JP2015161903A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress abnormal discharge energy while suppressing power consumption.SOLUTION: When a value of the current charge voltage CHG is equal to or lower than voltage thresholds, a CPU 51 determines that abnormal discharge is less likely to occur compared with the case where the value of CHG is larger than the voltage thresholds. Thus, the likelihood of the occurrence of abnormal discharge can be accurately determined compared with the case of not using an electrical change associated with the likelihood of the occurrence of abnormal discharge. When the CPU 51 has determined that abnormal discharge is less likely to occur, the CPU 51 reduces a value of resistance of a resistance part 67 compared with the case of having determined that abnormal discharge is more likely to occur. Thus, abnormal discharge energy can be suppressed while power consumption is suppressed compared with the case where a value of resistance of a suppression resistance is a fixed value sufficient to suppress abnormal discharge.

Description

  The present invention relates to a technique of an image forming apparatus including an electric unit that performs at least one of charging and discharging on a photosensitive member.

  In an electrophotographic image forming apparatus, for example, a photosensitive member is charged by a charging unit having a discharge wire and a grid. In such an image forming apparatus, for example, when toner concentrates and adheres to a specific portion of the discharge wire, abnormal discharge due to dielectric breakdown such as sparks may occur. Therefore, conventionally, there is an image forming apparatus in which a suppression resistor is provided in a grid current path in order to suppress this abnormal discharge energy (see Patent Document 1).

JP 2012-53168 A

  However, in the conventional image forming apparatus provided with the suppression resistor, the charging current always flows to the suppression resistor having a relatively high resistance value that can suppress the abnormal discharge even when the possibility of abnormal discharge is low. Therefore, there is a problem that power is wasted. Such a problem may occur not only in the charging unit but also in an image forming apparatus having a charge eliminating unit.

  The present specification discloses a technique capable of suppressing abnormal discharge energy while suppressing power consumption.

  An image forming apparatus disclosed in this specification includes an electric load, an applying unit that outputs an applied voltage, and an electric that performs at least one of charging and discharging on the electric load by applying the applied voltage. And a resistance part that is provided in a path of a current flowing through the electrical part and that can change a resistance value, and a control part, and determines whether the electrical part is likely to cause abnormal discharge. In the determination process and the height determination process, when it is determined that the possibility of occurrence of abnormal discharge is low, the resistance value of the resistance portion is made smaller than when it is determined that the possibility of occurrence of abnormal discharge is high. A resistance changing process to be executed.

  In this image forming apparatus, when it is determined that the possibility of abnormal discharge is low, the resistance value of the resistance portion is made smaller than when it is determined that the possibility of abnormal discharge is high. Thereby, it is possible to suppress abnormal discharge energy while suppressing power consumption compared to a case where the resistance value of the suppression resistor is a fixed value that can suppress abnormal discharge.

  The image forming apparatus includes: a current detection unit that outputs a signal corresponding to the current flowing through the electrical unit; and a voltage detection unit that outputs a signal corresponding to the applied voltage, and the control unit includes the current detection unit. Based on a signal from the unit, an application process is performed to control the application unit so that the current becomes constant. In the level determination process, the applied voltage is less than a voltage threshold based on a signal from the voltage detection unit. In this case, it is determined that the abnormal discharge is less likely to occur than when the applied voltage is greater than the voltage threshold.

  In this image forming apparatus, when the applied voltage is equal to or lower than the voltage threshold, it is determined that the possibility of abnormal discharge is lower than when the applied voltage is greater than the voltage threshold. Thereby, compared with the case where the electrical change accompanying the level of possibility that abnormal discharge will generate | occur | produce is not utilized, the level of possibility that abnormal discharge will generate | occur | produce can be judged more correctly.

  In the image forming apparatus, when the control unit determines that the abnormal discharge is unlikely to occur in the height determination process in the resistance changing process, and the possibility that the abnormal discharge is likely to occur is high. In at least one of the cases where the determination is made, the resistance value of the resistance section may be increased as the applied voltage is increased.

  In this image forming apparatus, the resistance value of the resistance portion is increased as the applied voltage is increased. Thereby, the resistance value of a resistance part can be changed according to the level of possibility that abnormal discharge will generate | occur | produce.

  In the image forming apparatus, the control unit executes a cleaning determination process for determining whether or not the electrical unit has been cleaned, and in response to determining that the cleaning is performed in the cleaning determination process in the height determination process. Further, it may be determined that the possibility of occurrence of the abnormal discharge is low, and it is determined that the possibility of occurrence of the abnormal discharge is high in response to determining that the cleaning is not performed.

  The image forming apparatus determines that the possibility of abnormal discharge is low in response to determining that the electrical unit has been cleaned, and may generate abnormal discharge in response to determining that the electrical unit has not been cleaned. Judgment is high. Thereby, it is possible to determine whether or not there is a possibility of abnormal discharge depending on the presence or absence of cleaning.

  The image forming apparatus includes a voltage detection unit that outputs a signal corresponding to the applied voltage, and a storage unit, and the control unit is configured to charge and discharge the electric unit based on a signal from the voltage detection unit. In accordance with the fact that the voltage difference between the current applied voltage and the previously stored applied voltage is larger than the reference difference in the storage process for storing the applied voltage in the storage unit every time at least one of the following is performed and the cleaning determination process The electrical unit may be determined to have been cleaned.

  The image forming apparatus determines that the electrical unit has been cleaned in response to the voltage difference between the current applied voltage and the previously stored applied voltage being greater than the reference difference. Accordingly, it is possible to more accurately determine the presence or absence of cleaning as compared to the case where the electrical change associated with the presence or absence of cleaning of the electrical portion is not used.

  In the image forming apparatus, the resistance unit may include a first resistance unit having a fixed resistance value and a second resistance unit capable of changing the resistance value.

  In this image forming apparatus, the resistance portion has a first resistance portion whose resistance value is fixed and a second resistance portion whose resistance value can be changed. Accordingly, an abnormal current due to, for example, a short circuit of a load can be suppressed by the resistance component of the first resistance portion regardless of the level of possibility of abnormal discharge.

  In the image forming apparatus, the second resistance unit may include a switching element, and may include a shunt circuit in which an on-resistance of the switching element is changed by the control of the control unit.

  In this image forming apparatus, the second resistance unit has a shunt circuit in which the on-resistance of the switching element changes under the control of the control unit. Thereby, a 2nd resistance part can be comprised, without using a variable resistance.

  In the image forming apparatus, the control unit may execute the resistance changing process during a non-image forming period in which the electric unit is neither charging nor discharging with respect to the electric load.

  The image forming apparatus executes the resistance changing process in a non-execution period in which neither charging nor charge removal is performed on the electric load. Thereby, it can suppress that it becomes impossible to charge or neutralize normally by execution of resistance change processing.

  In the image forming apparatus, the non-execution period may be a warm-up period before an execution period in which the electric unit performs at least one of charging and discharging on the electric load.

  In this image forming apparatus, the non-execution period is a warm-up period before the execution period in which the electric unit performs at least one of charging and discharging on the electric load. Thus, during the execution period, it is possible to suppress abnormal discharge energy while suppressing power consumption compared to a case where the resistance value of the suppression resistor is a fixed value that can suppress abnormal discharge.

  The image forming apparatus includes an abnormality detection unit that detects that an overcurrent exceeding a current threshold flows in the electrical unit, and the control unit determines whether an abnormal discharge has occurred based on a detection result of the abnormality detection unit. In the abnormality determination process for determining whether the abnormal discharge is low, the abnormality determination process and the height determination process are compared with the case where it is determined that the possibility of the abnormal discharge is high. Sensitivity change processing that lowers at least one of the detection sensitivity of the detection unit and the determination sensitivity of the abnormality determination processing may be executed.

  In this image forming apparatus, when it is determined that the possibility of abnormal discharge is low, the detection sensitivity of the abnormality detection unit and the abnormality determination are compared to when it is determined that the possibility of abnormal discharge is high. Decrease at least one of processing sensitivity. Accordingly, it is possible to suppress erroneous determination that the abnormal discharge has occurred when the possibility that the abnormal discharge occurs is low.

  In the image forming apparatus, in the abnormality determination process, the control unit determines that an abnormal discharge has occurred in response to the number of times of detection of the overcurrent reaching a reference number, and in the sensitivity change process, If it is determined in the height determination process that the possibility of occurrence of the abnormal discharge is low, the reference count may be made larger than that in the case where it is determined that the possibility of occurrence of the abnormal discharge is high.

  In this image forming apparatus, when it is determined that the possibility of occurrence of abnormal discharge is low, the reference number of times for determining whether or not abnormal discharge has occurred is greater than when it is determined that the possibility of occurrence of abnormal discharge is high. Increase Thereby, when the possibility of occurrence of abnormal discharge is low, the sensitivity of determination regarding abnormal discharge is reduced, and it is possible to suppress erroneous determination that abnormal discharge has occurred.

  The present invention is realized in various modes such as an image forming apparatus, a resistance changing method, an abnormal discharge detection method, a computer program for realizing the functions of these methods or apparatuses, and a recording medium on which the computer program is recorded. can do.

  According to the invention disclosed in this specification, it is possible to suppress abnormal discharge energy while suppressing power consumption.

1 is a schematic diagram illustrating an internal configuration of a printer according to an embodiment. Schematic circuit diagram of the high-voltage power supply Flow chart showing control processing Flow chart showing warm-up process Flow chart showing abnormal discharge detection processing

  A printer 1 according to an embodiment will be described with reference to FIGS. The printer 1 is an electrophotographic color printer and is an example of an image forming apparatus. In the following description, when distinguishing each component for each color, subscripts of Y (yellow), M (magenta), C (cyan), and K (black) are added to the reference numerals of the respective parts, and they are not distinguished. Omits subscripts.

(Mechanical configuration of the printer)
The printer 1 includes a supply unit 3, an image forming unit 5, a transport mechanism 7, a fixing unit 9, and a high voltage power supply device 50. For example, the printer 1 forms a toner image made of toner of one or a plurality of colors (four colors of yellow, magenta, cyan, and black in this embodiment) according to image data input from the outside on the sheet 15. Note that the sheet 15 is, for example, paper, an OHP sheet, or the like.

  The supply unit 3 is provided at the lowermost part of the printer 1 and includes a tray 17 for storing sheets 15 and a pickup roller 19. The sheets 15 accommodated in the tray 17 are taken out one by one by a pickup roller 19 and are sent to the transport mechanism 7 via the transport roller 11 and the registration roller 12.

  The conveyance mechanism 7 is for conveying the sheet 15, and includes a driving roller 31, a driven roller 33, and a belt 34, and the belt 34 is bridged between the driving roller 31 and the driven roller 33. . When the drive roller 31 rotates, the surface of the belt 34 facing the photosensitive drum 44 moves to the left in FIG. As a result, the sheet 15 sent from the registration roller 12 is conveyed to the image forming unit 5. Further, the transport mechanism 7 has four transfer rollers 33.

  The image forming unit 5 includes four process units 40K, 40Y, 40M, and 40C and four exposure devices 45. Each process unit 40 includes a charger 41, a photosensitive drum 44, a unit case 46, a developing roller 47, and a supply roller 48. The process units 40K, 40Y, 40M, and 40C are arranged in the printer 1 along the transport direction of the transport mechanism 7. The charger 41 is an example of an electric unit, and the photosensitive drum 44 is an example of an electric load and a photoconductor.

  The photosensitive drum 44 is formed, for example, by forming a positively chargeable photosensitive layer on an aluminum substrate, and the aluminum substrate is connected to the ground of the printer 1 via, for example, a conductive shaft 44A. Connected to the line. The charger 41 is a scorotron charger, and includes a discharge wire 42 and a grid 43. The charging voltage CHG is applied to the discharge wire 42, and the grid voltage GRID of the grid 43 is controlled so that the surface of the photosensitive drum 44 has substantially the same potential (for example, + 700V).

  The exposure device 45 includes, for example, a plurality of light emitting elements (for example, LEDs) arranged in a line along the rotational axis direction of the photosensitive drum 44, and the plurality of light emitting elements are selected according to image data input from the outside. By controlling the light emission, an electrostatic latent image is formed on the surface of the photosensitive drum 44. The exposure device 45 is fixedly installed in the printer 1. The exposure device 45 may use a laser.

  The unit case 46 stores toner of each color (in this embodiment, for example, a positively chargeable non-magnetic one-component toner), and includes a developing roller 47 and a supply roller 48. The toner is supplied to the developing roller 47 by the rotation of the supply roller 48 and is positively frictionally charged between the supply roller 48 and the developing roller 47. Further, the developing roller 47 supplies toner onto the photosensitive drum 44 to develop the electrostatic latent image, thereby forming a toner image on the photosensitive drum 44.

  Each transfer roller 33 is disposed at a position where the belt 34 is sandwiched between each transfer drum 33. Each transfer roller 33 receives a toner image formed on the photosensitive drum 44 by applying a transfer voltage (in this case, negative polarity) opposite to the toner charging polarity to the photosensitive drum 44. 15 is transferred. Thereafter, the sheet 15 is conveyed to the fixing unit 9 by the conveying mechanism 7, and the toner image is thermally fixed by the fixing unit 9 and is discharged onto the upper surface of the printer 1.

(Configuration of high-voltage power supply)
As illustrated in FIG. 2, the high-voltage power supply device 50 includes a CPU 51, a high-voltage power supply circuit 52 connected to the CPU 51, a storage unit 53, and a reception unit 54. The CPU 51 is an example of a control unit, and controls the entire printer in addition to the control of the high-voltage power supply circuit 52. The control unit is not limited to the CPU, and may be a hardware circuit for a specific application such as an ASIC.

  The high voltage power supply circuit 52 includes a charging voltage generation circuit 60, a resistance unit 67, an abnormal discharge detection circuit 70, a grid current detection circuit 80, and a charging voltage detection circuit 90. Note that the high-voltage power supply circuit 52 is provided for each of the chargers (41K to 41C). Since the configuration is the same, only one high-voltage power supply circuit 52 is shown in FIG.

  The charging voltage generation circuit 60 is an example of an application unit, and includes a transformer drive circuit 61 and a booster circuit 62. The charging voltage generation circuit 60 generates a charging voltage CHG to be applied to the discharge wire 42 of the charger 41. Along with the application of the charging voltage CHG to the discharge wire 42, corona discharge from the discharge wire 42 to the grid 43 occurs. The grid voltage GRID is generated in the grid 43 by the corona discharge. The charging voltage CHG is an example of an applied voltage, and is, for example, 5.5 kV to 8 kV, and the grid voltage GRID is, for example, about 700V.

  The transformer drive circuit 61 receives, for example, a PWM (Pulse Width Modulation) signal from the port PWM1 of the CPU 51, smoothes the PWM signal, and based on the smoothed PWM signal, the transformer 63 of the booster circuit 62 An oscillating current is passed through the primary winding 63A. Here, the value of the charging voltage CHG is controlled according to the duty ratio of the PWM signal. In the following description, it is assumed that the charging voltage CHG generated by the booster circuit 62 increases as the duty ratio of the PWM signal increases.

  The booster circuit 62 includes, for example, a transformer 63, a rectifier diode 64, and a smoothing capacitor 65. With such a configuration, the voltage of the primary side winding 63A of the transformer 63 is boosted via the secondary side winding 63B, rectified and smoothed by the rectifier diode 64 and the smoothing capacitor 65, and the charging voltage CHG is generated. The The charging voltage CHG is applied to the discharge wire 42 of the charger 41.

  The abnormal discharge detection circuit 70 is an example of an abnormality detection unit, and an overcurrent that instantaneously flows through the charger 41 due to the abnormal discharge is generated when an abnormal discharge due to a dielectric breakdown such as a spark occurs in the charger 41. It detects by detecting. The abnormal discharge detection circuit 70 can be composed of various known circuits, and an example thereof is shown in FIG.

  The abnormal discharge detection circuit 70 includes, for example, a coupling capacitor 71, a capacitor 72, resistors 73 and 74, bias resistors 75 and 76, a transistor Q1, and the like. The coupling capacitor 71 receives an overcurrent caused by abnormal discharge in the charger 41, in other words, an abnormal discharge current exceeding the current threshold. That is, when an abnormal discharge occurs between the discharge wire 42 and the grid 43, the grid current IG flowing through the grid 43 changes greatly intermittently.

  Then, an AC component of the grid current IG is extracted by the coupling capacitor 71, and the transistor Q1 is turned on / off according to the AC component. That is, the transistor Q1 is turned on each time an abnormal discharge of a predetermined level or more occurs between the discharge wire 42 and the grid 43. The CPU 51 reads the off signal from the transistor Q1 from the input port IN and detects the occurrence of abnormal discharge.

  The grid current detection circuit 80 is an example of a current detection unit, has detection resistors 81 and 82, and supplies a detection signal corresponding to the grid current IG flowing through the grid 43 to the port A / D1 of the CPU 51. The grid current IG is an example of a current that flows through the electric part. The charging voltage detection circuit 90 is an example of a voltage detection unit, has voltage dividing resistors 91 and 92, and supplies a detection signal corresponding to the charging voltage CHG to the port A / D2 of the CPU 51.

  The resistance unit 67 is provided in the path of the grid current IG and has a configuration in which the resistance value can be changed. The resistance portion 67 functions as a suppression resistor that suppresses abnormal discharge energy when abnormal discharge occurs in the charger 41 by increasing the resistance value, and suppresses abnormal discharge energy by decreasing the resistance value. It does not function as a suppressing resistor, but functions as a resistor that suppresses a short circuit or the like of an electric load.

  Specifically, the resistance unit 67 has a configuration in which a fixed resistor 68 and a shunt circuit 69 are connected in series. The fixed resistor 68 is an example of a first resistor unit, and the resistance value is fixed. The resistance component of the fixed resistor 68 can suppress an abnormal current due to, for example, a short circuit of an electric load such as the photosensitive drum 44, regardless of the possibility of abnormal discharge.

  The shunt circuit 69 is an example of a second resistance unit and has a configuration in which the resistance value can be changed. Specifically, the shunt circuit 69 includes a transistor Q2 and a resistor 69A, receives a PWM signal from the port PWM2 of the CPU 51, and changes the on-resistance of the transistor Q2 according to the duty ratio of the PWM signal. It is. The transistor Q2 is an example of a switching element. Thereby, a 2nd resistance part can be comprised, without using a variable resistance.

  The storage unit 53 is, for example, a ROM, a RAM, a non-volatile memory, and the like, and includes a program for executing control processing to be described later and a program for controlling the operation of each unit such as the image forming unit 5. The accepting unit 54 includes an operation unit that has a plurality of buttons and can accept various input instructions by the user, and a communication unit that communicates with an external device (not shown) by a wireless communication method or a wired communication method.

(Control content)
When the power of the printer 1 is turned on, the CPU 51 determines whether or not the reception unit 54 has received a print instruction (S1). If it is determined that the print instruction has not been received (S1: NO), the CPU 51 waits for printing. If it is determined that the instruction has been accepted (S1: YES), warm-up processing is executed (S2).

(1) Warming up process The warming up process will be described with reference to FIG. The CPU 51 causes the transport mechanism 7 or the like to start a transport operation, causes the charge voltage generation circuit 60 to generate the charge voltage CHG, and applies it to the discharge wire 42 (S11). Next, the CPU 51 starts to control the charging voltage generation circuit 60 so that the grid current IG becomes constant based on the detection value by the grid current detection circuit 80. That is, the CPU 51 starts constant current control for the charging voltage generation circuit 60 (S12). Thereby, the photosensitive drum 44 can be charged stably. The process of S12 is an example of an application process.

  After starting the constant current control, the CPU 51 acquires the value of the current charging voltage CHG from the detection signal from the charging voltage detection circuit 90 and stores it in the storage unit 53 (S13). The process of S13 is an example of a storage process.

  Next, the CPU 51 determines whether or not an abnormal discharge is likely to occur in the charger 41 (S14, S15). These processes are examples of the height determination process. Specifically, the CPU 51 determines whether or not the discharge wire 42 has been cleaned after the previous warm-up process (S14). The process of S14 is an example of a cleaning determination process. Here, when the toner or the like adhering to the discharge wire 42 is cleaned, the resistance value of the discharge wire 42 decreases, and the value of the charging voltage CHG changes greatly between the previous time and the current time in order to maintain the constant current control. To do.

  Therefore, the CPU 51 determines whether or not the voltage difference Δ between the value of the charging voltage CHG stored during the previous warm-up process and the value of the current charging voltage CHG is larger than the reference difference (S14). When the voltage difference Δ is larger than the reference difference, it is considered that the discharge wire 42 is likely to be cleaned, and the possibility that abnormal discharge occurs is low. When the voltage difference Δ is less than the reference difference, the discharge wire 42 is cleaned. It is considered that the possibility of abnormal discharge is high. As a result, it is possible to more accurately determine the presence or absence of cleaning as compared to the case where an electrical change associated with the presence or absence of cleaning of the discharge wire 42 is not used.

  Therefore, when the CPU 51 determines that the voltage difference Δ is larger than the reference difference (S14: YES), the CPU 51 sets the reference number to a relatively large number because the possibility of abnormal discharge is low (S19). This reference number is the number of overcurrent detection times for determining that an abnormal discharge error has occurred in an abnormal discharge detection process described later. The greater the reference number, the lower the sensitivity for determining abnormal discharge. Accordingly, it is possible to suppress an easy determination that an abnormal discharge error has occurred when the possibility of abnormal discharge is low.

  Further, the CPU 51 sets the resistance value of the resistance unit 67 to a small value (S19). For example, the CPU 51 sets the resistance value of the resistance unit 67 to about 1 KΩ. Thereby, when the possibility that abnormal discharge occurs is low, it is possible to suppress the wasteful consumption of electric power at the resistance portion 67.

  If the CPU 51 determines in S14 that the voltage difference Δ is less than or equal to the reference difference (S14: NO), the CPU 51 determines whether or not the current charging voltage CHG is greater than the first voltage threshold (S15). The first voltage threshold is an example of a voltage threshold, and is a value that is slightly smaller than the value of the charging voltage CHG when an abnormal discharge occurs in the discharge wire 42, for example, and can be obtained by experiments or the like. If the CPU 51 determines that the value of the current charging voltage CHG is greater than the first voltage threshold (S15: YES), the CPU 51 sets the reference number to a relatively small number because there is a high possibility of abnormal discharge. (S17). Thereby, when the possibility of occurrence of abnormal discharge is high, the determination sensitivity of abnormal discharge becomes high, and it can be detected early that an abnormal discharge error has occurred.

  Further, the CPU 51 increases the resistance value of the resistance unit 67 (S17). For example, the CPU 51 sets the resistance value of the resistance unit 67 to about 1 MΩ. Thereby, when there is a high possibility that abnormal discharge occurs, abnormal discharge energy can be suppressed.

  If it is determined in S15 that the current charging voltage CHG is equal to or lower than the first voltage threshold (S15: NO), it is determined whether or not the current charging voltage CHG is greater than the second voltage threshold (S16). ). The second voltage threshold is an example of a voltage threshold and is smaller than the first voltage threshold. When the CPU 51 determines that the value of the current charging voltage CHG is greater than the second voltage threshold (S16: YES), the possibility of occurrence of abnormal discharge is somewhat high, so the reference number is set to an intermediate number ( S18). Thereby, compared with the case where the reference number is set to the same value as in the process of S17, it is possible to suppress an easy determination that an abnormal discharge error has occurred, and to set the same number as the process of S19. Compared to the above, it is possible to detect early that an abnormal discharge error has occurred.

  Further, the CPU 51 sets the resistance value of the resistance unit 67 to an intermediate value (S19). For example, the CPU 51 sets the resistance value of the resistance unit 67 to a value between 1 KΩ and 1 MΩ. Thereby, compared with the case where resistance value of resistance part 67 is made into the same value as processing of S17, abnormal discharge energy can be controlled, and resistance part is compared with the case where it makes the same value as processing of S19. 67, it is possible to suppress the wasteful consumption of power.

  After executing any of the processes from S17 to S19, the CPU 51 waits until the warm-up operation ends (S20: NO). For example, when the warming-up operation ends (S20: YES) because the transport speed of the transport mechanism 7 becomes constant, the CPU 51 ends the warm-up process, proceeds to S3 in FIG. 3, and performs an operation for forming an image on the sheet. Then, an image forming process to be performed by the image forming unit 5 is executed. When the CPU 51 completes the image formation on the sheet (S4: YES), the CPU 51 stops the generation of the charging voltage CHG in the charging voltage generation circuit 60 (S5) and ends the control process.

(2) Abnormal Discharge Detection Processing The CPU 51 executes the abnormal discharge detection processing shown in FIG. 5 while the printer 1 is powered on, for example. The CPU 51 determines whether or not the number of times that the overcurrent has been detected by the abnormal discharge detection circuit 70 has reached the reference number set in any of the processes of S17 to S19 (S31). This process is an example of an abnormality determination process.

  When the CPU 51 determines that the number of abnormal discharge detections has not reached the reference number (S31: NO), the CPU 51 stands by, and when it determines that the number of abnormal discharge detections has reached the reference number (S31: YES), error processing is performed. Is executed (S32), and the process returns to S31. This error processing is, for example, processing for displaying error information on a display unit (not shown), notifying an external device via the receiving unit 54, or stopping the conveyance operation or the image forming operation. Thereby, it can be notified to the user or the like that an abnormal discharge has occurred.

(Effect of this embodiment)
As described above, the CPU 51 determines that the possibility of abnormal discharge is lower when the value of the current charging voltage CHG is less than or equal to each of the voltage threshold values, compared to when it is greater than the voltage threshold value. Thereby, compared with the case where the electrical change accompanying the level of possibility that abnormal discharge will generate | occur | produce is not utilized, the level of possibility that abnormal discharge will generate | occur | produce can be judged more correctly.

  Further, when the CPU 51 determines that the possibility of abnormal discharge is low, the CPU 51 causes the resistance value of the resistance unit 67 to be smaller than when it is determined that the possibility of abnormal discharge is high. Thereby, it is possible to suppress abnormal discharge energy while suppressing power consumption compared to a case where the resistance value of the suppression resistor is a fixed value that can suppress abnormal discharge. The process of S17 to S19 is an example of a resistance change process and a sensitivity change process.

  Further, the CPU 51 increases the resistance value of the resistance portion 67 as the current charging voltage CHG increases. Thereby, the resistance value of the resistance part 67 can be changed according to the level of possibility that abnormal discharge will occur.

  Further, the CPU 51 executes resistance change processing during a non-execution period when printing is not performed on the photosensitive drum 44. Thereby, it can suppress that it becomes impossible to charge normally by execution of resistance change processing. Moreover, this non-execution period is a warm-up period before the execution period in which the photosensitive drum 44 is charged. Thereby, during the charging execution period, abnormal discharge energy can be suppressed while suppressing power consumption compared to a case where the resistance value of the suppression resistor is a fixed value that can suppress abnormal discharge.

  When the CPU 51 determines that the possibility of occurrence of abnormal discharge is low, the CPU 51 reduces the determination sensitivity of abnormal discharge as compared to the case where it is determined that the possibility of occurrence of abnormal discharge is high. Accordingly, it is possible to suppress erroneous determination that the abnormal discharge has occurred when the possibility that the abnormal discharge occurs is low. In addition, when the CPU 51 determines that the possibility of abnormal discharge is low, the CPU 51 determines the reference number for determining whether or not abnormal discharge has occurred, as compared with the case where it is determined that the possibility of abnormal discharge is high. Enlarge. Thereby, when the possibility of occurrence of abnormal discharge is low, the sensitivity of determination regarding abnormal discharge is reduced, and it is possible to suppress erroneous determination that abnormal discharge has occurred.

<Other embodiments>
The technology disclosed in the present specification is not limited to the embodiments described with reference to the above description and drawings, and includes, for example, the following various aspects.

  The image forming apparatus is not limited to a single printer, for example, a copying machine having a reading function and a printing function, a facsimile having a facsimile function, and a multifunction machine having a plurality of functions such as a copying function and a facsimile function. Good. Further, the image forming apparatus is not limited to color, and may be a monochrome printer. Further, the image forming apparatus may be another electrophotographic method such as a polygon scanning exposure method.

  The electrical unit is not limited to the scorotron charger, and may be a corotron charger without a grid. The electrical unit is not limited to the charger, and may be a static eliminator that removes charges on the photosensitive drum 44, for example. In short, the electric unit may be any unit that performs at least one of charging and discharging on the electric load by applying a voltage. Further, the electric load is not limited to the photoconductor, and may be, for example, a conveyance belt that electrostatically attracts the sheet.

  Although the resistance part 67 was connected between the charging voltage generation circuit 60 and the discharge wire 42, it is not restricted to this. The resistance unit 67 may be, for example, between the grid 43 and the abnormal discharge detection circuit 70 or between the photosensitive drum 44 and the ground. In short, the resistance portion 67 may be provided in a path through which the grid current IG flows.

  The first resistance portion is not limited to the resistance itself, but may be an element having a resistance component. The second resistance unit is not limited to the shunt circuit 69 but may be a variable resistance element or the like.

  In the height determination process, for example, the CPU 51 may generate an abnormal discharge when the number of printed sheets of the discharge wire 42, the charging time, the rotational speed of the photosensitive drum 44, etc. exceed a predetermined value. You may judge that the nature is high.

  In the cleaning process, for example, the CPU 51 may determine that the discharge wire 42 has been cleaned on the condition that the receiving unit 54 has received a cleaning execution instruction from the user. Further, the CPU 51 displays a cleaning sign that prompts execution of cleaning on a display unit (not shown), and determines that the discharge wire 42 has been cleaned on the condition that the receiving unit 54 has received an instruction to clear the cleaning sign. Good.

  In the processing of S17 to S19, the CPU 51 changes the current threshold in the abnormal discharge detection circuit 70 or changes the detection value of the grid current IG in the abnormal discharge detection circuit 70 in addition to changing the determination sensitivity of the abnormal discharge detection processing. The detection sensitivity of the abnormal discharge detection circuit 70 may be changed by changing it.

  In FIG. 4, the CPU 51 may not execute any one of the process of S14 and the processes of S15 and S16. For example, the CPU 51 may proceed to S15 without performing the process of S14 after executing the process of S13. Further, when the CPU 51 makes an affirmative determination in S14 (S14: YES), it may proceed to S17 without performing the processes of S15 and S16. Further, if the CPU 51 makes a negative determination in S15 (S15: NO), it may proceed to S18 or S19 without performing S16.

  DESCRIPTION OF SYMBOLS 1: Printer 41: Charger 44: Photosensitive drum 51: CPU 53: Memory | storage part 54: Reception part 60: Charging voltage generation circuit 67: Resistance part 70: Abnormal discharge detection circuit 80: Grid current detection circuit 90: Charging voltage detection circuit

Claims (11)

Electrical load,
An application unit for outputting an applied voltage;
An electric unit that performs at least one of charging and discharging on the electric load by applying the applied voltage;
A resistor part provided in a path of a current flowing through the electric part, the resistance value of which can be changed;
A control unit,
High / low determination processing for determining the level of possibility of abnormal discharge occurring in the electrical part,
When it is determined that the abnormal discharge is unlikely to occur in the height determination process, the resistance changing process for reducing the resistance value of the resistance unit is more than when it is determined that the abnormal discharge is likely to occur. And an image forming apparatus. The image forming apparatus according to claim 1,
A current detection unit that outputs a signal corresponding to a current flowing through the electrical unit;
A voltage detection unit that outputs a signal according to the applied voltage,
The controller is
Based on the signal from the current detection unit, execute an application process for controlling the application unit so that the current becomes constant,
In the level determination process, when the applied voltage is equal to or lower than a voltage threshold based on a signal from the voltage detection unit, the possibility that the abnormal discharge is generated is lower than when the applied voltage is greater than the voltage threshold. The image forming apparatus determines that The image forming apparatus according to claim 2,
The controller is
In the resistance change process,
In the case where it is determined that the possibility of occurrence of the abnormal discharge is low in the height determination process, and in at least one of the cases where it is determined that the possibility of occurrence of the abnormal discharge is high, the larger the applied voltage, An image forming apparatus that increases a resistance value of the resistance portion. The image forming apparatus according to any one of claims 1 to 3,
The controller is
Performing a cleaning determination process for determining whether or not the electrical unit has been cleaned;
In the height determination process, it is determined that the possibility of occurrence of the abnormal discharge is low in response to determining that the cleaning is performed in the cleaning determination process, and in response to the determination that the cleaning is not performed, the abnormal discharge An image forming apparatus that determines that there is a high probability of occurrence. The image forming apparatus according to claim 4,
A voltage detector that outputs a signal corresponding to the applied voltage;
A storage unit,
The controller is
A storage process of storing the applied voltage in the storage unit every time the electrical unit performs at least one of charging and discharging based on a signal from the voltage detection unit;
In the cleaning determination process, an image forming apparatus that determines that the electrical unit has been cleaned in response to a voltage difference between a current applied voltage and a previously stored applied voltage being greater than a reference difference. An image forming apparatus according to any one of claims 1 to 5,
The resistance portion is
An image forming apparatus having a first resistance portion having a fixed resistance value and a second resistance portion capable of changing the resistance value. The image forming apparatus according to claim 6,
The image forming apparatus, wherein the second resistance unit includes a switching element, and includes a shunt circuit in which an on-resistance of the switching element is changed by the control of the control unit. The image forming apparatus according to any one of claims 1 to 7,
The controller is
The image forming apparatus, wherein the resistance changing process is executed in a non-image forming period in which the electric unit is not charged or neutralized with respect to the electric load. The image forming apparatus according to claim 8, wherein
The image forming apparatus, wherein the non-execution period is a warm-up period before an execution period in which the electric unit performs at least one of charging and discharging on the electric load. An image forming apparatus according to any one of claims 1 to 9,
Comprising an abnormality detection unit for detecting that an overcurrent exceeding a current threshold flows in the electrical unit;
The controller is
An abnormality determination process for determining whether an abnormal discharge has occurred based on the detection result of the abnormality detection unit;
In the height determination process, when it is determined that the possibility of occurrence of the abnormal discharge is low, the detection sensitivity of the abnormality detection unit, compared with the case where it is determined that the possibility of occurrence of the abnormal discharge is high, and An image forming apparatus that executes sensitivity change processing that lowers at least one of the determination sensitivity of the abnormality determination processing. The image forming apparatus according to claim 10, wherein
The controller is
In the abnormality determination process, it is determined that an abnormal discharge has occurred in response to the number of times of detection of the overcurrent reaching a reference number.
In the sensitivity change process, when it is determined in the height determination process that the possibility of occurrence of the abnormal discharge is low, the reference count is made larger than when it is determined that the possibility of occurrence of the abnormal discharge is high. , Image forming apparatus.

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