JP2013137410A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of efficiently detecting abnormal discharge generated when activating a high voltage application circuit.SOLUTION: An image forming apparatus 1 comprises: a high voltage application circuit 62 for generating a high voltage Vcg and applying the high voltage Vcg on a photoreceptor 27; a determination part 61 for determining whether or not the possibility of abnormal discharge is high attributed to the application of the high voltage Vcg on the photoreceptor, before activating the high voltage application circuit 62; an excessive current detection parts (61, 64) for detecting an excessive current in activating the high voltage application circuit 62; and a detection regulation part 61 for regulating the detection of the excessive current by the excessive current detection parts (61, 64) when the determination part 61 determines that the possibility of abnormal discharge is not high.

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for detecting an overcurrent generated when a charging voltage is activated in an image forming apparatus.

  Conventionally, as a technique for detecting an overcurrent generated when a charging voltage is started in an image forming apparatus, for example, a technique described in Patent Document 1 is known. In that prior art document, when a charging current greater than an overcurrent value is detected when a charging voltage is started, more specifically, when a high-voltage circuit that generates a charging voltage is detected, the charging roller and A technique for protecting a photosensitive drum from an overcurrent is disclosed.

JP-A-7-84425

However, when starting the high voltage circuit, the output value of the charging voltage varies greatly depending on conditions such as humidity, and even if the output value reaches the target charging voltage without abnormal discharge, the overshoot current output value is In some cases, a threshold value that is determined to be an overcurrent is exceeded. In this case, although it is desired to detect an overcurrent in the case of abnormal discharge, an overcurrent due to an overshoot in the case of no abnormal discharge is detected. For this reason, even in a normal state where no abnormal discharge occurs, there is a possibility that an inconvenience that an overcurrent is detected and an abnormal discharge error occurs.
The present invention provides a technique capable of efficiently detecting an abnormal discharge that occurs when a high voltage application circuit is started.

  The image forming apparatus disclosed in this specification includes a photoconductor, a high voltage application circuit that generates a high voltage and applies the high voltage to the photoconductor, and before the high voltage application circuit is activated. A determination unit that determines whether or not there is a high possibility of abnormal discharge due to application of the high voltage to the photoconductor, an overcurrent detection unit that detects an overcurrent at the start of the high voltage application circuit; A detection regulation unit that regulates detection of the overcurrent by the overcurrent detection unit when the judgment unit determines that the possibility of the abnormal discharge is not high.

  In the image forming apparatus, the detection restricting unit may prohibit the overcurrent detection unit from detecting the overcurrent when the determination unit determines that the possibility of the abnormal discharge is not high. . At this time, the detection restricting unit prohibits the overcurrent detection unit from detecting the overcurrent in a period until the current flowing by applying the high voltage to the photoconductor reaches a target current value. It may be.

  In the image forming apparatus, when the detection restricting unit determines that the possibility of the abnormal discharge is not high by the determining unit, at least a current that flows due to application of the high voltage to the photoconductor is a target current. In the period until the value is reached, the detection threshold for detecting the overcurrent by the overcurrent detection unit may not be set.

  Further, in the image forming apparatus, when the determination restricting unit determines that the possibility of the abnormal discharge is high by the determining unit, the detection restricting unit uses the high voltage applying circuit as a detection threshold for detecting the overcurrent. When the first threshold value higher than the overshoot value at the time of starting is set and the determination unit determines that the possibility of the abnormal discharge is not high, the detection threshold value is not set, and the overcurrent detection unit You may make it detect the overcurrent at the time of starting of the said high voltage application circuit using the said 1st threshold value set by the detection control part. In this case, when the determination unit determines that the possibility of abnormal discharge is high, the detection regulation unit sets the detection threshold to the first threshold at least during a period until the current reaches a target current value. After that, the detection threshold value may be set to a second threshold value lower than the first threshold value.

  The image forming apparatus may further include a humidity measuring unit that measures humidity inside the image forming apparatus, and the determination unit may detect the abnormal discharge when the humidity measured by the humidity measuring unit is lower than a predetermined humidity. It may be determined that the possibility is high, and when the humidity is equal to or higher than the predetermined humidity, it is determined that the possibility of the abnormal discharge is not high.

  Further, in the image forming apparatus, a photosensitive member cartridge including the photosensitive member and detachable from the image forming apparatus, a developer cartridge including a developer and detachable from the photosensitive member cartridge, and the developer cartridge. A developer cartridge detection unit for detecting the presence or absence of the developer cartridge, wherein the determination unit detects the developer cartridge by the developer cartridge detection unit before the activation of the high-voltage application circuit; If it is not possible to detect the abnormal discharge, it is determined that the possibility of abnormal discharge is high, and the detection regulation unit is higher than the overshoot value at the time of starting the high voltage application circuit as a detection threshold for detecting the overcurrent A first threshold may be set.

  The image forming apparatus further includes a humidity measuring unit that measures humidity inside the image forming apparatus, the photoconductor, a photoconductor cartridge that can be attached to and detached from the image forming apparatus, a developer, and the photoconductor. A developer cartridge that can be attached to and detached from the cartridge; and a developer cartridge detection unit that detects the presence or absence of the developer cartridge; and the determination unit is configured such that the humidity measured by the humidity measurement unit is equal to or higher than a predetermined humidity. However, if the developer cartridge is detected by the developer cartridge detection unit before the high voltage application circuit is activated, and the presence or absence of the photosensitive cartridge cannot be detected, the possibility of abnormal discharge is high. The detection restricting unit determines whether or not the high voltage application circuit is activated as a detection threshold for detecting the overcurrent. It may be set the first threshold value higher than the over shoot value.

  In the image forming apparatus, when the overcurrent is detected, the overcurrent detection unit may stop application of the high voltage to the photoconductor by the high voltage application circuit.

  The image forming apparatus further includes a charger for charging the photoconductor, wherein the high voltage is a charge voltage applied to the photoconductor via the charger, and the high voltage application circuit A charging voltage generation circuit that generates a voltage may be used.

  According to the image forming apparatus of the present invention, when the determination unit determines that the possibility of abnormal discharge is not high, the overcurrent detection by the overcurrent detection unit is restricted. Therefore, it is suppressed that the inrush current (overshoot current) at the start of the high voltage application circuit is erroneously detected as an overcurrent although the possibility of abnormal discharge is not high. As a result, it is possible to efficiently detect abnormal discharge that occurs when the high voltage application circuit is started.

1 is a side sectional view showing an internal configuration of a laser printer according to the present invention. Block diagram schematically showing the high voltage generation circuit The flowchart which shows roughly the electric current detection process in Embodiment 1. Time chart schematically showing charging current at start-up of charging voltage application circuit The flowchart which shows the electric current detection process in Embodiment 2 roughly.

<Embodiment 1>
Embodiment 1 of an image forming apparatus will be described with reference to FIGS. Here, a monochrome laser printer is exemplified as the image forming apparatus. Note that the image forming apparatus is not limited to a monochrome laser printer, and may be, for example, a color laser printer, an LED printer, a facsimile machine, or a multifunction machine having a copy function and a scanner function.

1. FIG. 1 is a schematic sectional side view of a main part of a monochrome laser printer. In FIG. 1, a monochromatic printer (hereinafter simply referred to as “printer”) 1 forms an image on a feeder section 4 for feeding paper 3 or a fed paper 3 in a main body casing 2. The image forming unit 5 and the like are provided.

(1) Feeder unit The feeder unit 4 is provided at the bottom of the main body casing 2, and the one end side (hereinafter, one end side (the right side in FIG. 1)) of the sheet feed tray 6 is the front side and the opposite side. The sheet feeding roller 8 provided above the end (the left side in FIG. 1 is the rear side in FIG. 1), the registration roller 12 provided on the downstream side in the conveyance direction of the sheet 3 with respect to the sheet feeding roller 8, and the like.

  The uppermost sheet 3 of the sheet feeding tray 6 is fed one by one by the rotation of the sheet feeding roller 8. The fed paper 3 is sent to the registration roller 12. The registration roller 12 sends the paper 3 to the image forming position after registration. The image forming position is a contact position between the photosensitive drum (an example of “photosensitive member”) 27 and the transfer roller 30.

(2) Image Forming Unit The image forming unit 5 includes a scanner unit 16, a process unit 17, and a fixing unit 40.
The scanner unit 16 is provided at an upper portion in the main body casing 2 and includes a laser light emitting unit (not shown), a polygon mirror, a reflecting mirror, and the like. A laser beam based on the image data emitted from the laser light emitting unit is irradiated on the surface of the photosensitive drum 27 by high-speed scanning through a polygon mirror, a reflecting mirror, and the like as indicated by a chain line.

  The process unit 17 is provided below the scanner unit 16 and includes a photosensitive member cartridge 18 and a developing cartridge 19 accommodated in the photosensitive member cartridge 18. The process unit 17, in other words, the photoreceptor cartridge 18 is detachably accommodated in the laser printer 1. Further, the developing cartridge 19 is detachably accommodated with respect to the photosensitive cartridge 18 and includes, for example, a developing roller 31, a supply roller 33, a toner hopper 34, and the like.

  The toner hopper 34 is filled with toner (developer). A supply roller 33 is provided at a position behind the toner hopper 34, and a developing roller 31 is provided so as to face the supply roller 33. A predetermined developing bias voltage is applied to the developing roller 31 during development. The toner discharged from the toner hopper 34 is supplied to the developing roller 31 by the rotation of the supply roller 33.

  The photoreceptor cartridge 18 includes a photoreceptor drum 27, a scorotron charger 29, a transfer roller 30, and the like. The photosensitive drum 27 is disposed to face the developing roller 31 and includes a cylindrical drum main body and a metal drum shaft 27a that is grounded to the shaft center of the drum main body. A positively chargeable photosensitive layer is formed on the surface of the drum body. An exposure window is provided above the photosensitive drum 27 as a laser beam path.

  The charger 29 is disposed above the photoconductor drum 27 so as to face the photoconductor drum 27 at a predetermined interval so as not to contact the photoconductor drum 27. The charger 29 includes a charging wire 29a and a grid 29b, and the surface of the photosensitive drum 27 is uniformly charged to, for example, positive polarity (for example, about 700V) through the grid 29b by discharging from the charging wire 29a. Let A predetermined charging voltage Vcg (for example, 5 kV to 8 kV) is applied to the charging wire 29a.

  The surface of the photosensitive drum 27 is first uniformly charged positively by the charger 29 as the photosensitive drum 27 rotates. Thereafter, the charged surface is exposed by high-speed scanning of the laser beam from the scanner unit 16, and an electrostatic latent image based on the image data is formed. Next, by the rotation of the developing roller 31, the toner carried on the surface of the developing roller 31 and charged positively is supplied to the electrostatic latent image on the surface of the photosensitive drum 27, and the electrostatic latent image is Developed.

  The transfer roller 30 has a metal roller shaft 30 a and is disposed below the photosensitive drum 27 so as to face the photosensitive drum 27. The roller shaft 30a is covered with a roller made of, for example, a conductive rubber material.

  A high voltage generating circuit 60 as shown in FIG. 2 is connected to the roller shaft 30 a of the transfer roller 30. During a transfer operation for transferring the toner image carried on the developing roller 31 to the paper 3 at the transfer position, a transfer bias voltage (for example, −6 kV) is applied to the roller shaft 30 a of the transfer roller 30 from the high voltage generation circuit 60. High voltage) Vtp is applied.

  As shown in FIG. 1, the fixing unit 40 is provided on the rear downstream side of the process unit 17. In the fixing unit 40, the toner transferred onto the paper 3 is thermally fixed, and then the paper 3 is discharged onto the paper discharge tray 46.

  A photosensitive cartridge sensor 13 is provided in the main casing 2. The photoconductor cartridge sensor 13 is, for example, based on contact with the surface of the photoconductor cartridge 18 in a state in which the process unit 17, specifically, the photoconductor cartridge 18 is in the normal mounting state shown in FIG. The presence or absence of 18 is detected. The photoreceptor cartridge sensor 13 may not be provided.

  A developing cartridge sensor 14 is provided in the main casing 2. The developing cartridge sensor 14 is, for example, based on engagement with a detection member (not shown) provided on the developing cartridge 19 in a state where the developing cartridge 19 is in the normal mounting state shown in FIG. The presence or absence of 1 is detected.

  Further, a humidity sensor 15 (an example of a humidity measuring unit) for measuring the humidity in the printer 1 is provided in the main casing 2. The detection signal of the humidity sensor 15 is supplied to the high voltage generation circuit 60.

2. High Voltage Generation Circuit Next, the high voltage generation circuit 60 will be described with reference to FIG. FIG. 2 is a block diagram schematically showing a high voltage generation circuit 60 that applies the charging voltage Vcg to the charger 29. The developing cartridge 19 shown in FIG. 2 schematically shows a case where it is erroneously attached to the printer 1, that is, a case where it is directly attached to the printer 1 without being attached to the photosensitive cartridge 18.

  The high voltage generation circuit 60 generates each high voltage applied to the transfer roller 30, the developing roller 31, the charging wire 29 a of the charger 29, and the like. Note that FIG. 2 shows only the configuration related to the charging voltage Vcg for convenience of explanation. The photosensitive drum 27 is charged by applying a high voltage, for example, a charging voltage Vcg of 5 kV to 8 kV to the charging wire 29a of the charger 29 by the high voltage generation circuit 60, and via the grid 29b of the charger 29. This is done by generating a corona discharge on the surface of 27. The charging voltage Vcg is applied to the charging wire 29a through, for example, an output terminal T1 provided on the frame portion 2a in the main body casing 2 and an input terminal P1 provided on the photosensitive cartridge 18.

  The high voltage generation circuit 60 includes a CPU 61, a charging voltage application circuit 62, a charging voltage detection circuit 63, and a charging current detection circuit 64. The CPU 61 is an example of a determination unit, an overcurrent detection unit, and a detection regulation unit. The charging voltage application circuit 62 is an example of a high voltage application circuit, and the charging current detection circuit 64 is an example of an overcurrent detection unit. The determination unit, the overcurrent detection unit, and the detection regulation unit are not limited to being configured by the CPU 61, and may be configured by, for example, an ASIC (specific application IC) or may be configured by individual circuits. .

  The CPU 61 basically determines whether or not there is a high possibility of abnormal discharge due to application of a high voltage to the photosensitive drum 27 before the high voltage application circuit is activated. Further, when the CPU 61 detects an overcurrent at the time of starting the high voltage application circuit and determines that the possibility of abnormal discharge is not high, the CPU 61 restricts the detection of the overcurrent at the time of starting the high voltage application circuit. Restriction of overcurrent detection includes prohibiting overcurrent detection and not setting a detection threshold for overcurrent detection.

  The charging voltage application circuit 62 includes, for example, a PWM signal smoothing circuit, a step-up transformer, a smoothing rectification circuit, and the like, and is subjected to constant current control by a PWM (Pulse Width Modulation) signal from the CPU 61. That is, the CPU 61 controls the generation of the charging voltage Vcg by the charging voltage application circuit 62 so that the charging current Icg becomes a predetermined constant current.

  The charging voltage detection circuit 63 is constituted by, for example, a voltage dividing resistor, divides the charging voltage Vcg, generates a charging voltage detection signal Sv, and supplies the charging voltage detection signal Sv to the CPU 61. The CPU 61 may control the charging voltage application circuit 62 so that the charging voltage Vcg becomes a predetermined constant voltage instead of the constant current control of the charging current Icg.

  The charging current detection circuit 64 is constituted by, for example, a resistor connected between the secondary winding of the step-up transformer of the charging voltage application circuit 62 and the power supply voltage Vcc, and the charging current is connected to one end of the resistance on the secondary winding side. A detection signal (voltage signal) Si is generated, and the charging current detection signal Si is supplied to the CPU 61. In this case, the charging current Icg flows from the power source Vcc through the charging current detection circuit 64, the secondary winding of the step-up transformer, the charger 29, and the photosensitive drum 27, and the high voltage generation circuit via the common ground. Return to 60. At this time, the power supply voltage Vcc is divided by the charging current detection circuit (resistance) 64 and the load resistance (discharge path and photosensitive drum 27). That is, the charging current detection circuit 64 detects the charging current Icg as a divided value of the power supply voltage Vcc.

  In normal charging control, the CPU 61 receives a charging current detection signal (feedback signal) Si, and controls the charging voltage application circuit 62 so that the charging current detection signal Si becomes a predetermined value as described above. The charging current Icg is controlled at a constant current.

  On the other hand, if an abnormal discharge occurs between the charger 29 and the photosensitive drum 27 during the charge control, or an abnormal discharge occurs between the output terminal T1 and the developing cartridge 19 when the charging voltage application circuit 62 is activated. In this case, since the charging current Icg is increased compared to that during normal discharging, the value of the charging current detection signal Si is different from that during normal discharging. Therefore, the CPU 61 determines whether or not an abnormal discharge has occurred according to a change in the charging current detection signal Si. Specifically, when an abnormal discharge occurs, the resistance value of the discharge path decreases, and thereby the divided value of the power supply voltage Vcc, that is, the value of the charging current detection signal Si decreases. Therefore, here, when the value (voltage value) of the charging current detection signal Si becomes equal to or less than a predetermined reference value, the CPU 61 determines that the charging current Icg is equal to or higher than the predetermined value and abnormal discharge has occurred.

  Further, the CPU 61 receives the charging voltage detection signal Sv and monitors whether or not the desired charging voltage Vcg is generated by the charging voltage application circuit 62 based on the charging voltage detection signal Sv. Note that the CPU 61 controls not only the high voltage generation circuit 60 but also processing related to image formation.

3. Next, the overcurrent detection process at the time of starting the charging voltage according to the first embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 is a flowchart showing the overcurrent detection process. The overcurrent detection process is executed by the CPU 61 according to a predetermined program, for example, according to a user's print instruction. FIG. 4 is a time chart showing the transition of the charging current when the charging voltage is activated.

  In the overcurrent detection process, the CPU 61 basically determines whether or not there is a high possibility of abnormal discharge due to application of the charging voltage Vcg to the photosensitive drum 27 before the charging voltage application circuit 62 is activated. Judging. If the CPU 61 determines that the possibility of abnormal discharge is not high, the CPU 61 restricts detection of overcurrent when the charging voltage application circuit 62 is activated.

  When the user issues a print instruction, the CPU 61 first determines whether the humidity in the printer 1 is less than 20% based on the detection signal from the humidity sensor 15 (step S100). When it determines with humidity being less than 20% (step S100: YES), 1st threshold value Ith1 is set as a detection threshold value which detects overcurrent (step S110; refer FIG. 4).

  The first threshold value Ith1 is set to a value that does not detect a current overshoot when the charging voltage application circuit 62 is activated. That is, the first threshold value Ith1 is set to a value that is higher than the overshoot current value Ios at startup and lower than the maximum value (overcurrent value) Imx of the abnormal current due to abnormal discharge (see FIG. 4). Here, the time of starting the charging voltage application circuit 62 means a time until the charging current Icg reaches the target current Ita, and corresponds to a period from time t0 to almost time t1 in FIG. The determination humidity (predetermined humidity) is not limited to 20%. The determination humidity may be appropriately determined based on the installation environment of the printer 1, the occurrence rate of abnormal discharge, the protection of the printer 1, and the like.

  On the other hand, when it is determined that the humidity is not less than 20%, that is, the humidity is 20% or more (step S100: NO), the detection threshold value for detecting the overcurrent is not set (step S105; see FIG. 4).

  Usually, when the humidity is low, the occurrence voltage of abnormal discharge due to the charging voltage Vcg is lower than that when the humidity is high, and it can be said that the possibility of occurrence of abnormal discharge is high. For this reason, the CPU 61 determines that the possibility of abnormal discharge is high when the humidity measured by the humidity sensor 15 is lower than the predetermined humidity (20%), and the possibility of abnormal discharge is high when the humidity is equal to or higher than the predetermined humidity. Judge that there is no. Then, the CPU 61 sets the detection threshold to the first threshold Ith1 when it is determined that the possibility of abnormal discharge is high, and does not set the detection threshold when it is determined that the possibility of abnormal discharge is not high.

  Thus, when the possibility of abnormal discharge is not high, the detection threshold value is not set, so that the overshoot current (see FIG. 4) at the start of the charging voltage application circuit 62 is erroneously detected as an overcurrent due to abnormal discharge. Can be suppressed. As a result, it is possible to reduce erroneous detection of overcurrent due to abnormal discharge that occurs when the charging voltage application circuit 62 is started, and to improve the efficiency of detection of overcurrent due to abnormal discharge.

  Next, the CPU 61 activates the charging voltage application circuit 62 and starts generating the charging voltage Vcg (step S120). This time corresponds to time t0 in FIG. Next, the CPU 61 compares the first threshold value Ith1 and the charging current Icg using the detection signal Si, and determines whether or not the charging current Icg exceeds the first threshold value Ith1, that is, whether there is an abnormal discharge. (Step S130). However, if the first threshold value Ith1 is not set in S105, the determination in S130 is not performed.

  If there is no abnormal discharge (step S130: NO), it is determined whether a specified time K1 for reaching the target current value Ita has elapsed (step S135). When it is determined that the specified time K1 has elapsed (step S135: YES), the CPU 61 sets the detection threshold to a second threshold Ith2 that is lower than the first threshold Ith1 (step S140). Here, the specified time K1 corresponds to a period from time t0 to time t2 in FIG. 4, and is at least a period until the charging current Icg reaches the target current value Ita.

  In step S140, when the first threshold value Ith1 is set in step S110, the setting is changed from the first threshold value Ith1 to the second threshold value Ith2. On the other hand, if the first threshold value Ith1 is not set in step S105, a second threshold value Ith2 is newly set. That is, when it is determined that the possibility of abnormal discharge is not high, the CPU 61 does not set a detection threshold for detecting an overcurrent at least during the period K1 until the charging current Icg reaches the target current value Ita. Therefore, even if there is a variation in the charging voltage Vcg or an overshoot of the charging current Icg when the charging voltage application circuit 62 is activated, the application operation can be continued without causing an error, and the abnormal current after the charging voltage application circuit 62 is activated. Can be detected. The period during which the detection threshold is not set is not necessarily limited to the period K1 when the charging voltage application circuit 62 is activated. The period may be longer than the period K1, or may be shorter than the period K1.

  On the other hand, if there is an abnormal discharge within the specified time K1 (step S130: YES), the generation of the charging voltage Vcg is stopped (step S150), and an abnormality in the charging current Icg is detected, for example, on a display unit (not shown). 2), an abnormal discharge process is performed to notify the user (step S160).

4). Effects of First Embodiment According to the configuration of the first embodiment, when the CPU 61 determines that the possibility of abnormal discharge is not high, detection of overcurrent is restricted. Specifically, when the humidity in the printer 1 is 20% or more, a detection threshold for detecting an overcurrent is not set. That is, no overcurrent is detected. Therefore, it is possible to suppress erroneous detection of an inrush current (overshoot current) at the start of the charging voltage application circuit 62 as an overcurrent although the possibility of abnormal discharge is not high. When the humidity is less than 20%, a first threshold value Ith1 for detecting abnormal discharge is set. As a result, the detection of abnormal discharge that occurs when the charging voltage application circuit 62 is started can be made more efficient.

  In addition, the detection threshold is not set in the period K1 when the charging voltage application circuit 62 is started, which is likely to vary greatly in the charging voltage Vcg. Therefore, it is possible to more effectively prevent erroneous detection of overcurrent.

  Further, since the charging voltage Vcg has the highest voltage value among the high voltages generated in the printer 1, abnormal discharge is likely to occur due to the charging voltage Vcg. Therefore, it is possible to accurately determine abnormal discharge due to application of the charging voltage Vcg.

<Embodiment 2>
Next, Embodiment 2 will be described with reference to FIG. FIG. 5 is a flowchart showing an overcurrent detection process in the second embodiment. The second embodiment is different from the first embodiment only in overcurrent detection processing. Therefore, only the overcurrent detection process of the second embodiment will be described here. The same members and processes as those in the first embodiment are denoted by the same member numbers and step numbers, and the description thereof is omitted.

  Specifically, the method for determining whether or not there is a high possibility of occurrence of abnormal discharge in the overcurrent detection process is different. In other words, in the first embodiment, the CPU 61 determines whether or not the possibility of abnormal discharge is high, based on the humidity in the printer 1, but in the second embodiment, the photoconductor cartridge 18 and the developing cartridge 19. This is done in connection with the detection.

  When the user issues a print instruction, the CPU 61 first determines whether or not the developing cartridge 19 is present, that is, whether or not the developing cartridge 19 is detected by the developing cartridge sensor 14 (step S200). When there is no developing cartridge 19 (step S200: NO), for example, an error is displayed on a display unit (not shown) of the operation unit, and error processing is performed (step S205).

  On the other hand, when the developing cartridge 19 is present (step S200: YES), the CPU 61 determines whether or not the presence or absence of the photosensitive cartridge 18 can be detected before the charging voltage applying circuit 62 is started, that is, before the charging voltage Vcg is applied. (Step S210). This determination is performed before the charging voltage application circuit 62 is activated, for example, based on whether or not the detection signal from the photosensitive cartridge sensor 13 can be received. In this embodiment, since it is possible to receive a detection signal from the photosensitive cartridge sensor 13, it is determined that the presence or absence of the photosensitive cartridge 18 can be detected (step S210: YES), and a detection threshold value for detecting an overcurrent is detected. Is not set (step S105).

  On the other hand, when it is not determined that the presence / absence of the photoconductor cartridge 18 can be detected, that is, when the presence / absence of the photoconductor cartridge 18 cannot be detected (step S210: NO), the first detection threshold value for detecting the overcurrent is set. A threshold value Ith1 is set (step S110: see FIG. 4). This is due to the following reason.

  If the developer cartridge 19 removed from the photosensitive cartridge 18 is erroneously attached to the printer 1, the output terminal T1 of the charging voltage Vcg is not connected to the input terminal P1 of the photosensitive cartridge 18. Therefore, when the presence or absence of the photoconductor cartridge 18 cannot be detected and the charging voltage Vcg is applied without the photoconductor cartridge 18 being mounted, the output terminal T1 of the charging voltage Vcg and the metal portion of the developer cartridge 19 (See FIG. 2). Accordingly, when the mounting of the developing cartridge 19 is detected and the presence / absence of the photosensitive cartridge 18 cannot be detected, the first threshold value Ith1 is set to detect an abnormal discharge when the charging voltage application circuit 62 is started. it can.

  In the case where it is possible to detect the presence / absence of the photosensitive cartridge 18, when the photosensitive cartridge 18 is not detected, it is processed as an error, and when the photosensitive cartridge 18 is detected, the output terminal T1 is input. Since it is connected to the terminal P1, the possibility of abnormal discharge is not high. Therefore, it is not necessary to set a detection threshold for detecting overcurrent, and no detection threshold is set, that is, detection of overcurrent is restricted.

  Next, the CPU 61 activates the charging voltage application circuit 62 to start generating the charging voltage Vcg (step S120), and the same processing as in the first embodiment is performed thereafter.

5. Effect of Embodiment 2 When the mounting of the developing cartridge 19 is detected and it is not possible to detect the presence or absence of the photosensitive cartridge 18, the first threshold value Ith1 is set to detect abnormal discharge when the charging voltage application circuit 62 is started. can do. That is, it is possible to preferably detect abnormal discharge caused by erroneous mounting of the developing cartridge 19. Further, when the presence / absence of the photosensitive cartridge 18 can be detected, the threshold value is not set. As a result, the detection of abnormal discharge that occurs when the charging voltage application circuit 62 is started can be made more efficient.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.

  (1) In the first embodiment, even when the humidity is 20% (predetermined humidity) or higher, the CPU 61 detects the developer cartridge 19 by the developer cartridge detection unit before the charging voltage application circuit 62 is activated. If the presence / absence of the photoconductor cartridge 18 cannot be detected, it is determined that the possibility of abnormal discharge is high, and the detection threshold for detecting the overcurrent is higher than the overshoot value at the start of the charging voltage application circuit 62. One threshold may be set. In this case, the possibility of abnormal discharge can be determined based on both the humidity and the presence / absence of cartridge detection.

  (2) In each of the above embodiments, when it is determined that the possibility of abnormal discharge is not high, an example in which overcurrent detection is restricted without setting a threshold value in each step S105 is not limited thereto. . In each step S105, detection of overcurrent may be restricted by prohibiting detection of overcurrent by the CPU 61 (overcurrent detection unit).

  (3) In each of the above embodiments, the example in which the charging voltage application circuit 62 is controlled at a constant current has been described. it can.

  (4) In each of the above embodiments, the example of the charging voltage application circuit 62 has been described as the high voltage application circuit for applying a high voltage to the photosensitive drum 27, but is not limited thereto. In the present invention, the high voltage application circuit, for example, generates a transfer bias and applies a transfer bias to the photosensitive drum 27, or generates a cleaning bias and applies a cleaning bias to the photosensitive drum 27. It can also be applied to a circuit.

  DESCRIPTION OF SYMBOLS 1 ... Laser printer, 13 ... Photoconductor cartridge sensor, 14 ... Developer cartridge sensor, 15 ... Humidity sensor, 18 ... Photoconductor cartridge, 19 ... Developer cartridge, 27 ... Photoconductor drum, 27 ... Photoconductor drum, 29 ... Charger 61 ... CPU, 62 ... charge voltage application circuit, 64 ... current detection circuit

Claims (11)

A photoreceptor,
A high voltage application circuit for generating a high voltage and applying the high voltage to the photoreceptor;
A determination unit that determines whether or not there is a high possibility of abnormal discharge due to application of the high voltage to the photoconductor before the high voltage application circuit is activated;
An overcurrent detection unit for detecting an overcurrent at the start of the high voltage application circuit;
When the determination unit determines that the possibility of abnormal discharge is not high, a detection regulation unit that regulates detection of the overcurrent by the overcurrent detection unit;
An image forming apparatus. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the detection regulation unit prohibits the overcurrent detection unit from detecting the overcurrent when the determination unit determines that the possibility of the abnormal discharge is not high. The image forming apparatus according to claim 2.
The detection restricting unit prohibits detection of the overcurrent by the overcurrent detection unit in a period until at least a current flowing through application of the high voltage to the photoconductor reaches a target current value. . The image forming apparatus according to claim 1.
In the period until the current flowing through the application of the high voltage to the photoconductor reaches a target current value when the determination restricting unit determines that the possibility of the abnormal discharge is not high by the determining unit An image forming apparatus that does not set a detection threshold for detecting the overcurrent by the overcurrent detection unit. The image forming apparatus according to claim 1.
The detection restricting unit is higher than an overshoot value at the time of starting the high voltage application circuit as a detection threshold for detecting the overcurrent when the determination unit determines that the possibility of the abnormal discharge is high When the first threshold value is set and the determination unit determines that the possibility of the abnormal discharge is not high, the detection threshold value is not set.
The overcurrent detection unit is an image forming apparatus that detects an overcurrent when the high voltage application circuit is activated using the first threshold set by the detection regulation unit. The image forming apparatus according to claim 5.
The detection restricting unit sets the detection threshold to the first threshold at least during a period until the current reaches a target current value when the determination unit determines that the possibility of the abnormal discharge is high. Thereafter, the detection threshold is set to a second threshold lower than the first threshold. The image forming apparatus according to any one of claims 1 to 6,
A humidity measuring unit for measuring the humidity inside the image forming apparatus;
The determination unit determines that the possibility of the abnormal discharge is high when the humidity measured by the humidity measurement unit is lower than a predetermined humidity, and the possibility of the abnormal discharge when the humidity is equal to or higher than the predetermined humidity. An image forming apparatus that determines that the price is not high. The image forming apparatus according to any one of claims 1 to 6,
A photosensitive cartridge including the photosensitive member and detachable from the image forming apparatus;
A developer cartridge that includes a developer and is detachable from the photoreceptor cartridge;
A developer cartridge detector for detecting the presence or absence of the developer cartridge;
Further comprising
If the developer cartridge is detected by the developer cartridge detection unit before the high voltage application circuit is activated and the presence / absence of the photoconductor cartridge cannot be detected, the determination unit has a high possibility of the abnormal discharge. Judging
The image forming apparatus, wherein the detection restricting unit sets a first threshold value that is higher than an overshoot value when the high voltage application circuit is activated as a detection threshold value for detecting the overcurrent. The image forming apparatus according to any one of claims 1 to 6,
A humidity measuring unit for measuring the humidity inside the image forming apparatus;
A photosensitive cartridge including the photosensitive member and detachable from the image forming apparatus;
A developer cartridge that includes a developer and is detachable from the photoreceptor cartridge;
A developer cartridge detector for detecting the presence or absence of the developer cartridge;
Further comprising
The determination unit
Even when the humidity measured by the humidity measuring unit is equal to or higher than a predetermined humidity, the developer cartridge detecting unit detects the developer cartridge before starting the high voltage application circuit, and the photosensitive member cartridge If the presence or absence cannot be detected, it is determined that the possibility of the abnormal discharge is high,
The image forming apparatus, wherein the detection restricting unit sets a first threshold value that is higher than an overshoot value when the high voltage application circuit is activated as a detection threshold value for detecting the overcurrent. The image forming apparatus according to any one of claims 1 to 9,
The overcurrent detection unit, when detecting the overcurrent, stops application of the high voltage to the photoconductor by the high voltage application circuit. The image forming apparatus according to any one of claims 1 to 10,
Comprising a charger for charging the photoreceptor;
The high voltage is a charging voltage applied to the photoconductor via the charger,
The image forming apparatus, wherein the high voltage application circuit is a charging voltage generation circuit that generates the charging voltage.

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