JP5021692B2 - Image forming apparatus and method for detecting open / closed state of shutter of potential sensor used in image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus and a shutter open / closed state detection method of a photoreceptor surface potential sensor used in the image forming apparatus.

  The surface potential sensor unit includes a potential sensor probe having a potential detection unit, a shutter that moves between a position at which the potential detection unit is exposed and a position that covers the potential detection unit, and a shutter mechanism that moves the shutter. The potential detector detects the surface potential of the photosensitive drum.

  A CPU (Central Processing Unit) controls driving of the shutter mechanism. The timing at which the CPU measures the surface potential is determined in advance, such as immediately after the image forming apparatus is activated.

  When the CPU does not measure the surface potential, it instructs the shutter mechanism to close the shutter. When measuring the potential, the CPU instructs the shutter mechanism to open the shutter.

  When the shutter exposes the potential detector, the potential sensor probe detects the surface potential of the photosensitive drum. The potential sensor probe outputs the detected voltage value to the CPU.

  Based on the voltage value, the CPU adjusts the charging bias of the charger, the developing bias of the developing device, and the intensity of the laser beam for exposure.

  When the potential sensor is provided between the charger and the developing device, the potential sensor is located upstream of the developing device in the drum rotation direction. The surface potential sensor unit is not soiled by toner scattered from the developing device. Since the shutter can be opened only when necessary, the detection surface of the potential detection unit is not soiled.

  However, when the potential sensor is provided downstream of the developing device in the drum rotation direction, toner from the developing device may adhere to the surface potential sensor unit. While the shutter is open, toner scattered from the developing device adheres to the potential detection unit.

  When toner adheres in the vicinity of the potential detection unit, the charged potential of the toner causes disturbance of the electric field. The surface potential sensor unit cannot accurately detect the surface potential. The accuracy of detection of the surface potential by the surface potential sensor unit deteriorates.

  When the potential sensor is located downstream of the developing device, the shutter needs to be closed at an unnecessary timing.

  The CPU is required to recognize that the shutter is opened only at the timing when the potential sensor measures the surface potential and that the shutter is closed at other timings.

  The CPU is required to recognize that the shutter is open as an error during the time when the shutter must be closed.

  Patent Document 1 discloses a surface potential sensor having a metal box-shaped shield member, a detection electrode in the shield member, and a detection window provided on a surface with respect to the photosensitive drum.

  U.S. Pat. No. 6,057,049 teaches an electrostatic voltmeter. An electrostatic voltmeter disclosed in Patent Document 2 includes a detection probe assembly, a shutter movable between a first position where the detection probe assembly is exposed and a second position where the detection probe assembly is covered, A shutter driver that selectively moves the shutter between a first position and a second position.

  Patent Document 3 discloses that the detection means detects the surface potential of the photoconductor by the minimum exposure amount and the surface potential of the photoconductor by the maximum exposure amount when three kinds of predetermined voltages are applied to the grid. To do.

  The control means controls the voltage applied to the grid based on each detected surface potential so that the difference between the surface potential of the photoconductor due to the minimum exposure amount and the surface potential of the photoconductor due to the maximum exposure amount becomes a predetermined value. To do.

  Conventionally, a mechanism for shuttering a detector of a potential sensor generally detects whether a shutter is normally opened and closed and exists at a steady position using an optical sensor or a mechanical sensor sensor.

  The optical sensor detects the presence or absence of a shutter when the light receiving element detects that the light beam is blocked.

  The mechanical sensor has a contact provided at a position where the shutter is closed and a contact attached to an end of the shutter. When the shutter is in the closed position, the two contacts come into contact. When the shutter is in the open position, the two contacts are separated. The mechanical sensor detects the position according to the state of energization between the two contacts.

  The CPU uses the sensor output from the optical sensor or the mechanical sensor to check whether the shutter is positioned at the open position and the closed position at an accurate timing.

Japanese Patent Laying-Open No. 2002-62326 (FIG. 7) JP 2000-147035 A Japanese Patent No. 2641050

  However, using an optical sensor or a mechanical sensor as a shutter opening / closing detection sensor complicates the apparatus and leads to an increase in cost.

  The optical sensor or the mechanical sensor needs to detect the opening / closing state of the shutter with high accuracy. It is necessary to adjust the mounting position of the optical sensor or mechanical sensor component.

  Since the space in the apparatus is limited, if a shutter and a shutter mechanism are arranged in the apparatus, a space for the optical sensor or the mechanical sensor cannot be secured in the apparatus.

  When an optical sensor or a mechanical sensor is used as a shutter opening / closing detection sensor, the detection accuracy of the shutter opening / closing state by the optical sensor or the mechanical sensor is deteriorated. The optical sensor or the mechanical sensor has a problem that low cost, high accuracy, space saving, and high durability cannot be realized.

  Therefore, in view of the above problems, the present invention provides an image forming apparatus using a surface potential sensor device having a space-saving, low-cost, high-precision, high-durability shutter mechanism, and a shutter of a potential sensor used in the image forming device. An object is to provide an open / closed state detection method.

  In order to solve such problems, according to one aspect of the present invention, a photoconductor on which an electrostatic latent image is formed, a charger having a grid and charging the photoconductor, and a grid bias on the grid A potential sensor having a potential detection unit that is disposed opposite to the photoconductor and detects a surface potential of the photoconductor, and an open position where the potential detection unit of the potential sensor is exposed to the photoconductor And a shutter that takes a closed position where the potential detection unit is shielded from the photoconductor, a driving mechanism that opens and closes the shutter, timing of opening and closing the shutter by the driving mechanism, a value of the grid bias, and the grid Each of the bias application timings is controlled, and the grid potential is set to a predetermined grid voltage at the timing when the shutter should be closed. And measuring the surface potential of the photoconductor with respect to the grid potential of the predetermined value based on the sensor detection value from the potential sensor at that time, and based on the grid potential of the predetermined value and the potential reading value of the potential sensor An image forming apparatus is provided that includes a control unit that determines whether or not the shutter is in a closed state.

  According to another aspect of the present invention, the opening / closing timing of the shutter by the driving mechanism for opening / closing the shutter of the potential sensor used in the image forming apparatus, and the value of the grid bias applied to the grid of the charger. And a control unit for controlling the application timing of the grid bias so that the potential detection unit for detecting the surface potential of the photosensitive member is located at an open position exposed to the photosensitive member with respect to the driving mechanism. The shutter is driven, and the control unit causes the potential sensor to measure the surface potential of the photoconductor when the shutter is open, and the control unit detects the potential detection unit to the drive mechanism. The shutter should be driven to be in a closed position shielded from the photoconductor, and the control unit should close the shutter In imming, the grid potential is set to a predetermined grid potential, and the potential sensor detects the surface potential of the photoconductor, and the control unit sets the predetermined grid potential and the potential read value of the potential sensor. Based on this, there is provided a shutter open / close state detection method for a potential sensor used in an image forming apparatus, wherein the shutter detects whether the shutter is open or closed.

  According to the present invention, an image forming apparatus using a surface potential sensor device having a shutter mechanism that is space-saving, low-cost, highly accurate, and highly durable can be obtained.

1 is a configuration diagram of an image forming apparatus. FIG. 3 is an enlarged longitudinal sectional view showing one image forming process unit. It is a disassembled perspective view of a surface potential sensor. It is a block diagram which shows the control system which made the main control of the charger. It is a flowchart for demonstrating the process which detects opening and closing of the shutter by a control part. (A) is a perspective view of the surface potential sensor with the shutter closed, and (b) is a perspective view of the surface potential sensor with the shutter open. (A) It is a diagram which shows transition of the detection value of the grid potential which the surface potential sensor output, (b) shows the list of the relationship between a grid bias voltage and the detection value of a grid potential in the same figure (a). FIG. It is a table | surface figure which shows the example of determination of the opening / closing detection of the shutter by a control part.

  Hereinafter, an image forming apparatus and a method for detecting the open / closed state of a shutter will be described in detail with reference to the accompanying drawings. In the drawings, the same portions are denoted by the same reference numerals, and redundant description is omitted.

(A) Overall Configuration The image forming apparatus according to the embodiment is a quadruple tandem type image forming apparatus. FIG. 1 is a configuration diagram of the image forming apparatus 1. FIG. 2 is an enlarged longitudinal sectional view showing one image forming process unit.

  The image forming apparatus 1 includes an image forming process unit 2 that forms a black image, an image forming process unit 3 that forms a cyan image, an image forming process unit 4 that forms a magenta image, and an image forming process that forms a yellow image. Unit 5 is provided.

  The image forming process unit 2 includes a photosensitive drum 2a, a drum cleaner 2b, a charger 2c, a developing device 2d, a surface potential sensor 2e, and an intermediate transfer roller 2f.

  The photoconductor drum 2a is a photoconductor on which an electrostatic latent image is formed. The photosensitive drum 2a rotates in the direction of arrow P as shown in FIG.

  The drum cleaner 2 b includes a roller 6 and a drum cleaning blade 7. The drum cleaner 2b brings the edge of the drum cleaning blade 7 into contact with the surface of the photosensitive drum 2a to remove the toner remaining on the photosensitive drum 2a.

  A neutralizing lamp (not shown) is provided downstream of the drum cleaner 2b in the drum rotation direction.

  The charger 2c uniformly charges the surface of the photosensitive drum 2a. The charger 2 c includes a wire 8 and a charging charger grid 9.

  A high voltage transformer 10 is connected to the wire 8. The high-voltage transformer 10 generates a voltage that is large enough to generate corona discharge.

  A voltage stabilizing circuit 11 is connected to the charging charger grid 9. The voltage stabilization circuit 11 is a power source that supplies a grid bias voltage.

  The charger 2c charges the surface voltage of the photosensitive drum 2a to a predetermined value by generating corona discharge from the wire 8 to the photosensitive drum 2a.

  When the voltage stabilization circuit 11 applies a grid bias voltage to the charging charger grid 9, the charger 2c changes the amount of charge on the surface of the photosensitive drum 2a, and the surface potential of the photosensitive drum 2a is stabilized to a predetermined value. To do.

  The control unit 12 gives a command to the voltage stabilization circuit 11 so that the voltage stabilization circuit 11 applies a grid bias voltage to the charging charger grid 9. The control unit 12 notifies the voltage stabilization circuit 11 of a voltage signal indicating the start of application of the grid bias voltage.

  For the control unit 12, a CPU, a ROM (Read Only Memory), and a RAM (Random Access Memory) are used.

  The developing device 2d develops the electrostatic latent image formed on the surface of the photosensitive drum 2a with black toner. The container 13 of the developing device 2d contains a developer.

  The augers 14 and 15 convey the developer and send the developer to the magnet roller 16. As the magnet roller 16 rotates, the magnet roller 16 supplies toner to the electrostatic latent image on the photoreceptor of the photoreceptor drum 2a.

  The surface potential sensor 2 e detects the surface potential of the photosensitive drum 2 a and outputs the measurement result to the control unit 12.

  FIG. 3 is an exploded perspective view of the surface potential sensor 2e. In the figure, the same reference numerals as those described above represent the same elements.

  The surface potential sensor 2 e includes a potential sensor probe 17, a shutter 18 that covers the potential sensor probe 17 and can slide on the potential sensor probe 17, and a shutter mechanism 19 (drive mechanism) that opens and closes the shutter 18. .

  The potential sensor probe 17, the shutter 18, and the shutter mechanism 19 are unitized. The surface potential sensor 2 e further includes a surface potential sensor control board 21 having a surface potential control circuit 20.

  The potential sensor probe 17 is a chopper type surface potential sensor, for example. The potential sensor probe 17 measures the intensity of the electric field incident from the photosensitive drum 2a.

  The potential sensor probe 17 has a probe housing 17a. The probe housing 17 a has a potential detection unit 22. The probe housing 17a is provided in the image forming unit 2 so that the potential detection unit 22 faces the surface of the photosensitive drum 2a.

  The potential sensor probe 17 includes a measurement electrode 23, a tuning fork-shaped vibrator (not shown) disposed between the potential detector 22 and the measurement electrode 23, a piezoelectric element (not shown) that vibrates the vibrator, and a comparator 24.

  The measurement electrode 23 receives the lines of electric force from the photosensitive drum 2 a via the potential detector 22. The comparator 24 amplifies the voltage difference between the voltage signal output from the measurement electrode 23 and the reference voltage signal input from the surface potential control circuit 20.

  The surface potential control circuit 20 is a shutter driver. The surface potential control circuit 20 causes the shutter mechanism 19 to open and close. The surface potential control circuit 20 sends the detection value from the potential sensor probe 17 to the control unit 12.

The surface potential control circuit 20 performs integral analysis on the amplified signal. A signal from the surface potential control circuit 20 is output to the control unit 12 as a V _O sensor signal.

  The potential detector 22, the measurement electrode 23, the vibrator, the piezoelectric element, and the comparator 24 constitute a potential detection sensor (or detector) that detects the potential of the surface of the photosensitive drum 2a.

  The shutter 18 is made of metal to shield the electric field. The shutter 18 has an opening 25. The shutter 18 moves between a closed position where the potential detector 22 is covered with respect to the photosensitive drum 2a and an open position where the potential detector 22 is exposed with respect to the photosensitive drum 2a.

  The shutter mechanism 19 reciprocates the shutter 18 along the probe housing 17a. The shutter mechanism 19 includes a spring 19a and a solenoid 19b.

  One end of the spring 19 a is locked to the shutter 18. The other end of the spring 19a is locked to a fastener fixed to the probe housing 17a. The spring 19a applies a force to the shutter 18 so that the shutter 18 moves toward the closed position.

  The solenoid 19b is excited by the surface potential control circuit 20. The solenoid 19b acts on the shutter 18 to move the shutter 18 from the closed position to the open position against the force of the spring 19a.

  When the energization of the solenoid 19b is off, the shutter 18 remains at the position where the potential detection unit 22 is closed. When energization to the solenoid 19b is on, the shutter 18 is displaced to a position where the potential detector 22 is open.

  An intermediate transfer roller 2f is provided downstream of the surface potential sensor 2e in FIG. 1 in the drum rotation direction.

  The intermediate transfer roller 2 f transfers the toner image on the photosensitive drum 2 a to the intermediate transfer belt 26. The intermediate transfer belt 26 is wound endlessly between a plurality of rollers 27.

  A motor (not shown) is connected to one of the rollers 27. The intermediate transfer belt 26 travels as the motor is driven to rotate by the CPU.

  The cyan image forming process unit 3 includes a photosensitive drum 3a, a drum cleaner 3b, a charger 3c, a developing unit 3d, a surface potential sensor unit 3e, and an intermediate transfer roller 3f.

  The magenta image forming process unit 4 includes a photosensitive drum 4a, a drum cleaner 4b, a charger 4c, a developing unit 4d, a surface potential sensor unit 4e, and an intermediate transfer roller 4f.

  The yellow image forming process unit 5 includes a photosensitive drum 5a, a drum cleaner 5b, a charger 5c, a developing unit 5d, a surface potential sensor unit 5e, and an intermediate transfer roller 5f.

  The configuration of the image forming process units 3, 4, and 5 is substantially the same as that of the image forming process unit 2.

  Further, the image forming apparatus 1 includes a laser unit 28, a paper feed cassette 29, a secondary transfer roller 30, and a fixing device 31.

  The laser unit 28 is an exposure device that forms an electrostatic latent image on the photosensitive drum 2a by irradiating the photosensitive drum 2a charged by the charger 2c with image light according to image information.

  The laser unit 28 modulates the laser beam according to the image data for writing input from the control unit 12, and irradiates the photosensitive drum 2a with one laser beam.

  The laser unit 28 also irradiates the photosensitive drums 3a, 4a, and 5a with laser beams, respectively.

  The paper feed cassette 29 is provided below the laser unit 28 and can be inserted into the case of the image forming apparatus 1 and pulled out of the case. A plurality of sheets 32 are set in the sheet feeding cassette 29.

  A conveyance path 33 is defined between the outlet of the paper feed cassette 29 and the fixing device 31.

  The secondary transfer roller 30 sandwiches the sheet 32 conveyed along the conveyance path 33 together with the intermediate transfer belt 26. The secondary transfer roller 30 transfers the toner image on the intermediate transfer belt 26 to the paper 32.

  The secondary transfer roller 30 can be in contact with the surface on the intermediate transfer belt 26 where the toner is carried and can be separated from the surface.

  The fixing device 31 is provided on the downstream side in the paper conveyance direction, and fixes the color image on the paper 32. The fixing device 31 includes a heating roller 31a, a pressure roller 31b, and a driving mechanism (not shown).

  The heating roller 31a is heated by a heater. The pressure roller 31b can take a position in contact with the heating roller 31a and a position away from the heating roller 31a.

  The drive mechanism applies a force toward the heating roller 31a to the pressure roller 31b. The paper 32 on which the color image is formed is conveyed between the heating roller 31a and the pressure roller 31b.

  The control unit 12 converts the writing image data to be printed into 4-print color data.

  The control unit 12 outputs black image data to the image forming process unit 2.

  The photosensitive drum 2a, the charger 2b, the laser unit 28, and the developing unit 2d form a black toner image on the photosensitive drum 2a. The primary transfer roller 2 f forms an intermediate transfer image on the intermediate transfer belt 26.

  The image forming process units 3, 4, and 5 form cyan, magenta, and yellow toner images on the intermediate transfer belt 26, respectively.

  The secondary transfer roller 30 performs secondary transfer on the paper 32 fed by the paper feed cassette 29. After the secondary transfer, the toner is fixed on the paper 32 by the fixing device 31. The fixed paper 32 is discharged.

  Each drum cleaning blade 7 cleans residual toner on the photosensitive drums 2a, 3a, 4a, and 5a after the primary transfer.

  FIG. 4 is a block diagram showing a control system that mainly controls the charger 2c. In the figure, the same reference numerals as those described above represent the same elements.

  The feedback circuit 34 feedback controls the charging of the charger 2c so that the surface potential of the photosensitive drum 2a converges to a target value. The feedback circuit 34 includes the photosensitive drum 2a, the potential sensor probe 17, the analog-digital converter 35, the control unit 12, the high-voltage transformer 10, and the charger 2c.

The analog / digital converter 35 A / D converts the analog V _O sensor signal output from the potential sensor probe 17 and outputs the signal.

  The control unit 12 includes a main CPU 36, logic LSIs (Large Scale Integration) 37, 38, a digital-analog converter 39, and a memory (not shown).

The memory stores a V _O sensor detection value used when the control unit 12 determines the open / closed state of the shutter 18, a numerical value range for detection, a threshold value, and the like.

  The configuration of the control system of the chargers 3c, 4c, and 5c (not shown) is substantially the same as the example of FIG.

(B) Operation The operation for determining the open / closed state of the shutter 18 of the surface potential sensor 2e performed by the control unit 12 will be described with reference to FIGS. In FIG. 6, those having the same reference numerals as those described above represent the same elements.

  The CPU determines the start timing of the process for determining the open / closed state of the shutter 18. The CPU stores in advance one or more conditions for starting the process in the memory, and the CPU determines whether the conditions are satisfied.

  The control unit 12 executes a mode for adjusting the surface potential of the charger 2c immediately after the image forming apparatus 1 is activated, for example, when the image forming apparatus 1 is powered on. It is timing.

  Alternatively, the start timing is a timing at which the control unit 12 detects that the number of printed sheets 32 has reached a certain value, and the control unit 12 executes a mode for adjusting the surface potential of the charger 2c.

  FIG. 5 is a flowchart for explaining processing for detecting opening / closing of the shutter 18 by the control unit 12.

  In step 100, the control unit 12 calculates an operating condition necessary for controlling the surface potential sensor 2e.

  FIG. 6A is a perspective view of the surface potential sensor 2e with the shutter 18 closed. Since the potential detection unit 22 of the potential sensor probe 17 is covered with the shutter 18, the potential detection unit 22 is not contaminated with toner or dust.

  In step 200, the control unit 12 sends a command to the surface potential control circuit 20 of the surface potential sensor control board 21 so as to open the shutter 18. The surface potential control circuit 20 instructs the shutter mechanism 19 to open the shutter.

  The shutter mechanism 19 slides the opening 25 provided in the shutter 18 to the position of the potential detection unit 22 of the potential sensor probe 17. The shutter 18 is displaced in the direction in which the potential detector 22 and the opening 25 overlap.

  FIG. 6B is a perspective view of the surface potential sensor with the shutter opened. The state of the shutter 18 is such that the internal measurement electrode 23 can enter the lines of electric force from the photosensitive drum 2a.

  The size of the opening 25 of the shutter 18 is larger than the size of the potential detector 22 of the potential sensor probe 17. Only when the shutter 18 is opened, the surface potential sensor 2e can correctly measure the surface potential of the photosensitive drum 2a.

  Subsequently, in step 300 of FIG. 5, the control unit 12 sends a command to the surface potential control circuit 20 to measure the surface potential of the photosensitive drum 2a. The surface potential control circuit 20 causes the potential sensor probe 17 to measure the surface potential. The surface potential control circuit 20 returns the measured surface potential to the control unit 12.

  In step 400, the control unit 12 sends a command to close the shutter 18 to the surface potential control circuit 20. The shutter mechanism 19 closes the shutter 18. Again, the state of the shutter 18 returns to the state of FIG.

  In step 500, the control unit 12 sends a command for measuring the surface potential of the photosensitive drum 2 a to the surface potential control circuit 20. The surface potential control circuit 20 measures the surface potential and returns the surface potential to the control unit 12.

  In step 600, the control unit 12 determines whether the operation state of the surface potential sensor 2e is OK or NG.

  If the controller 12 determines in step 700 that the surface potential sensor 2e is normal, the Yes route is passed, and in step 800, the controller 12 determines whether or not the shutter 18 is closed.

  If the control unit 12 determines in step 800 that the shutter 18 is closed, the control unit 12 passes the Yes route, and in step 900, the control unit 12 performs an operation for determining the surface potential control condition. The control unit 12 stores the determined condition in the memory.

  Subsequently, the control unit 12 executes the image quality maintaining process of the image forming unit 2 using the determined surface potential control condition. The quality of the image generated by the image forming apparatus 1 is controlled.

  Further, when the controller 12 determines that the surface potential sensor 2e is abnormal in step 700, the route passes No route, and in step 1000, the controller 12 displays a warning or adjustment error on the machine display. Notify device drivers.

  The content displayed on the display alerts the person to repair the surface potential sensor 2e. Alternatively, the display content prompts the person to replace the surface potential sensor 2e.

  If the control unit 12 determines in step 800 that the shutter 18 is not closed, the route passes No route, and in step 1100, the control unit 12 performs substantially the same processing as the processing in step 1000. Also in this case, the contents displayed on the display for a person urge the repair or replacement of the surface potential sensor 2e.

  The important point is that, in the image forming apparatus 1 according to the embodiment, the grid bias voltage is applied to the charger 2 c when the control unit 12 closes the shutter 18. The control unit 12 applies a bias when the shutter is closed, which is different from the prior art in which the CPU does not apply a bias when the shutter is closed.

  In the detection method of the open / closed state of the shutter 18 according to the embodiment, the control unit 12 applies a plurality of different grid bias voltages to the charger 2c one by one in order with the shutter 18 closed.

The control unit 12 reads the detection value of the V _O sensor signal corresponding to each grid bias voltage.

Based on each detected value of the obtained V _O sensor signal, the controller 12 determines whether or not the open / close state of the shutter 18 is normal by a detection method described in detail below and detects it.

(B1) Details of the method for detecting the open / closed state of the shutter.

  The surface potential sensor 2e mounted on the image forming apparatus 1 includes a shutter mechanism 19 and a shutter 18 to prevent the potential detection unit 22 from being contaminated with toner or dust. The surface potential sensor 2e opens and closes the shutter 18 when measuring the photoreceptor potential.

  The grid bias voltage applied by the charger 2c to the charging charger grid 9 when the shutter 18 is open is defined as Vg1. A reading value of the surface potential when the surface potential sensor 2e measures the surface potential using the grid bias voltage Vg1 is defined as α1.

  The control unit 12 outputs a timing signal indicating the timing at which the shutter 18 should be closed to the charger 2c. At the same timing, the charger 2c applies the grid bias voltage Vg1 to the charging charger grid 9.

  The controller 12 causes the surface potential sensor 2e to read simultaneously with the application. Let the obtained potential sensor reading at that time be β1.

  The control unit 12 compares α1 and β1. If α1 ≠ β1, the control unit 12 recognizes that the shutter 18 is closed.

  Further, the control unit 12 calculates the difference between α1 and β1. The memory in the control unit 12 stores a threshold value for comparing the magnitudes of the differences. The control unit 12 compares the numerical value of the difference with the threshold value, and recognizes that the shutter 18 is closed when it is determined that the difference is larger than the threshold value.

  When the shutter 18 is opened, the controller 12 is less likely to be mistaken for the shutter being closed. The frequency of misidentification, which is incorrect recognition, is reduced. More accurate detection can be performed.

  Further, the control unit 12 performs measurement in the same manner as the measurement example of Vg1 using another grid bias voltage Vg2 (Vg1 ≠ Vg2).

  When the shutter 18 is open, the controller 12 causes the surface potential sensor 2e to read the surface potential simultaneously with the application of the grid bias voltage Vg2. The obtained potential sensor reading is α2.

  The controller 12 applies the grid bias voltage Vg2 at the timing when the shutter 18 should be closed. Simultaneously with the application, the controller 12 causes the surface potential sensor 2e to read the surface potential. Let the obtained potential sensor reading be β2.

  The control unit 12 compares α2 and β2. When α1 ≠ α2 and α2 ≠ β2, the control unit 12 recognizes that the shutter 18 is closed.

  Alternatively, the control unit 12 calculates the difference between α1 and β1 and calculates the difference between α2 and β2. The memory stores in advance two reference values each having a certain amount. One reference value is a large value and the other reference value is a small value.

  When both the difference between α1 and β1 is larger than the larger reference value and the difference between α2 and β2 is larger than the larger reference value, the control unit 12 closes the shutter 18. Recognize that there is.

  If both the difference between α1 and β1 is smaller than the smaller reference value and the difference between α2 and β2 is smaller than the smaller reference value, the control unit 12 causes the shutter 18 to Recognize that it is open.

  The controller 12 compares the difference with a numerical range such as two reference values, thereby enabling more accurate opening / closing detection.

  The feedback circuit 34 can detect the open / closed state of the shutter 18 without using an optical sensor or a mechanical sensor using the detection result obtained through the opening / closing control of the shutter mechanism 19.

  Further specific examples will be described.

FIG. 7A is a diagram showing the transition of the detected value of the grid potential output from the surface potential sensor 2e. The detected value of the grid potential is represented by a solid line 40 indicating the voltage detected and output as the V _O sensor signal.

  1 to 8 represent the order. In each order, the control unit 12 controls the high-voltage transformer 10 so that a grid bias voltage is applied to the charger 2c for a predetermined period.

  FIG. 7B is a table showing a list of relationships between the grid bias voltage and the detected value of the grid potential in FIG. The state in which the shutter 18 is open or closed at each time is also shown in FIG. Orders 1 to 8 are the same between FIGS. 7A and 7B.

  The control unit 12 changes the grid bias voltage Vg and the state (open, closed) of the shutter 18 with respect to the charger 2c in order from order 1 to order 8. The above-described grid bias voltages Vg1 and Vg2 are 500 (−V) and 900 (−V), respectively.

  In order 1, the control unit 12 does not apply the grid bias voltage Vg. In order 2, the control unit 12 applies the grid bias voltage Vg for the pre-run operation.

In order 3, the control unit 12 opens the shutter 18 and applies a grid bias voltage of 500 (−V) to the charger 2 c. The controller 12 reads the detected value of the surface potential of the V _O sensor signal.

  In order 4, the control unit 12 measures the surface potential of the photosensitive drum 2a as an original process. The control unit 12 newly adds the order 3 and the following orders 5 to 8 to the process of the order 4. Processing in order 3, 5 to 8 is processing of the open / closed state detection method of the shutter 18 according to the embodiment.

  In order 3 and order 5, the control unit 12 measures the surface potential of the photosensitive drum 2a when the shutter 18 is open.

  In order 6, the control unit 12 closes the shutter 18.

  Further, thereafter, in order 7 and 8, the control unit 12 reads the sensor value when the shutter 18 should be closed.

  The current potential sensor readings (measured potential, detected value) obtained in the sequences 3, 4, 5, 7, and 8 are indicated by a, b, c, d, and e, respectively.

  When the grid bias voltage Vg is 500 [−V], the control unit 12 obtains a difference | a−e | between the value a when the shutter 18 is open and the value e when the shutter 18 is closed. .

  Further, when the grid bias voltage Vg is 900 [−V], the controller 12 determines the difference | c−d | between the value c when the shutter 18 is open and the value d when the shutter 18 is closed. Ask for.

  The control unit 12 compares the differences | a−e | and | c−d | thus obtained with γ stored in advance in the memory. γ is information indicating the range of allowable error.

  When | a−e | <γ and | c−d | <γ, the control unit 12 determines that the shutter 18 is not closed. The control unit 12 determines that the shutter 18 remains open.

  In other words, | a−e | <γ corresponds to the sensor detection value being within the value range 41 in FIG. | C−d | <γ corresponds to the sensor detection value being within the value range 42 in FIG.

  The sensor detection value is within the error range when the shutter 18 is open and 900 (−V) is applied, and the sensor detection value is when the shutter 18 is open and 500 (−V) is applied. If both are within the error range, the control unit 12 determines that the shutter 18 remains open.

  γ can be changed depending on the accuracy of the surface potential sensor 2e and the accuracy of the image forming system. The control unit 12 should give an appropriate numerical value to γ. The controller 12 uses γ = 60 (V).

  Desirably, γ is in the range of 0 to 100 (V). In consideration of reducing false detection and obtaining high detection accuracy, γ is more preferably in the range of 10 to 30 (V).

  In this way, the control unit 12 recognizes that the shutter 18 is closed when 0 <γ ≦ 100.

  Furthermore, in order to reduce false detection, the control part 12 increases the frequency | count of a measurement. When the shutter 18 is open, the controller 12 applies N (N ≧ 2) grid bias voltages Vg1 to the charger 2c, and reads the surface potential corresponding to each grid bias voltage Vg1.

  Similarly, when the shutter 18 is closed, the controller 12 reads the surface potential using N grid bias voltages Vg1.

  When the shutter 18 is open, the control unit 12 divides the voltage range of the upper limit value and the lower limit value of the grid bias voltage Vg1 used in the image forming process by the image forming unit 2 into N, and the voltage obtained by the N division Find the width of change.

  The control unit 12 changes the grid bias voltage Vg1 from the lower limit value to the upper limit value for each change width. The controller 12 reads the surface potential each time the voltage is changed.

  The control unit 12 performs the same processing when the shutter 18 is closed.

  The width for changing the voltage will be described.

  When the control unit 12 sets the grid bias voltage in the electrometer measurement when the shutter is opened and the surface potentials Vg1, Vg2,... Vgn (n: natural number) when the electrometer is detected when the shutter is closed, N times (N ≧ 2) Set measurement is performed.

  Let the lower limit value be L (| v |) and the upper limit value be U (| V |).

  When the shutter 18 is opened, [L + (N-1) * (UL) / N] ± 100, [L + (N-2) * (UL) / N] ± 100, [L + (N -3) * (UL) / N] ± 100,..., [L + (Nn) * (UL) / N] ± 100 N grid bias voltages Vg are supplied to the charger 2c. The control part 12 controls so that it may be applied.

  The controller 12 measures the surface potential corresponding to a series of N grid bias voltages Vg1.

  Similarly, when the shutter 18 is closed, [L + (N-1) * (UL) / N] ± 100, [L + (N-2) * (UL) / N] ± 100, [ L + (N−3) * (U−L) / N] ± 100,..., [L + (N−n) * (U−L) / N] ± 100 N grid bias voltages Vg are charged. The control unit 12 controls to be applied to the device 2c.

  The controller 12 measures the surface potential corresponding to a series of N grid bias voltages Vg1.

  It is desirable that the control unit 12 increase the number of measurement sets when the shutter 18 is open and the number of measurement sets when the shutter 18 is closed.

  Increasing the number of times of setting causes an increase in measurement time for reading the surface potential.

  In consideration of increasing the probability reliability that no false detection occurs and shortening the measurement time, the number of sets is preferably 2 to 5. In the present embodiment, the measurement time is given priority over the occurrence probability of erroneous detection. The number of sets was 2.

(B2) Explanation in the case of using another shutter structure.

  The shutter structure can be different from the structure of the shutter 18.

  The shutter 18 itself maintains a conduction state with the potential detector 22, the potential sensor probe 17, or the housing surface of the probe housing 17a. A shutter open / close detection method when the potential of the shutter 18 and the potential of the potential detector 22 are the same will be described.

  In this case, due to the characteristics of the potential sensor, in most cases, the control unit 12 obtains the upper limit value or the lower limit value of the voltage range that can be measured as the sensor detection potential when the shutter 18 is closed.

  Considering all situations, the sensor detection potential when the shutter 18 is closed hardly takes a value other than the value between the upper limit value and the lower limit value in the voltage range. It is limited that the value becomes indefinite between the upper limit value and the lower limit value.

  In many situations, the sensor detection potential outputs an upper limit value or a lower limit value, and thus values such as α1 and β1 can be determined. Also, a difference value calculated using α1, β1, etc. is obtained.

  Therefore, according to the shutter open / close detection method when the potential of the shutter 18 is the same as the potential of the potential detection unit 22 or the like, erroneous detection can be reduced. For this reason, the function of detecting the closed state of the shutter 18 described above is more effective from the viewpoint of reducing erroneous detection.

  In the embodiment, the voltage range that can be measured by the potential sensor is 0 to 1020 (V).

  A method for detecting that the shutter 18 is in the open state will be described.

In order 3, 4 and 5 in FIG. 7B, the control unit 12 obtains the detected values a, b and c of the V _O sensor signal. The control unit 12 sets and stores appropriate threshold values for the detection values a, b, and c of the V _O sensor signal.

The control unit 12 determines whether or not the shutter 18 is in an open state by determining whether or not the detection values a, b, and c of the V _O sensor signal are within a threshold range.

  By adopting such a configuration, it is possible to determine and approve the detection determination as to whether the shutter of the potential sensor normally opens and closes and is in an open state or a closed state.

  The controller 12 can determine without using a detection sensor such as an optical sensor or a mechanical sensor.

  The control operation of the control unit 12 for the image forming units 3, 4, and 5 is substantially the same as the control operation for the image forming unit 2.

  In this way, a surface potential sensor device having a space-saving, low-cost, high-precision, high-durability shutter mechanism and an image forming apparatus using the surface potential sensor device can be realized.

(B3) An example of a measurement result.

  FIG. 8 is a table showing a determination example of opening / closing detection of the shutter 18 by the control unit 12. For the measurement results 1 to 4 out of the measurement results 1 to 9, the control unit 12 determines whether α1 and β1 are equal.

  The control unit 12 determines whether the shutter 18 has been opened. Since the measurement results 1 to 4 are all α1 = β1, the control unit 12 detects that the shutter 18 is not open, and outputs a determination result indicating that the operation is abnormal.

  Regarding the measurement results 1 to 4, the difference between α1 and β1 and the difference between α2 and β2 may be 0 or a value larger than a threshold value as a detection factor. The control unit 12 determines that the shutter 18 is not open and detects an abnormal operation.

  Whether the shutter 18 is closed or not is not determined by the control unit 12.

  Moreover, about the measurement results 5-8, the control part 12 compares whether (alpha) 1 and (alpha) 2 are equal and whether (alpha) 2 and (beta) 2 are equal.

  For the measurement results 5 to 8, since α1 and α2 are not equal, the control unit 12 determines that the shutter 18 is open, and detects normal operation.

  Whether the shutter 18 is closed is also detected as to whether the shutter 18 is closed.

  Regarding the measurement result 9, since α1 and β1 are equal and α2 and β2 are equal, the control unit 12 determines that the shutter 18 is not closed.

  Thus, since the CPU can detect opening / closing of the shutter using the surface potential sensor 2e mounted on the image forming apparatus 1, it is possible to detect opening / closing of the shutter without separately providing an optical sensor or a mechanical sensor. Become.

  By adding a process in which the control unit 12 reads values such as α1, β1, etc., an error in the operation of the shutter 18 can be detected without using mechanical parts.

  Since the open / closed state of the shutter 18 can be detected electrically, a failure that occurs when mechanical parts are used does not occur.

  In the above embodiment, the surface potential sensor 2e is a chopper type potential sensor, but a capacitance variation type potential sensor may be used as the surface potential sensor 2e.

  The shutter mechanism 19 is composed of a spring 19a and a solenoid 19b. However, a force driving source for displacing the shutter 18 and a structure for transmitting the force can be variously modified. The advantage of the present invention is not impaired at all with respect to the embodiment and the invention in which the structure of the shutter mechanism 19 is merely changed.

  DESCRIPTION OF SYMBOLS 1 ... Image formation apparatus, 2-5 ... Image formation process unit, 2a, 3a, 4a, 5a ... Photosensitive drum (photosensitive body), 2b, 3b, 4b, 5b ... Drum cleaner, 2c, 3c, 4c, 5c ... Charger, 2d, 3d, 4d, 5d ... developer, 2e, 3e, 4e, 5e ... surface potential sensor, 2f, 3f, 4f, 5f ... intermediate transfer roller, 6 ... roller, 7 ... drum cleaning blade, 8 ... Wire 9, charging charger grid 10, high voltage transformer 11 voltage control circuit 12 control unit 13 container 14 15 auger 16 magnet roller 17 potential sensor probe 17 a probe housing Body, 18 ... Shutter, 19 ... Shutter mechanism (drive mechanism), 19a ... Spring, 19b ... Solenoid, 20 ... Surface potential control circuit, 21 ... Surface potential sensor control board DESCRIPTION OF SYMBOLS 22 ... Potential detection part, 23 ... Measuring electrode, 24 ... Comparator, 25 ... Opening, 26 ... Intermediate transfer belt, 27 ... Roller, 28 ... Laser unit, 29 ... Paper feed cassette, 30 ... Secondary transfer roller, 31 ... Fixing 31a ... heating roller, 31b ... pressure roller, 32 ... paper, 33 ... transport path, 34 ... feedback circuit, 35 ... analog-digital converter, 36 ... main CPU, 37, 38 ... logic LSI, 39 ... digital-analog converter , 40 ... solid line, 41, 42 ... value range.

Claims (5)

A photoreceptor on which an electrostatic latent image is formed;
A charger having a grid and charging the photoreceptor;
A power supply for applying a grid bias to the grid;
An electric potential sensor having an electric potential detection unit disposed opposite to the photoconductor to detect a surface electric potential of the photoconductor;
A shutter that takes an open position where the potential detector of the potential sensor is exposed to the photoreceptor and a closed position where the potential detector is shielded from the photoreceptor;
A drive mechanism for opening and closing the shutter;
The timing of opening and closing the shutter by the driving mechanism, the value of the grid bias, and the timing of applying the grid bias are respectively controlled, and the grid potential is set to a predetermined grid potential at the timing when the shutter should be closed. And measuring the surface potential of the photoconductor with respect to the grid potential of the predetermined value based on the sensor detection value from the potential sensor at that time, and based on the grid potential of the predetermined value and the potential reading value of the potential sensor An image forming apparatus comprising a control unit that determines whether or not a shutter is in a closed state.   The control unit sets the first grid potential at a timing at which the shutter should be closed, and a first potential reading value measured by the potential sensor with respect to a first grid potential when the shutter is open. The image forming apparatus according to claim 1, wherein the shutter is opened or closed using a second potential reading value detected by the potential sensor.   The controller is configured to detect a first potential reading value measured by the potential sensor with respect to a first grid potential when the shutter is open, and a first potential different from the first grid potential when the shutter is open. A second potential reading value measured by the potential sensor with respect to two grid potentials, and a third potential reading detected by the potential sensor with respect to the first grid potential at a timing when the shutter should be closed. And determining whether the shutter is open or closed using a value and a fourth potential reading value detected by the potential sensor with respect to the second grid potential at a timing when the shutter should be closed. The image forming apparatus according to claim 1. A developing device for developing the electrostatic latent image on the photoreceptor;
The position of the potential sensor is such that, during a plurality of steps of the electrophotographic process, the potential detection by the potential sensor is later than the development by the developing device, and the potential detection by the potential sensor is more than the charging by the charger. The image forming apparatus according to claim 1, wherein the image forming apparatus is a front side. Controlling the opening / closing timing of the shutter by the driving mechanism for driving the shutter of the potential sensor used in the image forming apparatus, the value of the grid bias applied to the grid of the charger, and the timing of applying the grid bias, respectively. The controller causes the drive mechanism to drive the shutter so that a potential detection unit that detects the surface potential of the photoconductor is located at an open position exposed to the photoconductor,
The control unit causes the potential sensor to measure the surface potential of the photoconductor when the shutter is open,
The control unit causes the driving mechanism to drive the shutter so that the electric potential detection unit is positioned at a closed position shielded from the photoconductor;
The control unit sets the grid potential to a predetermined grid potential at a timing when the shutter should be closed, and causes the potential sensor to detect the surface potential of the photoconductor,
The control unit detects whether the shutter is in an open state or a closed state based on the predetermined grid potential and the potential reading value of the potential sensor. A method for detecting the open / closed state of a shutter of a potential sensor.

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