JP2017032747A - Image forming apparatus and control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a phenomenon in which a developer is attached to a non-exposed portion of a photoreceptor during a period to decelerate the photoreceptor.SOLUTION: An image forming apparatus comprises: a photoreceptor (photoreceptor drum 61); a charger 62 that charges the photoreceptor; a developing roller 71 that is in contact with the photoreceptor to supply a developer; and a control part 100. The control part 100 executes image formation control of rotating the photoreceptor and developing roller 71 to apply an image formation voltage to the developing roller 71, deceleration control of gradually decelerating the photoreceptor and developing roller 71 to a halt, and first voltage control of applying, to the developing roller 71, a post-image formation voltage larger than the image formation voltage during the deceleration control.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus having a voltage applied to a developing roller for supplying a developer to a photosensitive member, a controller for controlling rotation of the photosensitive member and the developing roller, and a control method by the controller.

  Conventionally, during the deceleration period in which the photoconductor is gradually decelerated while rotating by inertia when the motor is turned off after printing, the development voltage is maintained at the same value as at the time of printing or smaller than the value at the time of printing. There is known an image forming apparatus including a control unit that performs control (see Patent Document 1). In this technique, by controlling the developing voltage as described above during the deceleration period, the potential difference between the photosensitive member and the developing roller becomes the same value or more than that during printing.

JP 2001-257216 A

  By the way, the inventor of the present application develops the image on the developing roller when the potential difference between the photosensitive member and the developing roller is relatively large during the deceleration period and the charge amount of the developer on the developing roller is reduced. It was confirmed by experiments and the like that a phenomenon occurs in which the agent adheres to the non-exposed portion of the photoreceptor. Therefore, in the conventional technology in which the potential difference between the photosensitive member and the developing roller is relatively large during the deceleration period, when the charge amount of the developer on the developing roller is reduced, the developer is not in contact with the photosensitive member. There is a possibility that a phenomenon of adhering to the exposed portion may occur.

  Accordingly, an object of the present invention is to suppress a phenomenon in which a developer adheres to a non-exposed portion of a photoreceptor during a deceleration period.

In order to solve the above problems, an image forming apparatus according to the present invention includes a photoconductor, a charger that charges the photoconductor, a developing roller that contacts the photoconductor and supplies a developer, and a control unit. .
The control unit rotates the photosensitive member and the developing roller, applies image forming voltage to the developing roller, decelerates the photosensitive member and the developing roller to decelerate toward the stop, and decelerates the developing roller. And a first voltage control for applying a post-image voltage larger than the image voltage.

  The control method according to the present invention is a control method for controlling the development voltage applied to the developing roller for supplying the developer to the photosensitive member and the rotation of the photosensitive member and the developing roller, the rotating the photosensitive member and the developing roller. In the image forming process for applying an image forming voltage to the developing roller, the decelerating process for decelerating the photosensitive member and the developing roller toward the stop, and the deceleration control, a post-image forming voltage larger than the image forming voltage is applied to the developing roller. And a voltage control process to be applied.

  According to each configuration described above, in the section in which the photosensitive member and the developing roller are decelerated toward the stop, the post-image forming voltage larger than that at the time of image formation is applied to the developing roller, so that there is a gap between the photosensitive member and the developing roller. Therefore, it is possible to suppress the developer from adhering to the non-exposed portion of the photoreceptor due to a decrease in the charge amount of the developer.

  According to the present invention, it is possible to suppress the phenomenon that the developer adheres to the non-exposed portion of the photoconductor in the section where the photoconductor and the developing roller are decelerated toward the stop.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. It is an expanded sectional view which expands and shows the structure of the rear part of a process cartridge. It is a figure which shows the relationship between a control part and each member to which a voltage is applied by a control part. It is a figure which shows the relationship between the motor and drive mechanism for driving each member of a process cartridge, and a control part. It is a figure which shows an environment judgment table. It is a flowchart which shows preparation rotation control and image formation control. It is a flowchart which shows each voltage control in deceleration control. It is a time chart which shows an example of operation | movement of the control part at the time of high humidity and non-high humidity. It is a flowchart which shows the modification of preparatory rotation control. It is a flowchart which shows the modification of 1st voltage control. It is a time chart which shows an example of operation | movement of the control part according to the flowchart of FIG. 9 and FIG.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, the schematic configuration of the image forming apparatus according to the embodiment will be described first, and then the detailed configuration of the characteristic part of the present invention will be described. Moreover, in the following description, a direction is demonstrated by the direction shown in FIG. Specifically, the right side of FIG. 1 is “front”, the left side of FIG. 1 is “rear”, the front side of FIG. 1 is “left”, and the back side of FIG. 1 is “right”. Further, the vertical direction in FIG.

  As shown in FIG. 1, a laser printer 1 as an example of an image forming apparatus includes a main body housing 2, a paper feeding unit 3 that supplies paper S, and an image forming unit that forms an image on the fed paper S. G mainly.

  The paper feed unit 3 is provided at a lower portion in the main body housing 2 and mainly includes a paper feed tray 31 that accommodates the paper S, a paper pressing plate 32, a paper feed mechanism 33, and a registration roller 34. Yes. The paper feed unit 3 brings the paper S in the paper feed tray 31 upward by the paper pressing plate 32, feeds the paper S one by one by the paper feed mechanism 33, and supplies it to the image forming unit G.

  The image forming unit G includes an exposure device 4, a process cartridge 5, and a fixing device 8.

  The exposure apparatus 4 is disposed in the upper part of the main body housing 2 and includes a laser light emitting unit (not shown), a polygon mirror, a lens, a reflecting mirror, and the like that are not shown. The exposure device 4 exposes the surface of the photoconductive drum 61 by scanning the surface of the photoconductive drum 61 with laser light (refer to the chain line) based on the image data emitted from the laser light emitting unit at high speed.

  The process cartridge 5 is disposed below the exposure apparatus 4 and is configured to be detachable from the main body housing 2 through an opening formed when the front cover 21 provided on the main body housing 2 is opened. The process cartridge 5 includes a drum unit 6 and a developing unit 7. The drum unit 6 mainly includes a photoreceptor drum 61 as an example of a photoreceptor, a scorotron charger 62, and a transfer roller 63. The developing unit 7 includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, a storage portion 74 that stores positively chargeable toner as a developer, and an agitator 75 that rotates in the storage portion 74. Has mainly.

  In the process cartridge 5, the surface of the photosensitive drum 61 that is rotationally driven is uniformly charged by the charger 62 and exposed by the laser beam from the exposure device 4, so that the photosensitive drum 61 is based on the image data. An electrostatic latent image is formed. The agitator 75 rotates in the container 74 to convey the toner in the container 74 toward the developing roller 71 while stirring. The supply roller 72 rotates in contact with the developing roller 71 to supply the toner discharged from the storage portion 74 by the agitator 75 to the developing roller 71. The developing roller 71 rotates in contact with the layer thickness regulating blade 73 so as to carry the toner regulated to a certain thickness with the layer thickness regulating blade 73 on the surface.

  Thereafter, the developing unit 7 supplies the toner carried on the developing roller 71 to the photosensitive drum 61 to visualize the electrostatic latent image, and forms a toner image on the photosensitive drum 61. Then, the paper S supplied from the paper supply unit 3 is conveyed between the photosensitive drum 61 and the transfer roller 63, whereby the toner image on the photosensitive drum 61 is transferred to the paper S.

  The fixing device 8 is disposed behind the process cartridge 5 and sandwiches the fixing belt 81B between a heating unit 81 having a halogen heater 81A, a fixing belt 81B, a nip plate 81C, and the nip plate 81C of the heating unit 81. A pressure roller 82 is mainly provided. The fixing device 8 heat-fixes the toner image on the paper S by conveying the paper S on which the toner image is transferred between the heating unit 81 and the pressure roller 82. The paper S on which the toner image has been thermally fixed is discharged onto a paper discharge tray 22 by a paper discharge roller 23.

  As shown in FIG. 2, the process cartridge 5, specifically, the drum unit 6 constituting the process cartridge 5 includes a photosensitive drum 61, a charger 62, a transfer roller 63, and the like, as well as a cleaning unit 64, a static elimination lamp. 90 and a drum frame 200. Note that the charger 62 according to the present embodiment includes a charging wire 62A and a grid electrode 62B disposed between the charging wire 62A and the photosensitive drum 61.

  The photosensitive drum 61 is a member in which a photosensitive layer is formed on the outer peripheral surface of a cylindrical drum body 61B having conductivity, and is provided in a state where a shaft 61A conducting to the drum body 61B is grounded. The charger 62 is disposed above the photosensitive drum 61 so as to face the photosensitive drum 61 with respect to the photosensitive drum 61, and the transfer roller 63 contacts the photosensitive drum 61 below the photosensitive drum 61. Are arranged. Further, the developing roller 71 of the developing unit 7 is downstream of the position where the photosensitive drum 61 and the charger 62 face each other in the rotational direction indicated by the arrow of the photosensitive drum 61, and is transferred to the photosensitive drum 61. It is arranged in contact with the photosensitive drum 61 on the upstream side of the position facing the roller 63. The rotation direction of the developing roller 71 is a direction in which the surface moves in the same direction at the contact portion with the photosensitive drum 61 as indicated by an arrow. In other words, the direction of rotation around the rotation axis is opposite between the photosensitive drum 61 and the developing roller 71. The supply roller 72 is disposed in contact with a portion of the developing roller 71 opposite to the photosensitive drum 61.

  The cleaning unit 64 is a unit for collecting deposits such as toner and paper dust attached to the outer peripheral surface of the photosensitive drum 61 after the transfer of the toner image, and includes a cleaning roller 64A, a collection roller 64B, and a scraping member. 64C and a cleaning frame 64D that supports the cleaning roller 64A and the like. The cleaning roller 64A is downstream of the position where the photosensitive drum 61 and the transfer roller 63 face each other in the rotational direction of the photosensitive drum 61, and more than the position where the photosensitive drum 61 and the charger 62 face each other. On the upstream side, it is arranged close to the photosensitive drum 61 to such an extent that deposits can be collected.

  The cleaning unit 64 collects deposits on the photosensitive drum 61 by the cleaning roller 64A, and collects deposits deposited on the cleaning roller 64A by the collection roller 64B. Then, the adhering matter adhering to the collection roller 64B is scraped off from the collection roller 64B by the scraping member 64C and stored in the storage section 64E formed in the cleaning frame 64D.

  The static elimination lamp 90 has a light emitting portion 91 that faces the surface of the photosensitive drum 61, and emits light from the light emitting portion 91 to the surface of the photosensitive drum 61, thereby remaining on the surface of the photosensitive drum 61 after transfer. It is configured so as to attenuate the electric charge. The light emitting portion 91 of the charge removal lamp 90 is downstream of the position where the photosensitive drum 61 and the transfer roller 63 face in the rotation direction of the photosensitive drum 61, and the photosensitive drum 61 and the cleaning roller 64A face each other. It is disposed on the upstream side of the position where it is opposed to the photosensitive drum 61.

  The drum frame 200 is a member that forms a frame of the drum unit 6. The drum frame 200 supports the photosensitive drum 61, the transfer roller 63, and the like in a rotatable manner, and supports the cleaning unit 64. The drum frame 200 is configured such that the developing unit 7 is detachably mounted.

Next, features of the present invention will be described in detail.
As shown in FIG. 1, an in-machine temperature sensor SE <b> 1 as an example of a temperature sensor, a humidity sensor SE <b> 2, and a control unit 100 (see FIG. 3) are provided in the main body housing 2.

  The in-machine temperature sensor SE1 is, for example, a thermistor, and is configured to detect an in-machine temperature that is the temperature in the main body housing 2. The in-machine temperature sensor SE1 is arranged at a position between the fixing device 8 and the process cartridge 5 in the main body housing 2 in the front-rear direction. That is, the in-machine temperature sensor SE <b> 1 is disposed outside the process cartridge 5 in the main body housing 2.

  The humidity sensor SE <b> 2 is a sensor that detects relative humidity, for example, and is disposed to face the inside of the air inlet 24 formed in the main body housing 2. The humidity sensor SE <b> 2 is configured to detect the humidity outside the main body housing 2 by detecting the humidity of the air taken in from the intake port 24. The temperature detected by the in-machine temperature sensor SE1 and the humidity detected by the humidity sensor SE2 are output to the control unit 100 shown in FIG.

  The control unit 100 includes a CPU, a RAM, a ROM, an input / output circuit, and the like, and functions to apply a voltage to the charger 62, the developing roller 71, the transfer roller 63, the supply roller 72, the cleaning roller 64A, the charge removal lamp 90, and the like. have. As shown in FIG. 4, the control unit 100 also has a function of controlling a motor 210 and a speed change mechanism 220 provided in the main body housing 2.

  The motor 210 is a driving source for supplying driving force to the photosensitive drum 61, the developing roller 71, the supply roller 72, the agitator 75, the cleaning roller 64A, and the like. It is controlled by the control unit 100 to rotate at a large second rotation speed. Since the photosensitive drum 61 is connected to the motor 210 at a fixed gear ratio, when the motor 210 is set to the first rotation speed, the photosensitive drum 61 rotates at the first drum peripheral speed corresponding to the first rotation speed, and the motor Assuming that 210 is the second rotation speed, the second rotation speed corresponds to the second rotation speed and rotates at a second drum peripheral speed larger than the first drum peripheral speed. In the following description, the first rotation speed and the first drum peripheral speed are also referred to as “low speed”, and the second rotation speed and the second drum peripheral speed are also referred to as “high speed”.

  The motor 210 is connected to the photosensitive drum 61 and the cleaning roller 64A via a predetermined number of gears, and the developing roller 71, the supply roller 72, and the agitator 75 are rotated at a rotational speed of the developing roller 71 and the like. Are connected via a speed change mechanism 220 for changing. Specifically, the developing roller 71, the supply roller 72, and the agitator 75 are connected via a predetermined gear, and are configured to rotate simultaneously at a predetermined peripheral speed ratio.

  The speed change mechanism 220 is a mechanism for switching the gear ratio between the motor 210 and the developing roller 71. When the motor 210 rotates at a low speed, the speed change mechanism 220 switches the circumferential speed v of the developing roller 71 between a first roller circumferential speed v1 and a second roller circumferential speed v2 that is larger than the first roller circumferential speed v1. . Here, the first roller circumferential speed v1 is set to a value larger than zero. When the peripheral speed v of the developing roller 71 is switched by the speed change mechanism 220, the peripheral speed ratio of the developing roller 71 with respect to the photosensitive drum 61 is switched. In the present embodiment, the second roller circumferential speed v2 is a value greater than the circumferential speed of the photosensitive drum 61, and the first roller circumferential speed v1 is a value smaller than the circumferential speed of the photosensitive drum 61. . That is, when the peripheral speed v of the developing roller 71 is set to the first roller peripheral speed v1, the peripheral speed ratio of the developing roller 71 to the photosensitive drum 61 is less than 1, and the peripheral speed v of the developing roller 71 is changed to the second roller peripheral speed v1. When the speed is v2, the peripheral speed ratio of the developing roller 71 to the photosensitive drum 61 is 1 or more.

  The speed change mechanism 220 includes a first transmission mechanism 221 having a first gear ratio for rotating the developing roller 71 at the second roller circumferential speed v2, and a mechanism for rotating the developing roller 71 at the first roller circumferential speed v1. A second transmission mechanism 222 configured with a second gear ratio and an electromagnetic clutch 223 for switching the transmission path of the driving force from the motor 210 to the first transmission mechanism 221 or the second transmission mechanism 222 are provided. In this speed change mechanism 220, when the electromagnetic clutch 223 is turned off, the driving force from the motor 210 is transmitted to the developing roller 71 via the second transmission mechanism 222, and when the electromagnetic clutch 223 is turned on, the driving force from the motor 210 is transmitted. Is transmitted to the developing roller 71 via the first transmission mechanism 221.

  The control unit 100 performs preparation rotation control for rotating the photosensitive drum 61 and the developing roller 71 before forming the electrostatic latent image on the photosensitive drum 61 and forms the electrostatic latent image on the photosensitive drum 61. Image forming control, and deceleration control for gradually decelerating the photosensitive drum 61 and the developing roller 71 toward the stop. In addition, when applying a voltage to the charger 62, the control unit 100 applies a wire voltage Vw to the charging wire 62 </ b> A of the charger 62, so that a positive voltage as an example of a charging voltage is applied to the grid electrode 62 </ b> B. A grid voltage Vg is applied. Further, when applying a voltage to the developing roller 71, the control unit 100 applies a positive developing voltage Vb having the same polarity as the grid voltage Vg to the developing roller 71.

  The control unit 100 is configured to execute preparatory rotation control when receiving a print command. In the preparatory rotation control, the control unit 100 rotates the motor 210 at a low speed and switches the electromagnetic clutch 223 on and off according to the temperature and humidity detected by the sensors SE1 and SE2, so that the circumference of the developing roller 71 is increased. Switching speed.

  Specifically, in the preparation rotation control, when the humidity at a predetermined temperature is equal to or lower than the predetermined humidity, the control unit 100 turns off the electromagnetic clutch 223 to rotate the developing roller 71 at the first roller circumferential speed v1. Further, in the preparatory rotation control, when the humidity at a predetermined temperature is higher than the predetermined humidity, the control unit 100 turns on the electromagnetic clutch 223 to move the developing roller 71 to the second roller peripheral speed greater than the first roller peripheral speed v1. Rotate at speed v2. In the following description, an environment where the humidity at a predetermined temperature is higher than the predetermined humidity is described as high humidity, and an environment where the humidity at the predetermined temperature is equal to or lower than the predetermined humidity is described as non-high humidity.

  The control unit 100 refers to the environment determination table shown in FIG. 5 to determine whether or not the humidity is high. If the control unit 100 determines that the humidity is not high, that is, non-high humidity, the control unit 100 moves the developing roller 71 to the first level. When the roller is rotated at the peripheral speed v1 of one roller and it is determined that the humidity is high, the developing roller 71 is rotated at the peripheral speed v2 of the second roller. Specifically, when the temperature is less than 10 ° C., the control unit 100 determines that the humidity is less than 80% and the humidity is less than 80%, and the humidity is greater than 80%. Judge.

  When the temperature is 10 ° C. or more and less than 20 ° C., the control unit 100 determines that the humidity is non-high humidity when the humidity is less than 70%, and the humidity is high when the humidity is 70% or more. Judge that there is. When the temperature is 20 ° C. or more and less than 30 ° C., the control unit 100 determines that the humidity is non-high humidity when the humidity is less than 60%, and the humidity is high when the humidity is 60% or more. Judge that there is.

  In the preparatory rotation control, when the temperature is 30 ° C. or higher, the control unit 100 determines that the humidity is less than 50% and the humidity is less than 50%, and the humidity is 50% or more. Judge. The environment determination table is used to examine the relationship between temperature, humidity, peripheral speed of the developing roller 71, grid voltage Vg and developing voltage Vb, which will be described later, and toner adhesion to the non-exposed portion of the photosensitive drum 61. It is set by experiment and simulation. Specifically, the temperature / humidity range in which the toner does not adhere to the non-exposed portion of the photosensitive drum 61 when preparatory rotation control is performed with the peripheral speed of the developing roller 71 as the first roller peripheral speed v1 is shown in FIG. A range indicated by white and a range of temperature / humidity in which the toner may adhere to the non-exposed portion is a range indicated by hatching in FIG.

  Further, in the preparatory rotation control, the control unit 100 applies the first grid voltage Vg1 to the grid electrode 62B and applies the first development voltage Vb1 smaller than the first grid voltage Vg1 to the developing roller 71. It is configured.

  The control unit 100 is configured to execute image formation control after completion of the preparation rotation control. In the image formation control, the control unit 100 rotates the motor 210 at a high speed and turns on the electromagnetic clutch 223 to rotate the photosensitive drum 61 at a higher speed than in the preparation rotation control, thereby causing the developing roller 71 to rotate. It has a function of rotating at a third roller peripheral speed v3 that is greater than the second roller peripheral speed v2. Specifically, when the image forming control is started, the control unit 100 switches the motor 210 from a low speed to a high speed, and when the electromagnetic clutch 223 remains OFF in the preparation rotation control, the electromagnetic clutch 223 is turned ON from OFF. When the electromagnetic clutch 223 is turned on in the preparation rotation control, the electromagnetic clutch 223 is maintained in the ON state. Thus, by always turning on the electromagnetic clutch 223 in the image formation control, the peripheral speed ratio of the developing roller 71 to the photosensitive drum 61 is 1 or more in the image forming control, that is, the developing roller 71 is more than the photosensitive drum 61. The peripheral speed is increased.

  Further, in the image formation control, the control unit 100 applies a second grid voltage Vg2 as an example of an image forming charging voltage, which is higher than the first grid voltage Vg1, to the grid electrode 62B, and also applies a second to the developing roller 71. The second developing voltage Vb2 as an example of the image forming voltage that is higher than the first developing voltage Vb1 is applied. The second development voltage Vb2 is a voltage smaller than the second grid voltage Vg2.

  The control unit 100 is configured to start the deceleration control by stopping the power supply to the motor 210 after the end of the image formation control. In the deceleration control, the control unit 100 turns off the electromagnetic clutch 223 so that the circumferential speed ratio of the developing roller 71 to the photosensitive drum 61 is less than 1, that is, the circumferential speed of the developing roller 71 is higher than that of the photosensitive drum 61. Make it smaller.

  The control unit 100 is configured to control the grid voltage Vg and the development voltage Vb according to the temperature and humidity detected by the sensors SE1 and SE2 in the deceleration control. Specifically, in the deceleration control, when the humidity at a predetermined temperature is higher than the predetermined humidity, the control unit 100 applies the grid electrode 62B to the first post-image charging voltage that is smaller than the second grid voltage Vg2. The first voltage control is performed in which the first grid voltage Vg1 is applied and the developing roller 71 is applied with a third developing voltage Vb3 that is larger than the second developing voltage Vb2 and is an example of a post-image forming voltage. The third development voltage Vb3 is a voltage smaller than the first grid voltage Vg1. In addition, when the humidity at the predetermined temperature is equal to or lower than the predetermined humidity, the control unit 100 applies the first grid voltage Vg1 to the grid electrode 62B, and the developing roller 71 is smaller than the second developing voltage Vb2. Second voltage control for applying the first development voltage Vb1 as an example of the voltage is executed.

  That is, the control unit 100 refers to the environment determination table shown in FIG. 5 to determine whether or not the humidity is high. When the control unit 100 determines that the humidity is not high, the control unit 100 executes the second voltage control and determines the high humidity. If it is determined that, the first voltage control is executed. In the present embodiment, whether the humidity is high is determined using the same environment determination table as in the preparation rotation control, but the present invention is not limited to this, and is different from that used in the preparation rotation control. A determination may be made using a table. Specifically, when the second voltage control is executed in the deceleration control, the temperature / humidity range in which the toner does not adhere to the non-exposed portion of the photosensitive drum 61 may be set as non-high humidity.

  Further, the control unit 100 is configured to stop the application of voltage to the charger 62 and the developing roller 71 when the rotation speed of the photosensitive drum 61 becomes a predetermined speed or less, for example, 0 in the deceleration control. ing.

  In addition to the control described above, the control unit 100 is configured to appropriately control the transfer voltage applied to the transfer roller 63, the cleaning voltage applied to the cleaning roller 64A, the ON / OFF of the charge removal lamp 90, and the like.

Next, a control method by the control unit 100 will be described in detail.
As shown in FIG. 6, the control unit 100 first determines whether or not a print command has been issued (S1). If it is determined in step S1 that a print command has been issued (Yes), the control unit 100 turns on the motor 210 and rotates the motor 210 at a low speed (S2), thereby starting preparation rotation control. Specifically, the control unit 100 rotates the motor 210 at a low speed by supplying the first current A1 to the motor 210. As a result, the photosensitive drum 61 rotates at the first drum peripheral speed, and the developing roller 71 rotates at the first roller peripheral speed v1.

  After step S2, the control unit 100 acquires the temperature from the in-machine temperature sensor SE1 and the humidity from the humidity sensor SE2 (S3). After step S3, the control unit 100 determines whether or not the environment is a high humidity environment based on the temperature and humidity and the environment determination table shown in FIG. 5 (S4). Specifically, the control unit 100 determines whether or not the humidity detected by the humidity sensor SE2 is equal to or higher than a humidity threshold that is changed according to the temperature detected by the in-machine temperature sensor SE1. Judgment whether or not.

  If it is determined in step S4 that the humidity is high (Yes), the control unit 100 turns on the electromagnetic clutch 223 (S5), thereby changing the circumferential speed of the developing roller 71 from the first roller circumferential speed v1 to the first. Switch to 2-roller circumferential speed v2. If it is determined in step S4 that the humidity is not high (No), the control unit 100 keeps the electromagnetic clutch 223 OFF (S6), so that the circumferential speed of the developing roller 71 is the first roller circumferential speed. Keep at v1.

  After step S5 or step S6, the controller 100 applies the first grid voltage Vg1 to the grid electrode 62B, and applies the first development voltage Vb1 to the developing roller 71 (S7). Note that the application timing of each voltage is such that the development voltage is applied when a part of the surface of the photosensitive drum 61 whose surface potential has changed due to the application of the grid voltage reaches the developing roller 71. The development voltage is applied after a predetermined time of application. This application timing is similar when a second grid voltage Vg2 or a second development voltage Vb2 described later is applied.

  After the specified time has elapsed since step S7 was executed, the control unit 100 supplies the motor 210 with the second current A2 that is larger than the first current A1, thereby rotating the motor 210 at high speed (S8). Here, the specified time is set to a time required for the preparation rotation control. That is, in step S8, the control unit 100 determines that the specified rotation time has elapsed, determines that the preparation rotation control has ended, and rotates the motor 210 at a high speed to start image formation control.

  After step S8, the control unit 100 turns on the electromagnetic clutch 223 (S9). Specifically, in step S9, the control unit 100 maintains the electromagnetic clutch 223 in the ON state when the electromagnetic clutch 223 is already ON, and the electromagnetic clutch 223 when the electromagnetic clutch 223 is in the OFF state. Set to ON.

  After step S9, the control unit 100 applies a second grid voltage Vg2 larger than the first grid voltage Vg1 to the grid electrode 62B, and applies a second development voltage Vb2 larger than the first development voltage Vb1 to the developing roller 71. Is applied (S10). After step S10, the control unit 100 determines whether or not the image formation control is finished (S11). Here, the end of the image formation control is determined, for example, based on whether or not images have been formed on all the sheets for the number of sheets designated by the print command and all the sheets have been discharged. The

  In step S11, if the control unit 100 determines that the image formation control has not ended (No), the process of step S11 is repeated, and if it is determined that the image formation control has ended (Yes), By stopping power supply to the motor 210, the motor 210 is turned off (S12). After step S12 or when determining No in step S1, the control unit 100 ends this control.

  Moreover, the control part 100 performs deceleration control by stopping the electric power supply to the motor 210 in step S12. In the deceleration control, as shown in FIG. 7, the control unit 100 first determines whether or not the environment is a high humidity environment based on the temperature, humidity, and the environment determination table shown in FIG. 5 (S21).

  When it is determined in step S21 that the humidity is high (Yes), the control unit 100 executes the first voltage control (S22). That is, in step S22, the control unit 100 applies the first grid voltage Vg1 smaller than the second grid voltage Vg2 to the grid electrode 62B, and applies a third development voltage larger than the second development voltage Vb2 to the developing roller 71. Vb3 is applied.

  If it is determined in step S21 that the humidity is not high (No), the control unit 100 executes the second voltage control (S23). That is, in step S23, the control unit 100 applies the first grid voltage Vg1 to the grid electrode 62B, and applies the first development voltage Vb1 smaller than the second development voltage Vb2 to the development roller 71.

  After step S22 or step S23, the control unit 100 determines whether or not the rotational speed of the photosensitive drum 61 has become equal to or lower than a predetermined speed (S24). Here, the determination as to whether or not the rotational speed of the photosensitive drum 61 has become equal to or lower than a predetermined speed may be performed using, for example, a sensor that detects the rotational speed of the photosensitive drum 61 or power to the motor 210. You may judge based on the elapsed time after stopping supply.

  If it is determined in step S24 that the rotational speed of the photosensitive drum 61 is greater than the predetermined speed (No), the control unit 100 repeats the process of step S24. If it is determined in step S24 that the rotation speed of the photosensitive drum 61 has become equal to or lower than the predetermined speed (Yes), the control unit 100 stops applying the grid voltage Vg to the grid electrode 62B and applies to the developing roller 71. The application of the developing voltage Vb is stopped and this control is finished.

Next, an example of the operation of the control unit 100 will be described with reference to a time chart shown in FIG.
As shown in FIG. 8, when receiving a print command (time t0), the control unit 100 supplies a first current A1 to the motor 210. As a result, the rotational speed of the motor 210 gradually increases toward the low speed, the peripheral speed of the photosensitive drum 61 gradually increases toward the low speed, and the peripheral speed of the developing roller 71 becomes the first roller peripheral speed v1. It gradually rises toward. Since the peripheral speed of the photosensitive drum 61 is proportional to the rotational speed of the motor 210, only the graph of the rotational speed of the motor 210 is shown, and the peripheral speed graph of the photosensitive drum 61 is not shown. .

  Further, the control unit 100 determines whether or not the environment is a high humidity environment based on the temperature, humidity, and environment determination table. If it is determined that the environment is a non-high humidity environment, the control unit 100 maintains the electromagnetic clutch 223 in the OFF state as shown by a broken line in the drawing, thereby causing the developing roller 71 to move to the first roller circumferential speed v1. Rotate with If it is determined that the environment is in a high humidity environment, the controller 100 turns on the electromagnetic clutch 223 to turn the developing roller 71 at the second roller circumferential speed v2 as indicated by the solid line in the figure. Rotate.

  In addition, after receiving the print command, the control unit 100 starts the rotation of the motor 210 (time t1), and then applies the first grid voltage Vg1 to the grid electrode 62B and the first cleaning voltage Vs1 to the cleaning roller 64A. Is applied. The controller 100 applies the first developing voltage Vb1 to the developing roller 71 after a predetermined time (time t2) from the start of applying the first grid voltage Vg1. Time t2 is the time when the surface of the photosensitive drum 61 charged at time t1 reaches the contact portion with the developing roller 71.

  When the preparatory rotation control is completed (time t3), the control unit 100 switches the current supplied to the motor 210 from the first current A1 to the second current A2, and switches the electromagnetic clutch 223 from OFF to ON, thereby forming an image. Start control. As a result, the rotational speed of the motor 210 and the peripheral speed of the photosensitive drum 61 gradually increase from low speed to high speed, and the peripheral speed of the developing roller 71 changes from the first roller peripheral speed v1 to the second roller peripheral speed. After switching to v2, it gradually increases from the second roller circumferential speed v2 toward the third roller circumferential speed v3.

  At time t3, the control unit 100 switches the grid voltage Vg applied to the grid electrode 62B from the first grid voltage Vg1 to the second grid voltage Vg2 larger than the first grid voltage Vg1. At time t3, the control unit 100 switches the cleaning voltage applied to the cleaning roller 64A from the first cleaning voltage Vs1 to the second cleaning voltage Vs2 that is higher than the first cleaning voltage Vs1. After a predetermined time from the start of applying the second grid voltage Vg2 (time t4), the control unit 100 increases the developing voltage Vb applied to the developing roller 71 from the first developing voltage Vb1 to the first developing voltage Vb1. Switch to the second development voltage Vb2. Time t4 is the time when the surface of the photosensitive drum 61 charged at time t3 reaches the contact portion with the developing roller 71.

  After time t4, the control unit 100 applies a negative transfer voltage to the transfer roller 63 after a predetermined time (time t5), and turns on the charge removal lamp 90 after the predetermined time (time t6). Time t5 is the time when the surface of the photosensitive drum 61 developed at time t4 reaches the contact portion with the transfer roller 63. Time t6 is the time when the surface of the photosensitive drum 61 that has passed through the transfer roller 63 at time t5 reaches a portion facing the static elimination lamp 90. After the completion of image formation, the control unit 100 switches the grid voltage Vg applied to the grid electrode 62B from the second grid voltage Vg2 to the first grid voltage Vg1 after a predetermined time (time t7).

  After time t7, the control unit 100 turns off the electromagnetic clutch 223 and stops power supply to the motor 210 (time t8). As a result, the motor 210, the photosensitive drum 61, and the developing roller 71 rotate by inertia, and the rotational speed of the motor 210, the peripheral speed of the photosensitive drum 61, and the peripheral speed of the developing roller 71 gradually decrease toward the stop. Deceleration control is started.

  When the deceleration control is started (time t8), the control unit 100 changes the developing voltage Vb applied to the developing roller 71 according to the humidity environment. Specifically, when the control unit 100 determines that the humidity is not high, the development voltage Vb is changed from the second development voltage Vb2 to the first smaller than the second development voltage Vb2, as indicated by a broken line in the figure. Switching to the development voltage Vb1. When the controller 100 determines that the humidity is high, the development voltage Vb is changed from the second development voltage Vb2 to the third development voltage Vb3 that is higher than the second development voltage Vb2, as indicated by a solid line in the figure. Switch to.

  At time t8, the control unit 100 turns off the transfer voltage and switches the cleaning voltage from the second cleaning voltage Vs2 to the first cleaning voltage Vs1. After time t8, the control unit 100 turns off the charge removal lamp 90 (time t9).

  When the rotational speed of the photosensitive drum 61 becomes equal to or lower than the predetermined speed after time t9 (time t10), the control unit 100 turns off all of the grid voltage Vg, the development voltage Vb, and the cleaning voltage.

According to the above, the following effects can be obtained in the present embodiment.
In the preparatory rotation control at high humidity, the developing roller 71 is rotated at the second roller peripheral speed v2, that is, at a high speed, so that the toner frictionally charged on the upstream side of the nip portion between the developing roller 71 and the photosensitive drum 61 is niped. It is possible to suppress a decrease in the charge amount of the toner until it reaches the part. Therefore, it is possible to suppress a phenomenon in which toner adheres to the non-exposed portion of the photosensitive drum 61 in the preparation rotation control at high humidity. Further, since the developing roller 71 is rotated at the first roller circumferential speed v1, that is, at a low speed in the preparatory rotation control at the time of non-high humidity, it is possible to suppress the deterioration of the toner as the number of rotations of the developing roller 71 increases. .

  In the preparatory rotation control at high humidity, toner consumption is suppressed by suppressing the toner from adhering to the non-exposed portion of the photosensitive drum 61, and the toner stored in the storage portion 64E of the cleaning unit 64 can be reduced. Therefore, the life of the cleaning unit 64 can be extended.

  In the preparation rotation control, the grid voltage Vg and the development voltage Vb are set to values smaller than those at the time of image formation control, so that power consumption can be suppressed.

  Since the developing roller 71, the supply roller 72, and the agitator 75 are configured to rotate simultaneously at a predetermined peripheral speed ratio, the supply roller 72 and the agitator 75 are moved at a high speed together with the developing roller 71 in the preparatory rotation control at high humidity. Can be rotated. Therefore, frictional charging of the toner between the developing roller 71 and the supply roller 72 can be promoted, and stirring and charging of the toner can be promoted by high-speed rotation of the agitator 75.

  In the deceleration control at high humidity, the potential difference between the photosensitive drum 61 and the developing roller 71 can be reduced by applying the third developing voltage Vb3 larger than that at the time of image formation to the developing roller 71. It is possible to suppress adhesion of the toner to the non-exposed portion of the photosensitive drum 61 caused by a decrease in the toner charge amount at high humidity. In the deceleration control at the time of non-high humidity, the development voltage Vb is set to the first development voltage Vb1 that is smaller than that at the time of high humidity. Therefore, the voltage difference between the grid voltage Vg and the development voltage Vb is small at the time of non-high humidity. Thus, the adhesion of the toner to the non-exposed portion of the photosensitive drum 61 can be suppressed.

  By applying the first grid voltage Vg1 smaller than that at the time of image formation control to the grid electrode 62B in the first voltage control, the voltage difference between the grid voltage Vg and the development voltage Vb can be further reduced in the first voltage control. Therefore, it is possible to satisfactorily suppress the adhesion of toner to the non-exposed portion of the photosensitive drum 61.

  If the grid voltage Vg is applied to the grid electrode 62B in a state where the rotational speed of the photosensitive drum 61 is low, the surface potential of the photosensitive drum 61 becomes too high. On the other hand, in the present embodiment, when the rotation speed of the photosensitive drum 61 becomes a predetermined speed or less, the application of the grid voltage Vg to the grid electrode 62B is stopped, so that the surface potential of the photosensitive drum 61 is increased. It can suppress becoming high.

  The present invention is not limited to the embodiments shown in FIGS. 6 to 8 and can be used in various forms as exemplified below. In the following description, members having substantially the same structure as the embodiment shown in FIGS. 6 to 8 and processes (steps) in the control are denoted by the same reference numerals, and description thereof is omitted.

  In the embodiment shown in FIGS. 6 to 8, the developing roller 71 is rotated at the second roller circumferential speed v2 by turning on the electromagnetic clutch 223 in the preparatory rotation control at high humidity. For example, the developing roller 71 may be rotated at the second roller circumferential speed v2 by switching the rotation speed of the motor 210 from a low speed to a high speed while the electromagnetic clutch 223 remains OFF. Specifically, the control unit 100 may be operated according to the flowchart shown in FIG.

  Here, in the flowchart shown in FIG. 9, the process of step S2 is deleted from the flowchart shown in FIG. 6, a new step S31 is provided instead of step S5, and a new step S32 is provided instead of step S6. In step S31, the control unit 100 rotates the motor 210 at a high speed by supplying the motor 210 with the second current A2 that is larger than the first current A1. At this time, the electromagnetic clutch 223 is OFF. As a result, the photosensitive drum 61 rotates at a second drum peripheral speed, which is an example of the fourth peripheral speed, which is greater than the first drum peripheral speed, and the developing roller 71 is greater than the first roller peripheral speed v1. Rotates at a 2-roller circumferential speed v2.

  In step S <b> 32, the control unit 100 supplies the first current A <b> 1 to the motor 210 to rotate the motor 210 at a low speed. At this time, the electromagnetic clutch 223 is OFF. As a result, the photosensitive drum 61 rotates at a first drum peripheral speed as an example of the third peripheral speed, which is smaller than the second drum peripheral speed, and the developing roller 71 rotates at the first roller peripheral speed v1.

  Further, in the embodiment shown in FIG. 7 and FIG. 8, in the first voltage control, the development voltage Vb is increased from the second development voltage Vb2 to the third development voltage Vb3 at a stretch. However, the present invention is not limited to this. In the first voltage control, the developing voltage Vb applied to the developing roller 71 may be gradually increased from the second developing voltage Vb2 toward the third developing voltage Vb3 in accordance with a decrease in the rotation speed of the developing roller 71. Specifically, the control unit 100 may be operated according to the flowchart shown in FIG.

  Here, in the flowchart shown in FIG. 10, instead of step S22 in the flowchart shown in FIG. 7, new processes of steps S41 and S42 are provided. In step S41, the control unit 100 applies the first grid voltage Vg1 to the grid electrode 62B, and changes the development voltage Vb applied to the development roller 71 to a value obtained by adding a predetermined amount α to the second development voltage Vb2. Here, the predetermined amount α is set so as to gradually increase each time step S41 is repeated in a range where Vb2 + α is equal to or less than Vb3.

  After step S41, the control unit 100 determines whether or not the current development voltage Vb is the third development voltage Vb3 (S42). If it is determined in step S42 that Vb = Vb3 is not satisfied (No), the control unit 100 returns to the process of step S41. As described above, by repeating the processes of steps S41 and S42 at predetermined time intervals, the development voltage Vb gradually increases from the second development voltage Vb2 toward the third development voltage Vb3. If it is determined in step S42 that Vb = Vb3 (Yes), the control unit 100 proceeds to the process of step S24.

  FIG. 11 is a time chart showing an example of the operation of the control unit 100 according to the flowcharts of FIGS. 9 and 10. The description of the control similar to the embodiment shown in FIG. 8 such as the control of the transfer voltage, the charge removal lamp, and the cleaning voltage is omitted.

  As shown in FIG. 11, when receiving a print command (time t20), the control unit 100 determines whether or not the humidity is high. If the humidity is not high, as shown by a broken line in FIG. The first current A1 is supplied to the motor 210 to rotate the motor 210 at a low speed. As a result, the developing roller 71 rotates at the first roller circumferential speed v1.

  When the humidity is high, the control unit 100 supplies the second current A2 to the motor 210 and rotates the motor 210 at a high speed, as indicated by a solid line in the figure. As a result, the developing roller 71 rotates at the second roller circumferential speed v2.

  Here, in the preparatory rotation control before starting the image formation control, the electromagnetic clutch 223 is kept OFF. Thereby, in the preparatory rotation control, the peripheral speed ratio of the developing roller 71 to the photosensitive drum 61 is less than 1, that is, the peripheral speed of the developing roller 71 is smaller than that of the photosensitive drum 61.

  Thereafter, similarly to the embodiment shown in FIG. 8, the control unit 100 applies the first grid voltage Vg1 to the grid electrode 62B after starting the rotation of the motor 210 (time t21), and performs the first development on the developing roller 71. The voltage Vb1 is applied (time t22). When the preparation rotation control is completed (time t23), the control unit 100 turns on the electromagnetic clutch 223 to start the image formation control. As a result, the peripheral speed of the developing roller 71 is switched from the first roller peripheral speed v1 or the second roller peripheral speed v2 to the third roller peripheral speed v3. Further, when the electromagnetic clutch 223 is turned on, the peripheral speed ratio of the developing roller 71 with respect to the photosensitive drum 61 is switched to 1 or more, that is, the peripheral speed of the developing roller 71 is larger than that of the photosensitive drum 61.

  At time t23, the control unit 100 switches the grid voltage Vg from the first grid voltage Vg1 to the second grid voltage Vg2, and then after a predetermined time, changes the development voltage Vb from the first development voltage Vb1 to the second development voltage Vb2. (Time t24). After the end of image formation, the control unit 100 switches the grid voltage Vg from the second grid voltage Vg2 to the first grid voltage Vg1 after a predetermined time (time t25).

  After time t25, control unit 100 turns off electromagnetic clutch 223 and stops power supply to motor 210 (time t26). As a result, the motor 210, the photosensitive drum 61, and the developing roller 71 rotate by inertia, and the rotational speed of the motor 210, the peripheral speed of the photosensitive drum 61, and the peripheral speed of the developing roller 71 gradually decrease toward the stop. Deceleration control is started.

  When starting the deceleration control (time t26), if the environment is not high humidity, the controller 100 changes the development voltage Vb from the second development voltage Vb2 to the first development voltage Vb1, as indicated by a broken line in the figure. Lower. In addition, when the environment is high when the deceleration control is started, the control unit 100 changes the development voltage Vb from the second development voltage Vb2 to the third development voltage Vb3 as shown by a solid line in the figure. Gradually increase.

As mentioned above, according to the form shown in FIGS. 9-11, the following effects can be acquired.
9 to 11, when the developing roller 71 is rotated at the first roller circumferential speed v1, that is, at a low speed, the photosensitive drum 61 is rotated at the first drum circumferential speed, that is, at a low speed, and the developing roller 71 is moved. When rotating at the second roller peripheral speed v2, that is, at a high speed, the photosensitive drum 61 is rotated at the second drum peripheral speed, that is, at a high speed. That is, since the electromagnetic clutch 223 is always turned off in the preparation rotation control, the peripheral speed ratio of the developing roller 71 with respect to the photosensitive drum 61 is kept constant in both high humidity and non-high humidity environments. Can do. For example, when the peripheral speed ratio at this time is set to a value that makes it difficult for toner to adhere to the non-exposed portion of the photosensitive drum 61, the ratio to the non-exposed portion of the photosensitive drum 61 is set. Toner adhesion can be suppressed.

  In the preparation rotation control, the amount of toner supplied from the developing roller 71 to the photosensitive drum 61 can be reduced by making the peripheral speed of the developing roller 71 smaller than that of the photosensitive drum 61. It is possible to satisfactorily suppress toner adhesion to the non-exposed portion.

As the rotation speed of the developing roller 71 decreases, the charge amount of the toner on the developing roller 71 decreases significantly, and the toner tends to adhere to the non-exposed portion of the photosensitive drum 61. In the forms shown in FIGS. 9 to 11, the developing voltage Vb is gradually increased as the rotation speed of the developing roller 71 is decreased. Therefore, the grid voltage is increased as the toner charge amount is gradually decreased. The potential difference between Vg and the development voltage Vb can be gradually reduced, and toner adhesion to the non-exposed portion of the photosensitive drum 61 can be satisfactorily suppressed.

  In the above-described embodiment, the development voltage at non-high humidity in the deceleration control is the first development voltage Vb1, but the present invention is not limited to this, and the development voltage at non-high humidity in the deceleration control is the same as that at the time of image formation. Any value smaller than the development voltage may be used. That is, for example, in the above-described embodiment, the developing voltage at the time of non-high humidity in the deceleration control may be set to a value lower than the first developing voltage Vb1 or higher than the first developing voltage Vb1.

  In the above embodiment, the photosensitive drum 61 is exemplified as the photosensitive member, but the present invention is not limited to this, and may be, for example, a belt-shaped photosensitive member.

  In the embodiment, the exposure apparatus 4 that emits laser light is exemplified as the exposure unit. However, the present invention is not limited to this, and may be an exposure unit that uses, for example, an LED.

  In the above-described embodiment, the scorotron type charger 62 is exemplified as the charger. However, the present invention is not limited to this, and the charger may be, for example, a charging roller that contacts the photoconductor.

  In the above embodiment, the present invention is applied to the laser printer 1. However, the present invention is not limited to this, and the present invention may be applied to other image forming apparatuses such as a copying machine and a multifunction machine.

  In the embodiment, the positively chargeable toner is exemplified as the developer. However, the present invention is not limited to this and may be a negatively chargeable toner. In this case, the grid voltage, the development voltage, and the like need only be changed to a negative polarity in accordance with the negative toner, and the magnitude (absolute value) has the same relationship as in the above embodiment. Good.

DESCRIPTION OF SYMBOLS 1 Laser printer 61 Photosensitive drum 71 Developing roller 100 Control part 4 Exposure apparatus

Claims (9)

A photoreceptor,
A charger for charging the photoreceptor;
A developing roller for supplying developer in contact with the photoreceptor;
A control unit,
The controller is
Image forming control for rotating the photosensitive member and the developing roller and applying an image forming voltage to the developing roller;
Deceleration control for decelerating the photoconductor and the developing roller toward a stop,
In the speed reduction control, an image forming apparatus that executes first voltage control for applying a post-image forming voltage larger than the image forming voltage to the developing roller. The controller is
In the image formation control, an image forming charging voltage is applied to the charger,
The image forming apparatus according to claim 1, wherein, in the first voltage control, a post-image-forming charging voltage smaller than the image-forming charging voltage is applied to the charger.   3. The image formation according to claim 2, wherein in the deceleration control, the control unit stops the application of a voltage to the charger when the rotational speed of the photoconductor becomes a predetermined speed or less. apparatus.   The control unit according to claim 2 or 3, wherein, in the first voltage control, the voltage applied to the developing roller is gradually increased in accordance with a decrease in the rotation speed of the developing roller. Image forming apparatus. The controller is
In the image formation control, the peripheral speed of the developing roller is made larger than that of the photoconductor,
5. The image forming apparatus according to claim 2, wherein, in the deceleration control, a peripheral speed of the developing roller is made smaller than that of the photosensitive member. Equipped with humidity sensor,
In the deceleration control, the control unit executes the first voltage control when the humidity is higher than a predetermined humidity, and when the humidity is equal to or lower than the predetermined humidity, 6. The image formation according to claim 2, wherein a second voltage control is performed in which a charging voltage is applied and a voltage smaller than the image forming voltage is applied to the developing roller. apparatus. A humidity sensor;
A temperature sensor;
In the deceleration control, the control unit executes the first voltage control when the humidity at a predetermined temperature is higher than the predetermined humidity, and when the humidity at the predetermined temperature is equal to or lower than the predetermined humidity, 6. The second voltage control is executed by applying a post-image charging voltage to a charger and applying a voltage lower than the post-image voltage to the developing roller. 6. The image forming apparatus according to claim 1. A motor for driving the photosensitive member and the developing roller;
The image forming apparatus according to claim 1, wherein the control unit starts the deceleration control by stopping power supply to the motor. A control method for controlling a developing voltage applied to a developing roller for supplying a developer to a photosensitive member, and rotation of the photosensitive member and the developing roller,
An image forming step of rotating the photosensitive member and the developing roller and applying an image forming voltage to the developing roller;
A decelerating step of decelerating the photoconductor and the developing roller toward a stop;
And a voltage control step of applying a post-image forming voltage larger than the image forming voltage to the developing roller in the deceleration control.

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