JP2007286382A - Transfer apparatus, and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, capable of suppressing the disturbance and color shift of an image in second and subsequent printout paper due to the speed fluctuation of an intermediate transfer belt 41 at the advancing of the recording paper P into secondary transfer nips. <P>SOLUTION: A pressing force adjusting means, consisting of a cam 55 and an energizing coil spring, etc., for adjusting the pressing force of a secondary transfer roller 51 forming the secondary transfer nips by abutting against the intermediate transfer belt 41, is provided, and a controller 11 which is a pressing force control means is constituted so as to execute the control to make the pressing force weaker than that immediately before advance, at the advancing of the recording paper P into the secondary transfer nips. According to such a configuration, the torque up of a belt-driving motor, by advancing of the recording paper P into secondary transfer nips is offset by the torque down due to the decrease of the pressing force by the secondary transfer roller 51 and the abrupt decrease of the rotating speed of the belt-driving roller at the time of advancing is suppressed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, a visible image developed on the surface of a latent image carrier is transferred from the latent image carrier to the front surface of an intermediate transfer belt, and then sandwiched in a transfer nip formed by contact between the belt and a transfer member. The present invention relates to a transfer device for transferring to a recording member. The present invention also relates to an image forming apparatus such as a printer, a copying machine, and a facsimile using the transfer device.

  In this type of image forming apparatus, when a speed fluctuation occurs in the intermediate transfer belt that is endlessly moved while being stretched by a plurality of stretching rollers, the visible image being transferred from the latent image carrier to the belt Will be disturbed. In particular, in a multicolor image forming apparatus in which visible images of different colors are sequentially superimposed and transferred onto the intermediate transfer belt, color misregistration occurs due to belt speed fluctuations.

  Accordingly, an image forming apparatus that stabilizes the speed of the intermediate transfer belt by detecting the speed fluctuation of the intermediate transfer belt and feeding back the result to the driving speed of the belt drive motor (hereinafter referred to as feedback control). Various are known. As a method of detecting the speed fluctuation of the intermediate transfer belt, for example, as disclosed in Patent Document 1, there is a method of detecting marks provided at a predetermined pitch in the circumferential direction of the intermediate transfer belt with an optical sensor or the like. There is also a method in which the rotational angular velocity of a belt driving roller that moves the intermediate transfer belt endlessly with its own rotational drive is detected by an encoder, and the speed fluctuation of the intermediate transfer belt is detected based on the detection result. Further, as disclosed in Patent Document 2, there is a method using these methods in combination.

JP 11-24507 A Japanese Patent Laid-Open No. 10-232565

  However, even if such feedback control is performed, in the continuous print mode in which images are continuously output to a plurality of recording papers, two image disturbances that may be caused by belt speed fluctuations are detected. It may cause the recording paper after the first. The present inventors have conducted intensive research on the cause of such inconvenience, and have found the following. That is, in general, in an image forming apparatus using an intermediate transfer belt, a transfer nip is formed by contacting the belt front surface with a contact member such as a secondary transfer roller. Then, the visible image transferred from the latent image carrier such as a photosensitive member to the intermediate transfer belt is secondarily transferred to a recording member such as a recording sheet sandwiched between transfer nips. Prior to the secondary transfer, when the leading end side of the recording paper enters the transfer nip, the torque with respect to the belt drive motor increases rapidly. And it turned out that the rotational speed of the belt drive motor is greatly reduced for a moment and the speed of the belt is rapidly reduced.

  The feedback control described above is control for returning the belt speed to the original speed by adjusting the driving speed of the belt driving motor based on the detection result when the belt speed fluctuation occurs. Such control is effective for relatively gradual speed fluctuations, but if a rapid speed fluctuation occurs, the image is disturbed before the fluctuation result is fed back to the belt drive motor. In the continuous print mode, when the recording paper enters the transfer nip, a visible image for secondary transfer onto the subsequent recording paper is primarily transferred from the latent image carrier to the intermediate transfer belt. For this reason, image disturbance has occurred in the second and subsequent recording sheets due to a rapid decrease in the belt speed when the recording sheet enters the transfer nip.

  In addition, when the trailing edge of the recording member sandwiched in the transfer nip is discharged from the transfer nip, if the torque with respect to the belt drive motor suddenly decreases, the rotational speed of the belt drive motor increases greatly for a moment, and the belt Speed increases rapidly. At this time, the rate of increase in speed is smaller than the rate of decrease in speed when the recording member enters the transfer nip.

  The present invention has been made in view of the above background, and an object thereof is to provide the following transfer device and an image forming apparatus using the same. That is, a transfer device or the like that can suppress image disturbance caused by a change in the speed of the intermediate transfer belt when the recording member enters the transfer nip or the trailing end of the recording member is discharged from the transfer nip.

In order to achieve the above object, the invention of claim 1 functions as an endless intermediate transfer belt that is endlessly moved while being stretched by a plurality of stretching rollers, and functions as one of the stretching rollers. A transfer nip forming roller that forms a transfer nip to the recording member by abutting from the belt front surface side on the belt wrapping position with respect to the nip backside stretching roller, and developed on the surface of the latent image carrier. In the transfer device for transferring the visual image from the surface to the front surface of the intermediate transfer belt and then transferring the image to a recording member sandwiched in the transfer nip, at least one of the plurality of stretching rollers, or A contact member that contacts the intermediate transfer belt; a pressing force adjusting means that adjusts a pressing force of the contact member against the tension member or the intermediate transfer belt; When entering the flop and is characterized by comprising a pressing force control means for controlling the pressing force adjusting means to weaken than in the immediately preceding entry of the pressing force.
According to a second aspect of the present invention, there is provided an endless intermediate transfer belt that is endlessly moved while being stretched by a plurality of stretching rollers, and a nip backside stretching roller that functions as one of the stretching rollers. A transfer nip forming roller that forms a transfer nip to the recording member by abutting from the belt front surface side to the belt wrapping position with respect to the belt, and a visible image developed on the surface of the latent image carrier is removed from the surface. In the transfer device for transferring to the recording member sandwiched in the transfer nip after transferring to the front surface of the intermediate transfer belt, at least one of the plurality of stretching rollers, or the intermediate transfer belt, An abutting member that abuts, a pressing force adjusting unit that adjusts a pressing force of the contact member against the tension member or the intermediate transfer belt, and a rear end of the recording member is discharged from the transfer nip. When that is characterized in that provided a pressing force control means for controlling the pressing force adjusting means so as enhance than in the immediately preceding discharge the pressing force.
According to a third aspect of the present invention, there is provided a latent image carrier for carrying a latent image, developing means for developing a latent image carried on the latent image carrier to obtain a visible image, and the latent image carrier. In an image forming apparatus including a transfer device for transferring the upper visible image to a recording member, the transfer device according to claim 1 or 2 is used as the transfer device.
According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, a contact roller is used as the contact member.
According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, the transfer nip forming roller that contacts the intermediate transfer belt is used as the contact roller.
According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect, the nip back-side stretching roller is also used as a belt driving roller that moves the intermediate transfer belt endlessly with its own rotational driving. It is what.
According to a seventh aspect of the present invention, in the image forming apparatus according to the third aspect of the present invention, the contact member is a surface immovable member.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the third to seventh aspects, a recording member detecting means for detecting the recording member passing through a position facing the self is provided, and the recording member detection is performed. The pressing force control means so as to perform control for obtaining the timing at which the recording member enters the transfer nip or the timing at which the rear end of the recording member is discharged from the transfer nip based on the detection result by the means. It is characterized by comprising.
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the third to seventh aspects, a thickness information acquisition unit that acquires thickness information of the recording member is provided, and the recording member enters the transfer nip. The pressing force control means is arranged so that control is performed to vary the degree of change of the pressing force according to the thickness information when the recording member is discharged from the transfer nip. It is characterized by comprising.
According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, the thickness information acquiring unit is a thickness detecting unit that detects the thickness of the recording member.
According to an eleventh aspect of the present invention, in the image forming apparatus according to the tenth aspect, at least one of the pair of conveying members that conveys the recording member sandwiched between conveying nips obtained by bringing the surfaces that move endlessly into contact with each other. Drive current detection means for detecting the drive current of the motor that is the drive source of the member is provided, and the thickness detection means detects the thickness of the recording member based on the detection result by the drive current detection means. It is characterized by being used.
According to a twelfth aspect of the present invention, in the image forming apparatus according to the eleventh aspect, the driving current detecting means is a driving source for a conveying member disposed upstream of the transfer nip in the recording member conveying direction. The present invention is characterized in that a sensor that detects the drive current of the motor is used.
The invention according to claim 13 is the image forming apparatus according to claim 10, wherein the driving source of the belt driving roller is configured to endlessly move the intermediate transfer belt by its own rotational drive while functioning as one of the plurality of stretching rollers. Drive current detection means for detecting the drive current of the motor is provided, and as the thickness detection means, what detects the thickness of the recording member based on the detection result by the drive current detection means is used. It is a feature.
According to a fourteenth aspect of the present invention, in the image forming apparatus according to the tenth aspect, the thickness detecting unit detects a thickness of the recording member based on a light transmittance with respect to the recording member. To do.
The invention according to claim 15 is the image forming apparatus according to claim 10, wherein at least one of the pair of conveying members that conveys the recording member sandwiched between conveying nips obtained by bringing the surfaces that move endlessly into contact with each other. Displacement amount detection means for detecting the displacement amount of the member is provided, and the thickness detection means is one that detects the thickness of the recording member based on the detection result by the displacement amount detection means. It is.
According to a sixteenth aspect of the present invention, in the image forming apparatus according to the tenth aspect, at least one of the pair of conveying members that conveys the recording member sandwiched between conveying nips obtained by bringing the surfaces that move endlessly into contact with each other. A surface speed detecting means for detecting a surface moving speed of the member is provided, and a means for detecting the thickness of the recording member based on a detection result by the surface speed detecting means is used as the thickness detecting means. Is.
According to a seventeenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, an input means for performing an operation of inputting thickness information by an operator is used as the thickness information acquiring means.
According to an eighteenth aspect of the present invention, in the image forming apparatus according to any one of the third to seventh aspects, width information acquisition means for acquiring width information that is length information in a direction orthogonal to the conveying direction of the recording member. And the degree of change in the pressing force when the recording member enters the transfer nip or when the trailing end of the recording member is discharged from the transfer nip is made different according to the width information. The pressing force control means is configured to perform control.
According to a nineteenth aspect of the present invention, in the image forming apparatus according to the eighteenth aspect, the width information acquiring unit is a width detecting unit that detects the width of the recording member.
According to a twentieth aspect of the present invention, in the image forming apparatus according to the nineteenth aspect, a plurality of recording member detecting means are provided for detecting the recording member that passes through a position facing the recording member while being arranged in the width direction of the recording member. In addition, as the width detecting means, a means for detecting the width of the recording member based on the detection result by the recording member detecting means is used.
According to a twenty-first aspect of the present invention, in the image forming apparatus of the eighteenth aspect, the width information acquiring unit uses an input unit that allows an operator to perform a width information input operation.
According to a twenty-second aspect of the present invention, in the image forming apparatus according to any one of the third to seventh aspects, a gap information obtaining unit is provided for obtaining the gap information which is the gap information of the recording member. When the recording member enters the transfer nip or when the rear end of the recording member is discharged from the transfer nip, control is performed to vary the degree of change in the pressing force according to the gap information. Thus, the pressing force control means is configured.
The invention of claim 23 is characterized in that, in the image forming apparatus of claim 22, an input means for performing a clearance information input operation by an operator is used as the clearance information acquisition means. .
According to a twenty-fourth aspect of the present invention, in the image forming apparatus according to any one of the third to seventh aspects, an inclination detecting unit that detects an inclination of the recording member being conveyed from the direction orthogonal to the conveying direction of the recording member being conveyed. And the degree of change in the pressing force when the recording member enters the transfer nip or when the rear end of the recording member is discharged from the transfer nip is varied according to the inclination. The pressing force control means is configured to perform control.
According to a twenty-fifth aspect of the present invention, in the image forming apparatus according to the twenty-fourth aspect, a plurality of recording member detecting means are provided for detecting the recording member that passes through the position facing the recording member while being arranged in the width direction of the recording member. In addition, as the tilt detection unit, a unit that detects the tilt of the recording member based on a detection result by the recording member detection unit is used.
According to a twenty-sixth aspect of the present invention, in the image forming apparatus of the twentieth or twenty-fifth aspect, an optical sensor for optically detecting the recording member is used as each of the plurality of recording member detection means. Is.
According to a twenty-seventh aspect of the present invention, in the image forming apparatus according to the twentieth or twenty-fifth aspect, as the plurality of recording member detecting means, a switch member that connects / disconnects an electrical contact with the contact / separation with the recording member. It is characterized by being used.
The invention according to claim 28 is the image forming apparatus according to any one of claims 3 to 27, wherein, as the transfer device, the latent image carrier is brought into contact with the back surface of the intermediate transfer belt through the intermediate transfer belt. And applying a transfer voltage to the latent image facing member opposite to the latent image bearing member, and transferring the visible image on the latent image carrier to the intermediate transfer belt, and applying the transfer voltage to the latent image facing member is started. In this case, the pressing force control means is configured so that control is performed to weaken the pressing force immediately before the start of application.
The invention according to claim 29 is the image forming apparatus according to any one of claims 3 to 28, wherein, as the transfer device, the latent image carrier is brought into contact with the back surface of the intermediate transfer belt through the intermediate transfer belt. Using a transfer device that transfers a visible image on the latent image carrier to the intermediate transfer belt while applying a transfer voltage to the latent image facing member, and stops applying the transfer voltage to the latent image facing member. In this case, the pressing force control means is configured so that the control for increasing the pressing force immediately before stopping the application is performed.
A thirty-third aspect of the invention is the image forming apparatus according to any one of the third to thirty-ninth aspects, wherein the intermediate transfer belt is moved endlessly by its own rotational drive while functioning as one of the plurality of stretching rollers. Drive current detection means for detecting the drive current of the motor that is the drive source of the drive roller is provided, and when the recording member enters the transfer nip, and the rear end of the recording member is discharged from the transfer nip. The pressing force control means is configured to perform control to change the pressing force in accordance with a detection result by the driving current detection means within a predetermined period not including the time when the driving current is detected. Is.
According to a thirty-first aspect of the present invention, in the image forming apparatus according to any one of the third to thirty-ninth aspects, a roller speed detecting unit that detects a rotational speed or an angular speed of any one of the plurality of stretching rollers is provided. In addition, the pressing force control means is configured to perform control to change the pressing force in accordance with a detection result by the roller speed detection means.
According to a thirty-second aspect of the present invention, in the image forming apparatus according to any one of the third to thirty-ninth aspects, a surface speed detecting means for detecting a surface speed of the intermediate transfer belt is provided, and a detection result by the surface speed detecting means. According to the present invention, the pressing force control means is configured so that the control for changing the pressing force is performed.
According to a thirty-third aspect of the present invention, in the image forming apparatus according to any one of the third to thirty-second aspects, the pressing force adjusting means adjusts the pressing force as the motor is driven. To do.
The invention according to claim 34 is the image forming apparatus according to any one of claims 3 to 33, wherein the plurality of developing means are arranged to face one latent image carrier, and development is performed by different developing means. The visible image thus formed is sequentially transferred onto the intermediate transfer belt.
The invention according to claim 35 is the image forming apparatus according to any one of claims 3 to 33, wherein a plurality of combinations of the latent image carrier and the developing means are opposed to the front surface of the intermediate transfer belt. The visible image developed and developed on each latent image carrier is superimposed on the intermediate transfer belt and transferred.

In these inventions, all of the invention specific matters of claim 1 are provided, and when a recording member such as recording paper enters the transfer nip, it is brought into contact with the intermediate transfer belt or a stretching roller for stretching the recording belt. The pressing force of the abutting member on the roller or belt is made weaker than that immediately before entering. In such a configuration, the torque increase of the belt drive motor due to the recording member entering the transfer nip is offset by the torque reduction due to the decrease in the pressing force by the abutting member, and the rotation speed of the belt drive motor at the time of entry suddenly increases. Suppresses the decline. Accordingly, it is possible to suppress image disturbance caused by the speed fluctuation of the intermediate transfer belt when the recording member enters the transfer nip.
Further, in the invention having all of the matters specified in the invention of claim 2, when the rear end of the recording member is discharged from the transfer nip, the contact is made to contact the intermediate transfer belt or a tension roller for stretching the intermediate transfer belt. The pressing force of the member against the roller or belt is made stronger than that immediately before entering. In such a configuration, the torque reduction of the belt drive motor due to the trailing end of the recording member being discharged from the transfer nip is offset by the torque increase due to the increase of the pressing force by the contact member, and the belt drive motor is Suppresses rapid increase in rotation speed. Accordingly, it is possible to suppress image disturbance due to the speed fluctuation of the intermediate transfer belt when the trailing end of the recording member is discharged from the transfer nip.

Hereinafter, a first embodiment of an electrophotographic copying machine (hereinafter simply referred to as a copying machine) will be described as an image forming apparatus to which the present invention is applied.
First, the basic configuration of the copier according to the first embodiment will be described. FIG. 1 is a schematic configuration diagram showing a copying machine according to the first embodiment. The copier shown in FIG. 1 includes a printer unit 100 that forms an image, a scanner 200 fixed above the printer unit 100, and an automatic document feeder (ADF) 300 fixed above the printer unit 100. The scanner 200 optically reads an image of a document by a known technique. The automatic document feeder 300 automatically conveys a document to the reading unit of the scanner 200 using a known technique.

  The printer unit 100 includes four process units 1Y, 1C, 1M, and 1K for yellow, magenta, cyan, and black (hereinafter referred to as Y, C, M, and K) as process units as toner image forming units. Yes. These use Y, C, M, and K toners of different colors as image forming substances for forming an image, but the other configurations are the same. Taking a process unit 1Y for generating a Y toner image as an example, this includes a photoconductor unit 2Y and a developing device 7Y as shown in FIG.

  As shown in FIG. 3, the photosensitive unit 2Y and the developing device 7Y are integrally attached to and detached from the printer unit body as a process unit 1Y. However, in a state where it is detached from the printer unit main body, the developing device 7Y can be attached to and detached from the photosensitive unit (not shown) as shown in FIG.

  In FIG. 2 described above, the photoconductor unit 2Y includes a drum-shaped photoconductor 3Y serving as a latent image carrier, a drum cleaning device 4Y, a static eliminator (not shown), a charging device 5Y, and the like.

  The charging device 5Y uniformly charges the surface of the photoreceptor 3Y that is driven to rotate in the clockwise direction in the drawing by a driving unit (not shown). In the figure, the charging roller 6Y that is driven to rotate counterclockwise in the drawing while a charging bias is applied by a power source (not shown) is brought close to the photosensitive member 3Y, thereby charging the photosensitive member 3Y uniformly. Device 5Y is shown. Instead of the charging roller 6Y, a roller that contacts a charging brush may be used. Further, a charger that uniformly charges the photoreceptor 3Y by a charger method, such as a scorotron charger, may be used. The surface of the photoreceptor 3Y uniformly charged by the charging device 5Y is exposed and scanned by a laser beam emitted from an optical writing unit to be described later, and carries a Y electrostatic latent image.

  The developing device 7Y as developing means has a first agent accommodating portion 9Y in which a first conveying screw 8Y is disposed. Further, it also has a second agent storage portion 14Y in which a toner concentration sensor (hereinafter referred to as a toner concentration sensor) 10Y composed of a magnetic permeability sensor, a second conveying screw 11Y, a developing roll 12Y, a doctor blade 13Y, and the like are disposed. . In these two agent storage portions, a Y developer (not shown) composed of a magnetic carrier and a negatively chargeable Y toner is included. The first transport screw 8Y is driven to rotate by a driving unit (not shown), thereby transporting the Y developer in the first agent storage unit 9Y from the near side to the far side in the direction perpendicular to the drawing sheet. And it penetrates into the 2nd agent accommodating part 14Y through the communication port which is not shown in the partition wall between the 1st agent accommodating part 9Y and the 2nd agent accommodating part 14Y.

  The second transport screw 11Y in the second agent storage portion 14Y is driven to rotate by a driving means (not shown), thereby transporting the Y developer from the back side to the front side in the drawing. The toner concentration of the Y developer being conveyed is detected by the toner concentration sensor 10Y fixed to the bottom of the first agent storage portion 14Y. In this manner, the developing roll 11Y is arranged in a posture parallel to the second transport screw 11Y above the second transport screw 11Y that transports the Y developer. The developing roller 11Y includes a magnet roller 16Y in a developing sleeve 15Y made of a non-magnetic pipe that is driven to rotate counterclockwise in the drawing. A part of the Y developer conveyed by the second conveying screw 11Y is pumped up to the surface of the developing sleeve 15Y by the magnetic force generated by the magnet roller 16Y. Then, after the layer thickness is regulated by the doctor blade 13Y disposed so as to maintain a predetermined gap from the developing sleeve 15Y as a developing member, the layer thickness is regulated and conveyed to the developing area facing the photosensitive member 3Y. Y toner is adhered to the Y electrostatic latent image. This adhesion forms a Y toner image on the photoreceptor 3Y. The Y developer that has consumed the Y toner by the development is returned to the second conveying screw 11Y as the developing sleeve 15Y of the developing roll 12Y rotates. And if it conveys to the near end in a figure, it will return in the 1st agent accommodating part 9Y via the communication port which is not shown in figure.

  The result of detecting the magnetic permeability of the Y developer by the toner concentration sensor 10Y is sent as a voltage signal to a control unit (not shown). Since the magnetic permeability of the Y developer shows a correlation with the Y toner density of the Y developer, the toner density sensor 10Y outputs a voltage having a value corresponding to the Y toner density. The control unit includes a RAM, in which a Y Vtref which is a target value of an output voltage from the toner density sensor 10Y and a C, M, and K toner density sensor mounted on another developing device. The data of C Vtref, M Vtref, and K Vtref, which are target values of the output voltage, are stored. For the Y developing device 7Y, the value of the output voltage from the toner density sensor 10Y is compared with the Y Vtref, and the Y toner supply device (not shown) is driven for a time corresponding to the comparison result. By this driving, an appropriate amount of Y toner is supplied to the Y developer whose Y toner density has been reduced by consumption of Y toner accompanying development in the first agent storage portion 9Y. For this reason, the Y toner concentration of the Y developer in the second agent container 14Y is maintained within a predetermined range. Similar toner supply control is performed for the developers in the process units (1C, M, K) for other colors.

  The Y toner image formed on the photoreceptor 3Y is intermediately transferred to an intermediate transfer belt described later. The drum cleaning device 4Y of the photoreceptor unit 2Y removes the toner remaining on the surface of the photoreceptor 3Y after the intermediate transfer process. As a result, the surface of the photoreceptor 3Y that has been subjected to the cleaning process is neutralized by a neutralizing device (not shown). By this charge removal, the surface of the photoreceptor 3Y is initialized and prepared for the next image formation. In FIG. 1 described above, in the process units 1C, M, and K for other colors, C, M, and K toner images are similarly formed on the photoreceptors 3C, M, and K, and the intermediate transfer belt is formed. Intermediate transfer.

  An optical writing unit 20 is arranged below the process units 1Y, 1C, 1M, and 1K in the drawing. The optical writing unit 20 serving as a latent image forming unit irradiates the photoreceptors 3Y, C, M, and K of the process units 1Y, C, M, and K with the laser light L emitted based on the image information. Thereby, electrostatic latent images for Y, C, M, and K are formed on the photoreceptors 3Y, 3C, 3M, and 3K. The optical writing unit 20 deflects the laser light L emitted from the light source by the polygon mirror 21 that is rotationally driven by a motor, and passes through the photosensitive members 3Y, 3C, 3M, and 3K via a plurality of optical lenses and mirrors. Is irradiated. In place of such a configuration, an optical scanning device using an LDE array may be employed.

  A first paper feed cassette 31 and a second paper feed cassette 32 are disposed below the optical writing unit 20 so as to overlap in the vertical direction. In each of these paper feed cassettes, a plurality of recording papers P as recording members are accommodated in a stack of recording papers. The uppermost recording paper P includes a first paper feed roller 31a, The second paper feed rollers 32a are in contact with each other. When the first paper feed roller 31a is driven to rotate counterclockwise in the figure by a driving means (not shown), the uppermost recording paper P in the first paper feed cassette 31 is vertically oriented on the right side of the cassette in the figure. The paper is discharged toward the paper feed path 33 arranged so as to extend. Further, when the second paper feed roller 32 a is driven to rotate counterclockwise in the figure by a driving means (not shown), the uppermost recording paper P in the second paper feed cassette 32 is directed toward the paper feed path 33. Discharged. A plurality of transport roller pairs 34 are arranged in the paper feed path 33, and the recording paper P fed into the paper feed path 33 is sandwiched between the rollers of the transport roller pair 34 while being fed between the paper feed paths 33. 33 is conveyed from the lower side to the upper side in the figure.

  A registration roller pair 35 is disposed at the end of the paper feed path 33. The registration roller pair 35 temporarily stops the rotation of both rollers as soon as the recording paper P fed from the conveyance roller pair 34 is sandwiched between the rollers. Then, the recording paper P is sent out toward a later-described secondary transfer nip at an appropriate timing.

  Above each of the process units 1Y, 1C, 1M, and 1K, there is disposed a transfer device 40 that can endlessly move the intermediate transfer belt 41, which is an endless moving body, counterclockwise in the drawing. In addition to the intermediate transfer belt 41, the transfer device 40 serving as transfer means includes a belt cleaning unit 42, a first bracket 43, a second bracket 44, and the like. Also provided are four primary transfer rollers 45Y, 45M, 45K, a nip backside stretching roller 46, a tension roller 47, an auxiliary roller 48, a nip upstream roller 49, and the like. The intermediate transfer belt 41 is endlessly moved in the counterclockwise direction in the figure by the rotational drive of any one of the tension rollers while being tensioned by these eight tension rollers.

  The four primary transfer rollers 45Y, 45C, 45M, 45K each sandwich the intermediate transfer belt 41 moved endlessly in this manner from the photoreceptors 3Y, 3C, 3M, and 3K to form primary transfer nips. ing. Then, a transfer bias having a polarity opposite to that of the toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 41. The intermediate transfer belt 41 sequentially passes through the primary transfer nips for Y, C, M, and K along with its endless movement, and on the photoreceptor 3Y, C, M, and K on the front surface. The Y, C, M, and K toner images are superimposed and primarily transferred. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 41.

  The intermediate transfer belt 41 is sandwiched between the nip back-side stretching roller 46 and the secondary transfer roller 51 disposed outside the loop of the intermediate transfer belt 41. By this sandwiching, a secondary transfer nip is formed in which the front surface of the intermediate transfer belt 41 and the secondary transfer roller 51 as a transfer nip forming roller come into contact with each other.

  The registration roller pair 35 described above feeds the recording paper P sandwiched between the rollers toward the secondary transfer nip at a timing at which the recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 41. The four-color toner image on the intermediate transfer belt 41 is influenced by the secondary transfer electric field formed between the secondary transfer roller 51 to which the secondary transfer bias is applied and the nip backside stretching roller 46, and the nip pressure. The secondary transfer is batch-transferred onto the recording paper P in the secondary transfer nip. Then, combined with the white color of the recording paper P, a full color toner image is obtained.

  Untransferred toner that has not been transferred to the recording paper P adheres to the intermediate transfer belt 41 after passing through the secondary transfer nip. This is cleaned by the belt cleaning unit 42. In the belt cleaning unit 42, the cleaning blade 42a is brought into contact with the front surface of the intermediate transfer belt 41, whereby the transfer residual toner on the belt is scraped off and removed.

  The first bracket 43 of the transfer device 40 swings at a predetermined rotation angle about the rotation axis as the solenoid (not shown) is turned on / off. When forming a monochrome image, the printer unit 100 of the copying machine rotates the first bracket 43 a little counterclockwise in the drawing by driving the solenoid described above. By this rotation, the Y, C, M primary transfer rollers 45Y, C, M are revolved counterclockwise in the drawing around the rotation axis, so that the intermediate transfer belt 41 is for Y, C, M. Separated from the photoreceptors 3Y, 3C, 3M. Of the four process units 1Y, 1C, 1M, and 1K, only the K process unit 1K is driven to form a monochrome image. As a result, it is possible to avoid exhaustion of the process units due to wastefully driving the process units for Y, C, and M during monochrome image formation.

  A fixing unit 95 is disposed above the secondary transfer nip in the drawing. The fixing unit 95 includes a fixing roller 96 that rotates in a counterclockwise direction in the drawing while including a heat source such as a halogen lamp, and a pressure roller 97 that rotates in a clockwise direction in the drawing while contacting the fixing roller 96. The fixing nip is formed by the contact of both rollers.

  A temperature sensor (not shown) is disposed in the vicinity of the fixing roller 96 so as to face the fixing roller 96 with a predetermined gap, and detects the surface temperature of the fixing roller 96 immediately before entering the fixing nip. This detection result is sent to a fixing power supply circuit (not shown). The fixing power supply circuit performs on / off control of power supply to the heat source included in the fixing roller 96 based on the detection result of the temperature sensor. As a result, the surface temperature of the fixing roller 96 is maintained at about 140 [°].

  The recording paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 41 and then sent into the fixing unit 95. Then, in the process of being conveyed from the lower side to the upper side in the figure while being sandwiched between the fixing nips in the fixing unit 95, the full color toner image is fixed by being heated or pressed by the fixing roller 96.

  The recording paper P subjected to the fixing process in this manner is discharged outside the apparatus after passing between the rollers of the paper discharge roller pair 98. A stack unit 99 is formed on the upper surface of the housing of the printer unit 100, and the recording paper P discharged to the outside by the discharge roller pair 98 is sequentially stacked on the stack unit 99.

  Above the transfer device 40, four toner cartridges 90Y, 90C, 90M, and 90K that store Y, C, M, and K toners are disposed. The Y, C, M, and K toner in the toner cartridges 90Y, 90C, 90M, and 90K are appropriately supplied to the developing devices of the process units 1Y, 1C, 1M, and 1K. These toner cartridges 90Y, 90C, 90M, and 90K are detachable from the printer unit 100 independently of the process units 1Y, 1C, 1M, and 1K.

Next, a characteristic configuration of the copying machine will be described.
The copier has an abutting member that abuts at least one of the above-described stretching rollers that stretch the intermediate transfer belt 41, or the intermediate transfer belt 41. Further, a pressing force adjusting means for adjusting the pressing force of the contact member against the stretching roller or the intermediate transfer belt 41 is provided. Furthermore, it has a control unit (not shown), which is a pressing force control unit that changes the pressing force by controlling the pressing force adjusting unit.

  The control unit includes a CPU (Central Processing Unit) as a calculation unit, a RAM (Random Access Memory) as a data storage unit, a data storage unit (Read Only Memory), and the like. I am in control. And the following control is performed with respect to the above-mentioned pressing force adjustment means. That is, when the recording paper P enters the above-described secondary transfer nip, the pressing force adjusting means is controlled so that the pressing force of the secondary transfer roller 51 against the intermediate transfer belt 41 is weaker than the value immediately before entering.

  In such a configuration, when the recording paper P enters the secondary transfer nip, the pressing force applied to the roller or the belt of the contact member that is in contact with the intermediate transfer belt 41 or the tension roller that stretches the intermediate transfer belt 41 is entered. By making it weaker than the previous value, you can: That is, the torque increase of the belt drive motor due to the recording paper P entering the secondary transfer nip is offset by the torque decrease due to the decrease in the pressing force by the contact member, and the rotation speed of the belt drive motor at the time of entry is reduced. Reduce sudden drop. As a result, it is possible to suppress image disturbance caused by a rapid speed reduction of the intermediate transfer belt 41 when the recording paper P enters the secondary transfer nip. In addition, it is possible to suppress color misregistration caused by the speed variation of the intermediate transfer belt 41. Such image distortion and color misregistration are primarily transferred from the photoreceptors of the respective colors to the intermediate transfer belt 41 due to fluctuations in the belt speed when the first recording sheet P enters the secondary transfer nip, for example. This occurs on the second and subsequent recording sheets P in the continuous print mode, such as disturbing the toner image for each second color in the middle. The belt driving motor described above transmits a driving force to a belt driving roller that moves the belt endlessly with its own rotational driving among a plurality of stretching rollers that stretch the intermediate transfer belt 41. Motor.

Next, a description will be given of the copying machine of each example in which a more characteristic configuration is added to the copying machine according to the first embodiment.
[First embodiment]
In this copying machine, a secondary transfer roller 51 that rotates while contacting the intermediate transfer belt 41 is used as the contact member, and the pressing force against the belt is adjusted. FIG. 5 is an enlarged configuration diagram showing the secondary transfer roller unit 50 in the transfer device 40 of the copying machine according to the first embodiment together with its peripheral configuration. In the figure, the secondary transfer roller unit 50 of the transfer device 40 includes a secondary transfer roller 51, a holding body 52, an urging coil spring 53, a cam shaft 54, a cam 55, a holding body rotating shaft 56, an optical sensor 57, and an illustration. It has a cam motor that does not. The secondary transfer roller 51 described above is rotatably held by the holding body 52.

  The holding body 52 of the secondary transfer roller unit 50 is supported by a support body (not shown) so that the holding body 52 can be rotated around a holding body rotation shaft 56 provided on the upper portion thereof. At the side of the holding body 52, the holding body 54 is urged toward the intermediate transfer belt 41 while the urging coil spring 53 is supported by the above-described supporting body. By this urging, the secondary transfer roller 51 rotatably held by the holding body 54 is pressed toward the intermediate transfer belt 41 while being brought into contact with the intermediate transfer belt 41. The urging direction of the holding body 52 by the urging coil spring 53 is, as shown by a one-dot chain line in the figure, its own coil axis, the rotation center of the secondary transfer roller 51, and the nip backside tension that is one of the stretching rollers. The rotation center of the pedestal roller 46 is positioned in a straight line.

  A cam 55 that rotates about a cam shaft 54 by a driving force from a cam motor (not shown) is disposed in the vicinity of the holding body 52, and its own cam surface is abutted against the lower portion of the holding body 52. . By this abutment, movement of the holding body 52 urged toward the intermediate transfer belt 41 by the urging coil spring 53 in the urging direction is restricted.

  When a cam motor (not shown) is driven to rotate forward or reversely, the cam 55 rotates about the cam shaft 54 and moves its own cam surface closer to or away from the holding body 52. As a result, the contact position between the cam surface and the lower portion of the holding body 52 moves in the left-right direction in the drawing relative to the printer unit 100, and the holding body 52 rotates counterclockwise in the drawing about the holding body rotation shaft 56. Rotate slightly in the direction or slightly in the clockwise direction in the figure. When the holding body 52 rotates in this way, the secondary transfer roller 51 moves slightly away from or slightly closer to the intermediate transfer belt 41, and the pressing force of the secondary transfer roller 51 against the intermediate transfer belt 41 is weak. It gets stronger and stronger. That is, in this copying machine, the holding body 52, the urging coil spring 53, the cam shaft 54, the cam 55, the holding body rotating shaft 56, the cam motor (not shown), etc. exert the pressing force of the secondary transfer roller 51 on the intermediate transfer belt 41. It functions as a pressing force adjusting means for adjusting.

  When the cam motor is driven to rotate forward for a predetermined time, as shown in FIG. 6, the cam 55 rotates counterclockwise in the drawing by a predetermined angle around the cam shaft 54, and the holding body 52 The lower part is overcome from the urging force of the urging coil spring 53 and pushed from the left side to the right side in the figure. As a result, the holding body 52 rotates about the holding body rotating shaft 56 by a predetermined angle in the counterclockwise direction in the figure, and the pressing force of the secondary transfer roller 51 against the intermediate transfer belt 41 is slightly weakened. On the other hand, when the cam motor is driven in the reverse direction, the holding body 52 rotates about the holding body rotation shaft 56 in the counterclockwise direction in the drawing, and the secondary transfer roller 51 is pushed against the intermediate transfer belt 41. Pressure increases.

  An optical sensor 57 is fixed to a portion of the holding body 52 facing the paper feed path. The optical sensor 57 is composed of a reflection type photosensor, and reflects light emitted from a light emitting element (not shown) by the surface of the recording paper P and receives it by the light receiving element. Then, based on the change in the amount of light received by the light receiving element, the front end of the recording paper P immediately before entering the secondary transfer nip is detected, and a front end detection signal is sent to the above-described control unit. In other words, the optical sensor 57 functions as a recording member detection unit that detects the recording paper P passing through the position facing the optical sensor 57, and enters the secondary transfer nip upstream of the secondary transfer nip in the recording paper conveyance direction. The leading edge of the recording paper P immediately before entering is detected. Instead of the reflective photosensor, a transmissive photosensor that exchanges light between the light-emitting element and the light-receiving element with the sheet feeding path interposed therebetween may be used.

  Based on the timing at which the leading edge detection signal is sent from the optical sensor 57, the control unit estimates the timing at which the leading edge of the recording paper P enters the secondary transfer nip and drives the cam motor to rotate forward for a predetermined time. In this copying machine, a high-speed print mode and a high-quality print mode for forming an image at a slower print speed can be switched by key input to an operation display unit (not shown). Based on the leading edge detection signal, the timing at which the leading edge of the recording paper P enters the secondary transfer nip can be obtained. Specifically, the optical sensor 57 is disposed so as to detect the leading edge of the recording paper P upstream of the recording paper transport direction by a predetermined distance (ΔL) from the secondary transfer nip in the recording paper transport direction. ing. Since the recording paper conveyance speed (V1) in the high-speed print mode is known in advance, the leading edge of the recording paper P is 2 after a period of “Δt1 = ΔL / V1” seconds after the leading edge detection signal is sent to the control unit. Enter the next transfer nip. Further, since the recording paper conveyance speed (V2) in the high image quality print mode is also known in advance, “Δt2 = ΔL / V2” seconds after the leading edge detection signal is sent to the control unit, The leading edge enters the secondary transfer nip. At these timings (hereinafter referred to as “entry timing”), the controller drives the cam motor to rotate forward for a predetermined time to weaken the pressing force of the secondary transfer roller 51 against the intermediate transfer belt 41. That is, in this copying machine, the control unit that controls the driving of the cam motor functions as a pressing force control unit that controls the pressing force adjusting unit.

  Based on the leading edge detection signal, the control unit also obtains a timing at which the leading end side of the recording paper P enters the secondary transfer nip by a predetermined amount (hereinafter referred to as a predetermined amount entering timing) in addition to the above-described entering timing. When a predetermined amount approach timing arrives, the cam motor is driven in reverse rotation for a predetermined time to slightly increase the pressing force of the secondary transfer roller 51 against the intermediate transfer belt 41. As a result, before the image transfer area of the recording paper P enters the secondary transfer nip, a nip pressure necessary for the secondary transfer can be secured, and secondary transfer failure due to insufficient nip pressure can be suppressed. . In the continuous print mode, the series of adjustment of the pressing force is performed for each sheet passing.

  In such a configuration, by using the secondary transfer roller 51 as the contact member, the recording paper P is brought into the secondary transfer nip without using a new contact member for adjusting the speed of the intermediate transfer belt 41. It is possible to suppress color misregistration due to a rapid change in belt speed when entering or discharging from the secondary transfer nip.

  The attachment of the cam 55 to the cam shaft 54 is preferably performed by press fitting or screw fixing. This is because by fixing in this way, it is possible to avoid subtle fluctuations in the pressing force due to rattling of the cam 55 on the cam shaft 54.

  In this copying machine, a belt drive that moves the intermediate transfer belt 41 endlessly with the rotation of the nip backside stretching roller 46 that wraps the intermediate transfer belt 41 around its surface on the back side of the secondary transfer nip. Also used as a roller. In such a configuration, among the plurality of stretching rollers, the nip back side roller 46 that first tends to change the rotational speed as the recording paper P enters the secondary transfer nip is used as a belt driving roller. As a result, the belt speed can be adjusted more accurately by quickly reflecting the change in the pressing force in the change in the torque of the belt drive motor as compared with the case where the other tension roller is a belt drive roller.

  The present inventors have prepared an experimental machine having the configuration of the copying machine, and the second and subsequent printout papers when the pressing force is lowered at the entry timing and when the pressing force is not changed. An experiment was conducted to examine the difference in color misregistration. The result is shown in FIG. As shown in the figure, it is understood that when the pressing force is lowered at the entry timing, the amount of color misregistration is suppressed better than when the pressing force is not changed.

  Although the example using the cam 55 or the like as the pressing force adjusting means has been described, any mechanism may be used as long as the pressing force of the secondary transfer roller 51 or the like can be adjusted.

  In a general image forming apparatus, rotation of the registration roller pair (35) is temporarily stopped with the recording paper P sandwiched between rollers, and the recording paper P is placed on the intermediate transfer belt 41 at the secondary transfer nip. The timing that can be synchronized with the four-color toner image is estimated. Then, the recording paper that protrudes from the registration nip of the registration roller pair toward the secondary transfer nip so as not to cause an error for each paper passing in the distance between the leading edge of the recording paper P and the entrance of the secondary transfer nip at this time. A registration sensor including an optical sensor for detecting the tip of P is provided. This copier also has such a registration sensor. In addition to the registration sensor, the secondary transfer roller unit 50 is provided with an optical sensor 27 for the following reason. That is, as described above, the distance between the leading edge of the recording paper P sandwiched between the pair of registration rollers whose rotation has stopped and the entrance of the secondary transfer nip is substantially constant for each sheet passing. It is also possible to obtain the entry timing based on the timing at which the recording paper P starts to be fed from to the secondary transfer nip. However, there is an error in the strength of the recording paper P depending on the material, thickness, etc., and the lower the strength of the recording paper P, the more the leading edge is bent, and it is sent to the secondary transfer nip. For this reason, there is a slight error in the time from when the recording paper P is first fed out from the registration roller pair until the leading edge reaches the entrance of the secondary transfer nip, depending on the strength of the recording paper P. In the present copying machine, the optical sensor 57 detects the leading edge of the recording paper P in the vicinity of the entrance of the secondary transfer nip in order to prevent the occurrence of improper timing of the pressing force due to this error.

  From the viewpoint of cost reduction, the four-color toner image in the secondary transfer nip and the transfer paper P are synchronized only by the paper feed timing from the paper feed cassette without adjusting the feed timing by the registration roller pair. It can be considered to measure. Even if it does in this way, if the optical sensor 57 is provided, an approach timing etc. can be calculated | required correctly.

  Also, from the viewpoint of further cost reduction, it is conceivable to omit the optical sensor 57, but even in such a case, it is possible to obtain the entry timing and the predetermined amount entry timing with a certain degree of accuracy depending on the device. is there.

  For example, a pair of registration rollers (35) and a pair of conveyance rollers (34), such as a pair of conveyance rollers (34), the recording paper P is placed in a conveyance nip obtained by abutting surfaces that endlessly move toward each other upstream of the secondary transfer nip. Drive current detecting means for detecting a drive current of a motor that is a drive source of at least one member of the pair of transport members that are sandwiched and transported is provided. The detection result of the drive current by the drive current detection means rises greatly at the moment when the recording paper P is sandwiched between the conveying member pair. Therefore, it is possible to obtain the entry timing and the like with a certain degree of accuracy based on the detection result by the drive current detection means. The drive current detection means is a drive source for at least one of the pair of conveying rollers disposed on the upstream side of the secondary transfer nip and the registration roller pair closest to the secondary transfer nip. It is desirable to detect the drive current of the motor. This is because it is possible to obtain the entry timing and the like more accurately than in the case of detecting the drive current of the motor that is the drive source of the roller upstream of the registration roller pair. Note that a servo motor is used as a motor that is a detection target of the drive current.

  Further, for example, surface movement speed detecting means for detecting the surface movement speed of at least one member of the conveying member pair disposed upstream of the secondary transfer nip in the paper conveying direction may be provided. The detection result of the surface moving speed by the surface moving speed detecting means greatly decreases at the moment when the recording paper P is sandwiched between the pair of conveying members. Therefore, it is possible to obtain the entry timing and the like with a certain degree of accuracy based on the detection result by the surface moving speed detection means.

[Second Embodiment]
FIG. 8 is an enlarged configuration diagram showing the secondary transfer roller unit 50 and its peripheral configuration in the copying machine. This copying machine has the same configuration as that of the copying machine according to the first embodiment, except that the method of driving the cam shaft 54 is different. Specifically, in the copying machine according to the first embodiment, the rotating shaft of the cam motor is directly connected to the cam shaft 54, and the cam motor is moved (rotated) together with the holding body 52. On the other hand, in this copying machine, the cam motor 58 is fixed to the printer unit 100 side and is separated from the holding body 52. A helical gear is fixed to the rotating shaft of the cam motor 58. A helical gear is formed at one end of the cam shaft 54. These gears mesh with each other so that the rotational driving force of the cam motor 58 is transmitted to the cam 55. Control of forward rotation and reverse rotation of the cam motor 58 is performed by the control unit 110 as described above.

[Third embodiment]
FIG. 9 is an enlarged configuration diagram showing the secondary transfer roller unit 50 and its peripheral configuration in the copying machine. In this copying machine, the pressing force of the secondary transfer roller 51 against the intermediate transfer belt is adjusted by adjusting the biasing force by the biasing coil spring 53 instead of pushing back the biasing coil spring 53 with a cam. This is different from the copying machine according to the first embodiment. Specifically, the secondary transfer roller unit 50 of this copying machine does not have a cam shaft or an eccentric cam. Instead, a first worm screw 59, a second worm screw 60, a pressure adjusting plate 61, and the like are provided. The second worm screw 60 takes a posture of extending in the coil axis direction while being passed through the coil of the urging coil spring 53. The pressure adjusting plate 61 has a female screw cut in a through hole (not shown) and is screwed to a second worm screw 60 passed through the through hole. The first worm screw 59 is engaged with the second worm screw 60 in a posture extending in a direction orthogonal to the axial direction of the second worm screw 60. Further, the end portion of the first worm screw 59 meshes with a helical gear provided on the rotating shaft of the cam motor 58.

  When the cam motor 58 rotates, the rotational driving force is transmitted to the second worm screw 60 via the first worm screw 59, and the second worm screw 60 rotates. Then, the pressure adjusting plate 61 moves along the axial direction on the second worm screw 60. Then, the distance between the pressure adjusting plate 61 and the holding body 52 changes, and the urging coil spring 53 located between them expands and contracts. By this expansion and contraction, the urging force of the urging coil spring 53 against the holding body 52 is adjusted, and the pressing force of the secondary transfer roller 51 against the intermediate transfer belt changes.

[Fourth embodiment]
In this copying machine, a contact member different from the secondary transfer roller 51 is provided, and the pressing force of the contact member against the intermediate transfer belt 41 is adjusted.
FIG. 10 is a schematic configuration diagram showing the transfer device 40 of the copying machine. In the drawing, a brake mechanism 62 is disposed above a tension roller 47 that is a tension roller that stretches the intermediate transfer belt 41. The brake mechanism 62 includes a rubbing member 63 that is a contact member that cannot move on the surface, a biasing coil spring 64, a pressure adjusting plate 65, a first worm screw 66, a second worm screw 67, a screw motor 68, and the like. Yes.

  The rubbing member 63 is disposed so as to come into contact with the tension roller 47 on the intermediate transfer belt 41 from the belt front surface side. A biasing coil spring 64 biases the rubbing member 63 toward the intermediate transfer belt 41. A second worm screw 67 is disposed inside the coil of the urging coil spring 64 so as to extend in the coil axis direction, and is screwed into a screw hole of the pressure adjusting plate 65. The first worm screw 66 meshes with the second worm screw 67 in a posture extending in a direction orthogonal to the axial direction of the second worm screw 67. Further, the end portion of the first worm screw 66 is meshed with a helical gear provided on the rotating shaft of the screw motor 68.

  When the screw motor 68 rotates, the rotational driving force is transmitted to the second worm screw 67 via the first worm screw 66, and the second worm screw 67 rotates. Then, the pressure adjusting plate 63 moves on the second worm screw 67 along the axial direction thereof. Then, the distance between the pressure adjusting plate 63 and the rubbing member 63 changes, and the biasing coil spring 64 located between the two expands and contracts. By this expansion and contraction, the urging force of the urging coil spring 64 against the rubbing member 63 is adjusted, and the pressing force of the rubbing member 63 against the intermediate transfer belt 41 changes.

  The copying machine normally starts a print job with the rubbing member 63 pressed against the intermediate transfer belt 41 with a certain pressing force. By this pressing, the torque for the belt drive motor is increased in advance. Then, at the above entry timing, the pressing force of the rubbing member 63 against the intermediate transfer belt 41 is made weaker than the value immediately before entering, and the torque increase due to the recording sheet P entering the nip is reduced by the torque reduction by reducing the pressing force. cancel. Thereafter, the pressing force is slightly increased at the above-described predetermined amount entry timing to avoid an increase in belt speed due to a reduction in the pressing force.

  In such a configuration, by using the rubbing member 63 that cannot move on the surface as the abutting member, the torque change rate accompanying the change in the pressing force can be increased as compared with the case where a surface movable roller or the like is used. The torque can be adjusted with a small change in the pressing force.

[Fifth embodiment]
In the experimental machine having the configuration of the copying machine according to the first embodiment described above, the inventors used a relatively thick recording paper P and a case using a normal thickness paper. An experiment was conducted to compare the difference in color misregistration at the approach timing. The pressing force of the secondary transfer roller 51 was not adjusted. The results are shown as a graph in FIG. In the figure, the graph drawn with a solid line shows the result when 90K paper (normal thickness) is used as the recording paper P. Further, the graph drawn with a dotted line shows the result when 210K paper (thick paper) is used as the recording paper P. As shown in the drawing, it can be seen that the larger the thickness of the recording paper P, the larger the amount of color misregistration due to the belt speed fluctuation at the above-described approach timing. This is because the torque increase amount at the approach timing increases as the thickness increases.

  Therefore, in this copying machine, the following additional characteristic configuration is added to the copying machine according to the first embodiment. That is, a thickness information acquisition unit that acquires the thickness information of the recording paper P is provided, and control is performed to vary the degree of change in the pressing force (the amount of change in pressing force) at the approach timing according to the thickness information. The controller 110 is a pressing force control means. In such a configuration, the belt speed variation is further suppressed by varying the amount of change in the pressing force according to the difference in the belt speed variation due to the difference in the thickness of the recording paper P at the entry timing. As a result, the color misregistration amount at the entry timing in the second and subsequent printout sheets can be further suppressed.

  There are various thickness information acquisition means for acquiring the thickness information of the recording paper P. In this copying machine, a thickness detection means for detecting the thickness is used. There are various thickness detection means. In this copying machine, at least any of the pair of conveyance members that convey the recording paper P between conveyance nips obtained by bringing the surfaces that move endlessly into contact with each other. What detects thickness based on the detection result by the drive current detection means which detects the drive current of the motor which is the drive source of one member is used. Specifically, the pair of conveyance rollers 34, the pair of registration rollers 35, the pair of the fixing roller 96 and the pressure roller 97 shown in FIG. 1 function as a pair of conveyance members that form a conveyance nip while moving relative to each other. ing. When the recording paper P is sandwiched between the transport nips of these transport member pairs, the drive current of the motor that supplies the drive force to the transport member increases as shown in FIG. It has been found that as the thickness of the recording paper P increases, the increase rate of the drive current of the motor increases.

  Therefore, this copying machine is provided with an ampermeter as drive current detection means for detecting the drive current of the motor. Then, a data table in which the increase rate of the drive current and the thickness of the recording paper P are associated, an algorithm for obtaining the thickness from the increase rate, and the like are constructed based on a previous experiment, and based on this, the thickness of the recording P The above-described control unit 110 serving as a thickness detection unit is configured. Note that a servo motor is used as a motor to be detected by the drive current.

  FIG. 13 is a schematic diagram showing various motors in the copying machine. In the figure, a motor denoted by reference numeral 121 is a registration motor that supplies driving force to any one of the registration roller pair (35) that is a conveying member. A motor denoted by reference numeral 120 is a belt drive motor that supplies a driving force to the belt in the pair of the intermediate transfer belt (41) and the secondary transfer roller (51) as a conveying member. A motor denoted by reference numeral 122 is a transport motor that supplies a driving force to a transport roller pair 34) that is a transport member. A motor denoted by reference numeral 123 is a fixing drive motor that supplies a driving force to at least one of the pair of the fixing roller 96 and the pressure roller 97 as a conveying member. Of these motors, an ampere meter 111 that detects any one of the drive currents is provided, and the detection result is sent to the control unit 110, so that the control unit 110 can have a pressing force corresponding to the thickness of the recording paper P. Adjustment control can be performed.

  However, in a motor for supplying a driving force to a pair of conveyance members that convey the recording paper P after the secondary transfer nip in the recording paper conveyance direction, the recording paper P is in accordance with the thickness after entering the secondary transfer nip. It shows a change in driving current. For this reason, in the continuous print mode, when the control unit 110 detects the thickness of the first recording sheet P based on the increase rate of the drive current, the recording sheet P has already entered the secondary transfer nip. . Therefore, at the entry timing of the first recording sheet P, the braking force cannot be adjusted according to the thickness, and the color shift in the second sheet cannot be suppressed according to the thickness. For three or more continuous printouts, the thickness detection result of the first sheet is reflected at the entry timing of the second sheet, so that color misregistration in the third and subsequent printout sheets can be controlled by the braking force corresponding to the thickness. It can be further suppressed by adjustment.

  However, it is desirable to further improve the image quality by adjusting the pressing force according to the thickness from the second printed sheet. Therefore, in the present copying machine, an ampermeter 111 that detects a drive current of a motor that is a drive source of a conveyance member disposed upstream of the secondary transfer nip in the recording paper conveyance direction is used. Yes. More specifically, in the present copying machine, as shown in FIG. 1, there are a registration roller pair 35 and a conveyance roller pair 34 as conveyance member pairs disposed upstream of the secondary transfer nip. Therefore, the ampere meter 111 is made to detect the drive current of the registration motor 121 or the conveyance motor 122 shown in FIG. Thereby, it is possible to further improve the image quality by adjusting the pressing force according to the thickness from the second printout paper.

[Sixth embodiment]
Similarly to the fifth embodiment, this copying machine is also provided with a thickness detecting means for detecting the thickness of the recording paper P, and controls the amount of change in the pressing force at the entry timing to be different according to the thickness information. Thus, the control part 110 which is a pressing force control means is comprised. However, the structure of the thickness detecting means is different from that of the fifth embodiment. Specifically, in the present copying machine, the ampere meter 111 shown in FIG. 13 is caused to detect the driving current of the belt driving motor 120 and the thickness of the recording paper P is detected based on the detection result. Thus, the control part 110 which is a pressing force control means is comprised. In such a configuration, it is possible to further improve the image quality by adjusting the pressing force according to the thickness based on the change in the driving current of the belt driving motor. However, the thickness of the first recording sheet P cannot be detected before entering the secondary transfer nip. For this reason, after obtaining the thickness of the first recording sheet P based on the drive current value when entering the secondary transfer nip, the pressing force at the entry timing of the second and subsequent recording sheets P depends on the thickness. Will be adjusted. Therefore, it is possible to further suppress deterioration in image quality after the third sheet. A servo motor is used as the belt drive motor.

[Seventh embodiment]
Similarly to the fifth embodiment, this copying machine is also provided with a thickness detecting means for detecting the thickness of the recording paper P, and controls the amount of change in the pressing force at the entry timing to be different according to the thickness information. Thus, the control part 110 which is a pressing force control means is comprised. However, this copying machine is also different from the fifth embodiment in the structure of the thickness detecting means. Specifically, in this copying machine, a transmission type photosensor that detects the thickness of the recording paper P based on the light transmittance with respect to the recording paper P is used as the thickness detection means. On the upstream side of the secondary transfer nip, light is emitted from the light emitting element of the transmissive photosensor toward the recording paper P being conveyed. Then, after passing through the recording paper P in the thickness direction, the light receiving element receives the light. The amount of received light (light transmittance) decreases as the thickness of the recording paper P increases. Therefore, the transmissive photosensor that outputs a voltage corresponding to the amount of received light from the light receiving element functions as a thickness detecting unit. In such a configuration, the thickness of the recording paper P can be detected in finer units than when the thickness is detected based on the drive current. However, when transparent paper or an OHP sheet is used, the thickness cannot be detected properly. On the other hand, when the thickness is detected based on the drive current, the thickness unit that can be detected is larger than that of the transmission type photosensor, but the thickness can be appropriately detected even with transparent paper or an OHP sheet.

[Eighth embodiment]
Similarly to the fifth embodiment, this copying machine is also provided with a thickness detecting means for detecting the thickness of the recording paper P, and controls the amount of change in the pressing force at the entry timing to be different according to the thickness information. Thus, the control part 110 which is a pressing force control means is comprised. However, this copying machine is also different from the fifth embodiment in the structure of the thickness detecting means. Specifically, this copying machine is provided with a laser displacement meter as displacement amount detection means for detecting the displacement amount of at least one member of the conveying member pair. When the recording paper P is sandwiched in the conveyance nip formed by the conveyance member pair, the position of the conveyance member is slightly displaced. As the thickness of the recording paper P increases, the amount of displacement of the transport member increases. Therefore, the thickness of the recording paper P can be obtained based on the detection result by a laser displacement meter that detects the displacement of the test object by a known technique. it can. Therefore, in the present copying machine, the control unit 110 serving as a thickness detection unit is configured to obtain the thickness of the recording paper P based on the detection result by the laser displacement meter.

  Even in such a configuration, even when a transparent paper or an OHP sheet is used as the recording paper P, the thickness thereof can be appropriately detected. Furthermore, it is possible to detect the thickness in finer units as compared with the case where the thickness is detected based on the drive current.

  The object to be detected for the amount of displacement by the laser displacement meter is preferably a conveyance member disposed upstream of the secondary transfer nip in the paper conveyance direction. By doing so, as described above, it is possible to further improve the image quality by adjusting the pressing force according to the thickness from the second printout paper. Therefore, in this copying machine, a laser displacement meter is provided so as to detect the displacement amount of any one roller in the registration roller pair (35) or any one roller in the conveyance roller pair (34). Yes.

[Ninth embodiment]
Similarly to the fifth embodiment, the present copying machine is also provided with a thickness detecting means for detecting the thickness of the recording paper P, and controls to change the approach timing pressing force variation amount according to the thickness information. Further, a control unit 110 serving as a pressing force control unit is configured. However, this copying machine is also different from the fifth embodiment in the structure of the thickness detecting means. Specifically, the copying machine is provided with surface speed detecting means for detecting the surface moving speed of at least one member of the conveying member pair. When the recording paper P is sandwiched in the conveyance nip formed by the conveyance member pair, the surface moving speed of the conveyance member is slightly displaced. As the thickness of the recording paper P becomes larger, the surface moving speed of the conveying member becomes slower. Therefore, the thickness of the recording paper P can be obtained based on the detection result by the surface speed detecting means. Therefore, in the present copying machine, the control unit 110 serving as the thickness detecting unit is configured to obtain the thickness of the recording paper P based on the detection result by the surface speed detecting unit that detects the surface moving speed of the conveying member.

  Even in such a configuration, even when a transparent paper or an OHP sheet is used as the recording paper P, the thickness thereof can be appropriately detected.

  When the conveyance member pair is a roller pair, a complete exchange relationship is established between the surface movement speed of the conveyance member and the rotation speed or the rotation angular speed. For this reason, as surface speed detection means, in addition to detecting the surface movement speed directly by detecting mark patterns arranged at a predetermined pitch on the roller peripheral surface, the rotational speed and rotational angular speed of the roller such as an encoder can be detected. What detects the surface moving speed indirectly by detecting can be used. In the present copying machine, since the object to be inspected for the surface moving speed is a roller, a device that detects the rotational speed of the roller is used.

  It is desirable to use a conveyance member disposed on the upstream side of the secondary transfer nip in the paper conveyance direction for the surface movement speed test target. By doing so, as described above, it is possible to further improve the image quality by adjusting the pressing force according to the thickness from the second printout paper. Therefore, in this copying machine, the rotational speed of one of the rollers in the registration roller pair (35) is detected.

  FIG. 14 is a perspective view showing one roller 35a and the encoder 70 in the registration roller pair to be detected for the rotational speed. The encoder 70 is a transmission type photo that detects passages for a plurality of slits 71a formed at a predetermined pitch in a circular direction of a test disk 71 that is fixed to the rotation shaft of the roller 35a and rotates with the rotation shaft. Sensor 72. As the rotation speed of the roller 35a increases, the detection time timing after passing through each slit 71a becomes earlier, so that the rotation speed of the roller 35a can be obtained based on the detection time timing.

  When detecting the surface moving speed of the conveying belt as the conveying member, the rotational speed of the belt driving roller for driving the conveying belt and the surface moving speed of the conveying belt are not completely correlated. This is because the conveying belt may slip on the peripheral surface of the belt driving roller. Therefore, the surface moving speed of the conveyor belt is directly detected. Specifically, as shown in FIG. 15, the conveyance belt 73 is provided with marks 74 at a predetermined pitch over the entire area in the circumferential direction in the non-contact area (end part) with the paper in the width direction. Use things. Then, each mark 74 is detected by an optical sensor 75 composed of a reflective photosensor or a transmissive photosensor, and the surface moving speed is detected based on the detection time interval.

[Tenth embodiment]
Similarly to the fifth embodiment, this copying machine is also provided with a thickness information acquisition means for acquiring the thickness information of the recording paper P, and controls the amount of change in the pressing force at the approach timing to be different according to the thickness information. The control unit 110 serving as a pressing force control unit is configured so as to be implemented. However, in the present copying machine, an operation display unit serving as an input unit in which an operator performs an input operation of thickness information is used as the thickness information acquisition unit, instead of the thickness detection unit that detects the thickness. The thickness information of the recording paper P is acquired by an input operation to various keys such as a numeric keypad of the operation display unit (not shown). In such a configuration, the thickness information of the recording paper P can be acquired without providing a special optical sensor, ampere meter, encoder or the like for detecting the thickness.

[Eleventh embodiment]
In the experimental machine having the configuration of the copier according to the first embodiment described above, the present inventors use a recording paper P having a relatively large sheet passing width (length in a direction perpendicular to the transport direction). An experiment was conducted to compare the difference in the amount of color misregistration at the approach timing between the case where there was a small amount and the case where a relatively small one was used. The pressing force of the secondary transfer roller 51 was not adjusted. The results are shown as a graph in FIG. In the drawing, a graph drawn with a solid line shows a result when the recording paper P is conveyed with a paper passing width of 210 [mm]. Further, the graph drawn with a dotted line shows the result when the recording paper P is conveyed with a paper passing width of 420 [mm]. As shown in the drawing, it can be seen that the larger the sheet passing width of the recording paper P, the larger the amount of color misregistration due to the belt speed fluctuation at the above-described approach timing. This is because the torque increase amount at the entry timing increases as the sheet passing width increases.

  Therefore, in this copying machine, the following additional characteristic configuration is added to the copying machine according to the first embodiment. That is, a width information acquisition unit that acquires width information that is a sheet passing width is provided. And the control part 110 which is a pressing force control means is comprised so that the control which changes the degree (change amount) of the said pressing force in the said approach timing according to width | variety information may be implemented. In such a configuration, the belt speed variation is further suppressed by varying the amount of change in the pressing force in accordance with the difference in the belt speed variation due to the difference in the sheet passing width at the entry timing. As a result, the amount of color misregistration in the second and subsequent printout sheets can be further suppressed.

  There are various width information acquisition means for acquiring the width information. In this copying machine, a width detection means for detecting the width is used. There are various width detection means, but in this copying machine, a plurality of recording member detections are detected for detecting the recording paper P that passes through the position facing the recording paper P while being arranged in the width direction of the recording paper P. In addition, a means for detecting the width of the recording paper P based on the detection result of the recording member detection means is used as the width detection means. Furthermore, an optical sensor is used as each of the plurality of recording member detection means. These optical sensors may be either reflection type photo sensors or transmission type photo sensors as long as they are arranged so that the recording paper P conveyed in the conveyance path can be detected. However, it is desirable to dispose upstream of the secondary transfer nip. By doing so, it is possible to further improve the image quality by adjusting the pressing force according to the sheet passing width from the second printed sheet.

[Twelfth embodiment]
Similarly to the eleventh embodiment, this copying machine is also provided with a width detecting means for detecting the width of the recording paper P, and controls the amount of change in pressing force at the entry timing to be different according to the thickness information. Thus, the control part 110 which is a pressing force control means is comprised. However, the configuration of the width detecting means is different from that of the eleventh embodiment. Specifically, in the present copying machine, switches as shown in FIG. 17 are used as a plurality of recording member detection means for detecting the recording paper P that passes through the position facing each other while being aligned in the width direction of the recording paper P. The member 76 is used. The switch member 76 can swing about a swing shaft 76a provided on the rear end side. Normally, however, the switch member 76 is in a posture as shown in FIG. 17A by a biasing force of a spring (not shown). Have taken. When the leading end comes into contact with the recording paper P that has been transported into the transport path, the recording paper P is rotated by a predetermined angle in the direction of the arrow in the figure as shown in FIG. The recording paper P is detected by connecting and disconnecting an electrical contact (not shown) along with such swinging.

  In such a configuration, even when a transparent paper, an OHP sheet, or the like is used as the recording paper P, the paper passing width can be accurately detected.

[Thirteenth embodiment]
Similarly to the eleventh embodiment, this copying machine is also provided with width information acquisition means for acquiring the width information of the recording paper P, and controls the amount of change in the pressing force at the approach timing to be different according to the width information. The control unit 110 serving as a pressing force control unit is configured so as to be implemented. However, in the present copying machine, an operation display unit serving as an input unit in which an operator performs an input operation of width information is used as the width information acquisition unit, instead of the width detection unit that detects the width. The width information of the recording paper P is acquired by an input operation to various keys such as a numeric keypad of the operation display unit (not shown). In such a configuration, the width information of the recording paper P can be acquired without providing a special optical sensor or switch member for detecting the width.

[14th embodiment]
The inventors of the present invention have used the copying machine according to the first embodiment described above, and the difference in the amount of color misregistration at the entry timing in the case where different recording media are used as the recording paper P. The experiment which compares was conducted. The pressing force of the secondary transfer roller 51 was not adjusted. The results are shown as a graph in FIG. As shown in the figure, it can be seen that the amount of color misregistration varies depending on the state of the gap (direction of threading (vertical threading, lateral threading) and roughness) (dotted line, alternate long and short dash line, solid line). Eye condition is different). Similarly, at the discharge timing, the amount of color misregistration differs depending on the state of the gap.

  Therefore, in this copying machine, the following additional characteristic configuration is added to the copying machine according to the first embodiment. That is, a gap information acquisition unit that acquires the gap information that is the gap information of the recording paper P is provided. And the control part 110 which is a pressing force control means is comprised so that the change which changes the pressing force in the said approach timing according to gap information may be implemented. In such a configuration, the belt speed fluctuation is further suppressed by varying the amount of change in the pressing force according to the difference in the belt speed change amount due to the difference in the clearance at the approach timing. As a result, the amount of color misregistration in the second and subsequent printout sheets can be further suppressed.

  As the gap information detecting means, an operation display unit is used as an input means for performing an operation of inputting gap information by an operator. The width information of the recording paper P is acquired by an input operation to various keys such as a numeric keypad of the operation display unit (not shown). In such a configuration, the gap information of the recording paper P can be acquired without providing a special sensor for detecting the gap.

[Fifteenth embodiment]
The inventors of the present invention described the relationship between the inclination θ of the recording paper P and the color misregistration amount when entering the secondary transfer nip in the experimental machine having the configuration of the copying machine according to the first embodiment described above. An experiment to investigate was conducted. The inclination θ is an inclination from a direction perpendicular to the conveyance direction of the recording paper P conveyed on the conveyance path in the copying machine. In this experiment, recording immediately before entering the secondary transfer nip. The inclination of the paper P is shown. The pressing force of the secondary transfer roller 51 was not adjusted. The results are shown as a graph in FIG. In the figure, the inclination θ is “solid line graph> dot-dot line bluff> dotted line graph”. As shown in the figure, it can be seen that the smaller the inclination θ, the larger the amount of color misregistration caused by the belt speed fluctuation at the above approach timing. This is because as the inclination θ decreases, the paper area at the moment of entering the secondary transfer nip increases, and the amount of torque increase increases.

  Therefore, in this copying machine, the following additional characteristic configuration is added to the copying machine according to the first embodiment. That is, there is provided an inclination detecting means for detecting the inclination θ of the recording paper P immediately before entering the secondary transfer nip. And the control part 110 which is a pressing force control means is comprised so that control which changes the change degree of the said pressing force in the said approach timing according to inclination (theta) may be implemented. In such a configuration, the belt speed fluctuation is further suppressed by varying the amount of change in the pressing force according to the difference in the belt speed change amount due to the difference in the inclination θ at the approach timing. As a result, the amount of color misregistration in the second and subsequent printout sheets can be further suppressed.

  There are various methods for detecting the inclination θ. This copying machine is provided with a plurality of recording member detection means for detecting the recording paper P that passes through the position facing the recording paper P while being arranged in the width direction of the recording paper P, and the detection by the recording member detection means is used as the inclination detection means. The control unit 110 is configured to obtain the inclination θ based on the result. Further, as shown in FIG. 20, an optical sensor 77 is used as each of the plurality of recording member detection means. These optical sensors 77 may be either reflection type photo sensors or transmission type photo sensors as long as they are arranged so that the recording paper P conveyed in the conveyance path can be detected. However, it is necessary to dispose near the nip on the upstream side of the secondary transfer nip. By detecting the recording member by the optical sensor 77, the inclination θ can be detected without hooking the recording paper P on the recording member detection means. Note that a switch member as shown in FIG. 17 may be used in place of the optical sensor 77 as the plurality of recording member detection means.

[Sixteenth embodiment]
In FIG. 1 described above, the transfer device 40 has the following configuration. That is, the primary transfer bias as a transfer voltage is applied to the primary transfer rollers 45Y, 45M, 45K, which are latent image facing members facing the respective photoreceptors via the intermediate transfer belt 41 while being in contact with the back surface of the intermediate transfer belt 41. In this configuration, the toner image on each photoconductor is transferred to the belt while being applied. In this configuration, the toner image on each photoconductor can be transferred onto the belt by an electrostatic transfer method. However, when the primary transfer bias is applied to the primary transfer rollers 45Y, 45C, 45M, 45K, a load is applied to the intermediate transfer belt 41 due to the electrostatic force generated between the roller and the photosensitive member. As a result, the torque of the belt drive motor increases, and the belt moving speed slightly decreases. On the contrary, after the application of the primary transfer bias is stopped, the belt moving speed slightly increases.

  Therefore, in this copying machine, the following additional characteristic configuration is added to the copying machine according to the first embodiment. That is, the pressing force control means is adapted to perform control to weaken the pressing force immediately before the start of application at the start of application of the primary transfer bias to the primary transfer rollers 45Y, 45C, 45M, 45K as the latent image facing member. A control unit 110 is configured. Further, the control unit 110 is configured to perform control to increase the pressing force immediately before stopping the application when the application of the primary transfer bias is stopped. With such a configuration, it is possible to suppress color misregistration due to belt speed fluctuations associated with application or stop of application of the primary transfer bias.

[Seventeenth embodiment]
In this copying machine, the following additional characteristic configuration is added to the copying machine according to the first embodiment. That is, an ampere meter as drive current detection means for detecting the drive current of the belt drive motor is provided. Then, the pressing force is changed according to the detection result by the ampere meter during the period excluding the entry timing in the print job and the discharge timing at which the trailing edge of the recording paper P is discharged from the secondary transfer nip. The control unit 110 serving as a pressing force control unit is configured to perform the control. More specifically, the detection result of the ampermeter, that is, torque up or torque down of the belt drive motor is fed back to the control unit 110, and in the case of torque up, the pressing force is reduced by an amount corresponding to the amount of torque increase. In the case of torque reduction, the pressing force is increased by an amount corresponding to the torque reduction amount. In such a configuration, in addition to the belt speed fluctuation caused by the recording paper P being sandwiched in the secondary transfer nip, the belt speed fluctuation due to a different cause can be suppressed to further suppress the color misregistration. A servo motor is used as the belt drive motor.

[Eighteenth embodiment]
In this copying machine, the following additional characteristic configuration is added to the copying machine according to the first embodiment. That is, an encoder is provided as a roller speed detecting means for detecting a rotational speed or angular speed fluctuation in any one of the plurality of stretching rollers. And the control part 110 which is a pressing force control means is comprised so that the control which changes the said pressing force according to the detection result by an encoder may be implemented. More specifically, when the detection result by the encoder, that is, when the belt moving speed becomes slower than normal, the pressing force is reduced by an amount corresponding to the speed reduction amount. Further, when the belt moving speed becomes faster than usual, the pressing force is increased by an amount corresponding to the speed increase amount. Even in such a configuration, in addition to the belt speed fluctuation caused by the recording paper P being sandwiched in the secondary transfer nip, the belt speed fluctuation caused by a different cause can be suppressed to further suppress the color misregistration. However, since the intermediate transfer belt 41 may slip on the circumferential surface of the tension roller, the detection result by the encoder and the belt moving speed are not completely correlated.

[Nineteenth embodiment]
In this copying machine, the following additional characteristic configuration is added to the copying machine according to the first embodiment. That is, surface speed detection means for detecting the surface speed of the intermediate transfer belt 41 is provided. And the control part 110 which is a pressing force control means is comprised so that the control which changes the said pressing force according to the detection result by this surface speed detection means may be implemented. More specifically, when the belt moving speed becomes slower than usual, the pressing force is reduced by an amount corresponding to the speed reduction amount. Further, when the belt moving speed becomes faster than usual, the pressing force is increased by an amount corresponding to the speed increase amount. Even in such a configuration, in addition to the belt speed fluctuation caused by the recording paper P being sandwiched in the secondary transfer nip, the belt speed fluctuation caused by a different cause can be suppressed to further suppress the color misregistration. In addition, even if the intermediate transfer belt 41 slips on the circumferential surface of the stretching roller, the belt moving speed can be accurately detected.

  As the surface speed detecting means for detecting the surface speed of the intermediate transfer belt 41, as shown in FIG. 21, a plurality of marks 79 attached to the front surface of the intermediate transfer belt 41 at a predetermined pitch in the circumferential direction are detected. An optical sensor 78 composed of a reflective photosensor is used. The mark 79 may be formed on the intermediate transfer belt 41 in advance, or a plurality of toner images may be formed by a process unit on a toner image non-formation region at the end of the belt in the width direction. It may be used as the mark 79.

Next, a copying machine according to a second embodiment to which the present invention is applied will be described. The basic configuration of the copier according to the second embodiment is the same as that of the copier according to the first embodiment, and a description thereof will be omitted.
The copier has an abutting member that abuts at least one of the above-described stretching rollers that stretch the intermediate transfer belt 41, or the intermediate transfer belt 41. Further, a pressing force adjusting means for adjusting the pressing force of the contact member against the stretching roller or the intermediate transfer belt 41 is provided. Furthermore, it has a control part (110) which is a pressing force control means for changing the pressing force by controlling the pressing force adjusting means. This control part (110) performs the following control with respect to a pressing force adjustment means. That is, when the trailing edge of the recording paper P is discharged from the secondary transfer nip, the pressing force is increased more than the value immediately before the discharge.

  In such a configuration, when the trailing edge of the recording paper P is discharged from the secondary transfer nip, the contact member that is in contact with the intermediate transfer belt 41 or the stretching roller that stretches the intermediate transfer belt 41 is pressed against the roller or belt. By increasing the pressure above the value immediately before discharge, the following becomes possible. That is, the belt drive motor torque reduction due to the trailing edge of the recording paper P being discharged from the secondary transfer nip is offset by the torque increase due to the decrease in the pressing force by the contact member, and the belt drive motor at the time of discharge Suppresses a rapid increase in the rotation speed. Accordingly, it is possible to suppress image disturbance caused by a rapid speed increase of the intermediate transfer belt 41 when the trailing edge of the recording paper P is discharged from the secondary transfer nip. In addition, it is possible to suppress color misregistration caused by the speed variation of the intermediate transfer belt 41.

  Such image disturbance and color misregistration also occur on the second and subsequent recording sheets P in the continuous print mode.

  In this copying machine, a secondary transfer roller 51 that rotates while being in contact with the intermediate transfer belt 41 is used as the contact member, and the pressing force on the belt is adjusted. Specifically, the secondary transfer roller 51 is slightly moved away from the intermediate transfer belt 41 by the same configuration as the secondary transfer roller unit 50 of the copying machine according to the first embodiment shown in FIG. The pressing force of the secondary transfer roller 51 against the intermediate transfer belt 41 is adjusted by bringing them closer. That is, in this copying machine as well as the copying machine according to the first embodiment, the holding body 52, the biasing coil spring 53, the cam shaft 54, the cam 55, the holding body rotating shaft 56, the cam motor (not shown), It functions as a pressing force adjusting means for adjusting the pressing force of the secondary transfer roller 51 against the transfer belt 41.

  The timing at which the trailing edge of the recording paper P is discharged from the secondary transfer nip (hereinafter referred to as discharge timing) is determined by the control unit based on the detection result by the optical sensor 57 in FIG. Specifically, the moment when the optical sensor 57 switches from the state in which the recording paper P is detected to the state in which the recording paper P is no longer detected is the moment when the trailing edge of the recording paper P passes through the position facing the optical sensor 57. The trailing edge of the recording paper P is discharged from the secondary transfer nip after a predetermined time has elapsed from this moment (a time depending on the length of the recording paper P and the conveyance speed). The discharge timing is obtained by measuring the timing after elapse of a predetermined time. That is, the control unit obtains the discharge timing based on the signal indicating that the recording paper P sent from the optical sensor 57 is not detected, that is, the trailing edge detection signal. As in the case of the copying machine according to the first embodiment, it is possible to appropriately obtain the discharge timing that varies depending on the difference between the high-speed print mode and the high-quality print mode. Further, as the optical sensor 57, a transmissive photosensor may be used instead of the reflective photosensor.

  In addition, when a predetermined time has elapsed from the discharge timing, the control unit returns the pressing force, which was stronger than the value immediately before discharge, to the initial value. This is for the reason explained below. That is, the present inventors prepared an experimental machine having the configuration of the copying machine, and the second and subsequent prints were obtained when the pressing force was increased at the discharge timing and when the pressing force was not changed. An experiment was conducted to examine the difference in color misregistration on out paper. The result is shown in FIG. As shown in the figure, when the pressing force is not changed at the discharge timing (no pressing force adjustment), a large color shift occurs only momentarily at the discharge timing, but no color shift occurs thereafter. This is because the belt moving speed suddenly increases for a moment at the discharge timing, but then the belt moving speed returns to the vicinity of the initial value. If the pressing force increased at the discharge timing is left as it is, the belt moving speed does not return to the vicinity of the initial value, but settles at a slower value than usual, and color shift occurs over time. Therefore, after a predetermined time has elapsed from the discharge timing, the pressing force is returned to the initial value. By doing so, as shown by the solid line in the figure, it is possible to avoid subsequent color shifts caused by continuing to increase the pressing force while suppressing color shifts occurring at the discharge timing. Although the example using the cam 55 or the like as the pressing force adjusting means has been described, any mechanism can be used as long as the pressing force of the secondary transfer roller 51 or the like can be adjusted. Good.

  In a general image forming apparatus, as described above, a registration sensor is provided. Instead of the detection result by the optical sensor 57, it is also possible to cause the control unit to obtain the discharge timing based on the detection result from the registration sensor. However, in this case, as described above, there is a risk of generating an ejection timing calculation error due to an approach timing error caused by a difference in waist strength of the recording paper P.

  Further, in the case where the approach timing is obtained based on the change in the drive current of the motor that is the drive source of the transport member pair, the drive source of the transport member pair disposed upstream of the secondary transfer nip. It has been described above that it is desirable to detect the drive current. However, when obtaining the above discharge timing, it is not always necessary to detect the drive current of the drive source of the pair of conveying members disposed upstream of the secondary transfer nip. For example, depending on the distance between the secondary transfer nip and the fixing nip, even when the recording paper P is relatively short, such as a postcard, the leading end of the recording paper P passes through the secondary transfer nip after entering the fixing nip. There is. In such a case, the recording paper to the fixing nip is based on the driving current of the motor that is the driving source of at least one of the conveying member pair consisting of the fixing roller (96) and the pressure roller (97). If the entry timing of P is detected, the discharge timing can be accurately obtained based on the detection result. Also, when the discharge timing is obtained based on the detection result of the surface movement speed and rotation speed of the conveying member pair, the surface speed and rotation speed of the conveying member pair are set upstream of the secondary transfer nip for the same reason. You may make it detect.

Next, a description will be given of the copying machine of each example in which a more characteristic configuration is added to the copying machine according to the second embodiment.
[20th embodiment]
In the experimental machine equipped with the configuration of the copying machine according to the second embodiment, the present inventors have used discharge timings when a relatively thick recording paper P is used and when a normal thickness is used. An experiment was conducted to compare the differences in color misregistration. The pressing force of the secondary transfer roller 51 was not adjusted. The results are shown as a graph in FIG. In the figure, the graph drawn with a solid line shows the result when 90K paper (normal thickness) is used as the recording paper P. Further, the graph drawn with a dotted line shows the result when 210K paper (thick paper) is used as the recording paper P. As shown in the drawing, it can be seen that the larger the thickness of the recording paper P, the larger the amount of color misregistration caused by the belt speed fluctuation at the discharge timing. This is because the torque reduction amount at the discharge timing increases as the thickness increases.

  Therefore, in this copying machine, the following additional characteristic configuration is added to the copying machine according to the second embodiment. That is, a thickness information acquisition unit that acquires thickness information of the recording paper P is provided, and a control is performed to vary the degree of change in pressing force at the discharge timing (the amount of change in pressing force) according to the thickness information. A control unit 110 serving as a pressing force control unit is configured. In such a configuration, the belt speed variation is further suppressed by varying the amount of change in the pressing force according to the difference in the belt speed variation due to the difference in the thickness of the recording paper P at the discharge timing. As a result, the color misregistration amount at the discharge timing of the second and subsequent printout sheets can be further suppressed.

  In this copying machine, thickness detecting means for detecting the thickness of the recording paper P is used as thickness information acquiring means. As the thickness detection means, as in the copying machine according to the fifth embodiment, the detection by the drive current detection means for detecting the drive current of the motor that is the drive source of at least one member of the conveying member pair. Based on the result, the thickness is detected. In the copying machine according to the fifth embodiment, it is desirable to detect the thickness based on the detection result of the driving current before the recording paper P enters the secondary transfer nip. A material that is a drive source for the pair of conveying members upstream of the secondary transfer nip is employed. If this is not done, it is possible to obtain the effect of further suppressing the color shift at the approach timing that occurs from the second and subsequent sheets by adjusting the pressing force according to the thickness. On the other hand, in this copying machine, for the reasons already described, even when the drive current of the secondary transfer nip and the drive source of the conveying member pair disposed downstream of this is detected, the discharge timing is not reached. In addition, the thickness of the recording paper P can be detected. Therefore, even if the detection target of the drive current is not used as the drive source for the pair of conveying members disposed upstream of the secondary transfer nip, the color shift at the discharge timing that occurs from the second and subsequent sheets is increased in thickness. The effect of further suppressing by adjusting the corresponding pressing force can be obtained from the second sheet.

  An example has been described in which the thickness detection means is provided that detects the thickness of the recording paper P based on the detection result of the drive current. However, even when using a device that detects the thickness based on the detection result of the transmission type photosensor as in the copying machine of the seventh embodiment, it is not limited to the upstream side of the secondary transfer nip, It may be provided on the downstream side. Further, even when a laser displacement meter is used as the thickness detecting means as in the copying machine of the eighth embodiment, it may be provided not only upstream but also downstream from the secondary transfer nip. Further, as in the ninth embodiment, the thickness detecting means is one that detects the thickness based on the moving speed of the conveying member, and is not limited to the upstream side of the secondary transfer nip, but the downstream side. May be provided. Furthermore, even when a device that detects the thickness based on the rotation speed of the conveying member is used, it may be provided not only on the upstream side of the secondary transfer nip but also on the downstream side. This is because, even if they are provided on the downstream side, the effect of further suppressing the color shift at the discharge timing that occurs from the second and subsequent sheets by adjusting the pressing force according to the thickness can be obtained from the second sheet. .

  As the thickness information acquisition means, instead of the thickness detection means, there may be provided a means for acquiring the thickness information of the recording paper P by an input operation with respect to various keys like the copying machine of the tenth embodiment.

[Twenty-first embodiment]
In the experimental machine having the configuration of the copying machine according to the second embodiment, the present inventors discharged paper when a recording paper P having a relatively large sheet passing width is used and when a relatively small sheet is used. An experiment was conducted to compare the difference in color misregistration amount at the timing. The pressing force of the secondary transfer roller 51 was not adjusted. The results are shown as a graph in FIG. In the drawing, a graph drawn with a solid line shows a result when the recording paper P is conveyed with a paper passing width of 210 [mm]. Further, the graph drawn with a dotted line shows the result when the recording paper P is conveyed with a paper passing width of 420 [mm]. As shown in the drawing, it can be seen that the larger the sheet passing width of the recording paper P, the larger the amount of color misregistration caused by the belt speed fluctuation at the above-described discharge timing. This is because the torque reduction amount at the discharge timing increases as the sheet passing width increases.

  Therefore, in this copying machine, the following additional characteristic configuration is added to the copying machine according to the second embodiment. That is, a width information acquisition unit that acquires width information that is a sheet passing width is provided. And the control part 110 which is a pressing force control means is comprised so that the control which changes the degree of the change of the said pressing force in discharge | emission timing according to width information may be implemented. In such a configuration, the belt speed variation is further suppressed by varying the amount of change in the pressing force in accordance with the difference in the belt speed variation due to the difference in the sheet passing width at the discharge timing. Thereby, it is possible to further suppress the color misregistration amount from the second printout paper.

  In the present copying machine, as in the copying machine according to the eleventh embodiment, a plurality of recording member detecting means are provided for detecting the recording paper P that is aligned in the width direction of the recording paper P and passes through the position facing the recording paper P. Yes. Further, as the width detecting means, a means for detecting the width of the recording paper P based on the detection result by the recording member detecting means is used. Furthermore, an optical sensor is used as each of the plurality of recording member detection means.

  These optical sensors may be either reflection type photo sensors or transmission type photo sensors as long as they are arranged so that the recording paper P conveyed in the conveyance path can be detected. Unlike the copying machine of the eleventh embodiment, these optical sensors are not necessarily provided upstream of the secondary transfer nip, and may be provided downstream. This is because the effect of further suppressing the color shift at the discharge timing that occurs from the second and subsequent sheets by adjusting the pressing force according to the sheet width can be obtained from the second sheet. When a plurality of switch members are provided instead of a plurality of optical sensors as in the copying machine of the twelfth embodiment, they can be disposed downstream of the secondary transfer nip for the same reason. It is.

  As the width information acquisition means, instead of the width detection means, there may be provided a means for acquiring the width information of the recording paper P by an input operation with respect to various keys as in the copying machine according to the thirteenth embodiment.

[Twenty-second embodiment]
The inventors of the present invention conducted an experiment comparing the difference in color misregistration amount at the discharge timing in the case of using a paper having different gaps as the recording paper P in an experimental machine having the configuration of the copying machine according to the second embodiment. Went. The pressing force of the secondary transfer roller 51 was not adjusted. The results are shown as a graph in FIG. As shown in the figure, it can be seen that the amount of color misregistration varies according to the state of the gap (the state of the gap is different for each of the dotted line, the alternate long and short dash line, and the solid line).

  Therefore, in this copying machine, the following additional characteristic configuration is added to the copying machine according to the second embodiment. That is, a gap information acquisition unit that acquires the gap information that is the gap information of the recording paper P is provided. And the control part 110 which is a pressing force control means is comprised so that control which changes the change degree of the pressing force in discharge timing according to gap information may be implemented. In such a configuration, the belt speed fluctuation is further suppressed by varying the amount of change in the pressing force in accordance with the difference in the belt speed change amount due to the difference in the gap at the discharge timing. As a result, the amount of color misregistration in the second and subsequent printout sheets can be further suppressed. As the gap information detecting means, an operation display unit is used as an input means for performing an operation for inputting the gap information by the operator.

[Twenty-third embodiment]
The inventors conducted an experiment to examine the relationship between the inclination θ of the recording paper P and the amount of color misregistration when discharged from the secondary transfer nip using an experimental machine having the configuration of the copying machine according to the second embodiment. went. The pressing force of the secondary transfer roller 51 was not adjusted. The results are shown as a graph in FIG. In the figure, the inclination θ is “solid line graph> dot-dot line bluff> dotted line graph”. As shown in the figure, it can be seen that the smaller the inclination θ, the larger the amount of color misregistration caused by the belt speed fluctuation at the discharge timing. This is because as the inclination θ decreases, the area of the trailing edge of the recording paper discharged from the secondary transfer nip increases, and the amount of torque reduction increases.

  Therefore, in this copying machine, the following additional characteristic configuration is added to the copying machine according to the second embodiment. In other words, an inclination detecting means for detecting the inclination θ of the recording paper P is provided. And the control part 110 which is a pressing force control means is comprised so that the control which changes the change degree of the said pressing force in discharge | emission timing according to inclination (theta) may be implemented. In such a configuration, the belt speed fluctuation is further suppressed by varying the amount of change in the pressing force according to the difference in the belt speed change amount due to the difference in the inclination θ at the discharge timing. As a result, the amount of color misregistration in the second and subsequent printout sheets can be further suppressed.

  In this copying machine, like the copying machine according to the fifteenth embodiment, there are provided a plurality of recording member detecting means for detecting the recording paper P that is aligned in the width direction of the recording paper P and passes through the position facing each other. Yes. The control unit 110 is configured to obtain the inclination θ based on the detection result by the recording member detection means as the inclination detection means. Furthermore, the optical sensor 77 previously shown in FIG. 20 is used as a plurality of recording member detection means. These optical sensors 77 may be either reflection type photo sensors or transmission type photo sensors as long as they are arranged so that the recording paper P conveyed in the conveyance path can be detected.

  In the copying machine according to the fifteenth embodiment, in order to detect the inclination θ of the recording sheet P immediately before entering the secondary transfer nip, a plurality of optical sensors 77 are arranged near the secondary transfer nip and upstream of the secondary transfer nip. Provided. In this copying machine, the optical sensor 77 may be provided in this way. This is because after entering the secondary transfer nip, the inclination θ of the recording paper P does not change until the recording paper P is discharged from the secondary transfer nip. Even if the optical sensor 77 is provided on the downstream side of the secondary transfer nip, it is possible to detect the inclination θ of the recording paper P immediately before the trailing edge is discharged from the secondary transfer nip.

  Note that a switch member as shown in FIG. 17 may be used in place of the optical sensor 77 as the plurality of recording member detection means.

  Further, as in the copier according to the sixteenth embodiment, the pressing force is weakened when the primary transfer bias is started than before the application is started, or the pressing force is increased when the application is stopped. The control unit 110 may be configured so as to perform control.

  Similarly to the copying machine according to the seventeenth embodiment, control is performed to change the pressing force in accordance with the detection result of the ampere meter during a period not including the entry timing and the discharge timing in the print job. In addition, the control unit 110 may be configured.

  Further, similarly to the copying machine according to the eighteenth embodiment, an encoder as roller speed detecting means for detecting the rotational speed or the angular speed of any one of the plurality of stretching rollers is provided, and the above-described operation is performed according to the detection result. The control unit 110 may be configured to perform control to change the pressing force.

  Further, similarly to the copying machine according to the nineteenth embodiment, there is provided an encoder as roller speed detecting means for detecting the rotational speed or the angular speed speed of any one of the plurality of stretching rollers, and the above-mentioned according to the detection result by the encoder. The control unit 110 may be configured to perform control to change the pressing force.

Next, a third embodiment of a copying machine to which the present invention is applied will be described. Note that the basic configuration of the copying machine according to the third embodiment is the same as that of the copying machine according to the first embodiment, and thus the description thereof is omitted.
This copier also has the same pressing force adjusting means as the copiers according to the first and second embodiments. In addition, a control unit (110) serving as a pressing force control unit that changes the pressing force by controlling the pressing force adjusting unit is provided. And a control part (110) performs the following control with respect to a pressing force adjustment means. That is, the pressing force is made weaker than the value immediately before entering at the approach timing. This suppresses the occurrence of color misregistration at the entry timing. Next, when a predetermined amount approach timing arrives, the pressing force is slightly increased. Thus, before the image transfer area of the recording paper P enters the secondary transfer nip, a nip pressure necessary for the secondary transfer is ensured, and secondary transfer failure due to insufficient nip pressure is suppressed. When the discharge timing comes, the pressing force is strengthened more than the hit immediately before the discharge. This suppresses the occurrence of color misregistration at the discharge timing. Further, after a predetermined time has elapsed from the discharge timing, the pressing force is returned to the initial value. This avoids the occurrence of color shift over time due to the fact that the pressing force is not returned to the initial value after the discharge timing. A series of adjustments of the pressing force is performed for each sheet passing.

  In such a configuration, it is possible to suppress both a color shift that occurs at the time of entry and a color shift that occurs at the time of discharge.

  Note that when the entry timing and the discharge timing are obtained based on the detection result of the recording paper P by the optical sensor, it is necessary to dispose the optical sensor upstream of the secondary transfer nip. Further, the entry timing and the discharge timing are obtained based on the detection result of the driving current of the driving source of the conveying member pair, the surface moving speed of the conveying member pair, the rotational speed of the conveying member pair, or the displacement of the conveying member pair. In this case, it is necessary to employ a pair of conveying members to be detected that is disposed upstream of the secondary transfer nip.

  In this copying machine as well, as in the copying machines according to the fifth and twentieth embodiments, the degree of change in the pressing force at the entry timing and the discharge timing is made different depending on the thickness of the recording paper P. Thus, the color shift can be further suppressed. When the thickness detection unit is used as the thickness information acquisition unit, an optical sensor for thickness detection is provided on the upstream side of the secondary transfer nip, or the driving current, surface moving speed, rotational speed, or displacement amount is measured. It is necessary to employ a pair of conveying members to be detected that are disposed upstream of the secondary transfer nip. By doing so, it is possible to obtain from the second sheet the effect of further reliably suppressing the color shift that occurs from the second sheet and thereafter by adjusting the pressing force according to the thickness.

  Also in this copying machine, as in the copying machines according to the eleventh embodiment and the twenty-first embodiment, the degree of change in the pressing force at the entry timing and the ejection timing is made different depending on the sheet passing width. The color shift can be further suppressed. When using a width detection unit as the width information acquisition unit, it is necessary to dispose it on the upstream side of the secondary transfer nip. By doing so, it is possible to obtain from the second sheet the effect of more reliably suppressing the color misregistration that occurs from the second and subsequent sheets by adjusting the pressing force according to the paper width. .

  Also in this copying machine, as in the copying machines according to the 14th embodiment and the 22nd embodiment, the degree of change of the pressing force at the entry timing and the discharge timing is made different depending on the gap. The color shift can be further suppressed.

  Also in the present copying machine, as in the copying machines according to the fifteenth embodiment and the twenty-third embodiment, the degree of change in the pressing force at the entry timing and the discharge timing is varied according to the inclination θ. The color shift can be further suppressed. In this case, the means for detecting the inclination θ needs to be arranged so as to detect the inclination of the recording sheet P immediately before entering the secondary transfer nip. This is because it is possible to detect the inclination θ of the recording paper P both immediately before entering the secondary transfer nip and immediately before the trailing edge is discharged from the secondary transfer nip.

  Further, as in the copier according to the sixteenth embodiment, the pressing force is weakened when the primary transfer bias is started than before the application is started, or the pressing force is increased when the application is stopped. The control unit 110 may be configured so as to perform control.

  Similarly to the copying machine according to the seventeenth embodiment, control is performed to change the pressing force in accordance with the detection result of the ampere meter during a period not including the entry timing and the discharge timing in the print job. In addition, the control unit 110 may be configured.

  Further, similarly to the copying machine according to the eighteenth embodiment, an encoder as roller speed detecting means for detecting the rotational speed or the angular speed of any one of the plurality of stretching rollers is provided, and the above-described operation is performed according to the detection result. The control unit 110 may be configured to perform control to change the pressing force.

  Further, similarly to the copying machine according to the nineteenth embodiment, there is provided an encoder as roller speed detecting means for detecting the rotational speed or the angular speed speed of any one of the plurality of stretching rollers, and the above-mentioned according to the detection result by the encoder. The control unit 110 may be configured to perform control to change the pressing force.

  As described above, in the copiers according to the first example and the second embodiment, the secondary transfer roller 51 which is a contact roller capable of endless surface movement is used as a contact member that contacts the stretching roller or the intermediate transfer belt 41. ing. With such a configuration, it is possible to avoid belt deterioration due to friction between the contact member and the intermediate transfer belt 41.

  Further, in the copying machine according to the first example or the second embodiment, the secondary transfer roller 51 that is a transfer nip forming roller that contacts the intermediate transfer belt 41 is used as the contact roller. In such a configuration, the moving speed of the intermediate transfer belt 41 can be adjusted without providing a new contact roller for adjusting the belt moving speed. Further, unlike a case where a roller different from the secondary transfer roller 51 is newly provided as a contact roller, it is possible to suppress a sudden torque increase itself when the recording paper P enters the secondary transfer nip. The belt speed fluctuation can be surely suppressed.

  Further, in the copiers according to the first example and the second embodiment, the nip backside stretching roller 46 is also used as a belt driving roller that moves the intermediate transfer belt 41 endlessly with its own rotational driving. In this configuration, as described above, the belt speed can be more accurately adjusted by quickly reflecting the change in the pressing force in the change in the torque of the belt drive motor as compared with the case where the other tension roller is a belt drive roller. It can be performed.

  Further, in the copying machine according to the fourth embodiment, the rubbing member 63 that cannot move on the surface is used as the contact member. In this configuration, as described above, the torque change rate associated with the change in the pressing force can be increased and the torque can be adjusted with a smaller change in the pressing force, compared to the case where a roller capable of moving the surface is used. it can.

  Further, in the copiers according to the first example and the second embodiment, the optical sensor 57 serving as a recording member detecting unit that detects the recording paper P passing through the position facing the self is transported by the recording paper more than the secondary transfer nip. The control unit 110 is configured to perform control for determining the entry timing and the discharge timing based on the detection result by being arranged on the upstream side in the direction. In such a configuration, when the leading edge of the recording paper immediately before entering the secondary transfer nip is detected by the optical sensor 57 and the entry timing and the discharge timing are obtained based on the timing, the timing based on the feed timing from the registration roller pair 35 is used. Compared to, it is possible to accurately determine the entry timing and the discharge timing. When the pressing force is changed only by the discharge timing, it is not always necessary to provide the optical sensor 57 in the vicinity of the secondary transfer nip and upstream of the secondary transfer nip.

  Further, in the copying machines according to the fifth to ninth embodiments or the twentieth embodiment, thickness information acquisition means for acquiring the thickness information of the recording paper P is provided, and the pressing at the entry timing and the discharge timing is performed. The control part 110 is comprised so that the control which changes the change degree of a pressure according to the thickness information may be implemented. In this configuration, as described above, the belt speed variation is further suppressed by varying the amount of change in the pressing force according to the difference in the belt speed variation due to the difference in the thickness of the recording paper P at the entry timing and the ejection timing. . As a result, the amount of color misregistration in the second and subsequent printout sheets can be further suppressed.

  In the copiers according to the fifth to eighth embodiments or the twentieth embodiment, thickness detecting means for detecting the thickness of the recording paper P is used as thickness information acquiring means. In such a configuration, unlike the case where the thickness information is acquired by an input operation to the operation display unit, it is possible to avoid improper pressing force adjustment control due to an input error of the thickness information.

  In the copiers according to the fifth and twentieth embodiments, at least one member of the pair of conveying members that conveys the recording paper P sandwiched between the conveying nips obtained by bringing the endlessly moving surfaces into contact with each other. An ampere meter 111 as drive current detection means for detecting the drive current of the motor serving as the drive source is provided. And the control part 110 is comprised so that the thickness of the recording paper P may be detected based on the detection result by the ampere meter 111 as a thickness detection means. In such a configuration, the thickness of the recording paper P can be detected without providing a thickness detection sensor for detecting the thickness of the recording paper P. Unlike the case of using an optical sensor for detecting the thickness of the recording paper P, the thickness of the recording paper P can be accurately detected even when a transparent paper or an OHP sheet is used as the recording paper P. it can.

  In the copier according to the fifth embodiment, the ampere meter 111 detects a drive current of a motor that is a drive source of a conveyance member disposed upstream of the secondary transfer nip in the recording paper conveyance direction. Use what you want. In such a configuration, as described above, it is possible to further improve the image quality by adjusting the pressing force according to the thickness at the entry timing from the second printed sheet.

  In the copying machine according to the sixth embodiment, a belt driving roller (nip nip) that moves the intermediate transfer belt 41 endlessly by its own rotational drive while functioning as one of a plurality of stretching rollers with respect to the ampere meter 111. The drive current of the belt drive motor that is the drive source of the back-side stretching roller 46) is detected. The control unit 110 is configured to detect the thickness of the recording paper P based on the detection result by the ampermeter 111 as the thickness detection means. In such a configuration, it is possible to further improve the image quality by adjusting the pressing force according to the thickness based on the change in the driving current of the belt driving motor.

  In the copier according to the seventh embodiment, a transmission type photosensor that detects the thickness of the recording paper P based on the light transmittance with respect to the recording paper P is used as the thickness detecting means. In such a configuration, the thickness of the recording paper P can be detected in finer units than when the thickness is detected based on the drive current.

  Further, in the copier according to the eighth embodiment, the displacement amount of at least one member in the conveying member pair that conveys the recording paper P sandwiched in the conveying nip obtained by bringing the endlessly moving surfaces into contact with each other is set. A laser displacement meter as a displacement amount detecting means for detection is provided. And the control part 110 is comprised so that the thickness of the recording paper P may be detected as a thickness detection means based on the detection result by this laser displacement meter. Even in such a configuration, even when a transparent paper or an OHP sheet is used as the recording paper P, the thickness thereof can be appropriately detected. Furthermore, it is possible to detect the thickness in finer units as compared with the case where the thickness is detected based on the drive current.

  Further, in the copying machine according to the ninth embodiment, the surface moving speed of at least one member of the conveying member pair that conveys the recording paper P sandwiched between the conveying nips obtained by bringing the surfaces that move endlessly into contact with each other. Surface speed detecting means for detecting the above is provided. The control unit 110 is configured to detect the thickness of the recording paper P based on the detection result of the surface speed detection unit as the thickness detection unit. Even in such a configuration, even when a transparent paper or an OHP sheet is used as the recording paper P, the thickness thereof can be appropriately detected.

  Further, in the copying machine according to the tenth embodiment, an operation display unit serving as an input unit for performing thickness information input operation by an operator is used as the thickness information acquisition unit. In this configuration, as described above, the thickness information of the recording paper P can be acquired without providing a special optical sensor, ampermeter, encoder, or the like for detecting the thickness.

  In the copiers according to the eleventh embodiment and the twenty-first embodiment, there is provided width information acquisition means for acquiring width information that is the sheet passing width. And the control part 110 is comprised so that the control which changes the change degree of the said pressing force in the said approach timing and discharge | emission timing according to the width information may be implemented. In such a configuration, the belt speed fluctuation is further suppressed by varying the amount of change in the pressing force according to the difference in the belt speed change amount due to the difference in the sheet passing width at the entry timing and the discharge timing. As a result, the amount of color misregistration in the second and subsequent printout sheets can be further suppressed.

  In the copying machine according to the eleventh embodiment, the twelfth embodiment, or the twenty-first embodiment, a width detection unit that detects the width of the recording paper P is used as the width information acquisition unit. In such a configuration, unlike when width information is acquired by an input operation to the operation display unit, improper pressing force adjustment control due to an input error of width information can be avoided.

  In the copying machine according to the eleventh embodiment, the twelfth embodiment, or the twenty-first embodiment, a plurality of recordings are detected that detect the recording paper P that passes through the position facing the recording paper P while being aligned in the width direction of the recording paper P. Member detection means is provided. And the control part 110 is comprised so that the width | variety of the recording paper P may be detected as a width | variety detection means based on the detection result by these recording member detection means. Even in such a configuration, unlike the case of acquiring the width information by an input operation to the operation display unit, it is possible to avoid improper pressing force adjustment control due to an input error of the width information.

  Further, in the copying machine according to the thirteenth embodiment, an operation display unit which is an input unit for performing width information input operation by an operator is used as the width information acquisition unit. In such a configuration, the width information of the recording paper P can be acquired without providing a special optical sensor or switch member for detecting the width.

  The copiers according to the fourteenth embodiment and the twenty-second embodiment are provided with a gap information acquisition unit that acquires gap information that is the gap information of the recording paper P. And the control part 110 is comprised so that the control which changes the change degree of the said pressing force in the said approach timing and discharge | emission timing according to the gap information may be implemented. In such a configuration, the belt speed variation is further suppressed by varying the amount of change in the pressing force according to the difference in the belt speed change amount due to the difference in the gaps at the entry timing and the discharge timing. As a result, the amount of color misregistration in the second and subsequent printout sheets can be further suppressed.

  In the copiers according to the fourteenth and twenty-second embodiments, an operation display unit serving as an input means for performing a clearance information input operation by the operator is used as the clearance information acquisition means. In such a configuration, the gap information of the recording paper P can be acquired without providing a special sensor for detecting the gap.

  Further, in the copying machines according to the fifteenth embodiment and the twenty-third embodiment, there are provided inclination detecting means for detecting the inclination θ from the direction orthogonal to the conveying direction of the recording paper P being conveyed in the copying machine. And the control part 110 is comprised so that the control which changes the change degree of the said pressing force in the said approach timing or discharge | emission timing according to inclination (theta) may be implemented. In such a configuration, the belt speed variation is further suppressed by making the amount of change in the pressing force different according to the difference in the belt speed change amount due to the difference in the inclination θ at the entry timing and the discharge timing. As a result, the amount of color misregistration in the second and subsequent printout sheets can be further suppressed.

  In the copying machines according to the fifteenth embodiment and the twenty-third embodiment, there are provided a plurality of recording member detecting means for detecting the recording paper P that passes through the position facing the recording paper P while being arranged in the width direction of the recording paper P. ing. The control unit 110 is configured to detect the inclination θ of the recording paper P based on the detection result by the recording member detection means as the inclination detection means. In such a configuration, the inclination θ of the recording paper P can be actually measured based on the detection results by the plurality of recording member detection means.

  In the copying machine according to the eleventh embodiment, the fifteenth embodiment, or the twenty-third embodiment, an optical sensor that optically detects the recording paper P is used as each of the plurality of recording member detection means. In such a configuration, unlike the case where a switch member is used as the plurality of recording member detection means, the recording paper P can be detected without hooking the recording paper P on the recording member detection means.

  Further, in the copier according to the twelfth embodiment, a switch member that connects / disconnects the electrical contact with the contact / separation with the recording paper P is used as the plurality of recording member detecting means. In such a configuration, even when a transparent paper, an OHP sheet, or the like is used as the recording paper P, the paper passing width can be accurately detected.

  Further, in the copying machine according to the sixteenth embodiment, the transfer device 40 is a latent image facing member that faces the photoreceptor as a latent image carrier through the intermediate transfer belt 41 while contacting the back surface of the intermediate transfer belt 41. A roller that transfers a toner image on the photosensitive member to a belt while applying a primary transfer bias to a certain primary transfer roller 45Y, 45C, 45M, 45K, 45K is used. Then, the control unit 110 is configured to perform a control to weaken the pressing force at the start of application of the primary transfer bias to the primary transfer rollers 45Y, 45C, 45M, 45K. With such a configuration, it is possible to suppress color misregistration due to a decrease in belt speed accompanying application of the primary transfer bias.

  Further, in the copying machine according to the sixteenth embodiment, when the application of the primary transfer bias to the primary transfer rollers 45Y, 45C, 45M, and 45K is stopped, control is performed to increase the pressing force more than immediately before the application is stopped. In addition, the control unit 110 is configured. With such a configuration, it is possible to suppress color misregistration due to an increase in belt speed accompanying the stop of application of the primary transfer bias.

  In the copier according to the seventeenth embodiment, a belt motor serving as a drive source for a belt drive roller that functions as one of a plurality of stretching rollers and moves the intermediate transfer belt 41 endlessly by its own rotational drive. An ampermeter serving as a drive current detection means for detecting the drive current is provided. The control unit 110 is configured to perform control to change the pressing force in accordance with the detection result by the ampere meter during a period not including the entry timing and the discharge timing in the print job. In such a configuration, in addition to the belt speed fluctuation caused by the recording paper P being sandwiched in the secondary transfer nip, the belt speed fluctuation due to a different cause can be suppressed to further suppress the color misregistration.

  The copier according to the eighteenth embodiment is provided with an encoder as roller speed detecting means for detecting the rotational speed or angular speed of any one of the plurality of stretching rollers. And the control part 110 is comprised so that the control which changes the said pressing force according to the detection result by this encoder may be implemented. Even in such a configuration, in addition to the belt speed fluctuation caused by the recording paper P being sandwiched in the secondary transfer nip, the belt speed fluctuation caused by a different cause can be suppressed to further suppress the color misregistration.

  In the copying machine according to the nineteenth embodiment, surface speed detecting means for detecting the surface speed of the intermediate transfer belt 41 is provided. And the control part 110 is comprised so that the control which changes the said pressing force according to the detection result by this surface speed detection means may be implemented. Even in such a configuration, in addition to the belt speed fluctuation caused by the recording paper P being sandwiched in the secondary transfer nip, the belt speed fluctuation caused by a different cause can be suppressed to further suppress the color misregistration. In addition, even if the intermediate transfer belt 41 slips on the circumferential surface of the stretching roller, the belt moving speed can be accurately detected.

  Further, in the copying machine according to the first embodiment and each example, since the pressing force adjusting means that adjusts the pressing force as the motor is driven is used, the pressing force is adjusted by adjusting the driving amount of the motor. The pressure can be adjusted accurately.

  Up to now, a plurality of process units having a combination of a photosensitive member and a developing device as a developing means have been arranged to face the front surface of the intermediate transfer belt 41, and toner images developed on the respective photosensitive members are used as belts. A so-called tandem type copying machine has been described in which the images are superimposed and transferred. However, if the present invention is applied to a single-color image forming apparatus that forms only a single-color image, image disturbance due to speed fluctuations of the intermediate transfer belt 41 can be suppressed. Even if the present invention is applied to the following image forming apparatus, color misregistration due to belt speed fluctuations can be suppressed. That is, an image forming apparatus in which a plurality of developing units are arranged to face one latent image carrier and visible images developed by different developing units are sequentially superimposed and transferred onto an intermediate transfer belt. is there.

1 is a schematic configuration diagram showing a copier according to a first embodiment. FIG. 2 is an enlarged configuration diagram showing a process unit for Y in the printer unit of the copier. The perspective view which shows the process unit. The perspective view which shows the image development apparatus of the process unit. FIG. 3 is an enlarged configuration diagram illustrating a secondary transfer roller unit in the transfer device of the copier according to the first embodiment, along with its peripheral configuration. FIG. 3 is an enlarged configuration diagram illustrating the secondary transfer roller unit in a state where the pressing force of the secondary transfer roller against the intermediate transfer belt is weakened. The graph which shows the relationship between the presence or absence of adjustment of the same pressing force in approach timing, and a color shift amount. FIG. 9 is an enlarged configuration diagram showing a secondary transfer roller unit and its peripheral configuration in a copying machine according to a second embodiment. FIG. 9 is an enlarged configuration diagram showing a secondary transfer roller unit and its surrounding configuration in a copying machine according to a third embodiment. FIG. 10 is a schematic configuration diagram illustrating a transfer device of a copying machine according to a fourth embodiment. 6 is a graph showing the relationship between the thickness of recording paper and the amount of color misregistration at the approach timing. The graph which shows the change of the motor drive current before and behind approach timing. FIG. 10 is a schematic diagram showing various motors in a copying machine according to a fifth embodiment. The perspective view which shows one roller and the encoder in the registration roller pair in the copying machine based on 9th Example. The perspective view which shows an example of a conveyance belt and a means to detect the surface moving speed of this. The graph which shows the relationship between the paper passing width | variety and color shift amount in approach timing. (A), (b) is an expanded block diagram which shows the switch member in the copying machine based on 12th Example. The graph which shows the relationship between the state of a crevice, and the amount of color shifts in approach timing. The graph which shows the relationship between inclination (theta) and the color shift amount in approach timing. The top view which shows the secondary transfer roller in the copying machine based on 15th Example, and the some optical sensor arrange | positioned upstream from this. FIG. 20 is a perspective view showing an optical sensor as a surface speed detecting means together with an intermediate transfer belt in a copying machine according to a nineteenth embodiment. The graph which shows the relationship between the presence or absence of adjustment of the same pressing force in discharge timing, and the amount of color shift. 6 is a graph showing the relationship between the thickness of recording paper and the amount of color misregistration at the discharge timing. 6 is a graph showing a relationship between a sheet passing width and a color misregistration amount at a discharge timing. The graph which shows the relationship between the state of a crevice, and the amount of color shifts in discharge timing. The graph which shows the relationship between inclination (theta) and the color shift amount in discharge timing.

Explanation of symbols

3Y, C, M, K: photoconductor (latent image carrier)
7Y: Developing device (developing means)
40: transfer device 41: intermediate transfer belt 45Y, C, M, K: primary transfer roller (stretching roller)
46: Nip back tension roller (stretch roller, belt drive roller)
47: Tension roller (stretching roller)
48: Auxiliary roller (stretching roller)
49: Nip upstream roller (stretching roller)
50: Secondary transfer roller unit 51: Secondary transfer roller (transfer nip forming roller)
52: Holding body (part of pressing force adjusting means)
53: Energizing coil spring (part of pressing force adjusting means)
54: Cam shaft (a part of the pressing force adjusting means)
56: Holding body rotating shaft (a part of the pressing force adjusting means)
110: Control unit (pressing force control means)

Claims (35)

An endless intermediate transfer belt that is endlessly moved while being stretched by a plurality of stretching rollers, and a belt strap at a belt wrapping position with respect to the nip-side stretching roller that functions as one of the stretching rollers. A transfer nip forming roller that forms a transfer nip to the recording member by abutting from the surface side, and a visible image developed on the surface of the latent image carrier from the surface to the front surface of the intermediate transfer belt In the transfer device for transferring to a recording member sandwiched in the transfer nip after being transferred to
A contact member that contacts at least one of the plurality of stretching rollers or the intermediate transfer belt, and a pressing force adjusting unit that adjusts the pressing force of the corresponding contact member against the stretching member or the intermediate transfer belt And a pressing force control means for controlling the pressing force adjusting means so that the pressing force is weaker than that immediately before the recording member enters the transfer nip. apparatus. An endless intermediate transfer belt that is endlessly moved while being stretched by a plurality of stretching rollers, and a belt strap at a belt wrapping position with respect to the nip-side stretching roller that functions as one of the stretching rollers. A transfer nip forming roller that forms a transfer nip to the recording member by abutting from the surface side, and a visible image developed on the surface of the latent image carrier from the surface to the front surface of the intermediate transfer belt In the transfer device for transferring to a recording member sandwiched in the transfer nip after being transferred to
A contact member that contacts at least one of the plurality of stretching rollers or the intermediate transfer belt, and a pressing force adjusting unit that adjusts the pressing force of the corresponding contact member against the stretching member or the intermediate transfer belt And a pressing force control means for controlling the pressing force adjusting means so that the pressing force is increased when the rear end of the recording member is discharged from the transfer nip as compared to the time immediately before discharging. Characteristic transfer device. A latent image carrier that carries a latent image, developing means for developing a latent image carried on the latent image carrier to obtain a visible image, and a visible image on the latent image carrier used as a recording member In an image forming apparatus comprising a transfer device for transferring,
An image forming apparatus using the transfer device according to claim 1 or 2 as the transfer device. The image forming apparatus according to claim 3.
An image forming apparatus using a contact roller as the contact member. The image forming apparatus according to claim 4.
An image forming apparatus using the transfer nip forming roller contacting the intermediate transfer belt as the contact roller. The image forming apparatus according to claim 5.
An image forming apparatus, wherein the nip backside stretching roller is also used as a belt driving roller that moves the intermediate transfer belt endlessly in accordance with its rotational driving. The image forming apparatus according to claim 3.
An image forming apparatus characterized in that a surface immovable member is used as the contact member. The image forming apparatus according to any one of claims 3 to 7,
Recording member detection means for detecting the recording member passing through a position facing the recording medium is provided, and based on the detection result by the recording member detection means, the timing at which the recording member enters the transfer nip, or the recording member An image forming apparatus, wherein the pressing force control means is configured to perform control for obtaining a timing at which a rear end of a member is discharged from the transfer nip. The image forming apparatus according to any one of claims 3 to 7,
Thickness information acquisition means for acquiring thickness information of the recording member is provided, and the pressing is performed when the recording member enters the transfer nip or when the rear end of the recording member is discharged from the transfer nip. An image forming apparatus, wherein the pressing force control unit is configured to perform control to vary the degree of pressure change according to the thickness information. The image forming apparatus according to claim 9, wherein
An image forming apparatus, wherein the thickness information acquiring unit is a thickness detecting unit that detects the thickness of the recording member. The image forming apparatus according to claim 10.
Drive current detection for detecting a drive current of a motor that is a drive source of at least one member of a conveyance member pair that conveys the recording member by sandwiching the recording member in a conveyance nip obtained by bringing the surfaces that move endlessly into contact with each other. An image forming apparatus characterized in that a means for detecting the thickness of the recording member based on a detection result by the drive current detecting means is used as the thickness detecting means. The image forming apparatus according to claim 11.
Image forming characterized in that the drive current detecting means detects a drive current of a motor that is a drive source of a transport member disposed upstream of the transfer nip in the recording member transport direction. apparatus. The image forming apparatus according to claim 10.
Drive current detection means for detecting a drive current of a motor serving as a drive source of a belt drive roller that functions as one of the plurality of stretching rollers and moves the intermediate transfer belt endlessly by its own rotational drive is provided. An image forming apparatus using the thickness detecting unit that detects the thickness of the recording member based on a detection result of the driving current detecting unit. The image forming apparatus according to claim 10.
An image forming apparatus, wherein the thickness detecting means detects a thickness of the recording member based on a light transmittance with respect to the recording member. The image forming apparatus according to claim 10.
Displacement amount detection means for detecting the displacement amount of at least one member of the pair of conveyance members that convey the recording member between the conveyance nips obtained by contacting the surfaces that move endlessly with each other, and the thickness detection An image forming apparatus characterized in that, as the means, one that detects the thickness of the recording member based on a detection result by the displacement amount detection means is used. The image forming apparatus according to claim 10.
Surface speed detecting means is provided for detecting the surface moving speed of at least one member of the conveying member pair that conveys the recording member by sandwiching the recording member in a conveying nip obtained by abutting surfaces that move endlessly with each other. An image forming apparatus characterized in that, as the detecting means, a means for detecting the thickness of the recording member based on a detection result by the surface speed detecting means is used. The image forming apparatus according to claim 9.
An image forming apparatus using an input means for performing thickness information input operation by an operator as the thickness information acquisition means. The image forming apparatus according to any one of claims 3 to 7,
Width information acquisition means for acquiring width information that is length information in a direction orthogonal to the conveying direction of the recording member is provided, and when the recording member enters the transfer nip, or at the rear end of the recording member An image forming apparatus, wherein the pressing force control means is configured to perform control to vary the degree of change of the pressing force according to the width information when the toner is discharged from the transfer nip. . The image forming apparatus according to claim 18, wherein
An image forming apparatus, wherein the width information acquisition unit is a width detection unit that detects the width of the recording member. The image forming apparatus according to claim 19.
A plurality of recording member detection means for detecting the recording member passing through the position facing each other while being arranged in the width direction of the recording member are provided, and the detection result by the recording member detection means is used as the width detection means. An image forming apparatus using a device that detects the width of the recording member on the basis thereof. The image forming apparatus according to claim 18.
An image forming apparatus using an input unit for performing width information input operation by an operator as the width information acquisition unit. The image forming apparatus according to any one of claims 3 to 7,
Provided is a gap information acquisition means for acquiring gap information which is the gap information of the recording member, and when the recording member enters the transfer nip, or the rear end of the recording member is separated from the transfer nip. An image forming apparatus characterized in that the pressing force control means is configured to perform a control to vary the degree of change of the pressing force when discharged, according to the gap information. The image forming apparatus according to claim 22, wherein
An image forming apparatus characterized in that an input means for performing a clearance information input operation by an operator is used as the clearance information acquisition means. The image forming apparatus according to any one of claims 3 to 7,
Inclination detecting means for detecting the inclination of the recording member being conveyed in the image forming apparatus from the direction orthogonal to the conveying direction is provided, and when the recording member enters the transfer nip or after the recording member. An image forming apparatus characterized in that the pressing force control means is configured to control to vary the degree of change of the pressing force according to the inclination when the end is discharged from the transfer nip. . 25. The image forming apparatus according to claim 24.
A plurality of recording member detecting means for detecting the recording member passing through the position facing each other while being arranged in the width direction of the recording member are provided, and the detection result by the recording member detecting means is used as the inclination detecting means. An image forming apparatus using the recording member that detects the inclination of the recording member based on the above. The image forming apparatus according to claim 20 or 25.
An image forming apparatus characterized in that an optical sensor for optically detecting the recording member is used as each of the plurality of recording member detection means. The image forming apparatus according to claim 20 or 25.
An image forming apparatus according to claim 1, wherein each of the plurality of recording member detecting means includes a switch member that contacts / disconnects an electric contact with the recording member. The image forming apparatus according to any one of claims 3 to 27.
As the transfer device, a visible voltage on the latent image bearing member is applied while applying a transfer voltage to a latent image facing member facing the latent image bearing member through the intermediate transfer belt while contacting the back surface of the intermediate transfer belt. The pressing force is used so that an image is transferred to the intermediate transfer belt, and control is performed to weaken the pressing force immediately before the start of application at the start of application of the transfer voltage to the latent image facing member. An image forming apparatus comprising a control means. The image forming apparatus according to any one of claims 3 to 28.
As the transfer device, a visible voltage on the latent image bearing member is applied while applying a transfer voltage to a latent image facing member facing the latent image bearing member through the intermediate transfer belt while contacting the back surface of the intermediate transfer belt. The pressing force is used so that an image is transferred to the intermediate transfer belt, and control is performed so that the pressing force is stronger than that immediately before the application is stopped when the application of the transfer voltage to the latent image facing member is stopped. An image forming apparatus comprising a control means. The image forming apparatus according to any one of claims 3 to 29.
Provided is a drive current detection means for detecting a drive current of a motor that is a drive source of a belt drive roller that functions as one of the plurality of stretching rollers and moves the intermediate transfer belt endlessly by its own rotational drive, And according to the detection result by the drive current detection means within a predetermined period not including when the recording member enters the transfer nip and when the trailing end of the recording member is discharged from the transfer nip. An image forming apparatus characterized in that the pressing force control means is configured to perform control to change the pressing force. The image forming apparatus according to any one of claims 3 to 29.
Roller speed detection means for detecting the rotational speed or angular speed speed of any one of the plurality of stretching rollers is provided, and control for changing the pressing force according to the detection result by the roller speed detection means is performed. As described above, an image forming apparatus comprising the pressing force control means. The image forming apparatus according to any one of claims 3 to 29.
A surface speed detecting means for detecting the surface speed of the intermediate transfer belt is provided, and the pressing force control means is configured to perform control to change the pressing force in accordance with a detection result by the surface speed detecting means. An image forming apparatus. The image forming apparatus according to any one of claims 3 to 32.
An image forming apparatus using the pressing force adjusting means that adjusts the pressing force as the motor is driven. 34. The image forming apparatus according to claim 3, wherein
A plurality of the developing means are arranged so as to face one latent image carrier, and visible images developed by different developing means are sequentially superimposed and transferred onto the intermediate transfer belt. An image forming apparatus. 34. The image forming apparatus according to claim 3, wherein
A plurality of combinations of the latent image carrier and the developing means are arranged to face the front surface of the intermediate transfer belt, and visible images developed on the respective latent image carriers are attached to the intermediate transfer belt. An image forming apparatus, wherein the image is superimposed and transferred.

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