JP2007078831A - Belt conveying device, transfer device and color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent failure from occurring when a motor is started in driving a belt. <P>SOLUTION: The belt conveying device has: an intermediate transfer belt 10 driven to be rotated by a motor 10d; a scale formed on the belt 10; a belt scale sensor 10b for reading the scale; and a motor control part 10c for performing feed-back control to the motor 10d on the basis of the read signal of the scale read by the sensor 10b, and is equipped with an encoder for detecting the rotating speed of the motor 10d. The motor control part 10c corrects the rotating speed of the motor 10d on the basis of a detection signal from the encoder when starting up the rotation of the motor 10d. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention includes a belt conveyance device that rotationally drives an endless belt having an image transferred on its surface, a transfer device that transfers an image conveyed by the belt conveyance device to a recording sheet, and an intermediate transfer system including the transfer device. The present invention relates to a tandem type color image forming apparatus such as a copying machine, a printer, a facsimile, and a digital multi-function peripheral (MFP) that combines these functions.

  Today, with the demand from the market, many electrophotographic apparatuses, such as color copying machines and color printers, form images in color. A color electrophotographic apparatus is provided with a developing device of a plurality of colors around one photoconductor, and a toner is attached by these developing devices to form a composite toner image on the photoconductor, and the toner image is transferred. A so-called one-drum type recording a color image on a sheet and a plurality of photosensitive members individually provided with a developing device are juxtaposed to form a monochrome toner image on each photosensitive member, and the monochrome toner images are There is a so-called tandem type that sequentially transfers and records a composite color image on a recording sheet. Comparing the 1-drum type and the tandem type, the former has the advantage that it can be made relatively small and cost can be reduced because there is only one photoconductor, but it can be reduced more than once (usually 4 times). ) Since a full-color image is formed by repeating image formation, there is a drawback that it is difficult to speed up image formation. The latter, on the contrary, has the advantage that it is easy to increase the speed of image formation, although there is a drawback that the apparatus becomes large and the cost is high. Recently, tandem type has been attracting attention because the demand for full-color monochrome speed is desired.

  As shown in FIG. 5, the tandem type electrophotographic apparatus includes a direct transfer system that sequentially transfers an image on each photoconductor 40 to a sheet s conveyed by a sheet conveying belt 10 ′ by a transfer device 62. As shown in FIG. 2, the images on the respective photoreceptors 40 are once transferred sequentially to the intermediate transfer belt 10 by the primary transfer device 62, and then the images on the intermediate transfer belt 10 are recorded on the recording sheet by the secondary transfer device 22. There are indirect transfer systems that perform batch transfer on s. The secondary transfer device 22 is a transfer conveyance belt, but there are also roller shapes and methods. Comparing the direct transfer type and the indirect transfer type, the former arranges the paper feeding device 6 on the upstream side of the tandem type image forming apparatus T in which the photoconductors 40 are arranged, and the fixing device 7 on the downstream side. There is a drawback in that the size increases in the sheet conveying direction. On the other hand, in the latter case, the secondary transfer position 22 can be set relatively freely, and the paper feeding device 6 and the fixing device 7 can be arranged so as to overlap the tandem image forming device T, thereby reducing the size. There is an advantage that becomes possible.

  In the former, in order not to increase the size in the sheet conveying direction, the fixing device 7 is arranged close to the tandem type image forming apparatus T. For this reason, the fixing device 7 cannot be disposed with a sufficient margin that allows the recording sheet s to bend, and an impact (particularly with a thick sheet) when the leading edge of the recording sheet s enters the fixing device 7 or the like. The fixing device 7 tends to affect upstream image formation due to the difference in speed between the sheet conveyance speed when passing through the fixing device 7 and the sheet conveyance speed by the transfer conveyance belt. On the other hand, since the latter can arrange the fixing device 7 with a sufficient margin that the recording sheet s can bend, the fixing device 7 can hardly affect the image formation.

  In this type of color electrophotographic apparatus, as shown in FIG. 2, the transfer residual toner remaining on the photosensitive member 1 after the primary transfer is removed by the photosensitive member cleaning device 8 to clean the surface of the photosensitive member 1 again. Ready for image formation. In addition, the transfer residual toner remaining on the intermediate transfer belt 10 after the secondary transfer is removed by the intermediate transfer body cleaning device 9 to clean the surface of the intermediate transfer belt 10 to prepare for image formation again.

  In view of the above, recently, an indirect transfer type of tandem type electrophotographic apparatus has attracted attention.

  However, in such a color image forming apparatus, when colors are superimposed, the position is shifted from a target position, and a problem such as color unevenness may occur on the image. As one of the causes of this color misregistration, it has been found that some image forming apparatuses using intermediate transfer are caused by uneven speed of the intermediate transfer member.

As a technique for solving such color misregistration, for example, the invention disclosed in Patent Document 1 is known. The present invention provides a scale on the intermediate transfer belt, detects the speed of the intermediate transfer belt by reading the scale with a sensor, controls the belt driving motor based on the detection result, reduces the speed unevenness, This is intended to prevent deviation. As other related techniques, for example, inventions described in Patent Documents 2 to 4 are also known.
JP 11-24507 A JP 2004-191815 A JP 2004-220006 A Japanese Patent Laying-Open No. 2005-062826

  In the invention described in Patent Document 1, the belt scale is read by a sensor, and feedback control is performed based on the sensor detection output. This control is effective after the motor rises to the target speed. During the rising period up to the target speed, the sensor output becomes unstable, the rising may fail, and the target speed may not be reached stably. In addition, in the inventions according to Patent Documents 2 to 4, no particular consideration is given to stably leading from the rising to the target speed.

  The present invention has been made in view of such a state of the art, and an object of the present invention is to prevent occurrence of problems at the time of starting a motor when driving a belt.

  In order to achieve the object, the first means includes an endless belt driven to rotate by a motor, a scale formed on the belt, a reading means for reading the scale, and the reading means read by the reading means. And a control unit that feedback-controls the motor based on a scale reading signal. The belt conveyance device includes a detection unit that detects a rotation speed of the motor, and the control unit is configured to detect the rotation speed of the motor when the motor starts rotating. The rotational speed of the motor is corrected based on the detection signal.

  The second means is the first means, wherein the control means controls the rotation speed of the motor based on a read signal of the scale and a detection signal of the detection means when the motor is driven at a steady speed. It is characterized by correcting.

  A third means is the second means, wherein the control means, from the correction by the detection signal at the time when the motor reaches a speed within a range set in advance with respect to the target speed of the steady speed at the time of startup of the motor, The correction is switched to the correction based on the read signal of the scale and the detection signal of the detection means.

  A fourth means is any one of the first to third means, wherein a slit is formed in the scale, and the reading means reads the slit forming part and the non-slit part and outputs a reading signal. It is characterized by.

  A fifth means is any one of the first to third means, wherein the detection means outputs a detection signal by detecting an encoder that rotates in synchronization with the rotation of the motor.

  The sixth means comprises a belt conveying apparatus according to any one of the first to fifth means, and a transfer means for transferring an image to the endless belt.

  A seventh means is characterized in that, in the sixth means, the endless belt is an intermediate transfer belt for further transferring the image once transferred onto a recording sheet and superimposing a plurality of color images.

  According to an eighth means, in the seventh means, the transfer means transfers the images on the plurality of photosensitive members arranged in parallel along the moving direction of the intermediate transfer belt to the same position on the intermediate transfer belt. And a second transfer unit that transfers an image on which a plurality of color images are superimposed by the first transfer unit to a recording sheet.

  A ninth means is characterized in that the image forming apparatus includes the transfer device according to any one of the sixth to eighth aspects.

  In the embodiments described later, the motor is the belt drive motor 10d, the endless belt is the intermediate transfer belt 10, the scale is the reference numeral 10a, the reading means is the belt scale sensor 10b, and the control means is the motor controller 10c. The slit is the scale slit 10e, the encoder is the reference numeral 10i, the transfer means is the primary transfer device 62, the secondary transfer device 22, the first transfer means is the primary transfer device 62, and the second transfer means is 2 Each corresponds to the next transfer device 22.

  According to the present invention, the control means corrects the rotation speed of the motor based on the detection signal at the start of the rotation of the motor, so that it is possible to prevent the occurrence of problems when starting the motor of the belt conveying device. As a result, it is possible to prevent the occurrence of problems at the time of starting the motor that rotationally drives the intermediate transfer belt of the transfer device or the image forming apparatus.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram of a color copying machine which is an image forming apparatus using an electrophotographic system according to an embodiment of the present invention. This color copying machine includes a printer unit 100, a paper feeding unit 200, a scanner unit 300, and a document conveying unit 400 which are copying machine main bodies. The scanner unit 300 is mounted on the copying apparatus main body 100, and a document transport unit 400 including an automatic document transport device (ADF) is mounted on the scanner unit 300. A control unit (not shown) for controlling the operation of each device in the color copying machine is also provided. The control unit includes a CPU, a RAM, a ROM, an I / O interface unit, and the like.

  The scanner unit 300 reads the image information of the document placed on the contact glass 32 by the reading sensor 36 and sends the read image information to the control unit. Based on the image information received from the scanner unit 300, the control unit controls a laser, an LED, and the like (not shown) disposed in the exposure device 21 of the printer unit 100 to face the photosensitive drums 40Bk, 40Y, 40M, and 40C. Then, the laser writing light L is irradiated. By this irradiation, electrostatic latent images are formed on the surfaces of the photosensitive drums 40Bk, 40Y, 40M, and 40C, and the latent images are developed into toner images through a predetermined development process.

  In addition to the exposure device 21, the printer unit 100 includes a primary transfer device 62, a secondary transfer device 22, a fixing device 25, a paper discharge device, a toner supply device (not shown), a toner supply device, and the like. The development process will be described in detail later.

  The paper feed unit 200 separates the paper cassette 43 provided in multiple stages in the paper bank 43, the paper feed roller 42 that feeds transfer paper as a recording medium from the paper feed cassette 44, and the fed transfer paper P to the paper feed path 46. A separation roller 45 that feeds out, a transport roller 47 that transports the transfer paper P to the paper feed path 48 of the printer unit 100, and the like are provided. In the present embodiment, in addition to the paper feeding unit, manual paper feeding is also possible. One sheet of the manual feed tray 51 for manual feeding and the transfer paper P on the manual tray 51 toward the manual paper feed path 53 are provided. Separation rollers 52 for separating each one are also provided on the side of the apparatus. The registration roller 49 discharges only one sheet of transfer paper P placed on the paper feed cassette 44 or the manual feed tray 51, and is positioned between the intermediate transfer belt 10 as the intermediate transfer member and the secondary transfer device 22. To the secondary transfer nip.

  As shown in FIG. 4, the intermediate transfer belt 10 has a base layer 11 made of, for example, a base layer made of a material that hardly stretches, such as a fluorine resin or a rubber material that stretches a little, and an elastic layer thereon. 12 is provided. The elastic layer 12 is made of, for example, fluorine rubber or acrylonitrile-butadiene copolymer rubber. The surface of the elastic layer 12 is coated with a coat layer 13 having good smoothness by coating, for example, a fluorine-based resin.

  In the above configuration, when copying a color image, the document is set on the document table 30 of the document conveying unit 400 or the document conveying unit 400 is opened and the document is set on the contact glass 32 of the scanner unit 300. The document feeder 400 is closed and the document is pressed. When a start switch (not shown) is pressed, the original is conveyed onto the contact glass 32 when the original is set on the original conveying unit 400, and immediately after the original is set on the other contact glass 32, the scanner unit 300 is driven to travel on the first traveling body 33 and the second traveling body 34.

  Then, the first traveling body 33 emits light from the light source and further reflects the reflected light from the document surface toward the second traveling body 34, and is reflected by the mirror of the second traveling body 34 and passes through the imaging lens 35. It puts in the reading sensor 36 and reads image information. When image information is received from the scanner unit, a laser image as described above or a development process described later is performed to form a toner image on the photosensitive drums 40Bk, 40Y, 40M, and 40C, and according to the image information. One of the four registration rollers is operated to feed the transfer paper P having a different size.

  Along with this, one of the support rollers 14, 15, 16 is rotated by a drive motor (not shown), the other two support rollers are driven to rotate, and the intermediate transfer belt 10 is rotated and conveyed. At the same time, the photosensitive drums 40Bk, 40Y, 40M, and 40C are rotated by the individual image forming units 18 to form black, yellow, magenta, and cyan single-color images on the photosensitive drums 40Bk, 40Y, 40M, and 40C, respectively. Form. Then, along with the conveyance of the intermediate transfer belt 10, the monochrome images are sequentially transferred to form a composite color image on the intermediate transfer belt 10.

  On the other hand, one of the paper feed rollers 42 of the paper feed unit 200 is selectively rotated, the transfer paper P is fed out from one of the paper feed cassettes 44, separated one by one by the separation roller 45, and put into the paper feed path 46. The transfer roller 47 is guided to a paper feed path 48 in the copying machine main body 100, and the transfer paper P is abutted against the registration roller 49 and stopped. Alternatively, the sheet feeding roller 50 is rotated to feed the transfer paper P on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual sheet feed path 53, and abutted against the registration roller 49 and stopped. Then, the registration roller 49 is rotated in time with the composite color image on the intermediate transfer belt 10, and the transfer paper P is fed into the secondary transfer nip portion where the intermediate transfer belt 10 and the roller 23 are in contact with each other. The color image is secondarily transferred under the influence of the transfer electric field and contact pressure formed on the transfer sheet P, and the color image is recorded on the transfer paper P. In general, the registration roller 49 is often used while being grounded, but it is also possible to apply a bias for removing paper dust from the sheet.

  After the image transfer, the transfer paper P is sent to the fixing device 25 by the conveying belt (secondary transfer belt) 24 of the secondary transfer device 22, and the pressure applied by the pressure roller 27 and the heat generated by the fixing belt 26 are transferred by the fixing device 25. After fixing the toner image by the application, if the switching claw 55 is in the paper discharge direction, it is discharged from the discharge roller 56 onto the paper discharge tray 57.

  Next, details of the printer unit 100 in the color copying machine of this embodiment will be described.

  FIG. 2 is an enlarged view showing a main part of the printer unit 100. The printer unit 100 is provided side by side with an intermediate transfer belt 10 supported by three support rollers 14, 15, and 16 as an intermediate transfer belt so as to face the intermediate transfer belt, and has black, yellow, magenta, and cyan on the surface. Four photosensitive drums 40Bk, 40Y, 40M, and 40C as latent image carriers each carrying one of the color toner images, and a developing unit 61Bk as developing means for forming a toner image on the surface of the photosensitive drum. , 61Y, 61M, 61C. Further, photoconductor cleaning devices 63Bk, 63Y, 63M, and 63C are provided for removing toner remaining after the primary transfer from the surface of the photoconductor drum. The four photosensitive drums 40Bk, 40Y, 40M, and 40C, the developing units 18Bk, 18Y, 18M, and 18C, and the four image forming units 18Bk, 18Y, 18M, and the photosensitive member cleaning devices 63Bk, 63Y, 63M, and 63C, The tandem image forming apparatus 20 is configured by 18C. Further, a belt cleaning device 17 for removing residual toner remaining on the intermediate transfer belt 10 after the toner image is transferred onto the transfer paper is provided on the left side of the support roller 15.

  A secondary transfer device 22 is provided on the opposite side of the intermediate transfer belt 10 from the tandem image forming device 20. In the present embodiment, the secondary transfer device 22 is configured such that a secondary transfer belt 24 is stretched between two rollers 23 and pressed against the third support roller 16 via the intermediate transfer belt 10. Then, a secondary transfer nip portion is formed, and the color toner image on the intermediate transfer belt 10 is secondarily transferred onto the transfer paper. The intermediate transfer belt 10 after the secondary transfer is prepared by the belt cleaning device 17 to remove residual toner remaining on the intermediate transfer belt 10 after image transfer, and to prepare for the image formation again by the tandem image forming apparatus 20.

  The secondary transfer device 22 described above is also provided with a transfer paper P transport function for transporting the transfer paper P after image transfer to the fixing device 25. Of course, a transfer roller or a non-contact charger may be disposed as the secondary transfer device 22, and in such a case, it is difficult to provide this transfer paper P conveyance function together.

  In the present embodiment, transfer is performed under the secondary transfer device 22 and the fixing device 25 so as to invert the transfer paper P so as to record images on both sides of the transfer paper P in parallel with the tandem image forming device 20 described above. A paper reversing device 28 is provided. As a result, after the image is fixed on one side of the transfer paper, the transfer paper path is switched to the transfer paper reversing device 28 side by the switching claw 55, and the toner image is transferred again at the secondary transfer nip after being reversed. The paper may be discharged onto the tray 57.

  Next, the tandem image forming apparatus 20 will be described.

  FIG. 3 is a partially enlarged view of the tandem image forming apparatus 20. Since the four image forming units 18Bk, 18Y, 18M, and 18C have the same configuration, the details of the configuration of one unit will be described with the four color symbols Bk, Y, M, and C omitted. The image forming unit includes a charging device 60 as a charging unit, a developing device 61, a primary transfer device 62 as a primary transfer unit, a photosensitive member cleaning device 63, around the photosensitive drums 40Bk, 40Y, 40M, and 40C. A neutralizing device 64 is provided. In the illustrated example, the photosensitive drums 40Bk, 40Y, 40M, and 40C have a drum shape in which a photosensitive organic photosensitive material is applied to a base tube such as aluminum to form a photosensitive layer. There may be.

  Although not shown, at least the photosensitive drums 40Bk, 40Y, 40M, and 40C are provided, and a process cartridge is formed by all or a part of the parts forming the image forming unit 18, and the copier main body 100 is collectively. Then, it may be detachable to improve maintenance. In addition, among the parts constituting the image forming unit 18, the charging device 60 is formed in a roller shape in the illustrated example, and contacts the photosensitive drums 40Bk, 40Y, 40M, and 40C to apply a voltage to the photosensitive drum. 40Bk, 40Y, 40M, and 40C are charged. Of course, charging can be performed by a non-contact scorotron charger.

  The developing device 61 may use a one-component developer, but in the illustrated example, a two-component developer composed of a magnetic carrier and a non-magnetic toner is used. Then, the agitation unit 66 conveys the two-component developer while stirring and supplies and adheres the two-component developer to the developing sleeve 65, and the toner of the two-component developer attached to the developing sleeve 65 is transferred to the photosensitive drum. 40Bk, 40Y, 40M, and 40C are provided, and the stirring unit 66 is positioned lower than the developing unit 67.

  The stirring unit 66 is provided with two parallel screws 68, and the two screws 68 are partitioned by a partition plate 69 except for both ends. Further, a toner density sensor 71 is provided in the developing case 70.

  The developing portion 67 is provided with a developing sleeve 65 facing the photosensitive drums 40Bk, 40Y, 40M, and 40C through the opening of the developing case 70, and a magnet 72 is fixedly provided in the developing sleeve 65. Further, a doctor blade 73 is provided with the tip approaching the developing sleeve 65. The developing sleeve 65 has a non-magnetic rotatable sleeve shape, and a plurality of magnets 72 are disposed therein. Since the magnet 72 is fixed, a magnetic force can be applied when the developer passes through a predetermined place.

  The magnet 72 has, for example, five magnetic poles N1, S1, N2, S2, and S3 in the rotation direction of the developing sleeve 65 from the position of the doctor blade 73. The developer forms a magnetic brush by the magnet 72 and is carried on the developing sleeve 65. The developing sleeve 65 is disposed in a region on the S1 side of the magnet 72 that forms a developer magnetic brush so as to face the photosensitive drums 40Bk, 40Y, 40M, and 40C.

  With the above configuration, the two-component developer is conveyed and circulated while being stirred by the two screws 68 and supplied to the developing sleeve 65. The developer supplied to the developing sleeve 65 is pumped and held by the magnet 72 to form a magnetic brush on the developing sleeve 65. The magnetic brush is trimmed to an appropriate amount by the doctor blade 73 as the developing sleeve 65 rotates. The developer that has been cut off is returned to the stirring unit 66.

  Of the developer carried on the developing sleeve 65, the toner is transferred to the photosensitive drums 40Bk, 40Y, 40M, and 40C by the developing bias voltage applied to the developing sleeve 65, and the photosensitive drums 40Bk, 40Y, 40M, The electrostatic latent image on 40C is visualized. After the visualization, the developer remaining on the developing sleeve 65 leaves the developing sleeve 65 and returns to the stirring unit 66 where there is no magnetic force of the magnet 72. When the toner concentration in the stirring unit 66 becomes light by this repetition, it is detected by the toner concentration sensor 71 and the stirring unit 66 is replenished with toner.

  The primary transfer device 62 is constituted by a roller-shaped primary transfer roller 62 and is provided by being pressed against the photosensitive drum 40 with the intermediate transfer belt 10 interposed therebetween. A conductive roller 74 is provided between the primary transfer rollers 62 in contact with the base layer 11 side of the intermediate transfer belt 10. The conductive roller 74 prevents a bias applied by each primary transfer roller 62 during transfer from flowing into the adjacent image forming units 18 via the intermediate resistance base layer 11.

  The photoconductor cleaning device 63 uses, for example, a cleaning blade 75 made of polyurethane rubber, and the front end thereof is pressed against the photoconductor drum 40. Further, in this embodiment, a contact conductive fur brush 76 whose outer periphery is in contact with the photosensitive drum 40 is rotatably provided in the direction of the arrow in order to improve the cleaning performance. Further, a metal electric field roller 77 for applying a bias to the fur brush 76 is rotatably provided in the direction of the arrow, and the tip of the scraper 78 is pressed against the electric field roller 77. Further, a collection screw 79 for collecting the removed toner is also provided.

  Residual toner on the photosensitive drum 40 is removed with the fur brush 76 that rotates in the counter direction with respect to the photosensitive drum 40 by the photosensitive member cleaning device 63 configured as described above. The toner adhering to the fur brush 76 is removed by the electric field roller 77 to which a bias that rotates in contact with the fur brush 76 in the counter direction is applied. The toner adhering to the electric field roller 77 is cleaned by the scraper 78. The toner collected by the photoconductor cleaning device 63 is brought to one side of the photoconductor cleaning device 63 by the collection screw 79 and returned to the developing device 61 by the toner recycling device 80 for reuse.

The static eliminator 64 uses a static elimination lamp, and irradiates light to initialize the surface potential of the photosensitive drum 40.

  The image forming process in the tandem image forming apparatus 20 configured as described above is performed as follows. As the photosensitive drum 40 rotates, the surface of the photosensitive drum 40 is first uniformly charged by the charging device 60, and the writing light L is irradiated to form an electrostatic latent image on the photosensitive drum 40. Thereafter, development is performed by attaching toner to the electrostatic latent image by the developing device 61 to form a toner image, and the toner image is primarily transferred onto the intermediate transfer belt 10 by the primary transfer roller 62. Residual toner is removed from the surface of the photoconductive drum 40 after the image transfer by the photoconductive cleaning device 63, and the charge is removed by the static eliminating device 64 to prepare for image formation again. On the other hand, the residual toner removed from the surface of the photosensitive drum is used again for development by a toner recycling device described later. Here, the order of colors for forming an image is not limited to the above, but varies depending on the aim and characteristics of the image forming apparatus.

  Conventionally, fluororesin, polycarbonate resin, polyimide resin, and the like have been used for the intermediate transfer belt. However, in recent years, an elastic belt in which the entire belt layer or a part of the belt is an elastic member has been used. A color image is usually formed with four colored toners. On one color image, toner layers of 1 to 4 layers are formed. The toner layer receives pressure by passing through the primary transfer (transfer from the photosensitive member to the intermediate transfer belt) and the secondary transfer (transfer from the intermediate transfer belt to the sheet), and the cohesive force between the toners increases. When the cohesive force between the toners increases, the phenomenon of missing characters in the characters and missing edges in the solid portion image tends to occur. Since the resin belt has a high hardness and does not deform according to the toner layer, the toner layer is easily compressed, and the character dropout phenomenon is likely to occur. Recently, there is an increasing demand for forming full-color images on various papers, for example, Japanese paper, intentionally irregularities, and forming images on paper. However, a paper with poor smoothness is liable to generate toner and voids at the time of transfer, and transfer loss is likely to occur. When the transfer pressure at the secondary transfer portion is increased to improve the adhesion, the condensing power of the toner layer is increased, and the above-mentioned character void is generated.

  Since the transfer of a color image using a resin belt includes such problems, the use of the elastic belt described above is increasing. The elastic belt is deformed at the transfer portion corresponding to the toner layer and the paper having poor smoothness. In other words, since the elastic belt deforms following local irregularities, the paper does not have excessive flatness and does not excessively increase the transfer pressure with respect to the toner layer. In contrast, a transfer image with excellent uniformity can be obtained.

  FIG. 6 is a schematic configuration diagram illustrating an example of an intermediate transfer unit of the indirect transfer type tandem type image forming apparatus according to the present embodiment. In this embodiment, a scale (also referred to as a belt scale) 10a is provided on the intermediate transfer belt 10 as shown in FIG. The scale 10a is read by a belt scale sensor 10b provided facing the scale 10a. The motor control unit 10c detects the speed of the belt surface from the output value, calculates an ideal belt speed from the detected speed, and feeds back to the belt drive motor 10d to enable accurate belt driving. Yes. The belt drive motor 10d drives the intermediate transfer belt drive roller 14 to rotate the intermediate transfer belt 10 in a predetermined direction. The belt scale 10a provided on the surface of the intermediate belt 10 is provided with a scale slit 10e. The belt scale sensor 10b is laid out at a position where the belt scale slit 10e can be read. The belt scale 10a is provided on the opposite surface of the photosensitive drum 40 in FIG. 6, but may be anywhere as long as the belt scale can be read.

  FIG. 8 is a diagram showing the relationship between the belt scale sensor 10b and the belt scale 10a. In this embodiment, the belt scale sensor 10b uses a reflection type optical sensor having a pair of light emitting / receiving elements 10b-1 and 2, and the reflectance is different between the slit portion 10e of the scale on the belt 1 scale and other portions. It is configured. As the output value of the belt scale sensor 10b, a binary signal of High or Low is output depending on the difference in the reflectance of the scale as shown in the figure. For example, when the belt scale sensor 10a is of a type that outputs a High signal when the light receiving element 10b-1 receives light, in the example of FIG. 9, the reflectance of the slit portion 10e of the belt scale 10a is higher than that of other portions. If it is a material, the output signal from the belt scale sensor 10b is an output during the period t when the slit portion 10e passes the sensor 10a, and the detection range of the sensor 10a is increased as the intermediate transfer belt 10 rotates. Depending on the presence or absence of the slit portion 10e passing therethrough, the output of the sensor 10a is repeated as shown in High and Low. Accordingly, the surface speed of the intermediate transfer belt 10 can be detected by obtaining the time T from the time when the signal changes from Low to High until the next signal changes from Low to High. These are merely examples, and it goes without saying that the type of sensor, the type of scale, the detection method, and the like may be different as long as the belt scale can be detected.

  FIG. 9 is a control block diagram showing an example of a control circuit when the belt scale sensor 10b having the configuration shown in FIG. 8 is used. As described above with reference to FIG. 6, the motor control unit 10c first controls the belt drive motor 10d to rotate at a basic speed. By rotating the belt drive motor 10d, the intermediate transfer belt 10 rotates and the scale 10a on the belt surface also rotates. Therefore, the scale 10a is read by the belt scale sensor 10b, and the value is controlled by the motor. This is fed back to the unit 10c. In the motor control unit 10c, if the fed back speed is the same as the basic speed, the control is performed at the basic speed as it is. If there is a difference in speed, the difference is calculated and added to the basic speed. To control the motor.

FIG. 10 is a flowchart showing a control procedure executed by the motor control unit 10c. In this control procedure, the motor control unit 10c first turns on the motor to rotate at the basic speed V with respect to the belt drive motor 10d (step S1). Thereafter, the next control is repeated until the timing for turning off the motor occurs (step S2-Y). In other words, the motor control unit 10c detects the feedback output from the belt scale sensor 10b and grasps the speed V ′ of the currently rotating belt surface. (Step S4). Next, the speed V ′ is compared with the basic speed V (step S5). In this comparison,
V = V '
If so (step S6-N), since it can be determined that the belt surface is rotating at the same speed as the basic speed V, the control is performed at the basic speed as it is (return to step S2). if,
V ≠ V '
If so (step S6-Y), the belt surface speed is different from the basic speed V.

In this case, the difference V ″ between the basic speed V and the surface speed V ′ is calculated (step S7),
V ''> 0
If so (step S8-Y), it can be determined that the belt surface speed V ′ is slower than the basic speed V, so the motor is controlled at a speed obtained by adding V ″ to V ″ (step S9). → S2). In contrast,
V ''<0
If so, it can be determined that the belt surface speed V ′ is faster than the basic speed V, so the motor is controlled at a speed obtained by subtracting V ″ from the basic speed V (step S10-N → S2). By repeating such a procedure, it becomes possible to operate the belt surface speed constantly at the basic speed.

  The speed fluctuation (difference between the basic speed and the surface speed) of the intermediate transfer belt described above is caused by several factors. The fluctuation frequency of the speed fluctuation includes high frequency and low frequency as shown in the characteristic diagram of FIG. There are fluctuations. That is, as shown in FIG. 11, when the rotation time of the belt is taken on the horizontal axis and the speed fluctuation amount is taken on the vertical axis, and the target speed that is the basic speed (ideal speed) is shown in the center, the intermediate transfer belt 10 is 1 While rotating, the fluctuation of the low frequency component whose speed changes relatively slowly and the fluctuation of the high frequency component whose speed changes instantaneously coexist. With the conventional image forming apparatus described above, it is possible to correct the speed fluctuation of these two frequency components. However, in order to correct both the low frequency component and the high frequency component, it is necessary to adjust the correction frequency range to the high frequency side, and a highly accurate and complicated control circuit is required. This is because the correction accuracy has a problem with the control loop period and the detection accuracy of the sensor.

  If the series of controls shown in FIG. 12 is a motor drive feedback loop period A, as shown in FIG. 13, if the control loop period A is sufficiently earlier than the low frequency period C, as shown in FIG. The amount can be detected, and at the end of one loop, the amount of speed deviation can be corrected and returned to the target speed.

  That is, A >> C is sufficient. As can be seen from FIG. 12, the motor drive feedback loop period A is read by the belt scale sensor (step S101), phase detection (step S102), phase comparison with the target value (step S103), deviation amount detection (step S104), and control. This is a loop of amount calculation (step S105), addition to the target value (step S106), and motor control (step S107). However, since the speed fluctuation cannot be detected for the high frequency period B that is earlier than the control loop period A, it cannot be corrected. That is, when B> A, control is impossible. Therefore, in order to correct the high-frequency cycle B, it is necessary to configure the control loop cycle with a cycle earlier than that.

  In general, in order to be within the control range, it is necessary to perform correction with a period of several tens of times the target correction frequency. Therefore, in order to correct the high-frequency cycle B, the control loop cycle must be considerably shortened. For this purpose, it is necessary to suppress the accuracy and variation of the constituent parts. Accordingly, it is necessary to improve the accuracy of the belt scale sensor 10b to be detected. Further, the scale 10a on the belt 10 needs to have high resolution and high accuracy, which makes it difficult to process. Therefore, in order to achieve these, it becomes necessary to construct a high-cost system. The present invention focuses on this point and limits the correction target to fluctuations in the low frequency period.

  In general, the high frequency period is several kHz or more, while the low frequency period is several tens of Hz or less, so that a sufficiently low-cost system can be constructed. A description will be given below of not correcting the speed fluctuation in the high frequency cycle.

  The tandem type image forming apparatus cannot transfer toner to the same position on the intermediate transfer belt 10 at the same time due to its configuration. That is, as shown in FIG. 14, the four photosensitive drums 10 are arranged with a predetermined distance from each other. Therefore, after being transferred from the first photosensitive drum 40C, the four photosensitive drums 10 are transferred from the next photosensitive drum 40M. In the meantime, a time difference will occur. For example, when printing four color dots on the same position on the transfer paper P, first, the toner transferred from the first photosensitive drum 40C onto the intermediate transfer belt 10 is rotated by the rotation of the intermediate transfer belt 10. The second color is transferred onto the intermediate transfer belt 10 for the first time when the transfer position on the next photosensitive drum 10M is reached. This means that there is a time difference from the first transfer to the next transfer. Thereafter, the third color and the fourth color are sequentially transferred with a time difference, and the four colors are transferred to the same position for the first time.

  At this time, if a speed fluctuation with a low frequency period slower than the transfer time difference between the adjacent photosensitive drums 40 occurs, the next transfer position is reached later or earlier from the first transfer position by the speed fluctuation. As a result, the transfer position is different, and as a result, the image is affected as a color shift. However, even if a speed fluctuation of a high frequency cycle with a period faster than the time difference from the first transfer position to the next transfer position occurs, if the speed returns to the original when the next transfer position is reached, It will not appear as a displacement. Accordingly, even if there is a slight misalignment, the color misregistration is hardly noticeable on the image. In view of the above, it is obvious that the effect can be sufficiently exerted in this type of image forming apparatus.

  As a factor that the speed fluctuation appears as a low frequency cycle, a factor caused by one belt cycle is large. This is because the image forming apparatus is of a tandem type and forms an image on a relatively large transfer paper such as an A3 size, and therefore, it is necessary to increase the peripheral length of the intermediate transfer belt 10. This is because it takes much longer time to complete one cycle than the time period of the belt speed control loop. For this reason, generally, a factor that causes an increase or decrease in speed during one rotation of the belt 10 due to a belt thickness deviation or a mechanical layout stacking tolerance affects the image.

  FIG. 15 is a diagram showing the relationship between the fluctuation frequency, the speed fluctuation amount, and the factors. From this figure, it can be seen that the frequency due to one belt period has a great influence on the speed fluctuation amount, and the influence of the frequency due to one belt period is extremely small. As a factor of the speed fluctuation of the high frequency period not caused by one round of the belt, there is a pitch fluctuation of the gear teeth for driving transmission. In the image forming apparatus, the target factors to be corrected are limited to factors caused by one belt revolution. As a result, speed fluctuations in a high frequency cycle that do not appear on the image can be ignored, so that a low-cost system can be configured.

  In the present invention, attention is paid to the thickness unevenness of the intermediate transfer belt as a factor causing the speed fluctuation of the intermediate transfer belt, and the speed fluctuation due to this is corrected.

Hereinafter, this mechanism will be described.

  FIG. 16 is a diagram showing the outline of the intermediate transfer unit in a case where the thickness of the intermediate transfer belt 10 is uneven. Here, in order to simplify the description, the configuration of the rollers is two, that is, a driving roller and a driven roller, but the configuration is the same for two or more rollers. Further, in order to simplify the explanation, the belt thickness unevenness shown in the figure is one thick portion and one thin portion, but the same is true in the case where there are a plurality of such unevennesses.

In the figure, the intermediate transfer belt 10 is held by a driving roller 14 and a driven roller 15. The intermediate transfer belt 10 is rotated in the direction of the arrow in the drawing by the driving roller 14. The point D on the surface of the intermediate transfer belt 10 is the thickest part of the belt, and the point E shows the thinnest part. The state of the belt when the point D is at the illustrated position on the drive roller 14 side and the point E is at the illustrated position on the driven roller 15 side is indicated by a solid line, the belt 10 rotates, and conversely, the D point is the driven roller 15. The state of the belt when the point E is at the position shown on the drive roller 14 side at the position shown on the side is indicated by a broken line. The thickness of the belt when the point D is on the driving roller side is X, and the thickness of the belt when the point E is on the driving roller side is x. That is, here
X> x
It is. Further, since the radius of the driving roller 14 does not change, the belt rotation radii from the center point of the driving roller 14 to the points D and E that are the belt surface are R and r, respectively, and the difference between X−x and X−x Be the same. That is,
(R−r) = (X−x)
It becomes. Here, the belt surface speeds at the points D and E are different from each other as described above, so that the point D is faster than the point E. This means that when the belt 10 rotates and the portion D where the thickness of the belt 10 is thicker than the other portions comes to the position of the driving roller 14, the surface speed of the belt 10 becomes the highest, and then Further, as the belt 10 rotates, the speed gradually decreases. When the thinnest portion E of the belt 10 reaches the position of the driving roller 14, the belt surface speed becomes the slowest. Therefore, this difference appears as belt speed unevenness.

  In general, it is impossible to make all the belt thickness uniform from the standpoint of belt manufacture and process. For this reason, this speed unevenness always occurs. Furthermore, since the thickness unevenness has a relatively small number of irregularities, the belt speed unevenness appears as a low frequency cycle. Therefore, as described above, the position shifts and the color appears on the image. This belt thickness unevenness is usually several Hz or less because of the accuracy in the manufacturing process. Therefore, by focusing attention on this factor, it is possible to configure a lower cost system. Further, by limiting the frequency to be corrected, the phase detection range in the feedback control can naturally be limited, and as a result, phase comparison with respect to the target speed and speed deviation amount detection can be performed with higher accuracy. As a result, more stable speed control can be performed.

  Further, as a factor causing the speed fluctuation of the intermediate transfer belt 10, there is an eccentricity of the driving roller 14 of the intermediate transfer belt 10. In this embodiment, the speed fluctuation due to the eccentricity of the drive roller 14 is corrected. Hereinafter, this mechanism will be described.

  FIG. 17 is a diagram showing a simplified outline of the intermediate transfer unit when the intermediate transfer belt drive rollers 14 and 15 have eccentricity. The basic configuration is the same as that shown in FIG. However, as shown in FIG. 17, when the drive roller 14 is eccentric, the radius from the center to the belt contact surface when the drive roller 14 swells most in the direction of the belt contact surface is R, and conversely, the belt contact surface. Let r be the radius from the center of the drive roller to the belt contact surface when it swells most on the opposite side. Assuming that the belt thickness is uniform (X = x), the belt surface speed will produce a speed difference of (R−r). Then, the belt surface speed fluctuation is generated by the speed difference. Generally, the radius of the drive roller 14 is often large, and this speed fluctuation appears as a relatively low frequency cycle. Color irregularities appear on the image. Since this low frequency period is generally about several Hz to several tens Hz, correcting this reduces the correction error due to the limitation of the correction frequency and realizes more stable speed control at a lower cost. Can do.

  There are a variety of factors that induce belt speed fluctuation. Among them, correction of speed fluctuation due to a low frequency cycle is as described above. At this time, what is actually the cause of the low frequency cycle depends on the system configuration of the target system, for example, the belt material, belt circumference, number of rollers, photoreceptor pitch, component accuracy, etc. Come different. Therefore, it may be difficult to correct each factor. In general, speed fluctuations often appear on an image at low frequencies, and it is sufficient that these can be corrected to about 100 Hz.

  FIG. 18 is a diagram showing the relationship between the speed fluctuation amount with respect to the fluctuation frequency and the influence on the image. As shown in this figure, if the correction range is limited to about 0 to 100 Hz, the configuration of the feedback system can be realized at low cost.

  FIG. 19 is a block diagram showing an example of a control circuit for correcting the fluctuation frequency according to the present embodiment. In this block diagram, the motor control unit 10 in FIG. 10 includes a correction controller 10f, a target speed input unit 10g, a drive circuit 10h, and an encoder 10i. The correction controller 10f includes a filter unit 10f-1 and a proportional gain unit 10f-2, and the encoder signal of the encoder 10i for detecting the rotation state of the motor 10d and the output from the belt scale sensor 10b together with the target belt position signal 10k. The result is input to the first adder 10j, and the added result is input to the correction controller 10f. That is, with respect to the target belt position information, the belt scale sensor signal and the encoder signal are input as error information to the correction controller 10f, and the internally calculated output is input to the second adder 10l and input separately. Correction is performed on the target speed (reference drive frequency) 10g of the motor 10d. The rate at which the scale sensor signal and encoder signal are fed back is controlled by the sequence and mode. In the case of the encoder signal 100%, the belt position information is not known, and the deviation of the belt itself cannot be corrected. However, the motor control accuracy can be increased by increasing the resolution of the encoder (number of pulses per revolution). In this embodiment, the corrected PWM signal output is input to the drive circuit 10h, and the motor 10d is driven while controlling the speed.

  As described above, the correction controller 10f includes the filter unit 10f-1 and the proportional gain unit 10f-2. The filter unit 10f-1 sets a filter coefficient according to the control band and filters the error signal. Actually cuts over a certain frequency. The proportional gain unit 10f-2 sets the proportional gain according to the control band and determines the magnitude of the correction amount. Actually, the higher the control band, the faster it is necessary to correct the fluctuation, so the gain is increased. In this embodiment, the correction controller 10f is composed of the filter unit 10f-1 and the proportional gain unit 10f-2, but all algorithm controllers having parameters are included. Further, the type of motor is not limited to a DC servo motor, and a speed-controllable motor such as a pulse motor is a target.

  FIG. 20 is a flowchart showing a control procedure of control performed by the motor control unit 10c of FIG. In this control, it is not necessary to perform belt position control at the time of acceleration when the belt drive motor 10d is started, and the scale sensor signal of the intermediate transfer belt which shows unstable behavior is not used at the time of start. Control is performed only by a signal (step S201). By this control, the motor speed is accelerated to the vicinity of the target value until the rise ends (step S202-N), and when it is determined that the rise ends (step S202-Y), the steady speed control is switched to the control based on the scale sensor signal and the encoder signal. (Step S204).

  FIG. 21 is a flowchart showing a determination procedure for determining the end of rising in the flowchart of FIG. After detecting the current speed V during the rising period (step S301), it is compared with the range of the target speed Vt ± E (step S202). If it is out of the range (step S202-N), the rising operation is continued (step S202). S203)), if it is within the range, it is determined that the rising edge has ended (step S204).

  FIG. 22 is a characteristic diagram showing a speed curve from the start of the motor in FIG. As can be seen from the figure, the speed V of the belt drive motor 10d is accelerated toward the target speed Vt, and it is determined that the rising end has been completed at Tc that has entered the range of Vt ± E, and the control is switched from encoder control to scale sensor control and encoder control. . Thereby, the process of step S204 in FIG. 20 is executed.

As described above, according to this embodiment,
(1) By performing feedback control on the intermediate transfer belt drive motor by the encoder signal and the belt scale sensor signal provided in the motor itself to correct the belt speed, the correction control is performed only by the encoder signal when the motor starts up. It is possible to prevent a start-up failure at startup.
(2) At the motor steady speed, correction control is performed using the encoder signal and the scale sensor signal. That is, in addition to the stable motor speed control by the encoder signal, the belt speed fluctuation can be suppressed by performing the speed control for correcting the belt fluctuation by the scale sensor signal.
(3) When the motor starts up, the correction control is switched when it reaches within a certain range with respect to the target speed of the steady speed. Therefore, it becomes possible to add to the correction control when the scale sensor output is stable. Speed fluctuation at the time can be prevented.
There is an effect.

1 is a configuration diagram of a color copying machine that is an image forming apparatus using an electrophotographic system according to an embodiment of the present invention. FIG. 2 is an enlarged view showing a main part of a printer unit in FIG. 1. FIG. 3 is a partially enlarged view of the tandem image forming apparatus in FIG. 2. FIG. 3 is a cross-sectional view illustrating a configuration of an intermediate transfer belt. 1 is a schematic configuration diagram illustrating an example of a direct transfer tandem color image forming apparatus. 1 is a schematic configuration diagram illustrating an example of an intermediate transfer unit of an indirect transfer tandem image forming apparatus according to an embodiment of the present invention. FIG. 6 is a plan view showing a state of a scale provided on the intermediate transfer belt. It is a figure which shows the relationship between a belt scale sensor and a scale. It is a control block diagram which shows an example of the control circuit at the time of using the belt scale sensor of FIG. It is a flowchart which shows the control procedure performed with the motor control part of FIG. It is a characteristic view which shows the state of the fluctuation speed in which the fluctuation | variation of a high frequency and a low frequency exists. It is a block diagram which shows an example of the control loop of motor control. It is a figure which shows the correction principle of this invention. FIG. 3 is a diagram illustrating a relationship between a tandem intermediate transfer belt, a photosensitive drum, and an image. It is a figure which shows the relationship of the fluctuation frequency over the belt 1 round, speed fluctuation amount, and its factor. FIG. 3 is a diagram illustrating a simplified outline of an intermediate transfer unit when there is a thickness unevenness in the intermediate transfer belt. FIG. 3 is a diagram illustrating a simplified outline of an intermediate transfer unit when an intermediate transfer belt drive roller has eccentricity. It is a figure which shows the relationship between the speed fluctuation amount with respect to a fluctuation frequency, and the influence on an image. It is a block diagram which shows an example of the control circuit for correct | amending the fluctuation frequency which concerns on this embodiment. It is a flowchart which shows the control procedure of the control performed by the motor control part of FIG. It is a flowchart which shows the judgment procedure of the rise end judgment in the flowchart of FIG. It is a characteristic view showing the speed curve from the motor starting in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Intermediate transfer belt 10b Belt scale sensor 10c Motor controller 10d Belt drive motor 10e Scale slit 10f Correction controller 10h Drive circuit 21 Exposure device 22 Secondary transfer device 25 Fixing device 40 Photosensitive drum 62 Primary transfer device 100 Printer unit 200 Paper feed unit 300 Scanner unit 400 Document transport unit

Claims (9)

An endless belt that is rotationally driven by a motor;
A scale formed on the belt;
Reading means for reading the scale;
Control means for feedback-controlling the motor based on a read signal of the scale read by the reading means;
In a belt conveyance device having
Comprising detection means for detecting the rotational speed of the motor;
The belt conveyance device according to claim 1, wherein the control means corrects the rotation speed of the motor based on the detection signal when the rotation of the motor rises.   2. The control unit according to claim 1, wherein when the motor is driven at a steady speed, the control unit corrects the rotation speed of the motor based on a read signal of the scale and a detection signal of the detection unit. Belt conveyor.   The control means, at the time of starting up the motor, from the correction by the detection signal when reaching a speed within a preset range with respect to the target speed of the steady speed, the scale read signal and the detection signal of the detection means The belt conveyance device according to claim 2, wherein the correction is switched to correction based on the above.   4. The belt according to claim 1, wherein a slit is formed in the scale, and the reading unit reads the slit forming portion and the non-slit portion and outputs a reading signal. Conveying device.   The belt conveying apparatus according to claim 1, wherein the detection unit outputs a detection signal by detecting an encoder that rotates in synchronization with rotation of the motor. A belt conveying device according to any one of claims 1 to 5,
A transfer device comprising transfer means for transferring an image to the endless belt.   7. The transfer apparatus according to claim 6, wherein the endless belt is an intermediate transfer belt that further transfers an image once transferred onto a recording sheet and superimposes images of a plurality of colors. The transfer means is a first transfer means for transferring images on a plurality of photoconductors arranged side by side along the moving direction of the intermediate transfer belt to the same position of the intermediate transfer belt;
8. The transfer apparatus according to claim 7, further comprising: a second transfer unit that transfers an image on which a plurality of color images are superimposed by the first transfer unit to a recording sheet.   An image forming apparatus comprising the transfer device according to claim 6.

Images