JP6021757B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a photoreceptor having a photosensitive layer provided on the surface, and a method for measuring the surface potential of the photosensitive layer.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses such as copying machines, printers, and facsimiles are known. This image forming apparatus includes a drum-type photosensitive member, and a charging device, an exposure device, a developing device, a transfer device, and the like arranged along the outer peripheral surface thereof. A general image forming process by the image forming apparatus is as follows. First, the surface of the photoconductor is charged to a predetermined reference potential by the charging device, and then a laser beam is irradiated onto the surface of the photoconductor from the exposure device. As a result, an electrostatic latent image having a different potential only at the irradiated portion is formed on the surface of the photosensitive member. Then, the toner charged to a potential higher than the potential of the electrostatic latent image is attached to the electrostatic latent image by the developing device, and then reversely from the reference potential by the transfer device from the back surface of the sheet conveyed to a predetermined transfer position. The toner image is transferred onto the surface of the sheet.

  In this type of image forming apparatus, the photosensitive layer provided on the photoreceptor is worn by repeated image formation. As the photosensitive layer wears, the discharge start voltage at which current starts to flow from the charging device to the photosensitive layer varies. Therefore, even when the photosensitive layer is worn, when the photosensitive layer is always charged by the charging device at the same voltage value, the surface potential of the photosensitive layer does not become the reference potential. As a result, the image density becomes unstable. Therefore, it is necessary to adjust the voltage value of the voltage applied from the charging device to the photosensitive layer so that the surface potential of the photosensitive layer becomes the reference potential. In Patent Document 1, the discharge start voltage when charging the photosensitive member by the charging device is measured, and the differential voltage value obtained by subtracting the discharge start voltage from the applied voltage of the charging device is regarded as equal to the surface potential of the photosensitive member. A technique for adjusting the applied voltage of the charging device so that the differential voltage value becomes equal to a reference potential is disclosed. Patent Document 2 discloses a technique for detecting a current value flowing from a charged photoconductor to a transfer device in contact with the photoconductor, and measuring the surface potential of the photoconductor from the detected current value and the resistance value of the transfer device. It is disclosed.

JP-A-6-194933 JP 2006-65113 A

  However, in general, in an image forming apparatus, the potential of the charged region is lowered due to dark decay before the charged region of the photosensitive member charged to the reference potential by the charging device reaches the developing device. Therefore, in the image forming apparatus described in Patent Document 1, the difference between the differential voltage value and the surface potential of the photoconductor during development is large, and it is difficult to keep the surface potential of the photoconductor in an appropriate state. . Further, the process cartridge device described in Patent Document 2 requires a current measuring device that directly detects a current value flowing from the photosensitive member to the transfer device. For this reason, there is a problem that not only the number of accessories increases and the entire apparatus becomes complicated, but also the unit price of the apparatus increases.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image forming apparatus capable of measuring the surface potential of a photosensitive layer provided on the surface of a photoreceptor with high accuracy, and a photosensitive layer. The object is to provide a surface potential measurement method.

  An image forming apparatus according to an aspect of the present invention includes a photoreceptor, a voltage application unit, a current detection unit, a first measurement unit, a second measurement unit, and a third measurement unit. The photoreceptor has a photosensitive layer on the surface. The voltage application unit applies a voltage to the photosensitive layer. The current detection unit detects a current flowing through the photosensitive layer. The first measuring means flows in the photosensitive layer acquired from the current detection unit when the voltage is applied and the voltage applied to the photosensitive layer from the voltage application unit in an uncharged state where the photosensitive layer is not charged. Based on the correlation with the current, a first discharge start voltage for starting discharge in the uncharged photosensitive layer is measured. The second measuring means includes a voltage applied to the photosensitive layer from the voltage application unit in a charged state in which the photosensitive layer is charged by applying a first voltage, and the current detection unit when the voltage is applied. Based on the acquired correlation with the current flowing through the photosensitive layer, a second discharge start voltage for starting discharge in the charged photosensitive layer is measured. The third measuring unit is configured to determine whether the first voltage is based on the first discharge starting voltage measured by the first measuring unit and the second discharge starting voltage measured by the second measuring unit. The surface potential of the photosensitive layer when applied to is measured.

  A method for measuring the surface potential of a photosensitive layer according to another aspect of the present invention includes the following first to seventh steps. In the first step, a voltage is applied to the photosensitive layer from the voltage application unit in an uncharged state where the photosensitive layer provided on the surface of the photoreceptor is not charged. In the second step, a current flowing through the photosensitive layer when a voltage is applied in the first step is acquired from a current detection unit. The third step is a first discharge start voltage for starting discharge in the uncharged photosensitive layer based on the correlation between the voltage applied in the first step and the current acquired in the second step. Measure. In the fourth step, a voltage is applied from the voltage application unit to the photosensitive layer in a charged state in which the photosensitive layer is charged by applying the first voltage. In the fifth step, the current flowing through the photosensitive layer when a voltage is applied in the fourth step is acquired from the current detection unit. In the sixth step, based on the correlation between the voltage applied in the fourth step and the current acquired in the fifth step, a second discharge start voltage for starting discharge in the charged photosensitive layer. taking measurement. In the seventh step, the photosensitive layer when the first voltage is applied based on the first discharge start voltage measured in the third step and the second discharge start voltage measured in the sixth step. Measure the surface potential.

  According to the present invention, the surface potential of the photosensitive layer in the photoreceptor can be measured with high accuracy.

1 is a diagram schematically illustrating a schematic configuration of a multifunction peripheral according to a first embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration around a photosensitive drum of a multifunction machine. FIG. 2 is a block diagram illustrating a configuration of a control unit and a power supply system of the multifunction machine. It is a graph which shows the relationship between the voltage which a charging device applies, and the charging current which flows into a charging device. It is a graph which shows the relationship between the voltage which a transfer apparatus applies, and the inflow current which flows into a transfer apparatus. It is a flowchart which shows the procedure of the surface potential measurement process performed by the control part. It is a flowchart which shows the procedure of the 1st discharge start voltage measurement process which concerns on 2nd Embodiment of this invention.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings as appropriate. In addition, the following 1st Embodiment is only an example which actualized this invention, and does not limit the technical scope of this invention.

[Schematic configuration of MFP 1]
First, a schematic configuration of a multifunction machine 1 (an example of an image forming apparatus of the present invention) according to an embodiment of the present invention will be described with reference to FIG.

  A multifunction device 1 shown in FIG. 1 is an image forming apparatus having functions such as a printer, a copying machine, and a facsimile. The multifunction device 1 prints an image on a printing paper (sheet) using a developing material such as toner based on the input image data. The multi-function device 1 includes an image reading unit 10 that reads an image of a document at the top, and an electrophotographic image forming unit 22 at the bottom. In the present embodiment, the multifunction device 1 is described as an example of the image forming apparatus of the present invention. However, the present invention is not limited to this, and for example, a printer, a facsimile machine, and a copying machine also correspond to the image forming apparatus of the present invention. .

[Image Reading Unit 10]
The image reading unit 10 includes a contact glass 11 that constitutes a document placement surface, and a document cover 20 that opens and closes the contact glass 11. When the multifunction device 1 functions as a copying machine, when a copy start instruction is input from an operation panel (not shown) after a document is set on the contact glass 11 and the document cover 20 is closed, the image reading unit 10 The reading operation is started, and the image data of the original is read. Inside the image reading unit 10, an optical system device such as a reading unit 12 including an LED light source 121 and a mirror 122, mirrors 13 and 14, an optical lens 15, and a CCD 16 is provided. The reading unit 12 is moved in the sub-scanning direction 45 by a motor or the like, and light irradiated from the LED light source 121 toward the contact glass 11 during the movement is scanned in the sub-scanning direction 45, and this reflected light is input to the CCD 16. The Thereby, the image of the document on the contact glass 11 is read.

  The document cover 20 is provided with an ADF 21. The ADF 21 sequentially conveys a plurality of documents set on the document setting unit 21 </ b> A by a plurality of conveyance rollers (not shown) so that the reading position determined on the contact glass 11 passes rightward in the sub-scanning direction 45. Move the document to. When the document is moved by the ADF 21, the reading unit 12 is arranged below the reading position, and the image of the moving document is read by the reading unit 12 at this position.

[Image forming unit 22]
The image forming unit 22 is an electrophotographic image forming unit that executes image forming processing (printing processing) based on image data read by the image reading unit 10 or image data input from an external information processing apparatus. is there. As shown in FIGS. 1 and 2, the image forming unit 22 includes a paper feeding cassette 25, a photosensitive drum 31 (an example of the photosensitive member of the present invention), a charging device 32, a developing device 33, a transfer device 34, and a cleaning blade. 35, a static elimination device 40 (an example of a static elimination unit of the present invention), a fixing device 36, an exposure device 39, a paper discharge unit 27, and the like.

  Further, as shown in FIG. 3, the image forming unit 22 includes a transfer voltage applying unit 57 that applies a transfer voltage to the transfer device 34 (an example of the voltage applying unit and the second voltage applying unit of the present invention), A charging voltage application unit 52 (an example of the voltage application unit and the first voltage application unit of the present invention) that applies a DC voltage for charging to the charging device 32, and a photosensitive layer of the photosensitive drum 31 (an example of the photosensitive layer of the present invention). The current detection unit 59 (an example of the current detection unit of the present invention) that detects a direct current flowing through the device (hereinafter also referred to as “charging current” or “inflow current”) and the entire multifunction device 1 are comprehensively controlled. A control unit 62 and the like are provided.

  As shown in FIG. 1, the paper feed cassette 25 is provided below the image forming unit 22. In the present embodiment, three paper feed cassettes 25 are arranged in the vertical direction. Each sheet cassette 25 stores a plurality of sheet-like printing sheets (sheets) in a stacked state. The printing paper stored in the paper feeding cassette 25 is taken out one by one by a feeding means 17 such as a feeding roller, and then conveyed toward a transfer device 34 through a conveyance path 18 inside the image forming unit 22. Is done.

  As shown in FIG. 2, the photosensitive drum 31 is a rotating body formed in a drum shape, and is rotatably supported by a frame or the like inside the image forming unit 22. A driving force is transmitted from a driving source such as a motor (not shown) and is rotated in the clockwise direction in FIG. The photosensitive drum 31 has a structure in which a single photosensitive layer is provided on the surface. Specifically, the photosensitive drum 31 has a single layer structure in which only a photosensitive layer such as an organic photoconductor made of an organic compound whose conductivity is increased by irradiation with light is deposited. Since the photosensitive drum 31 of the present embodiment realizes functions such as charge generation and charge transport only with a single photosensitive layer, stable quality image formation is possible as long as the photosensitive layer is not worn out. . The photoreceptor drum 31 having a photosensitive layer having a single layer structure is exemplified as the photoreceptor of the present invention. However, the present invention can also be applied to an organic photoreceptor drum in which a plurality of layers are laminated. For example, the organic photosensitive drum may have a three-layer structure including an undercoat layer, a charge generation layer, and a charge transport layer from the inside.

A charging device 32, a developing device 33, a transfer device 34, a cleaning blade 35, and a static elimination device 40 are arranged in this order along the outer peripheral surface of the photosensitive drum 31.

  The charging device 32 is provided above the photosensitive drum 31 so as to face the outer peripheral surface of the photosensitive drum 31. The charging device 32 uniformly distributes the photosensitive layer on the outer peripheral surface of the photosensitive drum 31 to a surface potential having a predetermined polarity in accordance with a predetermined DC voltage applied from an after-mentioned voltage application unit 52 during image formation. Charge. The charging device 32 has a charging roller 32 </ b> A (see FIG. 2) that rotates in contact with the outer peripheral surface of the photosensitive drum 31. The charging roller 32 </ b> A energizes the voltage when the charged voltage application unit 52 applies the photosensitive drum 31. By applying a voltage from the charged voltage application unit 52 to the photosensitive drum 31 via the charging roller 32A, a current flows through the charging roller 32A, and the photosensitive layer of the photosensitive drum 31 is applied according to the applied voltage. Charged to surface potential. In the present embodiment, the charged voltage application unit 52 applies a DC voltage set in the range of +1000 [V] to +1400 [V] to the charging roller 32A. When this positive DC voltage is applied, corona discharge occurs between the charging roller 32A and the photosensitive layer, and surrounding gas molecules are ionized positively, which adheres to the photosensitive layer and accumulates positive static electricity. It is done. The charging device 32 receives a charging current corresponding to the voltage applied from the charged voltage application unit 52. Note that the charging device 32 is not limited to a contact type using a charging roller 32A, and may be a non-contact type strolon. Any type of charging device can be used as long as the photosensitive layer on the surface of the photosensitive drum 31 is charged with static electricity.

  The developing device 33 is provided downstream of the charging device 32 in the rotation direction of the photosensitive drum 31. The developing device 33 has a developing roller 33A (see FIG. 2) to which a bias voltage lower than the surface potential is applied. The toner carried from a toner container (not shown) is supplied to the photosensitive drum 31 by the developing roller 33A. The toner used may be a one-component developer only for toner or a two-component developer in which a carrier and toner are mixed.

  The exposure device 39 irradiates the photosensitive drum 31 with a laser beam from between the charging device 32 and the developing device 33 to expose the outer peripheral surface of the photosensitive drum 31. As a result, an electrostatic latent image corresponding to image information included in the laser beam is formed on the outer peripheral surface of the photosensitive drum 31. When the outer peripheral surface of the photosensitive drum 31 is irradiated with a laser beam, the potential of the irradiated exposed portion is discharged, and an electrostatic latent image is formed by the exposed portion. When toner is supplied to the photosensitive drum 31 by the developing device 33, the toner adheres to the electrostatic latent image due to an electrostatic force due to a potential difference between the electrostatic latent image and the toner.

  The transfer device 34 is provided downstream of the developing device 33 in the rotation direction of the photosensitive drum 31. The transfer device 34 is provided below the photosensitive drum 31 so as to face the outer peripheral surface of the photosensitive drum 31. The transfer device 34 has a transfer roller 34 </ b> A (see FIG. 2) that rotates in contact with the outer peripheral surface of the photosensitive drum 31. The transfer roller 34 </ b> A energizes the voltage when the transfer voltage application unit 57 applies the photosensitive drum 31. A constant current having a predetermined value is supplied from the transfer voltage application unit 57 to the transfer roller 34A. As a result, when the printing paper is nipped between the photosensitive drum 31 and the transfer roller 34A during image formation, the toner image on the photosensitive drum 31 adheres (transfers) to the surface of the printing paper. That is, the toner image on the photosensitive drum 31 is positively charged, and there is printing paper between the photosensitive drum 31 and the transfer device 34. The transfer device 34 negatively charges the printing paper from the back side, thereby attracting the toner to the printing paper and copying the toner image onto the printing paper. In the present embodiment, at the time of measuring the surface potential, a voltage is applied to the photosensitive drum 31 from a transfer voltage applying unit 57 described later via the transfer roller 34A. As a result, the transfer device 34 can cause a current to flow from the charged photosensitive layer of the photosensitive drum 31 to the transfer roller 34 </ b> A according to the DC voltage applied from the transfer voltage application unit 57. At that time, a current flows from the charged photosensitive layer of the photosensitive drum 31 to the transfer device 34 including the transfer roller 34A. Note that the polarity of the voltage applied by the transfer voltage applying unit 57 to the photosensitive layer of the photosensitive drum 31 is different from the polarity of the voltage applied by the charged voltage applying unit 52 to the photosensitive layer of the photosensitive drum 31. In the present embodiment, the transfer voltage application unit 57 applies a DC voltage set in the range of −800 [V] to −600 [V] to the transfer roller 34A. When this negative DC voltage is applied, corona discharge occurs between the transfer roller 34A and the photosensitive layer, and positive static electricity stored in the photosensitive layer flows into the transfer device 34. The amount of current flowing into the transfer device 34 is the amount of current corresponding to the voltage applied to the transfer roller 34A.

  As shown in FIG. 1, the fixing device 36 is provided downstream of the transfer device 34 in the conveyance direction of the printing paper. The fixing device 36 fixes the toner transferred to the printing paper onto the printing paper, and includes a heating roller 37 and a pressure roller 38 disposed to face the heating roller 37. The toner transferred to the printing paper is heated and melted when passing through the fixing device 36 to be fixed on the printing paper. The printing paper that has passed through the fixing device 36 is discharged to the paper discharge unit 27.

  As shown in FIG. 2, the cleaning blade 35 is provided downstream of the transfer device 34 in the rotation direction of the photosensitive drum 31. The cleaning blade 35 removes toner remaining on the outer peripheral surface of the photosensitive drum 31 without being transferred to the paper, and is formed of silicon rubber or the like. By rotating the photosensitive drum 31 with the cleaning blade 35 in contact with the outer peripheral surface of the photosensitive drum 31, the remaining toner is scraped off to the toner receiver 35A.

  The static eliminator 40 is provided downstream of the cleaning blade 35 in the rotation direction of the photosensitive drum 31. The static eliminator 40 removes the charge remaining on the photosensitive layer of the photosensitive drum 31. The static eliminator 40 of the present embodiment neutralizes the photosensitive layer at a range of about 60 degrees with respect to the rotation center of the photosensitive drum 31 at a time. As the charge eliminating device 40, various devices such as a device that removes electricity by irradiating the outer peripheral surface of the photosensitive drum 31 with uniform light, a device that removes electricity by alternating current discharge, or a device that removes electricity by a conductive charge removing brush are used. Can do.

[Battery voltage application unit 52]
The charged voltage application unit 52 applies a DC voltage to the photosensitive layer via the charging roller 32 </ b> A according to a control signal from the control unit 62. The charged voltage application unit 52 is a DC voltage Vdc5 (this voltage level for charging) that can charge the photosensitive layer to a reference potential necessary for image formation when the multifunction device 1 is in an image forming mode in which an image can be formed on a printing paper. An example of the first voltage of the invention, for example, +1400 [V]) is applied. On the other hand, when the multifunction device 1 is in the surface potential measurement mode described later, DC voltages Vdc1 and Vdc2 that can charge the photosensitive layer of the photosensitive drum 31 are applied to the photosensitive layer of the photosensitive drum 31 via the charging roller 32A. . The surface potential measurement mode is an operation mode of the multi-function device 1 that is shifted when a surface potential measurement process described later for measuring the surface potential of the photosensitive layer of the photosensitive drum 31 is executed. In the present embodiment, the multifunction device 1 operates in one of the operation modes of the surface potential measurement mode and the image forming mode.

  Upon receiving a predetermined control signal from the control unit 62, the charged voltage application unit 52 converts the DC voltage applied from the DC power source 63 into a constant voltage corresponding to the control signal, and the charging roller 32A of the charging device 32. Output to. In the present embodiment, the charged voltage application unit 52 performs measurement required in the later-described surface potential measurement process according to a predetermined control signal input when the multi-function device 1 is in a later-described surface potential measurement mode. As the direct current voltage, the direct current voltage Vdc1 and the direct current voltage Vdc2 are sequentially applied to the photosensitive layer through the charging roller 32A. The charging voltage application unit 52 applies a DC voltage Vdc5, which is a DC voltage for charging required for image formation, according to a predetermined control signal input when the multifunction device 1 is in the image forming mode. Application to the photosensitive layer via 32A.

[Transfer voltage applying unit 57]
The transfer voltage application unit 57 applies a DC voltage to the photosensitive layer via the transfer roller 34 </ b> A according to a control signal from the control unit 62. The transfer voltage application unit 57 applies a voltage at a transfer voltage level at which the toner image formed on the photosensitive layer can be transferred to the printing paper when the multifunction device 1 is in an image forming mode capable of forming an image on the printing paper. To do. On the other hand, when the multi-function device 1 is in a surface potential measurement mode, which will be described later, the transfer voltage applying unit 57 supplies the DC voltages Vdc3 and Vdc4 that can be discharged from the charged photosensitive layer of the photosensitive drum 31 via the transfer roller 34A. Applied to the photosensitive layer of the photosensitive drum 31.

  When the transfer voltage application unit 57 receives a predetermined control signal from the control unit 62, the transfer voltage application unit 57 converts the DC voltage applied from the DC power source 63 into a constant voltage corresponding to the control signal, thereby transferring the transfer roller 34A of the transfer device 34. Output to. In the present embodiment, the transfer voltage application unit 57 is required for a surface potential measurement process described later in accordance with a predetermined control signal input when the multi-function device 1 is in a surface potential measurement mode described later. As the measurement DC voltage, a DC voltage Vdc3 and a DC voltage Vdc4 are sequentially applied to the photosensitive layer via the charging roller 32A. Further, the transfer voltage application unit 57 is configured to transfer a DC voltage (for example, DC-100 [V]) required for image formation in accordance with a predetermined control signal input when the multi-function device 1 is in the image formation mode. ] To -200 [V]) is applied to the photosensitive layer via the transfer roller 34A.

  The current detector 59 shown in FIG. 3 detects the current flowing through the photosensitive layer of the photosensitive drum 31. The current detector 59 is for detecting a direct current value that flows through the photosensitive layer when a direct current voltage is applied to the photosensitive layer. The current detection unit 59 is a well-known current detection circuit composed of electronic elements such as an internal resistor and an internal capacitor, and is provided between the photosensitive drum 31 and the ground potential. The current detection unit 59 is connected to the control unit 62, and the detection value (current value) detected by the current detection unit 59 is sent to the control unit 62. The control unit 62 can detect the current value flowing through the photosensitive layer based on the detection value from the current detection unit 59. This current value is used for the surface potential measurement process described later. In the present embodiment, in the surface potential measurement mode, the current value acquired using the current detection unit 59 when the DC voltage Vdc3 and the DC voltage Vdc4 are applied from the transfer voltage application unit 57 to the photosensitive layer. Is used for the surface potential measurement process. In the surface potential measurement mode, when the DC voltage Vdc1 and the DC voltage Vdc2 are applied from the charged voltage application unit 52 to the photosensitive layer, the current value acquired using the current detection unit 59 is used for the surface potential measurement process. Used.

[Configuration of Control Unit 62]
The control unit 62 performs overall control of the multifunction machine 1. As shown in FIG. 1, the control unit 62 is configured as a microcomputer including a CPU 62A, a ROM 62B, a RAM 62C, and the like as main components. The control unit 62 may be configured by an electronic circuit such as an integrated circuit (ASIC, DSP).

  The control unit 62 is connected to the image reading unit 10, the ADF 21, the image forming unit 22, the feeding unit 17, and the like inside the multifunction device 1, and controls these components. The control unit 62 also configures each element constituting the image forming unit 22, specifically, the charging device 32, the developing device 33, the transfer device 34, the cleaning blade 35, the fixing device 36, the fixing roller 37, and the pressure roller 38. , The exposure device 39, the charge removal device 40, and the like. The ROM 62B stores a program for executing image forming processing. The CPU 62A executes each control program in the ROM 62B, thereby controlling each element connected to the control unit 62 and printing an image on printing paper.

  In the present embodiment, the ROM 62B of the control unit 62 stores a program for executing a surface potential measurement process described later. The CPU 62A executes the surface potential measurement process by executing this program. In addition, when the CPU 62A executes the program, in the surface potential measurement mode, the control unit 62 includes a first measurement unit 71 (an example of the first measurement unit of the present invention) and a second measurement unit 72 (the present invention. It functions as an example of the second measuring unit, a third measuring unit 73 (an example of the third measuring unit of the present invention), and a uniformizing unit 75 (an example of the uniforming unit of the present invention) (see FIG. 3). The voltage correction unit 74 (an example of the voltage correction unit of the present invention) will be separately described in the surface potential correction process which is one of the modifications of the first embodiment.

  In addition to the program, the ROM 62B stores voltage values, calculation formulas, threshold values, and the like used for the surface potential measurement process. For example, a first discharge start voltage calculation formula for calculating a direct current voltage Vdc2 and a first discharge start voltage Vcs1 that are applied to acquire a current value in the first measurement unit 71 is stored in the ROM 62B. Further, the ROM 62B stores a second discharge start voltage calculation formula for calculating the DC voltage Vdc3 and the second discharge start voltage Vcs2 applied in order to acquire the current value by the second measuring unit 72. A surface potential calculation formula for calculating the surface potential in the third measuring unit 73 is stored in the ROM 62B. The ROM 62B also stores a threshold value for correcting the voltage applied by the charged voltage application unit 52 to the photosensitive layer during the image forming process. The RAM 62C temporarily stores current values measured by the first measurement unit 71 and the second measurement unit 72, and the like.

  The first measuring unit 71 applies a voltage from the charged voltage applying unit 52 to the uncharged photosensitive layer, and the current detecting unit 59 detects the current flowing through the photosensitive layer when the voltage is applied. The voltage value and the current value are acquired. Subsequently, the first measuring unit 71 starts discharge in the uncharged photosensitive layer based on the correlation between the acquired voltage value and current value (relation shown by the straight line 81 in FIG. 4). 1 Discharge start voltage Vcs1 is measured. A specific measurement method will be described later.

  The second measuring unit 72 applies a voltage from the charged voltage applying unit 52 to the charged photosensitive layer, and the current detecting unit 59 detects the current flowing through the photosensitive layer when the voltage is applied. The voltage value and the current value are acquired. Subsequently, the second measurement unit 72 starts discharge in the charged photosensitive layer based on the correlation between the acquired voltage value and current value (relation shown by the straight line 82 in FIG. 5). 2 Measure the discharge start voltage Vcs2. A specific measurement method will be described later.

  The third measurement unit 73 measures the surface potential of the photosensitive layer based on the first discharge start voltage Vcs1 measured by the first measurement unit 71 and the second discharge start voltage Vcs2 measured by the second measurement unit 72. . A specific measurement method will be described later.

  The uniformizing unit 75 causes the static eliminator 40 to neutralize the entire area of the photosensitive layer and applies a voltage to the charged voltage applying unit 52 before the measurement in the first measuring unit 71 and the second measuring unit 72 is performed. By charging the entire region of the photosensitive layer, the surface potential of the entire region of the photosensitive layer is made uniform. A specific equalization process will be described later.

[Measurement method of surface potential]
Here, the first discharge start voltage Vcs1, the second discharge start voltage Vcs2, and the surface potential will be described with reference to FIG. 4 and FIG. First, the first discharge start voltage Vcs1 will be described with reference to the graph shown in FIG. In general, in the contact charging method in which the photosensitive drum 31 is charged in contact with the charging roller 32A, the voltage applied to the photosensitive layer via the charging roller 32A and the charging current flowing from the charging device 32 to the photosensitive drum 31 are charged. It is known that there is a linear relationship (correlation) between For this reason, the control unit 62 can detect a voltage value at which the charging current does not flow by measuring the charging current flowing through the photosensitive drum 31 at that time by changing the voltage applied to the photosensitive layer to a plurality of different voltages. it can. The voltage value at which the charging current stops flowing is the first discharge start voltage Vcs1. Specifically, a DC voltage Vdc1 (+1200 [V]) is applied from the charged voltage application unit 52 to the photosensitive layer via the charging roller 32A. At this time, a current value (about 27.5 [μA]) of the charging current Idc 1 flowing from the charging device 32 to the photosensitive drum 31 is acquired by the current detection unit 59. Similarly, a DC voltage Vdc2 (+1400 [V]) is applied from the charged voltage application unit 52 to the photosensitive layer via the charging roller 32A. At that time, a current value (about 35 [μA]) of the charging current Idc 2 flowing from the charging device 32 to the photosensitive drum 31 is acquired by the current detection unit 59. As shown in FIG. 4, a straight line 81 obtained by connecting the point P1 of the DC voltage Vdc1 and the point P2 of the DC voltage Vdc2 is a linear relationship between the DC voltage Vdc1, the charging current Idc1, the DC voltage Vdc2, and the charging current Idc2. Indicates. The straight line 81 intersects with a line where the charging current indicates 0 [μA]. The intersecting point is a point indicating the first discharge start voltage Vcs1 (+600 [V]).

  Next, the second discharge start voltage Vcs2 will be described with reference to the graph shown in FIG. In general, in the contact discharge method in which the photosensitive drum 31 is contacted and discharged, such as the transfer roller 34A, linearity is generated between the voltage applied to the photosensitive layer and the inflow current flowing from the photosensitive drum 31 to the transfer device 34. It is known that there is a relationship (correlation). Therefore, the control unit 62 detects the voltage value at which the inflow current does not flow by measuring the inflow current flowing from the photoconductive drum 31 at that time by changing the voltage applied to the photosensitive layer to a plurality of different voltages. be able to. The voltage value at which this inflow current does not flow is the second discharge start voltage Vcs2. Specifically, the DC voltage Vdc3 (−600 [V]) is applied from the transfer voltage applying unit 57 to the photosensitive layer via the transfer roller 34A. At this time, a current value (about 3.4 [μA]) of the inflow current Idc3 flowing from the photosensitive drum 31 to the transfer device 34 is acquired by the current detection unit 59. Similarly, a DC voltage Vdc4 (−800 [V]) is applied from the transfer voltage application unit 57 to the photosensitive layer via the transfer roller 34A. At this time, a current value (about 4.75 [μA]) of the inflow current Idc4 flowing from the photosensitive drum 31 to the transfer device 34 is acquired by the current detection unit 59. As shown in FIG. 5, a straight line 82 obtained by connecting the point P3 of the DC voltage Vdc3 and the point P4 of the DC voltage Vdc4 includes the DC voltage Vdc3 and the inflow current Idc3, and the DC voltage Vdc4 and the inflow current Idc4. The linear relationship is shown. The straight line 82 intersects the line where the inflow current indicates 0 [μA]. The intersecting point is a point indicating the second discharge start voltage Vcs2 (−50 [V]).

  Next, the surface potential of the photosensitive layer of the photosensitive drum 31 will be described. It is known that the surface potential of the photosensitive layer charged by the charging device 32 decreases with time. This decrease in surface potential is due to so-called dark decay. Dark decay refers to a phenomenon in which the surface potential of the charged photosensitive layer of the photosensitive drum 31 is lowered by injected carriers (electrons, holes), thermally excited carriers, and the like in a dark place. Due to the dark decay, the surface potential rapidly decreases immediately after charging, and gradually decreases after a certain period of time. Therefore, it is considered that the surface potential of the photosensitive layer of the charged photosensitive drum 31 is largely different between the vicinity of the charging device 32 and the vicinity of the developing device 33, but is not significantly different between the vicinity of the developing device 33 and the vicinity of the transfer device 34. Therefore, the second discharge start voltage Vcs2 obtained by the voltage applied to the photosensitive layer via the transfer roller 34A and the inflow current flowing into the transfer device 34 is the second discharge when the photosensitive layer is located near the developing device 33. It is very close to the starting voltage. Utilizing this fact, in the present embodiment, a voltage value (+550) obtained by adding the first discharge start voltage Vcs1 (+600 [V]) and the second discharge start voltage Vcs2 (−50 [V]). [V]) is measured as the actual surface potential of the photosensitive layer of the photosensitive drum 31 at the development timing. Thereby, the surface potential of the photosensitive layer of the photosensitive drum 31 can be obtained with high accuracy.

[Surface potential measurement process]
Next, the surface potential measurement method for the photosensitive layer of the present invention will be described together with the surface potential measurement processing procedure executed by the control unit 62 with reference to the flowchart of FIG. In the figure, S11, S12,... Represent processing procedure (step) numbers. Processing in each step is performed by the control unit 62, more specifically, by the CPU 62A executing a program in the ROM 62B. In the following description, it is assumed that the multifunction device 1 is in an image forming mode in which an image can be formed on printing paper at the time of step S11.

  First, in step S <b> 11, the control unit 62 determines whether or not a surface potential measurement request is input to the multifunction device 1. Here, the surface potential measurement request includes, for example, that the main power of the multifunction device 1 is turned on, a surface potential measurement instruction is input to the multifunction device 1, and an image on the printing paper using the photosensitive drum 31. When the number of times of forming the toner exceeds the predetermined number, when the operation time of the multifunction machine 1 exceeds the preset time, the charging time when the photosensitive drum 31 is charged exceeds the preset time. The start condition is met. By measuring the surface potential of the photosensitive layer when such a predetermined start condition is satisfied, an accurate surface potential can be measured according to the use environment and use situation of the multifunction machine 1. When the surface potential measurement request is input, the control unit 62 switches the operation mode of the multifunction machine 1 from the image forming mode to the surface potential measurement mode for measuring the surface potential of the photosensitive layer of the photosensitive drum 31.

  In the next step S12, the control unit 62 applies voltage to the photosensitive layer from the charged voltage application unit 52 to charge the entire region of the photosensitive layer, and operates the static eliminator 40 to discharge the entire region of the photosensitive layer. The surface potential of the photosensitive layer is made uniform. The control unit 62 equalizes the surface potential of the photosensitive layer by executing the charging and discharging process during the period in which the photosensitive drum 31 is rotated three times by the motor. After this homogenization, the control unit 62 can charge the photosensitive layer so as to have a uniform surface potential by applying a voltage to the photosensitive layer from the charged voltage applying unit 52 and charging it. Therefore, the control unit 62 can suppress variations in the current value detected by the current detection unit 59. Here, the control part 62 which performs the process of step S12 is an example of the equalization means of this invention. The period during which the control unit 62 performs the charging and discharging process is not limited to the period in which the photosensitive drum 31 rotates three times, as long as the photosensitive drum 31 rotates at least once.

  In the next step S <b> 13, the control unit 62 operates the static eliminator 40 before applying a voltage from the charged voltage application unit 52 to the photosensitive layer of the photosensitive drum 31, and temporarily sets the photosensitive layer of the photosensitive drum 31. Remove all charge. Thereafter, the controller 62 stops the static eliminator 40 so as not to remove the charge on the photosensitive drum 31.

  In the next step S14, the control unit 62 applies the DC voltage Vdc1 from the charged voltage applying unit 52 to the photosensitive layer to charge the photosensitive layer. At that time, in step S <b> 15, the control unit 62 acquires the charging current Idc <b> 1 flowing from the charging device 32 to the photosensitive drum 31 from the current detection unit 59.

  Thereafter, in step S16, in order to charge the entire photosensitive layer of the photosensitive drum 31, the control unit 62 waits for one rotation of the photosensitive drum 31 with the DC voltage Vdc1 applied. That is, the charged voltage application unit 52 continues to apply the DC voltage Vdc1 to the photosensitive layer via the charging roller 32A until the entire area of the photosensitive layer is charged. The current detection unit 59 continues to measure the charging current Idc1, and the control unit 62 acquires the average value. Thereby, the control part 62 can suppress the dispersion | variation in the charging current Idc1 measured.

  In the next step S17, as in step S13, the control unit 62 operates the static eliminator 40 before applying a voltage from the charged voltage application unit 52 to the photosensitive layer of the photosensitive drum 31, and thereby the photosensitive drum 31. The electrification of the photosensitive layer is removed. Note that the controller 62 operates the static eliminator 40 in accordance with a period in which the photosensitive drum 31 is rotated once in a process of step S19 described later.

  In step S18, the control unit 62 raises the voltage applied from the charged voltage applying unit 52 to the DC voltage Vdc2, and applies the DC voltage Vdc2 from the charged voltage applying unit 52 to the photosensitive layer to charge the photosensitive layer. Here, step S14 and step S18 are examples of the first step of the present invention. At that time, in step S <b> 19, the control unit 62 acquires the charging current Idc <b> 2 flowing from the charging device 32 to the photosensitive drum 31 from the current detection unit 59. Here, step S15 and step S19 are an example of the second step of the present invention. Thereafter, in step S20, as in step S16, the controller 62 waits for one rotation of the photosensitive drum 31 with the DC voltage Vdc2 applied to charge the entire area of the photosensitive layer of the photosensitive drum 31. . Here, in order to reduce the processing time by reducing the surface potential measurement processing procedure, the DC voltage Vdc2 is set to 1400 [V], which is the same as the DC voltage Vdc5, but the DC voltage Vdc2 is set to the same value as the DC voltage Vdc5. do not have to.

  In the next step S21, the control unit 62 stops the static eliminator 40 so that the voltage on the photosensitive drum 31 is not removed. If there is an uncharged region on the photosensitive layer of the photosensitive drum 31, then, the control unit 62 applies a DC voltage Vdc5 from the charged voltage applying unit 52 to the photosensitive layer of the photosensitive drum 31. The entire photosensitive layer is charged with a DC voltage Vdc5. That is, the control unit 62 equalizes the surface potential of the photosensitive layer before applying the DC voltage Vdc3 from the charged voltage applying unit 52 to the photosensitive layer. As a result, the control unit 62 can proceed to the next processing without charging all the regions of the photosensitive layer of the photosensitive drum 31 again. Further, the controller 62 can suppress variations in the current value detected by the current detector 59 when a voltage is applied from the transfer device 34 to the photosensitive layer when the charged photosensitive layer is discharged.

  In the next step S22, the controller 62 determines the DC voltage Vdc1 applied in step S14, the charging current Idc1 acquired in step S15, the DC voltage Vdc2 applied in step S18, and the charging current acquired in step S19. Based on Idc2, the first discharge start voltage Vcs1 of the photosensitive layer of the photosensitive drum 31 is measured. Specifically, as shown in FIG. 4, the control unit 62 connects a point P1 determined by the DC voltage Vdc1 and the charging current Idc1 and a point P2 determined by the DC voltage Vdc2 and the charging current Idc2 to form a straight line 81 ( Determine the linear relationship). The control unit 62 obtains the voltage value at the point where the straight line 81 and the straight line where the charging current becomes 0 [μA] intersect. The obtained voltage value is the first discharge start voltage Vcs1. Here, step S22 is an example of the third step of the present invention. Moreover, the control part 62 which performs the process of step S14, S15, S18, S19, S22 is an example of the 1st measurement means of this invention.

  In the next step S23, the control unit 62 applies the DC voltage Vdc3 from the transfer voltage applying unit 57 to the photosensitive layer to discharge the photosensitive layer. Note that the DC voltage Vdc3 applied by the transfer voltage application unit 57 in step S23 has an electrical polarity opposite to the voltage applied by the charging voltage application unit 52 in steps S14 and S18. At that time, in step S <b> 24, the control unit 62 acquires an inflow current Idc <b> 3 that flows from the photosensitive drum 31 into the transfer device 34 from the current detection unit 59.

  Thereafter, in step S25, in order to discharge the entire photosensitive layer of the photosensitive drum 31, the control unit 62 waits until the photosensitive drum 31 rotates once with the DC voltage Vdc3 applied. That is, the transfer voltage applying unit 57 applies the DC voltage Vdc3 until the entire photosensitive layer is charged. Meanwhile, the current detection unit 59 continues to measure the inflow current Idc3, and the control unit 62 acquires the average value. Thereby, the control part 62 can suppress the dispersion | variation in the inflow current Idc3 measured.

  In the next step S26, the controller 62 applies the DC voltage Vdc5 from the voltage application unit 52 to the photosensitive layer before applying the DC voltage Vdc4 from the voltage application unit 52 to the photosensitive layer. Charge the area. As a result, the control unit 62 sets the charged state in which the entire region of the photosensitive layer is charged by the application of the DC voltage Vdc5.

  In step S27, the control unit 62 applies the DC voltage Vdc4 from the transfer voltage applying unit 57 to the photosensitive layer by setting the voltage applied from the transfer voltage applying unit 57 to the DC voltage Vdc4. Note that the DC voltage Vdc4 applied by the transfer voltage application unit 57 in step S27 is opposite in electrical polarity to the voltage applied by the charging voltage application unit 52 in steps S14 and S18. Here, step S23 and step S27 are an example of the fourth step of the present invention. At that time, in step S <b> 28, the control unit 62 acquires the inflow current Idc <b> 4 flowing from the photosensitive drum 31 into the transfer device 34 from the current detection unit 59. Here, step S24 and step S28 are an example of the fifth step of the present invention. Thereafter, in step S29, as in step S24, the controller 62 waits for one rotation of the photosensitive drum 31 with the DC voltage Vdc4 applied to discharge the entire region of the photosensitive layer of the photosensitive drum 31. .

  In the next step S30, the control unit 62 determines the DC voltage Vdc3 applied in step S23, the inflow current Idc3 acquired in step S24, the DC voltage Vdc4 applied in step S27, and the current acquired in step S28. Based on the built-in current Idc4, the second discharge start voltage Vcs2 of the photosensitive layer of the photosensitive drum 31 is measured. Specifically, as shown in FIG. 5, the control unit 62 is a straight line connecting a point P3 determined by the DC voltage Vdc3 and the inflow current Idc3 and a point P4 determined by the DC voltage Vdc4 and the inflow current Idc4. 82 (linear relationship) is determined. Next, the control unit 62 obtains a voltage value at a point where the straight line 82 and the straight line where the inflow current becomes 0 [μA] intersect. The obtained voltage value becomes the second discharge start voltage Vcs2. Here, step S30 is an example of the sixth step of the present invention. Moreover, the control part 62 which performs the process of step S23, S24, S27, S28, S30 is an example of the 2nd measurement means of this invention.

  Next, in step S31, the controller 62 determines the surface potential of the photosensitive layer of the photosensitive drum 31 based on the first discharge start voltage Vcs1 obtained in step S22 and the second discharge start voltage Vcs2 obtained in step S30. Is measured and the processing is terminated. Specifically, the control unit 62 obtains a surface potential obtained by adding the first discharge start voltage Vcs1 and the second discharge start voltage Vcs2. The obtained potential difference is the surface potential. Here, step S31 is an example of the seventh step of the present invention. Moreover, the control part 62 which performs the process of step S31 is an example of the 3rd measurement means of this invention.

  As described above, in the present embodiment, during the surface potential measurement process by the control unit 62, the first discharge start voltage Vcs1 at which discharge from the charging device 32 to the photosensitive layer of the photosensitive drum 31 is started, The second discharge start voltage Vcs2 at which the discharge from the photosensitive layer of the photosensitive drum 31 to the transfer device 34 after the change in the surface potential due to the attenuation becomes gentle is used. As a result, the surface potential including the influence of dark decay can be obtained, and the surface potential close to the actual surface potential when the photosensitive layer of the photosensitive drum 31 is in a position facing the developing device 33 is measured with high accuracy. can do.

  Further, the stress on the photosensitive layer in the surface potential processing mode can be reduced by reversing the polarities of the voltage applied by the charged voltage applying unit 52 and the voltage applied by the transfer voltage applying unit 57 to the photosensitive layer. Can do. This can prevent the life of the photosensitive layer from being reduced.

[Modification of First Embodiment]
Further, although the polarity of the voltage applied to the photosensitive layer by the charged voltage applying unit 52 and the voltage applied to the photosensitive layer by the transfer voltage applying unit 57 are reversed, the present invention is not limited to this. As long as the voltage resistance of the photosensitive layer is high, the voltage applied to the photosensitive layer of the photosensitive drum 31 by the voltage application unit 52 and the transfer voltage application unit 57 may be the same polarity. Thereby, the configuration of the charged voltage application unit 52 and the transfer voltage application unit 57 can be shared. In this case, the second measuring unit 72 applies a voltage having the same electrical polarity as the voltage applied by the first measuring unit 71. In addition, the first discharge start voltage Vcs1 and the second discharge start voltage Vcs2 have the same electrical polarity. Therefore, the voltage value obtained by subtracting the first discharge start voltage Vcs1 and the second discharge start voltage Vcs2 is set as the surface potential of the photosensitive layer of the photosensitive drum 31.

  In the first embodiment described above, in the surface potential measurement process, the DC voltage applied to the photosensitive layer in order to measure the first discharge start voltage Vcs1 is binary, and the first discharge start voltage Vcs1 is measured. Therefore, the DC voltage applied to the photosensitive layer is binary, but is not limited thereto. By setting the first discharge start voltage Vcs1 and the second discharge start voltage Vcs2 to a large number of values that are two or more of the voltage values applied to measure the first discharge start voltage Vcs1 and the second discharge start voltage Vcs2, It becomes possible to measure the value more accurately.

  In the first embodiment described above, in the surface potential measurement process, the charged voltage application unit 52 first applies the positive DC voltages Vdc1 and Vdc2, and then the transfer voltage application unit 57 applies the negative DC voltage. Although an example in which the voltages Vdc3 and Vdc4 are applied has been described, the present invention is not limited to this. First, the transfer voltage application unit 57 may apply the negative DC voltages Vdc3 and Vdc4 and measure the second discharge start voltage Vcs2 first. Alternatively, the charging voltage application unit 52 may first apply the negative DC voltages Vdc1 and Vdc2, and then the transfer voltage application unit 57 may apply the positive DC voltages Vdc3 and Vdc4. Alternatively, the transfer voltage application unit 57 may first apply the positive DC voltages Vdc3 and Vdc4, and then the charging voltage application unit 52 may apply the negative DC voltages Vdc1 and Vdc2.

  In the first embodiment described above, the DC voltages Vdc1 and Vdc2 are applied to the photosensitive layer of the photosensitive drum 31 via the charging roller 32A, and the DC voltages Vdc3 and Vdc4 are applied to the photosensitive drum 31 via the transfer roller 34A. Although the example applied to a photosensitive layer was demonstrated, it is not restricted to this. The charging roller 32A and the transfer roller 34A are provided separately if voltage application units such as the charging voltage application unit 52 and the transfer voltage application unit 57 can be energized when applying a voltage to the photosensitive layer of the photosensitive drum 31. The energized member may be used.

  In the first embodiment, in the surface potential measurement process, the discharge in the charging layer 32 and the charged photosensitive layer and the discharge in the transfer device 34 and the non-charged photosensitive layer are measured. Although the case where the first discharge start voltage Vcs1 and the second discharge start voltage Vcs2 are measured has been described as an example, the present invention is not limited thereto. In the surface potential measurement process, the first discharge start voltage Vcs1 and the second discharge start voltage Vcs2 may be measured using only one of the charging device 32 and the transfer device 34. Specifically, in step S23 of the surface potential measurement process, the charged voltage applying unit 52 applies the DC voltage Vdc3 to the photosensitive layer, and in step S27, the charged voltage applying unit 52 applies the DC voltage Vdc4 to the photosensitive layer. Conceivable. On the contrary, in step S14, the transfer voltage applying unit 57 applies the DC voltage Vdc1 to the photosensitive layer, and in step S18, the transfer voltage applying unit 57 applies the DC voltage Vdc2 to the photosensitive layer. It is done. Accordingly, the surface potential measurement process can be executed using only one of the charging device 32 and the transfer device 34.

  In the first embodiment described above, the example in which the control unit 62 performs the surface potential measurement process to measure the surface potential of the photosensitive layer by the control unit 62 has been described. However, the control unit 62 performs measurement. Based on the surface potential, a voltage correction process for correcting the DC voltage Vdc5 applied from the charged voltage applying unit 52 for charging the photosensitive layer may be executed. Specifically, the control unit 62 executes a voltage correction process, which will be described later, following step S30 of the surface potential measurement process.

  Following step S31 of the surface potential measurement process, the control unit 62 determines whether or not the surface potential extracted in step S31 is equal to or less than a predetermined first threshold value (an example of the first threshold value of the present invention). Here, the first threshold value is a threshold value for determining whether or not the voltage has decreased so that the photosensitive layer of the photosensitive drum 31 cannot maintain a predetermined print quality. For example, it is conceivable that the minimum surface potential capable of maintaining the print quality is measured in advance by experiments and the measurement result is used as the first threshold value. When it is determined that the surface potential is equal to or lower than the first threshold value, the control unit 62 corrects the DC voltage Vdc5 by increasing the voltage applied to the photosensitive layer by the charged voltage application unit 52 during the image forming process. If the surface potential is greater than the first threshold, the control unit 62 determines that the quality can be maintained by the voltage applied by the charged voltage application unit 52 and ends the process. The control unit 62 that executes these voltage correction processes is the voltage correction unit 74, which is an example of the voltage correction unit of the present invention.

  In this way, by adding the voltage correction process to the surface potential measurement process, the DC voltage Vdc5 optimum for the charged potential of the photosensitive drum 31 is set based on the measured surface potential. Therefore, the charged potential of the photosensitive drum 31 can always be stably maintained so as to be a predetermined reference potential. This prevents variations in print quality due to variations in charging potential, and stabilizes print quality.

[Second Embodiment]
In the description of the first embodiment, the case where a direct current voltage is applied from the charged voltage application unit 52 to the photosensitive layer of the photosensitive drum 31 is described, but the present invention is not limited to this example. In the second embodiment, a case where an AC voltage is applied from the charged voltage application unit 52 to the photosensitive layer of the photosensitive drum 31 will be described. Here, a difference from the configuration of the first embodiment is that a DC / AC power supply is provided instead of the DC power supply 63, and the voltage applied by the charging voltage applying unit 52 is a voltage obtained by superimposing the AC voltage on the DC voltage. It is. The current detector 59 can also measure an alternating current. Further, the difference from the processing of the first embodiment is that the voltage application method in steps S14 and S18 and the current measurement method in steps S15 and S19 in the surface potential measurement processing procedure are different, and in step S22. The method of obtaining the first discharge start voltage Vcs1 is different. Since other parts are common to the configuration and processing of the first embodiment, only different parts will be described here, and description of common parts will be omitted.

  As shown in FIG. 7, the surface potential measurement processing procedure of the second embodiment includes steps S14 and S15 of the surface potential measurement processing procedure of the first embodiment as steps S114 and S115, and step S18. , S19 are replaced with steps S118 and S119, step S22 is replaced with step S122, steps S23 and S24 are replaced with steps S123 and S124, steps S27 and S28 are replaced with steps S127 and S128, and step S30 is replaced with step S130. .

  In step S114 following step S13, the control unit 62 applies the superimposed voltage Vac1 from the charged voltage application unit 52 to the photosensitive layer. The superimposed voltage Vac1 is a voltage obtained by superimposing a predetermined first DC voltage and a first AC voltage that is a sine wave. At that time, as step S115, the control unit 62 acquires the charging current Iac1 flowing through the photosensitive drum 31 from the current detection unit 59 and obtains an effective value.

  In step S118 following step S17, the control unit 62 applies the superimposed voltage Vac2 from the charged voltage application unit 52 to the photosensitive layer. The superimposed voltage Vac2 is a voltage obtained by superimposing the first DC voltage, the first AC voltage, and the second AC voltage that is a sine wave having a different voltage value. At that time, as step S119, the control unit 62 acquires the charging current Iac2 flowing through the photosensitive drum 31 from the current detection unit 59, and obtains an effective value.

  In step S122 following step S21, the control unit 62 determines the superimposed voltage Vac1 applied in step S114, the effective value of the charging current Iac1 acquired in step S115, the superimposed voltage Vac1 applied in step S118, and the charging acquired in step S119. Based on the correlation (linear relationship) of the effective value of the current Iac2, the voltage value when the current amount becomes zero is obtained, and the first discharge start voltage Vcs1 is measured.

  In subsequent step S123, the control unit 62 applies the superimposed voltage Vac3 from the charged voltage application unit 52 to the photosensitive layer. The superimposed voltage Vac3 is a voltage obtained by superimposing a predetermined second DC voltage and a third AC voltage that is a sine wave. At that time, as step S124, the control unit 62 uses the current detection unit 59 to measure the charging current Iac3 flowing through the photosensitive drum 31 to obtain an effective value.

  In step S127 following step S26, the control unit 62 applies the superimposed voltage Vac4 from the charged voltage application unit 52 to the photosensitive layer. The superimposed voltage Vac4 is a voltage obtained by superimposing the fourth DC voltage, which is a sine wave having a voltage value different from that of the second DC voltage and the third AC voltage. At that time, as step S127, the control unit 62 uses the current detection unit 59 to measure the charging current Iac4 flowing through the photosensitive drum 31 to obtain an effective value.

  In step S130 subsequent to step S29, the control unit 62 controls the superimposed voltage Vac3 applied in step S123, the effective value of the charging current Iac3 acquired in step S124, the superimposed voltage Vac3 applied in step S127, and the charging acquired in step S128. Based on the correlation (linear relationship) of the effective value of the current Iac4, the voltage value when the current amount becomes zero is obtained, and the second discharge start voltage Vcs2 is measured. Thereafter, in step S31, the control unit 62 measures the surface potential and ends the process.

  As described above, in the second embodiment, when the control unit 62 performs the first discharge start voltage measurement process, the voltage at which the charged voltage application unit 52 charges the photosensitive layer of the photosensitive drum 31 is changed to a DC voltage. Are superimposed. As a result, the applied voltage can be made uniform, and variations due to measurement can be suppressed.

  Since the scope of the present disclosure is defined not by the detailed description preceding the description of the claims but by the description of the appended claims, the embodiments described herein are merely exemplary and non-limiting I want to be understood. Therefore, all the changes which do not deviate from a claim, or an equivalent are included in a claim.

1: MFP 10: Image reading unit 22: Image forming unit 31: Photoconductor drum 32: Charging device 33: Developing device 34: Transfer device 39: Exposure device 40: Charge eliminating device 52: Charge voltage applying unit 57: Transfer voltage Application unit 59: current detection unit 62: control unit 71: first measurement unit 72: second measurement unit 73: third measurement unit 74: voltage correction unit 75: equalization unit

Claims (8)

A photoreceptor having a photosensitive layer on the surface;
A voltage application unit for applying a voltage to the photosensitive layer;
A current detection unit that is provided between the photosensitive member and a ground potential and detects a current flowing through the photosensitive layer;
Correlation between the voltage applied to the photosensitive layer from the voltage application unit when the photosensitive layer is not charged and the current flowing through the photosensitive layer acquired from the current detection unit when the voltage is applied. First measurement means for measuring a first discharge start voltage for starting discharge in the photosensitive layer in the uncharged state,
A voltage applied to the photosensitive layer from the voltage application unit in a charged state in which the photosensitive layer is charged by applying the first voltage, and the photosensitive layer acquired from the current detection unit when the voltage is applied. Second measurement means for measuring a second discharge start voltage for starting discharge in the charged photosensitive layer based on a correlation with a flowing current;
The first voltage applied to the photosensitive layer based on the first discharge start voltage measured by the first measurement unit and the second discharge start voltage measured by the second measurement unit. A third measuring means for measuring the surface potential of the photosensitive layer;
Equipped with a,
The voltage application unit applies voltages having different polarities to the photosensitive layer during measurement of the first measurement unit and the second measurement unit, and the potential required for image formation of the photosensitive layer during image formation. A first voltage applying unit that applies the first voltage that can be charged to the surface, and a second voltage applying unit that applies a voltage capable of transferring the toner image formed on the photosensitive layer to the sheet during image formation,
The first measuring means includes a voltage applied to the photosensitive layer from the first voltage application unit and a current flowing through the photosensitive layer acquired from the current detection unit until the voltage is applied to the entire area of the photosensitive layer. Based on the correlation with the average value of the first discharge start voltage,
The second measuring means includes a voltage applied to the photosensitive layer from the second voltage application unit and a current flowing through the photosensitive layer acquired from the current detection unit until the voltage is applied to the entire area of the photosensitive layer. The second discharge start voltage is measured based on the correlation with the average value of
The third measuring means adds a voltage value obtained by adding the first discharge starting voltage measured by the first measuring means and the second discharge starting voltage measured by the second measuring means to the the image forming apparatus shall be the surface potential.   The first measuring unit and the second measuring unit obtain a linear relationship which is the correlation from at least a binary voltage and at least a binary current flowing in the photosensitive layer when each of the voltages is applied, 2. The image forming apparatus according to claim 1, wherein voltage values when the current value becomes zero in the linear relationship are the first discharge start voltage and the second discharge start voltage, respectively. The voltage application unit applies a superimposed voltage obtained by superimposing an AC voltage on a DC voltage to the photosensitive layer,
The first measuring means includes the superposed voltage applied from the voltage application unit to the photosensitive layer in the non-charged state, and a current flowing through the photosensitive layer acquired from the current detection unit when the superposed voltage is applied. Based on the correlation, the first discharge start voltage is measured,
The second measuring means correlates the superimposed voltage applied from the voltage application unit to the photosensitive layer in the charged state and a current flowing through the photosensitive layer acquired from the current detection unit when the superimposed voltage is applied. The image forming apparatus according to claim 1, wherein the second discharge start voltage is measured based on a relationship. Voltage correction means for correcting the voltage value of the first voltage applied to the photosensitive layer when the surface potential measured by the third measurement means is equal to or lower than a predetermined first threshold value is further provided. the image forming apparatus according to any one of claims 1-3. A charge eliminating portion for eliminating the charge on the photosensitive layer of the photoreceptor;
Before each measurement of the first measurement unit and the second measurement unit is performed, a voltage is applied from the voltage application unit to the photosensitive layer to charge the entire region of the photosensitive layer, and the neutralization unit Uniformizing means for neutralizing the surface potential of the photosensitive layer by neutralizing the entire area of the photosensitive layer;
Further comprising an image forming apparatus according to any one of claims 1-4 a. 6. The uniformizing unit according to claim 5 , wherein, before the voltage is applied from the voltage application unit to the photosensitive layer during the measurement by the first measurement unit, the neutralization unit neutralizes the entire region of the photosensitive layer. Image forming apparatus. The uniformizing unit applies the first voltage from the voltage application unit to the photosensitive layer before the voltage is applied from the voltage application unit to the photosensitive layer during the measurement by the second measurement unit. The image forming apparatus according to claim 5 , wherein the entire region of the layer is charged. The measurement of each of the first measurement unit and the second measurement unit is performed when a predetermined start condition is satisfied,
The start condition is that the number of times of forming an image on a sheet using the photoconductor exceeds a predetermined number of times, the time when the photoconductor is charged exceeds a predetermined time, and The image forming apparatus according to any one of claims 1 to 7 , wherein any one of the conditions when the time from when the power is applied to the image forming apparatus exceeds a predetermined time is satisfied.

Images