Image forming apparatus

Abstract

To provide a technique that can prevent an excessive increase in grid voltage even when the type of a high-voltage power supply substrate comprising an electrification voltage generation circuit and a grid voltage adjustment circuit is changed.SOLUTION: An ASIC 61 discriminates the type of a high-voltage power supply substrate 62 based on a signal output from the high-voltage power supply substrate, when causing an electrification voltage generation circuit 70 and a grid voltage adjustment circuit 81 to start operating, controls the electrification voltage generation circuit 70 to generate an electrification voltage at which a current value of a grid current becomes constant, determines a prescribed time according to the discriminated type of the high-voltage power supply substrate 62, controls the grid voltage adjustment circuit 81 so that a grid voltage becomes a first target voltage during the determined prescribed time, and after the lapse of the prescribed time, controls the grid voltage adjustment circuit 81 so that the grid voltage becomes a second target voltage.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] This application relates to a technique for supplying power to a charger that charges a photoreceptor included in an image forming apparatus.

Background Art

[0002] Patent Document 1 describes an image forming apparatus including a plurality of chargers that charge respective ones of a plurality of photoreceptors corresponding to respective colors, supplying a high-voltage charging voltage from a single charging voltage generation circuit to a charging wire of each charger, and controlling the charging voltage supplied from the charging voltage generation circuit to each charging wire based on the current value of a grid current generated in a grid of each charger. Further, this image forming apparatus includes a grid voltage adjustment circuit that controls the grid voltage generated in each grid to a constant voltage value. And in this image forming apparatus, in order to deal with the case where the grid voltage excessively increases when the charging voltage generation circuit and the grid voltage adjustment circuit are simultaneously activated, when starting the operations of the charging voltage generation circuit and the grid voltage adjustment circuit, after starting a process of adjusting the current value of the grid current to a target current value, a process of adjusting the voltage value of the grid voltage to a target voltage value is started.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the image forming apparatus described in Patent Document 1, when the type of high-voltage power supply board equipped with a charging voltage generation circuit and a grid voltage adjustment circuit is changed, differences in how the charging voltage rises occur depending on the type of high-voltage power supply board after the change. As a result, simply starting the process of adjusting the grid voltage value to a target voltage value after starting the process of adjusting the grid current value to a target current value may not prevent the grid voltage from increasing excessively.

[0005] The present invention aims to provide a technology that can suppress an excessive increase in grid voltage even when the type of high-voltage power supply board equipped with a charging voltage generation circuit and a grid voltage adjustment circuit is changed. [Means for solving the problem]

[0006] To achieve the above objective, the image forming apparatus of the present invention comprises a photoreceptor, a charger having a charging wire and a grid for charging the photoreceptor, a high-voltage power supply board connected to the charger and having a charging voltage generation circuit that generates a charging voltage which is a voltage applied to the charging wire of the charger, a grid voltage adjustment circuit that adjusts a grid voltage which is a voltage applied to the grid, and a grid current detection circuit that detects a grid current which is a current flowing through the grid, and a control unit, wherein one type of high-voltage power supply board is selected and installed from among a plurality of types of high-voltage power supply boards, and each of the plurality of types of high-voltage power supply boards outputs a different signal according to its type, and the control unit determines the type of high-voltage power supply board based on the signal output from the high-voltage power supply board, controls the charging voltage generation circuit to generate a charging voltage such that the current value of the grid current is constant when starting the operation of the charging voltage generation circuit and the grid voltage adjustment circuit, determines a predetermined time according to the determined type of high-voltage power supply board, controls the grid voltage adjustment circuit for the determined predetermined time so that the grid voltage becomes a first target voltage, and controls the grid voltage adjustment circuit after the predetermined time has elapsed so that the grid voltage becomes a second target voltage.

[0007] This allows for the determination of a predetermined time based on the type of high-voltage power supply board, and the control of the grid voltage adjustment circuit to reach a second target voltage according to that determined predetermined time, thereby suppressing an excessive increase in grid voltage.

[0008] Furthermore, the control unit may be configured to determine the type of high-voltage power supply board installed in response to the power being turned on to the image forming apparatus.

[0009] This allows the system to detect the type of high-voltage power supply board when powering on, even if a service technician replaces it with a different type during troubleshooting of an image forming machine. This prevents an excessive increase in grid voltage.

[0010] Furthermore, the image forming apparatus may be a color image forming apparatus, and the photoreceptor and charger may each consist of multiple photoreceptors and chargers corresponding to multiple colors, and the charging voltage generation circuit may consist of a first charging voltage generation circuit that generates a charging voltage to be applied to the charging wire of a charger corresponding to one predetermined color among the multiple colors, and a second charging voltage generation circuit that generates each charging voltage to be applied to each charging wire of the multiple chargers corresponding to multiple colors excluding the predetermined color, using a single circuit.

[0011] This allows for a reduction in the number of times the charging voltage is applied to each charging wire of multiple chargers corresponding to multiple colors other than the predetermined single color when image formation is frequently used, thereby extending the service life of the image forming apparatus.

[0012] Furthermore, the grid voltage adjustment circuit and grid current detection circuit are each composed of multiple grid voltage adjustment circuits and grid current detection circuits corresponding to multiple colors excluding one predetermined color from a plurality of colors, and the control unit controls the second charging voltage generation circuit to generate a charging voltage such that the grid current with the lowest current value among the multiple grid current values ​​detected from each of the multiple grid current detection circuits becomes a constant value, and also controls the multiple grid voltage adjustment circuits so that the grid voltage applied to each of the multiple grids corresponding to multiple colors excluding one predetermined color from a plurality of colors becomes a constant value.

[0013] This ensures that even when there are variations in the amount of change in each grid current, the current values ​​of all grid currents can be reliably increased to a magnitude greater than or equal to the target current value.

[0014] Furthermore, the grid current detection circuit is composed of multiple grid current detection circuits corresponding to multiple colors, including a grid current detection circuit corresponding to a predetermined single color; the grid voltage adjustment circuit does not include a grid voltage adjustment circuit corresponding to a predetermined single color, but is composed of multiple grid voltage adjustment circuits corresponding to multiple colors excluding the predetermined single color; the control unit may perform two-stage control from a first target voltage to a second target voltage for each grid voltage applied to the multiple grids corresponding to multiple colors excluding the predetermined single color, but may not perform two-stage control for the grid voltage applied to the grid corresponding to the predetermined single color. The predetermined single color is black.

[0015] Furthermore, the system may include an AD conversion circuit that receives an analog signal output from a high-voltage power supply board and converts the input analog signal into a digital signal. The control unit may then determine the type of installed high-voltage power supply board by comparing the signal value input to the AD conversion circuit and converted into a digital signal with a predetermined threshold. This allows for easy and reliable determination of the type of installed high-voltage power supply board.

[0016] Furthermore, the control unit may be provided with an input terminal for receiving an analog signal, which is a signal output from the high-voltage power supply board, and may determine the type of installed high-voltage power supply board depending on whether the signal input from the input terminal is a high signal or a low signal. This makes it possible to easily and reliably determine the type of installed high-voltage power supply board. [Brief explanation of the drawing]

[0017] [Figure 1] This is a cross-sectional view showing the schematic configuration of a color laser printer according to one embodiment of the present invention. [Figure 2] Figure 1 is a schematic block diagram relating to the high-voltage power supply unit of the printer. [Figure 3] This is a schematic block diagram relating to the high-voltage power supply unit corresponding to the black color. [Figure 4] This figure shows an example of a circuit for identifying the type of high-voltage power supply board. [Figure 5] This figure shows the changes in grid voltage and other parameters before and after two-stage control of the grid voltage. [Figure 6] This is a flowchart showing the control process steps performed by the ASIC in Figure 1. [Figure 7] This flowchart shows the steps of the control process executed by the ASIC in Figure 1, in parallel with the control process in Figure 6. [Modes for carrying out the invention]

[0018] Hereinafter, an embodiment of the present application will be described in detail based on the drawings. As shown in FIG. 1, a laser printer 1 according to an embodiment of the present application is a color laser printer that forms a color image on a sheet P or the like by an electrophotographic method, and is a so-called tandem type laser printer that uses four colors of toner. Hereinafter, the laser printer 1 will be simply referred to as the printer 1. In the following description, as shown in FIG. 1, the right side of the drawing is defined as the front side of the laser printer 1, and the left side of the drawing is defined as the rear side. Also, the front side of the drawing in FIG. 1 is defined as the left side when viewed from the front side of the printer 1, and the back side of the drawing is defined as the right side. Further, the upper side of the drawing in FIG. 1 is defined as the upper side of the printer 1, and the lower side of the drawing is defined as the lower side.

[0019] As shown in FIG. 1, the printer 1 has a substantially box-shaped main body housing 2, and houses a paper feeding unit 10, an image forming unit 20, etc. inside the main body housing 2. An ejection tray 5 for storing the sheets P on which images are formed in a stacked state is provided on the upper surface of the main body housing 2. The paper feeding unit 10 has a paper feeding tray 11 in which the sheets P are stored and various rollers, and drives the various rollers to feed the sheets P to the image forming unit 20. Also, the paper feeding tray 11 is configured to be detachable from the lower part of the main body housing 2.

[0020] The image forming unit 20 includes a conveyance unit 21, four process cartridges 30C, 30M, 30Y, 30K, an exposure unit 35, and a fixing unit 50. The conveyance unit 21 is provided between the paper feeding unit 10 and the process cartridges 30C etc. in the vertical direction, and has a conveyance belt 23, four transfer rollers 25 etc. The conveyance belt 23 is an endless belt configured with the belt in a loop shape, and is wound around a driving roller 27 located below the rear end side of the image forming unit 20 and a driven roller 29 located below the front end side. The upper surface of the conveyance belt 23 extends substantially horizontally directly below the process cartridges 30C etc., and abuts against the back surface of the paper P supplied from the paper feeding unit 10. The driving roller 27 rotates the conveyance belt 23 in a predetermined direction. Also, when a transfer bias is applied to each transfer roller 25, the conveyance belt 23 is negatively charged and adsorbs the paper P with electrostatic force onto the upper surface, and conveys the adsorbed paper P along the conveyance path R toward the discharge tray 5.

[0021] Each of the process cartridges 30C, 30M, 30Y, 30K corresponds to the four colors of cyan (C), magenta (M), yellow (Y), and black (K). Each of the process cartridges 30C, 30M, 30Y, 30K contains toner of the corresponding color (C, M, Y, K). Also, the four process cartridges 30C, 30M, 30Y, 30K are provided in the order of process cartridges 30K, 30Y, 30M, 30C from the front to the rear of the printer 1.

[0022] The process cartridge 30C has a drum-shaped photoreceptor 31, a charger 41, a toner cartridge 33, etc. Note that the configurations of the other process cartridges 30M, 30Y, 30K are the same as that of the process cartridge 30C except that toner of a different toner color is contained. For this reason, in the following description, the process cartridge 30C will be described as a representative, and the descriptions of the other process cartridges 30M, 30Y, 30K will be omitted as appropriate.

[0023] The photoreceptor 31 is located above the transfer roller 25, with a conveyor belt 23 sandwiched between it and the transfer roller 25 in the vertical direction. The charger 41 is a Scorotron-type charger, for example, in which a charging wire 42 and a grid 43 are housed in a shield case 45. The charging wire 42 is made of metal, for example, gold-plated tungsten, or plain tungsten. The shield case 45 is formed in a roughly rectangular tubular shape, elongated in the left-right direction. An opening is formed in the portion of the shield case 45 facing the photoreceptor 31. The grid 43 is constructed by stretching conductive wires in a mesh pattern within the opening of the shield case 45. The charging wire 42 is stretched along the left-right direction within the shield case 45 and is positioned at a distance from the photoreceptor 31 at the upper rear position. Therefore, the grid 43 is positioned between the photoreceptor 31 and the charging wire 42.

[0024] The charger 41 uniformly positively charges the surface of the photoreceptor 31 during image formation. Specifically, when a voltage is applied to the charging wire 42 and the grid 43, an electric field is formed between the charging wire 42 and the photoreceptor 31, causing corona discharge. When the electric field is formed between the charging wire 42 and the grid 43, a different voltage is applied to the grid 43 than that of the charging wire 42, thereby controlling the strength of the electric field and controlling the amount of charge on the photoreceptor 31.

[0025] The exposure unit 35 is located at the top of the inside of the main housing 2 and forms an electrostatic latent image based on image data on the surface of each charged photoreceptor 31. The toner cartridge 33 supplies toner to the surface of the photoreceptor 31 by loading the toner it contains onto the surface of the developing roller 47. As a result, a toner image is formed (developed) on the surface of the photoreceptor 31. The transport unit 21 transports the paper P toward the fixing unit 50 and applies a transfer bias to the transfer roller 25 to transfer the toner image developed on the surface of the photoreceptor 31 to the paper P.

[0026] The fixing unit 50 is located downstream of the transport path R compared to the transport unit 21. The fixing unit 50 has a heating roller 51 and a pressure roller 52. The heating roller 51 is positioned on the image-forming surface side of the paper P and rotates in sync with the transport belt 23, etc., heating the toner transferred to the paper P while transporting the paper P. The pressure roller 52 rotates in a driven manner, sandwiching the paper P between itself and the heating roller 51 and pressing the paper P towards the heating roller 51. As a result, the fixing unit 50 heats and melts the toner transferred to the paper P and fixes it to the paper P while transporting the paper P along the transport path R.

[0027] Next, the electrical configuration of the printer 1 related to this invention will be described with reference to Figures 2 and 3. Figures 2 and 3 show a schematic block diagram of the high-voltage power supply unit 60 built into the printer 1 and the connection configuration related to the high-voltage power supply unit 60. In the following description, when distinguishing each component by color, the subscripts Y (yellow), M (magenta), C (cyan), K (black), or subscripts such as "1 to 4" (for example, grid voltage GRID1 to GRID4) will be added to the symbols of each part, and when not distinguishing, the subscripts will be omitted (for example, written as grid voltage GRID).

[0028] The high-voltage power supply unit 60 includes an ASIC (Application-Specific Integrated Circuit) 61, a high-voltage power supply board 62 connected to the ASIC 61, a ROM 63, and a RAM 64. The ASIC 61 (an example of a control unit) controls the high-voltage power supply board 62 as well as the entire printer 1. The ROM 63 is a storage medium that stores various operation programs executed by the ASIC 61. In this embodiment, the ROM 63 stores a program PG for realizing the control processing shown in Figures 6 and 7, which will be described later. The RAM 64 stores temporary data for various processes and image data used for printing.

[0029] The high-voltage power supply board 62 has a charging voltage generation circuit 70 and a grid voltage adjustment circuit 81 equipped with a grid current detection circuit 82. The charging voltage generation circuit 70 is connected to a power line PL. Each charger 41 (41Y~41C) is connected in parallel to the power line PL. The charging voltage generation circuit 70 applies a charging voltage CHG to each charger 41 via the power line PL. The grid voltage adjustment circuits 81Y~81C and grid current detection circuits 82Y~82C are provided corresponding to each charger 41Y~41C.

[0030] The charging voltage generation circuit 70 includes, for example, a PWM signal control circuit 71, a transformer drive circuit 72, a boost circuit 73, and an output voltage detection circuit 78. The charging voltage generation circuit 70 generates a charging voltage CHG to be applied to the charging wires 42Y to 42C of each charger 41Y to 41C. The grid voltages GRID1 to GRID3 applied to the grid 43 are adjusted by the respective grid voltage adjustment circuits 81Y to 81C. The charging voltage CHG is, for example, approximately 5.5kV to 7kV. The grid voltage GRID is, for example, approximately 700V.

[0031] The PWM signal control circuit 71 includes, for example, a resistor and a capacitor (not shown), and smooths the PWM (Pulse Width Modulation) signal Sp1 from the ASIC 61's port PWM1, and supplies the smoothed PWM signal Sp1 to the transformer drive circuit 72. The transformer drive circuit 72, for example, supplies the smoothed PWM signal Sp1 supplied from the PWM signal control circuit 71 to a drive transistor (not shown), and supplies an oscillation current to the boost circuit 73.

[0032] The transformer 74 of the boost circuit 73 is equipped with a primary winding 74a, a secondary winding 74b, and an auxiliary winding 74c. The transformer drive circuit 72 supplies an oscillation current from a drive transistor to the primary winding 74a of the transformer 74. The transformer 74 changes the voltage value of the output voltage (charging voltage CHG) output from the secondary winding 74b according to the duty cycle of the oscillation current. For example, the transformer 74 generates a charging voltage CHG with a larger voltage value as the duty cycle of the PWM signal Sp1 increases. A rectifier diode 75, a smoothing capacitor 76, and an output resistor 77 are connected to the secondary winding 74b. As a result, the boost circuit 73 boosts and rectifies the voltage generated in the primary winding 74a of the transformer 74 and applies it as a charging voltage CHG to the charging wires 42Y~42C of each charger 41Y~41C.

[0033] Furthermore, the output voltage detection circuit 78 is connected between the auxiliary winding 74c of the transformer 74 and the ASIC 61. The output voltage detection circuit 78 includes, for example, a smoothing circuit and a voltage divider resistor (not shown). The output voltage detection circuit 78 detects the output voltage v1 generated in the auxiliary winding 74c in conjunction with the generation of the charged voltage CHG. The output voltage detection circuit 78 smooths and divides the output voltage v1 and supplies it as an output voltage detection signal Sv1 to port A / D1 of the ASIC 61.

[0034] Furthermore, each of the grid voltage adjustment circuits 81 has a voltage detection circuit 83 and an operational amplifier OP1. Since the circuit configurations of the grid voltage adjustment circuits 81Y to 81C are the same, the following explanation will focus on the grid voltage adjustment circuit 81Y corresponding to the color Y (yellow), and explanations of the other grid voltage adjustment circuits 81Y to 81C will be omitted as appropriate. The voltage detection circuit 83Y has two voltage divider resistors R7 and R8 connected in series. A divided current Id1 of the grid current Ig1 flowing through the grid 43Y flows through the voltage divider resistors R7 and R8. The voltage detection circuit 83Y outputs a detection voltage Vgr1 corresponding to the grid voltage GRID1 applied to the grid 43Y from the connection point of the two voltage divider resistors R7 and R8. The voltage detection circuit 83Y supplies the detection voltage Vgr1 as a voltage divider detection signal Sid1 to the non-inverting input (+) of the operational amplifier OP1 via the output resistor R6. Capacitor C3, when connected in parallel with voltage divider resistor R8, constitutes an RC filter.

[0035] Furthermore, the inverting input (-) of the operational amplifier OP1 is connected to the port PWM2 of the ASIC61 via the output resistor R9. The output side of the output resistor R9 is grounded to GND via the capacitor C4. The ASIC61 supplies the PWM signal Spp1 from port PWM2 and supplies the PWM signal Spp1 to the operational amplifier OP1 via the output resistor R9. Therefore, the ASIC61 is configured to allow the reference voltage of the operational amplifier OP1 to be changed.

[0036] A smoothing circuit, including a voltage divider resistor R4 and a capacitor C2, is connected to the output terminal of the operational amplifier OP1. The connection point of the voltage divider resistor R4 on the grid 43Y side (opposite the output terminal of the operational amplifier OP1) is grounded to GND via capacitor C2. The base of transistor Q1, which is used to stabilize the grid voltage GRID1, is connected to the connection point of the voltage divider resistor R4 on the grid 43Y side. Transistor Q1 is connected to a voltage control line Ln1, which is connected to the connection point between the voltage divider resistor R7 and the grid 43Y. Transistor Q1 is, for example, an NPN transistor, with its collector connected to the connection point on the grid 43Y side (voltage control line Ln1) and its emitter connected to the grid current detection circuit 82Y (resistor R3). Note that transistor Q1 is not limited to a bipolar transistor; for example, it may be an FET (field-effect transistor).

[0037] The base current of transistor Q1 is controlled by the output of operational amplifier OP1. The collector resistance of transistor Q1 changes with the base current, so transistor Q1 functions as a variable resistor. Here, collector resistance is the resistance value obtained by dividing the collector-emitter voltage by the collector current. For example, increasing the base current decreases the resistance, and conversely, decreasing the base current increases the resistance. This changes the collector-emitter voltage.

[0038] The operational amplifier OP1 changes the base voltage of transistor Q1 and the grid voltage GRID1 based on the difference between the detected voltage Vgr1 (voltage divider detection signal Sid1) detected by the voltage detection circuit 83Y and the PWM signal Spp1 from ASIC61. Therefore, ASIC61 can change the voltage value of the grid voltage GRID1 to a predetermined target voltage value by changing the duty cycle of the PWM signal Spp1. A capacitor C1 is provided between the voltage control line Ln1 and the grid 43Y, which charges the grid voltage GRID.

[0039] Furthermore, a grid current detection circuit 82Y is connected to the voltage control line Ln1 to detect a line current Ir1 corresponding to the grid current Ig1 flowing through the grid 43Y. The resistor R3 of the grid current detection circuit 82Y is connected between the emitter of transistor Q1 and GND. The grid current detection circuit 82Y supplies the voltage of the positive terminal of resistor R3 as a line voltage detection signal Sir1 to the A / D2 port of the ASIC61.

[0040] In this embodiment, the ASIC 61 controls the voltage value of the charging voltage CHG supplied from the charging voltage generation circuit 70 based on the current value of the grid current Ig. For example, the ASIC 61 controls the charging voltage CHG based on the grid current Ig with the smallest current value among the three grid currents Ig1 to Ig3. For example, due to the adhesion of toner to the charging wire 42, variations occur in the increase of the current values ​​of the grid currents Ig1 to Ig3. Therefore, the control of the charging voltage CHG is performed using the grid current Ig with the smallest increase in current value as a reference. This ensures that when there are variations in the amount of change of the grid currents Ig1 to Ig3, the current values ​​of all grid currents Ig1 to Ig3 can be reliably increased to a magnitude greater than or equal to the target current value.

[0041] For example, let's consider the case where the grid current Ig1 is the minimum current value (the current to be controlled). ASIC61 calculates the line current Ir1 (grid current Ig1) from, for example, the resistance value of resistor R3 and the voltage value of the line voltage detection signal Sir1. Based on the calculated grid current Ig1, ASIC61 controls the charging voltage generation circuit 70 to match the grid current Ig1 to the desired target current value. ASIC61 changes the duty cycle of the PWM signal Sp1 output from port PWM1 to match the grid current Ig1 to the desired target current value. This ensures that the current values ​​of all grid currents Ig1 to Ig3 are increased to a magnitude greater than or equal to the target current value.

[0042] Furthermore, the ASIC61 does not necessarily have to control the charging voltage generation circuit 70 (charging voltage CHG) based on the smallest grid current Ig. For example, the ASIC61 may control the charging voltage CHG based on the grid current Ig with the largest current value (maximum value) among the three grid currents Ig1 to Ig3. Alternatively, the ASIC61 may control the charging voltage CHG based on the average value of the three grid currents Ig.

[0043] Figure 3 shows a schematic block diagram of the charge voltage generation circuit 70K, which is provided specifically for K, and the connection configuration related to the charge voltage generation circuit 70K. The configuration in Figure 3 is actually included in the configuration in Figure 2, but for convenience it has been made into a separate diagram. Therefore, in Figure 3, components that are the same as those in Figure 2 are denoted by the same reference numerals, and their explanations are omitted as appropriate.

[0044] The charging voltage generation circuit 70K has the same configuration as the charging voltage generation circuit 70 in Figure 2, so its configuration will be omitted. The charging voltage generation circuit 70K is connected to the power line PLK. Only the charger 41K is connected to the power line PLK. The charging voltage generation circuit 70K applies the charging voltage CHGK to the charger 41K via the power line PLK.

[0045] A grid current detection circuit 82K is connected to the voltage control line Ln4 via resistor R11 to detect a line current Ir4 corresponding to the grid current Ig4 flowing through the grid 43K. Resistor R11, along with resistor R3 included in the grid current detection circuit 82K, generates the grid voltage GRID4 as the line current Ir4 flows through it. The grid voltage GRID4 is, for example, about 700V, similar to the grid voltages GRID1 to 3, but unlike the other line currents Ir1 to 3, the line current Ir4 can be matched to a desired target value. In other words, while it is possible to match one of the other line currents Ir1 to 3 to a desired target value, it is difficult to match all of the line currents Ir1 to 3 to their respective target values. This is because, as described above, a single charging voltage generation circuit 70 applies a charging voltage CHG to multiple chargers 41. For this reason, a grid voltage adjustment circuit 81 is provided to control each grid voltage GRID1 to 3 at a constant voltage. In contrast, since the line current Ir4 can be adjusted to the desired target value, the desired grid voltage GRID4 can be obtained simply by providing a resistor R11 with a predetermined resistance value. Therefore, the grid voltage adjustment circuit 81 for K is unnecessary.

[0046] ASIC61 controls the voltage value of the charging voltage CHGK supplied from the charging voltage generation circuit 70K based on the current value of the grid current Ig4. ASIC61 calculates the line current Ir4 (grid current Ig4) from the resistance value of resistor R3 included in the grid current detection circuit 82K and the voltage value of the line voltage detection signal Sir4. ASIC61 controls the charging voltage generation circuit 70K based on the calculated grid current Ig4 to match the current value of the grid current Ig4 to the desired target current value. ASIC61 changes the duty cycle of the PWM signal Sp2 output from port PWM5 to match the current value of the grid current Ig4 to the desired target current value. This makes it possible to set the grid voltage GRID4 to the desired voltage value.

[0047] The control processes performed by printer 1, configured as described above, will be explained in detail based on Figures 4 to 7. Figure 6 shows the procedure for control processes (excluding K) performed by ASIC 61, and Figure 7 shows the procedure for control process (K) performed by ASIC 61. Control processes (excluding K) and control process (K) are started in parallel, for example, when printer 1 is powered on. Hereafter, in the explanation of the procedure for each process, the step will be denoted as "S".

[0048] In Figure 6, the ASIC61 first checks the input voltage of the board identification input port (S10). Figure 4(a) shows an example of the input voltage input to port A / D8 of the ASIC61. An AD conversion circuit is connected to port A / D8, and the ASIC61 can convert the input voltage value of port A / D8 and detect it as a digital value. In the example in Figure 4(a), the input voltage value of port A / D8 is the analog value of R2 × V / (R1 + R2).

[0049] Next, ASIC61 determines whether the input voltage value, that is, the analog value of R2 × V / (R1 + R2) in the example of Figure 4(a), is greater than or equal to the threshold X (S12). In this determination, if the input voltage value ≥ the threshold X (S12: YES), ASIC61 determines that the high-voltage power supply board 62 currently built into printer 1 is board 62A, sets the switching time to 40ms, and sets the parameters of board 62A (S14), after which the process proceeds to S18. On the other hand, in the determination in S12, if the input voltage value < the threshold X (S12: NO), ASIC61 determines that the high-voltage power supply board 62 currently built into printer 1 is board 62B, sets the switching time to 60ms, and sets the parameters of board 62B (S16), after which the process proceeds to S18. Here, the switching time is the time to switch from the first stage control to the second stage control when controlling the grid voltages GRID1~3 in two stages. In other words, it is the time from the start to the end of the first stage of control. The setting values ​​for the switching time and the parameter settings can be read from the ROM 63 or RAM 64 mentioned above for each board 62A, 62B, which have been stored in advance.

[0050] Figures 4(b) and 4(c) show an example of a method for determining board 62A and board 62B when the general-purpose I / O port of the ASIC61 is used as the input port for board identification. When board 62A is built into printer 1, a high (H) signal is input to the general-purpose I / O port of the ASIC61, while when board 62B is built into printer 1, a low (L) signal is input to the general-purpose I / O port of the ASIC61. Therefore, in this case, the ASIC61 can determine whether the high-voltage power supply board 62 currently built into printer 1 is board 62A or board 62B by determining the level of the signal input to the general-purpose I / O port.

[0051] In S18 above, ASIC61 waits until it is instructed to start charging (S18:NO), and when it is instructed to start charging (S18:YES), ASIC61 activates the charging voltage generation circuit 70 and the grid voltage adjustment circuits 81Y, 81M, and 81C (S20). Next, ASIC61 sets the grid voltages GRID1 to 3 to 80% of their respective target voltages (S22), and then controls the charging voltage CHG so that the lowest grid current becomes the target current value, and controls the grid voltages GRID1 to 3 to the set voltage values ​​(S24). Then, ASIC61 continues to execute the control process in S24 until the switching time after the start of charging has elapsed (S26:NO), and when the switching time after the start of charging has elapsed (S26:YES), ASIC61 proceeds to process S28. For example, if the target voltages for grid voltages GRID1 to GRID3 are 750, 740, and 740V respectively, then in S22, 600, 592, and 592V will be set. Then, in S24, ASIC61 supplies PWM signals Spp1, Spp2, and Spp3 with duty cycles such that grid voltages GRID1 to GRID3 become 600, 592, and 592V respectively to grid voltage adjustment circuits 81Y to 81C. Note that the processing in S24 has already been described in detail, so it will not be repeated here.

[0052] In S28, ASIC61 sets the grid voltages GRID1 to GRID3 to 100% of their respective target voltages. Then, ASIC61 continues the process in S30, which is the same as in S24, until it receives an instruction to end charging (S32: NO). When it receives an instruction to end charging (S32: YES), it terminates the control process (except for K).

[0053] Figure 5 shows an example of the changes in grid voltage, etc., before and after implementing two-stage control of the grid voltage. Figure 5(a) shows the situation before implementing two-stage control of the grid voltage, and Figure 5(b) shows the situation after implementing two-stage control of the grid voltage.

[0054] As shown in Figure 5(a), if two-stage grid voltage control is not performed, depending on the type of high-voltage power supply board 62 currently built into the printer 1, an overshoot occurs around time T3 during the process of constant voltage control of the grid voltage to the target voltage, where the grid voltage exceeds the target voltage. In contrast, if two-stage control is performed, where the grid voltage is controlled to 80% of the target voltage value from time T0, when charging begins, to time T2, and then raised to the target voltage value (100%), no overshoot occurs, as shown in Figure 5(b). By performing this two-stage control, it is possible to suppress an excessive increase in grid voltage.

[0055] In the control process (K) shown in Figure 7, the grid voltage GRID4 is not controlled in two stages. Therefore, after the instruction to start charging is given (S40: YES), the ASIC61 controls the charging voltage CHGK so that the grid current Ig4 reaches the target current value (S42) until the instruction to end charging is given (S44: NO).

[0056] As described above, the printer 1 of this embodiment includes a photoreceptor 31, a charger 41 having a charging wire 42 and a grid 43 for charging the photoreceptor 31, a high-voltage power supply board 62 connected to the charger 41 and having a charging voltage generation circuit 70 that generates a charging voltage which is the voltage applied to the charging wire 42 of the charger 41, a grid voltage adjustment circuit 81 that adjusts the grid voltage which is the voltage applied to the grid 43, and a grid current detection circuit 82 that detects the grid current which is the current flowing through the grid 43, and an ASIC 61.

[0057] The high-voltage power supply board 62 is one of several types of high-voltage power supply boards 62A and 62B, and each of the several types of high-voltage power supply boards 62A and 62B outputs a different signal depending on the type. The ASIC 61 determines the type of high-voltage power supply board 62 based on the signal output from the high-voltage power supply board 62 and starts the operation of the charging voltage generation circuit 70 and the grid voltage adjustment circuit 81. The ASIC 61 controls the charging voltage generation circuit 70 to generate a charging voltage such that the grid current value is constant, determines a predetermined time according to the determined type of high-voltage power supply board 62, controls the grid voltage adjustment circuit 81 so that the grid voltage becomes the first target voltage during the determined predetermined time, and controls the grid voltage adjustment circuit 81 so that the grid voltage becomes the second target voltage after the predetermined time has elapsed.

[0058] Thus, in the printer 1 of this embodiment, a predetermined time is determined according to the type of high-voltage power supply board 62, and the grid voltage adjustment circuit 81 is controlled so that the voltage reaches a second target voltage according to the determined predetermined time, thereby suppressing an excessive increase in grid voltage. Incidentally, in this embodiment, the printer 1 is an example of an "image forming apparatus," and the ASIC 61 is an example of a "control unit."

[0059] Furthermore, the ASIC61 determines the type of high-voltage power supply board 62 installed in response to the printer 1 being powered on.

[0060] As a result, even if a service technician replaces the high-voltage power supply board 62 with a different type during troubleshooting of printer 1, the type of high-voltage power supply board 62 can be identified when the power is turned on, thus preventing an excessive increase in grid voltage.

[0061] Furthermore, printer 1 is a color laser printer 1, and the photoreceptor 31 and charger 41 are each composed of multiple photoreceptors 31Y, 31M, 31C and chargers 41Y, 41M, 41C corresponding to multiple colors, respectively, and the charging voltage generation circuit 70 is composed of a charging voltage generation circuit 70K that generates a charging voltage to be applied to the charging wire 42K of the charger 41K corresponding to black among the multiple colors, and a charging voltage generation circuit 70 that generates each charging voltage to be applied to the respective charging wires 42Y, 42M, 42C of the multiple chargers 41Y, 41M, 41C corresponding to multiple colors other than black, in a single circuit. Incidentally, color laser printer 1 is an example of a "color image forming apparatus". Black is an example of a "predetermined single color". Charging voltage generation circuit 70K is an example of a "first charging voltage generation circuit". Charging voltage generation circuit 70 is an example of a "second charging voltage generation circuit".

[0062] This reduces the number of times the charging voltage is applied to the charging wires 42Y, 42M, and 42C of the multiple chargers 41Y, 41M, and 41C, which correspond to multiple colors other than black, when black printing is frequently used, thereby extending the lifespan of the printer 1.

[0063] Furthermore, the grid voltage adjustment circuit 81 and the grid current detection circuit are each composed of multiple grid voltage adjustment circuits 81Y, 81M, 81C and grid current detection circuits 82Y, 82M, 82C, corresponding to multiple colors excluding black among the multiple colors. The ASIC 61 controls the charging voltage generation circuit 70 to generate a charging voltage such that the grid current with the lowest current value among the multiple grid currents Ig1 to Ig3 detected from the multiple grid current detection circuits 82Y, 82M, 82C becomes a constant value. The ASIC 61 also controls the multiple grid voltage adjustment circuits 81Y, 81M, 81C so that the grid voltages applied to the multiple grids 43Y, 43M, 43C corresponding to multiple colors excluding black become a constant value.

[0064] This ensures that even when there is variation in the change amounts of each grid current Ig1 to Ig3, the current values ​​of all grid currents Ig1 to Ig3 can be reliably increased to a magnitude greater than or equal to the target current value.

[0065] Furthermore, the grid current detection circuit is composed of multiple grid current detection circuits corresponding to multiple colors, including a grid current detection circuit corresponding to black; the grid voltage adjustment circuit 81 does not include a grid voltage adjustment circuit corresponding to black, but is composed of multiple grid voltage adjustment circuits corresponding to multiple colors excluding black; the ASIC 61 performs two-stage control from a first target voltage to a second target voltage for each grid voltage applied to the multiple grids corresponding to multiple colors excluding black, but does not perform two-stage control for the grid voltage applied to the grid corresponding to black.

[0066] Furthermore, printer 1 is equipped with an AD conversion circuit that receives an analog signal output from the high-voltage power supply board 62 and converts the input analog signal into a digital signal. ASIC 61 determines the type of installed high-voltage power supply board by comparing the signal value, which has been input to the AD conversion circuit and converted into a digital signal, with a predetermined threshold. This makes it possible to easily and reliably determine the type of installed high-voltage power supply board 62.

[0067] Furthermore, printer 1 is equipped with a general-purpose I / O port for inputting analog signals, which are signals output from the high-voltage power supply board 62. The ASIC 61 determines the type of high-voltage power supply board installed based on whether the signal input from the general-purpose I / O port is a high (H) or low (L) signal. Incidentally, the general-purpose I / O port is an example of an "input terminal." This allows for easy and reliable identification of the type of high-voltage power supply board 62 installed.

[0068] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0069] (1) In the above embodiment, the switching time was set to 40ms and 60ms depending on substrate 62A and substrate 62B, but the switching time is not limited to this time. Also, there may be more than two types of substrates.

[0070] (2) In the above embodiment, when the grid voltage GRID is controlled in two stages, it is set to 80% of the target voltage value in the first stage and to 100% of the target voltage value in the second stage, but the setting value is not limited to this.

[0071] (3) In the above embodiment, the charging voltage CHG applied to the chargers 41Y to 41C corresponding to the three colors Y, M, and C other than K is generated by one charging voltage generation circuit 70, and the charging voltage CHGK applied to the charger 41K corresponding to the color K is generated by a charging voltage generation circuit 70K independent of the charging voltage generation circuit 70. However, the embodiment is not limited to this, and the charging voltage CHG applied to the chargers 41Y to 41K corresponding to four colors including K may be generated by one charging voltage generation circuit 70. Also, the number of colors is not limited to four.

[0072] (4) In the above embodiment, a color laser printer was used as an example for printer 1, but a monochrome printer equipped only with a photoreceptor 31K corresponding to black may also be used. Furthermore, it is not limited to a printer, but may also be a multifunction device, facsimile machine, copier, etc. [Explanation of Symbols]

[0073] 1...Printer, 31...Photoconductor, 41...Charger, 42...Charging wire, 43...Grid, 60...High voltage power supply, 61...ASIC, 62...High voltage power supply board, 63...ROM, 64...RAM, 70...Charging voltage generation circuit, 81...Grid voltage adjustment circuit, 82...Grid current detection circuit.

Claims

1. Photoreceptor and A charger having a charging wire and a grid, which charges the photoreceptor, A high-voltage power supply board having a charging voltage generation circuit connected to the charger that generates a charging voltage which is a voltage applied to the charging wire of the charger, a grid voltage adjustment circuit that adjusts the grid voltage which is a voltage applied to the grid, and a grid current detection circuit that detects the grid current which is a current flowing through the grid, Control unit and An image forming apparatus capable of forming a color image comprising: The photoreceptor and the charger are each composed of multiple photoreceptors and chargers corresponding to multiple colors. The charging voltage generation circuit comprises a first charging voltage generation circuit that generates a charging voltage to be applied to the charging wire of a charger corresponding to one predetermined color among the plurality of colors, and a second charging voltage generation circuit that generates each charging voltage to be applied to each charging wire of a plurality of chargers corresponding to multiple colors excluding the predetermined color, using a single circuit. The grid voltage adjustment circuit and the grid current detection circuit are each composed of a plurality of grid voltage adjustment circuits and grid current detection circuits corresponding to a plurality of colors, excluding the predetermined one color from the plurality of colors. The aforementioned high-voltage power supply board is one type of high-voltage power supply board selected from among several types of high-voltage power supply boards and installed accordingly. The aforementioned multiple types of high-voltage power supply boards output different signals according to their respective types. The control unit, Based on the signal output from the aforementioned high-voltage power supply board, the type of the high-voltage power supply board is determined. When starting the operation of the charging voltage generation circuit and the grid voltage adjustment circuit, the charging voltage generation circuit is controlled to generate a charging voltage such that the current value of the grid current becomes constant. A predetermined time is determined according to the type of high-voltage power supply board that has been identified. During the predetermined time, the grid voltage adjustment circuit is controlled so that the grid voltage becomes the first target voltage, and after the predetermined time has elapsed, the grid voltage adjustment circuit is controlled so that the grid voltage becomes the second target voltage. With respect to the multiple colors excluding the predetermined one color, the second charging voltage generation circuit is controlled to generate a charging voltage such that the grid current with the lowest current value among the multiple grid current values ​​detected by the multiple grid current detection circuits becomes a constant value, and the multiple grid voltage adjustment circuits are controlled so that the grid voltage applied to each of the multiple grids corresponding to the multiple colors excluding the predetermined one becomes a constant value. An image forming apparatus characterized by the following:

2. Photoreceptor and A charger having a charging wire and a grid, which charges the photoreceptor, A high-voltage power supply board having a charging voltage generation circuit connected to the charger that generates a charging voltage which is a voltage applied to the charging wire of the charger, a grid voltage adjustment circuit that adjusts the grid voltage which is a voltage applied to the grid, and a grid current detection circuit that detects the grid current which is a current flowing through the grid, Control unit and An image forming apparatus capable of forming a color image comprising: The photoreceptor and the charger are each composed of multiple photoreceptors and chargers corresponding to multiple colors. The charging voltage generation circuit comprises a first charging voltage generation circuit that generates a charging voltage to be applied to the charging wire of a charger corresponding to one predetermined color among the plurality of colors, and a second charging voltage generation circuit that generates each charging voltage to be applied to each charging wire of a plurality of chargers corresponding to multiple colors excluding the predetermined color, using a single circuit. The grid current detection circuit is composed of a plurality of grid current detection circuits corresponding to a plurality of colors, including a grid current detection circuit corresponding to a predetermined single color. The grid voltage adjustment circuit does not include a grid voltage adjustment circuit corresponding to one predetermined color, but is composed of multiple grid voltage adjustment circuits corresponding to multiple colors excluding the predetermined color from the multiple colors. The aforementioned high-voltage power supply board is one type of high-voltage power supply board selected from among several types of high-voltage power supply boards and installed accordingly. The aforementioned multiple types of high-voltage power supply boards output different signals according to their respective types. The control unit, Based on the signal output from the aforementioned high-voltage power supply board, the type of the high-voltage power supply board is determined. When starting the operation of the charging voltage generation circuit and the grid voltage adjustment circuit, the charging voltage generation circuit is controlled to generate a charging voltage such that the current value of the grid current becomes constant. A predetermined time is determined according to the type of high-voltage power supply board that has been identified. During the predetermined time, the grid voltage adjustment circuit is controlled so that the grid voltage becomes the first target voltage, and after the predetermined time has elapsed, the grid voltage adjustment circuit is controlled so that the grid voltage becomes the second target voltage. For each grid voltage applied to the grids corresponding to multiple colors, excluding the predetermined one color, a two-stage control is performed from the first target voltage to the second target voltage, while the grid voltage applied to the grid corresponding to the predetermined one color is not subjected to the two-stage control. An image forming apparatus characterized by the following:

3. Photoreceptor and A charger having a charging wire and a grid, which charges the photoreceptor, A high-voltage power supply board having a charging voltage generation circuit connected to the charger that generates a charging voltage which is a voltage applied to the charging wire of the charger, a grid voltage adjustment circuit that adjusts the grid voltage which is a voltage applied to the grid, and a grid current detection circuit that detects the grid current which is a current flowing through the grid, An AD conversion circuit that receives an analog signal output from the aforementioned high-voltage power supply board and converts the input analog signal into a digital signal, Control unit and Equipped with, The aforementioned high-voltage power supply board is one type of high-voltage power supply board selected from among several types of high-voltage power supply boards and installed accordingly. The aforementioned multiple types of high-voltage power supply boards output different signals according to their respective types. The control unit, The type of installed high-voltage power supply board is determined by comparing the signal value of the signal output from the high-voltage power supply board, input to the AD conversion circuit, and converted into a digital signal with a predetermined threshold. When starting the operation of the charging voltage generation circuit and the grid voltage adjustment circuit, the charging voltage generation circuit is controlled to generate a charging voltage such that the current value of the grid current becomes constant. A predetermined time is determined according to the type of high-voltage power supply board that has been identified. During the predetermined time, the grid voltage adjustment circuit is controlled so that the grid voltage becomes the first target voltage, and after the predetermined time has elapsed, the grid voltage adjustment circuit is controlled so that the grid voltage becomes the second target voltage. An image forming apparatus characterized by the following:

4. The control unit determines the type of the installed high-voltage power supply board in response to the power being turned on to the image forming apparatus. The image forming apparatus according to any one of claims 1 to 3.

5. The aforementioned predetermined color is black. The image forming apparatus according to claim 1 or 2.

6. The system further includes an input terminal for inputting the analog signal, which is the signal output from the high-voltage power supply board, The control unit determines the type of the installed high-voltage power supply board depending on whether the signal input from the input terminal is an H signal or an L signal. The image forming apparatus according to claim 1 or 2.

7. The second target voltage is a voltage value higher than the first target voltage. The image forming apparatus according to any one of claims 1 to 3.

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