JP2012242434A - Image forming device - Google Patents

Abstract

To provide an image forming apparatus capable of suppressing the torque fluctuation of a motor when transferring a toner image and ensuring the stability of image quality.
A peripheral speed of a photosensitive drum is slightly larger than a peripheral speed of an intermediate transfer belt, a torque command value for driving a motor that rotates the photosensitive drum, and a motor that rotates the intermediate transfer belt. The rotational speed target value of the photosensitive drum 100 is corrected so that the torque command value for driving falls within the predetermined fluctuation ranges DD and BB, respectively.
[Selection] Figure 5

Description

  The present invention relates to an image forming apparatus using an electrophotographic process, and more particularly to a drive control technique that suppresses torque fluctuation when rotating a photosensitive drum.

  Image forming apparatuses using an electrophotographic process are widely used. In general, in the electrophotographic process, first, each photosensitive drum of four colors (yellow, magenta, cyan, black) is uniformly charged, and then each photosensitive drum is exposed in accordance with an image signal. An electrostatic latent image is formed on the drum. Thereafter, each electrostatic latent image is developed with each color toner, whereby each color toner image is formed on each photosensitive drum.

  A primary transfer roller is disposed so as to sandwich the intermediate transfer belt with respect to each photosensitive drum, and the toner images of each color formed on each photosensitive drum are transferred onto the intermediate transfer belt by the respective primary transfer rollers. . The toner image transferred onto the intermediate transfer belt in this way is transferred onto a sheet-like recording material (paper) by a secondary transfer roller.

  Here, for example, when the peripheral speed of the photosensitive drum is smaller than the peripheral speed of the intermediate transfer belt, a force for pushing the intermediate transfer belt between the photosensitive drum and the primary transfer roller acts on the intermediate transfer belt. (Refer to FIG. 3 (a) as appropriate). Due to this force, the intermediate transfer belt is bent, and the toner image is not accurately transferred to the intermediate transfer belt due to the bending, and this causes the toner image in the recording material to be lost.

  In order to prevent this hollow-out, a technique for controlling the difference in peripheral speed between the photosensitive drum and the intermediate transfer belt has been proposed (see Patent Document 1). In the technique described in Patent Document 1, for example, the peripheral speed of the photosensitive drum is adjusted by controlling the rotational speed of the motor so that the peripheral speed of the photosensitive drum is larger than the peripheral speed of the intermediate transfer belt. .

JP-A-11-102100

  By the way, in recent years, an intermediate transfer belt (elastic belt) having more flexibility (elasticity) than a conventional transfer belt using polyimide has been used in order to cope with a wide variety of recording materials (paper). ing.

  However, since the elastic belt has a larger coefficient of friction than the conventional transfer belt made of polyimide, it has a weak point that image deterioration easily occurs due to this. In addition, the magnitude of the frictional force between the photosensitive drum and the elastic belt changes depending on the difference in peripheral speed between the photosensitive drum and the elastic belt, and also changes depending on whether toner is contained between the photosensitive drum and the elastic belt. To do. Therefore, this change in frictional force causes, for example, fluctuations in the peripheral speed of the photosensitive drum.

  Even if the fluctuation in the peripheral speed of the photosensitive drum is controlled by feedback control, a delay always occurs, so that the fluctuation in the peripheral speed cannot be completely cancelled, and this appears as a positional deviation in the toner image. Further, the fluctuation in the peripheral speed of the photosensitive drum is directly connected to the torque fluctuation of the motor that rotates the photosensitive drum and the motor that rotates the intermediate transfer belt. Torque fluctuations of these motors cause the drive control system to become unstable, which causes the transfer accuracy to the elastic belt to be lowered and the image quality stability to be lowered.

  The present invention has been made in view of such circumstances, and it is possible to ensure stability of image quality by suppressing torque fluctuations of motors respectively driving a photosensitive drum and an intermediate transfer belt when transferring a toner image. An object is to provide an image forming apparatus.

  An image forming apparatus according to the present invention is an image forming apparatus that transfers a toner image formed on a photosensitive drum to an intermediate transfer belt, and transfers the toner image transferred to the intermediate transfer belt to a recording material. A first motor for rotating the drum, a second motor for rotating a rotating body for rotating the intermediate transfer belt, and the first motor so that the photosensitive drum rotates at a first rotation speed target value. Computing means for computing a first torque command value for driving and a second torque command value for driving the second motor so that the rotating body rotates at a second target rotational speed value; A calculating means for calculating a fluctuation range of the first torque command value and a fluctuation range of the second torque command value; and a first value obtained by subtracting the first fluctuation range from the fluctuation range of the first torque command value. The absolute value of the difference is the first threshold Comparing means for determining whether or not the absolute value of the second difference obtained by subtracting the second fluctuation range from the fluctuation range of the second torque command value exceeds a second threshold; When the absolute value of the first difference exceeds the first threshold or when the absolute value of the second difference exceeds the second threshold, the first difference is a negative value. When the second difference is a positive value or when the first difference is a positive value and the second difference is a negative value, the fluctuation range of the first torque command value Correction for correcting the first target rotational speed value so that the fluctuation range of the second torque command value falls within the range of the second fluctuation range. Means.

  According to the present invention, it is possible to suppress the torque fluctuations of the motors respectively driving the photosensitive drum and the intermediate transfer belt when transferring the toner image, and to ensure the stability of the image quality.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration of a photosensitive drum driving system and an intermediate transfer belt driving system in the image forming apparatus of FIG. 1. FIG. 2 is a diagram illustrating a configuration example of a photosensitive drum and an intermediate transfer belt in the image forming apparatus of FIG. FIG. 15 is a diagram illustrating a relationship between a peripheral speed difference between the photosensitive drum and the intermediate transfer belt illustrated in FIG. 14 and torque generated by the motor. FIG. 3 is a block diagram illustrating a configuration of a drive control system that corrects a target rotation speed value of the photosensitive drum according to the present exemplary embodiment. 6 is a flowchart showing an overall image of a process for correcting a target rotational speed value of a photosensitive drum by the drive control system of FIG. 5. 7 is a process flowchart for determining that toner has entered between the photosensitive drum and the intermediate transfer belt for step S1200 in FIG. 6. It is a flowchart of the pre-process performed before execution of the process according to the flowchart of FIG. FIG. 5 is a diagram illustrating a change in PWM value when a printing operation is performed with a peripheral speed difference at a correction target point in FIG. 4. FIG. 9 is a diagram illustrating a state of a photosensitive drum and a primary transfer roller during a normal printing operation and during the processing in steps S1002 and S1003 in FIG. It is an example which shows the change of the PWM value of the motor which drives an intermediate transfer belt regardless of a peripheral speed difference. It is an example which shows the change of the PWM value of the motor which drives a photosensitive drum irrespective of a peripheral speed difference. FIG. 10 is a block diagram illustrating a configuration of a conventional drive control system for a photosensitive drum and an intermediate transfer belt. FIG. 4 is a diagram showing a change in PWM value when there is a difference in peripheral speed between the photosensitive drum and the intermediate transfer belt in the configuration of FIG.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Schematic structure of image forming apparatus>
FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus using an electrophotographic process according to the present embodiment. This image forming apparatus has a plurality of image forming units, that is, four image forming units of yellow (Y), magenta (M), cyan (C), and black (K). The configuration is equivalent. Therefore, Y, M, C, and K (for example, “Y” of “100Y”) attached after the reference numerals in FIG. 1 correspond to yellow, magenta, cyan, and black image forming portions, respectively. In the following description, Y, M, C, and K are omitted as appropriate.

  The image forming apparatus includes a photosensitive drum 100 as an image carrier, a primary charger 12, an exposure unit 10, a developing device 11, and a primary transfer roller 103 that is a transfer roller disposed so as to face the photosensitive drum 100. ing. The image forming apparatus also includes a cleaner 13 (for the photosensitive drum), an intermediate transfer belt 101, a cleaner 16 (for the intermediate transfer belt), secondary transfer rollers 104 and 105, and a fixing device 20.

  After the photosensitive drum 100 is uniformly charged by the primary charger 12, exposure according to the image signal is performed on the photosensitive drum 100 by the exposure unit 10, whereby an electrostatic latent image is formed on the photosensitive drum 100. It is formed. The electrostatic latent image is developed by the developing device 11 to form a toner image. Each toner image on the photosensitive drum 100 is superimposed on the intermediate transfer belt 101 by pressing a primary transfer roller 103 disposed so as to face the photosensitive drum 100 with the intermediate transfer belt 101 interposed therebetween. Transcribed.

  The toner image superimposed on the intermediate transfer belt 101 is further transferred onto the recording material P by the secondary transfer rollers 104 and 105. Residual toner remaining on the photosensitive drum 100 is collected by the cleaner 13, and residual toner remaining on the intermediate transfer belt 101 is collected by the cleaner 16. The toner image transferred to the recording material P is fixed by the fixing device 20 to obtain a color image.

<Drive System of Photosensitive Drum 100 and Drive System of Intermediate Transfer Belt 101>
FIG. 2 is a diagram illustrating the configuration of the drive system (a) of the photosensitive drum 100 and the drive system (b) of the intermediate transfer belt 101. In the drive system of the photosensitive drum 100, as shown in FIG. 2A, the torque of the motor 120, which is the first motor, is transmitted to the drum shaft 122 via the gear 121. The drum shaft 122 is directly connected to the photosensitive drum 100 and a rotary encoder 123 that detects the rotational speed of the photosensitive drum 100. Note that detecting the rotational speed of the photosensitive drum 100 is equivalent to detecting the peripheral speed of the photosensitive drum 100.

  In the drive system of the intermediate transfer belt 101, as shown in FIG. 2B, the torque of the motor 130 as the second motor is transmitted to the belt roller shaft 132 via the gear 131. A belt roller 102 that is a rotating body that rotates the intermediate transfer belt 101 and a rotary encoder 133 that detects the rotational speed of the belt roller 102 are directly connected to the belt roller shaft 132. In the drive system of the intermediate transfer belt 101, the motor 130 rotates the belt roller 102 so that the intermediate transfer belt 101 rotates. Note that detecting the rotational speed of the belt roller 102 is equivalent to detecting the peripheral speed of the intermediate transfer belt 101.

<Configuration Example of Photosensitive Drum 100 and Intermediate Transfer Belt 101>
FIG. 3 is a diagram illustrating a configuration example of the photosensitive drum 100 and the intermediate transfer belt 101. In the configuration of FIG. 3A, the belt roller 102a is a belt roller 102 (see FIG. 2B) driven by a motor 130, and the belt roller 106a is not driven by the motor. On the other hand, in the configuration of FIG. 3B, the belt roller 106b is the belt roller 102 (see FIG. 2B) driven by the motor 130, and the belt roller 102b is not driven by the motor.

  Here, in each of the configurations of FIGS. 3A and 3B, the influence of the difference between the peripheral speed of the intermediate transfer belt 101 and the peripheral speed of the photosensitive drum 100 on the intermediate transfer belt 101 will be briefly described. 3A, when the peripheral speed of the photosensitive drum 100 is smaller than the peripheral speed of the intermediate transfer belt 101 (hereinafter referred to as “the peripheral speed difference is negative”), the belt roller 102a causes the intermediate transfer belt 101 to move to the photosensitive drum 100. And the primary transfer roller 103. As a result, as shown by a broken line in FIG. 3A, the intermediate transfer belt 101 is bent 110 before coming into contact with the photosensitive drum 100, which causes a transfer failure of the toner image. This causes the toner image to fall out.

  In the case of FIG. 3B, the relationship of the bending due to the difference in peripheral speed between the photosensitive drum 100 and the intermediate transfer belt 101 is opposite to that in the case of FIG. That is, when the peripheral speed of the photosensitive drum 100 is larger than the peripheral speed of the intermediate transfer belt 101 in the configuration shown in FIG. Try to push out to the side. As a result, the intermediate transfer belt 101 bends 110 shown by a broken line when it passes through the photosensitive drum 100.

  The present invention is applied to the structure shown in FIG. Therefore, in the following description, it is assumed that the configuration of FIG. 3A is applied to the image forming apparatus shown in FIG.

  As a method of avoiding the occurrence of the bending 110 in the intermediate transfer belt 101 described above, there is a method of eliminating the peripheral speed difference between the photosensitive drum 100 and the intermediate transfer belt 101. When there is no difference in peripheral speed, even when toner having a small friction coefficient enters the contact surface between the photosensitive drum 100 and the intermediate transfer belt 101, the frictional force does not change rapidly. Therefore, a rapid torque fluctuation does not occur in the motor that rotates the photosensitive drum 100, and stable primary transfer of the toner image becomes possible.

  In order to rotate the photosensitive drum 100 and the intermediate transfer belt 101 at the same peripheral speed, the drum shaft 122 and the belt roller shaft 132 must be rotated at a specified rotational speed. However, in the drive system of the photosensitive drum 100 and the intermediate transfer belt 101, the peripheral speeds of the photosensitive drum 100 and the intermediate transfer belt 101 are equalized due to variations in the diameters of the rotary encoders 123 and 133 and the photosensitive drum 100 and changes over time. May not be possible. Therefore, in the present invention, the rotational speed target value of the photosensitive drum 100 is corrected in order to suppress a difference in peripheral speed between the photosensitive drum 100 and the intermediate transfer belt 101.

  Before describing the specific embodiment, a conventional method for controlling the peripheral speed of the photosensitive drum 100 will be described below. This is because the prior art described below is also used in the embodiment of the present invention, and also contributes to an understanding of the present embodiment.

  FIG. 13 is a block diagram showing the configuration of a conventional drive control system for a photosensitive drum and an intermediate transfer belt. The arithmetic unit 320 acquires the rotational speeds of the photosensitive drum 100 and the belt roller 102 by the rotary encoder 123 and the rotary encoder 133, respectively, in order to detect the peripheral speeds of the photosensitive drum 100 and the intermediate transfer belt 101. The arithmetic device 320 obtains a deviation between the rotational speed target value of the photosensitive drum 100 stored in advance in the storage device 321 and the current rotational speed, and obtains a torque command value (first torque command value) based on the deviation. Input to the drive driver 300. Similarly, the arithmetic device 320 obtains a deviation between the rotational speed target value of the belt roller 102 stored in advance in the storage device 321 and the current rotational speed, and a torque command value (second torque command) based on the deviation. Value) is input to the drive driver 310.

  Each torque command value is represented by a duty ratio (applied pulse width) magnitude (hereinafter referred to as “PWM value”) or a current value of a PWM (Pulse Width Modulation) signal capable of adjusting an average voltage applied by a switching operation. Is done. Here, since the torque is proportional to the current value supplied to the motor, and the current value is proportional to the applied voltage, the torque is proportional to the PWM value. Therefore, in this embodiment, the PWM value is used as the torque command value.

  The drive drivers 300 and 310 to which the PWM value as the torque command value is input respectively input drive signals to the motor 120 that rotates the photosensitive drum 100 and the motor 130 that rotates the belt roller 102. Thereby, the rotational speed control of the photosensitive drum 100 and the belt roller 102, that is, the peripheral speed control of the photosensitive drum 100 and the intermediate transfer belt 101 is performed.

  FIG. 14 is a diagram showing a change in PWM value when there is a difference in peripheral speed between the photosensitive drum 100 and the intermediate transfer belt 101 in the configuration of FIG. FIG. 14A shows a change in PWM value when the printing operation (primary transfer) is executed in a state where the peripheral speed difference is negative. Since the peripheral speed of the photosensitive drum 100 is smaller than the peripheral speed of the intermediate transfer belt 101, a force pulled by the intermediate transfer belt 101 acts on the photosensitive drum 100.

  If toner having a small friction coefficient enters between the photosensitive drum 100 and the intermediate transfer belt 101 in this state, the intermediate transfer belt 101 pulls the photosensitive drum 100 due to slippage between the intermediate transfer belt 101 and the photosensitive drum 100. Get smaller. As a result, the PWM value 211 for driving the motor 120 that rotates the photosensitive drum 100 increases (maximum value: Dp_ton), and the PWM value 212 for driving the motor 130 that rotates the intermediate transfer belt 101 decreases ( Average of minimum values: Bp_ton). On the other hand, when the toner runs out between the photosensitive drum 100 and the intermediate transfer belt 101, the force with which the intermediate transfer belt 101 pulls the photosensitive drum 100 is recovered. As a result, the PWM value 211 for driving the motor 120 for rotating the photosensitive drum 100 decreases (average value of minimum values: Dp_toff), and the PWM value 212 for driving the motor 130 for rotating the intermediate transfer belt 101 is Increase (maximum value: Bp_toff).

  FIG. 14B shows a change in the PWM value when the printing operation (primary transfer) is executed with the peripheral speed difference being positive. Since the peripheral speed of the photosensitive drum 100 is higher than the peripheral speed of the intermediate transfer belt 101, the intermediate transfer belt 101 is pulled between the photosensitive drum 100 and the primary transfer roller 103 (the photosensitive drum 100 moves the intermediate transfer belt 101. Pulling force) is acting. If toner having a small friction coefficient enters between the photosensitive drum 100 and the intermediate transfer belt 101 in this state, the photosensitive drum 100 and the intermediate transfer belt 101 slip, whereby the PWM value 211 of the photosensitive drum 100 decreases, and the intermediate The PWM value 212 of the transfer belt 101 increases. On the other hand, when the toner runs out between the photosensitive drum 100 and the intermediate transfer belt 101, the force that the photosensitive drum 100 pulls the intermediate transfer belt 101 is restored, so that the PWM value 211 of the photosensitive drum 100 increases and the PWM of the intermediate transfer belt 101 increases. The value 212 decreases.

  Therefore, when the drive control system of FIG. 13 is applied to the configuration of FIG. 3A, when the peripheral speed difference is positive, the intermediate transfer belt 101 does not bend, but when the peripheral speed difference is large, the primary transfer Large torque fluctuations occur during transfer. For this reason, a delay occurs in the feedback control, which is the rotational speed control, so that the rotational speed fluctuation at the moment when the rotational speed fluctuates cannot be canceled, and this appears as a positional deviation in the toner image. In addition, torque fluctuations may cause the drive control system to become unstable and may deteriorate the image.

  FIG. 4 is a diagram showing the relationship between the circumferential speed difference between the photosensitive drum 100 and the intermediate transfer belt 101 described with reference to FIG. 14 and the torque generated by the motors 120 and 130. The intersection point 200 of the torque 201 generated by the motor 120 that rotates the photosensitive drum 100 and the torque 202 generated by the motor 130 that rotates the belt roller 102 is the peripheral speed at the surface where the photosensitive drum 100 and the intermediate transfer belt 101 contact each other. It is a point that becomes equal.

  Considering the above-described prevention of hollowing out, the peripheral speed of the photosensitive drum 100 and the intermediate transfer belt 101 is determined by a peripheral speed difference 203 (hereinafter referred to as “correction target point”) 203 that is slightly larger than the intersection 200. It is desirable to control. For this purpose, a rotational speed target value (first rotational speed target value) of the photosensitive drum 100 and a rotational speed target value (second rotational speed target value) of the belt roller 102 for obtaining a target peripheral speed difference are determined. . Then, the rotational speed target value of the photosensitive drum 100 is corrected so that the difference in peripheral speed between the photosensitive drum 100 and the intermediate transfer belt 101 is small and the torque fluctuation in the motors 120 and 130 is minimized. The method will be described in detail below.

<Control of the rotational speed of the motor 120 that rotates the photosensitive drum 100>
[Block diagram of drive control system]
FIG. 5 is a block diagram showing a configuration of a drive control system for correcting the target rotational speed value of the photosensitive drum 100 according to the present embodiment. This drive control system has a configuration in which a comparator 322 for determining the presence or absence of a peripheral speed difference is newly added to the conventional drive control system shown in FIG. Therefore, the description of the configuration common to FIG. 13 is omitted.

  The target rotational speed value of the photosensitive drum 100 is stored in the storage device 321. During correction processing of the rotational speed target value of the photosensitive drum 100 (hereinafter referred to as “target value correction processing” as appropriate), the PWM value is output from the arithmetic unit 320 in the same manner as the rotational speed control described with reference to FIGS. Is output. The arithmetic device 320 adds some of the PWM values to the drive drivers 300 and 310 and causes the storage device 321 to store them. When the stored PWM values reach a predetermined number (predetermined number). The average value is calculated.

  The comparator 322 determines how the calculated average value changes depending on the presence or absence of toner. Based on the determination result, the arithmetic device 320 determines whether or not to perform target value correction processing. When it is determined that the target value correction process is to be performed, the arithmetic device 320 overwrites the rotation speed target value of the photosensitive drum 100 stored in the storage device 321 with the corrected value.

  Specifically, generally, the comparator 322 separately acquires the average value of the upper limit value and the average value of the lower limit value of the fluctuation of the PWM value during the printing operation illustrated in FIG. 14, and outputs the PWM value from the acquired average value. Find the magnitude of the change in value. Then, the fluctuation widths of the PWM values of the photosensitive drum 100 and the intermediate transfer belt 101 are within the predetermined fluctuation width DD (first fluctuation width) and fluctuation width BB (second fluctuation width), respectively. In addition, the arithmetic unit 320 corrects the target rotational speed value of the photosensitive drum 100. The fluctuation ranges DD and BB will be described later with reference to FIG.

[Correction Processing of Rotational Speed Target Value of Photosensitive Drum 100]
FIG. 6 is a flowchart showing an overall image (overall flow) of the correction process of the rotational speed target value of the photosensitive drum 100. The processing shown in the flowchart of FIG. 6 is performed not in a normal printing operation but in a state where the toner is continuously supplied (a state where the toner is placed on the intermediate transfer belt).

  Note that the average PWM value Dp_toff for driving the motor 120 that rotates the photosensitive drum 100 and the average PWM value Bp_toff for rotating the intermediate transfer belt 101 have already been obtained in a state where toner is not supplied. Shall. Further, it is assumed that three times the standard deviation (Dp_std3 (first threshold value), Bp_std3 (second threshold value)) indicating the variation (noise) of these PWM values has already been obtained. The triple value (Dp_std3, Bp_std3) of the standard deviation will be described later with reference to FIG.

  Further, the fluctuation ranges of the PWM values for driving the motor 120 and the motor 130 for rotating the photosensitive drum 100 and the intermediate transfer belt 101 are DD and BB, respectively. The values of these fluctuation ranges DD and BB are obtained in advance, and are written in the storage device 321 when the product (image processing apparatus) is produced. FIG. 9 shows changes in the PWM value when the printing operation is performed with the peripheral speed difference at the correction target point 203 in FIG.

  In the target value correction process, first, the arithmetic unit 320 obtains a PWM value Dp_ton for driving the motor 120 that rotates the photosensitive drum 100 and a PWM value Bp_ton for driving the motor 130 that rotates the intermediate transfer belt 101. (Step S1200). That is, the PWM duty ratio corresponding to Dp_ton and Bp_ton shown in FIG. For the processing in step S1200, the arithmetic device 320 samples the PWM values used for driving the motors 120 and 130 when toner is between the photosensitive drum 100 and the intermediate transfer belt 101 at regular intervals. Since the sampled values include noise components, they are averaged. Details of step S1200 will be described later in detail with reference to FIG.

  Next, with respect to the photosensitive drum 100, the arithmetic unit 320 preliminarily calculates a difference (variation width) between the known average value of the PWM value when there is no toner and the average value of the PWM value when there is toner determined in step S 1200. A difference dDp (first difference) obtained by subtracting the determined fluctuation range DD is obtained. Further, regarding the intermediate transfer belt 101, a predetermined fluctuation width is determined from a difference (fluctuation width) between the known average value of the PWM value when there is no toner and the average value of the PWM value obtained when the toner is obtained in step S1200. A difference dBp (second difference) obtained by subtracting BB is obtained (step S1201). Specifically, the difference dDp = Dp_ton−Dp_toff−DD and the difference dBp = Bp_toff−Bp_ton−BB.

  Next, for the photosensitive drum 100, the comparator 322 compares the difference between the PWM value obtained in step S1201 and the triple value Dp_std3 (first threshold) of the standard deviation indicating the variation of the PWM value obtained in advance. Contrast with absolute value | dDp | (first absolute value) of dDp. Similarly, for the intermediate transfer belt 101, the triple value Bp_std3 (second threshold value) is compared with the absolute value | dBp | (second absolute value) of the PWM value difference dBp obtained in step S1201 (step S1202). ). This is to eliminate erroneous detection due to variations in the PWM value. Specifically, the first absolute value | dDp | is larger than the triple value Dp_std3 or the second absolute value | dBp | It is determined whether the value is larger than the triple value Bp_std3.

  When | dDp | is not larger than Dp_std3 and | dBp | is not larger than Bp_std3 (“NO” in S1202), the arithmetic unit 320 determines that the variation is within the range of the PWM value, and corrects the target value. The process is terminated without performing the process. If | dDp | is greater than Dp_std3, or | dBp | is greater than Bp_std3 (“YES” in S1202), arithmetic unit 320 advances the process to step S1203.

  In step S1203, the arithmetic unit 320 determines whether the change in the PWM value is a fluctuation as shown in FIG. 14 depending on whether each value of dDp and dBp obtained in step S1201 is positive or negative. . Specifically, it is determined whether dDp is negative and dBp is positive, or dDp is positive and dBp is negative. If this condition is not satisfied (“NO” in S1203), the arithmetic device 320 Determines that the PWM value does not fluctuate due to the peripheral speed difference, and ends the target value correction process. On the other hand, when dDp is negative and dBp is positive, or dDp is positive and dBp is negative (“YES” in S1203), the arithmetic unit 320 corrects the target value Vref of the rotational speed of the photosensitive drum 100. (Step S1204).

  In step S1204, the arithmetic unit 320 specifically corrects the rotational speed target value before correction using the change in the PWM value caused by the toner. A value obtained by further dividing the quotient obtained by dividing the difference dDp by Dp_toff by 2 ((dDp / Dp_toff) / 2) is added to the rotation speed target value before correction to obtain a rotation speed target value after correction. That is, the rotation speed target value is corrected by Vref [after correction] = Vref [before correction] + (dDp / Dp_toff) / 2). In this way, by correcting the target value of the rotational speed of the photosensitive drum 100, it is possible to suppress a change in the peripheral speed difference between the photosensitive drum 100 and the intermediate transfer belt 101.

[Related Processing in Step S1200]
In step S1200 in FIG. 6, when toner is present between the photosensitive drum 100 and the intermediate transfer belt 101, PWM values for driving the motors 120 and 130 to rotate the photosensitive drum 100 and the intermediate transfer belt 101 are set. Need to get. FIG. 7 is a process flowchart for determining that toner has entered between the photosensitive drum 100 and the intermediate transfer belt 101.

  First, the arithmetic device 320 starts a process of transferring toner to the intermediate transfer belt 101 (step S1100). The arithmetic device 320 uses the exposure start signal in step S1100 as a toner transfer start signal, and counts the elapsed time from the start signal (step S1101). Then, the arithmetic unit 320 estimates the time (transfer time Ton) from the target rotational speed of the photosensitive drum 100 until the toner is transferred to the intermediate transfer belt 101 (step S1102). For example, since the exposure is performed on the upper part of the photosensitive drum 100, the time that the photosensitive drum 100 makes a half turn is set as the transfer time Ton.

  Next, the arithmetic unit 320 determines whether or not a predetermined time has elapsed since the start of toner transfer (step S1103). This predetermined time is determined on the basis of the transfer time Ton. In this embodiment, a time obtained by doubling the transfer time Ton is used to ensure that the toner is between the photosensitive drum 100 and the intermediate transfer belt 101. It is a predetermined time.

  If the elapsed time has passed the predetermined time (“YES” in S1103), the arithmetic unit 320 determines that the toner is in the state between the photosensitive drum 100 and the intermediate transfer belt 101, ends this processing, and performs step. The process of S1200 is executed. Until the elapsed time has passed the predetermined time (“NO” in S1103), the arithmetic device 320 is in a standby state (the process returns to step S1103) until the elapsed time has passed the predetermined time. It should be noted that the toner transferred to the intermediate transfer belt 101 in this process is not output onto the paper but is transferred onto the intermediate transfer belt 101 until the correction process of the rotational speed target value of the photosensitive drum 100 is completed. Maintained.

[Pre-start process of step S1200]
FIG. 8 is a flowchart of preprocessing performed before execution of processing according to the flowchart of FIG. 6. In the processing according to the flowchart of FIG. 8, the PWM values Dp_toff and Bp_toff described with reference to FIG. Further, the noise magnitudes Dp_std3 and Bp_std3 of these PWM values are obtained.

  First, the arithmetic device 320 determines whether or not the image processing device is in a preparatory operation when the power is turned on (step S1000). When it is not in the state of the preparatory operation (“NO” in S1000), the arithmetic unit 320 ends this process and does not perform the process for correcting the target rotational speed value of the photosensitive drum 100. If it is in the preparatory operation state (“YES” in S1000), the arithmetic device 320 determines whether or not the counter value of the current number of printed sheets has exceeded a predetermined value (step S1001).

  If the counter value does not exceed the predetermined value (“NO” in S1001), the arithmetic unit 320 determines the speed of the photosensitive drum 100 and the intermediate transfer belt 101 after the previous correction processing of the rotational speed target value of the photosensitive drum 100. The change in driving characteristics is considered small. Therefore, the arithmetic unit 320 ends this process without performing the correction process of the rotation speed target value of the photosensitive drum 100. If the counter value exceeds the predetermined value (“YES” in S1001), the arithmetic unit 320 advances the process to step S1002.

  In step S <b> 1002, the arithmetic unit 320 applies the primary transfer roller 104 </ b> K corresponding to one photosensitive drum (here, “photosensitive drum 100 </ b> K”) whose peripheral speed is to be corrected to the same as that during the printing operation. The photosensitive drum 100K is pressed with pressure. At the same time, the primary transfer rollers 104Y, 104M, and 104C corresponding to the other photosensitive drums that are not correction targets, that is, the photosensitive drums 100Y, 100M, and 100C, are moved away from the intermediate transfer belt 101 (step S1003). ).

  FIG. 10 is a diagram illustrating the states of the photosensitive drum 100 and the primary transfer roller 104 during a normal printing operation and during the processing in steps S1002 and S1003. Note that the operation of the primary transfer roller 104 as shown in FIG. 10 is performed by operating means (not shown). The pressing / separating operation of the primary transfer rollers 104Y, 104M, 104C, and 104K can be performed independently.

  Next, the arithmetic unit 320 samples PWM values for driving the motor 120K and the motor 130K at regular intervals in order to rotate the photosensitive drum 100K and the intermediate transfer belt 101 in a state where toner is not flowing. And the arithmetic unit 320 calculates the average value of the sampled PWM value, and memorize | stores the calculated average value temporarily. Then, the average value (Dp_toff, Bp_toff) of the PWM value is further obtained from the stored average value data, and the triple value (Dp_std3, Bp_std3) of the standard deviation, which is a variation index, is obtained from the average value of the PWM values thus obtained. (Step S1004). These values are used in steps S1201 and S1202 in FIG.

  As described above, in this embodiment, the peripheral speed difference between the photosensitive drum 100 and the intermediate transfer belt 101 is controlled using changes in both PWM values for rotating the photosensitive drum 100 and the intermediate transfer belt 101.

  On the other hand, for example, the frictional force in the cleaner 16 (see FIG. 1) varies depending on the amount of toner on the intermediate transfer belt 101, so that the motor 130 for rotating the intermediate transfer belt 101 is driven. Only the PWM value changes.

  FIG. 11 shows an example of changes in the PWM value of the motor 130 that drives the intermediate transfer belt 101 regardless of the peripheral speed difference. The increase of the PWM value 212 in FIG. 11A is an example of torque fluctuation of the motor 130 that occurs when the toner is not flowing on the intermediate transfer belt 101 and the period is flowing. A motor that drives the intermediate transfer belt 101 since the frictional force between the cleaner 16 that scrapes off the toner and the intermediate transfer belt 101 decreases due to excess toner remaining on the intermediate transfer belt 101 without being transferred after the secondary transfer. The PWM value of 130 becomes smaller.

  On the other hand, the decrease in the PWM value 212 in FIG. 11B is an example of torque fluctuation of the motor 130 that occurs when the period from when the toner flows to the intermediate transfer belt 101 is shifted to the period when it does not flow. In this case, contrary to FIG. 11A, the excess toner on the intermediate transfer belt 101 decreases, so that the PWM value of the motor 130 that drives the intermediate transfer belt 101 increases. As another example, a shock caused when a sheet enters between the intermediate transfer belt 101 and the secondary transfer rollers 104 and 105 during the secondary transfer is caused by the PWM of the motor 130 that drives the intermediate transfer belt 101. The value may be changed.

  FIG. 12 is an example showing a change in the PWM value of the motor 120 that drives the photosensitive drum 100 regardless of the peripheral speed difference. The decrease of the PWM value 211 in FIG. 12A is an example of torque fluctuation of the motor 120 that occurs when the period from the time when no toner flows to the photosensitive drum 100 to the period when it flows. After the primary transfer, the excess toner remaining on the photosensitive drum 100 without being transferred reduces the frictional force of the cleaner 13 that scrapes off the excess toner on the photosensitive drum 100, and the PWM value of the motor 120 that drives the photosensitive drum 100 is Get smaller.

  On the other hand, the increase in the PWM value 211 in FIG. 12B is an example of torque fluctuation of the motor 120 that occurs when the toner flows from the photosensitive drum 100 to the non-flowing period. In this case, contrary to FIG. 12A, the PWM value of the motor 120 that drives the photosensitive drum 100 increases as the excess toner on the photosensitive drum 100 decreases.

  In this way, when the peripheral speed difference is controlled using only one of the PWM value changes for driving the photosensitive drum 100 and the intermediate transfer belt 101, only the PWM value change caused by the change in the peripheral speed difference is performed. In addition, the PWM value changes due to other factors. In the present embodiment, this problem is solved by controlling the difference in peripheral speed between the photosensitive drum 100 and the intermediate transfer belt 101 by using both PWM value changes for rotating the photosensitive drum 100 and the intermediate transfer belt 101. Is avoiding.

  As described above, according to the present embodiment, the torque fluctuation of the photosensitive drum 100 at the time of primary transfer can be suppressed to a small value, whereby the toner image is transferred from the photosensitive drum 100 to the intermediate transfer belt 101. The accuracy can be kept stable and high. Thereby, the image quality when transferred onto the recording material (paper) can be stabilized. The present invention is particularly useful for an image forming apparatus in which torque fluctuation of the photosensitive drum 100 easily occurs during primary transfer, that is, an image forming apparatus using an elastic belt having a large friction coefficient as the intermediate transfer belt 101. .

<Other embodiments>
Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. Furthermore, each embodiment mentioned above shows only one embodiment of this invention, and it is also possible to combine each embodiment suitably.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program code. It is a process to be executed. In this case, the program and the storage medium storing the program constitute the present invention.

100 Photosensitive drum 101 Intermediate transfer belt 102 Belt roller 103 Primary transfer roller 120 Motor (for photosensitive drum rotation)
130 Motor (for intermediate transfer belt rotation)
203 correction target point 320 arithmetic unit 322 comparator

Claims (6)

An image forming apparatus for transferring a toner image formed on a photosensitive drum to an intermediate transfer belt, and transferring the toner image transferred to the intermediate transfer belt to a recording material,
A first motor for rotating the photosensitive drum;
A second motor for rotating a rotating body for rotating the intermediate transfer belt;
A first torque command value for driving the first motor so that the photosensitive drum rotates at a first rotation speed target value and the rotation body so as to rotate at a second rotation speed target value. Computing means for computing a second torque command value for driving the second motor;
Calculating means for calculating a fluctuation range of the first torque command value and a fluctuation range of the second torque command value;
Whether or not the absolute value of the first difference obtained by subtracting the first fluctuation range from the fluctuation range of the first torque command value exceeds the first threshold, and from the fluctuation range of the second torque command value Comparing means for determining whether the absolute value of the second difference obtained by subtracting the second fluctuation range exceeds a second threshold;
When the absolute value of the first difference exceeds the first threshold or when the absolute value of the second difference exceeds the second threshold, the first difference is a negative value. When the second difference is a positive value or when the first difference is a positive value and the second difference is a negative value, the fluctuation range of the first torque command value Correction for correcting the first target rotational speed value so that the fluctuation range of the second torque command value falls within the range of the second fluctuation range. And an image forming apparatus.   A peripheral speed when the photosensitive drum is rotated at the first rotation speed target value is larger than a peripheral speed of the intermediate transfer belt when the rotating body is rotated at the second rotation speed target value. The image forming apparatus according to claim 1.   The first motor so that the photosensitive drum and the rotating body rotate at the first rotation speed target value and the second rotation speed target value, respectively, when toner is present on the intermediate transfer belt. And the difference between the average value of the maximum value and the average value of the minimum value of the torque command value calculated for the first motor when the second motor is driven is the first torque command value. And the difference between the average value of the maximum value of the torque command value calculated for the second motor and the average value of the minimum value is set as the fluctuation range of the second torque command value. The image forming apparatus according to claim 1 or 2.   When there is no toner on the intermediate transfer belt, the photosensitive drum and the rotating body rotate at the first rotation speed target value and the second rotation speed target value, respectively. Torque that is calculated for the second motor with the first threshold value being a value that is three times the standard deviation of the torque command value that is calculated for the first motor. The image forming apparatus according to claim 1, wherein a value that is three times the standard deviation of the command value is set as the second threshold value.   The correction unit is configured to cause the photosensitive drum and the rotating body to rotate at the first rotation speed target value and the second rotation speed target value, respectively, when there is no toner on the intermediate transfer belt. A value obtained by further dividing a quotient obtained by dividing the first difference by an average value of torque command values calculated for the first motor when the motor and the second motor are driven is divided by 2. The image forming apparatus according to claim 1, wherein the first rotation speed target value after correction is added to the first rotation speed target value. A transfer roller having a plurality of the photosensitive drums and arranged to sandwich the intermediate transfer belt so as to face each of the plurality of photosensitive drums; an operation of pressing the plurality of transfer rollers against the photosensitive drum; An operation means for independently performing an operation of separating from the intermediate transfer belt;
At the same time as pressing the transfer roller corresponding to one photosensitive drum that is the correction target of the first rotational speed target value among the plurality of photosensitive drums against the photosensitive drum that is the correction target. 2. The first torque command value and the second torque command value are calculated by the calculation means by separating the transfer roller corresponding to the photosensitive drum from the intermediate transfer belt. 6. The image forming apparatus according to any one of items 1 to 5.

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