JP4949671B2 - Belt drive control device, belt device and image forming apparatus - Google Patents

Description

  The present invention relates to a belt drive control device that performs drive control of a belt that is stretched over a plurality of support rotating bodies, a belt device that uses the belt drive control device, and an image forming apparatus that uses the belt device. is there.

  Conventionally, as an apparatus that uses such a belt, there is an image forming apparatus that uses a belt such as a photosensitive belt, an intermediate transfer belt, and a paper conveying belt. In such an image forming apparatus, high-precision drive control of the belt is essential to obtain a high-quality image. In particular, a direct transfer tandem type image forming apparatus that is excellent in image forming speed and suitable for downsizing requires high-precision drive control of a conveyance belt that conveys a recording sheet as a recording material. In this image forming apparatus, a recording sheet is transported using a transport belt, and sequentially passes through a plurality of image forming units that form different monochrome images arranged along the transport direction. As a result, it is possible to obtain a color image by superimposing single color images on a recording sheet.

Here, an example of an electrophotographic direct transfer type tandem type image forming apparatus will be specifically described with reference to FIG. In this image forming apparatus, for example, image forming units 18Y, 18M, 18C, and 18K that form monochrome images of yellow, magenta, cyan, and black are sequentially arranged in the conveyance direction of the recording paper. The electrostatic latent images formed on the surfaces of the photosensitive drums 40Y, 40M, 40C, and 40K by a laser exposure unit (not shown) are developed by the image forming units 18Y, 18M, 18C, and 18K, thereby developing toner images ( A visible image is formed. Then, after being sequentially superimposed and transferred onto a recording paper (not shown) that is attached to the transport belt 210 and transported by an electrostatic force, the toner is melted and pressed by the fixing device 25, whereby a color image is formed on the recording paper. It is formed. The conveyor belt 210 is stretched around the driving roller 215 and the driven roller 214 arranged in parallel with each other with an appropriate tension. The drive roller 215 is rotationally driven at a predetermined rotational speed by a drive motor (not shown), and accordingly, the transport belt 210 also moves endlessly at a predetermined speed. The recording paper is supplied to the image forming units 18Y, 18M, 18C, and 18K of the transport belt 210 at a predetermined timing by the paper feed mechanism, and is moved and transported at the same speed as the transport speed of the transport belt 210. The image forming unit sequentially passes.
In such an image forming apparatus, color shift occurs if the moving speed of the recording paper, that is, the moving speed of the conveying belt 210 is not maintained at a constant speed. This color misalignment occurs when the transfer positions of the single color images superimposed on the recording paper are relatively misaligned. When color misalignment occurs, for example, a fine line image formed by overlapping images of multiple colors appears blurred, or around the outline of a black character image formed in a background image formed by overlapping images of multiple colors White spots may occur on the screen.
As shown in FIG. 14, the single color images formed on the surfaces of the photosensitive drums 40Y, 40M, 40C, and 40K of the image forming units 18Y, 18M, 18C, and 18K are temporarily sequentially placed on the intermediate transfer belt 10. There is also a tandem type image forming apparatus that employs an intermediate transfer method in which the images are transferred so as to overlap each other and then collectively transferred onto a recording sheet. Also in this apparatus, if the moving speed of the intermediate transfer belt 10 is not maintained at a constant speed, a color shift similarly occurs.

  In addition to the tandem type image forming apparatus described above, a belt as an image carrier such as a recording material conveyance member that conveys a recording material, or a photosensitive member or an intermediate transfer member that carries an image transferred to the recording material. In the image forming apparatus using the belt, banding occurs if the moving speed of the belt is not maintained at a constant speed. This banding is image density unevenness caused by the belt moving speed becoming faster or slower during image transfer. That is, the image portion transferred when the belt moving speed is relatively high has a shape that is stretched in the belt circumferential direction from the original shape, and conversely, the image transferred when the belt moving speed is relatively slow. The portion has a shape reduced in the belt circumferential direction rather than the original shape. As a result, the density of the stretched image portion is reduced, and the density of the reduced image portion is increased. As a result, image density unevenness occurs in the belt circumferential direction, and banding occurs. This banding is noticeable to human eyes when forming a light monochromatic image.

  The belt moving speed varies depending on various causes. Among the causes, in the case of a single layer belt, there is belt thickness unevenness in the belt circumferential direction. This unevenness in the belt thickness is caused by, for example, uneven thickness in the belt circumferential direction seen in a belt produced by a centrifugal firing method using a cylindrical mold. When such uneven belt thickness exists in the belt, the belt moving speed increases when a portion with a thick belt is wound around the driving roller that drives the belt, and conversely when the portion with a thin belt is wound. The moving speed becomes slow. As a result, the belt moving speed varies. Hereinafter, the reason will be specifically described.

  FIG. 15 is a graph showing an example of belt thickness unevenness (belt thickness deviation distribution) in the circumferential direction of the intermediate transfer belt 10 used in the image forming apparatus as shown in FIG. The horizontal axis of this graph is obtained by replacing the length of one belt circumference (belt circumference) with an angle of 2π [rad]. The vertical axis represents the deviation value of the belt thickness with reference to the average belt thickness (100 [μm]) in the belt circumferential direction (reference value 0). Hereinafter, in the belt having such belt thickness unevenness, the deviation distribution for one round in the belt circumferential direction, which is a problem in the present invention, is referred to as belt thickness fluctuation. Here, the terms “belt thickness unevenness” and “belt thickness fluctuation” used in this specification will be described. First, “belt thickness unevenness” refers to the belt thickness deviation distribution measured by a film thickness measuring instrument, etc., and there is belt thickness unevenness in the belt circumferential direction (conveyance path direction) and depth direction (roller axis direction). To do. On the other hand, “belt thickness fluctuation” means that the belt rotation speed of the driven roller relative to the rotational angular speed of the drive roller and the rotational angular speed of the driven roller relative to the belt conveyance speed are affected when the belt drive control device is mounted. 2 shows a belt thickness deviation distribution resulting from the above.

FIG. 16 is an enlarged view of the belt portion wound around the drive roller as viewed from the axial direction of the drive roller.
The moving speed of the belt 103 is determined by the distance from the roller surface to the belt pitch line, that is, the pitch line distance (hereinafter referred to as “PLD (Pitch Line Distance)”). In the PLD, when the belt 103 is a single-layer belt made of a uniform belt material and the absolute values of the degree of expansion and contraction between the inner peripheral surface side and the outer peripheral surface side of the belt 103 are substantially the same, Is equivalent to the distance between the belt inner peripheral surface, that is, the roller surface. Therefore, in the case of a single-layer belt, the relationship between the PLD and the belt thickness is substantially constant, so that the moving speed of the belt 103 can be determined by the belt thickness variation. However, in a belt composed of a plurality of layers and the like, the stretchability differs between the hard layer and the soft layer. As a result, the distance between the position shifted from the center in the belt thickness direction and the roller surface becomes PLD. Further, the PLD may change depending on the belt winding angle with respect to the driving roller 105.

“PLD _ave ” in the formula shown in the above equation 1 is an average value of PLD over one belt revolution. For example, in the case of a single layer belt having an average thickness of 100 [μm], PLD _ave is 50 [μm]. Further, “f (d)” is a function indicating the fluctuation of the PLD over one belt revolution. Here, “d” indicates the position from the reference point on the belt circumference (phase when the belt circumference is 2π). f (d) is a periodic function having a high correlation with the belt thickness deviation value shown in FIG. If the PLD fluctuates in the belt circumferential direction, the rotational angular velocity or rotational angular displacement of the driven roller with respect to the rotational angular velocity or rotational displacement of the driving roller, or the belt traveling speed or the belt traveling distance with respect to the belt traveling speed or the belt traveling distance. Will fluctuate.

以下、本明細書において、上記数２に示す式中{ }内をローラ実効半径といい、その定常部分（ｒ＋ＰＬＤ_ave）をローラ実効半径Ｒとする。そして、ｆ（ｄ）をＰＬＤ変動という。 The relationship between the belt moving speed V and the rotational angular speed ω of the driving roller 105 is expressed by the following equation (2). “R” in this equation is the radius of the drive roller 105. In addition, the degree of influence of f (d) indicating the fluctuation of the PLD on the relationship between the belt moving speed or belt moving distance and the rotational angular velocity or rotational angular displacement of the roller varies depending on the contact state of the belt with the roller and the winding amount. There is a case. This degree of influence is expressed by a PLD fluctuation effective coefficient κ.

Hereinafter, in the present specification, the inside of {} in the formula shown in Equation 2 is referred to as the effective roller radius, and the steady portion (r + PLD _ave ) is referred to as the effective roller radius R. F (d) is referred to as PLD fluctuation.

From the equation shown in the above equation 2, it can be seen that the presence of the PLD fluctuation f (d) changes the relationship between the belt moving speed V and the rotational angular speed ω of the driving roller 105. That is, even if the driving roller 105 rotates at a constant rotational angular velocity (ω = constant), the moving speed V of the belt 103 changes due to the PLD fluctuation f (d). Here, for example, in the case of a single layer belt, when a belt portion thicker than the average belt thickness is wound around the driving roller 105, the PLD fluctuation f (d) having a high correlation with the thickness deviation of the belt 103 takes a positive value, Roller effective radius increases. Therefore, even if the drive roller 105 rotates at a constant rotational angular velocity (ω = constant), the belt moving speed V increases. Conversely, when a belt portion thinner than the average belt thickness is wound around the drive roller 105, the belt thickness fluctuation f (d) takes a negative value, and the effective roller radius decreases. Therefore, even if the drive roller 105 rotates at a constant rotational angular velocity (ω = constant), the belt moving speed V decreases.
Therefore, even if the rotational angular velocity ω of the driving roller 105 is constant, the moving speed of the belt 103 is not constant due to the PLD fluctuation f (d). Therefore, even if the driving of the belt 103 is controlled only from the rotational angular velocity ω of the driving roller 105, the belt 103 cannot be driven at a desired moving speed.

Further, the relationship between the belt moving speed V and the rotational angular velocity of the driven roller is the same as the relationship between the belt moving speed V and the rotational angular velocity ω of the driving roller 105 described above. That is, when the rotational angular velocity of the driven roller is detected by a rotary encoder or the like and the belt moving velocity V is obtained from the detected rotational angular velocity, the equation shown in the above equation 2 can be used. Therefore, for example, in the case of a single-layer belt, when a belt portion thicker than the average belt thickness is wound around the driven roller, as in the case of the driving roller 105, the PLD fluctuation f (d ) Takes a positive value, and the roller effective radius increases. Therefore, even if the belt 103 moves at a constant moving speed (V = constant), the rotational angular speed of the driven roller decreases. On the contrary, when the belt portion thinner than the average belt thickness is wound around the driven roller, the PLD fluctuation f (d) takes a negative value and the effective roller radius decreases. Therefore, even if the belt 103 is moving at a constant moving speed, the rotational angular speed of the driven roller increases.
Therefore, even if the moving speed of the belt 103 is constant, the rotational angular speed of the driven roller is not constant due to the PLD fluctuation f (d). Therefore, even if it is attempted to control the driving of the belt 103 only from the rotational angular velocity of the driven roller, the belt 103 cannot be driven at a desired moving speed.

As an apparatus capable of performing belt drive control in consideration of such PLD fluctuation f (d), there are image forming apparatuses described in Patent Document 1 and Patent Document 2.
In Patent Document 1, before a belt formed by a centrifugal molding method in which PLD fluctuations are likely to be generated by a sine wave over one circumference of the belt is incorporated into the apparatus main body, a thickness profile (belt thickness unevenness) in the entire belt circumference in advance in the manufacturing process An image forming apparatus is disclosed in which data is measured and the data is stored in a flash ROM. In this image forming apparatus, a reference mark serving as a home position, which is a reference position for matching the phase between the thickness profile data of the entire circumference and the actual belt thickness unevenness, is attached and detected based on the position. The belt drive control is performed so as to cancel the fluctuation of the belt moving speed due to the belt thickness fluctuation.
Patent Document 2 discloses an image forming apparatus that detects periodic fluctuations in belt movement speed by forming a detection pattern on a belt and detecting the pattern with a detection sensor. In this image forming apparatus, the rotational speed of the drive roller is controlled so as to cancel the detected fluctuations in the periodic belt moving speed.

JP 2000-310897 A Japanese Patent No. 3186610

However, the image forming apparatus described in Patent Document 1 requires a measuring process for measuring belt thickness unevenness in the belt manufacturing stage, and a highly accurate belt thickness measuring instrument is required in the measuring process. Therefore, there is a problem that the manufacturing cost increases significantly. In addition, when a belt is replaced with a new one, there is a problem that it is necessary to input thickness profile data unique to the new belt to the apparatus. Furthermore, since this image forming apparatus uses uneven belt thickness without using the PLD fluctuation f (d), accurate belt drive control is possible in the case of a single-layer belt, but in the case of a multi-layer belt. Accurate belt drive control is not possible.
Further, in the image forming apparatus described in Patent Document 2, it is necessary to form a detection pattern for at least one round of the belt on the belt in order to detect fluctuations in the belt moving speed. Therefore, there is a problem that a large amount of toner is consumed for forming this detection pattern. In particular, in order to detect fluctuations in belt movement speed with higher accuracy, if the average value of belt movement speed fluctuation information for multiple belt rotations is to be grasped as belt movement speed fluctuations, detection for multiple belt rotations is required. Therefore, the problem of toner consumption becomes more serious.

The present applicant has proposed a belt drive control device that can solve these problems in Japanese Patent Application No. 2005-230537 (hereinafter referred to as “prior application”).
More specifically, when the present inventors moved the belt endlessly due to the difference in the size of the diameter of the support rotating body, the winding angle of the belt with respect to the support rotating body, the material of the belt, the layer structure of the belt, etc. It has been found that the proportion of the PLD fluctuation component generated in the rotational angular velocity of the support rotator is different. That is, it has been found that when two rotating supports rotate with respect to the same belt, the magnitudes of the PLD fluctuations detected as the rotational angular velocity fluctuations of the respective rotating supports differ. If this is utilized, PLD fluctuation | variation can be specified from the rotation angle displacement or rotation angular velocity of two support rotary bodies. Therefore, based on the detection result of the rotational angular displacement or rotational angular velocity of these two supporting rotating bodies, the rotation control of the driving supporting rotating body is performed so that the fluctuation of the belt moving speed caused by the PLD fluctuation in the circumferential direction of the belt becomes small. It can be performed.
And in the invention which concerns on the said prior application, PLD fluctuation | variation is specified from the detection result of the rotation angle displacement or rotation angular velocity of said two support rotary body. This eliminates the need for a measurement process for measuring belt thickness unevenness in the belt manufacturing stage, so that the manufacturing cost does not increase. Further, when replacing the belt with a new one, there is no need to input data regarding unevenness of the belt thickness to the apparatus. Further, since it is not necessary to form a detection pattern, toner is not consumed for belt drive control. Further, it is not necessary to know in advance how the PLD fluctuation or the belt thickness fluctuation occurs over one belt circumference.

  Furthermore, in the invention according to the previous application, the PLD fluctuation specified from the rotational angular displacement or rotational angular velocity of the two support rotators is the two support rotations if the support rotator is a driven support rotator. The influence of the contact state between the body and the belt is taken into consideration. On the other hand, the belt thickness unevenness measured by the belt thickness measuring device as in the device described in Patent Document 1 does not take into consideration the influence of the contact state between the support rotating body and the belt. The belt thickness unevenness actually exists not only in the belt circumferential direction but also in the belt width direction orthogonal thereto. Here, when a belt having belt thickness unevenness also in the belt width direction is stretched over the support rotator, the relationship between the moving speed of the belt portion wound around the support rotator and the rotation angular speed of the support rotator is The belt portion largely depends on the thickest portion in the belt width direction. That is, the relationship between the moving speed of the belt portion and the rotational angular velocity of the support rotator varies depending on the belt thickness unevenness in the belt width direction of the belt portion wound around the support rotator. This is because the thickest portion in the belt width direction comes into contact with the support rotator with the largest frictional force with the support rotator. Therefore, if belt drive control is performed based on the belt thickness unevenness measured by the belt thickness measuring instrument in which the influence of the contact state between the support rotating body and the belt is not considered, a control error due to the belt thickness unevenness in the belt width direction occurs. . On the other hand, in the invention according to the prior application, belt drive control can be performed based on PLD fluctuation or belt thickness fluctuation in consideration of the influence of the contact state between the support rotating body and the belt. Control errors due to uneven belt thickness can be prevented. Therefore, according to the invention according to the prior application, belt drive control can be performed with higher accuracy.

  In the prior application, three methods have been proposed as methods for recognizing PLD fluctuations. The first method is a method of recognizing PLD fluctuations by arranging the two supporting rotating bodies in close proximity and regarding the rotational angular displacement or rotational angular velocity of these supporting rotating bodies as the same phase. The second method is a method of recognizing PLD fluctuations using FIR filter processing or IIR filter processing regardless of the arrangement of the two support rotating bodies. The third method is a method of recognizing PLD fluctuations using FIR filter processing after the ratio between the distance between the two supporting rotating bodies and the total belt circumference is 2 Nb (even number ratio). It is.

  The present invention provides a belt drive control device capable of performing drive control by recognizing PLD fluctuation by a new method different from the PLD fluctuation recognition method proposed in the previous application, a belt device using this belt drive control device, An object of the present invention is to provide an image forming apparatus using the belt device.

In order to achieve the above object, a first aspect of the present invention provides a plurality of support rotators including a driven support rotator that rotates along with the movement of the belt and a drive support rotator that transmits a driving force to the belt. the belt drive controller for controlling the driving of the over passed the belt, included in the rotational angular displacement or rotation information of the rotational angular velocity of two supporting rotating bodies the plurality of supporting rotating bodies caries Chi diameter that different, two rotational fluctuation component caused by fluctuations in the pitch line distance belt part wound around the respective supporting rotator performs a process of calculating the fluctuation information of the pitch line distance of one of the belt portions wound around the supporting rotator , And a control means for performing the drive control so as to reduce fluctuations in the moving speed of the belt caused by fluctuations in the pitch line distance in the circumferential direction of the belt using the processing result The two support rotators are arranged such that the ratio of the belt moving path length between the two support rotators and the belt total circumference is 2Nb + 1 (Nb is a natural number), The delay time, which is the belt passing time required for the belt to move the distance between the two support rotators on the belt movement path, and the diameters of the two support rotators with respect to the two rotation fluctuation components be one that addition processing for adding the processing result of the ratio based gain and the time of the first processing Ru respectively supplied to (2Nb + 1) -th processing, first as the gain of the n-th process 1 with gain times th processing those th power (n-1) that is intended to as a delay time of the n-th process is performed using that the belt passage time (n-1) multiplied by It is characterized by.
Further, the invention of claim 2, The belt drive controller as claimed in claim 1, over the period corresponding to the time required for the belt rotates one round, variation information storing fluctuation information calculated by the process It has a memory means.
Further, the invention of claim 3, The belt drive controller as claimed in claim 2, wherein said control means, the difference is allowable range of the fluctuation information obtained newly with fluctuations information stored in the fluctuation information storage unit at a timing beyond, it is characterized in carrying out the process for obtaining the above SL fluctuation information again.
Further, the invention of claim 4, The belt drive controller as claimed in any one of claims 1 to 3, wherein the control means, to perform the process of obtaining again on SL fluctuation information at a predetermined timing It is a feature.
Further, an invention according to claim 5, The belt drive controller as claimed in any one of claims 1 to 3, wherein said control means, while the process of obtaining the above SL fluctuation information, performs the driving control It is characterized by this.
The invention of claim 6 has the belt drive controller according to any one of claims 1 to 5, the historical information storage means for at least one revolution of the belt component storing past fluctuations information, the control means uses the one obtained from the said past information fluctuations information newly obtained and past fluctuations information stored in the storage means, is characterized in that performing the drive control.
According to a seventh aspect of the present invention, there is provided a belt stretched around a plurality of support rotators including a driven support rotator that rotates along with the movement of the belt and a drive support rotator that transmits a driving force to the belt. And a belt drive control device for controlling the driving of the belt in a belt device comprising: a driving source that generates a rotational driving force for driving the belt; becomes, and the ratio between belt movement path length and belt total circumference between mutual supporting rotator is 2Nb + 1 (Nb is a natural number) rotation angular displacement or rotation angular velocity of two supporting rotating body disposed so as to it has a detection means for detecting a degree, as the belt driving controller, and is characterized in that a belt drive controller as claimed in any one of claims 1 to 6.
The invention according to claim 8 is the belt device according to claim 7, wherein all of the two supporting rotating bodies are driven supporting rotating bodies that rotate along with the movement of the belt. It is.
The invention of claim 9 is the belt device of claim 8, wherein
The drive source includes feedback control means for detecting its own rotational angular displacement or rotational angular velocity and feeding back the rotational angular displacement or rotational angular velocity.
According to a tenth aspect of the present invention, in the belt device of the seventh aspect, the two support rotators include the drive support rotator.
According to an eleventh aspect of the present invention, in the belt device according to any one of the seventh to tenth aspects, a mark indicating the reference position on the belt is detected in order to grasp the reference belt movement position of the belt. The belt drive control device is characterized in that the control means of the belt drive control device acquires the rotation fluctuation component based on the detection timing of the mark detection means and performs the drive control. is there.
According to a twelfth aspect of the present invention, in the belt device according to any one of the seventh to tenth aspects, the control means of the belt drive control device provides the relationship information between the variation in the pitch line distance and the belt moving position. The drive control is performed after grasping on the basis of the average time required for the belt to make one revolution or the belt circumference known in advance.
The invention of claim 13 is the belt device according to any one of claims 7 to 12, wherein the belt has a joint at at least one place in the belt circumferential direction. It is.
The invention according to claim 14 is the belt device according to any one of claims 7 to 13, wherein the belt has a plurality of layers in the belt thickness direction. is there.
The invention according to claim 15 is a latent image carrier comprising a belt stretched over a plurality of support rotating members, a latent image forming means for forming a latent image on the latent image carrier, and the latent image carrier. An image forming apparatus comprising: a developing unit that develops the latent image on the image; and a transfer unit that transfers a visible image on the latent image carrier to a recording material. Item 15. The belt device according to any one of Items 7 to 14 is used.
According to a sixteenth aspect of the present invention, there is provided a latent image carrier, a latent image forming unit that forms a latent image on the latent image carrier, a developing unit that develops the latent image on the latent image carrier, An intermediate transfer member composed of a belt stretched over a support rotating member, a first transfer means for transferring a visible image on the latent image carrier to the intermediate transfer member, and a visible image on the intermediate transfer member. an image forming apparatus and a second transfer means for transferring the wood, as a belt device for driving the intermediate transfer body, the use of a belt device according to any one of claims 7 to 14 It is a feature.
According to a seventeenth aspect of the present invention, there is provided a latent image carrier, a latent image forming unit that forms a latent image on the latent image carrier, a developing unit that develops the latent image on the latent image carrier, A recording material conveying member comprising a belt stretched around a support rotating member, and a visible image on the latent image bearing member via the intermediate transfer member or directly without using the intermediate transfer member; an image forming apparatus having a transfer unit that transfers the recording material being conveyed, as a belt device for driving the recording material transporting member, a belt device according to any one of claims 7 to 14 It is characterized by using.

  In the present invention, the rotation information used for drive control includes two supports arranged such that the ratio of the belt movement path length between the support rotating bodies and the belt total circumference is 2Nb + 1 (Nb is a natural number). Although the rotation information of the rotating body will be described in detail later, PLD fluctuation can be recognized based on the rotation information.

  As described above, according to the present invention, there is also an excellent effect that the drive control can be performed by recognizing the PLD fluctuation by a new method different from the PLD fluctuation recognition method proposed in the previous application.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 is a schematic configuration diagram showing an example of a copying machine as an image forming apparatus to which the present invention is applied. In FIG. 2, reference numeral 100 denotes a copying machine main body, reference numeral 200 denotes a paper feed table on which the copying machine is placed, reference numeral 300 denotes a scanner mounted on the copying machine main body 100, and reference numeral 400 further denotes an automatic document transport mounted thereon. Device (ADF). This copier is a tandem type electrophotographic copier that employs an intermediate transfer (indirect transfer) system.

  In the center of the copying machine main body 100, an intermediate transfer belt 10 including a belt which is an intermediate transfer member serving as an image carrier is provided. The intermediate transfer belt 10 is stretched around support rollers 14, 15, and 16 as three support rotating bodies, and rotates in the clockwise direction in the drawing. An intermediate transfer belt cleaning device 17 for removing residual toner remaining on the intermediate transfer belt 10 after image transfer is provided on the left side of the second support roller 15 in the drawing among these three support rollers. Further, among the three support rollers, a belt portion stretched between the first support roller 14 and the second support roller 15 has yellow (Y), magenta (M), A tandem image forming unit 20 in which four image forming units 18 of cyan (C) and black (K) are arranged side by side is arranged oppositely. In the present embodiment, the third support roller 16 is a drive roller. An exposure device 21 as a latent image forming unit is provided above the tandem image forming unit 20.

  A secondary transfer device 22 as a second transfer unit is provided on the opposite side of the tandem image forming unit 20 with the intermediate transfer belt 10 interposed therebetween. In the secondary transfer device 22, a secondary transfer belt 24 that is a belt as a recording material conveying member is stretched between two rollers 23. The secondary transfer belt 24 is provided so as to be pressed against the third support roller 16 via the intermediate transfer belt 10. The secondary transfer device 22 transfers an image on the intermediate transfer belt 10 to a sheet as a recording material. A fixing device 25 for fixing the image transferred on the sheet is provided on the left side of the secondary transfer device 22 in the drawing. The fixing device 25 has a configuration in which a pressure roller 27 is pressed against a fixing belt 26 that is a belt. The secondary transfer device 22 described above also has a sheet conveyance function for conveying the sheet 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 sheet conveying function together. In the present embodiment, a sheet reversing device for reversing the sheet so as to record images on both sides of the sheet is provided below the secondary transfer device 22 and the fixing device 25 in parallel with the tandem image forming unit 20 described above. 28 is also provided.

When making a copy using the copying machine, a document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it. Thereafter, when a start switch (not shown) is pressed, when the document is set on the automatic document feeder 400, the document is conveyed and moved onto the contact glass 32. On the other hand, when an original is set on the contact glass 32, the scanner 300 is immediately driven. Next, the first traveling body 33 and the second traveling body 34 travel. 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. The document is placed in the reading sensor 36 and the original content is read.
In parallel with this document reading, the drive roller 16 is rotated by a drive motor which is a drive source (not shown). As a result, the intermediate transfer belt 10 moves in the clockwise direction in the drawing, and the remaining two support rollers (driven rollers) 14 and 15 rotate along with the movement. At the same time, the photosensitive drums 40Y, 40M, 40C, and 40K as the latent image carriers are rotated in the individual image forming units 18 so that yellow, magenta, cyan, and black are separately provided on the photosensitive drums. Each information is exposed and developed to form a single color toner image (visualized image). Then, the toner images on the photosensitive drums 40Y, 40M, 40C, and 40K are sequentially transferred onto the intermediate transfer belt 10 so as to overlap each other, thereby forming a composite color image on the intermediate transfer belt 10.

In parallel with such image formation, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated, and the sheet is fed out from one of the paper feed cassettes 44 provided in the paper bank 43 in multiple stages. The sheets are separated one by one and placed in the paper feed path 46, transported by the transport roller 47, guided to the paper feed path in the copying machine main body 100, and abutted against the registration roller 49 and stopped. Alternatively, the sheet feed roller 50 is rotated to feed out the sheets on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual feed path 53, and abutted against the registration roller 49 and stopped. Then, the registration roller 49 is rotated in synchronization with the composite color image on the intermediate transfer belt 10, the sheet is fed between the intermediate transfer belt 10 and the secondary transfer device 22, and transferred by the secondary transfer device 22. A color image is transferred onto the sheet. The image-transferred sheet is conveyed by the secondary transfer belt 24 and sent to the fixing device 25. The fixing device 25 applies heat and pressure to fix the transferred image, and then the switching roller 55 is used to switch the discharge image. The paper is discharged at 56 and stacked on the paper discharge tray 57. Alternatively, it is switched by the switching claw 55 and put into the sheet reversing device 28, where it is reversed and guided again to the transfer position, and an image is recorded also on the back surface, and then discharged onto the discharge tray 57 by the discharge roller 56.
The intermediate transfer belt 10 after the image transfer is removed by the intermediate transfer belt cleaning device 17 to remove residual toner remaining on the intermediate transfer belt 10 after the image transfer, so that the tandem image forming unit 20 can prepare for another image formation. Here, the registration roller 49 is generally used while being grounded, but it is also possible to apply a bias for removing paper dust from the sheet.

  This copier can be used to make a black and white copy. In that case, the intermediate transfer belt 10 is separated from the photosensitive drums 40Y, 40M, and 40C by means not shown. These photosensitive drums 40Y, 40M, and 40C are temporarily stopped from driving. Only the black photosensitive drum 40K is brought into contact with the intermediate transfer belt 10 to perform image formation and transfer.

Next, the configuration of the intermediate transfer belt 10 of the present embodiment will be described. The following description is not limited to the intermediate transfer belt, but is the same for a belt that is widely driven and controlled.
As the intermediate transfer belt, a single-layer belt mainly composed of a fluorine-based resin, a polycarbonate resin, a polyimide resin, or the like, or a multi-layer elastic belt having an entire belt layer or a part of the belt as an elastic member is used. In general, the belt used in the image forming apparatus is not limited to the intermediate transfer belt, and a plurality of functions are required. In recent years, in order to simultaneously achieve a plurality of required functions, a multi-layer belt having a plurality of layers in the belt thickness direction is often used. For example, the intermediate transfer belt 10 is required to have a plurality of functions such as toner releasability, photosensitive member nip property, durability, tensile property, high driving roller friction property, and photosensitive member low friction property.

The toner releasability is a function necessary for improving the transferability from the intermediate transfer belt 10 to the recording paper and improving the cleaning performance for the transfer residual toner remaining on the intermediate transfer belt.
The photoconductor nip property is a function necessary for improving transferability to the intermediate transfer belt 10 by being in close contact with the photoconductor drums 40Y, 40M, 40C, and 40K.
Durability is a function necessary for reducing running costs by enabling long-term use with less cracking and wear due to use over time.
The tensile property is a function necessary for controlling the belt moving speed and the belt moving position with high accuracy by preventing expansion and contraction in the belt circumferential direction when the belt is driven.
The high friction property with respect to the driving roller is a function necessary for realizing a stable and highly accurate driving by preventing slipping between the driving roller 16 and the intermediate transfer belt 10.
Low friction against the photoconductor is necessary to suppress load fluctuation by causing slippage between the photoconductor drums 40Y, 40M, 40C, and 40K and the intermediate transfer belt 10 even if a speed difference occurs between them. Function.
In order to simultaneously realize these functions at a high level, for example, an intermediate transfer belt composed of a multi-layer belt as described below is used.

FIG. 3 is an explanatory diagram showing an example of the layer structure of the intermediate transfer belt 10.
The intermediate transfer belt 10 of this example is an endless belt having a five-layer structure made of different materials, and is formed so that the thickness of the belt is 500 to 700 [μm] or less. The first layer, the second layer, the third layer, the fourth layer, and the fifth layer are sequentially formed from the belt surface side (the surface side in contact with the photosensitive drum).
The first layer is a polyurethane resin coat layer filled with fluorine. By this layer, low friction between the photosensitive drums 40Y, 40M, 40C, and 40K and the intermediate transfer belt 10 (anti-photosensitive member low friction) and toner releasability are realized.
The second layer is a silicon-acrylic copolymer coat layer that plays a role in improving the durability of the first layer and preventing the third layer from aging.
The third layer is a rubber layer (elastic layer) made of chloroprene having a thickness of about 400 to 500 [μm], and has a Young's modulus of 1 to 20 [Mpa]. Since the third layer is deformed in the secondary transfer portion according to local unevenness due to a toner image or recording paper having poor smoothness, the transfer pressure is not excessively increased with respect to the toner image. Occurrence of omission is suppressed. In addition, since good adhesion to a recording paper with poor smoothness is obtained, a transfer image with excellent uniformity can be obtained.
The fourth layer is a polyvinylidene fluoride layer having a thickness of about 100 [μm] and serves to prevent expansion and contraction in the belt circumferential direction. The Young's modulus is 500 to 1000 [Mpa].
The fifth layer has a polyurethane coat layer and realizes a high friction coefficient with the drive roller 16.

Examples of other materials include the following.
In the first layer and the second layer, prevention of contamination of the photosensitive member by an elastic material, improvement in cleaning performance by reducing surface friction resistance to the surface of the intermediate transfer belt 10 and reducing toner adhesion force, One or more types of polyurethane, polyester, epoxy resin and the like may be used in order to improve the secondary transfer property to the recording paper. Also, in order to reduce the surface energy and improve the lubricity, one or more kinds of powders or particles of fluororesin, fluorine compound, fluorocarbon, titanium dioxide, silicon carbide, etc., or particles of each other are used. The same type having different diameters may be dispersed. Moreover, you may use the thing which formed the fluorine rich layer on the surface by performing heat processing like a fluorine-type rubber material, and made surface energy small.
In the third elastic layer, butyl rubber, fluorine rubber, acrylic rubber, EPDM, NBR, acrylonitrile-butadiene-styrene rubber natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, ethylene-propylene rubber, ethylene-propylene ter Polymer, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, urethane rubber, syndiotactic 1,2-polybutadiene, epichlorohydrin rubber, ricone rubber, fluorine rubber, polysulfide rubber, polynorbornene rubber, hydrogenated nitrile rubber , One type selected from the group consisting of thermoplastic elastomers (for example, polystyrene-based, polyolefin-based, polyvinyl chloride-based, polyurethane-based, polyamide-based, polyurea, polyester-based, fluororesin-based). It may be used two or more kinds.
As the fourth layer, polycarbonate, fluororesin (ETFE, PVDF), polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer Polymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-acrylic acid Octyl copolymer and styrene-phenyl acrylate copolymer), styrene-methacrylic acid ester copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-phenyl methacrylate copolymer) Coalesce etc.), styrene-α-chloroacrylic acid Styrenic resins such as methyl copolymers, styrene-acrylonitrile-acrylic acid ester copolymers (monopolymers or copolymers containing styrene or styrene-substituted products), methyl methacrylate resins, butyl methacrylate resins, ethyl acrylate Resin, butyl acrylate resin, modified acrylic resin (silicone-modified acrylic resin, vinyl chloride resin-modified acrylic resin, acrylic / urethane resin, etc.), vinyl chloride resin, styrene-vinyl acetate copolymer, vinyl chloride-vinyl acetate copolymer Rosin-modified maleic acid resin, phenolic resin, epoxy resin, polyester resin, polyester polyurethane resin, polyethylene, polypropylene, polybutadiene, polyvinylidene chloride, ionomer resin, polyurethane resin, silicone resin, ketone resin, ethylene - it can be used ethyl acrylate copolymer, xylene resin and polyvinyl butyral resin, polyamide resin, one kind or two kinds or more selected from the group consisting of modified polyphenylene oxide resin.

As a method for preventing elongation as an elastic belt, there are a method of forming a rubber layer in a core resin layer that is less stretched as in the fourth layer, a method of putting a material for preventing elongation in the core layer, etc. It is not related to the manufacturing method.
Examples of materials constituting the core layer for preventing elongation include natural fibers such as cotton and silk, polyester fibers, nylon fibers, acrylic fibers, polyolefin fibers, polyvinyl alcohol fibers, polyvinyl chloride fibers, polyvinylidene chloride fibers, polyurethane 1 or 2 types selected from the group consisting of synthetic fibers such as fibers, polyacetal fibers, polyfluoroethylene fibers and phenol fibers, inorganic fibers such as carbon fibers, glass fibers and boron fibers, and metal fibers such as iron fibers and copper fibers By using the above, it is possible to use a woven fabric or yarn. Of course, the material is not limited to the above. The yarn may be twisted in any manner, such as one or a plurality of filaments twisted, a single twisted yarn, various twisted yarns, a double yarn or the like. Further, for example, fibers of a material selected from the above material group may be blended. Of course, the yarn can be used after being subjected to an appropriate conductive treatment. On the other hand, the woven fabric can be any woven fabric such as knitted weave. Of course, a woven fabric that has been woven can also be used, and naturally conductive treatment can be applied.
The manufacturing method for providing the core layer is not particularly limited. For example, a method in which a woven fabric woven in a cylindrical shape is covered with a mold and a coating layer is provided thereon, a woven fabric woven in a cylindrical shape is immersed in liquid rubber or the like, and a coating layer is formed on one or both sides of the core layer Examples of the method include a method of providing a coating layer on a spirally wound thread around a mold or the like at an arbitrary pitch.

  Depending on the layer, a conductive material for adjusting the resistance value may be included, for example, carbon black, graphite, metal powder such as aluminum or nickel, tin oxide, titanium oxide, antimony oxide, indium oxide, potassium titanate, antimony oxide- Conductive metal oxides such as tin oxide composite oxide (ATO) and indium oxide-tin oxide composite oxide (ITO), and conductive metal oxides are made of insulating fine particles such as barium sulfate, magnesium silicate, and calcium carbonate. It may be coated. However, it is a matter of course that the present invention is not limited to these materials.

  By the way, in the case of a single layer belt having a uniform belt material, since the degree of expansion and contraction of the inner peripheral surface and the outer peripheral surface of the belt coincides, the belt pitch line that determines the moving speed of the belt as shown in FIG. It becomes the center in the thickness direction. However, in the case of the multi-layer belt as described above, the belt pitch line does not become the central portion in the belt thickness direction. In the multi-layer belt, when there is a layer with a large Young's modulus protruding from among the plurality of layers constituting the belt, the belt pitch line is present at substantially the center of the layer. This is because a layer having a high Young's modulus (hereinafter referred to as “tensile layer”) is used as a core wire to prevent expansion and contraction in the belt circumferential direction, and other layers expand and contract and wind around the support roller. In the case of the intermediate transfer belt 10, the fourth layer which is the tensile layer protrudes and has a large Young's modulus, and therefore the belt pitch line exists inside the fourth layer. When there is a tensile layer having a large Young's modulus and protruding in this way, the thickness unevenness of the tensile layer in the belt circumferential direction greatly affects the fluctuation of the PLD. In short, in a multi-layer belt, the PLD is determined mainly by the influence of a layer having a large Young's modulus among the plurality of layers constituting the belt.

In addition, the PLD also varies when the position of the fourth layer (tensile layer) is displaced in the belt thickness direction over the entire circumference of the belt. For example, if the thickness of the fifth layer existing between the fourth layer (tensile layer) and the support roller is uneven, the position of the fourth layer (tensile layer) in the belt thickness direction depends on the thickness unevenness. Change and the PLD fluctuates.
Also, in the case of an endless belt (seam belt) with a joint, the manufacturing method is to create a fourth layer of polyvinylidene fluoride sheet, and overlap the end of the sheet by about 2 [mm] for fusion bonding In many cases, however, the other layers are sequentially formed after endlessness. In this case, the melt-bonded part (joint part) changes in physical properties due to melting and differs in elasticity from other parts. Therefore, even if the thickness is the same as the other part, the PLD of the joint part is different from that of the other part. It deviates greatly from PLD. In such a portion, even if there is no belt thickness variation, PLD variation occurs, and when this portion is wound around the drive roller, belt speed variation occurs. In addition, seam belts with joints do not require such molds and can adjust the belt circumference compared to seamless belts that require unique molds for products with different belt circumferences. There is an advantage that the manufacturing cost can be suppressed in that it is free.

Next, drive control of the intermediate transfer belt 10 will be described.
In the copying machine of this embodiment, it is necessary to move the intermediate transfer belt 10 at a constant speed. In practice, however, the belt moving speed varies due to component errors, environment, and changes over time. When the belt moving speed of the intermediate transfer belt 10 fluctuates, the actual belt moving position deviates from the target belt moving position, and the leading edge position of each toner image on the photosensitive drums 40Y, 40M, and 40C is the intermediate transfer belt 10. A color shift occurs due to a shift. Further, when the belt moving speed is relatively high, the toner image portion transferred onto the intermediate transfer belt 10 has a shape that is stretched in the belt circumferential direction rather than the original shape, and conversely, the belt moving speed is relatively high. At a later time, the toner image portion transferred onto the intermediate transfer belt 10 has a shape reduced in the belt circumferential direction from the original shape. In this case, in the image finally formed on the sheet, a periodic change in image density (banding) appears in a direction corresponding to the belt circumferential direction.
Therefore, the configuration and operation for maintaining the intermediate transfer belt 10 at a constant speed with high accuracy will be described below. Note that the following description is not limited to the intermediate transfer belt 10, but is the same for a belt that is widely driven and controlled.

In the present embodiment, the rotational angular velocities ω _{1 of} two rollers having different roller diameters or different degrees of influence of the PLD of the belt portion wound around the belt on the relationship between the moving speed of the belt and the rotational angular speed of the belt are different. , Ω ₂ are continuously detected, and the PLD fluctuation f (t) is obtained from the two types of rotational angular velocities ω ₁ , ω ₂ . In the case of a single-layer belt, the PLD has a certain relationship with the belt thickness, and the PLD variation has a certain relationship with the belt thickness variation, so that the belt portion having a different roller diameter or wound around itself. Continuously detecting the rotational angular velocities of two rollers having different degrees of influence of the thickness of the belt on the relationship between the moving speed of the belt and the rotational angular speed of the belt, and obtaining the belt thickness fluctuation from these two rotational angular velocities. It may be. The PLD fluctuation f (t) is a periodic function indicating the time change of the PLD of the belt portion that passes through a specific point on the belt moving path while the belt makes one round. Since the PLD fluctuation f (t) greatly affects the belt moving speed V as described above, the PLD fluctuation f (t) is obtained with high accuracy from the rotational angular velocities ω ₁ and ω _{2 of the} two support rollers. If belt drive control is performed based on the PLD fluctuation f (t), the belt moving speed V can be controlled with high accuracy.
In the present embodiment, as a method for obtaining the PLD fluctuation f (t) with high accuracy, the arrangement relationship of the two rollers (the belt conveyance distance between the two rollers) is set to an odd number with respect to one belt period, A method of performing filtering is used.

[Method for recognizing PLD fluctuation]
FIG. 4 is a schematic diagram showing the main part of the belt device. The belt device includes a belt 103 and a first roller 101 and a second roller 102 as support rotating bodies around which the belt 103 is stretched. The belt 103 is wound around the first roller 101 at a belt winding angle θ ₁ and is wound around the second roller 102 at a belt winding angle θ ₂ . The belt 103 moves endlessly in the direction of arrow A in the figure. The first roller 101 and the second roller 102 are each provided with a rotary encoder as a detecting means. As these rotary encoders, any encoder capable of detecting the rotational angular displacement or rotational angular velocity of each of the rollers 101 and 102 may be used. In the present embodiment, a roller that can detect the rotational angular velocities ω ₁ and ω ₂ of the rollers 101 and 102 is used. As this rotary encoder, for example, timing marks at regular intervals are formed on concentric circles on a disk made of a transparent member such as transparent glass or plastic, and are fixed coaxially to the rollers 101 and 102. A known optical encoder that optically detects the timing mark can be used. Also, for example, a timing mark is magnetically recorded on a concentric circle on a disk made of a magnetic material, is fixed coaxially to each of the rollers 101 and 102, and the timing mark is detected by a magnetic head. An encoder can also be used. A known tacho generator can also be used. In the present embodiment, the rotational angular velocity can be obtained, for example, by measuring a time interval of pulses continuously output from the rotary encoder and reciprocal thereof. The rotation angle displacement can be obtained by counting the number of pulses continuously output from the rotary encoder.

ここで、「ω₁」は第１ローラ１０１の回転角速度であり、「ω₂」は第２ローラ１０２の回転角速度であり、「Ｖ」はベルト移動速度であり、「Ｒ₁」は第１ローラ１０１のローラ実効半径であり、「Ｒ₂」は第２ローラ１０２のローラ実効半径である。
また、「κ₁」は、第１ローラ１０１のベルト巻付角θ₁、ベルト材質、ベルト層構造等によって決まる第１ローラ１０１のＰＬＤ変動実効係数であり、ＰＬＤがベルト移動速度Ｖに影響する度合いを決定するパラメータである。同様に、「κ₂」は、第２ローラ１０２のＰＬＤ変動実効係数である。ローラ１０１，１０２それぞれの関係式である上記数３及び上記数４において互いに異なるＰＬＤ変動実効係数を設定しているのは、ベルト巻付状態（変形曲率）が異なることや、各ローラに対するベルト巻付量が異なることなどが原因で、ＰＬＤ変動が、ベルト移動速度（ベルト移動量）とローラの回転角速度（回転角変位）との関係に影響する度合いが異なる場合があるためである。なお、これらのＰＬＤ変動実効係数κ₁，κ₂は、一般に、ベルト材質が均一で一層構造のベルトを用い、かつ、ベルト巻付角θ₁，θ₂が十分に大きいとき、いずれも同じ値となる。
また、「ｆ（ｔ）」は、ベルト移動経路上の特定地点を通過するベルト部分のＰＬＤの時間変化を示すベルトが１周する周期と同じ周期をもった周期関数であり、ベルト１周にわたるベルト周方向のＰＬＤの平均値ＰＬＤ_aveからの偏差を示すものである。ここでは、上記特定地点を、第１ローラ１０１に巻き付いた箇所とする。したがって、時間ｔ＝０のとき、第１ローラ１０１に巻き付いたベルト部分のＰＬＤ変動量はｆ（０）となる。なお、ＰＬＤ変動の関数としては、時間関数ｆ（ｔ）ではなく、上述した関数ｆ（ｄ）を用いてもよい。ｆ（ｔ）とｆ（ｄ）は相互に変換することができる。
また、「τ」は、第１ローラ１０１から第２ローラ１０２までベルト１０３が移動するのに要する平均時間であり、以下、「遅れ時間」という。この遅れ時間τは、第１ローラ１０１に巻き付いたベルト部分におけるＰＬＤ変動ｆ（ｔ）と、第２ローラ１０２に巻き付いたベルト部分におけるＰＬＤ変動ｆ（ｔ−τ）との位相差としての意味をもつ。 The relationship between the rotational angular velocities of the first roller 101 and the second roller 102 and the belt moving speed V is expressed by the following equations (3) and (4), respectively.

Here, “ω ₁ ” is the rotational angular velocity of the first roller 101, “ω ₂ ” is the rotational angular velocity of the second roller 102, “V” is the belt moving speed, and “R ₁ ” is the first angular velocity. “R ₂ ” is the effective roller radius of the roller 101, and “R ₂ ” is the effective roller radius of the second roller 102.
“Κ ₁ ” is a PLD fluctuation effective coefficient of the first roller 101 determined by the belt winding angle θ _{1 of} the first roller 101, the belt material, the belt layer structure, etc., and PLD affects the belt moving speed V. It is a parameter that determines the degree. Similarly, “κ ₂ ” is a PLD fluctuation effective coefficient of the second roller 102. The different PLD fluctuation effective coefficients in the above equations 3 and 4 which are the relational expressions of the rollers 101 and 102 are set because the belt winding state (deformation curvature) is different and the belt winding for each roller is different. This is because the degree of influence of the PLD fluctuation on the relationship between the belt moving speed (belt moving amount) and the rotational angular velocity (rotational angular displacement) of the roller may be different due to different attachment amounts. These PLD fluctuation effective coefficients κ ₁ and κ ₂ are generally the same value when the belt material is uniform and a _single- layer belt is used and the belt winding angles θ ₁ and θ ₂ are sufficiently large. It becomes.
Further, “f (t)” is a periodic function having the same cycle as the cycle in which the belt makes one turn indicating the time change of the PLD of the belt portion passing through a specific point on the belt movement path, and covers one belt turn. It shows the deviations from the mean PLD _ave of the belt circumferential direction of the PLD. Here, the specific point is a place wound around the first roller 101. Therefore, when the time t = 0, the PLD fluctuation amount of the belt portion wound around the first roller 101 is f (0). Note that the function f (d) described above may be used instead of the time function f (t) as a function of PLD fluctuation. f (t) and f (d) can be converted into each other.
“Τ” is an average time required for the belt 103 to move from the first roller 101 to the second roller 102, and is hereinafter referred to as “delay time”. The delay time τ has a meaning as a phase difference between the PLD fluctuation f (t) in the belt portion wound around the first roller 101 and the PLD fluctuation f (t−τ) in the belt portion wound around the second roller 102. Have.

The average value PLD _ave of PLD is difficult to obtain only from the layer structure of the belt and the material and physical properties of each layer. Can be sought. That is, the average value of the belt moving speed when the driving roller is driven at a constant rotational angular velocity is {(radius r of driving roller + PLD _ave ) × constant rotational angular speed ω ₀₁ of the driving roller}. The average value of the belt moving speed when the driving roller is driven at a constant rotational angular speed is obtained from (belt circumference) / (time required for one revolution of the belt). The belt circumference and the time required for one round of the belt can be accurately measured. Therefore, the average value of the belt moving speed when the driving roller is driven at a constant rotational angular speed can be accurately calculated. Further, since the radius r of the driving roller and the constant rotational angular velocity ω ₀₁ of the driving roller can be accurately grasped, PLD _ave can be accurately calculated. The method for calculating PLD _ave is not limited to this.

そして、ローラ実効半径Ｒ₁，Ｒ₂に対し、ＰＬＤ変動ｆ（ｔ）は十分小さいことから、上記数５に示す式を下記数６に示す式に近似することができる。

The belt moving speed V at the time t of the belt portion wound around the second roller 102 is the same as the belt moving speed V at the time t of the belt portion wound around the first roller 101. From the equation, the following equation 5 can be derived.

Since the PLD fluctuation f (t) is sufficiently small with respect to the roller effective radii R ₁ and R ₂ , the above equation 5 can be approximated to the following equation 6.

In this recognition method, the PLD fluctuation f (t) is obtained with high accuracy from the rotational angular velocities ω ₁ and ω _{2 of the} two rollers 101 and 102. In the following example, the case where the diameters of these rollers 101 and 102 are larger in the second roller 102 than in the first roller 101 is taken as an example, but the same principle can be used in the reverse case. Strictly speaking, when the value obtained by dividing the roller effective radius R by the PLD fluctuation effective coefficient κ is compared as described below, the roller 102 is larger than the roller 101.

このようにｆ（ｔ）の係数が１となるように規格化された上記数７の式の右辺をｇｆ（ｔ）と定義すると、下記の数８に示す式が得られる。ただし、この数８の式中の「Ｇ」は、下記の数９に示すものである。

各ローラ１０１，１０２間におけるローラ実効半径ＲとＰＬＤ変動実効係数κとの関係から、Ｇは１より小さい値をとる。また、上記数７の式からわかるように、ｇｆ（ｔ）は、ローラ実効半径Ｒ₁，Ｒ₂及びＰＬＤ変動実効係数κ₁，κ₂を用い、各ローラ１０１，１０２の回転角速度ω₁，ω₂から得られるものである。このｇｆ（ｔ）からＰＬＤ変動ｆ（ｔ）を求める。 The relationship between the rotational angular velocities ω ₁ and ω ₂ between the first roller 101 and the second roller 102 is expressed by the formula shown in the above formula 6, and when this formula is modified, the formula shown in the following formula 7 is obtained.

When the right side of the equation (7) normalized so that the coefficient of f (t) is 1 is defined as gf (t), the following equation (8) is obtained. However, “G” in the equation (8) is as shown in the following equation (9).

From the relationship between the roller effective radius R between the rollers 101 and 102 and the PLD fluctuation effective coefficient κ, G takes a value smaller than 1. Further, as can be seen from the equation (7), gf (t) uses the roller effective radii R ₁ and R ₂ and the PLD fluctuation effective coefficients κ ₁ and κ _2, and the rotational angular velocities ω ₁ , It is obtained from ω ₂ . The PLD fluctuation f (t) is obtained from this gf (t).

In the PLD fluctuation recognition method described below, the ratio of the belt conveyance section (distance) between the rollers and the belt total conveyance section (peripheral length) is 1: (2Nb + 1) in the arrangement of the two rollers 101 and 102. as the obtained rotational angular velocity omega ₁ of the two rollers 101 and 102, PLD fluctuation f in a short time from omega ₂ (t) to a high precision. However, “Nb” is a natural number.

  In this recognition method, first, the two roller arrangements are set so that the ratio of the belt conveyance section (distance) between the rollers and the entire belt conveyance section (circumferential length) is 1: (2Nb + 1). That is, when Nb = 1, the ratio of the conveyance section is 1: 3. Therefore, the arrangement of the two rollers 101 and 102 is the belt conveyance between these two rollers when the entire belt circumference is 1500 [mm]. The section (distance) is 500 [mm]. Similarly, when Nb = 2, the belt conveyance section (distance) between the two rollers is 300 [mm]. Thus, by adding conditions to the layout of the roller arrangement, the belt PLD fluctuation f (t) can be obtained with high accuracy by the arithmetic processing described below.

Hereinafter, the process of this recognition method will be described.
First, the case of Nb = 1 will be described. In this case, the first roller 101 and the second roller 102 are installed at a distance of 1/3 of the entire belt conveyance path. Then, gf (t) shown in the above equation 8 is obtained from the respective rotational angular velocities ω ₁ and ω ₂ .

  FIG. 5 is a calculation block diagram for explaining the recognition method. In this figure, F (s) obtained by Laplace transform of f (t), which is a time function, is used, and “s” in the figure is a Laplace operator. F (s) = L {f (t)} (where L {x} represents the Laplace transform of x). Further, in FIG. 5, the calculation from F (s) to gF (s) shown at the top of the figure expresses the equation shown in the above equation 8 for convenience, and is surrounded by a broken line in the figure. The part is a filter part.

The filter section has a time delay element of “τ” based on the coefficient based on “G” shown in Equation 9 and the distance between the two rollers. When gF (s), that is, the left side of the equation shown in Equation 7 (data obtained from the detected rotational angular velocities ω ₁ and ω ₂ ) is input to this filter unit, the time function m of the output M (s) of the filter unit. (T), that is, L ⁻¹ {M (s)} (where L ⁻¹ {y} represents the inverse Laplace transform of y) is as shown in the following Expression 10.

The PLD fluctuation f (t) is calculated by FIR filter processing (non-feedback processing) in the portion surrounded by a broken line in the figure. However, the required filter length is 2Nb + 1. That is, when Nb = 1, the filter length is 3, and therefore, as shown in FIG. 5, the process of calculating the addition result M (s) of three operation values is performed. This processing result is shown in the above equation 10 as described above. Here, assuming that the rotation angle of the belt is one rotation [pi] [rad], the positional relationship between the two rollers is 2 [pi] / 3 [rad]. The τ time indicates the belt conveyance time between the two rollers when the belt is conveyed at a predetermined specified speed. Therefore, the 3τ time is 2π [rad] when converted to the belt rotation angle. Since the PLD fluctuation f (t) is a periodic function that repeats every rotation of the belt, f (t−3τ) included in the second term on the right side in the final expression shown in Equation 10 is f (t). Can do. Therefore, in this recognition method, when Nb = 1, the above equation (10) can be transformed into the following equation (11).

ここで、５τ時間は、ベルト回転角に変換すると２π［ｒａｄ］となる。よって、上記数１２に示す式において、右辺第２項に含まれるｆ（ｔ−５τ）はｆ（ｔ）とすることができる。よって、上記数１２に示す式は、下記の数１３に示す式に変形することができる。
＜数式１３＞

Therefore, by dividing the output data m (t) of the FIR filter by ( 1− G ³ ), the PLD fluctuation f (t) can be obtained without error. The time required to execute this calculation process is 2τ hours because data of 2τ hours past is used.
Similarly, when Nb = 2, the FIR process of FIG. 6 is performed because the FIR process has a filter length of 5. The processing result is as shown in the following Expression 12.
<Formula 12>

Here, the time 5τ is 2π [rad] when converted to the belt rotation angle. Therefore, f (t−5τ) included in the second term on the right side can be set to f (t) in the formula shown in Equation 12 above. Therefore, the formula shown in the above formula 12 can be transformed into the formula shown in the following formula 13.
<Formula 13>

Therefore, by dividing the output data n (t) of the FIR filter by (1−G ⁵ ), the PLD fluctuation f (t) can be obtained without error. The time required to execute this calculation process is 4τ time. As described above, according to this recognition method, when Nb = 2, it is possible to obtain a highly accurate PLD fluctuation f (t) without a recognition error in a processing time of 3τ time.

  As described above, in the present recognition method, the above-described two roller arrangements are set so that the ratio between the belt conveyance section (distance) between the rollers and the entire belt conveyance section (peripheral length) is 1: (2Nb + 1). Thus, the PLD fluctuation f (t) can be obtained with high accuracy without any recognition error from the data of the FIR filter processing with the filter length of (2Nb + 1).

The PLD fluctuation f (t) is calculated using the data on the left side of the equation shown in the above equation 7 which is data obtained from the detected rotational angular velocities ω ₁ and ω ₂ according to the following calculation procedure that generalizes the above results. If obtained, the PLD fluctuation f (t) can be obtained with high accuracy from the detected rotational angular velocities ω ₁ and ω ₂ .
(First line)
gf (t).
(Second line)
Data obtained by multiplying gf (t) by G and delaying by the delay time τ is obtained.
(3rd line)
Data obtained by multiplying gf (t) by G ² and delaying by the delay time 2τ is obtained.
・
・
・
(Nth line)
Data obtained by multiplying gf (t) by G ^n-1 and delaying by the delay time (n-1) τ is obtained.
When the data of each line is obtained in this way, the operation data from the first line to the (2Nb + 1) th line are added. By dividing the addition result n (t) by (10−G ^{2Nb + 1} ), the PLD fluctuation f (t) can be obtained without error.

FIG. 7 is an operation block diagram obtained by Z-transforming the operation block diagram of FIG. In FIG. 7, gf (n) is expressed as gfn, and f (n) is expressed as fn.
The sampling time of the input data input to the filter unit (FIR filter) surrounded by the broken line shown in FIG. It is assumed that the time Tb required for this is N × Ts (N is a natural number). In this case, the number of samplings during one revolution of the belt 103 is N. The PLD fluctuation f (t) obtained according to the control block diagram shown in FIG. 7 is composed of a data string of N PLD fluctuation values f (n) obtained every sampling time Ts. Since the process in the filter unit at this time is a digital process, the filter process can be executed using a DSP (Digital Signal Processor), a μCPU, or the like.

As described above, the rotational angular velocities ω ₁ and ω ₂ of the _two rollers 101 and 102 rotate under the influence of PLD fluctuations f (t) and f (t−τ) having different phases. Since the effective radius R of the roller and / or the PLD fluctuation effective coefficient κ are different from each other, the proportion of the PLD fluctuation component in the roller effective radius is different. Therefore, the magnitudes of rotational angular velocity fluctuations due to detected PLD fluctuations are different from each other. The present inventors paid attention to this point and found that the PLD fluctuation f (t) can be derived with high accuracy without depending on the frequency characteristics by using the above-described FIR filter and algorithm processing similar to these filters. . Here, in order to derive the PLD fluctuation f (t), normalization is performed so that the coefficient of f (t) is 1. However, the standard is set so that the coefficient of the PLD fluctuation f (t−τ) is 1. The PLD fluctuation f (t−τ) may be derived by the same algorithm processing. At this time, the coefficient on the PLD fluctuation f (t) side is the reciprocal of G. That is, t ′ = t−τ, τ ′ = Tb−τ (Tb is the time for one round of the belt). ) − (1 / G) f (t′−τ ′), the PLD fluctuation can be detected using the FIR filter in the same manner as described above.

  In this recognition method, since the belt PLD fluctuation f (t) is derived as f (t−3τ) = f (t) in the above equation 10, if 3τ is not exactly one revolution of the belt, the belt moving speed is increased. A control error occurs. Therefore, even if an attempt is made to suppress belt movement speed fluctuation due to PLD fluctuation by this recognition method, some belt movement speed fluctuation remains. The reason why such (2Nb + 1) τ is not exactly one round of the belt is that the ratio of the belt conveyance section (distance) between the rollers to the entire belt conveyance section (circumferential length) is 1: (2Nb + 1). ), A change in the belt circumference over time, an environmental change, a manufacturing error in the belt circumference, and the like. The error in the positional relationship between the two rollers is desirably suppressed to about 10% with respect to the entire belt circumference. The roller installation position may be set within an allowable range of belt speed fluctuation described below.

  In general, the belt movement speed fluctuation generated in the belt 103 is caused not only by the PLD fluctuation but also by the eccentricity of gears and the accumulated pitch error in the drive transmission system. Therefore, the permissible range of the belt movement speed variation due to the PLD variation is an allowable range assigned to the PLD variation in design. Here, in the drive control of the intermediate transfer belt 10 in the copying machine of the present embodiment, as described above, color misregistration and banding occur due to fluctuations in the belt moving speed. Such color misalignment and banding are caused by the actual belt moving position deviating from the target belt moving position due to fluctuations in the belt moving speed. Getting worse. The color misregistration and banding are perceived by humans who have seen the image on the sheet, and the allowable range for suppressing the level to practically no problem is, for example, the banding change interval (for banding) ( It can be defined by a spatial frequency fs indicating (distance). Since this spatial frequency fs has a fixed relationship {f = F × fs (F: constant)} with the temporal frequency f, it seems to be within the allowable range of the spatial frequency fs determined as the allowable range of banding. In addition, an allowable range of the deviation amount of the belt moving position can be defined. As a result, an allowable range of fluctuations in the belt moving speed can be defined.

Next, specific belt drive control for suppressing fluctuations in the belt moving speed due to PLD fluctuations using the PLD fluctuations f (t) obtained by the above recognition method will be described.
For specific belt drive control using the PLD fluctuation f (t), a plurality of control methods are conceivable depending on the apparatus configuration. Here, a control example (belt drive control example 1) for a device configuration having a mechanism for detecting the home position of the belt 103 and a control example (belt drive control example 2) for a device configuration without such a mechanism. Take two examples.

[Belt drive control example 1]
In order to perform appropriate belt drive control according to the PLD fluctuation using the PLD fluctuation f (t), it is necessary to grasp the phase of the PLD fluctuation on the belt 103 (phase when the belt circumference is 2π). There is. As a method of grasping this phase, first, as in this belt drive control example 1, the home position mark of the belt 103 is determined in advance and detected, and time measurement information by a timer, drive motor rotation angle information, There is a method for grasping this phase by using any one of the rotation angle information by the rotary encoder output.

FIG. 8 is a schematic diagram showing an apparatus configuration for detecting the home position mark of the belt 103 in this belt drive control example 1. As shown in FIG.
In the present control example 1, the home position mark 103a is provided on the belt 103, and this is detected by the mark detection sensor 104 as a mark detection means, thereby grasping the phase that is the reference for one round of the belt. In this example, a metal film affixed to a predetermined position on the belt 103 is used as the home position mark 103a, and a reflective photosensor provided on a fixed member is used as the mark detection sensor 104. The mark detection sensor 104 outputs a pulse signal when the home position mark 103a passes the detection area. The position where the home position mark 103a is provided is the belt inner peripheral surface or the belt width direction end of the belt outer peripheral surface so as not to affect image formation. An image forming substance such as toner or ink may adhere to the home position mark 103 a or the sensor surface of the mark detection sensor 104. In this case, the home position of the belt 103 may be erroneously recognized. Therefore, in order to eliminate such erroneous recognition, it is desirable to add a function for accurately detecting the belt home position while managing the sensor output amplitude, pulse width, and pulse interval to the mark detection sensor 104. . Although at least one home position mark 103a is required, a plurality of home position marks 103a may be provided and patterned so as to easily eliminate erroneous recognition.

FIG. 9 is an explanatory diagram for explaining the control operation of the first belt drive control example. In the illustrated example, the position of the mark detection sensor 104 is different from the position shown in FIG. 8 for convenience of explanation.
The rotational driving force generated by the driving motor 106 is transmitted to the driving roller 105 through a speed reduction mechanism including a driving gear 106a and a driven gear 105a. As a result, the driving roller 105 rotates and the belt 103 moves in the direction of arrow A in the figure. As the belt 103 moves, the first roller 101 and the second roller 102 rotate together. These rollers 101 and 102 are provided with rotary encoders 101a and 102a, respectively, and output signals thereof are input to the angular velocity detection units 111 and 112 of the digital signal processing unit. This rotary encoder may be connected via a speed reducer such as a gear. The first roller 101 and the second roller 102 are subjected to surface treatment so as not to slip between the inner peripheral surface of the belt 103 and set a belt winding angle or the like. In this example, the diameter of the second roller 102 is larger than that of the first roller 101. The motor control signal calculated and output by the digital signal processing unit is input to the servo amplifier 117 via the DA converter 116, and the servo amplifier 117 drives the drive motor 106 according to the control signal.
In the digital signal processing unit, the first angular velocity detection unit 111 detects the rotational angular velocity ω ₁ of the first roller 101 from the output signal of the first rotary encoder 101a. Similarly, the second angular velocity detection unit 112 detects the rotational angular velocity ω ₂ of the second roller 102 from the output signal of the second rotary encoder 102a. The controller 110 calculates a control target value ω _ref1 according to the PLD fluctuation data of the belt 103 according to the target belt speed command from the copying machine main body. Specifically, first, the belt 103 is driven so that the rotational angular velocity ω1 of the first roller 101 is maintained at the command control target value _ωref1 based on the target belt speed command from the copying machine main body. That is, the belt 103 is driven so that the rotational angular velocity ω ₁ of the first roller 101 is constant. Accordingly, the command control target value ω _{ref1 at} this time is the above-described constant rotational angular velocity ω ₀₁ . When the rotational angular velocity ω1 of the first roller 101 becomes constant, based on the pulse signal from the mark detection sensor 104, by the recognition method, the data of the PLD fluctuation f (t) from the rotational angular velocity omega ₂ of the second roller 102 get. Then, an appropriate correction control target value ω _ref1 according to the data of the PLD fluctuation f (t) is generated and output.

The correction control target value ω _ref1 output from the controller 110 in this way is compared with the rotational angular velocity ω ₁ of the first roller 101 by the comparator 113, and the deviation is output from the comparator 113. This deviation is input to the gain (K) 114 and the phase compensator 115, and a motor control signal is output from the phase compensator 115. The deviation input to the gain (K) 114 is a deviation between the control target value ω _ref1 obtained by correcting the PLD fluctuation of the belt 103 and the detected rotational angular velocity ω ₁ of the first roller 101. In this embodiment, this deviation is caused by a slip between the driving roller 105 and the belt 103, a drive transmission error due to the eccentricity of the driving gear 106a and the driven gear 105a, a belt moving speed fluctuation due to the eccentricity of the driving roller 105, and the like. . The drive motor 106 is driven so that the deviation is reduced by the motor control signal and the belt 103 moves at a constant speed. For this purpose, for example, a PID controller is used so that the deviation of the belt 103 to be controlled from the target speed is reduced and the motor control signal is output so as to be stable without overshoot and oscillation. The

In order to maintain the belt moving speed V at a constant speed V ₀ , the rotational angular speed ω ₁ of the first roller 101 may be controlled to be an expression derived as shown in the following equation (14). If the rotational angular velocity ω ₂ of the second roller 102 is controlled, the control is performed so that the following equation 15 is obtained.

In this belt drive control example 1, even if the belt 103 has a PLD fluctuation in the belt circumferential direction, as described above, the correction control in which the rotational angular velocity ω ₁ of the first roller 101 is corrected by the PLD fluctuation f (t). Control is performed to achieve the target value ω _ref1 . Therefore, fluctuations in the belt moving speed due to PLD fluctuations can be suppressed.

[Belt drive control example 2]
Next, a belt drive control example 2 in which the mechanism for detecting the home position as shown in FIG. 8 is eliminated and the cost is reduced will be described.
The basic process is the same as in the belt drive control example 1 described above, but in this belt drive control example 2, instead of the pulse signal of the mark detection sensor 104, the home position of the belt 103 is virtually specified. The home position of the belt 103 is grasped using the virtual home position signal. For example, using the cumulative rotation angle of the rollers obtained by the rotary encoders 101a, 102a, etc. as the virtual home position signal, it is predicted that the belt 103 has made one round from an arbitrary position. In this case, since the accumulated rotation angle when the roller rotates while the belt 103 makes one revolution can be grasped in advance, it can be predicted that the belt 103 has made one revolution from the accumulated rotation angle. At this time, the time at which the counting of the cumulative rotation angle is started is t = 0 of the PLD fluctuation f (t). This time corresponds to the time when a pulse signal is received from the mark detection sensor in the belt drive control example 1.

The virtual home position signal is set to be generated every rotation period of the belt 103. Various setting methods can be considered in addition to the cumulative rotation angle of the roller described above. For example, it is predicted that the belt 103 has made one revolution from an arbitrary position using the cumulative rotation angle of the drive motor 106, and a virtual home position signal is generated when the cumulative rotation angle corresponding to one revolution of the belt is reached. The method of setting to can be considered. In addition, if the belt 103 moves at a predetermined average moving speed, the time required to make one round of the belt is predicted from the average moving speed, and when the time corresponding to one round of the belt is reached, A method of setting to generate a virtual home position signal is conceivable.
In this belt drive control example 2, the prediction that the belt 103 has made one revolution is actual due to PLDave, which is the average PLD value of the belt, the accuracy of the parts such as the roller diameter, environmental changes, changes over time of the parts, etc. Error occurs.

If there is an error between the belt revolution estimated by the virtual home position signal and the actual belt revolution, the phase of the PLD fluctuation f (t) is cumulatively shifted. For this reason, if the belt drive control described above is performed based on the data of the PLD fluctuation f (t), the fluctuation of the belt moving speed occurs and becomes large.
This point will be described in detail. Even when the PLD fluctuation f (t) is obtained based on the virtual home position signal, when the target rotational angular velocity of the first roller 101 is controlled by ω _ref1 expressed by the above equation 14, The rotational angular velocity ω ₂ detected by the second roller 102 must be ω _ref2 shown in the above equation (15). Here, if the virtual home position obtained from the virtual home position signal is shifted from the actual home position by a time d, the belt moving speed Vd at this time is expressed by the following equation (16).

このときの第２ローラ１０２の回転角速度ω_2dは、下記の数１８に示すとおりである。

そして、この式に、上記数１７に示した式を代入して変形すると、下記の数１９に示す式となる。

By substituting the equation shown in the above equation 14 into this equation and transforming it, the following equation 17 is obtained.

The rotational angular velocity ω _2d of the second roller 102 at this time is as shown in the following _equation (18).

Then, by substituting the equation shown in Equation 17 into this equation and transforming it, the following Equation 19 is obtained.

Therefore, the deviation ω _2δ of the rotational angular velocity of the second roller 102 due to the deviation of the virtual home position obtained from the virtual home position signal by the time d from the actual home position is as shown in the following equation (20). It is. A deviation amount ω _2δ of the rotational angular velocity of the second roller is obtained as a difference between the rotational angular velocity detection data ω _2d of the second roller and the reference data ω _ref2 that should be in the second roller.

By substituting the equation shown in the above equation 16 and the equation shown in the above equation 19 into this equation, the following equation 21 is obtained.

The deviation amount ω _2δ expressed by the equation shown in the above equation 21 includes a fluctuation component (first term) generated when the virtual home position is shifted from the actual home position by the time d in the first roller 101, and the second Similarly, it can be seen that the roller 102 is also the result of superimposing the fluctuation component (second term) generated when the virtual home position is shifted from the actual home position by the time d.
When the absolute value of the deviation amount ω _2δ exceeds a certain value, or when the average of the absolute value of the deviation amount ω _2δ at one round of the belt, the root mean square, or the square root of the mean square exceeds a certain value. Then, the currently recognized PLD fluctuation f (t) is corrected. This correction is a state where the control was the rotational angular velocity omega ₁ of the first roller 101 at a constant rotational angular velocity omega ₀₁ detects the rotational angular velocity omega ₂ of the second roller 102, thereby obtaining a new PLD variation f (t) Then, using the data of f (t), control is performed so that the rotational angular velocity ω ₁ of the first roller 101 matches the reference rotational angular velocity ω _ref1 .

[Update of PLD fluctuation]
Next, a process for updating the PLD fluctuation f (t) obtained once will be described.
Depending on the belt material, the belt thickness changes due to changes in the environment (temperature and humidity) and wear due to use over time, or the Young's modulus changes due to repeated bending and stretching, so that the PLD of the belt 103 changes over time. The PLD fluctuation of the belt 103 may change. Further, when the belt 103 is replaced, the PLD variation may change from the PLD variation before the replacement. Further, as described in the belt drive control example 2 above, the virtual home position may deviate from the actual home position. In such a case, it is necessary to update the PLD fluctuation f (t).

  Regarding the method of updating the PLD fluctuation f (t), there are roughly two methods, that is, a method of updating intermittently and a method of updating continuously. As the former method, there is a method of monitoring whether the belt drive control based on the PLD fluctuation f (t) is appropriately performed and updating the PLD fluctuation f (t) only when it is determined that the belt driving control is not properly performed. . Further, there is a method of periodically updating the PLD fluctuation f (t) without performing such monitoring. As the latter method, there is a method in which the PLD fluctuation f (t) is always obtained and the PLD fluctuation f (t) is continuously updated.

Here, the principle of updating the PLD fluctuation f (t) once obtained will be described.
If the PLD fluctuation f (t) is obtained accurately once, the rotational angular velocity ω ₁ of the first roller 101 is maintained at ω _ref1 expressed by the above equation (14). Here, when the actual PLD fluctuation changes from f (t) to g (t), the change ω _2ε of the rotational angular velocity of the second roller 102 is expressed by the following equation (22).

  This is because, similarly to the equation shown in Equation 21, the fluctuation component (first term) generated when the PLD fluctuation f (t) changes to g (t) in the first roller 101, and the second roller 102. It can be said that this is the result of superimposing the fluctuation component (second term) generated when the PLD fluctuation f (t) changes to g (t). Therefore, the update method when the PLD fluctuation f (t) shown below changes to g (t) can be corrected including the error caused by the deviation of the virtual home position as in the belt drive control example 2 described above. it can.

When the equation shown in the equation 22 is transformed using the equation shown in the following equation 23, the equation shown in the following equation 24 is obtained. “G” in the equation (24) is the same as that shown in the equation (9).

The ε (t) can be obtained by detecting by filtering as in the recognition method based on the above-described deviation amount ω _2ε . After obtaining ε (t), a new PLD fluctuation f ′ (t) is obtained by adding ε (t) to the PLD fluctuation f (t) before the change. The new PLD fluctuation f ′ (t) is equal to the PLD fluctuation g (t) after the change as shown in the following equation (25).

Therefore, if belt drive control is performed using the newly obtained PLD fluctuation f ′ (t) instead of the PLD fluctuation f (t), appropriate belt drive control corresponding to the changed PLD fluctuation g (t) is performed. It can be carried out.
Here, the method of obtaining ε (t) from ω _2ε and correcting and updating the PLD fluctuation f (t) to g (t) using ε (t) has been described. A method in which (t) is directly obtained and updated may be used.

Next, the installation location of the rotary encoder for detecting the rotational angular velocities ω ₁ and ω ₂ of the two rollers 101 and 102 necessary for performing the belt drive control described above will be described.
In the belt drive control described above, if the rotational angular velocities of two rollers having different diameters (strictly speaking, G in Equation 9 is not 1) can be detected, the belt moving speed due to the PLD fluctuation of the belt 103 is detected. Variations can be suppressed. For example, the following three types of locations of the rotary encoder for detecting the rotational angular velocity are conceivable. First, as shown in FIG. 9, a rotary encoder is installed on two driven rollers having different diameters other than the driving roller 105 (installation example 1 of the rotary encoder). The second is a case where a rotary encoder is installed on the drive roller 105 and one driven roller having a diameter different from that of the drive roller (Installation Example 2 of the rotary encoder). Third, a rotary encoder is installed on the driving roller 105 and the two driven rollers 101 and 102 having different diameters, or the driving roller 105 and the driven rollers 101 and 102 having different diameters from each other. This is a case where a rotary encoder is installed at 102 (Rotary encoder installation example 3). When the rotary encoder is installed on the drive roller 105, not only the rotary encoder is provided on the roller shaft of the drive roller 105 but also the motor shaft of the drive motor 106 is included.

[Rotary encoder installation example 1]
In this installation example 1, as shown in FIG. 9, the rotary encoders are installed on two driven rollers 101 and 102 having different diameters. In this case, as described above, the first roller 101 has a function capable of feedback control so that the rotational angular velocity ω ₁ of the first roller 101 becomes the control target value ω _ref1 determined by the controller 110. Therefore, the PLD fluctuation f (t) can be obtained with high accuracy in a state where the transmission error of the drive transmission system and the slip between the drive roller and the belt are corrected. For example, in the state in which the driving roller is feedback-controlled in this way, the PLD fluctuation f (t) is obtained from the detection result of the rotational angular velocity ω ₂ of the second roller 101, so that the transmission error of the driving transmission system, the driving roller 105 and the belt The PLD fluctuation f (t) with high accuracy that does not depend on the slip with 103 can be obtained.

[Installation example 2 of rotary encoder]
FIG. 10 is an explanatory diagram for explaining a control operation in the present installation example 2.
In this installation example 2, the motor and the drive roller are connected via a gear, but a DC servo motor is used as the drive motor 106, and the encoder is attached to the motor shaft or the drive roller shaft is used as the rotational angular velocity. It has a function that can detect and feedback control. In addition to the DC servo motor, a stepping motor capable of controlling the rotational angular velocity with the input drive pulse frequency may be used. In this case, since the rotational angular velocity can be controlled by the input drive pulse frequency to the stepping motor without feedback from the encoder, it is not necessary to install an encoder on the motor shaft or the drive roller. Also in this installation example 2, the rotational angular velocities ω _m and ω ₂ of the driving roller 105 and the driven roller 102 can be detected. Further, the rotational angular velocity ω _m of the motor shaft and the rotational angular velocity of the drive roller 105 rotate with a fixed relationship. Accordingly, the rotational angular velocity omega _m of the motor shaft becomes equivalent to the rotational angular velocity omega ₁ of the first roller 101 in the installation example 1. However, when a reduction mechanism is provided, the equivalent to the rotational angular velocity ω ₁ is obtained in a state where the reduction ratio is taken into consideration. As a result, also in the installation example 2, the PLD fluctuation f (t) can be obtained with high accuracy as in the installation example 1. However, in the present installation example 2, the rotational angular velocity ω ₂ of the second roller 102 detected by the angular velocity detection unit 112 includes fluctuation due to a drive transmission system error and slip between the drive roller 105 and the belt 103. Therefore, it is necessary to reduce these fluctuations and obtain the PLD fluctuation f (t). In particular, the friction coefficient is increased by exposing the surface of the roller so as not to cause a slip between the driving roller 105 and the belt 103. However, in this installation example 2, since it is not necessary to provide the rotary encoder 101a on the driven roller 101, the number of parts can be reduced by that amount, and the cost can be reduced compared to the installation example 1. .

[Installation example 3 of rotary encoder]
FIG. 11 is an explanatory diagram for describing a control operation in the third installation example.
In this installation example 3, as in the installation example 2, a drive motor 106 that can drive and control the rotational angular velocity, such as a DC servo motor or a stepping motor, is employed. Further, in the third installation example, as in the first installation example, the rotary encoders 101a and 102a are installed on the two driven rollers 101 and 102 having different diameters. Therefore, in this installation example 3, similarly to the installation example 1, the PLD fluctuation f (t) can be obtained with the same high accuracy as the installation example 1. In addition, the third installation example has a configuration for acquiring the rotational angular velocity ω _m information of the motor shaft, that is, a configuration taking a minor loop, and a more stable control system can be designed.

Further, the motor shaft rotates at a constant rotational angular velocity, that is, the driving roller 105 is driven at a constant rotational angular velocity, and the average rotational angular velocity of the first roller 101 and the second roller 102 is obtained, whereby the first roller 101 And the diameter ratio of the 2nd roller 102 can be calculated | required correctly. As a result, for example, the diameters of the first roller 101 and the second roller 102 change due to manufacturing variations, environmental changes, aging, and the like, so that the effective roller radius R ₁ , R ₁ , Even if R ₂ deviates from the actual one, the diameter ratio can be corrected.
The effective roller radius R here indicates (r + PLD _ave ) as described above, and varies depending on the variation of the roller radius and the PLD _ave of the belt. In the above equation 7, the effective roller radius R is an important parameter. As the accuracy of this ratio increases, the detection accuracy of PLD fluctuations increases. This is the same when the recognition method 1 or the recognition method 3 is used. The ratio of the effective roller radius R between the first roller 101 and the second roller 102 is obtained by controlling the first roller 101 to a constant rotational angular velocity to obtain the rotational angular velocity ratio or rotational angle ratio between the first roller 101 and the second roller 102. Therefore, the same can be said for the rotary encoder installation examples 1 and 2. In the rotary encoder installation example 3, the PLD fluctuation effective coefficients κ ₁ and κ ₂ of the rollers 101 and 102 can be corrected. That is, the PLD fluctuation f ₂ (t) is obtained using the rotational angular velocities ω _d and ω ₂ of the drive roller 105 and the second roller 102. Further, the PLD fluctuation f ₁ (t) is obtained by using the rotational angular velocities ω _d and ω ₁ of the driving roller 105 and the first roller 101. The two PLD fluctuations f ₁ (t) and f ₂ (t) obtained in this way are for the same belt 103 and should be equal to each other. However, if the roller effective radii R ₁ and R _{2 of the} rollers 101 and 102 are accurate, they may not be equal to each other due to setting value errors of the PLD fluctuation effective coefficients κ ₁ and κ ₂ . In such a case, the ratio of the PLD fluctuation effective coefficients pκ ₁ = κ ₁ / κ _d and pκ ₂ = κ ₂ / κ _d such that the two PLD fluctuations f ₁ (t) and f ₂ (t) coincide with each other. By calculating (κ _d : PLD fluctuation effective coefficient at the driving roller section) and correcting the PLD fluctuation effective coefficient ratio κ ₂ / κ ₁ , the roller effective radius ratio R ₁ / R ₂ is calculated as described above. Since it can be obtained with high accuracy, it can be seen that the PLD fluctuation f (t) can be recognized with higher accuracy than the equation (7). This is effective when the effective roller radius of either the first roller 101 or the second roller and the PLD fluctuation effective coefficient are likely to fluctuate.

ただし、ω_dは駆動ローラの回転角速度、Ｒ_dは駆動ローラ実効半径、τ₁は駆動ローラ１０５と第１ローラ１０１間をベルトが通過することによって決まる遅延時間である。

ただし、τ₂は駆動ローラ１０５と第２ローラ１０２間をベルトが通過することによって決まる遅延時間である。 Here, a method for obtaining the ratio of the PLD fluctuation effective coefficient κ of the first roller 101 and the second roller 102 will be described. The relationship between the driving roller 105 and the first roller 101 can be expressed by the following equations (26) and (27) so that the equation (7) can be easily estimated. Further, the relationship between the driving roller 105 and the second roller 102 can be expressed by the following equations 28 and 29.

Here, ω _d is the rotational angular velocity of the driving roller, R _d is the effective radius of the driving roller, and τ ₁ is a delay time determined by the belt passing between the driving roller 105 and the first roller 101.

However, τ ₂ is a delay time determined by the belt passing between the driving roller 105 and the second roller 102.

Here, the roller effective radius ratios pR ₁ and pR ₂ are obtained by the method described above, and R ₂ on the left side of the equation (28) is replaced with R ₂ = (pR ₁ / pR ₂ ) R ₁ , and By changing the PLD fluctuation effective coefficient ratio pκ ₁ = κ ₁ / κ _d or pκ ₂ = κ ₂ / κ _d corresponding to the one where the PLD fluctuation effective coefficients κ ₁ and κ ₂ tend to fluctuate, the PLD fluctuation derivation result is f ₁ (t) = f ₂ (t). Then, the PLD fluctuation effective coefficient ratio κ ₂ / κ ₁ between the first roller and the second roller is obtained from the obtained effective coefficient ratios (pκ ₂ / pκ ₁ = (κ ₂ / κ _d ) / (κ ₁ ). / Κ _d ) = κ ₂ / κ ₁ ). Thereby, the PLD fluctuation f (t) can be recognized with higher accuracy. If the fluctuation of the roller effective radius R _{1 on} the left side of the equation (26) is small and obtained in advance, the accuracy becomes higher. Alternatively, if the variation of the effective roller radius R ₂ on the left side of the formula is obtained in advance less the number 28, likewise, more accuracy is high. However, in order to derive the roller effective radius ratio and the PLD fluctuation effective coefficient ratio, it is preferable to perform low speed driving so that there is no slip with the belt in the driving roller portion when detecting rotation information.

[Example 1]
Next, a specific embodiment (hereinafter, this embodiment is referred to as “embodiment 1”) for updating the PLD fluctuation f (t) will be described. The first embodiment uses the above-described method 2 for recognizing the PLD fluctuation f (t). Further, there is no mechanism for detecting the home position of the belt 103 as in the belt drive control example 2, and the rotary encoder is also provided on the motor shaft of the drive motor 106 as in the rotary encoder installation example 3. This is an example in which a controllable one is adopted and the rotary encoders 101a and 102a are respectively installed on two driven rollers 101 and 102 having different diameters. Of course, as described above, the present invention can be implemented even in a configuration in which the rotary encoder is not provided on the motor shaft.

FIG. 1 is an explanatory diagram for explaining an update process according to the first embodiment. In this figure, a rotary encoder 106 b installed in the drive motor 106 is provided in a DC servo motor employed as the drive motor 106. In addition, a digital signal processing unit as control means surrounded by a broken line in the figure is constituted by a digital circuit, a DSP, a μCPU, a RAM, a ROM, a FIFO (Fast In Fast Out), and the like. Of course, the specific hardware configuration is not limited to this configuration. Some control blocks in the figure are processed by calculation in firmware.
In the first embodiment, since there is no mechanism for detecting the home position of the belt 103, as described in the belt drive control example 2, the virtual home position shifts and a phase error occurs. Further, the actual PLD fluctuation of the belt 103 may change due to environmental changes and changes with time. Therefore, it becomes necessary to update the PLD fluctuation f (t) obtained in the past. In the first embodiment, whether to update intermittently or continuously can be arbitrarily determined according to the load of an arithmetic processing unit such as a CPU.

  In the case where the update is performed intermittently, in the first embodiment, by checking the fluctuation of the belt moving speed, it is monitored whether the accuracy of the PLD fluctuation f (t) is within a certain allowable range. When it exceeds, PLD fluctuation f (t) is updated. Specifically, as described above, the absolute value of the value of ε (t) shown in the above equation 23, the average of the absolute value, the root mean square, or the square root of the root mean square is a predetermined allowable range. If it exceeds the allowable range, a process for updating the PLD fluctuation f (t) is performed. Of course, a process of periodically updating may be performed in accordance with the operating time or operating amount of the copying machine. If the absolute value of the ε (t) value, the average of the absolute value, the root mean square, or the square root of the root mean square does not fall within the allowable range even after the update process is performed, the initial values that are assumed are incorrect. Since there is an error, an error is reported.

More specifically, first, the controller 410 turns off the switches SW1 and SW2, and the rotation angular velocity ω of the first roller 101 obtained by the rotation angular velocity reference signal data ω ₀₁ (= V ₀ / R ₁ ) and the angular velocity detection unit 111. ₁ and the belt 103 is driven so that the first roller 101 has a constant rotational angular velocity ω ₀₁ . The two phase compensators 115a and 115b function to eliminate steady-state errors and perform stable feedback control. When the rotational angular velocity ω ₁ of the first roller 101 becomes a constant rotational angular velocity ω ₀₁ , the rotational angular velocity ω ₂ of the second roller 102 obtained by the angular velocity detecting unit 112 is expressed by the following equation 30 It becomes like the formula shown. “G” in the equation of Equation 30 is the same as that shown in Equation 9 above. In the first embodiment, since digital processing is premised, tn representing time discretely is used instead of time t. Therefore, the PLD fluctuation f (t) described above is replaced with f (tn).

The PLD fluctuation f (tn) is obtained from the rotational angular velocity ω ₂ of the second roller 102, and data for one round of the belt is stored in the FIFO 419 as fluctuation information storage means. In this process, first, the fixed data (R ₁ · ω ₀₁ ) / R ₂ calculated in the block 1302 is obtained from the detected rotational angular velocity ω ₂ of the second roller 102 in a state where the switches SW1 and SW2 are OFF. , And subtracted by the subtractor 1313. The value output from the subtractor 1313 is multiplied by the fixed data R ₂ / (κ ₁ · ω ₀₁ ) in the block 1304, and the output data is input to the FIR filter in the block 1315. That is, the output data of the block 1304 is f (tn) −Gf (tn−τ), and this data is input to the FIR filter 1315. The output of this filter is each data (nth time discrete PLD fluctuation data) fn constituting a data string of the PLD fluctuation f (tn). The controller 410 observes the rotational angular velocity ω ₁ of the first roller 101, and after the time has elapsed when the rotational angular velocity ω ₁ is constant and accurate PLD fluctuation data fn is output from the FIR filter 1315, the switch SW1. Turn on. This is because the FIR filter 1315 includes a delay element, so that accurate PLD fluctuation data fn is not output at the initial stage of filter execution. Then, the controller 410 counts the number of encoder output pulses of the first roller 101 and confirms that the belt 103 has moved one round, and then turns off the switch SW1. The PLD fluctuation data fn output from the FIR filter 1315 is accumulated in a PLD fluctuation data FIFO 419 having a capacity capable of storing the PLD fluctuation data fn for exactly one belt revolution. In the first embodiment, when the data in the FIFO 419 is empty, the PLD fluctuation data fn is stored by turning on the switch SW1.

この数３１に示す式の中かっこ内の演算処理は、ブロック１３０９で行われる。そして、図１に示す２つのスイッチＳＷ２をオンにすることで、第１ローラ１０１の基準データω_ref1が減算部１３１０から出力されることになる。 As described above, the PLD fluctuation data fn is accumulated in the FIFO 419 in accordance with the rotation of the belt 103. If the PLD fluctuation data fn is used and the reference data ω _ref1 of the first roller 101 is generated according to the following equation 31, drive control corresponding to the PLD fluctuation f (tn) is performed.

The calculation processing in the curly braces of the expression shown in Expression 31 is performed in block 1309. 1 is turned on, the reference data ω _ref1 of the first roller 101 is output from the subtracting unit 1310.

Further, by turning on the switch SW2, processing for detecting the control error ω _2ε represented by the equation shown in the above equation 24 is performed. In this process, first, the rotation angular velocity fluctuation of the second roller 102 is calculated in block 1307 and 1308, a constant rotational angular velocity omega ₀₁ block 1301 is added predicted from PLD variation data fn are accumulated in the FIFO419 After that, it is calculated by the block 1302 and subtracted by the subtractor 1313 from the rotational angular velocity ω ₂ detected by each speed detector 112. The output from the subtractor 1313 is ω _{2ε in} the equation shown in the above equation 24. This is input to block 1304. As a result, the output of the FIR filter 1315 is input to the controller 410 as PLD fluctuation error data εn. Then, when the PLD fluctuation error data εn exceeds a predetermined value, the controller 410 turns on the switch SW1 for a time corresponding to one revolution of the belt to obtain new PLD fluctuation data fn, which is stored in the FIFO 419. Update. When the switches SW1 and SW2 are both turned on in the state where the PLD fluctuation data fn before update has already been stored in the FIFO 419, the adder 1306 corrects the PLD fluctuation shown in the above equation (25). The corrected PLD fluctuation data is re-stored in the FIFO 419.

  When the PLD fluctuation data fn is accumulated in the FIFO 419, the data fn for a plurality of belt circumferences may be taken and averaged to be stored in the FIFO 419. In this case, the FIFO 419 also functions as past information storage means. Similarly, PLD fluctuation error data εn is also obtained by taking data εn for a plurality of belt circumferences and using the averaged data to reduce errors due to random fluctuations caused by gear backlash and noise. You may make it do.

Next, the case of continuously updating will be described. In this case, the correction of the PLD fluctuation shown in the formula 25 is always performed. That is, in FIG. 1, both the switches SW1 and SW2 are turned on.
More specifically, first, compared when PLD fluctuation data FIFO419 is empty, the controller 410 turns off the switch SW1, and a rotational angular velocity omega ₁ of the first roller 101 determined by the reference signal omega ₀₁ and the angular velocity detecting section 111 Then, the belt 103 is driven so that the first roller 101 has a constant rotational angular velocity ω ₀₁ . When the output of the FIR filter 1315 is stabilized, the switch SW1 is turned on, and the PLD fluctuation data fn is accumulated in the FIFO 419 for one belt revolution. Thereafter, when both the switches SW1 and SW2 are turned on, the sum of the output data εn of the FIR filter 1315 and the output data of the FIFO 419 becomes new PLD fluctuation data fn input to the FIFO 419 again. This data εn is PLD fluctuation error data obtained from the output of the FIR filter from the relationship of the equations shown in the above equations 22 and 24. In this case, the PLD fluctuation data fn whose error has been corrected rotates corresponding to one belt cycle in the FIFO. When the PLD fluctuation data fn is used to generate the reference signal ω _ref1 of the first roller 101 according to the equation shown in the above equation 31, drive control corresponding to the PLD fluctuation f (tn) is performed. At this time, if the controller 410 determines that the PLD fluctuation error data εn exceeds a predetermined value, it notifies the copying machine main body of the abnormality.

  In the first embodiment, the storage input data of the PLD fluctuation data fn is realized by using the FIFO 419 that shifts by the clock signal and the memory function of the block 1307 that outputs the input data after being delayed for a certain time. It may be realized by a memory function.

[Example 2]
Next, another embodiment (hereinafter, this embodiment is referred to as “embodiment 2”) for updating the PLD fluctuation f (t) will be described. In the second embodiment, a case will be described in which the PLD fluctuation data fn newly calculated in the FIFO 419 is sequentially accumulated and controlled instead of correcting the PLD fluctuation data fn as in the first embodiment. Further, in the following description, an example will be described in which PLD fluctuation data fn newly obtained in the FIFO 419 is sequentially accumulated and continuously updated using the PLD fluctuation data fn before the belt.

First, each rotational speed ω ₂ of the second roller 102 is detected, and then PLD fluctuation data gn is newly obtained from data excluding the reference data ω _ref1 calculated from the PLD fluctuation data fn stored in the FIFO 419. That is, the rotational angular velocity ω ₂ ′ of the second roller 102 is detected based on the virtual home position while the belt is driven and controlled based on the PLD fluctuation data fn currently stored in the FIFO 419. Then, the reference data ω _ref1 at this time is _multiplied by (R ₁ / R ₂ ), subtracted from the rotation angular velocity ω ₂ ′, and new reference data is obtained by using the signal ω ₂ ″ obtained from this. Based on this, drive control is performed.

ここで、上記信号ω₂''は下記の数３３に示す式から求まる。

したがって、上記数３１及び上記数３２に示した式から、下記の数３４に示す式が得られる。この数３４の式中の「Ｇ」は、上記数２９に示したものと同じであり、本実施例２における第１ローラ１０１及び第２ローラ１０２のローラ径比の関係から１よりも小さい値をとる。

この数３４に示す式から、ＰＬＤ変動データｇ（ｔｎ）を求めることができる。具体的には、例えば上述したＦＩＲフィルタやにより、新たなＰＬＤ変動データｇｎのデータ列として得ることができる。 The rotational angular velocity ω ₂ ′ of the second roller 102 detected with reference to the virtual home position is expressed by the following equation (32).

Here, the signal ω ₂ ″ is obtained from the following equation 33.

Therefore, the following equation 34 is obtained from the equations 31 and 32. “G” in the equation (34) is the same as that shown in the above equation (29), and is smaller than 1 due to the relationship between the roller diameter ratios of the first roller 101 and the second roller 102 in the second embodiment. Take.

From the equation shown in Equation 34, the PLD fluctuation data g (tn) can be obtained. Specifically, it can be obtained as a data string of new PLD fluctuation data gn by, for example, the FIR filter described above.

FIG. 12 is an explanatory diagram for explaining an update process according to the second embodiment. In this figure, the rotary encoder 106b installed in the drive motor 106 is provided in the DC servo motor employed as the drive motor 106, as in the first embodiment. In addition, the digital signal processing unit surrounded by a broken line in the figure includes a digital circuit, a DSP, a μCPU, a RAM, a ROM, a FIFO (Fast In Fast Out), and the like. Of course, the specific hardware configuration is not limited to this configuration. Some control blocks in the figure are processed by calculation in firmware.
In the second embodiment, first, the controller 510 turns off the switch SW1, and compares the reference data ω ₀₁ (= V ₀ / R ₁ ) with the rotational angular velocity ω ₁ of the first roller 101 obtained by the angular velocity detection unit 111. Then, the belt 103 is driven so that the first roller 101 has a constant rotational angular velocity ω ₀₁ . When the rotation angular velocity ω ₁ of the first roller 101 becomes a constant rotation angular velocity ω ₀₁ , the rotation angular velocity ω ₂ of the second roller 102 obtained by the angular velocity detection unit 112 is expressed by the following equation (35).

Here, ω ₀₁ output from the subtractor 1310 is multiplied by (R ₁ / R ₂ ) in the block 1302, and the fixed data (R ₁ · ω ₀₁ ) / R ₂ is input to the subtractor 1313. The value output from the subtractor 1313 is multiplied by fixed data R ₂ / (κ ₁ · ω ₀₁ ) in block 1304. This output data is input to the FIR filter or IIR filter of block 1315. That is, the output data of the block 1304 is f (tn) −Gf (tn−τ), and this data is input to the FIR filter. The output of this filter becomes each PLD fluctuation data fn constituting a data string of PLD fluctuation f (tn). The controller 510 observes the rotational angular velocity ω ₁ of the first roller 101, and after the time when the rotational angular velocity ω ₁ is constant and accurate PLD fluctuation data fn is output from the FIR filter, the switch SW 1 is turned on. turn on. This is because the delay element is included in the FIR filter, so that the accurate PLD fluctuation data fn is not output at the initial stage of the filter execution. If the PLD fluctuation data fn is used to calculate the reference data ω _ref1 of the first roller 101 in the block 1309 according to the equation shown in the above equation 31, the drive control corresponding to the PLD fluctuation f (tn) is performed. Become.

In the second embodiment, the FIFO 419 is inserted when the digital signal processing including the derivation calculation of the PLD fluctuation data fn or the multiplication of the block 1309 takes time. That is, the reference signal ω _ref1 is generated from the PLD fluctuation data fn for one belt revolution. Further, since the rotational angular velocity ω ₁ of the first roller 101 is controlled by the reference data ω _ref1 , the rotational angular velocity detection data ω ₁ of the first roller 101 is directly blocked as shown by the one-dot chain line in the figure. It may be configured to input to 1302.
In the second embodiment, the signal ω ₂ ″ includes a variation in the roller diameters of the first roller 101 and the second roller 102, a change due to temperature, or a DC component error due to a calculation error. Then, an error occurs in the filter processing of the subsequent FIR filter. When this error becomes a problem, a high-pass filter for removing the DC component of the signal ω ₂ ″ is inserted before the filter processing of the FIR filter.

In the first and second embodiments described above, a 1 / (1-G ^{2Nb + 1} ) multiplication block is provided in or after the block 1315 that is an FIR filter. In the recognition method, when Nb = 1, the output data f (tn) −G ³ f (tn−3τ) of the block 1315 is approximated to f (tn) = f (tn−τ). This is because the PLD fluctuation data fn is calculated as (1-G ³ ) f (tn).
In the first and second embodiments described above, based on the rotational angular velocity ω ₂ of the second roller 102 detected by the angular velocity detection unit 112, the rotation cycle of the first roller 101 and the second roller 102, other cycle fluctuations, Furthermore, a low-pass filter may be inserted in order to remove fluctuations in the high frequency range including noise. Thereby, the correction control of the belt movement speed fluctuation due to the PLD fluctuation can be stably suppressed with higher accuracy. This low-pass filter may be provided before the FIR filter or after the angular velocity detector 112. In the first and second embodiments, averaging may be performed to reduce random detection errors caused by gear backlash or noise. In other words, the data fn for the belt N (natural number) rounds is fetched into a RAM (Random Access Memory) in the form of first-in first-out (FIFO: First In First Out), and the data for N belts or less in the RAM is averaged. This is used as PLD fluctuation data. When the PLD fluctuation data is continuously updated, the reference data is generated with data obtained by averaging the PLD fluctuation data from before one rotation of the belt to at most N rotations.
In the first and second embodiments, the reference data ω _ref1 indicating the rotational angular velocity is converted into data indicating the rotational angular displacement, which is obtained from the output of the rotary encoder 101 a provided on the first roller 101. It is also possible to perform control in comparison with rotational angular displacement.
In the first and second embodiments, the reference data ω _ref1 is converted into a pulse train so as to control the pulse phase that is continuously output based on the output of the rotary encoder 101a provided on the first roller 101. It may be converted to perform PLL control.

As described above, the belt drive control device in the embodiment is a drive roller 105 that is a drive support rotating body to which a rotational driving force is transmitted among the support rollers 101, 102, and 105 as a plurality of support rotating bodies around which the belt 103 is stretched. By controlling the rotation of the belt 103, the driving of the belt 103 is controlled. In this belt drive control device, the effective radius of the rollers is different among the plurality of support rollers, or the PLD of the belt portion wound around the belt is the moving speed V of the belt and the rotation angular velocities ω ₁ and ω _{2 of the} belt. Of the belt moving speed V caused by the PLD fluctuation in the circumferential direction of the belt 103 based on the detection result of the rotational angular displacement or rotational angular velocity of the two first rollers 101 and the second rollers 102 that have different degrees of influence on the relationship with each other. A digital signal processing unit is provided as control means for controlling the rotation of the drive roller 105 so that the fluctuation is reduced. In this embodiment, the digital signal processing unit obtains PLD fluctuation information f (t) using an arbitrary point on the moving path of the belt 103 as a virtual home position, and uses the PLD fluctuation information f (t). The rotation control is performed. According to this apparatus, as described above, the two driven rollers 101 depend on the size of the effective roller radii R ₁ and R ₂ , the wrapping angles θ ₁ and θ _{2 of} the belt, the material of the belt, the layer structure of the belt, and the like. , 102 using the difference in the magnitude of the PLD fluctuation in the belt circumferential direction detected from the rotational angular velocities ω ₁ , ω ₂ of the rollers 102, 102 from the rotational angular displacements or rotational angular velocities ω ₁ , ω _{2 of} these rollers 101, 102. The PLD fluctuation given to the relationship between the belt moving speed V and the rotational angular velocities ω ₁ and ω ₂ of the rollers 101 and 102 can be specified with high accuracy even if the fluctuation is complicated. As a result, the belt 103 can be driven and controlled with high accuracy so that fluctuations in the belt moving speed due to PLD fluctuations are reduced.
In this embodiment, as described in the method for recognizing PLD fluctuations, the ratio of the belt conveyance section (distance) between the two rollers 101 and 102 to the belt total conveyance section (circumferential length) is 1: (2Nb + 1). ) (Where “Nb” is a natural number) and the detection results of the rotational angular displacements or rotational angular velocities ω ₁ and ω ₂ of the two rollers 101 and 102 detected at the same time, respectively. (The data on the left side of the equation shown in Equation 7 above), or the rotation angle displacement or rotation speed ω ₂ of the other of the rollers 101 and 102 while maintaining one of the rollers 101 and 102 at the constant angular speed ω _01. Since the data obtained based on is detection information including two pieces of PLD fluctuation information f (t) and f (t−τ), the coefficient of one of the PLD fluctuation information is determined according to the equation shown in Equation 7 above. Is 1 Performs normalization that, the filter length is performed FIR filtering (2Nb + 1), performs the rotation control using 1 / processing result obtained by multiplying the ^{(1-G 2Nb +} 1) as the PLD variation information. The FIR filter process gives 2Nb different gains to the input time function, and at the delay time τ, which is the movement time required for the belt 103 to move between the two rollers 101, 102. Based on this, an addition process for adding (2Nb + 1) pieces of data including the input time function is performed on the input time function delayed or advanced in phase. As the gain before the addition processing, the n-th gain is obtained by raising G to the nth power, and the n-th phase delay (advance) amount is obtained by multiplying τ by n for the predetermined time τ. Is what you do. At this time, the PLD fluctuation effective coefficients κ ₁ and κ ₂ of the two support rotators and the effective radius R ₁ of the two support rotators are set so that the gain G expressed by the equation shown in Equation 9 is different from _1. , R ₂ are set. Since such processing can be performed using an FIR filter, stable processing is possible.
In the present embodiment, a PLD fluctuation data FIFO 419 is provided as fluctuation information storage means for storing PLD fluctuation information f (t) for a period corresponding to the time Tb required for the belt 103 to make one revolution. . Thereby, it is possible to secure the calculation time for recognition and correction of the PLD fluctuation information f (t) and the calculation time for other processing of the calculation device.
In the present embodiment, a process for obtaining the PLD fluctuation information f (t) again at a predetermined timing is performed. As a result, the PLD fluctuation f (t) can be obtained again at the timing when the PLD fluctuation of the belt 103 changes beyond the allowable range depending on the environment and use over time. As a result, even if the PLD fluctuation of the belt 103 changes, highly accurate belt drive control can be maintained. In particular, as described in the first embodiment, the predetermined timing is determined based on the difference between the PLD fluctuation data predicted based on the belt movement position of the belt 103 and the PLD fluctuation information f (t) and the actual PLD fluctuation data. If the timing exceeds the allowable range, the belt drive control can be maintained more stably and accurately.
In the present embodiment, as described in the second embodiment, the rotation control may be performed while performing the process of obtaining the PLD fluctuation information f (t). In this case, the belt drive control can be maintained more stably and accurately. In this case, it is not necessary to store the PLD fluctuation information f (t) for one rotation of the belt, so that such storage means is not necessary.
In the present embodiment, as described above, the PLD fluctuation data FIFO 419 is provided as past information storage means for storing the past PLD fluctuation information for at least one belt revolution, and the past PLD fluctuation information stored in the PLD fluctuation data FIFO 419 is stored. The rotation control may be performed by using the PLD fluctuation information f (t) obtained by performing an averaging process or the like from the newly obtained PLD fluctuation information. In this case, the PLD fluctuation information obtained in the past and the newly obtained PLD fluctuation information can be averaged, so that the PLD fluctuation information f (t) can be obtained with higher accuracy. As a result, the influence of detection errors due to random fluctuations caused by gear backlash or noise can be reduced.
Further, the belt device in this embodiment includes a belt 103 that is stretched around a plurality of rollers including support rollers 101, 102, and 105, and a drive motor 106 as a drive source that generates a rotational drive force for driving the belt 103. Among these rollers, the roller radius is different, or the degree to which the PLD of the belt portion wound around the roller affects the relationship between the moving speed V of the belt and the rotation angular velocities ω ₁ and ω ₂ of the belt. Rotational encoders 101a, 102a and angular velocity detectors 111, 112 as detection means for detecting rotational angular displacements or rotational angular velocities ω ₁ , ω ₂ in two different first rollers 101 and second rollers 102; Among these rollers, the driving of the belt 103 is controlled by controlling the rotation of the driving roller 105 to which the rotational driving force is transmitted. As gate drive control device, and using the above-described belt driving controller. Thereby, as described above, a belt device capable of controlling the driving of the belt 103 with high accuracy is realized.
Moreover, in the installation example 1 of the rotary encoder according to the present embodiment, the two rollers 101 and 102 are all driven rollers that rotate along with the movement of the belt 103. In this case, when obtaining the PLD fluctuation f (t), it does not depend on fluctuation components (such as slip between the driving roller 105 and the belt 103) that cause the recognition error. Therefore, the PLD fluctuation f (t) can be obtained with higher accuracy.
In particular, as described in the installation example 3 of the rotary encoder of the present embodiment, the drive motor 106 detects its own rotational angular displacement or rotational angular velocity ω _m , and the rotational angular displacement or rotational angular velocity ω _m is the target. If a device having a feedback control means for performing feedback control so as to achieve a rotational angular displacement or a rotational angular velocity is used, a more stable control system can be designed. In addition, since the PLD fluctuation effective coefficients κ ₁ and κ ₂ of the driven rollers 101 and 102 described above can be corrected, the PLD fluctuation f (t) can be obtained with higher accuracy.
In the installation example 2 of the rotary encoder of the present embodiment, the driving roller 105 is included in the two rollers related to the rotational angular displacement or rotational angular velocity for obtaining the PLD fluctuation information f (t). The detection means for detecting the rotational angular displacement or rotational angular velocity of the driving roller 105 detects the rotational angular displacement or rotational angular velocity ω _m of the driving motor 106 or the target rotational angle input to the driving motor 106. A device that detects a displacement or a target rotational angular velocity is used. Thus, for example, if a pulse motor is used as the drive motor, it is sufficient to provide at least one rotary encoder, so that the cost can be reduced. That is, one of the rotational angular displacement or rotational angular velocity for obtaining the PLD fluctuation information f (t) is the rotational angular displacement or rotational angular velocity of the driving roller 105 that can guarantee the rotational angular displacement or rotational angular velocity to be constant. The PLD fluctuation information f (t) can be obtained only by the rotational angular displacement or rotational angular velocity ω ₂ of the roller 102, and the recognition process can be simplified.
In the present embodiment, as described in the belt drive control example 1, in order to grasp the reference belt movement position of the belt 103, the home position mark 103a that is a mark indicating the reference position on the belt 103 is set. A mark detection sensor 104 is provided as mark detection means for detection. Then, after grasping the relationship between the belt movement position corresponding to the obtained PLD fluctuation information f (t) and the actual belt movement position based on the detection timing by the mark detection sensor 104, the rotation control is performed. Thereby, since the reference position in the belt circumference can be determined, the obtained PLD fluctuation information f (t) can be used for the belt drive control in a state adapted to the PLD fluctuation of the belt 103, and the belt drive control is appropriately performed. It can be carried out.
In the present embodiment, as explained in the belt drive control example 2 above, the relationship between the belt movement position corresponding to the obtained PLD fluctuation information f (t) and the actual belt movement position is grasped in advance. The above rotation control is performed after grasping based on the average time required for the belt 103 to make one revolution or the belt circumferential length grasped in advance. As a result, the reference position (virtual home position) in one circumference of the belt can be determined without providing the home position mark 103a on the belt 103 or the mark detection sensor 104. Therefore, cost reduction can be achieved.
In addition, when the belt 103 is a seam belt having a joint at at least one place in the belt circumferential direction, the joint portion is thicker than the other portions, or the physical properties have changed and the other portions. The elasticity may be different. In such a case, even if the joint part has the same thickness as the other part, the PLD of the joint part is greatly deviated from the PLD of the other part. According to the belt drive control device of the present embodiment, as described above, the PLD fluctuation can be specified with high accuracy even for the belt having the protruding PLD fluctuation. Therefore, even such a seam belt can be controlled with high accuracy by suppressing sudden belt speed fluctuation that may occur when the joint portion is wound around the driving roller.
Further, when the belt 103 is a multi-layer belt having a plurality of layers in the belt thickness direction, even if the belt thickness is the same, the PLD varies depending on the layer structure or the like, and belt speed variation occurs. According to the belt drive control device of the present embodiment, as described above, the PLD fluctuation is specified and the drive control is performed based on the PLD fluctuation. Therefore, it is possible to drive and control the multi-layer belt with high accuracy.

The above description is the same even if the rotational angular velocity is converted into rotational angular displacement. This is because the rotational angular velocity is obtained by integrating the rotational angular velocities, and the relationship between the PLD fluctuation f (t) and the rotational angular displacement of the roller is obtained similarly. Specifically, the rotational angular displacement fluctuation is obtained by removing the average increase (the inclination component of the rotational angular displacement) from the detected rotational angular displacement, and the recognition method described above for the rotational angular velocity fluctuation is obtained from the rotational angular displacement fluctuation. The PLD fluctuation f (t) is acquired by the same method.
Further, in the above-described embodiment, when the belt 103 moves in the reverse direction, considering that the belt is rotating, the above-described explanation is that the delay time τ is Tb−τ (Tb: belt one rotation time). Replace it. At this time, 2 (Tb−τ) = 2Tb−2τ = Tb−2τ, and N (Tb−τ) (N: natural number), N (Tb−τ) = Tb−Nτ. That is, when trying to detect the PLD fluctuation f (t) using the FIR filter described in the present recognition method 2, if the delay time is processed as N (Tb−τ) time, the delay time processing becomes longer. The same applies to the delay time processing of Tb−Nτ time.
The embodiment described above is an example of driving control of the intermediate transfer belt of the tandem type image forming apparatus. The present invention is useful for driving control of belts (paper conveyance belts, photoconductor belts, intermediate transfer belts, fixing belts, etc.) used in image forming apparatuses using electrophotographic technology, ink jet technology, and printing technology. Just as you did. This is because very high accuracy is required for drive control of the belt of such an image forming apparatus. Therefore, the present invention is also useful for an image forming apparatus other than a tandem type image forming apparatus or an apparatus other than an image forming apparatus for those requiring very high accuracy for belt drive control.

FIG. 3 is a block diagram of a portion that performs drive control of the copier according to the embodiment. 1 is a schematic configuration diagram of the entire copier. FIG. 3 is an explanatory diagram illustrating an example of a layer structure of an intermediate transfer belt provided in the copier. FIG. 2 is a schematic diagram illustrating a main part of a belt device provided in the copier. The control block diagram for demonstrating the recognition method of the PLD fluctuation | variation in embodiment. The other control block diagram for demonstrating the recognition method of the PLD fluctuation | variation in embodiment. FIG. 6 is a control block diagram obtained by Z-transforming the control block diagram of FIG. 5. FIG. 3 is a schematic diagram showing a device configuration for detecting a belt home position in belt drive control example 1; Explanatory drawing for demonstrating control operation | movement of the same belt drive control example 1. FIG. Explanatory drawing for demonstrating the control action in the installation example 2 of a rotary encoder. Explanatory drawing for demonstrating the control action in the installation example 3 of a rotary encoder. Explanatory drawing for demonstrating the update process in Example 2. FIG. 1 is a schematic configuration diagram showing an example of a direct transfer tandem image forming apparatus. 1 is a schematic configuration diagram illustrating an example of an intermediate transfer type tandem image forming apparatus. 6 is a graph showing an example of belt thickness unevenness (belt thickness deviation distribution) in the circumferential direction of an intermediate transfer belt of an intermediate transfer type tandem type image forming apparatus. The enlarged view when the belt part wound around the drive roller is seen from the axial direction of the drive roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Intermediate transfer belt 14,15,16 Support roller 18 Image formation part 40Y, 40M, 40C, 40K Photosensitive drum 101 1st roller 102 2nd roller 101a, 102a, 106b Rotary encoder 103 Belt 103a Home position mark 104 Mark detection Sensor 105 Drive roller 106 Drive motor 110, 410, 510 Controller 111, 112 Angular velocity detector 210 Conveying belt 214 Followed roller 215 Drive roller 419 PLD fluctuation data FIFO
610 Carriage 611 Recording head 617 Drive pulley 618 Driven pulley 619 Timing belt 1315 FIR filter

Claims (17)

Belt drive control for performing drive control of the belt spanned across a plurality of support rotators including a driven support rotator that rotates along with the movement of the belt and a drive support rotator that transmits driving force to the belt. In the device
The plurality of supporting rotating bodies caries Chi diameter is included in the two rotational angular displacement or rotation information of the rotational angular velocity in the supporting rotator that different, results from a change in the pitch line distance belt part wound around the respective supporting rotator From the two rotational fluctuation components , a process for calculating the fluctuation information of the pitch line distance of the belt portion wound around one of the supporting rotating bodies is performed, and the fluctuation of the pitch line distance in the circumferential direction of the belt is performed using the processing result. Control means for performing the drive control so as to reduce fluctuations in the moving speed of the belt caused by
The two support rotators are arranged so that the ratio of the belt movement path length between the two support rotators and the belt total circumference is 2Nb + 1 (Nb is a natural number),
The above processing includes a delay time that is a belt passing time required for the belt to move a distance between the two support rotators on the belt movement path with respect to the two rotation fluctuation components , and the two support rotators. be one that addition processing for adding the processing result of the diameter of the ratio based gain and the time of the first processing Ru respectively supplied to (2Nb + 1) th processing, the gain of the n-th process that as the gain of the first process used after multiplication (n-1), carried out using that the belt passage time (n-1) multiplied by a delay time of n-th processing A belt drive control device. In the belt drive control device according to claim 1,
Over a period corresponding to the time required for the belt rotates one round, the belt drive controlling apparatus characterized by having a change information storing means for storing the variation information calculated by the above process. In the belt drive control device according to claim 2 ,
The control means at a timing difference exceeds the allowable range between the fluctuation information storage unit fluctuation information and fluctuations information newly obtained which is stored in, to carry out a process for obtaining the above SL fluctuation information again A belt drive control device. In the belt drive control device according to any one of claims 1 to 3 ,
It said control means, a belt drive controller and performs a process for obtaining again on SL fluctuation information at a predetermined timing. In the belt drive control device according to any one of claims 1 to 3 ,
It said control means, while the process of obtaining the above SL fluctuation information, the belt drive controller and performs the driving control. In the belt drive control device according to any one of claims 1 to 5 ,
It has a past information storage means for at least one revolution of the belt component storing past fluctuations information,
It said control means, said last information using the one obtained from the stored past fluctuations information and fluctuations information newly obtained in the storage means, a belt drive control and performs the drive control apparatus. A belt stretched over a plurality of support rotating bodies including a driven support rotating body that rotates along with the movement of the belt and a driving support rotating body that transmits a driving force to the belt, and for driving the belt In a belt device comprising a drive source that generates a rotational drive force and a belt drive control device that performs drive control of the belt,
Among the plurality of supporting rotating bodies, diameter becomes different, and the ratio is 2Nb + 1 the belt movement path length and belt total circumference between mutual supporting rotator (Nb is a natural number) arranged to be 2 One of a detecting means for detecting a rotation angular displacement or rotation angular velocity of the rotary support member,
A belt device using the belt drive control device according to any one of claims 1 to 6 as the belt drive control device. The belt device according to claim 7, wherein
All of the two support rotators are driven support rotators that rotate along with the movement of the belt. The belt device according to claim 8, wherein
The belt device according to claim 1, wherein the driving source includes a feedback control unit that detects its own rotational angular displacement or rotational angular velocity and feeds back the rotational angular displacement or rotational angular velocity. The belt device according to claim 7, wherein
The belt device characterized in that the two support rotators include the drive support rotator. The belt device according to any one of claims 7 to 10 ,
In order to grasp the reference belt movement position of the belt, it has mark detection means for detecting a mark indicating the reference position on the belt,
The belt device according to claim 1, wherein the control means of the belt drive control device acquires the rotation fluctuation component based on a detection timing by the mark detection means and performs the drive control. The belt device according to any one of claims 7 to 10 ,
The control means of the belt drive control device is configured to obtain, in advance, the average time required for the belt to make one revolution of the information on the relationship between the variation in the pitch line distance and the belt movement position, or the belt circumference that is known in advance. A belt device that performs the above-described drive control after grasping based on the above. The belt device according to any one of claims 7 to 12 ,
The belt device according to claim 1, wherein the belt has a joint at at least one place in the belt circumferential direction. The belt device according to any one of claims 7 to 13 ,
The belt device according to claim 1, wherein the belt has a plurality of layers in a belt thickness direction. A latent image carrier comprising a belt stretched over a plurality of support rotating members, a latent image forming unit for forming a latent image on the latent image carrier, and a developing unit for developing a latent image on the latent image carrier And an image forming apparatus comprising: a transfer unit that transfers a visible image on the latent image carrier to a recording material;
As a belt device for driving the image bearing member, an image forming apparatus which comprises using a belt device according to any one of claims 7 to 14. A latent image carrier, a latent image forming unit for forming a latent image on the latent image carrier, a developing unit for developing a latent image on the latent image carrier, and a belt stretched around a plurality of support rotating members An intermediate transfer member, a first transfer unit that transfers a developed image on the latent image carrier to the intermediate transfer member, and a second transfer unit that transfers the developed image on the intermediate transfer member to a recording material. An image forming apparatus comprising:
As a belt device for driving the intermediate transfer member, the image forming apparatus, which comprises using a belt device according to any one of claims 7 to 14. A latent image carrier, a latent image forming unit for forming a latent image on the latent image carrier, a developing unit for developing a latent image on the latent image carrier, and a belt stretched around a plurality of support rotating members The recording material conveying member comprising the above and a visible image on the latent image carrier are directly transferred to the recording material conveyed by the recording material conveying member via the intermediate transfer member or not via the intermediate transfer member. An image forming apparatus comprising transfer means,
As a belt device for driving the recording material transporting member, an image forming apparatus which comprises using a belt device according to any one of claims 7 to 14.

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