JP2018010132A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a deterioration in image caused by an increase in frictional force between photoreceptors and an intermediate transfer body.SOLUTION: Driving motors each drive to rotate photoreceptor drums and an intermediate transfer belt. A speed setting controller controls each of the driving motors to adjust a surface peripheral speed of each of the photoreceptor drums and intermediate transfer belt to a target surface peripheral speed. While a fogging toner is present/absent at primary transfer parts (nip parts), first torque and second torque are detected. A correction timing is determined as a timing at which an increase in temperature from the previous execution of correction processing of correcting the target surface peripheral speed of the photoreceptor drums (change in speed setting value) exceeds a predetermined temperature TS, and a difference in torque between the presence and absence of toner exceeds a predetermined value TQ, and the correction processing is executed.SELECTED DRAWING: Figure 12

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.

  Conventionally, an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic method generally has a photosensitive drum and an intermediate transfer belt that are driven to rotate, and a toner image formed on the photosensitive drum is used as an intermediate transfer belt. Transcribed. Then, the toner image transferred to the intermediate transfer belt is transferred to transfer paper. The accuracy of the speed of the photosensitive drum and the intermediate transfer belt affects the image reproducibility on the transfer paper, and even if the rotation speed unevenness is very small, density fluctuation unevenness called banding is caused by the image expansion / contraction caused by the unevenness of the transfer paper. Appear in the image and contribute to image degradation. In particular, in a tandem apparatus, a deviation from the original position of image formation or transfer occurs due to the speed variation of each color photosensitive drum. Further, the transfer position shifts from each drum due to the speed fluctuation of the intermediate transfer belt. As a result, each color image formed on the transfer paper shifts from its original position, so-called color misregistration, which contributes to image degradation.

  Even if the motor speed is constant, the rotational speed may not be constant due to the eccentricity of the gear in the mechanism for rotationally driving the photosensitive drum or the intermediate transfer belt. Therefore, instead of constant speed control of the drive motor, a method is known in which the rotational speed of a load shaft (photosensitive drum or drive roller for driving an intermediate transfer belt) is feedback controlled using a detection result by an encoder or the like. However, even when the constant speed control is performed using the encoder on the load shaft, the surface circumference may be reduced due to the tolerance of the photosensitive drum diameter, the driving roller diameter for the intermediate transfer belt, the thickness tolerance of the intermediate transfer belt, etc. It is not easy to control the speed (surface speed) at a target value.

  Here, the target surface peripheral speed of the photosensitive drum and the surface peripheral speed of the intermediate transfer belt will be described. From the viewpoint of image quality, a toner image transferred in a state where the surface peripheral speeds of the two coincide with each other is transferred without rubbing, so that the fine line reproducibility is high. However, the phenomenon of so-called hollowing out in which the central part of the image such as characters and lines is not transferred and is whitened out can be reduced by giving a difference in surface peripheral speed between the photosensitive drum and the intermediate transfer belt. Also, from the mechanical mechanism point of view, if the magnitude relationship between the surface peripheral speeds is switched interchangeably due to the tolerance of eccentricity and roundness, the transmission of the drive becomes discontinuous due to gear and coupling play, so constant speed rotation Adversely affects. For this reason, the surface peripheral speed difference is preferably given to such an extent that the magnitude relationship between the surface peripheral speeds does not change. Conventionally, in order to satisfy these requirements, the surface peripheral speed difference is set to about 0.3% as a target value of the encoder on the load shaft. This target value is a value that is determined so that the degradation of the image quality is within a range that satisfies the product requirement specifications even if there is a tolerance of the mechanism that drives the photosensitive drum and the intermediate transfer belt.

  However, since the surface peripheral speed difference is provided, if the frictional force between the photosensitive drum and the intermediate transfer belt during transfer is large, the speed unevenness between the photosensitive drum and the intermediate transfer belt is likely to occur, and the image quality is improved. Affect. For example, in a case where a multilayer elastic belt in which elastic rubber is stretched on the transfer surface of a polyimide belt is used as the intermediate transfer belt, the frictional force is large because the contact portion with the photosensitive drum is elastic rubber. Further, the frictional force between the two can be changed successively. For example, even if the intermediate transfer belt is not a multilayer elastic belt, the frictional force against the photosensitive drum may increase due to endurance use or temperature rise in the apparatus.

  For these reasons, the driving speed of the photosensitive drum and the intermediate transfer belt is set so that the target value of the surface peripheral speed difference is set to a minimum value, and the magnitude relation of the surface peripheral speed is not changed by tolerance. There is a need to set it. For example, the target value of the surface peripheral speed difference is 0 to 0.15%. When the tolerances of each part are accumulated, the error of the surface peripheral speed becomes ± 0.15% with a steady speed error. Even if the rotational speed of the drive shaft is detected by an encoder and controlled to a target value, the influence of tolerances at various places cannot be excluded. Further, due to factors other than tolerances, for example, the outer shape of the driving roller of the photosensitive drum or the intermediate transfer belt changes due to a change in ambient temperature, and the surface peripheral speed changes from a desired value. As a result, the surface peripheral speed difference is increased, and color unevenness, banding, and the like may be caused due to an increase in speed unevenness. In order to detect the surface peripheral speed, there are methods of marking the photosensitive drum and the intermediate transfer belt at equal intervals and reading the passing time of the marking with an optical sensor, or using a Doppler velocimeter, but this increases the cost. It leads to.

  For such a problem, Patent Document 1 proposes a technique for driving the photosensitive drum and the intermediate transfer belt at the same speed without detecting the surface peripheral speed. That is, in Patent Document 1, the intermediate transfer belt is driven while changing the speed of the photosensitive drum while the intermediate transfer belt is driven at a predetermined speed, and the speed corresponding to the inflection point of the torque characteristic at the time of control accompanying the speed change of the photosensitive drum is set. The speed at which the photosensitive drum should be driven is determined. In addition, the timing for executing the speed control of the photosensitive member and the transfer member is as follows. Time is given. It has also been proposed to perform color registration adjustment (color misregistration adjustment) as necessary after executing speed control when the power is on.

JP 2012-32515 A

  However, if the speed control as in Patent Document 1 is performed alone, it itself causes downtime. Therefore, in order to avoid excessive downtime, it is desirable that the speed control is originally performed at a timing at which downtime occurs, for example, at the timing of color misregistration adjustment for each predetermined number of image formations.

  However, if the speed control is only performed every time the number of image formations reaches a predetermined number, it cannot cope with a situation where the load for maintaining the surface peripheral speed difference fluctuates greatly. That is, depending on the operation mode in image formation, the in-machine temperature may increase rapidly. For example, the frictional force between the photosensitive drum and the intermediate transfer belt suddenly increases due to the temperature rise in the apparatus, the speed control cannot follow, and there is a problem that a color shift or a shock image occurs.

  An object of the present invention is to suppress image deterioration caused by an increase in frictional force between a photosensitive member and an intermediate transfer member.

  In order to achieve the above object, the present invention provides a motor, an image forming means for forming an image on a photosensitive member rotated by the motor, an intermediate transfer member to which the image on the photosensitive member is transferred, Control means for controlling the motor, change means for changing the target speed, temperature detection means for detecting temperature, and from the photoreceptor to the intermediate transfer body so that the rotational speed of the photoreceptor becomes the target speed. In the first period during which the image is transferred, the first information on the rotational torque of the motor in a state where the photoconductor is rotated is acquired, and in the second period in which the image is not transferred from the photoconductor to the intermediate transfer body. Acquisition means for acquiring second information relating to the rotational torque of the motor in a state where the photosensitive member is rotated, and the changing means is based on the temperature detected by the temperature detecting means. Come, and controlling whether or not to change the target speed of the photosensitive body based on the acquired first information and the second information by the acquisition unit.

  According to the present invention, it is possible to suppress image deterioration due to an increase in frictional force between the photosensitive member and the intermediate transfer member.

1 is a schematic cross-sectional view of a main part of an image forming apparatus. It is an enlarged view of the vicinity of a photosensitive drum and a developing device. 1 is a block diagram of an image forming apparatus. It is a perspective view of the mechanism which drives a photosensitive drum. FIG. 6 is a perspective view of a mechanism that drives an intermediate transfer belt. It is a figure which shows an example of the image for a measurement. It is a figure which shows the transition of the load of the drum drive motor by durability. It is a figure which shows the transition of the load of the drum drive motor by durability. It is a flowchart of an image formation process. It is a figure which shows the transition of the torque before durability in a temperature rising state. It is a figure which shows the transition of the torque after the endurance in a temperature rising state. It is a flowchart of a correction | amendment and adjustment process. It is a figure which shows transition of the load of a drum drive motor. It is a figure which shows transition of the load of a drum drive motor. It is a figure which shows the transition of the load of the drum drive motor of a comparative example.

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

  FIG. 1 is a schematic cross-sectional view of a main part of an image forming apparatus according to an embodiment of the present invention. This image forming apparatus includes four image forming units 1200 (1200Y, 1200M, as image forming means for forming four color images of yellow (Y), magenta (M), cyan (C), and black (K). 1200C, 1200K). That is, this image forming apparatus is a tandem color image forming apparatus using an electrophotographic system in which image forming units 1200 of respective colors are arranged side by side on an intermediate transfer belt 24 that is an intermediate transfer member. Since the constituent elements of each image forming unit 1200 are the same, hereinafter, the same reference numerals are used when not distinguishing the constituent elements for each image forming part, and Y, M, C, and K are appended after the reference numerals when distinguishing. .

  Each image forming unit 1200 includes a photosensitive drum 10 (10Y, 10M, 10C, 10K) as a rotatable photosensitive member. In consideration of the case where a large number of monochrome images are formed, a photosensitive drum 10K having a larger diameter than the photosensitive drums 10 of other colors is employed, and only the photosensitive drum 10K is prevented from reaching the end of its life. doing. The photosensitive drum 10 includes an aluminum cylinder and a photosensitive layer formed on the surface of the aluminum cylinder. The photosensitive layer functions as a photoreceptor. Around each photosensitive drum 10, a charger 21 (21Y, 21M, 21C, 21K), an exposure device 22 (22Y, 22M, 22C, 22K), a developing device 1 (1Y, 1M, 1C, 1K), a cleaning device 26 (26Y, 26M, 26C, 26K) are arranged. Further, a toner supply tank 20 (20Y, 20M, 20C, 20K) is disposed adjacent to each developing device 1.

  The intermediate transfer belt 24 is an endless belt member, and is an image carrier that carries a toner image transferred from the photosensitive drum 10. The intermediate transfer belt 24 is stretched by a plurality of rollers and is driven to rotate by a belt driving roller 40. The intermediate transfer belt 24 circulates (rotates) in the clockwise direction in FIG. 1 while being in contact with the surface of each photosensitive drum 10. A primary transfer roller 23 (23Y, 23M, 23C, 23K) is disposed opposite to each photosensitive drum 10 with the intermediate transfer belt 24 interposed therebetween. A detection sensor 1004 is disposed in the vicinity of the intermediate transfer belt 24 on the downstream side of the image forming unit 1200K.

  The photosensitive drum 10 is uniformly charged by the charger 21 and is exposed by the laser beam emitted from the exposure device 22 to form an electrostatic latent image on the surface (on the photoreceptor). The latent image is visualized as a toner image by the developing device 1 through a process described below. Next, the visualized toner image is transferred to the intermediate transfer belt 24 by the primary transfer roller 23 at a primary transfer portion (nip portion) N (see FIG. 2) formed by each photosensitive drum 10 and the primary transfer roller 23. Is transcribed. The toner image transferred to the intermediate transfer belt 24 is transferred to the transfer paper 30 by the secondary transfer roller 29, and the unfixed image transferred to the transfer paper 30 is fixed by the fixing device 25. The toner (developer) remaining on the photosensitive drum 10 is removed by the cleaning device 26. Further, the toner remaining on the intermediate transfer belt 24 is removed by the cleaning member 28 on the downstream side of the secondary transfer roller 29. As the toner is consumed in image formation, the toner is supplied from the toner supply tank 20 to the developing device 1.

  FIG. 2 is an enlarged view of the vicinity of the photosensitive drum 10 and the developing device 1. The developing device 1 includes a developing sleeve 8 as a developer carrying member that is rotatably disposed facing the photosensitive drum 10. The inside of the developing container 2 is divided into a developing chamber 3 and a stirring chamber 4 by a partition wall 7. In the developing chamber 3 and the stirring chamber 4, stirring screws 5 and 6 are arranged, respectively. The agitation screws 5 and 6 are driven by an agitation drive unit 46 that is a drive motor. The developing sleeve 8 is driven by a sleeve driving unit 43 that is a driving motor. The stirring drive unit 46, the sleeve drive unit 43, and the toner supply tank 20 are controlled by the controller 1001.

  In the developing device 1, a two-component developer including a nonmagnetic toner and a low magnetization high resistance carrier is used. These developers are accommodated in the developing container 2. The non-magnetic toner is configured by using an appropriate amount of a binder resin such as a styrene resin or a polyester resin, a colorant such as carbon black, a dye or a pigment, a release agent such as wax, a charge control agent, or the like. Such a non-magnetic toner can be produced by a conventional method such as a pulverization method or a polymerization method. As the carrier and toner are frictionally charged in the developing device 1, the toner is charged. A developing bias is applied to the charged toner, and the latent image on the photosensitive drum 10 is visualized by a potential difference with the photosensitive drum 10. In this embodiment, negatively charged toner is used.

  Next, the image forming operation will be described with reference to FIGS. The photosensitive drum 10 is charged to a negative potential (for example, −700 V) by the charger 21, and the exposure portion by the exposure unit 22 is discharged to 0 V (for example, −200 V). A developer containing toner that is triboelectrically charged to negative polarity in the developing device 1 is conveyed to the vicinity of the photosensitive drum 10 by the developing sleeve 8. At this time, the developing bias applied to the developing sleeve 8 is a potential (for example, −500 V) between the charging potential and the exposure site potential. In the above state, the negatively charged toner existing on the developing sleeve 8 flies to an exposed portion that is relatively closer to the positive potential than the charging potential and developing bias of the photoreceptor. The negatively charged toner flying to the photosensitive drum 10 is transferred to the intermediate transfer belt 24 in the primary transfer portion N by the pressure and electric field force between the primary transfer roller 23 and the intermediate transfer belt 24. At this time, a primary transfer bias (for example, +1500 V) having a positive polarity opposite to that of the toner is applied to the primary transfer roller 23.

  FIG. 3 is a block diagram of the image forming apparatus. The controller 1001 includes a CPU 100, a CR (color registration) controller 1003, a speed setting controller 1002, and an image forming controller 1100 (1100Y, 1100M, 1100C, 1100K). The controller 1001 further includes a torque detector 45 (45Y, 45M, 45C, 45K, 45b). A temperature detection unit 1005 (not shown in FIG. 1) is a temperature detection unit that detects the temperature (in-machine temperature) in the image forming apparatus and supplies the detection information to the speed setting controller 1002. The detection sensor 1004 reads a measurement image (described later in FIG. 6) formed on the intermediate transfer belt 24 and outputs the read information to the CR controller 1003.

  Each image forming controller 1100 controls the image forming operation of the corresponding image forming unit 1200. The speed controller 1300 (1300Y, 1300M, 1300C, 1300K) is controlled by the controller 1001 to control the speed of the drum drive motor 41 (41Y, 41M, 41C, 41K) by feedback control. The speed controller 1300b is controlled by the controller 1001 to control the speed of the belt drive motor 42 by feedback control. The controller 1001 controls the drive motors 41 and 42 by controlling the speed setting controller 1002 so that the surface peripheral speed of the photosensitive drum 10 and the surface peripheral speed of the intermediate transfer belt 24 become the respective target surface peripheral speeds. The controller 1001 serves as a control unit in the present invention.

  Each drum drive motor 41 rotationally drives the corresponding photosensitive drum 10. The belt drive motor 42 drives the intermediate transfer belt 24 to rotate. Each torque detection unit 45 extracts the PWM output value of the speed controller 1300 and averages it for a predetermined time, thereby detecting a duty ratio (%) proportional to the drive torque, which is the output torque at that time, as a load. Accordingly, each torque detector 45 detects the load of each of the drive motors 41 and 42. The controller 1001 stores the detected load in a storage unit (not shown).

  FIG. 4 is a perspective view of a mechanism for driving the photosensitive drum 10. Since the configuration of the drive mechanism for each photosensitive drum 10 is common, only one will be described as a representative. A drum drive gear 35 is connected to the drum shaft of the photosensitive drum 10, and the motor gear 31 is engaged with the drum drive gear 35. The driving force of the drum drive motor 41 is transmitted to the drum shaft via the motor gear 31 and the drum drive gear 35, and the photosensitive drum 10 rotates. An encoder 34 is disposed on the drum shaft, and the two speed detectors 32 and 33 monitor the rotation of the encoder 34. The speed detection units 32 and 33 count the rotation of the encoder 34 as a pulse, and send the rotation speed of the photosensitive drum 10 to the speed controller 1300 as a speed detection signal. The speed controller 1300 performs feedback control calculation based on the supplied speed detection signal, and outputs a PWM drive signal that is a drive command to the drum drive motor 41.

  FIG. 5 is a perspective view of a mechanism for driving the intermediate transfer belt 24. A belt drive gear 48 is connected to the roller shaft of the belt drive roller 40, and the belt drive gear 47 meshes with the belt drive gear 48 and the motor gear 36 meshes with the belt drive gear 47. The driving force of the belt driving motor 42 is transmitted to the roller shaft via the motor gear 36 and the belt driving gears 47 and 48, and the belt driving roller 40 rotates to rotate the intermediate transfer belt 24. An encoder 39 is disposed on the roller shaft, and the two speed detectors 37 and 38 monitor the rotation of the encoder 39. The speed detectors 37 and 38 count the rotation of the encoder 39 as a pulse, and send the rotational speed of the belt driving roller 40 to the speed controller 1300b as a speed detection signal. The speed controller 1300b performs a feedback control calculation based on the supplied speed detection signal, and outputs a PWM drive signal, which is a drive command, to the belt drive motor 42.

  Next, a sequence when two images are formed (two-sheet printing) in the image forming apparatus will be described. Here, each period will be described by roughly dividing it into pre-rotation, image formation, paper interval, and post-rotation. The pre-rotation is a period in which each drive unit and bias is turned on to achieve a stable state in order to perform image formation. The image forming period is a period for exposing the photosensitive drum 10 and visualizing the electrostatic latent image. The interval between sheets refers to a period between one image formation period and the next image formation period in continuous image formation, and is a period in which image formation is not performed. The post-rotation is a period for turning off each drive unit and bias.

  In the pre-rotation period, first, the controller 1001 drives the photosensitive drum 10 and the intermediate transfer belt 24. Since the photosensitive drum 10 and the intermediate transfer belt 24 have a large inertia, it takes 500 msec, for example, for the rising time from the start of driving until the target speed is reached and the rotation can be stably controlled at a constant speed. The driving method of the photosensitive drum 10 and the intermediate transfer belt 24 will be described later. Thereafter, the controller 1001 applies the charging bias after the photosensitive drum 10 and the intermediate transfer belt 24 can be controlled to rotate at a constant speed. The controller 1001 applies the primary transfer bias at an arbitrary timing after the charged portion on the photosensitive drum 10 reaches the primary transfer portion N. The development drive and the development bias may be at a desired rotational speed and a desired bias before the latent image exposed on the photosensitive drum 10 reaches the position of the developing device 1. However, it is desirable to apply the developing bias at a timing that is as late as possible in order to further prevent developer deterioration.

  During the image forming period, the controller 1001 exposes the charged photosensitive drum 10 by the exposure unit 22 at a timing determined by a color registration adjustment mode (hereinafter referred to as a color misregistration adjustment mode) described later to form a latent image. Form. Further, the controller 1001 visualizes the latent image with toner on the developing sleeve 8 of the developing device 1, and then transfers the toner image to the intermediate transfer belt 24 at the primary transfer portion N. Between the sheets, the controller 1001 maintains the drive and bias in the state at the time of image formation. In the post-rotation period, the controller 1001 turns off exposure, development drive, development bias, primary transfer bias, and charging bias in this order, and then stops driving the photosensitive drum 10 and the intermediate transfer belt 24.

  Next, the color misregistration adjustment mode will be described. The color misregistration adjustment mode is a mode for correcting an image writing position shift due to manufacturing variations of the image forming apparatus and a change with time of the image writing position due to a temperature rise in the apparatus. The color misregistration adjustment mode is performed at a predetermined timing, such as when an instruction is given from the user, when the image forming apparatus is started up, or after every predetermined number of prints (for example, every 1000 image forming images are formed). . In the color misregistration adjustment mode, the controller 1001 forms an image for measurement on the intermediate transfer belt 24 and adjusts the image forming timing for each color based on the result of reading the image for measurement by the detection sensor 1004 (image writing position). Correct).

  FIG. 6 is a diagram illustrating an example of a measurement image formed on the intermediate transfer belt 24. When it is time to execute the color misregistration adjustment mode, driving of the intermediate transfer belt 24 is started, and measurement images 702 (702Y, 702M, 702C, 702K) as test images (patch images) are placed on the intermediate transfer belt 24. Are formed continuously. The detection sensor 1004 reads each measurement image 702 at a reading position CL in the main scanning direction of the measurement image 702 (direction orthogonal to the conveyance direction of the intermediate transfer belt 24). The controller 1001 determines the relative position of the measurement image 702 for each color in the main scanning direction and the sub-scanning direction (conveying direction of the intermediate transfer belt 24) from the time required for each measurement image 702 to pass the reading position CL. Calculate the relationship.

  For example, when the measurement image 702Y passes the reading position CL, the interval Lys is calculated from the passage time between the image portions of the measurement image 702Y. Similarly, the interval Lms is calculated from the passage time between the image portions of the measurement image 702M. The intervals Lys and Lms are intervals in the sub-scanning direction of the measurement image 702. From the relationship between the interval Lys and the interval Lms, the relative positional relationship between the measurement image 702Y and the measurement image 702M in the main scanning direction is calculated. On the other hand, the relative positional relationship between the measurement image 702Y and the measurement image 702M in the sub-scanning direction is calculated from the interval Lym between the intermediate position of the interval Lys and the intermediate position of the interval Lms in the sub-scanning direction. The

  In this way, the relative positional relationship between the color images is calculated. Normally, an average value obtained by forming and reading a plurality of sets of measurement images 702 with the four color measurement images 702 shown in FIG. 6 as a set is employed as a relative positional relationship. This is to increase the accuracy because various disturbances are applied to each set of measurement images 702 and slight variations in image position can occur. When the data acquisition by forming and reading the measurement image 702 is repeated a predetermined number of times, the CR controller 1003 calculates the color misregistration adjustment value that averages the relative misregistration of each color and corrects the average misregistration. The timing of laser exposure by the exposure unit 22 is determined based on the color misregistration adjustment value.

  In this embodiment, in the initial setting, a speed difference (that is, a peripheral speed difference) is provided for the target surface peripheral speeds of the photosensitive drum 10 and the intermediate transfer belt 24, and the photosensitive drum 10 is set slightly faster. . Note that the surface peripheral speed of the photosensitive drum 10 when the surface peripheral speed of the intermediate transfer belt 24 is 1, that is, the ratio of the surface peripheral speed of the photosensitive drum 10 to the surface peripheral speed of the intermediate transfer belt 24 is the peripheral speed difference. Define. The difference between the two may be defined as a peripheral speed difference. The photosensitive drum 10 is controlled to a target surface peripheral speed (hereinafter also abbreviated as “drum target surface peripheral speed”) by adjusting the duty ratio of the PWM drive signal output to the drum drive motor 41. The intermediate transfer belt 24 is adjusted to a target conveyance speed, that is, a target surface peripheral speed (hereinafter sometimes abbreviated as “belt target surface peripheral speed”) by adjusting a duty ratio of a PWM drive signal output to the belt drive motor 42. Be controlled. Since there is a difference in peripheral speed between the photosensitive drum 10 and the intermediate transfer belt 24, a frictional force is generated between them (primary transfer portion N). The dynamic friction coefficient between the two is referred to as a friction coefficient μb. 7 and 8, the transition of the load due to durability (multiple prints) when the target surface peripheral speed is not changed will be described.

  7 and 8 are diagrams showing transition of the load of the drum drive motor 41 due to durability. In these figures, the horizontal axis represents the number of durable images (number of prints), and the vertical axis represents the output PWM duty ratio (drum drive load) to the drum drive motor 41. If image formation is continued in a temperature-raised state (for example, a state in which the temperature of the machine is raised to 40 ° C.), the friction coefficient μb increases, and the drum driving load is indicated by the solid line in FIG. To rise. On the other hand, even if image formation is continued in a room temperature state (for example, the state where the inside of the apparatus is 30 ° C.), as shown by a dotted line in FIG.

  However, when image formation is started at room temperature and the mode is switched to a mode in which the in-machine temperature reaches 40 ° C. when the number of durable images reaches 10,000, as shown by the dotted line in FIG. The same level as the drum driving load when image formation is continued in this state. That is, the friction coefficient μb not only changes according to the number of durable images, but also has a characteristic that it becomes particularly large when the ambient temperature is high. It was found that when the drum driving load enters an area where the PWM duty ratio of the motor exceeds 60%, image defects such as color misregistration and banding are likely to occur. Preventing this is one of the objects of the present invention.

  FIG. 9 is a flowchart of the image forming process. The processing in this flowchart is realized by the CPU 100 reading and executing a program stored in a storage unit such as a ROM (not shown) provided in the controller 1001. This process is started when the apparatus power is turned on.

  In this process, first, “torque measurement” will be described. The torque measurement is an operation for measuring the driving load of the photosensitive drum 10 when the photosensitive drum 10 and the drum driving motor 41 are controlled to the respective target surface peripheral speeds. Torque measurement is performed for each color (each photosensitive drum 10). In the torque measurement, the drum detection torque 45 corresponding to the photosensitive drum 10 causes the drum drive torque T, which is the output torque of the drum drive motor 41, to be the first torque Ta (first information) and the second torque Tb (second Information). The first torque Ta is information regarding the rotational torque of the drum drive motor 41 and is the drum drive torque T in the “predetermined operation state” of the developing device 1. The predetermined operation state is a state in which the developing sleeve 8 is rotationally driven and the developing bias is on during the post-rotation period. Even during a period when image formation is not intended, a little toner adheres to the non-image forming area of the photosensitive drum 10. Then, the toner is supplied to the primary transfer portion N. Such toner is referred to as fog toner.

  On the other hand, the second torque Tb is information relating to the rotational torque of the belt drive motor 42, and is the drum drive torque T in a state where the rotational drive of the developing sleeve 8 is stopped and the developing bias is off in the post-rotation period. In this state, since fog toner hardly occurs, the amount of toner supplied to the primary transfer portion N is smaller than in the predetermined operation state. Note that the second torque Tb may be measured in a state where either the rotation driving of the developing sleeve 8 or the developing bias is stopped (off). The dynamic friction coefficient between the photosensitive drum 10 and the intermediate transfer belt 24 changes between when the toner is present and when there is no toner, and the friction coefficient μb is smaller when the toner is present. Therefore, when the drum target surface peripheral speed is higher than the belt target surface peripheral speed, the second torque Tb is usually larger than the first torque Ta (Ta <Tb).

  Note that the period of the predetermined operation state is included in the first period in which the image is transferred from the photosensitive drum 10 to the intermediate transfer belt 24. The first torque Ta is acquired with the photosensitive drum 10 rotating in the first period. The second torque Tb is acquired in a state where the photosensitive drum 10 is rotated in a second period in which no image is transferred from the photosensitive drum 10 to the intermediate transfer belt 24.

  The flowchart of FIG. 9 will be described. First, in step S101, the controller 1001 waits for the input of an image forming job from the user, and starts the processing of the image forming job when the image forming job is input. Next, the controller 1001 determines whether or not a predetermined number (for example, 200 images) of images have been output since the previous torque measurement (step S102). Information about the number of output images is stored in a nonvolatile memory (not shown). If a predetermined number of images have not been output since the previous torque measurement, the controller 1001 determines whether or not the image forming job has ended (step S103). As a result of the determination, if the image forming job has not ended as a result of the determination, the controller 1001 returns the process to step S102. On the other hand, when the image forming job is completed, the controller 1001 performs the first torque for each color in a predetermined operation state of the developing device 1 in the post-rotation period, that is, in a state where the primary transfer portion N has fog toner. Ta is measured (step S104).

  Next, the controller 1001 stops the development drive (step S105). Then, the controller 1001 measures the second torque Tb for each color at least after the rotation of the developing sleeve 8 is stopped and the developing bias is turned off, that is, in the state where there is almost no fog toner in the primary transfer portion N. (Step S106). Next, the controller 1001 determines whether or not the power of the image forming apparatus is turned off (step S112). If the power is not turned off, the process returns to step S101 while the power is turned off. In the case where it is found, the process of FIG. 9 is terminated.

  As a result of the determination in step S102, when a predetermined number of images are output from the previous torque measurement, the controller 1001 controls the image forming controller 1100 to temporarily stop the image forming operation (step S107). That is, exposure and visualization of the electrostatic latent image are stopped. Immediately thereafter, the developing device 1 is in a predetermined operating state in a state where the developing drive is operating. The controller 1001 measures the first torque Ta for each color in a predetermined operation state of the developing device 1, that is, in a state where the primary transfer portion N has fog toner (step S108). Next, the controller 1001 stops the development drive (step S109). In step S110, the controller 1001 measures the second torque Tb for each color in the same manner as in step S106. Thereafter, the controller 1001 controls the image forming controller 1100 to restart the image forming operation (step S111), and returns the process to step S102. Information on the first torque Ta and the second torque Tb measured by this process is stored in a storage unit (not shown).

  FIGS. 10 and 11 respectively show the first torque Ta and the second torque when the drum target surface peripheral speed is constant and the drum target surface peripheral speed is changed before and after the endurance in the temperature rising state. It is a figure which shows the transition of Tb. In these figures, the horizontal axis represents the speed setting value (%) of the photosensitive drum 10, and the vertical axis represents the output PWM duty ratio to the drum drive motor 41. Here, the speed set value corresponds to a target value of the peripheral speed difference, and when the speed set value is 0%, the target value of the peripheral speed difference is zero. However, the actual peripheral speed difference is not always zero due to the tolerances of each part and the change of friction. In the initial setting, the speed setting value is, for example, + 0.15% (the drum target surface peripheral speed is faster).

  Since the friction coefficient μb is not so large in the initial state before the endurance progress, as shown in FIG. 10, both the changes in the first torque Ta and the second torque Tb are not large even if the speed set value is changed. In addition, when the primary transfer portion N has fog toner, the friction coefficient μb is not so large. Therefore, as shown by the dotted lines in FIGS. 10 and 11, the change in the first torque Ta does not change even if the speed set value is changed. not big. However, in the temperature rise state, if the speed setting value is increased in a state in which the durability has advanced and the primary transfer portion N has almost no fog toner, as shown by the solid line in FIG. The torque Ta of 1 greatly increases.

  In FIG. 11, the speed setting value (about + 0.05%) when the diagram of the first torque Ta and the diagram of the second torque Tb intersect is when the actual peripheral speed difference is zero. It is considered that this is the speed setting value. The speed setting controller 1002 uses the torques Ta and Tb obtained in the process of FIG. 9 to change the speed setting values described in FIG. 12, so that the point at which the torques Ta and Tb intersect, that is, the peripheral speed difference is zero. Move the speed setting value closer to the point. This avoids an excessive increase in drum driving torque. In the process of FIG. 12, the photosensitive drum 10 is targeted for correction, and the speed setting controller 1002 executes a correction process for correcting the target surface peripheral speed of the photosensitive drum 10, but the target surface peripheral speed of the intermediate transfer belt 24 is Keep constant.

  The correction process for correcting the drum target surface peripheral speed and the color misregistration adjustment will be described with reference to FIG. FIG. 12 is a flowchart of the correction / adjustment process. The processing in this flowchart is realized by the CPU 100 reading and executing a program stored in a storage unit such as a ROM (not shown) provided in the controller 1001. This process is started when the apparatus power is turned on. Steps S202 to S205 and S207 to S210 are performed for each color.

  First, the controller 1001 determines whether or not the temperature rise in the machine since the previous execution of the correction process (change of the speed setting value) has exceeded a predetermined temperature TS (T−Th> TS?) (Step S201). . The predetermined temperature TS is, for example, 2 ° C. The temperature rise is a difference (T−Th) between the current temperature T and the change temperature Th. If T−Th> TS is established, the temperature inside the apparatus has increased so as to greatly affect the friction coefficient μb. Therefore, the controller 1001 determines whether or not the torque difference ΔT with and without toner exceeds a predetermined value TQ. (ΔT> TQ) is determined (step S202). The torque difference ΔT is a difference (Tb−Ta) between the second torque Tb and the first torque Ta, and is acquired by the speed setting controller 1002 from the stored values of the torque Ta and Tb. The speed setting controller 1002 serves as an acquisition unit in the present invention. The predetermined value TQ is, for example, 10%.

  Then, the controller 1001 advances the process to step S211 when ΔT> TQ is not satisfied. On the other hand, if ΔT> TQ is satisfied, it can be determined that the friction coefficient μb has increased, so the controller 1001 determines that the correction timing for executing the correction processing has come, and executes step S203 and subsequent steps. . Here, the controller 1001 determines the correction timing based on the current temperature T and the acquired torque difference ΔT. In step S203, the controller 1001 controls the speed setting controller 1002 to update the speed setting value of the photosensitive drum 10 according to Equation 1. This is the correction process. The controller 1001 serves as a changing unit that changes the speed setting value.

[Equation 1]
Sd (n + 1) = Sd (n) -g (Tb-Ta)
Here, Sd (n) is the speed setting value before the change, and Sd (n + 1) is the speed setting value after the change. g is a feedback gain. A value obtained by subtracting the drum target surface peripheral speed corresponding to Sd (n + 1) from the drum target surface peripheral speed corresponding to Sd (n) is a correction amount determined by the controller 1001. As the feedback gain g, a value is adopted so that the speed set value is corrected in a direction in which the peripheral speed difference is reduced. For example, when the difference (Tb−Ta) that is the torque difference ΔT is positive, the gain g is set to a value that satisfies Sd (n + 1) ≦ Sd (n). The gain g is determined by the speed setting controller 1002 as a value that satisfies the above-described condition, or may be a fixed value with a sufficient margin for satisfying the above-described condition.

  In determining the gain g, it is desirable to set a value determined according to the current belt target surface peripheral speed of the intermediate transfer belt 24 on the non-correction side as a limit in the correction direction of the speed setting value. This is because it is not preferable that the magnitude relationship between the drum target surface peripheral speed and the belt target surface peripheral speed is reversed. The value determined according to the belt target surface peripheral speed is a speed setting value corresponding to the belt target surface peripheral speed, or a speed setting value corresponding to a value faster than the belt target surface peripheral speed by a predetermined margin value. There may be.

  Next, the controller 1001 acquires the current temperature T, which is the current in-flight temperature detected by the temperature detection unit 1005, and stores this current temperature T in the storage unit (not shown) as the current change temperature Th (Step S100). S204). Next, the controller 1001 controls the CR controller 1003 to correct the image forming timing in accordance with the correction amount of the drum target surface peripheral speed obtained by correcting the speed setting value in the correction process performed in step S203. (Step S205). That is, the CR controller 1003 calculates the exposure position shift amount associated with the change of the drum target surface peripheral speed, and changes the image writing timing so as to correct it. This avoids image degradation. By executing the processes of steps S201 to S205, the speed set value can be updated based on the temperature change and the torque difference ΔT even when the color misregistration adjustment timing does not arrive.

  Next, the controller 1001 determines whether or not the power of the image forming apparatus is turned off (step S211). If the power is not turned off, the process returns to step S201 while the power is turned off. In the event that there is a failure, the processing in FIG. 12 is terminated.

  If T−Th> TS is not satisfied as a result of the determination in step S201, the controller 1001 executes step S206 and subsequent steps because the temperature inside the apparatus does not increase so much as to significantly affect the friction coefficient μb. In step S206, the controller 1001 determines whether or not the execution timing of the color misregistration adjustment mode has arrived. As described above, the execution timing of the color misregistration adjustment mode is a predetermined timing determined by an instruction from the user, execution of a predetermined number of prints, or the like.

  Then, when the execution timing of the color misregistration adjustment mode has arrived, the controller 1001 determines whether or not the torque difference ΔT with or without toner exceeds a predetermined value TQ (ΔT> TQ), as in step S202. Step S207). Then, the controller 1001 advances the process to step S210 when ΔT> TQ is not satisfied. On the other hand, if ΔT> TQ is satisfied, the controller 1001 determines that the correction timing for executing the correction process has come, and executes step S208 and subsequent steps. In steps S208 and S209, the controller 1001 executes correction processing, storage of the changed temperature Th, and the like, as in steps S203 and S204. Next, the controller 1001 controls the CR controller 1003 to execute the color misregistration adjustment mode for each color (step S210). Thereafter, the process proceeds to step S211.

  7, 8, 13, and 14, the case where the correction process (change of the drum target surface peripheral speed) is performed and the case where the correction process is not performed are compared by the process of FIG. 12. FIGS. 13 and 14 are diagrams showing the transition of the load of the drum drive motor 41 due to durability when the correction process is performed. In these figures, the definitions of the horizontal axis and the vertical axis are the same as those in FIGS.

  When image formation is continued in the temperature rise state (in-machine temperature 40 ° C.), the drum driving load increases as shown by the solid line in FIG. 7 unless correction processing is performed. On the other hand, when the correction process is performed, as shown in FIG. 13, the drum driving load does not become extremely high and remains in a substantially constant range. Also, when image formation is started at room temperature and the interior temperature suddenly rises when the number of durable images reaches 10,000, if the correction process is not performed, the drum driving load is as shown by the dotted line in FIG. Soaring. On the other hand, when the correction process is performed, as shown in FIG. 14, the sudden increase in the drum driving load is suppressed and remains in a substantially constant range. In this embodiment, since the drum driving load does not exceed 60% in terms of the PWM duty ratio, image defects such as color misregistration and banding are less likely to occur, and a high-quality image is maintained.

  As a comparative example with respect to the present embodiment, the correction process (change of the drum target surface peripheral speed) is not performed in response to the temperature rise, and the correction process is performed only when the timing of the color misregistration adjustment mode arrives. The transition of the drum driving load in this case will be described with reference to FIG. Although not shown, the speed setting value change sequence of the comparative example corresponds to a flowchart composed of steps S206 to S211 by omitting steps S201 to S205 from the flowchart of FIG. That is, the speed setting value can be updated only when the timing for executing the color misregistration adjustment mode has arrived.

  FIG. 15 is a diagram illustrating a load transition of the drum drive motor 41 due to durability when the speed setting value change sequence of the comparative example is performed. In these drawings, the definitions of the horizontal axis and the vertical axis are the same as those in FIG. When image formation is started at room temperature and the number of durable images reaches 10,000, the temperature inside the apparatus suddenly rises. If the correction process corresponding to the temperature rise is not performed, the drum driving load is shown by the dotted line in FIG. Soaring as shown. The drum driving load is not as high as that indicated by the dotted line in FIG. 8, but is higher than that shown in FIG. As a result, the drum driving load may exceed 60% in PWM duty ratio. That is, the control cannot follow the change in the friction coefficient μb accompanying the sudden rise in the in-machine temperature, and color misregistration and banding may occur.

  According to the present embodiment, whether to change the speed setting value of the photosensitive drum 10 based on the torques Ta and Tb is controlled based on the detected temperature. That is, it is determined that the temperature rise from the previous execution of the correction process (change of the speed setting value) exceeds the predetermined temperature TS, and the torque difference ΔT (Tb−Ta) with or without toner exceeds the predetermined value TQ. The timing is determined to be the correction timing. Then, correction processing is executed at the correction timing. In the correction process, the speed set value is corrected in a direction in which the peripheral speed difference becomes smaller based on the torque difference ΔT. As a result, the peripheral speed difference is reduced when the friction increases due to temperature change or durability, so image degradation such as banding and color misregistration due to an increase in frictional force between the photosensitive drum 10 and the intermediate transfer belt 24 is suppressed. Can do.

  In addition, when the timing at which the color misregistration adjustment mode should be performed has arrived and the torque difference ΔT exceeds a predetermined value TQ, correction processing is executed before the color misregistration adjustment mode is performed. Thus, the correction process is originally executed at the timing when the downtime occurs, so that the occurrence of the downtime can be suppressed.

  Further, since the value determined according to the current belt target surface peripheral speed of the intermediate transfer belt 24 during the correction process is set as a limit in the correction direction of the speed setting value, the drum target surface peripheral speed, the belt target surface peripheral speed, It is possible to avoid image degradation caused by reversal of the magnitude relationship between the two. Further, the photosensitive drum 10 exists for each color, and the correction process is executed for each photosensitive drum 10, so that the target surface peripheral speed can be optimally corrected in each photosensitive drum 10.

  The acquisition timing of the torque difference ΔT (Tb−Ta) is not limited to the time when the image forming job is completed as described with reference to FIG. 9 or the time when a predetermined number of images are output from the previous torque measurement. For example, in the processing of FIG. 12, it may be acquired before the correction processing (steps S203 and S208).

  In the present embodiment, in the correction process, the photosensitive drum 10 is targeted for correction, and the drum target surface peripheral speed is corrected based on the torque difference ΔT acquired from the drum driving load. However, the present invention is not limited to this, and the torque difference ΔT to be used may be acquired from the driving torque (belt driving load) of the intermediate transfer belt 24.

  Further, either the photosensitive drum 10 or the intermediate transfer belt 24 may be set as a correction target, and the intermediate transfer belt 24 may be set as a correction target. In this case, for example, in an image forming apparatus having a single photosensitive drum 10, the torque difference ΔT is acquired from the drum driving load or the belt driving load, and the belt target surface peripheral speed is corrected based on the torque difference ΔT in the correction process. To do. Further, the limit in the correction direction of the speed setting value may be a value determined according to the target surface peripheral speed on the non-correction target side (the other of the photosensitive drum 10 and the intermediate transfer belt 24).

  The present invention can be applied to various image forming apparatuses such as a copying machine, a printer, and a facsimile using an electrophotographic system.

  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.

DESCRIPTION OF SYMBOLS 1 Developing device 10 Photosensitive drum 24 Intermediate transfer belt 41 Drum drive motor 42 Belt drive motor 45 Torque detection unit 1001 Controller 1002 Speed setting controller 1005 Temperature detection unit

Claims (24)

A motor,
Image forming means for forming an image on a photosensitive member driven to rotate by the motor;
An intermediate transfer member to which the image on the photosensitive member is transferred;
Control means for controlling the motor such that the rotational speed of the photoconductor becomes a target speed;
Changing means for changing the target speed;
Temperature detection means for detecting temperature;
In the first period during which the image is transferred from the photosensitive member to the intermediate transfer member, first information on rotational torque of the motor in a state where the photosensitive member is rotated is acquired, and the photosensitive member is transferred to the intermediate transfer member. Obtaining means for obtaining second information relating to a rotational torque of the motor in a state where the photoconductor is rotated in a second period in which the image is not transferred,
Whether the changing unit changes the target speed of the photoconductor based on the first information and the second information acquired by the acquiring unit based on the temperature detected by the temperature detecting unit. An image forming apparatus characterized by controlling the above.   The change means determines a correction timing based on the temperature, the first information, and the second information, and changes the target speed of the photoconductor at the determined correction timing. The image forming apparatus according to 1.   The changing unit is configured to detect a timing at which a temperature increase from the previous change of the target speed of the photoconductor exceeds a predetermined temperature and a difference between the first information and the second information exceeds a predetermined value. The image forming apparatus according to claim 2, wherein the timing is determined to be correction timing.   The said changing means determines a correction amount based on the first information and the second information, and changes the target speed of the photoconductor by the determined correction amount. The image forming apparatus according to any one of the above.   5. The image formation according to claim 1, wherein the first period includes a period in which the developer carrying member of the developing unit is rotationally driven and the developing bias is on. apparatus. The control unit controls the conveyance speed of the intermediate transfer member to be a target speed;
The changing unit is configured to change the target speed of the photoconductor in a direction in which the speed difference is reduced when there is a speed difference between the target speed of the photoconductor and the target speed of the intermediate transfer body. The image forming apparatus according to any one of claims 1 to 5.   The image forming apparatus according to claim 6, wherein the changing unit changes the target speed of the photoconductor using a value determined according to the target speed of the intermediate transfer member as a limit in a correction direction. .   8. The apparatus according to claim 1, wherein the acquisition unit acquires the first information and the second information every time a predetermined number of images are formed by the image forming unit. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the acquisition unit acquires the first information and the second information when an image forming job ends.   10. The image forming timing according to claim 1, wherein when the target speed of the photoconductor is changed, the control unit corrects the image forming timing in accordance with a correction amount of the target speed of the photoconductor. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the acquisition unit acquires the first information and the second information from a load of the motor. The photoreceptor exists for each color,
The image forming apparatus according to claim 1, wherein the changing unit controls whether to change the target speed for each photoconductor. The photoreceptor exists for each color,
The control unit is capable of performing an adjustment mode in which an image for measurement is formed on the intermediate transfer member and an image forming timing for each color is adjusted based on a result of reading the image for measurement.
The changing unit determines that the timing before the adjustment mode is performed is the correction timing when the timing at which the adjustment mode should be performed has arrived and the difference exceeds the predetermined value. The image forming apparatus according to claim 3. A motor,
Image forming means for forming an image on the photoreceptor;
An intermediate transfer member that is rotationally driven by the motor and to which the image on the photosensitive member is transferred;
Control means for controlling the motor so that the conveyance speed of the intermediate transfer member becomes a target speed;
Changing means for changing the target speed;
Temperature detection means for detecting temperature;
In the first period during which the image is transferred from the photosensitive member to the intermediate transfer member, first information on rotational torque of the motor in a state where the photosensitive member is rotated is acquired, and the photosensitive member is transferred to the intermediate transfer member. Obtaining means for obtaining second information relating to a rotational torque of the motor in a state where the photoconductor is rotated in a second period in which the image is not transferred,
Whether the changing unit changes the target speed of the intermediate transfer body based on the first information and the second information acquired by the acquiring unit based on the temperature detected by the temperature detecting unit. An image forming apparatus that controls whether or not.   The change unit determines a correction timing based on the temperature, the first information, and the second information, and changes the target speed of the intermediate transfer member at the determined correction timing. Item 15. The image forming apparatus according to Item 14.   The changing means is a timing at which the temperature rise from the previous change of the target speed of the intermediate transfer member exceeds a predetermined temperature and the difference between the first information and the second information exceeds a predetermined value, The image forming apparatus according to claim 15, wherein the correction timing is determined.   The change means determines a correction amount based on the first information and the second information, and changes the target speed of the intermediate transfer member by the determined correction amount. The image forming apparatus according to any one of 16.   18. The image formation according to claim 14, wherein the first period includes a period in which the developer carrying member of the developing unit is rotationally driven and the developing bias is on. apparatus. The control means controls the rotational speed of the photoconductor to be a target speed,
The changing unit changes the target speed of the intermediate transfer member in a direction in which the speed difference decreases when there is a speed difference between the target speed of the photosensitive member and the target speed of the intermediate transfer member. The image forming apparatus according to claim 14, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 19, wherein the changing unit changes the target speed of the intermediate transfer member using a value determined according to the target speed of the photosensitive member as a limit in a correction direction. .   21. The apparatus according to claim 14, wherein the acquisition unit acquires the first information and the second information every time a predetermined number of images are formed by the image forming unit. Image forming apparatus.   21. The image forming apparatus according to claim 14, wherein the acquisition unit acquires the first information and the second information at the end of the image forming job.   15. The image forming timing is corrected according to a correction amount of the target speed of the intermediate transfer body when the target speed of the intermediate transfer body is changed. 23. The image forming apparatus according to any one of 22 above.   24. The image forming apparatus according to claim 14, wherein the acquisition unit acquires the first information and the second information from a load of the motor.

Images