JP2020020875A - Image forming apparatus - Google Patents

Abstract

To prevent a developer with a low charge amount from being scattered from a developing roller.SOLUTION: A control unit can execute, before starting formation of an electrostatic latent image on a photoreceptor, preparative rotation control (time t1 to t7) of rotating the photoreceptor and a developing roller, and image formation control of forming the electrostatic latent image on the photoreceptor. In the preparative rotation control, the control unit sets the peripheral speed of the photoreceptor to a first speed V1 and subsequently changes to a second speed V2 larger than the first speed V1, when the elapsed time from the completion of previous image formation control is less than a predetermined time, sets the ratio of the peripheral speed of the developing roller to that of the photoreceptor to a first peripheral speed ratio being less than 1, after changing the peripheral speed of the photoreceptor from the first speed V1 to the second speed V2 (after time t4), sets the peripheral speed ratio to a second peripheral speed ratio being 1 or more (developing electromagnetic clutch ON), and when the elapsed time is equal to or more than the predetermined time, sets the peripheral speed ratio to the second peripheral speed ratio before changing the peripheral speed of the photoreceptor from the first speed V1 to the second speed V2 (before time t4) (developing electromagnetic clutch ON).SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus including a control unit that can change the rotation speed of a photoconductor and a developing roller.

  Conventionally, as an image forming apparatus, a control unit capable of switching a peripheral speed of a photosensitive member between a low speed and a high speed and switching a peripheral speed ratio of a developing roller to a photosensitive member between a low peripheral speed ratio and a high peripheral speed ratio There is known a device provided with (see Patent Document 1).

JP 2017-32746 A

  Incidentally, when the image forming apparatus has been left for a long time since the previous printing, the charge amount of the developer carried on the developing roller may be reduced. In this case, if the peripheral speed ratio of the developing roller to the photosensitive member is set to be a low peripheral speed ratio when the peripheral speed of the photosensitive member is low, the peripheral speed of the developing roller becomes slow, and the peripheral speed of the developing roller is reduced. In some cases, the charge amount of the developer may not be sufficiently increased. Further, after that, if the peripheral speed of the photoconductor is switched to a high speed, and then the peripheral speed ratio is switched to a high peripheral speed ratio, the peripheral speed of the developing roller rapidly increases, and the developer having a low charge amount is developed. There is a risk of scattering from the rollers.

  Therefore, an object of the present invention is to suppress a developer having a low charge amount from scattering from a developing roller.

In order to solve the above problems, an image forming apparatus according to the present invention includes a photoconductor, a developing roller that supplies a developer to the photoconductor, and a control unit.
The control unit includes: a preparation rotation control for rotating the photoconductor and the developing roller before starting the formation of the electrostatic latent image on the photoconductor; and an image forming apparatus for forming an electrostatic latent image on the photoconductor. And in the preparatory rotation control, the peripheral speed of the photoconductor is set to a first speed, and then changed to a second speed greater than the first speed, and the previous image forming control is performed. If the elapsed time from the end is less than the predetermined time, the peripheral speed ratio of the developing roller to the photosensitive member is set to a first peripheral speed ratio of less than 1, and the peripheral speed of the photosensitive member is set to the first speed. After changing from the second speed to the second speed, the peripheral speed ratio is set to a second peripheral speed ratio of 1 or more. If the elapsed time is equal to or longer than the predetermined time, the peripheral speed of the photoconductor is changed to the first speed. Before changing from the second speed to the second speed, the peripheral speed ratio is set to the second peripheral speed ratio.

  According to the configuration described above, when the elapsed time is equal to or longer than the predetermined time, the peripheral speed ratio is changed to the second peripheral speed before the peripheral speed of the photoconductor is switched to the second speed, that is, when the peripheral speed is lower than the second speed. Since the peripheral speed can be switched to the two peripheral speed ratio, a sharp increase in the peripheral speed of the developing roller can be suppressed, the scattering of the developer can be suppressed, and the peripheral speed of the developing roller increases in the initial stage of the preparation rotation control. Thus, the charge amount of the developer on the developing roller can be increased. Therefore, even when the charge amount of the developer on the developing roller is reduced due to the elapsed time being equal to or longer than the predetermined time, it is possible to suppress the developer having a low charge amount from scattering from the developing roller. .

  Further, when the elapsed time is equal to or longer than the predetermined time, the control unit may set the peripheral speed ratio to the second peripheral speed ratio when starting rotation of the photoconductor.

  According to this, the peripheral speed ratio is set to the second peripheral speed ratio when the rotation of the photoconductor is started. Therefore, for example, the peripheral speed ratio is changed from the first peripheral speed ratio to the second peripheral speed ratio during the rotation of the photoconductor. Since the peripheral speed of the developing roller can be further suppressed from suddenly increasing as compared with the mode of switching to, the scattering of the developer can be further suppressed.

  Further, when the elapsed time is equal to or longer than the predetermined time, the control unit sets the peripheral speed ratio to the first peripheral speed ratio when starting rotation of the photoconductor, and sets the photoconductor to the first peripheral speed ratio. During the rotation at the first speed, the peripheral speed ratio may be the second peripheral speed ratio.

  In addition, when the elapsed time is less than a predetermined time, the control unit sets the timing of changing the peripheral speed ratio from the first peripheral speed ratio to the second peripheral speed ratio earlier as the elapsed time is longer. May be.

  According to this, when the elapsed time is shorter than the predetermined time, the speed of setting the second peripheral speed ratio is earlier as the elapsed time is longer, so that the speed of the developing roller can be increased earlier. Therefore, the charge amount of the developer can be increased to a charge amount suitable for image formation.

  Further, when the elapsed time is equal to or longer than the predetermined time, the control unit may set a longer period for rotating the photoconductor at the first speed as the elapsed time is longer.

  According to this, when the elapsed time is equal to or longer than the predetermined time, the longer the elapsed time, the longer the period for rotating the photoconductor at the first speed. Therefore, the longer the elapsed time, the longer the developing roller can be rotated. As a result, the charge amount of the developer can be favorably increased.

  Further, the image forming apparatus is a motor, a drive train for transmitting a driving force of the motor to the photoconductor, and a transmission for transmitting the driving force of the motor to the developing roller, wherein the transmission for the photoconductor is performed. A transmission that switches a peripheral speed ratio of the developing roller between the first peripheral speed ratio and the second peripheral speed ratio, wherein the control unit controls the transmission to reduce the peripheral speed ratio. May be set.

  According to this, the photosensitive member and the developing roller can be driven by the same motor, and the peripheral speed ratio can be switched.

  Further, the first peripheral speed ratio may be 1/5 or less of the second peripheral speed ratio.

  According to this, by setting the first peripheral speed ratio to 1/5 or less of the second peripheral speed ratio, the peripheral speed of the developing roller when the first peripheral speed ratio is set can be reduced, The cumulative number of rotations of the developing roller can be kept low.

Further, an image forming apparatus according to the present invention includes a photoconductor, a developing roller for supplying a developer to the photoconductor, a motor, a drive train for transmitting a driving force of the motor to the photoconductor, A transmission for transmitting a driving force to the developing roller, wherein the transmission switches a peripheral speed ratio of the developing roller with respect to the photoconductor between a first peripheral speed ratio of less than 1 and a second peripheral speed ratio of 1 or more. And a control unit.
The control unit includes: a preparation rotation control for rotating the photoconductor and the developing roller before starting the formation of the electrostatic latent image on the photoconductor; and an image forming apparatus for forming an electrostatic latent image on the photoconductor. And in the preparatory rotation control, the motor is driven to change the peripheral speed of the photoconductor to a first speed, and then to a second speed greater than the first speed. And a process of setting the peripheral speed ratio to the first peripheral speed ratio or the second peripheral speed ratio by switching the transmission, and ending the previous image forming control. If the elapsed time after the change is less than the predetermined time, the peripheral speed of the photoconductor is changed from the first speed to the second speed, and then the peripheral speed ratio is set to the second peripheral speed ratio. If the elapsed time is equal to or longer than the predetermined time, the peripheral speed of the photoconductor is reduced to the first speed. Before changing to the second speed from the time, setting the peripheral speed ratio to the second circumferential speed ratio.

  According to this, when the elapsed time is equal to or longer than the predetermined time, before the peripheral speed of the photoconductor is switched to the second speed, that is, when the peripheral speed is lower than the second speed, the peripheral speed ratio is changed to the second peripheral speed. Since the speed ratio can be switched, a rapid increase in the peripheral speed of the developing roller can be suppressed, and the scattering of the developer can be suppressed. The charge amount of the developer on the roller can be increased. Therefore, even when the charge amount of the developer on the developing roller is reduced due to the elapsed time being equal to or longer than the predetermined time, it is possible to suppress the developer having a low charge amount from scattering from the developing roller. .

  According to the present invention, it is possible to suppress the developer having a low charge amount from scattering from the developing roller.

FIG. 1 is a diagram illustrating an image forming apparatus according to an embodiment of the present disclosure. FIG. 3 is a diagram illustrating a relationship between a motor, a transmission, a supply electromagnetic clutch, and a control unit for driving each member of the image forming apparatus. 4 is a flowchart illustrating an operation of a control unit. 6 is a flowchart illustrating first print control. 9 is a flowchart illustrating a second print control. 5 is a time chart illustrating an operation of a control unit according to an elapsed time. 9 is a flowchart illustrating a first modification of the second print control. 9 is a time chart illustrating a first modification of the second print control. 9 is a time chart illustrating a second modification of the second print control.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate.
As shown in FIG. 1, a laser printer 1 as an example of an image forming apparatus includes a main body housing 2, a sheet supply unit 3 that supplies a sheet S, and an image forming unit G that forms an image on the supplied sheet S. And the main.

  The sheet supply unit 3 is provided at a lower portion in the main body housing 2 and mainly includes a sheet tray 31 that stores sheets S, a pressing plate 32, and a sheet supply mechanism 33. The sheet feeding mechanism 33 includes a pickup roller 33A, a separation roller 33B, a separation pad 33C, and a registration roller 33D. The sheet supply unit 3 supplies the sheet S in the sheet tray 31 to the separation roller 33B by the pickup roller 33A, and separates the sheet S into one sheet between the separation roller 33B and the separation pad 33C. More specifically, the pickup roller 33A is a roller that can switch between a stopped state and a conveyed state of the sheet S. The pickup roller 33A starts rotating from a state in which the sheet S in the sheet tray 31 is stopped after coming into contact with the sheet S. Out of the sheet S. The registration roller 33D conveys the sheet S toward the image forming unit G after aligning the position of the leading end of the sheet S.

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

  The exposure device 4 is disposed at an upper part in the main body housing 2 and includes a laser light emitting unit (not shown), a polygon mirror, a lens, a reflector, and the like, which are omitted from reference numerals. The exposure device 4 exposes the surface of the photoconductor 61 by scanning the surface of the photoconductor 61 at high speed with a laser beam (see a chain line) based on image data emitted from the laser light emitting unit.

  The process cartridge 5 is disposed below the exposure device 4, and is configured to be detachable from the main housing 2 through an opening formed when the front cover 21 provided on the main housing 2 is opened. The process cartridge 5 includes a drum unit 6 and a developing unit 7. The drum unit 6 mainly has a photoreceptor 61, a scorotron-type charger 62, and a transfer roller 63. The photoreceptor 61 is a photoreceptor drum having a cylindrical drum main body having conductivity and a photosensitive layer formed on the outer peripheral surface of the drum main body. The developing unit 7 includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, an accommodating section 74 for accommodating a positively charged toner as a developer, and an agitator 75 rotating in the accommodating section 74. Mainly have.

  The process cartridge 5 uniformly charges the surface of the photoconductor 61, which is rotationally driven, by the charger 62, and exposes the surface of the photoconductor 61 with the laser beam from the exposure device 4. Form a latent image. The agitator 75 rotates in the storage unit 74 to convey the toner in the storage unit 74 toward the developing roller 71 while stirring the toner. The supply roller 72 rotates while being in contact with the developing roller 71, and supplies the toner discharged from the storage unit 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 that the surface of the developing roller 71 carries the toner regulated to a certain thickness with the layer thickness regulating blade 73.

  After that, the developing unit 7 supplies the toner carried on the developing roller 71 to the photoconductor 61 to visualize the electrostatic latent image to form a toner image on the photoconductor 61. Then, the sheet S supplied from the sheet supply unit 3 is conveyed between the photoconductor 61 and the transfer roller 63, so that the toner image on the photoconductor 61 is transferred to the sheet S.

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

  As shown in FIG. 2, a motor M, a drive train GM, a transmission 9, a supply electromagnetic clutch C, and a control unit 100 are provided in the main body housing 2.

  The motor M is a drive source for supplying a driving force to the photoconductor 61, the developing roller 71, the supply roller 72, the agitator 75, the pickup roller 33A, and the like, and is connected to the photoconductor 61 via a drive train GM. . In addition, the motor M is connected to the developing roller 71 and the like via the transmission 9 and is connected to the pickup roller 33A via the supply electromagnetic clutch C.

  The drive train GM is a drive train having a plurality of gears for transmitting the driving force of the motor M to the photoconductor 61, and is connected to the motor M and the photoconductor 61. That is, the photoconductor 61 is connected to the motor M at a fixed gear ratio.

  The transmission 9 is a transmission that transmits the driving force of the motor M to the developing roller 71, and sets the peripheral speed ratio of the developing roller 71 to the photoconductor 61 to a first peripheral speed ratio of less than 1 and a first peripheral speed ratio of 1 or more. This is a mechanism for switching between two peripheral speed ratios. Specifically, the developing roller 71, the supply roller 72, and the agitator 75 are connected via a predetermined gear provided in the developing unit 7, and are configured to simultaneously rotate at a predetermined gear ratio. Then, the driving force of the motor M is input to the developing unit 7 via the transmission 9 and the developing roller 71 and the like are rotated, whereby the peripheral speed of the developing roller 71 (the peripheral speed ratio with respect to the photosensitive member 61) is changed by the transmission 9. ) Can be switched. The photoconductor 61 and the developing roller 71 rotate so that the peripheral surface moves in the same direction at the contact portion. In the present embodiment, the first peripheral speed ratio is set to 1/5 or less of the second peripheral speed ratio.

  The transmission 9 includes a first transmission mechanism 91 having a first gear ratio for setting a peripheral speed ratio of the developing roller 71 to the photoconductor 61 to a first peripheral speed ratio, and a peripheral portion of the developing roller 71 to the photoconductor 61. In order to set the speed ratio to the second peripheral speed ratio, the second transmission mechanism 92 configured with the second gear ratio and the transmission path of the driving force from the motor M are switched to the first transmission mechanism 91 or the second transmission mechanism 92. And a developing electromagnetic clutch 93. In this transmission 9, when the developing electromagnetic clutch 93 is turned off, the driving force from the motor M is transmitted to the developing roller 71 via the first transmission mechanism 91, and the developing roller 71 rotates at the first peripheral speed ratio. . When the developing electromagnetic clutch 93 is turned on, the driving force from the motor M is transmitted to the developing roller 71 via the second transmission mechanism 92, and the developing roller 71 rotates at the second peripheral speed ratio.

  The supply electromagnetic clutch C is an electromagnetic clutch for switching transmission / disconnection of the driving force from the motor M to the pickup roller 33A.

  The control unit 100 includes a CPU, a RAM, a ROM, an input / output circuit, and the like, and has a function of controlling the motor M, the transmission 9, and the supply electromagnetic clutch C. The control unit 100 also has a function of applying a voltage (bias) to the developing roller 71 and the like, and a function of controlling the exposure device 4 and the like.

  The control unit 100 performs a preparatory rotation control for rotating the photoconductor 61 and the developing roller 71 before starting the formation of the electrostatic latent image on the photoconductor 61, and an image forming operation for forming an electrostatic latent image on the photoconductor 61. Control and can be executed. The control unit 100 is configured to execute a preparatory rotation control upon receiving a print command.

  In the preparation rotation control, the control unit 100 drives the motor M to set the peripheral speed of the photoconductor 61 to the first speed V1, and then to change the peripheral speed to the second speed V2 higher than the first speed V1. And a peripheral speed ratio setting process of setting the peripheral speed ratio of the developing roller 71 to the photoconductor 61 to the first peripheral speed ratio or the second peripheral speed ratio by switching the transmission 9. Has become.

  Specifically, in the peripheral speed changing process, the control unit 100 drives the motor M at the first rotational speed, thereby setting the peripheral speed of the photoconductor 61 to the first speed V1, and then increasing the rotational speed of the motor M to the first rotational speed. By switching from one rotation speed to a second rotation speed higher than the first rotation speed, the peripheral speed of the photoconductor 61 is changed to a second speed V2 higher than the first speed V1. In the following description, the first rotation speed, which is the rotation speed of the motor M, is also referred to as “low speed”, and the second rotation speed is also referred to as “high speed”.

  In the peripheral speed ratio setting process, the control unit 100 sets the peripheral speed ratio based on the elapsed time T from the end of the previous image forming control. Specifically, when the elapsed time T is less than the predetermined time Tth, the control unit 100 changes the peripheral speed of the photoconductor 61 from the first speed V1 to the second speed V2, and then changes the peripheral speed ratio to the second peripheral speed. Set the speed ratio.

  Specifically, when the elapsed time T is shorter than the predetermined time Tth, the control unit 100 turns off the developing electromagnetic clutch 93 when the rotation of the photoconductor 61 is started, that is, when the rotation of the motor M is started. In this state, the peripheral speed ratio is set to the first peripheral speed ratio. Thereafter, the control unit 100 changes the peripheral speed of the photoconductor 61 from the first speed V1 to the second speed V2 and then turns on the developing electromagnetic clutch 93 to set the peripheral speed ratio to the second peripheral speed ratio. I do.

  Further, when the elapsed time T is shorter than the predetermined time Tth, the control unit 100 has a function of increasing the timing of changing the peripheral speed ratio from the first peripheral speed ratio to the second peripheral speed ratio as the elapsed time T is longer. have. Specifically, when the elapsed time T is less than the first threshold value TH1 smaller than the predetermined time Tth, the control unit 100 sets the peripheral speed ratio to the first peripheral speed ratio after the lapse of the first time TM1 from the start of the supply of the sheet S. The peripheral speed ratio is switched to the second peripheral speed ratio. When the elapsed time T is equal to or longer than the first threshold value TH1, the control unit 100 sets the peripheral speed ratio to the first rotation speed after a lapse of a second time TM2 shorter than the first time TM1 from the start of the supply of the sheet S. The speed ratio is switched to the second peripheral speed ratio.

  When the elapsed time T is equal to or longer than the predetermined time Tth, the control unit 100 sets the peripheral speed ratio to the second peripheral speed before changing the peripheral speed of the photoconductor 61 from the first speed V1 to the second speed V2. Set the speed ratio. In the present embodiment, when the elapsed time T is equal to or longer than the predetermined time Tth, the control unit 100 activates the developing electromagnetic clutch 93 when the rotation of the photoconductor 61 is started, that is, when the rotation of the motor M is started. Turn on to set the peripheral speed ratio to the second peripheral speed ratio.

  Next, the operation of the control unit 100 will be described in detail. The control section 100 constantly executes the control shown in FIG. 3 repeatedly.

  In the control shown in FIG. 3, the control unit 100 first determines whether or not there is a print command (S1). If it is determined in step S1 that there is no print command (No), the control section 100 ends this control.

  If it is determined in step S1 that there is a print command (Yes), the control unit 100 acquires the elapsed time T from the previous image forming control (S2). More specifically, the control unit 100 starts counting the elapsed time T when the previous image forming control ends, and ends counting the elapsed time T when the print command is received, thereby acquiring the elapsed time T. .

  After step S2, the control unit 100 determines whether the elapsed time T is less than the predetermined time Tth (S3). If it is determined in step S3 that T <Tth (Yes), the control unit 100 executes the first print control (S4).

  If it is determined in step S3 that T <Tth is not satisfied (No), the control unit 100 executes the second print control (S5). The first print control and the second print control will be described later in detail. After steps S4 and S5, control unit 100 ends the present control.

  As shown in FIG. 4, in the first printing control, the control unit 100 first rotates the motor M at a low speed and applies a charging bias to the charger 62 (S11). After step S11, the controller 100 applies a developing bias to the developing roller 71 (S12). Here, the time from the start of the application of the charging bias to the start of the application of the developing bias can be set as appropriate. For example, the portion where the surface potential of the photoconductor 61 becomes higher due to the start of the application of the charging bias is The time can be longer than the time required to move from the charger 62 to the developing roller 71.

  After step S12, the control unit 100 switches the rotation speed of the motor M from low speed to high speed (S13). Here, the time from the start of the application of the developing bias to the switching of the rotation speed of the motor M can be set as appropriate.

  After step S13, the control unit 100 turns on the supply electromagnetic clutch C (S14). Here, the time from the start of switching the rotation speed of the motor M to the ON of the supply electromagnetic clutch C can be set as appropriate.

  After step S14, control unit 100 determines whether elapsed time T is less than first threshold value TH1 (S15).

  If it is determined in step S15 that T <TH1, the control unit 100 turns on the developing electromagnetic clutch 93 after the start of the supply of the sheet S, that is, the first time TM1 after the supply electromagnetic clutch C is turned on. (S16). If it is determined in step S15 that T <TH1 is not satisfied, that is, if the elapsed time T is in the range of TH1 ≦ T <Tth, the control unit 100 sets the second time TM2 (TM2 < After the elapse of TM1), the developing electromagnetic clutch 93 is turned on (S17). That is, the longer the elapsed time T is (S15: No), the earlier the control unit 100 sets the timing of changing the peripheral speed ratio from the first peripheral speed ratio to the second peripheral speed ratio, that is, the timing of turning on the developing electromagnetic clutch 93. (TM2 <TM1). Note that the first time TM1 may be an elapsed time from the timing when a sheet is detected by a sensor provided in the sheet supply unit 3.

  After steps S16 and S17, the control section 100 executes image forming control on one sheet S (S18). Specifically, in the image forming control, the control unit 100 executes exposure control for exposing the photoconductor 61 by the exposure device 4 and transfer control for applying a transfer bias to the transfer roller 63. Note that the start timing of the exposure control and the transfer control can be set as appropriate.

  After step S18, the control unit 100 determines whether printing for the number of sheets specified by the print command has been completed (S19). If it is determined in step S19 that printing has not been completed (No), the control unit 100 returns to step S18.

  If it is determined in step S19 that printing has been completed (Yes), the control unit 100 turns off the developing electromagnetic clutch 93 (S20). After step S20, the control unit 100 turns off the motor M (S21). Here, the time from the OFF of the developing electromagnetic clutch to the OFF of the motor M can be set as appropriate.

  After step S21, the control unit 100 turns off the charging bias and the developing bias (S22). Here, the time from when the motor M is turned off to when the charging bias or the like is turned off can be set as appropriate.

  After step S22, the control section 100 starts counting the elapsed time T (S23), and ends this control. Here, the time from the turning off of the motor M to the start of counting the elapsed time T can be set as appropriate. The timing to start counting the elapsed time T may be simultaneous with the turning off of the motor M.

  In the second print control shown in FIG. 5, the control unit 100 sets the timing to turn on the developing electromagnetic clutch earlier than the timing of the first print control. In the second print control shown in FIG. 5, a new process of step S31 is provided in place of the process of step S11 in the first print control, and the process in steps S15 to S17 in the first print control is deleted. ing.

  Specifically, in the second printing control, the control unit 100 first turns on the developing electromagnetic clutch, rotates the motor M at a low speed, and applies a charging bias to the charger 62 (S31). After step S31, the control unit 100 executes steps S12 to S14 similar to the first print control. After step S14, the control unit 100 executes steps S18 to S23 similar to the first print control.

Next, the operation of the control unit 100 according to the elapsed time T will be described with reference to the time chart of FIG.
When the elapsed time T is less than the predetermined time Tth, that is, when much time has not passed since the previous image forming control, the control unit 100 receives a print command as shown by a solid line in FIG. At time t1), the application of the charging bias is started, and the rotation of the motor M is started while the developing electromagnetic clutch 93 is kept OFF. As a result, the photoconductor 61 starts to rotate, and the developing roller 71 starts to rotate with respect to the photoconductor 61 at the first peripheral speed ratio.

  When the rotation speed of the motor M reaches the first rotation speed, the peripheral speed of the photoconductor 61 becomes the first speed V1 (time t2). At this time, the peripheral speed of the developing roller 71 is the first roller speed V11 obtained by multiplying the first speed V1 by the first peripheral speed ratio. At this time, the application of the developing bias is also started.

  Thereafter, when the control unit 100 switches the rotation speed of the motor M from the first rotation speed to the second rotation speed at a predetermined timing (time t3), the peripheral speeds of both the photoconductor 61 and the developing roller 71 increase. Go. When the rotation speed of the motor M reaches the second rotation speed, the peripheral speed of the photoconductor 61 becomes the second speed V2, and the peripheral speed of the developing roller 71 is the second roller speed V12 higher than the first roller speed V11. (Time t4).

  Next, the control unit 100 turns on the supply electromagnetic clutch C to execute the supply of one sheet S (time t4). Thereafter, the control unit 100 turns on the developing electromagnetic clutch 93 at a timing corresponding to the elapsed time T (time t5 or time t6). More specifically, when the elapsed time T is less than the first threshold value TH1, the control unit 100 determines that the developing electromagnetic force has elapsed after the lapse of the first time TM1 from the start of sheet S supply (time t4), as indicated by the solid line in the figure. The clutch 93 is turned on (time t6).

  When the elapsed time T is equal to or longer than the first threshold value TH1, the control unit 100 determines that the elapsed time T is shorter than the first time TM1 from the start of the supply of the sheet S (time t4) as indicated by a two-dot chain line in FIG. After the elapse of two hours TM2, the developing electromagnetic clutch 93 is turned on (time t5). When the developing electromagnetic clutch 93 is turned on in this way, the peripheral speed of the developing roller 71 is rapidly switched from the second roller speed V12 to the fourth roller speed V14 (time t5 or time t6).

  Here, when the elapsed time T is less than the first threshold value TH1, that is, when the elapsed time T is very short, the charge amount of the toner on the developing roller 71 does not decrease, so that the time from t1 to t6 is long. During this time, even if the developing roller 71 is rotated at a low speed (V11, V12), the charge amount is a high charge amount suitable for image formation. Therefore, in this case, even if the peripheral speed of the developing roller 71 is switched at the timing of the time t6, the toner of an appropriate charge amount is held by the developing roller 71, so that the toner does not scatter from the developing roller 71. Further, the number of rotations of the developing roller 71 until immediately before performing image formation (time t7) can be reduced.

  On the other hand, when the elapsed time T is equal to or longer than the first threshold value TH1, the charge amount of the toner on the developing roller 71 is slightly reduced as compared with the case where T <TH1. If the developing roller 71 is rotated at a low speed (V11, V12) during this time, the charge amount may not rise to a high charge amount suitable for image formation during this time. In this case, if the peripheral speed of the developing roller 71 is switched at the time t6, there is a possibility that good image formation may not be performed. Therefore, when the elapsed time T is equal to or longer than the first threshold value TH1, the timing for switching the peripheral speed of the developing roller 71 is made earlier (time t5) than when T <TH1, so that the developing roller Since 71 can be the fourth roller speed V14, the charge amount of the toner can be satisfactorily increased to a charge amount suitable for image formation during the period from time t5 to t6. When the peripheral speed of the developing roller 71 is switched at time t5, the peripheral speed of the developing roller 71 sharply increases. At this time, that is, the charge amount of the toner on the developing roller 71 when TH1 ≦ T <Tth is: Since the charge amount is higher than that at which toner scattering occurs, toner does not scatter from the developing roller 71.

  After that, the control unit 100 performs image formation control such as exposure control (time t7) and application of a transfer bias (time t8) based on the timing of starting supply of the sheet S (time t4). After ending the image forming control, the controller 100 turns off the developing electromagnetic clutch 93 (time t9).

  Thereafter, the control unit 100 turns off the motor M (time t10). Next, the control unit 100 turns off the charging bias and the developing bias (time t11).

  When the elapsed time T is equal to or longer than the predetermined time Tth, that is, when a long time has elapsed since the previous image forming control, the control unit 100 receives a print command as shown by a broken line in FIG. t1) The developing electromagnetic clutch 93 is turned on to start the rotation of the motor M. As a result, the photoconductor 61 starts to rotate, and the developing roller 71 starts to rotate with respect to the photoconductor 61 at the second peripheral speed ratio. The control of the charging bias and the like is the same as the case where the elapsed time T is shorter than the predetermined time Tth, and thus will not be described below.

  When the rotation of the developing roller 71 is started at the second peripheral speed ratio in this manner, the peripheral speed of the developing roller 71 is steeper at a larger gradient than when the rotation of the developing roller 71 is started at the first peripheral speed ratio (T <Tth). Will increase. Then, when the rotation speed of the motor M reaches the first rotation speed and the peripheral speed of the photosensitive member 61 becomes the first speed V1 (time t2), the peripheral speed of the developing roller 71 is changed to the first speed V1 by the second rotation speed. The third roller speed V13 obtained by multiplying the speed ratio is obtained. In the present embodiment, the third roller speed V13 is set to a value higher than the above-described second roller speed V12, but may be V13 ≦ V12.

  As described above, when T ≧ Tth, the peripheral speed of the developing roller 71 can be increased in the initial stage of the preparatory rotation control as compared with the case where T <Tth. Accordingly, when T ≧ Tth, that is, when the charge amount of the toner on the developing roller 71 is low, the peripheral speed of the developing roller 71 is increased at the initial stage of the preparation rotation control, and You can increase the amount. In this embodiment, by setting the peripheral speed ratio to the second peripheral speed ratio before the rotation of the photoconductor 61 is started, the peripheral speed of the developing roller 71 is sharply increased as compared with the case where T <Tth. It does not rise, but gradually rises with the acceleration of the motor M. Therefore, scattering of toner from the developing roller 71 due to a rapid increase in the peripheral speed of the developing roller 71 can be suppressed.

  Thereafter, when the control unit 100 switches the rotation speed of the motor M from the first rotation speed to the second rotation speed at a predetermined timing (time t3), the peripheral speeds of both the photoconductor 61 and the developing roller 71 increase. Go. When the rotation speed of the motor M reaches the second rotation speed, the peripheral speed of the photoconductor 61 becomes the second speed V2, and the peripheral speed of the developing roller 71 becomes the fourth roller speed V14 higher than the third roller speed V13. (Time t4).

  As described above, when the peripheral speed of the developing roller 71 reaches the fourth roller speed V14, since the charge amount of the toner on the developing roller 71 is increased between the times t1 and t4, the toner from the developing roller 71 is Can be suppressed. Note that the subsequent control is the same as in the case of T <Tth, and a description thereof will be omitted.

According to the above, the following effects can be obtained in the present embodiment.
When the elapsed time T is equal to or longer than the predetermined time Tth, before the peripheral speed of the photoconductor 61 is switched to the second speed V2, that is, when the peripheral speed is lower than the second speed V2, the peripheral speed ratio becomes the second peripheral speed. Since the speed ratio can be switched, a sharp increase in the peripheral speed of the developing roller 71 can be suppressed, and the scattering of toner can be suppressed. Further, when T ≧ Tth, the peripheral speed of the developing roller 71 is increased in the initial stage of the preparation rotation control, so that the charge amount of the toner on the developing roller 71 can be increased. Therefore, even if the charge amount of the toner on the developing roller 71 decreases due to T ≧ Tth, the charge amount should be increased before the peripheral speed of the developing roller 71 reaches the fourth roller speed V14. Therefore, it is possible to suppress the toner having a low charge amount from scattering from the developing roller 71.

  When T ≧ Tth, the peripheral speed ratio is set to the second peripheral speed ratio when the rotation of the photoconductor 61 is started. Therefore, for example, as described later, the peripheral speed ratio is set to the first peripheral speed ratio during the rotation of the photoconductor 61. Compared with a mode in which the peripheral speed ratio is switched from the peripheral speed ratio to the second peripheral speed ratio (see FIG. 9), it is possible to further suppress the peripheral speed of the developing roller 71 from sharply increasing, so that the scattering of toner can be further suppressed.

  If T <Tth, the longer the elapsed time T, the earlier the timing for setting the second peripheral speed ratio, so that the speed of the developing roller 71 can be increased at an earlier timing. Can be increased to a charge amount suitable for image formation.

  Since the motor M is connected to the photoconductor 61 via the drive train GM and to the developing roller 71 via the transmission 9, the photoconductor 61 and the developing roller 71 can be driven by the same motor M. At the same time, the peripheral speed ratio can be favorably switched.

  Since the first peripheral speed ratio is set to 1/5 or less of the second peripheral speed ratio, the peripheral speed of the developing roller 71 when the first peripheral speed ratio is set can be sufficiently reduced. The cumulative number of rotations can be kept low.

  Note that the present invention is not limited to the above embodiment, but can be used in various forms as exemplified below. In the following description, members and steps having substantially the same structure as those of the above embodiment are denoted by the same reference numerals, and description thereof will be omitted.

  In the above embodiment, one type of control is performed when the elapsed time T is equal to or longer than the predetermined time Tth, but the present invention is not limited to this. For example, when the elapsed time T is equal to or longer than the predetermined time Tth, the control unit 100 may be configured such that the longer the elapsed time T, the longer the period during which the photoconductor 61 is rotated at the first speed V1. Good.

  In this case, the control unit 100 can execute the second print control according to, for example, the flowchart shown in FIG. Here, in the control of FIG. 7, new processes of steps S41 and S42 are added to the control of FIG.

  In the second print control shown in FIG. 7, the control unit 100 first determines whether or not the elapsed time T is equal to or greater than a second threshold TH2 that is longer than a predetermined time Tth (S41). If it is determined in step S41 that T ≧ TH2 (Yes), the control unit 100 rotates the motor M at a low speed for a specified time and applies a charging bias (S42).

  More specifically, in step S42, the control unit 100 rotates the motor M at a low speed with the developing electromagnetic clutch 93 OFF for a specified time (between times t01 and t02), as indicated by the thick line in FIG. The motor M is stopped later, but after the charging bias is turned on at time t01, the charging bias is kept on until the image forming control ends.

  Returning to FIG. 7, after step S42, or if it is determined in step S41 that T ≧ TH2 is not satisfied (No), control unit 100 executes the above-described processing from step S31.

  In this embodiment, as shown in FIG. 8, when T ≧ TH2 in the second print control, the control unit 100 switches the developing electromagnetic clutch 93 to ON (at time Before t1), the photoconductor 61 is rotated at the first speed V1, and the developing roller 71 is rotated at the first roller speed V11. After that, the control unit 100 executes the control indicated by the broken line in the figure. Further, in the second print control, if T ≧ TH2, the control unit 100 executes the control indicated by the solid line in the figure and then executes the control indicated by the broken line in the figure during the period from time t01 to t1.

  According to the above, when the elapsed time T is equal to or longer than the predetermined time Tth, the longer the elapsed time T, the longer the period during which the photoconductor 61 is rotated at the first speed V1. 71 can be rotated for a long time, and the charge amount of the toner can be satisfactorily increased.

  In the above embodiment, when the elapsed time T is equal to or longer than the predetermined time Tth, the peripheral speed ratio is set to the second peripheral speed ratio when rotating the photoconductor 61, but the present invention is not limited to this. is not. For example, when the elapsed time T is equal to or longer than the predetermined time Tth, the control unit 100 sets the peripheral speed ratio to the first peripheral speed ratio when starting rotation of the photoconductor 61, and sets the photoconductor 61 to the first speed. During the rotation at V1, the peripheral speed ratio may be set to the second peripheral speed ratio.

  Specifically, for example, as shown by a broken line in FIG. 9, when the elapsed time T is equal to or longer than the predetermined time Tth, the control unit 100 starts rotating the photoconductor 61 (time t1). By keeping the developing electromagnetic clutch 93 in the OFF state, the peripheral speed ratio is set to the first peripheral speed ratio. Thereafter, the control unit 100 turns on the developing electromagnetic clutch 93 (time t20) during the period in which the photoconductor 61 is rotating at the first speed V1 (time t2 to t3), thereby setting the peripheral speed ratio. This is the second peripheral speed ratio.

  Note that the flowchart in this embodiment may be slightly modified from the flowchart in FIG. Specifically, in FIG. 5, the timing for turning on the developing electromagnetic clutch 93 may be set, for example, between step S12 and step S13 instead of step S31.

  In the above-described embodiment, the starting point for starting the counting of the first time TM1 and the second time TM2 is the time when the supply of the sheet S is started. However, the present invention is not limited to this, and for example, when the print command is received. Or it may be at the start of the motor M.

  In the above embodiment, the first peripheral speed ratio is set to 1/5 or less of the second peripheral speed ratio. However, the present invention is not limited to this. For example, the first peripheral speed ratio is equal to or less than the second peripheral speed ratio. It may be 1/4 or less, or 1/3 or less.

  In the embodiment of FIG. 6, when T> Tth, the developing electromagnetic clutch 93 is turned on when the rotation of the photoconductor 61 is started. However, the present invention is not limited to this, and the rotation of the photoconductor 61 is started. In this case, the peripheral speed ratio should be the second peripheral speed ratio. For example, the developing electromagnetic clutch 93 may be turned on before the rotation of the photoconductor 61, and the peripheral speed ratio may be set to the second peripheral speed ratio.

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

  In the above embodiment, when T <Tth, two types of control, that is, control when T <TH1 and control when T ≧ TH1, can be executed, but the present invention is not limited to this. Not something. For example, when T <Tth, three or more types of control may be executed by comparing the elapsed time T with two or more types of thresholds. That is, three or more types of timings at which the peripheral speed ratio is changed may be set such that the longer the elapsed time T, the earlier the timing at which the peripheral speed ratio is changed from the first peripheral speed ratio to the second peripheral speed ratio.

  In the embodiment of FIG. 7, in the case of T ≧ Tth, two types of control, that is, control when T ≧ TH2 and control when T <TH2, can be executed. However, the present invention is not limited to this. Not something. For example, when T ≧ Tth, three or more types of control may be executed by comparing the elapsed time T with two or more types of thresholds. In other words, three or more low-speed periods may be set such that the longer the elapsed time T is, the longer the period during which the photoconductor 61 rotates at the first speed V1 (hereinafter, also referred to as “low-speed period”).

  In the above-described embodiment, the present invention is applied to the laser printer 1, but the present invention is not limited to this, and the present invention may be applied to other image forming apparatuses, for example, a copier or a multifunction peripheral.

  In the above-described embodiment, a positively charged toner is exemplified as the developer, but the present invention is not limited to this, and a negatively charged toner may be used.

  The components described in the embodiment and the modified examples described above may be implemented in any combination.

Reference Signs List 1 laser printer 61 photoconductor 71 developing roller 100 control unit T elapsed time Tth predetermined time V1 first speed V2 second speed

Claims (8)

A photoreceptor,
A developing roller for supplying a developer to the photoconductor,
And a control unit,
The control unit includes:
Before starting formation of an electrostatic latent image on the photoconductor, preparation rotation control for rotating the photoconductor and the developing roller,
Image forming control to form an electrostatic latent image on the photoreceptor,
In the preparation rotation control,
After setting the peripheral speed of the photoconductor to a first speed, the peripheral speed is changed to a second speed higher than the first speed,
If the elapsed time from the end of the previous image forming control is less than the predetermined time, the peripheral speed ratio of the developing roller to the photosensitive member is set to a first peripheral speed ratio of less than 1, and the peripheral speed ratio of the photosensitive member is reduced. After changing the speed from the first speed to the second speed, setting the peripheral speed ratio to a second peripheral speed ratio of 1 or more;
When the elapsed time is equal to or longer than the predetermined time, the peripheral speed ratio is set to the second peripheral speed ratio before changing the peripheral speed of the photoconductor from the first speed to the second speed. An image forming apparatus comprising:   The control unit sets the peripheral speed ratio to the second peripheral speed ratio when starting rotation of the photoconductor when the elapsed time is equal to or longer than the predetermined time. 2. The image forming apparatus according to 1.   When the elapsed time is equal to or longer than the predetermined time, the control unit sets the peripheral speed ratio to the first peripheral speed ratio when starting rotation of the photoconductor, and sets the photoconductor to the first peripheral speed ratio. 2. The image forming apparatus according to claim 1, wherein the peripheral speed ratio is set to the second peripheral speed ratio during a period in which the image forming apparatus is rotating at a speed.   When the elapsed time is less than a predetermined time, the control unit may advance the timing of changing the peripheral speed ratio from the first peripheral speed ratio to the second peripheral speed ratio as the elapsed time is longer. The image forming apparatus according to any one of claims 1 to 3, wherein:   The control unit according to claim 1, wherein, when the elapsed time is equal to or longer than the predetermined time, the longer the elapsed time, the longer the period during which the photoconductor is rotated at the first speed. The image forming apparatus according to claim 4. Motor and
A drive train for transmitting the driving force of the motor to the photoconductor,
A transmission for transmitting a driving force of the motor to the developing roller, wherein the transmission switches a peripheral speed ratio of the developing roller with respect to the photoconductor between the first peripheral speed ratio and the second peripheral speed ratio; ,
6. The image forming apparatus according to claim 1, wherein the control unit sets the peripheral speed ratio by controlling the transmission. 7.   The image forming apparatus according to any one of claims 1 to 6, wherein the first peripheral speed ratio is equal to or less than 1/5 of the second peripheral speed ratio. A photoreceptor,
A developing roller for supplying a developer to the photoconductor,
Motor and
A drive train for transmitting the driving force of the motor to the photoconductor,
A transmission for transmitting a driving force of the motor to the developing roller, wherein a peripheral speed ratio of the developing roller to the photosensitive member is set to a first peripheral speed ratio of less than 1 and a second peripheral speed ratio of 1 or more. A transmission to switch,
And a control unit,
The control unit includes:
Before starting formation of an electrostatic latent image on the photoconductor, preparation rotation control for rotating the photoconductor and the developing roller,
Image forming control to form an electrostatic latent image on the photoreceptor,
In the preparation rotation control,
A process of driving the motor to change the peripheral speed of the photoconductor to a first speed, and then to a second speed greater than the first speed;
Switching the transmission to set the peripheral speed ratio to the first peripheral speed ratio or the second peripheral speed ratio,
If the elapsed time from the end of the previous image forming control is less than the predetermined time, the peripheral speed of the photoconductor is changed from the first speed to the second speed, and then the peripheral speed ratio is changed. Set to the second peripheral speed ratio,
If the elapsed time is equal to or longer than the predetermined time, the peripheral speed ratio is set to the second peripheral speed ratio before changing the peripheral speed of the photoconductor from the first speed to the second speed. An image forming apparatus comprising:

Images