JP2013238763A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus in which when image formation is performed on an extremely thin recording material or the like, deterioration of an image, which is likely to occur when a loop amount is caused to be made small before a rear end of the recording material passes through a transfer part, can be prevented.SOLUTION: An image forming apparatus includes loop detection means (S1 and S2) for detecting a loop amount of a recording material and environment detection means (35) for detecting a humidity of installation environment. Control means (37) controls basis weight determination means (37) for determining a basis weight of the recording material, and a difference between conveyance speeds of the transfer part and a fixing part on the basis of a loop detected by the loop detection means, a humidity detected by the environment detection means, and a basis weight determined by the basis weight determination means, so as to adjust the loop amount of the recording material. The control means controls so that a large loop is changed to a small loop in the process of conveying the recording material when it is under a high humidity environment of a prescribed humidity (Hh) or more with a basis weight of a prescribed value or more, and controls the difference in the conveyance speeds so that a large loop is maintained in the processing of conveying the recording material when it is under a high humidity environment with a basis weight of a value less than a prescribed value.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a fax machine using an electrophotographic system.

  Conventionally, a transfer unit that transports a recording material while transferring an unfixed toner image on an image carrier onto the recording material, and an unfixed toner image (unfixed image) on the recording material is heated and pressed to form a recording material. There is known an electrophotographic image forming apparatus including a fixing unit that conveys a recording material while fixing. In such an image forming apparatus, an image defect may occur when a recording material conveyance speed difference occurs between the transfer unit and the fixing unit.

  In other words, the heat that is temporarily removed from the fixing roller of the fixing unit by performing the fixing process using the heating method is the amount of developer that forms an unfixed image transferred to the recording material, and the unit time that passes through the fixing unit. It varies depending on the number of passing recording materials and the heat capacity of the recording materials. The temperature of the fixing roller and the pressure roller of the fixing unit fluctuates due to a temporary temperature change in the amount of heat taken from the fixing roller, so that the amount of thermal expansion changes depending on the situation and appears as a change in the outer diameter. For this reason, the conveyance speed of the fixing unit changes, and a difference occurs between the conveyance speed and the transfer unit.

  For example, when the fixing roller or the pressure roller is thermally expanded with the fixing motor rotated so that the conveyance speed of the fixing unit is the same as that of the transfer unit without being affected by heat, fixing is performed at the same rotational speed. When the motor is rotated, the conveyance speed of the fixing unit is faster than the conveyance speed of the transfer unit. If there is a difference in the conveyance speed of the recording material between the fixing unit and the transfer unit in this way, there is a possibility that image deterioration will be caused. Specifically, when the conveyance speed of the fixing unit is faster than the conveyance speed of the transfer unit, the recording material is pulled between the fixing unit and the transfer unit by the fixing unit, and the image is transferred when the image is transferred to the recording material by the transfer unit. May cause disturbance.

  On the other hand, when the recording material conveyance speed by the fixing unit is slower than the recording material conveyance speed of the transfer unit, the amount of the recording material conveyed by the transfer unit is less than the amount of the recording material conveyed by the fixing unit. It will exceed. For this reason, the recording material begins to slack in the direction of the conveyance guide between the fixing unit and the transfer unit. Hereinafter, the phenomenon that the recording material is slack is described as “the recording material forms a loop”.

  When the recording material forms a loop as described above, if the loop becomes excessive, the recording material is strongly pressed against the conveyance guide and rubbed, or the recording material develops into a loop in the direction opposite to the recording material state. It rubs against the transport guide on the side or the cover of the fixing unit. As a result, the transferred unfixed image may be disturbed, resulting in image deterioration. Therefore, the following proposals to reduce image degradation by forming a predetermined loop in the recording material between the transfer portion and the fixing portion, thereby preventing the recording material from being pulled or loosened too much are proposed. Has been made.

  That is, a loop detection sensor for detecting the loop amount of the recording material and a loop detection flag for turning on / off the loop detection sensor are provided in the conveyance guide between the fixing unit and the transfer unit. Then, according to the detection result of the loop detection sensor, the conveyance speed of the fixing unit is switched between a first speed that is slower than the conveyance speed of the transfer unit and a second speed that is faster than the conveyance speed of the transfer unit. Maintain the loop amount. As a result, while the recording material is nipped and conveyed by both the transfer unit and the fixing unit, image formation can be performed while the loop amount is kept substantially constant (see Patent Documents 1 and 2).

  Further, when the recording material passes through the transfer portion, the holding force at the transfer portion is lost, so that the loop formed so far is released. At this time, if the set value of the loop that is kept substantially constant is large, the trailing edge of the recording material may jump depending on the type of the recording material, and the unfixed image may be rubbed against, for example, a conveyance guide and the like to cause image deterioration. There is a fear.

  In order to cope with this, a plurality of loop detection sensors are provided, and the sensor to be used is switched in accordance with the information relating to the recording material, and the amount of loop of the recording material that has been largely maintained until the trailing edge passes through the transfer portion is determined by the trailing edge. There is also proposed a configuration in which the toner is controlled to be small before passing through the transfer portion. With this configuration, it is possible to prevent image degradation that occurs when the trailing edge of the recording material bounces off the transfer portion (see Patent Document 3).

JP 05-107966 A Japanese Patent Application Laid-Open No. 07-234604 JP 2006-309188 A

  However, in recent years, the types of recording materials used in the market have been diversified. For example, a thin recording material having an extremely small basis weight (weight of recording material per unit area), a thick recording material having an extremely large basis weight, and a material using a reproducing material have been used. In addition, recording materials that are generally used have the property that the water content changes according to changes in humidity and the rigidity varies, and when the humidity is relatively low, the rigidity increases and the humidity increases. According to this, the rigidity becomes low. In addition, even if the recording materials used in recent years have the same basis weight, when the usage environment changes, for example, in a high temperature and high humidity environment such as a temperature of 30 ° C. and a humidity of 80%, other types of recording materials are used. Some of the recording materials have extremely low rigidity compared to other recording materials.

  Further, the recording material conveyance speed required for the image forming apparatus is increasing year by year. Due to such a background, while the recording material passes through the transfer portion and is conveyed only by the fixing portion, the recording material is pulled out without receiving a holding force by the transfer portion or a supporting force by the conveyance guide. Become. Therefore, according to the technique of Patent Document 3 in which the recording material whose rigidity is extremely low at least in a high humidity environment as described above performs control to reduce the loop amount before the trailing edge passes through the transfer portion, the trailing edge is used. May go wild when trying to rush into the fusing unit.

  As described above, when the recording material is largely exposed in the vicinity of the entrance of the fixing unit at least in a high humidity environment, the image surface may be rubbed against a cover, a conveyance guide, or the like in the vicinity of the recording material to cause image distortion. In addition, the recording material may first hit the heated fixing roller before entering the fixing nip portion between the fixing roller and the pressure roller. In such a case, the image may be disturbed or gloss unevenness may occur, and the above method is not sufficient for image deterioration.

  Therefore, the present invention, when forming an image using an extremely thin recording material or the like, causes image deterioration that is likely to occur when the loop amount is reduced before the trailing end of the recording material passes through the transfer portion, at least in an environment of high humidity. An object of the present invention is to provide an image forming apparatus having a preventable configuration.

  The present invention includes a transfer unit that transfers a recording material by transferring an unfixed image, and a fixing unit that is disposed on the downstream side of the transfer unit and conveys the recording material and fixes the unfixed image to the recording material. A recording material formed between the transfer unit and the fixing unit in an image forming apparatus that controls a conveyance speed difference between the transfer unit and the fixing unit to adjust a loop amount of the recording material A loop detection unit that detects the loop amount of the recording medium as a plurality of loop amounts, an environment detection unit that detects humidity in the installation environment of the image forming apparatus main body, and a basis weight determination unit that determines the basis weight of the recording material to be conveyed A control means for adjusting the loop amount of the recording material by controlling the transport speed difference based on a detection loop by the loop detection means, a humidity detected by the environment detection means, and a determination basis weight by the basis weight determination means; And the system The means conveys the recording material between the transfer unit and the fixing unit when the basis weight determined by the basis weight determination unit is a predetermined basis weight or more in a high humidity environment where the detected humidity is a predetermined humidity or more. In the process, the conveyance speed difference is controlled so that a large loop equal to or larger than a predetermined loop amount becomes a small loop smaller than the predetermined loop amount, and when the determination basis weight is less than a predetermined basis weight, In the image forming apparatus, the conveyance speed difference is controlled so that the large loop is maintained in the process of conveying the recording material to and from the fixing unit.

  According to the present invention, the trailing edge of the recording material conveyed between the transfer unit and the fixing unit is transferred based on the detection loop by the loop detection unit, the humidity detected by the environment detection unit, and the determination basis weight by the basis weight determination unit. It is possible to appropriately adjust the loop amount when exiting from the section. As a result, when transporting thin recording materials with a determined basis weight of less than the specified basis weight in a high humidity environment, maintaining a large loop before and after the trailing edge comes out of the transfer section will add stiffness to the thin recording material. Therefore, it is possible to avoid a large rampage when the rear end enters the fixing portion. Therefore, it is possible to effectively prevent image degradation that may occur on the recording material when conveyed between the transfer unit and the fixing unit.

1 is a schematic diagram showing the overall configuration of an image forming apparatus according to the present invention. FIG. 3 is a cross-sectional view illustrating the posture of a recording material between a transfer unit and a fixing unit in an embodiment according to the invention. The posture of the recording material at the time of loop detection control in the present embodiment is shown, (a) is a cross-sectional view (at the time of using S1) showing the posture of the recording material at the time of loop detection control using the first loop detection sensor, (b). FIG. 6 is a cross-sectional view showing the posture of a recording material during loop detection control using a second loop detection sensor. The loop detection sensor in this embodiment and a loop detection flag are shown, (a) is a perspective view which shows the state at the time of detection by a 1st loop detection sensor, (b) respectively shows the state at the time of detection by a 2nd loop detection sensor. The block diagram which shows the control system in this embodiment. (A) is a timing chart showing each timing of loop detection control when the detected humidity is higher than the threshold value Hh, and (b) is when the detected humidity is lower than the threshold value Hl. The flowchart figure shown about the operation | movement in this embodiment. The timing chart figure of the loop detection control in a comparative example.

  Hereinafter, exemplary embodiments of the present invention will be exemplarily described with reference to FIGS. 1 to 8. However, the material, arrangement, dimensions, shape, and the like of the component parts described in the following embodiments should be appropriately changed depending on the configuration of the apparatus to which the present invention is applied and various conditions, and the modes shown below It is not limited to.

  First, an overall schematic configuration of an image forming apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram showing the overall configuration of an electrophotographic color image forming apparatus (full color printer) 50 to which the present invention is applied.

  That is, the image forming apparatus 50 includes an image forming apparatus main body 50a (hereinafter also referred to as “apparatus main body 50a”), and controls the difference in the conveyance speed between the transfer unit 30 and the fixing unit 40 to adjust the loop amount of the recording material. Have the function of conveying. A photosensitive drum a which is an image carrier (electrophotographic photosensitive member) that is arranged in a line at regular intervals and forms toner images of yellow, magenta, cyan, and black colors inside the apparatus main body 50a. An image forming unit 102 in which four to d are arranged is provided. A charging unit, a developing unit, and a cleaning unit are disposed around each of the photosensitive drums a to d. The photosensitive drums a to d, the charging unit, and the like are arranged in the process cartridge 1 (1a, 1b, 1c, 1d). ) As a unit.

  Above these process cartridges 1a, 1b, 1c, and 1d, an intermediate transfer belt 2 that is an intermediate transfer member is disposed in contact with the photosensitive drums a to d. Further, four transfer rollers 301 as primary transfer portions are disposed inside the intermediate transfer belt 2 so as to be in contact with the photosensitive drums a to d via the intermediate transfer belt 2. Here, the intermediate transfer belt 2 is supported by a secondary transfer counter roller 303 and the like, and rotates by a drive input to the secondary transfer counter roller 303.

  The secondary transfer counter roller 303 is disposed so as to be in contact with the secondary transfer roller 302 via the intermediate transfer belt 2. The secondary transfer counter roller 303 and the secondary transfer roller 302 constitute a transfer unit 30 that is a secondary transfer unit that transfers and conveys an unfixed toner image (unfixed image) to the recording material. Further, on the downstream side of the transfer unit 30 in the recording material conveyance direction, a fixing unit 40 that has a fixing roller 100 and a pressure roller 101 and conveys the recording material and fixes an unfixed toner image on the recording material is installed. ing.

  In FIG. 1, reference numeral 6 denotes an exposure device disposed below the process cartridge 1, and the exposure device 6 selectively irradiates the photosensitive drums a to d with laser light in accordance with image signals. I do. Then, by exposing the photosensitive drums a to d in this way, electrostatic latent images of respective colors corresponding to the image information are formed on the surfaces of the photosensitive drums a to d charged by the charging unit.

  The exposure device 6 includes a light emitting member (not shown) that emits laser light, and a polygon mirror 6a that scans the laser light from the light emitting member in the longitudinal direction (main scanning direction) of the photosensitive drums a to d. . Further, the exposure apparatus 6 includes a reflection mirror 6b that reflects various lenses and the photosensitive drums a to d, and the like. Then, the exposure device 6 irradiates each of the photosensitive drums a to d with laser light through a slit formed in the housing 6c.

  When duplex printing is required, the recording material P on which the toner image is fixed by the fixing unit 40 is sent from the conveyance path 42 to the reverse conveyance paths 46 and 47 by switching the switching member 103 and reversing the discharge roller pair 11. The paper is transported by the transport roller pairs 12 and 15 and joined from the re-transport path 48 to the transport path 49. That is, the recording material P is reversed in the conveyance path 42 so that the leading and trailing ends are replaced, and the recording material P is conveyed again to the reverse conveyance paths 46 and 47 by switching the switching member 103. Examples of the recording material include transfer recording material, electrofax recording material, electrostatic recording paper, OHP recording material, printing paper, format paper, and the like.

  After that, the re-conveyance path 48 changes to the conveyance path 49 in synchronism with the timing of the recording material P of the subsequent job conveyed from the paper feed cassette (recording material stacking unit) 4 via the conveyance path 45 by the pickup roller 8. They are merged and sent to the transfer unit 30 through the registration roller pair 9. Then, an unfixed toner image is formed on the recording material P in the same manner as described above.

  In addition, a loop detection unit 31 and conveyance guides 32 and 33 that form the conveyance path 29 are disposed in the conveyance path 29 between the transfer unit 30 and the fixing unit 40. These will be described later.

  Next, an image forming operation in the image forming apparatus 50 having such a configuration will be described. First, when an image formation start signal is issued, each of the photosensitive drums a to d that is rotationally driven at a predetermined process speed is uniformly charged to a negative polarity by the charging unit.

  The exposure device 6 emits laser light from the light emitting member in accordance with image signals obtained by separating image information input from the outside for each color. Then, the laser light is irradiated onto the photosensitive drums a to d via the polygon mirror 6a, the reflection mirror 6b, and the like, and electrostatic latent images of the respective colors are formed on the photosensitive drums a to d.

  Next, first, yellow toner is attached to the electrostatic latent image formed on the photosensitive drum a to visualize the electrostatic latent image on the photosensitive drum a as a yellow toner image. This yellow toner image is driven by a transfer roller 301 to which a primary transfer bias (positive polarity) opposite in polarity to the toner is applied in a primary transfer portion between the photosensitive drum a and the transfer roller 301. Primary transfer is performed on the intermediate transfer belt 2.

  The intermediate transfer belt 2 to which the yellow toner image has been transferred next moves to the photosensitive drum b side where the magenta toner image is formed. The magenta toner image formed on the photosensitive drum b is superimposed on the yellow toner image on the intermediate transfer belt 2 and transferred at the primary transfer portion.

  Similarly, cyan and black toner images formed by the photosensitive drums c and d are sequentially superimposed on the yellow and magenta toner images superimposed and transferred on the intermediate transfer belt 2 at each primary transfer unit. As a result, a full-color toner image is formed on the intermediate transfer belt 2.

  Next, the recording material P stored in the paper feed cassette 4 is conveyed to the registration roller pair 9 by the pickup roller 8. Then, the recording material P is conveyed to the transfer unit 30 by the registration roller pair 9 in accordance with the timing when the leading edge of the full color toner image formed on the intermediate transfer belt 2 reaches the transfer unit 30. Then, a full-color toner image is secondarily transferred to the recording material P conveyed to the transfer unit 30 by a secondary transfer roller 302 to which a secondary transfer bias (positive polarity) opposite in polarity to the toner is applied. The

  The recording material P to which the toner image has been transferred is guided by conveyance guides 32 and 33, introduced into the fixing nip of the fixing unit 40, and heated to a predetermined temperature by a halogen heater 105 included therein and a pressure roller. Then, the recording material P is fixed to the recording material P.

  As a result, the toners of the respective colors are melted and mixed and fixed on the recording material P as a full-color print image. Thereafter, the recording material P on which the image is fixed is discharged onto the discharge tray 7 by the discharge roller pair 10 and 11 provided downstream of the fixing unit 40.

  In the image forming apparatus 50, a paper feed heating member (heating member) 23 is installed in the paper feed cassette (recording material stacking unit) 4 in order to improve the product grade. Thereby, the paper cassette 4 on which a plurality of recording materials P are stacked is heated, and the amount of moisture can be reduced by heating the stacked recording materials P before passing paper.

  Next, the configuration in the vicinity of the transfer unit 30 and the fixing unit 40 in the image forming apparatus will be described with reference to FIG. FIG. 2 is a cross-sectional view showing the configuration of the portion from the transfer unit 30 to the fixing unit 40 in the present embodiment and showing the posture of the recording material for defining the loop amount described in the present invention.

  That is, the recording material P onto which the toner image (unfixed image) has been transferred is guided by the conveyance guides 32 and 33 and guided to the fixing unit 40. The fixing unit 40 includes a fixing roller 100 including a halogen heater 105 as a heat source, and a pressure roller 101. The fixing roller 100 and the pressure roller 101 are pressed against each other by applying a load of 300 N, for example, to form a fixing nip portion N. The pressure roller 101 is driven by a drive motor (not shown) (hereinafter referred to as a fixing motor). Is rotated, and the recording material P is conveyed at the fixing nip portion N.

  In the present embodiment, the pressure roller 101 side is described as being configured to rotate and convey the recording material P, but the side that is rotationally driven in the fixing unit 40 is either the pressure roller 101 or the fixing roller 100. I do not care. In other words, the fixing unit 40 is not limited to the pressure roller 101 side, and can be used in a configuration in which the fixing roller 100 side is rotationally driven, or in a configuration in which both the fixing roller 100 and the pressure roller 101 are rotationally driven. It is.

  As shown in FIG. 2, the image forming apparatus 50 includes an environmental sensor 35 for measuring environmental conditions for image formation such as temperature and humidity. The environmental sensor 35 is disposed on the back side of the conveyance guides 32 and 33 in FIG. 2, but the arrangement position is not limited to this. The environmental sensor 35 may be located anywhere on the image forming apparatus as long as it is installed on the image forming apparatus, and the measurement target may be the temperature and humidity outside the image forming apparatus, or the temperature and humidity inside the image forming apparatus. What is necessary is just to be able to determine the temperature and humidity for utilization according to the embodiment to be implemented.

  Next, detection of the loop amount of the recording material P performed between the transfer unit 30 and the fixing unit 40 will be described with reference to FIGS. FIG. 4A is a perspective view showing a state at the time of detection by the first loop detection sensor, and FIG. 4B is a perspective view showing a state at the time of detection by the second loop detection sensor.

  First, the loop amount to be formed is defined using FIG. In FIG. 2, each posture of the recording material P is indicated by three lines P0, P1, and P2. P0 is a reference loop detection position indicated by a straight line connecting the exit of the transfer section 30 and the entrance of the fixing section 40, and the distance from the reference loop detection position P0 is defined as a loop amount L.

P1 is a first loop detection position indicating the posture of the recording material P when detected and controlled by the first loop detection sensor S1, and the loop amount at the first loop detection position P1 is defined as a first loop amount L1. . P2 is a second loop detection position indicating the posture of the recording material P when the detection control is performed by the second loop detection sensor S2, and the loop amount at the second loop detection position P2 is defined as a second loop amount L2. To do. in this case,
L1 <L2
It is.

  In the following, such a loop amount is described as “a loop is deep” when the loop amount L is large, and “loop is shallow” when a loop amount L is small. The first and second loop detection sensors S1 and S2 use the loop amount of the recording material P formed between the transfer unit 30 and the fixing unit 40 as a loop amount in a plurality of stages (in this embodiment, two stages). The loop detection means of the present invention to detect is configured.

  Next, a detailed configuration of the loop detection unit 31 will be described with reference to FIGS. 2 and 4A and 4B. 4A shows a state in which the first loop detection sensor S1 has detected the loop detection flag 26 (turned ON), and in FIG. 4B, the second loop detection sensor S2 has turned the loop detection flag 26 on. The detected state (turned on) is shown. 4A and 4B depict the state at the time of loop detection control as viewed from the oblique rear side (right side in FIG. 2) of the conveyance guides 32 and 33. FIG.

  As shown in FIG. 2, the loop detection unit 31 disposed in the conveyance path 29 between the transfer unit 30 and the fixing unit 40 has a rotation shaft 25 that is rotatably supported on the back side of the conveyance guide 32. And a loop detection flag 26, a light shielding plate 28, and a light shielding plate 27, which are sequentially fixed to the rotating shaft 25.

  As shown in FIGS. 4A and 4B, the loop detection flag 26 and the light shielding plates 27 and 28 are arranged on a straight line via the rotation shaft 25. The loop detection flag 26 has a rear end on the rotary shaft 25 so that the front contact portion 26a protrudes in a direction opposite to the front ends of the light shielding plates 28 and 27 whose rear ends are fixed to the rotary shaft 25. The part is fixed.

  The light shielding plates 27 and 28 are formed so that the tip end portions spread in a substantially fan shape. First and second loop detection sensors S1 and S2 that have light emitting and light receiving portions at the portions facing the respective tip portions of the light shielding plates 27 and 28 and that output detection signals according to the operation of the loop detection flag 26 are provided. They are arranged at different positions. Further, a torsion spring (not shown) for urging the rotation shaft 25 is provided so as to rotate the loop detection flag 26 in the clockwise direction of FIGS. 4 (a) and 4 (b).

  The loop detection flag 26 is configured to rotate in the clockwise direction and the counterclockwise direction in FIGS. 4A and 4B with the rotation shaft 25 supported on the apparatus body 50a side as a fulcrum. Yes. The loop detection flag 26 is restricted from rotating beyond the home position by a rotation stop member (not shown) supported on the apparatus main body 50a side.

  When the transported recording material P passes over the loop detection unit 31 and the contact portion 26a of the loop detection flag 26 is pushed and rotated, the posture of the recording material P is changed by the first and second loop detection sensors S1 and S2. Detected. The state detected in this way is described as “the loop detection sensor is ON”, and the state where the light shielding plates 27 and 28 do not reach the first and second loop detection sensors S1 and S2 is described as “loop detection”. “Sensor is OFF”.

  The loop detection flag 26 projects the contact portion 26 a into the conveyance path 29 between the transfer unit 30 and the fixing unit 40 so as to be able to contact the recording material P conveyed through the conveyance path 29. Since the detection positions of the first and second loop detection sensors S1 and S2 are different, when both the sensors S1 and S2 are not ON, only when the sensor S1 is ON, both when both the sensors S1 and S2 are ON In addition, the loop amount can be detected at a plurality of locations (three locations in the present embodiment).

  The first loop detection sensor S1 is located at a position where the slit between the light emitting and light receiving portions is shielded by the light shielding plate 27 that rotates together with the loop detection flag 26 that is rotated by the recording material P that has reached the first loop detection position P1. Has been placed. The second loop detection sensor S2 is located at a position where the slit between the light emitting and light receiving portions is shielded by the light shielding plate 28 that rotates together with the loop detection flag 26 that is rotated by the recording material P that has reached the second loop detection position P2. Has been placed.

  When the loop detection flag 26 is rotated in contact with the recording material P, the light shielding plates 27 and 28 are integrally rotated via the rotation shaft 25 and enter the slit to shield between the light emitting / receiving portions. Thus, detection signals are output from the first and second loop detection sensors S1 and S2. As described above, the detection of the first and second loop detection sensors S1 and S2, which are photo interrupters, detects the movement of the loop detection flag 26 that operates by the contact with the recording material P between the transfer unit 30 and the fixing unit 40. .

  Next, a control system for loop detection control in the present embodiment will be described with reference to FIG. FIG. 5 is a block diagram showing a control system in the present embodiment.

  That is, as shown in FIG. 5, the control unit 37 provided in the image forming apparatus 50 includes a timer 39, a CPU 38, a memory 43, a first loop detection masking Q1, and a second loop detection masking Q2. The control unit 37 includes a paper feed heating member ON / OFF detection sensor 36 that detects on / off of the paper feed heating member 23, an environmental sensor 35, a registration sensor 44, the first and second loop detection sensors S1, S2, and the like described above. And a fixing motor M is connected. In the control unit 37, paper (recording material) type information 24 such as user setting values such as the size and weight (basis weight) of the recording material and paper feed detection values is set in the setting information input unit provided in the image forming apparatus 50. It is input by setting input (not shown) or the like or detected by a detection means (not shown).

  The control unit 37 constitutes the basis weight determination means of the present invention that determines the basis weight of the recording material to be conveyed based on the input information regarding the weight (basis weight) of the recording material. Further, the control unit 37 controls the conveyance speed difference between the transfer unit 30 and the fixing unit 40 based on the detection loops of the first and second loop detection sensors S1 and S2, the humidity detected by the environment sensor 35, and the determination basis weight. Thus, the control means of the present invention for adjusting the loop amount of the recording material is configured.

  The timer 39 counts (measures) each timing necessary for the control of the control unit 37. The CPU 38 executes various calculations necessary for the control of the control unit 37. The memory 43 stores information necessary for the control unit 37 to control paper (recording material) type information and the like.

  The first and second loop detection masking Q1 and Q2 are a plurality of mask means capable of disabling the first and second loop detection sensors S1 and S2. The first loop detection masking Q1 applies a mask so that the detection signal from the first loop detection sensor S1 is not used for control. The second loop detection masking Q2 applies a mask so that the detection signal from the second loop detection sensor S2 is not used for control.

  The paper feed heating member ON / OFF detection sensor 36 detects the ON / OFF state of the paper feed heating member 23. The environmental sensor 35 measures the environmental conditions of image formation such as temperature and humidity, and constitutes the environmental detection means of the present invention that detects the humidity in the installation environment of the image forming apparatus main body 50a. The registration sensor 44 detects the leading end position of the recording material fed from the registration roller pair 9 and outputs the detected position to the control unit 37. The fixing motor M is rotationally driven so as to drive the fixing unit 40 according to the control of the control unit 37.

  The control unit 37 selects a loop detection sensor that detects a loop having a size corresponding to the paper (recording material) type information related to the recording material from the first and second loop detection sensors S1 and S2. Then, either one of the first and second loop detection masking Q1 and Q2 is masked so that the signal from the unselected loop detection sensor is not used for control, and according to the detection signal of the selected loop detection sensor. Control is performed so as to keep the loop amount formed by the recording material substantially constant.

  The paper (recording material) type information includes the size and weight (basis weight) of the recording material. Paper (recording material) type information is stored in advance in the memory 43, and is selected and set before image formation by information input from a setting information input unit (not shown) provided in the image forming apparatus 50. The setting information input unit is an automatic input of information detected by a size detection means (not shown) provided in the paper feed cassette 4 or a recording material being conveyed when input from the setting information input unit Including automatic input of information detected by the detecting means. Each piece of input information is sent to the control unit 37.

  Next, loop detection control performed using the above-described loop detection unit 31 and the like will be described. That is, the control unit 37 determines which one of the first and second loop detection sensors S1 and S2 is to be used according to the information of the recording material set or detected at the beginning of image formation.

  When the loop detection sensor is turned on according to the detection signal of the selected loop detection sensor, the control unit 37, for example, sets the conveyance speed of the fixing unit 40 to the first conveyance speed V1 that is faster than the conveyance speed Vt of the transfer unit 30. As described above, the rotational speed (rotational speed) of the fixing motor M is driven and controlled to Mhigh. In this case, the loop becomes shallow by conveying the recording material P at the first conveyance speed V1. On the other hand, for example, the control unit 37 drives and controls the rotation speed of the fixing motor M to Mlow so that the conveyance speed of the fixing unit 40 becomes the second conveyance speed V2 that is slower than the conveyance speed Vt of the transfer unit 30. The loop is deepened by transporting P at the second transport speed V2.

Summarizing the above-described first and second transport speeds V1 and V2, when the transport speed of the transfer section 30 is Vt, the control unit 37
V1>Vt> V2
The speed control of the fixing unit 40 is executed based on the loop detection of the first and second loop detection sensors S1 and S2 so as to satisfy the above.

  Accordingly, the conveyance speed of the fixing unit 40, that is, the rotation speed of the fixing motor M is switched around the desired loop amount (the loop amount at the position where the loop detection sensor is switched ON / OFF), and the loop amount is made substantially constant. Can be controlled.

  The loop amount adjustment of the recording material by the loop detection control according to the present invention may be performed by controlling the conveyance speed difference between the transfer unit 30 and the fixing unit 40. Therefore, it is possible to adjust the conveyance speed of the transfer unit 30 while keeping the conveyance speed of the fixing unit 40 constant, or to adjust the conveyance speeds of the fixing unit 40 and the transfer unit 30. Is possible.

  Next, the posture of the recording material when it is detected by the loop detection sensors S1 and S2 will be described with reference to FIGS. 3 (a) and 3 (b). 3A is a cross-sectional view showing the state of the recording material when the first loop detection sensor S1 is used by switching the contact type first and second loop detection sensors S1 and S2, and FIG. These are sectional views showing the state of the recording material when the second loop detection sensor S2 is used. In FIG. 3A, the second loop detection sensor S2 is omitted, and in FIG. 3B, the first loop detection sensor S1 is not shown.

  In FIG. 3A, since the control is performed using the detection signal of the first loop detection sensor S1, the posture of the recording material P becomes the first loop detection position P1. In this case, the control unit 37 controls the conveyance speed of the fixing unit 40 so that the recording material P is substantially constant at the first loop detection position P1. The loop amount at this time is the first loop amount L1 described above.

  Depending on the detection and non-detection of the first loop detection sensor S1, the rotation speed (rotation speed) of the fixing unit 40 by the fixing motor M is changed between Mlow and Mhigh, so that the recording material P has the first loop amount. Control is performed so as to be carried within a certain range from L1.

  In FIG. 3B, since the control is performed using the detection signal of the second loop detection sensor S2, the posture of the recording material P becomes the second loop detection position P2. In this case, the control unit 37 controls the conveyance speed of the fixing unit 40 so that the recording material P is substantially constant at the second loop detection position P2. The loop amount at this time is the second loop amount L2 deeper than the first loop amount L1.

  Next, the control content using the detection result by the environment sensor 35 will be described in detail with reference to FIGS. 3 (a) and 3 (b) and FIGS. 6 (a) and 6 (b). FIG. 6A is a timing chart showing each timing of loop detection control when the detected humidity is higher than the threshold value Hh, and FIG. 6B is a timing chart when the detected humidity is lower than the threshold value Hl.

  First, the detected humidity H detected by the environmental sensor 53 is less than a preset lower threshold value H1 (see FIG. 6B), for example, the humidity of the outside air at a location where the image forming apparatus 50 is installed is 30%. If the recording material is lower, such as less than the recording material, the recording material does not contain much moisture, so that the rigidity becomes high. When the rigidity is high in this way, the influence of the movement of the trailing edge of the recording material jumps as the trailing edge of the recording material passes through the transfer portion 30 and the loop formed so far is released. It becomes larger than the bouncing action at the condition.

  Further, when the recording material passes through the transfer portion 30 and enters from the front end and is pulled into the fixing portion 40, the recording material has high rigidity so that the recording material does not move close to the conveyance guides 32 and 33. However, the recording material is less likely to rampage. For this reason, an image is rubbed against a part such as a cover near the fixing unit 40 or the conveyance guide 34 and image deterioration occurs, or a phenomenon such as hitting the fixing roller 100 before entering the fixing nip N properly is less likely to occur. . The phenomenon is that when a part of the recording material hits the fixing roller 100 before entering the fixing nip portion N, the unfixed toner image is preheated by the heat of the fixing roller 100 and has a recording portion thereof. The material is heated in the fixing nip portion N as usual and is overmelted, resulting in an image defect.

  As described above, when the detected humidity H is lower than the lower threshold value H1 (FIG. 6B), the rear end of the recording material passing through the transfer unit 30 is transferred to the transfer unit 30 regardless of the basis weight of the recording material. Before reaching, the recording material is switched to a shallow loop at an earlier timing than the trailing edge of the recording material passes through the transfer portion 30. That is, when the detected humidity is less than the threshold value Hl (less than the second predetermined humidity) lower than the threshold value Hh (predetermined humidity), the control unit 37 uses the transfer unit 30 and the fixing unit 40 to record the recording material regardless of the determination basis weight. In the process of conveyance, the conveyance speed difference is controlled so that a deep loop becomes a shallow loop.

  As described above, when the detected humidity H is lower than the lower threshold value H1, the control using the second loop detection sensor S2 is switched to the control using the first loop detection sensor S1, and the deep loop (large loop) to the shallow loop is switched. Switch to (small loop). After the trailing edge of the recording material passes through the transfer unit 30, the control by the first loop detection sensor S1 is continued until the fixing unit 40 is completely passed (see T3 in FIG. 6B).

  On the other hand, the detected humidity H detected by the environmental sensor 35 is equal to or higher than a preset upper threshold value Hh (see FIG. 6A). For example, the humidity of the outside air at the location where the image forming apparatus 50 is installed is 60%. If it is higher, such as above, the recording material contains a very large amount of moisture and the rigidity becomes low. When the rigidity is low in this way, especially with a very thin recording material having a small basis weight, even if the rear end passes through the transfer portion 30 and the holding force at the transfer portion 30 is lost, the loop formed so far is removed. The power to release is small. For this reason, image deterioration is unlikely to occur even if control for switching to a shallow loop is not performed before exiting the transfer section 30 as in the low humidity state described above.

  However, in a recording material having a small basis weight and a very thin recording medium, after the trailing edge passes through the transfer portion 30, the recording material enters the fixing portion 40 from the leading edge and reaches the fixing nip portion N as follows. May cause serious problems. That is, when a very thin recording material is transported in a shallow loop, it is transported without being supported by the transport guides 32 and 33, and therefore when entering the fixing nip portion N due to low rigidity. The rear end is prone to rampage.

  When controlling to switch to the shallow loop, the control unit 37 controls the rotation speed of the fixing motor M to Mhigh so that the conveyance speed of the fixing unit 40 becomes the first conveyance speed V1 so as to make the deep loop shallow. become. For this reason, the rapid pull-in of the fixing unit 40 promotes the above-described rampage when the trailing edge of the recording material enters the fixing unit 40. The extremely thin and damp recording material is further pulled by the fast pulling of the fixing unit 40 while the holding force is lost after the trailing edge has passed through the transfer unit 30, so that the fixing nip remains in an accelerated state. Part N will be drawn.

  Therefore, when the detected humidity H is higher than the preset upper threshold value Hh, the deep loop conveyance control using the second loop detection sensor S2 is continued even after the leading edge of the recording material enters the fixing unit 40. By doing so, it is possible to reduce the fluctuation of the recording material when passing through the transfer section 30. In addition to this, when the trailing edge of the recording material is extremely thin and wet, the conveyance guides 32 and 33 for guiding conveyance are close when the rear end enters the fixing nip portion N, so that the amount of fluctuation is further reduced.

  Therefore, in the present embodiment, when a very thin recording material is conveyed at high humidity when the detected humidity H is higher than the upper threshold value Hh, the recording material leading end enters the fixing nip portion N of the fixing unit 40 from the beginning. A deep loop is controlled using the loop detection sensor S2. According to the present embodiment, in the case of a recording material in which the stiffness is extremely weak as described above, image deterioration due to the trailing edge of the recording material jumping when passing through the transfer unit 30 is also recorded at the time of entering the fixing nip N. Image degradation due to the ramp of the rear end of the material can be reduced at the same time.

As described above, when the determination basis weight is equal to or higher than the predetermined basis weight (Mg / m ² ) in the high humidity environment where the detected humidity is equal to or higher than the upper threshold value Hh (predetermined humidity), the control unit 37 Control like this. That is, in the process of conveying the recording material between the transfer unit 30 and the fixing unit 40, the conveyance speed difference is set so that a deep loop (large loop) greater than or equal to a predetermined loop amount becomes a shallow loop (small loop) less than the predetermined loop amount. Control. Further, when the determination basis weight is less than the predetermined basis weight in the high humidity environment, the control unit 37 has a deep loop (large loop) in the process of transporting the recording material between the transfer unit 30 and the fixing unit 40. The conveyance speed difference is controlled so as to be maintained.

Even when the humidity is high, in the information regarding the recording material obtained at the beginning of image formation, the basis weight is equal to or higher than a predetermined upper limit (Mg / m ² in the present embodiment). Under the conditions where it can be determined that the rigidity is high, the following is performed. In this case, after the leading edge of the recording material enters the fixing unit 40, the deep loop control by the second loop detection sensor S2 until then is performed as the loop amount detection control equivalent to that at the time of low humidity, and the first loop detection sensor S1. Switch to shallow loop control. In other words, regardless of the basis weight of the recording material, before the trailing edge of the recording material passing through the transfer portion 30 reaches the transferring portion 30, the recording material trailing edge enters the shallow loop at an earlier timing than passing through the transfer portion 30. Switch.

  However, when the detected humidity is not higher than the upper threshold Hh or lower than the lower threshold Hl (between the threshold Hh and the threshold Hl), loop detection control corresponding to the basis weight of the recording material is executed. That is, when the basis weight is equal to or greater than a predetermined upper limit, the timing at which the recording material rear end passes through the transfer portion 30 before the rear end of the recording material passing through the transfer portion 30 reaches the transfer portion 30. Then, control is performed to switch from a deep loop to a shallow loop. On the other hand, when the basis weight is less than a predetermined upper limit, control is performed to maintain a deep loop before and after the trailing edge of the recording material exits the transfer portion 30.

  In the image forming apparatus 50, the control unit 37 detects the ON / OFF operation of the paper feed heating member 23 with the CPU 38, and considers the decrease in the amount of moisture by the paper feed heating member 23, and detects the humidity by the environmental sensor 35. The threshold value Hh (predetermined humidity) can be reduced (changed). In this case, the control unit 37 sets a value obtained by subtracting a predetermined predetermined humidity value from the threshold value Hh in accordance with the operating state (on / off state) of the paper feed heating member 23, and based on the set value, A transport speed difference between the fixing unit 40 and the transfer unit 30 (in this embodiment, speed adjustment of the fixing unit 40) is controlled. In that case, the control unit 37 also reduces (changes) the threshold value Hl (second predetermined humidity) under the humidity detection by the environment sensor 35 in consideration of the decrease in the amount of moisture by the paper feed heating member 23.

  The above loop detection control in the present embodiment will be described with reference to FIGS. 6 (a), 6 (b) and FIG. FIG. 7 is a flowchart showing the operation in this embodiment.

  That is, when rotation driving of the fixing motor M is started (step S1), the control unit 37 determines whether the humidity detected by the environment sensor 35 is equal to or higher than the upper threshold value Hh (step S2). In step S2, if the detected humidity is equal to or higher than the upper threshold value Hh (FIG. 6A), the process proceeds to step S3. If the detected humidity is not equal to or higher than the upper threshold value Hh, the process proceeds to step S6.

In step S3, the basis weight of the recording material is determined whether a predetermined value Mg / ^{m 2} or more and is not a predetermined value Mg / ^{m 2} or more process proceeds to step S4, a predetermined value Mg / ^{m 2} or more If there is, the process proceeds to step S7.

  In step S <b> 4, it is determined whether or not the rear end of the recording material has started to enter the transfer unit 30. This determination is made, for example, by the timer 39 counting a predetermined time after the leading edge position of the recording material P delivered from the registration roller pair 9 is detected by the registration sensor 44 (t1).

  If it is determined in step S4 that the trailing edge of the recording material has started to enter the transfer portion 30, the process proceeds to step S5. In step S5, the first loop detection masking Q1 is masked so that the signal from the first loop detection sensor S1 is not used for control (T1 to T3). In FIG. 6A, t2 indicates the time when the first loop detection sensor S1 is turned on, t3 indicates the time when the second loop detection sensor S2 is turned on, and t4 indicates the rotation speed of the fixing motor M. It shows the time when it was set to Mhigh.

  Subsequently, in step S10, it is determined whether or not the fixing by the fixing unit 40 has been completed. If it is determined that the fixing has been completed, the process proceeds to step S15, where the rotation of the fixing motor M is stopped and the process is terminated. On the other hand, when it is determined that the fixing is not completed, the process proceeds to step S11, and it is determined whether or not the detection by the second loop detection sensor S2 is ON.

  If it is determined in step S11 that the detection by the second loop detection sensor S2 is ON, in step S13, the conveyance speed of the fixing unit 40 is controlled to be the first conveyance speed V1. On the other hand, if it is determined in step S11 that the detection by the second loop detection sensor S2 is not ON, in step S12, the conveyance speed of the fixing unit 40 is controlled to be the second conveyance speed V2.

  On the other hand, in step S6, it is determined whether the humidity detected by the environmental sensor 35 is less than the lower threshold value H1. As a result, when the detected humidity is lower than the lower threshold value H1 (FIG. 6B), the process proceeds to step S7, and when the detected humidity is not lower than the lower threshold value H1 (that is, between the threshold values H1 and Hh). Proceeding to step S9, the loop detection control described above corresponding to the basis weight of the recording material is executed.

  In step S <b> 7, it is determined whether or not the rear end of the recording material has started to enter the transfer unit 30. If it is determined that the rush has started, the process proceeds to step S8, and the second loop detection masking Q2 is masked so that the signal from the second loop detection sensor S2 is not used for control (T2 to T3). Proceed to S14. If it is determined in step S7 that the trailing edge of the recording material does not start entering the transfer portion 30, step S7 is repeated.

  In step S14, it is determined whether or not the fixing by the fixing unit 40 is completed. If it is determined that the fixing is completed, the process proceeds to step S15, where the rotation of the fixing motor M is stopped and the process is terminated. On the other hand, when it is determined that the fixing is not completed, the process proceeds to step S16, and it is determined whether or not the detection by the first loop detection sensor S1 is ON.

  If it is determined in step S16 that the detection by the first loop detection sensor S1 is ON, in step S17, the conveyance speed of the fixing unit 40 is controlled to be the first conveyance speed V1. On the other hand, if it is determined in step S16 that the detection by the first loop detection sensor S1 is not ON, in step S18, the conveyance speed of the fixing unit 40 is controlled to be the second conveyance speed V2.

  In contrast to the loop detection control of the present embodiment, the following control is performed in FIG. FIG. 8 is a timing chart of loop detection control in the comparative example.

  That is, in the comparative example in which the conventional control is performed, the detected humidity of the installation environment detected by the environment sensor 35 as in the present embodiment and the judgment basis weight of the recording material are not taken into consideration, and in any environment However, only loop detection control for changing the loop amount is executed. Therefore, the control is such that the recording medium is transported in a deep loop until the trailing edge of the recording material is removed from the transfer section 30 and is simply switched to a shallow loop before the trailing edge of the recording material is removed from the transfer section 30. For this reason, it is difficult to avoid a large rampage when the trailing edge of the recording material enters the fixing unit 40, and it is difficult to prevent image deterioration that may occur in the recording material.

  On the other hand, according to this embodiment mentioned above, based on the detection loop by 1st, 2nd loop detection sensor S1, S2, the humidity detected by the environmental sensor 35, and the determination basis weight by the control part (basis weight determination means) 37. The following can be done. That is, it is possible to appropriately adjust the loop amount when the trailing edge of the recording material P conveyed by the transfer unit 30 and the fixing unit 40 comes out of the transfer unit 30.

  Accordingly, when a very thin recording material having a determination basis weight of less than a predetermined basis weight is conveyed in a high humidity environment, the deep end (large loop) is maintained before and after the rear end of the transfer material 30 is removed. The recording material can be stiffened to give rigidity. As a result, it is possible to avoid a large rampage when the trailing edge of the recording material enters the fixing unit 40. Therefore, image degradation that may occur in the recording material when transported between the transfer unit 30 and the fixing unit 40 is achieved. Can be effectively prevented.

  DESCRIPTION OF SYMBOLS 4 ... Recording material stacking part (paper feeding cassette), 23 ... Heating member (paper feeding heating member), 30 ... Transfer part, 35 ... Environment detection means (environment sensor), 37 ... Control means, Basis weight judgment means (control part) ), 40... Fixing unit, 50... Image forming apparatus, 50 a... Image forming apparatus main body, Hh... Predetermined humidity (upper threshold), Hl second predetermined humidity (lower threshold), L, L1, L2. (Loop amount, first loop amount, second loop amount), P ... recording material, S1, S2 ... loop detection means (first loop detection sensor, second loop detection sensor), V1, V2 ... conveying speed ( (1st transport speed, 2nd transport speed)

Claims (3)

A transfer unit configured to transfer a recording material by transferring an unfixed image; and a fixing unit disposed downstream of the transfer unit and configured to convey the recording material and fix the unfixed image on the recording material. In an image forming apparatus that transports by adjusting a loop amount of a recording material by controlling a transport speed difference between the fixing unit and the fixing unit,
Loop detection means for detecting a loop amount of a recording material formed between the transfer unit and the fixing unit as a loop amount of a plurality of stages;
Environment detection means for detecting humidity in the installation environment of the image forming apparatus main body;
A basis weight determining means for determining a basis weight of the recording material to be conveyed;
Control means for adjusting the loop amount of the recording material by controlling the transport speed difference based on the detection loop by the loop detection means, the humidity detected by the environment detection means, and the determination basis weight by the basis weight determination means; Have
The control means includes
In a high humidity environment where the detected humidity is equal to or higher than a predetermined humidity, when the basis weight determined by the basis weight determination unit is equal to or higher than a predetermined basis weight, in the process of transporting the recording material between the transfer unit and the fixing unit, The conveyance speed difference is controlled so that a large loop equal to or larger than a predetermined loop amount becomes a small loop smaller than the predetermined loop amount, and the transfer unit and the fixing unit In the process of transporting the recording material, the transport speed difference is controlled so that the large loop is maintained.
An image forming apparatus. The control means includes
When the detected humidity is less than a second predetermined humidity lower than the predetermined humidity, the recording material is transported between the transfer unit and the fixing unit regardless of the basis weight determined by the basis weight determination unit. Controlling the transport speed difference so that the small loop becomes the large loop,
The image forming apparatus according to claim 1. The image forming apparatus main body includes a recording material stacking unit for stacking a plurality of recording materials, and a heating member for heating the recording material stacking unit,
The control means includes
Corresponding to the operating state of the heating member, a value obtained by subtracting a predetermined predetermined humidity value from the predetermined humidity is set, and the conveyance speed difference is controlled based on the set value.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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