JP5887909B2 - Image forming apparatus and control method thereof - Google Patents

Description

  The present invention provides a monochrome unit having a function of pressing a transfer unit against an image carrier carrying a toner image and transferring the toner image on the image carrier onto a sheet through the sheet between the image carrier and the transfer unit. The present invention relates to an image forming apparatus suitable for being applied to a color printer, a copying machine, and a composite machine of these, and a control method thereof.

  In recent years, there have been color printers that form color images based on color image information, color copiers that have a scan function that reads an image of an original and outputs an image signal for color image reproduction, and multifunction devices. It has been increasingly used. For example, digital color image forming apparatuses that acquire RGB (Red), Green (G), and Blue (B) RGB image data and form a color image based on the image data are widely used. Yes.

  In this type of image forming apparatus, RGB image data is color-converted into yellow (Y), magenta (M), cyan (C), and black (BK) YMCK image data. A color toner image is formed on the basis of YMCK image data by an image forming unit employing an electrophotographic method. The image forming unit includes image forming units that share Y, M, C, and BK image forming output functions. The image forming unit stores image data on a photosensitive drum that is uniformly charged by a charging unit for each image forming color. Based on this, an electrostatic latent image is formed by an optical writing unit (PH: Printer Head) using a polygon mirror or the like.

  The electrostatic latent image is developed by the developing device for each image forming color. The color toner image formed on the photosensitive drum by performing such charging, exposure and development is superimposed on the intermediate transfer belt, and the superimposed color toner image is transferred onto the sheet by the transfer unit. The sheet is transported from the sheet feeding tray to the transfer section by the sheet feeding section. The toner image transferred onto a predetermined sheet is fixed by a fixing device. Thereby, a color image based on the image data can be formed on a predetermined sheet.

  FIG. 13 is a diagram illustrating a configuration example of a transfer system of an image forming apparatus 300 according to a conventional example. The transfer system of the image forming apparatus 300 shown in FIG. 13 includes an intermediate transfer belt 1, a transfer pressure contact / separation mechanism 15, and a secondary transfer unit 70. The intermediate transfer belt 1 has an endless belt shape and carries a toner image formed by an image forming unit (not shown). The intermediate transfer belt 1 is stretched around an intermediate transfer roller 2, a driven roller 3, and other driven rollers (not shown).

  A secondary transfer unit 70 is disposed below the intermediate transfer belt 1. The secondary transfer unit 70 is disposed in the vicinity of the intermediate transfer belt 1 and can be pressed against and separated from the intermediate transfer belt 1, and the toner image carried on the intermediate transfer belt 1 is transferred onto the paper P when pressed. To be made.

  The secondary transfer unit 70 includes a secondary transfer roller 10, a transfer driving roller 11, a driven roller 12, a secondary transfer belt 13, and a transfer unit driving motor (not shown). A secondary transfer belt 13 is stretched around the secondary transfer roller 10 via a transfer driving roller 11 and a driven roller 12.

  A transfer cleaning unit 14 is provided below the secondary transfer roller 10, and the transfer cleaning unit 14 has a cleaning blade 14a. The cleaning blade 14 a is in contact with the secondary transfer roller 10 and has a structure capable of cleaning the toner agent remaining on the surface of the secondary transfer roller 10.

  A transfer pressure contact / separation mechanism 15 is disposed below the secondary transfer unit 70. The transfer pressure contact / separation mechanism 15 has a structure in which the secondary transfer unit 70 can be pressed against and separated from the intermediate transfer belt 1. The secondary transfer portion 70 shown in FIG. 13 is in a state of being pressed against the intermediate transfer belt 1. These constitute the transfer system of the image forming apparatus 300.

  Based on the constant speed / constant current (torque) switching drive system of the secondary transfer unit 70, the transfer system of the image forming apparatus 300 adopts the FB control system of the sheet passing cycle in order to cope with the load change at the beginning of the operation. doing. This FB control method is based on the average speed of the secondary transfer roller 10 during the first sheet passing after the secondary transfer unit 70 is pressed against the intermediate transfer belt 1, and is applied to the second and subsequent sheets of paper P. With respect to the magnification of the formed image, the same image magnification as that of the first image can be compensated.

  FIG. 14A and FIG. 14B are diagrams showing a relationship example (part 1) between the transfer load and the image magnification versus elapsed time. The vertical axis shown in FIG. 14A is the transfer load, and the horizontal axis is the elapsed time T. In the figure, a solid line is a transfer load curve, and shows a change transition of the transfer load with respect to the elapsed time T. The transfer load is generated when the secondary transfer unit 70 is in pressure contact with the intermediate transfer belt 1. A broken line in the figure is a torque command value of the motor for driving the transfer unit. A torque command value for driving the motor for driving the transfer unit is stored and fixed in a storage unit (not shown).

  The vertical axis shown in FIG. 14B is the image magnification, and the horizontal axis is the elapsed time T. In the figure, a solid line is an image magnification change curve, and shows a change transition of the image magnification with respect to the elapsed time T. The change in image magnification occurs when the secondary transfer unit 70 is pressed against the intermediate transfer belt 1. A one-dot chain line in the figure is a reference value of the image magnification, and is an image magnification when the first page 1 image is transferred after the secondary transfer unit 70 is pressed against the intermediate transfer belt 1.

  After the operation is started, a constant torque command value read from the storage unit is set in the transfer unit driving motor, and constant torque and constant speed control is executed. With this constant torque and constant speed control, the second page 2 image transfer, the third page 3 image transfer, the fourth page 4 image transfer, etc. are shown in FIG. 14A. As the transfer load is reduced, the image magnification tends to increase.

  The increasing tendency of the image magnification is constant torque control of the torque command value stored in the storage unit after the press contact with respect to the torque command value acquired in the constant speed state before the press contact of the secondary transfer unit 70 and stored in the storage unit. In FIG. 14, since the load of the transfer cleaning unit 14 changes, it is considered that a change in image magnification as shown in FIG. 14B occurs.

  The change in the transfer load itself was sufficiently slow, and it was assumed that the change in the material of the secondary transfer belt 13 and the transfer cleaning unit 14 changes with time (changes gradually throughout life). However, in reality, the transfer load is a phenomenon in which the material change throughout the life is large and changes in a short time (several tens of sheets) depending on the cleaning configuration (such as lubricant application) of the secondary transfer roller 10. I found out.

  According to the constant speed / constant current (torque) switching drive system of the secondary transfer unit 70 described above, if the load on the secondary transfer unit 70 changes in a short time, the intermediate transfer belt 1-the paper P-the secondary transfer unit 70. Each sliding state also changes, and there is a problem that the image magnification on the paper P changes.

  Therefore, as a solution to this problem, the average speed of the secondary transfer roller 10 measured during the nip in the constant torque state after the secondary transfer unit 70 is pressed is stored as a reference value. Then, for the second and subsequent sheets, the average speed of the secondary transfer roller 10 during each sheet passing period is measured, and the measurement result of the average speed is compared with the reference value of the average speed stored in the storage unit. A control system that determines the constant torque command value for the next sheet from the difference was adopted. This control method is FB control of the sheet passing period with reference to the average speed of the secondary transfer roller 10 when the first sheet is passed after the secondary transfer unit 70 is pressed.

  FIG. 15A and FIG. 15B are diagrams showing a relationship example (part 2) between the transfer load and the image magnification versus elapsed time. According to the countermeasure example for preventing the change in the image magnification, in order to prevent the tendency of the image magnification to increase with the reduction of the transfer load shown in FIG. 15A, the first sheet after the press contact of the secondary transfer unit 70 is performed. The average speed of the transfer driving motor during the sheet passing is measured and stored as a reference value in the storage unit.

  Similarly, for the second and subsequent sheets, the average speed of the motor during the sheet passing period is measured, and the difference between the reference value stored in the storage unit and the average speed of the motor is measured and fed back to the constant torque command value of the next sheet. (FB) A control method. When this FB control works normally, as a result, the load torque corresponding to the average load of the motor during the sheet passing period is set as the torque command value of the next sheet. It becomes possible to maintain the same image magnification as the image magnification of the first sheet.

  According to this FB control, since a command value changing method in the sheet passing cycle is adopted, the speed of the intermediate transfer belt 1 due to the torque change from the secondary transfer unit 70 to the intermediate transfer belt 1 which is the original purpose of constant torque control. Image degradation due to fluctuations does not occur. That is, by this FB control, it is possible to adopt a configuration in which the same image magnification as that of the first sheet can be compensated for during the continuous sheet passing period after press contact. Note that the mechanism for transferring the toner image from the intermediate transfer belt 1 to the secondary transfer unit 70 does not achieve the effect because the FB control is not in time for the transfer of the second Page 2 image in the figure. I understood.

  FIG. 16 is a diagram illustrating an example of FB control after the secondary transfer unit 70 is separated and re-pressed. The vertical axis shown in FIG. 16 is the image magnification, and the horizontal axis is the elapsed time T. In the figure, three alternate long and short dash lines are, in order from the bottom, the lower limit image magnification V− ′, the center image magnification V0, and the upper limit image magnification V + ′. The square marks indicate the corresponding number of sheets P. In the drawing, a rectangular portion surrounded by a broken line is a section (period) in which the secondary transfer portion 70 is separated and re-pressed. According to the FB control after the start of the operation, the image magnification changes with reference to the center image magnification V0. According to the FB control after the separation and re-pressure contact of the secondary transfer unit 70 for the first time, the image magnification is changed with reference to the lower limit image magnification V- '. According to the FB control after the second secondary transfer unit 70 separated and re-pressed, the image magnification changes with the upper limit image magnification V + ′ as a reference.

  Differences such as the lower limit image magnification V− ′ and the upper limit image magnification V + ′ with respect to the center image magnification V0 are generated every time the secondary transfer portion 70 is separated and re-pressed. This is because the FB control is executed based on the average speed of the subsequent first sheet.

  Note that, regarding an image forming apparatus having a function of cleaning a transfer portion, the image forming apparatus disclosed in Patent Document 1 includes an image carrier, a transfer rotating body, a cleaning unit, a driving unit, and a control unit. Is done. The image carrier carries a toner image, and the transfer rotator rotates by forming a transfer nip with the image carrier. The cleaning unit rubs the transfer rotator to remove toner attached to the transfer rotator.

  The driving unit applies a driving force to the transfer rotator so that the transfer rotator moves in the same direction as the image carrier at the transfer nip. The control unit controls the driving unit based on the usage history of the cleaning unit. Based on these assumptions, the control unit controls the driving force applied to the transfer unit by the driving unit in accordance with at least one of the usage history of the cleaning unit and the amount of moisture in the air. By configuring the image forming apparatus in this way, it is possible to increase the load on the intermediate transfer belt while preventing the occurrence of slippage on the transfer surface between the recording material and the intermediate transfer belt while maintaining high cleaning performance. .

  Further, regarding an image forming apparatus including an intermediate transfer belt, according to the image forming apparatus disclosed in Patent Document 2, a transfer roller and a secondary transfer roller for driving an intermediate transfer belt, a motor for driving a transfer unit, a torque command A value detection unit, a setting unit, a determination unit, and a control unit are included. The transfer roller drives the intermediate transfer belt. The transfer unit driving motor is connected to the control means and rotates the secondary transfer roller. The secondary transfer roller transfers the toner image formed on the intermediate transfer belt to the recording paper. The torque command value detection means is connected to the control means and detects a torque command value for the motor for driving the transfer section.

  The setting means is connected to the control means and sets a lower limit value of the torque command value. The determination means determines whether or not the torque command value detected by the torque command value detection means exceeds a lower limit value. The control means controls the motor based on the determination result to the determination means. Based on these assumptions, the control means performs a secondary operation so that when the torque command value exceeds the lower limit value, the difference between the surface speed of the intermediate transfer belt and the peripheral speed of the second rotating body is within a predetermined range. The drive of the transfer roller was controlled. By configuring the image forming apparatus in this way, it is possible to execute speed control so as to eliminate speed fluctuations in the peripheral speed of the secondary transfer roller and the surface speed of the intermediate transfer belt without causing an increase in parts or cost. Is.

JP 2008-304552 A (page 5 FIG. 2) JP 2009-009103 A (Page 6 FIG. 2)

By the way, according to the image forming apparatus provided with the separation pressure contact mechanism of the transfer portion according to the conventional example, there are the following problems.
i. According to the transfer control example after the separation re-pressure contact as shown in FIG. 16, a compensation configuration is adopted in which the same image magnification as that of the first sheet is obtained in the continuous sheet passing period after the pressure contact of the secondary transfer unit 70. However, when image density, registration correction, or the like is necessary during the execution of the image forming job, the secondary transfer unit 70 is once separated (opened) from the intermediate transfer belt 1 and is pressed again. In such a case, if the average speed of the first sheet after the press contact is used as a reference, a difference occurs in the reference value stored in the storage unit depending on the degree of change in the transfer load. As a result, the image magnification before and after the re-press contact is increased. There is a problem that a difference such as an upper limit image magnification V + ′ and a lower limit image magnification V− ′ occurs with respect to the center image magnification V0.

  ii. In the transfer control example after the above-mentioned separation re-pressure contact, after the first pressure contact operation is completed and the secondary transfer unit 70 is once separated (released), the reference value at the time of the next pressure contact becomes the same value. It does not compensate for this. This is because the reference value may be measured in a state where the load of the secondary transfer unit 70 is different from the load of the transfer cleaning unit 14 or the like. For this reason, during the execution of the image forming job, when the secondary transfer unit 70 is separated (released) under some condition and is pressed again, the image magnification changes before and after this, and is different before and after the separated pressure welding. There is a problem that an image is formed and output. As a result, there is a problem that the number of paper breaks increases, and the change width of the image magnification increases throughout the entire image forming job.

  iii. According to the image forming apparatus found in Patent Document 1, the control unit controls the driving force applied to the transfer unit by the driving unit according to at least one of the usage history of the cleaning unit and the amount of moisture in the air. I made it. Therefore, even if the load on the intermediate transfer belt can be increased and slippage on the transfer surface between the recording material and the intermediate transfer belt can be prevented while maintaining high cleaning performance, the change in image magnification throughout the entire job can be prevented. The current situation is that the width cannot be kept to a minimum.

  iv. According to the image forming apparatus disclosed in Patent Document 2, when the torque command value exceeds the lower limit value, the control unit determines that the difference between the surface speed of the intermediate transfer belt and the peripheral speed of the second rotating body is within a predetermined range. Thus, the drive of the secondary transfer roller is controlled. Accordingly, even if the speed control can be executed so as to eliminate the speed fluctuation of the peripheral speed of the secondary transfer roller and the surface speed of the intermediate transfer belt without increasing the number of parts and the cost, the intermediate transfer belt and the secondary transfer belt There is a problem that torque transfer between the transfer rollers (load fluctuation with respect to the intermediate transfer belt) occurs.

  In view of the above, the present invention solves the above-described problems, and can reduce the number of paper breaks to the minimum number even when the transfer unit is separated and re-pressed during execution of an image forming job. In addition, an object of the present invention is to provide an image forming apparatus and a control method therefor that can keep the change width of the image magnification throughout the entire job to a minimum.

In order to solve the above-mentioned problem, an image forming apparatus according to claim 1 is capable of pressing and separating an image carrier that carries a toner image, and the image carrier, and the image carrier during pressure contact. A transfer unit that transfers a toner image carried on the body onto a sheet; a transfer drive unit that rotationally drives the transfer unit based on a predetermined command value; and a command value that is set in the transfer drive unit and the transfer unit A control unit capable of constant speed control for rotationally driving at a constant speed and constant torque control for rotationally driving the transfer unit at a constant torque, and the control unit separates the transfer unit from the image carrier. In accordance with a constant speed driving torque detected when performing the constant speed control of the transfer driving unit in a state where the transfer unit is in constant contact, the transfer driving unit performs constant torque control with the transfer unit being pressed against the image carrier, After the pressure contact of the transfer driving unit, based on the image forming job. The average speed of the transfer driving unit obtained by measuring when the first first sheet is passed through the transfer unit is stored as a reference value in a predetermined storage unit, and the second and subsequent sheets When the sheet is passed through the transfer section, the average speed of the transfer drive section is measured, and the transfer of the next sheet is calculated from the difference between the measured average speed of the transfer drive section and the reference value of the average speed of the transfer drive section. A constant torque command value at the time is calculated and the command value is changed, and during the execution of the image forming job, it is monitored whether separation and re-pressure contact are performed in the transfer unit, An average speed of the transfer driving unit and a reference value of the average speed stored in the storage unit obtained by measuring when the first image based on the image forming job after the press contact is transferred onto the sheet are obtained. If the difference between the two is outside the allowable range, the first toner image after re-pressing is transferred. If the difference between the two is within an allowable range, the first toner image after re-pressing is transferred and fixed, and the sheet is fixed to the normal tray. It is characterized by being discharged.

According to the image forming apparatus of the first aspect, the image forming apparatus includes the image carrier, the transfer unit, the transfer driving unit, and the control unit. The image carrier carries a toner image. The transfer unit can be pressed against and separated from the image carrier, and transfers the toner image carried on the image carrier to the paper during the pressure contact. The transfer driving unit rotationally drives the transfer unit based on a predetermined command value. The control unit executes a constant speed control for setting a command value in the transfer driving unit and rotationally driving the transfer unit at a constant speed, and a constant torque control for rotating the transfer unit at a constant torque. The control unit is in a state in which the transfer unit is pressed against the image carrier in accordance with a constant speed driving torque detected when the transfer unit is controlled at a constant speed with the transfer unit being separated from the image carrier. Then, constant torque control of the transfer driving unit is performed. After the press contact, the average speed of the transfer driving unit obtained by measuring when the first first sheet based on the image forming job is passed through the transfer unit is stored as a reference value in a predetermined storage unit. The control unit measures the average speed of the transfer driving unit when the second and subsequent sheets are passed through the transfer unit, and measures the average speed of the transfer driving unit and the reference value of the average speed of the transfer driving unit. The constant torque command value at the time of transfer of the next sheet is calculated from the difference between and the command value is changed. Based on these assumptions, the control unit monitors whether or not separation and re-pressure contact have been performed in the transfer unit during execution of the image formation job, and performs a first operation based on the image formation job after separation re-pressure contact of the transfer unit. The average speed of the transfer driving unit obtained by measuring when the first image is transferred to the sheet is compared with the reference value of the average speed stored in the storage unit, and the difference between them is outside the allowable range. In this case, the sheet on which the first toner image after re-pressing is transferred and fixed is discharged to a waste tray. If the difference between the two is within an allowable range, the first toner after re-pressing is The sheet on which the image has been transferred and fixed is discharged to a normal tray (discharge control during re-press contact).

  By this paper discharge control at the time of re-pressing, the first toner image after the re-pressure contact is transferred and fixed, and the paper is discharged as a test paper without making a normal output, or the first sheet after the re-pressure contact. The sheet on which the toner image is transferred and fixed can be used as a normal output.

According to a second aspect of the present invention, in the first aspect, the control unit performs measurement when the first image based on the image forming job after the separation re-pressure contact of the transfer unit is transferred to a sheet. If by subtracting the reference value of the average speed and the average speed stored in the storage unit of the transfer drive portion thus obtained is outside the permissible range, further, a constant torque during the transfer of the next sheet from the difference A command value is calculated and the command value is changed.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the control unit performs measurement when the first image based on the image forming job after the separation re-pressure contact of the transfer unit is transferred to a sheet. If by subtracting the reference value of the average speed and the average speed stored in the storage unit of the transfer drive portion thus obtained is within the allowable range, further, a constant torque during the transfer of the next sheet from the difference A command value is calculated and the command value is changed.

  According to another aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier that carries a toner image; and a pressure image that can be pressed against and separated from the image carrier; A transfer unit that transfers to a sheet; a transfer drive unit that rotationally drives the transfer unit based on a predetermined command value; and a constant speed that sets the command value in the transfer drive unit and rotationally drives the transfer unit at a constant speed. And a control unit capable of constant torque control for rotationally driving the transfer unit with a constant torque, and the control unit is configured to move the transfer drive unit in a state where the transfer unit is separated from the image carrier. According to the constant speed driving torque detected when performing the constant speed control, the transfer driving part is controlled in constant torque while the transfer part is in pressure contact with the image carrier, and after the pressing of the transfer driving part , The first first sheet based on the image forming job When the average speed of the transfer driving unit obtained by measurement when passing through the transfer unit is stored as a reference value in a predetermined storage unit, and the second and subsequent sheets are passed through the transfer unit Then, the average speed of the transfer driving unit is measured, and a constant torque command value at the time of transfer of the next sheet is calculated from the difference between the measured value of the average speed of the transfer driving unit and the reference value of the average speed of the transfer driving unit. The command value is changed, and during the execution of the image forming job, it is monitored whether separation and re-pressure contact are performed in the transfer unit, and during the execution of the image forming job, the separation and separation of the transfer unit are monitored. When re-pressing is detected, it is determined whether the images based on the image forming jobs before and after the separation re-pressure contact of the transfer portion are the same, and the images based on the image forming jobs before and after the separation re-pressure contact of the transfer portion are determined. If they are not the same, when passing the first first sheet of the image forming job The stored reference value of the average speed of the transfer drive unit is read from the storage unit, and the first toner image after the re-press contact is transferred and fixed, and the sheet is discharged to a waste tray, The measured value of the average speed of the transfer driving unit obtained by measuring when the first sheet after press contact is passed through the transfer unit, and the average speed of the transfer driving unit read from the storage unit A constant torque command value at the time of transfer of the next sheet is calculated from a difference from a reference value, and the command value is changed.

According to a fifth aspect of the present invention, there is provided a method for controlling an image forming apparatus, comprising: an image carrier that carries a toner image; and the image carrier that can be pressed and separated from the image carrier; A transfer unit that transfers a toner image onto a sheet, a transfer drive unit that rotationally drives the transfer unit based on a predetermined command value, and a command value that is set in the transfer drive unit to drive the transfer unit at a constant speed. And a control unit capable of constant torque control for rotationally driving the transfer unit with a constant torque, the control unit comprising: The transfer unit is pressed against the image carrier in accordance with a constant speed drive torque detected when the constant speed control of the transfer drive unit is executed in this state. The step of constant torque control of the transfer drive unit, Passing the first first sheet based on the image forming job through the transfer unit and storing the average speed of the transfer drive unit obtained by measurement at that time in a predetermined storage unit as a reference value Passing the second and subsequent sheets through the transfer section and measuring the average speed of the transfer drive section; and the measured average speed of the transfer drive section and the average speed of the transfer drive section. A step of calculating a constant torque command value at the time of transfer of the next sheet from a difference from the reference value and changing the command value, and whether or not separation and re-pressure contact are performed at the transfer unit during execution of the image forming job And an average speed of the transfer driving unit obtained by measuring when the first image based on the image forming job after the separation re-pressure contact of the transfer unit is transferred to a sheet, and the comparing the reference value of the average speed stored in the storage unit If the difference between the two is outside the allowable range, the first toner image after re-pressing is transferred, and the paper after the toner image is transferred is discharged to a waste tray, and the difference between the two is within the allowable range. In this case, the first toner image after re-pressing is transferred, and the step of discharging the paper after the toner image transfer to a normal tray is executed.

  The control method of the image forming apparatus according to claim 6, wherein the image bearing member carrying a toner image and the image bearing member can be pressed and separated from the image bearing member, and are carried on the image bearing member at the time of pressing. A transfer unit that transfers a toner image onto a sheet, a transfer drive unit that rotationally drives the transfer unit based on a predetermined command value, and a command value that is set in the transfer drive unit to drive the transfer unit at a constant speed. And a control unit capable of constant torque control for rotationally driving the transfer unit with a constant torque, the control unit comprising: The transfer unit is pressed against the image carrier in accordance with a constant speed drive torque detected when the constant speed control of the transfer drive unit is executed in this state. The step of constant torque control of the transfer drive unit, Passing the first first sheet based on the image forming job through the transfer unit and storing the average speed of the transfer drive unit obtained by measurement at that time in a predetermined storage unit as a reference value Passing the second and subsequent sheets through the transfer section and measuring the average speed of the transfer drive section; and the measured average speed of the transfer drive section and the average speed of the transfer drive section. A step of calculating a constant torque command value at the time of transfer of the next sheet from a difference from the reference value and changing the command value, and whether or not separation and re-pressure contact are performed at the transfer unit during execution of the image forming job If the separation and re-pressure contact of the transfer unit are detected during execution of the image forming job and whether the images based on the image forming job before and after the separation re-pressure contact of the transfer unit are the same. To determine whether the transfer portion is separated When the images based on the subsequent image forming job are not the same, the reference value of the average speed of the transfer driving unit stored at the time of passing the first first sheet of the image forming job is read from the storage unit, Measured when the first toner image after the re-pressure contact is transferred and fixed is discharged to a waste tray and the first sheet after the re-pressure contact is passed through the transfer section. A constant torque command value at the time of transfer of the next sheet is calculated from a difference between the measured value of the average speed of the transfer driving unit obtained from the reference value of the average speed of the transfer driving unit read from the storage unit, and And a step of changing the command value.

According to the control method of the image forming apparatus according to claim 1 and the image forming apparatus according to claim 5, it is monitored whether separation and re-pressure contact are performed in the transfer unit during execution of the image forming job. A controller, and the controller is configured to measure the average speed of the transfer driver obtained by measuring when the first image based on the image forming job after the separation re-pressure contact of the transfer unit is transferred to the sheet. The reference value of the average speed stored in the storage unit is compared, and if the difference between the two is outside the allowable range, the first toner image after the re-press contact is transferred and fixed, and the paper used as a waste tray When the difference between the two is within an allowable range, the sheet on which the first toner image after re-pressing is transferred and fixed is discharged to a normal tray.

  With this configuration, the sheet on which the first toner image after re-pressing is transferred and fixed is discharged as a test paper without normal output, or the first toner image after re-pressing is transferred. The fixed sheet can be used as a normal output. Therefore, the torque relationship with the image carrier is appropriately adjusted not only for long-term changes in the environment of the load applied to the transfer portion, but also for the short-term fluctuations at the beginning of the image forming operation. Thus, it is possible to minimize a change in image magnification caused by a short-term load change while minimizing unnecessary load fluctuations on the image carrier to prevent deterioration in image quality.

  In addition, even if the transfer unit is separated and re-pressed during the execution of the image forming job, the number of paper breaks can be minimized, and the change width of the image magnification throughout the job can be kept to a minimum. become.

According to the image forming apparatus of the second aspect, the control unit performs transfer obtained by measuring the first image based on the image forming job after the separation re-pressure contact of the transfer unit is transferred to the sheet. If the difference between the reference value of the average speed and the average speed stored in the storage unit of the driving unit is outside the allowable range is further to calculate the constant torque command value at the time of transfer of the next sheet from the difference command value Therefore, the sheet on which the first toner image after re-pressing is transferred and fixed can be handled as a test sheet without making a normal output. In addition, after the re-pressing, the constant torque command value for the next sheet is calculated using only the measured value of the average speed of the transfer driving unit obtained by measuring when the first sheet is passed through the transfer unit. The command value can be changed.

According to the image forming apparatus of the third aspect, the control unit performs transfer obtained by measuring when the first image based on the image forming job after the separation unit is pressed again is transferred to the sheet. when the difference of the average speed of the drive unit and the reference value of the average speed stored in the storage unit is within the allowable range, further, it calculates a constant torque command value at the time of transfer of the next sheet from the difference command value Therefore, the first toner image after the re-pressure contact is transferred and fixed, and the sheet is discharged to the normal tray. Therefore, the first toner image after the re-pressure contact is transferred and fixed. Paper can be handled as regular output.

  According to the image forming apparatus according to claim 4 and the image forming apparatus control method according to claim 6, when the separation and re-pressure contact of the transfer unit are detected during execution of the image forming job, the transfer unit is separated again. It is determined whether or not the images based on the image forming jobs before and after the press contact are the same, and if the images based on the image forming jobs before and after the separated re-pressing are not the same, the first first sheet of the image forming job The reference value of the average speed of the transfer driving unit stored at the time of passing the sheet is read from the storage unit, and the first toner image after the re-press contact is transferred and fixed, and the sheet is discharged to a waste tray. A measurement value of the average speed of the transfer driving unit obtained by measuring when the first sheet after re-pressing is passed through the transfer unit, and a reference of the average speed of the transfer driving unit read from the storage unit The constant torque command value when transferring the next sheet is calculated from the difference from the value. Since changing the instruction value out, together it makes it possible to reduce Yabukami minimize number, comprising the range of change in image magnification through the entire job can be held to a minimum.

1 is a conceptual diagram showing a configuration example of an image forming apparatus 100 as a first embodiment according to the present invention. It is a figure which shows the FB control example of the 1st sheet after separation / re-pressure welding. 2 is a block diagram illustrating a configuration example of a transfer and paper discharge control system in the image forming apparatus 100. FIG. 3 is a flowchart illustrating an example of control in a transfer and paper discharge system of the image forming apparatus 100. 6 is a flowchart illustrating an example of transfer and paper discharge control after separation / re-pressing of the image forming apparatus 100. FIG. 6 is a conceptual diagram illustrating a configuration example of a transfer system and a paper discharge system in an image forming apparatus 200 as a second embodiment. It is explanatory drawing which shows the example of a press-contact state of an intermediate transfer and a secondary transfer system. (A) And (B) is a figure which shows the example of FB control after separation / re-pressure welding. 2 is a block diagram illustrating a configuration example of a transfer and paper discharge control system in the image forming apparatus 100. FIG. 5 is a flowchart illustrating an example of control in a transfer and paper discharge system of the image forming apparatus 200. 6 is a flowchart illustrating an example (part 1) of transfer and paper discharge control after separation / re-pressure contact in the image forming apparatus 200. 6 is a flowchart illustrating an example (part 2) of transfer and paper discharge control after separation / re-pressure contact in the image forming apparatus 200. FIG. 10 is a conceptual diagram illustrating a configuration example of a transfer system of an image forming apparatus 300 according to a conventional example. (A) And (B) is a figure which shows the example (the 1) of a relationship between transfer load and image magnification versus elapsed time. (A) And (B) is a figure which shows the example of a relationship (the 2) of transfer load and image magnification versus elapsed time. FIG. 6 is a diagram illustrating an example of FB control after separation and re-pressure contact of the secondary transfer unit.

  Hereinafter, an image forming apparatus and a control method thereof according to an embodiment of the present invention will be described with reference to the drawings. The description in this section does not limit the technical scope described in the claims, the meaning of terms, and the like.

  An image forming apparatus 100 shown in FIG. 1 is suitable for application to a black and white printer, a copying machine, or a complex machine thereof. The image forming apparatus 100, the transfer unit 16, the fixing device 17, and the normal and disposal devices are used. The trays 24 and 25 and the transfer pressure contact / separation mechanism 80 are provided.

  In this example, the image forming unit 7 that forms a monochrome image includes the photosensitive drum 4, the optical writing unit 8, the developing unit 9, the cleaning unit 18, and the charging unit 19. The photosensitive drum 4 constitutes an example of an image carrier and carries a toner image. For example, in the image forming unit 7, the photosensitive drum 4 is uniformly charged to a predetermined potential by the charger 19. An electrostatic latent image based on image information is formed on the photosensitive drum 4 after charging by the optical writing unit 8. The electrostatic latent image formed on the photosensitive drum 4 is developed by the developing device 9, and a toner image is formed on the photosensitive drum 4.

  A transfer unit 16 is disposed below the photosensitive drum 4. The transfer unit 16 is pressure-bonded to the photoconductive drum 4, and the toner image on the photoconductive drum 4 is transferred to the paper P through the paper P between the photoconductive drum 4 and the transfer unit 16. The transfer unit 16 includes, for example, a transfer unit driving motor 30, a transfer belt 32, a transfer driving roller 33, and a driven roller 34. A transfer belt 32 is stretched around the transfer drive roller 33 via a driven roller 34. The transfer unit 16 can be pressed against and separated from the photosensitive drum 4, and transfers the toner image formed on the photosensitive drum 4 onto the paper P during the pressing. The toner image remaining on the photosensitive drum 4 is removed by the cleaning unit 18.

  A transfer pressure contact / separation mechanism 15 is disposed below the transfer unit 16. The transfer pressure contact / separation mechanism 15 has a structure in which the transfer unit 16 can be pressed against and separated from the photosensitive drum 4. For example, the transfer pressure contact / separation mechanism 15 includes a transfer belt 32, a transfer drive roller 33, and a driven roller 34. It is possible to move downward. The transfer pressure contact / separation mechanism 15 presses the transfer portion 16 against the photosensitive drum 4 and transfers the toner image formed on the photosensitive drum 4 onto the paper P.

  A fixing device 17 is provided on the downstream side of the transfer unit 16. The fixing device 17 fixes the toner image transferred onto the paper P by the transfer unit 16. The fixing device 17 is provided with a pressure roller and a heating roller (not shown). The pressure roller and the heating roller heat-fix the toner image transferred to the paper P by applying heat.

  The normal and disposal trays 24 and 25 are provided on the downstream side of the fixing device 17. In this example, the tray 24 is pressed and separated from the tray 24, and then sequentially from the first sheet corresponding to the re-press contact discharge control. The fixed paper P is discharged as regular output paper. Alternatively, the fixed sheets P are discharged in order from the second sheet after the first sheet is discarded as a test sheet to the tray 25. After the press contact and separation to the tray 25, the first sheet P after fixing is discarded as a test sheet corresponding to the re-press contact discharge control.

  Note that p1 shown in FIG. 1 indicates a driving speed of the transfer unit 16 (hereinafter referred to as a transfer driving speed) when the paper P (first sheet: hereinafter also referred to as a front sheet) is passed through the transfer unit 16. It is a position where measurement of the average value of is started. The position p1 is set in the transport direction of the paper P. p2 is a position where the measurement of the average value of the transfer driving speed is completed. A section p1-p2 is a section in which an average value of the transfer driving speed is measured. p3 is the position of the leading end of the next sheet P (second sheet: hereinafter also referred to as the next sheet).

  Further, L1 shown in the drawing is a distance from the light irradiation position of the optical writing unit 8 to the nip position of the transfer unit 16 (hereinafter referred to as an exposure-transfer distance). The light irradiation position is the arrival position of the light beam irradiated from the optical writing unit 8 to the photosensitive drum 4. L2 is a distance between the positions p2 and p3, and is a distance from the position p2 at which the measurement / average speed of the previous sheet is completed to the leading edge position p3 of the next sheet. L3 is a distance between the positions p1 and p2, and is a distance from the position p1 to obtain the measurement / average speed of the front sheet to the position p2.

  In the monochrome image forming apparatus 100, a relationship such as L1 <L2 is set between the distance L1 and the distance L2. When such a relationship of L1 <L2 is set, in the image forming apparatus 100, after the measurement of the transfer driving speed of the transfer unit 16 of the front sheet and the acquisition of the average speed are completed, the exposure by the optical writing unit 8 is started. Even in this case, the image can be formed on the leading edge of the next sheet in time. That is, the measurement of the transfer driving speed of the front paper (paper P (first sheet)) and the detection result of the average speed acquisition, in particular, require time for preparing a soft image. This is a model that can be reflected in image formation of paper (paper P (second sheet)).

  Here, with reference to FIG. 2, an example of the first FB control after the separation / re-pressure contact in the photosensitive drum 4 and the transfer unit 16 according to the first embodiment will be described. In this embodiment, when separation and re-compression of the transfer unit 16 occur during execution of an image forming job, the average speed stored in the first sheet of the image forming job is used as a reference value. I made it. This reference value is not the average speed of the first sheet after each re-bonding.

  The vertical axis shown in FIG. 2 is the image magnification, and the horizontal axis is the elapsed time T. In the figure, three alternate long and short dash lines are, in order from the bottom, the lower limit image magnification V−, the center image magnification V0, and the upper limit image magnification V +. The square marks indicate the corresponding number of sheets P.

  The example of paper discharge control in this example is applied to the case where the measurement result of the transfer driving speed of the previous paper (paper P (first sheet)) and the acquisition result of the average speed is the next paper (paper P (second sheet) )) This model can be reflected in the image formation. That is, according to the monochrome image forming apparatus 100, the contents of the image forming job before and after the separation and re-pressing of the transfer unit 16 are excluded from the paper discharge control condition, and the first one at the start of the image forming job. The average speed of the transfer unit 16 stored in the eye is set as a reference value (see I in the figure).

  Furthermore, the measured value of the average speed of the motor 30 for driving the transfer unit obtained by measuring when the first sheet P after the separation / re-pressure contact of the transfer unit 16 is passed through the transfer unit 16, and the storage When the difference from the reference value of the average speed of the motor 30 read from the unit 6 is included in the speed allowable range, the sheet P on which the first toner image after the re-press contact is transferred and fixed is usually used. Then, a constant torque command value at the time of transferring the next sheet is calculated from the difference, and the command value is changed (see II and IV in the figure).

  In addition, the measured value of the average speed of the motor 30 for driving the transfer unit obtained by measuring when the first sheet P after the separation / re-pressing of the transfer unit 16 is passed through the transfer unit 16 is stored. When the difference from the reference value of the average speed of the motor 30 read from the unit 6 is out of the allowable speed range, the paper P on which the first toner image after the re-press contact is transferred and fixed is used as a waste tray. The constant torque command value at the time of transferring the next sheet is calculated from the difference and the command value is changed (see III in the figure). In the above-described discharge control example, a condition for discharging the first sheet P after the separation / re-pressure contact of the transfer unit 16 is set as a first re-pressure transfer condition.

  According to the first re-pressure contact transfer condition, regardless of the image based on the image forming job before and after the re-pressure contact, when the first image is OK, the first tray 24 is used as it is as a regular image formation output as it is. Eject the paper. If the first sheet is NG, the first sheet is discharged as a test sheet to the disposal tray 25, the first image is formed on the second sheet, and the second and subsequent sheets are used for normal use. The paper is discharged to the tray 24.

  Next, a configuration example of a transfer and discharge control system in the image forming apparatus 100 will be described with reference to FIG. The transfer and discharge control system of the image forming apparatus 100 shown in FIG. 3 includes the control unit 5, the storage unit 6, and the discharge switching unit 27, and includes a transfer unit driving motor 30 and a photosensitive drum. The drive motor 40, the pressure contact / separation drive motor 150, and the normal and waste trays 24 and 25 are controlled. The control unit 5, the storage unit 6, and the motors 30, 40, 150 constitute a transfer control system, and the paper discharge switching unit 27 and the trays 24, 25 constitute a paper discharge control system.

  The control unit 5 controls the motors 40, 150, 30 and the like that are driven corresponding to the photosensitive drum 4, the transfer pressure contact / separation mechanism 15, the transfer drive roller 33, and the like shown in FIG. A central processing unit (CPU) and a program for operating it are mainly configured.

  A storage unit 6 is connected to the control unit 5. The storage unit 6 includes a read only memory (ROM), a memory (Random Access Memory: RAM) in which information can be written and read as needed, and a nonvolatile memory. The storage unit 6 stores a system program for controlling the transfer control system and control information for controlling the paper discharge control system. For example, when the power is turned on, the control unit 5 that has detected the power-on information reads the system program from the storage unit 6 and develops it in the RAM, activates the transfer and discharge control system, and performs the transfer and discharge. The control system is controlled.

  A motor 40 for driving the photosensitive drum is connected to the control unit 5. The photosensitive drum 4 is connected to the drive shaft of the motor 40 via a drive force transmission mechanism 41. The motor 40 is a DC brushless motor. The control unit 5 transmits a predetermined torque command value to the motor 40. The torque command value includes a PWM signal S41 that controls the speed and torque of the motor 40.

  The motor 40 rotates the photosensitive drum 4 via the driving force transmission mechanism 41 based on the torque command value. A rotation sensor (not shown) is attached to the motor 40, the rotation sensor detects the rotation of the motor 40, and the speed information D 40 detected here is fed back to the control unit 5. Note that a known sensor such as a Hall element can be used as the rotation sensor, and the present invention is not limited to a specific sensor.

  In addition to the motor 40, the controller 5 is connected to a transfer unit drive motor 30 that constitutes an example of a transfer unit drive unit. A transfer drive roller 33 is connected to the drive shaft of the motor 30 via a drive force transmission mechanism 31. The motor 30 is a DC brushless motor. The control unit 5 transmits a predetermined torque command value to the motor 30. The torque command value includes a PWM signal S31 for controlling the speed and torque of the motor 30.

  The motor 30 rotates the transfer driving roller 33 via the driving force transmission mechanism 31 based on the torque command value. The transfer belt 32 is rotated in a predetermined direction by the rotation of the transfer driving roller 33. A rotation sensor (not shown) is also attached to the motor 30, the rotation sensor detects the rotation of the motor 30, and the speed information D <b> 30 detected here is fed back to the control unit 5. Note that a known sensor such as a Hall element can be used as the rotation sensor, and the present invention is not limited to a specific sensor.

  In addition to the motors 30, 40, a pressure contact / separation driving motor 150 is connected to the control unit 5. A transfer pressure contact / separation mechanism 15 is connected to a drive shaft of the motor 150 via a drive force transmission mechanism 151. The motor 150 is a DC brushless motor. The control unit 5 transmits a predetermined operation command value to the motor 150. The operation command value is a control signal S51 for controlling the pressure contact / separation operation of the transfer pressure contact / separation mechanism 15.

  The motor 150 drives the transfer pressure contact / separation mechanism 15 via the driving force transmission mechanism 151 based on the operation command value. The transfer pressure contact / separation mechanism 15 moves the transfer unit 16 upward and downward. A position detection sensor (not shown) is attached to the transfer pressure contact / separation mechanism 15, and the position detection sensor detects the position of the transfer unit 16 during pressure contact and separation, and the detected pressure contact / separation information D 15 is fed back to the control unit 5. Is done. Note that a known sensor such as a reflective or transmissive optical sensor can be used as the position sensor, and the present invention is not limited to a specific sensor.

  A paper discharge switching unit 27 is connected to the control unit 5. The paper discharge switching unit 27 performs paper discharge selection control based on the paper discharge control signal S27 during re-pressure contact paper discharge control. The paper discharge control signal S27 is a signal for selecting the normal and disposal trays 24 and 25, and is output from the control unit 5 to the paper discharge switching unit 27.

  In the paper discharge selection control during the re-pressure contact paper discharge control, for example, when the difference between the measured value of the average speed of the motor 30 for driving the transfer unit and the reference value of the average speed of the motor 30 is within the allowable speed range. Selects the normal tray 24 based on the paper discharge control signal S27, and discharges the paper P after the fixing process from the fixing device 17 to the normal tray 24. As a result, the sheet P (regular output) on which the first toner image after re-pressing is transferred and fixed is discharged to the normal tray 24.

  If the difference between the measured value of the average speed of the transfer section driving motor 30 and the reference value of the average speed of the motor 30 is out of the allowable speed range, the disposal is performed based on the paper discharge control signal S27. The tray 25 is selected, and the paper P after the fixing process is discharged from the fixing device 17 to the disposal tray 25. As a result, the sheet P on which the first toner image after the re-pressure contact is transferred and fixed can be handled as a test sheet without making a normal output.

  The control unit 5 sets a command value to the transfer unit driving motor 30 and executes constant speed control for rotating the transfer belt 32 at a constant speed and constant torque control for rotating the transfer belt 32 at a constant torque. . For example, the control unit 5 performs transfer according to a constant speed driving torque detected when performing constant speed control of the transfer unit driving motor 30 with the transfer belt 32 being separated from the photosensitive drum 4. The constant torque control of the transfer unit driving motor 30 is executed in a state where the belt 32 is in pressure contact with the photosensitive drum 4.

  The control unit 5 is obtained by measuring when the first first sheet P based on the image forming job is passed through the transfer unit 16 after the transfer belt 32 is pressed against the photosensitive drum 4. The average speed of the transfer unit driving motor 30 is stored in the predetermined storage unit 6 as a reference value. The control unit 5 measures the average speed of the motor 30 for driving the transfer unit when the second and subsequent sheets of paper P are passed through the transfer unit 16, and the measured value of the average speed of the motor 30 and the motor 30 are measured. The constant torque command value at the time of transferring the next sheet is calculated from the difference from the reference value of the average speed, and the command value is changed.

  Further, when the control unit 5 detects the separation and re-pressure contact of the transfer unit 16 during execution of the image forming job, the first re-pressure transfer condition is set when the first first sheet of the image forming job is passed. The stored reference value of the average speed of the transfer unit driving motor 30 is read from the storage unit 6, and is obtained by measurement when the first sheet P is passed through the transfer unit 16 after re-pressing. It is determined whether or not the difference between the measured value of the average speed of the transfer unit driving motor 30 and the reference value of the average speed of the motor 30 read from the storage unit 6 is included in the allowable speed range.

  When the difference is out of the allowable speed range, the control unit 5 discharges the sheet P on which the first toner image after re-pressing is transferred and fixed to the discard tray 25, and transfers the next sheet from the difference. The constant torque command value is calculated and the command value is changed. Further, when the difference is within the allowable speed range, the control unit 5 discharges the sheet P on which the first toner image after re-pressing is transferred and fixed to the normal tray 24, and from the difference, The constant torque command value at the time of transferring the next sheet is calculated and the command value is changed.

  Next, with reference to FIGS. 4 and 5, an example of control in the transfer and discharge system of the image forming apparatus 100 will be described. In this example, the first re-contact transfer condition is applied, and the measurement result of the transfer driving speed of the previous paper (paper P (first sheet)) and the average speed acquisition result are the following paper (paper P (two sheets) This is a model that can be reflected in the image formation of the eye)) and controls the transfer and discharge system in the monochrome image forming apparatus 100.

  Under these control conditions, in step ST1 shown in FIG. 4, the control unit 5 keeps the transfer unit 16 and the photosensitive drum 4 separated from each other, and the rotational speeds of the transfer unit 16 and the photosensitive drum 4 are constant. Thus, the control unit 5 performs constant speed control of the photosensitive drum driving motor 40 and the transfer unit driving motor 30 by feedback. At this time, the transfer unit 16 and the photosensitive drum 4 may be controlled to have the same rotation speed.

  The control unit 5 detects the constant speed driving torque of the motor 30 based on the PWM signal while the transfer unit driving motor 30 is controlled at a constant speed. The control unit 5 calculates an average torque command value from the detected constant speed driving torque. In addition, the torque command value can be determined by an appropriate method such as a center value, and the present invention is not limited to a specific method.

  Next, in step ST <b> 2, the control unit 5 activates a pressure contact / separation motor 150 to press the transfer unit 16 against the photosensitive drum 4. The transfer belt 32 is pressed against the photosensitive drum 4 in accordance with the constant speed driving torque detected at that time, and in this state, constant torque control of the transfer unit driving motor 30 is performed.

  Thereafter, in step ST3, the control unit 5 stops the operation of the press-separation motor 150 with the completion of the press-contact. When the press contact is completed, the control unit 5 continues the constant speed control of the motor 40 for driving the photosensitive drum and rotates the photosensitive drum 4 in step ST4. The control unit 5 performs constant torque control on the transfer unit driving motor 30 according to the constant speed driving torque detected in step ST2. By this constant torque control, the transfer unit 16 rotates. At this time, the control unit 5 passes the first first sheet P based on the image forming job after the press contact to the transfer unit 16 and measures the transfer unit driving motor 30 obtained by measurement at that time. The average speed is stored in a predetermined storage unit 6 as a reference value.

  Further, the control unit 5 passes the second and subsequent sheets of paper P through the transfer unit 16 and measures the average speed of the motor 30 for driving the transfer unit. Then, the control unit 5 calculates a constant torque command value at the time of transferring the next sheet from the difference between the measured value of the average speed of the motor 30 and the reference value of the average speed of the motor 30, and changes the command value.

  In step ST <b> 5, the control unit 5 monitors whether the separation unit and the re-pressure contact are performed in the transfer unit 16 during execution of the image forming job. If separation and re-press contact are not detected by the transfer unit 16 during execution of the image forming job, the process returns to step ST4 to continue control for changing the command value by calculating a constant torque command value at the time of transferring the next sheet. .

  During execution of the image forming job, when the controller 5 detects separation and re-pressure contact in the transfer unit 16 in step ST5 described above, separation re-pressure contact discharge control is executed in step ST6. For example, the process proceeds to step ST11 shown in FIG. In step ST11, the control unit 5 exposes the image of Page 1 onto the photosensitive drum 4 to form a toner image. Thereafter, the toner image is transferred from the photosensitive drum 4 to the paper P. At this time, the speed of the transfer unit driving motor 30 is measured. The control unit 5 updates the PWM value of the motor 30.

  Thereafter, in step ST12, the control unit 5 responds to whether or not the difference between the reference value of the average speed of the motor 30 for driving the transfer unit and the measured value of the average speed of the motor 30 is included in the allowable speed range. To branch control. At this time, the control unit 5 stores, as the first re-pressure contact transfer condition, the reference value of the average speed of the transfer unit driving motor 30 stored when the first sheet of the first image forming job is passed. After reading from the unit 6 and re-pressing, the measured value of the average speed of the motor 30 for driving the transfer unit obtained by measuring when the first sheet P is passed through the transfer unit 16, and from the storage unit 6 It is determined whether or not the difference between the read average speed of the motor 30 and the reference value is included in the allowable speed range.

  When the difference between the reference value of the average speed of the motor 30 and the measured value of the average speed of the motor 30 is out of the allowable speed range, the process proceeds to step ST13, and the control unit 5 re-executes according to the re-pressure contact transfer condition. The sheet P on which the first toner image after the pressure contact is transferred and fixed is discharged to a disposal tray 25. At this time, the paper discharge switching unit 27 selects the discard tray 25 based on the paper discharge control signal S27 output from the control unit 5. The controller 5 calculates a constant torque command value at the time of transferring the next sheet from the difference between the reference value of the average speed of the motor 30 and the measured value of the average speed of the motor 30, and changes the command value.

  Thereafter, in step ST14, the control unit 5 exposes the image [Reread] of Page 1 to the photosensitive drum 4 to form a toner image. Thereafter, the toner image is transferred from the photosensitive drum 4 to the paper P. At this time, the speed of the transfer unit driving motor 30 is measured. The control unit 5 updates the PWM value of the motor 30 for driving the transfer unit. Thereafter, the process proceeds to step ST16.

  If the difference between the reference value of the average speed of the motor 30 for driving the transfer unit and the measured value of the average speed of the motor 30 is included in the allowable speed range in step ST12 described above, the process proceeds to step ST15. The control unit 5 transfers the first toner image after re-pressing, fixes the toner image after transfer, and discharges the fixed paper P to the normal (regular) tray 24. At this time, the paper discharge switching unit 27 selects the normal tray 24 based on the paper discharge control signal S27 output from the control unit 50. Thereafter, the process proceeds to step ST16.

  In step ST <b> 16, the control unit 5 exposes the image [after page] 2 to the photosensitive drum 4 to form a toner image. Thereafter, the toner image is transferred from the photosensitive drum 4 to the paper P. At this time, the speed of the transfer unit driving motor 30 is measured. The control unit 5 updates the PWM value of the motor 30. Since the page P2 and the paper P after the image of the page 2 are fed back (FB), they are all discharged to the normal (regular) tray 24. At this time, the paper discharge switching unit 27 selects the normal tray 24 based on the paper discharge control signal S27 output from the control unit 5. Thereafter, the process proceeds to step ST17.

  In step ST17, the control unit 5 determines the end of the image forming operation. For example, when an EOF (end-off flag) indicating the last page of the image forming job is detected, the image forming operation (control) is terminated. If no EOF is detected, the process returns to step ST16 to repeat the image forming process.

  As described above, according to the image forming apparatus 100 according to the first embodiment, the difference between the measured value of the average speed of the transfer unit driving motor 30 and the reference value of the average speed of the motor 30 falls within the allowable speed range. In the case of deviation, the sheet P on which the first toner image after re-pressing is transferred and fixed can be handled as a test sheet without making a normal output. Moreover, after the re-pressing, only the measurement value of the average speed of the motor 30 for driving the transfer unit obtained by measuring when the first sheet P is passed through the transfer unit 16 is used for the next sheet. The constant torque command value can be calculated and the command value can be changed.

  In addition, when the difference between the measured value of the average speed of the motor 30 for driving the transfer unit and the reference value of the average speed of the motor 30 is included in the speed allowable range, the control unit 5 Since the paper P on which the first toner image is transferred and fixed is discharged to the normal tray 24, the paper P on which the first toner image after re-pressing is transferred and fixed is handled as a normal output. be able to.

  Next, a configuration example of the transfer system and the paper discharge system in the image forming apparatus 200 as the second embodiment will be described with reference to FIG. In this example, when the same and non-identical images based on the image forming job before and after the separation re-pressure contact of the secondary transfer unit 70 are transferred to the paper P as a second re-pressure contact transfer condition, Are not identical, the first sheet P after re-pressing is treated as a test sheet, and the second and subsequent sheets P are set as regular outputs. When the images are the same, the transfer system and the paper discharge system are controlled with the same contents as in the first embodiment.

  An image forming apparatus 200 shown in FIG. 6 includes an intermediate transfer belt 1, a transfer pressure contact / separation mechanism 15, a fixing device 17, normal and waste trays 24 and 25, an image forming unit 60, and a secondary transfer unit 70. Is done.

  For example, the image forming unit 60 includes an image forming unit for each image forming color of yellow, magenta, cyan, and black in order to form a color toner image. Each of the image forming units includes a photosensitive drum, a charger, an optical writing unit, a developing unit, a cleaning unit, and the like. In the image forming unit, the photosensitive drum is uniformly charged to a predetermined potential by the charger. An electrostatic latent image based on image information is formed on the photosensitive drum after charging by the optical writing unit. The electrostatic latent image formed on the photosensitive drum is developed by a developing device, and a toner image is formed on the photosensitive drum. The toner image formed on the photosensitive drum is transferred to the intermediate transfer belt 1 (primary transfer). The toner image remaining on the photosensitive drum is removed by the cleaning unit.

  Adjacent to the image forming unit 60, an intermediate transfer belt 1 constituting an example of an image carrier is provided. The intermediate transfer belt 1 has an endless belt shape and carries a toner image formed by the image forming unit 60. The intermediate transfer belt 1 is stretched around an intermediate transfer roller 2, a driven roller 3, and other driven rollers (not shown).

  Below the intermediate transfer belt 1, a secondary transfer unit 70 constituting an example of a transfer unit is disposed. The secondary transfer unit 70 is disposed in the vicinity of the intermediate transfer belt 1 and can be pressed against and separated from the intermediate transfer belt 1, and the toner image carried on the intermediate transfer belt 1 is transferred onto the paper P when pressed. To be made.

  The secondary transfer unit 70 includes a secondary transfer roller 10, a transfer driving roller 11, a driven roller 12, a secondary transfer belt 13, and a transfer unit driving motor 110. A secondary transfer belt 13 is stretched around the secondary transfer roller 10 via a transfer driving roller 11 and a driven roller 12.

  A transfer cleaning unit 14 is provided below the secondary transfer roller 10, and the transfer cleaning unit 14 has a cleaning blade 14a. The cleaning blade 14 a is in contact with the secondary transfer roller 10 and has a structure capable of cleaning the toner agent remaining on the surface of the secondary transfer roller 10.

  A transfer pressure contact / separation mechanism 15 is disposed below the secondary transfer unit 70. The transfer pressure contact / separation mechanism 15 has a structure in which the secondary transfer unit 70 can be pressed and separated from the intermediate transfer belt 1. For example, the secondary transfer roller 10, the transfer drive roller 11, the driven roller 12, 2, 2, 2. The next transfer belt 13 and the transfer cleaning unit 14 can be moved upward together.

  The secondary transfer unit 70 illustrated in FIG. 6 is in a state of being separated from the intermediate transfer belt 1. On the other hand, the secondary transfer unit 70 shown in FIG. 7 is in a state of being pressed against the intermediate transfer belt 1. A known configuration can be adopted for the transfer pressure contact / separation mechanism 15, and the configuration is not particularly limited in the present invention.

  A fixing device 17 is provided on the downstream side of the secondary transfer unit 70. The fixing device 17 fixes the toner image transferred onto the paper P by the secondary transfer unit 70. The fixing device 17 is provided with a pressure roller and a heating roller (not shown). The pressure roller and the heating roller heat-fix the toner image transferred to the paper P by applying heat.

  Normal and disposal trays 24 and 25 are provided on the downstream side of the fixing device 17, respectively. In this example, unlike the first embodiment, the tray 24 corresponds to re-pressure contact discharge control after being pressed and separated. After the first sheet is discarded as a test sheet in the tray 25, the fixed sheets P are discharged in order from the second sheet (first sheet reread). After the press contact and separation on the tray 25, the first sheet P after fixing is always discarded as a test sheet in accordance with the re-press contact discharge control.

  Here, with reference to FIGS. 8A and 8B, an example of the first FB control after separation / re-pressure contact in the intermediate transfer belt 1 and the secondary transfer unit 70 according to the second embodiment will be described. In this embodiment, when the separation and re-pressure contact of the secondary transfer unit 70 occurs during execution of the image formation job, the images related to the image formation job before and after the separation and re-pressure contact correspond to the same or not. Thus, the average speed stored in the first sheet of the image forming job is used as the reference value. This reference value is not the average speed of the first sheet after each re-bonding.

  Each vertical axis shown in FIGS. 8A and 8B is the image magnification, and the horizontal axis is the elapsed time T. In the figure, one dot-and-dash line is the center image magnification V0. The square marks indicate the corresponding number of sheets P. The example of paper discharge control in this example is applied to the case where the measurement result of the transfer driving speed of the previous paper (paper P (first sheet)) and the acquisition result of the average speed is the next paper (paper P (second sheet) )) This model cannot be reflected in the image formation. Even in a monochrome machine, a model having the intermediate transfer belt 1 cannot reliably perform feedback (FB) control, so this example is applied.

  For example, according to the tandem color image forming apparatus 200 having the intermediate transfer belt 1, the images related to the image forming jobs before and after the separation and re-pressure contact of the secondary transfer unit 70 are the same or not. Is included in the paper discharge control condition, and the transfer paper discharge control is executed using the average speed of the secondary transfer unit 70 stored in the first sheet at the start of the image forming job as a reference value (see I in the figure).

  As shown in FIG. 8A, when the images related to the image forming job before and after the separation and re-pressure contact of the secondary transfer unit 70 are the same, the first sheet after the separation / re-pressure contact of the secondary transfer unit 70 The measurement value of the average speed of the motor 30 for driving the transfer unit obtained by measuring when the paper P of the eye passes through the secondary transfer unit 70, and the reference of the average speed of the motor 30 read from the storage unit 6 When the difference from the value is included in the allowable speed range, the sheet P on which the first toner image after re-pressing is transferred and fixed is discharged to the normal tray 24, and the next sheet is calculated from the difference. The constant torque command value at the time of transfer is calculated and the command value is changed (see II in the figure).

  Further, when the images related to the image forming jobs before and after the separation and re-pressure contact of the secondary transfer unit 70 are the same, the first sheet P after the separation / re-pressure contact of the secondary transfer unit 70 is removed. A difference between a measured value of the average speed of the motor 30 for driving the transfer unit obtained by measuring when the paper is passed through the secondary transfer unit 70 and a reference value of the average speed of the motor 30 read from the storage unit 6 is obtained. When the speed is out of the allowable range, the sheet P on which the first toner image after re-pressing is transferred and fixed is discharged to the discard tray 25, and the constant torque command value at the time of transferring the next sheet is calculated from the difference. Calculate and change the command value (see III in the figure).

  As shown in FIG. 8B, when the images related to the image forming job before and after the separation and re-pressure contact of the secondary transfer unit 70 are not identical, the measured value of the average speed of the motor 30 for driving the transfer unit Including the case where the difference from the reference value of the average speed of the motor 30 is out of the allowable speed range, the paper P on which the first toner image after re-pressing is transferred and fixed is discarded regardless of the difference. The constant torque command value at the time of the next sheet transfer is calculated from the difference and the command value is changed (see II ′ and III in the figure). In the above-described discharge control example, the condition for discharging the first sheet P after the separation / re-pressure contact of the secondary transfer unit 70 is set as a second re-pressure contact transfer condition.

  According to the second re-pressure contact transfer condition, when the images based on the image forming jobs before and after re-pressure contact are the same, and the first image is OK, the first image is directly used as a regular image formation output. The paper is discharged onto a normal tray 24. When the images based on the image forming jobs before and after the re-pressing are the same, and the first sheet is NG, the first sheet is discharged as a test sheet to the disposal tray 25 and the second sheet The first image is formed on the sheet, and the second and subsequent sheets are discharged to the normal tray 24.

  If the images based on the image forming jobs before and after the re-pressing are not identical, the first sheet is surely discharged to the disposal tray 25 as a test sheet. In the case where the images based on the image forming job after the re-pressing are not the same, the second and subsequent sheets are discharged to the normal tray 24 without making a determination.

  Next, a configuration example of a transfer and paper discharge control system in the image forming apparatus 100 will be described with reference to FIG. The transfer and discharge control system of the image forming apparatus 100 shown in FIG. 9 includes the storage unit 6, the discharge switching unit 27, and the control unit 50, and includes an intermediate transfer belt driving motor 20 and a transfer unit. The driving motor 110, the pressure contact / separation driving motor 150, and the normal and waste trays 24 and 25 are controlled. The control unit 50, the storage unit 6, and the motors 20, 110, and 150 constitute a transfer control system, and the paper discharge switching unit 27 and the trays 24 and 25 constitute a paper discharge control system.

  The control unit 50 controls the intermediate transfer belt 1, the secondary transfer roller 10, the motors 20, 110, and 150 that drive the transfer pressure contact / separation mechanism 15 shown in FIG. ) And programs for operating the same.

  The storage unit 6 is connected to the control unit 50. The storage unit 6 includes a ROM, a RAM, and a nonvolatile memory. The storage unit 6 stores a system program for controlling the transfer control system and control information for controlling the paper discharge control system. For example, when the power is turned on, the control unit 50 that has detected the power-on information reads the system program from the storage unit 6 and develops it in the RAM, activates the transfer and discharge control system, and performs the transfer and discharge. The control system is controlled.

  The controller 50 is connected to a motor 20 for driving the intermediate transfer belt. The intermediate transfer roller 2 is connected to the drive shaft of the motor 20 via a drive force transmission mechanism 21. The motor 20 is a DC brushless motor.

  The control unit 50 transmits a predetermined torque command value to the motor 20. The torque command value includes a PWM signal S21 for controlling the speed and torque of the motor 20. The motor 20 rotates the intermediate transfer roller 2 via the driving force transmission mechanism 21 based on the torque command value. The intermediate transfer belt 1 is rotated in a predetermined direction by the rotation of the intermediate transfer roller 2.

  A rotation sensor (not shown) is attached to the motor 20, the rotation sensor detects the rotation of the motor 20, and the speed information D <b> 20 detected here is fed back to the control unit 50. Note that a known sensor such as a Hall element can be used as the rotation sensor, and the present invention is not limited to a specific sensor.

  In addition to the motor 20, the controller 50 is connected to a motor 110 for driving a transfer unit that constitutes an example of a transfer drive unit. A transfer driving roller 11 is connected to a driving shaft of the motor 110 via a driving force transmission mechanism 111. The motor 110 is a DC brushless motor.

  The control unit 50 transmits a predetermined torque command value to the motor 110. The torque command value includes a PWM signal S11 that controls the speed and torque of the motor 110. The motor 110 rotates the transfer driving roller 11 via the driving force transmission mechanism 111 based on the torque command value. The transfer driving roller 11 rotates the secondary transfer roller 10 via the secondary transfer belt 13.

  A rotation sensor (not shown) is also attached to the motor 110. The rotation sensor detects the rotation of the motor 110, and the detected speed information D11 is fed back to the control unit 50. Note that a known sensor such as a Hall element can be used as the rotation sensor, and the present invention is not limited to a specific sensor.

  In addition to the motors 20 and 110, a pressure contact / separation driving motor 150 is connected to the control unit 50. A transfer pressure contact / separation mechanism 15 is connected to a drive shaft of the motor 150 via a drive force transmission mechanism 151. The motor 150 is a DC brushless motor.

  The control unit 50 transmits a predetermined operation command value to the motor 150. The operation command value is a control signal S51 for controlling the pressure contact / separation operation of the transfer pressure contact / separation mechanism 15. The motor 150 drives the transfer pressure contact / separation mechanism 15 via the driving force transmission mechanism 151 based on the operation command value. The transfer pressure contact / separation mechanism 15 moves the secondary transfer unit 70 upward and downward.

  A position detection sensor (not shown) is attached to the transfer pressure contact / separation mechanism 15, and the position detection sensor detects the position of the secondary transfer unit 70 during pressure contact and separation, and the pressure contact separation information D 15 detected here is the control unit 50. Feedback. Note that a known sensor such as a reflective or transmissive optical sensor can be used as the position sensor, and the present invention is not limited to a specific sensor.

  A paper discharge switching unit 27 is connected to the control unit 50. The paper discharge switching unit 27 performs paper discharge selection control based on the paper discharge control signal S27 during re-pressure contact paper discharge control. The paper discharge control signal S27 is a signal for selecting the normal and disposal trays 24 and 25, and is output from the control unit 50 to the paper discharge switching unit 27.

  In the paper discharge selection control at the time of the re-pressure contact discharge control, for example, when the images related to the image forming job before and after the separation pressure contact are the same, the measured value of the average speed of the motor 110 for driving the transfer unit, When the difference from the reference value of the average speed of the motor 110 is within the allowable speed range, the normal tray 24 is selected based on the paper discharge control signal S27 and the image forming unit 60 moves to the normal tray 24. The paper P after image formation is discharged. As a result, the sheet P (regular output) on which the first toner image after re-pressing is transferred and fixed is discharged to the normal tray 24.

  The difference between the measured value of the average speed of the motor 110 for driving the transfer unit and the reference value of the average speed of the motor 110 is the speed when the images related to the image forming jobs before and after the separation pressure welding are the same. If it is outside the allowable range, the discard tray 25 is selected based on the discharge control signal S27, and the paper P after image formation is discharged from the image forming unit 60 to the discard tray 25. As a result, the sheet P on which the first toner image after the re-pressure contact is transferred and fixed can be handled as a test sheet without making a normal output.

  Further, when the images related to the image forming job before and after the separation pressure contact are not identical, the difference between the measured value of the average speed of the transfer unit driving motor 30 and the reference value of the average speed of the motor 30 is the speed allowable range. The paper P to which the first toner image after re-pressing is transferred and fixed is discharged to the discard tray 25 regardless of the difference.

  The control unit 50 sets a command value to the transfer unit driving motor 110 and drives the secondary transfer belt 13 to rotate at a constant speed, and a constant torque to drive the secondary transfer belt 13 to rotate at a constant torque. Execute control. Further, the control unit 50 responds to a constant speed driving torque detected when performing constant speed control of the motor 110 for driving the transfer unit with the secondary transfer belt 13 separated from the intermediate transfer belt 1. The constant torque control of the motor 110 for driving the transfer unit is executed in a state where the secondary transfer belt 13 is pressed against the intermediate transfer belt 1.

  The control unit 50 is obtained by measuring when the first first sheet P based on the image forming job is passed through the secondary transfer unit 70 after the secondary transfer belt 13 is pressed against the intermediate transfer belt 1. The average speed of the transfer section driving motor 110 is stored in the predetermined storage section 6 as a reference value. Further, the control unit 50 measures the average speed of the motor 110 for driving the transfer unit when the second and subsequent sheets of paper P are passed through the secondary transfer unit 70, and the measured value of the average speed of the motor 110 is measured. Then, a constant torque command value at the time of transferring the next sheet is calculated from the difference between the average speed of the motor 110 and the reference value of the average speed, and the command value is changed.

  Further, the control unit 50 monitors whether or not the separation and re-pressure contact is performed in the secondary transfer unit 70 during execution of the image forming job, and after the re-pressure contact according to the second re-pressure contact transfer condition. The paper P on which the first toner image is transferred and fixed is discharged to the disposal tray 25, or the paper P on which the first toner image after re-pressing is transferred and fixed is used for normal use. It is discharged to the tray 24.

  Here, the second re-pressure contact transfer condition is a condition for transferring an image based on the image forming job before and after the separation re-pressure contact of the secondary transfer unit 70 onto the paper P. This condition includes branch control corresponding to whether the image based on the image forming job before the separation and the image based on the image forming job after the press contact are the same or not.

  When the controller 50 detects the separation and re-pressure contact of the secondary transfer unit 70 during execution of the image forming job, the image formation before and after the separation re-pressure contact of the secondary transfer unit 70 is set as the second re-pressure contact transfer condition. It is determined whether the images based on the job are the same. For example, when the images based on the image forming jobs before and after the separation re-pressure contact of the secondary transfer unit 70 are the same, the control unit 50 determines the first first image forming job based on the first re-pressure transfer condition. The reference value of the average speed of the motor 110 for driving the transfer unit, which is stored when the first sheet is passed, is read from the storage unit 6.

  The control unit 50 measures the average speed of the transfer unit driving motor 110 obtained by measuring when the first sheet P is passed through the secondary transfer unit 70 after re-pressing, and a storage unit. It is determined whether or not the difference from the reference value of the average speed of the motor 110 read from 6 is within an allowable range. When the difference is out of the allowable range, the controller 50 discharges the sheet P on which the first toner image after re-pressing is transferred and fixed to the discard tray 25, and transfers the next sheet from the difference. The constant torque command value is calculated and the command value is changed.

  Next, an example of intermediate transfer, secondary transfer, and paper discharge control according to the second embodiment will be described with reference to FIGS. In this embodiment, the second re-contact transfer condition is applied, and the measurement result of the transfer driving speed of the preceding sheet (sheet P (first sheet)) and the acquisition of the average speed is the next sheet (sheet P (2). This is based on the premise that the transfer type and the paper discharge system in the color image forming apparatus 200 are controlled and cannot be reflected in the image formation of the first sheet)).

  Under these control conditions, in step ST21 shown in FIG. 9, the controller 50 determines the rotational speeds of the secondary transfer roller 10 and the intermediate transfer belt 1 in a state where the secondary transfer roller 10 and the intermediate transfer belt 1 are separated from each other. The controller 50 controls the motor 20 for driving the intermediate transfer belt and the motor 110 for driving the transfer unit at a constant speed by feedback so that the speed is constant. At this time, the rotation speed of the secondary transfer roller 10 and the intermediate transfer belt 1 may be controlled to be the same speed, and the rotation speed of the secondary transfer roller 10 is higher than the rotation speed of the intermediate transfer belt 1. You may control so that it may become large.

  While the transfer unit driving motor 110 is controlled at a constant speed, the control unit 50 detects the constant speed driving torque of the transfer unit driving motor 110 based on the PWM signal. The control unit 50 calculates an average torque command value from the detected constant speed driving torque. In addition, the torque command value can be determined by an appropriate method such as a center value, and the present invention is not limited to a specific method.

  Next, in step ST <b> 22, the control unit 50 starts the pressure contact / separation motor 150 to press the secondary transfer roller 10 against the intermediate transfer belt 1. The secondary transfer belt 13 is brought into pressure contact with the intermediate transfer belt 1 in accordance with the constant speed driving torque detected at that time, and the constant torque control of the transfer unit driving motor 110 is performed in this state.

  Thereafter, in step ST23, the control unit 50 stops the operation of the pressure separation / separation motor 150 with the completion of the pressure welding. When the press contact is completed, the control unit 50 continues the constant speed control of the motor 20 for driving the intermediate transfer belt and rotates the intermediate transfer belt 1 in step ST24. The control unit 50 performs constant torque control on the transfer unit driving motor 110 according to the constant speed driving torque detected in step ST2. By this constant torque control, the secondary transfer roller 10 rotates. At this time, the control unit 50 passes the first first sheet P based on the image forming job after press contact to the secondary transfer unit 70, and the transfer unit driving motor obtained by measurement at that time is obtained. The average speed 110 is stored in the predetermined storage unit 6 as a reference value.

  Further, the control unit 50 passes the second and subsequent sheets P through the secondary transfer unit 70 and measures the average speed of the motor 110 for driving the transfer unit. Then, the control unit 50 calculates a constant torque command value at the time of transferring the next sheet from the difference between the measured value of the average speed of the motor 110 for driving the transfer unit and the reference value of the average speed of the motor 110, and changes the command value. To do.

  In step ST <b> 25, the control unit 50 monitors whether or not the separation and re-pressure contact are performed in the secondary transfer unit 70 during execution of the image forming job. If separation and re-pressure contact are not detected by the secondary transfer unit 70 during execution of the image forming job, the process returns to step ST24 to perform control to calculate a constant torque command value at the time of transferring the next sheet and change the command value. continue.

  If the controller 50 detects separation and re-pressure contact in the above-described step ST25 during execution of the image forming job, separation / re-pressure contact discharge control is executed in step ST26. For example, the process proceeds to step ST31 shown in FIG. In step ST31, the control unit 50 inputs management information related to the image forming job before and after the separation re-pressure contact. The management information related to the image forming job includes the number of sheets for printing the same image continuously.

  In step ST32, the control unit 50 decodes (analyzes) the management information related to the image forming job, and branches control according to whether the images before and after the separation pressure contact are the same or not. When the images related to the image forming jobs before and after the separation pressure contact are the same, in step ST33, the control unit 50 calculates the reference value of the average speed of the transfer unit driving motor 110 and the measured value of the average speed of the motor 110. Control branches according to whether or not the difference is included within the allowable speed range. At this time, the control unit 50 stores the reference value of the average speed of the motor 110 for driving the transfer unit, which is stored when the first first sheet of the image forming job is passed, as the first re-pressure transfer condition. Read from unit 6.

  The control unit 50 measures the average speed of the transfer unit driving motor 110 obtained by measuring when the first sheet P is passed through the secondary transfer unit 70 after re-pressing, and a storage unit. It is determined whether or not the difference from the reference value of the average speed of the motor 110 read from 6 is within the speed allowable range.

  When the difference between the reference value of the average speed of the motor 110 and the measured value of the average speed of the motor 110 is out of the allowable speed range, the process proceeds to step ST35, and the control unit 50 re-executes according to the re-pressure contact transfer condition. The sheet P on which the first toner image after the pressure contact is transferred and fixed is discharged to a disposal tray 25. At this time, the paper discharge switching unit 27 selects the discard tray 25 based on the paper discharge control signal S27 output from the control unit 50. The control unit 50 calculates a constant torque command value at the time of transferring the next sheet from the difference between the reference value of the average speed of the motor 110 and the measured value of the average speed of the motor 110, and changes the command value.

  Thereafter, in step ST36, the control unit 50 exposes the image [read again] of Page 1 to a photosensitive drum (not shown) by the image forming unit 60, thereby forming a toner image. Thereafter, the toner image is transferred from the photosensitive drum to the intermediate transfer belt 1. At this time, the speed of the motor 110 for driving the transfer unit is measured. The control unit 50 updates the PWM value of the motor 110 for driving the transfer unit. Thereafter, the process proceeds to step ST41.

  When the difference between the reference value of the average speed of the motor 110 and the measured value of the average speed of the motor 110 is included in the allowable speed range in step ST34 described above, the process proceeds to step ST37, and the control unit 50 The sheet P on which the first toner image after re-pressing is transferred and fixed is discharged to the normal tray 25. At this time, the paper discharge switching unit 27 selects the normal tray 24 based on the paper discharge control signal S27 output from the control unit 50. The control unit 50 calculates a constant torque command value at the time of transferring the next sheet from the difference between the reference value of the average speed of the motor 110 and the measured value of the average speed of the motor 110, and changes the command value.

  If the images related to the image forming jobs before and after the separation pressure welding are not identical in step ST32 described above, the control unit 50 always makes a test image in step ST38 shown in FIG. Form. The control unit 50 exposes a test image for test passing through a photosensitive drum (not shown) by the image forming unit 60 to form a toner image related to the test image. Thereafter, the toner image is transferred from the photosensitive drum to the intermediate transfer belt 1. At this time, the speed of the motor 110 for driving the transfer unit is measured. The control unit 50 updates the PWM value of the motor 110 for driving the transfer unit.

  Thereafter, the process proceeds to step ST39, where the control unit 50 discharges the first sheet (test paper passing) to the discard tray 25. At this time, the paper discharge switching unit 27 selects the discard tray 25 based on the paper discharge control signal S27 output from the control unit 50. The control unit 50 calculates a constant torque command value at the time of transferring the next sheet from the difference between the reference value of the average speed of the motor 110 and the measured value of the average speed of the motor 110, and changes the command value.

  Thereafter, in step ST40, the control unit 50 exposes the image [page and later] of Page 2 to a photosensitive drum (not shown) by the image forming unit 60 to form a toner image. Thereafter, the toner image is transferred from the image forming unit 60 to the intermediate transfer belt 1. At this time, the speed of the motor 110 for driving the transfer unit is measured. The control unit 50 updates the PWM value of the motor 110. Since the page P2 and the paper P after the image of the page 2 are fed back (FB), they are all discharged to the normal (regular) tray 24. At this time, the paper discharge switching unit 27 selects the normal tray 24 based on the paper discharge control signal S27 output from the control unit 50. Thereafter, the process proceeds to step ST42.

  In step ST42, the control unit 50 determines the end of the image forming operation. For example, when an EOF (end-off flag) indicating the last page of the image forming job is detected, the image forming operation (control) is terminated. If no EOF is detected, the process returns to step ST41 and the image forming process is repeated.

  As described above, according to the image forming apparatus 200 according to the second embodiment, the images based on the image forming jobs before and after the separation re-pressure contact are the same, and the average speed of the motor 110 for driving the transfer unit is the same. When the difference between the measured value and the reference value of the average speed of the motor 110 is out of the allowable speed range, the sheet P on which the first toner image after re-pressing is transferred and fixed is not set as a normal output. Can be handled as test paper. Moreover, after the re-pressure contact, the measured value of the average speed of the transfer unit driving motor 110 obtained by measuring when the first sheet P is passed through the secondary transfer unit 70 is used for the next sheet. The constant torque command value can be calculated and the command value can be changed.

  Further, in the image forming apparatus 200, the control unit 50 determines that the difference between the measured value of the average speed of the motor 110 for driving the transfer unit and the reference value of the average speed of the motor 110 is within the allowable speed range. The sheet P on which the first toner image after the re-pressure contact is transferred and fixed is discharged to the normal tray 24, and a constant torque command value at the time of the next sheet transfer is calculated from the difference to change the command value. .

  Further, according to the image forming apparatus 200, the images based on the image forming jobs before and after the separation re-pressure contact are the same, and the control unit 50 calculates the average speed measurement value of the transfer unit driving motor 110. When the difference from the reference value of the average speed of the motor 110 is within the allowable speed range, the sheet P on which the first toner image after re-pressing is transferred and fixed can be handled as a normal output. .

  According to the image forming apparatus 100, when the images based on the image forming jobs before and after the separation re-pressure contact are not the same, the measured value of the average speed of the motor 110 for driving the transfer unit and the average speed of the motor 110 are calculated. Regardless of the difference from the reference value, the sheet P on which the first toner image after re-pressing is transferred and fixed can be handled as a test sheet without normal output. In addition, after the re-pressing, only the measurement value of the average speed of the motor 110 for driving the transfer unit, which is obtained by measuring when the first sheet P is passed through the transfer unit, is used for the next sheet. The command value can be changed by calculating the torque command value.

  By such paper discharge control during separation / re-pressure contact, the first toner image after re-pressure contact is transferred and fixed, and the paper P is discharged as a test paper without normal output. The paper P on which the subsequent first toner image is transferred and fixed can be used as a normal output. Accordingly, the torque relationship with the image carrier not only in the environment of the load applied to the secondary transfer belt 13, but also in the short-term fluctuation at the beginning of the image forming operation as well as in the long-term change over time. Is appropriately maintained, and unnecessary load fluctuations on the intermediate transfer belt 1 are minimized to prevent deterioration of the image quality, and a change in image magnification caused by a short-term load change can be minimized.

  In addition, even if the transfer unit is separated and re-pressed during the execution of the image forming job, the number of paper breaks can be minimized, and the change width of the magnification throughout the job can be minimized. It becomes like this.

  The present invention provides a monochrome unit having a function of pressing a transfer unit against an image carrier carrying a toner image and transferring the toner image on the image carrier onto a sheet through the sheet between the image carrier and the transfer unit. The present invention is extremely suitable when applied to color printers, copiers, and composite machines of these.

1 Intermediate transfer belt (image carrier)
2 Intermediate transfer roller 3, 12, 34 Driven roller 4 Photosensitive drum (image carrier)
5, 50 Control unit 6 Storage unit 7, 60 Image forming unit 8 Optical writing unit (image forming unit)
9 Developer (image forming unit)
DESCRIPTION OF SYMBOLS 10 Secondary transfer roller 11, 33 Transfer drive roller 13 Secondary transfer belt 14, 18 Transfer cleaning unit 15 Transfer pressure contact / separation mechanism 16 Transfer unit 17 Fixing device 19 Charger 20, 30, 40, 110, 150 Motor 21, 31, 41, 111 Driving force transmission mechanism 24, 25 Tray 27 Paper discharge switching unit 32 Transfer belt 33 Cleaning unit 70 Secondary transfer unit 100, 200 Image forming apparatus

Claims (6)

An image carrier for carrying a toner image;
A transfer unit that is capable of being pressed against and separated from the image carrier, and that transfers a toner image carried on the image carrier to the paper during the pressure contact;
A transfer driving unit that rotationally drives the transfer unit based on a predetermined command value;
A constant speed control that sets a command value in the transfer driving unit and rotationally drives the transfer unit at a constant speed and a control unit capable of constant torque control that rotationally drives the transfer unit at a constant torque, and
The controller is
The transfer unit is pressed against the image carrier in accordance with a constant speed driving torque detected when the transfer driving unit is controlled at a constant speed with the transfer unit being separated from the image carrier. In the state, perform a constant torque control of the transfer drive unit,
After the press contact of the transfer drive unit, a predetermined value is obtained by using an average speed of the transfer drive unit obtained by measuring when the first first sheet based on the image forming job is passed through the transfer unit as a reference value. Memorize in the memory,
When the second and subsequent sheets are passed through the transfer section, the average speed of the transfer drive section is measured,
The constant torque command value at the time of transfer of the next sheet is calculated from the difference between the measurement value of the average speed of the transfer driving unit and the reference value of the average speed of the transfer driving unit, and the command value is changed.
During the execution of the image forming job, it is monitored whether separation and re-pressure contact are performed at the transfer unit,
The average speed of the transfer driving unit obtained by measuring when the first image based on the image forming job after the separation re-pressing of the transfer unit is transferred to the sheet, and the average stored in the storage unit If the difference between the two is outside the allowable range, the first toner image after re-pressing is transferred and fixed, and the paper is discharged to a waste tray. An image forming apparatus, wherein when the difference is within an allowable range, the sheet on which the first toner image after re-pressing is transferred and fixed is discharged to a normal tray. The controller is
The average speed of the transfer driving unit obtained by measuring when the first image based on the image forming job after the separation re-pressing of the transfer unit is transferred to the sheet, and the average stored in the storage unit If the difference between the reference value of the speed is outside the allowable range, further, to claim 1 from the difference to calculate the constant torque command value at the time of transfer of the next sheet and changes the command value The image forming apparatus described. The controller is
The average speed of the transfer driving unit obtained by measuring when the first image based on the image forming job after the separation re-pressing of the transfer unit is transferred to the sheet, and the average stored in the storage unit If the difference between the reference value of the speed is within the allowable range, further, in claim 2 in which from the difference to calculate the constant torque command value at the time of transfer of the next sheet and changes the command value The image forming apparatus described. An image carrier for carrying a toner image;
A transfer unit that is capable of being pressed against and separated from the image carrier, and that transfers a toner image carried on the image carrier to the paper during the pressure contact;
A transfer driving unit that rotationally drives the transfer unit based on a predetermined command value;
A constant speed control that sets a command value in the transfer driving unit and rotationally drives the transfer unit at a constant speed and a control unit capable of constant torque control that rotationally drives the transfer unit at a constant torque, and
The controller is
The transfer unit is pressed against the image carrier in accordance with a constant speed driving torque detected when the transfer driving unit is controlled at a constant speed with the transfer unit being separated from the image carrier. In the state, perform a constant torque control of the transfer drive unit,
After the press contact of the transfer drive unit, a predetermined value is obtained by using an average speed of the transfer drive unit obtained by measuring when the first first sheet based on the image forming job is passed through the transfer unit as a reference value. Memorize in the memory,
When the second and subsequent sheets are passed through the transfer section, the average speed of the transfer drive section is measured,
The constant torque command value at the time of transfer of the next sheet is calculated from the difference between the measurement value of the average speed of the transfer driving unit and the reference value of the average speed of the transfer driving unit, and the command value is changed.
During the execution of the image forming job, it is monitored whether separation and re-pressure contact are performed at the transfer unit,
When the separation and re-pressure contact of the transfer part is detected during the execution of the image forming job, it is determined whether or not the images based on the image formation job before and after the separation re-pressure contact of the transfer part are the same,
When the images based on the image forming job before and after the separation re-pressure contact of the transfer unit are not the same, the reference of the average speed of the transfer driving unit stored at the time of passing the first first sheet of the image forming job Reading a value from the storage unit;
The first toner image after re-pressure contact is transferred and fixed, and the paper is discharged to a waste tray.
The measured value of the average speed of the transfer driving unit obtained by measuring when the first sheet after re-pressing is passed through the transfer unit, and the average speed of the transfer driving unit read from the storage unit An image forming apparatus characterized in that a constant torque command value at the time of transfer of the next sheet is calculated from a difference from the reference value to change the command value. An image carrier that carries a toner image, a transfer unit that can be pressed against and separated from the image carrier, and that transfers the toner image carried on the image carrier to the paper during pressure contact, and a predetermined command A transfer driving unit that rotationally drives the transfer unit based on the value, a constant speed control that sets a command value in the transfer driving unit and rotationally drives the transfer unit at a constant speed, and rotationally drives the transfer unit at a constant torque. A control unit capable of constant torque control, and a control method of an image forming apparatus comprising:
The controller is
The transfer unit is moved away from the image carrier, and the transfer unit is moved to the image carrier in accordance with a constant speed driving torque detected when constant speed control of the transfer driver is executed in this state. Pressing, and in this state, performing a constant torque control of the transfer drive unit;
After the press contact, the first first sheet based on the image forming job is passed through the transfer unit, and the average speed of the transfer drive unit obtained by measurement at that time is stored in a predetermined storage unit as a reference value. And steps to
Passing the second and subsequent sheets through the transfer section and measuring the average speed of the transfer drive section;
Calculating a constant torque command value at the time of transferring the next sheet from a difference between a measured value of the average speed of the transfer driving unit and a reference value of the average speed of the transfer driving unit, and changing the command value;
Monitoring whether or not separation and re-pressure contact are performed at the transfer unit during execution of the image forming job;
The average speed of the transfer driving unit obtained by measuring when the first image based on the image forming job after the separation re-pressing of the transfer unit is transferred to the sheet, and the average stored in the storage unit If the difference between the two is outside the allowable range, the first toner image after re-pressing is transferred, and the paper after the toner image transfer is discharged to a waste tray. When the difference between the two is within an allowable range, the first toner image after re-pressing is transferred, and the step of discharging the paper after the toner image transfer to a normal tray is executed. And a control method of the image forming apparatus. An image carrier that carries a toner image, a transfer unit that can be pressed against and separated from the image carrier, and that transfers the toner image carried on the image carrier to the paper during pressure contact, and a predetermined command A transfer driving unit that rotationally drives the transfer unit based on the value, a constant speed control that sets a command value in the transfer driving unit and rotationally drives the transfer unit at a constant speed, and rotationally drives the transfer unit at a constant torque. A control unit capable of constant torque control, and a control method of an image forming apparatus comprising:
The controller is
The transfer unit is moved away from the image carrier, and the transfer unit is moved to the image carrier in accordance with a constant speed driving torque detected when constant speed control of the transfer driver is executed in this state. Pressing, and in this state, performing a constant torque control of the transfer drive unit;
After the press contact, the first first sheet based on the image forming job is passed through the transfer unit, and the average speed of the transfer drive unit obtained by measurement at that time is stored in a predetermined storage unit as a reference value. And steps to
Passing the second and subsequent sheets through the transfer section and measuring the average speed of the transfer drive section;
Calculating a constant torque command value at the time of transferring the next sheet from a difference between a measured value of the average speed of the transfer driving unit and a reference value of the average speed of the transfer driving unit, and changing the command value;
Monitoring whether or not separation and re-pressure contact are performed at the transfer unit during execution of the image forming job;
When separation and re-pressure contact of the transfer unit are detected during execution of the image forming job, it is determined whether images based on the image formation job before and after separation re-pressure contact of the transfer unit are the same, and the transfer If the images based on the image forming job before and after the separation re-pressure contact of the parts are not the same, the reference value of the average speed of the transfer driving unit stored at the time of passing the first first sheet of the image forming job is used. The sheet read from the storage unit and transferred with the first toner image after re-pressing is fixed and discharged to a waste tray, and the first sheet after re-pressing is passed through the transfer unit. Constant torque command at the time of transfer of the next sheet from the difference between the measured value of the average speed of the transfer driving unit obtained by measuring when the paper is fed and the reference value of the average speed of the transfer driving unit read from the storage unit Calculating a value and changing the command value; Method of controlling an image forming apparatus and executes.

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