JP6617579B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a composite machine of these, and in particular, when a charging voltage in which a DC voltage and an AC voltage are superimposed is applied to the photosensitive body, the photosensitive layer of the photosensitive body. This is characterized in that the peak-to-peak voltage of the AC voltage is controlled in accordance with the film thickness to suppress the deterioration of film thickness unevenness.

  Conventionally, in an image forming apparatus such as a copying machine or a printer, toner is supplied from a developing device to an electrostatic latent image formed on a photoconductor to develop the electrostatic latent image formed on the photoconductor. ing. Further, residual toner is removed from the surface of the photoconductor by a cleaning device having a cleaning blade after transferring the toner image.

  According to the number of printed sheets, the photosensitive layer on the surface of the photosensitive member is scraped by the cleaning blade in contact with the photosensitive member, and the thickness of the photosensitive layer is reduced. When the photosensitive layer on the surface of the photosensitive member is charged with a charging voltage obtained by superimposing an AC voltage on a DC voltage, the amount of abrasion of the photosensitive layer increases as the amplitude of the charging voltage, that is, the peak voltage (Vpp) of the AC voltage increases. growing. This is because overloading increases the load applied to the photosensitive layer on the surface of the photoreceptor at the time of discharging, so that the photosensitive layer is easily scraped.

  On the other hand, if the peak-to-peak voltage (Vpp) of the AC voltage is too low, the photosensitive layer on the surface of the photosensitive member becomes insufficiently charged and image defects occur. For this reason, it is desirable to set the peak-to-peak voltage (Vpp) of the AC voltage as low as possible within a range where no image defect occurs. Here, the peak-to-peak voltage (Vpp) of the AC voltage suitable for image formation that does not cause insufficient charging and does not cause image defects varies depending on the film thickness of the photosensitive layer, and becomes smaller as the photosensitive film has a thinner photosensitive layer. Become. FIG. 13 shows the relationship between the film thickness of the photosensitive layer and the peak-to-peak voltage (Vpp) of the AC voltage suitable for image formation.

  However, since the film thickness of the photosensitive layer on the surface of the photoconductor is not necessarily uniform, an AC voltage with a constant peak-to-peak voltage (Vpp) is superimposed on the DC voltage and charged on the photoconductor with uneven film thickness. In such a case, the load on the surface of the photosensitive layer is increased where the photosensitive layer is thin, and the amount of abrasion of the photosensitive layer is increased. For this reason, the film thickness is further reduced where the film thickness is thin, and the unevenness of the film thickness increases.

  Here, FIG. 14 shows an initial state in which an AC voltage having a constant peak-to-peak voltage (Vpp) is superimposed on a DC voltage and charged when there is unevenness in the film thickness of the photosensitive layer in the circumferential direction of the photoreceptor. It shows the relationship of film thickness unevenness at the end of durability. In FIG. 14, the upward direction of the arrow indicates that the photosensitive layer is thick. When charging is performed by superimposing an alternating voltage with a constant peak-to-peak voltage (Vpp), an overdischarged state occurs at a portion where the film thickness is thin, and the load on the surface of the photosensitive layer increases. As a result, the shaving amount of the photosensitive layer is increased, the film thickness is gradually reduced, and the unevenness of the film thickness of the photosensitive layer is deteriorated. As shown in FIG. 14, at the end of the durability compared with the initial state, many portions where the photosensitive layer is thin are scraped, and the unevenness of the photosensitive layer is aggravated.

  As described above, when the photosensitive layer of the photoconductor is uneven, a difference occurs in the abrasion amount of the photoconductive layer of the photoconductor by superimposing an alternating voltage with a constant peak-to-peak voltage (Vpp) on the DC voltage. Unevenness of film thickness worsens. Conventionally, it has been dealt with so as not to cause a quality problem by exchanging the photoconductor while the film thickness unevenness of the photosensitive layer is slight. However, due to the recent increase in durability, a photosensitive member having a thick photosensitive layer has been used, so that at the end of the durability of the photosensitive member, unevenness in the thickness of the photosensitive layer becomes significant, resulting in a quality defect. There is a problem that occurs.

  On the other hand, even when the film thickness of the photosensitive layer is large, an image forming apparatus in which an optimum charging voltage is installed has been proposed (for example, see Patent Document 1).

  In this patent document 1, the peak-to-peak voltage (Vpp) of the alternating voltage superimposed on the direct current voltage is set according to the amount of change in the film thickness of the photosensitive layer depending on the usage frequency of the photosensitive member, and along the axial direction of the photosensitive member. Therefore, even if the film thickness varies, charging failure is prevented from occurring at a portion where the film thickness becomes thick. That is, in this Patent Document 1, when the film thickness of the photosensitive layer varies in the axial direction of the photoconductor, the peak-to-peak voltage (Vpp) of the AC voltage is prevented so that a portion having a large film thickness does not cause charging failure. Is set. For this reason, in the part where the film thickness of the photosensitive layer is thin, an overdischarge state occurs, the load on the surface of the photosensitive layer increases, and there is a problem that the amount of abrasion of the photosensitive layer increases.

JP2015-152850A

  Therefore, the present invention detects the film thickness in the circumferential direction of the photosensitive layer of the photoconductor, and controls the peak-to-peak voltage of the AC voltage in the charging voltage in the circumferential direction according to the film thickness. It is an object of the present invention to prevent deterioration in film thickness unevenness of the photosensitive layer by preventing the charging voltage from being excessive in a portion having a small thickness.

  In the image forming apparatus of the present invention, in order to solve the above-described problems, a photosensitive member provided with a photosensitive layer, a charging device for charging the photosensitive layer, and a charging voltage obtained by superimposing a DC voltage and an AC voltage. Is applied to the charging device, an exposure device that exposes the photosensitive layer according to image information, a cleaning device that cleans the surface of the photosensitive layer, and a circumferential position of the photoconductor. A position detecting unit that detects the film thickness of the photosensitive layer in the circumferential direction of the photoconductor based on the output of the position detecting unit and the output of the current measuring unit. A thickness detection unit, and a control unit that controls a peak-to-peak voltage of the AC voltage applied to the charging device, the control unit based on an output of the film thickness detection unit, the film in the circumferential direction of the photosensitive layer Applied to the charging device according to thickness And controlling the peak-to-peak voltage of the AC voltage that.

  In the present invention, the control unit controls the peak-to-peak voltage of the AC voltage of the charging power source unit according to the film thickness of the photosensitive layer at the position in the circumferential direction of the photoconductor determined by the film thickness detection unit. Control is performed so that the charged potential at the portion where the photosensitive layer is thin is not excessive. For this reason, an increase in the load on the photosensitive layer is suppressed, and an increase in the amount of abrasion of the photosensitive layer can be prevented.

  Further, when determining the film thickness of the photosensitive layer in the circumferential direction of the photoconductor, a position detection unit for detecting the circumferential position of the photoconductor and a current measurement unit for detecting the amount of current flowing through the photoconductor are provided. The film thickness detection means can determine the film thickness of the photosensitive layer in the circumferential direction of the photoconductor based on the output of the position detection unit and the output of the current measurement unit.

  The controller is provided with means for controlling the exposure amount of the exposure apparatus, and the controller controls the peak-to-peak voltage of the AC voltage that acts on the photosensitive member at a position where the photosensitive layer is thin. It is preferable to control so as to lower the voltage between the peaks of the AC voltage corresponding to the average film thickness and to increase the exposure amount at that position. As described above, in the portion where the film thickness of the photosensitive layer is small, the voltage between the peaks of the AC voltage is lowered, while the exposure amount is increased to suppress the abrasion of the photosensitive layer and to keep the charged potential level in the image portion constant. Thus, density unevenness can be eliminated.

  The position detection unit may include a rotary encoder attached to the photoconductor, and may be configured to detect a circumferential position of the photoconductor based on the output of the rotary encoder.

  In the case where a transfer belt to which the toner image formed on the surface of the photosensitive layer is transferred is provided, the position detection unit has a detection sensor for detecting the toner image transferred to the transfer belt, A toner image for position start point detection is formed on the photosensitive layer, the toner image for position start point detection transferred to the transfer belt is detected by the detection sensor, and the toner image for position start point detection is detected by the detection sensor. Based on this, the position detection unit can be configured to detect the circumferential position of the photoconductor.

  Further, when a contact charging roller is used in the charging device, the current measuring unit can calculate the film thickness based on the current value flowing between the photoconductor and the contact charging roller.

  Further, when a transfer belt on which the toner image formed on the surface of the photoconductor is transferred is provided, the current measurement unit calculates the film thickness based on the value of the current flowing through the photoconductor through the transfer belt. Can be configured to

  According to the present invention, by controlling the peak-to-peak voltage of the AC voltage applied to the charging device in accordance with the film thickness in the circumferential direction of the photoconductor, the charging potential at the portion where the film thickness of the photosensitive layer is thin becomes excessive. Prevents the photosensitive layer from increasing in load, prevents the photosensitive layer from being scraped off, and prevents the photosensitive layer from becoming uneven.

1 is a schematic explanatory diagram illustrating an internal structure of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic explanatory view showing an imaging cartridge using a developing device according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a circuit configuration of a charge control portion of the image forming apparatus illustrated in FIG. 1. In the above embodiment, the initial state and the state after endurance when the peak-to-peak voltage (Vpp) of the AC voltage is changed corresponding to the unevenness of the film thickness of the photosensitive layer in the circumferential direction of the photoreceptor are shown. It is explanatory drawing. In the above-described embodiment, the relationship between the exposure amount and the charging potential of the image portion when the peak-to-peak voltage (Vpp) of the AC voltage is changed corresponding to the uneven thickness of the photosensitive layer in the circumferential direction of the photoreceptor. It is a schematic explanatory drawing shown. In the above-described embodiment, the relationship between the peak voltage (Vpp) of the AC voltage and the charging potential of the image portion when the exposure amount is controlled corresponding to the unevenness of the film thickness of the photosensitive layer in the circumferential direction of the photosensitive member is shown. FIG. In the embodiment of the present invention, it is a schematic explanatory view showing an example of the film thickness profile of the photosensitive layer in the photoreceptor. In embodiment of this invention, it is the schematic explanatory drawing which showed an example of the profile of the correction amount of the peak voltage (Vpp) of the alternating voltage applied to a contact charging roller. In the embodiment of the present invention, it is a schematic explanatory diagram showing an example of the exposure amount correction amount profile. 4 is a flowchart of a detection control operation for detecting a film thickness of a photosensitive layer and correcting a peak-to-peak voltage and an exposure correction amount in one embodiment of the present invention. FIG. 5 is a block diagram illustrating a first modification of the circuit configuration of a charging control portion of the image forming apparatus illustrated in FIG. 1. FIG. 10 is a block diagram illustrating a second modification of the circuit configuration of the charge control portion of the image forming apparatus illustrated in FIG. 1. It is explanatory drawing which shows the relationship between the film thickness of the photosensitive layer of a photoreceptor, and the peak-to-peak voltage (Vpp) of the alternating voltage suitable for image formation. FIG. 5 is a schematic explanatory diagram showing an initial state and a state after endurance in a conventional example in which a constant peak voltage (Vpp) is applied when the film thickness of the photosensitive layer is uneven in the circumferential direction of the photoreceptor. is there.

  Next, an image forming apparatus according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. The image forming apparatus according to the present invention is not limited to the one shown in the following embodiment, and can be implemented with appropriate modifications within a range not changing the gist thereof.

  First, the overall configuration of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG. In the image forming apparatus of this embodiment, as shown in FIG. 1, four imaging cartridges 10 </ b> A to 10 </ b> D are mounted in the image forming apparatus 1.

  Here, in each of the imaging cartridges 10A to 10D, the photosensitive member 11, the charging device 12 for charging the surface of the photosensitive layer 11a of the photosensitive member 11, and the electrostatic latent image formed on the surface of the photosensitive layer 11a. A developing device 20 for supplying a toner to the surface of the photosensitive layer 11a and a cleaning device for removing the toner remaining after the toner image formed on the surface of the photosensitive layer 11a is transferred to the intermediate transfer belt 2 from the surface of the photosensitive layer 11a. A device 14 is provided. The surface of the charged photosensitive layer 11a is exposed according to image information from the exposure device 50, and an electrostatic latent image is formed on the surface of the photosensitive layer 11a. The exposure apparatus 50 performs exposure using, for example, a laser diode (light source) and a polygon mirror. The laser beam modulated in accordance with the image signal from the laser diode is scanned by the polygon mirror and irradiated onto the photosensitive layer 11a of the photosensitive member 11. The amount of exposure can be changed by changing the amount of current applied to the laser diode.

  In the image forming apparatus according to this embodiment, when full color image formation is performed, each developing device 20 in each of the imaging cartridges 10A to 10D has different colors of black, yellow, magenta, and cyan. The toner is accommodated, and a toner image of each color is formed on the surface of the photosensitive layer 11a of each photoconductor 11 in each of the imaging cartridges 10A to 10D.

  Next, the toner images of each color formed on the surface of the photosensitive layer 11a of the photosensitive member 11 in each of the imaging cartridges 10A to 10D in this manner are sequentially transferred to the intermediate transfer belt 2 by the primary transfer roller 13, respectively. A full-color toner image is formed on the intermediate transfer belt 2.

  On the other hand, the recording medium S is fed by the paper feed roller 3, and this recording medium S is guided between the intermediate transfer belt 2 and the transfer roller 5 at an appropriate timing by the timing roller 4, and on the intermediate transfer belt 2. The formed full color toner image is transferred to the recording medium S, while the toner remaining on the intermediate transfer belt 2 without being transferred to the recording medium S is removed from the intermediate transfer belt 2 by the belt cleaning device 6. .

  Then, the recording medium S on which the full-color toner image is transferred as described above is guided to the fixing device 7, and after fixing the full-color toner image on the recording medium S, the recording medium S is discharged by the paper discharge roller 8. The paper is discharged.

  The image forming apparatus is not limited to the one described above, and although not shown in the drawing, a rotary developing device holding a plurality of developing devices is rotated to sequentially guide each developing device to the photoreceptor. Thus, a full-color image forming apparatus configured to perform full-color image formation or an image forming apparatus performing black-and-white image formation may be used.

  Next, the imaging cartridges 10A to 10D in this embodiment will be specifically described. As shown in FIG. 2, the imaging cartridges 10 </ b> A to 10 </ b> D are composed of a developing device 20 and a photoreceptor unit 110.

  The photoconductor unit 110 includes a photoconductor 11, a charging device 12, and a cleaning device 14 including a cleaning blade 14a. The charging device 12 includes a contact charging roller 12a as a contact charging member and a cleaning roller 12b as a cleaning member for cleaning the surface of the contact charging roller 12a. The charging device 12 is provided with a charging voltage obtained by superimposing an AC voltage on a DC voltage.

  In the developing device 20, a developer containing toner and carrier is used. Here, in the developing device 20, as shown in FIG. 2, the developing roller 22 as a developing carrier having a magnet member 22 b provided on the inner peripheral side opposes the photoconductor 11 with a required interval. It is provided as follows. The developing roller 22 has a nonmagnetic cylindrical sleeve 22a. In the magnet member 22b, for example, five magnets are arranged along the peripheral surface at a predetermined interval.

  Further, in the developing device 20, as shown in FIG. 2, a first transport unit 23 for transporting the developer along the developing roller 22 is provided in the device main body 21. A first stirring member 24 provided with a screw-like blade member that transports the developer while being mixed and stirred around the rotation shaft is provided in the transport unit 23. And the 2nd conveyance part 26 which conveys the 1st conveyance part 23 and the above-mentioned developer in the reverse direction via the partition 25 under this 1st conveyance part 23 is provided, and in this 2nd conveyance part 26, A second stirring member 27 provided with a screw-like blade member that transports the developer while being mixed and stirred is provided around the rotation shaft.

  Further, a circulation port (see FIG. 5) for communicating the first transport unit 23 and the second transport unit 26 with an end of a partition wall 25 provided between the first transport unit 23 and the second transport unit 26. The developer is circulated between the first conveyance unit 23 and the second conveyance unit 26 through these circulation ports.

  Further, in the developing device 20, the first stirring member 24 rotates the first stirring member 24 provided in the first transport unit 23 to transport the developer while mixing and stirring the developing roller. The developer is supplied onto the cylindrical sleeve 22 a of 22, and the amount of developer conveyed is regulated by the regulating member 29 while the developer thus supplied is conveyed to a position facing the photoreceptor 11 by the developing roller 22. It is trying to regulate by. Then, the developer whose amount is regulated in this way is guided to the position facing the photoconductor 11 by the developing roller 22, and the toner in the developer is supplied to the photoconductor 11 to be formed on the photosensitive layer 11 a of the photoconductor 11. The developed electrostatic latent image is developed.

  As described above, the toner image formed on the surface of the photosensitive layer 11a of the photoreceptor 11 is transferred to the intermediate transfer belt 2, and the residual toner remaining on the photosensitive layer 11a is transferred to the cleaning device 14 provided with the cleaning blade 14a. To be removed.

  For example, the photoreceptor 11 has a configuration in which an undercoat layer and a photosensitive layer 11a for forming an electrostatic latent image are sequentially laminated on the outer surface of a conductive support. The photosensitive layer 11a of the photoreceptor 11 has a function-separated layer structure in which a charge generation layer having a charge generation function and a charge transport layer having a charge transport function are stacked.

  As shown in FIG. 3, a charging voltage obtained by superimposing an AC voltage on a DC voltage is applied to the contact charging roller 12 a of the charging device 12 by a charging power supply unit 250. The charging power supply unit 250 includes a DC power supply unit 251 for applying a DC voltage, an AC power supply unit 252 for applying an AC voltage to be superimposed on the DC voltage of the DC power supply unit 251, and a current for measuring a current value flowing through the contact charging roller 12a. A measurement unit 253.

  The control unit 200 controls each unit of the image forming apparatus 1 and gives a control signal to the charging power source unit 250 so as to set a charging voltage to be applied to the charging device 12. In order to set the charging voltage to be applied to the charging device 12, the control unit 200 sets a DC voltage by the DC power supply unit 251 and a peak-to-peak voltage (Vpp) of the AC voltage by the AC power supply unit 252. The peak-to-peak voltage (Vpp) of the AC voltage is set based on the peak-to-peak voltage (Vpp) of the AC voltage suitable for image formation corresponding to the average film thickness of the photoconductor 11.

  The control unit 200 receives an output from a position detection unit 280 that detects the circumferential position of the photoconductor 11. Based on the output of the position detection unit 280, the circumferential position of the photoconductor 11 is detected. Is calculated. The position detector 280 is provided with a rotary encoder (not shown) attached to the photoconductor 11, and a position in the circumferential direction of the photoconductor 11, that is, a rotation from the start of rotation, according to the output of the rotary encoder accompanying the rotation of the photoconductor 11. The direction position is output to the control unit 200 as angle information. The control unit 200 calculates position information at the time of detecting the film thickness of the photosensitive layer 11 a of the photoconductor 11 based on the output of the position detection unit 280.

  The control unit 200 receives the current value measured by the current measuring unit 253, detects the current value flowing through the photoconductor 11 and the contact charging roller 12a, and based on the detected result, the photoconductive layer 11a of the photoconductor 11. The film thickness is detected. The control unit 200, the position detection unit 280, and the current measurement unit 253 constitute a film thickness detection unit that detects the film thickness of the photosensitive layer 11 a in the circumferential direction of the photoconductor 11. That is, the control unit 200 calculates the film thickness of the photosensitive layer 11 a based on the current value of the current measurement unit 253 at the circumferential position of the photoconductor 11 detected by the position detection unit 280, and the circumferential position of the photoconductor 11. Is stored in the memory 290.

  In this way, the film thickness is calculated for one rotation of the photoconductor 11, and the film thickness profile in the circumferential direction of the photosensitive layer 11a is stored in the memory 290. For the film thickness profile, the control unit 200 sets the correction amount of the peak-to-peak voltage (Vpp) of the alternating voltage of the charging potential applied to the contact charging roller 12a according to the film thickness in the circumferential direction of the photoconductor 11. The correction data is calculated and stored in the memory 290.

  Further, the control unit 200 controls the transfer power supply unit 260 that supplies a voltage to be applied to the primary transfer roller 13, and causes the transfer power supply unit 260 to apply an appropriate transfer voltage to the primary transfer roller 13.

  Further, the control unit 200 controls the exposure power supply unit 270 in order to control the light amount of the exposure apparatus 50. That is, the control unit 200 controls the exposure power source unit 270 according to the film thickness of the photosensitive layer 11a in the photoreceptor 11, and appropriately controls the exposure amount from the exposure device 50 to the photosensitive layer 11a. Here, a reference supply voltage is set to, for example, 1000 mV according to the average film thickness of the photosensitive layer 11a, and a correction voltage for correcting the supply voltage based on a deviation in film thickness in the circumferential direction with respect to the average film thickness of the photosensitive layer 11a. Is calculated, and the control unit 200 controls the exposure power supply unit 270 so as to control the exposure amount according to the film thickness in the circumferential direction of the photosensitive layer 11a.

  Next, when applying the charging voltage from the charging power supply unit 250 to the contact charging roller 12a, the AC voltage from the AC power supply unit 252 is changed to the DC voltage output from the DC power supply unit 251 as shown in FIG. The superimposed charging voltage is applied from the charging power supply unit 250 to the contact charging roller 12a, and the photosensitive layer 11a on the surface of the rotating photoconductor 11 is charged to a predetermined potential.

  Here, the control unit 200 determines the DC voltage value of the DC voltage applied from the DC power supply unit 251 to the contact charging roller 12a and the peak-to-peak voltage (Vpp) of the AC voltage applied from the AC power supply unit 252 to the contact charging roller 12a. Control.

  The current measuring unit 253 measures the value of the current flowing through the contact charging roller 12 a via the photoconductor 11. The data of the current value measured by the current measurement unit 253 is input to the control unit 200, and the control unit 200 calculates the film thickness of the photosensitive layer 11a from the output of the current measurement unit 253. The calculated film thickness is related to the position of the photoconductor 11 by the position information from the position detection unit 280.

  The control unit 200 changes the peak-to-peak voltage (Vpp) of the alternating voltage applied during image formation according to the film thickness of the photosensitive layer 11a of the photoconductor 11, so that the photosensitive layer 11a is not overcharged. Is determined. The control unit 200 calculates the film thickness of the photosensitive layer 11a of the photoconductor 11 based on the current value information input from the current measurement unit 253, and is applied to the contact charging roller 12a by the calculated film thickness profile. An appropriate peak-to-peak voltage (Vpp) of the AC voltage is set.

In the system in which an AC voltage is superimposed on a DC voltage and applied to the contact charging roller 12a of the charging device 12 to charge the photoconductor 11, a positive side is provided between the contact charging roller 12a and the photoconductor 11. Discharge and negative discharge occur alternately, and the surface of the photosensitive layer 11a of the photoconductor 11 is uniformly charged. Further, during normal image formation, the DC voltage applied from the DC power supply unit 251 to the contact charging roller 12a is determined according to conditions determined by image density control or the like.
The peak-to-peak voltage (Vpp) is controlled.

  Further, as shown in FIG. 13, the image forming apparatus 1 has a peak-to-peak voltage (Vpp) of an AC voltage that is optimal at the time of image formation with respect to the film thickness of the photosensitive layer 11 a of the photoreceptor 11. Reference numeral 200 sets a peak-to-peak voltage (Vpp) of the reference AC voltage based on the average film thickness of the photosensitive layer 11a, and the photosensitive layer 11 of the photoconductor 11 with respect to the peak-to-peak voltage of the reference AC voltage. In response to the difference in the film thickness in the circumferential direction, the peak voltage (Vpp) of the AC voltage is corrected and the control of the charging power supply unit 250 is executed.

  Here, as shown in FIGS. 1 to 3, the cleaning device 14 brings a cleaning blade 14 a into contact with the surface of the photosensitive member 11, and residual toner remaining on the photosensitive layer 11 a without being transferred to the intermediate transfer belt 2. In this case, the photosensitive layer 11a on the surface of the photoconductor 11 is scraped by rubbing or the like with the cleaning blade 14a, and the film thickness of the photosensitive layer 11a gradually decreases as image formation increases. To go.

  Here, as described above, when the film thickness of the photosensitive layer 11a on the surface of the photoconductor 11 is uneven in the circumferential direction, when an AC voltage having a constant peak-to-peak voltage (Vpp) is applied to the photoconductor 11, In a portion where the film thickness is thin, the charging potential is high. Therefore, the load on the surface of the photosensitive layer 11a is large, the amount of shaving of the photosensitive layer 11a is increased, the film thickness is gradually reduced, and the unevenness of the film thickness of the photosensitive layer 11a is deteriorated.

  In this embodiment, as shown in FIG. 3, the direct current that flows when the photosensitive member 11 is charged is measured by the current measuring unit 253, and based on this current value, the control unit 200 The film thickness of the photosensitive layer 11a of the photoconductor 11 is calculated.

  Here, when the film thickness of the photosensitive layer 11a of the photoconductor 11 is reduced, the electrostatic capacity of the surface of the photoconductor 11 is increased, and it is necessary for charging the photoconductor 11 from the neutralized state to a predetermined charging potential. The current increases. For this reason, the film thickness of the photosensitive layer 11 a can be detected by measuring the direct current that flows when the photosensitive member 11 is charged by the current measuring unit 253.

  Then, a charging voltage obtained by superimposing an AC voltage on a DC voltage is applied from the charging power supply unit 250 to the contact charging roller 12a in contact with the photoconductor 11. The film thickness of the photosensitive layer 11a of the photoconductor 11 is detected by detecting the amount of current flowing from the contact charging roller 12a to the photoconductor 11 when the surface of the photoconductor 11 is charged to a predetermined potential by the current measuring unit 253. . The control unit 200 calculates the current film thickness of the photosensitive layer 11a of the photoconductor 11 based on the measured value.

  As shown in FIG. 4, the control unit 200 changes the peak-to-peak voltage (Vpp) of the AC power supply unit 250 according to the detected circumferential film thickness of the photosensitive layer 11a. That is, the peak-to-peak voltage (Vpp) at a position where the film thickness of the photosensitive layer 11a is thin is lowered to control the charging potential so as not to be excessive, so that the film thickness is not increased. By controlling in this way, control is performed so that unevenness in film thickness does not deteriorate even at the end of durability.

  FIG. 7 shows an example in which the change in the film thickness in the circumferential direction of the photosensitive layer 11a of the photoconductor 11 is measured based on the data from the position detection unit 280 and the data from the current measurement unit 253 given to the control unit 200. . The average film thickness of the photosensitive layer 11a is set to 0, and the nonuniformity of the film thickness of the photosensitive layer 11a is measured as the (+) direction and the (−) direction for one rotation of the photoreceptor 11, and the measurement result is stored in the memory 290. To do.

  The control unit 200 sets the peak-to-peak voltage (Vpp) of the AC voltage that is optimal for image formation during image formation corresponding to the average film thickness of the photosensitive layer 11a.

  Next, the control unit 200 calculates the difference from the average film thickness based on the measurement result of the film thickness unevenness of the photosensitive layer 11a measured as described above, and calculates the average film based on the difference from the average film thickness. An amplitude amount (Vpp correction amount) of the peak-to-peak voltage (Vpp) to be corrected is calculated from the peak-to-peak voltage (Vpp) corresponding to the thickness. Then, the Vpp correction amount corresponding to the film thickness unevenness in the circumferential direction in the calculated photosensitive layer 11 a shown in FIG. 7 is calculated, and the result is stored in the memory 290.

  Then, as shown in FIG. 8, the control unit 200 makes the Vpp correction amount (+) between the peaks of the AC voltage at a location where the film thickness of the photosensitive layer 11a shown in FIG. 7 is larger than the average film thickness. While increasing the voltage (Vpp), in the portion where the film thickness of the photosensitive layer 11a shown in FIG. 7 is smaller than the average film thickness, the Vpp correction amount is set to (−) and the peak voltage (Vpp) of the AC voltage is decreased. To do.

  In this way, the load applied to the surface of the photosensitive layer 11a is reduced in the portion where the film thickness of the photosensitive layer 11a is smaller than the average film thickness, compared to the portion where the film thickness of the photosensitive layer 11a is thicker than the average film thickness. The film thickness unevenness of the photosensitive layer 11a in the circumferential direction of the photoconductor 11 is suppressed.

  Here, when the peak-to-peak voltage (Vpp) of the AC voltage applied from the AC power supply unit 252 is corrected in this way, the DC voltage applied from the DC power supply unit 251 is corrected according to the film thickness of the photosensitive layer 11a. Not performed. The reason for this is that when the DC voltage correction control is performed according to the film thickness of the photosensitive layer 11a, the charging potential Vo of the non-image portion is not constant, and the noise of the non-image portion is deteriorated.

  However, in the case where the control is performed not to correct the DC voltage applied from the DC power supply unit 251 while correcting the peak-to-peak voltage (Vpp) of the AC voltage applied from the AC power supply unit 252 as shown in FIG. As shown in FIG. 4, when the photosensitive layer 11a is irradiated with a constant amount of light, the charged potential Vi of the image portion is not constant due to the electrostatic capacity depending on the film thickness of the photosensitive layer 11a. There will be a difference.

  For this reason, in this embodiment, as shown in FIG. 6, since the film thickness of the photosensitive layer 11a is thin, the exposure amount from the exposure device 50 is set at a location where the peak voltage (Vpp) of the AC voltage is reduced. In many cases, the charging potential Vi of the image portion is made constant.

  Specifically, when the correction amount of the peak-to-peak voltage (Vpp) of the AC voltage shown in FIG. 8 is set with respect to the calculated film thickness of FIG. 9, the voltage value output from the exposure power supply unit 270 to the exposure apparatus 50 in the circumferential direction of the photoconductor 11 is used as the reference exposure voltage at the portion where the film thickness of the photosensitive layer 11 a becomes the average film thickness. On the other hand, the voltage value output to the exposure apparatus 50 is corrected as the exposure correction amount (mV) in accordance with the film thickness of the photosensitive layer 11a. In a portion where the photosensitive layer 11a is thick and the peak-to-peak voltage (Vpp) of the AC voltage is corrected to the (+) side, the exposure correction amount (mV) is set to (−) in order to reduce the exposure amount. On the other hand, in the portion where the photosensitive layer 11a is thin and the peak-to-peak voltage (Vpp) is corrected to the (−) side, the exposure correction amount (mV) is set to (+) in order to increase the exposure amount. The charging potential Vi of the image portion is made constant so as to eliminate the occurrence of density unevenness.

  Here, in the image forming apparatus 1, the detection of the film thickness of the photosensitive layer 11 a in the photoconductor 11, the Vpp correction amount in the peak voltage (Vpp) of the AC voltage, and the exposure power output from the exposure power supply unit 270 to the exposure apparatus 50. The calculation control of the exposure correction amount (mV) at the voltage is executed, for example, at a preparation stage when the image forming apparatus 1 is started up, or the image interval is increased and interrupted every time a predetermined number (for example, 1000) of images is formed. To be executed.

  Next, in the image forming apparatus 1, the detection of the film thickness of the photosensitive layer 11 a in the photosensitive member 11, the Vpp correction amount in the peak-to-peak voltage (Vpp) of the AC voltage, and the exposure power output from the exposure power supply unit 270 to the exposure device 50. The calculation control of the exposure correction amount (mV) at the voltage will be described with reference to FIG.

  When the film thickness detection operation is started, in step S1, the control unit 200 controls the DC power supply unit 251 so that the DC voltage applied to the contact charging roller 12a is set to a constant voltage, and is superimposed on the DC voltage. The AC power supply unit 252 is controlled so that the peak-to-peak voltage (Vpp) of the AC voltage is also set to a constant voltage.

  In step S2, a charging potential obtained by superimposing a constant AC voltage on a constant DC voltage is applied to the contact charging roller 12a, the photoconductor 11 is rotated once, and a current value is measured by the current measuring unit 253. The position information is detected by the position detection unit 280, and these data are sent to the control unit 200 and stored in the memory 290.

  Subsequently, in step S <b> 3, the control unit 200 calculates the film thickness of the photosensitive layer 11 a of the photoconductor 11 based on the measured value for one rotation of the photoconductor 11 read from the memory 290. In step S 4, the calculated film thickness value is stored in the memory 290 in association with the position information of the photoconductor 11.

  In step S5, an average film thickness of the calculated photosensitive layer 11a is obtained, and a difference between the average film thickness and the calculated film thickness is calculated. In this embodiment, a film thickness profile of the average film thickness and the differential film thickness of the photosensitive layer 11a is obtained corresponding to the angle of one round of the photoconductor 11 as shown in FIG.

  Subsequently, in step S <b> 6, the control unit 200 sequentially reads out a difference value of the film thickness from 0 ° to 360 ° in the circumferential direction of the photoconductor 11 from the memory 290. In step S7, it is determined whether or not the difference of the photosensitive layer 11a at the read position is equal to or smaller than a predetermined value, for example, 0.5 μm. If the difference is equal to or smaller than the predetermined value, the process proceeds to step S10 without correction. In step S10, it is determined whether or not the reading of data for one rotation of the photoconductor 11 has been completed. If the reading has not been completed, the process returns to step S6 to read the difference value of the film thickness at the next position. .

  In step S7, when the control unit 200 determines that the read difference value exceeds the predetermined value, the process proceeds to step S8. In step S8, based on the read difference value of the film thickness, the control unit 200 calculates the Vpp correction amount (V) and the exposure correction amount (mV) in the peak-to-peak voltage (Vpp) of the AC voltage.

  In step S <b> 9, the control unit 200 stores the calculated Vpp correction amount (V) and exposure correction amount (mV) in the memory 290.

  Subsequently, in step S10, it is determined whether or not the reading of data for one rotation of the photoconductor 11 has been completed. If it has not been completed, the process returns to step S6, and the above operation is performed for one rotation of the photoconductor 11. Repeat until minutes are finished. In this way, the Vpp correction amount (V) profile in the peak-to-peak voltage (Vpp) of the AC voltage applied to the contact charging roller 12a shown in FIGS. 8 and 9 and the exposure correction in the exposure voltage output to the exposure apparatus 50. A quantity (mV) profile is calculated and this value is stored in the memory 290.

  When the reading of data for one rotation of the photoconductor 11 is completed, the film thickness detection operation is completed (step S11), and the AC is detected together with the film thickness detection of the photoconductive layer 11a of the photoconductor 11 in the image forming apparatus 1. The calculation operation of the Vpp correction amount (V) at the peak-to-peak voltage (Vpp) and the exposure correction amount (mV) at the exposure voltage output to the exposure apparatus 50 ends.

  Then, the result of detecting the film thickness in the circumferential direction of the photosensitive layer 11a in the photosensitive member 11 obtained by this calculation control operation, the Vpp correction amount (V) in the peak-to-peak voltage (Vpp) of the AC voltage, and the output to the exposure device 50. Based on the exposure correction amount (mV) in the exposure voltage, the control unit 200 controls the charging power source unit 250 to control the charging potential for the contact charging roller 12a. The control unit 200 also controls the exposure power supply unit 270 to control the exposure amount of the exposure apparatus 50. As described above, the peak-to-peak voltage (Vpp) of the AC voltage and the exposure amount are controlled according to the film thickness of the photosensitive layer 11a of the photoconductor 11, and an image is formed.

  FIG. 11 is a block diagram showing a first modification of the circuit configuration of the charging control portion. Here, in the circuit configuration shown in FIG. 3, the position of the photoconductor 11 is detected by a rotary encoder provided on the photoconductor 11. In the configuration shown in FIG. 11, the position detection unit 280 uses an IDC sensor 281. Position detection.

  Then, immediately after the end of the film thickness detection operation, the position detection unit 280 forms a start point position detection toner image on the photoconductor 11, and transfers the start point position detection toner image to the intermediate transfer belt 2. A position detection toner image is detected by a detection sensor 281. In this embodiment, an IDC sensor is used as the detection sensor 281. The position detection unit 280 detects the position information of the photoconductor 11 from the timing at which the film thickness detection operation ends and the timing at which the detection sensor 281 detects the position detection toner image. The control unit 200 stores the position information of the position detection unit 280 and the film thickness at the position in the memory 290 in association with each other. Since the other configuration is the same as that of FIG. 4, the same reference numeral is given to the same configuration and the description is omitted to avoid duplication of description.

  FIG. 12 is a block diagram showing a second modification of the circuit configuration of the charging control portion. Here, in the circuit configuration shown in FIG. 3, the control unit 200 detects the film thickness of the photoconductor 11 based on the output from the current measuring unit 253 of the charging voltage applied to the contact charging roller 12a. In contrast, in the configuration shown in FIG. 12, the current of the transfer bias applied to the primary transfer roller 13 is measured by the current measuring unit 261, and the value of the current flowing through the photoconductor 11 through the intermediate transfer belt 2 is measured. The The measurement value is given to the control unit 200, and the control unit 200 calculates the film thickness of the photosensitive layer 11 a of the photoconductor 11 based on the output of the current measurement unit 261.

  In the configuration shown in FIG. 12, the film thickness of the photosensitive layer 11 a of the photosensitive member 11 is detected by driving the photosensitive member 11 once while applying a transfer current at a constant voltage, and performing photosensitivity via the intermediate transfer belt 2. The control unit 200 stores the current value profile flowing through the body 11 in the memory 290. In addition, the control unit 200 calculates a film thickness profile in the circumferential direction of the photosensitive layer 11 a of the photoconductor 11 from the measured current value profile, and stores it in the memory 290 in association with the position information of the photoconductor 11. Since the other configuration is the same as that of FIG. 4, the same reference numeral is given to the same configuration and the description is omitted to avoid duplication of description.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Intermediate transfer belt 3 Paper feed roller 4 Timing roller 5 Transfer roller 6 Belt cleaning device 7 Fixing device 8 Paper discharge roller 10A Imaging cartridge 10B Imaging cartridge 10C Imaging cartridge 10D Imaging cartridge 11 Photoconductor 11a Photosensitive layer 12 Charging device 12a Contact charging roller 13 Primary transfer roller 14 Cleaning device 14a Cleaning blade 20 Developing device 22 Developing roller 50 Exposure device 200 Control unit 250 Charging power source unit 251 DC power source unit 252 AC power source unit 253 Current measuring unit 260 Transfer power source unit 270 Exposure power source unit 280 Position detection unit 290 Memory

Claims (7)

A photosensitive member provided with a photosensitive layer, a charging device for charging the photosensitive layer, a charging power supply unit for applying a charging voltage obtained by superimposing a DC voltage and an AC voltage to the charging device, and the photosensitive layer according to image information. An exposure apparatus for performing exposure, a cleaning apparatus for cleaning the surface of the photosensitive layer, a film thickness detecting means for determining a film thickness of the photosensitive layer in the circumferential direction of the photosensitive member, and a peak of an AC voltage applied to the charging device A control unit for controlling the voltage between,
The control unit controls the peak-to-peak voltage of the AC voltage applied to the charging device according to the film thickness in the circumferential direction of the photosensitive layer based on the output of the film thickness detecting means. .   The image forming apparatus according to claim 1, further comprising: a position detection unit that detects a circumferential position of the photoconductor; and a current measurement unit that detects an amount of current flowing through the photoconductor, and the film thickness detection unit. The image forming apparatus is characterized in that the film thickness of the photosensitive layer in the circumferential direction of the photosensitive member is obtained based on the output of the position detecting unit and the output of the current measuring unit. The image forming apparatus according to claim 2 , wherein the position detection unit includes a rotary encoder attached to the photoconductor, and detects a circumferential position of the photoconductor based on an output of the rotary encoder. Image forming apparatus. The image forming apparatus according to claim 2 , further comprising a transfer belt to which a toner image formed on the surface of the photosensitive layer is transferred, wherein the position detection unit includes a detection sensor that detects an image transferred to the transfer belt. A position start point detection toner image is formed on the photosensitive layer, the position start point detection toner image transferred to the transfer belt is detected by the detection sensor, and the position detection unit detects the position start point by the detection sensor. An image forming apparatus for detecting a circumferential position of the photosensitive member based on a timing at which a detection toner image is detected. The image forming apparatus according to claim 2 , wherein the charging device includes a contact charging roller, and the current measuring unit detects a current value flowing between the photosensitive member and the contact charging roller. The image forming apparatus according to claim 2 , further comprising: a transfer belt to which a toner image formed on the surface of the photosensitive layer is transferred, wherein the current measuring unit calculates a current value flowing through the photoconductor via the transfer belt. An image forming apparatus characterized by detecting. The image forming apparatus according to claim 1 , wherein the control unit includes a unit that controls an exposure amount of the exposure apparatus, and the control unit is configured to control a photosensitive layer of the photoconductor. The peak-to-peak voltage of the AC voltage at the position where the film thickness is thin is made lower than the peak-to-peak voltage of the AC voltage corresponding to the average film thickness of the photosensitive layer, and the exposure amount at that position is controlled to increase. Image forming apparatus.

Images