JP7483387B2 - Image forming device - Google Patents

Description

The present invention relates to control for correcting the widthwise position of an intermediate transfer belt in an image forming device.

Conventionally, in a tandem type intermediate transfer type color image forming device such as a copier or printer, images of each color, yellow (Y), magenta (M), cyan (C), and black (K), are formed and transferred in sequence to an endless intermediate transfer belt to form a color image on a recording material. During image formation, the intermediate transfer belt is driven to rotate together with the photosensitive drum. At that time, the belt may shift 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 a toner image, or the entry of a recording material. If the belt shifts or meanders during image formation, the transfer position between the colors YMCK may shift, resulting in color misalignment. To prevent this, a control (steering control) is known that uses a sensor (edge sensor) that detects the edge position of the belt and tilts some of the multiple rollers that stretch the belt based on the detection result to correct the shift or meander of the belt.

However, the detection information from the edge sensor contains components of the belt edge shape that are caused by cutting errors during belt manufacturing, etc. These components of the belt edge shape are components that are detected as if the belt position has fluctuated, even when the belt is actually traveling straight without meandering and has no effect on color misalignment. If steering control is performed based on these detection errors, the belt position will instead fluctuate.

Therefore, a method is known in which the belt edge shape is measured in advance, for example when changing the belt, the data is stored, and the edge shape components are removed from the detection results of the edge sensor (Patent Document 1). Also, a technology has been disclosed in which the edge shape components are suppressed and steering control is performed based on the average value of the belt position data for one revolution of the belt (Patent Document 2).

Japanese Patent Application Laid-Open No. 11-298948 JP 2016-008988 A

However, the edge shape of the belt changes depending on the installation environment of the device, the usage conditions, changes in temperature and humidity, plastic deformation over time due to long-term use, and deterioration such as belt wear and cracks. For this reason, when using the method of performing correction using stored edge shape data described in Patent Document 1, the data needs to be updated in accordance with changes in the edge shape over time, and needs to be reacquired. Acquiring edge shape data requires turning off steering control and interrupting image formation in order to eliminate the effects of disturbances during steering control and image formation. As image formation is interrupted, productivity decreases.

In addition, averaging the data for one revolution of the belt in the technology described in Patent Document 2 is equivalent to performing low-pass filtering, which reduces the responsiveness of the steering control and reduces the control performance for suppressing belt meandering.

SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to suppress belt meandering caused by changes in the belt edge shape over time.

In order to achieve the above object, the image forming apparatus according to claim 1 comprises an image forming means for forming an image, an endless belt on which the image is transferred , a plurality of belt tension rollers for tensioning the belt, a driving means for driving and transporting the belt, a transfer means for transferring the image on the belt to a sheet, a belt position detection means for detecting the position of an edge in a width direction perpendicular to a transport direction of the belt, a memory means for storing data relating to a shape of the edge of the belt, a correction means for performing a correction to remove an influence of the shape of the edge included in a detection result of the belt position detection means based on the data stored in the memory means, a calculation means for performing a filter calculation using a notch filter that reduces fluctuations that appear in the detection result of the belt position detection means in the rotation period of the belt in order to suppress an error in the correction by the correction means caused by a change over time in the shape of the edge of the belt, and a control means for controlling an inclination of a steering roller included in the plurality of belt tension rollers based on the detection result of the belt position detection means on which the correction by the correction means and the filter calculation by the calculation means have been performed so as to suppress meandering of the belt .

According to the present invention, erroneous correction of steering control caused by changes in the belt edge shape over time can be suppressed .

FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus. FIG. 2 is a diagram illustrating a control configuration of the image forming apparatus. FIG. 4 is a schematic explanatory diagram of a belt edge sensor. FIG. 11 is a perspective view illustrating a tilting operation of a steering roller and a belt correction direction. FIG. FIG. 2 is a block diagram of a steering control. 4 is a flowchart of a steering control. 5A and 5B are diagrams illustrating changes in belt edge shape over time. FIG. 1 is a block diagram of signal processing to realize a notch filter. 11A and 11B are diagrams illustrating differences in steering tilt operation depending on whether or not a notch filter is used; 11A and 11B are diagrams illustrating the results of evaluating color shift depending on whether or not a notch filter is used. FIG. 13 is a diagram illustrating the open-loop transfer characteristics of a notch filter and a moving average. FIG. 13 is a diagram showing the open-loop transfer characteristics of a notch filter and a moving average (after gain adjustment). FIG. 13 is a diagram showing sensitivity functions of a notch filter and a moving average (after gain adjustment). FIG. 11 is a block diagram of steering control when the mounting position of the notch filter is changed.

Below, the embodiment of the present invention will be described in detail with reference to the drawings.

Example 1
First, the configuration of an image forming apparatus according to an 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 a recording material S in accordance with image data received from an external source via a network.

First, toner images are formed on the photosensitive drums 1Y, 1M, 1C, and 1K based on image data. The toner images are formed separately for yellow (Y), magenta (M), cyan (C), and black (K), but the forming method for each color toner image is substantially the same except for the color. Therefore, the following describes the method for forming a yellow (Y) toner image, and the formation of magenta (M), cyan (C), and black (K) toner images will be described by replacing the suffix Y of the reference numerals of the components in the description with M, C, and K.
A yellow (Y) toner image is formed by a photosensitive drum 1Y, a charger 2Y, a laser scanner 3Y, a developing unit 4Y, and a primary transfer roller 5Y.

An image signal generated based on 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 the input image signal from the semiconductor laser. The laser beam output from the semiconductor laser is irradiated onto the surface of the photosensitive drum 1Y via the polygon mirror and the mirror, thereby exposing the photosensitive drum 1Y. An electrostatic latent image is formed on the photosensitive drum 1Y by exposing the photosensitive drum 1Y, whose surface is uniformly charged by the charger 2Y. The electrostatic latent image formed on the photosensitive drum 1Y is developed by the toner supplied from the developer 4Y, thereby forming a yellow toner image on the photosensitive drum 1Y. The toner image on the photosensitive drum 1Y moves to a position T1 facing the primary transfer roller 5Y as the photosensitive drum 1Y rotates. A primary transfer bias of the opposite polarity to the charging polarity of the toner is applied to the primary transfer roller 5Y by a bias voltage supply 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 uses a cleaning blade to rub against the photosensitive drum 1Y to collect residual toner remaining on the photosensitive drum 1Y.

The above toner image formation for each color is also performed for magenta (M), cyan (C), and black (K). The toner images of each color are then transferred in sequence onto the intermediate transfer belt 6, forming a full-color toner image. The full-color toner image is transported by the intermediate transfer belt 6 to the secondary transfer section T2, which is formed by the secondary transfer roller 8 and the opposing roller 9.

The recording material S drawn from the recording material cassette 10 is fed onto the transport path by the paper feed roller 11 and sent to the registration roller 12. The registration roller 12 receives the recording material S in a stopped state and keeps it waiting, then sends the recording material S to the secondary transfer section T2 in time with the toner image on the intermediate transfer belt 6.

During the process in which the recording material S is nipped and conveyed through the secondary transfer section T2 with the toner image superimposed thereon, a bias voltage is applied to the secondary transfer roller 8, so that the full-color toner image is transferred from the intermediate transfer belt 6 to the recording material S. Residual toner that is not transferred and remains on the surface of the intermediate transfer belt 6 is collected by the belt cleaning device 13.

The recording material S onto which the toner image has been transferred is transported to the fixing device 14, where it is heated and pressurized, and the toner image is fixed to the recording material. After fixing, the recording material S is discharged outside the device by the paper discharge rollers 15.

The above is the color image formation process using the tandem intermediate transfer method with the intermediate transfer belt 6.

The advantage of the intermediate transfer belt method, which indirectly transfers a toner image from an image carrier to a recording material using an intermediate transfer belt, is that it is less susceptible to fluctuations in the resistance value of the recording material due to changes in humidity, etc., because the toner images of each color are superimposed on the belt. In addition, compared to a method in which the toner images of each color are directly transferred to the recording material, it is easier to control the transfer conditions of the toner images when forming a color image. The recording material transport system is also simplified, which helps prevent sheet jams.

On the other hand, because multiple color toner images are superimposed on the intermediate transfer belt, it is important to minimize fluctuations in the belt position (meandering) in order to form high-quality color images without color shift. If the belt position fluctuates, the superposition of the toner images of each color will shift as the belt passes through the primary transfer sections for each color of YMCK, resulting in color shifts. To prevent this, a control called steering control is performed to stabilize the belt position. Steering control will be explained in more detail later.

<Control Configuration of Image Forming Apparatus>
Next, the control configuration of the image forming apparatus will be described.

Figure 2 is a block diagram showing an example of the control configuration of the image forming apparatus 100. The system controller 150 shown in Figure 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 is capable of exchanging data with each unit connected to it.

The CPU 150a reads and executes various programs stored in the ROM 150b to execute various sequences related to a predetermined image formation sequence. 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 in which various data is temporarily stored. The RAM 150c stores data such as setting values for the high voltage control unit 155, command values for the motor control unit 157, and information received from the operation unit 152.

The system controller 150 accepts settings made by the user via the operation unit 152 by controlling the operation unit 152 to display an operation screen on a display unit provided on the operation unit 152, which allows the user to make various settings. The system controller 150 receives information indicating the contents of settings made by the user via the operation unit 152 (such as the copy magnification setting value and the density setting value) from the operation unit 152. The system controller 150 also transmits data to the operation unit 152 to inform the user of the status of the image forming apparatus. The operation unit 152 displays information indicating the status 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 setting value data of each device in the image forming apparatus 100 that is required for image processing in the image processing unit 151. The system controller 150 also 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 setting values output from the system controller 150, the high voltage control unit 155 supplies the chargers 2Y, 2M, 2C, 2K, developers 4Y, 4M, 4C, 4K, primary transfer rollers 5Y, 5M, 5C, 5K, and secondary transfer roller 8 that constitute the high voltage unit 156 with the voltages required for their respective operations.

The A/D converter 153 receives a detection signal from a thermistor 154 for detecting the temperature of the fixing heater 161, converts the detection signal into a digital signal, and transmits it 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.

The system controller 150 also controls the driving of each motor via the motor control unit 157. The system controller 150 generates command signals such as the position and speed of the motor to be controlled, and outputs them to the motor control unit 157. The motor control unit 157 controls the driving of the motor according to the command signals provided by the CPU 150a.

The steering control, which is a feature of this patent and is a control for stabilizing the position of the intermediate transfer belt, is also performed by the control configuration shown in Figure 2. Based on information obtained from a sensor 159 that detects the position of the intermediate transfer belt in the width direction, a CPU 150a in the system controller 150 performs control calculations and drives a motor 158 that operates a mechanism for correcting the belt position via a motor control unit 157.

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

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

If the intermediate transfer belt 6 meanders during image formation, the toner images of each color will be misaligned when transferred from the drum to the belt, resulting in color misalignment. Therefore, the image forming device 100 performs steering control to stabilize the position of the intermediate transfer belt. In steering control, some of the rollers that tension the belt are configured as tiltable steering rollers, and the position of the belt in the width direction is corrected by adjusting the tilt direction and amount of tilt of the steering roller based on position information obtained from a sensor that detects the position of the belt.

Specifically, the configuration of the intermediate transfer belt drive device that realizes steering control will be described with reference to FIG. 1. It is equipped with a drive roller 20, a steering roller 21, driven rollers 22 and 23, a secondary transfer opposing roller 9, and primary transfer rollers 5Y, 5M, 5C, and 5K, and the intermediate transfer belt 6 is rotatably stretched around these rollers. The drive roller 20 is connected to a drive motor 24, and the intermediate transfer belt 6 is transported as the drive roller 20 rotates in the direction of the arrow in the figure.

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

Next, the belt position detection means will be described. The belt position detection sensor 25 (edge sensor) is disposed between the black photosensitive drum 1K and the driven roller 23. FIG. 3(a) is a view of the intermediate transfer belt as seen from the steering roller 21 side. FIG. 3(b) is a detailed cross-sectional view of the edge sensor. One end of the contact 25x is held in a pressed state against the end of the intermediate transfer belt 6 by the tension of the spring 25w. In this case, the pressing force of the contact 25x by the spring 25w is set to an appropriate magnitude so as not to deform the intermediate transfer belt 6. The contact 25x is supported at its middle portion by a support shaft 25y so as to be freely rotatable, and a displacement sensor 25z, which is a reflective photosensor, is disposed in an opposing state on the other end of the contact 25x across the support shaft 25y.

In this edge sensor 25, the change in position of the intermediate transfer belt 6 in the width direction (y direction in the figure) is converted into the movement (swinging motion) of the contact 25x that is pressed against the belt edge. At this time, the output level of the displacement sensor 25z changes in response to the movement (displacement) of the contact 25x, so 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 steering roller 21 and its vicinity in FIG. 1. The steering roller 21 is supported rotatably by a bearing holder 30. The bearing holder 30 is fixed to the movable side of a slide rail 31. A slider 32 is fixed to the same surface of the movable side of the slide rail 31. Meanwhile, the fixed side of the slide rail 31 is fixed to a steering arm (support member) 33. The slider 32 is biased in the direction of arrow T by a spring (biasing member) 34 hung on the steering arm 33. Therefore, the slider 32 slides on the steering arm 33, and as a result, the steering roller 21 is biased in the direction of arrow T, providing tension to the intermediate transfer belt 6.

On the other hand, the steering arm 33 on the front side of the page is supported so as to be able to swing about the swing shaft 35. A follower 36 is supported on the steering arm 33 in a direction symmetrical to the steering roller 21 with respect to the swing shaft 35. A cam 37 is provided so as to abut against the follower 36, and the cam 37 is configured to be rotatable by a steering motor (drive means) 26. 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 rotates in the direction of arrow E, and the alignment is changed. Conversely, 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, and the alignment is changed.

In this way, the steering roller 21 rotates as shown in Figures 5(a), (b), and (c). When the alignment of the steering roller 21 shifts in the direction of the arrow E, the intermediate transfer belt 6 moves into the page, and when it shifts in the direction of the arrow F, the intermediate transfer belt 6 moves into the page. This is based on the principle that when the steering roller 21 tilts, the start and end positions of the intermediate transfer belt 6 wrapping around the steering roller 21 shift in the axial direction of the belt, and the belt position is corrected as the belt is transported.

<Steering control calculation>
Next, the calculation process for steering control will be described. This calculation process is performed by the CPU 150b in the system controller 150 shown in Fig. 2. A detailed description will be given with reference to the control block diagram shown in Fig. 6 and the flow chart shown in Fig. 7.

As shown in FIG. 6, the steering control is composed of 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 in FIG. 6 is the control target of the steering control, and is represented by mathematical expressions and numerical data in the control block diagram representing the control information processing. The control plant 50 is composed of an intermediate transfer belt shift plant 54, a shift disturbance 55, and an edge shape 56. The intermediate transfer belt shift plant 54 is a transmission system that inputs the tilt position of the steering roller and outputs a belt position response according to the input. A shift disturbance 55 is added to the intermediate transfer belt shift plant 54, resulting in a belt position that affects the image. The steering control aims to stabilize this belt position. The shift disturbance 55 is a disturbance generated by the shift force due to the support mechanism of the intermediate transfer belt, the mechanical accuracy of the belt itself, the transfer of the toner image, the intrusion of the recording material, etc. The belt position is further added with a belt edge shape component 56 caused by cutting errors in belt manufacturing, etc., and is output from the control plant 50. The edge sensor 25 is configured to detect belt position information including the belt edge shape 56 and output it to the control controller 51.

Next, the processing of the control controller 51 will be described with reference to Figures 6 and 7. When a print job is started and the driving motor 24 that transports the intermediate transfer belt 6 starts to be driven, the steering control processing shown in Figure 7 is called.

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

Next, profile correction is performed (S102). This is a correction to remove the effect of the edge shape component 56 of the belt being included in the edge sensor detection value, which is caused by cutting errors during belt manufacturing, etc. If the belt position is corrected while this belt edge shape component 56 is included, it will be an erroneous correction, which will in fact cause the belt position to fluctuate and result in color misalignment. Therefore, the belt edge shape 56 is measured in advance and stored in the memory unit 57, and the edge shape component 56 is removed from the detection result of the edge sensor 25.

Next, a notch filter process is performed to remove the frequency components of one revolution of the belt, which is a feature of this patent (S103). This process is performed to prevent erroneous corrections in response to errors in profile correction caused by changes in the belt edge shape over time.

The necessity of the notch filter and how to realize it will be explained in more detail. If the belt edge shape 56 in the control plant 50 and the information in the edge shape storage unit 57 in the control controller 51 match, the detection noise due to the belt edge shape is suppressed by profile correction and does not affect the control. However, in reality, it has been found that the edge shape of an endless belt changes due to factors such as changes in temperature and humidity due to the installation environment and usage conditions of the device, plastic deformation over time due to long-term use, and deterioration such as wear and cracks of the belt. Figure 8 (a) shows belt edge shape data before and after the change over time. Figure 8 (b) is an enlarged view of the difference in the change over time. There is a particularly large change in the belt one revolution component. If the edge shape changes over time in this way, the belt edge shape 56 and the information in the edge shape data storage unit 57 will not match, and the difference will become a profile correction error.

At high frequencies where the steering control belt position correction is difficult to respond to, the belt position fluctuations caused by erroneous corrections in response to profile correction errors are small, and the color shift deterioration is minimal. However, it was found that the component of one revolution of the belt is a low frequency, and the control is activated, causing large position fluctuations.

One way to deal with changes in edge shape over time is to reacquire edge shape data, but when acquiring edge shape data, steering control must be turned off and the data must be acquired while no images are being formed in order to suppress unnecessary disturbances, resulting in reduced productivity of the image forming device.

In this patent, therefore, a notch filter is used to remove the frequency components of one revolution of the belt in order to suppress belt meandering caused by changes in the belt shape over time, without reacquiring the edge shape. A notch filter is a filter that blocks certain frequencies and passes other frequencies. A notch filter can be realized by signal processing using an IIR filter as shown in Figure 9. 1/z in Figure 9 is a delay device and memory that holds information. By adjusting the gains a1, a2, b0, b1, and b2 in Figure 9, a notch filter that removes the desired frequency band can be realized.

By using a notch filter in the feedback loop that removes the frequency band of the belt one revolution component, it is possible to prevent the profile correction error caused by the change over time of the belt one revolution component of the belt edge shape 56 from being transmitted to the PI controller 53, which is the downstream processing stage, and to prevent erroneous correction of the steering control.

After the notch filter processing, general feedback control calculation processing is performed. First, the target position ref and the detected value are compared to calculate the deviation e (S104). Next, a PI control calculation is performed to calculate the operation amount of the steering motor 26 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 expressed by 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 rotational position command for the steering motor, and the 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 offset position of the intermediate transfer belt 6 is corrected.

The process of S101 to S106 is continuously repeated while the drive motor 24 that transports the intermediate transfer belt 6 is driving (S107). Through the above process, the belt position can be stabilized while the intermediate transfer belt is being driven for transport during a print job, etc.

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

Figure 10 shows the difference in steering control operation with and without a notch filter that cuts out the frequency components of one revolution of the belt. In both cases, the belt shape changes over time. The thin line in Figure 10 shows the results without a notch filter, and the thick line shows the results with a notch filter. When there is no notch filter, the steering roller for one revolution of the belt tilts in response to the change in edge shape over time.

Figure 11 shows the results of evaluating color shift in the control state with and without the notch filter shown in Figure 10. As with Figure 10, the thin line shows the result without a notch filter, and the thick line shows the result with a notch filter. Without a notch filter, color shift worsens as a result of inverse correction being made in response to the edge shape. With a notch filter, the reaction to the edge shape of one revolution of the belt is suppressed, thereby suppressing the occurrence of color shift.

In this way, by introducing a notch filter that cuts out the frequency components of one revolution of the belt into the feedback loop of the steering control, it is possible to suppress color shifts caused by changes in the belt edge shape.

Here, in order to suppress the influence of the one-cycle belt component, it is also possible to consider a method of averaging one cycle of the belt (moving average processing) instead of using a notch filter. In this case, it is also possible to suppress the influence of profile correction errors caused by changes over time in the one-cycle belt component. However, when a moving average is used, the phase changes from low frequencies, deteriorating control stability. A detailed explanation will be given below.

Figure 12 shows the loop transfer characteristics of control when a notch filter is introduced and when a moving average of one revolution of the belt is performed. The solid line shows the case where a notch filter is used, and the dashed line shows the case where a moving average is used. The frequency of one revolution of the belt is 4.8 sec, and at this frequency of 0.21 Hz, both cut off the transmission. Therefore, in both cases, the effects of changes in the profile over time of one revolution of the belt can be suppressed.

Next, also using Figure 12, we compare the phase margin, which is an index of stability. The phase margin is a value that indicates how many degrees the phase at the frequency where the gain is 0 dB has a margin of -180 deg, and the smaller this value is, the more unstable the control is. 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 a moving average is used, the phase at a gain of 0 dB is P2, and the phase margin is 14 deg. In this way, when a moving average is used, the control stability is low. When control stability is low, when a disturbance is input to the belt position, the behavior will result in repeated large vibrations, which will cause color misregistration to worsen.

Therefore, we consider lowering the gain of the PI controller to ensure the stability of the control using the moving average. However, lowering the gain reduces the control responsiveness and makes it impossible to sufficiently suppress the disturbances that we want to suppress. We will explain in detail.

Figure 13 shows the open-loop transfer characteristics when a notch filter is used and when moving averages are performed and the gain is adjusted. The phase margin, which is an index of stability, was adjusted to 60 deg, as shown by P1 and P3 in Figure 13. In this case, the frequency at a gain of 0 dB, which indicates responsiveness, is approximately 0.9 Hz when a notch filter is used and approximately 0.3 Hz when the moving average is used, meaning that while the same stability is ensured, the frequency is lower when the moving average is used. The control performance against disturbances toward the belt is reduced to the extent that responsiveness is reduced.

A way to see disturbance suppression performance more clearly is the sensitivity function. The sensitivity function is a characteristic diagram that expresses the level to which the control can suppress a disturbance when it is introduced. For example, it shows how the belt position fluctuates when the control is applied when the fluctuation of the deviation disturbance 55 shown in Figure 6 is input. Figure 14 shows a comparison of the sensitivity functions when a notch filter is used and when a moving average is used. As an example, when a disturbance with a frequency of 0.02 Hz and an amplitude of 100 um is input, in the case of the notch filter, it is suppressed to 23 um, a reduction of 87%, at -12.8 dB, as shown in P4 of Figure 14, whereas in the case of using the moving average, it is only suppressed to 72 um, a reduction of 28%, at -2.8 dB, as shown in P5 of Figure 14.

In this way, by using a notch filter that targets the frequency components of one revolution of the belt, it is possible to respond to changes in the belt shape over time without compromising control stability or disturbance suppression performance, compared to using a moving average of one revolution of the belt.

Finally, we will discuss the relationship between notch filters and obtaining belt shape data for profile correction. Cutting steps during belt manufacturing can cause large movements of the steering roller, which can affect belt position fluctuations. In such cases, in addition to using a notch filter, it is a good idea to simultaneously perform corrections using belt edge shape data for components other than one revolution of the belt.

Belt edge shape data is acquired by turning off the steering control while the belt is being conveyed in a straight line without being pulled too far, and then turning on the SW shown in Figure 6. At this time, if data acquisition is performed using information before processing by the notch filter 57 as in Figure 6, profile correction during image formation must also be performed before notch filter processing. 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 when the belt shape data is acquired and when it is corrected, a correction error will occur. Also, as shown in Figure 15, in a configuration in which belt shape data acquisition is performed based on data after notch filter processing, profile correction must also be performed after notch filter processing.

By configuring it in this way, it is possible to achieve both profile correction and the effects of a notch filter.

S: recording material 6; intermediate transfer belt 20; driving 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 deviation plant 55 Deviation disturbance 56 Belt edge shape 57 Edge shape data storage unit 58 Notch filter 100 Image forming apparatus

Claims (3)

An image forming means for forming an image;
an endless belt onto which the image is transferred ;
A plurality of belt tension rollers for tensioning the belt;
A driving means for driving the belt;
a transfer means for transferring the image on the belt to a sheet;
a belt position detection means for detecting the position of an edge of the belt in a width direction perpendicular to the conveying direction of the belt;
a storage means for storing data relating to the shape of the edge of the belt;
a correction means for performing a correction based on the data stored in the storage means to remove an influence of the shape of the edge included in the detection result of the belt position detection means;
a calculation means for performing a filter calculation using a notch filter that reduces fluctuations appearing in the detection result of the belt position detection means during a rotation cycle of the belt in order to suppress an error in the correction by the correction means caused by a change over time in the shape of the edge of the belt;
and a control means for controlling an inclination of a steering roller included in the plurality of belt tension rollers based on the detection result of the belt position detection means in which the correction by the correction means and the filter calculation by the calculation means have been performed so as to suppress meandering of the belt . 2. The image forming apparatus according to claim 1, wherein the calculation means performs a filter calculation using the notch filter on the detection result of the belt position detection means after the correction by the correction means . 2. The image forming apparatus according to claim 1 , wherein the correction means corrects the detection result of the belt position detection means on which the filter calculation has been performed by the calculation means, based on the data stored in the storage means .

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