JP2007286383A - Transfer device, 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 fluctuation in the speed of an intermediate transfer belt 41 at the time of advancing the recording paper P into secondary transfer nips. <P>SOLUTION: A braking force imparting means 60 for directly imparting braking force to a revolving shaft of at least any one (in an example shown in the figure, a nip upstream roller 49) of a plurality of stretching rollers to stretch an intermediate transfer belt 41 is arranged and a control part 11 serving as a braking force control means is constituted so as to execute the control to make the braking force weaker than that immediate before advance when advancing the recording paper P into the secondary transfer nips. In such 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 in the pressing force by the secondary transfer roller 51 and the abrupt decrease in the rotating speed of the belt driving roller when advanced is suppressed. Thus, the disturbance and color shift of an image in second and subsequent printout paper is prevented. <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 a 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, the rotating shaft of at least one of the plurality of stretching rollers Braking force applying means for directly applying a braking force to the recording medium, and controlling the braking force applying means so that when the recording member enters the transfer nip, the braking force is weaker than that immediately before entering. In which it characterized in that a braking force control means.
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 a recording member sandwiched in the transfer nip after transferring to the front surface of the intermediate transfer belt, a braking force is applied to at least any one of the plurality of stretching rollers. A braking force applying unit that directly applies the braking force applying unit, and a braking force control unit that controls the braking force applying unit so that when the rear end of the recording member is discharged from the transfer nip, the braking force is stronger than immediately before the discharging. It is characterized in the provision of the means.
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, as at least one of the plurality of stretching rollers, a braking force is applied to the rotation shaft of the nip back-side stretching roller. The braking force applying means is configured.
According to a fifth aspect of the present invention, in the image forming apparatus of the fourth 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 sixth aspect of the present invention, in the image forming apparatus according to any one of the third to fifth aspects, the 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 braking force control means is configured 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 seventh aspect of the present invention, in the image forming apparatus according to any one of the third to fifth 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 braking force control means so that the degree of change of the braking force when the rear end of the recording member is discharged from the transfer nip is varied according to the thickness information. It is characterized by comprising.
The invention according to claim 8 is the image forming apparatus according to claim 7, wherein the thickness information acquisition means is a thickness detection means for detecting the thickness of the recording member.
According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth 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 tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, the drive current detecting means is a drive source for a conveyance member disposed upstream of the transfer nip in the recording member conveyance 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 11 is the image forming apparatus according to claim 8, wherein the driving source of the belt driving roller that functions as one of the plurality of stretching rollers and moves the intermediate transfer belt endlessly by its own rotational drive. 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 twelfth aspect of the present invention, in the image forming apparatus according to the eighth aspect of the present invention, 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 13 is the image forming apparatus according to claim 8, 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.
The invention according to claim 14 is the image forming apparatus according to claim 8, wherein at least one of the pair of conveyance members that conveys the recording member sandwiched between conveyance 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.
The invention of claim 15 is characterized in that, in the image forming apparatus of claim 7, an input means for performing thickness information input operation by an operator is used as the thickness information acquisition means.
According to a sixteenth aspect of the present invention, in the image forming apparatus according to any one of the third to fifth 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 when the recording member enters the transfer nip or when the trailing end of the recording member is discharged from the transfer nip, the degree of change in the braking force varies according to the width information. The braking force control means is configured to perform the control.
According to a seventeenth aspect of the present invention, in the image forming apparatus according to the sixteenth aspect, the width information acquiring unit is a width detecting unit that detects the width of the recording member.
The invention according to claim 18 is the image forming apparatus according to claim 17, further comprising a plurality of recording member detecting means for detecting the recording member passing 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 nineteenth aspect of the present invention, in the image forming apparatus according to the sixteenth aspect, an input means for performing width information input operation by an operator is used as the width information acquiring means.
According to a twentieth aspect of the present invention, in the image forming apparatus according to any one of the third to fifth aspects, a gap information acquisition unit that acquires gap information that is the gap information of the recording member is provided, and The braking force control so that the degree of change of the braking force when the recording member enters or is discharged from the transfer nip is controlled according to the gap information. It is characterized by comprising means.
The invention according to claim 21 is characterized in that, in the image forming apparatus according to claim 20, 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-second aspect of the present invention, in the image forming apparatus according to any one of the third to fifth 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 braking force when the recording member enters the transfer nip or when the rear end of the recording member is ejected from the transfer nip varies depending on the inclination. The braking force control means is configured to perform the control.
The invention according to claim 23 is the image forming apparatus according to claim 22, further comprising a plurality of recording member detecting means for detecting the recording member that passes through a position opposed to itself 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-fourth aspect of the present invention, in the image forming apparatus according to the eighteenth or twenty-third aspect, an optical sensor that optically detects the recording member is used as each of the plurality of recording member detection means. Is.
According to a twenty-fifth aspect of the present invention, in the image forming apparatus according to the eighteenth or twenty-third aspect, as the plurality of recording member detecting means, a switch member that connects / disconnects an electrical contact with each contact with the recording member. It is characterized by being used.
According to a twenty-sixth aspect of the present invention, in the image forming apparatus according to any one of the third to thirty-fifth aspects, 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 braking force control means is configured such that control is performed to weaken the braking force immediately before the start of application.
According to a twenty-seventh aspect of the present invention, in the image forming apparatus according to any one of the third to twenty-sixth aspects, 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 braking force control means is configured so that the control for increasing the braking force is performed more than immediately before stopping the application.
According to a twenty-eighth aspect of the present invention, in the image forming apparatus according to any of the third to twenty-seventh aspects, the intermediate transfer belt is driven 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 a roller drive source 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 braking force control means is configured to perform control to change the braking force in accordance with a detection result by the drive current detection means within a predetermined period not including It is.
The invention according to claim 29 is the image forming apparatus according to any one of claims 3 to 27, further comprising roller speed detecting means for detecting a rotational speed or an angular speed of any one of the plurality of stretching rollers, In addition, the braking force control unit is configured to perform control for changing the braking force in accordance with a detection result of the roller speed detection unit.
According to a thirty-third aspect of the present invention, in the image forming apparatus according to any one of the third to thirty-seventh 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. The braking force control means is configured so that the control for changing the braking force according to the above is implemented.
The invention according to a thirty-first aspect is the image forming apparatus according to any one of the third to thirty-third aspects, wherein a powder brake, a hysteresis brake, or a friction brake is used as the braking force applying 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-first aspects, 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 33 is the image forming apparatus according to any one of claims 3 to 31, 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, with all of the invention specific matters of claim 1, when a recording member such as recording paper enters the transfer nip, the braking force against the rotation shaft of the stretching roller that stretches the intermediate transfer belt Is weaker than that just before entering. In such a configuration, the belt drive motor torque increase due to the recording member entering the transfer nip is offset by the torque decrease due to a decrease in the braking force with respect to the rotation shaft of the tension roller, and the belt drive motor rotation during entry Suppresses a rapid drop in speed. 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.
According to the invention having all the matters specified in the second aspect of the invention, when the trailing end of the recording member is discharged from the transfer nip, the braking force against the rotation shaft of the stretching roller that stretches the intermediate transfer belt is applied immediately before entering. Strengthen than when. In this configuration, the belt drive motor torque reduction due to the trailing end of the recording member being discharged from the transfer nip is offset by torque increase due to an increase in the braking force against the rotation shaft of the tension roller, and the belt at the time of discharge Suppresses a sudden increase in the rotational speed of the drive motor. 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, which is driven to rotate counterclockwise in the figure 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, 45C, 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.

  FIG. 5 is an enlarged configuration diagram showing the secondary transfer roller unit 50 in the transfer device 40 of the copying machine 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 with respect 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, the cam 55 rotates counterclockwise in the drawing by a predetermined angle around the cam shaft 54, and the lower portion of the holding body 52 is moved by the biasing coil spring 53. Overcome the urging force and push from the left to the right 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.

  If the secondary transfer roller 51 is left pressed against the intermediate transfer belt 41 for a long period of time while the print job is stopped, the occurrence of curling of the intermediate transfer belt 41 is promoted or the secondary transfer roller 51 Or promote permanent deformation. Therefore, while the print job is stopped, the braking force of the secondary transfer roller 51 against the intermediate transfer belt 41 is weakened by the rotation of the cam 55, or the secondary transfer roller 51 is separated from the belt. Thereby, the curl and permanent deformation mentioned above can be suppressed.

Next, a characteristic configuration of the copying machine will be described.
The copying machine includes a braking force applying unit that directly applies a braking force to at least one of the plurality of stretching rollers that stretch the intermediate transfer belt 41. Furthermore, it has a control unit (not shown) which is a braking force control means for changing the braking force by controlling the braking force applying means.

  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 braking force provision means. That is, when the recording paper P enters the above-described secondary transfer nip, the braking force applying means is controlled so that the braking force with respect to the rotation shaft of the stretching roller is weaker than the value immediately before entering.

  In such a configuration, when the recording paper P enters the secondary transfer nip, the following can be achieved by making the braking force on the rotation shaft of the stretching roller weaker than the value immediately before entering. 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 braking force with respect to the rotating shaft of the stretching roller, and the belt drive motor at the time of entry is Suppresses sudden drop in rotation speed. 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]
FIG. 6 is a schematic configuration diagram showing the transfer device 40 and its peripheral configuration in the copying machine according to the first embodiment. In the figure, a nip upstream roller 49 is a driven roller that rotates as the intermediate transfer belt 41 moves endlessly. Further, the nip backside stretching roller 46 is a belt driving roller that moves the intermediate transfer belt 41 endlessly by being driven to rotate by receiving a driving force supplied from a belt driving motor (not shown).

  A braking force applying means 60 is connected to the rotation shaft of the nip upstream roller 49 via a coupling (not shown). The braking force applying means 60 is a powder brake, a hysteresis brake, or a friction brake, and is controlled by the braking force applying means 60 according to the voltage value or current value of the power supplied from the brake power supply circuit 110a of the control unit 110. The power can be changed freely. Instead of the coupling, the braking force applying means 60 may be connected to the rotating shaft of the nip upstream roller 49 through a gear.

  An optical sensor 57 is fixed to a portion of the holder of the secondary transfer roller unit 50 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 110 estimates the timing at which the leading edge of the recording paper P enters the secondary transfer nip, and outputs the output voltage value from the brake power circuit 110a or Adjust the output current value. 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.

  The control unit 110 reduces the output voltage value or output current value from the brake power supply circuit 110a at these timings (hereinafter referred to as the entry timing) to be smaller than the previous value, and the braking force on the rotation shaft of the nip upstream roller 49. The braking force by the applying means 60 is weakened. That is, in this copying machine, the control unit 110 that controls the output voltage value or the output current value from the brake power supply circuit 110a functions as a braking force control unit.

  Based on the leading edge detection signal, the control unit 110 obtains a timing at which the leading edge 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 the predetermined amount approach timing arrives, the output voltage value or output current value from the brake power supply circuit 110a is made larger than the previous value, and the braking force applied by the braking force applying means 60 to the rotation shaft of the nip upstream roller 49 is increased. Slightly strengthen. 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, a series of adjustments of the braking force are performed for each sheet passing.

  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 this copying machine, for the purpose of preventing the occurrence of improper braking force change timing due to this error, the leading edge of the recording paper P is detected by the optical sensor 57 in the vicinity of the secondary transfer nip entrance.

  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 to be detected by 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.

  The present inventors prepared an experimental machine having the configuration of the copying machine, and printed out the second and subsequent sheets when the braking force was weakened at the approach timing and when the braking force was not changed. An experiment was conducted to examine the difference in color misregistration on paper. When the braking force is not changed, as shown in the graph of FIG. 7, the load torque of the belt drive motor is determined at the nip entry timing that arrives Δt seconds after the optical sensor (57) detects the leading edge of the paper. It rises rapidly. At this time, as shown in the graph of FIG. 8, the amount of color misregistration increases rapidly. In the graph of FIG. 7, T <b> 1 indicates a steady load torque magnitude due to a factor different from the application of the braking force by the braking force applying means 60. This is load torque due to friction in the drive transmission system from the belt drive motor to the belt drive roller, load on the intermediate transfer belt 41, friction on the bearing, and the like.

  On the other hand, when the braking force is weakened at the approach timing, the load torque of the belt drive motor is rapidly reduced by weakening the braking force at the approach timing, as shown in the graph of FIG. To do. In the graph of FIG. 9, T <b> 2 indicates an initial braking load torque that is applied in advance to the belt drive motor by applying a braking force by the braking force applying unit 60 to the rotation axis of the nip upstream roller 49. In the figure, the steady load torque T1 described above is not reflected in the graph. Therefore, when the braking force is weakened, the load torque for the belt drive motor is a combination of the graph of FIG. 7 and the graph of FIG. 9, and as shown in FIG. It becomes constant. When the amount of color misregistration was examined under such load torque conditions, as shown in FIG. 11, a high-quality image can be formed with almost no sudden increase in the color misregistration amount at the approach timing. It was.

  In this copying machine, the braking force applying means 60 exhibits a braking force that can give a torque fluctuation larger than the sum of the steady load torque T1 and the initial braking load torque T2 shown in FIG. Used.

[Second Embodiment]
FIG. 12 is a schematic configuration diagram showing the transfer device 40 and its surrounding configuration in the copying machine according to the second embodiment. In the drawing, a tension roller 47, which is one of the stretching rollers, is urged toward the intermediate transfer belt 41 by a spring to give a predetermined tension to the belt, and the belt is endlessly moved. This is a driven roller that rotates with the rotation. Further, the nip backside stretching roller 46 is a belt driving roller that moves the intermediate transfer belt 41 endlessly by being driven to rotate by receiving a driving force supplied from a belt driving motor (not shown).

  A braking force applying means 60 including a powder brake, a hysteresis brake, or a friction brake is connected to the rotation shaft of the tension roller 47 through a coupling (not shown).

  At the entry timing, the control unit 110 reduces the output voltage value or output current value from the brake power supply circuit 110a to be less than the previous value, and weakens the braking force applied by the braking force applying means 60 on the rotation shaft of the tension roller 47. . As a result, it is possible to suppress a rapid decrease in the belt moving speed at the entry timing, and to suppress a color shift that occurs at the entry timing. Further, when the predetermined amount approach timing arrives, the output voltage value or output current value from the brake power supply circuit 110a is made larger than the previous value, and the braking force applied by the braking force applying means 60 to the rotating shaft of the tension roller 47 is increased. Slightly strengthen. 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. .

[Third embodiment]
FIG. 13 is a schematic configuration diagram showing the transfer device 40 and its peripheral configuration in the copying machine according to the third embodiment. In the drawing, a nip back-side stretch roller 46, which is one of the stretch rollers, is driven to rotate by receiving a driving force supplied from a belt drive motor (not shown), thereby driving the intermediate transfer belt 41 endlessly. It is a roller.

  A braking force applying means 60 composed of a powder brake, a hysteresis brake, or a friction brake is connected to the rotation shaft of the nip back-side stretching roller 46 through a coupling (not shown).

  At the entry timing, the control unit 110 reduces the output voltage value or output current value from the brake power supply circuit 110a to be less than the previous value, and weakens the braking force applied by the braking force applying means 60 on the rotation shaft of the tension roller 47. . As a result, it is possible to suppress a rapid decrease in the belt moving speed at the entry timing, and to suppress a color shift that occurs at the entry timing.

  In this copying machine, among the plurality of tension rollers, the nip back roller 46 that is likely to change the rotational speed first as the recording paper P enters and discharges from the secondary transfer nip is used as the belt driving roller. It is said. The control unit 110 adjusts the braking force for the rotation shaft of the belt driving roller. In this configuration, the belt speed can be adjusted more accurately by quickly reflecting the change in the braking force in the change in the torque of the belt drive motor, compared to the case where the other tension roller is a belt drive roller. .

  In this copying machine as well, when the predetermined amount approach timing comes, the output voltage value or output current value from the brake power supply circuit 110a is made larger than the previous value, and the braking force is applied to the rotating shaft of the tension roller 47. The braking force by means 60 is slightly increased. 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. .

[Fourth embodiment]
In the experimental machine having the configuration of the copying machine according to the third embodiment described above, the present inventors used a relatively thick recording paper P and a case using a normal thickness. An experiment was conducted to compare the difference in color misregistration at the approach timing. The braking force by the braking force applying means 60 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 third embodiment. That is, a thickness information acquisition unit that acquires thickness information of the recording paper P is provided, and control is performed to vary the degree of change in the braking force (braking force change amount) at the entry timing according to the thickness information. The control unit 110 serving as braking force control means is configured. In such a configuration, the belt speed variation is further suppressed by varying the amount of change in the braking 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 amount of color misregistration 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 conveyance nips of these conveyance member pairs, the drive current of the motor that supplies the drive force to the conveyance members 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.

  In view of this, the copying machine is provided with an ampermeter serving 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 prior experiment, and based on this, the thickness of the recording P is recorded. 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. 16 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. Among 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 be supplied with a braking 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 braking force according to the thickness from the second printed sheet. Therefore, in this copying machine, an ampere meter 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 braking force according to the thickness from the second printed sheet.

  The initial braking load torque by applying the braking force may be varied depending on the thickness. Specifically, FIG. 17 is a graph showing changes in the load torque of the registration motor when 80K paper is used as the recording paper P. FIG. 18 is a graph showing changes in the load torque of the registration motor when 180K paper is used as the recording paper P. FIG. 19 is a graph showing a change in load torque of the registration motor when 220K paper is used as the recording paper P. In these drawings, a graph indicated by a dotted line indicates a change in load torque with respect to the resist drive motor. Further, the graph shown by the solid line is a graph showing the initial control load torque T2 required in the fluctuation range of the load torque. The initial control load torque T2 needs to be set larger than the load torque fluctuation amount Ta at the approach timing. Otherwise, it is not possible to secure a torque reduction amount for offsetting a sudden increase in load torque. As the thickness of the recording paper P increases, such as 80K paper, 180K paper, 220 paper, etc., the amount of fluctuation Ta of the load torque at the entry timing increases. Therefore, as the thickness increases, the initial control load torque T2 required for cancellation also increases. . In other words, if the thickness is relatively small, the initial control load torque T2 can also be reduced to suppress deterioration of the registration motor. However, if the initial control load torque T2 is changed according to the thickness in this way, the average belt speed in the print job is changed according to the thickness. Even if there is such a change, the initial control load torque T2 may be changed according to the thickness as long as the overall expansion / contraction of the image does not occur so much. Further, if slight expansion / contraction occurs, the optical writing system, the photosensitive member linear velocity, and the like may be changed in accordance with the change amount of the initial control load torque T2.

[Fifth embodiment]
Similar to the fourth embodiment, this copying machine is also provided with a thickness detecting means for detecting the thickness of the recording paper P, and controls to vary the amount of change in the braking force at the entry timing according to the thickness information. Thus, the control part 110 which is a braking force control means is comprised. However, the structure of the thickness detection means is different from that of the fourth embodiment. Specifically, in the present copying machine, the ampere meter 111 shown in FIG. 16 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 braking force control means is comprised. In such a configuration, it is possible to further improve the image quality by adjusting the braking force according to the thickness based on the change in the drive current of the belt drive 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 braking force at the entry timing of the second and subsequent recording sheets P is determined according to 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.

[Sixth embodiment]
Similar to the fourth embodiment, this copying machine is also provided with a thickness detecting means for detecting the thickness of the recording paper P, and controls to vary the amount of change in the braking force at the entry timing according to the thickness information. Thus, the control part 110 which is a braking force control means is comprised. However, this copying machine is also different from the fourth embodiment in the configuration 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.

[Seventh embodiment]
Similar to the fourth embodiment, this copying machine is also provided with a thickness detecting means for detecting the thickness of the recording paper P, and controls to vary the amount of change in the braking force at the entry timing according to the thickness information. Thus, the control part 110 which is a braking force control means is comprised. However, this copying machine is also different from the fourth embodiment in the configuration 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 braking force in accordance with the thickness from the second printout sheet. 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.

[Eighth embodiment]
Similar to the fourth embodiment, this copying machine is also provided with a thickness detecting means for detecting the thickness of the recording paper P, and controls to vary the amount of change in the braking force at the entry timing according to the thickness information. Thus, the control part 110 which is a braking force control means is comprised. However, this copying machine is also different from the fourth embodiment in the configuration 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 increases, the surface moving speed of the conveying member decreases, so that 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 braking force in accordance with the thickness from the second printout sheet. Therefore, in this copying machine, the rotational speed of one of the rollers in the registration roller pair (35) is detected.

  FIG. 20 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. 21, as the conveyor belt 73, in the non-contact area (end part) with the paper in the width direction, marks 74 are attached at a predetermined pitch over the entire area in the circumferential 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.

[Ninth embodiment]
Similarly to the fourth embodiment, this copying machine is also provided with a thickness information acquisition means for acquiring the thickness information of the recording paper P, and performs control for varying the amount of change in the braking force at the entry timing according to the thickness information. The control part 110 which is a braking force control means is comprised so that it may implement. 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, an ampere meter, an encoder, or the like for detecting the thickness.

[Tenth embodiment]
In the experimental machine having the configuration of the copying machine according to the third 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 of using a relatively small one and the case using a relatively small one. The braking force by the braking force applying means 60 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 braking force control means is comprised so that the control which changes the degree (change amount) of the said braking 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 braking force according to the difference in the belt speed change amount 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 braking force according to the sheet passing width from the second printed sheet.

[Eleventh embodiment]
Similarly to the tenth embodiment, this copying machine is also provided with a width detecting means for detecting the width of the recording paper P, and controls to vary the amount of change in the braking force at the entry timing according to the thickness information. Thus, the control part 110 which is a braking force control means is comprised. However, the configuration of the width detecting means is different from that of the tenth embodiment. Specifically, in the present copying machine, switches as shown in FIG. 23 are used as 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. The member 76 is used. The switch member 76 is swingable about a swing shaft 76a provided on the rear end side. Normally, however, the switch member 76 has a posture as shown in FIG. 23 (a) 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 transporting 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.

[Twelfth embodiment]
Similar to the tenth embodiment, this copying machine is also provided with width information acquisition means for acquiring the width information of the recording paper P, and performs control for varying the amount of change in the braking force at the approach timing according to the width information. The control part 110 which is a braking force control means is comprised so that it may implement. 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.

[Thirteenth embodiment]
The inventors of the present invention have a difference in the amount of color misregistration at the entry timing when the recording paper P has different gaps in the experimental machine having the configuration of the copying machine according to the third embodiment described above. The experiment which compares was conducted. The braking force by the braking force applying means 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).

  Therefore, in this copying machine, the following additional characteristic configuration is added to the copying machine according to the third 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 braking force control means is comprised so that the control which changes the change degree of the braking force in the said approach timing according to gap information may be implemented. In such a configuration, the belt speed variation is further suppressed by varying the amount of change in the braking force according to the difference in the amount of change in the belt speed 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.

[14th embodiment]
The inventors of the present invention have 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 third 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, particularly, the recording paper immediately before entering the secondary transfer nip. The inclination of P is shown. The braking force by the braking force applying means 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 becomes smaller, the paper area at the moment of entering the secondary transfer nip becomes larger, thereby increasing the torque increase amount.

  Therefore, in this copying machine, the following additional characteristic configuration is added to the copying machine according to the third 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 braking force control means is comprised so that the control which changes the change degree of the said braking 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 braking 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. 26, 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. 23 may be used instead of the optical sensor 77 as the plurality of recording member detection means.

[Fifteenth 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 third embodiment. That is, the braking force control means is adapted to perform control to weaken the braking 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 braking force more immediately before stopping the application when the application of the primary transfer bias is stopped.

  FIG. 27 is a schematic configuration diagram showing the transfer device 40 and its peripheral configuration in the copying machine according to the fifteenth embodiment. In the figure, the primary transfer bias output from the primary transfer bias power supply circuit 115 is applied to the primary transfer rollers 45Y, 45C, 45M, 45K, respectively. The primary transfer bias power supply circuit 115 and the control unit 110 are communicably connected. The primary transfer bias power supply circuit 115 turns on and off the output of the primary transfer bias based on a control signal from the control unit 110. The control unit 110 performs control to weaken the braking force simultaneously with sending an output-on signal to the primary transfer bias power supply circuit 115 or after a predetermined time lag therefrom. In addition, the control for increasing the braking force is performed at the same time when the output-off signal is sent to the primary transfer bias power supply circuit 115 or after a predetermined time lag. 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.

[Sixteenth embodiment]
In this copying machine, the following additional characteristic configuration is added to the copying machine according to the first embodiment. In other words, an ampermeter is provided as a drive current detecting means for detecting the drive current of the belt drive motor. Then, the control unit 110 serving as a braking force control unit is configured to perform control to change the braking force according to the detection result by the ampere meter in a period excluding the entry timing and the discharge timing in the print job. Yes.

  FIG. 28 is a schematic configuration diagram showing the transfer device 40 and its peripheral configuration in the copying machine according to the sixteenth embodiment. In the drawing, the nip back side stretching roller 46 functioning as a belt driving roller is driven to rotate by the driving force of the belt driving motor 120. An amper meter 111 serving as drive current detection means is connected between the belt drive motor 120 and a motor power supply circuit (not shown), and outputs an output signal corresponding to the drive current to the control unit 110. Then, the control unit 110 weakens the braking force by an amount corresponding to the output signal from the ampere meter 111, that is, the amount of torque increase of the belt drive motor 120. In the case of torque reduction, the braking 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. Further, instead of feeding back the output signal from the ampermeter 111 to the braking force, it may be fed back to the drive amount (drive pulse signal) of the belt drive motor 120.

[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 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 braking force control means is comprised so that the control which changes the said braking force according to the detection result by an encoder may be implemented.

  FIG. 29 is a schematic configuration diagram showing the transfer device 40 and its peripheral configuration in the copying machine according to the sixteenth embodiment. In the figure, an encoder 70 is attached to the rotating shaft of the nip upstream roller 49 in addition to the braking force applying means 60. The detection result of the rotational speed of the nip upstream roller 49 by the trace coder 70 is output to the control unit 110. When the result of detection by the encoder 70, that is, when the belt moving speed becomes slower than usual, the control unit 110 weakens the braking force by an amount corresponding to the speed reduction amount. Further, when the belt moving speed becomes faster than usual, the braking 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. Instead of feeding back the detection result of the encoder 70 to the braking force, it may be fed back to the drive amount (drive pulse signal) of 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, 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 braking force control means is comprised so that the control which changes the said braking force according to the detection result by this surface speed detection means may be implemented.

  FIG. 30 is a schematic configuration diagram showing the transfer device 40 and its peripheral configuration in the copying machine according to the eighteenth embodiment. In the figure, one roller of the registration roller pair 35 is rotationally driven by the driving force from the registration motor 121. An ampere meter 111 is connected between the registration motor 121 and a motor power circuit (not shown), and an output signal corresponding to the drive current of the registration motor 121 is output to the control unit 110. The control unit 110 obtains the thickness of the recording paper P based on the output signal from the ampermeter 111. Then, the amount of change in braking force at the entry timing and the discharge timing is determined according to the thickness.

  Below the intermediate transfer belt 41, an optical sensor 78 serving as a surface speed detecting means is disposed. As shown in FIG. 31, the optical sensor 78 is formed of a reflective photosensor, and detects a plurality of marks 79 attached to the front surface of the intermediate transfer belt 41 at a predetermined pitch in the circumferential direction. 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.

  In FIG. 30 shown above, the control unit 110 grasps the belt moving speed based on the output signal from the optical sensor 78. When the belt moving speed becomes slower than usual, the braking force is weakened by an amount corresponding to the speed reduction amount. Further, when the belt moving speed becomes faster than usual, the braking 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.

  Instead of changing the braking force according to the belt moving speed, the driving amount of the belt drive motor may be changed according to the belt moving speed.

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.
This copying machine also includes a braking force applying unit that directly applies a braking force to at least one of the plurality of stretching rollers that stretch the intermediate transfer belt 41. Furthermore, it has a control unit (not shown) which is a braking force control means for changing the braking force by controlling the braking force applying means. This control part performs the following control with respect to a braking force provision means. That is, when the trailing edge of the recording paper P is discharged from the secondary transfer nip (hereinafter referred to as discharge timing), the control is performed to increase the braking force to a value immediately before discharge.

  In such a configuration, the following can be achieved by increasing the braking force at the discharge timing. That is, the torque reduction of the belt drive motor due to the discharge of the trailing edge of the recording paper P from the secondary transfer nip is offset by the torque increase due to the increase of the braking force, and the rotation speed of the belt drive motor at the time of discharge is reduced. Suppresses sudden rise. 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.

  Further, in the present copying machine, the braking force applying means 60 is connected to the rotating shaft of the nip upstream roller 49 as in the copying machine according to the first embodiment shown in FIG. The braking force applying means 60 is a powder brake, a hysteresis brake, or a friction brake, and is controlled by the braking force applying means 60 according to the voltage value or current value of the power supplied from the brake power supply circuit 110a of the control unit 110. The power can be changed freely

  The timing at which the trailing edge of the recording paper P is discharged from the secondary transfer nip (discharge timing) is obtained 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 present copying machine, and printed the second and subsequent sheets when the braking force was increased at the discharge timing and when the braking force was not changed. An experiment was conducted to examine the difference in color misregistration on out paper. Then, when the pressing force was not changed at the discharge timing, a large color shift occurred for a moment at the discharge timing, but no color shift occurred 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 braking 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 value slower than usual, and color shift occurs over time. Therefore, after a predetermined time has elapsed from the discharge timing, the braking force is returned to the initial value. By doing so, it is possible to avoid subsequent color shifts caused by continuing to increase the braking force thereafter while suppressing color shifts occurring at the discharge timing.

  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.
[Nineteenth 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 braking force at the discharge timing was not adjusted. As a result, it was found 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. In other words, 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 braking force at the discharge timing (braking force change amount) according to the thickness information. A control unit 110 serving as a braking force control unit is configured. In such a configuration, the belt speed variation is further suppressed by varying the amount of change in the braking force in accordance with 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 fourth embodiment, detection by a 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 fourth embodiment, it is desirable to detect the thickness based on the detection result of the drive 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 braking 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 copier of the sixth 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 seventh embodiment, it may be provided not only upstream but also downstream from the secondary transfer nip. Further, as in the eighth 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.

[20th 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 braking force at the discharge timing was not adjusted. As a result, it has been found 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 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 braking force control means is comprised so that the control which changes the degree of the change of the said braking force in discharge | emission 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 braking force according to the difference in the belt speed change amount 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, similarly to the copying machine according to the tenth 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 tenth 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 eleventh 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 to various keys as in the copying machine according to the twelfth embodiment.

[Twenty-first 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 braking force at the discharge timing was not adjusted. Then, it was found that the amount of color misregistration varies 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 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 braking force control means is comprised so that the control which changes the change degree of the said braking force in discharge | emission timing according to gap information may be implemented. In such a configuration, the belt speed variation is further suppressed by varying the amount of change in the braking force in accordance with the difference in the belt speed change amount due to the difference in the clearance 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-second 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 braking force at the discharge timing was not adjusted. Then, it was found 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 braking force control means is comprised so that the control which changes the change degree of the said braking force in discharge | emission timing according to inclination (theta) may be implemented. In such a configuration, the variation in the belt speed is further suppressed by varying the amount of change in the braking force according to the difference in the belt speed variation 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 the present copying machine, as in the copying machine according to the fourteenth 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. 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, an optical sensor is used as a 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.

  In the copying machine according to the fourteenth embodiment, in order to detect the inclination θ of the recording paper 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, an optical sensor 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 an optical sensor 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, as the plurality of recording member detection means, a switch member 76 as shown in FIG. 23 may be used instead of the optical sensor.

  Further, as in the copying machine according to the fifteenth embodiment, the braking force is weakened when the primary transfer bias is started than before the start of the application, or the braking force is increased when the application is stopped. The control unit 110 may be configured so as to perform control.

  Further, similarly to the copying machine according to the sixteenth embodiment, the control unit 110 may be configured to perform the control for changing the braking force in accordance with the detection result by the amperometer.

  Further, similarly to the copying machine according to the seventeenth 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 that changes the braking force.

  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 that changes the braking 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 copying machine also has the same braking force application means as the copying machine according to the first and second embodiments. Moreover, it has the control part (110) which is a braking force control means which changes braking force by controlling this braking force provision means. And a control part (110) performs the following control with respect to a braking force provision means. That is, the braking 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 the predetermined amount approach timing arrives, the braking 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 arrives, the braking force is made stronger 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 braking force is returned to the initial value. This avoids the occurrence of color shift over time due to the brake force not being 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.

  Also in the present copying machine, as in the copying machines according to the fourth and nineteenth embodiments, the degree of change in the braking 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 in this way, it is possible to obtain from the second sheet the effect of more reliably suppressing the color shift that occurs from the second sheet and thereafter by adjusting the braking force according to the thickness.

  Also in the present copying machine, as in the copying machines according to the tenth and twentieth embodiments, the degree of change in the braking force at the entry timing and the discharge 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 shift that occurs from the second sheet onward by adjusting the braking force according to the paper width. .

  Also in the present copying machine, as with the copying machines according to the thirteenth and twenty-first embodiments, the degree of change in the braking force at the entry timing and the discharge timing varies depending on the gap. The color shift can be further suppressed.

  Also in this copying machine, as in the copying machines according to the fourteenth and twenty-second embodiments, the degree of change in the braking force at the entry timing and the discharge timing is made different 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 paper 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 copying machine according to the fifteenth embodiment, the braking force is weakened when the primary transfer bias is started than before the start of the application, or the braking force is increased when the application is stopped. The control unit 110 may be configured so as to perform control.

  Further, similarly to the copying machine according to the sixteenth embodiment, the control unit 110 may be configured to perform the control for changing the braking force in accordance with the detection result by the amperometer.

  Further, similarly to the copying machine according to the seventeenth 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 that changes the braking force.

  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 that changes the braking force.

  In the copiers according to the third, tenth, thirteenth, and fourteenth embodiments, a braking force is applied to the rotation shaft of the nip backside stretching roller 46 as at least one of the plurality of stretching rollers. As described above, the braking force applying means 60 is configured. With such a configuration, a change in belt speed accompanying a change in braking force can be quickly reflected in the secondary transfer nip.

  In the copiers according to the third, tenth, thirteenth, and fourteenth embodiments, the nip back-side stretching roller 46 is also used as a belt driving roller that moves the intermediate transfer belt 41 endlessly with its own rotational drive. is doing. In this configuration, as described above, the belt speed can be more accurately adjusted by quickly reflecting the change in the braking 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 each embodiment, an optical sensor 57 serving as a recording member detection unit that detects the recording paper P passing through the position facing the self is disposed upstream of the secondary transfer nip in the recording paper conveyance direction. And the control part 110 is comprised so that control which calculates | requires approach timing and discharge | emission timing based on the detection result by it may be implemented. 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.

  In the copying machines according to the fourth to eighth embodiments and the nineteenth embodiment, thickness information acquisition means for acquiring the thickness information of the recording paper P is provided, and the braking force at the entry timing and the discharge timing is determined. The control part 110 is comprised so that the change degree may be controlled according to the thickness information. In this configuration, as described above, the belt speed variation is further suppressed by varying the amount of change in the braking 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 discharge timing. . As a result, the amount of color misregistration in the second and subsequent printout sheets can be further suppressed.

  Further, in the copying machines according to the fourth to seventh embodiments and the nineteenth 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, improper braking force adjustment control due to an input error of the thickness information can be avoided.

  In the copiers according to the fourth and nineteenth embodiments, at least one member in 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 amper meter 111 is provided as a drive current detection means for detecting the drive current of the motor that is the drive source of the motor. 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 a thickness detection unit. 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 fourth embodiment, the ampere meter 111 detects the drive current of the motor that is the drive source of the transport member disposed upstream of the secondary transfer nip in the recording paper transport direction. Use what you want. In such a configuration, as described above, it is possible to further improve the image quality by adjusting the braking force according to the thickness from the second printout sheet.

  In the copier according to the fifth embodiment, a driving roller (behind the 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 which is the drive source of the tension roller 46) is detected. The control unit 110 is configured to detect the thickness of the recording paper P based on the detection result of the ampere meter 111 as a thickness detection unit. In such a configuration, it is possible to further improve the image quality by adjusting the braking force according to the thickness based on the change in the drive current of the belt drive motor.

  In the copying machine according to the sixth embodiment, a transmission type photosensor that detects the thickness of the recording paper P based on the light transmittance of 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 copying machine according to the seventh embodiment, the displacement amount of at least one member in the conveying member pair that conveys the recording paper P by sandwiching the recording paper P in the conveying nip obtained by bringing the surfaces that move endlessly 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.

  In the copier according to the eighth 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.

  In the copier according to the ninth embodiment, an operation display unit serving as an input unit for performing an operation for inputting thickness information 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, an ampermeter, an encoder, or the like for detecting the thickness.

  In the copiers according to the tenth, eleventh, and twentieth embodiments, width information acquisition means for acquiring width information that is the sheet passing width is provided. And the control part 110 is comprised so that the control which changes the change degree of the said braking 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 variation is further suppressed by varying the amount of change in the braking 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 copiers according to the tenth, eleventh and twentieth embodiments, the width detection unit for detecting the width of the recording paper P is used as the width information acquisition unit. In such a configuration, unlike the case where the width information is acquired by an input operation to the operation display unit, improper braking force adjustment control due to an input error of the width information can be avoided.

  In the copiers according to the tenth, eleventh, and twentieth embodiments, a plurality of recordings that detect the recording paper P that passes through the position facing each other while being aligned in the width direction of the recording paper P are recorded. 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 where the width information is acquired by an input operation to the operation display unit, it is possible to avoid improper braking force adjustment control due to an input error of the width information.

  In the copier according to the twelfth embodiment, an operation display unit serving as an input means for performing width information input operation by an operator is used as the width information acquisition means. 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 thirteenth embodiment and the twenty-first embodiment are provided with a gap information acquisition means for acquiring 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 braking force in the said approach timing and discharge 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 braking 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 thirteenth embodiment and the twenty-first embodiment, 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.

  In the copiers according to the fourteenth and twenty-second embodiments, there is provided an inclination detecting means for detecting an inclination θ from a direction orthogonal to the conveyance direction of the recording paper P immediately before entering the secondary transfer nip. Yes. And the control part 110 is comprised so that the control which changes the change degree of the said braking 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 varying the amount of change in the braking force 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 fourteenth embodiment and the twenty-second embodiment, there are provided 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. 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 machines according to the fourteenth embodiment and the twenty-second embodiment, optical sensors that optically detect the recording paper P are used as the plurality of recording member detection units. 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.

  In the copier according to the eleventh embodiment, as the plurality of recording member detecting means, switch members that connect and disconnect the electrical contacts with the recording paper P are used. 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.

  In the copying machine according to the fifteenth 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 a 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 braking force immediately before the start of application when the application of the primary transfer bias to the primary transfer rollers 45Y, 45C, 45M, 45K is started. 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.

  In the copying machine according to the fifteenth embodiment, when the primary transfer bias for the primary transfer rollers 45Y, 45C, 45M, 45K is stopped, control is performed to increase the braking force more than immediately before the stop of application. 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 sixteenth embodiment, the belt motor serving as a drive source for a 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 as drive current detection means for detecting drive current is provided. Then, the control unit 110 is configured to perform control to change the braking force according to 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 seventeenth 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 braking 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 eighteenth 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 braking 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 each embodiment or each example, as the braking force applying means, a device that adjusts the braking force as the motor is driven is used. Therefore, the braking force can be adjusted by adjusting the driving amount of the motor. 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 copying machine 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 showing a secondary transfer roller unit in the transfer device of the copying machine according to the first embodiment, along with its peripheral configuration. 1 is a schematic configuration diagram showing a transfer device and its peripheral configuration in a copying machine according to a first embodiment. The graph which shows the fluctuation | variation of the load torque when not changing a braking force. The graph which shows the amount of color shift when not changing a braking force. The graph which shows the fluctuation | variation of the load torque accompanying the change of the braking force by a braking force provision means. The graph which shows the synthetic wave of the graph of FIG. 7, and the graph of FIG. The graph which shows the amount of color shift when changing braking force. FIG. 9 is a schematic configuration diagram showing a transfer device and its peripheral configuration in a copying machine according to a second embodiment. FIG. 10 is a schematic configuration diagram showing a transfer device and its peripheral configuration in a copying machine according to a third embodiment. The graph which shows the relationship between the presence or absence of the adjustment of the braking force in approach timing, and a color shift amount. 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 fourth embodiment. The graph which shows the change of the load torque of a registration motor at the time of using 80K paper as the recording paper P. FIG. The graph which shows the change of the load torque of a registration motor at the time of using 180K paper as the recording paper P. FIG. The graph which shows the change of the load torque of a registration motor at the time of using 220K paper as the recording paper P. The perspective view which shows one roller and the encoder in the registration roller pair in the copying machine based on 8th Example. The perspective view which shows an example of a conveyance belt and a means to detect the surface moving speed of this. 6 is a graph showing the relationship between the thickness of recording paper and the amount of color misregistration. (A), (b) is an expanded block diagram which shows the switch member in the copying machine based on 11th Example. The graph which shows the relationship between the state of a crevice, and the amount of color shift. 6 is a graph showing the relationship between the inclination θ and the amount of color misregistration. The top view which shows the secondary transfer roller in the copying machine based on 14th Example, and the some optical sensor arrange | positioned upstream from this. FIG. 18 is a schematic configuration diagram showing a transfer device and its peripheral configuration in a copying machine according to a fifteenth embodiment. FIG. 18 is a schematic configuration diagram showing a transfer device and its peripheral configuration in a copying machine according to a fifteenth embodiment. The schematic block diagram which shows the transfer apparatus and its surrounding structure in the copying machine based on 16th Example. The schematic block diagram which shows the transfer apparatus and its surrounding structure in the copying machine based on 18th Example. The perspective view which shows the optical sensor which is a surface speed detection means in the copying machine based on 18th Example with an intermediate transfer belt.

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)
60: Braking force applying means

Claims (33)

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 braking force applying means for directly applying a braking force to at least one of the plurality of stretching rollers; and when the recording member enters the transfer nip, immediately before the braking force is applied. And a braking force control means for controlling the braking force application means so as to be weaker than the above. 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 braking force applying means for directly applying a braking force to at least one of the plurality of stretching rollers; and a braking force applied when the rear end of the recording member is discharged from the transfer nip. A transfer device comprising: a braking force control unit that controls the braking force applying unit so as to be stronger than immediately before discharging. 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 comprising: the braking force applying means configured to apply a braking force to a rotation shaft of the nip back side stretching roller as at least one of the plurality of stretching rollers. The image forming apparatus according to claim 4.
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 any one of claims 3 to 5,
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 braking force control unit 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 5,
Thickness information acquisition means for acquiring thickness information of the recording member is provided, and the control 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 braking force control means is configured to perform control to vary the degree of power change according to the thickness information. The image forming apparatus according to claim 7, 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 8.
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 9.
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 8.
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 8.
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 8.
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 8.
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 7.
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 5,
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 characterized in that the braking force control means is configured to perform control to vary the degree of change of the braking force when the toner is discharged from the transfer nip according to the width information. . The image forming apparatus according to claim 16, comprising:
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 17.
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 16.
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 5,
A gap information acquisition unit that acquires gap information that is gap information of the recording member is provided, and when the recording member enters the transfer nip or is discharged from the transfer nip, An image forming apparatus, wherein the braking force control means is configured to perform control to vary the degree of change of braking force according to the gap information. The image forming apparatus according to claim 20, 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 5,
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 braking force control means is configured to control to vary the degree of change of the braking force when the end is discharged from the transfer nip according to the inclination. . The image forming apparatus according to claim 22, wherein
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 18 or 23.
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 18 or 23.
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 25,
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 braking force is used so that an image is transferred to the intermediate transfer belt and the braking force is controlled to be weaker than that immediately before the 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 26.
As the transfer device, a visible voltage on the latent image carrier is applied while applying a transfer voltage to a latent image facing member facing the latent image carrier through the intermediate transfer belt while contacting the back surface of the intermediate transfer belt. The braking force is used so that an image is transferred to the intermediate transfer belt, and the braking force is controlled to be stronger than immediately before stopping the application 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 27.
Drive current detection means for detecting a drive current of a motor serving as a drive source of a 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 Depending on 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, wherein the braking force control means is configured to perform control for changing the braking force. The image forming apparatus according to any one of claims 3 to 27.
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 is performed to change the braking force according to the detection result of the roller speed detection means. As described above, an image forming apparatus comprising the braking force control means. The image forming apparatus according to any one of claims 3 to 27.
The braking force control means is configured to provide surface speed detection means for detecting the surface speed of the intermediate transfer belt, and to perform control for changing the braking force in accordance with a detection result by the surface speed detection means. An image forming apparatus. The image forming apparatus according to any one of claims 3 to 30,
An image forming apparatus using a powder brake, a hysteresis brake, or a friction brake as the braking force applying means. 32. The image forming apparatus according to claim 3, wherein:
A plurality of the developing means are arranged 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. 32. 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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