JP2021117325A - Image forming apparatus - Google Patents

Abstract

To prevent the occurrence of color shift due to erroneous correction in belt position control caused by a change over time in the shape of the edges of an intermediate transfer belt.SOLUTION: An image forming apparatus has: an endless belt (6); a plurality of belt tension rollers (20, 21, 22, 23, 9) that stretches the belt; driving means (24) that drives to convey the belt; image forming means (1Y, 1M, 1C, 1K) that are provided opposite to the belt; the steering roller (21) that is the belt tension roller and changes a disposition angle with respect to the belt to correct the position in a width direction of the belt; and control operation means (150) that has a sensor (25) for detecting a position orthogonal to a conveyance direction of the belt, and calculates the disposition angle of the steering roller based on a detection value from the sensor. The control operation means calculates the disposition angle of the steering roller based on a value processed by a notch filter (58) that removes a frequency component for one revolution of the belt from the detection value from the sensor.SELECTED DRAWING: Figure 6

Description

The present invention relates to a control for correcting the position of the intermediate transfer belt in the width direction in the image forming apparatus.

Conventionally, in a tandem type intermediate transfer type color image forming apparatus such as a copier or a printer, images of each color of yellow (Y), magenta (M), cyan (C), and black (K) are formed, and the images are sequentially endless. A color image is formed on the recording material by transferring to the intermediate transfer belt of. During image formation, the intermediate transfer belt is orbitally driven with the photoconductor drum. At that time, the belt tends to lean or meander due to disturbances such as the support mechanism of the intermediate transfer belt, the mechanical accuracy of the belt itself, the transfer of the toner image, and the plunge of the recording material. If the belt is biased or meandering during image formation, the transfer position shifts between the YMCK colors, resulting in color shifts. In order to suppress this, a sensor (edge sensor) that detects the edge position of the belt is used, and based on the detection result, some of the multiple rollers that stretch the belt are tilted to prevent the belt from leaning or meandering. Control to correct (steering control) is known.

However, the detection information of the edge sensor includes the edge shape component of the belt due to the cutting error of the belt manufacturing or the like. This belt edge shape component is a component that is detected as if the belt position fluctuates even when the belt is actually conveyed straight without meandering and has no effect on color shift. .. If steering control is performed based on this detection error, the belt position will fluctuate on the contrary.

Therefore, there is known a method of measuring the belt edge shape in advance, such as when replacing the belt, storing the data, and removing the edge shape component from the detection result of the edge sensor (Patent Document 1). Further, a technique for controlling steering while suppressing an edge shape component based on an averaged value of belt position data around one belt is disclosed (Patent Document 2).

Japanese Unexamined Patent Publication No. 11-298948 Japanese Unexamined Patent Publication No. 2016-008988

However, the edge shape of the belt changes due to the installation environment and usage conditions of the device, changes in temperature and humidity, plastic deformation over time due to long-term use, deterioration such as wear and cracks of the belt, and the like. Therefore, when the method of performing correction using the stored edge shape data described in Patent Document 1 is used, it is necessary to update the data according to the change with time of the edge shape, and it is necessary to perform reacquisition. For the acquisition of edge shape data, it is necessary to turn off the steering control and interrupt the image formation in order to eliminate the influence of the disturbance during the steering control and the image formation. Since image formation is interrupted, productivity is reduced.

Further, averaging the data of one belt circumference of the technique described in Patent Document 2 is equivalent to performing low-pass filter processing, the responsiveness of steering control is lowered, and the control performance for suppressing belt meandering is lowered. do.

Therefore, an object of the present invention is to suppress belt meandering due to a change in the belt edge shape over time without causing reacquisition of edge shape data or deterioration of control performance.

In order to achieve the above object, the image forming apparatus according to claim 1 includes an endless belt, a plurality of belt tensioning rollers for tensioning the belt, a driving means for transporting and driving the belt, and the belt. An image forming means provided so as to face the belt, a steering roller which is a belt tensioning roller and corrects a position in the width direction of the belt by changing the arrangement angle with respect to the belt, and transport of the belt. It has a sensor that detects a position orthogonal to the direction, and has a control calculation means that calculates the arrangement angle of the steering roller based on the detection value of the sensor. It is characterized in that the arrangement angle of the steering roller is calculated based on the value processed by the notch filter that removes the frequency component around one circumference of the belt.

According to the present invention, it is possible to suppress the occurrence of belt meandering and the occurrence of color shift by suppressing erroneous correction of steering control due to a change in the shape of the belt edge over time. Moreover, since the frequency of edge shape reacquisition is not increased, the productivity is not reduced. Further, as compared with the case where the averaging process for one round of the belt is performed, it is possible to suppress the deterioration of the disturbance suppression performance.

It is a figure explaining the whole structure of an image forming apparatus. It is a figure explaining the control structure of an image forming apparatus. It is explanatory drawing of the outline of the belt edge sensor. It is an enlarged view of the vicinity of a steering roller. It is a perspective view explaining the tilting operation of a steering roller and the belt correction direction. It is a block diagram of steering control. It is a flowchart of steering control. It is a figure explaining the time-dependent change of a belt edge shape. It is a block diagram of signal processing which realizes a notch filter. It is a figure which shows the difference of the steering tilting operation with and without a notch filter. It is a figure explaining the color shift evaluation result with and without a notch filter. It is a figure which shows the round-trip transmission characteristic of a notch filter and a moving average. It is a figure which shows the one-round transmission characteristic of a notch filter and a moving average (after gain adjustment). It is a figure which shows the sensitivity function of a notch filter and a moving average (after gain adjustment). It is a block diagram of steering control when the mounting position of a notch filter is changed.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

<Example 1>
First, the configuration of the image forming apparatus according to the embodiment of the present invention will be described with reference to FIG.
The image forming apparatus 100 is an apparatus that forms and outputs an image on the recording material S according to the image data received from the outside via the network.

First, a toner image is formed on the photosensitive drums 1Y, 1M, 1C, and 1K based on the image data. The toner image is divided into yellow (Y), magenta (M), cyan (C), and black (K), and the toner images are formed in substantially the same manner except that the colors are different. Will be done. Therefore, in the following, a method for forming a toner image of yellow (Y) will be described, and for forming a toner image of magenta (M), cyan (C), and black (K), the trailing Y of the reference numerals attached to the constituent members in the description will be added. It shall be explained by replacing it with M, C, and K.
The yellow (Y) toner image is formed by the photosensitive drum 1Y, the charger 2Y, the laser scanner 3Y, the developer 4Y, and the primary transfer roller 5Y.

The image signal generated based on the image data is input to the laser scanner 3Y. The laser scanner 3Y includes a semiconductor laser and a polygon mirror, and outputs a laser beam modulated by an input image signal from the semiconductor laser. The surface of the photosensitive drum 1Y is exposed by irradiating the surface of the photosensitive drum 1Y with the laser beam output from the semiconductor laser via the polygon mirror and the mirror. By exposing the photosensitive drum 1Y whose surface is uniformly charged by the charger 2Y, an electrostatic latent image is formed on the photosensitive drum 1Y. The electrostatic latent image formed on the photosensitive drum 1Y is developed by the toner supplied from the developing device 4Y, so that a yellow toner image is formed on the photosensitive drum 1Y. The toner image on the photosensitive drum 1Y moves to the position T1 facing the primary transfer roller 5Y as the photosensitive drum 1Y rotates. A primary transfer bias having a polarity opposite to the charging polarity of the toner is applied to the primary transfer roller 5Y by a bias voltage supplying means (not shown), and the toner image is transferred to the intermediate transfer belt 6 by this primary transfer bias. The drum cleaning device 7Y rubs the cleaning blade against the photosensitive drum 1Y to collect the transfer residual toner remaining on the photosensitive drum 1Y.

The toner image formation of each of the above colors is also performed in magenta (M), cyan (C), and black (K). Then, the toner images of each color are sequentially superimposed on the intermediate transfer belt 6 and transferred to form a full-color toner image. The full-color toner image is transferred to the secondary transfer unit T2 formed by the secondary transfer roller 8 and the opposing roller 9 by the transfer of the intermediate transfer belt 6.

The recording material S drawn out from the recording material cassette 10 is fed onto the transport path by the paper feed roller 11 and sent out to the resist roller 12. The resist roller 12 receives the recording material S in a stopped state and puts it on standby, and sends the recording material S to the secondary transfer unit T2 in time with the toner image of the intermediate transfer belt 6.

A bias voltage is applied to the secondary transfer roller 8 in the process in which the recording material S is sandwiched and conveyed by the secondary transfer unit T2 so as to overlap the toner image, so that the full-color toner image is transferred from the intermediate transfer belt 6 to the recording material S. Transcribed. The transfer residual toner that remains on the surface of the intermediate transfer belt 6 without being transferred is collected by the belt cleaning device 13.

The recording material S to which the toner image is transferred is conveyed to the fixing device 14, heated and pressurized in the fixing device, and the toner image is fixed to the recording material. The recording material S after fixing is discharged to the outside of the apparatus by the paper ejection roller 15.

The above is the color image forming process of the tandem type intermediate transfer method using the intermediate transfer belt 6.

The advantage of the intermediate transfer belt method, which indirectly transfers the toner image from the image carrier to the recording material using the intermediate transfer belt, is that the toner images of each color are superimposed on the belt, so that the recording material is subject to changes in humidity and the like. It is not easily affected by fluctuations in the resistance value of. Further, as compared with the method of directly transferring each color toner image to the recording material, it becomes easier to control the transfer conditions of the toner image when forming the color image. The transport system for the recording material is also simple, and the occurrence of sheet jam can be suppressed.

On the other hand, since the toner images of multiple colors are superimposed on the intermediate transfer belt, the position fluctuation (meandering) of the belt should be reduced to zero as much as possible in order to form a high-quality color image without color shift. It becomes important. If the position of the belt fluctuates, the overlay of the toner images of each color shifts when the belt passes through the primary transfer portion of each color of YMCK, resulting in color shift. In order to suppress this, the belt position stabilization control called steering control is performed. Steering control will be described in detail later.

<Control configuration of image forming device>
Next, the control configuration of the image forming apparatus will be described.

FIG. 2 is a block diagram showing a control configuration example of the image forming apparatus 100. The system controller 150 shown in FIG. 2 includes a CPU 150a, a ROM 150b, and a RAM 150c, and controls the entire image forming apparatus 100. The system controller 150 is connected to an image processing unit 151, an operation unit 152, an analog-to-digital (A / D) converter 153, a high-voltage control unit 155, a motor control unit 157, sensors 159, and an AC driver 160. The system controller 150 can exchange data with each connected unit.

The CPU 150a executes various sequences related to a predetermined image formation sequence by reading and executing various programs stored in the ROM 150b. The RAM 150c is a volatile storage device, and the CPU 150a is used as a work area for executing various programs or as a temporary storage area for temporarily storing various data. The RAM 150c stores, for example, data such as a set value for the high-voltage control unit 155, a command value for the motor control unit 157, and information received from the operation unit 152.

The system controller 150 controls the operation unit 152 so that the operation screen for the user to perform various settings is displayed on the display unit provided in the operation unit 152, so that the user can set the operation screen via the operation unit 152. Accept. The system controller 150 receives information from the operation unit 152 indicating the contents of settings (copy magnification setting value, density setting value, etc.) by the user via the operation unit 152. Further, the system controller 150 transmits data for notifying the user of the state of the image forming apparatus to the operation unit 152. The operation unit 152 displays information indicating the state of the image forming apparatus on the display unit based on the data received from the system controller 150.

The system controller 150 (CPU 150a) transmits to the image processing unit 151 the set value data of each device in the image forming apparatus 100 required for the image processing in the image processing unit 151. Further, the system controller 150 receives signals from each device (signals from sensors 159) and controls the high voltage control unit 155 based on the received signals. Based on the set value output from the system controller 150, the high-voltage control unit 155 comprises the chargers 2Y, 2M, 2C, 2K, the developer 4Y, 4M, 4C, 4K, and the primary transfer roller 5Y that constitute the high-voltage unit 156. The voltage required for each operation is supplied to the 5M, 5C, 5K, and the secondary transfer roller 8.

The A / D converter 153 receives a detection signal from the thermistor 154 for detecting the temperature of the fixing heater 161, converts the detection signal into a digital signal, and transmits the detection signal to the system controller 150. The system controller 150 controls the AC driver 160 based on the digital signal received from the A / D converter 153 to control the temperature of the fixing heater 161 to a desired temperature for the fixing process. The fixing heater is a heater included in the fixing device 14 and used for the fixing process.

Further, the system controller 150 controls the drive of each motor via the motor control unit 157. The system controller 150 generates a command signal such as the position and speed of the motor to be controlled and outputs the command signal to the motor control unit 157. The motor control unit 157 drives and controls the motor according to a command signal given from the CPU 150a.

Similarly, steering control, which is a control for stabilizing the position of the intermediate transfer belt, which is a feature of the present patent, is also carried out with the control configuration shown in FIG. A motor that operates a mechanism that corrects the belt position via the motor control unit 157 by the CPU 150a in the system controller 150 performing control calculations based on the information obtained from the sensor 159 that detects the position of the intermediate transfer belt in the width direction. Drive 158.

As described above, the system controller 150 shown in FIG. 2 controls the image forming apparatus 100.

<Steering control>
Next, the steering control for controlling the position of the intermediate transfer belt, which is a feature of the present patent, will be described.

If the intermediate transfer belt 6 meanders at the time of image formation, the position shift occurs when the toner image of each color is transferred from the drum to the belt, and the color shift occurs. Therefore, the image forming apparatus 100 performs steering control in order to stabilize the position of the intermediate transfer belt. In steering control, some of the rollers that stretch the belt are configured as steering rollers that can be tilted, and based on the position information obtained from the sensor that detects the position of the belt, the steering roller The position in the width direction of the belt is corrected by adjusting the tilt direction and the tilt amount.

Specifically, the configuration of the intermediate transfer belt drive device that realizes steering control will be described with reference to FIG. A drive roller 20, a steering roller 21, a driven roller 22/23, a secondary transfer opposing roller 9, a primary transfer roller 5Y, 5M, 5C, and 5K are provided, and the intermediate transfer belt 6 can rotate with respect to these rollers. It is stretched over. The drive roller 20 is connected to the drive motor 24, and the intermediate transfer belt 6 is conveyed according to the rotation of the drive roller 20 in the direction of the arrow in the drawing.

The driven rollers 22 and 23, which are a part of the support roller member, block the change in the inclination of the intermediate transfer belt 6 due to the inclination of the steering roller 21 and maintain the primary transfer surface in a constant horizontal state.

Next, the belt position detecting means will be described. The belt position detection sensor 25 (edge sensor) is arranged between the black photosensitive drum 1K and the driven roller 23. FIG. 3A is a view of the intermediate transfer belt when viewed from the steering roller 21 side. Further, FIG. 3B is a detailed cross-sectional view of the edge sensor. With the tensile force of the spring 25w, one end side of the contact 25x is held in a pressure contact state with the end of the intermediate transfer belt 6. In this case, the pressure contact force of the contactor 25x by the spring 25w is set to an appropriate magnitude so as not to deform the intermediate transfer belt 6. Further, the contact 25x is rotatably supported by a support shaft 25y at an intermediate portion thereof, and a displacement sensor 25z, which is a reflective photo sensor, faces the other end side of the contact 25x with the support shaft 25y as a boundary. Arranged in a state.

In the edge sensor 25, the position change of the intermediate transfer belt 6 in the width direction (y direction in the drawing) is replaced by the movement (swinging motion) of the contactor 25x that presses against the belt edge. At this time, since the output level of the displacement sensor 25z fluctuates according to the movement (displacement) of the contactor 25x, the position of the intermediate transfer belt 6 in the width direction can be continuously detected based on the sensor output. ..

Next, the tilting operation of the steering roller 21 will be described. FIG. 4 is an enlarged view of the vicinity of the steering roller 21 of FIG. The steering roller 21 is rotatably supported by the bearing holder 30. Further, the bearing holder 30 is fixed to the movable side of the slide rail 31. Further, the slider 32 is fixed to the same surface on the movable side of the slide rail 31. On the other hand, the fixed side of the slide rail 31 is fixed to the steering arm (support member) 33. Further, the slider 32 is urged in the arrow T direction by a spring (biasing member) 34 applied to the steering arm 33. Therefore, the slider 32 slides on the steering arm 33, and as a result, the steering roller 21 is urged in the arrow T direction to give tension to the intermediate transfer belt 6.

On the other hand, the steering arm 33 on the front side of the paper is oscillatingly supported around the oscillating shaft 35. A follower 36 is pivotally supported on the steering arm 33 in a direction symmetrical to the steering roller 21 with respect to the swing shaft 35. Further, a cam 37 is provided so as to come into contact with the follower 36, and the cam 37 is configured to be rotatable by a steering motor (driving means) 26. Here, when the cam 37 rotates in the direction of arrow A in FIG. 3, the follower 36 side of the steering arm 33 rotates in the direction of arrow C about the swing shaft 35, and as a result, the steering roller 21 side is in the direction of arrow E. The alignment is changed by rotating to. On the contrary, when the cam 37 rotates in the direction of arrow B, the follower 36 side of the steering arm 33 rotates in the direction of arrow D about the swing shaft 35, and as a result, the steering roller 21 side rotates in the direction of arrow F. It rotates and its alignment is changed.

In this way, the steering roller 21 rotates as shown in FIGS. 5A, 5B, and 5C. When the alignment of the steering roller 21 shifts in the direction of arrow E, the intermediate transfer belt 6 moves to the back side of the paper surface, and when it shifts in the direction of arrow F, the intermediate transfer belt 6 moves to the front side of the paper surface. This is because when the steering roller 21 is tilted, the winding start position and end position of the intermediate transfer belt 6 with respect to the steering roller 21 are displaced in the axial direction of the belt, and the belt position is corrected as the belt is conveyed. The principle is used.

<Steering control calculation>
Next, the arithmetic processing of steering control will be described. This arithmetic processing is performed by the CPU 150b in the system controller 150 shown in FIG. The control block diagram shown in FIG. 6 and the flowchart shown in FIG. 7 will be described in detail.

As shown in FIG. 6, the steering control includes a control plant 50, a control controller 51, an edge sensor 25, a motor driver 52, and a steering motor 26. The control plant 50 of FIG. 6 is a control target of steering control, and is represented by mathematical formulas and numerical data on a control block diagram representing control information processing. The control plant 50 is composed of a plant 54 near the intermediate transfer belt, a disturbance 55 near the intermediate transfer belt, and an edge shape 56. The intermediate transfer belt-side plant 54 is a transmission system that receives the tilt position of the steering roller as an input and outputs a response of the belt position in response to the input. A side disturbance 55 is added to the intermediate transfer belt side plant 54, and the belt position affects the image. Steering control aims to stabilize this belt position. The lean disturbance 55 is a disturbance generated by a leaning force such as the support mechanism of the intermediate transfer belt, the mechanical accuracy of the belt itself, the transfer of the toner image, and the plunge of the recording material. The edge shape component 56 of the belt due to a cutting error of belt manufacturing or the like is further added to the belt position, and the belt is output from the control plant 50. The edge sensor 25 is configured to detect the belt position information to which the belt edge shape 56 is added and output it to the control controller 51.

Next, the processing of the control controller 51 will be described with reference to FIGS. 6 and 7. When the print job is started and the drive of the drive motor 24 that conveys the intermediate transfer belt 6 is started, the steering control process shown in FIG. 7 is called.

First, the detection data is acquired from the edge sensor 25 (S101).

Next, profile correction is performed (S102). This is a correction for removing the influence that the detection value of the edge sensor includes the edge shape component 56 of the belt due to the cutting error of the belt manufacturing or the like. If the belt position is corrected while the belt edge shape component 56 is included, the correction will be erroneous, and conversely, the belt position will fluctuate and color shift will occur. Therefore, the belt edge shape 56 is measured in advance and stored in the storage unit 57, and the edge shape component 56 is removed from the detection result of the edge sensor 25.

Next, a notch filter process for removing the frequency component around the belt, which is a feature of the present patent, is performed (S103). This is a process for suppressing erroneous correction in response to an error in profile correction due to a change in the shape of the belt edge over time.

The necessity and implementation method of the notch filter will be explained in a little more detail. If the information of the belt edge shape 56 in the control plant 50 and the information of the edge shape storage unit 57 in the control controller 51 match, the detection noise due to the belt edge shape is suppressed by the profile correction, which affects the control. There is no. However, in reality, it was found that the edge shape of the endless belt changes due to factors such as changes in temperature and humidity depending on the installation environment and usage conditions of the device, plastic deformation over time due to long-term use, and deterioration such as belt wear and cracks. rice field. FIG. 8A is belt edge shape data before and after the change with time. FIG. 8B is an enlarged view taking the difference of the change with time. In particular, there is a large change in the one-round belt component. When the edge shape changes with time in this way, the information of the belt edge shape 56 and the edge shape data storage unit 57 do not match, and the difference becomes a profile correction error.

If the frequency is such that the belt position correction of the steering control is difficult to respond, the belt position fluctuation due to the erroneous correction in response to the profile correction error is small and the deterioration of color shift is slight. However, it was found that the one-round belt component has a low frequency, and the control works to cause a large positional fluctuation.

As a method of coping with the change of the edge shape with time, a method of reacquiring the edge shape data can be considered. However, at the time of acquiring the edge shape data, the steering control is turned off and the image is formed in order to suppress unnecessary disturbance. Since it is necessary to earn income without it, the productivity of the image forming apparatus is reduced.

Therefore, in this patent, a notch filter that removes the frequency component around one circumference of the belt is used in order to suppress the occurrence of belt meandering due to the change of the belt shape with time without reacquiring the edge shape. A notch filter is a filter that does not pass only a specific frequency but passes other frequencies. The notch filter can be realized by signal processing by the IIR filter as shown in FIG. 1 / z in FIG. 9 is a delay device and a memory for holding information. By adjusting the gains a1, a2, b0, b1 and b2 in FIG. 9, a notch filter that removes a desired frequency band can be realized.

By using a notch filter that removes the frequency band of the belt 1-circle component in the feedback loop, the profile correction error caused by the time-dependent change of the belt 1-circle component of the belt edge shape 56 can be corrected by the PI controller 53, which is a subsequent process. It is possible to suppress the transmission to the engine and suppress the erroneous correction of steering control.

After the notch filter processing, general feedback control arithmetic processing is performed. First, the deviation e is calculated by comparing the target position ref with the detected value (S104). Next, a PI control calculation for calculating the operating amount of the steering motor 26 is performed using the PI controller 53 based on the deviation e (S105). This is a commonly used proportional control and integral control, and the output str_pos of the PI controller 53 is represented by the equation (1).

式（１）のKpは比例ゲイン、Kiは積分ゲインである。

In equation (1), Kp is the proportional gain and Ki is the integral gain.

str_pos is a rotation position command of the steering motor, and the control controller 51 outputs this information to the motor driver 52 (S106). The motor driver operates the steering motor 53 based on this command. When the steering motor 26 rotates, the steering roller 21 tilts, and the position of the intermediate transfer belt 6 is corrected.

The processes S101 to S106 are continuously and repeatedly performed while the drive motor 24 that conveys the intermediate transfer belt 6 is being driven (S107). By the above processing, the belt position can be stabilized during the transfer drive of the intermediate transfer belt such as during the printing job.

<Effect of notch filter>
Next, the effect of using a notch filter that removes the frequency component around the belt, which is a feature of this patent, will be described.

FIG. 10 is a diagram showing a difference in steering control operation depending on the presence or absence of a notch filter that cuts a frequency component around one belt. Both conditions are a state in which the belt shape changes with time. The thin line in FIG. 10 is the result without the notch filter, and the thick line is the result with the notch filter. When there is no notch filter, the steering roller tilts around the belt in response to the change of the edge shape with time.

FIG. 11 is a result of evaluating the color shift in the controlled state with and without the notch filter shown in FIG. Similarly to FIG. 10, the thin line is the result without the notch filter, and the thick line is the result with the notch filter. When there is no notch filter, the color shift is exacerbated as a result of performing reverse correction in response to the edge shape. When there is a notch filter, the reaction to the edge shape around the belt is suppressed, so that the occurrence of color shift is suppressed.

In this way, by introducing a notch filter that cuts the frequency component around the belt into the feedback loop of the steering control, it is possible to suppress the occurrence of color shift due to the change in the shape of the belt edge.

Here, in order to suppress the influence of suppressing the belt one-lap component, a method of averaging the belt one-lap (moving average processing) instead of the notch filter is also conceivable. In this case as well, the influence of the profile correction error due to the change over time of the one-round belt component can be suppressed. However, when the moving average is used, the phase changes from a low frequency, and the control stability deteriorates. explain in detail.

FIG. 12 shows the one-round transmission characteristic of the control when the notch filter is introduced and when the moving average of one round of the belt is performed. The case where the notch filter is used is shown by a solid line, and the case where a moving average is used is shown by a broken line. The frequency of one circumference of the belt is 4.8 seconds, and at that frequency of 0.21 Hz, both of them block transmission. Therefore, in both cases, the influence of the change in the profile of one circumference of the belt with time can be suppressed.

Next, the phase margin, which is an index of stability, is compared with reference to FIG. The phase margin is a value indicating how many more margins the phase at the frequency at which the gain is 0 dB has with respect to −180 deg, and the smaller this value is, the more unstable the control becomes. When a notch filter is used, the phase at a gain of 0 dB is P1, and the phase margin is 60 deg. On the other hand, when the moving average is used, the phase at a gain of 0 dB is P2, and the phase margin is 14 deg. When the moving average is used in this way, the control stability is low. If the control stability is low, when a disturbance with respect to the belt position is input, a large vibration is repeated, which causes deterioration of color shift.

Therefore, consider lowering the gain of the PI controller in order to ensure the stability of the control performed by moving average. However, if the gain is lowered, the control responsiveness is lowered, and the disturbance that is originally desired to be dropped cannot be sufficiently suppressed. explain in detail.

FIG. 13 shows the one-round transmission characteristics when the notch filter is used and when the moving average is performed and the gain is adjusted. As shown in P1 and P3 of FIG. 13, the phase margin, which is an index of stability, was adjusted in gain so as to be 60 deg. In that case, the frequency with a gain of 0 dB, which represents responsiveness, is about 0.9 Hz when a notch filter is used, and about 0.3 Hz when a moving average is used, and moves when the same stability is ensured. If the average is used, it will be low. The lower the responsiveness, the lower the control performance against belt-side disturbance.

There is a sensitivity function as a way to see the disturbance suppression performance more clearly. The sensitivity function is a characteristic diagram showing how much the value can be suppressed by the control working when a disturbance enters. For example, when the fluctuation of the bias disturbance 55 shown in FIG. 6 is input, it shows how the fluctuation becomes at the belt position due to the action of the control. FIG. 14 shows a comparison of the sensitivity functions when the notch filter is used and when the moving average is used. As an example, when a disturbance with an amplitude of 100 um is input at a frequency of 0.02 Hz, in the case of a notch filter, as shown in P4 of FIG. 14, it is suppressed to 23 um, which is an 87% reduction at -12.8 dB, whereas it moves. When the average is used, as shown in P5 of FIG. 14, it can be suppressed to 72 um, which is a 28% reduction at -2.8 dB.

In this way, by using a notch filter that targets the frequency component of one circumference of the belt, the belt shape does not deteriorate in control stability and disturbance suppression performance as compared with the case of using the moving average of one circumference of the belt. It can respond to changes over time.

Finally, the relationship between the belt shape data acquisition for profile correction and the notch filter will be described. The cut step during manufacturing of the belt causes a large operation of the steering roller, which may affect the fluctuation of the belt position. In that case, it is advisable to use the notch filter and at the same time correct the belt edge shape data for the components other than the one-round belt component.

The belt edge shape data is acquired by turning off the steering control while the belt is being conveyed straight to the extent that the belt does not lean over, and then turning on the SW shown in FIG. At this time, when data acquisition is performed using the information before the processing of the notch filter 57 as shown in FIG. 6, it is necessary to perform profile correction during image formation before the processing of the notch filter. This is because there is some phase shift in the data before and after the notch filter, and if the presence or absence of the notch filter does not match at the time of acquiring the belt shape data and at the time of correction, a correction error will occur. Further, as shown in FIG. 15, in the case of a configuration in which the belt shape data acquisition is performed based on the data after the notch filter processing, the profile correction also needs to be performed after the notch filter processing.

With this configuration, the effects of profile correction and notch filter can be achieved at the same time.

S Recording material 6 Intermediate transfer belt 20 Drive roller 21 Steering roller 22 Driven roller (upstream)
23 Driven roller (downstream)
24 Drive motor 25 Edge sensor 26 Steering motor 53 PI controller 54 Intermediate transfer Belt-side plant 55 Side disturbance 56 Belt edge shape 57 Edge shape data storage 58 Notch filter 100 Image forming device

Claims (3)

With an endless belt,
A plurality of belt tension rollers for tensioning the belt, and
A driving means for transporting and driving the belt and
An image forming means provided so as to face the belt and
A steering roller that corrects the position of the belt in the width direction by changing the arrangement angle with respect to the belt, which is the belt tension roller.
It has a sensor that detects a position orthogonal to the transport direction of the belt.
It has a control calculation means for calculating the arrangement angle of the steering roller based on the detection value of the sensor.
In the control calculation means, based on the value processed by the notch filter that removes the frequency component around the belt with respect to the detected value of the sensor.
An image forming apparatus characterized by calculating the arrangement angle of the steering roller. It has a storage means for storing the edge shape data of the belt, and has a storage means.
The data for storing the edge shape is created based on the data before the processing of the notch filter, and is created.
The image forming apparatus according to claim 1, wherein the arrangement angle of the steering roller is driven based on the detection data of the edge position before the processing of the notch filter and the edge shape data stored in the storage means. It has a storage means for storing the edge shape data of the belt, and has a storage means.
The data for storing the edge shape is created based on the data after the processing of the notch filter.
The image forming apparatus according to claim 1, wherein the arrangement angle of the steering roller is driven based on the detection data of the edge position after the processing of the notch filter and the edge shape data stored in the storage means.

Images