JP5925155B2 - Image forming apparatus and method for measuring film thickness of photosensitive layer - Google Patents

Description

  The present invention relates to an image forming apparatus including a photoreceptor having a single photosensitive layer provided on the surface, and a method for measuring the film thickness 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 photoreceptor, 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 potential (hereinafter also referred to as “charging bias”) by the charging device, and then the laser beam is irradiated from the exposure device to the surface of the photoconductor. 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, a toner charged to a potential higher than the potential of the electrostatic latent image is attached to the electrostatic latent image by a developing device, and then charged from the back surface of the sheet material conveyed to a predetermined transfer position by the transfer device. A charge having the opposite polarity to the bias is applied, and the toner image is transferred to the surface of the sheet material.

  In this type of image forming apparatus, the photosensitive layer provided on the surface of the photoreceptor is worn by repeated image formation. When the photosensitive layer is worn and its film thickness becomes thinner than the reference value, sufficient image quality cannot be obtained. For this reason, when the film thickness of the photosensitive layer becomes less than the reference value, it is determined that the life of the photoconductor has expired, and the photoconductor is replaced. Conventionally, the film thickness used for determining the life of the photosensitive layer is measured by the methods described in Patent Documents 1 and 2, for example. The measurement method of Patent Document 1 uses the fact that the current value flowing into the photosensitive layer changes with a predetermined relationship depending on the film thickness of the photosensitive layer, measures the inflow current value to the photoconductor, and based on the measured value. This is a method for measuring the film thickness. The measuring method of Patent Document 2 is a method of measuring the current flowing through the photosensitive layer and measuring the film thickness of the photosensitive layer from the measurement result.

JP-A-9-179559 JP 2011-13431 A

  However, since the value of the current flowing through the photosensitive layer varies depending on the use environment and use state, the measurement method described in Patent Document 2 described above cannot accurately measure the film thickness. In addition, the measurement method described in Patent Document 1 is applied to a photoconductor in which the relationship between the voltage applied to the photoconductor and the current value of the photosensitive layer is constant even when the use environment or use state changes. For example, the present invention is applied to a so-called multi-layered photoreceptor or a photoreceptor composed of amorphous silicon. Therefore, a photoreceptor having a single photosensitive layer on its surface (hereinafter referred to as a “single-layer photoreceptor”) changes the voltage applied to the photoreceptor and the current value of the photosensitive layer when the usage environment or usage state changes. Therefore, the measurement method disclosed in Patent Document 2 cannot be applied to the single-layer photoconductor. For this reason, the conventional measurement method cannot accurately measure the film thickness of the photosensitive layer of the single-layer photoconductor, and cannot accurately determine the lifetime (replacement time) of the single-layer photoconductor.

  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 accurately measuring the thickness of a single photosensitive layer provided on the surface of a photoreceptor, and a photosensitive It is to provide a method for measuring the thickness of a layer.

The image forming apparatus of the present invention includes a photoconductor, a DC voltage supply unit, an AC voltage supply unit, a current value detection unit, an effective value change unit, and a film thickness measurement unit. The photoreceptor is provided with a single photosensitive layer on the surface. The DC voltage supply unit applies a DC voltage having a constant voltage value to the photosensitive layer. The AC voltage supply unit applies an AC voltage to the photosensitive layer by superimposing the AC voltage on the DC voltage. The current value detection unit detects a DC current value flowing through the photosensitive layer when the DC voltage and the AC voltage are applied. The effective value changing unit increases the effective value of the AC voltage stepwise. The film thickness measurement unit changes the effective value when the amount of change in the detection value by the current value detection unit in response to an increase in the effective value of the AC voltage is equal to or greater than a predetermined first threshold value. The film thickness of the photosensitive layer is determined based on the effective value of the AC voltage before the change by the unit.
The method for measuring the film thickness of the photosensitive layer of the present invention includes the following first to fourth steps. In the first step, a DC voltage having a constant voltage value is applied to a single photosensitive layer provided on the photosensitive member. In the second step, an AC voltage whose effective value increases stepwise is superimposed on the DC voltage and applied to the photosensitive layer. The third step detects the value of a direct current flowing through the photosensitive layer while the effective value is increased by the second step. The fourth step corresponds to the detection value when a fluctuation amount in which the detection value in the third step fluctuates in accordance with an increase in the effective value of the AC voltage becomes equal to or more than a predetermined first threshold value. The film thickness of the photosensitive layer is determined based on the effective value of the AC voltage.

  According to the present invention, the film thickness of a single photosensitive layer in a photoconductor can be accurately measured even when the use environment or use state changes. This makes it possible to accurately determine the life of the photoreceptor.

FIG. 1 is a diagram schematically illustrating a schematic configuration of a multifunction peripheral according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration around the photosensitive drum of the multifunction machine shown in FIG. FIG. 3 is a block diagram illustrating a configuration of a control unit and a power supply system of the multifunction peripheral illustrated in FIG. FIG. 4 is a graph showing the relationship between the surface potential, the applied AC voltage, and the current value flowing through the photosensitive layer in the photosensitive drum shown in FIG. 5A is a graph showing the relationship between the AC voltage applied to the photosensitive drum shown in FIG. 2 and the film thickness of the photosensitive layer, and FIG. 5B is a graph showing the relationship between the photosensitive drum shown in FIG. It is table data which shows the correspondence of the alternating voltage applied and the film thickness of a photosensitive layer. FIG. 6 is a flowchart showing the procedure of the film thickness measurement process executed by the control unit shown in FIG.

  Embodiments of the present invention will be described below with reference to the drawings as appropriate. In addition, the following 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 material) 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 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 supply unit 57 that supplies a transfer voltage to the transfer device 34, a charged voltage supply unit 52 that supplies a voltage to the charging device 32, and a photoconductor. A current value detection unit 59 (an example of a current value detection unit of the present invention) that detects a direct current flowing in the photosensitive layer of the drum 31 and a control unit 62 that controls the entire multifunction device 1 are provided. .

  As shown in FIG. 1, the paper feed cassette 25 is provided below the image forming unit. 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 (sheet materials) 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. A conventional organic photosensitive drum has a three-layer structure of an undercoat layer, a charge generation layer, and a charge transport layer from the inside, whereas the photosensitive drum 31 of the present embodiment has functions such as charge generation and charge transport. Is realized with only a single photosensitive layer. Therefore, stable quality image formation is possible as long as all the photosensitive layer is not worn.

  A charging device 32, a developing device 33, a transfer device 34, and a cleaning blade 35 are arranged 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 charges the outer peripheral surface of the photosensitive drum 31 to have a surface potential with a predetermined polarity in accordance with a predetermined voltage supplied from an after-mentioned voltage supply unit 52. 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. When a voltage is applied from the charged voltage supply unit 52 to the photosensitive drum 31 via the charging roller 32A, the photosensitive layer of the photosensitive drum 31 is charged to a surface potential corresponding to the applied voltage. The charging device 2 is not limited to a contact type using the charging roller 32A, and may be a non-contact type. Any type of charging device can be applied as long as it charges the photosensitive layer on the surface of the photosensitive drum 31.

  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. A constant current having a predetermined value is supplied from the transfer voltage supply unit 57 to the transfer roller 34A. As a result, when the printing paper is nipped at the nip portion between the photosensitive drum 31 and the transfer roller 34A, the toner on the photosensitive drum 32 adheres to the surface of the printing paper.

  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 38 and a pressure roller 39 disposed to face the heating roller 38. 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.

[Electrostatic voltage supply unit 52]
The charged voltage supply unit 52 supplies a DC voltage or an AC voltage to the charging roller 32 </ b> A according to a control signal from the control unit 62. As shown in FIG. 3, the charged voltage supply unit 52 includes a DC voltage supply circuit 53 (an example of the DC voltage supply unit of the present invention), an AC voltage supply circuit 54 (an example of the AC voltage supply unit of the present invention), and Have

  The DC voltage supply circuit 53 applies a DC voltage having a constant voltage value to the photosensitive layer of the photosensitive drum 31 through the charging roller 32A to charge the photosensitive layer 31. The voltage output from the DC voltage supply circuit 53 is controlled by a control signal input from the control unit 62. Specifically, when the DC voltage supply circuit 53 receives a predetermined control signal from the control unit 62, the DC voltage supply circuit 53 converts the DC voltage supplied from the DC power supply 63 into a constant voltage corresponding to the control signal, thereby charging the charging device. It outputs to 32 charging rollers 32A. In the present embodiment, the DC voltage supply circuit 53 is a measurement required for a film thickness measurement process described later according to a predetermined control signal input when the multi-function device 1 is in a film thickness measurement mode described later. DC voltage (for example, voltage of DC 500 [V]) is supplied to the charging roller 32A. The film thickness measurement mode is an operation mode of the multifunction device 1 that is shifted when a film thickness measurement process (described later) for measuring the film thickness of the photosensitive layer of the photosensitive drum 31 is executed. The multi function device 1 operates in one of an operation mode of the film thickness measurement mode and an image forming mode described later. The DC voltage supply circuit 53 is a charging DC voltage (for example, required for image formation) according to a predetermined control signal input when the multifunction device 1 is in an image forming mode capable of forming an image on a printing paper. DC voltage of 1000 [V] to 1200 [V]) is supplied to the charging roller 32A.

  The AC voltage supply circuit 54 superimposes the AC voltage on the DC voltage output from the DC voltage supply circuit 53 via the charging roller 32 </ b> A and applies the AC voltage to the photosensitive layer of the photosensitive drum 31 for charging. The voltage output from the AC voltage supply circuit 54 is controlled by a control signal input from the control unit 62. Specifically, upon receiving a predetermined control signal from the control unit 62, the AC voltage supply circuit 54 converts the AC voltage supplied from the AC power supply 64 into an AC voltage having an effective value corresponding to the control signal. Output to the charging roller 32 </ b> A of the charging device 32. In the present embodiment, the AC voltage supply circuit 54 is used for measurement that is required in the film thickness measurement process described later in accordance with a predetermined control signal that is input when the multifunction device 1 is in the film thickness measurement mode. An AC voltage is supplied to the charging roller 32A. When the multifunction device 1 is in the image forming mode, the AC voltage supply circuit 54 is controlled by the control unit 62 so as not to supply the AC voltage to the charging roller 32A.

The current value detection unit 59 detects a DC current value flowing through the photosensitive layer when a DC voltage and an AC voltage are applied to the photosensitive layer of the photosensitive drum 31. The current value 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 value detection unit 59 is connected to the control unit 62, and the detection value (current value) detected by the current value detection unit 59 is sent to the control unit 62 and used for film thickness measurement processing described later.

  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 ROM 62B stores a program for executing an image forming process for printing paper, a program for executing a film thickness measurement process described later, and the like. The CPU 62A executes the image forming process and the film thickness measuring process by executing these programs.

  In this embodiment, the control part 62 functions as an effective value change part of this invention by performing the below-mentioned film thickness measurement process. That is, the control unit 62 changes the effective value of the AC voltage supplied from the AC voltage supply circuit 53 to the charging roller 32A. Specifically, the control unit 62 outputs to the AC voltage supply circuit 53 a control signal for increasing the effective value stepwise within the range of 0 [V] to 2000 [V]. Upon receiving this control signal, the AC voltage supply circuit 53 changes the effective value of the output AC voltage stepwise from 0 [V] to 2000 [V] according to the control signal.

Moreover, the control part 62 functions as a film thickness measurement part of this invention by performing the below-mentioned film thickness measurement process. That is, when the detection value by the current value detection unit 59 varies in accordance with the change in the effective value of the AC voltage supplied to the charging roller 32A, the control unit 62 has a variation amount equal to or greater than a predetermined first threshold value. When the fluctuation amount is equal to or greater than the first threshold value, the film thickness of the photosensitive layer of the photosensitive drum 31 is determined based on the effective value of the AC voltage before the change. A specific determination method will be described later.

Moreover, the control part 62 functions as a replacement time determination part of this invention by performing the below-mentioned film thickness measurement process. That is, the control unit 62 determines that it is time to replace the photosensitive drum 31, that is, that the lifetime has expired, when the determined film thickness of the photosensitive layer is equal to or less than a predetermined second threshold value. A specific determination method will be described later.

Moreover, the control part 62 functions as a voltage setting part of this invention by performing the below-mentioned film thickness measurement process. That is, the control unit 62 determines a voltage value corresponding to the determined film thickness, and sets the voltage value to be applied to the photosensitive layer of the photosensitive drum 31. A specific setting method will be described later.

  The ROM 62B of the control unit 62 is an example of a first storage unit and a second storage unit according to the present invention, and includes a first threshold value, a second threshold value, and table data 76 (FIG. 5 ( B) and the like) are stored.

  Hereinafter, with reference to FIG. 4, the property of the photosensitive layer having a single layer structure provided in the photosensitive drum 31 will be described. In the photosensitive layer having a single layer structure provided in the photosensitive drum 31 of the present embodiment, the capacitor effect of the photosensitive layer composed of a plurality of layers does not occur. Here, the capacitor effect in the photosensitive layer means that in a plurality of photosensitive layers, a pseudo capacitor is formed between the layers, and the photosensitive layer itself functions as a capacitor. Therefore, the capacitor effect does not occur in the photosensitive layer having a single layer structure. Therefore, when a constant DC voltage is applied to the photosensitive layer having a single layer structure, and the effective value of the AC voltage is increased stepwise from 0 [V], as shown in FIG. The potential does not follow the saturation curve, but at first, it rises rapidly, and when it reaches a certain potential, the potential drops. That is, when the voltage value of the AC voltage is gradually increased, an inflection point (see 71A and 72A in FIG. 4) appears where the potential of the photosensitive layer starts to decrease. A curve 71 and a curve 72 in FIG. 4 show the charging potential when the AC voltage is increased stepwise while a constant DC voltage is applied to the photosensitive layer having a single layer structure. The characteristic of the photosensitive layer having a thickness of 38 μm is shown, and the curve 72 shows the characteristic of the photosensitive layer having a thickness of 19 μm.

  The above phenomenon occurs because the negative voltage value of the AC voltage is larger than the voltage value of the DC voltage, and both are canceled out, thereby substantially reducing the charging potential. As shown in FIG. 4, the voltage value (effective value) of the AC voltage when the inflection points 71A and 71B appear is determined by the charging potential (surface potential) of the photosensitive layer charged by the applied DC voltage. The Since the charging potential of the photosensitive layer is an element determined by the film thickness of the photosensitive layer, it can be said that the voltage value of the alternating voltage when the inflection point appears is determined by the film thickness of the photosensitive layer.

  Actually, a constant DC voltage (for example, 500 [V]) is applied to the photosensitive layer with a film thickness of 38 μm and the photosensitive layer with a film thickness of 19 μm, and the effective value of the AC voltage is gradually increased from 0 [V]. When an experiment was performed to increase the voltage, an inflection point 71A appeared at an AC voltage of 1500 [V] in the photosensitive layer having a film thickness of 38 μm as shown by a curve 71 in FIG. As can be seen, in the photosensitive layer having a film thickness of 19 μm, the inflection point 72A appears at an AC voltage of 1200 [V]. Further, in the experiment, as shown in FIG. 4, the value of the direct current flowing through the photosensitive layer increases in proportion to the alternating voltage, and after the inflection point, the photosensitivity increases as the charging potential decreases. It was confirmed that the rate of increase in the current value of the photosensitive layer increased rapidly because the current flowed easily through the layer. For example, in the experiment, as shown by the broken line 73 in FIG. 4, the rate of increase (variation) in the current value of the photosensitive layer with a film thickness of 38 μm is the AC voltage 1500 [V] at the inflection point 71A. It was confirmed that the current value Ia was gently inclined until the current value Ia was detected, but the inclination increased thereafter. Further, as shown by the broken line 74 in FIG. 4, the rate of increase (variation) of the current value of the photosensitive layer having a film thickness of 19 μm is the current value Ib (when the AC voltage is 1500 [V] at the inflection point 72A). It was confirmed that the slope was gently inclined until> Ia) was detected, but thereafter, the slope increased.

  In the present embodiment, by performing the above-described experiment on photosensitive layers having various thicknesses, the correspondence between the voltage value of the AC voltage superimposed on a constant DC voltage and the thickness of the photosensitive layer (the first embodiment of the present invention). 5 (A) and FIG. 5 (B)) are acquired, and a film thickness measurement process described later is performed based on this correspondence. In addition, the voltage value of the applied voltage at which the charging voltage in the photosensitive layer having various thicknesses becomes constant is measured in advance for each film thickness by experiments or the like, and the correspondence relationship between the applied voltage and the film thickness (second of the present invention). The film thickness measurement process described later is performed based on the correspondence relationship (see FIG. 5B). These correspondences are stored in the ROM 62A of the control unit 62 as the table data 76 shown in FIG.

  Next, the film thickness measurement method of the present invention will be described along with the procedure of the film thickness measurement process 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 film thickness measurement request is input to the multifunction device 1. Here, the film thickness measurement request includes, for example, that the main power supply of the multifunction device 1 has been turned on, a film thickness measurement instruction has been input to the multifunction device 1, and the cumulative number of prints has reached a preset number. In other words, the condition that the operation time of the multifunction device 1 has reached a preset time is satisfied. By measuring the film thickness of the photosensitive layer when such a condition is satisfied, the accurate film thickness can be measured according to the use environment and use situation of the multifunction machine 1. When the film thickness measurement request is input, the control unit 62 switches the operation mode of the multifunction machine 1 from the image forming mode to the film thickness measurement mode for measuring the film thickness of the photosensitive layer of the photosensitive drum 31.

  In the next step S <b> 12, the controller 62 applies a DC voltage having a constant voltage value to the photosensitive layer of the photosensitive drum 31 to charge the photosensitive layer. That is, the control unit 62 uses a DC voltage of DC 500 [V] (hereinafter referred to as “DC voltage for measurement”) as a DC voltage for measurement for measuring the film thickness of the photosensitive layer. To supply. Specifically, the control unit 62 outputs a control signal that causes the DC voltage supply circuit 53 to supply the DC voltage for measurement. By receiving this control signal, the DC voltage supply circuit 53 supplies the DC voltage for measurement to the charging roller 32A. Here, step S12 is an example of the first step of the present invention.

  In step S <b> 13, the control unit 62 applies an alternating voltage whose effective value is increased stepwise to the photosensitive layer of the photosensitive drum 31 by superimposing the alternating voltage on the measurement direct-current voltage. That is, the control unit 62 uses, as the AC voltage for measurement, an AC voltage whose effective value increases stepwise in the range from 0 [V] to 2000 [V] (hereinafter referred to as “measuring AC voltage”). It is superimposed on the direct current voltage and supplied to the charging roller 32A. Specifically, the control unit 62 outputs a control signal that causes the AC voltage supply circuit 54 to supply the AC voltage for measurement. This control signal is an instruction signal for increasing the effective value of the AC voltage step by step. By receiving this control signal, the AC voltage supply circuit 54 supplies the DC voltage for measurement to the charging roller 32A so that the effective value gradually increases from 0 [V]. Here, step S13 is an example of the second step of the present invention. Moreover, the control part 62 which performs step S13 is an example of the effective value change part of this invention.

  In next step S <b> 14, the control unit 62 detects the current value of the DC voltage flowing through the photosensitive layer from the detection value input from the current value detection unit 59. Then, based on the detected current value, a fluctuation amount of the current value that fluctuates in accordance with an increase in the effective value of the AC voltage is calculated. Specifically, a current value gradient indicating a fluctuation amount of the current value with respect to the elapsed time is calculated based on the detected current value. Here, step S14 is an example of a third step of the present invention.

In the next step S15, the control unit 62 determines whether or not the current value gradient calculated in step S14 is equal to or greater than a predetermined first threshold value. Here, the first threshold value is a threshold value for determining that the current value gradient has changed. For example, the value of the current value gradient calculated immediately after shifting to the film thickness measurement mode can be used as the first threshold value. By adopting such a first threshold value, it can be determined whether or not the current value gradient has changed. When it is determined that the current value gradient is equal to or greater than the first threshold value, the control unit 62 determines the photosensitive drum 31 based on the effective value of the AC voltage corresponding to the current value at the time when the current value gradient changes. The thickness of the photosensitive layer is determined (S16). Specifically, the control unit 62 determines the film thickness corresponding to the effective value of the AC voltage corresponding to the current value at the time when the current value gradient changes from the table data 76 (see FIG. 5B) in the ROM 62B. To extract. For example, when the effective value is 1200 [V], the corresponding film thickness 19 [μm] is extracted from the table data 79. When the effective value is 1000 [V], the film thickness 38 [μm] corresponding to the effective value is extracted from the table data 76. The film thickness extracted in this way is the film thickness of the photosensitive layer of the photosensitive drum 31. Here, steps S14 and S15 are an example of the fourth step of the present invention. Moreover, the control part 62 which performs step S14 and S15 is an example of the film thickness measurement part of this invention. In step S15, when the current gradient is less than the first threshold value, the process returns to step S14, and the processes after step S14 are repeated.

  In the next step S17, the control unit 62 determines whether or not the film thickness extracted in step S16 is equal to or less than a predetermined second threshold value. Here, the second threshold value is a threshold value for determining whether or not the photosensitive layer of the photosensitive drum 31 is worn to such an extent that the predetermined print quality cannot be maintained. For example, it is conceivable that the minimum film thickness that can maintain the print quality is measured in advance by an experiment or the like, and the measurement result is used as the second threshold value. If it is determined that the film thickness is equal to or less than the second threshold value, the control unit 62 proceeds to step S18 and outputs message information indicating that the photosensitive drum 31 is in the replacement period. For example, when the second threshold value is 19 [μm], the message information is output when the film thickness extracted in step S16 is determined to be 19 [μm]. The message information is output to, for example, an operation panel (not shown) of the multifunction device 1 or an external information processing apparatus connected to the multifunction device 1 by communication. After outputting the message information, the control unit 62 proceeds to step S19. Here, the control part 62 which performs step S17 and S18 is an example of the replacement time determination part of this invention. In step S17, if the extracted film thickness is larger than the second threshold value, and if the current gradient is less than the first threshold value, the controller 62 causes the photosensitive drum 31 to be replaced at the replacement time. It is determined that the number has not been reached, and the process proceeds to step S19.

In the next step 19, the voltage value of the applied voltage corresponding to the film thickness extracted in step S 16 is extracted from the table data 76 (see FIG. 5B) in the ROM 62 B, and the extracted voltage value is the photoreceptor. The applied voltage is set to be applied to the photosensitive layer of the drum 31. Specifically, the DC voltage of the extracted voltage value is set to a voltage value supplied from the DC voltage supply circuit 53. For example, when the film thickness extracted in step S16 is 19 [μm], the corresponding applied voltage 1000 [V] is set. The film thickness extracted in step S16 is 38 [μm.
], The corresponding applied voltage 1200 [V] is set. When the operation mode of the multifunction device 1 returns to the image forming mode, the control unit 62 generates a control signal for outputting a DC voltage having the voltage value set in step S19, and at a timing necessary for image formation. The control signal is output to the DC voltage supply circuit 53. Here, the control part 62 which performs step S19 is an example of the voltage setting part of this invention.

  Subsequently, the control unit 62 stops the supply of the AC voltage from the AC voltage supply circuit 54 and returns the operation mode of the multifunction machine 1 from the film thickness measurement mode to the image forming mode (S20). That is, when the multifunction device 1 is in the image forming mode, the AC voltage is not supplied to the charging roller 32A. Thereby, the film thickness measurement process performed in the film thickness measurement mode ends.

As described above, in the present embodiment, when the film thickness measurement processing is executed by the control unit 62, the measurement AC at the inflection point where the charged potential of the photosensitive layer changes from rising to falling in the film thickness measurement mode. The effective value of the voltage is specified, the film thickness corresponding to the effective value is extracted, and the extracted film thickness is measured as the film thickness of the photosensitive layer. Therefore, the film thickness of the photosensitive layer having a single layer structure on the photosensitive drum 31 can be accurately measured. In particular, the effective value of the AC voltage for measurement is not used in the image forming mode of the multifunction machine 1 and is not easily affected by the use environment or use conditions. Therefore, in the present embodiment, the actual film thickness of the photosensitive layer can be accurately measured from the effective value of the AC voltage for measurement regardless of the use environment or use situation.

  In addition, since the replacement time of the photosensitive drum 31 is determined based on the measured film thickness, the user can recognize the accurate replacement time of the photosensitive drum 31 in the multifunction machine 1. Further, the photosensitive drum 31 can be used without waste until the lifetime of the photosensitive drum 31 is exhausted.

  In addition, since the optimum applied voltage is set for the charging potential of the photosensitive drum 31 based on the measured film thickness, the charging potential of the photosensitive drum 31 is always stably maintained at a predetermined setting potential. be able to. This prevents variations in print quality due to variations in charging potential, and stabilizes print quality.

1: MFP 10: image reading unit 22: image forming unit 31: photosensitive drum 32: charging device 33: developing device 34: transfer device 39: exposure device 52: charging voltage supply unit 53: DC voltage supply circuit 54: AC Voltage supply circuit 59: current value detection unit 62: control unit

Claims (6)

A photoreceptor having a single photosensitive layer on its surface;
A DC voltage supply unit for applying a DC voltage having a constant voltage value to the photosensitive layer;
An AC voltage supply unit for applying an AC voltage to the photosensitive layer by superimposing the AC voltage on the DC voltage;
A current value detection unit for detecting a direct current value flowing in the photosensitive layer when the direct current voltage and the alternating current voltage are applied;
An effective value changing unit for gradually increasing the effective value of the AC voltage;
The AC before the change by the effective value change unit when the amount of change in the detection value by the current value detection unit according to the increase of the effective value of the AC voltage becomes equal to or greater than a predetermined first threshold. And a film thickness measuring unit that determines a film thickness of the photosensitive layer based on an effective value of the voltage. A first storage unit that stores first correspondence information indicating a correspondence relationship between the effective value of the AC voltage and the film thickness of the photosensitive layer;
The film thickness measurement unit corresponds to the effective value of the AC voltage before the change by the effective value change unit when the fluctuation amount of the detection value by the current value detection unit is equal to or greater than the first threshold value. The image forming apparatus according to claim 1, wherein the film thickness of the photosensitive layer is extracted from the first correspondence information in the first storage unit. 3. The replacement time determination unit according to claim 1, further comprising a replacement time determination unit that determines that the photoconductor is a replacement time when a film thickness determined by the film thickness measurement unit is equal to or less than a predetermined second threshold value. The image forming apparatus described. A second storage unit that stores second correspondence information indicating a correspondence relationship between a film thickness of the photosensitive layer and a voltage value of a DC voltage applied to the photosensitive layer during image formation;
A voltage setting unit that extracts the voltage value corresponding to the film thickness determined by the film thickness measurement unit from the second correspondence information of the second storage unit and sets the voltage to the photosensitive layer; The image forming apparatus according to claim 1, further comprising an image forming apparatus. The image forming apparatus operates in one of a film thickness measurement mode for measuring the film thickness of the photosensitive layer and an image formation mode for forming an image by applying a DC voltage necessary for image formation to the photosensitive layer. Is,
The effective value changing unit changes the effective value of the AC voltage within a predetermined range during the film thickness measurement mode, and stops the application of the AC voltage during the image forming mode. The image forming apparatus according to any one of the above. A first step of applying a DC voltage having a constant voltage value to a single photosensitive layer provided on the photoreceptor;
A second step of applying an alternating voltage, whose effective value increases stepwise, to the photosensitive layer by superimposing the alternating voltage on the direct current voltage;
A third step of detecting a direct current value flowing through the photosensitive layer during the increase of the effective value in the second step;
The effective value of the AC voltage corresponding to the detected value when the amount of change in the detected value in the third step according to the increase in the effective value of the AC voltage is equal to or greater than a predetermined first threshold value. And a fourth step of determining the film thickness of the photosensitive layer based on the method.

Images