JP6146176B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet.

  2. Description of the Related Art Conventionally, an ultrasonic double feed detection technique for detecting double feed in which two sheets of paper are overlapped and conveyed using a double feed detection sensor is known. This ultrasonic multi-feed detection utilizes the fact that the transmission amount (reflection amount) of ultrasonic waves differs between when one sheet is overlapped and when two sheets are overlapped (during multi-feed). The double feed detection is performed by comparing the measured value of the amount (reflection amount) with a predetermined threshold. Incidentally, there is an envelope as a type of paper on which an image is formed. Due to the structure of the envelope, the degree of overlap of the paper varies depending on the location, and it is difficult to detect the occurrence of double feed in the envelope being conveyed using a normal double feed detection sensor.

  For example, Patent Document 1 discloses a transmitter that emits ultrasonic waves from at least one of two directions with respect to a sheet to be conveyed, and a sound wave that is emitted from the paper in response to the irradiated ultrasonic waves. A sheet conveying device including a detection sensor for detecting the image is disclosed. The transmitter emits ultrasonic waves from the direction corresponding to the operation mode for each type of paper, and the CPU detects whether or not the paper is being double fed based on the intensity of the sound waves detected. For example, in the operation mode (envelope mode) for detecting three or more double feeds, the ultrasonic wave is applied to the paper at an angle set by changing the direction of the transmitter.

JP2013-63820A

  However, in an image forming apparatus that does not have a special configuration for detecting double feeding of envelopes as described in Patent Document 1, one envelope to be conveyed is erroneously detected as double feeding. For this reason, conventionally, when the envelope is passed, detection is not performed by the multilayer detection sensor. In such a case, there has been a problem that double feed cannot be detected when double feed occurs in the envelope to be conveyed.

  In view of the above situation, there has been a demand for a method of detecting a double feed of a sheet with high probability when passing a sheet that is difficult to detect the occurrence of a double feed unless a special sensor is used.

  An image forming apparatus according to an aspect of the present invention includes a registration roller that can be separated, a transfer unit that transfers a toner image onto a sheet conveyed from the registration roller, and a sheet that is provided between the registration roller and the transfer unit. The registration roller is separated after the leading edge of the sheet reaches the transfer unit according to the determination result of the sheet detection unit to detect, the sheet type determination unit to determine the paper type of the conveyed sheet, and the sheet type determination unit A timing determination unit for determining timing. The timing determination unit makes the timing for separating the registration rollers earlier when the paper is a specific paper type than when the paper is another paper type.

In the image forming apparatus having the above-described configuration, when passing a sheet of a specific sheet type, in order to speed up the timing at which the registration roller is separated after the leading edge of the sheet reaches the transfer unit, the preceding sheet of the sheets that are being multi-fed is sent. Only the sheet is conveyed by the transfer unit, and the subsequent sheet remains in place. The remaining paper is detected by the paper detection unit.
Is stable.

  According to the image forming apparatus of the present invention, it is possible to detect a double feed of paper such as an envelope, which is difficult to accurately detect double feed, with high probability.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 3 is an explanatory diagram illustrating a configuration around a registration roller and a secondary transfer unit according to an embodiment of the present invention. 2 is a block diagram illustrating a hardware configuration of each unit of the image forming apparatus according to the embodiment of the present disclosure. FIG. FIG. 6 is an explanatory diagram showing the timing of registration roller separation when the first paper type according to an embodiment of the present invention reaches the secondary transfer portion. FIG. 10 is an explanatory diagram illustrating the timing of registration roller separation when a second paper type according to an embodiment of the present invention reaches a secondary transfer unit. It is explanatory drawing which shows reverse rotation of the registration roller at the time of loop creation which concerns on one embodiment of this invention. It is explanatory drawing which shows the operation conditions of papermaking when the registration roller which concerns on one embodiment of this invention reversely rotates. FIG. 10 is an explanatory diagram illustrating a sheet in which a second sheet returns in the reverse direction when the registration roller according to the embodiment of the present invention rotates in the reverse direction. 6 is a flowchart illustrating image forming processing according to an embodiment of the present invention.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the common member in each figure.

[Configuration example of image forming apparatus]
First, an outline of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.
FIG. 1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the image forming apparatus 1 forms an image on a sheet by an electrophotographic method, and has four colors of yellow (Y), magenta (M), cyan (C), and black (Bk). This is a tandem color image forming apparatus that superimposes toner. The image forming apparatus 1 includes a document transport unit 10, a paper storage unit 20, an image reading unit 30, an image forming unit 40, an intermediate transfer belt 50, a secondary transfer unit 60, and a fixing unit 80. .

  The document transport unit 10 includes a document feed table 11 on which a document G is set, a plurality of rollers 12, a transport drum 13, a transport guide 14, a document discharge roller 15, and a document discharge tray 16. Yes. The documents G set on the document feeder 11 are conveyed one by one to the reading position of the image reading unit 30 by the plurality of rollers 12 and the conveying drum 13. The conveyance guide 14 and the document discharge roller 15 discharge the document G conveyed by the plurality of rollers 12 and the conveyance drum 13 to the document discharge tray 16.

  The image reading unit 30 reads an image of the document G transported by the document transport unit 10 or the document placed on the document table 31 and generates image data. Specifically, the image of the original G is irradiated by the lamp L. The reflected light from the document G is guided in the order of the first mirror unit 32, the second mirror unit 33, and the lens unit 34 and forms an image on the light receiving surface of the image sensor 35. The image sensor 35 photoelectrically converts incident light and outputs a predetermined image signal. The output image signal is created as image data by A / D conversion.

  The image reading unit 30 has an image reading control unit 36. The image reading control unit 36 performs processing such as shading correction, dither processing, and compression on the image data created by the A / D conversion, and stores the image data in the RAM 103 (see FIG. 3) of the control unit 100. The image data is not limited to data output from the image reading unit 30 and may be data received from an external device such as a personal computer connected to the image forming apparatus 1 or another image forming apparatus.

  The paper storage unit 20 is disposed at the lower part of the apparatus main body, and a plurality of paper storage units 20 are provided according to the size and type of paper. The sheet is fed by the sheet feeding unit 21 and sent to the transport unit 23, and is transported by the transport unit 23 to the secondary transfer unit 60 having a transfer position. Further, a manual feed portion 22 is provided in the vicinity of the paper storage portion 20. From the manual feed section 22, paper of a size not stored in the paper storage section 20, tag paper having a tag, special paper such as an OHP sheet is sent to the transfer position. In FIG. 1, a sheet S fed by the sheet feeding unit 21 is denoted by a symbol “S”.

  An image forming unit 40 and an intermediate transfer belt 50 are disposed between the image reading unit 30 and the paper storage unit 20. The image forming unit 40 includes four image forming units 40Y, 40M, 40C, and 40K in order to form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (Bk). .

  The first image forming unit 40Y forms a yellow toner image, and the second image forming unit 40M forms a magenta toner image. The third image forming unit 40C forms a cyan toner image, and the fourth image forming unit 40K forms a black toner image. Since these four image forming units 40Y, 40M, 40C, and 40K have the same configuration, only the first image forming unit 40Y will be described here.

  The first image forming unit 40Y includes a drum-shaped photoconductor 41, a charging unit 42 arranged around the photoconductor 41, an exposure unit 43, a developing unit 44, and a cleaning unit 45. The photoreceptor 41 is rotated by a drive motor (not shown). The charging unit 42 applies a charge to the photoconductor 41 and uniformly charges the surface of the photoconductor 41. The exposure unit 43 performs an exposure operation on the surface of the photoconductor 41 based on image data read from the original G or image data transmitted from an external device, thereby forming an electrostatic latent image on the photoconductor 41. Form.

  The developing unit 44 attaches yellow toner to the electrostatic latent image formed on the photoconductor 41 using, for example, a two-component developer composed of toner and carrier. As a result, a yellow toner image is formed on the surface of the photoreceptor 41.

  The developing unit 44 of the second image forming unit 40M attaches magenta toner to the photoconductor 41, and the developing unit 44 of the third image forming unit 40C attaches cyan toner to the photoconductor 41. Then, the developing unit 44 of the fourth image forming unit 40K adheres black toner to the photoconductor 41.

The toner image formed on the photoreceptor 41 is transferred to an intermediate transfer belt 50 that is an example of an image carrier. The intermediate transfer belt 50 is formed in an endless shape and is stretched around a plurality of rollers. The intermediate transfer belt 50 is rotationally driven in a direction opposite to the rotation (movement) direction of the photoconductor 41 by a drive motor (not shown).
The cleaning unit 45 removes the toner remaining on the surface of the photoreceptor 41 after the toner image is transferred to the intermediate transfer belt 50.

  A primary transfer portion 51 is provided at a position on the intermediate transfer belt 50 that faces the photoreceptor 41 of each of the image forming units 40Y, 40M, 40C, and 40K. The primary transfer unit 51 primarily transfers the toner image formed on the photoreceptor 41 to the intermediate transfer belt 50 by applying a voltage having a polarity opposite to that of the toner to the intermediate transfer belt 50.

  When the intermediate transfer belt 50 is driven to rotate, the toner images formed by the four image forming units 40Y, 40M, 40C, and 40K are sequentially transferred onto the surface of the intermediate transfer belt 50. As a result, yellow, magenta, cyan, and black toner images are superimposed on the intermediate transfer belt 50 to form a color toner image.

  A belt cleaning device 53 faces the intermediate transfer belt 50. The belt cleaning device 53 cleans the surface of the intermediate transfer belt 50 that has finished transferring the toner image onto the paper.

  A secondary transfer unit 60 is disposed in the vicinity of the intermediate transfer belt 50 and downstream of the transport unit 23 in the sheet transport direction. The paper transported to the secondary transfer unit 60 may be displaced from the reference position in the paper width direction (main scanning direction) to any of the paper width direction as it is transported. In the image forming apparatus 1, in order to correct the misalignment of the sheet, the misregistration detection sensor between the registration roller 71 and the secondary transfer unit 60 and the registration roller 71 on the upstream side of the secondary transfer unit 60 in the sheet conveyance direction. 72 is provided. Further, a sheet detection sensor 73 is provided on the downstream side of the deviation detection sensor 72 in the sheet conveyance direction.

The secondary transfer unit 60 brings the paper whose misalignment has been corrected by the registration roller 71 into contact with the intermediate transfer belt 50 and secondarily transfers the toner image formed on the outer peripheral surface of the intermediate transfer belt 50 onto the paper.
The secondary transfer unit 60 has a secondary transfer roller 61. The secondary transfer roller 61 is pressed against the opposing roller 52 with the intermediate transfer belt 50 interposed therebetween. A portion where the secondary transfer roller 61 and the intermediate transfer belt 50 come into contact becomes a secondary transfer nip portion 62. The secondary transfer nip portion 62 is a transfer position where the toner image formed on the outer peripheral surface of the intermediate transfer belt 50 is transferred to the paper S.

  A fixing unit 80 is provided on the paper discharge side of the secondary transfer unit 60. The fixing unit 80 pressurizes and heats the paper to fix the transferred toner image on the paper. The fixing unit 80 includes, for example, a fixing upper roller 81 and a fixing lower roller 82 which are a pair of fixing members. The upper fixing roller 81 and the lower fixing roller 82 are arranged in pressure contact with each other, and a fixing nip portion is formed as a pressing portion between the upper fixing roller 81 and the lower fixing roller 82.

  A heating unit is provided inside the fixing upper roller 81. The outer peripheral portion of the fixing upper roller 81 is warmed by the radiant heat from the heating portion. Then, the heat of the fixing upper roller 81 is transmitted to the sheet, whereby the toner image on the sheet is thermally fixed.

  The sheet is conveyed so that the surface on which the toner image is transferred by the secondary transfer unit 60 (the surface to be fixed) faces the fixing upper roller 81, and passes through the fixing nip. Accordingly, the sheet passing through the fixing nip portion is pressed by the upper fixing roller 81 and the lower fixing roller 82 and heated by the heat of the upper fixing roller 81.

  A switching gate 24 is disposed downstream of the fixing unit 80 in the sheet conveyance direction. The switching gate 24 switches the conveyance path of the sheet that has passed through the fixing unit 80. That is, the switching gate 24 moves the paper straight when performing face-up paper discharge in which the image forming surface is discharged upward in single-sided image formation. As a result, the paper is discharged by the pair of paper discharge rollers 25. Further, the switching gate 24 guides the sheet downward when performing face-down paper discharge and double-sided image formation in which the image forming surface in single-sided image formation is discharged downward.

When face-down paper discharge is performed, after the sheet is guided downward by the switching gate 24, the sheet reverse transport unit 26 reverses the front and back and transports the sheet upward. As a result, the sheet whose front and back sides are reversed and whose image forming surface faces downward is discharged by the pair of discharge rollers 25.
When performing double-sided image formation, after the sheet is guided downward by the switching gate 24, the front and back are reversed by the sheet reversing conveyance unit 26, and sent again to the transfer position of the secondary transfer unit 60 by the refeed path 27.

  A post-processing device that folds the paper or performs stapling processing or the like on the paper may be disposed on the downstream side of the pair of paper discharge rollers 25.

[Configuration around registration roller and secondary transfer unit]
Here, the configuration around the registration roller 71 and the secondary transfer unit 60 will be described in detail with reference to FIG.
FIG. 2 is a plan view showing the positional relationship among the registration roller 71, the deviation detection sensor 72, the paper detection sensor 73, and the secondary transfer unit 60. FIG. 2 illustrates a state in which the first sheet S1 and the second sheet S2 are double-fed to the secondary transfer unit 60. As shown in FIG. 2, a deviation detection sensor 72 is disposed in the vicinity of the registration roller 71 on the downstream side in the sheet conveyance direction. Further, a sheet detection sensor 73 is arranged at a predetermined distance from the deviation detection sensor 72 on the downstream side in the sheet conveyance direction.

The registration roller 71 includes a driving roller 71a and a driven roller 71b disposed to face the upper side across the sheet conveyance path. The driving roller 71a and the driven roller 71b of the registration roller 71 can be pressed and separated in the vertical direction by a separation driving unit (not shown), and the driving roller 71a and the driven roller 71b are in pressure contact with each other. A nip portion 71c is formed between the driven rollers 71b. In the following description, it is described that the driving roller 71a and the driven roller 71b are pressed and separated from each other, that the registration roller 71 is pressed and separated.
Each roller shaft is supported by a bearing member (not shown) so as to be slidable in the axial direction, that is, the paper width direction (front side and back side of the image forming apparatus: main scanning direction). The registration roller 71 moves in the paper width direction. The swing drive unit can be composed of, for example, a rack and pinion mechanism and a drive motor that rotates the pinion of the rack and pinion mechanism in forward and reverse directions.
The driving roller 71a is rotated in the forward direction and the reverse direction by a roller driving unit (not shown), and a stepping motor can be used as a driving source of the roller driving unit, for example. The forward direction is a rotation direction when the sheet is conveyed to the secondary transfer unit 60. The above-described separation drive unit, swing drive unit, and roller drive unit have configurations well known to those skilled in the art, and detailed description thereof with reference to the drawings is omitted here.

  Here, an outline of the operation of the registration roller 71 will be described. The registration roller 71 swings in the sheet width direction orthogonal to the sheet conveyance direction with the sheet S sandwiched between the nip portions 71c according to the position of the side edge of the sheet detected by the deviation detection sensor 72. Thereby, the deviation of the paper in the paper width direction is corrected. When attention is paid to the paper width direction after the end of the swinging, the paper is moved by the registration roller 71 from a position with a deviation to a position in which the deviation in the paper width direction is corrected. Thereafter, the sheet detection sensor 73 disposed at a predetermined distance away from the deviation detection sensor 72 in the sheet conveyance direction detects the leading edge of the sheet with the deviation corrected. Then, a predetermined time after the sheet detection sensor 73 detects the leading edge of the sheet, the leading edge of the sheet reaches the transfer position of the secondary transfer unit 60. After the leading edge of the paper reaches the secondary transfer portion 60 and the secondary transfer nip portion 62, the registration roller 71 is separated when a time set according to the paper type described later has elapsed.

  As the deviation detection sensor 72, a line sensor in which a plurality of photoelectric conversion elements are arranged linearly along the paper width direction or an image sensor in which photoelectric conversion elements are arranged in a matrix is used. As the line sensor and the image sensor, a CCD type image sensor or a CMOS type (including MOS type) image sensor can be used. For the paper detection sensor 73, for example, a transmissive photosensor in which a light emitting member and a light receiving member are arranged to face each other, a reflective photosensor that detects reflected light from an object of emitted light, and the like are used. The paper detection sensor 73 is also used as a paper detection unit when a specific paper such as an envelope is being passed.

  A double feed detection sensor 74, which is an example of a double feed detection unit, is disposed on the upstream side of the registration roller 71 in the sheet conveyance direction (see FIG. 1). The double feed detection sensor 74 detects the double feed of the paper by irradiating the paper with ultrasonic waves and detecting the sound wave that is radiated from the paper. The double feed detection sensor 74 may be configured by a combination of a transmitter and a receiver that are arranged to face each other across the paper conveyance path.

  The image forming apparatus 1 includes a paper transport mechanism (not shown) that is driven and controlled by the control unit 100 and transports the paper S on which an image is formed. The sheet transport mechanism includes a roller disposed between the sheet feeding unit 21 and the manual feeding unit 22 of the image forming apparatus 1 and the registration roller 71, and a rotation driving unit (not shown) that rotates each roller. The As the rotation driving unit, a combination of a motor and various mechanisms and various actuators can be employed.

[Configuration of control system of image forming apparatus]
Next, a control system of the image forming apparatus 1 will be described with reference to FIG.
FIG. 3 is a block diagram illustrating a control system of the image forming apparatus 1.

  As illustrated in FIG. 3, the image forming apparatus 1 includes a control unit 100. The control unit 100 includes a communication unit 108, an image reading unit 30, an image processing unit 106, an image forming unit 40, a paper feeding unit 21, a secondary transfer unit 60, a fixing unit 80, and a registration roller driving mechanism via a system bus 107. 70 and the double feed detection sensor 74. Further, the control unit 100 is connected to the HDD 104, the operation display unit 105, the deviation detection sensor 72, and the paper detection sensor 73 via the system bus 107.

  The control unit 100 includes, for example, a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102 for storing programs executed by the CPU 101, setting values, and the like, and a RAM (Random) used as a work area of the CPU 101. Access Memory) 103. As the ROM 102, for example, an electrically erasable programmable ROM is used. The control unit 100 controls each block, that is, controls the entire apparatus.

For example, based on the detection result of the deviation detection sensor 72, the control unit 100 presses the registration roller 71 to sandwich the paper, and the swing control unit swings the registration roller 71 in the main scanning direction. It is an example.
The control unit 100 is an example of a paper type determination unit that determines the paper type of the conveyed paper.
Further, the control unit 100 is an example of a timing determination unit that determines the timing at which the registration roller 71 is separated after the leading edge of the paper reaches the secondary transfer unit 60 according to the determination result as the paper type determination unit. It is. For example, the ROM 102 stores a set value of timing for separating the paper type and the registration roller 71 in association with each other. The control unit 100 acquires a set value of the separation timing corresponding to the paper type of the sheet from the ROM 102, and controls the separation of the registration rollers 71 based on the set value of the timing.

  The HDD 104 stores image data of an original image obtained by reading by the image reading unit 30, or stores output image data and the like. The operation display unit 105 is a touch panel including a display such as a liquid crystal display (LCD) or an organic ELD (Electro Luminescence Display). The operation display unit 105 displays an instruction menu for the user, information about the acquired image data, and the like. Further, the operation display unit 105 includes a plurality of keys, receives input of various instructions, data such as characters and numbers, and outputs an input signal to the control unit 100.

  Image data generated by the image reading unit 30 and image data transmitted from a PC (personal computer) 120 which is an example of an external device connected to the image forming apparatus 1 are sent to the image processing unit 106 for image processing. Is done. The image processing unit 106 performs processes such as analog processing, A / D conversion, shading correction, and image compression on the received image data.

  The communication unit 108 receives job information relating to image formation transmitted from the PC 120 which is an external information processing apparatus via a communication line. The received job information is sent to the control unit 100 via the system bus 107.

  As described above, the registration roller driving mechanism 70 includes the registration roller 71 and a swing driving unit, a roller driving unit, and a separation driving unit (not shown). The registration roller driving mechanism 70 is driven and controlled by the control unit 100. The registration roller 71 is rocked by the rocking mechanism portion of the registration roller driving mechanism 70, the driving roller 71a is rotated by the roller driving portion, and the registration roller 71 is pressed and separated by the separation driving portion. In general, the roller driving section stops the driving roller 71a when the leading edge of the sheet is brought into contact with the nip 71c of the registration roller 71 to lock the sheet, and the driving roller 71a is rotated otherwise. The swing drive unit returns the registration roller 71 to the reference position (home position) in the sheet width direction after the leading edge of the sheet reaches the secondary transfer unit 60. The separation driving unit separates the registration roller 71 based on a timing signal corresponding to the paper type of the paper output from the control unit 100. The timing for separating the registration roller 71 after the leading edge of the paper reaches the secondary transfer unit 60 will be described later.

  The deviation detection sensor 72 is driven and controlled by the control unit 100, and has a function as a deviation detection unit that detects deviation from the reference position of the conveyed paper. The deviation detection sensor 72 periodically reads the position of one side edge of the sheet parallel to the sheet conveyance direction, and outputs the read information to the control unit 100. Based on the information received from the deviation detection sensor 72, the control unit 100 calculates a deviation direction (displacement direction) and a deviation amount (displacement amount) from the reference position of the sheet. Then, the direction and amount of rocking of the registration roller 71 are determined based on the calculation result, and a control signal including an instruction based on this determination is output to the rocking drive unit.

  The paper detection sensor 73 is driven and controlled by the control unit 100 and has a function as a paper detection unit that detects the leading edge of the conveyed paper. The sheet detection sensor 73 periodically reads whether or not the leading edge of the sheet has passed, and outputs the read information to the control unit 100. Based on the information received from the paper detection sensor 73, the control unit 100 determines whether the leading edge of the paper has passed directly below the paper detection sensor 73. When the leading edge of the sheet passes directly below the sheet detection sensor 73, the control unit 100 detects the leading edge of the sheet and after a predetermined time, the registration roller 71 causes the sheet to reach the transfer position of the secondary transfer unit 60. Control the rotation of

  In this embodiment, an example in which a personal computer is applied as an external device has been described. However, the present invention is not limited to this, and various other devices such as a facsimile device can be applied as the external device. .

[Registration roller separation according to paper type]
Next, the timing of registration roller separation according to the paper type will be described.
FIG. 4 is an explanatory diagram showing the separation timing of the registration roller 71 when the first paper type according to the embodiment of the present invention reaches the secondary transfer unit 60. FIG. 5 is an explanatory diagram showing the separation timing of the registration roller 71 when the second paper type according to the embodiment of the present invention reaches the secondary transfer unit 60.

The paper classified as the first paper type is a paper set to be a paper that is difficult to detect double feeding. The paper that is difficult to detect double feeding is, for example, a paper that is configured such that a plurality of papers overlap each other. Examples of the paper that is configured by overlapping a plurality of papers in part include envelopes, label papers, and pressure-sensitive papers. A sheet that is difficult to detect these double feeds is set in advance as the first sheet type. For example, a flap or the like exists in an envelope, and a label paper is composed of a pedestal and a seal, and the paper state (paper overlap and thickness) differs depending on the location.
The paper classified as the second paper type is a paper that is more easily detected as a double feed than the first paper type, and is, for example, a thin paper such as plain paper.
At least information on the first paper type and other paper types and the timing of separation of the registration rollers 71 are associated with each other and stored in the storage means such as the ROM 102.

  As shown in FIG. 4, when the conveyed paper is an envelope E that is the first paper type, the registration roller 71 is reached at an early timing after the envelope E reaches the secondary transfer nip portion 62 of the secondary transfer portion 60. Separate them. At this time, a distance (distance from the leading end of the envelope E to the nip portion 62) conveyed while the registration roller 71 is separated after the envelope E reaches the secondary transfer nip portion 62 of the secondary transfer portion 60 is L1.

  On the other hand, as shown in FIG. 5, when the sheet to be conveyed is the thin paper T that is the second paper type, the first paper after the thin paper T reaches the secondary transfer nip portion 62 of the secondary transfer unit 60. The registration roller 71 is separated at a timing later than the seed. In this case, the conveyance time of the thin paper T by the secondary transfer unit 60 is longer than that of the envelope F, and during the time when the registration roller 71 is separated after the thin paper T reaches the secondary transfer nip 62 of the secondary transfer unit 60. The distance L2 (the distance from the leading end of the thin paper T to the nip portion 62) is longer than the distance L1.

  Here, for example, it is assumed that two sheets S1 and S2 are double-fed as shown in FIG. After the first sheet reaches the secondary transfer nip 62 of the secondary transfer unit 60, the registration roller 71 is separated at an early timing (before the second sheet reaches the secondary transfer nip 62). Since the first sheet S1 is nipped by the secondary transfer unit 60, it is continuously conveyed by the secondary transfer unit 60. On the other hand, since the second sheet S2 is not nipped by either the secondary transfer unit 60 or the registration roller 71, it loses its conveying force and stays there. By detecting the paper S2 remaining between the registration roller 71 and the secondary transfer unit 60 by the paper detection sensor 73 (jam detection), it is possible to detect double feeding.

  As described above, according to the present embodiment, the timing at which the registration roller 71 is separated after the leading edge of the paper reaches the secondary transfer nip 62 of the secondary transfer unit 60 is changed according to the type of paper to be conveyed. Yes. Therefore, in the case of paper that is difficult to detect double feed such as an envelope, only the subsequent paper can be left between the registration roller 71 and the secondary transfer unit 60, and the double feed of the paper is high. It becomes feasible to detect with probability.

There is another aspect in adopting a configuration in which the timing at which the registration roller 71 is separated after the leading edge of the paper reaches the secondary transfer unit 60 is changed according to the paper type of the paper.
From the viewpoint of productivity, it is desirable that the sheet is nipped by the secondary transfer unit 60 and then the registration roller 71 is immediately separated to return the secondary transfer unit 60 to the home position. By the way, in order to carry the paper while maintaining the posture of the paper, it is desirable to nip and carry the paper by the registration roller 71 in addition to nip the paper by the secondary transfer unit 60. Such a function of using the registration roller 71 as an aid for paper conveyance is called an assist function. In general, in the case of thin paper with weak stiffness (low rigidity), it is desirable to use the assist function of the registration roller 71 as well as the secondary transfer unit 60. On the other hand, a firm sheet such as an envelope is conveyed while maintaining the posture of the sheet even if it is conveyed by the secondary transfer unit 60 alone. In the case of stiff paper, if the registration roller 71 is strongly pressed, slippage may occur between the paper and the secondary transfer roller 61 or the belt 50 in the secondary transfer nip portion 62. Therefore, it is desirable that the assist function by the registration roller 71 is enhanced by separation at a later timing in a sheet such as thin paper, and the assist function is weakened by separation at an earlier timing in a sheet having stiffness such as an envelope.

  In the present embodiment, the timing at which the registration roller 71 is separated when the first paper type such as envelope, label paper, and pressure-bonded paper is advanced, and the timing at which the registration roller 71 is separated when the paper type is other than the first paper type is delayed. By doing so, the productivity mentioned above and the good conveyance by the assist function are made compatible.

[Reverse rotation of registration roller during registration loop creation]
In order to suppress variations in the leading edge of the paper, there is a mechanism that stops the rotation of the registration roller 71 and creates a loop (registration loop) in cooperation with the roller on the upstream side. May bite into the nip portion 71c of the registration roller 71. Therefore, there is also a mechanism for adjusting the position of the leading edge of the paper by rotating the registration roller 71 in the direction opposite to the paper conveyance direction when creating the registration loop. In the present embodiment, by using a mechanism that reversely rotates the registration roller 71, it is possible to more reliably detect double feeding. Hereinafter, the relationship between the reverse rotation of the registration rollers and double feed detection will be described.

  FIG. 6 is an explanatory diagram showing reverse rotation of the registration roller at the time of creating a loop according to an embodiment of the present invention. FIG. 7 is an explanatory diagram showing the operating conditions for papermaking when the registration roller according to the embodiment of the present invention rotates in the reverse direction. FIG. 8 is an explanatory diagram showing a state in which the second sheet located on the lower side returns in the reverse direction (upstream in the sheet conveyance direction) when the registration roller according to the embodiment of the present invention rotates in the reverse direction. is there.

For example, when the paper S1 and the paper S2 are double-fed to the registration roller 71 (see FIG. 6), the paper rolling operation condition, that is, the condition under which the second paper S2 positioned on the lower side returns in the reverse direction is It is expressed as follows.
μ (r) × P>F> μ (p) × P

  Here, the conveying force of the sheets S1 and S2 by the rollers on the upstream side of the registration roller 71 is F, the operating pressure (nip pressure) in the direction perpendicular to the axis of the registration roller 71 is P, and the friction coefficient between the drive roller 71a and the sheet S2. Is μ (r), and the coefficient of friction between the sheets S1 and S2 is μ (p).

  When the paper-making operation conditions are satisfied, the lower sheet S2 returns in the reverse direction, and a distance is generated between the leading edge of the upper first sheet S1 and the leading edge of the lower sheet S2. Even if this distance is small, when the sheet is conveyed by the registration roller 71 in this state, the timing at which the registration roller 71 is separated after the upper sheet S1 reaches the secondary transfer nip 62 of the secondary transfer unit 60 is reached. As soon as possible, the lower sheet S2 can be left between the registration roller 71 and the secondary transfer section 60. That is, by using the gap between the upper sheet S1 and the lower sheet S2 generated by the reverse rotation of the registration roller 71, it is possible to detect the double feed of the sheet with a higher probability.

[Operation of image forming apparatus]
Hereinafter, an outline of the operation of the image forming apparatus 1 will be described.
FIG. 9 is a flowchart showing image forming processing according to an embodiment of the present invention.

  First, the control unit 100 of the image forming apparatus 1 detects a job start related to image formation based on an operation signal input from the operation display unit 105 or job information transmitted from the PC 120 via the communication unit 108. When detecting the start of a job relating to image formation, the control unit 100 refers to the job information and determines whether or not the selected paper is the first paper type (step S1). If the paper is not the first paper type such as an envelope (NO in step S1), the process proceeds to step S13. If the paper is the first paper type (YES in step S1), the process proceeds to step S2.

  When the paper is the first paper type in the determination process of step S1, the control unit 100 operates the paper supply unit 21 to supply the paper from the paper storage unit 20 or the manual feed unit 22 to the conveyance path. Paper passing is started (step S2). At this time, the control unit 100 sets the double feed detection sensor 74 to invalid so as not to operate in order to prevent erroneous detection.

  After starting the conveyance, the control unit 100 drives and controls the roller driving unit of the registration roller driving mechanism 70 to rotate the registration roller 71 in the reverse direction (step S3). Thereby, the posture of the paper and the conveyance timing are adjusted. Although the reverse rotation of the registration roller 71 is preferable for increasing the probability of double feed detection, it is not essential. For example, the rotation of the registration roller 71 may be stopped, and the sheet may be brought into contact with the nip portion 71c of the registration roller 71 and stopped to align the leading edge of the sheet.

  When the leading edge of the paper arrives at the registration roller 71 (step S4), a registration loop is formed for a predetermined time between the registration roller 71 and the upstream roller (step S5). The control unit 100 determines the time from the start of paper conveyance until the leading edge of the paper arrives at the registration roller 71 based on a preset process speed and an output from a paper detection sensor (not shown) in the middle of the conveyance path. I know. The same applies to the time from the start of sheet conveyance until the sheet described later arrives at the secondary transfer unit 60.

  Thereafter, the control unit 100 starts to rotate the driving roller 71a of the registration roller 71, and the driven roller 71b rotates accordingly, and nips and conveys the sheet at the nip portion 71c (step S6). Then, the leading edge of the sheet passing directly under the deviation detection sensor 72 enters the nip portion 71 c of the registration roller 71.

  At this time, the deviation detection sensor 72 detects the position of one side edge of the paper and outputs it to the control unit 100 (step S7). The control unit 100 determines the deviation direction and deviation amount of the sheet from the detection result by the deviation detection sensor 72. The control unit 100 outputs a control signal to the rocking drive unit of the registration roller driving mechanism 70 based on the above-mentioned paper misalignment direction and misalignment amount, performs the rocking of the registration roller 71, and corrects the misalignment. (Step S8).

  After the registration roller 71 swings, the control unit 100 outputs a control signal to the roller driving unit of the registration roller driving mechanism 70 and a paper transport mechanism (not shown) to direct the paper to the secondary transfer unit 60. Transport. After the leading edge of the sheet is detected by the sheet detection sensor 73, the control unit 100 outputs a control signal to a sheet transport mechanism (not shown), and the sheet is transferred a predetermined time after the leading edge of the sheet is detected by the sheet detection sensor 73. Transport to position. That is, the paper reaches the transfer position after a predetermined time has elapsed from the start of paper passing. Then, the toner image formed on the intermediate transfer belt 50 is transferred to the sheet conveyed to the transfer position.

  When the control unit 100 determines that the leading edge of the sheet has reached the secondary transfer nip 62 of the secondary transfer unit 60 (step S9), the control unit 100 drives and controls the separation driving unit of the registration roller driving mechanism 70 to perform the first control. The registration rollers 71 are separated at an early timing according to the paper type (step S10).

  Here, the control unit 100 determines whether or not residual paper is detected based on the output of the paper detection sensor 73 (step S11). The residual paper detected at this time is paper that does not originally exist in this location unless double feeding has occurred. When the remaining paper is detected (YES in step S11), the control unit 100 determines that double feed is detected (jam detection) (step S12), and performs predetermined processing. For example, the conveyance of the paper is stopped and the operation display unit 105 notifies the user of the double feed. If no remaining paper is detected (NO in step S11), the control unit 100 performs a series of processing on the subsequent paper in the same manner.

  Here, the process returns to the determination process in step S1. When the paper is not the first paper type in the determination process of step S1, the control unit 100 performs the processes of steps S13 to S22. At this time, the control unit 100 performs detection by setting the double feed detection sensor 74 to be valid. In addition, since the process of step S13-step 19 is the same as the process of step S2-step S8, description is abbreviate | omitted.

  After the processing of step S19 (the swing of the registration roller 71) is completed, when the leading edge of the sheet reaches the secondary transfer nip 62 of the secondary transfer unit 60 (step S20), the sheet is placed on the intermediate transfer belt 50 with respect to the sheet. The formed toner image is transferred. At this time, the registration roller 71 is rotated in the forward direction, that is, in the sheet conveying direction (step S21).

  Thereafter, after the leading edge of the paper reaches the secondary transfer nip portion 62 of the secondary transfer portion 60, the control portion 100 drives and controls the separation drive portion of the registration roller drive mechanism 70 from the first paper type. The registration roller 71 is separated at a later timing (step S22). After this process is completed, the control unit 100 performs a series of processes on the subsequent sheets in the same manner.

  As described above, according to the present embodiment, the timing at which the registration roller 71 is separated after the leading edge of the paper reaches the secondary transfer nip 62 of the secondary transfer unit 60 is changed according to the type of paper to be conveyed. Yes. That is, the timing of separating the registration rollers 71 is advanced when a specific sheet such as an envelope that is difficult to detect double feeding is being passed. Therefore, only a subsequent sheet can remain between the registration roller 71 and the secondary transfer unit 60 when a specific sheet is passed. Therefore, it is possible to detect a double feed of a specific paper with a high probability by a normally used paper detection sensor without using a special sensor for detecting the double feed.

  In the present embodiment, the timing at which the registration roller 71 is separated after the leading edge of the paper reaches the secondary transfer nip 62 of the secondary transfer unit 60 is changed according to the paper type. The productivity and the assist function for the sheet conveyance of the registration roller 71 can be made compatible.

  The embodiment to which the invention made by the present inventor is applied has been described above. However, the present invention is not limited by the description and drawings which form part of the disclosure of the invention according to the above-described embodiments, and various modifications may be made without departing from the spirit of the invention described in the claims. Is possible.

  In the above-described embodiment, as an example of a sheet that is difficult to detect double feeding, a sheet having different sheet states such as a plurality of overlapping sheets is partially described. Good. Examples of the paper having a hole partially include punched paper.

  In the above-described embodiment, the example in which the remaining sheet is detected by the sheet detection sensor 73 has been described. However, the deviation detection sensor 72 may also serve as the remaining sheet detection function of the sheet detection sensor 73.

  In the above-described embodiment, the example in which the present invention is applied to the case where the sheet is conveyed to the secondary transfer unit 60 has been described. However, the present invention is not limited to this example. The present invention can be applied to an image forming apparatus that conveys a sheet that has passed through a registration roller to a transfer position. For example, the image forming apparatus includes a photosensitive member as an image carrier and transfers a toner image directly from the photosensitive member to the sheet. It is also applicable to the device.

  Furthermore, in the above-described embodiment, the image forming system 1 has been described as an example. However, a configuration in which a post-processing device and a paper feeding device are connected to the image forming device 1 or a configuration in which a separate fixing device is provided. It can also be applied to production printing machines.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 40 ... Image forming part, 50 ... Intermediate transfer belt, 60 ... Secondary transfer part, 61 ... Secondary transfer roller, 62 ... Secondary transfer nip part, 70 ... Registration roller drive mechanism, 71 ... Registration Roller, 71a ... Driving roller, 71b ... Driven roller, 71c ... Nip part, 72 ... Misalignment detection sensor, 73 ... Paper detection sensor, 74 ... Double feed detection sensor, 100 ... Control part, 101 ... CPU, 102 ... ROM, 103 ... RAM, S1, S2 ... paper, E ... envelope, T ... thin paper

Claims (6)

A resist roller that can be separated;
A transfer unit for transferring a toner image onto a sheet conveyed from the registration roller;
A paper detection unit provided between the registration roller and the transfer unit for detecting paper;
A paper type determination unit that determines the type of paper to be conveyed;
A timing determining unit that determines a timing for separating the registration rollers after the leading edge of the sheet reaches the transfer unit, according to a determination result of the sheet type determining unit;
The timing determination unit is configured to make the timing for separating the registration rollers earlier in the case of a paper type in which at least a part of the paper is configured by overlapping a plurality of sheets , as compared to the case of other paper types. . The image forming apparatus according to claim 1, wherein the paper type formed by overlapping a plurality of at least a part is an envelope. A double feed detector for detecting whether or not the paper is being double fed;
The image forming apparatus according to claim 1, wherein when the paper type of the paper is a paper type configured such that at least a part of the paper types overlaps, the multi- feed detection unit does not detect. The registration roller rotates in a direction opposite to a direction in which the sheet is conveyed when a loop is formed in the sheet in cooperation with a roller provided on the upstream side in the sheet conveyance direction. The image forming apparatus described in 1. The registration roller swings in the paper width direction orthogonal to the paper transport direction.
The image forming apparatus according to claim 1. When the paper type of the paper is a paper type in which at least a part of the paper is overlapped, the paper detection unit detects the double fed paper
The image forming apparatus according to claim 1.

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