JP6032524B2 - Belt drive device, transfer device, and image forming apparatus - Google Patents

Description

  The present invention relates to a belt driving device that moves an endless belt member endlessly while being stretched by a plurality of stretching members, and a transfer device and an image forming apparatus using the belt driving device.

  Conventionally, as this type of image forming apparatus, the one described in Patent Document 1 is known. This image forming apparatus forms a toner image on the surface of a drum-shaped photoreceptor by a known electrophotographic process. Then, the toner image on the photosensitive member is transferred to a recording sheet by a transfer device. The transfer device includes a belt drive device that moves an endless intermediate transfer belt while stretching an endless intermediate transfer belt by a plurality of stretching rollers, and transfers the toner image on the photosensitive member to the front surface (loop) of the intermediate transfer belt. After primary transfer to the outer surface), secondary transfer to the recording sheet.

  In the process of transferring in this way, the speed of the intermediate transfer belt is controlled based on the detection result by the scale sensor. Specifically, a scale having a plurality of scale marks arranged at a predetermined pitch in the belt circumferential direction is provided at one end in the width direction of the intermediate transfer belt. The control unit of the transfer device controls the belt drive motor drive speed so that the scale marks detected by the scale sensor composed of the reflective optical sensor become a predetermined cycle, thereby targeting the intermediate transfer belt. It is moving endlessly at speed.

  In such a configuration, when a scale mark having a significantly reduced light reflectivity due to adhesion of toner or dirt is generated, the scale mark is not detected by the scale sensor, so that the speed of the intermediate transfer belt is not correctly detected. Therefore, the image forming apparatus described in Patent Document 1 determines that a scale abnormality has occurred when the period in which the scale mark is detected by the scale sensor changes abruptly. When a scale abnormality occurs, the belt driving method is switched from the normal driving method based on the detection result by the scale sensor to the abnormal driving method. In the abnormal driving method, the rotational speed of the belt drive motor is detected by an encoder, and the drive speed of the belt drive motor is adjusted so that the result becomes a predetermined value. Thereby, even when the scale mark is abnormal, the intermediate transfer belt can be driven at a stable speed.

  However, such an abnormal driving method has a problem that the speed of the intermediate transfer belt is shifted from the target speed due to an error in the diameter of the driving roller. Specifically, the driving roller is disposed inside the loop of the intermediate transfer belt, and rotates the endless belt by receiving a driving force from a belt driving motor while the belt is wound around its surface. It is to be moved. When there is no processing error in the diameter of the drive roller, the drive roller can be rotated at a predetermined linear speed by rotating the belt drive motor at a predetermined speed. Then, the intermediate transfer belt can be moved endlessly at the target speed. However, due to the limit of processing accuracy, a processing error necessarily occurs in the diameter of the drive roller. Then, even if the belt drive motor is rotated at a predetermined speed, the linear speed of the drive roller does not become a predetermined speed, and the speed of the intermediate transfer belt deviates from the target speed.

  In the normal driving method, the configuration for grasping the speed of the intermediate transfer belt based on the detection result by the scale sensor has been described, but the intermediate driving belt is driven based on the speed of a follower member such as a driven roller that follows the belt and rotates. A similar problem may occur even in a configuration in which the speed of the transfer belt is grasped.

  In the abnormal driving method, the configuration for controlling the driving speed of the belt driving motor based on the rotational speed of the belt driving motor has been described. The configuration for controlling the driving speed of the belt driving motor based on the rotational speed of the driving roller. A similar problem may occur in

  Further, the image forming apparatus using the intermediate transfer belt has been described. However, in the case of a belt driving apparatus that drives an endless belt member, a similar problem of belt speed deviation caused by a processing error in the diameter of the driving roller occurs. .

  The present invention has been made in view of the above background, and an object of the present invention is to provide the following belt driving device, and a transfer device and an image forming apparatus using the belt driving device. That is, a belt driving device or the like that can reduce the deviation of the belt speed from the target speed due to a processing error in the diameter of the driving roller in the abnormal driving method.

To achieve the above object, the present invention provides an endless belt member, a plurality of stretching members that support the belt member while supporting the belt member inside a loop of the belt member, and one of the plurality of stretching members. And a first speed for detecting the speed of the surface movement of the belt member or the follower member following the endless movement of the belt member. and detecting means, speed of rotation speed or a second speed detecting means for detecting a rotational speed of the drive motor is a drive source of the drive roller, the first speed detecting means and the second speed detecting means of the drive roller based on the detection result, controls the driving speed of said drive motor and control means for adjusting a moving speed of the belt member, wherein the control means detects the speed of the first speed detecting means When it is determined that there is no abnormality in the first detection result that is the result, the first detection result or a predetermined first calculated value based on the first detection result is compared with a predetermined first target value. When the normal driving method for controlling the driving speed of the drive motor based on the above is adopted, and the first detection result is determined to be abnormal , the detection result of the speed by the second speed detection means. Employs an abnormal time control method for controlling the drive speed of the drive motor based on a comparison between a second detection result or a predetermined second calculated value based on the second detection result and a predetermined second target value. In the belt drive device, the drive speed of the drive motor is determined based on a comparison between the second detection result or the second calculated value and the second target value in a state where there is no abnormality in the first detection result. while controlling the multiple Acquiring the first detection result, after calculating the average speed of the belt member based on a plurality of the first detection result, based on a comparison result between the average speed and the first target value, the abnormality The control means is configured to execute a target value correction process for correcting the second target value at a predetermined timing so that the belt member can be driven at the same moving speed as the first target value in a temporal control method. It is characterized by comprising.

  In the present invention, when the drive speed of the drive motor is controlled so that the second detection result or the second calculated value reflecting the rotation speed of the drive roller is the same as the second target value in the target value correction processing, Due to the processing error of the roller diameter, the belt member moves endlessly at a speed deviating from the target speed. The amount of deviation is grasped based on the difference between the first detection result or the first calculated value reflecting the belt speed and the first target value. Then, based on the grasp result, the second target value is corrected so that the first detection result or the first calculated value reflecting the belt speed can be made equal to the first target value. This reduces the deviation of the belt speed from the target speed due to a processing error in the diameter of the driving roller in the abnormal driving method by setting the second target value to a value commensurate with the actual diameter of the driving roller. can do.

1 is a schematic configuration diagram showing a copier according to an embodiment. FIG. 2 is a partial configuration diagram illustrating an enlarged part of an image forming unit in the copier. FIG. 3 is a partially enlarged view showing a part of a tandem part composed of four process units in the image forming part. FIG. 2 is a perspective view showing a scanner and an ADF of the copier. The schematic diagram for demonstrating shape factor SF-1. The schematic diagram for demonstrating shape factor SF-2. FIG. 2 is a perspective view showing a transfer unit of the copier. The partial expansion perspective view which shows the front side board of the transfer unit. The perspective view which shows the transfer unit of the state which removed the two side plates with a control apparatus. The schematic diagram which shows the scale sensor of the transcription | transfer unit, and each scale mark SM of a scale. FIG. 3 is a block diagram showing a main part of an electric circuit of the transfer unit. The block diagram which shows the same electric circuit in detail from FIG. The flowchart which shows the processing flow of the control implemented by the same control apparatus. The graph which shows a time-dependent change of the belt speed measured value measured by a normal time drive system. The graph which shows the time-dependent change of the belt speed measured value measured by the drive system at the time of abnormality. FIG. 2 is a schematic configuration diagram showing the transfer unit from the side. The expansion block diagram for demonstrating the belt speed fluctuation | variation resulting from the deflection | deviation of a direction change roller. FIG. 3 is an enlarged configuration diagram for explaining belt speed fluctuations caused by the primary transfer roller runout. The principal part block diagram which shows the principal part structure of the copying machine which concerns on a modification.

Hereinafter, an embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter simply referred to as a copying machine) will be described.
First, a basic configuration of the copying machine according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating a copying machine according to an embodiment. This copier includes an image forming unit 1 as an image forming apparatus, a blank paper supply device 40, and an image reading unit 50. The image reading unit 50 as an image reading apparatus includes a scanner 150 fixed on the image forming unit 1 and an automatic document feeder (hereinafter referred to as ADF) 51 as a sheet conveying device supported by the scanner 150. ing.

  The blank paper supply device 40 is divided into two paper feed cassettes 42 arranged in a plurality of stages in the paper bank 41, a feed roller 43 that feeds the recording sheets from the paper feed cassettes, and the fed recording sheets one by one while conveying them. A pair of paper feed separating rollers 45 and the like. In addition, a plurality of conveyance rollers 47 that convey a recording sheet as a sheet member are provided in a paper feed path 37 as a conveyance path of the image forming unit 1. Then, the recording sheet in the paper feeding cassette is fed into the paper feeding path 37 in the image forming unit 1.

  The image forming unit 1 as an image forming unit includes an optical writing device 2 and four process units 3K, Y, M, and 4 that form toner images of black, yellow, magenta, and cyan (K, Y, M, and C). C, a transfer unit 24, a paper transport unit 28, a registration roller pair 33, a fixing device 34, a switchback device 36, a paper feed path 37, and the like. Then, a light source such as a laser diode or LED (not shown) disposed in the optical writing device 2 is driven to irradiate the four drum-shaped photosensitive members 4K, Y, M, and C with the laser light L. . By this irradiation, electrostatic latent images are formed on the surfaces of the photoreceptors 4K, Y, M, and C, and the latent images are developed into toner images via a predetermined development process.

  FIG. 2 is an enlarged partial configuration diagram illustrating a part of the internal configuration of the image forming unit 1. FIG. 3 is a partially enlarged view showing a part of a tandem part composed of four process units 3K, Y, M, and C. Since the four process units 3K, Y, M, and C have substantially the same configuration except that the colors of the toners to be used are different from each other, in FIG. The subscript is omitted.

  The process units 3K, 3Y, 3C, and 3C support the photosensitive member and the various devices disposed around it as a single unit on a common support, and with respect to the image forming unit 1 main body. Detachable. Taking the black process unit 3K as an example, this has a charging device 23, a developing device 6, a drum cleaning device 15, a static elimination lamp 22 and the like around the photosensitive member 4. This copying machine has a so-called tandem type configuration in which four process units 3K, Y, M, and C are arranged so as to face an intermediate transfer belt 25 (to be described later) along the endless movement direction. Yes.

  As the photoreceptor 4, a drum-shaped member is used in which a photosensitive layer is formed by applying a photosensitive organic photosensitive material to a base tube made of aluminum or the like. However, an endless belt may be used.

  The developing device 6 develops the latent image using a two-component developer containing a magnetic carrier and a nonmagnetic toner (not shown). In order to transfer the toner in the two-component developer carried on the developing sleeve 12 to the photosensitive member 4, the agitating unit 7 that conveys the two-component developer accommodated in the inside and supplies the developing sleeve 12 with stirring. Development section 11.

  The stirring unit 7 is provided at a position lower than the developing unit 11, and is provided on the bottom surface of the developing case 9, two conveying screws 8 arranged in parallel to each other, a partition plate provided between these screws. A toner density sensor 10 and the like are included.

  The developing unit 11 includes a developing sleeve 12 that faces the photosensitive member 4 through the opening of the developing case 9, a magnet roller 13 that is non-rotatably provided inside the developing sleeve 12, a doctor blade 14 that approaches the developing sleeve 12, and the like. ing. The developing sleeve 12 has a non-magnetic rotatable cylindrical shape. The magnet roller 12 has a plurality of magnetic poles that are sequentially arranged from the position facing the doctor blade 14 in the rotational direction of the sleeve. Each of these magnetic poles applies a magnetic force to the two-component developer on the sleeve at a predetermined position in the rotation direction. As a result, the two-component developer sent from the stirring unit 7 is attracted and carried on the surface of the developing sleeve 13 and a magnetic brush is formed along the magnetic field lines on the sleeve surface.

  The magnetic brush is regulated to an appropriate layer thickness when passing through the position facing the doctor blade 14 as the developing sleeve 12 rotates, and then conveyed to the developing region facing the photoconductor 4. Then, the toner is transferred onto the electrostatic latent image by the potential difference between the developing bias applied to the developing sleeve 12 and the electrostatic latent image on the photosensitive member 4, thereby contributing to development. Further, as the developing sleeve 12 rotates, the developing sleeve 12 is returned to the developing portion 11 again, and after being separated from the sleeve surface by the influence of the repulsive magnetic field formed between the magnetic poles of the magnet roller 13, the developing sleeve 12 is returned to the stirring portion 7. An appropriate amount of toner is supplied to the two-component developer in the stirring unit 7 based on the detection result of the toner density sensor 10. The developing device 6 may employ a one-component developer that does not include a magnetic carrier, instead of one that uses a two-component developer.

  As the drum cleaning device 15, a system in which the cleaning blade 16 made of an elastic body is pressed against the photoconductor 4 is used, but another system may be used. For the purpose of enhancing the cleaning property, this example employs a system having a contact conductive fur brush 17 whose outer peripheral surface is in contact with the photoreceptor 4 so as to be rotatable in the direction of the arrow in the figure. The fur brush 17 also serves to apply the lubricant to the surface of the photosensitive member 4 while scraping the lubricant from a solid lubricant (not shown) into a fine powder. A metal electric field roller 18 for applying a bias to the fur brush 17 is rotatably provided in the direction of the arrow in the figure, and the tip of the scraper 19 is pressed against it. The toner attached to the fur brush 17 is transferred to the electric field roller 18 to which a bias is applied while rotating in contact with the fur brush 17 in the counter direction. Then, after being scraped from the electric field roller 18 by the scraper 19, it falls onto the recovery screw 20. The collection screw 20 conveys the collected toner toward the end of the drum cleaning device 15 in the direction orthogonal to the drawing sheet surface, and transfers it to the external recycling conveyance device 21. The recycle conveyance device 21 sends the delivered toner to the developing device 15 for recycling.

  The neutralization lamp 22 neutralizes the photoreceptor 4 by light irradiation. The surface of the photoreceptor 4 that has been neutralized is uniformly charged by the charging device 23 and then subjected to optical writing processing by the optical writing device 2. As the charging device 23, a charging device that rotates a charging roller to which a charging bias is applied while contacting the photosensitive member 4 is used. A scorotron charger or the like that performs a non-contact charging process on the photoreceptor 4 may be used.

  In FIG. 2 described above, K, Y, M, and C toner images are formed on the photoreceptors 4K, Y, M, and C of the four process units 3K, Y, M, and C by the processes described above. Is done.

  A transfer unit 24 is disposed below the four process units 3K, Y, M, and C. The transfer unit 24 as a belt driving device moves the intermediate transfer belt 25 stretched by a plurality of rollers endlessly in the clockwise direction in the drawing while contacting the photoreceptors 4K, Y, M, and C. As a result, primary transfer nips for K, Y, M, and C in which the photoreceptors 4K, Y, M, and C abut the intermediate transfer belt 25 that is an endless belt member are formed. In the vicinity of the primary transfer nips for K, Y, M, and C, the intermediate transfer belt 25 is moved to the photoreceptors 4K, Y, M, and C by primary transfer rollers 26K, Y, M, and C disposed inside the belt loop. Pressing toward C. A primary transfer bias is applied to the primary transfer rollers 26K, Y, M, and C by a power source (not shown). As a result, a primary transfer electric field for electrostatically moving the toner images on the photoreceptors 4K, Y, M, and C toward the intermediate transfer belt 25 is formed in the primary transfer nips for K, Y, M, and C. Has been. In the drawing, a toner image is formed on each of the primary transfer nips on the front surface of the intermediate transfer belt 25 that sequentially passes through the primary transfer nips for K, Y, M, and C with endless movement in the clockwise direction. Are sequentially superimposed and primarily transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as a four-color toner image) is formed on the front surface of the intermediate transfer belt 25.

  Below the transfer unit 24 in the figure, a paper transport unit 28 is provided between the drive roller 30 and the secondary transfer roller 31 to endlessly move the endless paper transport belt 29. Then, the intermediate transfer belt 25 and the paper conveyance belt 29 are sandwiched between the secondary transfer roller 31 of itself and the lower stretching roller 27 a of the transfer unit 24. As a result, a secondary transfer nip is formed in which the front surface of the intermediate transfer belt 25 and the front surface of the paper transport belt 29 come into contact with each other. A secondary transfer bias is applied to the secondary transfer roller 31 by a power source (not shown). On the other hand, the lower stretching roller 27a of the transfer unit 24 is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip.

  A registration roller pair 33 is disposed on the right side of the secondary transfer nip in the drawing. A registration roller sensor (not shown) is disposed near the entrance of the registration nip of the registration roller pair 33. The recording sheet P conveyed toward the registration roller pair 33 from a blank paper supply device (not shown) is temporarily stopped after a predetermined time when the leading edge of the recording sheet P is detected by the registration roller sensor. Touch the tip to the resist nip. As a result, the posture of the recording sheet P is corrected, and preparations for synchronization with image formation are completed. In this way, the posture of the recording sheet P is corrected, but the correction may not be performed successfully. Then, the skew of the recording sheet P occurs on the downstream side of the registration roller pair 33.

  When the prior application of the recording sheet P hits the registration nip, the registration roller pair 33 resumes roller rotation driving at a timing at which the recording sheet P can be synchronized with the four-color toner image on the intermediate transfer belt 25, and the recording sheet P To the secondary transfer nip. In the secondary transfer nip, the four-color toner images on the intermediate transfer belt 25 are collectively transferred to the recording sheet due to the influence of the secondary transfer electric field and the nip pressure, and become a full-color image combined with the white color of the recording sheet. The recording sheet that has passed through the secondary transfer nip is separated from the intermediate transfer belt 25 and is conveyed to the fixing device 34 along with its endless movement while being held on the front surface of the paper conveyance belt 29.

  Transfer residual toner that has not been transferred to the recording sheet at the secondary transfer nip is attached to the surface of the intermediate transfer belt 25 that has passed through the secondary transfer nip. This transfer residual toner is scraped off and removed by a belt cleaning device in contact with the intermediate transfer belt 25.

The intermediate transfer belt 25 is a material in which a conductive material such as carbon black is dispersed in PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), or the like. Is shaped into a single-layer or multiple-layer endless belt by a casting method, a centrifugal molding method, or the like. The volume resistivity is adjusted to 10 ⁸ to 10 ¹² Ωcm, and the surface resistivity is adjusted to 10 ⁹ to 10 ¹³ Ωcm. If the volume resistivity exceeds the range, the value of the transfer bias at which an effective transfer rate can be obtained becomes high, resulting in an increase in power supply cost. Further, since the charging potential of the intermediate transfer belt 25 becomes high or the self-discharge becomes difficult in the transfer process, the transfer paper peeling process, etc., it becomes necessary to provide a static elimination means, resulting in an increase in cost and an increase in size. I will. Also, if the volume resistivity and surface resistivity are below the above-mentioned ranges, the rate of decay of the belt charging potential increases, which is advantageous for static elimination by self-discharge, but the current during transfer flows in the surface direction. As a result, toner scattering occurs.

  The volume resistivity and surface resistivity can be measured with a high resistivity meter (manufactured by Mitsubishi Chemical Corporation: Hiresta IP). An HRS probe (inner electrode diameter 5.9 mm, ring electrode inner diameter 11 mm) is connected to the measuring instrument body, and a predetermined voltage (100 V when measuring volume resistivity, 500 V when measuring surface resistivity) is applied to the front and back of the intermediate transfer belt 25. And the value after 10 seconds is adopted as the measurement result.

  A release promoting layer may be coated on the surface of the intermediate transfer belt 25 as necessary. Materials for the release promoting layer include ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluororesin), FEP ( Examples thereof include fluororesins such as tetrafluoroethylene-hexafluoropropylene copolymer) and PVF (vinyl fluoride).

  The primary transfer rollers 26K, Y, M, and C are obtained by coating the surface of a metal core made of iron, stainless steel, aluminum, or the like with an elastic layer made of a foamed resin. The thickness of the elastic layer is 2 to 10 [mm], but is not limited to this range.

  The recording sheet conveyed to the fixing device 34 is fixed to a full color image by pressurization or heating in the fixing device 34, and then sent from the fixing device 34 to the paper discharge roller pair 35 and then to the outside of the apparatus. Discharged.

  In FIG. 1 described above, a switchback device 36 is disposed under the paper transport unit 22 and the fixing device 34. As a result, the recording sheet that has undergone the image fixing process on one side is switched by the switching claw to the recording sheet reversing device side, where it is reversed and enters the secondary transfer transfer nip again. Then, after the secondary transfer process and the fixing process of the image are performed on the other side, the sheet is discharged onto a discharge tray.

  As the toner to be set in the image forming unit 1, a toner having a shape factor SF-1 of 100 to 180 and a shape factor SF-2 of 100 to 180 is used. FIG. 5 is a schematic diagram for explaining the shape factor SF-1. The shape factor SF-1 is an index value indicating the ratio of the roundness of the toner shape, and is obtained by a mathematical formula “SF-1 = {(MXNLNG) 2 / AREA} × (100π / 4)”. This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4. The shape of the toner having a shape factor SF-1 value of 100 is a true sphere, and the greater the value of SF-1, the worse the sphericity.

  FIG. 6 is a schematic diagram for explaining the shape factor SF-2. The shape factor SF-2 is an index value indicating the ratio of the unevenness of the toner shape, and is obtained by an equation “SF-2 = {(PERI) 2 / AREA} × (100π / 4)”. A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane by the figure area AREA and multiplying by 100π / 4. There is no unevenness on the surface of the toner having a shape factor SF-2 value of 100. As the shape factor SF-2 increases, the unevenness of the toner surface becomes more prominent. The shape factor can be obtained by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzing it. is there.

  When the shape of the toner is close to a spherical shape, the contact state between the toner and the toner or the toner and the photoconductor becomes a point contact, so that the adsorbing force between the toners becomes weak and the fluidity increases, and the toner and the photoconductor The attraction force becomes weaker and the transfer rate becomes higher. If either of the shape factor SF-1 or the shape factor SF-2 exceeds 180, the transfer rate is lowered and the cleaning property when attached to the transfer unit is also not preferred. The toner particle size is preferably in the range of 4 to 10 [μm] in terms of volume average particle size. When the particle size is smaller than this, it becomes a cause of background stains during development, fluidity is deteriorated, and the particles are more likely to be aggregated. On the other hand, when the particle size is larger than this, it is impossible to obtain a high-definition image due to toner scattering or resolution deterioration. In the copying machine according to the embodiment, a toner having a volume average particle diameter of 6.5 [μm] is set.

  In FIG. 1, a scanner 150 fixed on the image forming unit 1 and an ADF 51 fixed on the scanner 150 have a fixed reading unit and a moving reading unit 152. The moving reading unit 152 is disposed immediately below a second contact glass (not shown) fixed to the upper wall of the casing of the scanner 150 so as to come into contact with the document MS, and illustrates an optical system including a light source and a reflection mirror. It can be moved in the middle / left / right direction. Then, in the process of moving the optical system from the left side to the right side in the figure, the light emitted from the light source is reflected by a document (not shown) placed on the second contact glass and then passed through a plurality of reflecting mirrors. The light is received by the image reading sensor 153 fixed to the scanner body.

  On the other hand, the fixed reading unit includes a first surface fixed reading unit 151 disposed in the scanner 150 and a second surface fixed reading unit (not shown) disposed in the ADF 51. A first surface fixed reading unit 151 having a light source, a reflection mirror, an image reading sensor such as a CCD, etc. is arranged directly below a first contact glass (not shown) fixed to the upper wall of the casing of the scanner 150 so as to contact the document MS. It is installed. Then, when a document MS conveyed by the ADF 51 described later passes over the first contact glass, the light emitted from the light source is sequentially reflected on the document surface and received by the image reading sensor via a plurality of reflecting mirrors. To do. Thus, the first surface of the document MS is scanned without moving the optical system including the light source and the reflection mirror. The second surface fixed reading unit scans the second surface of the document MS after passing through the first surface fixed reading unit 151.

  An ADF 51 disposed on the scanner 150 includes a document placing table 53 for placing the document MS before reading on the main body cover 52, a transport unit 54 for transporting the document MS as a sheet member, and after reading. A document stacking table 55 for stacking the originals MS is held. As shown in FIG. 4, it is supported by a hinge 159 fixed to the scanner 150 so as to be swingable in the vertical direction. Then, by swinging, it moves like an open / close door, and the first contact glass 154 and the second contact glass 155 on the upper surface of the scanner 150 are exposed in the opened state. In the case of a single-sided original such as a book in which one corner of the original bundle is bound, the originals cannot be separated one by one and cannot be transported by ADF. Therefore, in the case of a single-sided original, the ADF 51 is opened as shown in FIG. 4, and then the single-sided original with the page to be read open is placed face down on the second contact glass 154, and then the ADF is close up. Then, the image of the page is read by the moving reading unit 152 shown in FIG.

  On the other hand, in the case of a document bundle in which a plurality of document MSs independent from each other are simply stacked, the document MS is automatically conveyed one by one by the ADF 51 while the first surface fixed reading unit 151 in the scanner 150 or the first document in the ADF 51. The two-surface fixed reading unit can sequentially read. In this case, after setting the document bundle on the document placing table 53, a copy start button (not shown) is pressed. Then, the ADF 51 sends the originals MS of the original bundle placed on the original placement table 53 into the conveyance unit 54 in order from the top, and conveys the original MS toward the original stack table 55 while inverting it. In the course of this conveyance, immediately after the document MS is reversed, the original MS is passed directly over the first surface fixed reading unit 151 of the scanner 150. At this time, the image on the first surface of the document MS is read by the first surface fixed reading unit 151 of the scanner 150.

Next, the transfer unit 24 as a transfer device will be described in detail.
FIG. 7 is a perspective view showing the transfer unit 24. The transfer unit 24 is attached to and detached from the copying machine main body in the state shown in the figure. In the transfer unit 24, a drive motor 203 and an encoder 202 are fixed to the front side plate of the two side plates that span a plurality of rollers, as shown in FIG. The drive motor 203 is a motor that is a drive source of the drive roller 27 c that is wound around the intermediate transfer belt 25. The encoder 202 detects the rotation speed of the drive roller 27c and functions as a second speed detection unit.

  FIG. 9 is a perspective view showing the transfer unit 24 together with the control device 201 with the two side plates removed. The transfer unit 24 has a belt driving device for driving the intermediate transfer belt 25. The belt driving device includes an intermediate transfer belt, a plurality of stretching rollers that support the intermediate transfer belt 25 while supporting the inner transfer belt 25 inside the loop, a control device 201, a drive motor 203, a speed reducer 204, a scale sensor 205, and the like. Yes.

  The driving force of the driving motor 203 is transmitted to the driving roller 27c, which is one of the plurality of stretching rollers, via the speed reducer 204. As a result, when the drive roller 27c rotates, the intermediate transfer belt 25 moves endlessly in the clockwise direction in FIG. As the driving roller 27c, a roller made of a rubber roller in which a rubber layer is coated on the surface of a metal core is used. The cored bar is made of extruded aluminum, but may be made of a material other than aluminum as long as it is metal. The rubber layer coated on the core metal is made of EP rubber, and is coated on the core metal with a thickness of 0.5 [mm].

  When a tension of 1 [N / cm] or more is applied to the intermediate transfer belt 25, it is desirable that the diameter of the drive roller 27c is 16 [mm] or more. When an intermediate transfer belt 25 made of PI material is used, winding wrinkles are likely to occur due to being left for a long time in a state of being wound around the peripheral surface of the roller, but if the diameter is 16 mm or more, This is because the occurrence of winding wrinkles can be suppressed. In the case where a configuration for loosening the tension of the intermediate transfer belt 25 during standby is added, the diameter of the drive roller 27c may be 16 [mm].

  At one end in the width direction of the intermediate transfer belt 25, a scale 209 having a plurality of scale marks arranged at a predetermined pitch over the entire circumference of the belt is provided. In the figure, an example in which the scale 209 is provided on the belt front surface (loop outer peripheral surface) is shown, but it may be provided on the belt rear surface (loop inner peripheral surface). The scale 209 has a scale mark printed on a tape made of a material having a higher reflectance than the belt surface or a material having a lower reflectance, and is attached so as to extend over the entire circumference of the belt. Yes.

  The scale sensor 205 as the first speed detecting means is composed of a reflection type photo sensor, reflects light emitted from the light emitting element on the scale mark surface of the scale 209, and detects the obtained reflected light with the light receiving element. Then, a detection signal corresponding to the amount of received light is output to the control device 201.

  FIG. 10 is a schematic diagram showing the scale sensor 205 and the scale marks SM of the scale 209. The plurality of scale marks SM are made of a light-reflective material and are arranged at a predetermined pitch P0 along the belt moving direction. When any one of the scale marks SM on the scale 209 moves directly below the scale sensor 205, the light emitted from the light emitting element of the scale sensor 205 is reflected by the surface of the scale mark SM, and the obtained reflected light is reflected. Light is received by the light receiving element of the scale sensor 205.

  The control device (201 in FIG. 9) controls the drive speed of the drive motor (203 in FIG. 9) so that the time interval at which each scale mark SM is detected by the scale sensor 205 is set to a predetermined period. The intermediate transfer belt (25) is driven at a target speed.

  FIG. 11 is a block diagram showing the main part of the electric circuit of the transfer unit (24). The control device 201 repeats the normal driving method and the abnormal driving method as a method of driving the drive motor 203 that is a driving source of the intermediate transfer belt 25. In the normal driving method, the driving speed of the driving motor 203 is adjusted based on the period of detecting each scale mark of the scale 209 by the scale sensor 205, that is, the result of detecting the belt moving speed. In the abnormal driving method, the drive speed of the drive motor 203 is adjusted based on the result of detecting the rotational speed of the drive roller 27c by the encoder 202 fixed to the shaft of the drive roller 27c.

  FIG. 12 is a block diagram showing the electric circuit in the transfer unit (24) in more detail than FIG. The control device 201 includes a first speed value conversion unit 201a, a first computing unit 201b, a target speed setting unit 201c, a controller 201d, a second speed value conversion unit 201e, a second computing unit 201f, a switching circuit 201g, and an abnormality determination unit 201h. Etc. Output signals from the scale sensor 205 are input to the first speed value conversion unit 201a, the target speed setting unit 201c, and the abnormality determination unit 201h of the control device 201, respectively.

  The output signal from the scale sensor 205 is an analog voltage signal, and the waveform has a shape in which rising and falling portions are alternately repeated. The rising portion is output from the scale sensor 205 when the reflected light obtained on the scale mark is received by the light receiving element. That is, it is a mark detection signal. On the other hand, the falling portion is output from the scale sensor 205 when the reflected light obtained on the scale mark is not received by the light receiving element. That is, it is a mark non-detection signal.

  The first speed value conversion unit 201a calculates the moving speed of the intermediate transfer belt based on the period in which the pulse rising in the output signal from the scale sensor 205 occurs, that is, the period in which the scale sensor 205 detects the scale mark SM. Then, the measured belt speed value is output as a digital signal to the first computing unit 201b. The target speed setting unit 201c outputs the target speed of the intermediate transfer belt to the first calculator 201b as a digital signal. The first computing unit 201b computes the difference between the measured belt speed value output from the first speed value conversion unit 201a and the target speed output from the target speed setting unit 201c, and the resulting belt speed difference. Is output to the switching circuit 201g.

  On the other hand, the second speed value conversion unit 201e calculates the rotation speed of the drive roller 27c based on the period in which the pulse rising in the output signal from the encoder 202 occurs, that is, the period in which the encoder scale scale mark is detected. Then, the measured roller rotation speed value is output as a digital signal to the second calculator 201f. The target speed setting unit 201c outputs the target rotation speed of the drive roller 27c to the second calculator 201f as a digital signal. The second computing unit 201f computes the difference between the roller rotational speed measurement value output from the second speed value conversion unit 201e and the target rotational speed output from the target speed setting unit 201c, and the resulting rotation. The speed difference is output to the switching circuit 201g.

  Further, the abnormality determination unit 201h determines the presence / absence of abnormality of the scale mark SM (hereinafter referred to as scale abnormality) based on the change state of the pulse falling period in the output signal from the scale sensor 205. Specifically, it is assumed that a scale mark SM whose light reflectivity is significantly lowered due to adhesion of dirt such as toner is generated, and the scale mark SM is not detected by the scale sensor 205. Then, before and after the scale mark SM passes just below the scale sensor 205 as the belt moves, the pulse rising period is approximately doubled. More specifically, for example, when the intermediate transfer belt is traveling near the target speed, the pulse rising period of the output signal from the scale sensor 205 is about 14 times the reference clock period. In such a state, when a scale mark SM (hereinafter referred to as an abnormal mark) with significantly reduced light reflectivity passes immediately below the scale sensor 205, the pulse rising period is 28 times the reference clock period only at that time. It rises rapidly to the extent. When the pulse fall period rises rapidly in this way, the abnormality determination unit 201h compares the next pulse fall period with the previous pulse fall period. When the moving speed of the intermediate transfer belt suddenly increases for some unexpected reason, the pulse falling period rapidly increases even if no abnormal mark is generated. In this case, however, the pulse falling period does not rise rapidly for a moment, but the increased state continues to some extent. For this reason, the next falling cycle is also significantly larger than the previous falling cycle. In such a case, the abnormality determination unit 201h determines that no mark abnormality has occurred. On the other hand, when the sudden rise in the pulse falling cycle is due to the abnormal mark, the next pulse falling cycle returns to the normal cycle. For this reason, the difference between the next pulse falling period and the previous falling period falls within a predetermined threshold. In this case, the abnormality determination unit 201h determines that an abnormality mark has occurred.

  FIG. 13 is a flowchart illustrating a control processing flow executed by the control device 201. The control device 201 determines whether or not the mark abnormality flag is being set when a predetermined start timing arrives (Y in Step 1; hereinafter, Step is referred to as S). If it is not set (N in S2), driving of the driving motor is started by a normal driving method in which the driving speed of the driving motor is adjusted based on the output signal from the scale sensor (S3). In the normal driving method, the presence or absence of a mark abnormality is determined based on the output signal from the scale sensor while feedback controlling the driving speed of the driving motor (S4). If a mark abnormality is recognized (Y in S5), after setting a mark abnormality flag (S6), the drive control system of the drive motor is switched from the normal driving system to the abnormal driving system (S7). If no mark abnormality is recognized (N in S5), drive control of the drive motor in the normal drive system is continued. Thereafter, when a predetermined stop timing comes (Y in S8), the drive motor is stopped (S9).

  On the other hand, if it is determined in step S2 that the mark abnormality flag is being set (Y in S2), the driving motor is driven by the abnormal time driving method in which the driving speed of the driving motor is adjusted based on the output signal from the encoder. Is started (S10). In the abnormal driving method, the drive speed of the drive motor is feedback-controlled based on the output signal from the encoder (S11). When a predetermined stop timing arrives (Y in S12), the drive motor is stopped (S9).

Next, experiments conducted by the present inventors will be described.
The inventors prepared a test machine having a basic configuration similar to the basic configuration of the copying machine according to the embodiment. Then, while driving the driving motor of the intermediate transfer belt of this testing machine in the normal driving method, the individual belt speed measurement values calculated based on the output signal from the scale sensor are stored in the data storage circuit to the control device. A process of sequentially storing them was performed.

  FIG. 14 is a graph showing the change with time in the measured belt speed obtained in this experiment. As the scale attached to the intermediate transfer belt, a scale in which scale marks SM are arranged at a pitch of 0.1 [mm] was used. The pitch error of the scale mark SM in this scale is 0.1 [mm] ± 0.005 [%]. For this reason, the speed detection error (the difference between the actual speed and the detected speed) does not exceed 0.005 [%]. The average belt speed calculated from the graph shown in FIG. 14 was 299.875 [mm / s]. On the other hand, the target speed was set to 299.86 [mm / s]. The numerical value of 29.875 [mm / s] is a numerical value in which an error of −0.0005 [%] is generated with respect to the target speed, and is within the range of the target speed ± 0.005 [%]. Therefore, it can be seen that the belt speed can be controlled with high accuracy.

  Next, the present inventors conducted a similar experiment by changing the drive control system of the drive motor from the normal drive system to the abnormal drive system. FIG. 15 is a graph showing the change with time in the measured belt speed obtained in this experiment. The average belt speed calculated from this graph was 299.5 [mm / s]. This is a numerical value in which an error of −0.120 [%] is generated with respect to the target of 299.86 [mm / s]. Moreover, it is a numerical value in which an error of −0.0125 [%] is generated with respect to the average speed of 299.875 [mm / s] in the previous experiment. It can be seen that the error is very large compared to the previous experiment. The cause of the large error is the tolerance of the diameter of the drive roller. Specifically, a drive roller having a diameter of 30 ± 0.05 [mm] is used. Such a driving roller varies in diameter in the range of 29.95 to 30.05 [mm] for each solid. The diameter of the drive roller mounted on the test machine was 29.964 [mm] as measured with a precision measuring instrument. This is a numerical value in which an error of −0.12 [%] is generated with respect to the target diameter. This numerical value coincides with a numerical value of −0.120 [%], which is an error of the average speed with respect to the target speed. In other words, the tolerance of the diameter of the driving roller increases the error from the target speed of the average speed in the abnormal driving method.

  As described above, in the abnormal driving method, a relatively large error is generated between the average speed and the target speed of the intermediate transfer belt, so that the amount of misalignment of the color toner images is increased.

Next, a characteristic configuration of the copier according to the embodiment will be described.
The control device 201 illustrated in FIG. 12 performs target value correction processing when a target value correction operation command is issued from the operator in a state where a print job is not performed. However, in the state where the mark abnormality flag is set, the target value correction process is not performed even if a target value correction operation command is issued. The mark abnormality flag being set is canceled based on the input of the mark abnormality elimination information from the operator who has replaced or cleaned the intermediate transfer belt.

  In the target value correction process, first, driving of the drive motor is started by the abnormal time driving method. Hereinafter, the target speed of the belt in the abnormal driving method is referred to as a target speed Vs. The target rotational speed of the driving roller in the normal driving method is referred to as target rotational speed ωs. The target speed Vs is 299.86 [mm / s], the initial value of the target rotational speed ωs is 190.99 [rpm], the design value of the diameter of the drive roller is 30 [mm], and the drive The target value correction process will be described by taking as an example a case where the actual diameter of the roller is 29.964 [mm].

  In the abnormal driving method, if there is no tolerance in the diameter of the driving roller, the average speed of the intermediate transfer belt is almost the same as the target speed Vs (299.86 mm / s). However, if there is a tolerance in the diameter of the drive roller, the average speed of the intermediate transfer belt deviates from the target speed Vs by an amount corresponding to the tolerance. Therefore, the controller 201d of the control device 201 drives the drive motor by the abnormal time drive method for at least a period in which the intermediate transfer belt is rotated one or more times. The target speed setting unit 201c of the control device 201 calculates the belt speed measurement value for each predetermined period based on the output signal from the scale sensor 205 during that period, and stores the result in the data storage circuit. When the drive motor is stopped, the average speed Vave of the intermediate transfer belt is calculated based on the plurality of belt speed measurements stored in the data storage circuit. Next, the normal target speed Vn is divided by the calculation result (Vs / Vave). The result reflects the amount of deviation of the average belt speed from the target speed Vs according to the tolerance of the diameter of the drive roller. The target speed setting unit 201c corrects the target rotational speed ωs by multiplying the result (ωs = ωs × Vs / Vave). As a result, the target rotational speed ωs is corrected to a value corresponding to the tolerance of the diameter of the drive roller.

  More specifically, the design value of the diameter of the drive roller is 30 [mm]. When there is no tolerance in the diameter of the driving roller, when the driving roller is rotated at 190.93 [rpm] which is the initial value of the target rotational speed ωs, the linear speed of the driving roller becomes about 299.86 [mm / s]. (30 × 3.141 × 190.93 / 60), which matches the target speed Vs. However, since the actual diameter is 29.964 [mm], when the driving roller is rotated at 190.93 [rpm] which is the initial value of the target rotational speed ωs, the linear speed of the driving roller is 299.5 [mm]. / S] (29.961 × 3.141 × 190.93 / 60), the speed does not coincide with the target speed Vs. However, the linear velocity can be detected as the average velocity Vave. That is, the average speed Vave is 299.5 [mm / s]. When the result of dividing the target speed Vs by the average speed Vave is multiplied by the initial value of the target rotational speed ωs, the corrected target rotational speed ωs becomes 191.17 [rpm] (299.86 / 299.5 × 190. 93). When the drive roller is rotated at the corrected target rotational speed ωs, the linear speed becomes 299.87 [mm / s] (191.17 / 60 × 29.964 × 3.141), so the target speed It almost coincides with Vs.

  Thus, in this copying machine, the drive speed of the drive motor is set so that the measured value of the roller rotational speed as the second calculated value is the same as the target rotational speed ωs as the second target value in the abnormal driving method. When controlled, the intermediate transfer belt moves at a speed deviating from the target speed Vs due to a processing error (tolerance) of the diameter of the drive roller. The amount of deviation is grasped based on the difference between the average speed Vave as the first calculated value and the target speed Vs as the first target value. Based on the grasped result, the target rotational speed ωs as the second target value is corrected so that the average speed Vave as the first calculated value is equal to the target speed Vs as the first target value. Thus, by setting the target rotational speed ωs to a value commensurate with the actual driving roller diameter, in the abnormal driving method, the deviation of the average speed Vave from the target speed Vs due to the processing error of the driving roller diameter is reduced. Can be reduced.

  Note that the initial target value correction processing may be performed at the time of shipment from the factory, or may be automatically performed when the initial operation is performed under the user. When the replacement operation of the driving roller is performed, the replacement operator performs a target value correction operation command by operating the operation display unit, thereby performing target value correction processing and replacing the abnormal target speed Va after replacement. Make it suitable for the diameter. Only the abnormal target speed Va is corrected, and the normal target speed Vn is maintained at the initial value.

  In the normal driving method, the example in which the drive speed of the drive motor is adjusted based on the comparison between the measured belt speed value that is the first calculated value and the target speed Vs that is the first target value has been described. The drive speed of the drive motor may be adjusted based on the rise period of the scale detection signal that is the result and the target period that is the first target value. In this case, in the target value correction process, the second detection result or the second calculated value may be corrected by multiplying the result obtained by dividing the target period by the rising period measurement value.

  In the abnormal driving method, the example in which the drive speed of the drive motor is adjusted based on the comparison between the measured value of the roller rotational speed as the second calculated value and the target rotational speed ωs as the second target value has been described. The drive speed of the drive motor may be adjusted based on the rising period of the encoder detection signal that is the second detection result and the target period that is the second target value.

  Moreover, although the example which provided the encoder 202 which detects the rotational speed of the drive roller 27c was demonstrated as a 2nd speed detection means, what detects the rotational speed of the drive motor 203 may be provided. For example, some DC brushless motors have a built-in FG signal generator that generates an FG signal representing the motor rotation speed. The FG signal generator may be used as the second speed detecting means.

  FIG. 16 is a schematic configuration diagram showing the transfer unit 24 from the side. In the figure, the primary transfer rollers 26K, Y, M, and C are disposed so as to satisfy the following conditions. That is, the intermediate transfer belt 25 is linearly moved from the position of the primary transfer roller 26K disposed on the most upstream side in the belt moving direction to the position of the primary transfer roller 26C disposed on the most downstream side. This is a condition of moving. In order to satisfy such conditions, the primary transfer rollers 26K, Y, M, and C wind the intermediate transfer belt 25 at the same winding angle, and the winding angle is a relatively small value. More specifically, the winding angle is 8.13 [°]. The winding angle is an angle formed by a line segment connecting the belt contact start point and the roller center point in the circumferential direction of the roller surface and a line segment connecting the belt separation start point and the roller center point in the circumferential direction of the roller surface. It is.

  Among a plurality of stretching rollers disposed inside the loop of the intermediate transfer belt 25, some wind the intermediate transfer belt 25 at a large winding angle with respect to its surface in order to greatly change the belt moving direction. It functions as a direction change roller. Specifically, the lower stretching roller 27a, the driving roller 27c, the tension roller 27b, and the like function as direction changing rollers.

  The intermediate transfer belt 25 that has passed through the position wound around the most downstream primary transfer roller 26C is eventually changed in direction by the direction changing roller. The driving roller 27c plays the role.

  In this copying machine, as shown in the figure, the scale sensor 205 serving as the first speed detection means is located downstream of the most upstream primary transfer roller 26K in the belt moving direction and downstream of the primary transfer roller 26K. It is disposed at a position upstream of the roller 26C in the belt moving direction. At this position, as described above, the intermediate transfer belt 25 moves substantially linearly. In the vicinity thereof, a plurality of primary transfer nips are formed. The speed of the intermediate transfer belt 25 is detected by the scale sensor 205 in the vicinity of a position where a plurality of primary transfer nips are formed, and the result is fed back to the drive control of the drive motor, thereby changing the belt speed in the primary transfer nip. Can be suppressed.

  In this copying machine, the primary transfer roller 26C is used as a direction change roller by making the belt winding angle with respect to the most downstream primary transfer roller 27c the same as the belt winding angle with respect to the other primary transfer rollers. Not functioning. With such a configuration, it is possible to suppress the overlay deviation due to the deflection of the direction change roller as compared with the case where the primary transfer roller 26C functions as the direction change roller. Specifically, the direction changing roller winds the intermediate transfer belt 25 at a large winding angle, and therefore, the force due to the belt tension is strongly applied, and the direction changing roller is likely to swing. And the belt speed fluctuation | variation accompanying the deflection | deviation of a direction change roller becomes large, so that a winding angle becomes large.

  FIG. 17 is an enlarged configuration diagram for explaining the belt speed fluctuation caused by the deflection of the direction changing roller. The intermediate transfer belt 25 is wound around the illustrated direction changing roller at a winding angle of 180 °. The direction change roller maximizes the speed fluctuation of the intermediate transfer belt 25 when it swings at the center of the winding angle. In the illustrated example, the shake is in the direction of arrow A. When the direction changing roller swings in the direction of the arrow A with a swing width of 0.5 [mm], the belt portion in the vicinity of the direction changing roller and upstream of the direction changing roller also follows that and moves to 0.5 [mm]. ] To cause displacement. Of course, the greater the displacement, the greater the change in the belt speed.

  FIG. 18 is an enlarged configuration diagram for explaining the belt speed fluctuation caused by the shake of the primary transfer roller 26C. The intermediate transfer belt 25 is wound around the primary transfer roller 26C at a very small winding angle of 8.13 [°]. For this reason, the primary transfer roller 26C does not function as a direction changing roller. In the configuration shown in the figure, when the primary transfer roller 26C is swung in the direction of arrow B, the belt speed fluctuation caused by the wobbling becomes the largest. When the primary transfer roller 26C swings in the direction of arrow B with a swing width of 0.5 [mm], the belt portion on the downstream side of the roller is displaced only 0.1138 [mm] with the swing. Compared to the configuration of FIG. 17 that is displaced by 0.5 [mm], the belt speed fluctuation amount is remarkably reduced.

  In this copying machine, the primary transfer roller 26C on the most downstream side does not function as a direction change roller, and a drive roller 27c as a direction change roller is disposed on the downstream side in the belt moving direction, thereby providing a primary. The primary transfer surface (from the primary transfer nip for K to the primary transfer nip for C) from the primary transfer surface of the intermediate transfer belt 25 caused by the deflection of the drive roller 27c, compared with the case where the transfer roller 26C functions as a direction change roller. Suppress the speed fluctuation of the surface. Thereby, it is possible to suppress overlay deviation due to speed fluctuation of the primary transfer surface.

  FIG. 19 is a main part configuration diagram showing a main part configuration of a copying machine according to a modification. In this copying machine, a driven encoder 208 is provided as a first speed detecting means instead of the scale sensor. The driven encoder 208 detects the rotational speed of the tension roller 27b that rotates following the endless movement of the intermediate transfer belt 25. Since the linear speed of the tension roller 27b is the same as the linear speed of the intermediate transfer belt 25, the moving speed of the intermediate transfer belt 25 can be obtained by detecting the rotational speed of the tension roller 27b.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
[Aspect A]
An endless belt member (for example, the intermediate transfer belt 25), a plurality of stretching members that support and stretch the belt member inside the loop of the belt member, and one of the plurality of stretching members, First speed detection for detecting a driving roller (e.g., 27c) that moves the belt member endlessly in accordance with the rotational driving of the belt, and a surface moving speed of the belt member or a driven member that follows the endless movement of the belt member. Means (for example, scale sensor 205), second speed detecting means (for example, encoder 202) for detecting the rotational speed of the driving roller, or the rotational speed of a driving motor (for example, 203) that is a driving source of the driving roller, Based on the detection results of the first speed detection means and the second speed detection means, the drive speed of the drive motor is controlled to adjust the moving speed of the belt member. Control means (for example, the control device 201), and when the control means determines that there is no abnormality with respect to the first detection result that is the detection result by the first speed detection means, the first detection result, or While adopting a normal driving method for controlling the driving speed of the driving motor based on a comparison between a predetermined first calculated value based on the first detection result and a predetermined first target value, When it is determined that there is an abnormality in one detection result, a second detection result that is a detection result by the second speed detection means, a predetermined second calculated value based on the second detection result, and a predetermined second In a belt driving apparatus that employs an abnormal time control method for controlling the drive speed of the drive motor based on a comparison with a target value, the second detection result without any abnormality in the first detection result. Or said 2 comparing the first detection result or the first calculated value with the first target value while controlling the driving speed of the drive motor based on the comparison between the calculated value and the second target value. The control means is configured to perform a target value correction process for correcting the second target value based on the above at a predetermined timing.

[Aspect B]
Aspect B is characterized in that, in aspect A, the drive roller is a rubber roller coated with a rubber layer. In such a configuration, it is possible to drive the belt member at a stable speed while suppressing the occurrence of belt slip on the surface of the drive roller as compared with the case where a drive roller that is not a rubber roller is used.

[Aspect C]
Aspect C uses, in aspect A or B, as the belt member, a belt member having a scale (for example, 209) having a plurality of marks arranged at a predetermined pitch in the belt circumferential direction, and as the first speed detection means. In this embodiment, a mark detecting means (for example, a scale sensor 205) for detecting the mark (for example, the scale mark SM) is used. In such a configuration, unlike the configuration in which the belt speed is detected based on the rotational speed of the driven roller, even if there is a tolerance in the diameter of the driven roller, the tolerance is not reflected in the speed detection accuracy. It is possible to avoid a decrease in speed detection accuracy due to the tolerance of the roller diameter.

[Aspect D]
Aspect D is a rotation speed detection means (for example, a driven speed) that detects the rotation speed of the driven roller as the driven member that rotates following the endless movement of the belt member as the first speed detection means in aspect A or B. This is characterized in that an encoder 208) is used. In such a configuration, unlike the case of using a scale sensor, it is possible to avoid a decrease in speed detection accuracy due to the expansion and contraction of the belt.

[Aspect E]
In the aspect E, a plurality of image carriers that carry visible images of different colors are provided as the image carrier (for example, the photosensitive member 4), and the visible images carried on the respective image carriers are transferred to the belt member. In order to individually transfer to the front surface, a plurality of transfer rollers (for example, primary transfer rollers 26K, Y,...) Disposed at positions corresponding to the respective image carriers inside the belt member. M, C), and the first speed detecting means is located downstream of the most upstream transfer roller (for example, the maintenance transfer roller 26K) in the belt moving direction and the most downstream transfer roller. It is characterized in that it is arranged at a position upstream of the belt moving direction (for example, the primary transfer roller 26C). In such a configuration, by detecting the belt speed fluctuation in the vicinity of the plurality of primary transfer nips, the belt speed fluctuation in the vicinity of the plurality of primary transfer nips is suppressed, and the occurrence of overlay deviation is more efficiently suppressed. be able to.

[Aspect F]
An aspect F is the aspect E in which the belt member is moved from the position of the transfer roller disposed on the most upstream side in the belt moving direction toward the position of the transfer roller disposed on the most downstream side. In order to move the member linearly, the belt member is wound around each transfer roller at the same winding angle, and the moving direction of the belt member is set downstream of the transfer roller on the most downstream side. In order to change the position, a direction changing roller (for example, a driving roller 27c) is provided to wind the belt member around its circumferential surface at a winding angle larger than the winding angle. In such a configuration, as described above, it is possible to suppress the occurrence of misalignment due to belt speed fluctuations as compared with the case where the most downstream transfer roller functions as a direction change roller.

4K, Y, C, M: photoconductor (image carrier)
24: Transfer unit (transfer device)
25: Intermediate transfer belt (belt member)
26K, Y, C, M: Primary transfer roller (transfer roller)
27b: Stretching roller (driven roller)
27c: Driving roller (direction changing roller)
201: Control device (control means)
202: Encoder (second speed detection means)
203: Drive motor 205: Scale sensor (first speed detection means, mark detection means)
208: driven encoder (first speed detection means, rotation speed detection means)
209: Scale SM: Scale mark (marker)

JP 2004-220006 A

Claims (8)

An endless belt member, a plurality of stretching members that support the belt member while supporting the belt member inside a loop of the belt member, and one of a plurality of stretching members. A driving roller that moves the belt member endlessly, a surface moving speed of the belt member, or a first speed detecting means that detects a speed of a driven member that follows the endless movement of the belt member, and a rotational speed of the driving roller, or A second speed detecting means for detecting a rotational speed of a driving motor which is a driving source of the driving roller, and driving of the driving motor based on a speed detection result by the first speed detecting means or the second speed detecting means; by controlling the speed and control means for adjusting a moving speed of the belt member, said control means, abnormal for the first detection result is the speed of detection results by the first speed detecting means Is determined, the drive speed of the drive motor is controlled based on a comparison between the first detection result or a predetermined first calculated value based on the first detection result and a predetermined first target value. While the normal driving method is employed, when it is determined that the first detection result is abnormal, the second detection result that is the detection result of the speed by the second speed detection means, or the second In the belt drive device that employs an abnormal time control method for controlling the drive speed of the drive motor based on a comparison between a predetermined second calculated value based on a detection result and a predetermined second target value,
In the absence of abnormality in the first detection result, while controlling the driving speed of the drive motor based on a comparison between the second detection result or the second target value and the second calculated value, a plurality of the first get the first detection result, after calculating the average speed of the belt member based on a plurality of the first detection result, based on a result of comparison between the first target value and the average speed, for when the abnormality The control means is configured to perform a target value correction process for correcting the second target value to a value that can drive the belt member at the same moving speed as the first target value in a control manner at a predetermined timing. A belt drive device characterized by that. The belt driving device according to claim 1, wherein
A belt driving device comprising a rubber roller coated with a rubber layer as the driving roller. In the belt drive device according to claim 1 or 2,
As the belt member, a belt member having a scale having a plurality of marks arranged at a predetermined pitch in the belt circumferential direction is used.
A belt driving apparatus comprising: a mark detecting means for detecting the mark as the first speed detecting means. In the belt drive device according to claim 1 or 2,
A belt drive comprising a rotation speed detection means for detecting a rotation speed of a driven roller as the driven member that rotates following the endless movement of the belt member as the first speed detection means. apparatus. The endless belt member is moved endlessly by the belt driving means, and the visible image carried on the surface of the image carrier is moved endlessly on the surface of the endless belt member or the recording sheet held on the surface. In a transfer device for transferring to
A transfer device using the belt drive device according to claim 1 as the belt drive means. In an image forming apparatus comprising: an image carrier that carries a visible image on a surface; and a transfer device that transfers a visible image on the image carrier to a transfer member.
An image forming apparatus using the transfer device according to claim 5 as the transfer device. The image forming apparatus according to claim 6.
As the image carrier, provided with a plurality of image carriers that carry visible images of different colors,
In order to individually transfer the visible image carried on each image carrier to the front surface of the belt member, the belt is arranged at a position corresponding to each image carrier inside the belt member. Provided with a plurality of transfer rollers,
In addition, the first speed detection unit is disposed at a position downstream of the transfer roller on the most upstream side in the belt movement direction and upstream of the transfer roller on the most downstream side in the belt movement direction. An image forming apparatus. The image forming apparatus according to claim 7.
The belt member is moved linearly from the position of the transfer roller disposed on the most upstream side in the belt moving direction toward the position of the transfer roller disposed on the most downstream side. In addition, the belt member is wound around each transfer roller at an equal winding angle,
In addition, in order to change the moving direction of the belt member on the downstream side of the transfer roller on the most downstream side, a direction changing roller for winding the belt member on its peripheral surface at a winding angle larger than the winding angle is provided. An image forming apparatus.

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