JP2012113117A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that reduces difference in the amount of discharge that is caused by difference in the degree of stains on respective scorotron chargers.SOLUTION: An image forming apparatus includes: a first photoreceptor drum 51K that corresponds to black developer; a plurality of second photoreceptor drums 51Y, 51M, 51C that correspond to respective developer for colors other than black; a first scorotron charger 52K that charges the first photoreceptor drum 51K; a plurality of second scorotron chargers 52Y, 52M, 52C that charge corresponding respective second photoreceptor drums 51Y, 51M, 51C; a first voltage application circuit 210 that is connected to the first scorotron charger 52K and applies voltage to the first scorotron charger 52K; and a second voltage application circuit 220 that is connected to the respective second scorotron chargers 52Y, 52M, 52C and applies voltage to the respective scorotron chargers 52Y, 52M, 52C.

Description

  The present invention relates to an image forming apparatus capable of executing monochrome printing and color printing.

  2. Description of the Related Art Conventionally, as a multicolor image forming apparatus such as a color laser printer, an apparatus including a photoconductor and a scorotron charger corresponding to each color developer and charging the photoconductor is known (for example, Patent Documents). 1). In the image forming apparatus disclosed in Patent Document 1, a single voltage application circuit for applying a voltage to each scorotron charger is made common, thereby reducing costs and downsizing the apparatus.

JP-A-3-142484

  However, in the above-described technique, since the voltage application circuit is shared, the voltage applied to each scorotron charger cannot be adjusted. On the other hand, the scorotron charger for black is used frequently, and dirt is likely to adhere to the wire compared to other scorotron chargers. Therefore, there is a large difference in the amount of discharge between the two, resulting in a decrease in image quality. It was.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that reduces a difference in discharge amount caused by a difference in the degree of contamination of each scorotron charger.

  In order to achieve the above object, an image forming apparatus of the present invention includes a first photosensitive member corresponding to a black developer, a plurality of second photosensitive members corresponding to developers of colors other than black, and the first photosensitive member. A first scorotron charger for charging one photoconductor, a plurality of second scorotron chargers for charging each corresponding second photoconductor, and the first scorotron charger; A first voltage application circuit that applies a voltage and a second voltage application circuit that is commonly connected to each of the second scorotron chargers and applies a voltage to each of the second scorotron chargers.

  According to the image forming apparatus configured as described above, since the voltage application circuit is divided between the first scorotron charger and the other second scorotron charger, where the wires are likely to become dirty, the degree of contamination of the wires of each scorotron charger. It is possible to reduce the difference in the amount of discharge caused by the difference.

  According to the present invention, a voltage application circuit for applying a voltage to a charger is divided into a voltage application circuit connected to a black scorotron charger that is frequently used and easily contaminated with a wire, and other scorotron charging that has little wire contamination. Since the voltage application circuit is commonly connected to the charger, the difference in the discharge amount caused by the difference in the degree of dirt on the wires of each scorotron charger can be reduced.

1 is a side sectional view showing a color printer according to a first embodiment of the present invention. It is a figure which shows the structure of the power supply device which concerns on 1st Embodiment of this invention. It is a flowchart which shows control of the 2nd voltage application circuit by the control apparatus which concerns on 1st Embodiment of this invention. It is a flowchart which shows control of the 2nd voltage application circuit by the control apparatus which concerns on a modification. It is a flowchart which shows control of the 2nd voltage application circuit by the control apparatus which concerns on 2nd Embodiment.

[First Embodiment]
Next, a first embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, first, the overall configuration of the color printer 1 (image forming apparatus) will be briefly described, and then the details of the features of the present invention will be described.

  Further, in the following explanation, explanation will be given in the direction based on the user when the color printer 1 is used. That is, in FIG. 1, the left side is the “front (front) side”, the right side is the “rear (back) side”, the back side in the vertical direction of the paper is the “left side”, and the front side in the vertical direction of the paper is “Right side”. In addition, the vertical direction toward the page is defined as the “vertical direction”.

<Overall configuration of color printer>
As shown in FIG. 1, the color printer 1 includes, in the apparatus main body 2, a paper feeding unit 20 that supplies paper S (recording sheet (transfer medium)) and image formation that forms an image on the fed paper S. The unit 30 and a paper discharge unit 90 that discharges the paper S on which an image is formed are provided.

  An opening 2 </ b> A is formed in the upper part of the apparatus main body 2. The opening 2A is opened and closed by an upper cover 3 that is rotatably supported by the apparatus main body 2. An upper surface of the upper cover 3 serves as a paper discharge tray 4 that accumulates the paper S discharged from the apparatus main body 2.

  The paper feeding unit 20 is provided at a lower portion in the apparatus main body 2, and a paper feeding tray 21 that is detachably attached to the apparatus main body 2, and a paper supply mechanism that conveys the paper S from the paper feeding tray 21 to the image forming unit 30. 22 is provided. The paper supply mechanism 22 is provided on the front side of the paper feed tray 21 and includes a paper feed roller 23, a separation roller 24, and a separation pad 25.

  In the paper feed unit 20 configured in this way, the paper S in the paper feed tray 21 is separated one by one and sent upward, and passes through between the paper dust removal roller 26 and the pinch roller 27 in the process. After the powder is removed, the direction is changed backward through a conveyance path (not shown) and supplied to the image forming unit 30.

  The image forming unit 30 includes four LED units 40, four process cartridges 50, a transfer unit 70, a fixing unit 80, and a power supply device 200.

  The LED unit 40 is swingably connected to an LED mounting member (not shown) provided below the upper cover 3, and is appropriately positioned and supported by a positioning member provided in the apparatus main body 2.

  The process cartridge 50 is arranged in parallel in the front-rear direction between the upper cover 3 and the paper feed unit 20, and includes a drum cartridge 58 and a developing cartridge 56 that can be attached to and detached from the drum cartridge 58.

  The developing cartridge 56 mainly includes a developing roller 53, a supply roller 54, a layer thickness regulating blade 57, and a toner storage chamber 55 that stores toner as an example of a developer.

  Further, in the normal state, the developing cartridge 56 is indicated by reference numerals 56K, 56Y, 56M, and 56C containing toners for black, yellow, magenta, and cyan from the upstream side in the transport direction of the paper S. They are arranged in this order.

  The drum cartridge 58 includes a photosensitive drum 51 as an example of a photosensitive member, a scorotron charger 52, and the like. In the present specification and drawings, when the photosensitive drum 51 and the scorotron charger 52 corresponding to the color of the toner are specified, K, Y, M are associated with black, yellow, magenta, and cyan, respectively. , C is attached.

  In the present embodiment, the photosensitive drum 51K corresponding to black toner is also referred to as “first photosensitive drum 51K” (first photosensitive member). Further, the photosensitive drums 51Y, 51M, and 51C corresponding to the toners of colors other than black are also referred to as “second photosensitive drums 51Y, 51M, and 51C” (second photosensitive members). Further, the black scorotron charger 52K for charging the first photosensitive drum 51K is referred to as “first scorotron charger 52K”, and a plurality of scorotron chargers other than black for charging the corresponding second photosensitive drums 51Y, 51M, 51C. 52Y, 52M, and 52C are also referred to as “second scorotron chargers 52Y, 52M, and 52C”.

  The scorotron charger 52 includes a wire 521 formed of metal, and a grid 522 that is disposed between the wire 521 and the photosensitive drum 51 and is formed of a metal plate member (see FIG. 2). . The scorotron charger 52 generates a corona discharge when a voltage is applied by a power supply device 200 to be described later, and ions generated by the corona discharge flow as a discharge current to the photosensitive drum 51 side. Is uniformly charged.

  The transfer unit 70 is provided between the paper feeding unit 20 and each process cartridge 50, and includes a driving roller 71, a driven roller 72, a conveyance belt 73, and a transfer roller 74.

  The driving roller 71 and the driven roller 72 are arranged in parallel with a space in the front-rear direction, and a conveying belt 73 formed of an endless belt is stretched between them. The outer surface of the conveyance belt 73 is in contact with each photosensitive drum 51. In addition, four transfer rollers 74 that sandwich the conveyor belt 73 with the respective photosensitive drums 51 are arranged inside the conveyor belt 73 so as to face the respective photosensitive drums 51. The transfer roller 74 is applied with a transfer bias (transfer voltage) having a polarity different from the charging polarity of the toner by constant current control during transfer.

  The fixing unit 80 is disposed on the rear side of each process cartridge 50 and the transfer unit 70, and includes a heating roller 81 and a pressure roller 82 that is disposed to face the heating roller 81 and presses the heating roller 81.

  In the image forming unit 30 configured as described above, in the color printing mode, first, the surface of each photosensitive drum 51 is uniformly charged by each scorotron charger 52 and then exposed by each LED unit 40. The As a result, the potential of the exposed portion is lowered, and an electrostatic latent image based on the image data is formed on each photosensitive drum 51. Further, the toner in the toner storage chamber 55 is supplied to the developing roller 53 via the supply roller 54 and enters between the developing roller 53 and the layer thickness regulating blade 57 to form a thin layer having a certain thickness. Supported on.

  The toner carried on the developing roller 53 is supplied from the developing roller 53 to the electrostatic latent image formed on the photosensitive drum 51. As a result, the electrostatic latent image is visualized and a toner image is formed on the photosensitive drum 51.

  The sheet S supplied on the conveyor belt 73 passes between the photosensitive drums 51 and the transfer rollers 74 arranged inside the conveyor belt 73, so that the toner formed on the photosensitive drums 51 is formed. The image is transferred onto the paper S. Then, as the sheet S passes between the heating roller 81 and the pressure roller 82, the toner image transferred onto the sheet S is thermally fixed.

  The paper discharge unit 90 includes a paper discharge-side transport path 91 formed so as to extend upward from the exit of the fixing unit 80 and reverse forward, and a plurality of pairs of transport rollers 92 that transport the paper S. . The sheet S on which the toner image has been transferred and heat-fixed is transported along a paper discharge side transport path 91 by a transport roller 92, discharged outside the apparatus main body 2, and accumulated in the paper discharge tray 4.

<Configuration of power supply>
Next, the configuration of the power supply device 200 will be described.
The power supply device 200 is a device for applying a voltage to each scorotron charger 52. As shown in FIG. 2, the power supply device 200 has a first voltage application circuit 210, a second voltage application circuit 220, a control device 230, a constant device. Mainly composed of voltage circuits D1, D2, D3, D4 and current detection units R1, R2, R3, R4.

  The first voltage application circuit 210 and the second voltage application circuit 220 include PWM signal smoothing circuits 211 and 221, transformer drive circuits 212 and 222, output circuits 213 and 223, and voltage detection circuits 214 and 224, respectively. Yes.

  The first voltage application circuit 210 is connected to the first scorotron charger 52K and applies a voltage to the first scorotron charger 52K. The second voltage application circuit 220 is commonly connected to the second scorotron chargers 52Y, 52M, and 52C, and applies a voltage to the second scorotron chargers 52Y, 52M, and 52C.

  The PWM signal smoothing circuits 211 and 221 smooth the PWM signal output from the control device 230 described later, and output the smoothed PWM signal to the transformer drive circuits 212 and 222.

  The transformer drive circuits 212 and 222 are composed of amplification elements such as transistors, for example, and apply a voltage corresponding to the PWM signal to the output circuits 213 and 223.

  The output circuits 213 and 223 are circuits that rectify the voltages input from the transformer drive circuits 212 and 222 and output the rectified voltages to the scorotron chargers 52K, 52Y, 52M, and 52C. The wire 521 of the first scorotron charger 52K is connected to the output circuit 213 of the first voltage application circuit 210, and the wire 521 of the second scorotron charger 52Y, 52M, 52C is the output of the second voltage application circuit 220. The circuit 223 is connected.

  The voltage detection circuits 214 and 224 detect the voltages generated in the output circuits 213 and 223 and input them to the control device 230. Thereby, the control device 230 can take in the data of the output voltage of the output circuits 213 and 223.

  The constant voltage circuits D1, D2, D3, D4 are composed of, for example, three Zener diodes connected in series, and make the voltage of the grid 522 of each Scorotron charger 52K, 52Y, 52M, 52C constant.

  The current detection units R1, R2, R3, R4 are composed of resistors, for example, and are connected to the constant voltage circuits D1, D2, D3, D4, respectively. Then, each A / D port (not shown) provided in the control device 230, which will be described later, connects signal lines between the current detection units R1, R2, R3, R4 and the constant voltage circuits D1, D2, D3, D4, respectively. Connected through. With this configuration, since a voltage proportional to the magnitude of the grid current value flowing through each grid 522 is input to each A / D port, the voltage input to each A / D port can be read. Each grid current value can be detected.

  The control device 230 includes a CPU, a ROM, a RAM, and the like, and is configured to control the first voltage application circuit 210 and the second voltage application circuit 220 according to a program prepared in advance. Note that the amount of discharge flowing from the scorotron charger 52 to the surface of the photosensitive drum 51 is substantially proportional to the grid current value flowing through the grid 522. Therefore, in the present embodiment, the control device 230 performs control such that each grid current value is equal to or greater than a predetermined value so that the charge amount on the surface of the photosensitive drum 51 is not insufficient.

<Control method by control device>
Next, a method for controlling the second voltage application circuit 220 by the control device 230 will be described in detail with reference to FIG.
The control of the second voltage application circuit 220 by the control device 230 includes initial control (constant voltage control) executed immediately after the start of the printing process and actual control (constant current control) executed until the end of the printing process after the initial control. The two-stage control.

  In the initial control, first, immediately after the start of the printing process, the control device 230 causes the output voltage of the second voltage application circuit 220, that is, the second voltage application circuit 220 to detect the second scorotron chargers 52Y, 52M, and 52C (each wire 521). ) Is set to the target value of the voltage to be applied (S10).

  Next, the control device 230 inputs the PWM signal to the PWM signal smoothing circuit 221 so that the output voltage of the second voltage application circuit 220 becomes the target value set in step S10. Based on the voltage value detected by the voltage detection circuit 224, the output voltage of the second voltage application circuit 220 is adjusted so as to be stabilized at the target value (S20).

  When the output voltage is stabilized in step S20, the control device 230 causes the current value flowing through each current detection unit R2, R3, R4 from the voltage input to each A / D port, that is, the grid current flowing through each grid 522. A value is calculated (detected) (S30). Then, it is determined whether or not each grid current value detected in step S30 is equal to or greater than a predetermined value (S40).

  If at least one grid current value is smaller than the predetermined value in step S40 (No), control device 230 increases the target value of the output voltage (S50). Thereafter, the processing from step S20 to step S40 is similarly performed until all the grid current values become equal to or greater than a predetermined value.

  In step S40, when all the grid current values are equal to or larger than the predetermined value (Yes), the control by the control device 230 shifts to actual control.

  In the actual control, first, the control device 230 detects a grid current value flowing through each grid 522 (S60). And the control apparatus 230 discriminate | determines the grid current value which shows the minimum current value among each grid current value detected by step S60 (S70).

  Then, the control device 230 controls the second voltage application circuit 220 so that the grid current indicating the minimum current value determined in step S70 becomes a constant current equal to or greater than a predetermined value (S80). Specifically, in step S80, the control device 230 outputs the PWM signal to the PWM signal smoothing circuit 221 based on the voltage input to the A / D port corresponding to the grid 522 indicating the minimum current value. The output voltage is adjusted so that the grid current indicating the minimum current value becomes a constant current. In this way, by performing constant current control on the grid current value indicating the minimum current value, other grid current values can also be maintained at a current value equal to or greater than a predetermined value.

  Then, the control device 230 determines whether or not to end the voltage application process (S90). When the voltage application process is continuously performed (No), it is determined whether it is the timing for detecting the grid current value (S100). Specifically, the control device 230 detects each grid current value for each predetermined number of printed sheets. When the number of printed sheets reaches a predetermined value (Yes), each grid current value is detected (S60), and the grid current value indicating the minimum current value is determined again (S70). On the other hand, if the number of printed sheets has not reached the predetermined value in step S100 (No), the constant current control is continued (S80).

  When the printing process by the color printer 1 is completed, it is determined in step S90 that the voltage application process is terminated (Yes), and the control of the second voltage application circuit 220 by the control device 230 is terminated.

  The control device 230 performs constant current control on the first voltage application circuit 210 after performing the above-described initial control so that the grid current value of the first scorotron charger 52K is equal to or greater than a predetermined value. .

According to the above, the following effects can be obtained in the present embodiment.
A first voltage application circuit 210 connected to the first scorotron charger 52K corresponding to the frequently used black toner, and a plurality of second scorotron chargers 52Y, 52M, and 52C respectively corresponding to toners of colors other than black. And the second voltage application circuit 220 connected in common to each other, the discharge amount of the first scorotron charger 52K and the second scorotron chargers 52Y, 52M, and 52C caused by the difference in the degree of contamination of the wire 521 is reduced. The difference can be reduced.

  Then, current detection units R2, R3, and R4 that detect the grid current value flowing through each grid 522, and a control device 230 that controls the second voltage application circuit 220 so that each grid current value becomes equal to or greater than a predetermined value are provided. As a result, the surfaces of the corresponding second photosensitive drums 51Y, 51M, 51C can be sufficiently charged.

  Further, the control device 230 determines a grid current value indicating the minimum current value among the grid current values, and the second voltage is set so that the grid current value indicating the minimum current value becomes a constant current equal to or greater than a predetermined value. By controlling the application circuit 220, constant current control of one grid current makes it possible to maintain another grid current value at a current value equal to or higher than a predetermined value.

  Since the control device 230 determines the grid current value indicating the minimum current value for each predetermined number of printed sheets, even if the scorotron charger indicating the minimum grid current value is replaced during printing, Constant current control can be performed according to the grid current value of the scorotron charger showing the minimum current value.

  In the above embodiment, the timing for determining the grid current value indicating the minimum current value in step S100 is set for each predetermined number of printed sheets. However, the present invention is not limited to this. For example, the determination timing of the grid current value indicating the minimum current value may be every predetermined time. As described above, even when the grid current value indicating the minimum current value is determined every predetermined time, it is possible to cope with the change in the rank order of the grid current value during printing.

  In the above-described embodiment, the voltage is controlled so that each grid current value is equal to or higher than a predetermined value while performing constant voltage control in the initial control, but the present invention is not limited to this. For example, the initial control may be simplified as shown in FIG.

  Specifically, the control device 230 first sets a minimum value (that is, a target current value) of each grid current value at the start of printing (S15).

  Next, the control device 230 controls the second voltage application circuit 220 so that each grid current value becomes the set current value, and the second voltage application circuit 220 controls each scorotron charger 52C, 52Y, 52M. A voltage is applied (S25). And after completion | finish of step S25, it transfers to real control (after step S60).

  Thus, by simplifying the initial control, the initial control can be completed in a short time.

[Second Embodiment]
Next, a second embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In this embodiment, the control method by the control device 230 is simplified in the power supply device 200 having the same configuration as that of the first embodiment. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the present embodiment, the control by the control device 230 is the same as that of the first embodiment in the processing up to step S40, and the processing after step S40 is not performed to determine the grid current value indicating the minimum current value. In addition, control is performed to keep each grid current value at or above a predetermined value.

  Specifically, when all the grid current values are equal to or greater than a predetermined value in step S40 (Yes), the control device 230 performs constant voltage control (S110). Thereafter, it is determined whether or not to end the voltage application process (S90), and when it is determined to end (Yes), the control by the control device 230 ends.

  If it is determined in step S90 that the voltage application process is not terminated (No), the control device 230 determines whether it is time to detect the grid current value (S100). When it is the detection timing of the grid current (Yes), the control device 230 detects each grid current value (S30), and determines whether each detected grid current value is equal to or greater than a predetermined value (S40). When any of the grid current values is less than a predetermined value (No), the control device 230 applies a voltage to be applied between the wire 521 and the grid 522 of each of the second scorotron chargers 52Y, 52M, and 52C. The second voltage application circuit 220 is controlled to increase (S50). On the other hand, if it is not the detection timing of the grid current in step S100 (No), the constant voltage control is continued (S110).

  According to this, since there is no step of discriminating the grid current value indicating the minimum current value, the control can be simplified as compared with the case of the first embodiment.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. About a concrete structure, it can change suitably in the range which does not deviate from the meaning of this invention.

  In the embodiment, the color printer 1 is exemplified as the image forming apparatus. However, the present invention can also be applied to a multifunction machine or a copier.

DESCRIPTION OF SYMBOLS 1 Color printer 2 Apparatus main body 51K 1st photoreceptor drum 51Y, 51M, 51C 2nd photoreceptor drum 52K 1st scorotron charger 52Y, 52M, 52C 2nd scorotron charger 200 Power supply device 210 1st voltage application circuit 220 2nd Voltage application circuit 230 Controller 521 Wire 522 Grid R1, R2, R3, R4 Current detection unit

Claims (8)

A first photoreceptor corresponding to a black developer;
A plurality of second photoreceptors respectively corresponding to developers of colors other than black;
A first scorotron charger for charging the first photoreceptor;
A plurality of second scorotron chargers for charging each corresponding second photoreceptor;
A first voltage application circuit connected to the first scorotron charger and applying a voltage to the first scorotron charger;
An image forming apparatus comprising: a second voltage application circuit that is commonly connected to each of the second scorotron chargers and applies a voltage to each of the second scorotron chargers. The first scorotron charger and the second scorotron charger each have a wire and a grid,
A current detector for detecting a grid current value flowing through the grid of each of the corresponding second scorotron chargers;
The image forming apparatus according to claim 1, further comprising a control device that controls the second voltage application circuit so that each grid current value is equal to or greater than a predetermined value.   The control device determines a grid current value indicating a minimum current value among the grid current values, and the second voltage so that the grid current indicating the minimum current value becomes a constant current equal to or greater than the predetermined value. The image forming apparatus according to claim 2, wherein the application circuit is controlled.   The image forming apparatus according to claim 3, wherein the control device determines a grid current value indicating the minimum current value for each predetermined number of printed sheets.   The image forming apparatus according to claim 3, wherein the control device discriminates a grid current value indicating the minimum current value every predetermined time.   The control device controls the second voltage application circuit so as to increase a voltage to be applied to each of the second scorotron chargers when any of the grid current values becomes less than a predetermined value. The image forming apparatus according to claim 2.   The image forming apparatus according to claim 6, wherein the control device detects each grid current value for each predetermined number of printed sheets.   The image forming apparatus according to claim 6, wherein the control device detects each grid current value at predetermined time intervals.

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