JP6589813B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a laser printer, and a facsimile. In particular, the image includes a corona charging type charging device, and drives a photosensitive drum and a fixing device with the same driving source. The present invention relates to a forming apparatus.

  In an image forming apparatus using an electrophotographic process, a toner image is formed on a photosensitive drum as an image carrier, and the toner image formed on the photosensitive drum is transferred onto a recording medium using a transfer member. Thereafter, an unfixed toner image is fixed on the recording medium by a fixing device including a fixing member such as a fixing roller or a fixing belt. When the fixing member is raised to a predetermined temperature (fixing temperature) or higher (hereinafter referred to as warm-up) when returning from the power saving mode or starting up from the standby state, the surface temperature of the fixing member is uniformly increased. It is necessary to perform warm-up while rotating the fixing member.

  On the other hand, there is a type in which the photosensitive drum and the fixing member are rotationally driven in synchronization by the same driving source (motor). In such a configuration, since the photosensitive drum rotates unnecessarily except during image formation, there is a problem that the photosensitive layer laminated on the surface of the photosensitive drum is worn.

  Therefore, for example, Patent Document 1 discloses that the heat roller and the photosensitive drum are rotated at a lower speed than the rotation speed at the time of image formation, thereby reducing noise and wear of the photosensitive layer on the surface of the photosensitive drum. An image forming apparatus for suppressing is disclosed.

JP-A-5-1955

  However, the method of Patent Document 1 does not describe anything about the setting of the charging voltage when rotating at low speed during the warm-up. It is known that when the photosensitive drum is driven to rotate without being charged, it is difficult to charge to a desired surface potential (charge is difficult to rise) during subsequent image formation.

  For this reason, it is necessary to apply a charging voltage even during rotational driving during warm-up. Here, when using a corona charging type charging device that generates a discharge by applying a voltage to the corona wire, if a charging voltage higher than necessary is applied, the surface potential of the photosensitive drum is set to the target value during image formation immediately after warm-up. And discharge products such as ozone, NOx, and SOx are generated in the same manner as in normal image formation.

  In view of the above problems, the present invention is provided with a corona charging type charging device, and in the configuration in which the image carrier and the fixing device are driven by the same drive source, the rising of the surface potential of the image carrier at the start of image formation. An object of the present invention is to provide an image forming apparatus capable of improving the quality and suppressing the generation of discharge products.

  In order to achieve the above object, a first configuration of the present invention includes an image carrier, a charging device, a transfer member, a fixing device, a voltage applying device, a driving device, and a control unit. Forming device. A photosensitive layer is formed on the surface of the image carrier. The charging device is a corona charging type in which the surface of the image carrier is charged by discharge from a corona wire. The transfer member is disposed on the downstream side of the charging device with respect to the rotation direction of the image carrier so as to be in contact with the image carrier, and transfers the toner image formed on the surface of the image carrier to the recording medium. The fixing device includes a heated rotating body heated by a heating unit and a pressure member pressed against the heated rotating body, and fixes the toner image transferred onto the recording medium. The voltage application device applies a charging voltage to the charging device. The driving device drives the image carrier and the fixing device in synchronization. The control unit controls the voltage application device and the driving device. The control unit rotates the image carrier and the heated rotating body at a lower speed than the time of image formation at the time of warming up to raise the surface temperature of the heated rotating body to a predetermined fixing temperature, and from the voltage application device to the corona wire. The applied wire voltage is made lower than that during image formation.

  According to the first configuration of the present invention, noise during wear-up and the wear of the photosensitive layer on the surface of the photosensitive drum are suppressed, and the rise of the surface potential of the image carrier is improved in printing immediately after the completion of warm-up. Can be made. Moreover, the production | generation of the discharge product by the discharge from the corona wire of a charging device can also be suppressed effectively. Furthermore, since it is possible to prevent the surface potential of the image carrier from becoming excessively high during printing immediately after warm-up, the occurrence of image defects due to overcharging of the image carrier can be improved.

1 is a side sectional view showing an internal structure of an image forming apparatus 100 according to an embodiment of the present invention. Partial enlarged view of the periphery of the image forming portion P in FIG. Block diagram showing a control path of the image forming apparatus 100 10 is a flowchart illustrating an example of control of the process linear velocity and the charging application voltage when executing warm-up in the image forming apparatus 100 of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view showing an internal structure of an image forming apparatus 100 according to an embodiment of the present invention, and FIG. 2 is an enlarged view of the vicinity of an image forming portion P in FIG. In the image forming apparatus (here, a monochrome printer) 100, an image forming portion P that forms a monochrome image by each process of charging, exposure, development, and transfer is disposed. In the image forming portion P, a photosensitive drum 5 that carries a visible image (toner image) is disposed. A charging device 4, a developing device 8, a transfer roller 14, a cleaning device 19, and a charge eliminating device 6 are disposed along the rotation direction of the photosensitive drum 5 (counterclockwise direction in FIG. 2). An exposure unit (laser scanning unit or the like) 7 is disposed above the image forming portion P.

  The photosensitive drum 5 includes a base tube 5a as a support and a photosensitive layer 5b formed on the surface of the base tube 5a. In the present embodiment, a positively charged single layer type in which a charge generating agent, a charge transporting agent, a binder resin (binder), and a filler are contained in the same layer as the photosensitive layer 5b on the outer peripheral surface of an aluminum cylindrical tube 5a. An organic photosensitive layer (OPC) is laminated. The photosensitive drum 5 rotates counterclockwise in FIG. 2 by a driving force from the main motor 50 (see FIG. 3). An amorphous silicon photosensitive layer may be laminated as the photosensitive layer 5b.

  The charging device 4 is disposed so as to face the photosensitive drum 5 over substantially the entire region in the longitudinal direction of the photosensitive drum 5 (direction perpendicular to the paper surface of FIG. 2). The charging device 4 is provided at a shield member (housing) having a U-shaped cross section having an open portion on the surface side of the photosensitive drum 5, a corona wire 21 to which a high voltage is applied, and an open portion of the shield member. This is a scorotron system having a grid 23, and the surface of the photosensitive drum 5 is charged to a predetermined positive potential (same polarity as the toner) through the grid 23 by corona discharge from the corona wire 21.

  The developing device 8 is a two-component developing type having two agitating / conveying screws (not shown) and a developing roller 25, and is formed on the surface of the developing roller 25 using a two-component developer containing a magnetic carrier and toner. A magnetic brush is formed, and the toner is attached by bringing the magnetic brush into contact with the surface of the photosensitive drum 5 in a state where a developing bias having the same polarity (positive) as that of the toner is applied to the developing roller 25.

  The transfer roller 14 transfers the toner image formed on the surface of the photosensitive drum 5 onto a sheet (recording medium). The cleaning device 19 includes a cleaning blade 27 that is in line contact with the photosensitive drum 5 in the longitudinal direction, and a recovery spiral (not shown) that discharges waste toner scraped from the surface of the photosensitive drum 5 by the cleaning blade 27. After the toner image is transferred to the paper, residual toner on the surface of the photosensitive drum 5 is removed. Further, a static elimination device 6 that removes residual charges on the surface of the photosensitive drum 5 is provided on the downstream side of the cleaning device 19 with respect to the rotation direction of the photosensitive drum 5. The static eliminator 6 irradiates the surface of the photosensitive drum 5 with static elimination light to remove residual charges.

  The fixing device 15 detects the temperature of the surface of the fixing roller 15a, the fixing roller 15a that is a heated rotating body, the pressure roller 15b that is a pressure member, the heater 30 disposed inside the fixing roller 15a. And a fixing temperature sensor 60 (see FIG. 3). The fixing roller 15a is rotated by a driving force from the main motor 50 (see FIG. 3), and the pressure roller 15b is rotated following the fixing roller 15a.

  When the image forming operation is performed, the photosensitive drum 5 rotating in the counterclockwise direction is uniformly charged by the charging device 4, and the electrostatic latent image is formed on the photosensitive drum 5 by the laser beam from the exposure unit 7 based on the image data. An image is formed, and toner is attached to the electrostatic latent image by the developing device 8 to form a toner image. The toner is supplied to the developing device 8 from the toner container 9. The image data is transmitted from a personal computer (hereinafter referred to as a personal computer).

  A sheet is conveyed from the sheet feeding cassette 10 or the manual sheet feeder 11 via the sheet conveying path 12 and the registration roller pair 13 toward the photosensitive drum 5 on which the toner image is formed as described above, and the transfer roller 14. As a result, the toner image formed on the surface of the photosensitive drum 5 is transferred to the sheet. The sheet on which the toner image has been transferred is separated from the photosensitive drum 5 and conveyed to the fixing device 15 to fix the toner image. The sheet that has passed through the fixing device 15 is conveyed to the upper part of the apparatus through the sheet conveying path 16, and is discharged to the discharge tray 18 by the discharge roller pair 17 when an image is formed on only one side of the sheet (during single-sided printing).

  Next, the control path of the image forming apparatus 100 of the present invention will be described. FIG. 3 is a block diagram illustrating an example of a control path used in the image forming apparatus 100 of the present invention. It should be noted that since various control of each part of the apparatus is performed when the image forming apparatus 100 is used, the control path of the entire image forming apparatus 100 becomes complicated. Therefore, here, a portion of the control path that is necessary for the implementation of the present invention will be mainly described.

  The control unit 90 includes a central processing unit (CPU) 91 as a central processing unit, a read only memory (ROM) 92 that is a read-only storage unit, a random access memory (RAM) 93 that is a readable / writable storage unit, A plurality of (here, two) I / Os that temporarily transmit control signals to and receive input signals from the operation unit 70. F (interface) 96 is provided at least. In addition, the control unit 90 can be arranged at any location inside the main body of the image forming apparatus 100.

  The ROM 92 stores a control program for the image forming apparatus 100, data necessary for control, and the like that are not changed during use of the image forming apparatus 100. The RAM 93 stores necessary data generated during the control of the image forming apparatus 100, data temporarily required for controlling the image forming apparatus 100, and the like. Further, the ROM 92 (or RAM 93) is applied to the corona wire 21 of the charging device 4 during the warm-up, and the rotational speed (process linear speed) of the photosensitive drum 5 and the fixing roller during the warm-up, as will be described later. A voltage value and the like are also stored.

  In addition, the control unit 90 transmits a control signal from the CPU 91 to the respective units and apparatuses in the image forming apparatus 100 through the I / F 96. In addition, a signal indicating the state and an input signal are transmitted from each part or device to the CPU 91 through the I / F 96. Examples of the parts and devices controlled by the control unit 90 include the image forming unit P, the exposure unit 7, the fixing device 15, the image input unit 40, the voltage control circuit 41, the main motor 50, the fixing temperature sensor 60, and the operation unit 70. Etc.

  The image input unit 40 is a receiving unit that receives image data transmitted from the personal computer or the like to the image forming apparatus 100. The image signal input from the image input unit 40 is converted into a digital signal and then sent to the temporary storage unit 94.

  The voltage control circuit 41 is connected to the charging voltage power source 42, the developing voltage power source 43, the transfer voltage power source 44, and the fixing voltage power source 45, and operates each of these power sources by an output signal from the control unit 90. Each of the power sources is controlled by a control signal from the voltage control circuit 41, the charging voltage power source 42 is supplied to the corona wire 21 and the grid 23 in the charging device 4, the developing voltage power source 43 is supplied to the developing roller 25 in the developing device 8, and A predetermined voltage is applied to the transfer roller 14, and a fixing voltage power supply 45 is applied to a heater 30 (see FIG. 1) built in the fixing roller 15 a of the fixing device 15.

  The main motor 50 drives driven members in the image forming apparatus 100 including the photosensitive drum 5 and the fixing device 15 (fixing roller 15a) based on a control signal from the control unit 90.

  The fixing temperature sensor 60 is disposed to face the fixing roller 15a and detects the surface temperature of the fixing roller 15a. As the fixing temperature sensor 60, a thermistor or the like that can detect the surface temperature of the fixing roller 15a in a non-contact manner is used.

  The operation unit 70 is provided with a liquid crystal display unit 71 and LEDs 72 indicating various states. The user operates the stop / clear button of the operation unit 70 to stop image formation, and operates the reset button to operate the image. Various settings of the forming apparatus 100 are set to a default state. The liquid crystal display unit 71 displays the state of the image forming apparatus 100, and displays the image forming status and the number of copies to be printed. Various settings of the image forming apparatus 100 are performed from a printer driver of a personal computer.

  Hereinafter, the control of the process linear velocity and the charging applied voltage during the warm-up, which is a characteristic part of the present invention, will be described. As described above, in order to improve the rising of the surface potential of the photosensitive drum 5 in printing immediately after warm-up, it is necessary to rotationally drive the photosensitive drum 5 with the charging voltage applied to the charging device 4. Further, in order to suppress wear of the photosensitive layer 5b, it is necessary to rotate the photosensitive drum 5 at a low speed. However, when the photosensitive drum 5 is rotated at a lower speed than usual and the same charging voltage is applied from the charging voltage power source 42 to the charging device 4 at the time of image formation, the surface of the photosensitive drum 5 is printed immediately after warm-up printing. The potential becomes higher than the target potential, which may cause image defects. Further, the discharge product of the same amount as that at the time of image formation is generated during the warm-up and adheres to the surface of the photosensitive layer 5b, so that the life of the photosensitive drum 5 is shortened.

  Therefore, in the image forming apparatus 100 according to the present invention, the photosensitive drum 5 and the fixing device 15 are driven at a lower speed than during image formation during warm-up, and the charging voltage applied to the charging device 4 is decreased as compared to during image formation. . Specifically, the voltage (grid voltage) applied to the grid 23 of the charging device 4 is the same as that during image formation, and the voltage (wire voltage) applied to the corona wire 21 is lower than that during image formation. The charging current (main charging current) flowing through the wire 21 is reduced as compared with that during image formation. At this time, the wire voltage applied to the corona wire 21 is set according to the rotational speed of the photosensitive drum 5 so that the surface potential of the photosensitive drum 5 becomes substantially the same as that at the time of image formation.

  Thereby, the rising of the surface potential of the photosensitive drum 5 is improved in printing immediately after the warm-up is completed, and the generation of discharge products can be effectively suppressed. Note that, instead of lowering the wire voltage applied to the corona wire 21, the surface potential of the photosensitive drum 5 can be charged to substantially the same potential as when the image is formed even if the grid voltage applied to the grid 23 is lowered. However, since the generation of ozone and discharge products is greatly affected by the discharge from the corona wire 21, it is possible to effectively suppress the generation of ozone and discharge products by reducing the wire voltage applied to the corona wire 21. it can. In addition, since only the wire voltage is varied without changing the grid voltage, the control of the charging voltage can be simplified.

  Alternatively, the grid voltage applied to the grid 23 can be higher than that during image formation. As a result, the wire voltage applied to the corona wire 21 can be further reduced when the surface potential of the photosensitive drum 5 is charged to substantially the same potential as during image formation during warm-up, generating ozone and discharge products. Can be more effectively suppressed.

  FIG. 4 is a flowchart illustrating an example of control of the process linear velocity and the charge application voltage when executing warm-up in the image forming apparatus 100 of the present invention. With reference to FIGS. 1 to 3 as necessary, the control procedure of the process linear velocity and the charge application voltage during the warm-up will be described along the steps of FIG. The image forming speed of the image forming apparatus 100 (process linear speed) is 240 mm / s, the main charging current flowing through the corona wire 21 during image formation is 310 μA, the grid voltage is 500 V, and the surface potential of the photosensitive drum 5 is 420 V. It is set to become. Further, it is assumed that the image forming apparatus 100 is in a standby state (print waiting state) at the start of FIG. 4 and the fixing roller 15a is maintained at a temperature lower than the fixing temperature.

  When a print command is input from the host device (host device) such as a personal computer to the control unit 90 (step S1), the control unit 90 sets the image forming speed (process linear speed) to 80 mm / s (step S2). Further, the controller 90 sets the main charging current flowing through the corona wire 21 to be 155 μA (step S3). Specifically, the control unit 90 transmits a control signal to the bias application circuit 41, and the corona wire 21 is supplied from the charging voltage power source 42 so that the main charging current is 155 μA while the grid voltage is the same as that at the time of image formation. Sets the wire voltage applied to.

  Next, warm-up is started by the control unit 90 (step S4). Specifically, a control signal is transmitted from the controller 90 to the main motor 50, and the photosensitive drum 5 and the fixing roller 15a are rotated at the speed (80 mm / s) set in step S2. Then, the temperature of the fixing roller 15a is increased by increasing the voltage applied from the fixing voltage power supply 45 to the heater 30 while the photosensitive drum 5 and the fixing roller 15a are rotated.

  Next, the control unit 90 determines whether or not the surface temperature of the fixing roller 15a has reached a predetermined fixing temperature based on a detection signal from the fixing temperature sensor 60 (step S5). When the surface temperature of the fixing roller 15a reaches a predetermined fixing temperature (Yes in Step S5), the control unit 90 sets the image forming speed (process linear speed) to 240 mm / s (Step S6). Further, the controller 90 sets the main charging current flowing through the corona wire 21 to 310 μA (step S7). Specifically, the control unit 90 transmits a control signal to the bias application circuit 41 and sets the wire voltage applied from the charging voltage power source 42 to the corona wire 21 so that the main charging current becomes 310 μA. Thereafter, printing is started (step S8).

  Then, it is determined whether or not the printing is finished (step S9). If the printing is finished (Yes in step S9), the image forming apparatus 100 is shifted to the standby state again (step S10) and the process is finished. To do.

  According to the above control, the main charging current flowing through the corona wire 21 is imaged while rotating the photosensitive drum 5 and the fixing roller 15a at a lower speed (80 mm / s) than during image formation (240 mm / s) during warm-up. By reducing (155 μA) from the formation (310 μA), the surface of the photosensitive drum 5 at the time of warm-up can be charged to a substantially target potential (substantially the same potential as the surface potential at the time of image formation).

  As a result, noise during the warm-up and the wear of the photosensitive layer 5b on the surface of the photosensitive drum 5 are suppressed, and the rise of the surface potential of the photosensitive drum 5 is improved. Also, the generation of discharge products during warm-up can be suppressed. Furthermore, since it is possible to prevent the surface potential of the photosensitive drum 5 from becoming excessively high during printing immediately after warm-up, it is possible to improve the occurrence of image defects due to overcharging of the photosensitive drum 5.

  Since the surface potential of the photosensitive drum 5 at the time of warm-up is not required to be as precise as the surface potential at the time of image formation (printing), there is no problem as long as it is approximately the same as the surface potential at the time of image formation. .

  In the above embodiment, the process linear velocity and charging application voltage control procedure at the time of warm-up from the standby state has been described, or the warm-up at the time of returning from the power saving mode (sleep mode) is exactly the same. I can explain. In the power saving mode, since the power supply to the fixing roller 15a is off, the warm-up time (the rotation time of the photosensitive drum 5) is longer than the warm-up from the standby state. Therefore, controlling the process linear velocity and the charge application voltage as in the above embodiment is particularly effective from the viewpoint of suppressing wear of the photosensitive drum 5 and generation of discharge products.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above embodiment, the photosensitive drum 5 and the fixing roller 15a are rotated at a speed 1/3 (80 mm / s) at the time of image formation at the time of warm-up. The rotational speed of 15a can be set arbitrarily.

  In the above embodiment, the scorotron charging device 4 including the corona wire 21 and the grid 23 is used. However, instead of the scorotron charging device 4, there is no grid and the corotron method includes only the corona wire. Even in an image forming apparatus equipped with the above-mentioned charging device, by adjusting the charging voltage applied to the corona wire during warm-up, the main charging current flowing through the corona wire is reduced compared with that during image formation, so that substantially the same effect is achieved. Thus, substantially the same effect can be obtained.

  Further, the present invention is not limited to the monochrome printer as shown in FIG. 1, and includes a corona charging type charging device such as a color printer, a digital multifunction peripheral, a color copying machine, etc., and the photosensitive drum and the fixing device are the same. The present invention can be applied to various image forming apparatuses that are driven by a driving source.

  The present invention can be used in an image forming apparatus in which a photosensitive drum and a fixing device are driven by the same drive source. By utilizing the present invention, the surface of the photosensitive drum in printing immediately after the end of warm-up can be accurately charged to a desired surface potential, the rise of the surface potential can be improved, and the generation of discharge products can also be suppressed. An image forming apparatus can be provided.

P Image forming unit 4 Charging device 5 Photosensitive drum (image carrier)
6 Static eliminating device 8 Developing device 14 Transfer roller (transfer member)
15 Fixing device 15a Fixing roller (heated rotating body)
15b Pressure roller (pressure member)
21 Corona wire 23 Grid 41 Voltage control circuit (voltage application device)
42 Charging voltage power supply (voltage application device)
50 Main motor (drive device)
90 control unit 100 image forming apparatus

Claims (3)

An image carrier having a photosensitive layer formed on the surface;
A corona charging type charging device for charging the surface of the image carrier by discharge from a corona wire;
A transfer member disposed on the downstream side of the charging device with respect to the rotation direction of the image carrier so as to contact the image carrier, and transferring a toner image formed on the surface of the image carrier to a recording medium;
A fixing device having a heated rotating body heated by a heating unit and a pressure member pressed against the heated rotating body, and fixing the toner image transferred onto the recording medium;
A voltage applying device for applying a charging voltage to the charging device;
One driving device for driving the image carrier and the fixing device in synchronization;
A control unit for controlling the voltage application device and the driving device;
In an image forming apparatus comprising:
The control unit rotates the image carrier and the heated rotating body at a lower speed than during image formation during warm-up to increase the surface temperature of the heated rotating body to a predetermined fixing temperature, and applies the voltage. Lower the wire voltage applied to the corona wire from the device than during image formation ,
The charging device is a scorotron system including the corona wire and a grid, and the voltage applying device applies a grid voltage to the grid,
The control unit makes the grid voltage higher than that at the time of image formation, and lowers the wire voltage than at the time of image formation.   The image forming apparatus according to claim 1, wherein the control unit sets the wire voltage so that a surface potential of the image carrier during the warm-up is substantially the same as that during image formation. The image forming apparatus according to claim 1 , wherein the image bearing member includes an amorphous silicon photosensitive layer formed as the photosensitive layer .

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