JP2023161185A - Image forming device - Google Patents

Abstract

To suppress erroneous detection of a rear end of a recording material even in the case where there is a possibility that a rotary member is rotated at a portion other than the rear end.SOLUTION: An image forming device includes: a first detection sensor which includes a rotary member capable of coming into contact with a recording material conveyed in a conveyance direction and which outputs a first signal in response to rotation of the rotary member, and which is configured to rotate in the case where the rotary member is pushed to a front end of the recording material in the conveyance direction and in the case where a rear end of the recording material passes; a second detection sensor which is different from the first detection sensor, and which outputs a second signal in response to the passing of the recording material; and an engine control unit which detects the rear end of the recording material based on the first signal, after the rotary member is rotated by the front end of the recording material. Based on the second signal, the engine control unit sets a detection section for detecting the rear end in the case where the first signal satisfies a predetermined condition. The engine control unit does not detect the rear end even when the first signal satisfies the predetermined condition before the detection section.SELECTED DRAWING: Figure 6

Description

The present invention relates to an image forming apparatus using an electrophotographic process or the like.

A conveyance path of an image forming apparatus may be provided with a shutter for correcting skew of a sheet fed from a paper feeding unit, and a conveyance path sensor for determining the position of the leading edge and trailing edge of the sheet. In Patent Document 1, when an image forming apparatus continuously conveys a plurality of sheets, in order to shorten the distance between the sheets as much as possible and improve productivity, a rotating shutter is used to transport the leading edge of the sheet. It is shown that it is equipped with a sensor that detects the position of the rear end. Here, productivity refers to the number of sheets conveyed per unit time.

Japanese Patent Application Publication No. 2015-231917

However, in an image forming apparatus equipped with a sensor that detects the trailing edge of a sheet using a rotating shutter (rotating member), if the rotating member rotates at a position other than the trailing edge of the sheet, the trailing edge of the sheet may be incorrectly detected. There is a possibility that

For example, so-called pressure-bonded paper may be used, in which glue is applied to the surface, and after printing, the sheet is folded along with the glue and pressed using a special processing machine to hide the printed surface. At this time, when the glue portion of the sheet reaches the rotating member, the rotating member may rotate due to friction between the rotating member and the glue portion. When this phenomenon occurs, the image forming apparatus may erroneously detect the glue portion as the trailing edge of the sheet.

The present invention was made under such circumstances, and an object of the present invention is to suppress false detection of the trailing edge of a recording material even when there is a possibility that the rotating member is rotated at a portion other than the trailing edge. shall be.

The present invention includes the following configuration.
(1) An image forming apparatus for forming an image on a recording material, including a rotating member that can come into contact with the recording material being conveyed in the conveying direction, and outputting a first signal in accordance with rotation of the rotating member. a first detection sensor configured to rotate when the rotating member is pushed by the leading end of the recording material in the transport direction and when the rear end of the recording material passes; a detection sensor, a second detection sensor different from the first detection sensor and outputting a second signal in response to passage of the recording material; and a second detection sensor in which the rotating member is rotated by the leading end of the recording material. a control unit configured to detect the trailing edge of the recording material based on the first signal, the control unit configured to detect the trailing edge of the recording material based on the first signal, the control unit configured to detect the trailing edge of the recording material based on the first signal; A detection section for detecting the rear end is set based on the second signal, and the control section is configured to set a detection section for detecting the rear end based on the second signal, and the control section does not detect the rear end even if the first signal satisfies the predetermined condition before the detection section. An image forming apparatus characterized in that it does not detect.
(2) An image forming apparatus for forming an image on a recording material, including a rotating member that can come into contact with the recording material being conveyed in the conveying direction, and outputting a first signal in accordance with rotation of the rotating member. a first detection sensor configured to rotate when the rotating member is pushed by the leading end of the recording material in the transport direction and when the rear end of the recording material passes; a detection sensor, a second detection sensor different from the first detection sensor and outputting a second signal in response to passage of the recording material; and a second detection sensor in which the rotating member is rotated by the leading end of the recording material. is configured to perform an operation related to at least one of conveying the recording material, forming an image on the recording material, and detecting a conveyance failure of the recording material in response to the first signal. a control unit configured to set a trigger period for executing the operation when the first signal satisfies a predetermined condition based on the second signal; The image forming apparatus is characterized in that the operation is not performed even if the first signal satisfies the predetermined condition before the trigger period.

According to the present invention, even when there is a possibility that the rotating member is rotated at a portion other than the rear end, erroneous detection of the rear end of the recording material can be suppressed.

Overall configuration diagram of the image forming apparatus of Examples 1 and 2 Diagram showing the cash register sensor of Examples 1 and 2 A cross-sectional view of the cash register sensor of Examples 1 and 2 and a diagram showing the sensor output results Block diagram of image forming apparatus of Examples 1 and 2 Timing chart of conventional image formation and paper feed control for comparison with examples A diagram showing an example of the pressure-bonded paper used in Examples 1 and 2, a cross-sectional view of the registration sensor during conveyance of the pressure-bonded paper, and a diagram showing the sensor output results. Timing chart showing conveyance control in Example 1 Flowchart showing conveyance control in Example 1 Flowchart showing conveyance control in Example 1 Timing chart showing conveyance control in Example 2 Flowchart showing conveyance control in Example 2 Flowchart showing conveyance control in Example 2

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail by way of examples with reference to the drawings.

[Image forming device]
In FIG. 1, the overall configuration of a laser printer will be described as an example of an image forming apparatus according to a first embodiment. The image forming apparatus of the first embodiment is capable of forming an image on a specific sheet. The specific sheet is a sheet that has a portion in a predetermined range from the trailing edge to the leading edge of the recording material that affects an output signal when detecting the trailing edge by a registration sensor, which will be described later. The image forming apparatus shown in FIG. 1 includes four image forming stations Sy, Sm, Sc, and Sk. Specifically, in the figure, from the left side, the image forming stations are Sy, Sm, Sc, and Sk, which have yellow (Y), magenta (M), cyan (C), and black (Bk) toners. Further, y, m, c, and k at the end of the symbols in the figure respectively mean yellow (Y), magenta (M), cyan (C), and black (Bk). The configurations of the image forming stations Sy, Sm, Sc, and Sk are the same, and in the following description, symbols y to k will not be attached unless particularly necessary.

(Image forming section)
In each image forming station S, the photosensitive drum 1, which is an image carrier, is driven by a drive motor (not shown) and rotated counterclockwise (in the direction of the arrow in the figure). A charging roller 2, which is a charging means, contacts the photosensitive drum 1 and uniformly charges the surface of the photosensitive drum 1 while rotating as the photosensitive drum 1 rotates. A DC voltage or a voltage obtained by superimposing a DC voltage and an AC voltage is applied to the charging roller 2, and the photosensitive drum 1 is charged at the abutting nip between the charging roller 2 and the surface of the photosensitive drum 1.

The exposure means 11 is a scanner unit that scans laser light with a rotating polygon mirror, and irradiates the photosensitive drum 1 with a scanning beam 12 modulated based on a video signal (image signal) to form an electrostatic latent image. . Note that as the exposure means 11, an LED unit including an LED array including LEDs (light emitting diodes) can also be used.

The developing unit 8, which is a developing means, includes a developing roller 4 in contact with the photosensitive drum 1, a developer (hereinafter referred to as toner) 5, and a developing blade 7 that regulates the thickness of the toner layer formed on the developing roller 4. . The developing unit 8 develops the electrostatic latent image formed on the photosensitive drum 1 with toner to form a toner image.

The waste toner container 3 collects toner remaining on the photosensitive drum 1 without being transferred to an intermediate transfer belt 80, which will be described later. The process cartridge 9 includes a photosensitive drum 1, a charging roller 2, a waste toner container 3, and a developing unit 8, and is an integrated cartridge that is detachable from the image forming apparatus. Further, the charging roller 2 is connected to a charging voltage power source 20 that is a means for supplying voltage to the charging roller 2 . The developing roller 4 is connected to a developing voltage power source 21 that is a means for supplying voltage to the developing roller 4 . By bringing the charging roller 2 into contact with the surface of the photosensitive drum 1 and applying a charging voltage to the charging roller 2 from a charging voltage power source 20, the surface of the photosensitive drum 1 is uniformly charged.

The intermediate transfer belt 80 is supported by three rollers, a secondary transfer opposing roller 86, a drive roller 14, and a tension roller 15, which are tension members, and is configured to maintain appropriate tension. By driving the drive roller 14, the intermediate transfer belt 80 moves in the direction of the arrow in the figure at substantially the same speed. Further, the primary transfer roller 81 is disposed on the opposite side of the photosensitive drum 1 with the intermediate transfer belt 80 interposed therebetween, and is connected to a primary transfer voltage power source 84 that is a means for supplying voltage to the primary transfer roller 81 . Then, by applying a primary transfer voltage to the primary transfer roller 81, the toner images on the photosensitive drum 1 (on the image carrier) are sequentially transferred to the intermediate transfer belt 80 in contact with the photosensitive drum 1, and the intermediate transfer A multicolor (full color) image is formed on the belt 80 (primary transfer). Furthermore, a neutralizing member 23 is arranged downstream of each primary transfer roller 81 in the moving direction of the intermediate transfer belt 80 . The drive roller 14, the tension roller 15, the static eliminating member 23, and the secondary transfer opposing roller 86, which will be described later, are electrically grounded.

(Cassette feeding section)
Sheets P, which are recording materials, are placed on a paper feed cassette 16, which is a stacking section. When feeding the sheet P, a stepping motor (hereinafter referred to as a paper feeding motor 420) drives the pickup roller 17, which is a paper feeding means, to raise the paper feeding cassette bottom plate 29. As a result, the sheet P placed in the paper feed cassette 16 is pushed up. The uppermost sheet of the pushed up sheets P comes into contact with the pickup roller 17, and the rotation of the pickup roller 17 separates and feeds the sheets P one by one. The fed sheet P is conveyed toward the registration roller pair 18.

The image forming apparatus includes a registration sensor (first detection sensor) 35 having a shutter member 35a, which will be described later. When the registration sensor 35 detects the leading edge of the sheet P, the paper feed motor 420 stops driving, and the conveyance of the sheet P is temporarily stopped. The sheet P, which has been temporarily stopped by the registration roller pair 18, is restarted (also called re-feeding) at a timing when the toner image formed on the intermediate transfer belt 80 and the sheet P match in the secondary transfer section. be done) The secondary transfer portion refers to a portion where the color toner image on the intermediate transfer belt 80 is transferred to the sheet P, and is a nip portion between a secondary transfer roller 82 and a secondary transfer opposing roller 86, which will be described later. Further, the size of the sheet P (the length in the conveyance direction) is determined based on the elapsed time from the timing (point in time) when the sheet P is re-fed to the timing (point in time) when the registration sensor 35 detects the trailing edge of the sheet P. (hereinafter referred to as sheet size) is determined.
Note that even if the paper feed motor 420 does not stop driving when the registration sensor 35 detects the leading edge of the sheet P and changes the transport speed of the sheet P to match the toner image and the sheet P at the secondary transfer section. good.

(Register sensor part)
FIG. 2(A) shows the configuration of the registration sensor 35, and FIG. 2(B) shows the relationship between the attitude and output of the registration sensor 35. (a) to (d) of FIG. 2(B) show the posture of the registration sensor 35, and (e) of FIG. 2(B) shows the output result (hereinafter also referred to as sensor output result) 200 of the registration sensor 35. Note that some symbols are omitted in (b) to (d) of FIG. 2(B). In addition, (e) of FIG. 2(B) is drawn to correspond to (a) to (d), and when the register sensor 35 outputs a low level, it is OFF, and when the register sensor 35 outputs a high level. It is considered ON when it is on.

As shown in FIG. 2A, the registration sensor 35 includes a shutter member (rotating member) 35a that can come into contact with the sheet P conveyed in the conveyance direction, a shutter shaft 35b, a detected portion 35f, and a detection portion 35g. In this embodiment, a plurality of shutter members 35a are provided in the width direction W perpendicular to the conveying direction D of the sheet P. Further, the shutter shaft 35b also serves as the rotation axis of one of the registration rollers 18.

The registration sensor 35 detects the leading edge of the sheet P by changing its output signal (first signal) when the leading edge of the sheet P fed by the pickup roller 17 contacts and rotates. The registration sensor 35 detects the rear end of the sheet P by changing its output signal again as the rear end of the sheet P passes and rotates. The register sensor 35 functions as a first detection means (first detection sensor).

A shutter member (rotating member) 35a having three shutter parts (contact parts) 35c, 35d, and 35e is fixed to a shutter shaft 35b. The shutter portions 35c, 35d, and 35e protrude in a radial direction centered on the shutter shaft 35b. The detected part 35f has the same shape as the shutter member 35a, has three light shielding flags having the same shape as the three shutter parts 35c, 35d, and 35e, and is attached to the shutter shaft 35b so as to rotate integrally with the shutter member 35a. Fixed. Note that the shutter member 35a and the detected portion 35f do not have to have the same shape, and may have a similar shape (for example, a similar shape) having the same number of light shielding flags as the shutter portions 35c, 35d, and 35e. The shapes of the shutter portions 35c, 35d, and 35e and the plurality of light shielding flags may be the same or similar, but may be different in shape. The number of the shutter parts 35c, 35d, 35e and the plurality of light shielding flags is not limited to three, but in order to narrow the interval between the plurality of sheets P and improve the detection accuracy of the sheets P, three or more are used. preferable.

On the other hand, the detection section 35g is an optical sensor in which an optical path is formed by a light emitting element and a light receiving element, and is attached to a frame that receives the shutter shaft 35b. The detection unit 35g can determine the presence or absence of the sheet P depending on whether the light blocking flag of the detected unit 35f, which rotates at the same timing as the shutter member 35a, blocks the optical path of the detection unit 35g. That is, in response to the rotation of the shutter member 35a, the registration sensor 35 outputs an output signal (first signal) to the CPU 304, which will be described later.

(a) of FIG. 2B shows a situation where the sheet P rushes into the shutter member 35a that is waiting at the sheet P standby position (hereinafter referred to as the sheet standby position). The sheet P conveyed in the conveyance direction D toward the registration roller pair 18 comes into contact with one of the three shutter parts 35c, 35d, and 35e of the shutter member 35a before the nip of the registration roller pair 18. The skew of the sheet P is corrected by the shutter member 35a. In the state of (a) of FIG. 2(B), the detection result of the detection unit 35g (hereinafter referred to as the sensor output result) is OFF as shown at 201 in (e) of FIG. 2(B).

The shutter member 35a is pushed by the leading end of the sheet P in the conveyance direction D, and is configured to rotate in the rotation direction R1 when the force received from the sheet P reaches a certain level or more. (b) of FIG. 2(B) shows that the shutter portion 35c of the shutter member 35a is pushed by the leading edge of the sheet P that has entered, and the shutter member 35a begins to rotate in the arrow direction (rotation direction R1) in the figure. . At this timing, the light blocking flag of the detection member blocks the optical path of the detection unit 35g, and the sensor output result turns ON as shown at 202 in (e) of FIG. 2(B).

(c) of FIG. 2(B) shows a state in which the sheet P is passing through the shutter member 35a. While the sheet P is passing, the sensor output result remains ON as shown at 203 in (e) of FIG. 2(B). Note that while the sheet P is passing, the shutter portion 35c does not receive any rotational force, or even if the shutter portion 35e attempts to rotate in the direction of arrow R1 in FIG. It is being Therefore, while the sheet P is passing, the rotation of the shutter member 35a is normally stopped.

The shutter member 35a is configured to rotate in the rotation direction R1 when the rear end of the sheet P in the conveyance direction D passes. That is, the rotation direction of the shutter member 35a when pushed by the leading edge of the sheet P is the same as the rotation direction of the shutter member 35a when the rear edge of the sheet P passes. By doing so, after the preceding sheet P has passed, the shutter member 35a can be quickly returned to a position where the leading edge of the following sheet P can be detected. Further, the registration sensor 35 is biased by a biasing member (not shown) in a direction in which one of the shutter portions 35c, 35d, and 35e is positioned at a contact position where it contacts the sheet P.

(d) of FIG. 2(B) shows the state when the sheet P passes through the shutter member 35a. When the sheet P passes, there is no longer anything that prevents the shutter portion 35e from rotating in the direction of the arrow R1. Therefore, the shutter member 35a begins to rotate in the direction of arrow R1, and the shutter portion 35e waits at the sheet standby position. At this time, as shown at 204 in (e) of FIG. 2(B), the sensor output result indicates OFF. As described above, one of the shutter sections 35c, 35d, and 35e waits for the arrival of the sheet P at the sheet standby position.

In the first embodiment, the light blocking flag does not block the optical path of the detection unit 35g at the sheet standby position and the sensor output result is low level, and when the leading edge of the sheet P reaches and is passing through, the light blocking flag does not block the optical path of the detection unit 35g. Although the optical path of the sensor is blocked and the sensor output result is at a high level, the present invention is not limited to this. Further, the fact that the leading edge of the sheet P presses the shutter portion 35c (35d, 35e) and the sensor output result is switched from OFF to ON is expressed as the registration sensor 35 detecting the leading edge of the sheet P. The fact that the rear end of the sheet P passes through the shutter section 35e (35c, 35d) and the sensor output result is switched from ON to OFF is expressed as the registration sensor 35 detecting the rear end of the sheet P.

(MP tray feeding section)
Returning to the explanation of FIG. A sheet P, which is a recording material, is placed on the MP tray 50. When feeding a sheet P (hereinafter also simply referred to as a sheet), the pickup roller 51 is driven by the paper feed motor 420 already explained in the paper feed cassette 16, and the topmost sheet of the sheet P is picked up. It comes into contact with the roller 51 and is fed into the machine. The image forming apparatus has an MP conveyance sensor 52 that is different from the registration sensor 35. Regarding the conveyance direction D of the sheet P, the MP conveyance sensor 52 is arranged upstream of the registration sensor 35. The fed sheet P passes through the MP conveyance sensor 52 in the conveyance path and is conveyed to the registration roller pair 18. Thereafter, printing (hereinafter also referred to as printing) is performed in the same manner as the operation described for the sheet P already fed from the paper feed cassette 16.

In this embodiment, the MP conveyance sensor 52 includes a contact member that contacts the sheet P, a detected member that operates in conjunction with the contact member, and a detection unit that detects movement of the detected member. An optical sensor can be used for the detection section. The MP conveyance sensor 52 outputs an output signal (second signal) in response to the passage of the sheet.

The MP conveyance sensor 52 in this embodiment has two directions: a moving direction of the abutting member when the abutting member moves while being pushed by the leading edge of the sheet P, and a moving direction of the abutting member when the rear end of the sheet P passes. is in the opposite direction. Therefore, when comparing the registration sensor 35 using the shutter member 35a and the MP conveyance sensor 52, the registration sensor 35 can more accurately detect the rear end of the sheet P.

(Transport control unit)
When the leading edge of the sheet P fed from the paper feed cassette 16 or the MP tray 50 is detected by the registration sensor 35, the conveyance of the sheet P is temporarily stopped. Once the stopped sheet P is re-fed, detection of a paper jam (hereinafter referred to as jam) at the fixing sensor 37, which is the next sensor provided on the conveyance path, starts. Specifically, parameters such as the distance from the registration sensor 35 to the fixing sensor 37, the conveyance speed, the startup curve of the paper feed motor 420, and the conveyance variation of the sheet P are used to calculate the timing at which the sheet P reaches the fixing sensor 37 (hereinafter referred to as the arrival time). timing) is calculated. In the conveyance control, it is determined whether a jam has occurred based on whether the sheet P arrives at this arrival timing. Similarly, jam detection is also started at the timing when the trailing edge of the sheet P is detected by the registration sensor 35 after the temporarily stopped sheet P is re-fed (hereinafter referred to as detection timing). Note that the fixing sensor 37 is provided downstream of the fixing section 19 in the transport direction.
Further, as described above, when the leading edge of the sheet P is detected by the registration sensor 35, the conveyance speed may be changed without stopping the conveyance.

(Secondary transfer section)
The intermediate transfer belt 80 to which the toner images formed on the photosensitive drums 1 of each image forming station S have been transferred is moved by the driving roller 14 . As a result, the full-color toner image transferred onto the intermediate transfer belt 80 is conveyed to the secondary transfer portion, which is the contact portion between the secondary transfer roller 82 and the intermediate transfer belt 80 . Then, the sheet P and the intermediate transfer belt 80 are sandwiched and conveyed by a secondary transfer roller 82 and a secondary transfer opposing roller 86 installed opposite to the secondary transfer roller 82, and a secondary A voltage is applied to the transfer roller 82. As a result, the toner image on the intermediate transfer belt 80 is transferred onto the sheet P (secondary transfer).

(Fusing part)
The fixing unit 19, which is a fixing unit, fixes the toner image on the sheet P by applying heat and pressure to the unfixed toner image formed on the sheet P. The fixing unit 19 includes a fixing belt 19a and a pressure roller 19b, and the pressure roller 19b sandwiches the fixing belt 19a and forms a fixing nip portion by a predetermined pressure contact with a belt guide member (not shown). . With the fixing nip section adjusted to a predetermined temperature, the sheet P on which an unfixed toner image is formed is placed between the fixing belt 19a and the pressure roller 19b in the fixing nip section with the image surface facing upward, that is, the sheet P is fixed. It is introduced facing the belt 19a surface. At the fixing nip, the image surface of the sheet P comes into close contact with the outer surface of the fixing belt 19a, and the sheet P is conveyed through the fixing nip. In the process of conveying the sheet P by the fixing belt 19a through the fixing nip, the toner image on the sheet P is heated by the fixing belt 19a, and the unfixed toner image on the sheet P is heated and fixed. The sheet P with the toner image fixed thereon is discharged onto the discharge tray 36. Further, the toner remaining on the intermediate transfer belt 80 without being transferred to the sheet P is charged to a predetermined polarity by a cleaning device 88 to which a predetermined voltage is applied by a power source 89, and is transferred from the intermediate transfer belt 80 onto the photosensitive drum 1. The waste toner is moved and collected in the waste toner container 3.

The image forming apparatus includes an operation display section 310. The operation display section 310 is provided with various known input means for inputting various information by the user and known display means for displaying various information. For example, the user can use the operation display unit 310 to set the sheet size and paper type (plain paper, thin paper, thick paper, etc.) of the sheet P to be printed. Further, the user can set the sheet size and paper type (plain paper, thin paper, thick paper, etc.) of the sheet P from an external device connected wirelessly or wired to the image forming apparatus.

[System configuration of image forming apparatus]
FIG. 3 is a block diagram for explaining the entire system configuration of the image forming apparatus. In FIG. 3, the image forming apparatus includes a controller section 301 and an engine section 302. The engine section 302 includes a video interface section 303 and an engine control section 302a as a control section. The engine control unit 302a includes a CPU (central processing unit) 304, a ROM (read only memory), a RAM (random access memory), and an image processing GA (gate array) 305. The ROM stores control programs and data executed by the CPU 304. The RAM is a memory used by the control program executed by the CPU 304 to temporarily store information.

The controller unit 301 is capable of communicating with a host computer 300 and an engine unit 302, which are external devices. The controller unit 301, which is an image signal output means, receives a print command including image information (print data) and printing conditions from the host computer 300, and develops bitmap data (image data) based on the received print data. . When the bitmap data has been developed, the controller unit 301 transmits image size information and a print reservation command to the CPU 304 via the video interface unit 303 in accordance with a print command from the host computer 300. Then, at the timing when the engine unit 302 is ready for printing (image formation possible), the controller unit 301 transmits a print start command to the CPU 304 of the engine control unit 302a.

The engine control unit 302a controls the conveying operation of the sheet P and/or the image forming operation on the sheet P based on the timing at which the rear end of the sheet P is detected by the registration sensor 35. The engine control unit 302a also detects a conveyance failure of the sheet P based on the timing at which the registration sensor 35 detects the rear end of the sheet P.

The engine control section 302a includes an image control section 306, a fixing control section 307, and a sheet conveyance section 308. The CPU 304, image processing GA 305, image control unit 306, fixing control unit 307, and sheet conveyance unit 308 are connected via a bidirectional bus, and mutually transmit and receive data via the bidirectional bus.

The video interface section 303 relays various signals between the engine section 302 and the controller section 301. The image control unit 306 controls the image forming unit described above. The fixing control unit 307 controls the fixing unit 19 described above, and the sheet conveyance unit 308 feeds the sheet P from the paper feed cassette 16 and MP tray 50 described above, and controls the paper feed motor 420. In this embodiment, conveyance rollers other than the pickup roller 51 are also driven by the paper feed motor 420. When the CPU 304, which sends and receives data such as commands to and from the controller unit 301, receives a sheet size specification command and a print reservation command from the controller unit 301, it prepares to execute a print job, and a print start command is sent from the controller unit 301. wait for. Upon receiving the print start command, the CPU 304 causes each control unit (image control unit 306, fixing control unit 307, sheet conveyance unit 308) to perform a print operation (hereinafter referred to as print) according to the information in the print reservation command, such as the specified sheet size. (also called an action).

Further, the engine section 302 has a timer, and the CPU 304 performs various timing controls based on the time measured by the timer. The engine section 302 also includes a register sensor counter 309, which will be described in the second embodiment. The register sensor counter 309 may be included in the engine control section 302a.

When the image control unit 306 receives the instruction to start the printing operation, it starts preparing for image formation. When the CPU 304 receives a notification from the image control unit 306 that preparations for image formation are complete, the CPU 304 sends a timing signal /TOP, which is a reference timing for outputting a video signal, to the controller unit 301 via the video interface unit 303. Output a signal. Upon receiving the /TOP signal from the CPU 304, the controller unit 301 performs the following processing. The controller unit 301 outputs the video signal generated from the bitmap data for the designated sheet size to the image processing GA 305 via the video interface unit 303 based on the timing at which the /TOP signal is received. Upon receiving the video signal from the controller unit 301, the image processing GA 305 converts the received video signal into data for image formation and transmits it to the image control unit 306. The image control unit 306 performs image formation based on image formation data received from the image processing GA 305. Note that during image formation when performing continuous printing, the image control unit 306 determines the time interval ( Determine the image forming interval (period). Then, in accordance with the image forming interval, the image control unit 306 instructs the CPU 304 to transmit the /TOP signal.

The sheet conveying unit 308 starts a paper feeding operation upon receiving an instruction to start a printing operation from the CPU 304 . The sheet conveyance unit 308 drives a paper feed motor 420 to convey the sheet P placed on the MP tray 50 or the paper feed cassette 16 (hereinafter also referred to as a paper feed unit) to a secondary transfer position, and also drives a registration sensor. 35 to detect the size of the sheet P (sheet size). Note that the size of the sheet P here refers to the length of the sheet P in the conveyance direction. Furthermore, when the registration sensor 35 detects the leading and trailing ends of the sheet P, the fixing sensor 37 located downstream of the registration sensor 35 in the conveying direction performs jam detection.

When the fixing control unit 307 receives an instruction to start a printing operation, it starts preparing for fixing processing. The fixing control unit 307 adjusts the temperature according to the paper type information (for example, the thickness of the sheet P) set in the print reservation command at the timing when the sheet P on which the secondary transfer has been performed is conveyed to the fixing unit 19. Start. Note that the paper type information may include, in addition to the thickness of the sheet P, indicators indicating the characteristics of the sheet P, such as the size of the sheet P, basis weight (g/m ² ), glossiness, and the like. After fixing the image (toner image) on the sheet P, the fixing control unit 307 transports (discharges) the sheet P out of the machine.

The engine control unit 302a of the engine unit 302 sets conditions for image forming operation based on information input through the operation display unit 310, for example, information such as the sheet size of the sheet P. Furthermore, if a jam or the like occurs during the image forming operation, the engine section 302 displays this fact on the operation display section 310 and notifies the user.

In summary, the engine control unit 302a includes a control unit configured to execute operations related to at least one of conveying the sheet P, forming an image on the sheet P, and detecting a conveyance failure of the sheet P. I can do it.

In this embodiment, the engine control unit 302a is configured to detect the rear end of the sheet P based on the output signal (first signal) of the registration sensor 35 after the rotating shutter 35a is rotated by the leading end of the sheet P. be done. The engine control unit 302a also detects the trailing edge of the sheet P, and performs operations related to at least one of forming an image on the sheet P and detecting a conveyance failure of the sheet P, using the trailing edge of the sheet P as a reference. (rear end reference operation). In other words, the engine control unit 302a is configured to perform the rear end reference operation based on the output signal (first signal) of the registration sensor 35 after the rotary shutter 35a is rotated by the leading edge of the sheet P. .
The operation controlled by the engine control unit 302a of the engine unit 302 will be described below, but it may be simply stated that the engine unit 302 controls the target.

[Overview of conventional printing operations]
FIG. 4 is a timing chart when, in control of the comparative example, the registration sensor 35 detects the trailing edge of the sheet P, and then the fixing sensor 37 detects a jam. In the printing operation, one sheet P of LTR size (215.9 mm x 279.4 mm) is printed from the MP tray 50. In FIG. 4, (i) is the waveform of the /TOP signal (410), (ii) is the driving status of the paper feed motor 420, (iii) is the paper feed pickup solenoid (drive of the pickup roller 51) (430), (iv ) shows the output waveform (440) of the MP conveyance sensor 52. In FIG. 4, (v) is the output waveform (450) of the registration sensor 35, (vi) is the output waveform (460) of the fixing sensor 37, and (vii) is the output waveform (460) of the fixing sensor 37 as an example of the above-mentioned specific sheet when pressure-bonded paper is conveyed. The output waveform (480) of the register sensor 35 is shown. The horizontal axis direction indicates time. Pressure-bonded paper is a sheet suitable for communicating highly confidential information.Glue is applied to the surface of the sheet, and after printing, the sheet is folded to match the glue and is pressed using a special processing machine.

In FIG. 4, the /TOP signal is a signal sent from the engine section 302 to the controller section 301. When the engine unit 302 receives a print start command from the controller unit 301, it performs an image formation preparation operation for a print operation. When the image formation preparation operation is completed, the /TOP signal for the first sheet P is output at /TOP timing 411. The controller unit 301 starts image formation based on the /TOP signal output from the engine unit 302.

The engine unit 302 starts the paper feed motor 420 in parallel with preparations for image formation control, and prepares for paper feeding operation. When the sheet feeding preparation operation is completed, the engine section 302 drives the pickup roller 51 to feed one sheet P at a pickup timing 431. The engine unit 302 detects the leading edge of the sheet P fed into the machine with the MP conveying sensor 52 at timing 441 when the leading edge of the sheet P reaches the MP conveying sensor 52 . Further, the engine unit 302 detects the rear end of the sheet P with the MP conveyance sensor 52 at timing 442 when the rear end of the sheet P reaches the MP conveyance sensor 52 .

When the engine unit 302 detects the leading edge of the sheet P fed from the MP tray 50 at a timing 451 when the leading edge of the sheet P reaches the registration sensor 35, it temporarily stops the paper feeding motor 420 at a timing 421. Timing 421 is the timing at which the sheet P reaches a position where its conveyance is temporarily stopped. Thereafter, the paper feed motor 420 is restarted at the sheet refeed timing 422 so that the toner image formed on the intermediate transfer belt 80 and the leading edge of the sheet P waiting at the registration sensor 35 match in the secondary transfer section. , refeed the sheet P. Depending on the position of the toner image on the intermediate transfer belt 80, the conveyance may not be stopped. In the first embodiment, a case will be described in which transport is temporarily stopped.

The leading edge of the re-fed sheet P reaches the fixing sensor 37 at timing 461. The rear end of the sheet P passes the registration sensor 35 at timing 452. Timing 452 is the timing at which the rear end of the sheet P passes the registration sensor 35. The engine unit 302 starts fixing retention jam detection by the fixing sensor 37 from timing t1 (452) when the rear end of the sheet P passes the registration sensor 35.

Specifically, the engine unit 302 starts from timing t1 (452) when the trailing edge of the sheet P passes the registration sensor 35 and starts detecting the trailing edge of the sheet P by the fixing sensor 37 at a time Tfsr (hereinafter simply referred to as detection). Wait until the start time Tfsr (470) elapses. The engine unit 302 uses the fixing sensor 37 to detect the trailing edge of the sheet P during a fixing sensor sheet trailing edge detection section Tfsr_window (hereinafter simply referred to as a detection section Tfsr_window) (471) from timing t2 when the detection start time Tfsr has elapsed. Detection of More specifically, the engine unit 302 waits to see whether the rear end of the sheet P can be detected by the fixing sensor 37 during the detection period Tfsr_window.

The detection start time Tfsr (470) and the detection interval Tfsr_window (471) can be calculated using the following equations (1) and (2), respectively.
Tfsr=(distance from registration sensor 35 to fixing sensor 37/transport speed)
-Fixing variation early arrival time Formula (1)
Tfsr_window = Fixing variation early arrival time + Fixing variation late arrival time Formula (2)
The fixing variation early arrival time used in equations (1) and equation (2) and the fixing variation late arrival time used in equation (2) will be explained.

The engine control unit 302a can calculate an ideal timing (also referred to as a center value) at which the rear end of the sheet P reaches the fixing sensor 37, or can read out a stored value. In equation (1), (distance from registration sensor 35 to fixing sensor 37/conveying speed) corresponds to the center value.
In reality, the rear end of the sheet P may arrive at the fixing sensor 37 earlier than the center value (early arrival), or conversely may arrive later than the center value (late arrival).

Normally, when conveying a sheet P in an image forming apparatus, the time for conveying a predetermined distance cannot be determined only by the dimensions of the conveyance path, and may be delayed or accelerated due to other factors, so there is variation. A possible reason for the variation in the time taken to convey a predetermined distance is that the sheets P are conveyed along different conveyance paths depending on the guide shape of the conveyance path. Furthermore, the diameter of the pressure roller 19b of the fixing unit 19 changes depending on how warm it is, which may affect the conveyance speed of the sheet P. After accumulating each variation factor, the difference between the time when the trailing edge of the sheet P reaches the fixing sensor 37 earliest from the registration sensor 35 and the center value is calculated as the fixing variation early arrival time, the time when the trailing edge of the sheet P reaches the fixing sensor 37 the latest, and the center value. The difference between the values is defined as the fixation variation delay time.

Therefore, the engine unit 302 sets the value obtained by subtracting the fixing variation early arrival time from the center value as the detection start time Tfsr (470). Further, the sum of the fixing variation early arrival time and the fixing variation late arrival time is set as the detection interval Tfsr_window (471).

Note that the detection start time Tfsr (470) can also be set as the time at which the trailing edge of the sheet P reaches the fixing sensor 37 from the registration sensor 35 earliest. The difference between the time when the trailing edge of the sheet P reaches the fixing sensor 37 from the registration sensor 35 the latest and the time when the trailing edge of the sheet P reaches the fixing sensor 37 from the registration sensor 35 earliest is determined by the detection interval Tfsr_window (471). It can be done.

If the rear end of the sheet P cannot be detected by the fixing sensor 37 during the detection period Tfsr_window (471), the engine section 302 causes the sheet P to stay near the fixing section 19 and the secondary transfer section. It is determined that printing cannot continue normally. In this case, the engine unit 302 stops the operation of the image forming apparatus. On the other hand, the engine unit 302 was able to normally detect the trailing edge of the sheet P with the fixing sensor 37 at timing 462 when the trailing edge of the sheet P passed the fixing sensor 37 during the detection period Tfsr_window (471). If so, the sheet P is directly discharged to the outside of the machine and the printing operation is ended. Note that in the following explanation, only the symbols (411, 421, etc.) representing each timing will be used unless newly explained.

(crimped paper)
Next, in the control of the comparative example, the operation when printing one sheet of LTR size pressure-bonded paper from the MP tray 50 will be described using FIGS. 4 and 5. FIG. 5(A) shows an example of pressure-bonded paper, and also shows the conveyance direction, leading edge, and trailing edge of the pressure-bonded paper. In the pressure-bonded paper of FIG. 5A, glue is arranged at a position X (501) from the rear end toward the front end in a direction perpendicular to the conveyance direction, and this part is called a glue portion 502.

(Jam detection when printing on pressure bonded paper)
Next, when printing the pressure-bonded paper shown in FIG. The process will be explained using FIG. 4. The engine unit 302 also performs the same control as the control already explained using FIG. 4 for the pressure-bonded paper in FIG. Paper operations (421, 431) and paper refeed operations (422) are performed. The leading edge of the pressure-bonded paper that has been re-fed reaches the fixing sensor 37 (461).

Next, the operation when the pressure-bonded paper reaches and passes the registration sensor 35 will be explained using FIG. 5(B). 5(B) (a) to (g) are given the same reference numerals as in FIG. 2(B)(a), etc., and FIG. 5(B)(h) is the same as FIG. Similarly to (e), the sensor output results are shown. The leading edge of the pressing paper reaches the registration sensor 35 at timing 481 when the leading edge of the pressing paper reaches the registration sensor 35 (FIG. 5(B)(a)). When the leading edge of the pressure bonding paper presses the shutter portion 35c, the shutter member 35a and the light shielding flag of the detection member rotate, and the sensor output changes from OFF to ON (FIG. 5(B)(b)). While the pressure-bonded paper is passing through the registration sensor 35, the sensor output result is maintained at ON (FIG. 5(B) (b) to (c)), similarly to the explanation in FIG. 2(B).

Thereafter, the adhesive portion 502 of the pressure bonding paper comes into contact with the shutter portion 35e that constitutes the registration sensor 35 (FIG. 5(B)(d)). The shutter portion 35e that has come into contact with the glue portion 502 is dragged by the glue portion 502 and rotates in the direction of arrow R1 (clockwise direction) due to friction with the glue portion 502 (FIG. 5(B)(e)). As a result, the shutter member 35a and the light-shielding flag of the detection member rotate to the sheet standby position as in FIGS. The result shows OFF. After that, the light shielding flag of the shutter member 35a and the detection member is turned ON at timing 485 when the pressure-bonded paper is re-detected by the registration sensor 35 of the pressure-bonded paper because the pressure-bonded paper passes at the same position as in FIGS. 5(B) and 5(c). (FIG. 5(B)(f)). FIGS. 5B and 5G show timing t12 (timing t1 described above) when the actual rear end of the pressure-bonded paper passes the registration sensor 35, and the sensor output result is OFF, that is, there is no sheet (452). Here, X from timing t11 to timing t12 in FIG. 4(vii) corresponds to X in 501 in FIG. 5(A).

The engine unit 302 determines that the timing t11 when the sensor output result is turned OFF due to the glue portion 502 on the pressure-bonded paper is the timing when the registration sensor 35 is added to the rear end of the pressure-bonded paper (482). Therefore, the engine unit 302 starts detecting the fixing retention jam using the fixing sensor 37.

The fixing sensor detection start time for the trailing edge of pressure bonded paper (hereinafter referred to as pressure bonded paper detection start time) Tfsrp (483) and the fixing sensor pressure bonded paper trailing edge detection period (hereinafter referred to as pressure bonded paper detection zone) Tfsrp_window (484) are as described above. It can be obtained using equations (1) and (2). The calculation results of equations (1) and (2) are the same as the detection start time Tfsr (470) and the detection interval Tfsr_window (471). The engine unit 302 waits to see whether the fixing sensor 37 can detect the trailing edge of the pressure-bonded paper during the pressure-bonded paper detection period Tfsrp_window (484).

Normally, when an LTR-sized sheet P is conveyed, the timing at which the rear end of the sheet P reaches the fixing sensor 37 is 462, as described above. However, the trailing edge of the pressure-bonded paper is detected (482) by the registration sensor 35 at a timing t11 that is X (501) earlier than the timing t1 (452) at which the trailing edge of the normal sheet P passes through the registration sensor 35. In the case of pressure-bonded paper, the engine unit 302 starts fixing retention jam detection at timing t13, which is X (501) earlier than usual. Therefore, the original trailing edge (462) of the pressure-bonded paper cannot reach the fixing sensor 37 during the detection period Tfsrp_window (484) of the pressure-bonded paper. Therefore, based on this detection result, the engine unit 302 erroneously detects that the sheet P has accumulated near the fixing unit 19 and the secondary transfer unit and that the printing operation cannot be continued normally, and stops the operation of the image forming apparatus. Stop. As described above, in the control of the comparative example, when a printing operation is performed on pressure-bonded paper, the engine section 302 incorrectly detects that there is a fixing retention jam.
Furthermore, even for sheets other than press-bonded paper, if the rotary shutter 35a is rotated at a timing different from the rear end of the sheet P, the control section of the engine section 302 may erroneously detect the rear end of the sheet P.

The rotary shutter 35 of the registration sensor 35 rotates in the same direction when pushed by the leading edge of the sheet P and when the trailing edge of the sheet P passes. Furthermore, the shutter sections 35c, 35d, and 35e are moved toward the downstream side in the conveying direction D of the sheet P when pushed by the leading edge of the sheet P and when the trailing edge of the sheet P passes. In such a configuration, even if the timing is different from the rear end of the sheet P, when a force in the conveyance direction D is applied to the rotary shutter 35a, rotation of the rotary shutter 35a is likely to occur.

[Overview of printing operation in Example 1]
In the first embodiment, in the image forming apparatus, the length of the sheet P measured by the MP conveyance sensor 52 disposed upstream of the registration sensor 35 in the conveyance direction is used to detect the trailing edge of the sheet P by the registration sensor 35. conduct.

The MP conveyance sensor 52 is provided upstream of the registration sensor 35 in the conveyance direction, and functions as a second detection means (second detection sensor) that detects the leading edge and trailing edge of the sheet P. Note that the detection means used to measure the length of the sheet P may be installed downstream of the registration sensor 35 in the conveyance direction D.

The engine control unit 302a of the engine unit 302 of the first embodiment determines the timing at which the registration sensor 35 starts detecting the rear end of the sheet P based on the measured length of the sheet P. In this embodiment, the engine control section 302a of the engine section 302 measures the length of the sheet P based on the detection result of the MP conveyance sensor 52. As a result, even when a specific sheet is used, it is possible to prevent the fixing sensor 37 from erroneously detecting a fixing retention jam, and to perform a normal printing operation.
In the following description, a case will be described in which pressure-bonded paper is used as the sheet P. For this reason, the sheet P is sometimes called pressure-bonded paper.

In the first embodiment, similar to the conventional example described with reference to FIG. 4, the operation when printing one sheet of LTR size pressure-bonded paper from the MP tray 50 will be described.
FIG. 6 is a timing chart showing image formation and paper feeding control in the first embodiment. FIGS. 6(i) to (iv) and (vi) show waveforms similar to those in FIGS. 4(i) to (iv) and (vii). Further, FIG. 6(v) corresponds to FIG. 4(vii), and when representing the same timing, only the symbols (711, 721, etc.) are used. Note that in FIG. 4, the numbers in the 400s are replaced by codes in the 700s in FIG. The engine unit 302 performs the same control as that described using FIG. 4, and outputs a /TOP signal (711) and feeds the first sheet of pressure-bonded paper (731). Further, the leading edge of the pressure-bonded paper is detected by the MP conveyance sensor 52 (741), and the leading edge is detected by the registration sensor 35 (751).

When the engine control unit 302a of the engine unit 302 detects the leading edge of the sheet P fed into the machine with the MP transport sensor 52 (741), the MP transport sensor 52 starts measuring the length of the sheet P from there. The length of the sheet P can be calculated using the time during which the MP conveyance sensor 52 is ON and the time during which conveyance is stopped (Formula (3)). The time during which the MP conveyance sensor 52 is ON is the time T1 from 741 to 742. The time during which the conveyance is stopped is the time T2 from 721 to 722.
Length = MP conveyance sensor ON time (T1-T2) excluding conveyance stop time / conveyance speed
Formula (3)

Similar to the description of FIG. 4, when the sheet P temporarily stopped by the registration sensor 35 is re-fed, the conveyance of the sheet P is restarted (722). At timing t21 of paper refeeding, the engine unit 302 determines the timing at which the trailing edge of the crimp paper passes the registration sensor 35. (754) is set.

The engine unit 302 waits for the registration sensor 35 to detect the trailing edge of the crimp paper during the registration sensor crimp paper trailing edge detection interval Treg_window (755) from timing t22 when the detection start time Treg (754) has elapsed. The detection start time Treg (754) and the registration sensor pressure-bonded paper trailing edge detection section (hereinafter referred to as the pressure-bonded paper detection section) Treg_window (755) can be determined using equations (4) and (5), respectively.
Treg = (sheet size/conveying speed) - registration variation early arrival time Formula (4)
Treg_window = Early arrival time due to cash register variation + Late arrival time due to cash register variation
Formula (5)

The sheet size used in equation (4) is the sheet size specified by the user or the length determined by equation (3). The seat size may be read from a value corresponding to the designated seat P stored in the ROM of the engine control unit 302a, or may be input in advance by the user via the operation display unit 310 or the like.

Note that the operation display section 310 described with reference to FIG. 1 functions as an input means that can input that the sheet P is a specific sheet (press-bonded paper). The engine control section 302a of the engine section 302 determines that the sheet P is a pressure-bonded paper based on the input result from the operation display section 310. Information indicating that the sheet P is pressure-bonded paper may be input from an external device connected to the image forming apparatus.

The concept of the registration variation early arrival time and the registration variation late arrival time is the same as the fixing variation early arrival time and the fixing variation late arrival time that have already been explained. In other words, considering the center value at which the rear end of the sheet P reaches the registration sensor 35, the case where the rear end of the sheet P reaches the registration sensor 35 the latest, and the case where the rear end of the sheet P reaches the registration sensor 35 the earliest. determined.

Note that the registration variation early arrival time needs to satisfy equation (6).
Registration variation early arrival time ≦X/conveying speed Formula (6)
X is the distance from the rear end of the pressure-bonded paper to the adhesive part 502 as explained in FIG. This is because there is a possibility that it will be detected.

Before the length of the sheet P is measured by the MP conveyance sensor 52, the sheet size to be used first is determined by using a value stored in the ROM of the engine control unit 302a or by inputting the sheet size in advance by the user. can be used.

The engine unit 302 finishes measuring the length of the pressure bonding paper at the timing (742) when the rear end of the re-fed pressure bonding paper passes the MP conveyance sensor 52. The engine unit 302 updates the detection start time Treg using the measured length of the pressure bonding paper. In other words, the start timing of the trailing edge detection section Treg_window (755) is updated. The engine unit 302 detects the trailing edge of the pressure bonded paper with the registration sensor 35 during the pressure bonded paper trailing edge detection section Treg_window (755) from timing t22 when the detection start time Treg (754) has elapsed since paper re-feeding.

That is, the engine control unit 302a sets a detection period (Treg_window) in which the rear end of the sheet P is detected when the output signal of the registration sensor 35 satisfies a predetermined condition, based on the output signal of the MP conveyance sensor 52. Note that the detection period (Treg_window) can also be called a trigger period for the engine control unit 302a to execute the rear end reference operation when the output signal of the registration sensor 35 satisfies a predetermined condition.
Here, in this embodiment, the predetermined condition refers to whether the magnitude of the output signal of the register sensor 35 exceeds a predetermined value (in this embodiment, whether it changes from OFF to ON).

Even if the output signal of the registration sensor 35 satisfies a predetermined condition before the rear end detection section Treg_window (before the detection start time Treg), the engine control unit 302a does not detect the rear end of the sheet P and performs the rear end reference operation. is not executed either. Thereafter, in the trailing edge detection section Treg_window, if the output signal of the registration sensor 35 satisfies a predetermined condition, the engine control unit 302a detects the trailing edge of the sheet P and executes the trailing edge reference operation.

When pressure bonding paper is used, as explained in FIGS. 4 and 5(B), the shutter parts 35c, 35d, and 35e of the registration sensor 35 are rotated by the adhesive part 502 of the pressure bonding paper, thereby crimping the registration sensor 35. Even though the paper is still passing through, the sensor output result is OFF (no sheet). However, the timing (752) at which the shutter sections 35c, 35d, and 35e are rotated by the glue section 502 is outside the trailing edge detection section Treg_window of the pressure-bonded paper. Therefore, the control is such that the fact that the sensor output result is OFF (no sheet) (Tα in FIG. 6(v)) is not detected.

In this way, even if the rotary shutter 35a rotates before the rear end detection section Treg_window, the engine control unit 302a does not detect the rear end of the seat P. Thereafter, when the rear end of the sheet P reaches the registration sensor 35 and the rotation of the rotary shutter 35a is detected in the rear end detection section Treg_window, the engine control unit 302a detects the rear end of the sheet P.

The engine unit 302 calls the timing 753 when the registration sensor 35 can normally detect the trailing edge of the sheet P during the trailing edge detection section Treg_window (755) of the bonded paper. Timing 753 is the timing at which the registration sensor 35 detects the rear end of the pressure-bonded paper. The engine control unit 302a controls the following operations based on timing 753. That is, as described in FIG. 4, the engine unit 302 starts fixing retention jam detection (756 Tfsr, 757 Tfsr_window) by the fixing sensor 37. The engine unit 302 normally detects the leading and trailing ends of the pressure-bonded paper (761, 762). The engine unit 302 directly discharges the pressure-bonded paper to the outside of the machine and ends the printing operation.

On the other hand, if the register sensor 35 cannot detect the trailing edge of the crimp paper during the crimp paper trailing edge detection section Treg_window (755), the engine unit 302 performs the following control. That is, the engine unit 302 determines that the pressure-bonded paper has accumulated near the registration sensor 35 and that the printing operation cannot be continued normally, and stops the operation of the image forming apparatus. Note that 756 in FIG. 6(vi) is similar to 483 in FIG. 4, and 757 is similar to 484 in FIG. Note that the conveyance failure of the crimped paper when the trailing edge of the crimped paper cannot be detected by the registration sensor 35 in the trailing edge detection section of the crimped paper Treg_window (755) is hereinafter referred to as a registration jam, and the detection of the registration jam is referred to as a registration jam. This is called jam detection.

(Transport control of Example 1)
7 and 8 are control flowcharts of the engine section 302 in the first embodiment when the sheet P is a pressure-bonded paper. Detection of the trailing edge of the sheet P by the registration sensor 35 will be described in detail with reference to FIG. When the engine unit 302 starts printing, it starts processing from step (hereinafter referred to as S) 800a. In S800a, the engine unit 302 sets an MP conveyance sensor ON detection request and a registration sensor ON detection request for detecting the leading edge of the sheet P with the registration sensor 35 and the MP conveyance sensor 52. In S801a, the engine unit 302 starts the paper feeding operation and outputs the /TOP signal.

In S802a, the engine unit 302 determines whether the sheet P has reached the MP conveyance sensor 52 and the MP conveyance sensor 52 has been turned on. In S802a, if the engine unit 302 determines that the MP conveyance sensor 52 is turned on, the process proceeds to S803a, and if it determines that it is not turned on, the engine unit 302 advances the process to S806a. In S803a, the engine unit 302 determines whether an MP conveyance sensor ON detection request is set. If the engine unit 302 determines in S803a that the MP conveyance sensor ON detection request has been set, the process proceeds to S804a, and if it determines that it has not been set, the engine unit 302 proceeds to S809a. In S804a, the engine unit 302 starts a length measurement timer in order to perform length measurement using the MP conveyance sensor 52. In S805a, the engine unit 302 cancels the MP conveyance sensor ON detection request and sets an MP conveyance sensor OFF detection request for detecting the rear end of the sheet P with the MP conveyance sensor 52.

In S806a, the engine unit 302 determines whether an MP conveyance sensor OFF detection request is set. If the engine unit 302 determines in S806a that the MP conveyance sensor OFF detection request has been set, the process advances to S807a, and if it determines that the MP conveyance sensor OFF detection request has not been set, the engine unit 302 advances the process to S809a. In S807a, when the MP conveyance sensor 52 changes from ON to OFF, the engine unit 302 cancels the MP conveyance sensor OFF detection request, stops the actual measurement timer, calculates and finalizes the length determined by the MP conveyance sensor 52. let In S808a, the engine unit 302 updates the pressure bonding paper detection start time Treg. The pressure-bonded paper detection start time Treg can be calculated using equation (4) described above. At this point, the sheet size used to calculate the pressure-bonded paper detection start time Treg is the length calculated in S807a.

At 809a, the engine unit 302 determines whether the sheet P has reached the registration sensor 35 and the registration sensor 35 has been turned on. In S809a, if the engine unit 302 determines that the registration sensor 35 is turned on, the process proceeds to S810a, and if it determines that it is not turned on, the engine unit 302 advances the process to S820a. In S810a, the engine unit 302 determines whether a registration sensor ON detection request is set. In S810a, if the engine unit 302 determines that the registration sensor ON detection request is set, the process proceeds to S811a, and if it determines that it has not been set, the engine unit 302 proceeds to S817a.

In S811a, the engine unit 302 temporarily stops transporting the sheet P. In S812a, the engine unit 302 stops the length measurement timer. In S813a, the engine unit 302 determines whether it is time to refeed the paper. If the engine unit 302 determines in S813a that it is not time to refeed the paper, the process returns to S813a, and if it determines that the time to refeed the paper has come, the engine unit 302 advances the process to S814a. In S814a, the engine unit 302 cancels the registration sensor ON detection request and resumes transporting the sheet P. In S815a, the engine unit 302 restarts the length measurement timer. In S816a, the engine unit 302 calculates the pressure-bonded paper detection start time Treg, starts a timer for the pressure-bonded paper detection start time Treg, and returns the process to S802a. The pressure-bonded paper detection start time Treg can be calculated using equation (4) described above. At this point, the sheet size used to calculate the pressure-bonded paper detection start time Treg is the sheet size specified by the controller unit 301 or input from the operation display unit 310. This is because at this point, the measurement of the length of the sheet P by the MP conveyance sensor 52 has not been completed (see FIG. 6).

In S817a, the engine unit 302 refers to the timer for the pressure-bonded paper detection start time Treg, and determines whether the pressure-bonded paper detection start time Treg has elapsed since the start of paper refeeding (Treg timer≧Treg). to decide. If the engine unit 302 determines in S817a that the pressure-bonded paper detection start time Treg has elapsed, the process proceeds to S818a, and if it determines that the time has not elapsed, the engine unit 302 returns the process to S802a. In S818a, the engine unit 302 sets a registration sensor OFF detection request. In S819a, the engine unit 302 starts detecting a jam at the register, and returns the process to S802a.

In S820a, the engine unit 302 determines whether a registration sensor OFF detection request is set. In S820a, if the engine unit 302 determines that the register sensor OFF detection request has been set, the process proceeds to S821a, and if it determines that it has not been set, the engine unit 302 returns the process to S802a. In S821a, the engine unit 302 determines that it is the timing when the pressure-bonded paper has passed through the registration sensor 35, and ends the registration jam detection. In S822a, the engine unit 302 starts fixing retention jam detection and ends the process.

The key point of the control in the first embodiment is that the detection start time Treg, which determines the timing at which the registration sensor 35 detects the trailing edge of the pressure-bonded paper being conveyed, is based on the MP conveyance sensor 52 rather than the sheet size specified by the controller unit 301. The point is to use the length measured using This makes it possible to invalidate the output result from the registration sensor 35 of the adhesive portion 502 within the length of the pressure-bonded paper, no matter what sheet size of pressure-bonded paper is placed on the MP tray 50.

(Register jam detection)
Referring to FIG. 8(a), the registration jam detection by the registration sensor 35 will be described in detail. When the engine unit 302 starts detecting a jam at the register in S819a, it starts processing from S800b onwards. In S800b, the engine unit 302 calculates a trailing edge detection interval Treg_window for detecting the trailing edge of the press-bonded paper by the registration sensor 35, and starts a timer for the trailing edge detection interval Treg_window. The trailing edge detection section Treg_window can be calculated using the equation (5) described above. In S801b, the engine unit 302 refers to the timer for the rear end detection interval Treg_window and determines whether the rear end detection interval Treg_window has elapsed (timer for Treg_window≧Treg_window). If the engine unit 302 determines in S801b that the rear end detection period Treg_window has not elapsed, the engine unit 302 returns the process to S801b and determines whether it is possible to detect the OFF state of the registration sensor 35. If the engine unit 302 determines in S801b that the rear end detection period Treg_window has elapsed, the engine unit 302 advances the process to S802b.

In S802b, if the engine unit 302 cannot detect that the registration sensor 35 is turned off before the trailing edge detection period Treg_window has elapsed, the engine unit 302 determines that a sticky paper jam has occurred near the registration sensor 35. In this case, the engine unit 302 stops the printing operation and ends the process of FIG. 8(a). On the other hand, in S802b, if the engine unit 302 is able to detect that the registration sensor 35 is turned off before the rear end detection period Treg_window elapses, the engine unit 302 returns to the process of FIG. 7 to continue the process.

(Fixing retention jam detection)
Referring to FIG. 8(b), the fixing retention jam detection by the fixing sensor 37 detecting the trailing edge of the pressure-bonded paper will be described in detail. Fixing retention jam detection is an example of the rear end reference operation. In S800c, the engine unit 302 calculates a detection start time Tfsr for starting detection of the trailing edge of the pressure-bonded paper by the fixing sensor 37, and starts a timer for the detection start time Tfsr. The detection start time Tfsr can be calculated using the equation (1) already explained. In S801c, the engine unit 302 refers to the detection start time Tfsr timer started in S800c, and determines whether the detection start time Tfsr has elapsed (Tfsr timer≧Tfsr).

If the engine unit 302 determines in S801c that the detection start time Tfsr has not elapsed, the process returns to S801c. If the engine unit 302 determines in S801c that the detection start time Tfsr has elapsed, the engine unit 302 advances the process to S802c. In S802c, the engine unit 302 calculates a detection period Tfsr_window for detecting the trailing edge of the pressure-bonded paper by the fixing sensor 37, and starts a timer for the detection period Tfsr_window. The detection interval Tfsr_window can be calculated using the equation (2) already explained.

In S803c, the engine unit 302 determines whether the fixing sensor 37 is turned off, and if it is determined that it is not turned off, the process advances to S804c. In S804c, the engine unit 302 refers to the detection interval Tfsr_window timer and determines whether the detection interval Tfsr_windo has been reached. If the engine unit 302 determines in S804c that the detection interval Tfsr_window has not been reached, the process returns to S803c, and if it determines that the detection interval Tfsr_window has been reached, the engine unit 302 advances the process to S805c. That is, if the engine unit 302 cannot detect that the fixing sensor 37 is turned off before the detection interval Tfsr_window timer reaches the detection interval Tfsr_window, the engine unit 302 advances to the process of S805c. In step S805c, the engine unit 302 determines that a stuck paper jam has occurred near the fixing sensor 37, stops the printing operation, and ends the process of FIG. 8(b). In step S803c, if the engine unit 302 can detect that the fixing sensor 37 is turned off before the detection interval Tfsr_window timer reaches the detection interval Tfsr_window, the engine unit 302 ends the process of FIG. 8B.

In this way, the engine section 302 measures the length of the sheet P according to the output of the MP conveyance sensor 52, which is different from the registration sensor 35, and the registration sensor 35 detects the rear end of the sheet P based on the length of the sheet P. judge whether it is the right time to do so. Even if there is a change in the output signal of the registration sensor 35 after the registration sensor 35 detects the leading edge of the sheet P, if the timing at which the trailing edge of the sheet P is not detected by the registration sensor 35 is not the same, the output signal will change. Ignore change. Furthermore, when the timing is such that the rear end of the sheet P is detected by the registration sensor 35, the engine section 302 detects the rear end of the sheet P according to a change in the output signal.

In the first embodiment, control was described in which the registration sensor 35 detects the trailing edge of the pressure-bonded paper using the size (length) of the sheet actually conveyed within the image forming apparatus.
In the first embodiment, control using the length measured by the MP conveyance sensor 52 has been described, but the present invention is not limited to this. As long as the conveyance sensor is installed upstream of the registration sensor 35 in the conveyance direction and is capable of measuring the length of the pressure-bonded paper, this control can be applied even if the tray on which the pressure-bonded paper is installed is not an MP tray. Can be done.

Further, in the first embodiment, a case has been described in which LTR size is specified from the controller unit and printing is performed in a state where LTR size pressure-bonded paper is installed in the paper feed unit. However, this control can also be applied to a print operation when the specification of the controller unit 301 and the sheet size installed in the paper feed unit do not match. Further, this control can also be applied to a printing operation in which the controller unit 301 specifies printing of an irregular size.
As described above, according to the first embodiment, even when there is a possibility that the rotating member is rotated at a portion other than the rear end, erroneous detection of the rear end of the recording material can be suppressed.

In the first embodiment, when the registration sensor 35 detects the trailing edge of the pressure-bonded paper, the length of the pressure-bonded paper measured by the MP transport sensor 52 disposed upstream of the registration sensor 35 in the transport direction is used. The control for detecting the trailing edge of the sheet by the registration sensor 35 has been described. In the second embodiment, control will be described in the case where there is no conveyance sensor capable of measuring the length of the sheet P upstream of the registration sensor 35. Specifically, when the registration sensor 35 detects the trailing edge of the pressure-bonded paper, the length of the pressure-bonded paper measured by the fixing sensor (second detection sensor) 37 located downstream of the registration sensor 35 in the transport direction is Control for detecting the trailing edge of the sheet by the registration sensor 35 will be described. That is, the fixing sensor 37 is provided downstream of the registration sensor 35 in the conveyance direction, and functions as a third detection means for detecting the leading edge and trailing edge of the sheet P. The engine unit 302 measures the length of the pressure-bonded paper based on the detection result of the fixing sensor 37.

Further, the engine control unit 302a detects the rear end of the sheet P when the output signal of the registration sensor 35 satisfies a predetermined condition. In the first embodiment, the predetermined condition was whether the magnitude of the output signal of the register sensor 35 exceeded a predetermined value. In this example, a method of detecting the rear end of the sheet P under conditions different from those in Example 1 will be described using the results after removing chattering, which will be described later.

The engine section 302 of the second embodiment includes a registration sensor counter 309 (counter) in order to remove chattering (see FIG. 3). The engine control unit 302a of the engine unit 302 ignores changes in the output signal from the time the output signal of the register sensor 35 changes until the count number counted by the register sensor counter 309 reaches a predetermined count number. As will be described later, the predetermined count number includes a first count number (high precision) and a second count number (low precision) that is larger than the first count number.

The engine control unit 302a of the engine unit 302 sets the timing at which the rear end of the sheet P is detected by the registration sensor 35 based on the length of the sheet P. If the timing is not such that the rear end of the sheet P is detected by the registration sensor 35, the engine control unit 302a sets the predetermined count number to the second count number. On the other hand, when the timing is such that the rear end of the sheet P is detected by the registration sensor 35, the engine control unit 302a sets the predetermined count number to the first count number. Note that the configuration of the image forming apparatus, the system configuration, and the registration sensor configuration are the same as those described in FIG. 1, FIG. 2(B), and FIG. 3 of the first embodiment, so detailed descriptions thereof will be omitted. However, in the second embodiment, a configuration without the MP conveyance sensor 52 described in FIG. 1 will be described.

[Overview of printing operation in Example 2]
In the second embodiment, an operation will be described as an example in which two sheets of LTR-sized pressure-bonded paper are printed from the MP tray 50 by specifying, for example, an irregular size from the controller unit 301. The image forming apparatus has a function that allows printing by specifying a custom size, assuming a user who uses a custom size. When printing an irregularly sized sheet P with the image forming apparatus, the engine unit 302 prints the sheet P installed in the MP tray 50 if the size (length of the sheet in the transport direction) is within the maximum support size. Appropriate printing can be performed according to the size of the sheet P. In this case, the engine unit 302 can print any size within the maximum support size without causing conveyance failures such as paper jams.

If the size of the sheet P placed on the MP tray 50 is unknown, the image forming apparatus performs image formation and transport control based on the maximum size of the sheet P placed on the MP tray 50. Therefore, when the length of the sheet P is not measured, the engine unit 302 uses the registration sensor 35 to specify the length of the sheet P based on the length of the largest sheet P among the sheets P on which an image forming operation is possible in the image forming apparatus. The timing to start detecting the trailing edge of the sheet may be determined. Then, at the timing when the sheet size of the sheet P is measured and determined by the conveyance sensor, image forming control and conveyance control are changed in accordance with the sheet size. Thereby, it is possible to perform a printing operation without causing transport defects and suppressing the occurrence of image defects. In the second embodiment, image formation and transport control are performed with the maximum support size that can be installed on the MP tray 50 being LGL size (215.9 mm x 355.6 mm).

FIG. 9 is a timing chart showing image formation and paper feeding control in the second embodiment. FIGS. 9(i) to (iii) are similar waveforms to FIGS. 6(i) to (iii), FIG. 9(iv) is similar to FIG. 6(v), and FIG. 9(vii) is similar to FIG. 6(vi), respectively. shows. FIG. 9(v) shows how the value of the register sensor counter 309 changes (970), which will be described later. FIG. 9(vi) shows the output result of the registration sensor 35 after chattering has been removed (980), which will be described later. Note that in FIG. 6, the numerals in the 700s are used as numerals in the 900s in FIG. 9, and only the numerals are used for those having the same meaning as the timing explained so far.

(Chattering removal control)
First, the chattering removal control in the second embodiment will be explained using FIG. 9. When the leading or trailing edge of the sheet P reaches the register sensor 35, electrical noise or mechanical sensor flag bouncing may occur due to the shape and characteristics of the sensor, which may cause the sensor output result to become unstable. There may be cases where it is not possible to do so. A similar problem may occur with the registration sensor 35, and if the output result of the registration sensor 35 is not stable, the conveyance control of the engine section 302 may be affected. Hereinafter, a state in which the output result of the register sensor 35 is not stable and repeatedly changes between ON and OFF in a short period of time will be referred to as chattering. Therefore, the engine section 302 does not directly use the output result (950) of the registration sensor 35 for control, but uses the sensor output result (980) after chattering has been removed. In the second embodiment, there are two types of detection thresholds used for chattering removal: a low-accuracy threshold (971) and a high-accuracy threshold (972).

Chattering removal is a control in which the output result of the register sensor 35 is determined when the same result is output for a predetermined period of time. For example, an example will be described in which chattering is removed from the leading edge of the sheet P using a high-precision threshold value (972). At the timing when the leading edge of the sheet P reaches the registration sensor 35, the output result of the registration sensor 35 turns ON (951). At this timing, the register sensor detection counter (970) starts counting. The engine unit 302 continues to count the register sensor detection counter while the output result of the register sensor 35 is ON. At chattering removal leading edge registration sensor arrival timing 981 (t31) when the registration sensor detection counter reaches the high precision threshold (972), the output result of the registration sensor 35 after chattering removal is turned ON. The engine section 302 performs the following control using the detection result (981) of the leading edge of the sheet P.

(Low precision threshold and high precision threshold)
Also, the difference between the low precision threshold (971) and the high precision threshold (972) will be explained. Depending on which threshold value is used, the time from the output result of the registration sensor 35 to determining the output result of the registration sensor (980) after chattering removal changes. In the second embodiment, the determination timing of the register sensor output result after chattering removal is earlier (shorter) for the high-accuracy threshold (972) than for the low-accuracy threshold (971). In other words, since the output result of the register sensor 35 is determined at a timing closer to that of the register sensor 35, the sensor output result whose chattering is removed using the high-precision threshold value (972) is more accurate.

The low accuracy threshold (971) and the high accuracy threshold (972) are thresholds for determining how long the state must continue after the output signal of the registration sensor 35 changes to determine that the registration sensor 35 has rotated. For example, if a high-accuracy threshold (972) is set, it is determined that the register sensor 35 has rotated when the time during which the magnitude of the output signal of the register sensor 35 exceeds a predetermined value reaches a first length. Ru. On the other hand, when the low accuracy threshold (971) is set, if the time during which the magnitude of the output signal of the register sensor 35 exceeds a predetermined value reaches a second length that is longer than the first length, It is determined that the registration sensor 35 has rotated. In other words, when the low accuracy threshold (971) is set, even if the time during which the magnitude of the output signal of the registration sensor 35 exceeds a predetermined value reaches the first length, it is not determined that the registration sensor has rotated.

The state in which the register sensor 35 becomes high level or the state in which it becomes low level can be a state in which the magnitude of the output signal of the register sensor 35 exceeds a predetermined value. Further, in this embodiment, the first length is 20 ms and the second length is 70 ms.

When the adhesive portion 502 of the pressure bonding paper comes into contact with the registration sensor 35, the registration sensor 35 rotates. However, at this time, the low level (or high level) of the output signal of the registration sensor 35 is shorter than the time when the low accuracy threshold (971) is set, and it is not determined that the registration sensor 35 has rotated.

In the second embodiment, whether this threshold is set to a low-accuracy threshold (971) or a high-accuracy threshold (972) is determined depending on whether or not it is time for the adhesive part 502 of the pressure-bonding paper to pass. . Note that if the low accuracy threshold (971) is set, in other words, the accuracy of chattering is constantly reduced, when the trailing edge of the crimp paper actually reaches and the registration sensor 35 rotates, it will take time as follows. Resulting in. In other words, when the high-accuracy threshold (972) is set, the trailing edge of the pressure-bonded paper can be detected in 20 ms, but when the low-accuracy threshold (971) is still set, 70 ms has elapsed. Otherwise, the trailing edge of the crimp paper cannot be detected. Therefore, if the low-accuracy threshold (971) is always set, the accuracy of detecting the position of the trailing edge of the pressure-bonded paper will decrease. Therefore, in the second embodiment, the threshold used for chattering removal (in other words, chattering accuracy) is changed from the low accuracy threshold (971) to the high accuracy threshold ( 972).

In the second embodiment, chattering is removed using a low-accuracy threshold (971) when the adhesive portion 502 of the pressure-bonded paper passes the registration sensor 35, thereby preventing false detection of the trailing edge of the pressure-bonded paper. However, if chattering removal using a low-accuracy threshold (971) is applied to the actual trailing edge of the sheet, the detection accuracy will decrease as described above, which may have a negative impact on sheet P conveyance control and image formation. be. Therefore, in the second embodiment, the low precision threshold (971) and the high precision threshold (972) are appropriately switched.

Next, image formation and paper feeding control in Example 2 will be explained using FIG. 9. The control according to the second embodiment makes it possible to prevent false detection of the trailing edge by the glue portion 502 without lowering the detection accuracy of the trailing edge of the pressure-bonded paper. In the second embodiment, regarding chattering removal, a high-precision threshold value (972) is used to detect the leading edge of the pressure-bonded paper. On the other hand, the trailing edge of the pressure bonded paper is detected while being controlled by switching between a low precision threshold (971) and a high precision threshold (972).

(1st photo)
The engine unit 302 performs the same control as that described using FIG. 4, and outputs a /TOP signal (911) and feeds the first sheet of pressure-bonded paper (931). The engine unit 302 removes chattering at the timing when the registration sensor 35 detects the leading edge of the sheet P fed from the MP tray 50 (951). The engine unit 302 determines the position of the tip of the pressure-bonded paper (981), and temporarily stops the paper feed motor 420 (921). After that, the paper feed motor 420 is restarted and the sheet P is fed again so that the toner image formed on the intermediate transfer belt 80 and the leading edge of the pressure-bonded paper waiting at the registration sensor 35 match in the secondary transfer section. (922).

The engine unit 302 measures Treg_max (954) at the paper refeed timing t32 (922), the maximum time to start detection by the pressure bonded paper trailing edge registration sensor (hereinafter referred to as the maximum time to start detection). The maximum detection start time Treg_max (954) can be determined using equation (7).
Treg_max = (maximum support size/conveying speed) - registration variation early arrival time
Formula (7)
The maximum supported size in the second embodiment is the LGL size. The registration variation early arrival time is as explained in the first embodiment.

The engine unit 302 sets the registration sensor trailing edge detection threshold used to remove chattering to a high precision threshold (972), assuming that the trailing edge of the pressure-bonded paper will arrive after the measurement of the maximum detection start time Treg_max is completed. . In other words, chattering is removed using the low accuracy threshold (971) until the measurement of the maximum detection start time Treg_max is completed.

As described in the first embodiment, when the adhesive portion 502 approaches the press-bonded paper while passing through the registration sensor 35, the output result of the registration sensor 35 changes from ON to OFF (952). The engine section 302 removes chattering at the timing when the output result of the registration sensor 35 changes from ON to OFF. However, as explained in the first embodiment, the output result of the register sensor 35 returns from OFF to ON before the register sensor detection counter reaches the low accuracy threshold (timing t33), so the output result of the register sensor 35 after chattering is removed remains ON. Thereby, the engine unit 302 can prevent erroneously detecting the rear end of the pressure-bonded paper.

Thereafter, at timing t34 when the actual trailing edge of the pressure-bonded paper reaches the registration sensor 35 (953), chattering is removed using a low accuracy threshold (971). The registration sensor output result after chattering is removed turns OFF at the rear end registration sensor passing timing 982 after chattering is removed.

In the case of specifying an irregular size, it is not known what sheet size the sheet P is placed on the MP tray 50. Therefore, in the case of a printing operation specifying an irregular size, the engine unit 302 performs control assuming that the trailing edge of the sheet P of the maximum support size is detected. Therefore, depending on the size of the sheet P actually placed on the MP tray 50, the trailing edge of the sheet P, which should originally be detected with high accuracy using the high-accuracy threshold (972), may be detected using the low-accuracy threshold (971). (982) Further, the trailing edge detection section Treg_window (955) is a section after the maximum detection start time Treg_max for the maximum support size has elapsed, and the trailing edge of the pressure-bonded paper in Example 2 is detected before this section.

When the pressure-bonded paper that has passed through the registration sensor 35 reaches the fixing sensor 37 (991), measurement of the length of the pressure-bonded paper by the fixing sensor 37 is started from there. The length measurement can be calculated using the time during which the fixing sensor 37 is ON (the time from 991 to 992) (Equation (8)).
Length = Fixing sensor ON time/Transportation speed Formula (8)

Thereafter, in the same way as the operation described with reference to FIG. 6, if the registration sensor 35 is able to normally detect the trailing edge of the pressure-bonded paper (982), the following control is performed. That is, the engine unit 302 starts fixing retention jam detection (993 Tfsr, 994 Tfsr_window) by the fixing sensor 37. After the engine unit 302 normally detects the leading and trailing ends of the pressure-bonded paper (991, 992), the engine unit 302 directly discharges the pressure-bonded paper to the outside of the machine and ends the printing operation for the first sheet. In this way, the maximum support size is used for the first sheet of pressure bonding paper.

(2nd photo)
Next, the second image will be explained. The engine unit 302 performs control so that printing can be performed normally even if a sheet P of LGL size, which is the maximum supported size, is placed on the MP tray 50 because of the irregular size specification. In other words, the image forming interval and paper feeding interval for the first and second sheets are both set assuming LGL size (912, 932).

The engine unit 302 removes chattering at the timing when the registration sensor 35 detects the leading edge of the pressure-bonded paper fed from the MP tray 50 (956). The engine unit 302 determines the position of the tip of the pressure-bonded paper (983), and temporarily stops the paper feed motor 420 (923). After that, the paper feed motor 420 is restarted and the pressure paper is re-feeded so that the toner image formed on the intermediate transfer belt 80 and the leading edge of the pressure paper waiting at the registration sensor 35 match in the secondary transfer section. (924).

Similarly to the first sheet, the engine unit 302 measures the detection start time Treg (959) at the paper refeed timing t35 (924). The detection start time Treg (959) is different from the maximum detection start time Treg_max for the first image, and can be determined by the equation (4) described in the first embodiment. As the sheet size, the length calculated by equation (8) when the first sheet of pressure-bonded paper passes the fixing sensor 37 (992) is used.

The engine unit 302 sets the registration sensor rear end detection threshold for chattering removal to a low accuracy threshold (971) during the period (959) until the measurement is completed at the detection start time Treg. Similarly to the first sheet, the engine section 302 does not detect the OFF output of the registration sensor 35 due to the glue section 502 as OFF (957). This makes it possible to prevent erroneous detection of the trailing edge position of the pressure-bonded paper.

The second image uses the length measurement results from the first image, and after completing the measurement of the detection start time Treg, changes the registration sensor rear end detection threshold for chattering removal from the low accuracy threshold (971) to the high accuracy threshold (972). Switch to The engine unit 302 detects the trailing edge of the press-bonded paper using the registration sensor 35 during the trailing edge detection section Treg_window (960).

At timing t36 when the actual trailing edge of the pressure-bonded paper reaches the registration sensor 35 (958), chattering is removed using a high-accuracy threshold (972). Then, the register sensor output result after chattering is removed becomes OFF (984). Thereby, the registration sensor 35 can detect the trailing edge of the pressure-bonded paper with higher accuracy than the first sheet, and it is possible to minimize the influence of subsequent control.

The engine unit 302 starts fixing retention jam detection (995 Tfsr, 996 Tfsr_window) by the fixing sensor 37. After the engine unit 302 normally detects the leading and trailing edges of the pressure-bonded paper (997, 998), the engine unit 302 directly discharges the pressure-bonded paper to the outside of the machine and ends the printing operation for the second sheet. In this way, for the second sheet of press paper, the length measurement result of the first sheet of press paper is used.

In this manner, in the second embodiment as well, the engine control unit 302a sets the detection period (Treg_window) in which the trailing edge of the sheet P is detected when the output signal of the registration sensor 35 satisfies a predetermined condition to the output signal of the fixing sensor 37. Set based on.
In the second embodiment, the predetermined condition is whether the time during which the output signal of the register sensor 35 exceeds a predetermined value has reached the first length (the count number has reached the first count number). whether or not).

Even if the output signal of the registration sensor 35 satisfies a predetermined condition before the rear end detection section Treg_window (before the detection start time Treg), the engine control unit 302a does not detect the rear end of the sheet P and performs the rear end reference operation. is not executed either.

On the other hand, the engine control unit 302a determines that the time during which the output signal of the registration sensor 35 exceeds a predetermined magnitude outside the rear end detection section Treg_window has reached a second length longer than the first length (count number reaches the second count), the trailing edge of the sheet P can be detected.

In this way, within the trailing edge detection section Treg_window, the output signal of the registration sensor 35 is processed based on the high precision threshold (972), and outside the trailing edge detection section Treg_window, the output signal of the registration sensor 35 is processed based on the low precision threshold (971). , detects the rear end of the sheet P.

As described above, the length of the first sheet P cannot be measured by the fixing sensor 37. In this case, the set sheet size is different from the actually used sheet P, and the time for the trailing edge of the sheet P to reach the registration sensor 35 may be outside the trailing edge detection section Treg_window. According to the control of this embodiment, even if the trailing edge of the sheet P reaches the registration sensor 35 outside the trailing edge detection section Treg_window, the trailing edge of the sheet P is detected using the low accuracy threshold (971). can do.

(Transport control of Example 2)
10 and 11 are control flowcharts of the engine section 302 in the second embodiment. The flowcharts in FIGS. 10 and 11 are flowcharts executed when printing one sheet. Detection of the leading and trailing ends of the press-bonded paper by the registration sensor 35 will be described in detail with reference to FIG. 10 . FIG. 10 is a flowchart when the registration sensor 35 detects the leading edge and trailing edge of the fed pressure-bonded paper. In other words, the engine unit 302 performs processing depending on whether the registration sensor 35 detects the leading edge of the pressure-bonded paper (S1001a), the paper is being conveyed (S1008a), or the trailing edge is detected (S1012a). Note that the output results of the registration sensor 35 explained in the flowchart are the results after chattering removal explained in FIG. 9(vi). First, detection of the leading edge of the pressure-bonded paper and its processing will be explained.

In step S1000a, upon receiving the sheet size designation command, print reservation command, and print start command from the controller unit 301, the engine unit 302 starts feeding paper and outputs a /TOP signal to the controller unit 301. In S1001a, the engine unit 302 determines whether the output of the registration sensor 35 on the conveyance path changes (registration sensor edge detected) and (&), and whether the change is from OFF to ON. If the engine unit 302 determines in S1001a that the output of the register sensor 35 has changed and that an edge change from OFF to ON has been detected, the engine unit 302 advances the process to S1002a. If the engine unit 302 determines in S1001a that the condition is not satisfied, the process advances to S1008a. In S1002a, the engine unit 302 stops the paper feed motor 420 and temporarily stops the conveyance in order to align the toner image formed on the intermediate transfer belt 80 with the leading edge of the pressure bonding paper being conveyed. Note that depending on the position of the toner image on the intermediate transfer belt 80, the conveyance may not be stopped. In the second embodiment, a case will be described in which transport is temporarily stopped, similar to the timing chart in FIG. 9 .

In S1003a, the engine unit 302 determines whether it is time to refeed paper. If the engine unit 302 determines in S1003a that it is not time to refeed the paper, the process returns to S1003a. In this case, the engine unit 302 waits until the paper refeeding timing occurs when the toner image formed on the intermediate transfer belt 80 and the leading edge of the pressure-bonded paper temporarily stopped at the position of the registration sensor 35 match at the secondary transfer unit. do.

If the engine unit 302 determines in S1003a that the paper refeeding timing has been reached, the process advances to S1004a. In S1004a, the engine unit 302 restarts the temporarily stopped conveyance of the pressure-bonded paper. In S1005a, the engine unit 302 calculates a detection start time Treg for starting detection of the trailing edge of the pressure-bonded paper by the registration sensor 35, and starts a Treg timer. The detection start time Treg can be determined by the equation shown in equation (4) when the length measurement by the fixing sensor 37, which will be described later, has been completed. On the other hand, if the length measurement of the pressure-bonded paper has not been completed, the maximum detection start time Treg_max is set as the detection start time Treg, as shown in equation (7). In S1006a, the engine unit 302 sets the registration sensor rear end detection threshold for chattering removal to a low accuracy threshold. In S1007a, the engine unit 302 starts measuring the length of the pressure-bonded paper using the fixing sensor 37. The process of S1007a will be explained with reference to FIG. 11(c). The above is the process performed when the registration sensor 35 detects the leading edge of the sheet.

Next, processing performed when the press-bonded paper is passing through the registration sensor 35 will be described. While the pressure-bonded paper is being conveyed, the output result of the registration sensor 35 is ON. This is the result after chattering was removed using the low accuracy threshold set in S1006a. In S1008a, the engine unit 302 determines whether there is no change in the output of the registration sensor 35 and whether it is maintained in the ON state. If the engine unit 302 determines in S1008a that there is no change in the output of the register sensor 35 and that it is ON, the engine unit 302 advances the process to S1009a. If the engine unit 302 determines in S1008a that the condition is not satisfied, the process advances to S1012a. While the output result of the registration sensor 35 is ON, in S1009a, the engine unit 302 determines whether the Treg timer started in S1005a has reached the detection start time Treg. In S1009a, if the engine unit 302 determines that the Treg timer has reached the detection start time Treg, the engine unit 302 advances the process to 1010a, and if it determines that the Treg timer has not reached the detection start time Treg, the engine unit 302 advances the process to 1012a.

In Example 2, in the case of the first sheet of pressure-bonded paper, the detection start time Treg is calculated by the detection start maximum time Treg_max. In the second embodiment, as shown in the description of FIG. 9, for the first sheet of pressure-bonded paper, the condition of S1009a is not met before the trailing edge of the pressure-bonded paper that is actually conveyed passes the registration sensor 35. This is because the detection start time Treg calculated in S1005a is calculated using equation (7). On the other hand, for the second sheet of pressure-bonded paper, the detection start time Treg is updated according to the length measured by the fixing sensor 37, as described in FIG. The condition of S1009a is met. In S1010a, the engine unit 302 switches the registration sensor rear end detection threshold for chattering removal from a low-accuracy threshold to a high-accuracy threshold. In S1011a, the engine unit 302 starts detecting a jam at the register. The process of S1011a will be explained with reference to FIG. 11(a).

Finally, the detection of the trailing edge of the pressure-bonded paper and its processing will be explained. In S1012a, the engine unit 302 determines whether the output of the registration sensor 35 on the conveyance path changes as a result of detecting the rear end, and whether the output result changes from ON to OFF (edge). If the engine unit 302 determines in S1012a that there is a change in the output of the register sensor 35 and that the change is from ON to OFF, the process proceeds to S1013a, and if the conditions are not met, the process proceeds to S1001a. Return to

In step S1013a, the engine unit 302 determines that the rear end has been successfully detected, and ends the registration jam detection started in step S1011a. In S1014a, the engine unit 302 starts fixing retention jam detection, and then ends the process. A flowchart of fixing retention jam detection in S1014a is shown in FIG. 11(b). Note that steps S1000c to S1005c in FIG. 11(b) have been explained in steps S800c to S805c in FIG. 8(b) of the first embodiment, so their explanation will be omitted. Further, FIG. 11(a) shows a flowchart regarding detection of a jam at the register. Note that the processing in S1000b to S1002b in FIG. 11A is the same as the control described in S800b to S802b in FIG.

(Length measurement process)
The length measurement process shown in FIG. 11(c) will be explained. In S1000d, the engine unit 302 determines whether there is a change in the output of the fixing sensor 37 and whether the change is from OFF to ON (that is, an ON edge). If the engine unit 302 determines in S1000d that it is not an ON edge, the process returns to S1000d, and if it determines that it is an ON edge, the engine unit 302 advances the process to S1001d. In S1001d, the engine unit 302 starts a length measurement timer. In S1002d, the engine unit 302 determines whether there is a change in the output of the fixing sensor 37 and the change is from ON to OFF (ie, OFF edge). If the engine unit 302 determines in S1002d that it is not an OFF edge, the process returns to S1002d, and if it determines that it is an OFF edge, the engine unit 302 advances the process to S1003d. In S1003d, the engine unit 302 stops the length measurement timer and calculates the length of the pressure bonding paper. The length of the pressure bonding paper can be calculated using equation (8).

In the second embodiment, control is performed in which the registration sensor 35 detects the trailing edge of the sheet P by measuring and using the sheet size (length) actually conveyed in the image forming apparatus with a conveyance sensor located downstream of the rotary shutter. explained. In the second embodiment, the control using the length measured by the fixing sensor 37 was explained, but if the conveyance sensor is installed downstream of the registration sensor 35 in the conveyance direction and is capable of measuring the length, the control in the second embodiment can be applied. can be applied. In addition, in Example 2, we have explained the control in printing on irregular size sheets, but even in printing of standard size as in Example 1, the controller unit specification and the sheet size installed in the paper feed unit can be controlled. This can also be applied to a print operation when there is a mismatch.
As described above, according to the second embodiment, even when there is a possibility that the rotating member is rotated at a portion other than the rear end, erroneous detection of the rear end of the recording material can be suppressed.

As described above, according to the control shown in each example of the present embodiment, the engine control unit 302a measures the length of the sheet P using a sensor (second detection sensor) different from the registration sensor 35, Based on the result, a trailing edge detection section Treg_window is set.

Note that even if there is a second detection sensor means installed upstream of the registration sensor 35, the output signal of the registration sensor 35 may be processed using the above-described chattering removal method. That is, for example, in the first embodiment, when detecting the trailing edge of the sheet P and performing the trailing edge reference operation according to the output signal of the registration sensor 35, the chattering removal control of the second embodiment can be used. Specifically, the engine control unit 302a uses a high-accuracy threshold (972) within the rear end detection section Treg_window (755) and uses a low-accuracy threshold (971) outside the rear end detection section Treg_window (755), based on the output signal of the registration sensor 35. Thus, the rear end of the sheet P can be detected.

The use of pressure-bonded paper is just one example of the reason why the rotary shutter 35a is rotated at a timing different from the rear end of the sheet P. According to the control shown in each example of the present embodiment described above, when the rotary shutter 35a is rotated at a timing different from that of the rear end of the seat P, the control unit of the engine section 302 controls the rear end of the seat P. False detection can be suppressed. The engine control unit 302a performs the control shown in each example of this embodiment only when a specific sheet such as pressure-bonded paper is used (for example, when a specific sheet is specified as the sheet P to be used). It's okay.

35 Registration sensor 51 Pick-up roller 302 Engine section 302a Engine control section

Claims (17)

An image forming apparatus for forming an image on a recording material,
A first detection sensor includes a rotating member that can come into contact with a recording material conveyed in a conveying direction, and outputs a first signal in accordance with rotation of the rotating member, wherein the rotating member a first detection sensor configured to rotate when pushed by the leading edge of the recording material and when the rear end of the recording material passes;
a second detection sensor that is different from the first detection sensor and outputs a second signal in response to passage of the recording material;
a control unit configured to detect the rear end of the recording material based on the first signal after the rotating member is rotated by the leading end of the recording material;
Equipped with
The control unit sets a detection section for detecting the rear end based on the second signal when the first signal satisfies a predetermined condition;
The image forming apparatus is characterized in that the control unit does not detect the trailing edge even if the first signal satisfies the predetermined condition before the detection period. The image forming apparatus according to claim 1, wherein the predetermined condition includes whether the magnitude of the first signal exceeds a predetermined value. The image forming apparatus according to claim 2, wherein the second detection sensor is arranged upstream of the first detection sensor in the transport direction. The image forming apparatus according to claim 1, wherein the predetermined condition includes whether or not a time period during which the magnitude of the first signal exceeds a predetermined value reaches a first length. The image forming apparatus according to claim 4, wherein the second detection sensor is disposed upstream of the first detection sensor in the transport direction. The image according to claim 4, wherein the control unit detects the rear end when the time reaches a second length that is longer than the first length outside the detection section. Forming device. 7. The image forming apparatus according to claim 6, wherein the second detection sensor is disposed upstream of the first detection sensor in the transport direction. The second detection sensor is arranged downstream of the first detection sensor in the transport direction,
If the detection section is not set based on the second signal, the control section sets the detection section based on the length of the largest recording material among the recording materials on which image formation is possible. The image forming apparatus according to claim 6, characterized in that: An image forming apparatus for forming an image on a recording material,
A first detection sensor includes a rotating member that can come into contact with a recording material conveyed in a conveying direction, and outputs a first signal in accordance with rotation of the rotating member, wherein the rotating member a first detection sensor configured to rotate when pushed by the leading edge of the recording material and when the rear end of the recording material passes;
a second detection sensor that is different from the first detection sensor and outputs a second signal in response to passage of the recording material;
After the rotating member is rotated by the leading end of the recording material, at least one of transporting the recording material, forming an image on the recording material, and detecting a transport failure of the recording material is performed in accordance with the first signal. a controller configured to perform an operation related to the one;
Equipped with
The control unit sets a trigger period for executing the operation when the first signal satisfies a predetermined condition, based on the second signal,
The image forming apparatus is characterized in that the control unit does not execute the operation even if the first signal satisfies the predetermined condition before the trigger period. The image forming apparatus according to claim 9, wherein the predetermined condition includes whether the magnitude of the first signal exceeds a predetermined value. The image forming apparatus according to claim 10, wherein the second detection sensor is arranged upstream of the first detection sensor in the transport direction. 10. The image forming apparatus according to claim 9, wherein the predetermined condition includes whether the time during which the magnitude of the first signal exceeds a predetermined value reaches a first length. The image forming apparatus according to claim 12, wherein the second detection sensor is arranged upstream of the first detection sensor in the transport direction. The image forming apparatus according to claim 12, wherein the control unit executes the operation when the time reaches a second length that is longer than the first length outside the trigger section. Device. The image forming apparatus according to claim 14, wherein the second detection sensor is arranged upstream of the first detection sensor in the transport direction. The second detection sensor is arranged downstream of the first detection sensor in the transport direction,
If the trigger section is not set based on the second signal, the control section sets the trigger section based on the length of the largest recording material among the recording materials on which image formation is possible. The image forming apparatus according to claim 14. 17. The rotating direction of the rotating member when pushed by the leading end is the same as the rotating direction of the rotating member when the rear end passes. The image forming apparatus described above.

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