JP7338290B2 - CONTROL DEVICE, CONTROL METHOD, AND IMAGE FORMING APPARATUS - Google Patents

Description

The present disclosure relates to an image forming apparatus that transfers a toner image formed on the peripheral surface of a photoreceptor drum to an intermediate transfer belt, and more particularly to technology for controlling the rotation of the photoreceptor drum.

In an image forming apparatus such as an electrophotographic printer, a toner image is formed on a photosensitive drum for each of a plurality of colors, and the toner images of multiple colors are superimposed and transferred to an intermediate transfer belt, which is then transferred to a recording sheet. A color image is obtained by fixing the toner image.

According to Patent Document 1, a rotational driving force is transmitted from a motor to a photosensitive drum via a reduction gear. At this time, even if control data for controlling the rotation of the motor at a constant speed is given to the motor, the photosensitive drum may rotation unevenness occurs. Since the rotation cycle of the reduction gear and the motor is set to be 1/integer of one rotation of the photoreceptor drum, the uneven rotation repeats at the rotation period of the photoreceptor drum.

Therefore, at the transfer position from the photoreceptor drum to the intermediate transfer belt, the relationship between the amount of movement of the peripheral surface of the photoreceptor drum and the amount of movement of the intermediate transfer belt differs for each color, and images of each color are superimposed. Sometimes they do not match, resulting in color shift (position shift). In order to solve this problem, the image forming apparatus is equipped with an encoder that outputs 1000 pulses for one rotation of the photosensitive drum. Based on the error data and the control step period of the motor in the (n-1)th rotation, the control step period of the motor in the nth rotation is controlled. In this way, based on the cycle of encoder pulses detected in the past, predicted fluctuations are predicted in advance, and the control step cycle of the motor in the next rotation is determined. Suppresses occurrence.

Here, a control method of predicting an assumed change in advance using a past detection signal and determining an output signal according to the prediction is called feedforward control.

Further, in Patent Documents 2 and 3, as in Patent Document 1, based on the period of encoder pulses detected in the past, predicted fluctuations are predicted in advance, and the control step period of the motor in the next rotation is predicted. have decided.

When the rotational fluctuation of the photoreceptor drum is good, the width of the change in the positional deviation amount of the toner image formed on the peripheral surface of the photoreceptor drum is within a certain range, as shown in FIG. In this figure, the horizontal axis indicates the passage of time, and the vertical axis indicates the displacement amount of the toner image formed on the peripheral surface of the photosensitive drum.

JP-A-2000-162941 JP-A-2004-53882 Japanese Unexamined Patent Application Publication No. 2005-80378 JP 2007-171241 A JP 2008-129346 A JP-A-2002-72592 JP 2010-237631 A JP 2013-160941 A

However, when the feedforward is repeatedly executed to control the peripheral speed of the photoreceptor drum, there is a problem that the restraining force generated between the photoreceptor drum and the intermediate transfer belt causes a large rotational fluctuation of the photoreceptor drum. .

Here, the constraint force means that the circumferential speed of the photosensitive drum and the circumferential speed of the intermediate transfer belt are almost the same, and there is almost no speed difference between the two. , the force that restricts the fluctuation of the circumferential movement of one against the other, as if static friction were acting. When viewed from the photoreceptor drum side, this binding force limits the rotational fluctuation of the photoreceptor drum.

When the binding force between the photoreceptor drum and the intermediate transfer belt is large, the feedforward is repeatedly executed so that, for example, when the peripheral speed of the photoreceptor drum is slow, the peripheral speed of the photoreceptor drum is increased. Even if the force is slightly increased, the peripheral speed of the photosensitive drum may not change due to a large restraining force. In this case, since the rotation of the photoreceptor drum does not follow the control, the gain is repeatedly applied by feedforward, the gain gradually increases, the difference from the target peripheral speed increases, and the rotational driving force exceeds the restraining force. Then, the peripheral speed of the photosensitive drum changes to a peripheral speed greatly exceeding the speed difference of the intermediate transfer belt (first change). As a result of this change, the peripheral velocity of the photosensitive drum deviates greatly from the target peripheral velocity by feedforward. Therefore, the reverse gain is then determined. In this case as well, it is controlled and largely changed in the opposite direction (second change) in the same manner as described above. When the feedforward is repeatedly performed, the first change and the second change occur repeatedly. As a result, hunting (large vibration) occurs.

FIG. 17 shows changes in the amount of positional deviation when the rotational fluctuation of the photosensitive drum is large. As shown in this figure, the positional deviation amount of the toner image formed on the peripheral surface of the photosensitive drum fluctuates greatly over time. In this figure, the horizontal axis indicates the passage of time, and the vertical axis indicates the displacement amount of the toner image formed on the peripheral surface of the photosensitive drum.

When the restraining force between the photoreceptor drum and the intermediate transfer belt increases in this manner, the photoreceptor drum undergoes a large rotational fluctuation, resulting in misalignment of the image on the circumferential surface of the photoreceptor drum.

FIG. 18 shows changes in the amount of misregistration when the rotational variation of the photosensitive drums of each color is large. In this figure, the horizontal axis indicates the position on the recording sheet when the image is transferred onto the recording sheet, and the vertical axis indicates Y (yellow), M (magenta), C (cyan), and K (black). Indicates the amount of color misregistration. As shown in this figure, different phase and amplitude fluctuations occur for each color, resulting in misregistration of Y, M, C, and K colors on the recording sheet.

When obtaining a color image, misalignment of images between colors becomes conspicuous as color misregistration, but misalignment of images also occurs when obtaining a monochrome image.

In order to solve such problems, the present disclosure provides a control device capable of suppressing an increase in the binding force between the photoreceptor drum and the intermediate transfer belt, thereby preventing the occurrence of image misalignment. An object of the present invention is to provide a control method and an image forming apparatus.

In order to achieve the above object, one embodiment of the present disclosure is a control device for controlling rotation of a photoreceptor that transfers a toner image formed on its peripheral surface to an intermediate transfer member, comprising : As a result of hunting occurring in the rotation of the toner image , the toner image is deviated from the prohibited area , which is the range of the speed difference between the peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer member, setting means for setting a target value of the peripheral speed of the photoreceptor so that it is adjacent to the prohibited region and belongs to the permitted region, which is a range of speed differences in which positional deviation exceeding an allowable value does not occur; speed control means for controlling the peripheral speed of the photoreceptor so that it rotates in unison; and the setting means further controls the photoreceptor and the intermediate transfer member under a plurality of reference speed differences. Drive control is performed, positional deviation amounts of the toner image formed on the circumferential surface of the photoreceptor are measured at each reference speed difference, and the allowable value is calculated by the hunting using a plurality of obtained measured positional deviation amounts. is estimated, and the estimated range is set as the prohibited area .
Further, another embodiment of the present disclosure is a control device for controlling rotation of a photoreceptor that transfers a toner image formed on its peripheral surface to an intermediate transfer member, wherein hunting occurs in the rotation of the photoreceptor. , outside the prohibited area, which is the range of the speed difference between the peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer member, which causes the positional deviation of the toner image exceeding the allowable value, adjacent to the prohibited area, and the allowable setting means for setting a target value of the peripheral speed of the photoreceptor so that it belongs to an allowable region, which is a range of speed differences in which positional deviation exceeding a value does not occur; a speed control means for controlling the peripheral speed of the photoreceptor, wherein the speed difference range in which the toner image is misaligned beyond an allowable value is defined as a large speed difference region; The setting means sets the target value so that the speed difference falls outside the large speed difference region and belongs to the allowable region, and further, based on a plurality of reference speed differences, the photoreceptor and the intermediate transfer member. are driven and controlled to measure the amount of positional deviation of the toner image formed on the circumferential surface of the photoreceptor at each reference speed difference, and the plurality of measured positional deviation amounts thus obtained are used to determine the distance between the photoreceptor and the intermediate Estimate the range of speed difference in which the positional deviation occurs beyond the allowable value without generating a binding force that limits the rotational fluctuation of the photoreceptor between the transfer body and the estimated range. It is characterized in that it is set as a large speed difference region.

Here, the range of the speed difference in which the hunting occurs may vary due to varying factors related to the photoreceptor, and the prohibited area may include the varied range of the speed difference.

Here, the fluctuating factor related to the photoreceptor may be component tolerance, assembly error, aging or environmental change of at least one of the photoreceptor and the intermediate transfer body.

Here, the peripheral speed of the photosensitive member is defined as the first speed, the peripheral speed of the intermediate transfer member is defined as the second speed, and the speed difference is calculated by (first speed−second speed)/first speed*100. Then, the width of the prohibited area may be within 0.1 percent.

Here, the setting means further drives and controls the photoreceptor and the intermediate transfer member under a plurality of reference speed differences, and the toner image formed on the peripheral surface of the photoreceptor at each reference speed difference. , and using the obtained plurality of measured positional deviation amounts, estimate the range of speed difference in which the positional deviation occurs due to the hunting exceeding the allowable value, and the range obtained by the estimation may be set as the prohibited area.

Here, the setting means plots a plurality of sets of the reference speed difference and the corresponding measured positional deviation amount on a virtual plane having the velocity difference as the horizontal axis and the positional deviation amount as the vertical axis. Calculation is performed to obtain an approximated curve representing the distribution of a plurality of plotted points, the speed difference corresponding to the allowable value is obtained in the obtained approximated curve, and the obtained speed difference is used as the boundary of the prohibited area. May be set as a value.

Here, the setting means may set the prohibited area according to an instruction from an operator or when an operating condition of the photoreceptor satisfies a predetermined condition.

Here, the predetermined condition may be that the cumulative number of rotations of the photoreceptor reaches a predetermined number.

Here, the setting means may further set a parameter indicating an image forming condition or a parameter indicating timing for starting image formation according to the set target value.

Here, the range of the speed difference in which the toner image is misaligned beyond an allowable value due to the speed difference is defined as a large speed difference region. The target value may be set so as to fall outside the allowable range.

Here, the setting means further drives and controls the photoreceptor and the intermediate transfer member under a plurality of reference speed differences, and the toner image formed on the peripheral surface of the photoreceptor at each reference speed difference. , and using the obtained plurality of measured positional deviation amounts, estimate the range of speed differences in which the positional deviation occurs beyond the allowable value without generating the restraining force, and by estimating The obtained range may be set as the large speed difference region.

Here, the setting means may set the large speed difference region according to an instruction from an operator or when the working condition of the photoreceptor satisfies a predetermined condition.

Here, the predetermined condition may be that the cumulative number of rotations of the photoreceptor reaches a predetermined number.

Here, the speed difference is calculated by subtracting the peripheral speed of the intermediate transfer member from the peripheral speed of the photosensitive member. and a negative allowed area, the width of the negative allowed area being wider than the width of the positive allowed area.

Here, the negative permission area is a phenomenon in which a part of the toner image remains on the photoreceptor without being transferred to the intermediate transfer body when the toner image is transferred from the photoreceptor to the intermediate transfer body. may include a hollow suppression region that suppresses the

Here, in an image forming apparatus having a plurality of photoconductors and the intermediate transfer member, the control device controls the rotation of the plurality of photoconductors, and the toner image formed on the peripheral surface of each photoconductor is transferred to the intermediate transfer member. Further, for each of the plurality of photoconductors, the setting means sets the speed difference between the peripheral speed of the photoconductor and the peripheral speed of the intermediate transfer member to fall outside the prohibited region and fall within the permitted region. In addition, the target value of the peripheral speed of the photoreceptor may be set.

Here , in an image forming apparatus including the photoreceptor and the intermediate transfer member, the control device controls the rotation of the photoreceptor, and further controls the peripheral speed of the photoreceptor during image formation by the image forming apparatus. and a second speed, which is the peripheral speed of the intermediate transfer member; a calculating device, which calculates the speed difference between the first speed and the second speed; and the calculated speed determination means for determining whether the difference belongs to the prohibited area or the permitted area; and the setting means further determines whether the speed difference belongs to the permitted area when the speed difference belongs to the prohibited area. The target value of the peripheral speed of the photoreceptor may be corrected so as to belong to

Here, the control device further determines an output signal by estimating the rotation of the photoreceptor based on a detection signal detected by a sensor that detects the rotation of the photoreceptor. A feedforward control circuit may be provided to control by feedforward.

Here, the control device further uses, as a predetermined target signal, a detection signal detected by a sensor that detects rotation of the photoreceptor and rotation of a motor that transmits rotational driving force to the photoreceptor. A feedback control circuit may be included to control by feedback determining the output signal such that the detected signal matches the target signal.

Further, another embodiment of the present disclosure is a control method of a control device for controlling rotation of a photoreceptor that transfers a toner image formed on a peripheral surface to an intermediate transfer member, comprising : rotating the photoreceptor; As a result of hunting occurring in the toner image , the positional deviation of the toner image exceeding the allowable value will occur . a setting step of setting a target value of the peripheral speed of the photoreceptor so that it is adjacent to the region and belongs to a permitted region , which is a range of speed differences in which positional deviation exceeding an allowable value does not occur; and a speed control step of controlling a peripheral speed of the photoreceptor so that it rotates in the above-described manner, wherein the setting step further includes driving the photoreceptor and the intermediate transfer member under a plurality of reference speed differences. The amount of positional deviation of the toner image formed on the circumferential surface of the photoreceptor is measured for each reference speed difference, and the allowable value is adjusted by the hunting using the plurality of measured positional deviation amounts thus obtained. It is characterized by estimating a speed difference range beyond which positional deviation occurs, and setting the range obtained by estimation as the prohibited area .
Further, another embodiment of the present disclosure is a control method of a control device for controlling rotation of a photoreceptor for transferring a toner image formed on a peripheral surface to an intermediate transfer body, wherein hunting is caused in the rotation of the photoreceptor. As a result, the positional deviation of the toner image exceeding the allowable value is generated outside the prohibited area, which is the range of the speed difference between the peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer member, and is adjacent to the prohibited region. a setting step of setting a target value of the peripheral speed of the photoreceptor so that the photoreceptor belongs to an allowable region, which is a speed difference range in which positional deviation exceeding an allowable value does not occur; and a speed control step of controlling the peripheral speed of the photoreceptor, wherein the range of the speed difference in which the toner image positional deviation exceeding an allowable value is caused by the speed difference is defined as a large speed difference region. In the setting step, the target value is set so that the speed difference is outside the large speed difference region and belongs to the allowable region; The intermediate transfer member is driven and controlled, and the amount of positional deviation of the toner image formed on the circumferential surface of the photoreceptor is measured for each reference speed difference. and the intermediate transfer member, the range obtained by estimating the speed difference range in which the positional deviation exceeds the allowable value without generating a restraining force that limits the rotation fluctuation of the photoreceptor. is set as the large speed difference region.

Another embodiment of the present disclosure is an image forming apparatus for transferring a toner image formed on the circumferential surface of a photoreceptor to an intermediate transfer member, comprising the control device for controlling rotation of the photoreceptor. Characterized by

According to this embodiment, it is possible to suppress the increase in the binding force between the photoreceptor drum and the intermediate transfer belt, thereby preventing image misalignment.

1 is a diagram schematically showing the overall configuration of an image forming apparatus 1 as one embodiment; FIG. 3 shows the configuration of a control system that controls the rotational driving of the photosensitive drum 43 and the intermediate transfer belt 32. FIG. (a) is a graph showing a positional deviation amount corresponding to a speed difference between a drum speed and a belt speed; (b) shows an enlarged view of the first prohibited area 201; (c) shows the amount of positional deviation on the circumferential surface of the photosensitive drum 43; 3 shows a configuration of a control circuit 14; 3 is a block diagram showing the configuration of a controller 108b; FIG. 3 is a block diagram showing the configuration of a determination table 124; FIG. (a) A method of calculating the upper limit value 267 and the lower limit value 261 in the first prohibited area 201 is shown. (b) shows a mark image formed on the circumferential surface of the photosensitive drum 43; A calculation method for the upper limit value 214 in the second prohibited area 204 and the lower limit value 215 in the third prohibited area 205 is shown. 4 is a flowchart showing the overall operation of the image forming apparatus 1; 4 is a flowchart showing the operation of speed comparison processing; 7 is a flow chart showing the operation of manual setting processing of a prohibited area; 9 is a flowchart showing the operation of manual setting processing of the first prohibited area; 9 is a flowchart showing the operation of manual setting processing of the second prohibited area; 7 is a flowchart showing the operation of automatic setting processing of a prohibited area; 5 is a graph showing the positional deviation amount corresponding to the speed difference between the drum speed and the belt speed. In addition to the first, second and third prohibited areas and the first and second permitted areas, a blank suppression area is also shown. FIG. 10 shows changes in the amount of positional deviation when rotation fluctuations of the photoreceptor drum are good; FIG. FIG. 10 shows changes in the amount of positional deviation when the rotational fluctuation of the photoreceptor drum is large. FIG. 10 shows changes in the amount of misregistration when rotation fluctuations of the photoreceptor drums of respective colors are large.

1 Embodiment An embodiment will be described with reference to the drawings.

1.1 Image forming apparatus 1
The image forming apparatus 1 is a tandem-type color multifunction peripheral (MFP: MultiFunction Peripheral) having functions such as a scanner, a printer, and a copier.

In the image forming apparatus 1, as shown in FIG. 1, a sheet conveying section 50 that accommodates and conveys sheets is provided at the bottom of the housing. A print engine 13 for forming an image by electrophotography and a control circuit 14 for integrally controlling each block of the image forming apparatus 1 are provided above the sheet conveying unit 50 . is provided with a scanner 10 that reads a document and generates input image data, and an operation panel 20 that displays an operation screen and accepts an input operation from an operator.

(1) Scanner 10
As shown in FIG. 1, the scanner 10 includes an automatic document feeder (ADF) 11, a document image scanning device 12, and the like.

The automatic document feeder 11 transports the document placed on the document tray by the transport mechanism and sends it to the document image scanning device 12 .

The document image scanning device 12 optically scans the document conveyed onto the contact glass from the automatic document feeder 11 or the document placed on the contact glass, and converts the light reflected from the document into a CCD (Charge Coupled Device). ) An image is formed on the light-receiving surface of the sensor 12a, and the document image is read. The scanner 10 generates input image data based on the result of reading by the document image scanning device 12 . The scanner 10 writes the generated input image data to the image memory 104 (FIG. 4).

(2) Operation panel 20
The operation panel 20 includes a display section 21 and an operation section 22 (not shown).

The display unit 21 displays various operation screens, operation status of each function, and the like.

The operation unit 22 includes a touch panel and various operation keys such as a numeric keypad and a start key for receiving contact operations by the operator. It receives an instruction to automatically set the area, etc., and outputs an operation signal to the main control unit 100 (FIG. 4). The operation panel 20 is configured by, for example, a liquid crystal display (LCD) with a touch panel.

Further, the operation unit 22 receives a positional deviation amount tolerance value, which will be described later, and outputs the received positional deviation amount tolerance value to the main control unit 100 .

(3) Print engine 13
As shown in FIG. 1, the print engine 13 includes an image forming section 40 for forming an image by electrophotography and a fixing section 60 for fusing a toner image onto a sheet.

The image forming unit 40 includes image forming units 41Y, 41M, 41Y, 41M, 41Y, 41M, 41Y, 41M, 41Y, 41M, 41Y, 41M, 41Y, 41M, 41Y, 41M, 41Y, 41M, 41Y, 41M, 41Y, 41M, 41Y, 41M, 41Y, 41M, and 41M, respectively. 41C, 41K, an intermediate transfer unit 31, and the like.

Image forming units 41Y, 41M, 41C, and 41K for the Y, M, C, and K components have similar configurations. For convenience of illustration and description, common constituent elements are denoted by the same reference numerals, and Y, M, C, or K is added to the reference numerals to distinguish them. In FIG. 1, only the constituent elements of the image forming unit 41Y for the Y component are denoted by reference numerals, and the constituent elements of the other image forming units 41M, 41C, and 41K are omitted. Hereinafter, the image forming unit 41Y will be described as the image forming unit 41 as a representative of the image forming units 41Y, 41M, 41C, and 41K.

The image forming unit 41 includes an exposure device 48, a developing device 42, a photoreceptor drum 43 (photoreceptor), a charging device 44, a drum cleaning device 45, a sensor 46, and the like.

As shown in FIG. 2, the controller 108b (part of the control device) controls the drive current supplied to the drive motor 70 that rotates the photoreceptor drum 43, so that the photoreceptor drum 43 is driven at a predetermined drum speed. (first speed). Here, the drum speed is the speed (peripheral speed) on the peripheral surface of the photosensitive drum 43 . Specifically, the controller 108 b generates a PWM control signal and outputs the generated PWM control signal to the driving circuit 73 in order to rotate the photosensitive drum 43 at a predetermined drum speed. The drive circuit 73 generates a drive current according to the received PWM control signal and supplies the generated drive current to the drive motor 70 . The driving motor 70 transmits rotational driving force to the rotating shaft of the photosensitive drum 43 via a gear mechanism (not shown). As a result, the photosensitive drum 43 rotates at a predetermined drum speed. Due to the precision of the gear mechanism, the eccentricity of the photoreceptor drum 43, and the like, the rotational fluctuation of the drive motor 70 and the rotational fluctuation of the photoreceptor drum 43 are different. Rotation fluctuations due to eccentricity of the photoreceptor drum 43 often occur for each rotation, and have an undulation component over a relatively long period of time (for example, 0.5 seconds, in other words, 2 Hz).

An optical encoder 71 is provided on the rotating shaft of the photoreceptor drum 43 to detect the number of revolutions of the photoreceptor drum 43 and calculate the peripheral speed. The encoder 71 is composed of a light-emitting element, a light-receiving element, a code wheel, an arithmetic circuit, and the like. The code wheel rotates together with the rotating shaft of the photosensitive drum 43, and the code wheel is provided with a plurality of slits at regular intervals on a circle concentric with the rotating shaft. The light-emitting element is provided so as to face the light-receiving element, and the code wheel blocks or transmits light between the light-emitting element and the light-receiving element. The number of slits provided in the code wheel is, for example, 1000, and when the photosensitive drum 43 makes one rotation, the light receiving element outputs 1000 encoder pulses. The arithmetic circuit measures the number of rotations of the photosensitive drum 43 per unit time by counting the number of output encoder pulses per unit time. Since the diameter of the photosensitive drum 43 is known, the arithmetic circuit calculates and outputs the peripheral speed (drum speed) of the photosensitive drum 43 using the measured number of rotations per unit time.

The drive motor 70 is provided with an FG (Frequency Generator) 72 that measures the rotation speed of the drive motor 70 . The FG 72 rotates a magnetic pattern magnetized in multiple poles in the circumferential direction together with the driving motor 70, and induces an induced electromotive force in a circumferential comb-teeth-shaped line (FG pattern) formed at a position facing this magnetic pattern. The rotational speed (angular speed) of the drive motor 70 is detected and output. The drive motor 70 is rotatable at a constant rotational speed with feedback by PID control (Proportional-Integral-Differential Controller).

Returning to FIG. 1, the charging device 44 uniformly charges the circumferential surface of the photosensitive drum 43 to a negative polarity.

The exposure device 48 is composed of, for example, a semiconductor laser, and irradiates the photosensitive drum 43 with laser light corresponding to an image of each color component. An electrostatic latent image of each color component is formed on the circumferential surface of the photosensitive drum 43 by the irradiation of the laser light.

The developing device 42 is, for example, a two-component developing device, and forms a toner image by visualizing an electrostatic latent image by attaching toner of each color component to the circumferential surface of the photosensitive drum 43 .

The sensor 46 detects a mark image (FIG. 7B) formed as a toner image on the circumferential surface of the photosensitive drum 43. When the mark image is detected, the mark detected on the circumferential surface of the photosensitive drum 43 is detected. Outputs position information indicating the position where the image exists.

The drum cleaning device 45 has a drum cleaning blade that slides on the peripheral surface of the photosensitive drum 43, a lubricant applying portion, and the like. The drum cleaning blade removes transfer residual toner remaining on the circumferential surface of the photosensitive drum 43 after the primary transfer. The lubricant applying section applies a lubricant to the peripheral surface of the photoreceptor drum 43 after residuals such as transfer residual toner have been removed. As the photosensitive drum 43 rotates, the applied lubricant passes through the charging device 44, the developing device 42, and other parts in the circumferential direction, and reaches the drum cleaning device 45. It is supplied to the contact portion between the provided drum cleaning blade and the photosensitive drum 43 .

As a result, the friction between the drum cleaning blade and the photosensitive drum 43 is reduced, the early wear of the cleaning blade is prevented, and the cleaning performance can be improved over a long period of time. Longer life can be achieved by suppressing wear. In addition, since the lubricant film is interposed between the peripheral surface of the photosensitive drum 43 and the toner particles of the toner image after development, transferability can be improved over a long period of time.

The intermediate transfer unit 31 includes an intermediate transfer belt 32 (intermediate transfer body), a plurality of primary transfer rollers 47, a plurality of support rollers 33A-33D, secondary transfer rollers 34A and 34B, a belt cleaning device 36, and the like.

The intermediate transfer belt 32 is an endless belt, and is stretched in a loop shape by a plurality of support rollers 33A to 33D. Of the plurality of support rollers 33A-33D, the support roller 33A is a driving roller, and the support rollers 33B-33D are driven rollers. As shown in FIG. 2, the intermediate transfer belt 32 moves in the direction of arrow A at a predetermined belt speed (second speed) by controlling the drive current supplied to the drive motor 80 that rotates the support roller 33A. ) to cycle. Here, the belt speed is the speed on the circumferential surface of the intermediate transfer belt 32 . Specifically, the controller 108 b generates a PWM control signal and outputs the generated PWM control signal to the driving circuit 83 in order to rotate the intermediate transfer belt 32 at a predetermined belt speed. The drive circuit 83 generates a drive current according to the received PWM control signal and supplies the generated drive current to the drive motor 80 . Drive motor 80 is a brushless motor. The drive motor 80 transmits rotational driving force to the rotation shaft of the support roller 33A via a gear mechanism (not shown). As a result, the support roller 33A rotates, and the intermediate transfer belt 32 circulates at a predetermined belt speed.

The rotation shaft of the support roller 33D is provided with an optical encoder 81 that detects the number of rotations of the support roller 33D and calculates and outputs the peripheral speed, that is, the speed of the intermediate transfer belt 32 (belt speed). . The encoder 81 has the same configuration as the encoder 71, and the description thereof is omitted.

The drive motor 80 is provided with an FG 82 that measures and outputs the rotational speed of the drive motor 80 . The FG82 has the same configuration as the FG72, and its description is omitted.

Returning to FIG. 1, the primary transfer roller 47 for each color component is arranged on the inner circumferential surface side of the intermediate transfer belt 32 so as to face the photosensitive drum 43 for that color component. A transfer current corresponding to the applied voltage flows through the primary transfer roller 47 . The primary transfer roller 47 is pressed against the photoreceptor drum 43 with the intermediate transfer belt 32 interposed therebetween. A primary transfer nip is formed for transfer.

The secondary transfer rollers 34A and 34B are arranged on the outer peripheral side of the intermediate transfer belt 32 so as to face the support rollers 33A and 33B arranged on the inner peripheral side of the intermediate transfer belt 32 . A secondary transfer nip for transferring the toner image from the intermediate transfer belt 32 to the sheet S is formed by pressing the secondary transfer rollers 34A and 34B against the support rollers 33A and 33B, respectively, with the intermediate transfer belt 32 interposed therebetween. be done.

When the intermediate transfer belt 32 passes through the primary transfer nip of each color, the toner images on the photosensitive drums 43 of each color are superimposed on the intermediate transfer belt 32 and primarily transferred.

After that, when the sheet S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 32 is secondarily transferred onto the sheet S. The sheet S onto which the toner image has been transferred is conveyed toward the fixing section 60 .

The belt cleaning device 36 has a belt cleaning blade or the like that slides on the surface of the intermediate transfer belt 32, and removes transfer residual toner remaining on the surface of the intermediate transfer belt 32 after secondary transfer.

The fixing section 60 is provided on the downstream side in the sheet S conveying direction from the secondary transfer nip. The fixing unit 60 includes a fixing belt 60A arranged on the fixing surface of the sheet S (the surface on which the toner image is formed), and a pressure roller 60B arranged on the back surface of the sheet S (the surface opposite to the fixing surface). and a heat source 60C for applying heat to the fixing belt 60A. The pressure roller 60B is brought into pressure contact with the fixing belt 60A, thereby forming a fixing nip NP for nipping and conveying the sheet S. As shown in FIG.

The fixing section 60 heats and presses the sheet S conveyed from the secondary transfer nip at the fixing nip NP. The sheet S that has passed through the fixing nip NP is conveyed toward the paper discharge section 52 .

(4) Sheet conveying unit 50
The sheet conveying section 50 includes a sheet feeding section 51, a conveying path section 53, a sheet discharging section 52, and the like. The sheet conveying section 50 is controlled according to instructions from the control circuit 14 .

The paper feeding unit 51 is provided at the bottom of the housing of the image forming apparatus 1 , and the transport path unit 53 is provided on the downstream side in the transport direction of the sheets fed from the paper feeding unit 51 .

The paper feed section 51 includes three paper feed tray units 51a to 51c. Sheets are accommodated in the sheet feed tray units 51a to 51c, respectively. Sheets S accommodated in the paper feed tray units 51 a to 51 c are conveyed to the conveying path section 53 .

The transport path portion 53 has a plurality of transport roller pairs such as a registration roller pair 53a. When the sheet S is conveyed from the sheet feeding section 51 to the conveying path section 53, the registration roller pair 53a corrects the inclination of the sheet S and adjusts the conveying timing. After that, the sheet S is conveyed toward the secondary transfer nip.

The paper discharge section 52 includes a paper discharge roller 52a. The sheet S conveyed from the fixing section 60 is discharged out of the apparatus by the discharge rollers 52a.

(5) Positional deviation on the peripheral surface of the photoreceptor drum 43 On the peripheral surface of the photoreceptor drum 43, due to fluctuations in the number of rotations of the photoreceptor drum 43, the position where the toner image should be originally formed may shift. , there may be a positional deviation in which the toner image is formed in the circumferential direction of the photosensitive drum 43 .

FIG. 3C shows positional deviation of the toner image on the peripheral surface of the photosensitive drum 43 . As shown in this figure, due to fluctuations in the rotation speed of the photosensitive drum 43, a toner image 43b is formed at a position shifted in the circumferential direction of the photosensitive drum 43 from the toner image 43a that should be formed. there is Thus, there is a problem that a desired image cannot be obtained because the toner image is formed at a position shifted from the original position. In the case of color printing, this misregistration becomes conspicuous as color misregistration among Y, M, C and K colors.

Here, the distance 43c between the toner image 43a and the toner image 43b on the peripheral surface of the photosensitive drum 43 is the positional deviation amount.

FIG. 3A is a graph showing the positional deviation amount corresponding to the speed difference between the drum speed of the photosensitive drum 43 and the belt speed of the intermediate transfer belt 32 . In this figure, the horizontal axis indicates the speed difference, and the vertical axis indicates the amount of positional deviation. Here, the speed difference between the drum speed and the belt speed is calculated by the following formula.

Speed difference = (drum speed - belt speed) / (drum speed) x 100
As shown in this figure, the possible values of the speed difference between the drum speed and the belt speed are the second prohibited area 204 (large speed difference area), the first permitted area 202 (permitted area), and the first prohibited area 201 (forbidden area). area), a second allowed area 203 (allowed area) and a third prohibited area 205 (large speed difference area).

The second prohibited area 204 is an area below the upper limit value 214 (−0.50%), and the first prohibited area 201 is above the lower limit value 212 (−0.05%) and above the upper limit value 213 (+0.05%). ), and the third prohibited area 205 is an area equal to or greater than the lower limit value 215 (+0.30%). Also, the first permission region 202 is the region between the upper limit value 214 and the lower limit value 212 , and the second permission region 203 is the region between the upper limit value 213 and the lower limit value 215 .

The first prohibited area 201 is defined as a speed difference in which the toner image formed on the peripheral surface of the photoreceptor drum 43 is misaligned due to hunting that occurs during rotation control of the photoreceptor drum 43, exceeding the allowable value. Range. In other words, hunting occurs in the first prohibited area 201 due to the generation of a binding force between the peripheral surface of the photoreceptor drum 43 and the peripheral surface of the intermediate transfer belt 55 that restricts fluctuations in rotation of the photoreceptor drum 43 . is the range of speed differences that cause

The first prohibited area 201 is a range in which the drum speed and the belt speed are substantially constant. Here, as an example, the first prohibited area 201 is in the range of -0.05% or more and +0.05% or less. That is, the width of the first prohibited area 201 may be within 0.1%. When the speed difference exists within the first prohibited area 201, the force of constraint between the drum speed and the belt speed is strong, and the responsiveness to the rotation control of the drum is poor. Therefore, hunting occurs. In the first prohibited area 201, for example, as shown in FIG. 17, the rotation fluctuation is large, so the amount of positional deviation is large, and in some cases, the positional deviation exceeding 0.1 mm may occur. Moreover, in the case of a color image, color misregistration becomes conspicuous and the image quality deteriorates. Therefore, control is performed to avoid setting in the first prohibited area 201 .

As shown in FIG. 3B, the first prohibited area 201 includes a velocity difference 211 of "0", a positive prohibited area 222 where the velocity difference is positive, and a negative prohibited area 221 where the velocity difference is negative. include.

On the other hand, when the speed difference exists within the first permission area 202 or the second permission area 203, the rotational fluctuation of the photosensitive drum is small. The first allowable area 202 and the second allowable area 203 are speed difference ranges in which positional deviation exceeding the allowable value does not occur. In other words, the first permission area 202 and the second permission area 203 are restraints that limit variations in the rotation of the photoreceptor drum 43 between the peripheral surface of the photoreceptor drum 43 and the peripheral surface of the intermediate transfer belt 55, respectively. This is the range of speed differences in which no force is generated.

Here, as an example, the first permission area 202 is in the range of -0.50% or more and -0.05% or less, and the second permission area 203 is in the range of +0.05% or more and +0.30% as an example. The range is as follows. The first permission area 202 is the negative permission area and the second permission area 203 is the positive permission area. Within the first permission area 202 or the second permission area 203, the rotation variation of the photosensitive drum 43 is small, so as shown in FIG. It can be misaligned. In the first permission area 202 or the second permission area 203, only the influence of the eccentricity of the photosensitive drum needs to be corrected without being affected by the constraint force between the drum speed and the belt speed.

A second prohibited area 204 or a third prohibited area 205 is a range of speed differences in which the toner image formed on the peripheral surface of the photosensitive drum 43 is misaligned beyond the allowable value. No binding force is generated between the photosensitive drum 43 and the intermediate transfer belt 32 in the second prohibited area 204 or the third prohibited area 205 . The second prohibited area 204 is a large negative speed difference area, and the third prohibited area 205 is a large positive speed difference area. The large positive speed difference region exists on the side larger than the positive permission region, and the negative large speed difference region exists on the side smaller than the negative permission region.

If the speed difference exists within the second prohibited area 204 or the third prohibited area 205, the surface friction between the photoreceptor drum and the intermediate transfer belt exceeds the allowable amount due to the large speed difference, and the normal position is not stable. However, it is difficult to transfer the printed image, resulting in large misregistration and color misregistration.

Further, when the rotation of the photosensitive drum 43 is feedforward/feedback controlled, if the drum speed is higher than the belt speed due to the difference in surface friction between the photosensitive drum 43 and the intermediate transfer belt 32, that is, in the second permission area 203, With a small speed difference, sudden speed fluctuations may occur and control may be disturbed. In order to avoid this phenomenon, as described above, the boundary between the second prohibited area 204 and the first permitted area 202 is set to "-0.50%", and the boundary between the third prohibited area 205 and the second permitted area 203 is set to -0.50%. , “+0.30%”. That is, the width of the first permission area 202 and the width of the second permission area 203 are made different, and the width of the second permission area 203 is set narrower than the width of the first permission area 202 .

As described above, the speed difference between the drum speed and the belt speed exceeds the permissible value due to hunting that occurs during rotation control of the photosensitive drum 43, and toner is formed on the circumferential surface of the photosensitive drum 43. The drum speed of the photoreceptor drum 43 is adjusted so that it belongs within the first permitted region 202 or the second permitted region 203 where the positional deviation exceeding the allowable value does not occur, except for the first prohibited region 201 where the image is misaligned. Set a target value.

Further, when the speed difference exists within the first prohibited area 201 , the drum speed of the photosensitive drum 43 may be corrected so that the speed difference exists within the first permitted area 202 or the second permitted area 203 . Further, even when the speed difference exists within the second prohibited area 204 or the third prohibited area 205, the speed difference of the photosensitive drum 43 is adjusted so that the speed difference exists within the first permitted area 202 or the second permitted area 203. Correct the drum speed.

The area setting described above can be applied to both the formation of a color image and the formation of a monochrome image.

(6) Control circuit 14
As shown in FIG. 4, the control circuit 14 includes a main control unit 100, an image memory 104, a storage unit 105, an image processing unit 106, a network communication unit 107, an engine control unit 108, a scanner control unit 109, an input/output unit 110, and the like. consists of

(6-1) Main control unit 100
The main control unit 100 is composed of a CPU 101, a ROM 102, a RAM 103, and the like.

A RAM 103 is composed of a semiconductor memory, temporarily stores various control variables, and provides a work area when the CPU 101 executes a program.

The ROM 102 is composed of a semiconductor memory, and stores in advance control programs and the like for executing various jobs such as scan jobs, copy jobs, and print jobs.

The CPU 101 operates according to control programs stored in the ROM 102 .

Since it is composed of the CPU 101, the ROM 102, the RAM 103, and the like, as described above, the main control unit 100 controls the image memory 104, the storage unit 105, the image processing unit 106, and the network communication unit according to a scan job, a copy job, a print job, or the like. 107, the engine control unit 108, the scanner control unit 109, the input/output unit 110, and the like are controlled in a unified manner.

For example, when the main control unit 100 receives a print job through the network communication unit 107 by operating according to a control program, the main control unit 100 instructs the engine control unit 108 to instruct the print engine 13 to perform an image forming operation based on the print job. to run.

Further, the main control unit 100 configures a later-described setting unit 111 (FIG. 5, part of the control device) by operating according to the control program.

Further, the main control unit 100 receives a manual setting instruction of the prohibited area or an automatic setting instruction of the prohibited area from the operation panel 20 via the input/output unit 110 . Upon receiving the prohibited area manual setting instruction or the prohibited area automatic setting instruction, the main control unit 100 outputs the prohibited area manual setting instruction or the prohibited area automatic setting instruction to the setting unit 111 .

(6-2) Image memory 104 and storage unit 105
The image memory 104 is composed of a semiconductor memory and temporarily stores input image data such as a print job.

The storage unit 105 is composed of a nonvolatile semiconductor memory. Of course, the storage unit 105 may be composed of a hard disk drive. The storage unit 105 includes areas for storing tolerance values 112a, 112b, and 112c of the amount of positional deviation.

The allowable value 112a of the positional deviation amount is used to determine the upper limit value 213 and the lower limit value 212 of the first prohibited area 201 shown in FIG. Also, the allowable value 112b of the positional deviation amount is used to determine the upper limit value 214 of the second prohibited area 204 shown in FIG. Furthermore, the allowable value 112c of the positional deviation amount is used to determine the lower limit value 215 of the third prohibited area 205 shown in FIG.

(6-3) Image processing unit 106
The image processing unit 106 includes a circuit or the like for performing digital image processing on the input image data stored in the image memory 104 . For example, the image processing unit 106 performs gradation correction based on gradation correction data (gradation correction table) under the control of the main control unit 100 . Further, the image processing unit 106 performs various correction processes such as color correction, shading correction, compression process, etc. in addition to gradation correction on the input image data stored in the image memory 104 . Further, the image processing unit 106 performs multi-value printing of R (red), G (green), and B (blue) included in a print job received from an external terminal device or generated by scanning with the scanner 10, for example. Input image data composed of digital signals is subjected to various data processing, and converted into input image data of each of Y, M, C, and K color components. The print engine 13 is controlled based on the input image data subjected to these processes.

(6-4) Network communication unit 107, scanner control unit 109 and input/output unit 110
A network communication unit 107 receives a print job from an external terminal device via a network. The network communication unit 107 also outputs messages and the like to external terminal devices as necessary.

A scanner control unit 109 controls scanning of the document surface by the scanner 10 . For example, the scanner control unit 109 designates the resolution when the document surface is scanned by the scanner 10 . The scanner control unit 109 writes the image data received from the scanner 10 into the image memory 104 .

Input/output unit 110 relays data between main control unit 100 and operation panel 20 .

(6-5) Engine control unit 108
As shown in FIG. 4, the engine control section 108 includes an engine main control section 108a, a controller 108b, and the like.

(Engine main control unit 108a)
The engine main control section 108a is composed of a CPU, a ROM, a RAM, and the like. The RAM is composed of a semiconductor memory, temporarily stores various control variables, and provides a work area when a program is executed by the CPU. The ROM is composed of a semiconductor memory, and stores in advance a control program and the like for operating the engine control unit 108 . The CPU operates according to control programs stored in the ROM.

The engine main control unit 108a controls the feeding operation from the sheet conveying unit 50 and the image forming operation of the image forming unit for each color component of the print engine 13 in an integrated manner, and causes the image forming operation to be executed. Further, the engine main control section 108a controls the controller 108b.

(controller 108b)
The controller 108b controls the speed difference between the drum speed and the belt speed to fall within the first allowed area 202 or the second allowed area 203, except for the first forbidden area 201, the second forbidden area 204 and the third forbidden area 205. , to control the drum speed.

The controller 108b controls the rotation of the photoreceptor drums 43 of each color, and controls the circulation of the intermediate transfer belt 32. FIG. The controller 108b comprises four drum control circuits 121a, 121b, 121c, 121d and a belt control circuit 131, as shown in FIG.

The drum control circuits 121a, 121b, 121c, and 121d correspond to the Y-, M-, C-, and K-color photosensitive drums 43, respectively, and control the rotation of the photosensitive drums 43 for each color. A belt control circuit 131 corresponds to the intermediate transfer belt 32 and controls the circulation of the intermediate transfer belt 32 .

In FIG. 5, descriptions of FGs, encoders, drive motors, drive circuits, etc. corresponding to the drum control circuits 121b, 121c, and 121d are omitted.

Further, as shown in FIG. 5, the setting unit 111 (setting means) and the controller 108b constitute a control device 113 that controls the rotation of the photosensitive drum 43. As shown in FIG.

(6-6) Drum control circuit 121a
Here, the drum control circuit 121a will be described. Note that the drum control circuits 121b, 121c, and 121d have the same configuration as the drum control circuit 121a, respectively, so the description of the drum control circuits 121b, 121c, and 121d is omitted.

The drum control circuit 121a comprises an arithmetic circuit 122 (acquisition means), a speed command circuit 123, a determination table 124, and a speed comparison control circuit 125, as shown in FIG.

(Determination table 124)
As shown in FIG. 6, the determination table 124 includes an upper limit value 124a of the second prohibited area 204, a lower limit value 124b of the first prohibited area 201, an upper limit value 124c of the first prohibited area 201, and a lower limit value of the third prohibited area 205. 124d is a data table with areas for storing .124d.

Upper limit 124a, lower limit 124b, upper limit 124c, and lower limit 124d correspond to upper limit 214, lower limit 212, upper limit 213, and lower limit 215 shown in FIG. 3, respectively.

(arithmetic circuit 122)
The arithmetic circuit 122 (speed control means) controls the peripheral speed of the photosensitive drum 43 so that it rotates in accordance with the target value as described below.

Arithmetic circuit 122 receives the rotation speed of drive motor 70 from FG 72 and the drum speed of photosensitive drum 43 from encoder 71 .

The arithmetic circuit 122 is composed of a feedback control circuit 122a, a feedforward control circuit 122b and a speed arithmetic circuit 122c.

The feedback control circuit 122a compares the rotation speed of the drive motor 70 received from the FG 72 with a predetermined target speed, calculates the difference between the rotation speed and the target speed, and determines whether the rotation speed of the drive motor 70 matches the target speed. , the calculated difference is added to or subtracted from the rotation speed received from the FG 72 to calculate a new rotation speed.

The feedforward control circuit 122b controls the drum speed of the photosensitive drum 43 received from the encoder 71 and the past predetermined period (for example, if the current rotation of the photosensitive drum 43 is the n-th rotation, the n-1th rotation In the period of one rotation), based on the drum speed of the photosensitive drum 43 received from the encoder 71 and stored, predicted fluctuations are predicted and a correction amount is calculated.

Feedback control is suitable for removing the fluctuation component of about several tens of Hz immediately before, but it is difficult to feed back the fluctuation component in a long cycle. Therefore, feedforward control is also used. As described above, the rotation speed for one rotation of the photoreceptor drum 43 is stored, and the regular variation of the photoreceptor drum 43 is grasped. By superimposing the deviation of the rotation speed fluctuation for one rotation of the photoreceptor drum 43 on the feedback for the next one rotation, the low-frequency It is possible to suppress the rotational fluctuation by removing the rotational fluctuation component due to the eccentricity of the photosensitive drum 43 .

The speed calculation circuit 122c corrects the new rotational speed calculated by the feedback control circuit 122a with the correction amount calculated by the feedforward control circuit 122b, and calculates the drum speed of the photosensitive drum 43 after correction. The corrected drum speed obtained and calculated is output to the speed comparison control circuit 125 .

(Speed comparison control circuit 125)
A speed comparison control circuit 125 receives the corrected drum speed from the arithmetic circuit 122 and the belt speed from the belt control circuit 131 . The speed comparison control circuit 125 outputs the corrected drum speed received from the arithmetic circuit 122 to the speed command circuit 123 .

Upon receiving the drum speed and belt speed, the speed comparison control circuit 125 (calculating means) calculates the speed difference according to the following equation.

Speed difference=(Drum speed after correction−Belt speed)/(Drum speed after correction)×100
Next, the speed comparison control circuit 125 (judgment means) uses the determination table 124 to determine whether the obtained speed difference is the second prohibited area 204, the first permitted area 202, the first prohibited area 201, the first prohibited area 201, and the second prohibited area 204 shown in FIG. It is determined in which of the second permitted area 203 and the third prohibited area 205 the area is entered.

When it is determined that the speed difference falls within the second prohibited area 204 (speed difference≦upper limit 124a), the speed comparison control circuit 125 (setting means) adjusts the drum speed so that the speed difference falls within the first permitted area 202. speed up the target value of For example, the speed comparison control circuit 125 sets the target value of the drum speed such that the speed difference is -0.25.

When it is determined that the speed difference falls within the third prohibited region 205 (speed difference≧lower limit 124d), the speed comparison control circuit 125 sets the target value of the drum speed so that the speed difference falls within the second permitted region 203. slow down. For example, the speed comparison control circuit 125 sets the target value of the drum speed such that the speed difference is +0.25.

When determining that the speed difference falls within the first prohibited area 201 (lower limit value 124b≤speed difference≤upper limit value 124c), the speed comparison control circuit 125 further determines whether the speed difference is 0 or more. If the speed difference is greater than or equal to 0, the drum speed target value is increased so that the speed difference falls within the second permission area 203 . For example, the speed comparison control circuit 125 sets the target value of the drum speed such that the speed difference is +0.25. On the other hand, if the speed difference is less than 0, the target value of the drum speed is decreased so that the speed difference falls within the first allowable region 202 . For example, the speed comparison control circuit 125 sets the target value of the drum speed such that the speed difference is -0.25.

When it is determined that the speed difference falls within the first allowable region 202 or the second allowable region 203 (upper limit value 124a<speed difference<lower limit value 124b or upper limit value 124c<speed difference<lower limit value 124d), the speed comparison control circuit 125 , does not change the target value of the drum speed.

As described above, the speed comparison control circuit 125 (correction means) corrects the target value of the drum speed so that the speed difference falls within the first permission area 202 or the second permission area 203 . Next, the speed comparison control circuit 125 outputs the corrected target value of the drum speed to the arithmetic circuit 122 so that the speed difference falls within the first permission area 202 or the second permission area 203 .

In this way, even during image formation, when the speed difference does not enter the first permission area 202 or the second permission area 203, the speed difference is set to enter the first permission area 202 or the second permission area 203. Furthermore, since the target value of the drum speed is corrected, it is possible to prevent the positional deviation on the circumferential surface of the photosensitive drum 43 from occurring.

(Speed command circuit 123)
Speed command circuit 123 receives the drum speed from speed comparison control circuit 125 . Next, the speed command circuit 123 generates a PWM control signal that is set to rotate the photosensitive drum 43 according to the received drum speed. Next, speed command circuit 123 outputs the generated PWM control signal to drive circuit 73 .

(6-7) Belt control circuit 131
The belt control circuit 131 comprises an arithmetic circuit 132 (acquisition means) and a speed command circuit 133, as shown in FIG.

(arithmetic circuit 132)
Arithmetic circuit 132 receives the rotation speed of drive motor 80 from FG 82 and the belt speed of intermediate transfer belt 32 from encoder 81 .

The arithmetic circuit 132 is composed of a feedback control circuit 132a, a feedforward control circuit 132b and a speed arithmetic circuit 132c.

The feedback control circuit 132a compares the rotation speed of the drive motor 80 received from the FG 82 with a predetermined target speed, calculates the difference between the rotation speed and the target speed, and determines whether the rotation speed of the drive motor 80 matches the target speed. , the calculated difference is added to or subtracted from the rotation speed received from the FG82 to calculate a new rotation speed.

The feedforward control circuit 132b controls the belt speed of the intermediate transfer belt 32 received from the encoder 81 and the past predetermined period (for example, if the current rotation of the intermediate transfer belt 32 is the m-th rotation, the m-1th rotation One rotation period), based on the belt speed of the intermediate transfer belt 32 received from the encoder 81 and stored, predicted fluctuations are predicted and a correction amount is calculated.

The speed calculation circuit 132c corrects the new rotation speed calculated by the feedback control circuit 132a with the correction amount calculated by the feedforward control circuit 132b, and calculates the belt speed of the intermediate transfer belt 32 after correction. Then, the calculated corrected belt speed is output to the speed command circuit 133 and the speed comparison control circuit 125 .

(Speed command circuit 133)
The speed command circuit 133 receives the belt speed from the speed calculation circuit 132c. Next, the speed command circuit 133 generates a PWM control signal that is set so that the intermediate transfer belt 32 runs around according to the received belt speed. Next, speed command circuit 133 outputs the generated PWM control signal to drive circuit 83 .

(6-8) Setting unit 111
(6-8-1) Setting Target Belt Speed and Target Drum Speed When the operator gives an instruction to execute printing, the setting unit 111 selects from the determination table 124 the upper limit value 124a of the second prohibited area 204, the first The lower limit value 124b of the prohibited area 201, the upper limit value 124c of the first prohibited area 201, and the lower limit value 124d of the third prohibited area 205 are read. When the operator issues a print execution instruction, the determination table 124 contains the upper limit value 124a of the second prohibited area 204, the lower limit value 124b of the first prohibited area 201, the upper limit value 124c of the first prohibited area 201, and the Assume that the lower limit value 124d of the third prohibited area 205 is set.

A setting unit 111 sets a target belt speed of the intermediate transfer belt 32 . The target belt speed is set based on image forming conditions and the like.

The setting unit 111 removes the first prohibited area 201 defined by the read upper limit value 124c and the lower limit value 124b, and sets the first permitted area defined by the upper limit value 124a, the lower limit value 124b, the upper limit value 124c, and the lower limit value 124d. 202 and the speed difference belonging to the second allowable area 203 are set. For example, the setting unit 111 sets “−0.25” as the speed difference from the first permission area 202 .

Next, the setting unit 111 (correcting means) sets (corrects) the target drum speed (target value) so that the difference from the target belt speed becomes the set speed difference.

target drum speed=target belt speed/(1-speed difference/100)
Next, the setting unit 111 converts the target belt speed into the target speed of the drive motor 80 and outputs the target speed to the arithmetic circuit 132 of the belt control circuit 131 . The setting unit 111 also converts the target drum speed into the target speed of the drive motor 70, and outputs the target speed to the arithmetic circuit 122 of the drum control circuits 121a to 121d.

The intermediate transfer belt 32 is driven and controlled so as to run in a circle in accordance with the target belt speed set in this way. Further, the photosensitive drum 43 is driven and controlled so as to rotate at the target drum speed set in this manner.

Therefore, the speed difference falls within the ranges of the first permission area 202 and the second permission area 203, and it is possible to prevent the occurrence of positional deviation on the circumferential surface of the photosensitive drum 43. FIG.

(6-8-2) Setting of Determination Table 124 The setting unit 111 sets the first prohibited area 201, the second prohibited area 204, and the third prohibited area 205 as described below. That is, the determination table 124 is set. It is assumed that the first prohibited area 201, the second prohibited area 204, and the third prohibited area 205 are set before the operator issues a print execution instruction.

The setting unit 111 sets a plurality of reference speed differences, drives and controls the photoreceptor drum 43 and the intermediate transfer belt 32 based on each reference speed difference that has been set, and at each reference speed difference, the photoreceptor drum 43 Measure the amount of misalignment of the toner image formed on the . Using a plurality of obtained measured positional deviation amounts, the range of velocity difference in which the positional deviation occurs exceeding the allowable value due to hunting is estimated, and the estimated range is set as the first prohibited area 201. . Further, using the obtained plural measured positional deviation amounts, the range of velocity difference in which the positional deviation occurs beyond the permissible value without generating a restraining force is estimated, and the range obtained by the estimation is A second prohibited area 204 and a third prohibited area 205 are set. Further, the setting unit 111 sets the first prohibited area 201, the second prohibited area 204, and the third prohibited area 205 according to an instruction from the operator or when the operating status of the photosensitive drum 43 satisfies a predetermined condition. Here, the predetermined condition is, for example, that the cumulative number of rotations of the photosensitive drum 43 reaches a predetermined number.

Specifically, it is as follows.

The setting unit 111 receives from the main control unit 100 an instruction to manually set the prohibited area or an instruction to automatically set the prohibited area. Here, the prohibited area is any one of the first prohibited area 201 , the second prohibited area 204 and the third prohibited area 205 .

Upon receiving the prohibited area manual setting instruction, the setting unit 111 executes the prohibited area manual setting process. The manual setting process of the prohibited area will be described later.

Upon receiving the prohibited area automatic setting instruction, the setting unit 111 sets the prohibited area automatic setting mode. Next, the setting unit 111 determines whether or not the cumulative number of printed sheets by the print engine 13 exceeds 10,000 sheets, for example. Here, the cumulative number of printed sheets may be reset to "0" each time it is determined that it exceeds 10,000 sheets. Instead of determining the number of prints, the setting unit 111 may determine whether or not the total number of rotations of the photosensitive drum 43 exceeds 10,000 times, for example. It may be reset to "0" each time it is determined that the count exceeds 10,000. The setting unit 111 also determines whether or not the prohibited area automatic setting mode is set.

When the cumulative number of prints exceeds 10,000 and the prohibited area automatic setting mode is set, the setting unit 111 executes the prohibited area automatic setting process. Since the cumulative number of rotations is reset to "0" each time it is determined that it exceeds 10,000, if the prohibited area automatic setting mode is set, the cumulative number of prints will exceed 10,000. Each time it exceeds, the setting unit 111 executes automatic setting processing of the prohibited area. The automatic setting processing of the prohibited area will be described later.

In this way, when the automatic setting mode is set, the automatic setting process of the prohibited area is executed every time the cumulative number of prints exceeds 10,000, that is, every time a predetermined period elapses, which will be described later. As described above, there is a case where the range of the speed difference between the peripheral surface of the photoreceptor drum 43 and the peripheral surface of the intermediate transfer belt 32, in which the restraining force for limiting the fluctuation of the rotation of the photoreceptor drum 43 is generated, fluctuates. Because there is By executing the automatic setting process of the prohibited area every time the predetermined period is exceeded, the range of the changed prohibited area is newly set, and by using the newly set prohibited area, the peripheral surface of the photosensitive drum 43 It is possible to prevent the occurrence of upward positional deviation.

If the cumulative number of prints does not exceed 10,000, the setting unit 111 does not execute the automatic setting process of the prohibited area. If the total number of prints exceeds 10,000 but the prohibited area automatic setting mode is not set, the setting unit 111 does not execute the prohibited area automatic setting process.

(Manual setting processing of prohibited area)
The setting unit 111 receives the allowable value for the positional deviation amount of the first prohibited area 201 from the operation unit 22 via the main control unit 100 . Next, the setting unit 111 executes manual setting processing of the first prohibited area 201, which will be described later. The setting unit 111 writes the received allowable value of the positional deviation amount of the first prohibited area 201 to the storage unit 105 as the allowable value 112a.

The setting unit 111 also receives the allowable value for the positional deviation amount of the second prohibited area 204 from the operation unit 22 via the main control unit 100 . Next, the setting unit 111 executes manual setting processing of the second prohibited area 204, which will be described later. The setting unit 111 writes the received allowable value of the positional deviation amount of the second prohibited area 204 to the storage unit 105 as the allowable value 112b.

Further, the setting unit 111 receives the allowable value of the positional deviation amount of the third prohibited area 205 from the operation unit 22 via the main control unit 100 . Next, the setting unit 111 executes manual setting processing of the third prohibited area 205, which will be described later. The setting unit 111 writes the received allowable value for the amount of misalignment of the third prohibited area 205 to the storage unit 105 as the allowable value 112c.

(Manual setting processing of the first prohibited area 201)
As an example, the manual setting process of the first prohibited area 201 will be described using FIGS. 7(a) and 7(b).

FIG. 7(a) is an enlarged display of the first prohibited area 201 in FIG. 3, where the horizontal axis indicates the speed difference and the vertical axis indicates the amount of positional deviation.

In the first prohibited area 201, as shown in this figure, a plurality of reference speed differences 262 "-0.02", 263 "-0.01", 264 "0.0", 265 "+0" are plotted along the horizontal axis. .01" and 266"+0.02" are shown. A plurality of reference speed differences 262, 263, 264, 265 and 266 are preset. Note that the plurality of reference speed differences 262, 263, 264, 265, and 266 shown in FIG. may be set with a plurality of reference speed differences.

In addition, one allowable value 251 is indicated in the first prohibited area 201 as shown in this figure. A permissible value 251 is a value that is permissible as a positional deviation amount. The allowable value 251 is entered by the operator.

As an example, the setting unit 111 sets each of the plurality of reference speed differences 262, 263, 264, 265, and 266 shown in FIG. are the reference speed differences 262, 263, 264, 265 and 266, respectively, and the drum speed of the photosensitive drum 43 is set, and the following steps 1 to 3 are repeated.

(a) Procedure 1
The setting unit 111 instructs the engine control unit 108 to form a plurality of mark images for measuring the amount of misregistration on the circumferential surface of the photosensitive drum 43 . At this time, a transfer current corresponding to the applied voltage is applied to the primary transfer roller 47 .

FIG. 7B shows mark images 250a, 250b, . A sensor 46 shown in FIG. 7B is used to detect the circumferential position of each mark image formed on the circumferential surface of the photosensitive drum 43 .

(b) Procedure 2
A sensor 46 measures the positions of a plurality of mark images on the peripheral surface of the photosensitive drum 43 . As shown in FIG. 7B, the sensor 46 measures by detecting the circumferential positions of the mark images 250a, 250b, . .

(c) Procedure 3
The setting unit 111 compares the measured positions of the plurality of mark images with the positions where each mark image should originally exist, and calculates the amount of positional deviation.

In the above, a mark image is formed on the photosensitive drum, and the positional deviation amount is detected by detecting the position of the formed mark image in the circumferential direction. However, it is not limited to this method. The peripheral speed of the photosensitive drum 43 is obtained from the encoder 71, and the position on the photosensitive drum is detected by integrating the obtained peripheral speed, and the detected position is compared with the original position. Then, the amount of positional deviation may be calculated.

After repeating steps 1 to 3 for a plurality of speed differences, the setting unit 111 plots the reference speed difference and the corresponding measurement on a virtual plane with the speed difference on the horizontal axis and the positional deviation amount on the vertical axis. A calculation is performed to plot a plurality of sets consisting of the amount of positional deviation and an approximated curve representing the distribution of the plotted points, and the speed difference corresponding to the allowable value is determined on the obtained approximated curve. , the obtained velocity difference is set as the boundary value of the first prohibited area 201 .

Specifically, the setting unit 111 plots pairs of the velocity difference and the positional deviation amount on the XY coordinate plane. Plotted points 271, 272, 273, 274 and 275 are shown in FIG. 7(a). The plotting of the points on the XY coordinate plane is for the purpose of facilitating understanding, and it is not necessary to actually plot the points on the XY coordinate plane.

Next, the setting unit 111 obtains two approximate straight lines from a plurality of points plotted on the XY coordinate plane. Specifically, as shown in FIG. 7A, an approximate straight line 276 is obtained by linear approximation from plotted points 271 and 272, and an approximate straight line 276 is obtained from plotted points 273, 274, and 275 by linear approximation. An approximate straight line 277 is obtained.

Next, the setting unit 111 calculates the speed difference corresponding to the allowable value of the positional deviation amount for each of the two approximate straight lines as the upper limit value and the lower limit value of the first prohibited area 201 .

Specifically, as shown in FIG. 7A, the setting unit 111 draws a straight line on the XY coordinate plane that passes through the point indicated by the allowable value 251 of the positional deviation amount and is parallel to the horizontal axis. Next, the intersection point of the straight line parallel to the horizontal axis and the approximate straight line 276 is obtained, and the intersection point is extended downward in parallel with the vertical axis. It is calculated as the lower limit value 261 . The setting unit 111 also draws a straight line on the XY coordinate plane that passes through the point indicated by the allowable value 251 of the positional deviation amount and is parallel to the horizontal axis. Next, the intersection point of the straight line parallel to the horizontal axis and the approximate straight line 277 is obtained, and the intersection point is extended downward in parallel with the vertical axis. It is calculated as the upper limit value 267.

Next, the setting unit 111 writes the calculated upper limit value and lower limit value into the determination table 124 . Specifically, the setting unit 111 writes the calculated upper limit value 267 and lower limit value 261 shown in FIG. Accordingly, the setting unit 111 sets the first prohibited area 201 (the positive prohibited area 222 and the negative prohibited area 221 shown in FIG. 3B).

This completes the description of the manual setting process of the upper limit value and the lower limit value of the first prohibited area 201 .

(Specific example of allowable value)
When the allowable value 251 shown in FIG. 7A is set to "0.02 mm", the speed difference points at which the positional deviation increases from the allowable value 251 are the speed difference (-0.04%) and the speed difference (+0.04%). 04%), the speed difference range “−0.04% to +0.04%” may be set as the first prohibited area 201 .

In this case, since the allowable value "0.02 mm" corresponding to the speed difference "±0.04%" is set, the first prohibited area of the speed difference range "-0.04% to +0.04%" By setting the speed difference between the drum speed of the photosensitive drum and the belt speed of the intermediate transfer belt so as to avoid 201, the positional deviation of the image can be suppressed within the allowable value “0.02 mm”.

In the above, the allowable value “0.02 mm” and the speed difference “±0.04%” are examples, respectively, and are not limited to these values, and may take other values. .

Here, the lower limit value and the upper limit value of the first prohibited area 201 are respectively set at the design stage of the image forming apparatus, the manufacturing stage of each image forming apparatus, and the use environment of each image forming apparatus. , may be

Further, the upper limit value of the second prohibited area 204 and the lower limit value of the third prohibited area 205 are also set at the design stage of the image forming apparatus, the manufacturing stage of each image forming apparatus, and the use environment of each image forming apparatus. , may be set.

(Manual setting processing of the second prohibited area 204)
As an example, the manual setting process of the second prohibited area 204 will be described with reference to FIG.

FIG. 8 shows in detail the first permitted area 202 and the second prohibited area 204 in FIG. 3, where the horizontal axis indicates the speed difference and the vertical axis indicates the amount of positional deviation.

In the first allowed area 202 and the second forbidden area 204, a plurality of reference speed differences 291a, 292a, 293a, 294a, 295a and 296a are shown on the horizontal axis as shown in this figure. A plurality of reference speed differences are set in advance at predetermined intervals (for example, 0.2%). It should be noted that the plurality of reference speed differences shown in this figure is an example, and is not limited to this example. A difference may be set.

In addition, one allowable value 281 is indicated in the second prohibited area 204 as shown in this figure. A permissible value 281 is a value that is permissible as a positional deviation amount. The allowable value 281 is entered by the operator.

As an example, the setting unit 111 sets each of the plurality of reference speed differences 291a to 296a shown in FIG. 296a, and repeat steps 1 to 3, which are the same as steps 1 to 3 described in the manual setting process of the first prohibited area 201 above. Here, description of procedures 1 to 3 is omitted.

After repeating steps 1 to 3 for a plurality of reference speed differences, the setting unit 111 plots pairs of reference speed differences and positional deviation amounts on the XY coordinate plane. Specifically, FIG. 8 shows plotted points 291-296. Even in this case, the plotting of the points on the XY coordinate plane is for the purpose of facilitating understanding, and it is not necessary to actually plot the points on the XY coordinate plane.

Next, the setting unit 111 obtains one approximate curve from a plurality of points plotted on the XY coordinate plane. Specifically, as shown in FIG. 8, an approximated curve 297 is obtained from plotted points 291-296.

Next, the setting unit 111 calculates the speed difference corresponding to the allowable value of the amount of positional deviation in the one obtained approximated curve as the upper limit value of the second prohibited area 204 .

Specifically, as shown in FIG. 8, the setting unit 111 draws a straight line on the XY coordinate plane that passes through the point indicated by the allowable value 281 of the positional deviation amount and is parallel to the horizontal axis. Next, the intersection point of the straight line parallel to the horizontal axis and the approximated curve 297 is obtained, and the intersection point is extended downward in parallel with the vertical axis, and the intersection point that intersects the horizontal axis is placed in the second prohibited area 204. It is calculated as the upper limit value 214 .

Next, the setting unit 111 writes the calculated upper limit value to the determination table 124 . Specifically, the setting unit 111 writes the calculated upper limit value 214 shown in FIG.

This completes the description of the manual setting process of the upper limit value of the second prohibited area 204 .

(Manual setting process of the third prohibited area 205)
As an example, the manual setting process of the third prohibited area 205 will be described with reference to FIG.

FIG. 8 shows in detail the second allowed area 203 and the third prohibited area 205 in FIG.

In the second allowed area 203 and the third forbidden area 205, a plurality of reference speed differences 301a, 302a, 303a, 304a, 305a and 306a are shown on the horizontal axis as shown in this figure. A plurality of reference speed differences are set in advance at predetermined intervals (for example, 0.2%). It should be noted that the plurality of reference speed differences shown in this figure is an example, and is not limited to this example. may be set.

In addition, one allowable value 282 is indicated in the third prohibited area 205 as shown in this figure. A permissible value 282 is a value that is permissible as the amount of positional deviation. Tolerance 282 is entered by the operator.

As an example, the setting unit 111 sets the reference speed difference 301a for each of the plurality of reference speed differences 301a to 306a shown in FIG. 306a, and repeat steps 1 to 3, which are the same as steps 1 to 3 described in the manual setting process of the first prohibited area 201 above. Here, description of procedures 1 to 3 is omitted.

After repeating steps 1 to 3 for a plurality of reference speed differences, the setting unit 111 plots pairs of reference speed differences and positional deviation amounts on the XY coordinate plane. Specifically, FIG. 8 shows plotted points 301-306. Even in this case, the plotting of the points on the XY coordinate plane is for the purpose of facilitating understanding, and it is not necessary to actually plot the points on the XY coordinate plane.

Next, the setting unit 111 obtains one approximate curve from a plurality of points plotted on the XY coordinate plane. Specifically, as shown in FIG. 8, an approximated curve 307 is obtained from the plotted points 301-306.

Next, the setting unit 111 calculates the speed difference corresponding to the allowable value of the positional deviation amount as the lower limit value of the third prohibited area 205 in the one obtained approximated curve.

Specifically, as shown in FIG. 8, the setting unit 111 draws a straight line on the XY coordinate plane that passes through the point indicated by the allowable value 282 of the positional deviation amount and is parallel to the horizontal axis. Next, the intersection point of the straight line parallel to the horizontal axis and the approximated curve 307 is obtained, and the intersection point is extended downward in parallel with the vertical axis, and the intersection point that intersects the horizontal axis is the third prohibited area 205. Calculated as the lower limit value 215 .

Next, the setting unit 111 writes the calculated lower limit value to the determination table 124 . Specifically, the setting unit 111 writes the calculated lower limit value 215 shown in FIG.

This completes the description of the manual setting process for the lower limit value of the third prohibited area 205 .

(Automatic setting processing of prohibited area)
The setting unit 111 reads from the storage unit 105 the allowable value of the positional deviation amount of the first prohibited area 201 . Next, the setting unit 111 executes automatic setting processing of the first prohibited area 201 . Here, since the automatic setting process of the first prohibited area 201 is the same as the manual setting process of the first prohibited area 201, description thereof is omitted.

The setting unit 111 also reads out the allowable value of the positional deviation amount of the second prohibited area 204 from the storage unit 105 . Next, the setting unit 111 executes automatic setting processing of the second prohibited area 204 . Here, since the automatic setting process of the second prohibited area 204 is the same as the manual setting process of the second prohibited area 204, description thereof is omitted.

Also, the setting unit 111 reads out the allowable value of the positional deviation amount of the third prohibited area 205 from the storage unit 105 . Next, the setting unit 111 executes manual setting processing of the third prohibited area 205 . Here, since the automatic setting process of the third prohibited area 205 is the same as the manual setting process of the third prohibited area 205, description thereof is omitted.

1.2 Operations of Image Forming Apparatus 1 Operations of the image forming apparatus 1 will be described.

(1) Overall Operation of Image Forming Apparatus 1 Overall operation of the image forming apparatus 1 will be described with reference to the flowchart shown in FIG.

The operation unit 22 of the operation panel 20 receives an operator's instruction (step S101).

The main control unit 100 determines the content of the instruction (step S102).

If the content of the instruction is a print execution instruction ("print execution instruction" in step S102), the setting unit 111 determines the upper limit value 124a of the second prohibited area 204, the lower limit value of the first prohibited area 201 from the determination table 124, The value 124b, the upper limit value 124c of the first prohibited area 201, and the lower limit value 124d of the third prohibited area 205 are read (step S111). Next, the setting unit 111 sets the target belt speed of the intermediate transfer belt 32 (step S112). Next, the setting unit 111 removes the first prohibited area 201 defined by the read upper limit value 124c and the lower limit value 124b, and removes the first prohibited area 201 defined by the upper limit value 124a, the lower limit value 124b, the upper limit value 124c, and the lower limit value 124d. A speed difference belonging to the first permission area 202 and the second permission area 203 is set (step S113). Next, the setting unit 111 sets the target drum speed so that the difference from the target belt speed becomes the set speed difference (step S114). Next, the engine control unit 108 causes the print engine 13 to perform image formation. In image formation, the intermediate transfer belt 32 is driven and controlled so as to rotate in accordance with the target belt speed, and the photosensitive drums 43 are driven and controlled so as to rotate in accordance with the target drum speed. (step S103). Further, the engine control unit 108 causes the controller 108b to repeatedly execute speed comparison processing during image formation (step S104). When the image formation is completed, the main controller 100 returns control to step S101.

If the content of the instruction is an instruction to manually set the prohibited area (“instruction to manually set prohibited area” in step S102), the main control unit 100 causes the setting unit 111 to execute the manual setting process of the prohibited area ( step S105). When the prohibited area manual setting process ends, the main control unit 100 returns the control to step S101.

If the content of the instruction is an instruction to automatically set a prohibited area ("instruction to automatically set prohibited area" in step S102), the main control unit 100 sets the automatic setting mode of the prohibited area (step S106). Next, the main control unit 100 determines whether or not the cumulative number of prints exceeds 10,000 (step S107).

If the cumulative number of prints exceeds 10,000 ("YES" in step S107), main control unit 100 determines whether or not the prohibited area automatic setting mode is set (step S108). If the prohibited area automatic setting mode is set ("YES" in step S108), the main control unit 100 causes the setting unit 111 to execute the prohibited area automatic setting process (step S109). When the prohibited area automatic setting process ends, the main control unit 100 returns the control to step S101.

If the prohibited area automatic setting mode is not set ("NO" in step S108), the main control unit 100 returns the control to step S101.

If the cumulative number of prints does not exceed 10,000 ("NO" in step S107), the main control unit 100 returns control to step S101.

If the content of the instruction is other ("other" in step S102), main control unit 100 executes other processing (step S110). When other processes are completed, the main control unit 100 returns control to step S101.

(2) Speed Comparison Processing Speed comparison processing will be described with reference to the flowchart shown in FIG.

It should be noted that the procedure of the speed comparison processing described here is the detailed operation of step S104 in FIG.

The speed comparison control circuit 125 obtains the drum speed from the arithmetic circuit 122 (step S121) and the belt speed from the belt control circuit 131 (step S122).

Next, the speed comparison control circuit 125 calculates the speed difference using the following formula.

Speed difference=(drum speed−belt speed)/(drum speed)×100 (step S123)
Next, the speed comparison control circuit 125 uses the determination table 124 to determine whether the obtained speed difference is the second prohibited area 204, the first permitted area 202, the first prohibited area 201, and the second permitted area 203 shown in FIG. and the third prohibited area 205 (step S124).

If it is determined that the speed difference is within the first prohibited area 201 ("first prohibited area" in step S124), the speed comparison control circuit 125 further determines whether the speed difference is 0 or more (step S125). ). If the speed difference is 0 or more ("YES" in step S125), the target value of the drum speed is increased so that the speed difference falls within the second permission area 203 (step S127). On the other hand, if the speed difference is less than 0 ("NO" in step S125), the drum speed target value is decreased so that the speed difference falls within the first permission area 202 (step S126).

If it is determined that the speed difference falls within the second prohibited area 204 ("second prohibited area" in step S124), the speed comparison control circuit 125 adjusts the drum speed so that the speed difference falls within the first permitted area 202. The target value is increased (step S128).

If it is determined that the speed difference is within the third prohibited area 205 ("third prohibited area" in step S124), the speed comparison control circuit 125 adjusts the drum speed so that the speed difference is within the second permitted area 203. The target value is delayed (step S128).

If it is determined that the speed difference falls within the first permitted region 202 or the second permitted region 203 ("first or second permitted region" in step S124), the speed comparison control circuit 125 does not change the target value of the drum speed. .

As described above, the speed comparison control circuit 125 adjusts the drum speed so that the speed difference falls within the first permission area 202 or the second permission area 203 .

(3) Manual setting process of prohibited area Manual setting process of prohibited area will be described with reference to the flowchart shown in FIG. 11 .

It should be noted that the procedure of the manual setting process of the prohibited area described here is the detailed operation of step S105 in FIG.

The operation unit 22 receives the allowable value for the positional deviation amount of the first prohibited area 201 (step S141). Next, the setting unit 111 executes manual setting processing of the first prohibited area 201 (step S142).

Next, the operation unit 22 receives the allowable value for the positional deviation amount of the second prohibited area 204 (step S143). Next, the setting unit 111 executes manual setting processing of the second prohibited area 204 (step S144).

Next, the operation unit 22 receives the allowable value for the positional deviation amount of the third prohibited area 205 (step S145). Next, the setting unit 111 executes manual setting processing of the third prohibited area 205 (step S146).

The above completes the manual setting process of the prohibited area.

(4) Manual setting process of first prohibited area Manual setting process of the first prohibited area 201 will be described with reference to the flowchart shown in FIG.

It should be noted that the procedure of manual setting processing of the first prohibited area 201 described here is the detailed operation of step S142 in FIG.

The setting unit 111 repeats steps S162 to S164 for a plurality of reference speed differences (steps S161 to S165).

The setting unit 111 instructs the engine control unit 108 to form a plurality of mark images for measuring the amount of misregistration (step S162).

The sensor 46 measures the position of the mark image on the circumferential surface of the photosensitive drum 43 (step S163).

The setting unit 111 calculates the positional deviation amount using the measured positions of the plurality of mark images (step S164).

After repeating steps S161 to S165, the setting unit 111 plots a set of the reference speed difference and the positional deviation amount on the XY coordinate plane (step S166).

Next, the setting unit 111 obtains two approximate straight lines from a plurality of points plotted on the XY coordinate plane (step S167).

Next, the setting unit 111 calculates the speed difference corresponding to the allowable value of the positional deviation amount for each of the two approximate straight lines as the upper limit value and the lower limit value of the first prohibited area 201 (step S168).

Next, the setting unit 111 writes the calculated upper limit value and lower limit value to the determination table 124 (step S169).

This completes the description of the manual setting of the upper limit value and the lower limit value of the first prohibited area 201 .

(5) Manual setting process of second prohibited area Manual setting process of the second prohibited area 204 will be described with reference to the flowchart shown in FIG.

It should be noted that the procedure of the manual setting process of the second prohibited area 204 described here is the detailed operation of step S144 in FIG. Also, the manual setting process of the third prohibited area 205 is the same as the following procedure, so the description thereof will be omitted.

The setting unit 111 repeats steps S162 to S164 for a plurality of reference speed differences (steps S161 to S165).

Since steps S161 to S165 are the same as steps S161 to S165 in FIG. 12, detailed description thereof will be omitted.

After repeating steps S161 to S165, the setting unit 111 plots a set of the reference speed difference and the positional deviation amount on the XY coordinate plane (step S166).

Next, the setting unit 111 obtains one approximate curve from a plurality of points plotted on the XY coordinate plane (step S167a).

Next, the setting unit 111 calculates the speed difference corresponding to the allowable value of the positional deviation amount on the approximated curve as the upper limit value of the second prohibited area 204 (step S168a).

Next, the setting unit 111 writes the calculated upper limit value to the determination table 124 (step S169a).

This completes the description of the manual setting of the upper limit value of the second prohibited area 204 .

(6) Automatic setting process of prohibited area The automatic setting process of prohibited area will be described with reference to the flowchart shown in FIG. 14 .

It should be noted that the procedure of the automatic setting process of the prohibited area described here is the detailed operation of step S109 in FIG.

The setting unit 111 reads the allowable value of the positional deviation amount of the first prohibited area 201 from the storage unit 105 (step S181). Next, the setting unit 111 executes automatic setting processing of the first prohibited area 201 (step S182).

Next, the setting unit 111 reads the allowable value of the positional deviation amount of the second prohibited area 204 from the storage unit 105 (step S183). Next, the setting unit 111 executes automatic setting processing of the second prohibited area 204 (step S184).

Next, the setting unit 111 reads the permissible value of the positional deviation amount of the third prohibited area 205 from the storage unit 105 (step S185). Next, the setting unit 111 executes automatic setting processing of the third prohibited area 205 (step S186).

With the above, the automatic setting processing of the prohibited area is completed.

Note that steps S182, S184, and S186 may be performed in the same manner as steps S142, S144, and S146 in the flowchart of FIG. 11, and detailed description thereof will be omitted.

1.3 Summary As described above, the speed difference between the drum speed and the belt speed exceeds the permissible value due to hunting that occurs during rotation control of the photoreceptor drum 43, and a The rotation speed of the photosensitive drum 43 is set so that it belongs to the first permitted region 202 or the second permitted region 203, in which the toner image to be printed is not misaligned, except for the first prohibited region 201, in which misalignment occurs. to control the drum speed. Also, the drum speed is corrected so that the speed difference does not enter the first prohibited area 201 during image formation. As a result, it is possible to prevent large fluctuations in the rotation speed of the photosensitive drum and to prevent misregistration (color misregistration) of the image.

2 Modification (1)
Modification (1) of the embodiment will be described.

FIG. 15, like FIG. 3A, is a graph showing the positional deviation amount corresponding to the speed difference between the drum speed of the photosensitive drum 43 and the belt speed of the intermediate transfer belt 32. In FIG. In this figure, the horizontal axis indicates the speed difference, and the vertical axis indicates the amount of positional deviation.

Further, as shown in FIG. 15, between the speed difference 216 "-0.25" and the lower limit 212 "-0.05" in the first permitted area 202, below the first prohibited area 201, A blank suppression area 206 is provided.

Here, according to Japanese Patent Laid-Open No. 2002-200003, the void means a phenomenon in which the toner does not move from the intermediate transfer belt to the recording sheet at the transfer position where the toner image is transferred to the recording sheet, and there is a portion where the transfer is not performed. To tell. This phenomenon also occurs when the toner image on the photosensitive drum is primarily transferred onto the intermediate transfer belt.

This is because the toner image on the photoreceptor drum is strongly pressed by the transfer nip between the photoreceptor drum and the intermediate transfer belt during transfer. It is considered that the toner to be transferred is mechanically pressed against the photoreceptor drum and remains on the photoreceptor drum without being transferred onto the intermediate transfer belt.

As one of the measures for preventing this void, when the toner image on the photosensitive drum is transferred to the intermediate transfer belt, a method is used in which the drum speed of the photosensitive drum and the belt speed of the intermediate transfer belt are different. It is By providing a difference between the drum speed and the belt speed in this manner, a shearing force is imparted to the toner, which tends to stick to the photoreceptor drum, to separate the toner from the surface of the photoreceptor drum. . That is, when the toner image is transferred onto the intermediate transfer belt, a slight lateral (almost horizontal) force is applied so that the toner image rubs against the intermediate transfer belt so that the toner image is well transferred onto the intermediate transfer belt. It is intended to

As described above, the blank suppression area 206 is provided within the first permission area 202 between the speed difference "-0.25" and the speed difference "-0.05". If the binding force with respect to the intermediate transfer belt is not strong and the speed difference is within the void suppression region 206, the occurrence of the void phenomenon can be suppressed.

It should be noted that no void suppression area is provided in the second permission area 203 . This is because the drum speed is higher than the belt speed in the second permission area 203, and a shearing force that peels off the toner on the photoreceptor drum from the surface of the photoreceptor drum cannot be expected.

In order to suppress the occurrence of the dropout, the speed comparison control circuit 125 slows down the drum speed so that the speed difference enters the dropout suppression region 206 when determining that the speed difference falls within the first prohibited region 201 . may In addition, in order to suppress the occurrence of a dropout, the speed comparison control circuit 125 controls the speed difference to enter the dropout suppression region 206 when the speed difference enters the first permission region 202 but does not enter the dropout suppression region 206. As such, the drum speed may be increased.

As described above, it is possible to suppress the occurrence of voids.

3. Other Modifications and Supplementary Explanations (1) As described above, the restraining force is generated between the photoreceptor drum and the intermediate transfer belt when the peripheral speed of the photoreceptor drum and the intermediate transfer belt are approximately the same. is the case.

This restraining force is obtained when the peripheral speed of the photoreceptor drum and the intermediate transfer belt are approximately the same, and in addition, when the transfer current flows through the intermediate transfer belt, static electricity is generated between the photoreceptor drum and the intermediate transfer belt. This also occurs when the electrical attracting force is large, or when there are few toner images on the intermediate transfer belt and the electrostatic attracting force between the photosensitive drum and the intermediate transfer belt is large.

(2) In the case of monochrome printing, among the Y, M, C, and K photosensitive drums, only the K photosensitive drum rotates. , the belt speed may be controlled by setting a target value of the belt speed so that the speed difference belongs to the first permission region 202 or the second permission region 203 .

(3) The range of speed difference between the peripheral surface of the photoreceptor drum 43 and the peripheral surface of the intermediate transfer belt 32 may fluctuate in which the restraining force that limits the variation in the rotation of the photoreceptor drum 43 is generated. be. In other words, the speed difference range in which hunting occurs in the rotation of the photosensitive drum 43 may vary.

Factors for this fluctuation are component tolerances, assembly errors, changes over time, and changes in the environment of the rollers on which the intermediate transfer belt is stretched. Due to these fluctuation factors, the roller diameter may fluctuate. Also, the diameter of the photosensitive drum may vary due to variations in temperature, humidity, and the like. Therefore, due to these fluctuation factors, the speed difference between the drum speed of the photosensitive drum and the belt speed of the intermediate transfer belt may differ.

Therefore, the positive prohibited area 222 and the negative prohibited area 221 of the first prohibited area 201 may each include the changed range of the speed difference as a result of the change of the range of the speed difference.

As shown in FIG. 3(b), for example, the positive prohibited area 222 has a width of 0.05% obtained by adding a width 234 of 0.03% to the basic width 233 of 0.02%. may have Similarly, the negative forbidden region 221 may have a basic width 232 of 0.02% plus an additional width 231 of 0.03% due to the variable factor, which is 0.05%.

(4) A target value may be set in advance as a reference for measuring the positional deviation amount of the toner image formed on the photosensitive drum 43 .

Further, for example, the transfer current flowing through the primary transfer roller 47 is turned off, and the image is formed on the photoreceptor drum 43 under the condition that the electrostatic binding force between the photoreceptor drum 43 and the intermediate transfer belt 32 is excluded. The result of measuring the amount of positional deviation of the toner image may be used as a reference. As a result, it is possible to know the characteristics of the rotational fluctuation of the photoreceptor drum in a state in which the electrostatic binding force is removed.

(5) The setting unit 111 may further change the parameter indicating the image forming condition or the parameter indicating the timing of starting image formation according to the corrected drum speed.

For example, when the drum speed is increased, as one of the image forming conditions, the lubricant application unit sets a parameter indicating the amount of lubricant applied so that the amount of lubricant applied to the peripheral surface of the photosensitive drum 43 increases. You can change it.

For example, when the drum speed is increased, the relationship between the drum speed and the belt speed changes. Therefore, as a parameter indicating the timing of starting image formation, the start position of the toner image arrangement on the recording sheet is changed with the changed drum speed. It may be changed according to the belt speed relationship.

(6) As described above, the image forming apparatus incorporates a computer system having a microprocessor and memory. The memory stores computer programs, and the microprocessor may operate according to the computer programs.

A microprocessor consists of a fetch section, a decode section, an execution section, a register file, an instruction counter, and so on. The fetch unit reads each instruction code included in the computer program one by one from the computer program stored in the memory. The decoding unit decodes the read instruction code. The execution part operates according to the decoding result. Thus, the microprocessor operates according to computer programs stored in memory.

Here, the computer program is constructed by combining a plurality of instruction codes indicating instructions to the computer in order to achieve a predetermined function.

Also, the computer program may be recorded on a computer-readable recording medium such as a flexible disk, hard disk, optical disk, or semiconductor memory.

Also, the computer program may be transmitted via a wired or wireless telecommunication line, a network represented by the Internet, data broadcasting, or the like.

(7) The above embodiments and modifications may be combined.

The control device according to the present disclosure can suppress an increase in the binding force between the photoreceptor drum and the intermediate transfer belt, prevent the occurrence of image misalignment, and control the rotation of the photoreceptor drum. It is useful as a technique for

1 image forming apparatus 10 scanner 11 automatic document feeder 12 document image scanner 12a CCD sensor 13 print engine 14 control circuit 20 operation panel 21 display section 22 operation section 31 intermediate transfer unit 32 intermediate transfer belt 33A to 33D support roller 34A, 34B secondary transfer roller 36 belt cleaning device 40 image forming section 41, 41Y to 41K image forming unit 42 developing device 43 photoreceptor drum 44 charging device 45 drum cleaning device 46 sensor 47 primary transfer roller 48 exposure device 50 sheet conveying section 51 feeding Paper section 51a to 51c Paper feed tray unit 52 Paper discharge section 53 Transport path section 60 Fixing section 70 Drive motor 71 Encoder 72 FG
73 drive circuit 80 drive motor 81 encoder 82 FG
83 drive circuit 100 main controller 101 CPU
102 ROMs
103 RAM
104 image memory 105 storage unit 106 image processing unit 107 network communication unit 108 engine control unit 108a engine main control unit 108b controller 109 scanner control unit 110 input/output unit 111 setting unit 121a to 121d drum control circuit 122 arithmetic circuit 122a feedback control circuit 122b Feedforward control circuit 122c Speed arithmetic circuit 123 Speed command circuit 124 Judgment table 125 Speed comparison control circuit 131 Belt control circuit 132 Arithmetic circuit 132a Feedback control circuit 132b Feedforward control circuit 132c Speed arithmetic circuit 133 Speed command circuit

Claims (20)

A control device for controlling rotation of a photoreceptor that transfers a toner image formed on a peripheral surface to an intermediate transfer member,
A prohibited area , which is a range of speed difference between the peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer member , in which a positional deviation of the toner image exceeding an allowable value occurs as a result of hunting occurring in the rotation of the photoreceptor. a setting means for setting a target value of the peripheral speed of the photoreceptor so that the target value of the peripheral speed of the photoreceptor is adjacent to the prohibited region and belongs to the permitted region , which is a range of speed differences in which a positional deviation exceeding an allowable value does not occur;
speed control means for controlling the peripheral speed of the photoreceptor so that it rotates in accordance with the target value;
with
The setting means further drives and controls the photoreceptor and the intermediate transfer member based on a plurality of reference speed differences, and controls positional deviation of the toner image formed on the peripheral surface of the photoreceptor for each reference speed difference. Using a plurality of measured positional deviation amounts obtained, a range of speed differences in which positional deviation occurs due to hunting exceeding the allowable value is estimated, and the range obtained by estimation is Set as keep out area
A control device characterized by: A control device for controlling rotation of a photoreceptor that transfers a toner image formed on a peripheral surface to an intermediate transfer member,
From the prohibition area, which is the range of the speed difference between the peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer member, where hunting occurs in the rotation of the photoreceptor, resulting in positional deviation of the toner image exceeding an allowable value. setting means for setting a target value of the peripheral speed of the photoreceptor so that it is adjacent to the prohibited region and belongs to the permitted region, which is a range of speed differences in which positional deviation exceeding an allowable value does not occur;
speed control means for controlling the peripheral speed of the photoreceptor so that it rotates in accordance with the target value;
with
defining a range of the speed difference in which the toner image is misaligned beyond an allowable value as a large speed difference region;
The setting means sets the target value so that the speed difference falls outside the large speed difference region and belongs to the allowable region, and further, based on a plurality of reference speed differences, the photoreceptor and the intermediate transfer By controlling the driving of the body, the amount of positional deviation of the toner image formed on the circumferential surface of the photoreceptor is measured for each reference speed difference, and the obtained plural measured positional deviation amounts are used to determine the position of the photoreceptor and the Estimate the range of speed difference in which positional deviation occurs beyond the permissible value without generating a binding force that restricts the rotation fluctuation of the photoreceptor between the intermediate transfer member and the range obtained by the estimation, Set as the large speed difference area
A control device characterized by: varying factors associated with the photoreceptor vary the range of the velocity difference that causes the hunting;
The control device according to claim 1 or 2 , wherein the prohibited area includes a range of varied speed differences. 4. The control device according to claim 3 , wherein the fluctuating factor related to the photoreceptor is component tolerance, assembly error, aging, or environmental change of at least one of the photoreceptor and the intermediate transfer body. setting the peripheral speed of the photoreceptor to a first speed, and setting the peripheral speed of the intermediate transfer member to a second speed;
When the speed difference is calculated by (first speed - second speed) / first speed * 100,
The control device according to claim 1 or 2 , wherein the width of the prohibited area is within 0.1 percent. The setting means performs an operation of plotting a plurality of sets of the reference speed difference and the corresponding measured positional deviation amount on a virtual plane having the velocity difference as the horizontal axis and the positional deviation amount as the vertical axis. , obtaining an approximated curve representing the distribution of the plurality of plotted points, obtaining a speed difference corresponding to the allowable value in the obtained approximated curve, and setting the obtained speed difference as the boundary value of the prohibited area. The control device according to claim 1 or 2, characterized in that: 3. The control device according to claim 1, wherein the setting unit sets the prohibited area according to an instruction from an operator or when an operating condition of the photoreceptor satisfies a predetermined condition. 8. The control device according to claim 7, wherein the predetermined condition is that the cumulative number of rotations of the photoreceptor reaches a predetermined number. 3. The setting device according to claim 1, wherein the setting unit further sets a parameter indicating an image forming condition or a parameter indicating timing for starting image formation according to the set target value. controller. 3. The control device according to claim 2 , wherein the setting unit sets the large speed difference region according to an instruction from an operator or when an operating condition of the photoreceptor satisfies a predetermined condition. 11. The control device according to claim 10 , wherein the predetermined condition is that the cumulative number of rotations of the photoreceptor reaches a predetermined number. The speed difference is calculated by subtracting the peripheral speed of the intermediate transfer member from the peripheral speed of the photosensitive member,
The allowable area includes a positive allowable area in which the speed difference is positive and a negative allowable area in which the speed difference is negative, and the width of the negative allowable area is wider than the width of the positive allowable area. The control device according to claim 1 or claim 2 . The negative permission area suppresses occurrence of a phenomenon in which a part of the toner image remains on the photoreceptor without being transferred to the intermediate transfer body when the toner image is transferred from the photoreceptor to the intermediate transfer body. 13. The control device according to claim 12, further comprising a blank suppression area. The control device controls rotation of a plurality of photoreceptors in an image forming apparatus having a plurality of photoreceptors and the intermediate transfer body,
The toner image formed on the peripheral surface of each photoreceptor is transferred to the intermediate transfer member,
The setting means further controls each of the plurality of photoreceptors such that the difference between the peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer member is outside the prohibited area and belongs to the permitted area. 3. The control device according to claim 1 or 2, wherein a target value of the peripheral speed of is set. The control device controls rotation of the photoreceptor in an image forming apparatus including the photoreceptor and the intermediate transfer body,
moreover,
acquisition means for acquiring a first speed, which is the peripheral speed of the photoreceptor, and a second speed, which is the peripheral speed of the intermediate transfer member, during image formation by the image forming apparatus;
calculating means for calculating the speed difference between the first speed and the second speed;
determining means for determining whether the calculated speed difference belongs to the prohibited area or the allowed area;
3. The setting means further corrects the target value of the peripheral speed of the photosensitive member so that the speed difference belongs to the permitted region when the speed difference belongs to the prohibited region. 3. A control device according to claim 1 or claim 2 . The control device further
A feedforward control circuit that controls the rotation of the photoreceptor by a feedforward that determines an output signal by predicting a presupposed variation based on a detection signal detected by a sensor that detects the rotation of the photoreceptor. 3. The control device according to claim 1 or 2, comprising: The control device further
A detection signal detected by a sensor that detects the rotation of the photoreceptor and the rotation of a motor that transmits rotational driving force to the photoreceptor is compared with a predetermined target signal, and the detection signal matches the target signal. 3. A control device according to claim 1 or claim 2, comprising a feedback control circuit for controlling by feedback determining the output signal so as to. A control method for a control device for controlling rotation of a photoreceptor that transfers a toner image formed on a peripheral surface to an intermediate transfer member, comprising:
A prohibited area , which is a range of speed difference between the peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer member , in which a positional deviation of the toner image exceeding an allowable value occurs as a result of hunting occurring in the rotation of the photoreceptor. a setting step of setting a target value of the peripheral speed of the photoreceptor so that it is adjacent to the prohibited region and belongs to the permitted region , which is a range of speed differences in which a positional deviation exceeding an allowable value does not occur ;
a speed control step of controlling the peripheral speed of the photoreceptor so that it rotates in accordance with the target value;
including
In the setting step, the photoreceptor and the intermediate transfer member are driven and controlled based on a plurality of reference speed differences, and positional deviation of the toner image formed on the peripheral surface of the photoreceptor is controlled for each reference speed difference. Using a plurality of measured positional deviation amounts obtained, a range of speed differences in which positional deviation occurs due to hunting exceeding the allowable value is estimated, and the range obtained by estimation is Set as keep out area
A control method characterized by: A control method for a control device for controlling rotation of a photoreceptor that transfers a toner image formed on a peripheral surface to an intermediate transfer member, comprising:
From the prohibition area, which is the range of the speed difference between the peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer member, where hunting occurs in the rotation of the photoreceptor, resulting in positional deviation of the toner image exceeding an allowable value. a setting step of setting a target value of the peripheral speed of the photoreceptor such that it is outside the prohibited region and belongs to the permitted region, which is a speed difference range in which a positional deviation exceeding an allowable value does not occur;
a speed control step of controlling the peripheral speed of the photoreceptor so that it rotates in accordance with the target value;
including
defining a range of the speed difference in which the toner image is misaligned beyond an allowable value as a large speed difference region;
In the setting step, the target value is set so that the speed difference is outside the large speed difference region and belongs to the allowable region, and further, the photoreceptor and the intermediate transfer speed are set based on a plurality of reference speed differences. By controlling the driving of the body, the amount of positional deviation of the toner image formed on the circumferential surface of the photoreceptor is measured for each reference speed difference, and the obtained plural measured positional deviation amounts are used to determine the position of the photoreceptor and the Estimate the range of speed difference in which positional deviation occurs beyond the permissible value without generating a binding force that restricts the rotation fluctuation of the photoreceptor between the intermediate transfer member and the range obtained by the estimation, Set as the large speed difference area
A control method characterized by: An image forming apparatus for transferring a toner image formed on a peripheral surface of a photoreceptor to an intermediate transfer member,
3. An image forming apparatus, comprising: the control device according to claim 1, which controls rotation of the photoreceptor.

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