Image forming device

Abstract

To reduce ripples generated by an output voltage when a positive polarity voltage and a negative polarity voltage are superposed and applied to a load.SOLUTION: An image formation device comprises a positive voltage control part 200b, a negative voltage control part 200c, a brush 16, a discharge needle 18, PWM control parts 331 and 341, a voltage detection circuit 238, a voltage detection circuit 258, a gain setting part 334, and a gain setting part 344. The gain setting part 334, in a state in which the negative voltage control part 200c is applied to the discharge needle 18 with a discharge needle voltage V2, switches a setting of a first gain on the basis of a second gain when a voltage with a voltage V1 and the discharge needle voltage V2 superposed is applied to the brush 16 (t503).SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, and more particularly to a high-voltage power supply device used in, for example, an electrophotographic image forming apparatus, and an image forming apparatus equipped with the same. [Background technology]

[0002] In a high-voltage power supply device for an electrophotographic image forming apparatus, in order to reduce the size and cost of the apparatus, there is a configuration in which the output of one high-voltage power supply is applied to multiple loads. For example, Patent Document 1 proposes a configuration in which one high-voltage power supply that outputs a negative voltage supplies voltage to two loads. Also proposed is a configuration in which a positive high-voltage power supply (first power supply) and a negative high-voltage power supply (second power supply) are connected to one load.

[0003] Patent Document 2 proposes a configuration in which a single high-voltage power supply that outputs a negative voltage supplies voltage to three loads. Patent Document 3 proposes a method for controlling the output voltage of a high-voltage power supply, and proposes a high-voltage power supply device equipped with gain setting means for setting the gain of a high-voltage output control means based on the deviation between a target voltage value of the high-voltage power supply and a voltage value detected by a voltage detection means. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-078252 A [Patent Document 2] JP 2015-184340 A [Patent Document 3] JP 2007-189880 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the conventional technology has the following problems. In positive / negative superposition control in which a negative power supply is superimposed while a positive power supply is applied, if the control gain of the high-voltage power supply control means is set based on the difference between the target voltage value and the detected voltage value of the power supply output, voltage ripples occur at the start of positive / negative superposition control. FIG. 8 shows the transition of the power supply state when positive / negative superposition control is performed on the brush. In FIG. 8, when a negative voltage is applied to perform positive / negative superposition control at time t1503, the deviation between the target voltage value and the current output voltage value of the negative voltage is large, so the power supply start-up control starts in a state where the control gain is large. As a result, the voltage control of the positive power supply applied to the brush cannot follow the start-up control of the negative power supply, and ripples occur in the output voltage supplied to the brush during the period from time t1503 to time t1504. If ripples occur in the output to the brush, it becomes difficult for the brush to stably hold the toner remaining on the surface of the intermediate transfer belt during the print sequence.

[0006] The present invention has been made under these circumstances, and has an object to reduce the ripple that occurs in the output voltage when positive and negative voltages are superimposed and applied to a load. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0008] (1) A first power source that generates a first voltage of a first polarity, a second power source that generates a second voltage of a second polarity opposite to the first polarity, a first member to which the first voltage or a voltage obtained by superimposing the first voltage and the second voltage is applied, a second member to which the second voltage is applied, a first control means that controls the first power source, a second control means that controls the second power source, a first voltage detection means that detects the voltage applied to the first member, a second voltage detection means that detects the voltage applied to the second member, and a control method for controlling the first control means based on the voltage detected by the first voltage detection means and a first target voltage. and second setting means for setting a second gain for controlling the second power source by the second control means, based on a voltage detected by the second voltage detection means and a second target voltage, wherein the first setting means switches a setting of the first gain based on the second gain when a voltage obtained by superimposing the first voltage and the second voltage is applied to the first member in a state in which the second power source applies the second voltage to the second member. Effect of the Invention

[0010] According to the present invention, it is possible to reduce ripples occurring in the output voltage when a positive voltage and a negative voltage are superimposed and applied to a load. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing an image forming apparatus according to first and second embodiments; [Diagram 2] FIG. 1 is a diagram showing an outline of the configuration of an image forming apparatus and a high-voltage power supply according to first and second embodiments; [Diagram 3] FIG. 1 is a diagram showing an outline of a high-voltage power supply circuit according to first and second embodiments. [Figure 4] FIG. 1 is a diagram showing a start-up waveform of a high-voltage power supply according to the first embodiment. [Diagram 5] Timing chart of positive / negative superposition control in the first embodiment [Figure 6] FIG. 13 is a diagram showing output voltage characteristics versus drive frequency of the piezoelectric transformers of Examples 1 and 2. [Figure 7] Timing chart of positive / negative superposition control in the second embodiment [Figure 8] Timing chart of positive / negative superposition control in the conventional example DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] In this embodiment, a configuration for reducing ripples in a positive output voltage when a negative (second polarity) voltage is superimposed on a positive (first polarity) voltage and applied to a load in a high-voltage power supply capable of positive and negative superimposed outputs is described below. EXAMPLES

[0013] A positive / negative superposition control method in the high voltage power supply of the image forming apparatus according to the first embodiment will be described.

[0014] [Explanation of the configuration of the image forming device] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. The configuration and operation of the image forming apparatus of the first embodiment will be described with reference to FIG. 1. First, the image forming apparatus 100 is composed of first to fourth (a to d) image forming stations, the first being yellow (hereinafter referred to as Y), the second being magenta (hereinafter referred to as M), the third being cyan (hereinafter referred to as C), and the fourth being black (hereinafter referred to as Bk). Each station is replaceable with respect to the image forming apparatus 100 main body. Each station is sufficient to include at least a photosensitive drum, and there is no particular limitation as to which members are included in the image forming station and made replaceable. In the following, the operation of the first image forming station (Y)a will be described as a representative of each station.

[0015] The image forming station a includes a photosensitive drum 1a, which is a photoconductor, and a memory member 309 that stores, for example, the cumulative number of rotations of the photosensitive drum 1a as information related to the life of the photosensitive drum 1a. The memory member 309 may be provided as a ROM or RAM inside the control unit 303, instead of being provided in the image forming station. The photosensitive drum 1a is rotated at a predetermined peripheral speed (process speed) in the direction of the arrow (counterclockwise direction). During the rotation process, the photosensitive drum 1a is uniformly charged to a charging potential of a predetermined polarity by the charging roller 2a. Next, the surface of the photosensitive drum 1a corresponding to the image portion is exposed to light by scanning with a laser beam 6a of the exposure device 3a based on image data (image signal) supplied from the outside, thereby removing the charge, and forming an exposure potential VL on the surface of the photosensitive drum 1a. Next, toner is developed in the exposure potential VL portion, which is the image portion, by the potential difference between the development voltage Vdc applied to the yellow developing device 4a, which is the developing means, and the exposure potential VL, and the image is visualized. The image forming apparatus 100 of the first embodiment is an image forming apparatus of a reversal development type in which an image is exposed by the exposure device 3a and developed with toner on the exposed portion.

[0016] The intermediate transfer belt 10, which is an intermediate transfer body, is stretched by tension members 11, 12, and 13 and is in contact with the photosensitive drum 1a. At the contact position, the intermediate transfer belt 10 rotates in the same direction as the photosensitive drum 1a at approximately the same peripheral speed. The yellow toner image formed on the photosensitive drum 1a passes through the contact portion between the photosensitive drum 1a and the intermediate transfer belt 10 (hereinafter referred to as the primary transfer nip portion). In the process, the yellow toner image is transferred onto the intermediate transfer belt 10 by the primary transfer voltage applied to the primary transfer roller 14a by the primary transfer power source 15a (primary transfer). The toner remaining on the surface of the photosensitive drum 1a is cleaned and removed by the cleaning device 5a, and the image formation process after the charging described above is repeated. Thereafter, a magenta toner image (M) of the second color, a cyan toner image (C) of the third color, and a black toner image (Bk) of the fourth color are formed in the same manner and transferred onto the intermediate transfer belt 10 in a superimposed manner, thereby obtaining a composite color image. The four-color toner images on the intermediate transfer belt 10 (on the intermediate transfer body) pass through a contact portion (hereinafter referred to as a secondary transfer nip portion) between the intermediate transfer belt 10 and a secondary transfer roller 20, which is a transfer means. In the process, the four-color toner images are transferred collectively onto the surface of the recording material P fed by the paper feed roller 50 by a voltage (hereinafter referred to as a secondary transfer voltage) applied to the secondary transfer roller 20 by a secondary transfer power source 21. Note that, only in FIG. 1, a to d are added to the symbols to distinguish the colors, but in the following description, except when a specific color is described, the suffixes a to d indicating the colors added to the ends of the symbols shown in FIG. 1 may be omitted.

[0017] The charge eliminating needle 18 is disposed on the discharge side of the recording material P in the secondary transfer nip portion, that is, downstream of the secondary transfer roller 20 in the conveying direction of the recording material P. The charge eliminating needle 18, which is the second member, eliminates the charge of the recording material P that has passed through the secondary transfer nip portion (hereinafter, simply referred to as "discharging the recording material P") by a voltage for charge eliminating (hereinafter, referred to as "charge eliminating needle voltage") applied by a charge eliminating needle power source 19. The charge eliminating needle voltage applied to the charge eliminating needle 18 is a potential of opposite polarity to the transfer voltage applied to the secondary transfer roller 20. The charge eliminating needle 18 promotes separation of the recording material P electrostatically attracted to the intermediate transfer belt 10.

[0018] Thereafter, the recording material P carrying the four color toner image is introduced into the fixing device 30, where it is heated and pressurized so that the four color toners melt, mix, and are fixed to the recording material P. Through the above operations, a full-color toner image is formed on the recording material P. In addition, the toner remaining on the surface of the intermediate transfer belt 10 is temporarily collected by the brush 16, which is the first member, due to the brush voltage applied by the brush power supply 17 to the brush 16.

[0019] Thereafter, when image formation is completed, a voltage of the opposite polarity to the voltage used when the toner was temporarily collected is applied to the brush 16, causing the brush 16 to expel the toner onto the intermediate transfer belt 10. Thereafter, the toner expelled onto the intermediate transfer belt 10 is transferred (i.e., reverse-transferred) from the intermediate transfer belt 10 to the photosensitive drum 1a, and is cleaned and removed by the cleaning device 5a.

[0020] [Block diagram of image forming device] 2 is a functional block diagram of an engine control unit of a laser printer as the image forming apparatus 100. The controller unit 302 is capable of communicating with the host computer 301 and the engine control unit 303. When the controller unit 302 receives (inputs) print data from the host computer 301, it develops the print data and converts it into image data for forming an image. Then, based on the image data, it generates video signals for exposure of four colors for exposure. When the controller unit 302 completes the generation of the video signals, it instructs the video interface unit 304 of the engine control unit 303 to start printing. The engine control unit 303 has a microcomputer 303a with built-in ROM 303b and RAM 303c, and exchanges information with the controller unit 302 through serial communication, and performs the control described below based on the information exchanged from the controller unit 302.

[0021] When the video interface unit 304 receives a print start instruction from the controller unit 302, it transmits the print start instruction to the image formation control unit 305. Based on the received print start instruction, the image formation control unit 305 activates various actuators by the actuator driving unit 306 and starts preparation for image formation. When the image formation control unit 305 is ready for image formation, it notifies the controller unit 302 of completion of image formation preparation via the video interface unit 304. When the controller unit 302 receives the image formation preparation completion notification, it starts transmitting a video signal to the video interface unit 304 based on a vertical synchronization signal output from the engine control unit 303. The image formation control unit 305 performs image formation based on the video signal received by the video interface unit 304 by the image formation operation control unit 307.

[0022] The engine control unit 303 transfers the toner image developed on the photosensitive drum 1 (photosensitive member) to the recording material P via the intermediate transfer belt 10 by the image forming operation control unit 307 and the high voltage control unit 201. At this time, the high voltage control unit 201 controls the high voltage power supply unit 308. Here, the high voltage power supply unit 308 has a positive voltage control unit 200a, a positive voltage control unit 200b as a first power supply, a negative voltage control unit 200c as a second power supply, a negative voltage control unit 200d, a secondary transfer power supply 21, a brush power supply 17, and a static elimination needle power supply 19. The high voltage control unit 201 determines the timing to control the positive voltage control unit 200a, the positive voltage control unit 200b, the negative voltage control unit 200c, and the negative voltage control unit 200d in accordance with the position of the recording material P. The high voltage control unit 201 controls the positive and negative superimposed voltages of the secondary transfer roller 20, the brush 16, and the static elimination needle 18.

[0023] [Explanation of high voltage circuit] In a high-voltage power supply device for an image forming apparatus, there is a configuration in which the output of one high-voltage power supply is applied to multiple loads, thereby making the device smaller and reducing costs. For example, a configuration has been proposed in which a voltage is supplied to two loads from one high-voltage power supply that outputs negative polarity. Here, for example, a cleaning member (hereinafter referred to as a brush) for an intermediate transfer belt and a secondary transfer roller are considered to be two loads.

[0024] Also proposed is a configuration in which a high voltage power supply (first power supply) that generates a voltage of a first polarity, that is, positive polarity, and a high voltage power supply (second power supply) that generates a voltage of a second polarity, that is, negative polarity, opposite to the first polarity, are connected to one load. In this configuration, a positive polarity voltage is applied to the brush during image formation, so that the toner that remains without being transferred from the intermediate transfer belt to the recording material is collected by the brush. Then, after image formation is completed, a negative polarity is applied to the brush, so that the toner collected by the brush is discharged onto the intermediate transfer belt, and the discharged toner is collected in a waste toner container.

[0025] Also, a configuration has been proposed in which a voltage is supplied to three loads from one high-voltage power source that outputs negative polarity. Here, for example, a brush, a secondary transfer roller, and a charge-removing needle are considered as the three loads. The charge-removing needle is a member used to separate the recording material from the intermediate transfer belt. For example, the charge-removing needle uses a corona discharger arranged downstream in the conveying direction of the recording material, and irradiates the recording material immediately after it is discharged from the transfer section with charged particles generated by corona discharge, thereby separating the recording material from the intermediate transfer belt. In an image forming apparatus configured in this way, a positive voltage is applied to the brush during image formation, and the toner that remains without being transferred is collected, while a negative voltage is applied to the charge-removing needle, thereby separating the recording material from the intermediate transfer belt. Here, since the negative power source is connected to the charge-removing needle and the brush, a positive voltage and a negative voltage are applied to the brush. Hereinafter, the output in which a positive voltage and a negative voltage are superimposed and applied to one component will be referred to as "positive-negative superimposed output," and this type of control will be referred to as "positive-negative superimposed control." At this time, in order to apply a positive voltage to the brush, the output of the positive voltage is increased by the amount of the voltage applied from the negative power source. This allows control to apply the desired positive voltage to the brush.

[0026] As for a method for controlling the output voltage of a high-voltage power supply, a high-voltage power supply device has been proposed that includes a gain setting means for setting the gain of a control means for high-voltage output based on the deviation between a target voltage value of the high-voltage power supply and a detected voltage value that is the detection result of a voltage detection means. This power supply device includes a gain switching means for switching the gain so as to increase the gain setting of the control means when the detected voltage value of the voltage detection means is smaller than a predetermined threshold value in order to speed up the rise time of the high-voltage power supply. By controlling the gain switching based on the deviation between the target voltage value and the current detected voltage value, the gain is small during steady state, thereby suppressing ripples in the output voltage of the high-voltage power supply, and the gain is large during power start-up, thereby shortening the power supply start-up time.

[0027] 2 shows the configurations of the secondary transfer power supply 21, the brush power supply 17, and the static elimination needle power supply 19 of the image forming apparatus 100 of the embodiment 1. The relationship between the positive voltage control unit 200a, the positive voltage control unit 200b, the negative voltage control unit 200c, and the negative voltage control unit 200d and each power supply is shown below. Secondary transfer power supply 21: positive voltage control unit 200a + negative voltage control unit 200d (Positive and negative superimposed power supply) Brush power supply 17 ··· Positive voltage control unit 200b + Negative voltage control unit 200c (Positive and negative superimposed power supply) Negative voltage control unit 200c

[0028] The high voltage control unit 201 is controlled by a microcomputer 303a having built-in ROM 303b and RAM 303c, detects the current and voltage flowing through the secondary transfer roller 20, the brush 16, and the static elimination needle 18, and controls the voltage applied to the secondary transfer roller 20, the brush 16, and the static elimination needle 18. The circuits of the positive voltage control unit 200a, the positive voltage control unit 200b, the negative voltage control unit 200c, and the negative voltage control unit 200d that constitute the secondary transfer power supply 21, the brush power supply 17, and the static elimination needle power supply 19 will be described below with reference to FIG.

[0029] [Circuit explanation of secondary transfer power supply 21] The positive voltage control unit 200a (secondary transfer positive power supply) of the secondary transfer power supply 21 is configured to apply a voltage by a flyback transformer 202. The transformer driving unit 251 is a driving unit that drives the flyback transformer 202. The transformer driving unit 251 is driven at a predetermined frequency according to an analog signal 280 (e.g., a PWM signal) output from a PWM control unit 321 of the high voltage control unit 201 and a CLK signal 281 from a CLK control unit 323. The flyback transformer 202 has an internal capacitor 254 and a bleeder resistor 206, is turned on by the control of the transformer driving unit 251, and applies a positive voltage to the secondary transfer roller 20 as the secondary transfer power supply 21. The voltage detection circuit 208 divides the voltage applied to the secondary transfer roller 20 by resistors (not shown), and inputs the divided output to an AD converter 322 to detect the voltage applied to the secondary transfer roller 20. Here, a circuit configuration using a flyback transformer as the high voltage control generation means has been described, but other configurations of the high voltage power supply generation circuit may also be used.

[0030] [Circuit explanation for brush power supply 17] A positive voltage control unit 200b (brush positive power supply) of the brush power supply 17 is configured to apply a voltage by a piezoelectric transformer 210, which is a first piezoelectric transformer. A transformer driving unit 252 is a driving unit that drives the piezoelectric transformer 210. The transformer driving unit 252 drives the piezoelectric transformer 210 to output a predetermined voltage at a driving frequency based on a control signal 282 (frequency setting signal) (PWM signal) output from a PWM control unit 331 of the high voltage control unit 201. The piezoelectric transformer 210 is turned on by the control of the transformer driving unit 252, and applies a positive voltage to the brush 16 as the brush power supply 17. Diodes 261, 262, and a capacitor 263 form a rectifier circuit that rectifies the output of the piezoelectric transformer 210. A resistor 205 is a bleeder resistor. Voltage detection circuit 238, which is a first voltage detection means (voltage detection means), divides the voltage applied to brush 16 using resistors (not shown) and inputs the divided output to AD converter 332 to detect the voltage applied to brush 16. Here, a circuit configuration using a piezoelectric transformer is described as the high voltage control means, but other configurations of high voltage power supply generation circuits may also be used.

[0031] [Circuit explanation of static elimination needle power supply 19] The negative voltage control section 200c and the negative voltage control section 200d of the brush 16 and the static electricity elimination needle 18 are configured to apply voltages by a piezoelectric transformer 204 of a negative power supply, which is a second piezoelectric transformer. The transformer driving section 253 is a driving section that drives the piezoelectric transformer 204 for the negative power supply. The transformer driving section 253 drives the piezoelectric transformer 204 to output a predetermined voltage at a driving frequency based on a control signal 283 (frequency setting signal) (PWM signal) output from the PWM control section 341 of the high voltage control section 201. The output of the piezoelectric transformer 204 for the negative power supply is separated into a current path to the secondary transfer roller 20 and a current path to the brush 16 and the static electricity elimination needle 18 by passing through two rectifier circuits 271 and 272 connected in parallel. With this configuration, the reference voltages Vref1 and Vref2 on the non-grounded sides of the current detection circuit 237(i1) and the current detection circuit 207(i2) are also separated at the same time.

[0032] The piezoelectric transformer 204 is turned on by the control of the transformer driving unit 253, applies a negative voltage to the brush 16 and the static elimination needle 18 via the rectifier circuit 271, and applies a negative voltage to the secondary transfer roller 20 via the rectifier circuit 272. The rectifier circuit 271 is composed of diodes 273 and 274 and a capacitor 275, and the rectifier circuit 272 is composed of diodes 276 and 277 and a capacitor 278, and each rectifies the output from the piezoelectric transformer 204. The resistors 234 and 235 are bleeder resistors. The voltage detection circuit 258, which is the second voltage detection means, divides the voltage applied to the static elimination needle 18 by resistors (not shown), and inputs the divided output to the AD converter 342 to detect the voltage applied to the static elimination needle 18. Here, a circuit configuration using a piezoelectric transformer as the high voltage control means is described, but other configurations of high voltage power supply generation circuits may be used.

[0033] [Explanation of the current paths of the secondary transfer power supply 21, the brush power supply 17, and the static elimination needle power supply 19] The secondary transfer positive current flows into the GND of the photosensitive drum 1a via the secondary transfer roller 20, the intermediate transfer belt 10, and the photosensitive drum 1a by the charge pump of the capacitor 254 in the flyback transformer 202. Then, the secondary transfer positive current that has flowed into the GND of the photosensitive drum 1a passes from the GND of the current detection circuit 207 through the current detection circuit 207 and the bleeder resistor 235, and returns to the capacitor 254 in the flyback transformer 202.

[0034] The brush positive current flows into the GND of the photosensitive drum 1a via the brush 16, the intermediate transfer belt 10, and the photosensitive drum 1a by the charge pump of the capacitor 263. Then, the brush positive current that has flowed into the GND of the photosensitive drum 1a passes from the GND of the current detection circuit 237 through the current detection circuit 237 and the bleeder resistor 234 and returns to the capacitor 263.

[0035] The secondary transfer negative current flows into the current detection circuit 207 and the GND of the current detection circuit 207 by the charge pump of the capacitor 278. Then, the secondary transfer negative current that has flowed into the GND of the current detection circuit 207 returns to the capacitor 278 from the GND of the photosensitive drum 1a via the photosensitive drum 1a, the intermediate transfer belt 10, the secondary transfer roller 20, and the bleeder resistor 206 in the flyback transformer 202.

[0036] The brush negative current flows into the current detection circuit 237 and the GND of the current detection circuit 237 by the charge pump of the capacitor 275. Then, the brush negative current that has flowed into the GND of the current detection circuit 237 returns to the capacitor 275 from the GND of the photosensitive drum 1a via the photosensitive drum 1a, the intermediate transfer belt 10, the brush 16, and the bleeder resistor 205.

[0037] Similarly, the static elimination needle negative current flows into the current detection circuit 237 and the GND of the current detection circuit 237 by the charge pump of the capacitor 275. Then, the static elimination needle negative current that has flowed into the GND of the current detection circuit 237 returns to the capacitor 275 from the GND of the photosensitive drum 1a via the photosensitive drum 1a, the intermediate transfer belt 10, the recording material P, and the static elimination needle 18.

[0038] [Explanation of constant voltage control of the secondary transfer power supply 21, brush power supply 17, and static elimination needle power supply 19] The output voltage control of the secondary transfer power supply 21, the brush power supply 17, and the static elimination needle power supply 19 is performed by PID control units 320, 330, and 340 provided in each power supply circuit. The PID control units 320, 330, and 340 perform constant voltage control by PID control based on the deviation between a target voltage value set in advance as the operation of the image forming apparatus 100 and the voltage detection value of each power supply circuit captured by AD converters 322, 332, and 342. The high voltage control unit 201 has gain setting units 324, 334, and 344 that set arbitrary feedback gains for each parameter of the P term, I term, and D term of the PID control units 320, 330, and 340.

[0039] In the secondary transfer power supply 21, the high voltage control unit 201 applies a positive voltage to the secondary transfer roller 20 in synchronization with the arrival timing of the recording material P in order to transfer the toner image to the recording material P. Fig. 4(i) shows the secondary transfer voltage, and (ii) shows the gain (set gain) (high gain or low gain) set in the secondary transfer power supply 21. Both horizontal axes indicate time, with t401 and t402 indicating times (timing).

[0040] As shown in FIG. 4, the gain setting unit 324 sets the gain of the P term high at time t401 when a voltage is applied to the secondary transfer roller 20. The gain setting unit 324 switches the gain of the P term to a low gain at time t402 when the deviation between the output voltage of the secondary transfer power supply 21 and the target voltage becomes smaller than the desired value. This shortens the power supply rise time when applying a voltage to the secondary transfer roller 20, and can suppress the ripple of the voltage applied to the secondary transfer roller 20 to a small value after the desired voltage is applied to the secondary transfer roller 20. Here, the explanation has been given of switching the gain setting only for the P term, but it is desirable to optimize the gain setting for the D term and the I term in the same manner in order to suppress the ripple of the voltage during voltage application to a small value while shortening the power supply rise time.

[0041] In the brush power supply 17, the high voltage control unit 201 applies a positive voltage in accordance with the timing of the arrival of the toner remaining on the intermediate transfer belt 10 in order to recover the toner that has not been transferred from the intermediate transfer belt 10 to the recording material P to the brush 16. In addition, in the charge removal needle power supply 19, a negative voltage is applied to the charge removal needle 18 in accordance with the timing of the arrival of the recording material P in order to promote separation of the recording material P electrostatically adsorbed to the intermediate transfer belt 10. The PID control at the time of power up in the brush power supply 17 and the charge removal needle power supply 19 is similar to the constant voltage control by the PID control of the secondary transfer power supply 21. The brush power supply 17 is also subjected to constant voltage control by the PID control unit 330, which is the first control unit, based on the set gain set by the gain setting unit 334, which is the first setting unit (setting unit). The charge removal needle power supply 19 is also subjected to constant voltage control by the PID control unit 340, which is the second control unit, based on the set gain set by the gain setting unit 344, which is the second setting unit. That is, the gain setting unit 334 sets a first gain (gain) when controlling the positive voltage control unit 200b based on the voltage detected by the voltage detection circuit 238 and a target voltage Vt1 described later. The gain setting unit 344 sets a second gain when controlling the negative voltage control unit 200c based on the voltage detected by the voltage detection circuit 258 and a target voltage Vt2 described later.

[0042] [Explanation of positive and negative superposition control of high voltage power supply] In the configuration of the first embodiment, as shown in Fig. 3, the positive voltage control unit 200b and the negative voltage control unit 200c of the brush power supply 17 are connected to each other at a connection point A. When the negative voltage control unit 200c is put into an output state while the positive voltage control unit 200b is outputting and the output voltages are superimposed, the reference potential of the positive voltage control unit 200b is lowered by the absolute value of the negative voltage output by the negative voltage control unit 200c. In other words, when a positive voltage is output to the brush 16 to collect the toner remaining on the intermediate transfer belt 10, the positive voltage control unit 200b outputs a positive voltage that is larger by the absolute value of the negative voltage output by the negative voltage control unit 200c.

[0043] Here, FIG. 5 shows the transition of the power supply state when performing positive and negative superposition control on the brush 16. (i) shows the brush voltage, with the target voltage (first target voltage) being Vt1, and 0V being the off voltage. (ii) shows the output of the positive voltage control unit 200b outputted to the brush 16, and also shows the voltage V3 (=V1+|V2|) during positive and negative superposition control. (iii) shows the gain settings (low gain, high gain) of the positive voltage control unit 200b. (iv) shows the output of the negative voltage control unit 200c outputted to the brush 16, i.e., the static elimination needle voltage, with the target voltage (second target voltage) of the negative voltage being Vt2. (v) shows the gain setting of the negative voltage control unit 200c. t501 to t506 show each timing.

[0044] As a specific example, as shown in FIG. 5, a case will be described where it is desired to superimpose a voltage V1 (+1000V (first voltage)) for recovering toner remaining on the intermediate transfer belt 10 and a static elimination needle voltage V2 (-1000V (second voltage)) and output them. In this case, it is necessary to control the positive voltage control unit 200b to output a voltage V3 = V1 + |V2| = +2000V (=1000V + |-1000V|). Note that the voltage V1 (first voltage) is a voltage generated by the positive voltage control unit 200b when positive / negative superimposition control is not being performed, and the static elimination needle voltage V2 (second voltage) is a voltage generated by the negative voltage control unit 200c.

[0045] 3, the positive voltage control unit 200b detects the voltage that has dropped by the negative voltage as the detection result, and the high voltage control unit 201 converts the detection result of the positive voltage control unit 200b by the AD converter 332 and feeds it back to the PID control unit 330. In other words, by increasing the output from the positive voltage control unit 200b by the amount of the drop in the voltage applied to the brush 16, the desired positive voltage is applied to the brush 16 even during the positive and negative superimposed output.

[0046] FIG. 8 shows the transition of the power supply state when positive and negative superposition control is performed on the brush. (i) shows the voltage applied to the brush (hereinafter referred to as brush voltage), with the target voltage being Vt1, and 0V being the off voltage. (ii) shows the positive voltage output to the brush (positive voltage output), and also shows the voltage V3 (=V1+|V2|) during positive and negative superposition control. (iii) shows the gain settings (low gain, high gain) when applying a positive voltage. (iv) shows the negative voltage output to the brush, with the target voltage for the negative voltage being Vt2. (v) shows the gain settings when applying a negative voltage. The horizontal axis indicates time in all cases. t1501 to t1506 indicate each timing.

[0047] At time t1501, a positive polarity output to the brush is started. From time t1501 to time t1502 when the brush voltage reaches the target voltage Vt1, the gain of the positive polarity voltage is set to a high gain. In the period from time t1502 to t1503 when the target positive polarity voltage is applied to the brush, the positive polarity output is already close to the target voltage Vt1. For this reason, in order to suppress the ripple of the output voltage, the gain of the positive polarity voltage is set to a small setting value (low gain) and voltage control is performed. When the application of the negative polarity voltage is started at time t1503 to perform the positive / negative superposition control, the deviation of the negative polarity voltage between the target voltage Vt2 and the current output voltage value is large, so the gain is set to a large state (high gain) and the start-up control of the power supply is started. As a result, the positive polarity voltage control of the brush voltage cannot follow the start-up control of the negative polarity voltage, and ripples are generated in the brush voltage in the period around time t1504. Note that time t1505 is the time when the application of the negative voltage ends, and time t1506 is the time when the positive voltage returns to the target voltage Vt1.

[0048] If ripples occur in the brush voltage, it becomes difficult for the brush to stably hold the toner remaining on the surface of the intermediate transfer belt during the print sequence.

[0049] Therefore, a control method for reducing the ripple of the output voltage applied to the brush 16 in the first embodiment will be described when a positive-negative superimposed output state is set in which a positive voltage is applied to the brush 16 from the positive voltage control unit 200b and a negative voltage is applied from the negative voltage control unit 200c. The high voltage control unit 201 starts starting up the positive voltage control unit 200b at time t501, and the PID control unit 330 starts PID control to achieve the target voltage Vt1. At time t501, the voltage applied to the brush 16 is V0 (0V), and the deviation from the target voltage Vt1 is large. For this reason, the gain setting unit 334 sets a high gain setting value. At time t502 when the voltage applied to the brush 16 reaches the target voltage Vt1, the gain setting unit 334 sets a low gain setting value to suppress the ripple of the voltage applied to the brush 16.

[0050] Next, the high voltage control unit 201 starts to start up the negative voltage control unit 200c at time t503 in accordance with the timing of time t504 when the recording material P reaches the static electricity removal needle 18. At time t503, the voltage applied to the static electricity removal needle 18 is 0V, and since the deviation from the target voltage Vt2 is large, the gain setting unit 334 sets a high gain setting value. In addition, in order to prevent voltage ripples occurring in the brush 16, the gain setting unit 324 also sets a high gain setting value for the positive voltage control unit 200b. The PID control unit 340 of the negative voltage control unit 200c starts PID control so that the target voltage Vt2 is reached. At this time, constant voltage control is performed so that the output voltage applied to the brush 16 becomes the target voltage Vt1, and the positive voltage control unit 200b outputs a voltage of V1 + |V2| (=V3). The PID control unit 330 of the positive voltage control unit 200b performs PID control in a state where the gain is balanced with the gain setting unit 344 of the PID control unit 340 of the negative voltage control unit 200c. This makes it possible to maintain the positive voltage applied to the brush 16 at the target voltage Vt1 without generating ripples.

[0051] At time t504 when the voltage applied to the static elimination needle 18 reaches the target voltage Vt2, the gain setting unit 344 sets a low gain setting value in order to suppress ripples in the voltage applied to the static elimination needle 18. At the same time, the gain setting unit 344 of the positive voltage control unit 200b also sets a low gain setting value.

[0052] Thereafter, the high voltage control unit 201 stops applying the negative voltage at time t505 when the recording material P passes the charge removal needle 18. At this time, the negative voltage control unit 200c is also connected to the brush 16 and applies a negative voltage, so that at time t506 when the output of the negative voltage control unit 200c becomes V0 (0 V), the voltage control of the brush 16 switches from the positive-negative superimposed output to the positive voltage output.

[0053] In this manner, when the static elimination needle power supply 19 starts applying the static elimination needle voltage V2 to the static elimination needle 18, so that the voltage V1 and the static elimination needle voltage V2 are superimposed and applied to the brush 16, the gain setting unit 334 switches the setting of the first gain. More specifically, when the brush power supply 17 starts applying the voltage V1 to the brush 16, the gain setting unit 334 sets the first gain to a first set value (high gain) (t501). When the voltage V1 reaches the target voltage Vt1, the gain setting unit 334 switches the first gain to a second set value (low gain) lower than the first set value (t502). In addition, when the voltage V1 and the static elimination needle voltage V2 are superimposed and applied to the brush 16, the gain setting unit 334 switches the first gain from the second set value (low gain) to the first set value (high gain) (t503).

[0054] On the other hand, when the static elimination needle power supply 19 starts applying the static elimination needle voltage V2 to the static elimination needle 18, the gain setting unit 344 sets the second gain to a third set value (high gain) (t503). When the static elimination needle voltage V2 reaches the target voltage Vt2, the gain setting unit 344 sets the second gain to a fourth set value (low gain) lower than the third set value (high gain) (t504). When the static elimination needle voltage V2 reaches the target voltage Vt2, the gain setting unit 334 switches the first gain to the second set value in response to the switching of the second gain by the gain setting unit 344 (t504).

[0055] As described above, according to the first embodiment, when a positive and negative superimposed output is applied to the voltage application unit, the gain setting value of the PID control unit of the positive voltage control unit is increased, so that the ripples generated in the voltage application unit can be reduced even in a transient state in which the positive and negative superimposed output is started. As a result, the toner remaining on the surface of the intermediate transfer belt 10 during the print sequence of the image forming apparatus 100 can be stably collected by the brush 16. Note that, although the control of the positive and negative superimposed output to the brush 16 has been described in the first embodiment, the application location of the positive and negative superimposed output is not limited. Also, a configuration may be used in which a positive voltage is applied from the positive voltage control unit to the voltage application unit while a negative voltage is applied from the negative voltage control unit to the voltage application unit, and a positive voltage is applied from the positive voltage control unit to perform the positive and negative superimposed output.

[0056] As described above, according to the first embodiment, when a positive voltage and a negative voltage are superimposed and applied to a load, it is possible to reduce ripples occurring in the output voltage. EXAMPLES

[0057] In Example 2, a different embodiment will be described regarding a gain setting method set in the PID control units of the positive voltage control unit and the negative voltage control unit during positive / negative superposition control. Regarding the outline of the configuration of the image forming apparatus 100 in Example 2 and the configuration of the high voltage power supply circuit, the description of the same parts as in Example 1 will be omitted, and the specific description will be given of the differences.

[0058] [Explanation of the characteristics of piezoelectric transformers] Fig. 6 shows the relationship between the drive frequency and the output voltage when a PWM signal is input to the piezoelectric transformers 210, 204 used in the brush power supply 17 and the static elimination needle power supply 19. Fig. 6(a) shows the output characteristics of the positive voltage control unit 200b, and Fig. 6(b) shows the output characteristics of the negative voltage control unit 200c. In both cases, the horizontal axis shows the drive frequency f, and the vertical axis shows the output voltage Vout (or -Vout).

[0059] The piezoelectric transformer has the characteristic that it outputs the maximum voltage when the driving frequency is the resonance frequency fp of the piezoelectric transformer (generally around 160 kHz). When performing voltage control on the positive voltage control unit 200b and the negative voltage control unit 200c of the brush power supply 17, the PWM control units 331 and 341 input PWM signals with driving frequencies f of f600 and f610 (approximately 180 kHz) to the transformer driving units 252 and 253 and start voltage control. Hereinafter, f600 and f610 are referred to as driving start frequencies. Thereafter, while the driving frequency f is swept to the low frequency side by the PWM control units 331 and 341, voltage control is performed by the PID control units 330 and 340 so that the detection results of the voltage detection circuits 238 and 259 become the desired target voltage.

[0060] The output voltage characteristic of the piezoelectric transformer with respect to the driving frequency f is non-linear. For this reason, the displacement amount of the output voltage with respect to the driving frequency f is insensitive (the displacement amount is small) when the driving frequency f is near the driving start frequencies f600 and f610, but becomes steep (the displacement amount becomes large) when the driving frequency f approaches the resonance frequency fp. Therefore, in the second embodiment, in order to suppress the overshoot of the output voltage at the time of power supply startup, instead of setting the gain setting for the PID control unit at the time of power supply startup to a fixed value, power supply startup control is performed while switching in multiple stages.

[0061] As shown in FIG. 6, in the sections f600 to f601 and f610 to f611 where the displacement amount of the output voltage with respect to the driving frequency f is insensitive, the gain settings are set to high gains G601 and G611. Also, in the sections f601 to f602 and f611 to f612, PID control is implemented by setting gain setting values G602 (<G601) and G612 (<G611) lower than G601 and G611. Further, in the frequency band higher than f602 and f612 where the displacement amount of the output voltage with respect to the driving frequency f becomes the steepest, PID control is implemented by setting gain setting values G603 (<G602) and G613 (<G612) even lower than G602 and G612.

[0062] The right side of the graphs in Figures 6(a) and (b) show the gains (selected gains) (G601 to G603, G611 to G613) that are selected corresponding to each section of the drive frequency. Note that in the selected gains, the lower the gain in the graph (a), the higher the gain, and the higher the gain in the graph (b), the lower the selected gain.

[0063] As shown in Fig. 6(a), the piezoelectric transformer 210 outputs a voltage V1 at a drive frequency f between drive frequencies f601 and f602, and outputs a voltage V3 at a drive frequency f between drive frequencies f602 and resonant frequency fp. As shown in Fig. 6(b), the piezoelectric transformer 204 outputs a voltage V2 to the static elimination needle at a drive frequency f between drive frequencies f611 and f612. When the output voltage reaches the target voltage, the PWM control units 331 and 341 stop sweeping the drive frequency f of the PWM signal to the low frequency side.

[0064] [Explanation of positive and negative superposition control of high voltage power supply] Fig. 7 is a timing chart before and after the start of positive and negative superposition output, where (i) to (v) show graphs similar to (i) to (v) in Fig. 5. Note that (iii) and (v) show gain setting values ​​G0, G601, etc. Also, t601 to t608 show each timing.

[0065] The high voltage control unit 201 starts the startup of the positive voltage control unit 200b at time t601, and the PID control unit 330 starts PID control so as to reach the target voltage Vt1. At time t601, the voltage applied to the brush 16 is V0 (0V), and since there is a large deviation from the target voltage Vt1, the gain setting unit 334 is set to a gain setting value G601. The PWM control unit 331 sweeps the driving frequency f of the PWM signal to the low frequency side until the target voltage Vt1 is reached. The PID control is started, and at time t602 when the driving frequency f of the PWM signal reaches f601, the gain setting unit 334 is set to a minimum gain setting value G0 to suppress the ripple in the voltage applied to the brush 16 at time t603 when the voltage applied to the brush 16 reaches the target voltage Vt1. Here, the relationship of the gain setting values ​​in the positive voltage control unit 200b is as follows: High gain: G601>G602>G603>G0: Low gain

[0066] Next, the high voltage control unit 201 starts to start up the negative voltage control unit 200c at time t604, in time with time t606 when the recording material P reaches the static elimination needle 18. At time t604, the voltage applied to the static elimination needle 18 is 0 V, and since there is a large deviation from the target voltage Vt2, a high gain setting value G611 is set in the gain setting unit 334. The PWM control unit 341 sweeps the drive frequency f of the PWM signal to the low frequency side until the target voltage Vt2 is reached.

[0067] In order to prevent voltage ripples occurring in the brush 16, the gain setting unit 324 of the positive voltage control unit 200b also sets a gain setting value G602 corresponding to the current drive frequency f601-f602 (drive frequency corresponding to voltage V1). The PWM control unit 331 sweeps the drive frequency f of the PWM signal to the low frequency side until the output voltage becomes voltage V3. Meanwhile, the PID control unit 340 of the negative voltage control unit 200c starts PID control so as to reach the target voltage Vt2.

[0068] A gain setting value G603 is set at time t605 when the driving frequency f of the PWM signal of the positive voltage control unit 200b reaches f602. Similarly, for the negative voltage control unit 200c, a gain setting value G612 is set at time t605 when the driving frequency f of the PWM signal reaches f611. At this time, in order to perform constant voltage control so that the output voltage applied to the brush 16 becomes the target voltage Vt1, the positive voltage control unit 200b outputs a voltage of V3=V1+|V2|. The PID control unit 330 of the positive voltage control unit 200b performs PID control in a state where the control gain is balanced with the gain setting unit 344 of the PID control unit 340 of the negative voltage control unit 200c, so that the positive voltage applied to the brush 16 can be maintained at V1. In FIG. 7, the time when the drive frequency f reaches f602 due to the sweep of the PWM control unit 331 and the time when the drive frequency f reaches f611 due to the sweep of the PWM control unit 341 are the same, but they may be different times.

[0069] In order to suppress ripples in the voltage applied to the static electricity elimination needle 18 at time t606 when the voltage applied to the static electricity elimination needle 18 reaches the target voltage Vt2, a minimum gain setting value G1 is set in the gain setting unit 344. At the same time, a minimum gain setting value G0 is also set in the gain setting unit 344 of the positive voltage control unit 200b. Here, the relationship of the gain setting values ​​in the negative voltage control unit 200c is as follows. High gain: G611>G612>G613>G1: Low gain

[0070] Thereafter, the high voltage control unit 201 stops applying the negative voltage at time t607 when the recording material P passes the charge removal needle 18. At this time, the negative voltage control unit 200c is also connected to the brush 16 and applies a negative voltage, so that at time t608 when the output of the negative voltage control unit 200c becomes V0 (0 V), the voltage control of the brush 16 switches from the positive-negative superimposed output to the positive voltage output.

[0071] In this way, the piezoelectric transformer 210 has an output characteristic in which the voltage change in the vicinity of the resonance frequency fp, which is lower than the drive start frequency f600, is steeper than the voltage change in the vicinity of the drive start frequency f600 at which drive is started. The gain setting unit 334 performs the following during the period from when the voltage V1 and the static elimination needle voltage V2 are superimposed and applied to the brush 16 until the static elimination needle voltage V2 reaches the target voltage Vt2. That is, the gain setting unit 334 switches the setting of the first gain according to the drive frequency so that the first gain becomes lower as the drive frequency of the piezoelectric transformer 210 becomes smaller in the range from the drive start frequency f600 to the resonance frequency fp (t604 to t606). Note that the gain setting unit 334 switches the setting of the first gain according to the drive frequency during the period from when the brush power supply 17 starts applying the voltage V1 to the brush 16 until the voltage V1 reaches the target voltage Vt1 (t601 to t603).

[0072] On the other hand, the piezoelectric transformer 204 also has output characteristics in which the voltage change in the vicinity of a resonance frequency fp lower than the drive start frequency f610 at which driving is started is steeper than the voltage change in the vicinity of the drive start frequency f610 at which driving is started. The gain setting unit 344 performs the following during the period from when the static elimination needle power supply 19 starts applying the static elimination needle voltage V2 to the static elimination needle 18 until the static elimination needle voltage V2 reaches the target voltage Vt2. That is, the gain setting unit 344 switches the setting of the second gain in accordance with the drive frequency (t604 to t606).

[0073] As described above, according to the second embodiment, particularly in the case of using a high voltage circuit using a piezoelectric transformer, the gain of the PID control corresponding to the drive frequency of each piezoelectric transformer is set during positive and negative superposition control. This makes it possible to reduce ripples occurring in the voltage application section during positive and negative superposition output. As a result, the toner remaining on the surface of the intermediate transfer belt 10 during the print sequence of the image forming apparatus 100 can be stably collected by the brush 16. Note that, although the above-mentioned second embodiment has been described with respect to the control of performing positive and negative superposition output to the brush 16, the application location of the positive and negative superposition output is not limited. Also, a configuration may be used in which a positive voltage is applied from the positive voltage control section to the voltage application section while a negative voltage is applied from the negative voltage control section, and a positive voltage is applied from the positive voltage control section to perform positive and negative superposition output.

[0074] As described above, according to the second embodiment, when a positive voltage and a negative voltage are superimposed and applied to a load, it is possible to reduce ripples occurring in the output voltage. [Explanation of symbols]

[0075] 16 Brushes 18 Static electricity removal needle 200b Positive voltage control section 200c Negative voltage control section 238 Voltage Detection Circuit 258 Voltage Detection Circuit 330 PID control unit 340 PID control unit 334 Gain setting section 344 Gain setting section

Claims

1. a first power supply generating a first voltage of a first polarity; a second power supply generating a second voltage of a second polarity opposite to the first polarity; a first member to which the first voltage or a voltage obtained by superimposing the first voltage and the second voltage is applied; a second member to which the second voltage is applied; a first control means for controlling the first power source; A second control means for controlling the second power source; a first voltage detection means for detecting a voltage applied to the first member; A second voltage detection means for detecting a voltage applied to the second member; a first setting means for setting a first gain when the first control means controls the first power supply based on the voltage detected by the first voltage detection means and a first target voltage; a second setting means for setting a second gain when the second control means controls the second power supply based on the voltage detected by the second voltage detection means and a second target voltage; An image forming apparatus comprising: The image forming apparatus is characterized in that the first setting means switches the setting of the first gain based on the second gain when a voltage obtained by superimposing the first voltage and the second voltage is applied to the first member while the second power source is applying the second voltage to the second member.

2. The first setting means is when the first power supply starts applying the first voltage to the first member, the first gain is set to a first set value, and when the first voltage reaches the first target voltage, the first gain is switched to a second set value lower than the first set value; 2. The image forming apparatus according to claim 1, wherein when a voltage in which the first voltage and the second voltage are superimposed is applied to the first member, the first gain is switched from the second set value to the first set value.

3. 3. The image forming apparatus according to claim 2, wherein the second setting means sets the second gain to a third set value when the second power source starts applying the second voltage to the second member, and sets the second gain to a fourth set value lower than the third set value when the second voltage reaches the second target voltage.

4. 4. The image forming apparatus according to claim 3, wherein the first setting unit switches the first gain to the second set value when the second voltage reaches the second target voltage.

5. the first power source includes a first piezoelectric transformer; the first piezoelectric transformer has an output characteristic in which a voltage change in the vicinity of a resonance frequency lower than a drive start frequency at which drive is started is steeper than a voltage change in the vicinity of the drive start frequency, The image forming apparatus according to claim 1, characterized in that the first setting means switches the setting of the first gain depending on the drive frequency so that the first gain becomes lower as the drive frequency of the first piezoelectric transformer becomes smaller in the range from the drive start frequency to the resonant frequency, from the time when the superimposed voltage of the first voltage and the second voltage is applied to the first member until the second voltage reaches the second target voltage.

6. 6. The image forming apparatus according to claim 5, wherein the first setting means switches the setting of the first gain in accordance with the drive frequency during a period from when the first power source starts applying the first voltage to the first member until when the first voltage reaches the first target voltage.

7. the second power source includes a second piezoelectric transformer; the second piezoelectric transformer has an output characteristic in which a voltage change in the vicinity of a resonance frequency lower than a drive start frequency at which drive is started is steeper than a voltage change in the vicinity of the drive start frequency, 6. The image forming apparatus according to claim 5, wherein the second setting means switches the setting of the second gain in accordance with the drive frequency during a period from when the second power source starts applying the second voltage to the second member until when the second voltage reaches the second target voltage.

8. A photoconductor; an intermediate transfer body onto which the toner image on the photoreceptor is transferred; a transfer means for transferring the toner image on the intermediate transfer body to a recording material; a brush for collecting toner that has not been transferred to the recording material by the transfer means and remains on the intermediate transfer body; a charge removing needle for separating the recording material after the toner image is transferred from the intermediate transfer body; Equipped with the first member is the brush, 8. The image forming apparatus according to claim 1, wherein the second member is the charge eliminating needle.

Images