JP2007140351A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform high-speed image forming operation without adversely influencing a following electrifying step even when performing a destaticizing step for destaticizing the surface of an image carrier before a cleaning step. <P>SOLUTION: The image forming part 20 of the image forming apparatus 1 performs the destaticizing step for eliminating the residual charge of a photoreceptor drum 22 before removing toner remaining on the surface of the drum. In the image forming part 20, the quantity of destaticizing light with which a toner non-remaining spot on the surface of the photoreceptor drum 22 is irradiated by a destaticizing means 70 is controlled to be different from the quantity of destaticizing light with which a toner remaining spot is irradiated when performing a refreshing step for a developing means 60 by supplying the toner to the photoreceptor drum 22 in a non-transfer period of paper P. Thus, potential at the toner non-remaining spot is intentionally increased with the toner remaining spot where the potential of the surface of the photoreceptor is increased in the electrifying step in following image forming operation, so that the surface potential of the photoreceptor drum 22 after the destaticizing step is made uniform. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus represented by a copying machine or a printer. In particular, the present invention relates to an image forming apparatus that executes a charge eliminating step for removing charged charges on an image carrier before cleaning toner remaining on the surface of the image carrier.

  In an electrophotographic image forming apparatus such as a copying machine or a printer, a photosensitive drum is widely used as an image carrier. A general image forming operation using the photosensitive drum is as follows. The surface of the photosensitive drum is uniformly charged with a predetermined potential by a charging unit, and by irradiating the LED light or the like of the exposure unit there, the potential is partially attenuated to form an electrostatic latent image of an original image. Is done. Then, a toner image is formed by developing this electrostatic latent image with developing means. After the toner image is transferred onto the paper, the remaining toner is cleaned by the cleaning unit on the surface of the photosensitive drum, and the charge removal is performed by irradiating the neutralizing light by the neutralizing unit in preparation for the next image forming operation. Is called.

  Here, when an amorphous silicon photoconductor is used as the photoconductor, there is a concern about the occurrence of an exposure memory in which the pattern of the electrostatic latent image formed in the current image forming operation adversely affects the next image forming operation. Yes. The exposure memory is a major problem in increasing the speed of recent image forming apparatuses, mainly due to the short time from the charge removal process to the charging process. In order to solve such a problem, a method is proposed in which the charge removal step is executed before the cleaning step and the time from charge removal to charging is suitably set, and an example thereof can be seen in Patent Document 1.

On the other hand, if the image forming apparatus continuously performs low density printing or leaves the printer without performing printing for a long time, the charge amount of the toner stored in the developing unit increases. As a result, the toner becomes difficult to be separated from the developing means, and the amount of movement of the toner to the photosensitive drum is reduced. If printing is performed as it is, there arises a problem that the image density is lowered. In order to solve such problems and maintain the performance of the developing means, toner is supplied from the developing means to the photosensitive drum during the non-transfer period to the paper on the condition that the toner occupation ratio on the image is lowered. Thus, a method of refreshing the developing means has been proposed, and an example of this can be seen in Japanese Patent Application Laid-Open No. 2003-228620.
JP 2003-295563 A (page 2-4, FIG. 4) JP 2000-310909 A (page 3-7, FIG. 1-3)

  However, the neutralization process is executed before the cleaning process as in the image forming apparatus described in Patent Document 1, and the refreshing process of the developing unit is performed in the non-transfer period to the paper as in the image forming apparatus described in Patent Document 2. In this case, the image carrier is irradiated with static elimination light in a state where the toner is placed on the surface of the image carrier in the static elimination process, so that the toner shields the static elimination light. As a result, the static elimination light does not reach the surface of the photoreceptor of the image carrier, the generation of photocarriers in the photosensitive layer becomes insufficient, and the surface potential of the photoreceptor rises above a predetermined potential in the next charging step. Occurs. Therefore, in order to obtain a predetermined surface potential at a level where there is no problem, it is necessary to further increase the time by rotating the image carrier once. As a result, the number of printed sheets per unit time is reduced, which hinders speeding up of the image forming apparatus.

  The present invention has been made in view of the above points, and in an image forming apparatus that performs a charge eliminating process on the surface of an image carrier in an image forming operation before a cleaning process, a refresh process is performed to maintain the performance of the developing unit. It is an object of the present invention to provide an image forming apparatus capable of executing a high-speed image forming operation without adversely affecting the next charging process.

  In order to solve the above problems, the present invention comprises an image carrier, a charging unit for charging the surface of the image carrier, an exposure unit for exposing the charged image carrier surface to form an electrostatic latent image, Developing means for supplying toner to the electrostatic latent image to form a toner image on the surface of the image carrier, neutralizing means for removing residual charges on the image carrier, and cleaning means for cleaning the toner remaining on the surface of the image carrier And an image forming apparatus that executes a charge eliminating step for removing residual charges on the image carrier before cleaning the toner remaining on the surface of the image carrier. The control means executes a refresh process for refreshing the developing means by supplying toner from the developing means to the image carrier within a non-transfer period to the paper. The neutralization amount of light irradiated to the toner non-residual portion of the surface of the image bearing member by discharging means, and a controlling differently from the neutralization amount of light applied to the toner remaining locations.

  According to the configuration of the present invention, in the image forming apparatus that executes the charge eliminating step for removing the residual charge on the image carrier before cleaning the toner remaining on the surface of the image carrier, the control unit includes the non-transfer to the sheet. Within this period, a refresh process is performed in which toner is supplied from the developing means to the image carrier and the developing means is refreshed. In this refresh process, the toner remaining on the surface of the image carrier is irradiated by the charge eliminating means. The amount of charge removed is controlled so as to be different from the amount of charge removed to the remaining toner location, so that the remaining toner location where the potential on the surface of the photoconductor rises during the charging process during the next image forming operation. In addition, the potential of the toner non-remaining portion can be increased intentionally. As a result, the surface potential of the image carrier after the static elimination step can be made uniform, and the surface of the image carrier can be easily charged to a predetermined potential by controlling the charging means. Therefore, in order to obtain a predetermined surface potential even if the generation of the photocarrier in the charge removal process is insufficient at the toner remaining portion on the surface of the image carrier formed in the refresh process of the developing means, There is no need to make a single turn to earn time. As a result, it is possible to execute a high-speed image forming operation.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  First, an image output operation of an image forming apparatus according to an embodiment of the present invention will be described while explaining an outline of the structure with reference to FIG. FIG. 1 is a schematic vertical sectional front view of an image forming apparatus. This image forming apparatus is of a color printing type in which a toner image is transferred onto a sheet using an intermediate transfer belt.

  As shown in FIG. 1, a paper cassette 3 is disposed below the inside of the main body 2 of the image forming apparatus 1. Inside the paper cassette 3, paper P such as cut paper before printing is stacked and accommodated. The sheets P are separated and sent one by one toward the upper left of the sheet cassette 3 in FIG. The paper cassette 3 can be pulled out horizontally from the front side of the main body 2.

  A paper transport unit 4 is provided inside the main body 2 and on the left side of the paper cassette 3. The paper P delivered from the paper cassette 3 is transported vertically upward along the side surface of the main body 2 by the paper transport unit 4 and reaches the secondary transfer unit 40.

  On the other hand, a document feeding unit 5 is provided on the upper surface of the image forming apparatus 1, and a document image reading unit 6 is provided below the document feeding unit 5. When a user copies a document, a document on which an image such as a character, a figure, or a pattern is drawn is stacked on the document feeding unit 5. The document feeding unit 5 separates the documents one by one and sends the document, and the document image reading unit 6 reads the image data. Information on the image data is sent to a laser irradiation unit 7 which is an exposure unit disposed above the paper cassette 3. The laser irradiation unit 7 irradiates the image forming unit 20 with laser light L controlled based on the image data.

  A total of four image forming units 20 are provided above the laser irradiation unit 7, and an intermediate transfer belt 8 using an intermediate transfer member in the form of an endless belt is provided above each image forming unit 20. The intermediate transfer belt 8 is wound around and supported by a plurality of rollers, and is rotated clockwise in FIG. 1 by a driving device (not shown).

  The four image forming units 20 are arranged in a line along the intermediate transfer belt 8 from the upstream side toward the downstream side in the rotation direction. The four image forming units 20 are an image forming unit 20B for black, an image forming unit 20C for cyan, an image forming unit 20M for magenta, and an image forming unit 20Y for yellow in order from the upstream side. To supplement the image forming unit 20 with toner, toner supply containers 21B, 21C, 21M, and 21Y corresponding to the image forming units 20B, 20C, 20M, and 20Y are provided above the intermediate transfer belt 8 and are not shown. Thus, toner is supplied to each image forming unit 20. In the following description, the identification symbols “B”, “C”, “M”, and “Y” are omitted unless particularly limited.

  In each image forming unit 20, an electrostatic latent image of a document image is created by the laser light L emitted by the laser irradiating unit 7 serving as an exposure unit, and a toner image is formed from the electrostatic latent image. A primary transfer unit 30 provided with a primary transfer roller 31 is provided above each image forming unit 20 with the intermediate transfer belt 8 therebetween. The primary transfer roller 31 is movable in the vertical direction in FIG. 1, and is pressed against and separated from the intermediate transfer belt 8 as necessary. As the primary transfer roller 31 comes into pressure contact with the intermediate transfer belt 8, the intermediate transfer belt 8 comes into pressure contact with the image forming portion 20 from above to form a primary transfer nip portion, and the toner image formed by the image forming portion 20 is intermediate. The image is transferred to the surface of the transfer belt 8. The toner image of each image forming unit 20 is transferred to the intermediate transfer belt 8 at a predetermined timing along with the rotation of the intermediate transfer belt 8, so that the surface of the intermediate transfer belt 8 has four colors, magenta, cyan, yellow, and black. A color toner image is formed by superimposing the toner images.

  A secondary transfer unit 40 is disposed at a position where the intermediate transfer belt 8 is suspended on the sheet conveyance path. The secondary transfer unit 40 includes a secondary transfer roller 41. The color toner image on the surface of the intermediate transfer belt 8 is a secondary transfer nip formed by the intermediate transfer belt 8 and the secondary transfer roller 41 being pressed against the sheet P sent in synchronization by the sheet transport unit 4. It is transcribed at the part. The toner remaining on the surface of the intermediate transfer belt 8 after the secondary transfer is cleaned by the cleaning device 9 for the intermediate transfer belt 8 provided on the upstream side of the intermediate transfer belt 8 in the rotation direction of the magenta image forming unit 20M. The

  A fixing unit 10 is provided above the secondary transfer unit 40. The sheet P carrying the unfixed toner image in the secondary transfer unit 40 is sent to the fixing unit 10 where the toner image is heated and pressed by the fixing roller and the pressure roller to be fixed.

  A branch portion 11 is provided above the fixing portion 10. The paper P discharged from the fixing unit 10 is discharged from the branching unit 11 to the in-body sheet discharge tray 12 provided in the cylinder of the image forming apparatus 1 when double-sided printing is not performed.

  The discharge port portion from which the paper P is discharged from the branching portion 11 toward the in-body paper discharge tray 12 functions as the switchback portion 13. When performing duplex printing, the switchback unit 13 switches the transport direction of the paper P discharged from the fixing unit 10. Then, the paper P is sent downward through the branching unit 11, the left side of the fixing unit 10, and the left side of the secondary transfer unit 40, and is sent again to the secondary transfer unit 40 through the paper transport unit 4. .

  Next, a detailed configuration around the image forming unit 20 of the image forming apparatus 1 will be described with reference to FIG. FIG. 2 is a partially enlarged view of a vertical section showing the periphery of the image forming unit and a schematic diagram of a control circuit. Since the four color image forming units 20 have the same structure, the identification symbols “B”, “C”, “M”, and “Y” are omitted as described above.

  As shown in FIG. 2, the image forming unit 20 includes a photosensitive drum 22 as an image carrier at the center thereof. In the vicinity of the photosensitive drum 22, a charging unit 50, a developing unit 60, a charge eliminating unit 70, and a cleaning unit 80 are arranged in order along the rotation direction. The primary transfer unit 30 is provided between the developing unit 60 and the charge eliminating unit 70 along the rotation direction of the photosensitive drum 22.

  The photosensitive drum 22 is an inorganic photosensitive drum in which amorphous silicon, which is an inorganic photoconductive material, is provided on the outside of a conductive roller-shaped substrate made of aluminum or the like by vacuum deposition or the like, and has a diameter of 30 mm. is there. The photosensitive drum 22 is rotated by a driving device (not shown) so that the peripheral speed thereof is substantially the same as the paper conveyance speed (for example, 210 mm / sec).

  The charging unit 50 includes a charging roller 52 that contacts the photosensitive drum 22 inside the housing 51. The charging roller 52 includes a cored bar, a conductive layer provided on the outside thereof, and a resistance layer provided on the outside thereof. The charging roller 52 is brought into pressure contact with the photosensitive drum 22 with a predetermined pressure, and rotates according to the rotation of the photosensitive drum 22. By this charging roller 52, the surface of the photosensitive drum 22 is uniformly charged with a predetermined polarity and potential. In the housing 51, a cleaning brush 53 is provided at a position where the charging roller 52 is separated from the photosensitive drum 22.

  The developing means 60 is provided with a photosensitive member non-contact type developing roller 61 in the vicinity of the photosensitive drum 22. A bias having the same polarity as the charging polarity of the photosensitive drum 22 is applied to the developing roller 61. The developing roller 61 charges the toner, which is a developer, and causes the toner to fly to the electrostatic latent image on the surface of the photosensitive drum 22 to develop the electrostatic latent image. As the toner, a non-magnetic one-component toner is used, but a two-component developer obtained by mixing a magnetic carrier and a non-magnetic toner may be used. The toner is accommodated in a toner supply container 21 (see FIG. 1), conveyed to a developing unit 60 by a conveying unit (not shown), and replenished by a screw 62. The developing roller may be a photoreceptor contact type.

  The primary transfer unit 30 is provided with a primary transfer roller 31 that comes into contact with the photosensitive drum 22 via the intermediate transfer belt 8. The primary transfer roller 31 includes a core metal 32 and a conductive elastic layer 33 provided on the outside thereof. The conductive elastic layer 33 is made of polyurethane rubber or the like in which a conductive material such as carbon is dispersed. The primary transfer roller 31 is supported by a frame (not shown) via an arm 34. The arm 34 can rotate around its shaft portion 34a, and the primary transfer roller 31 moves up and down by this rotation. The primary transfer roller 31 moves downward at a predetermined timing and comes into contact with the intermediate transfer belt 8, and the intermediate transfer belt 8 is pushed down according to this and comes into contact with the photosensitive drum 22 to form a primary transfer nip portion. When the primary transfer roller 31 moves upward, the intermediate transfer belt 8 is separated from the photosensitive drum 22. The primary transfer roller 31 does not have a driving device, and rotates according to the rotation of the intermediate transfer belt 8 by contacting the intermediate transfer belt 8. Further, a transfer bias is applied to the primary transfer roller 31 as necessary.

  The neutralizing unit 70 is disposed further downstream of the primary transfer unit 30 along the rotation direction of the photosensitive drum 22. The static elimination means 70 includes an LED (light emitting diode) 71 and a reflector 72. The LED 71 is attached to the upper surface of the housing 81 of the cleaning device 80. Instead of the LED 71, an EL (electroluminescence) light source, a fluorescent lamp, or the like can be used. The reflector 72 is provided above the LED 71 so as to cover the LED 71. The neutralizing means 70 irradiates the photosensitive drum 22 with the neutralizing light from the LED 71 to remove the charged charges on the surface.

  The cleaning unit 80 includes a cleaning roller 82 as a cleaning member, a cleaning blade 83, a scraper 84, and a discharge screw 85 inside the housing 81. The cleaning roller 82 and the cleaning blade 83 have substantially the same axial length as the photosensitive drum 22 and are provided so as to contact the photosensitive drum 22. After the toner image on the surface of the photosensitive drum 22 is transferred to the intermediate transfer belt 8, the cleaning roller 82 and the cleaning blade 83 remove the toner remaining on the surface of the photosensitive drum 22 and perform cleaning. The scraper 84 is provided in contact with the cleaning roller 82 from above in FIG. 2, and removes excess toner adhering to the surface of the cleaning roller 82 to make the toner layer uniform. The toner removed from the surface of the photosensitive drum 22 is sent to the discharge screw 85 according to the action of gravity and the rotation of the cleaning roller 82, and is conveyed to the outside of the housing 81 by the discharge screw 85.

  Further, the image forming apparatus 1 is provided with a control unit 90. The control unit 90 controls each of the units provided in the image forming unit 20, the primary transfer unit 30, and the like to form a toner image, and primarily transfers the toner image to the intermediate transfer belt 8.

  Here, a series of operations of the image forming unit 20 and the transfer unit 30 will be described.

  First, the control unit 90 uniformly charges the surface of the photosensitive drum 22 with a predetermined polarity and potential by the charging roller 52 of the charging unit 50. The charging potential at this time is usually about 200 to 1000V.

  Next, based on the image data read by the document image reading unit 6 (see FIG. 1), the photosensitive drum 22 is irradiated with the laser light L controlled by the laser irradiation unit 7 (see FIG. 1), and the irradiated portion is irradiated. Is attenuated to form an electrostatic latent image of the original image. The control unit 90 supplies the toner charged by the developing unit 60 to the surface of the photosensitive drum 22 by the developing roller 61, and develops the toner image from the electrostatic latent image.

  On the other hand, the intermediate transfer belt 8 is synchronized with the toner image formation on the surface of the photosensitive drum 22 by the control unit 90 and is brought into contact with the photosensitive drum 22 by being pushed down by the primary transfer roller 31. At this time, a negative transfer bias having a polarity opposite to that of the photosensitive drum 22 and the toner is applied to the primary transfer roller 31. Thus, the toner image is contact-transferred to the intermediate transfer belt 8 as the toner moves from the photosensitive drum 22 toward the primary transfer roller 31.

  Then, the controller 90 irradiates the surface of the photosensitive drum 22 after the toner image has been transferred to the intermediate transfer belt 8 with the discharging light of the LED 71 by the discharging unit 70. By this charge removal operation, the charged charges on the surface of the photosensitive drum 22 are removed, and preparation for the charging process in the next image forming operation is made.

  After neutralizing the photosensitive drum 22, the control unit 90 controls the cleaning unit 80 so that the toner remaining on the surface of the photosensitive drum 22 is removed by the cleaning roller 82 and the cleaning blade 83. Then, the toner collected in the housing 81 is conveyed to the outside of the cleaning unit 80 by the discharge screw 85.

  Subsequently, as described above, in the configuration in which the static elimination process of the photosensitive drum 22 is performed before the cleaning process, toner is supplied from the developing unit 60 to the photosensitive drum 22 within the non-transfer period to the paper P. The effect of the amount of toner remaining on the surface of the photosensitive drum 22 during the charge removal process on the drum surface potential during the next charging process when the refresh process for refreshing the developing unit 60 is executed will be described with reference to FIG. . FIG. 3 is a graph showing the effect of the amount of toner remaining on the drum surface during the charge removal process on the drum surface potential during the next charging process when black toner is used.

  The horizontal axis in FIG. 3 indicates the amount of toner remaining on the surface of the photosensitive drum 22 during the static elimination process, and the toner amount increases toward the right. The vertical axis shows the potential difference between the surface potential of the surface of the photosensitive drum 22 in the next charging step and the portion of the surface potential where the toner remained in the charge removal step and the portion where the toner did not remain. Becomes larger.

As usual, a refreshing process for refreshing the developing unit 60 was performed, and in the subsequent neutralizing process, the LED 71 that applied the neutralizing light was turned on, and the neutralizing operation of the photosensitive drum 22 by the neutralizing unit 70 was performed. As shown in FIG. 3, when the amount of residual toner on the surface of the photosensitive drum 22 is changed between about 0.2 to 0.9 mg / cm ² , the locations where the toner remains and the residual amount during the static elimination process The surface potential difference at the next charging step with the portion that was not changed varies between about 15 to 45V. That is, the surface potential difference is relatively small when the residual toner amount is small, but the surface potential difference becomes very large when the residual toner amount is large in order to maintain the suitable performance of the developing unit 60. Thus, in order to obtain a predetermined uniform surface potential, it is necessary to further increase the time by rotating the photosensitive drum 22 once. Accordingly, the number of printed sheets per unit time is reduced, and the speeding up of the image forming apparatus 1 is hindered.

  Next, a method for making the surface potential of the photosensitive drum 22 uniform after the static elimination process even when the refresh process of the developing unit 60 is performed on the image forming unit 20 as described above will be described with reference to FIG. In addition to FIG. 3, it demonstrates using FIG.4 and FIG.5. FIG. 4 is a graph and a schematic diagram showing the transition of the surface potential of the photosensitive drum while the toner remaining portion moves from the upstream side of the static eliminating unit to the downstream side of the charging unit according to the rotation of the photosensitive drum. FIG. 5 is a graph showing the relationship between the static elimination energy and the photosensitive drum surface potential.

  4 is a diagram in which the surface of the photosensitive drum 22 is schematically extended in the lateral direction from the upstream side of the static elimination unit 70 in FIG. 2 to the downstream side of the charging unit 50. In FIG. 4, the surface of the photosensitive drum 22 moves from the left to the right in the drawing. A one-dot chain line rectangle on the surface of the photosensitive drum 22 indicates a toner remaining portion. The drawing of the cleaning roller 82 is omitted.

  In the central part and the lower part of FIG. 4, a graph showing the transition of the surface potential of the photosensitive drum 22 while the toner remaining portion moves from the upstream side of the static elimination unit 70 to the downstream side of the charging unit 50 according to the rotation of the photosensitive drum 22. Is drawn. In the central part of FIG. 4, a graph in the case where the charge removal amount is not controlled in the charge removal process is shown in the lower part for each of the toner remaining place and the toner non-remaining place on the surface of the photosensitive drum 22 after the refresh process. Shows a graph in the case of controlling the amount of static elimination according to the embodiment of the present invention.

  Further, in the schematic diagram of the surface of the photosensitive drum 22 and the graph showing the transition of the surface potential, the upstream side of the static elimination means 70 is the section A, the section from the cleaning means 80 to the charging means 50 is the section B, and the downstream of the charging means 50. The side is defined as section C.

  First, as a comparative example with respect to the embodiment of the present invention, the amount of charge removed in the charge removal step is applied to each of the remaining toner location and non-remaining location on the surface of the photosensitive drum 22 after the refresh process as in the past. The case where the control is not performed will be described using the graph in the center of FIG.

  In the section A on the upstream side of the charge removal means 70, the surface potential of the photosensitive drum 22 is V1 at the toner remaining portion and V2 at the toner non-remaining portion. In order to supply the toner from the developing means 60 to the surface of the photosensitive drum 22, the surface potential of the toner remaining portion is lower than that of the toner non-residual portion. Then, when the remaining toner portion reaches the portion of the charge removal unit 70, the amount of charge removal is not individually controlled for each of the remaining toner portion and the non-toner remaining portion. That is, the static elimination process is executed with a uniform static elimination light amount on the surface of the photosensitive drum 22.

  As a result, the surface potential of the photosensitive drum 22 in the section B after the toner is removed by the cleaning blade 83 decreases to V0 at the toner non-remaining portion, whereas the toner remaining portion has a slightly lower potential. It remains high V1. As described above, this is caused by the remaining toner shielding the static elimination light. If the toner remaining portion passes through the portion of the charging unit 50 in the charging process at the next image forming operation, the surface potential of the photosensitive drum 22 is changed with respect to V2 of the toner non-remaining portion as shown in the section C. The toner remaining portion becomes V3 having a higher potential. That is, a surface potential difference as shown in FIG. 3 occurs. Therefore, the surface potential of the photosensitive drum 22 is not uniform, and adversely affects subsequent image formation.

  Next, in order to solve such a problem, the amount of charge to be removed is controlled in the charge removal step for each of the toner remaining portion and the toner non-remaining portion on the surface of the photosensitive drum 22 after the refresh process. Will be described using the graph at the bottom of FIG.

  In the section A on the upstream side of the charge eliminating means 70, the surface potential of the photosensitive drum 22 is V1 at the toner remaining portion and V2 at the toner non-residual portion, as in the comparative example. Then, when the remaining toner portion reaches the portion of the charge removal unit 70, the control unit 90 (see FIG. 2) uses the charge removal unit 70 to reduce the amount of charge removed from the surface of the photosensitive drum 22 to the remaining toner remaining amount. It controls so that it differs from the static elimination light quantity irradiated to a location. That is, the neutralization process was performed on the surface of the photosensitive drum 22 where no toner remained, by reducing the amount of neutralization light compared with the remaining toner.

Here, details of the control of the charge removal amount will be described with reference to FIG. According to FIG. 5, when the energy of the neutralizing light applied to the photosensitive drum 22 where the surface potential of the toner non-remaining portion before the neutralizing light irradiation is about 260 V is gradually increased, that is, when the neutralizing light amount is gradually increased, It can be seen that the surface potential is approximately constant 25 V exceeding 0.5 μJ / cm ² and cannot be further reduced. If the amount of residual toner on the surface of the photosensitive drum 22 in the refresh process is about 0.6 mg / cm ² , the next charging process between the location where the toner remained and the location where the toner did not remain during the static elimination process. The surface potential difference at the time is about 35V as shown in FIG. Therefore, it can be seen that the surface potential of the remaining toner portion at the time of the static elimination process is about 60 V by adding 35 V to the previous 25 V.

On the other hand, in the charge removal step, the amount of charge removed may be controlled so that the surface potential of the non-remaining toner after irradiation with the removal light is substantially the same as about 60 V of the remaining toner. According to FIG. 5, the surface potential of the photosensitive drum 22 becomes about 60 V when the amount of static elimination light, that is, the static elimination energy is about 0.3 μJ / cm ² . Therefore, in the charge removal step, the charge removal light amount exceeding 0.5 μJ / cm ^2, for example, 0.8 μJ / cm ^{2 for} the remaining toner portion, and 0.3 μJ / cm ² charge removal amount for the toner non-remaining portion. Thus, it is only necessary to irradiate the photosensitive drum 22 with static elimination light.

The timing of switching the amount of charge to be removed for the toner remaining portion and the toner non-remaining portion is executed as follows. As shown in FIG. 2, if the laser beam L irradiation spot on the surface of the photosensitive drum 22 is X and the charge removal light irradiation spot is Y, the rotation angle between XY is about 200 ° and the photosensitive member has a diameter of 30 mm. In the case of the drum 22, the distance is 52.3 mm. If the peripheral speed of the photosensitive drum 22 is 210 mm / sec, the movement time between X and Y is about 0.25 sec. As a result, in the charge removal process, irradiation is performed with a charge removal light amount of 0.3 μJ / cm ² for a normal toner non-remaining portion, and the charge removal light quantity is 0.25 seconds after the start of laser light L irradiation for the refresh process. Switch to 0.8 μJ / cm ² . As a result, 0.8 μJ / cm ² of neutralizing light is applied to the remaining toner portion. Then, after the photosensitive drum 22 is rotated by the length of the toner remaining portion in the drum rotation direction, the charge removal light amount is switched to 0.3 μJ / cm ² again to irradiate the non-toner remaining portion with the charge removing light.

  As shown in FIG. 4, the surface potential of the photosensitive drum 22 in the section B after the toner is removed by the cleaning blade 83 is the surface potential of the non-residual portion as shown in FIG. Thus, the surface potential becomes V1 which is uniform at both the toner remaining portion and the toner non-remaining portion. When the remaining toner portion passes through the charging means 50 in the charging process at the next image forming operation, as shown in the section C, the remaining toner portion and the non-toner remaining portion can be charged with uniform V2. it can.

  In the image forming apparatus 1 that executes the charge eliminating step for removing the residual charge on the photosensitive drum 22 as the image carrier in this way before cleaning the toner remaining on the surface of the photosensitive drum 22, the control unit 90 includes: In the non-transfer period to the paper P, a refreshing process is performed in which toner is supplied from the developing unit 60 to the photosensitive drum 22 to refresh the developing unit 60. Since the amount of charge neutralized on the toner non-remaining spot on the surface of the drum 22 is controlled so as to be different from the amount of charge neutralized on the remaining toner spot, the potential on the surface of the photoconductor is changed in the charging process during the next image forming operation. The potential of the toner non-remaining portion can be intentionally increased in accordance with the toner remaining portion that rises. As a result, the surface potential of the photosensitive drum 22 after the charge eliminating step can be made uniform, and the surface of the photosensitive drum 22 can be easily charged to a predetermined potential by the control of the charging unit 50. Therefore, in order to obtain a predetermined surface potential even in the case where the generation of the photocarrier in the charge removal process is insufficient at the toner remaining portion on the surface of the photosensitive drum 22 formed in the refresh process of the developing unit 60, the photoconductor. There is no need to make time by rotating the drum 22 once. As a result, it is possible to execute a high-speed image forming operation.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

  For example, in the embodiment of the present invention, the image forming apparatus is of a color printing type in which a toner image is transferred onto a sheet using an intermediate transfer belt, but the type of the image forming apparatus is not limited to this. Alternatively, a model that does not use an intermediate transfer belt or a model for monochrome printing may be used.

  Further, in the description using FIG. 4, the charge removal amount control is individually executed for each of the toner remaining portion and the toner non-remaining portion. However, the toner remaining portion is irradiated with the discharge light. Instead, it is possible to irradiate only the non-remaining portion of the toner with the charge removal light.

  The present invention can be used in general image forming apparatuses.

1 is a schematic vertical sectional front view of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a partially enlarged view of a vertical section showing the periphery of an image forming unit of the image forming apparatus of FIG. 1 and a schematic diagram of a control circuit. 6 is a graph showing the influence of the amount of toner remaining on the drum surface during the charge removal process on the drum surface potential during the next charging process. FIG. 6 is a graph and a schematic diagram showing the transition of the surface potential of the photosensitive drum while the toner remaining portion moves from the upstream side of the static elimination unit to the downstream side of the charging unit according to the rotation of the photosensitive drum. 6 is a graph showing the relationship between static elimination energy and photosensitive drum surface potential.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 8 Intermediate transfer belt 20 Image forming part 22 Photosensitive drum (image carrier)
30 Primary transfer section 31 Primary transfer roller 50 Charging means 60 Developing means 70 Static elimination means 71 LED
80 Cleaning means 90 Control means

Claims (1)

An image carrier, a charging unit for charging the surface of the image carrier, an exposure unit for exposing the charged image carrier surface to form an electrostatic latent image, and supplying toner to the electrostatic latent image to carry the image A developing means for forming a toner image on the surface of the body, a charge removing means for removing the residual charge on the image carrier, a cleaning means for cleaning the toner remaining on the surface of the image carrier, and a control means for controlling the means. In the image forming apparatus, the charge removing step for removing the residual charge on the image carrier is performed before cleaning the toner remaining on the surface of the image carrier.
The control means executes a refresh step of refreshing the developing means by supplying toner from the developing means to the image carrier within a non-transfer period to the paper. An image forming apparatus comprising: controlling an amount of static electricity irradiated to a non-residual portion of toner on a surface of an image carrier so as to be different from an amount of static electricity irradiated to a residual portion of toner.

Images