JP2019028276A - Image formation device - Google Patents

Abstract

To provide an image formation device that enables an optimal control gain to be set, and enables responsiveness of fixation loop control and accuracy thereof to be ensured.SOLUTION: An image formation device comprises: an image carrier that carries toner images; transfer means that transfers the toner image to a transfer material; conveyance means that conveys the transfer material; fixation means that fixes the toner image on the transfer material conveyed by the conveyance means to the transfer material with the toner image thereon held and conveyed by a fixation nip part composed of a fixation rotor and pressure rotor in which a drive unit rotatingly drives; loop-amount detection means that detects an amount of loop generated in the transfer material while being conveyed from the conveyance means to the fixation means; and loop-amount control means that varies the fixation rotor and pressure rotor on the basis of detection information of the loop-amount detection means, and controls the amount of loop of the transfer material, in which the image formation device has: control gain switch means of rotation velocity control of the drive unit; and rotation velocity detection means of the drive unit. In accordance with response time of the drive unit, a control gain of the rotation velocity control is made variable.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus including a fixing unit.

  In a conventional electrophotographic image forming apparatus, due to factors such as thermal expansion of the fixing roller and manufacturing errors, an image defect may occur due to excessive pulling or bending of the transfer material between the fixing device and the photosensitive drum. In order to prevent this, it is necessary to drive the fixing roller at an appropriate speed.

  In Patent Document 1, the first conveyance speed that is lower than the conveyance speed of the transfer material in the transfer unit and the second conveyance speed that is no longer than the first conveyance speed are used as the conveyance speed of the fixing unit. As a result, the transfer material is bent (looped) between the transfer portion and the fixing roller. When the amount of bending (also referred to as loop amount) formed on the transfer material is greater than or equal to a predetermined height, the transfer material is conveyed at the second conveyance speed, and when the amount is less than the predetermined height, the first conveyance is performed. Control is performed so that the transfer material is conveyed at a speed and the loop amount is kept within a certain range (also referred to as loop control).

  A DC brushless motor is often used to drive the fixing unit, but optimal control is performed according to the characteristics of the motor used and the load torque of the motor so as to keep the loop amount within a certain range with high accuracy. The gain is set.

Japanese Patent Laid-Open No. 5-107966

  In recent years, cost competition with manufacturers in the same industry has become severe, and it is desirable to reduce the cost of relatively expensive parts such as motors. As a device manufacturer, load torque can be reduced to reduce the required specifications for motors and control motors. In addition to simplifying the circuit, the company is taking measures such as making it possible to copy and purchase motors with equivalent specifications. In order to copy and purchase parts with the same specifications as well as motors, it is necessary to ensure the same performance and quality of the equipment even if parts from different manufacturers are mounted.

  On the other hand, cost competition is also active among motor manufacturers, and motor manufacturers' technological developments have proposed smaller and cheaper motors with equivalent performance. As the motor becomes smaller, the motor inertia also becomes smaller, so the optimum control gain is different, but it is not always possible to achieve the same performance with the same inertia for each motor manufacturer.

  If a motor with different inertia is used without changing the control gain, the speed response of the motor, that is, the response of the loop control will change, causing image defects such as pitch unevenness, gloss unevenness, or unfixed toner image rubbing. It becomes. For this reason, it has been difficult to copy and purchase motors having different characteristics.

  An object of the present invention is to provide an image forming apparatus that can set an optimum control gain and ensure the responsiveness and accuracy of fixing loop control.

  To achieve the above object, an image forming apparatus according to the present invention transfers an image carrier that carries a toner image formed according to image information, and a toner image formed on the image carrier to a transfer material. And a fixing nip portion constituted by a fixing rotator and a pressure rotator in which a driving unit rotates and drives a toner image on the transfer material conveyed by the conveying unit. Fixing means for nipping and conveying and fixing to a transfer material, loop amount detecting means for detecting a loop amount generated in the transfer material while being conveyed from the conveying means to the fixing means, and detection information of the loop amount detecting means An image forming apparatus comprising: a loop amount control unit configured to control a loop amount of the transfer material by varying a rotation speed of the fixing rotator and the pressure rotator based on the rotation speed of the driving unit. Control gain of control And Toggles means has a rotation speed detecting means of the drive unit, characterized by varying the control gain of the speed control according to the response time of the drive unit.

  According to the present invention, it is possible to provide an image forming apparatus that can set an optimum control gain and ensure the responsiveness and accuracy of fixing loop control.

Overall view of the device Arrangement of fixing unit and secondary transfer unit Schematic diagram of fixing loop control Fixing loop control block diagram Motor speed control block diagram Control gain adjustment flowchart

(First Embodiment 1)
(Configuration of the entire image forming apparatus)
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a color digital printer as an example of an image forming apparatus to which the paper conveying device of the present invention is applied.

  First, the image forming unit will be described. The four laser scanner units 1Y, 1M, 1C, and 1Bk form electrostatic latent images on the four photosensitive drums 2Y, 2M, 2C, and 2Bk, respectively, and toner images are formed by the four developing units 3Y, 3M, 3C, and 3Bk, respectively. Form. The color toner images formed on the four photosensitive drums 1Y, 1M, 1C, and 1Bk are transferred onto the intermediate transfer belt ITB by the four primary transfer portions 4Y, 4M, 4C, and 4Bk, respectively, thereby forming a full-color toner image. At the same time, it is transported to the secondary transfer portion R11 and transferred to the printing paper.

  The printing paper is fed from one of the paper feeding cassettes CST1 to CST3 by the respective pickup units PU1 to PU3 and is conveyed toward the registration roller pair R10 by the conveying roller pairs R5 to R9. Further, the paper fed from the manual feeding unit MF is conveyed to the registration roller pair R10.

  The sheet conveyed by the registration roller pair R10 is controlled so that there is no deviation from the toner image on the intermediate transfer body belt ITB. The toner image is transferred onto the sheet by the secondary transfer unit R11. Thereafter, the toner image transferred onto the paper is heated and pressurized by the fixing device UN3 driven by the motor 225, and is fixed onto the paper. Thereafter, the paper is decurled by the decurling unit UN5 from the paper discharge reversing unit UN4, and then discharged from the paper discharge roller pair R15 to the outside of the apparatus main body. In addition, after printing on the first side during duplex printing, the paper is fed again from the reverse paper discharge unit UN4 to the registration unit UN1 via the double-side reverse unit UN6 and the double-sided conveyance path UN8, and similarly printed and discharged.

(Explanation of secondary transfer unit to fixing unit)
The fixing unit UN3 will be described with reference to FIG. The stay 220 has a function of fixing the fixing heater and a function of guiding the rotation of the fixing film 223 from the inside, and is a rigid body having heat resistance and heat insulation. The stay 220 is a horizontally long member having a longitudinal direction (a direction orthogonal to the transport direction) crossing the transport path of the printing paper S. The fixing heater 221 is made of ceramic and is fixed along the longitudinal direction of the stay 220.

  The fixing thermistor 222 is a sensor that is installed on the back surface of the fixing heater 221 and detects the temperature of the fixing heater 221 and functions as a fixing temperature measuring unit. Fixing temperature adjustment control is executed by adjusting the power supplied to the fixing heater 221 based on the temperature detected by the fixing thermistor 222.

  The fixing film 223 as a rotating member is formed of a cylindrical heat resistant film material and is loosely fitted on the stay 220. The fixing film 223 is also called a fixing sleeve. The pressure roller 224, which is a rotating member, is in pressure contact with the fixing sleeve 223 and is driven to rotate at a predetermined peripheral speed in the direction of arrow B by the fixing motor 225. The fixing sleeve 223 rotates following the rotation of the pressure roller 224. When the printing paper S is nipped by the fixing nip formed by the pressure roller 224 and the fixing sleeve 223, the printing paper S is nipped and conveyed together with the fixing sleeve 223.

  As a result, heat from the fixing heater 221 is applied to the unfixed image on the printing paper S via the fixing sleeve 223, and the unfixed image on the printing paper S is heated and fixed on the surface of the printing paper S. The printing paper S that has passed through the fixing nip is separated from the surface of the fixing sleeve 223 and conveyed downstream. Note that the arrow C in FIG.

  Next, a part for transferring the transfer material from the secondary transfer unit 140 to the fixing unit UN3 will be described. Intermediate transfer body ITB is conveyed at a constant speed in the direction of arrow A by secondary transfer counter roller 201 driven by ITB motor 200. The printing paper S is nipped and conveyed between the intermediate transfer body ITB driven by the secondary transfer counter roller 201 and the secondary transfer roller 202, and is conveyed toward the fixing unit UN3. While the printing paper S is being conveyed by both the secondary transfer unit 140 and the fixing unit UN3, the conveyance speed of the fixing unit UN3 is adjusted by the loop sensor 162 in order to adjust the loop amount (deflection amount) of the transfer material. Be controlled. The control of the loop amount will be described later.

  By controlling the conveyance speed of the fixing unit UN3, the transfer material is conveyed in a state where the loop amount of the transfer material is appropriately held. The loop sensor 162 is an optical sensor having a light emitting unit and a light receiving unit, and determines whether or not the loop sensor flag 210 as a rotating moving member blocks light from the light emitting unit. When the printing paper S bends a predetermined amount or more (the loop amount becomes a predetermined amount or more), the printing paper S comes into contact with the loop sensor flag 210 and moves to a position where the loop sensor flag 210 does not block the light from the light emitting unit. A loop sensor 162 is arranged. That is, the loop sensor 162 and the loop sensor flag 210 function as detection means for detecting the amount of bending of the transfer material.

  FIG. 3 is a diagram showing the loop amount of the printing paper S and the state of the loop sensor flag. (A) represents the case where the loop amount is 0, (B) represents the case where the loop amount is appropriate, and (C) represents the case where the loop amount is large. When the loop amount between the fixing unit UN3 and the secondary transfer unit 140 is 0 as shown in FIG. 3A, the loop sensor flag 210 stops at a position where the loop sensor flag 210 can reliably shield the loop sensor 162. To do. For this reason, the loop sensor 162 detects OFF.

  When the loop amount between the fixing unit UN3 and the secondary transfer unit 140 is appropriate as shown in FIG. 3B, the loop sensor flag 210 is pushed downward by the printing paper S and the inclination is small. As a result, the loop sensor 162 is in a state where the loop sensor flag 210 is slightly shielded. Also in this case, the loop sensor 162 detects OFF. When the loop amount between the fixing unit UN3 and the secondary transfer unit 140 is larger than the appropriate amount as shown in FIG. 3C, the loop sensor flag 210 is pushed down greatly by the printing paper S and the inclination is further reduced. Yes. The loop sensor flag 210 does not shield the loop sensor 162 and is in a transmissive state. For this reason, the loop sensor 162 detects ON.

(Description of the control block of the configuration related to loop amount control)
FIG. 4 is a control block diagram of a configuration relating to loop amount control of the image forming apparatus. The control unit 300 is used as a work area necessary for the CPU 301 that controls all of the image forming apparatus, the ROM 302 that stores the control contents of the image forming apparatus to be executed by the CPU 301, and the CPU 301 to control the image forming apparatus. A RAM 303 is included. The CPU 301 acquires information related to image formation such as the print mode and size of the printing paper S input from the operation / display unit 310 by the operator, and an instruction to start image formation.

  In addition, the CPU 301 displays necessary information on the operation / display unit 310. The CPU 301 controls the fixing heater 221 so that the temperature acquired by the fixing thermistor 222 becomes the target temperature. The fixing motor 225 drives the pressure roller 224. Further, the CPU 301 controls the fixing motor 225 based on the detection result of the loop sensor 162, and executes the loop amount control of the transfer material.

(Explanation of motor rotation speed control)
Next, control of the rotational speed of the motor 39 will be described with reference to the block diagram of FIG. The function shown in the block diagram of FIG. 5 may be configured by the CPU 40 (including the DSP) executing a program, an analog circuit, or a digital circuit. It is good or you may comprise by those combination.

  The CPU 40 sends a drive signal (acceleration / deceleration signal) instructing to accelerate or decelerate the rotational speed of the motor to the motor control circuit unit 42 in the motor drive circuit unit 41 as necessary. The motor control circuit unit 42 includes a charge pump circuit (not shown) inside, and changes the voltage value of the charge pump circuit in accordance with an acceleration / deceleration signal from the CPU 40. Further, the PWM drive unit 66 PWM-drives the FET (not shown) in the motor drive circuit unit 41 based on the voltage value output from the charge pump circuit, whereby the rotor 58 rotates.

  Here, the rotation speed detection unit 68 detects the rotation speed of the rotor 58 and outputs an FG signal corresponding to the detected rotation speed to the error amplification section 76 in the CPU 40. The cycle of the FG signal is output in synchronization with the rotation operation of the motor 39, and represents the rotation speed of the motor 39. This FG signal can be rephrased as a speed signal or speed information of the motor 39.

  Further, a target period corresponding to the target rotation speed is set in the target speed setting unit 78 of the CPU 40 in advance. A signal indicating the set target period is output to the error amplifier 76. Here, the signal output to the error amplifying unit 76 is assumed to be a rectangular wave signal, for example, similarly to the FG signal, but may be any signal as long as the error amplifying unit 76 can handle it. Then, the error amplifying unit 76 measures the cycle of the FG signal based on the count number of the internal clock between the falling edges of the FG signal. Further, the target period is also measured based on the count number of the internal clock between the falling edges of the signal output from the target speed setting unit 78.

  The error amplifying unit 76 has an actual rotation cycle (corresponding to the count number) according to the signal output from the rotation speed detection unit 68 and a target rotation cycle (corresponding to the count number) according to the signal output from the target speed setting unit 78. The error is amplified according to the gain setting value from the gain setting unit 77. Specifically, for example, the detected real cycle is Creal, the target rotational speed is Cref, and the gain setting value is G. In this case, the error amplifying unit 76 multiplies the gain setting value G by (Creal−Cref) and sets the multiplied value to the width of the acceleration / deceleration signal.

  The gain setting value G is, for example, a proportional gain in the case of proportional control, and an integral gain or a differential gain in the case of PID control. Then, the error amplification unit 76 outputs the amplified signal to the acceleration / deceleration signal generation unit 75. The acceleration / deceleration signal generation unit 75 adjusts the width of the acceleration / deceleration signal using the signal output from the error amplifying unit 76 and feeds back the adjusted signal to the motor control circuit unit 42. As described above, the rotation speed of the motor 39 is controlled by closed loop control.

  FIG. 6 is a flowchart showing a method for adjusting the control gain G of the fixing motor 225. When the operator in the manufacturing process at the time of manufacturing the apparatus or the service person at the time of maintenance of the apparatus selects the gain G adjustment mode from the operation / display unit 310, the gain setting of the fixing motor 225 is started (Step 101). The target speed Vtrgt of the fixing motor 225 is set (Step 102), and the motor is turned on (Step 103). The target speed arrival time T until the rotation speed Vf of the fixing motor 225 reaches the target speed Vtrgt (Step 104) is acquired (Step 105), the control gain G is calculated (Step 106), and the gain adjustment mode is ended (Step 107). .

  The method for calculating the gain G is not limited in the present invention. For example, the gain G may be calculated as follows using a predetermined coefficient a and offset b.

G = a · T + b
In the above description, the operator or service person selects and adjusts the gain adjustment mode. However, the adjustment may be performed after the apparatus is turned on or during printing preparation after the apparatus door is opened or closed.

  Further, in the case of an apparatus that prints by switching a plurality of fixing motor speeds depending on a medium to be printed, a control gain G may be set for each of the plurality of motor speeds.

  As explained above, by adjusting and varying the control gain of the fixing motor according to the target arrival time at the time of starting the motor, a plurality of motors having different motor inertias, that is, different responsiveness, are used for copy purchase. However, an appropriate control gain can be set, and a printed matter with good image quality can be obtained without causing image defects such as pitch unevenness, gloss unevenness, or unfixed toner image rubbing.

  Alternatively, even when a small and inexpensive motor is adopted after the launch of the device, it is easy to reduce the cost by using an inexpensive motor regardless of the difference in response due to the difference in inertia.

77..Gain setting part, 162..Fusing loop sensor

Claims (4)

An image carrier that carries a toner image formed according to image information;
Transfer means for transferring the toner image formed on the image carrier to a transfer material;
Conveying means for conveying the transfer material;
Fixing means for nipping and conveying the toner image on the transfer material conveyed by the conveying means at a fixing nip portion constituted by a fixing rotator and a pressure rotator, which are driven by a drive unit, and fixing the toner image on the transfer material; A loop amount detecting means for detecting a loop amount generated in the transfer material while being conveyed from the conveying means to the fixing means;
Loop amount control means for controlling the loop amount of the transfer material by varying the rotational speeds of the fixing rotator and the pressure rotator based on the detection information of the loop amount detector;
An image forming apparatus comprising:
Control gain switching means for rotational speed control of the drive unit;
A rotational speed detection means of the drive unit;
Have
An image forming apparatus, wherein a control gain of the rotational speed control is made variable in accordance with a response time of the drive unit.   2. The image forming apparatus according to claim 1, wherein the response time of the drive unit is such that a control gain of the rotation speed control is made variable by counting a start time or a stop time of the drive unit.   The image forming apparatus according to claim 1, further comprising an adjustment mode different from that during normal printing, wherein a control gain of the rotational speed control is made variable by an operation in the adjustment mode.   The image forming apparatus according to claim 1, wherein a control gain of the rotation speed control is made variable during a printing preparation operation of the apparatus.