JP2015007696A - Image forming apparatus and charging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to prevent reduction in image quality due to changes in thickness of an outer layer of an image holding body, and to provide a charging apparatus configured to prevent a charging failure due to changes in thickness of an outer layer of an object to be charged.SOLUTION: An image forming apparatus includes: a photoreceptor 102 having a film part 106 and holding an image; a charging member 204 having a part coming into contact with the photoreceptor 102 and another part forming a gap with the film part 106, to charge the film part 106; and support means 210 for supporting the charging member 204 so as to change at least one of a position and a size of the gap.

Description

  The present invention relates to an image forming apparatus and a charging device.

  In Patent Document 1, in a contact charging device that charges a photosensitive member by bringing the charging member into contact with the surface of the photosensitive member, the charging member is formed in a belt shape, and one end side of the belt-shaped charging member is wound up. A feeding roller for winding, a winding roller for winding the other end, and a conductive roller for bringing the belt-shaped charging member into contact with the surface of the photoreceptor and applying a voltage. A contact charging device is disclosed.

  In Patent Document 2, a charging electrode in which a semiconductive film-like member having flexibility is formed in a substantially cylindrical shape, and held inside the cylindrical charging electrode at a distance from the object to be charged, Insulating electrode support for supporting the charging electrode so that it moves around by an electrostatic force acting between the charged body and the charged electrode, with the peripheral surface of the charging electrode being in contact with the charged body A member, a feeding electrode that is pressed almost uniformly in the width direction from the outside of the charging electrode, and is supported so as to sandwich the charging electrode between the electrode supporting member and the charging electrode via the feeding electrode. There has been disclosed a charging device having a power source for applying a charging potential to an electrode.

JP-A-5-333665 Japanese Patent Laid-Open No. 10-239946

  The present invention relates to an image forming apparatus capable of suppressing deterioration in image quality associated with a change in the thickness of an outer layer of an image carrier, and a charging failure associated with a change in the thickness of an outer layer of an object to be charged. It is an object of the present invention to provide a charging device capable of suppressing the above.

  The present invention according to claim 1 has an outer layer, and an image holding body that holds an image, a part of the image holding body is in contact with the image holding body, and another part forms a gap between the outer layer, An image forming apparatus comprising: a charging member that charges the outer layer; and a support unit that supports the charging member so that at least one of a position of the gap and a size of the gap can be changed.

  According to a second aspect of the present invention, when the thickness of the outer layer is equal to or greater than a predetermined value, the supporting unit includes the charging member and the image holding body in the moving direction of the image holding body. When the gap is formed on the downstream side of the contact position where the contact is made and the thickness of the outer layer is smaller than the predetermined value, the gap is formed on the upstream side and the downstream side of the contact position in the moving direction. The image forming apparatus according to claim 1, wherein the charging member is supported so as to be formed.

  According to a third aspect of the present invention, the support means can change at least one of the position of the gap and the size of the gap according to the number of images formed using the image carrier. The image forming apparatus according to claim 1, wherein the charging member is supported on the image forming apparatus.

  According to a fourth aspect of the present invention, the charging member is a plate-like or film-like member that is in contact with the outer layer and forms a convex curved surface on the image carrier side, and the support means includes the charging member. The image forming apparatus according to claim 1, further comprising a moving mechanism that moves the image holding member.

  According to the fifth aspect of the present invention, there is provided a charging member that partially contacts an outer layer of an object to be charged and that forms a gap between the other part and the outer layer, and charges the outer layer, and the position of the gap And a supporting means for supporting the charging member so that at least one of the sizes of the gaps can be changed.

  According to the first aspect of the present invention, it is possible to provide an image forming apparatus capable of suppressing a decrease in image quality due to a change in the thickness of the outer layer of the image carrier.

  According to the second aspect of the present invention, it is possible to provide an image forming apparatus capable of suppressing deterioration in image quality due to wear of the outer layer of the image carrier.

  According to the third aspect of the present invention, there is provided an image forming apparatus capable of detecting the state of wear of the outer layer of the image carrier and suppressing deterioration in image quality due to wear of the outer layer of the image carrier. can do.

  According to the fourth aspect of the present invention, there is provided an image forming apparatus capable of suppressing a decrease in image quality due to a change in the outer layer of the image holding member with a simple configuration as compared with the case where the present configuration is not provided. be able to.

  According to the fifth aspect of the present invention, it is possible to provide a charging device that can suppress a charging failure associated with a change in the thickness of the outer layer of an object to be charged.

1 is a diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2A is a diagram showing a state where the charging member is in the first position, and FIG. 2B is a diagram where the charging member is in the second position. It is a figure which shows a certain state. FIG. 2 is a block diagram illustrating a control unit of the image forming apparatus illustrated in FIG. 1. A phenomenon that occurs when the photosensitive member is charged according to the position of the charging member and the film thickness of the photosensitive member included in the charging device illustrated in FIG. 2 will be described. FIG. 4A illustrates the charging member at the second position. FIG. 4B is a diagram illustrating a phenomenon that occurs when the film thickness of the photoconductor is relatively large. FIG. 4B is a diagram when the charging member is in the second position and the film thickness of the photoconductor is relatively small. FIG. 4C is a diagram for explaining a phenomenon that occurs when the charging member is in the first position and the film thickness of the photosensitive member is relatively small. 3 is a flowchart for explaining the operation of the image forming apparatus shown in FIG. 1. When the charging device shown in FIG. 2 performs the operation shown in the flowchart shown in FIG. 5 to charge the photosensitive member, whether or not a minute black line is generated in the image and potential unevenness are generated for each number of images formed. It is a chart shown. FIG. 5 is a diagram illustrating, for each number of sheets on which images are formed, whether minute black lines are generated in an image and potential unevenness is generated in the photoconductor when the photoconductor is charged by the charging device according to the first comparative example. FIG. 10 is a diagram showing, for each number of sheets on which images are formed, whether minute black lines are generated in an image and potential unevenness occurs in the photosensitive member when the photosensitive member is charged in a charging device according to a second comparative example. It is a figure which shows the charging device which the image forming apparatus which concerns on a 3rd comparative example has. 10 is a chart showing, for each number of sheets on which images are formed, whether minute black lines are generated in an image and potential unevenness is generated in the photosensitive member when the photosensitive member is charged in a charging device according to a third comparative example.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an image forming apparatus 10 according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 10 includes an image forming apparatus main body 12, and an image forming unit 100, a paper feeding apparatus 300, and a control apparatus 400 used as a control unit in the image forming apparatus main body 12. Is provided. In the image forming apparatus main body 12, a conveyance path 350 used for conveying a sheet used as a recording medium is formed. Further, the image forming apparatus main body 12 is formed with a discharge port 14 used for discharging the sheet.

  The image forming unit 100 forms, for example, a monochromatic image and employs an electrophotographic system. The image forming unit 100 irradiates light onto the surface of the photoconductor 102, the charging device 200 that charges the photoconductor 102, and the surface of the photoconductor 102 that is charged by the charging device 200. The latent image forming apparatus 110 for forming the photosensitive member 102, the latent image formed on the photosensitive member 102 is developed using a developer, and a developer image is formed on the surface of the photosensitive member 102. A transfer device 116 for transferring the developer image formed on the surface of the body 102 to the paper, a cleaning device 120 for cleaning the photoconductor 102 after the developer image is transferred to the paper by the transfer device 116, and a transfer device 116. And a fixing device 126 that fixes the developer image transferred onto the paper on the paper.

  The photosensitive member 102 has, for example, a cylindrical shape, and is used as an object to be charged and is also used as an image holding member that holds an image. The photosensitive member 102 includes a cylindrical base 104 made of, for example, aluminum, and the outer surface of the base 104 is covered with a film unit 106. The film part 106 is used as an outer layer and also as a charge holding part for holding charges. For example, the film part 106 is made of an organic photosensitive layer, and includes, for example, a charge generation material that generates charges and a resin as a binder. And a charge transport layer that includes a charge transport material that transports charges and that uses a resin as a final material, and may have an undercoat layer, a protective layer, and the like.

  The charging device 200 includes a charging member 204. A part of the charging member 204 is in contact with the photoconductor 102, and the other part forms a downstream gap S1 (see FIG. 2) and an upstream gap S2 (see FIG. 2) with the photoconductor 102. Form. Further, the charging member 204 is charged with, for example, a direct current voltage to charge the photosensitive member 102. Details of the charging device 200 will be described later.

  The developing device 114 includes a developing device main body 136, and a cylindrical developer conveying member 138 is attached to the developing device main body 136. Further, a developer including toner and a carrier is accommodated in the developing device main body 136, and the toner in the developer is conveyed toward the photosensitive member 102 by the developer conveying member 138.

  The transfer device 116 includes a transfer roll 118. The transfer roll 118 is disposed so as to be in contact with the photoconductor 102, for example, and is applied with a voltage for transfer and is used as a transfer member.

  The cleaning device 120 has a cleaning member 122. The cleaning member 122 has one end pressed against the photoconductor 102, removes toner and the like from the surface of the photoconductor 102 at the pressed end, and cleans the photoconductor 102. Since the cleaning member 122 is pressed against the photosensitive member 102 in this way, the film portion 106 of the photosensitive member 102 is worn by the cleaning member 122 as the number of images formed using the photosensitive member 102 increases. The thickness of the film part 106 is reduced. The film portion 106 is also worn by the developer conveying member 138, the transfer roll 118, and the charging member 204 coming into contact with the film portion 106.

  The fixing device 126 includes a heating roll 128 having a heat source therein, and a pressure roll 130 that comes into contact with the heating roll 128, and the toner transferred to the paper at the contact portion between the heating roll 128 and the pressure roll 130. Heat and press to fix the image on the paper.

  The paper feeding device 300 supplies paper toward the image forming unit 100. In addition, the paper feeding device 300 includes a paper storage container 302 that stores paper in a stacked state, and a delivery roll 304 that sends out the paper from the paper storage container 302.

  The conveyance path 350 conveys the sheet from the sheet feeding device 300 toward the transfer device 116, conveys the sheet from the transfer device 116 toward the fixing device 126, passes through the discharge port 14, and from the inside of the image forming apparatus main body 12. This is a conveyance path for conveying a sheet so as to discharge the sheet. The feed roll 304, the transport roll 354, the registration roll 356, the transfer device 116, and the fixing device 126 are arranged in this order along the transport path 350 from the upstream side in the paper transport direction.

  The registration roll 356 temporarily stops the movement of the leading end portion of the paper conveyed toward the contact position N1 where the photoconductor 102 and the transfer roll 118 are in contact with each other toward the contact position N1, and develops the photoconductor 102 on the photoconductor 102. The movement of the leading edge of the sheet toward the contact position N1 is resumed so as to coincide with the timing at which the agent image is formed.

  FIG. 2 shows a charging device 200. The charging device 200 includes the charging member 204 as described above. 2A shows the charging device 200 with the charging member 204 in the first position, and FIG. 2B shows the charging device 200 with the charging member 204 in the second position. Show.

  As shown in FIGS. 2A and 2B, the charging member 204 is formed of a curved plate-like member, for example, contacting the film portion 106 of the photoconductor 102 and protruding toward the photoconductor 102. The discharge surface 206 is a surface that is used as a curved surface and generates a discharge with respect to the photosensitive member 102. Further, the charging member 204 partially contacts the photoconductor 102 so as to form at least one of a downstream gap S1 and an upstream gap S2 that are, for example, wedge-shaped spaces. Has been placed. The charging member 204 is connected to a voltage applying device 270 for applying a DC voltage, for example, to the charging member 204. Thus, the charging member 204 is used as a charging electrode for charging the photosensitive member 102. Instead of using a plate-like member as the charging member 204, a film-like member may be used as the charging member 204.

  Further, the charging member 204 is supported by the supporting means 210. The support unit 210 is used as a support unit that supports the charging member 204 so that at least one of the position of the gap (the downstream gap S1 and the upstream gap S2) and the size of the gap can be changed. The support unit 210 is a support member 212 that is a member to which the charging member 204 is attached, and a moving mechanism that is used as a moving mechanism that moves the charging member 204 and the support member 212 together with the photosensitive member 102. 280.

  A driving source 282 made of, for example, a motor or a solenoid is connected to the moving mechanism 280, and the driving from the driving source 282 is transmitted to the supporting member 212, and the supporting member 212 and the charging member 204 are integrated as shown in FIG. ) To the second position shown in FIG. 2B. As the moving mechanism 280, for example, a mechanism having a cam, a mechanism having a crank, a mechanism having a link, or the like can be used.

  In the charging device 200, when the charging member 204 is in the first position shown in FIG. 2A, the moving direction of the photosensitive member 102 indicated by the arrow a in FIGS. 2A and 2B is obtained. The downstream gap S1 is formed downstream of the contact position N2 where the charging member 204 and the photosensitive member 102 are in contact with each other. Thus, in the state where the charging member 204 is in the first position, the upstream gap S2 is not formed. On the other hand, when the charging member 204 is positioned at the second position shown in FIG. 2B, a downstream gap S1 is formed on the downstream side of the contact position N2 in the moving direction of the photosensitive member indicated by the arrow a. At the same time, an upstream gap S2 is formed on the upstream side of the contact position N2 in the moving direction of the photosensitive member indicated by the arrow a.

  FIG. 3 is a block diagram showing the control device 400. The control device 400 is used as a control means for controlling the support means 210 so that at least one of the position of the gap (the downstream gap S1 and the upstream gap S2) and the size of the gap can be changed. Further, when the thickness of the film unit 106 is equal to or greater than a predetermined value, the control device 400 forms only the downstream side gap S1, and the thickness of the film unit 106 of the photoconductor 102 is determined in advance. When it is smaller than the predetermined value, it is used as a control means for controlling the support means 210 so as to form the downstream gap S1 and the upstream gap S2.

  As illustrated in FIG. 3, the control device 400 includes a control circuit 402 including a CPU or the like, for example, and an image signal is input to the control circuit 402 via the communication interface 404. The control circuit 402 counts the number of images formed using the photoconductor 102 from the start of use of the photoconductor 102 from the input image signal, and stores this value in the image number storage unit 406. Let Further, the image forming unit 100 and the moving mechanism 280 are controlled by the output from the control circuit 402.

  FIG. 4 illustrates a phenomenon that occurs when the photosensitive member 102 is charged in accordance with the position of the charging member 204 and the thickness of the film portion 106. FIG. FIG. 4B is a diagram for explaining a phenomenon that occurs when the thickness of the film portion 106 is relatively large at the position of FIG. 4, and FIG. 4B is a diagram in which the charging member 204 is at the second position and the thickness of the film portion 106 is compared. FIG. 4C is a diagram for explaining a phenomenon that occurs when the charging member 204 is in the first position and the thickness of the film portion 106 is relatively small. is there.

  As shown in FIG. 4A, when the thickness of the film portion 106 is large, the capacitance of the film portion 106 becomes smaller than when the thickness of the film portion 106 is thin. Therefore, abnormal discharge is likely to occur between the charging member 204 and the photosensitive member 102 as compared with the case where the film portion 106 is thin. When a DC bias is applied to the charging member 204 as the charging bias, it is known that abnormal discharge is unlikely to occur in the downstream gap S1, but abnormal discharge is likely to occur in the upstream gap S2. Therefore, as shown in FIG. 4A, the charging member 204 is disposed at the second position even though the film portion 106 is not worn so much and the thickness of the film portion 106 is relatively thick. Then, abnormal discharge occurs in the upstream gap S2, and there is a possibility that an image defect such as a minute black line occurs in an image formed due to the abnormal discharge may occur.

  As shown in FIG. 4B, when the thickness of the film portion 106 is small, the capacitance of the film portion 106 becomes larger than when the thickness of the film portion 106 is thick. For this reason, in order to sufficiently charge the film portion 106 having a relatively large capacitance, it is desirable to secure a sufficient region where discharge occurs between the charging member 204 and the photosensitive member 102. For this reason, when the film portion 106 is worn and the thickness of the film portion 106 is relatively thin, the charging member 204 is disposed at the second position as shown in FIG. It is desirable to form not only the downstream side gap S1 but also the upstream side gap S2 as a region where the above occurs.

  Therefore, as shown in FIG. 4B, when the thickness of the film portion 106 is small, the capacitance of the film portion 106 is larger than that when the thickness of the film portion 106 is large. Abnormal discharge hardly occurs in the gap S2, and even if the charging member 204 is disposed at the second position, image quality deterioration due to abnormal discharge occurring in the upstream gap S2 hardly occurs.

  As shown in FIG. 4C, when the thickness of the film portion 106 is small, the capacitance of the film portion 106 becomes larger than when the thickness of the film portion 106 is thick. Therefore, the charging member 204 is moved to the first position as shown in FIG. 4C even though the thickness of the film portion 106 is relatively thin and the capacitance of the film portion 106 is relatively large. If only the downstream gap S1 is formed as a region where discharge occurs, the film portion 106 may be insufficiently charged. If the charging of the film portion 106 is insufficient, uneven charging occurs in the film portion 106, and there is a possibility that an image formed due to the uneven charging is defective.

  FIG. 5 is a flowchart showing control by the control device 400. At the time when a series of controls is started, the charging member 204 is in the first position shown in FIG. For this reason, at the time when this control is started, only the downstream gap S1 is formed between the photosensitive member 102 and the charging member 204, and no upstream gap S2 is formed.

  When an image signal is input from the communication interface 404 and a series of controls starts, in step S10, the control device 400 determines that the number of images formed using the photosensitive member 102 after the start of use is a predetermined number. It is determined whether or not it is larger than a certain number N. If it is determined that the number of images formed using the photoconductor 102 is not larger than the number N, that is, the number of images formed using the photoconductor 102 is less than the number N. If a determination is made, the process proceeds to step S30. On the other hand, if it is determined in step S10 that the number of images formed using the photoreceptor 102 is greater than the number N, the process proceeds to step S20.

  Here, the predetermined number N is, for example, 100K (K is × 1000). The number N is the hardness of the film portion 106 of the photoconductor 102, the hardness of the cleaning member 122 of the cleaning device 120, the magnitude of the force pressing the cleaning member 122 against the photoconductor 102, and the like. For example, in this embodiment, the number N of images formed in which the thickness of the film part 106 having an initial thickness of 26 μm is 20 μm is N. It has been established.

  In step S20, the control device 400 controls the moving mechanism 280 to move the charging member 204 to the second position shown in FIG. As a result, both the downstream gap S1 and the upstream gap S2 are formed between the photosensitive member 102 and the charging member 204.

  In step S <b> 30, the control device 400 controls the image forming unit 100 to cause the image forming unit 100 to form an image.

  In step S40, the control device 400 determines whether the image formed in step S30 is the last image in a series of image forming operations from the image data or the like input from the communication interface 404. When the determination is made, the process returns to step S10. When the determination is made that the image is the last image, the control device 400 ends the series of controls.

  As described above, in the image forming apparatus 10, the position of the gap formed between the photoconductor 102 and the charging member 204 changes according to the change in the thickness of the film portion 106 of the photoconductor 102. It has become.

  FIG. 6 shows the thickness of the film portion 106 in the image forming apparatus 10 according to the present embodiment described above, the position of the gap formed between the photosensitive member 102 and the charging member 204, and the photosensitive member 102 with the charging device 200. Formation of an image after the use of the photoconductor 102 is started, whether or not a minute black line is generated in an image formed by the image forming apparatus 10 when the photoconductor 102 is charged, and whether or not potential unevenness occurs in the photoconductor 102. It is a chart shown for every number of sheets.

  The first column in FIG. 6 shows the number of images formed using the photoconductor 102 after the use of the photoconductor 102 is started. The second column in FIG. 6 shows the film thickness of the film part 106. Here, the thickness of the film portion 106 is the image formed when the film portion 106 is worn with use of the photoconductor 102 because the cleaning member 122 or the like is in contact with the photoconductor 102 as described above. As the number of increases, it becomes thinner. The third row in FIG. 6 shows the position of the gap formed by the photosensitive member 102 and the charging member 204. More specifically, whether or not the downstream gap S1 is formed and the upstream gap Whether or not S2 is formed is shown.

  Further, the fourth column in FIG. 6 indicates whether or not a minute black line is generated in the formed image. “◯” in the fourth column indicates that a minute black line has not occurred and the image quality is improved. Indicates that there is no problem. The fifth column in FIG. 6 shows the degree of potential unevenness in the photoconductor 102 when the photoconductor 102 is charged. “◯” in the fifth column indicates the potential unevenness in the photoconductor 102. Is 10 V or less, indicating that there is no problem in image quality in the formed image.

  As shown in FIG. 6, in the image forming apparatus 10, a minute black line is not generated when the number of images formed using the photosensitive member 102 is 100K or less. When the number of images formed using the photoreceptor 102 is 100K or less, the wear of the film part 106 has not progressed, the thickness of the film part 106 is relatively large, and the capacitance of the film part 106 is relatively high. Small. For this reason, compared with the case where the thickness of the film portion 106 is relatively thin and the capacitance of the film portion 106 is large, abnormal discharge is likely to occur between the charging member 204 and the photosensitive member 102, and this abnormal discharge is caused. It tends to occur in an image on which a minute black line is formed. When a DC bias is applied to the charging member 204 as the charging bias, abnormal discharge is likely to occur in a region upstream of the contact position N2, that is, the position of the upstream gap S2.

  In this image forming apparatus 10, when the number of images formed using the photosensitive member 102 is 100K or less, the charging member 204 is disposed at the first position shown in FIG. Thus, only the downstream gap S1 is formed, and the upstream gap S2, which is a region where abnormal discharge is particularly likely to occur, is not formed to suppress abnormal discharge and the occurrence of minute black lines due to abnormal discharge. Yes.

  Further, in the image forming apparatus 10, when the number of images formed using the photoconductor 102 is 100K or less, the potential unevenness of the photoconductor 102 is within a range in which no image quality problem occurs. This is because the film portion 106 is not worn, the film portion 106 is relatively thick, and the capacitance of the film portion 106 is relatively small. This is because even if the gap S <b> 2 is not formed, a sufficient charging region is secured to charge the photosensitive member 102 without potential unevenness.

  Further, in the image forming apparatus 10, when the number of images formed using the photosensitive member 102 is from 100K to 200K, the minute black line is formed despite the formation of the upstream gap S2, which is a region where abnormal discharge is likely to occur. Has not occurred. This is because the wear of the film portion 106 proceeds, the thickness of the film portion 106 becomes relatively thin, and the capacitance of the film portion 106 becomes relatively large. Therefore, the charging member 204 is shown in FIG. This is because abnormal discharge does not occur in the upstream gap S2 even if the upstream gap S2 is formed by moving to the second position.

  Further, in the image forming apparatus 10, when the number of images formed using the photosensitive member 102 is from 100K to 200K, the potential unevenness of the photosensitive member 102 is in a range where no image quality problem occurs. When the number of images formed using the photoconductor 102 is from 100K to 200K, the wear of the film portion 106 proceeds, the thickness of the film portion 106 becomes relatively thin, and the capacitance of the film portion 106 becomes relatively small. Therefore, the photosensitive member 102 is likely to have uneven potential.

  For this reason, in the image forming apparatus 10, when the number of images formed using the photoconductor 102 is 100K to 200K, the upstream side gap S2 is formed together with the downstream side gap S1, and the photosensitive member 102 is moved in the moving direction. Increasing the charging area for charging the photoconductor 102 prevents potential unevenness of the photoconductor 102 from occurring.

  FIG. 7 shows the thickness of the film portion 106 in the image forming apparatus 10 (not shown) according to the first comparative example, the position of the gap formed by the photosensitive member 102 and the charging member 204, and the photosensitive member by the charging device 200. Whether or not a minute black line is generated in an image formed by the image forming apparatus 10 when the image forming apparatus 10 is charged and whether or not potential unevenness occurs in the image forming apparatus 10 are determined for each number of images formed using the image forming apparatus 102. It is a chart shown.

  In the image forming apparatus 10 according to the embodiment of the present invention described above, only the downstream gap S1 is formed until the number of images formed using the photoconductor 102 is 100K or less, and the image formed using the photoconductor 102 is formed. Both the downstream side gap S1 and the upstream side gap S2 were formed from 100K to 200K. On the other hand, in the image forming apparatus 10 according to the first comparative example, as shown in the third column of FIG. 7, even when the number of images formed using the photoconductor 102 is 100K or less, the photoconductor. Even when the number of images formed using 102 is 100K to 200K, only the downstream gap S1 is formed, and the upstream gap S2 is not formed. Except for the above points, the image forming apparatus 10 according to the first comparative example is the same as the image forming apparatus 10 according to the above-described embodiment of the present invention.

  The items shown in the first to fifth columns in FIG. 7 are the same as those in FIG. Further, “x” in the fifth column in FIG. 7 indicates that the potential unevenness of the photosensitive member 102 is larger than 10 V, and there is a possibility that a problem in image quality may occur in the formed image.

  In the image forming apparatus 10 according to the first comparative example, when the number of images formed using the photosensitive member 102 is up to 100K, as in the image forming apparatus 10 according to the embodiment of the present invention described above, Lines have not occurred, and the potential unevenness of the photoconductor 102 is in a range where no image quality problems occur.

  On the other hand, when the number of images formed using the photoconductor 102 is 100K to 200K, the minute black line is not generated as in the image forming apparatus 10 according to the first embodiment, but the photoconductor. The potential unevenness of 102 is larger than 10V. This is because the upstream gap S2 is not formed even though the wear of the film part 106 progresses, the thickness of the film part 106 becomes relatively thin, and the capacitance of the film part 106 becomes relatively large. For this reason, the charging region for charging the photosensitive member 102 in the moving direction of the photosensitive member 102 becomes insufficient, and the photosensitive member 102 is not sufficiently charged.

  FIG. 8 shows the thickness of the film portion 106 in the image forming apparatus 10 (not shown) according to the second comparative example, the position of the gap formed between the photosensitive member 102 and the charging member 204, and the photosensitive member with the charging device 200. Whether or not a minute black line is generated in an image formed by the image forming apparatus 10 when the image forming apparatus 10 is charged and whether or not potential unevenness occurs in the image forming apparatus 10 are determined for each number of images formed using the image forming apparatus 102. It is a chart shown.

  In the image forming apparatus 10 according to the above-described embodiment of the present invention, only the downstream gap S1 is formed until the number of images formed using the photoconductor 102 is 100K or less, and the image formed using the photoconductor 102 is formed. Both the downstream side gap S1 and the upstream side gap S2 were formed from 100K to 200K. On the other hand, in the image forming apparatus 10 according to the second comparative example, as shown in the third column of FIG. 8, even when the number of images formed using the photoconductor 102 is 100K or less, the photoconductor. Even when the number of images formed using 102 is from 100K to 200K, both the downstream gap S1 and the upstream gap S2 are formed. Except for the above points, the image forming apparatus 10 according to the second comparative example is the same as the image forming apparatus 10 according to the above-described embodiment of the present invention.

  Items shown in the first to fifth columns in FIG. 8 are the same as those in FIGS. Further, “x” in the fourth column in FIG. 8 indicates that a minute black line is formed in the formed image.

  In the image forming apparatus 10 according to the second comparative example, when the number of images formed using the photoconductor 102 is 100K to 200K, as in the image forming apparatus 10 according to the embodiment of the present invention described above, A minute black line has not occurred, and the potential unevenness of the photosensitive member 102 is in a range where no image quality problem occurs.

  On the other hand, when the number of images formed using the photoconductor 102 is 100K or less, the potential unevenness of the photoconductor 102 does not occur in the same manner as the image forming apparatus 10 according to the first embodiment described above. A minute black line will be generated. This is because the number of images formed using the photoconductor 102 is 100K or less, the wear of the film part 106 is not progressing, the film part 106 is relatively thick, and the electrostatic capacity of the film part 106 is large. This is because the upstream gap S2, which is a region where abnormal discharge is particularly likely to occur, is formed even though abnormal discharge is likely to occur between the charging member 204 and the photosensitive member 102 because it is relatively small.

  FIG. 9 shows a charging device 200 included in the image forming apparatus 10 according to the third comparative example. In the image forming apparatus 10 according to the above-described embodiment of the present invention, the charging member 204 is disposed so that the support member 212 is located downstream of the contact position N2 in the moving direction of the photosensitive member 102. On the other hand, in the image forming apparatus 10 according to the third comparative example, the charging member 204 is arranged so that the support member 212 is positioned upstream of the contact position N2 in the moving direction of the photosensitive member 102. Yes. Further, in the image forming apparatus 10 according to the third comparative example, even when the number of images formed using the photoconductor 102 is 100K or less, the number of images formed using the photoconductor 102 starts from 100K. Even up to 200K, only the upstream gap S2 is formed between the photosensitive member 102 and the charging member 204, and the downstream gap S1 is not formed. Except for the above points, the image forming apparatus 10 according to the third comparative example is the same as the image forming apparatus 10 according to the above-described embodiment of the present invention.

  FIG. 10 shows the thickness of the film portion 106 in the image forming apparatus 10 according to the third comparative example, the position of the gap formed by the photosensitive member 102 and the charging member 204, and the photosensitive member 102 charged by the charging device 200. 4 is a chart showing, for each number of images formed using the photoconductor 102, whether or not a minute black line is generated in an image formed by the image forming apparatus 10 and whether or not potential unevenness occurs in the photoconductor 102. . The items shown in the first to fifth columns in FIG. 10 are the same as those in FIGS.

  In the image forming apparatus 10 according to the third comparative example, when the number of images formed using the photoconductor 102 is 100K or less, potential unevenness does not occur as in the image forming apparatus 10 according to the above-described embodiment of the present invention. . However, when the number of images formed using the photosensitive member 102 is 100K or less, fine black lines that are not generated in the image forming apparatus 10 according to the above-described embodiment of the present invention are generated. This is because the number of images formed using the photosensitive member is 100K or less, the wear of the film part 106 is not progressing, the film part 106 is relatively thick, and the capacitance of the film part 106 is compared. This is because the upstream gap S2, which is a region in which abnormal discharge is particularly likely to occur, is formed between the charging member 204 and the photosensitive member 102 because abnormal discharge is likely to occur.

  Further, in the image forming apparatus 10 according to the third comparative example, when the number of images formed using the photosensitive member 102 is 100K to 200K, the minute black as in the image forming apparatus 10 according to the above-described embodiment of the present invention is used. No line is generated. However, when the number of images formed using the photosensitive member 102 is 100K to 200K, potential unevenness that has not occurred in the image forming apparatus 10 according to the above-described embodiment of the present invention occurs. This is because the downstream gap S1 is not formed even though the wear of the film part 106 progresses, the thickness of the film part 106 becomes relatively thin, and the capacitance of the film part 106 becomes relatively large. For this reason, the charging region for charging the photosensitive member 102 in the moving direction of the photosensitive member 102 becomes insufficient, and the photosensitive member 102 is not sufficiently charged.

  In the embodiment described above, an example has been described in which the position where the gap is formed at the position between the photosensitive member 102 and the charging member 204 is changed in accordance with the change in the thickness of the film portion 106. The size of the gap at the position between the photosensitive member 102 and the charging member 204 may be changed according to the change in the thickness of the film part 106. Further, a position where a gap is formed at a position between the photoconductor 102 and the charging member 204 according to a change in the thickness of the film unit 106 and a size of the gap at a position between the photoconductor 102 and the charging member 204. Both of them may be changed.

  Further, in the embodiment described above, an example in which a single color image is formed as the image forming unit 100 is shown as an example. However, the present invention is also applied to an apparatus that forms a multicolor image as the image forming unit 100. Can be applied.

  As described above, the present invention can be applied to at least an image forming apparatus such as a printer, a facsimile machine, and a copying machine, and a charging device used in such an image forming apparatus.

DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 102 ... Photoconductor 106 ... Film | membrane part 200 ... Charging apparatus 204 ... Charging member 206 ... Discharge surface 210 ... Support means 212 ... Support member 270 ... Voltage application device 280 ... Movement mechanism 282 ... Drive source 400 ... Control device 410 ... Rotational speed measurement device N2 ... Contact position S1 ... Downstream clearance S2 ... Upstream Side gap

Claims (5)

An image carrier having an outer layer and holding an image;
A charging member that partially contacts the image carrier and forms a gap between the other part and the outer layer and charges the outer layer;
Support means for supporting the charging member so that at least one of the position of the gap and the size of the gap can be changed;
An image forming apparatus. The support means is
When the thickness of the outer layer is equal to or greater than a predetermined value, the gap is formed on the downstream side of the contact position where the charging member and the image carrier are in contact with each other in the moving direction of the image carrier. Let
The image according to claim 1, wherein when the thickness of the outer layer is smaller than the predetermined value, the charging member is supported so that the gap is formed on the upstream side and the downstream side of the contact position in the moving direction. Forming equipment.   The said support means supports the said charging member so that at least one of the position of the said clearance gap and the magnitude | size of the said clearance gap can be changed according to the number of the images formed using the said image holding body. The image forming apparatus according to 1 or 2. The charging member is a plate-like or film-like member that contacts the outer layer and forms a convex curved surface on the image carrier side,
The image forming apparatus according to claim 1, wherein the support unit includes a moving mechanism that moves the charging member relative to the image holding member. A charging member that partially contacts the outer layer of the object to be charged, and forms a gap between the other part and the outer layer, and charges the outer layer;
Support means for supporting the charging member so that at least one of the position of the gap and the size of the gap can be changed;
Charging device having

Images