JP2007003714A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain variations in depth magnification caused by the elongation of an intermediate transfer body, when a toner image is transferred from the intermediate transfer body to a recording paper, and to stabilize the image quality. <P>SOLUTION: The feedforward compensation is carried out, by forecasting the elongation volume of an intermediate transfer belt 22 at a secondary transfer part T2 according to the kinds of applied paper P, etc., and gradually changing the pressure applied by a secondary transfer roller 30, starting from high to low so as to eliminate the forecasted elongation volume. As a result, pressure which would cause elongation in the intermediate transfer belt 22 will not be generated, thereby restraining variations in depth magnification by the elongation. Changes in the transfer bias voltage with the change (compensation) in pressure is taken into consideration, and the transfer bias voltage is adjusted, thereby avoiding deterioration in the image quality and maintaining the state with high image quality. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is provided between a photoreceptor and a recording medium physically separated from each other, and a primary transfer unit in which a toner image is transferred from the photoreceptor by a predetermined transfer bias voltage in contact with the photoreceptor. The toner image circulated between the recording medium and a secondary transfer section that transfers the toner image received by the primary transfer section to the recording medium to the recording medium with a predetermined transfer bias voltage. The present invention relates to an image forming apparatus including an intermediate transfer body having a surface formed of a material having elasticity.

  Intermediate transfer in which the toner image formed on the photoconductor is primarily transferred to an intermediate transfer body such as an elastic intermediate transfer belt by electrophotographic technology, and the toner image on the intermediate transfer body is secondarily transferred to paper. In a solid-state image forming apparatus, the degree of freedom of the movement path of the intermediate transfer belt is increased, and variations in component arrangement and toner image handling (moving to the transfer position on the recording paper) when the apparatus is configured are increased. Can do.

In the image forming apparatus using the intermediate transfer belt as described above, when the toner image on the intermediate transfer belt is transferred to the recording paper (that is, secondary transfer), based on the type, thickness, and transfer speed of the recording paper. It has been proposed to improve the transferability by providing a function of switching the contact pressure and electric field at the secondary transfer position of the toner image in several steps (see Patent Document 1 and Patent Document 2).
JP 2002-214943 A JP2003-131494A

  However, in the techniques of Patent Document 1 and Patent Document 2 described above, since the intermediate transfer belt has elasticity, the pressure applied to the recording paper is fixed. As a result, the intermediate transfer belt stretches, and as a result, the image magnification changes.

  More specifically, the extension of the intermediate transfer belt varies depending on the type and material of the recording paper and the pressure applied to the recording paper, but is stable in a state where the intermediate transfer belt is extended by a predetermined conveyance amount. In the transition period from the initial state until the elongation becomes stable, the image magnification changes.

  It is an object of the present invention to obtain an image forming apparatus capable of stabilizing image quality by suppressing fluctuations in vertical magnification due to elongation of an intermediate transfer member when transferring a toner image from the intermediate transfer member to a recording sheet.

  A first invention is a primary transfer unit that is interposed between a photoconductor and a recording medium that are physically separated from each other, contacts the photoconductor and transfers a toner image from the photoconductor by a predetermined transfer bias voltage. And a secondary transfer unit that contacts the recording medium and transfers the toner image received by the primary transfer unit to the recording medium to the recording medium with a predetermined transfer bias voltage, and the toner image An image forming apparatus including an intermediate transfer body formed of a material having an elastic force on a transfer surface of the intermediate transfer body between the intermediate transfer body and the recording medium at the time of transfer to the recording medium in the secondary transfer portion The pressure change means which changes the pressure concerning to from a high state to a low state is provided.

  According to the first invention, the transfer efficiency of the toner image is enhanced by applying a predetermined pressure between the intermediate transfer member and the recording medium in the secondary transfer portion.

  On the other hand, the intermediate transfer member having elasticity is stretched by this pressure, and the magnification (vertical magnification) in the conveyance direction of the recording medium varies.

  Therefore, the pressure applied between the intermediate transfer member and the recording medium is changed from a high state to a low state at the time of transfer.

  As a result, fluctuations in the vertical magnification can be suppressed.

  In the first invention, the image forming apparatus further includes a transfer bias correction unit that corrects the transfer bias voltage that changes due to the pressure change by the pressure change unit.

  The change in pressure causes a change in transfer bias voltage that affects the image quality together with the pressure.

  Therefore, the image quality can be maintained by correcting the transfer bias voltage in accordance with the change in pressure.

  According to a second aspect of the present invention, a primary transfer unit is interposed between a photosensitive member and a recording medium that are physically separated from each other, and contacts with the photosensitive member to transfer a toner image from the photosensitive member with a predetermined transfer bias voltage. And a secondary transfer unit that contacts the recording medium and transfers the toner image received by the primary transfer unit to the recording medium to the recording medium with a predetermined transfer bias voltage, and the toner image An image forming apparatus including an intermediate transfer body formed of a material having an elastic force on a transfer surface thereof, wherein a correlation between a transfer bias voltage in the secondary transfer portion and an extension amount of the intermediate transfer body in a circumferential movement direction is provided A correlation storage means for storing the relationship; a transfer bias voltage detection means for detecting a transfer bias voltage at the secondary transfer section; and a transfer via of the secondary transfer section detected by the transfer bias voltage detection means. From the voltage, based on the correlation stored in the correlation storage means, an elongation amount acquisition means for acquiring the elongation amount of the intermediate transfer member, and the intermediate transfer according to the elongation amount acquired by the elongation amount means Pressure adjusting means for adjusting the pressure applied between the body and the recording medium.

  According to the second invention, there is a correlation between the transfer bias voltage applied to the secondary transfer portion and the amount of elongation of the intermediate transfer member caused by the pressure applied between the intermediate transfer member and the recording medium. The correlation is stored, the amount of elongation of the intermediate transfer member is acquired based on the fluctuation of the transfer bias voltage, and the pressure applied between the intermediate transfer member and the recording medium is corrected so that the elongation is corrected. By adjusting, the fluctuation of the vertical magnification can be suppressed and the image quality can be improved.

  As described above, the present invention has an excellent effect that when the toner image is transferred from the intermediate transfer member to the recording paper, the fluctuation in the vertical magnification due to the elongation of the intermediate transfer member can be suppressed and the image quality can be stabilized.

(First embodiment)
An image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, the image forming apparatus 10 of the first embodiment is provided with a photoconductor 12 that is driven to rotate in the direction of arrow A (clockwise direction) in the figure at the approximate center in the apparatus. . A charging roll 14 for charging the surface of the photoconductor 12 is arranged around the photoconductor 12, and further, a laser beam L is irradiated on the surface of the photoconductor 12 charged by the charging roll 14 at a lower portion in the apparatus main body. An exposure device 16 for forming an electrostatic latent image is provided.

  A rotary developing device 18 that develops an electrostatic latent image formed on the photoconductor 12 into a toner image is disposed adjacent to the lower left of the photoconductor 12 in FIG. The rotary developing device 18 includes developing units 20Y, 20M, 20C, and 20K that respectively form toner images of four colors of yellow, yellow, magenta, cyan, and black.

  An intermediate transfer belt 22 as an intermediate transfer member to which a toner image visualized by the rotary developing device 18 is transferred is wound around a predetermined area on the peripheral surface of the photosensitive member 12 and on the upper right. , 26 holds the winding state.

  This winding area is the primary transfer portion T1.

  The intermediate transfer belt 22 is wound around a plurality of rollers 28A, 28B, and 28C to form a substantially triangular loop. The intermediate transfer belt 22 is rotated by the rotational force of the photosensitive member 12 by the winding region (that is, driven rotation). ).

  The intermediate transfer belt 22 is rotated four times so that the toner image on the photoconductor 12 is primarily transferred in the order of yellow, magenta, cyan, and black in the primary transfer portion T1, and the primary transferred toner image is transferred as follows. It is transported toward the secondary transfer portion T2.

  The secondary transfer portion T2 includes one of the rollers 28A, 28B, and 28C around which the intermediate transfer belt 22 is wound (the rightmost roller 28A in FIG. 1 in the first embodiment) and the secondary transfer roller. 30 between the secondary transfer roll 30 and the intermediate transfer belt 22 is a secondary transfer position.

  A paper feed tray 64 for storing paper P is provided at the lower part of the image forming apparatus 10. In the vicinity of the right side of the paper feed tray 64, a feed roll 66 for sending the paper P from the paper feed tray 64 to the transport path 40 is disposed. The paper P is taken out from the paper feed tray 64 by the feed roll 66 and is transported to the secondary transfer portion T2 through a predetermined transport path.

  In the conveyance path 40 of the sheet P having the secondary transfer portion T2 as an intermediate point, a fixing device 70 provided with a heating roll 72 and a pressure roll 74 on the downstream side of the secondary transfer portion T2, and further, A pair of discharge rolls 76 and 78 are provided on the downstream side. A discharge port 80 is formed in the left side wall portion of the discharge rolls 76 and 78, and a discharge tray 82 extending from the discharge port 80 to the left side (outside) in FIG.

  Here, in the secondary transfer portion T2 in the first embodiment, an adjustment mechanism portion 100 (see FIG. 2) for adjusting the contact pressure of the transfer roller 30 to the intermediate transfer belt 22 is provided. .

  As shown in FIG. 2, the adjustment mechanism unit 100 includes a stepping motor 102 as a drive source. The adjustment mechanism unit 100 is controlled by a controller 101. The controller 101 is equipped with data for obtaining a pressure adjustment amount from information such as the type of paper P and a memory such as a lookup table. Has been.

  An elliptical eccentric cam 104 is attached to the rotating shaft 102 </ b> A of the stepping motor 102, and a rotating arm 106 is disposed so as to contact the outer periphery of the eccentric cam 104. The eccentric cam 104 is not limited to an elliptical shape, and may be a disc shape with an eccentric mounting position of the rotating shaft 102A, or various polygons with corners having an R shape.

  The rotation arm 106 is attached to the casing 102 </ b> B of the stepping motor 102 through the shaft 108 at the center in the longitudinal direction. For this reason, the rotating arm 106 can be rotated around the shaft 108.

  One end (upper end) of the tension coil spring 110 is attached to the right end portion of the rotary arm 106 in FIG. The other end (lower end) of the tension coil spring 110 is fixed to a base 112 on which the stepping motor 102 is placed. Thereby, the rotary arm 106 is urged by the tension coil spring 110 so as to rotate in the clockwise direction in FIG. 2 (in the direction of arrow B in FIG. 2) as the center of the shaft 108.

  At this time, a part of the rotation arm 106 (between the shaft 108 and the attachment end of the tension coil spring 110) is in contact with the outer periphery of the eccentric cam 104, and the eccentric cam 104 rotates, whereby the tension coil spring is rotated. It is possible to rotate about the shaft 108 in a state in which the contact with the eccentric cam 104 is maintained by the urging force 110.

  The secondary transfer roller 30 is attached to the left end of the rotating arm 106 in FIG. For this reason, when the rotary arm 106 rotates, the shaft 114 moves in an arc shape, and accordingly, the secondary transfer roller 30 moves in an arc shape (see the solid line position and the imaginary line position in FIG. 2). . In the first embodiment, the movement range of the secondary transfer roller 30 is a range between the solid line position and the imaginary line position in FIG.

  Here, the arc-shaped movement of the secondary transfer roller 30 changes the distance from the intermediate transfer belt 22.

  In the first embodiment, the position where the secondary transfer roller 30 is located at the solid line position in FIG. 2 is the position farthest from the intermediate transfer belt 22 (retract position), and the position when the secondary transfer roller 30 is located at the imaginary line position in FIG. The position is close to the intermediate transfer belt 22. When the secondary transfer roller 30 is at the imaginary line position in FIG. 2, the pressure is the highest (maximum pressure position / initial advance position). When the secondary transfer roller 30 is gradually moved from this position toward the solid line position in FIG. In the middle, the sheet P is separated from the sheet P sandwiched between the intermediate transfer belt 22 (minimum pressure position).

  In the stepping motor 102, the movement range from the maximum pressure position to the minimum pressure position is set to a plurality of stages, and the pressure is changed stepwise from the start to the end of the secondary transfer. This pressure change has a function of correcting the vertical magnification fluctuation caused by the elongation of the intermediate transfer belt 22 that may occur during the secondary transfer.

  That is, in the secondary transfer portion T2, by applying a predetermined pressure and applying a predetermined transfer bias voltage between the paper P and the intermediate transfer belt 22, the toner image is properly transferred. This is an important requirement that greatly affects the image quality after transfer.

  However, this pressure causes the intermediate transfer belt 22 having elasticity to extend in the transport direction, and the vertical magnification of the image varies due to the extension.

  The elongation converges when it reaches a certain level, but the change in the longitudinal magnification occurs during the period from the beginning of the elongation to the convergence (transition period).

  Therefore, in order to reduce this elongation, the maximum pressure is applied at the initial stage of transfer (secondary transfer), and this pressure is gradually decreased to eliminate the elongation of the intermediate transfer belt 22.

  The number of pressure change stages and the pressure change timing vary depending on the type of paper P to be applied. In the first embodiment, the vertical magnification is set in advance using paper type, paper size, thickness information, and transfer speed as parameters. The setting value for correction control is determined.

  The set values for vertical magnification correction control are an initial advance position (initial secondary transfer roller 22 position) α, a step division number n, an advance correction interval time x, and an advance cancellation step number y based on the paper size.

  That is, secondary transfer is started in a state where the secondary transfer roller 22 is positioned at the initial advance position α (sheet leading edge entry), and the stepping motor 102 is set to a predetermined value based on the step division number n at every advance correction interval time x. Driving for the advance cancellation step number y is repeated n times (not necessarily up to the trailing edge of the paper) (see FIG. 3).

  The operation of the first embodiment will be described below.

  First, a color image forming operation by the image forming apparatus 10 of the first embodiment will be described.

  When an image forming signal is input to the image forming apparatus 10, the photosensitive member 12 is uniformly charged by the charging device 14, and the charged photosensitive member 12 is irradiated with laser light from the exposure device 16 based on the image forming signal. L is irradiated. With the laser light L, the surface of the photoconductor 12 is exposed to form an electrostatic latent image. The electrostatic latent image formed on the photoreceptor 12 is developed with yellow, magenta, cyan, and black toner images by the developing devices 20Y, 20M, 20C, and 20K of the rotary developing device 18, and is subjected to intermediate transfer at the primary transfer portion T1. Primary transfer is performed on the belt 22. The transfer residual toner remaining on the photoreceptor 12 after the primary transfer is scraped off and removed by a cleaning blade or the like.

  On the other hand, the paper P stored in the paper feed tray 64 is sent out by the feed roll 66, and only the uppermost paper P of the paper feed tray 64 is guided to the transport path 40, and is sent to the secondary transfer portion T2 at a predetermined timing. It is sent. The toner image primarily transferred to the intermediate transfer belt 22 is secondarily transferred to the paper P at the secondary transfer portion T2. The sheet P on which the toner image is transferred is guided to the fixing device 70 through a predetermined conveyance path, and the toner image is fixed by the thermal pressure by the heating roll 72 and the pressure roll 74. The paper P on which the image is formed by fixing the toner image is discharged from the discharge port 80 to the discharge tray 82 by the discharge rollers 76 and 78.

  Next, the position adjustment control of the secondary transfer roller 30 accompanying printing will be described with reference to the flowcharts of FIGS.

  FIG. 4 is a main routine for print start control. In step 150, image formation is started and conveyance of the paper P is started, and the process proceeds to step 152.

  In step 152, it is determined whether or not the sheet P has reached the secondary transfer standby position. If an affirmative determination is made, the process proceeds to step 154 to acquire various control information.

  The various types of control information vary depending on the paper P, and information on the paper type to be applied, paper size, thickness information, and transfer speed is acquired.

  In the next step 156, a setting value for vertical magnification correction control is determined based on the various control information.

  That is, the initial advance position α, the division number n, the advance correction time interval x, and the advance cancellation step number y are determined, and the process proceeds to step 158.

  In the next step 158, it is determined whether or not the image formation on the photoconductor 12 is completed, the toner image is transferred onto the intermediate transfer belt 22 by the primary transfer, and the secondary transfer timing is reached. In step 160, the stepping motor 102 is driven so as to position the secondary transfer roller 30 to the initial advance position (the imaginary line position in FIG. 2 in the first embodiment).

  By driving the stepping motor 102 (here, rotating in the counterclockwise direction in FIG. 2), the eccentric cam 104 is moved from the solid line position in FIG. 2 to the imaginary line position.

  With this movement, the rotating arm 106 rotates counterclockwise in FIG. 2 (the direction opposite to the arrow B direction in FIG. 2) about the shaft 108 against the urging force of the tension coil spring 110. Then, the secondary transfer roller 30 is moved to the imaginary line position (initial advance position) in FIG.

  As a result, the secondary transfer roller 30 is closest to the intermediate transfer belt 22 and the pressure on the paper P is maximized.

  In step 162, it is determined whether or not the initial advance position has been reached. If an affirmative determination is made, the process proceeds to step 164, the drive of the stepping motor 102 is stopped, and the process proceeds to step 166.

  In step 166, the correction number counter is reset, and then the process proceeds to step 168 to execute the vertical magnification correction process. Details of the vertical magnification correction processing will be described later (the flowchart of FIG. 5).

  When the vertical magnification correction process (for one time) in step 168 is completed, the process proceeds to step 170, where it is determined whether or not the transfer has been completed. If the negative determination is made, it is determined that further vertical magnification correction processing is necessary. Then, the process returns to step 168.

  If the determination in step 170 is affirmative, it is determined that all the vertical magnification correction processing has been completed, and the process proceeds to step 172.

  In step 172, the stepping motor 102 is driven so as to position the secondary transfer roller to the retract position.

  By driving the stepping motor 102 (here, the clockwise rotation in FIG. 2), the eccentric cam 104 is moved from the current position to the solid line position in FIG.

  Along with this movement, the rotating arm 106 follows the urging force of the tension coil spring 110 and rotates about the shaft 108 in the clockwise direction in FIG. 2 (in the direction of arrow B in FIG. 2). 30 is moved to the solid line position (retract position) in FIG.

  As a result, the secondary transfer roller 30 is separated from the intermediate transfer belt 22 and the pressure on the paper P is also zero.

  In the next step 174, it is determined whether or not the secondary transfer roller 30 has reached the retract position. If an affirmative determination is made, the process proceeds to step 176 to stop driving the stepping motor 102, and the process proceeds to step 178. .

  In step 178, it is determined whether or not there is the next printing. If an affirmative determination is made, the process returns to step 150 to repeat the above affirmation. If the determination in step 178 is negative, this routine ends.

  Next, details of the vertical magnification correction processing in step 168 of FIG. 4 will be described with reference to the flowchart of FIG.

  In step 180, it is determined whether or not the count value cnt exceeds the stage division number n (cnt ≧ n). If the determination is affirmative, it is determined that the vertical magnification correction processing has ended, and this routine is executed. finish.

  If a negative determination is made in step 180, the process proceeds to step 182 to continue the vertical magnification correction process.

  Step 182 sets a correction interval timing counter T. This correction interval timing counter T is determined by the number of times of vertical magnification correction, and x (n) is substituted.

  In the next step 184, the set correction interval timing counter T is started (counted down), and the process proceeds to step 186. In step 186, it is determined whether or not the correction interval timing counter T has become 0. If the determination is affirmative, the process proceeds to step 188 to move the secondary transfer roller toward the retract position (driving of the stepping motor 102). ).

  In the next step 190, it is determined whether or not the movement has been performed for y pulses. If the determination is affirmative, the process proceeds to step 192, the driving of the stepping motor 102 is stopped, and the process proceeds to step 194. In step 194, the count value cnt is incremented. At this time, the vertical magnification correction process for one time is finished, and this routine is finished.

  As described above, at the time of the secondary transfer in the secondary transfer portion T2, the secondary transfer roller 30 is caused to shift the pressure from a higher level to a lower level in a plurality of steps based on information previously set according to the type of the paper P or the like. Therefore, the elongation of the intermediate transfer belt 22 due to the pressure can be reduced, and fluctuations in the vertical magnification can be suppressed.

  In the above description, the pressure is adjusted by paying attention only to the correction of the vertical magnification caused by the extension of the intermediate transfer belt 22, but the transfer bias voltage at the secondary transfer portion T2 is changed by the change of the pressure. May change.

  This transfer bias voltage has a great influence on the transfer efficiency of the toner image, like the above-mentioned pressure, and is one of parameters that cannot be ignored when high image quality is required. Therefore, by correcting the transfer bias voltage according to the change in pressure, it becomes possible to correct the vertical magnification while maintaining the image quality.

  Since the correction of the transfer bias voltage has a correlation with the pressure, for example, the pressure value is correlated with the number of steps of the stepping motor 102, and the current value of the secondary transfer roller 30 is calculated by the correlation. The most optimal transfer bias voltage at the position may be obtained and corrected.

  As described above, in the first embodiment, the extension amount of the intermediate transfer belt 22 in the secondary transfer portion T2 is predicted according to the type of the paper P to be applied, and the predicted extension amount is eliminated. The feedforward correction is performed so that the pressure applied by the secondary transfer roller 30 is gradually changed from a higher value to a lower value. As a result, no pressure is applied to the intermediate transfer belt 22 to cause elongation, and fluctuations in the vertical magnification due to the elongation can be suppressed. In addition, by considering the change of the transfer bias voltage accompanying the change (correction) of the pressure, and adjusting this transfer bias voltage, it is possible to eliminate the deterioration of the image quality and maintain the high image quality state.

(Second Embodiment)
The second embodiment will be described below. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description of the configuration is omitted.

  The second embodiment corresponds to the second invention, whereas the first embodiment corresponds to the first invention.

  That is, the feature is that the extension amount of the intermediate transfer belt 22 is correlated with the transfer bias voltage applied to the secondary transfer portion T2, and the extension amount of the intermediate transfer belt 22 is determined based on the transfer bias voltage value. Thus, the pressure applied by the secondary transfer roller 30 is adjusted based on the amount of elongation.

  In other words, in the first embodiment, the amount of elongation is predicted in advance and the pressure applied by the secondary transfer roller 30 is feedforward corrected, whereas in the second embodiment, feedback correction is performed. To do.

  Since the image forming apparatus 10 and the pressure adjusting mechanism 100 applied to the second embodiment are the same as those of the first embodiment (see FIGS. 1 and 2), they are omitted, and according to FIGS. The pressure adjustment feedback control associated with the printing process according to the second embodiment will be described.

  FIG. 6 is a main routine of print control according to the second embodiment. In step 200, image formation is started and conveyance of the paper P is started, and the process proceeds to step 202.

  In step 202, it is determined whether or not the paper P has reached the secondary transfer standby position. If an affirmative determination is made, the process proceeds to step 204 to acquire various control information.

  The various types of control information vary depending on the paper P, and information on the paper type to be applied, paper size, thickness information, and transfer speed is acquired.

  In the next step 206, a setting value for vertical magnification correction control is determined based on the various control information. That is, the initial advance position α is determined and the routine proceeds to step 208.

  In the next step 208, it is determined whether the image formation on the photoconductor 12 is completed, the toner image is transferred onto the intermediate transfer belt 22 by the primary transfer, and the secondary transfer timing is reached. Then, the process proceeds to step 210, and the stepping motor 102 is driven so as to position the secondary transfer roller 30 to the initial advance position (the imaginary line position in FIG. 2 in the second embodiment).

  By driving the stepping motor 102 (here, rotating in the counterclockwise direction in FIG. 2), the eccentric cam 104 is moved from the solid line position in FIG. 2 to the imaginary line position.

  With this movement, the rotating arm 106 rotates counterclockwise in FIG. 2 (the direction opposite to the arrow B direction in FIG. 2) about the shaft 108 against the urging force of the tension coil spring 110. Then, the secondary transfer roller 30 is moved to the imaginary line position (initial advance position) in FIG.

  As a result, the secondary transfer roller 30 is closest to the intermediate transfer belt 22 and the pressure on the paper P is maximized.

  In step 212, it is determined whether or not the initial advance position has been reached. If an affirmative determination is made, the process proceeds to step 214 to stop driving the stepping motor 102, and the process proceeds to step 216 to monitor the transfer bias voltage. And the process proceeds to step 218.

  In step 218, transfer bias monitoring vertical magnification correction processing is executed. Details of this vertical magnification correction processing will be described later (flow chart of FIG. 7).

  When the vertical magnification correction process (one time) in step 218 is completed, the process proceeds to step 220, where it is determined whether or not the transfer has been completed. If a negative determination is made, it is determined that further vertical magnification correction processing is necessary. Then, the process returns to step 218.

  If the determination in step 220 is affirmative, it is determined that all the vertical magnification correction processing has been completed, and the process proceeds to step 222.

  In step 222, the stepping motor 102 is driven so as to position the secondary transfer roller to the retract position.

  By driving the stepping motor 102 (here, the clockwise rotation in FIG. 2), the eccentric cam 104 is moved from the current position to the solid line position in FIG.

  With this movement, the rotating arm 106 follows the urging force of the tension coil spring 110 and rotates about the shaft 108 in the clockwise direction in FIG. 2 (in the direction of arrow B in FIG. 2). 30 is moved to the solid line position (retract position) in FIG.

  As a result, the secondary transfer roller 30 is separated from the intermediate transfer belt 22 and the pressure on the paper P is also zero.

  In the next step 224, it is determined whether or not the secondary transfer roller 30 has reached the retract position. If an affirmative determination is made, the process proceeds to step 226, the driving of the stepping motor 102 is stopped, and the process proceeds to step 228. Then, the monitoring of the transfer bias voltage is terminated, and the process proceeds to Step 230.

  In step 230, it is determined whether or not there is the next printing. If an affirmative determination is made, the process returns to step 200 to repeat the above affirmation. If a negative determination is made in step 230, this routine ends.

  Next, details of the transfer bias voltage monitoring vertical magnification correction process in step 218 of FIG. 6 will be described with reference to the flowchart of FIG.

  In step 232, it is determined whether or not the transfer bias voltage change amount ΔB exceeds the transfer bias voltage change allowable upper limit Bmax. If the determination is negative, the process proceeds to step 234, and the transfer bias voltage change amount is determined. It is determined whether or not ΔB is below the transfer bias voltage change allowable lower limit Bmin. If a negative determination is made in this step 234, it is determined that the amount of change in the transfer bias voltage is within the allowable range, so that it is not subject to pressure correction, and this routine ends.

  If the determination in step 232 is affirmative, it is determined that the amount of change in the transfer bias voltage exceeds the upper limit value, and the process proceeds to step 236 to move the secondary transfer roller 30 in the retract direction.

  In step 236, it is determined whether or not the secondary transfer roller 30 is at the limit position in the retract direction (ynow ≧ ymin). If the determination is affirmative (limit position), the correction cannot be made and the routine ends. If a negative determination is made in step 236, the process proceeds to step 238, where the secondary transfer roller 30 is started to move in the retract direction, and the driving of the stepping motor 102 is started.

  In the next step 240, it is determined whether or not the stepping motor 102 has been driven by a predetermined pulse. If an affirmative determination is made, the process proceeds to step 242 to stop the driving of the stepping motor 102 and this routine ends. .

  On the other hand, if an affirmative determination is made in step 234, it is determined that the amount of change in the transfer bias voltage exceeds the lower limit, and the process proceeds to step 244 to move the secondary transfer roller 30 in the advance direction.

  In step 244, it is determined whether or not the secondary transfer roller 30 is in the limit position in the advance direction (ynow ≧ ymax). If the determination is affirmative (limit position), the correction cannot be made and the routine ends. If the determination in step 244 is negative, the process proceeds to step 246, where the stepping motor 102 is started to start moving the secondary transfer roller 30 in the advance direction.

  In the next step 248, it is determined whether or not the stepping motor 102 has been driven by a predetermined pulse. If an affirmative determination is made, the routine proceeds to step 250 where the driving of the stepping motor 102 is stopped and this routine ends. .

  As described above, in the second embodiment, paying attention to the correlation between the transfer bias voltage at the secondary transfer portion T2 and the elongation amount of the intermediate transfer belt 22, the change is based on the change in the transfer bias voltage. Since the elongation amount of the intermediate transfer belt 22 is acquired and the pressure by the secondary transfer roller 30 in the secondary transfer portion T2 is feedback-corrected so that the acquired elongation amount is corrected, the intermediate transfer belt due to the pressure is corrected. 22 can be reduced, and fluctuations in the vertical magnification can be suppressed.

  In the second embodiment, the allowable amount of change in the transfer bias voltage is determined and feedback correction is performed within the allowable amount. However, the first bias is set so as not to exceed the allowable amount. You may make it use the feedforward correction | amendment of embodiment together.

1 is a configuration diagram illustrating an overall configuration of an image forming apparatus according to a first embodiment. It is the schematic of the pressure adjustment mechanism in the secondary transfer part which concerns on 1st Embodiment. It is a front view of the paper which shows the timing of the pressure adjustment which concerns on 1st Embodiment. 4 is a flowchart illustrating a main routine of print processing control according to the first embodiment. It is a flowchart which shows the vertical magnification correction control routine which concerns on 1st Embodiment. 10 is a flowchart illustrating a main routine of print processing control according to the second embodiment. It is a flowchart which shows the transfer bias voltage monitoring vertical magnification correction control routine which concerns on 2nd Embodiment.

Explanation of symbols

T1 Primary transfer portion T2 Secondary transfer portion P Paper 10 Image forming device 12 Photoconductor 14 Charging roll 16 Exposure device 18 Rotary developing device 20Y, 20M, 20C, 20K Developer 22 Intermediate transfer belt (intermediate transfer member)
23, 24, 26 Roller 28A, 28B, 28C Roller 30 Secondary transfer roll 40 Transport path 64 Paper feed tray 66 Feed roll 70 Fixing device 72 Heating roll 74 Pressure roll 76, 78 Discharge roll 80 Discharge port 100 Adjustment mechanism ( Pressure changing means, pressure adjusting means)
101 controller (correlation storage means, transfer bias voltage detection means, elongation acquisition means)
102 Stepping motor 102A Rotating shaft 102B Casing 104 Eccentric cam 106 Rotating arm 108 Shaft 110 Tension coil spring 112 Base 114 Shaft

Claims (3)

A primary transfer unit that is interposed between a photosensitive member and a recording medium physically separated from each other, contacts the photosensitive member, and transfers a toner image from the photosensitive member with a predetermined transfer bias voltage; and the recording medium; The toner image transferred to the recording medium by a predetermined transfer bias voltage, and the transfer surface of the toner image is elasticized. An image forming apparatus comprising an intermediate transfer member formed of a material having
An image forming apparatus comprising pressure changing means for changing a pressure applied between the intermediate transfer member and the recording medium from a high state to a low state at the time of transfer to the recording medium in the secondary transfer unit.   2. The image forming apparatus according to claim 1, further comprising a transfer bias correcting unit that corrects the transfer bias voltage that changes due to a pressure change by the pressure changing unit. A primary transfer unit that is interposed between a photosensitive member and a recording medium physically separated from each other, contacts the photosensitive member, and transfers a toner image from the photosensitive member with a predetermined transfer bias voltage; and the recording medium; The toner image transferred to the recording medium by a predetermined transfer bias voltage, and the transfer surface of the toner image is elasticized. An image forming apparatus comprising an intermediate transfer member formed of a material having
Correlation storage means for storing the correlation between the transfer bias voltage in the secondary transfer portion and the amount of elongation of the intermediate transfer member in the circumferential movement direction;
Transfer bias voltage detection means for detecting a transfer bias voltage in the secondary transfer portion;
An elongation amount acquisition means for acquiring an elongation amount of the intermediate transfer body from the transfer bias voltage of the secondary transfer portion detected by the transfer bias voltage detection means based on the correlation stored in the correlation storage means; ,
Pressure adjusting means for adjusting the pressure applied between the intermediate transfer member and the recording medium in accordance with the amount of elongation acquired by the amount of stretching means;
An image forming apparatus.

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