Image forming apparatus

Abstract

To provide an image formation device that has a plurality of charging members, and that can determine completion of cleaning of all of the charging members by a small number of times of determination.SOLUTION: Judging that in at least one charging wire 521, a voltage difference between a wire voltage right before detecting irregularity and a wire voltage after detecting the irregularity is greater than a threshold, a control device 10 judges whether a difference between a maximum value of a grid current flowing through each of a plurality of grids and a minimum value thereof falls within a prescribed range on the basis of a grid current detection signal. When the maximum value of the grid current and the minimum value thereof falls within the prescribed range, the control device 10 judges all of the plurality of charging wires 521 have been cleaned.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for forming an image by charging a photoconductor with a charging member. [Background Art]

[0002] Patent Document 1 describes an image forming apparatus having a plurality of charging members that prompts a user to clean the charging members when abnormal discharge occurs. In the image forming apparatus, after the charging member is cleaned, if the current flowing through a grid can be stabilized at a target current while maintaining the voltage applied to the charging wire constituting the charging member, it is determined that the charging wire has been cleaned. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2019-012233 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] In a configuration where an image forming apparatus includes a plurality of charging members, even when cleaning of one charging member is completed, cleaning of other charging members may not have been performed. In this case, driving the image forming apparatus may cause abnormal discharge to recur due to the charging member that has not been cleaned.

[0005] The present invention has been made in view of the above problem, and an object of the present invention is to provide an image forming apparatus having a plurality of charging members, which can determine that cleaning has been completed for all target charging members in a small number of determinations. [Means for Solving the Problem]

[0006] To solve the above problems, the image forming apparatus disclosed herein includes a plurality of chargers for charging the plurality of photoreceptors, a charging wire, and a grid positioned between the charging wire and the photoreceptors, a voltage output circuit that outputs a voltage to the charging wire to generate a corona discharge between the charging wire and the photoreceptor and generates a voltage on the grid in conjunction with the corona discharge, a wire voltage detection circuit that outputs a wire voltage detection signal according to the magnitude of the wire voltage which is the voltage applied to the charging wire, a grid current detection circuit that outputs a grid current detection signal according to the grid current which is the current flowing through the grid, and a control unit. When the control unit detects an abnormality in the charger, it notifies the user to clean the charging wire, and thereafter performs a cleaning confirmation process to determine whether or not cleaning has been performed on the plurality of charging wires. In the cleaning confirmation process, wire voltages are output to multiple charged wires so that each set voltage is applied to multiple grids. Based on the wire voltage detection signals corresponding to the wire voltages of the multiple charged wires, it is determined whether the voltage difference between the wire voltage immediately before detecting an abnormality in the charger and the wire voltage after detecting an abnormality in the charger is greater than a predetermined threshold. If it is determined that the wire voltage difference is greater than the threshold for at least one charged wire, it is determined, based on the grid current detection signal, whether the difference between the maximum and minimum values ​​of the grid current flowing through each of the multiple grids is within a predetermined range. If the difference between the maximum and minimum values ​​of the grid current is within the predetermined range, it is determined that all of the multiple charged wires have been cleaned.

[0007] In the above configuration, based on the wire voltage detection signal, it is determined whether the difference between the wire voltage immediately before the detection of an abnormality in the charger and the wire voltage after the detection of the abnormality in the charger is greater than a predetermined threshold. Voltage is output to multiple charged wires so that the wire voltage, which is the voltage applied to the charged wires, approaches the target voltage. If it is determined that the difference in wire voltage is greater than the threshold for at least one charged wire, it is determined based on the grid current detection signal whether the difference between the maximum and minimum values ​​of the multiple grid currents is within a predetermined range. If the difference between the maximum and minimum values ​​of the multiple grid currents is within the predetermined range, it is determined that all of the multiple charged wires have been cleaned. This makes it possible to determine that cleaning has been completed for all charged wires in an image forming apparatus with multiple charged wires in a small number of steps.

[0008] In the cleaning confirmation process, the control unit of the image forming apparatus determines, based on grid current detection signals corresponding to the grid currents of multiple grids, whether the current difference between the grid current immediately before detecting an abnormality in the charger and the grid current after detecting an abnormality in the charger is greater than a predetermined threshold. If it determines that the difference in grid current is greater than the threshold in at least one grid, it determines, based on the grid current detection signals, whether the difference between the maximum and minimum values ​​of the grid current flowing through each of the multiple grids is within a predetermined range. If the difference between the maximum and minimum values ​​of the grid current is within a predetermined range, it may determine that all of the multiple charged wires have been cleaned.

[0009] In a configuration where two or more chargers are connected in parallel to the voltage output circuit, the internal resistance of each charger differs depending on the amount of deposits that accumulate. Therefore, it may not be possible to determine whether cleaning has been completed for all chargers based solely on the change in current or voltage before and after a charger malfunction. Even in such cases, it is possible to determine whether cleaning has been completed for all chargers being evaluated.

[0010] The control unit includes multiple grid voltage adjustment circuits that adjust the grid voltage, which is the voltage applied to the grid. Even with this configuration, it is possible to determine whether or not cleaning has been completed for all the chargers being evaluated.

[0011] The control unit can perform constant current control based on the grid current detection signal, causing the voltage output circuit to control the output to the charged wire so that the grid current flowing through the grid approaches the target current. In the cleaning confirmation process, after detecting an abnormality in the charger, the voltage output circuit is controlled to a constant current when the wire voltage detection signal is acquired. With the above configuration, in the cleaning confirmation process, the change in wire voltage after detecting an abnormality in the charger can be determined while the grid current is controlled to a constant value, thus improving the accuracy of determining whether or not cleaning has been performed.

[0012] The control unit can perform constant voltage control, which causes the voltage output circuit to control the output to the charged wire so that the wire voltage, which is the voltage applied to the charged wire, approaches the target voltage, based on the wire voltage detection signal. In the cleaning confirmation process, after detecting an abnormality in the charger, the voltage output circuit is controlled to a constant voltage when the grid current detection signal is acquired. With the above configuration, in the cleaning confirmation process, since the change in grid current after detecting an abnormality in the charger can be determined while the wire voltage is controlled to a constant value, the accuracy of determining whether or not cleaning has been performed can be improved.

[0013] The system includes a grid voltage detection circuit that outputs a grid voltage detection signal corresponding to the magnitude of the grid voltage generated on the grid. In the cleaning confirmation process, based on the wire voltage detection signal, grid voltage detection signal, and grid current detection signal output immediately before detecting an abnormality in the charger, a first relational expression showing the relationship between the grid current and the voltage difference between the charged wire and the grid is determined. In the determined first relational expression, a first voltage prediction value showing the voltage difference between the charged wire and the grid corresponding to a specific grid current is obtained. After detecting an abnormality in the charger, based on the wire voltage detection signal, grid voltage detection signal, and grid current detection signal obtained, a second relational expression showing the relationship between the grid current and the voltage difference between the charged wire and the grid is determined. In the determined second relational expression, a second voltage prediction value, which is the voltage difference between the charged wire and the grid corresponding to a specific grid current, is obtained. If the difference between the first voltage prediction value and the second voltage prediction value is greater than a predetermined threshold, it is determined that the wire voltage difference is greater than a predetermined threshold. In the above configuration, even if there are voltage variations between multiple charged wires, the determination can be made using the voltage prediction value, which is a standardized comparison target. This improves the accuracy of determining whether or not cleaning has been performed on all chargers.

[0014] In the cleaning confirmation process, if it is determined that the wire voltage difference in at least one charged wire is greater than a threshold, the maximum and minimum values ​​of the second voltage prediction values ​​for each of the multiple grids are obtained. If the difference between the maximum and minimum values ​​of the obtained second voltage prediction values ​​is within a predetermined range, it is determined that all of the multiple charged wires have been cleaned. With the above configuration, the accuracy of determining whether or not cleaning has been performed on all chargers can be improved.

[0015] The system includes a grid voltage detection circuit that outputs a grid voltage detection signal corresponding to the magnitude of the grid voltage generated on the grid. In the cleaning confirmation process, based on the wire voltage detection signal, grid voltage detection signal, and grid current detection signal output immediately before detecting an abnormality in the charger, a first relational expression between the grid current and the voltage difference between the charged wire and the grid is determined. In the determined first relational expression, the grid current corresponding to a specific voltage difference is obtained as the first current prediction value. Based on the wire voltage detection signal, grid voltage detection signal, and grid current detection signal obtained after detecting an abnormality in the charger, a second relational expression between the grid current and the voltage difference between the charged wire and the grid is determined. In the determined second relational expression, the grid current corresponding to a specific voltage difference is obtained as the second current prediction value. If the difference between the first current prediction value and the second current prediction value is greater than a predetermined threshold, it is determined that the difference in grid current is greater than a predetermined threshold. With the above configuration, even if there is variation in grid current among multiple grids, the determination can be made using the current prediction value, which is a leveled comparison target, so it is possible to accurately determine whether or not cleaning has been performed on all chargers.

[0016] In the cleaning confirmation process, if it is determined that the wire voltage difference in at least one grid is greater than a threshold, the maximum and minimum values ​​of the second current prediction values ​​for each of the multiple grids are obtained. If the difference between the obtained maximum and minimum values ​​of the second current prediction values ​​is within a predetermined range, it is determined that all of the multiple charged wires have been cleaned. With the above configuration, the accuracy of determining whether or not cleaning has been performed on all chargers can be improved.

[0017] In the cleaning confirmation process, if the grid current is Ig, the wire voltage is Vw, the grid voltage is Vg, the voltage difference between the charged wire and the grid at the start of charging of the charged wire is Vth, and the proportionality constant is k, then the first and second relationships are determined as Vw - Vg = Ig × k + Vth.

[0018] A housing having an opening, a cover attached to the housing such that the opening can be opened and closed, and an open / close sensor that detects that the cover has changed from a closed position to an open position, wherein the photoreceptor and the charger are mountable in the housing through the opening, and the control unit starts cleaning confirmation processing when the open / close sensor detects that the cover has changed from the open position to the closed position. This makes it possible to start determining whether or not cleaning has been performed after the user moves the cover from the open position to the closed position and cleaning of the charger has been performed. Effects of the Invention

[0019] According to the present invention, in an image forming apparatus having a plurality of charging wires, it can be determined in a small number of determinations that cleaning of all charging wires has been completed. Brief Description of the Drawings

[0020] [Figure 1] It is a configuration diagram of a printer. [Figure 2] It is a diagram explaining the electrical configuration of the printer. [Figure 3] It is a flowchart explaining the procedure of processing executed by a control device. [Figure 4] It is a flowchart explaining the procedure of cleaning confirmation processing. [Figure 5] It is a graph explaining current / voltage characteristics. [Figure 6] It is a graph explaining variation in current of each charging member. [Figure 7] It is a flowchart explaining the procedure of cleaning confirmation processing according to a second embodiment. [Figure 8] It is a flowchart explaining the procedure of cleaning confirmation processing according to a third embodiment. [Figure 9] It is a flowchart explaining the procedure of processing according to a fourth embodiment. [Figure 10] It is a flowchart explaining the procedure of cleaning confirmation processing. [Figure 11] This graph illustrates the predicted voltage values. [Modes for carrying out the invention]

[0021] (First Embodiment) The image forming apparatus according to this embodiment will be described using the printer 100 shown in Figure 1 as an example. The printer 100 is a color laser printer that forms color images on paper or the like using an electrophotographic method, and is a so-called tandem laser printer that uses four toners.

[0022] As shown in Figure 1, the printer 100 mainly comprises a housing 90, an upper cover 91, a display device 80, an opening / closing sensor 81, a paper feeding unit (not shown), an image forming unit 60, a control device 10 which is an example of a control unit, and a paper discharge unit (not shown).

[0023] An opening 90A is formed on the top surface of the housing 90 for maintaining components housed inside the housing 90. Specific examples of component maintenance include replacing the charger 52 (described later) with a new one, or cleaning the charger 52. Since the specific methods and configurations for cleaning the charger 52 are publicly known, a detailed explanation is omitted in this specification. The upper cover 91 is located on the top of the housing 90 and rotates around a pivot axis, changing between a closed position that shields the opening 90A and an open position that exposes the opening 90A.

[0024] The opening / closing sensor 81 outputs a detection signal to the control device 10 when it detects that the upper cover 91 has changed from the closed position to the open position, or from the open position to the closed position. The opening / closing sensor 81 can be, for example, an optical sensor. The display device 80 is a device capable of displaying characters, such as a liquid crystal display, and is, for example, installed on the upper front of the printer 100. The display device 80 can display characters and icons under the control of the control device 10.

[0025] As shown in Figure 2, the control device 10 mainly comprises an ASIC20 (application-specific integrated circuit), a first charging voltage output circuit 30, a second charging voltage output circuit 35, and grid voltage adjustment circuits 40Y, 40M, and 40C. The ASIC20 is configured with a CPU (not shown), memory consisting of RAM, ROM, etc., and input / output interfaces, and controls each part of the printer 100 according to a pre-set program. The other components of the control device 10 will be described later.

[0026] The image forming unit 60 mainly comprises LED units (not shown) corresponding to each color, four process units 50C, 50M, 50Y, and 50K, and a transfer unit 70. The LED units are, for example, pivotably supported with respect to the upper cover 91 and are positioned above and facing the photoreceptor drum 51 when the upper cover 91 is in the closed position.

[0027] The process unit 50 mainly comprises a photoreceptor drum 51, a charger 52, a developing roller 53, a supply roller 54, and a toner storage unit 55. The process unit 50 has units containing black (K), yellow (Y), magenta (M), and cyan (C) toners arranged in this order from upstream to downstream of the paper transport path. When identifying the components corresponding to each toner color, the symbols Y, M, C, and K are assigned to correspond to yellow, magenta, cyan, and black, respectively.

[0028] The charger 52 is provided in conjunction with the photoreceptor drum 51 and mainly comprises a charging wire 521 as an example of a charging member and a grid 522. The charger 52 charges the surface of the corresponding photoreceptor drum 51 to a positive potential greater than the development bias applied to the developing roller 53 by corona discharge of the charging wire 521. The grid 522 is provided between the charging wire 521 and the photoreceptor drum 51.

[0029] The developing roller 53 is provided in accordance with each photoreceptor drum 51 and carries toner supplied from the toner storage unit 55 on its surface. When the developing roller 53 comes into sliding contact with the photoreceptor drum 51 while a positive developing bias is applied, it supplies the toner carried on the corresponding photoreceptor drum 51. The toner storage unit 55 contains toner as a recording agent inside. In this embodiment, the toner is positively charged, but is not limited to this. The transfer unit 70 is provided between the paper feed tray and the process unit 50 and is composed of transfer rollers corresponding to each color.

[0030] In the image forming unit 60, the surface of the photoreceptor drum 51 is uniformly charged by the charger 52 and then exposed by the LED unit, forming an electrostatic latent image based on image data on the photoreceptor drum 51. Toner in the toner storage unit 55 is supplied to the developing roller 53 via the supply roller 54, and the toner carried on the developing roller 53 is supplied to the exposed portion of the photoreceptor drum 51, making the electrostatic latent image visible and forming a toner image on the photoreceptor drum 51. Subsequently, paper supplied from a paper feeding unit (not shown) is transported, transferring the toner image formed on the photoreceptor drum 51 onto the paper. The paper on which the toner image has been transferred is heat-fixed by a fixing unit (not shown). The paper with the heat-fixed toner image is transported along the paper discharge path by the transport roller and discharged to the outside of the housing 90 and placed on the paper discharge tray.

[0031] Next, the electrical configuration of the printer 100 will be explained using Figure 2. The first charging voltage output circuit 30 of the control device 10 is connected in parallel to the three charging wires 521Y, 521M, and 521C, and is a circuit that applies a common wire voltage Vwymc to each of the charging wires 521C, 521M, and 521Y. The second charging voltage output circuit 35 is connected to the charging wire 521K for black, and is a circuit that applies a wire voltage Vwk to this charging wire 521K.

[0032] As shown in Figure 2, the first charging voltage output circuit 30 includes an abnormal discharge detection circuit 31 and a wire voltage detection circuit 32. The abnormal discharge detection circuit 31 detects whether or not an abnormal discharge has occurred based on the abnormal discharge current that instantaneously flows through the charger 52 and ground. Here, abnormal discharge refers to spark discharge or arc discharge caused by contamination of the charged wire with toner or paper dust, for example, unlike corona discharge. The wire voltage detection circuit 32 of the first charging voltage output circuit 30 detects the wire voltage Vwymc generated in the charged wires 521C, 521M, and 521Y. The wire voltage detection circuit 32 of the second charging voltage output circuit 35 detects the wire voltage Vwk generated in the charged wire 521K. The abnormal discharge detected by the abnormal discharge detection circuit 31 and the wire voltage Vw detected by each wire voltage detection circuit 32 are input to port A / D1 of the ASIC20.

[0033] The first charging voltage output circuit 30 receives a PWM (Pulse Width Modulation) signal Sp1 from the ASIC 20 via port PWM1 and applies a wire voltage Vwymc to each charging wire 521C, 521M, and 521Y according to the duty cycle of the PWM signal Sp1. The second charging voltage output circuit 35 receives a PWM signal Sp2 from the ASIC 20 via port PWM2 and applies a wire voltage Vwk to the charging wire 521K according to the duty cycle of the PWM signal Sp2. For example, the higher the duty cycle of each PWM signal Sp1 and Sp2, the larger the value of the wire voltage Vw, and the lower the duty cycle, the smaller the value of the wire voltage Vw.

[0034] The grid voltage adjustment circuit 40 is a circuit that adjusts the grid voltage Vg generated at the grid 522. Of the four grid voltage adjustment circuits 40Y to 40C, grid voltage adjustment circuit 40C is connected to the cyan grid 522C, grid voltage adjustment circuit 40M is connected to the magenta grid 522M, and grid voltage adjustment circuit 40Y is connected to the yellow grid 522Y. Since the circuit configurations of grid voltage adjustment circuits 40C, 40M, and 40Y are similar, the following explanation will focus on grid voltage adjustment circuit 40Y, which corresponds to yellow (Y), and will omit explanations of the other grid voltage adjustment circuits 40C and 40M as appropriate.

[0035] As shown in Figure 2, the grid voltage adjustment circuit 40Y has an input line L1, one end of which is connected to the grid 522Y. The collector of transistor Q1 is connected to input line L1 via connection point P1. Transistor Q1 is, for example, an NPN transistor, but may also be a FET (field-effect transistor). The emitter of transistor Q1 is connected to ground via the grid current detection circuit 403Y. The base of transistor Q1 is connected to the output terminal of operational amplifier OP1 via a smoothing circuit including resistor R1 and capacitor C1. The connection point P2 between the emitter of transistor Q1 and the grid current detection circuit 403Y is connected to one end of detection line L2. The other end of detection line L2 is connected to port A / D3 of ASIC20. Port PWM3 of ASIC20 is connected to the input terminal of operational amplifier OP1 via a smoothing circuit including output resistor R2 and capacitor C2.

[0036] The other end of input line L1 is connected to grid voltage detection circuit 402Y. Grid voltage detection circuit 402Y has a voltage divider circuit formed by series-connected resistors R3 and R4, and a capacitor C3. Capacitor C3 has one end connected to the connection point of resistors R3 and R4 in the voltage divider circuit, and the other end connected to ground, forming an RC filter. Furthermore, the connection point P3 of resistors R3 and R4 in the voltage divider circuit is connected to port A / D2 of ASIC20. As a result, when a grid voltage Vgy corresponding to the wire voltage Vwy of the charged wire 521Y is applied to input line L1, a grid voltage detection signal Vgr1 corresponding to the voltage division ratio of resistors R3 and R4 in the voltage divider circuit is input to port A / D2 of ASIC20. The grid voltage detection circuit 402Y also supplies the grid voltage detection signal Vgr1 to the operational amplifier OP1 as a voltage divider detection signal Sid1 via output resistor R5.

[0037] ASIC20 adjusts the PWM signal Spp1 output from port PWM3 in response to the grid voltage detection signal Vgr1 input via port A / D2, and supplies the adjusted PWM signal Spp1 to operational amplifier OP1. This controls the switching period of transistor Q1 and adjusts the grid voltage Vgy of grid 522Y. The wire voltage Vwy is controlled, for example, between approximately 5.5kV and 7kV. The grid voltage Vgy is controlled, for example, to around 700V.

[0038] The K-colored grid 522K is connected to a grid voltage detection circuit 402K and a grid current detection circuit 403K. The grid voltage detection circuit 402K outputs a grid voltage detection signal Vgr4 to port A / D8 of ASIC20, corresponding to the grid voltage Vw generated in the grid 522K. The grid current detection circuit 403 outputs a grid current detection signal Sir4 to port A / D9 of ASIC20, corresponding to the grid current Igk generated in the grid 522K. In other words, unlike the YMC colored grids 522Y, M, and C, the K-colored grid 522K is not subject to grid voltage adjustment by the grid voltage adjustment circuit.

[0039] Next, the printing process performed by the ASIC20 will be explained using Figure 3. The process shown in Figure 3 is executed when the ASIC20 receives a print command after receiving print job data from an external device such as a PC. Alternatively, the process may also be executed when the printer 100 has stored print job data in memory and the ASIC20 receives a print command for print job data via an operation through a user interface (not shown).

[0040] In step 10 (hereinafter referred to as "S"), the ASIC20 performs printing processing using print job data in accordance with the print command. The ASIC20 starts outputting PWM signals Sp1, Sp2 and PWM signals Spp1, Spp2 to initiate the operation of the first and second charging voltage output circuits 30, 35 and the grid voltage adjustment circuits 40Y~40C. The ASIC20 adjusts the duty cycle of PWM signals Sp1, Sp2 based on the values ​​of grid current detection signals Sir1~Sir4 to control the wire voltages Vwymc, Vwk output from the first and second charging voltage output circuits 30, 35. For example, the ASIC20 controls the grid current Ig of each YMC color so that the minimum current value is above a predetermined value, and controls the grid current Ig of the K color so that it is above a predetermined value. Furthermore, ASIC20 adjusts the duty cycle of the PWM signal Spp and controls the grid voltage adjustment circuits 40Y, 40M, and 40C to match the grid voltage Vg to a desired set voltage. For example, when ASIC20 receives a print command and starts a charge operation, it executes the received print command when the grid current Ig and grid voltage Vg reach the desired target values. Alternatively, when ASIC20 starts a charge operation in conjunction with a warm-up operation, it may terminate the warm-up operation when the grid current Ig and grid voltage Vg reach the desired target values.

[0041] In S11, the wire voltage Vw is acquired according to the wire voltage detection signal Vwr output from the wire voltage detection circuit 32 of the first charging voltage output circuit 30, and the grid currents Igy, Igm, and Igc for each YMC color are acquired from the grid current detection signals Sir1 to Sir3 output from the grid current detection circuits 403Y to 403C for each YMC color. Hereafter, the wire voltage Vw and grid current Ig acquired in S11 will be prefixed with "b". That is, the wire voltage Vwb is the voltage detected before the abnormality of the charger 52 is detected in S12, as will be described later, and the grid current Igb is the current detected before the abnormality of the charger 52 is detected in S12, as will be described later. In this embodiment, the grid voltage is not adjusted by the grid voltage adjustment circuit for the K-colored charging wire 521K, so the decision of whether or not to perform cleaning is not made together with the YMC-colored chargers 52. For this reason, the grid current Igk is not acquired in S11.

[0042] In S12, it is determined whether or not there is an abnormality in the charger 52. Here, it is determined whether or not the wire voltage Vwymc detected by the wire voltage detection circuit 32 in the first charging voltage output circuit 30 has exceeded the upper limit voltage. For example, if toner or paper dust adheres to the charged wire 521, the resistance of the charged wire 521 increases. As the resistance of the charged wire 521 increases, the grid voltage Vg and grid current Ig do not reach the target values, so the ASIC 20 controls the drive of the first charging voltage output circuit 30 to increase the wire voltage Vwymc. As a result, an abnormality occurs in the charger 52, such as an excessive increase in the wire voltage Vwymc or abnormal discharge. Here, the upper limit voltage is the lower limit of the wire voltage Vw that is expected when there is an abnormality in the discharge of the charger 52. In addition to this, in S12, if the abnormal discharge detection circuit 31 detects that an abnormal discharge is occurring from the value of the wire current flowing through the charged wire 521, S12 may be judged as positive. In addition, in S12, it may be determined whether the wire voltage Vwk detected by the wire voltage detection circuit 32 in the second charged voltage output circuit 35 has exceeded the upper limit voltage.

[0043] If the result of S12 is negative, the process shown in Figure 3 is terminated. On the other hand, if an abnormality is detected in the charger 52 (S12: YES), the process proceeds to S13, and the status flag indicating the status of the printer 100 is set to "error state". When the status flag is set to "error state", the execution of the printing process on the printer 100 is prohibited. In S14, the display device 80 issues a notification prompting cleaning of the charged wires 521. For example, the display device 80 displays text prompting wire cleaning to be performed on all charged wires 521.

[0044] In S15, the system determines whether the opening / closing of the upper cover 91 has been detected by the opening / closing sensor 81. Upon notification in S14, the user changes the upper cover 91 from the closed position to the open position and removes the process unit 50 from the opening 90A in order to start wire cleaning. After the wire cleaning is complete, the user installs the process unit 50 into the printer 100 and changes the upper cover 91 from the open position to the closed position. Therefore, if the system determines from the signal from the opening / closing sensor 81 that the upper cover 91 has changed from the closed position to the open position and then changed again from the open position to the closed position (S15: YES), the system proceeds to S16. In this embodiment, if the opening / closing of the upper cover 91 is not detected by the opening / closing sensor 81 (S15: NO), the system waits.

[0045] In S16, a cleaning confirmation process is performed to determine whether cleaning has been performed on all charged wires 521. Figure 4 is a flowchart illustrating the process performed in S16 of Figure 3. First, in S20, the chargers 52Y, 52M, and 52Y are operated. In this embodiment, a minimum value is set for the grid current Ig for each YMC color. The ASIC20 adjusts the duty cycle of the PWM signals Sp1 and Sp2 to control the drive of the first charging voltage output circuit 30 so that all grid currents for each YMC color are greater than or equal to the minimum value of the grid current Ig. As a result, the wire voltage Vw and grid current Ig for each YMC color become constant. As described above, the grid voltage Vgk is not adjusted by the grid voltage adjustment circuit for the K color charger 52, so in S20, the drive of the second charging voltage output circuit 35 is not controlled.

[0046] In S21, the grid current Ig is obtained using the grid current detection signals Sir1, Sir2, and Sir3 output from the grid current detection circuits 403 for each YMC color. Additionally, the wire voltage Vwymc is obtained using the wire voltage detection signal Vwr output from the wire voltage detection circuit 32 of the first charged voltage output circuit 30. Hereafter, the grid current Ig and wire voltage Vw obtained in S21 will be referred to as "Igt" and "Vwt" respectively to distinguish them from the grid current Igb and wire voltage Vwb obtained in S11.

[0047] In S22, the maximum value Igmax and minimum value Igmin of the grid current Igt for each color acquired in S21 during the cleaning confirmation process are obtained. In S23, the wire voltage Vwt acquired in S21 and the maximum value Igmax and minimum value Igmin of the grid current Igt acquired in S22 are stored in memory.

[0048] In S24, the wire voltage Vwb, voltage difference threshold Vos, and current difference determination value ΔIgt obtained in S11 are read from memory. The voltage difference threshold Vos is a threshold used in the determination in S25, which will be described later, and specifically represents the expected decrease in wire voltage Vw after cleaning of the charger 52. The current difference determination value ΔIgt is a value used in S26, which will be described later, and represents the maximum value of the variation range in the grid current Ig of each color after cleaning of the charger 52.

[0049] In S25, it is determined whether the value obtained by subtracting the voltage difference threshold Vos from the wire voltage Vwb read in S24 is greater than the wire voltage Vwt saved in S23 (i.e., the wire voltage Vwymc during the greening confirmation process). In other words, in S25, it is determined whether the difference between the wire voltages Vwb and Vwt obtained before and after the abnormality of the charger 52 is greater than the voltage difference threshold Vos.

[0050] Figure 5 is a graph showing the current / voltage characteristics, with the grid current Ig on the horizontal axis and the wire voltage Vw on the vertical axis. Contamination of the charged wire 521 with toner and paper dust increases the internal resistance of the charged wire 521, resulting in a higher value for the wire voltage Vwymc output from the first charged voltage output circuit 30. At this time, the wire voltage Vwb immediately before the abnormality of the charger 52 is detected is expected to be higher than in normal operating conditions. Cleaning or replacement of the charged wire 521 will cause the wire voltage Vwt to decrease compared to the wire voltage Vwb before cleaning, as indicated by the arrows in the figure. Therefore, if the charged wire 521 is cleaned after the abnormality of the charger 52 is detected in S12, the wire voltage Vw will be lower than when the abnormality of the charger 52 was detected.

[0051] In S26, it is determined whether the difference between the maximum value Igmax and the minimum value Igmin of the grid current obtained in S23 (Igmax-Igmin) is smaller than the current difference determination value ΔIgt. Figure 6 is a diagram illustrating the voltage difference (=Vw-Vg) between the charged wire 521 and the grid 522 and the variation in the grid current Ig flowing through each colored grid 522. The vertical axis is the voltage difference (Vw-Vg) between the charged wire 521 and the grid 522, and the horizontal axis is the grid current Ig. Figure 6 shows the grid current Igt for each YMC color. In the figure, among the grid currents Igc, Igm, and Igy for each YMC color, the maximum value at a predetermined voltage difference Vwt-Vg is the maximum grid current Igmax, and the minimum value at a predetermined voltage difference Vw-Vg is the minimum grid current Igmin. Note that "Vwt" is the wire voltage Vwymc acquired in S23 of Figure 4 during the cleaning confirmation process, and "Vgt" is the grid voltage Vg during the cleaning confirmation process. By performing cleaning on all charged wires 521, the difference in resistance values ​​among the charged wires 521 of each color becomes smaller, and therefore the variation in the grid currents Igc, Igm, and Igy for each YMC color also becomes smaller. As a result, the difference between the maximum value Igmax and the minimum value Igmin among the grid currents Igc, Igm, and Igy for each color falls within the range of the current difference determination value ΔIgt. On the other hand, if even one of the charged wires 521 is not cleaned, the variation range of the grid currents Igc, Igm, and Igy becomes larger within the rated voltage range, and the difference between the maximum value Igmax and the minimum value Igmin does not fall within the range of the current difference determination value ΔIgt.

[0052] Therefore, if the difference between the maximum value Igmax and the minimum value Igmin of the grid current Igb for each color of YMC during the cleaning confirmation process is less than the current difference determination value ΔIgt (S26: YES), the process proceeds to S17 in Figure 3. In S17, the value of the status flag is changed from "error state" to "normal state". That is, the error state of the printer 100 is cleared, assuming that cleaning has been performed on all charged wires 521. Then, the process in Figure 3 is terminated.

[0053] On the other hand, if the decision in S25 in Figure 4 is negative (S25: NO), the process proceeds to S27, and the display device 80 prompts the user to re-notify the user to perform cleaning. For example, the screen displayed on the display device 80 in S27 is the same as the screen displayed in S14 in Figure 3.

[0054] Even if S25 is judged positively, if in S26 the difference between the maximum value Igmax and the minimum value Igmin of the grid current Igt is greater than or equal to the current difference determination value ΔIgt, the process proceeds to S27, and the display device 80 re-notifies the user about cleaning. In this embodiment, since the charged wires 521Y~521C of each YMC color are connected in parallel to the first charged voltage output circuit 30, it is possible to proceed to S26 even if cleaning has not been performed on all charged wires 521.

[0055] In S28, it is determined whether or not the opening and closing of the upper cover 91 has been detected. If the opening and closing of the upper cover 91 is detected (S28: YES), the process returns to S20 and the series of operations from S20 to S24 are executed again. In other words, after the re-notification in S27, the user performs cleaning on all charged wires 521, and the wire voltage Vwt newly acquired in S23, as well as the maximum value Igmax and minimum value Igmin of the grid current Igt, are obtained, and the decisions in S25 and S26 are made again. If the decision in S26 is then affirmative, the process proceeds to S17, the status flag of the printer 100 is changed from the error state to the normal state, and the process in Figure 3 is terminated.

[0056] The embodiment described above can achieve the following effects. In the cleaning confirmation process, the control device 10 determines, based on the wire voltage detection signal Vwr, whether the difference in wire voltage Vw before and after the detection of an abnormality in the charger 52 is greater than a predetermined threshold. If it is determined that the difference in wire voltage Vw is greater than the voltage difference threshold Vos, the control device 10 determines, based on the grid current detection signal, whether the difference between the maximum value Igmax and the minimum value Igmin among the multiple grid currents Igt is within a predetermined range. This makes it possible to determine in a small number of attempts that cleaning has been completed for all charged wires 521 in a printer 100 having charged wires 521 of each color.

[0057] In a configuration where two or more chargers 52 are connected in parallel to the first charging voltage output circuit 30, the internal resistance of each charger 52 differs depending on the amount of deposits adhering to it. Therefore, it may not be possible to determine whether cleaning has been completed for all chargers based solely on the change in current or voltage before and after an abnormality in a charger is detected. Even in such cases, it is possible to determine whether cleaning has been completed for all charging wires 521.

[0058] The control device 10 includes a plurality of grid voltage adjustment circuits 40Y to 40C that adjust the grid voltage Vg, which is the voltage applied to the grid. Even with this configuration, it is possible to determine whether or not cleaning has been completed for each of the YMC color chargers 52.

[0059] The control device 10 starts the cleaning confirmation process when the opening / closing sensor 81 detects that the upper cover 91 has changed between the open and closed positions. This allows the control device 10 to start determining whether or not cleaning has been performed after the upper cover 91 has been operated by the user and cleaning has been performed on the charger 52.

[0060] (Second Embodiment) In the second embodiment, the configurations that differ from those of the first embodiment will be mainly described. In the second embodiment, the same reference numerals are used for parts that are the same as in the first embodiment, and their descriptions will not be repeated. In this embodiment, compared to the first embodiment, the ASIC 20 of the control device 10 has a different configuration in which it controls the current flowing through the charger 52 with a constant current during the cleaning confirmation process.

[0061] Figure 7 is a flowchart illustrating the procedure for the process performed in S16 of Figure 3 in the second embodiment. In S30, the target current Ti of the grid current Igt in the cleaning confirmation process is set. The target current Ti is the target value of the grid current Igt flowing through the charger 52 during the cleaning confirmation process. In this embodiment, the target current Ti is set to a value lower than the current flowing through the grid 522 during the printing process in S10.

[0062] In S31, the output of the first charging voltage output circuit 30 is controlled by constant current control so that the grid current Igt during the cleaning confirmation process approaches the target current Ti set in S30. In this embodiment as well, the K-colored charging wire 521K is not checked for cleaning along with the YMC-colored charging wires 521YMC, so constant current control is not performed on the second charging voltage output circuit 35. In constant current control, the ASIC20 first acquires the current deviation between the target current Ti and the YMC-colored grid current Igt input through ports A / D3, 5, and 7. Then, the ASIC20 adjusts the duty cycle of the PWM signal Sp1 output from port PWM1 so that the acquired current deviation for each YMC color approaches 0. At this time, the ASIC20 may also output PWM signals Spp1 to Spp3 from ports PWM3 to PWM5 based on the current deviation for each color, causing the YMC-colored grid voltage adjustment circuits 40C to 40Y to adjust the grid voltage Vgt.

[0063] In S22, the maximum value Igmax and minimum value Igmin of the grid current Igt for each YMC color are obtained. In this embodiment, in S31, the grid current Igt is controlled to a value lower than the grid current Ig that flows during the printing process, so the maximum value Igmax and minimum value Igmin are also limited to values ​​lower than those in the first embodiment.

[0064] After going through S23 and S24, in S25, it is determined whether the value obtained by subtracting the voltage difference threshold Vos from the wire voltage Vwb acquired in S11 is greater than the current wire voltage Vwt. At this time, because the grid current Igt is controlled to the target current Ti by constant current control, the wire voltage Vwt will also be lower than in the first embodiment if cleaning has been performed. Furthermore, by performing constant current control, it is possible to suppress the output difference of the wire voltage Vwt from the first charged voltage output circuit 30 to the charged wires 521 of each YMC color, and the variation in the grid current Igt. As a result, the difference between each wire voltage Vwb and Vwt before and after cleaning will be larger than in the first embodiment, and the variation in the wire voltage Vwt of each color and the grid current Igt will be suppressed, thereby improving the accuracy of determining whether cleaning has been performed or not.

[0065] If S25 is judged positively, the process proceeds to S26. If the difference between the maximum value Igmax and the minimum value Igmin of the grid current Igt (Igmax-Igmin) is smaller than the current difference determination value ΔIgt (S26: YES), the process proceeds to S17 in Figure 3. In this embodiment, since the grid current Igt is limited by constant current control, the current difference determination value ΔIgt used in S26 is a different value from the current difference determination value ΔIgt used in the first embodiment. In S17, the value of the status flag is changed from "error state" to "normal state". On the other hand, if S25 or S26 is judged negatively, the process proceeds to S27, and the display device 80 is notified again to perform cleaning.

[0066] In the embodiment described above, in the cleaning confirmation process, since the change in wire voltage Vwt after detecting an abnormality in the charger 52 can be determined while the grid current Igt is controlled to a constant value, the accuracy of determining whether or not cleaning has been performed on the charged wire 521 can be improved.

[0067] (Third embodiment) In the third embodiment, the configuration that differs from that of the first embodiment will be mainly described. In the third embodiment, the same reference numerals are used for parts that are the same as in the first embodiment, and their descriptions will not be repeated. In this embodiment, compared to the first embodiment, the ASIC20 has a different configuration in which the voltage applied to the charger 52 is controlled to a constant voltage during the cleaning confirmation process.

[0068] Figure 8 is a flowchart illustrating the procedure for the process performed in S16 of Figure 3 in the third embodiment. In S40, the target voltage Tv of the charger 52 in the cleaning confirmation process is obtained. The target voltage Tv is the target value of the wire voltage Vwt during the execution of the cleaning confirmation process. In this embodiment, the target voltage Tv is set to a value lower than the voltage generated in the charged wire 521 during the printing process in S10.

[0069] In S41, the first charged voltage output circuit 30 is controlled by constant voltage control so that the wire voltage Vwt during the cleaning confirmation process approaches the target voltage Tv acquired in S40. In constant voltage control, the ASIC20 first acquires the voltage difference between the target voltage Tv and the current wire voltage Vwt. Then, the ASIC20 adjusts the duty cycle of the PWM signal Sp1 output from port PWM1 so that the acquired voltage difference approaches 0.

[0070] In S42, the grid current Igb acquired in S11, the current difference threshold Ios, and the current difference determination value ΔIgt are read from memory. The grid current Igb read in S42 is the grid current Igb acquired just before the abnormality of the charger 52 was detected in S12.

[0071] In S43, it is determined whether the value obtained by subtracting the current difference threshold Ios from the grid current Igb acquired in S42 for each YMC color is greater than the current grid current Igt acquired in S21. In other words, in this embodiment, it is determined whether the difference between the grid currents Igb and Igt for each YMC color before and after the detection of an abnormality in the charger 52 is greater than the current difference threshold Ios. In this embodiment, if at least one of the grid currents Igb and Igt for each YMC color is judged positively in S43, the process proceeds to S26. In S26, if the difference between the maximum value Igmax and the minimum value Igmin of the grid current Igt for each YMC color (Igmax-Igmin) is less than the current difference determination value ΔIgt (S26:YES), the process proceeds to S17 in Figure 2, and the value of the status flag is changed from "error state" to "normal state". In this embodiment, since the wire voltage Vwt of each color of YMC is controlled at a constant voltage, the current difference determination value ΔIgt used in S26 will be a different value from the current difference determination value ΔIgt used in the first embodiment.

[0072] In the embodiment described above, when it is determined that the current difference between the grid currents Igb and Igt before and after detecting an abnormality in the charger 52 is greater than a predetermined current difference threshold Ios, it is determined, based on the grid current detection signal, whether the difference between the maximum value Igmax and the minimum value Igmin of the grid current is within a predetermined range. If the difference between the maximum value Igmax and the minimum value Igmin is within the predetermined range, it is determined that the charged wires 521 of each YMC color have been cleaned. This makes it possible to determine whether cleaning has been performed on the charged wires 512 of each YMC color based on the change in grid current Ig.

[0073] In the cleaning confirmation process, the change in grid current Igt after detecting an abnormality in the charger 52 can be determined while the wire voltage Vwt is controlled to a constant value, thus improving the accuracy of determining whether or not cleaning has been performed.

[0074] (Fourth embodiment) In the fourth embodiment, the configuration that differs from that of the first embodiment will be mainly described. In the fourth embodiment, the same reference numerals are used for parts that are the same as in the first embodiment, and their descriptions will not be repeated. In this embodiment, compared to the first embodiment, the control device 10 has a different configuration in that it uses a voltage prediction value as the value used to determine whether or not cleaning has been performed in the cleaning confirmation process.

[0075] The process shown in Figure 9 is executed when the ASIC20 receives print job data from an external device such as a PC and receives a print command. After executing the print process in S10, in S51, the wire voltage Vwymc is obtained using the wire voltage detection signal Vwr output from the wire voltage detection circuit 32 in the first charged voltage output circuit 30, and the grid voltages Vgy to Vgc corresponding to the obtained wire voltage Vwymc are obtained using the grid voltage detection signals Vgr1 to Vgr3 output from the grid voltage detection circuits 402 for each YMC color. In addition, the grid currents Igy to Igc corresponding to the obtained wire voltage Vwymc are obtained using the grid current detection signals output from the grid current detection circuit 403 for each YMC color. In this embodiment as well, the voltage and current obtained in S51 are prefixed with "b".

[0076] If an abnormality in the charger 52 is detected in S12 (S12:YES), the process proceeds to S13, and the status flag indicating the status of the printer 100 is set to "error state". In S14, the display device 80 issues a notification prompting wire cleaning. In S15, if the opening / closing sensor 81 detects the opening or closing of the upper cover 91 (S15:YES), the process proceeds to S52, and the cleaning confirmation process is executed.

[0077] Figure 10 is a flowchart illustrating the process performed in S52 of Figure 9. In S70, multiple target voltages Vgt' for the grid voltage in each YMC color are determined during the cleaning confirmation process.

[0078] In S71, multiple target voltages Vwt' for the wire voltage Vwt in each YMC color are determined during the cleaning confirmation process. For example, the target voltage Vwt' can be determined using the following equation (Equation 1). Vwt'=Vwb-ΔV-(Vgb-Vgt) … (Formula 1) Note that "ΔV" is the change in the voltage difference between the wire voltage Vw and the grid voltage Vg for each YMC color before and after the abnormality of the charger 52 is detected (Vwb - Vgb - (Vwt - Vgt)). In addition to using the above (Equation 1), the target voltage Vwt' may be one of several constants predetermined according to the desired judgment accuracy of the cleaning confirmation process.

[0079] In S72, the target voltage Vgt' of the K-color grid voltage Vgt is determined during the cleaning confirmation process.

[0080] In step S73, the first and second charging voltage output circuits 30 and 35 are driven by the target voltages Vwt' and Vgt' determined in steps S70, S71, and S72, respectively, to operate the charger 52.

[0081] In S74, a first voltage prediction value Vth1n is calculated for each YMCK color, corresponding to the voltage difference between the wire voltage Vwb and the grid voltage Vgb immediately before detecting an abnormality in the charger 52. In this embodiment, the first voltage prediction value Vth1n can be calculated using the following equation (Equation 2) based on the multiple values ​​obtained in S51. Vwbn-Vgbn=Igbn×k+Vth1n… (Formula 2) Here, the proportionality constant k is the coefficient between the grid current Igbn and the first voltage prediction value Vth1n. By combining the first voltage prediction value Vth1n on the left side of (Equation 2) above, it becomes possible to determine the relational expression for calculating the first voltage prediction value Vth1n for each color of YMC.

[0082] The above (Equation 2) is a linear approximation of the relationship between the voltage difference between the charged wire 521 and the grid 522 and the grid current Ig for each color of YMCK. Since a grid current Ig flows through the grid 522 according to the voltage difference between the wire voltage Vw and the grid voltage Vg, the relationship between the first predicted voltage Vth1 and the grid current Igb can be approximated by a linear relationship, as shown in Figure 11. In Figure 11, the intercept at the moment when discharge occurs in the charged wire 521 (i.e., grid current Igb = 0) is the first predicted voltage Vth1 in this embodiment. In S74, the first predicted voltage Vth1n is obtained for all colors of YMCK.

[0083] In S75, a second voltage prediction value Vth2n is calculated for each YMCK color, corresponding to the voltage difference between the wire voltage Vwt and the grid voltage Vgt during the cleaning confirmation process. The second voltage prediction value Vth2n can be calculated using the following equation (3), similar to the above equation (2). Vwtn-Vgtn=Igtn×k+Vth2n… (Formula 3) In the above equation (Equation 3), for each YMC color, "Vwtn" is the wire voltage Vw when the charger 52 is driven by the target voltages Vwt' and Vgt' determined in S70 and S71, and "Vgtn" is the grid voltage Vg when the charger 52 is driven by the target voltages Vwt' and Vgt' determined in S70 and S72. For the K color, "Vwtn" is the wire voltage Vw when the charger 52 is driven by the target voltage Vgt' determined in S72, and "Vgtn" is the grid voltage Vg when the charger 52 is driven by the target voltage Vgt' determined in S72. In the above equation (Equation 3), by combining the second voltage prediction value Vth2n on the left side, it becomes possible to determine the relational expression for calculating the second voltage prediction value Vth2n.

[0084] In the relational equation shown in Figure 11, the intercept at the moment when discharge occurs in the charged wire 521 (i.e., when the grid current Ig = 0) is the second voltage prediction value Vth2 in this embodiment. In S75, the second voltage prediction value Vth2n is obtained for all YMCK colors. Even if variations occur in the wire voltage Vw due to the processing in S74 and S75, the comparison targets are the first and second voltage prediction values ​​Vth1n and Vth2n calculated by the relational equation, so the comparison targets used in S77 and S78, described later, can be standardized.

[0085] In S76, the maximum value Vthmax and minimum value Vthmin are obtained from the second voltage prediction values ​​Vth2n for each YMCK color acquired in S75 and stored in memory.

[0086] In S77, it is determined whether there is a difference between the first voltage prediction value Vth1n and the second voltage prediction value Vth2n for each YMCK color that is greater than the voltage difference threshold ΔVth. After an abnormality in the charger 52 is detected, cleaning is performed, which reduces the overall voltage difference between the charging wire 521 and the grid 522. Therefore, if the difference in the voltage prediction value Vth of at least one color obtained before and after the detection of the abnormality in the charger 52 is greater than a predetermined voltage difference threshold ΔVth, it can be determined that cleaning has been performed.

[0087] If S77 is judged positively, the process proceeds to S79, where it is determined whether the difference between the maximum value Vthmax and the minimum value Vthmin (Vthmax-Vthmin) of the second voltage prediction values ​​Vth2n for each YMCK color is smaller than the prediction difference judgment value ΔVp. That is, cleaning is performed on the charged wires 521 of each YMCK color, which reduces the difference in resistance values ​​of the charged wires 521 for each YMCK color, and thus reduces the variation in the second voltage prediction values ​​Vth2 for each YMCK color. Therefore, in the cleaning confirmation process, the difference between the maximum value Vthmax and the minimum value Vthmin of the second voltage prediction values ​​Vth2n for each YMCK color falls within the range of the prediction difference judgment value ΔVp. On the other hand, if even one of the charged wires 521 of each YMCK color has not been cleaned, the difference between the maximum value Vthmax and the minimum value Vthmin will not fall within the range of the prediction difference judgment value ΔVp.

[0088] If S79 is judged positively (S79: YES), the process proceeds to S17 in Figure 9. In S17, the value of the status flag is changed from "error state" to "normal state," and the error state of the printer 100 is cleared, assuming that cleaning has been performed on all charged wires 521. Then, the process in Figure 9 is terminated.

[0089] On the other hand, if the judgment in S77 or S79 in Figure 10 is negative, the process proceeds to S78 to determine whether the total number of judgments in S77 and S78 is the third time. If the total number of judgments is not the third time, the process proceeds to S80 to re-notify the execution of cleaning. Then, in S81, it is determined whether the opening and closing of the upper cover 91 has been detected. If the opening and closing of the upper cover 91 is detected, the process returns to S70 and executes the series of processes from S70 to S76.

[0090] In S78, if the total number of judgment attempts is 3, the process proceeds to S17 in Figure 9, and the error state is cleared. This is because the ASIC20 uses a voltage prediction value different from the measured value to determine whether cleaning has been performed, and therefore determines whether cleaning has been performed based on the number of attempts. Note that it is not necessary to determine the total number of judgment attempts in S78. In this case, if either S77 or S79 is judged negatively, the process proceeds to S80, and a re-notification is issued. In other words, the process does not proceed to S17 in Figure 9 unless S79 is judged positively.

[0091] In the embodiment described above, the voltage prediction value used to determine whether or not cleaning has been performed can be calculated using the determined relational expression. Therefore, even if there is variation in the wire voltage Vw among multiple charged wires 521, the determination is made using the voltage prediction value, which is a standardized comparison target, thus improving the accuracy of determining whether or not cleaning has been performed for all charged wires 521.

[0092] In the cleaning confirmation process, if it is determined that the difference in voltage prediction values ​​for at least one charged wire 521 is greater than a threshold, the maximum value Vthmax and minimum value Vthmin are obtained from the second voltage prediction values ​​for each of the multiple grids. If the difference between the maximum value Vthmax and the minimum value Vthmin is within a predetermined range, it is determined that all of the multiple charged wires 521 have been cleaned. This improves the accuracy of determining whether or not cleaning has been performed on all charged wires 521.

[0093] (Modification of the fourth embodiment) In the fourth embodiment described above, instead of acquiring first and second voltage prediction values ​​Vth1n and Vth2n, first and second current prediction values ​​may be acquired, and the decision in S77 may be made based on the acquired first and second current prediction values. In this case, in S74, the ASIC20 acquires the grid current Igb corresponding to a specific voltage difference as the first current prediction value from (Equation 2) above. In S75, the ASIC20 acquires the grid current Igt corresponding to a specific voltage difference as the second current prediction value from (Equation 3) above. Then, in S77, if the difference between the first current prediction value and the second current prediction value is greater than a predetermined threshold, the decision in S77 is affirmed, and the process proceeds to S79. This makes it possible to equalize the current prediction values ​​to be compared even when there is variation in the grid current Ig between the multi-colored grids 522, so that it is possible to accurately determine whether or not cleaning has been performed on all charged wires 521.

[0094] Furthermore, in S76, the maximum and minimum values ​​of the second current prediction values ​​for each of the multi-colored grids 522 are obtained, and in S79, if the difference between the obtained maximum and minimum values ​​of the second current prediction values ​​is within a predetermined range, it may be determined that all charged wires 521 have been cleaned. This improves the accuracy of determining whether or not cleaning has been performed on all charged wires 521.

[0095] (Other embodiments) The technologies disclosed herein are not limited to the embodiments described above and can be modified in various forms without departing from their essence, for example, the following modifications are possible. In the above-described embodiment, the three colors (Y, M, C) were connected to a common first charging voltage output circuit 30. Alternatively, all four colors (YMCK) may be connected to a common charging voltage output circuit.

[0096] In the embodiment described above, the cleaning confirmation process was executed in S15 after detecting the opening and closing of the upper cover 91. Alternatively, in S15, the cleaning confirmation process may be executed on the condition that, for example, the attachment or detachment of the process unit is detected, or that the start operation for the cleaning confirmation process is received through an operation by a user interface (not shown).

[0097] In the above-described embodiment, notifications were made by the display device 80 in S14 and S27, but instead, information may be notified by voice, for example.

[0098] In the embodiments described above, an upper cover 91 was exemplified as a cover, but the invention is not limited thereto, and may be a front cover, a side cover, or the like. A photoreceptor drum 51 was exemplified as a photoreceptor, but the present invention is not limited thereto, and may be a belt-shaped photoreceptor, for example. A charging wire 521 was exemplified as a charging member, but the present invention is not limited thereto, and may be a member other than a wire, for example. In the above-described embodiment, the image forming apparatus was a printer 100, but it is not limited to this, and the image forming apparatus may be, for example, a copier or a multifunction device. [Explanation of symbols]

[0099] 10...Control device, 20...ASIC, 30...First charging voltage output circuit, 32...Wire voltage detection circuit, 35...Second charging voltage output circuit, 40...Grid voltage adjustment circuit, 51...Photoreceptor drum, 52...Charger, 100...Printer, 402...Grid voltage detection circuit, 403...Grid current detection circuit, 521...Charging wire, 522...Grid

Claims

1. Multiple photoreceptors, A plurality of chargers having a charging wire and a grid positioned between the charging wire and the photoreceptor, for charging the plurality of photoreceptors, Control unit and Equipped with, The control unit, A voltage output circuit outputs a voltage to the charging wire that generates a corona discharge between the charging wire and the photoreceptor, and generates a voltage on the grid in conjunction with the corona discharge. A wire voltage detection circuit that outputs a wire voltage detection signal corresponding to the magnitude of the wire voltage, which is the voltage applied to the charged wire, A grid current detection circuit that outputs a grid current detection signal corresponding to the grid current, which is the current flowing through the grid, Equipped with, The control unit, If an abnormality in the charger is detected, a notification prompting cleaning of the charging wires is issued, and then a cleaning confirmation process is performed to determine whether or not cleaning of the multiple charging wires has been carried out. In the aforementioned cleaning confirmation process, A wire voltage is output to the multiple charged wires so that each set voltage is applied to the multiple grids. Based on the wire voltage detection signal corresponding to the wire voltage of the multiple charged wires, it is determined whether the voltage difference between the wire voltage immediately before detecting an abnormality in the charger and the wire voltage after detecting an abnormality in the charger is greater than a predetermined threshold. If it is determined that the voltage difference in at least one of the charged wires is greater than the threshold, then, based on the grid current detection signal, it is determined whether the difference between the maximum and minimum values ​​of the grid current flowing through each of the plurality of grids is within a predetermined range. If the difference between the maximum and minimum values ​​of the grid current falls within the predetermined range, it is determined that all of the multiple charged wires have been cleaned. Image forming apparatus.

2. Multiple photoreceptors, A plurality of chargers having a charging wire and a grid positioned between the charging wire and the photoreceptor, for charging the plurality of photoreceptors, Control unit and Equipped with, The control unit, A voltage output circuit outputs a voltage to the charging wire that generates a corona discharge between the charging wire and the photoreceptor, and generates a voltage on the grid in conjunction with the corona discharge. A wire voltage detection circuit that outputs a wire voltage detection signal corresponding to the magnitude of the wire voltage, which is the voltage applied to the charged wire, A grid current detection circuit that outputs a grid current detection signal corresponding to the grid current, which is the current flowing through the grid, Equipped with, The control unit, If an abnormality in the charger is detected, a notification prompting cleaning of the charging wires is issued, and then a cleaning confirmation process is performed to determine whether or not cleaning of the multiple charging wires has been carried out. In the aforementioned cleaning confirmation process, Voltage is output to the plurality of charged wires so that the wire voltage approaches the target voltage. Based on the grid current detection signals corresponding to the grid currents of the multiple grids, it is determined whether the current difference between the grid current immediately before detecting an abnormality in the charger and the grid current after detecting an abnormality in the charger is greater than a predetermined threshold. The difference in grid currents in at least one of the grids is greater than the threshold. If this is determined, then, based on the grid current detection signal, it is determined whether the difference between the maximum and minimum values ​​of the grid current flowing through each of the plurality of grids is within a predetermined range. If the difference between the maximum and minimum values ​​of the grid current falls within the predetermined range, it is determined that all of the multiple charged wires have been cleaned. Image forming apparatus.

3. The image forming apparatus according to claim 1 or 2, wherein two or more of the plurality of chargers are connected in parallel to the voltage output circuit.

4. The image forming apparatus according to claim 3, wherein the control unit comprises a plurality of grid voltage adjustment circuits for adjusting the grid voltage, which is a voltage applied to the grid.

5. The control unit is capable of performing constant current control, which causes the voltage output circuit to control the output to the charged wire so that the grid current flowing through the grid approaches a target current, based on the grid current detection signal. The image forming apparatus according to claim 1, wherein, in the cleaning confirmation process, after detecting an abnormality in the charger, the voltage output circuit is controlled by constant current when acquiring the wire voltage detection signal.

6. The control unit is capable of performing constant voltage control, which causes the voltage output circuit to control the output to the charged wire so that the wire voltage, which is the voltage applied to the charged wire, approaches a target voltage, based on the wire voltage detection signal. The image forming apparatus according to claim 2, wherein, in the cleaning confirmation process, after detecting an abnormality in the charger, the voltage output circuit is controlled by constant voltage when acquiring the grid current detection signal.

7. Multiple photoreceptors, A plurality of chargers having a charging wire and a grid positioned between the charging wire and the photoreceptor, for charging the plurality of photoreceptors, Control unit and Equipped with, The control unit, A voltage output circuit outputs a voltage to the charging wire that generates a corona discharge between the charging wire and the photoreceptor, and generates a voltage on the grid in conjunction with the corona discharge. A wire voltage detection circuit that outputs a wire voltage detection signal corresponding to the magnitude of the wire voltage, which is the voltage applied to the charged wire, A grid current detection circuit that outputs a grid current detection signal corresponding to the grid current, which is the current flowing through the grid, A grid voltage detection circuit that outputs a grid voltage detection signal corresponding to the magnitude of the grid voltage generated in the grid, Equipped with, The control unit, If an abnormality in the charger is detected, a notification prompting cleaning of the charging wires is issued, and then a cleaning confirmation process is performed to determine whether or not cleaning of the multiple charging wires has been carried out. In the aforementioned cleaning confirmation process, A wire voltage is output to the multiple charged wires so that each set voltage is applied to the multiple grids. Based on the wire voltage detection signal, grid voltage detection signal, and grid current detection signal output immediately before detecting an abnormality in the charger, a relational expression showing the relationship between the grid current and the voltage difference between the charging wire and the grid is determined, and a first voltage prediction value indicating the voltage difference between the charging wire and the grid corresponding to a specific grid current is obtained in the determined relational expression. Based on the wire voltage detection signal, grid voltage detection signal, and grid current detection signal obtained after detecting an abnormality in the charger, a relational expression showing the relationship between the grid current and the voltage difference between the charging wire and the grid is determined, and a second voltage prediction value, which is the voltage difference between the charging wire and the grid corresponding to the specific grid current, is obtained in the determined relational expression. Determine whether the difference between the first voltage prediction value and the second voltage prediction value is greater than a predetermined threshold. If it is determined that the difference between the first predicted voltage and the second predicted voltage is greater than a predetermined threshold for at least one of the charged wires, and if the difference between the maximum value and the minimum value of the second predicted voltage for each of the plurality of grids is within a predetermined range, it is determined that all of the plurality of charged wires are in a cleaned state. The relational expression showing the relationship between the grid current and the voltage difference between the charging wire and the grid is: Vw-Vg=Ig×k+Vth Therefore, in the above relation, Vw is the wire voltage, Vg is the grid voltage, Ig is the grid current, k is the proportionality constant, Vth is, In the case of the first voltage prediction value, in a graph approximating the relationship between the first voltage prediction value and the grid current using a linear relation, the voltage difference between the charging wire and the grid at the moment discharge occurs in the charging wire is: In the case of the second voltage prediction value, in a graph approximating the relationship between the second voltage prediction value and the grid current using a linear relationship, the voltage difference between the charging wire and the grid at the moment discharge occurs in the charging wire is: Image forming apparatus.

8. A housing having an opening, A cover is attached to the housing so as to be able to open and close the opening, An opening / closing sensor that detects when the cover changes from a closed position to an open position, Equipped with, The photoreceptor and the charger can be mounted inside the housing through the opening. The image forming apparatus according to claim 1 or 2, wherein the control unit starts the cleaning confirmation process when the opening / closing sensor detects that the cover has changed from the open position to the closed position.

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