JP2014137395A - Control device controlling stretching attitude of endless belt, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a stretching attitude of an endless belt while minimizing an increase in settling time.SOLUTION: A control device controls a stretching attitude of an endless belt, and includes: a plurality of deviation calculating means that are multi-input multi-output systems for controlling a plurality of outputs with a plurality of inputs, and calculates, for each of the plurality of inputs, deviation between each of the inputs and a target value corresponding to each of the inputs; a plurality of gain means that are arranged immediately after the plurality of respective deviation calculating means; and control means that calculates a plurality of output values from the plurality of inputs. The control device includes a first control mode intended to bring a deviation position of a belt to a reference position, and a second control mode intended to simultaneously reduce the deviation speed and skew of the belt to zero, and further includes gain setting means that calculates gain values of the plurality of gain means according to the control modes.

Description

  The present invention relates to a control device that controls the tension posture of an endless belt, and an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine having these functions. is there.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a configuration in which an endless belt is used as an intermediate transfer member that is a transfer medium or a sheet conveying unit that is a transfer medium is known. Such a belt is stretched around a plurality of rollers and is driven to circulate. However, the belt position shifts in the direction perpendicular to the belt conveyance direction (main scanning direction) and the stretched area with the belt is subjected to main scanning. A “belt skew” may occur that inclines in the direction. If the belt is deviated, the belt may come off the roller, or the end of the belt may come into contact with the side plate supporting the roller shaft. Further, when a belt skew occurs in the primary transfer area of the intermediate transfer belt, which is an intermediate transfer member, or when a belt skew occurs in the transfer area of the paper conveying belt, which is a conveying means, the intermediate transfer belt or the recording paper on the transfer medium A shift occurs in the image forming position, resulting in image distortion. In forming a color image, black (hereinafter referred to as “K”), yellow (hereinafter referred to as “Y”), magenta (hereinafter referred to as “M”), and cyan (hereinafter referred to as “C”) monochromatic images are formed, and these are transferred onto a transfer medium. A color image is obtained by superimposing the image above. In such color image formation, a shift in image forming position appears as a color shift between toner images of each color. All of these lead to degradation of image quality, and it is necessary to take some measures with respect to the belt shift and belt skew in order to obtain a high-quality image.

  Japanese Patent Application Laid-Open No. 2004-151867 discloses that a belt conveying device that suppresses belt deviation and belt skew by adjusting two of the rollers that stretch the intermediate transfer belt as tiltable steering rollers and adjusting the inclination of the steering rollers. Is described. Specifically, based on the detection result of the position detecting means for detecting the position of the belt in the belt width direction, one of the two steering rollers is tilted to correct the belt shift. Further, based on the detection result of the two position detection means arranged at a predetermined interval in the sub-scanning direction in the primary transfer area of the belt, the belt skew in the primary transfer area is detected, and based on the detection result. The other steering roller is tilted to correct the belt skew in the primary transfer area.

  However, in Patent Document 1, switching between the control mode in which the shift position is brought to the reference position and the control mode in which the shift speed and the stretching posture inclination are simultaneously reduced to zero cannot be performed smoothly, and the startup time of the image forming apparatus There was a problem that it took extra. The reason will be described below.

  In the belt steering system, there are a control mode in which the position of the belt is moved to the reference position (middle in the direction of displacement; hereinafter referred to as the home position), and a mode in which the shift speed and the tension posture tilt are controlled simultaneously. . The former control mode is a control mode in which the belt end does not easily fall even if a slight deviation occurs by bringing the belt to the vicinity of the center position in the main scanning direction before forming an image on the belt. . The latter control mode is a control mode for avoiding abnormal images such as misalignment at the same time as preventing the belt from falling by simultaneously performing color misregistration and belt misalignment in the main scanning direction.

  Basically, the former control mode only needs to control the shift position, but when switching from the former to the latter, there is generally a stretching posture tilt, and this must be reduced. Color misregistration in the main scanning direction may occur or it may take more time to settle. In addition, it has been found that if the former control mode, that is, the mode of bringing to the home position is attempted to make the tilt of the stretching posture zero at the same time, it will generally take a long time to use any controller. .

  Therefore, there has been a problem that when the inclination is not reduced to some extent during the process of bringing to the home position, color misregistration eventually occurs or a long time is required for the settling time.

  An object of the present invention is to control the tension posture of an endless belt while minimizing an increase in the settling time.

  The above-described problem is a control device that controls the tension posture of an endless belt, and this control device is a multi-input multi-output system that controls a plurality of outputs by a plurality of inputs, and corresponds to each of the plurality of inputs. A plurality of deviation calculating means for calculating a deviation between each input and a target value for each input, a plurality of gain means arranged immediately after each of the plurality of deviation calculating means, and a plurality of outputs from the plurality of inputs Control means for calculating a value, and a first control mode that aims to make the belt shift position reach the reference position, and simultaneously zeroing the belt shift speed and skewing This is solved by providing a gain setting unit that has a target second control mode and calculates gain values of the plurality of gain units according to each control mode.

  According to the present invention, the first control mode for the purpose of causing the belt shift position to reach the reference position, and the second control mode for the purpose of simultaneously reducing the belt shift speed and the skew to zero. Therefore, the gain setting means calculates the gain values of the plurality of gain means, so that the multi-input multi-output system control can be performed with a combination of gains in which one control is neglected in comparison with the other control in each control mode. Therefore, when the first control mode is completed, the inclination of the belt tension posture is approaching zero to some extent, and the increase in the settling time can be minimized.

1 is a schematic diagram illustrating a configuration example of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a schematic view of an end portion of an intermediate transfer belt. It is a schematic perspective view of a transfer unit. It is a figure which shows the structure of a control part.

  In FIG. 1, the image forming apparatus includes a transfer unit 20 serving as a belt conveyance device. The transfer unit 20 includes an intermediate transfer belt 200 supported by a driving roller 211, a steering roller 215, a tension roller 214, a secondary transfer counter roller 213, and a driven roller 212 with a predetermined tension. Above the intermediate transfer belt 200 in the figure, an image forming unit 1Y as a toner image forming unit corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K) according to the belt running direction. , 1M, 1C, 1K are arranged in this order. Each of the image forming units 1Y, 1M, 1C, and 1K has photoreceptors 10Y, 10M, 10C, and 10K, and image writing units 12Y, 12M, 12C, and 12K that expose and scan the surfaces of the photoreceptors with a laser beam or the like. doing. Further, around each photosensitive member, the chargers 11Y, 11M, 11C, and 11K, the developing devices 13Y, 13M, 13C, and 13K, and the primary transfer roller 14Y are arranged in accordance with the rotation direction of the drums (counterclockwise in the drawing). , 14M, 14C, 14K are arranged in this order. In the following, Y, M, C, and K indicating colors are omitted as appropriate.

  The photosensitive member 10 is rotated counterclockwise, and the surface thereof is uniformly charged by the charger 11, and then the image writing unit 12 performs exposure scanning according to the input image information to form an electrostatic latent image. To do. Each color developing device 13 causes each color toner to adhere to the electrostatic latent image on the photoreceptor to develop each color toner image. The toner images of these colors are primarily transferred onto the intermediate transfer belt 200 that contacts the photoreceptor 10 and rotates in the direction of the arrow.

  At the primary transfer nip for Y, M, C, and K where the photoreceptor 10 and the intermediate transfer belt 200 abut, the intermediate transfer belt 200 is moved by the primary transfer rollers 14Y, 14M, 14C, and 14K disposed inside the belt loop. It is pressed toward the photoconductor 10. A primary transfer bias is applied to the primary transfer rollers 14Y, 14M, 14C, and 14K by a power source (not shown). Thus, a primary transfer electric field for electrostatically moving the color toner images on the photoreceptor 10 toward the intermediate transfer belt 200 is formed in the primary transfer nips for Y, M, C, and K. The Y, M, C, and K primary transfer nips pass through the Y, M, C, and K primary transfer nips sequentially as the belt moves endlessly. The M, C, and K toner images are sequentially superimposed and primarily transferred. By this superimposing primary transfer, a four-color superimposed toner image is formed on the outer peripheral surface of the intermediate transfer belt 200.

  Below the transfer unit 20 in the figure, there is provided a paper transport unit 30 that is a belt transport device that spans an endless paper transport belt 30c between the driving roller 30a and the secondary transfer roller 30b and moves endlessly. . The intermediate transfer belt 200 and the paper transport belt 30c are sandwiched between the secondary transfer roller 30b and the secondary transfer counter roller 213. As a result, a secondary transfer nip is formed in which the outer peripheral surface of the intermediate transfer belt 200 and the outer peripheral surface of the sheet conveying belt 30c come into contact with each other. A secondary transfer bias is applied to the secondary transfer roller 30b by a power source (not shown). On the other hand, the secondary transfer counter roller 213 of the transfer unit 20 is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip. Note that a secondary transfer bias may be applied to the secondary transfer counter roller 213 to ground the secondary transfer roller 30b.

  On the right side of the secondary transfer nip in the drawing, a registration roller pair 33 serving as a timing adjustment and skew correction roller is disposed. A registration roller sensor (not shown) is disposed near the entrance of the registration nip of the registration roller pair 33. The paper P conveyed from the paper supply device (not shown) toward the registration roller pair 33 abuts the leading end against the registration nip of the registration roller pair 33. As a result, the posture of the paper P is corrected, and preparations for synchronizing with image formation are completed. Thereafter, the registration roller pair 33 sends the sheet to the secondary transfer nip at a timing at which the sheet can be synchronized with the superimposed toner image on the intermediate transfer belt 200. In the secondary transfer nip, the superposed toner image on the intermediate transfer belt 200 is secondarily transferred to the paper collectively by the influence of the secondary transfer electric field and the nip pressure, and becomes a full color image combined with the white color of the paper P. The sheet P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 200 and is conveyed to the fixing device 34 along with its endless movement while being held on the outer peripheral surface of the sheet conveying belt 30c. On the surface of the intermediate transfer belt 200 that has passed through the secondary transfer nip, transfer residual toner that has not been transferred to the paper P at the secondary transfer nip is attached. This transfer residual toner is scraped and removed by a belt cleaning device (not shown) that contacts the intermediate transfer belt 200.

  The sheet P conveyed into the fixing device 34 is sandwiched between fixing nips by contact between a fixing roller 34a including a heat source such as a halogen lamp and a pressure roller 34b. Then, after the full color image is fixed on the surface by pressurization or heating in the fixing nip, the paper P is discharged from the fixing device 34. Thereafter, the paper is discharged out of the apparatus by a pair of paper discharge rollers 35.

  In the vicinity of one end of the intermediate transfer belt 200, as shown in FIG. 2, a detection line 201 is formed over the entire circumference in the transport direction. In addition, two detectors 205a and 205b are provided at a predetermined interval in the belt moving direction in a stretching region (hereinafter referred to as a primary transfer region) in which the image forming units 1Y to 1K of the intermediate transfer belt 200 are sequentially arranged. Are arranged to face the detection line 201 (see FIG. 1). A control unit (not shown) detects the belt shift by sequentially detecting the position of the detection line 201 in the main scanning direction on one of the detectors 205a and 205b. That is, any one of the detectors 205a and 205b and a control unit (not shown) constitute a shift detection means. In addition, the control unit (not shown) has a difference between the main scanning direction position of the detection line 201 detected by the first detector 205a and the main scanning direction position of the detection line 201 detected by the second detector 205b. Are sequentially calculated to detect belt skew in the primary transfer region. That is, the detectors 205a and 205b and a control unit (not shown) constitute skew detection means.

  In the present embodiment, belt deviation and skew are detected by detecting movement in the belt main scanning direction of the detection line 201 formed in advance on the intermediate transfer belt 200 with high accuracy. Therefore, there is no need to refer to edge data measured in advance or to store data obtained by averaging periodic fluctuations in the edge position in the storage means. Therefore, it is possible to detect a belt shift and belt skew detection at high speed with a low cost configuration and no dead time.

  FIG. 3 is a schematic perspective view of the transfer unit 20. The intermediate transfer belt 200 travels when the driving roller 211 is rotationally driven by a motor (not shown) as belt driving means. The tension roller 214 and the steering roller 215 correct misalignment and skew generated in the intermediate transfer belt 200. Both ends of the rotation shafts of the rollers 214 and 215 are pivot bearings (not shown) in the direction perpendicular to the roller rotation axis. It is supported so that it can swing. Further, one end of each of the tension roller 214 and the steering roller 215 is supported by an actuator (not shown) serving as a belt shift / skew correction unit so as to be reciprocally movable in a direction perpendicular to the belt surface and perpendicular to each other. ing.

  The control unit (not shown) drives an actuator (not shown) based on the belt deviation detection information and the belt skew detection information detected by the detectors 205a and 205b (FIG. 1), and tilts the tension roller 214 and the steering roller 215. . As a basic control method for calculating the control input value from each deviation of the detected value of the belt deviation and the belt inclination and the deviation and the target value of the inclination, as will be described later, a feedback of two inputs and two outputs that is obvious to those skilled in the art. It is sufficient to use a type writing system.

  FIG. 4 shows a configuration of a control unit which is a control device in the present embodiment. The control unit includes first and second deviation calculation means 301 and 302, a control means 303 that holds a 2-input 2-output control algorithm that is a multi-input multi-output system, and first and second gain means 304. , 305 and gain setting means 306. The first and second deviation calculation means 301 and 302 calculate the difference value between the measured value and the target value of the belt deviation amount and the skew amount, respectively. In the 2-input 2-output control algorithm of the control means 303, the difference values between the measured values of the belt deviation amount and the skew amount and the target values are input, and the inclination amounts of the tension roller 214 and the steering roller 215 are used as output values. To do. As a 2-input 2-output control algorithm, it may be designed using a conventional multi-input multi-output control design method such as model predictive control, or a plurality of single-input single-output control algorithms are configured in parallel. May be. The first and second gain means 304 and 305 are arranged immediately after the first and second deviation calculation means 301 and 302 and before the respective input terminals of the control means 303. The gain setting means 306 receives the control mode and outputs the gain value.

  The operation of the control unit having such a configuration will be described below. As described above, the belt tension posture control largely requires two modes. The first control mode is a control mode in which the belt shift position is brought to the reference position (home position) in the belt steering system. The second control mode simultaneously controls the shift speed and the tension posture inclination. It is a mode to do.

  Both control modes can be handled by the same controller (feedback controller). That is, both control modes can be supported if simultaneous control by two axes is performed so that the shift position and skew are always zero at the same time. However, generally, when two parameters by two axes are controlled simultaneously, the settling time for convergence to the target value becomes longer than when only one is controlled. Since the settling time has a great influence on the warm-up time of the image forming apparatus, it is desirable that the settling time be shorter. For this reason, in the first control mode, it is conceivable that the skew control is not performed and only the shift position control is performed.

  However, in this case, the following problem occurs. In such a first control mode, the shift position quickly converges and reaches the home position. However, since the skew is not controlled at all, the shift position has an inclination when the shift position converges. If drawing is started as it is, a color shift in the main scanning direction occurs. For this reason, if it is attempted to simultaneously control the shift position and the skew from this point, further stabilization time is required, and it is no longer meaningful to control only the shift position in order to shorten the initial stabilization time. End up.

  In the second control mode, in consideration of color misregistration in the main scanning direction, it is desirable that the skew is near zero, but for the shift position, if the shift speed is even near zero, If it is within a certain range, it need not be exactly zero.

  In a double loop configuration with the shift position control loop as the outer loop and the shift speed control loop as the inner loop, if the controller of the outer loop introduces a controller with only proportional gain, the control of shift position is neglected if the proportional gain is small. However, it is important to control the shifting speed.

  Therefore, in the present invention, two-axis simultaneous control is performed in both the first control mode and the second control mode, but in the first control mode, the skew control is performed with neglected control, In the second control mode, the shift position control is neglected. Specifically, in the first control mode, the gain of the first gain unit 304 is reduced, and the difference value of the apparent skew amount is reduced and input to the control unit 303, thereby neglecting this difference. Execute control. In the second control mode, the gain of the second gain unit 305 is reduced, the difference value of the apparent shift position is reduced and input to the control unit 303, so that this difference is neglected and the shift speed is emphasized. Control is executed.

  The gain setting means 306 may hold a combination of gains appropriate for each control mode and output the gain value to each gain means 304 and 305 in accordance with the control mode.

  In addition, in this way, when the control mode is switched by changing only the gain value with the same controller, the control mode is switched without resetting those state values when the control means includes an integrator or a filter. be able to. As a result, the behavior of the controller becomes continuous, and there is also an advantage that there is no sudden change in output.

  The above embodiment has been described as controlling the tension posture of the intermediate transfer belt. However, the present invention can naturally be applied even if the control target is another endless belt such as a paper conveyance belt. It is.

200 Intermediate Transfer Belt 201 Detection Line 205a, 205b Detector 211 Drive Roller 212 Driven Roller 213 Secondary Transfer Counter Roller 214 Tension Roller 215 Steering Rollers 301, 302 Deviation Calculation Unit 303 Control Unit 304, 305 Gain Unit 306 Gain Setting Unit

Japanese Patent No. 3976924

Claims (6)

  A control device for controlling the tension posture of the endless belt, wherein the control device is a multi-input multi-output system that controls a plurality of outputs by a plurality of inputs, corresponding to each of the plurality of inputs, A plurality of deviation calculating means for calculating a deviation from a target value for each input, a plurality of gain means arranged immediately after each of the plurality of deviation calculating means, and a plurality of output values from the plurality of inputs. And a first control mode for the purpose of causing the belt shift position to reach the reference position, and for the purpose of simultaneously reducing the belt shift speed and skewing to zero. And a gain setting unit that calculates gain values of the plurality of gain units according to each control mode.   The control device according to claim 1, wherein the input is a belt offset position and a belt skew.   In the first control mode, the gain setting means sets the gain of the first gain means arranged immediately after the deviation calculation means corresponding to the belt shift position to be lower than the value in the second control mode. The control device according to claim 2, wherein:   In the second control mode, the gain setting means sets the gain of the second gain means arranged immediately after the deviation calculating means corresponding to the belt skew to be lower than the value in the first control mode. The control device according to claim 2, wherein the control device is a control device.   The control device according to claim 1, wherein the endless belt is an intermediate transfer belt.   An image forming apparatus comprising the control device according to claim 1.

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