JP2017032744A - Image forming apparatus, control method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an increase in image density when the potential of an exposed portion of a photoreceptor is reduced due to a reduction in charging voltage.SOLUTION: An image forming apparatus comprises: an image forming part including a photoreceptor (photoreceptor drum 61), a charging part (charger 62) that charges the photoreceptor, and a developing part (developing roller 71) that supplies a developer to the photoreceptor; and a control part 100. The control part 100 performs a charging voltage application processing of applying a charging voltage to the charging part, developing voltage application processing of applying a developing voltage to the developing part; and reduction processing of, when determining that a predetermined time or more has elapsed from when the drive of the photoreceptor or the developing part is stopped, reducing absolute values of the charging voltage and developing voltage compared with a case of determining that the predetermined time or more has not elapsed.SELECTED DRAWING: Figure 3

Description

  The present invention provides an image forming apparatus having a control unit capable of changing a charging voltage applied to a charger and a developing voltage applied to a developing roller, a control method by the control unit, and a method for operating the control unit Regarding the program.

  2. Description of the Related Art Conventionally, there is known an image forming apparatus including a control unit that makes an absolute value of a charging voltage during image formation control smaller than a standard value when an elapsed time from the previous image formation is a certain value or more (patent) Reference 1).

JP 2010-72246 A

  By the way, in the prior art, when the charging voltage is lowered, the surface potential of the photoconductor may be lowered, and the potential of the exposed portion of the photoconductor may also be lowered. In this case, the potential difference between the developing roller and the exposed portion becomes large, which may increase the image density.

  Accordingly, an object of the present invention is to suppress an increase in image density when the potential of an exposed portion of a photoreceptor is lowered due to a decrease in charging voltage.

In order to solve the above problems, an image forming apparatus according to the present invention includes a photoconductor, a charging unit that charges the photoconductor, a developing unit that supplies a developer to the photoconductor, a control unit, .
The control unit includes a charging voltage applying process for applying a charging voltage to the charging unit, a developing voltage applying process for applying a developing voltage to the developing unit, and an elapsed time after driving of the photosensitive member or the developing unit is stopped for a predetermined time. In the case where it is determined as described above, a reduction process is performed in which the absolute values of the charging voltage and the developing voltage are reduced as compared with the case where it is determined that the elapsed time is not longer than the predetermined time.

  The control method according to the present invention is a control method for controlling a charging voltage applied to a charging unit for charging a photosensitive member and a developing voltage applied to a developing unit for supplying a developer to the photosensitive member. The absolute value of the charging voltage and development voltage is lower than when the elapsed time is determined not to be longer than the predetermined time when it is determined that the elapsed time since the drive of the body or the developing unit is stopped is longer than the predetermined time. Let

  The program according to the present invention is a program for operating a control unit that controls a charging voltage applied to a charging unit that charges the photosensitive member and a developing voltage applied to a developing unit that supplies developer to the photosensitive member. The control unit includes a charging voltage applying unit that applies a charging voltage to the charging unit, a developing voltage applying unit that applies a developing voltage to the developing unit, and an elapsed time after the driving of the photosensitive member or the developing unit is stopped. When it is determined that the time is longer than the predetermined time, the absolute values of the charging voltage and the developing voltage are made to function as a lowering unit that reduces the elapsed time as compared with the case where it is determined that the elapsed time is not longer than the predetermined time.

  When the elapsed time since the driving of the photosensitive member or the developing unit is stopped for a predetermined time or more, the charge amount of the developer is likely to be low. Therefore, in this case, the adhesion of the developer to the non-exposed part of the photoreceptor can be suppressed by reducing the absolute value of the charging voltage. At this time, even if the potential of the exposed portion of the photoreceptor decreases due to a decrease in the absolute value of the charging voltage, the potential difference between the exposed portion and the developing portion can be reduced by reducing the absolute value of the developing voltage. Therefore, it is possible to suppress an increase in image density.

  According to the present invention, when the charging voltage is lowered, the developing voltage is also lowered. Therefore, even if the potential of the exposed portion of the photoreceptor is lowered due to the lowering of the charging voltage, an increase in image density can be suppressed. .

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 a grid voltage, a surface potential, and a development voltage. It is a flowchart which shows operation | movement of a control part. It is a time chart which shows operation of a control part, and change of each voltage. 10 is a flowchart illustrating an operation of a control unit according to Modification 1. 10 is a time chart showing changes in voltages according to Modification 2.

  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 feed unit 3 that supplies paper S as an example of a recording sheet, and an image on the fed paper S. And an image forming part G for forming the image.

  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 as an example of an exposure unit, a process cartridge 5, and a fixing device 8 as an example of a fixing unit.

  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 photosensitive drum 61 as an example of a photosensitive member, a scorotron charger 62 as an example of a charging unit, and a transfer roller 63. The developing unit 7 mainly includes a developing roller 71 as an example of a developing unit, a supply roller 72, a layer thickness regulating blade 73, a container 74 that stores positively chargeable toner as a developer, and an agitator 75. Have.

  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 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, a temperature sensor SE1, a humidity sensor SE2, a fixing temperature sensor SE3, and a control unit 100 (see FIG. 3) are provided in the main body housing 2.

  The temperature sensor SE <b> 1 is a thermistor, for example, and is disposed facing the inside of the air inlet 24 formed by the main body housing 2. The temperature sensor SE <b> 1 is configured to detect the temperature outside the main body housing 2 by detecting the temperature of air taken in from the intake port 24.

  The humidity sensor SE <b> 2 is a sensor that detects relative humidity, for example, and is disposed facing the inside of the air inlet 24. 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 fixing temperature sensor SE3 is a thermistor, for example, and is provided in the fixing device 8. The fixing temperature sensor SE3 is configured to detect the temperature in the fixing device 8, for example, the temperature of the nip plate of the heating unit 81. The temperature detected by the temperature sensor SE1, the humidity detected by the humidity sensor SE2, and the temperature detected by the fixing temperature sensor SE3 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 controls a voltage applied to the charger 62, the developing roller 71, the transfer roller 63, the supply roller 72, the cleaning roller 64A, the static elimination lamp 90, and the like. It has a function to do. In particular, 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 smaller than the grid voltage Vg to the developing roller 71.

  In the present embodiment, the surface voltage of the photosensitive drum 61 is controlled by controlling the grid voltage Vg. However, the present invention is not limited to this, and for example, a voltage applied to the charging wire 62A is used. You may control.

  The control unit 100 includes a determination unit 110, a reduction unit 120, a development voltage increase unit 130, a charging voltage application unit 140, a development voltage application unit 150, a storage unit 160, a reception unit 170, and a timer 180. doing. In other words, the control unit 100 functions as the above-described units 110 to 150 by operating based on a program stored in the storage unit 160.

  The control unit 100 also has a function of performing known image formation control for forming an image on the paper S. Here, the image formation control is performed from the start of feeding of the first sheet S out of the number of image formations designated in the image formation command to the discharge of the last sheet S to the discharge tray 22. Control. Briefly, in the image formation control, the control unit 100 performs a paper feed process for feeding the paper S, an exposure process for exposing the photosensitive drum 61 by the exposure device 4 to form an electrostatic latent image, Development processing for supplying toner from the developing roller 71 to the electrostatic latent image on the photosensitive drum 61, transfer processing for transferring the toner image on the photosensitive drum 61 to the paper S, and thermal fixing of the toner image to the paper S Perform fixing processing.

  The accepting unit 170 has a function of accepting an image formation command from a personal computer or the like. When receiving the image formation command, the receiving unit 170 outputs the image formation command to the determination unit 110.

  Upon receiving an image formation command from the accepting unit 170, the determination unit 110 performs a reduction process, which will be described later, based on each information sent from the temperature sensor SE1, the humidity sensor SE2, etc. before starting image formation control. It has a function of performing determination processing for determining whether or not to execute development voltage increase processing. Specifically, the determination unit 110 determines the following four conditions in the determination process.

  In the determination process, the determination unit 110 determines whether or not the first condition that the elapsed time since the driving of the photosensitive drum 61 has been a predetermined time or longer is satisfied. Here, in this embodiment, the stop of the driving of the photosensitive drum 61 is determined based on, for example, the stop of the drive signal output to the motor 210 (see FIG. 2) that drives the photosensitive drum 61, and the elapsed time. Is counted by the timer 180 or the like.

  In the determination process, the determination unit 110 determines whether or not a second condition such that the temperature detected by the temperature sensor SE1 is equal to or higher than the first temperature is satisfied. Here, the first temperature is a relatively high temperature of, for example, 30 ° C. or more, and is appropriately determined by experiment, simulation, or the like.

  In the determination process, the determination unit 110 determines whether or not a third condition such that the humidity detected by the humidity sensor SE2 is equal to or higher than the first humidity is satisfied. Here, the first humidity is a relatively high humidity of, for example, 80% or more, and is appropriately determined by experiment, simulation, or the like.

  In the determination process, the determination unit 110 determines whether or not a fourth condition such that the temperature detected by the temperature sensor SE1 is equal to or lower than a second temperature lower than the first temperature is satisfied. Here, the second temperature is a relatively low temperature of, for example, 20 ° C. or less, and is appropriately determined by experiment, simulation, or the like.

  When the determination unit 110 determines that the first condition, the second condition, and the third condition are satisfied in the determination process, the determination unit 110 outputs a decrease instruction for executing the decrease process to the decrease unit 120. In other words, the determination unit 110 determines whether or not the first condition, the second condition, and the third condition are satisfied in the determination process, so that the charge amount of the toner in the developing unit 7 is lower than the predetermined amount. If the charge amount is determined to be low, a reduction instruction is output to the reduction means 120.

  If the determination unit 110 determines that the first condition and the fourth condition are satisfied in the determination process, the determination unit 110 outputs an increase instruction for executing the development voltage increase process to the development voltage increase unit 130. Further, when neither the lowering process nor the developing voltage raising process is executed, for example, when the judging unit 110 judges that the first condition is not satisfied, a non-execution signal indicating that is sent to the charging voltage applying unit 140 and the developing unit. The voltage is output to the voltage applying means 150.

  When receiving a reduction instruction from the determination unit 110, the reduction unit 120 has a function of performing a reduction process for reducing the grid voltage Vg and the development voltage Vb as compared with the case where the reduction instruction is not received. Specifically, the reduction unit 120 receives a reduction instruction before the start of the image formation control, thereby starting the reduction process before the start of the image formation control, and continuing the reduction process during the image formation control, that is, during the exposure process. When the predetermined conditions are met during the exposure process, the lowering process is stopped. When performing the reduction process, the reduction unit 120 acquires the first grid voltage Vg1 and the first development voltage Vb1 for the reduction process from the storage unit 160, and outputs the first grid voltage Vg1 to the charging voltage application unit 140. The first development voltage Vb1 is output to the development voltage application unit 150.

  When receiving the increase instruction from the determination unit 110, the development voltage raising unit 130 sets the grid voltage Vg to a value during the lowering process, that is, a value larger than the first grid voltage Vg1, and the development voltage Vb satisfies the first condition. It has a function of performing development voltage increase processing for increasing the voltage more than the case where it is determined that there is no. Specifically, when performing the development voltage increase process, the development voltage increase unit 130 acquires the second grid voltage Vg2 and the second development voltage Vb2 for the increase process from the storage unit 160, and obtains the second grid voltage Vg2. The charging voltage applying unit 140 outputs the second developing voltage Vb2 to the developing voltage applying unit 150. In the present embodiment, the second grid voltage Vg2 is described as the same value as a reference value VG described later.

  The charging voltage application unit 140 has a function of performing a charging voltage application process for applying the grid voltage Vg to the grid electrode 62B. Specifically, when receiving the non-execution signal output from the determination unit 110, the charging voltage application unit 140 sets the grid voltage Vg to the grid voltage reference value VG stored in the storage unit 160. Applied to the grid electrode 62B. Here, the reference value VG may be a fixed value or a value set based on humidity, temperature, or the like. In the present embodiment, the reference value VG will be described as a fixed value. The same applies to a reference value VB of a developing voltage described later.

  When the charging voltage application unit 140 receives the first grid voltage Vg1 for reduction processing from the reduction unit 120, the charging voltage application unit 140 sets the grid voltage Vg to the first grid voltage Vg1 and applies it to the grid electrode 62B. When changing the first grid voltage Vg1 to the reference value VG, the charging voltage applying unit 140 gradually increases the grid voltage Vg toward the reference value VG. When the charging voltage applying unit 140 receives the second grid voltage Vg2 (VG) for increasing processing from the developing voltage increasing unit 130, the charging voltage applying unit 140 sets the grid voltage Vg to the second grid voltage Vg2 and applies it to the grid electrode 62B. Apply.

  The development voltage application unit 150 has a function of performing development voltage application processing for applying the development voltage Vb to the development roller 71. Specifically, when the development voltage application unit 150 receives the non-execution signal output from the determination unit 110, the development voltage application unit 150 sets the development voltage Vb to the reference value VB of the development voltage stored in the storage unit 160. Applied to the developing roller 71.

  When the development voltage application unit 150 receives the first development voltage Vb1 for the reduction process from the reduction unit 120, the development voltage application unit 150 sets the development voltage Vb to the first development voltage Vb1 and applies it to the development roller 71. When the development voltage application unit 150 receives the second development voltage Vb2 for the increase process from the development voltage increase unit 130, the development voltage application unit 150 sets the development voltage Vb to the second development voltage Vb2 and applies it to the development roller 71. The development voltage application means 150 gradually increases the development voltage Vb when changing from the first development voltage Vb1 to the reference value VB, and the development voltage when changing from the second development voltage Vb2 to the reference value VB. Vb is gradually decreased.

  The storage unit 160 stores the reference values VG and VB, the first grid voltage Vg1, the first development voltage Vb1, the second grid voltage Vg2, the second development voltage Vb2, the temperature or humidity threshold values, and the like. Yes. Here, the relationship among the reference values VG, VB, the first grid voltage Vg1, the first development voltage Vb1, the second grid voltage Vg2, and the second development voltage Vb2 is as shown in FIG.

  As shown in FIG. 4, the first grid voltage Vg1 is set to a value lower than the reference value VG by the first reduction amount α. On the other hand, the first development voltage Vb1 is set to a value lower than the reference value VB by the second decrease amount β. The second decrease amount β is a value corresponding to the first decrease amount α, and is set to a value smaller than the first decrease amount α. Here, the second reduction amount β being a value corresponding to the first reduction amount α includes, for example, satisfying a relationship such as β = Xα with respect to the predetermined value X. The predetermined value X can be set within a range of 0 <X <1, for example.

  Here, when the grid voltage Vg is set to the reference value VG, the surface potential V0 of the photosensitive drum 61 becomes the reference potential Vx as shown by the solid line in the figure, and the potential of the exposed portion is higher than the reference potential Vx. Becomes a small potential Vy. On the other hand, when the grid voltage Vg is set to the first grid voltage Vg1, the surface potential V0 of the photosensitive drum 61 becomes a potential Vx1 smaller than the reference potential Vx as shown by a broken line in the drawing, and the exposed portion. Becomes a potential Vy1 smaller than the potential Vy. Then, by setting the first development voltage Vb1 so that an appropriate amount of toner is supplied to the exposed portion having such a small potential Vy1, the second reduction amount β is changed to the first reduction amount α. The value is in accordance. That is, the reference values VG and VB, the first grid voltage Vg1, and the first development voltage Vb1 described above are set as appropriate through experiments, simulations, and the like.

  Further, the surface potential Vx2 indicated by a two-dot chain line in the figure is a surface potential when the grid voltage Vg is set to the second grid voltage Vg2, that is, the reference value VG at a low temperature, and is a surface potential at a normal temperature and humidity. It is higher than Vx. The potential Vy2 of the exposed portion at this time is also higher than the potential Vy at normal temperature and humidity. The second development voltage Vb2 is set to a high value such that an appropriate amount of toner is supplied to the exposed portion that has a high potential Vy2 at low temperatures. That is, the second development voltage Vb2 is also set as appropriate through experiments, simulations, and the like.

  Next, the operation of the control unit 100 will be described in detail. Note that the ON / OFF timing of each voltage by the control unit 100 may be a well-known method, and a description thereof will be omitted.

  The control unit 100 starts the flowchart shown in FIG. 5 when the power of the laser printer 1 is turned on. When the flowchart of FIG. 5 is started, the control unit 100 determines whether there is an image formation command, that is, whether the reception unit 170 has received the image formation command (S1). If it is determined in step S1 that there is no image formation command (No), the control unit 100 ends this control. If it is determined in step S1 that there is an image formation command (Yes), the control unit 100 determines whether or not the elapsed time after the drive of the photosensitive drum 61 is stopped is equal to or longer than a predetermined time ( S2).

  Here, the driving of the photosensitive drum 61 is started, for example, in response to an image forming command received by the receiving unit 170, and is stopped after the above-described image forming control is completed. In the case of performing cooling control that idles the photosensitive drum 61 after the image formation control, the driving of the photosensitive drum 61 is stopped after the cooling control.

  If it is determined in step S2 that the elapsed time is equal to or longer than the predetermined time (Yes), the control unit 100 determines whether the temperature is equal to or higher than the first temperature and the humidity is equal to or higher than the first humidity. By doing so, it is judged whether it is a high-temperature, high-humidity environment (S3).

  If it is determined in step S3 that the environment is a high temperature and high humidity environment (Yes), the control unit 100 sets the grid voltage Vg to the first grid voltage Vg1 and sets the development voltage Vb to the first development voltage Vb1. Then, the lowering process is executed (S4). When it is determined in step S3 that the environment is not a high-temperature and high-humidity environment (No), the control unit 100 determines whether or not the temperature is a low-temperature environment by determining whether or not the temperature is equal to or lower than the second temperature. (S5).

  When it is determined in step S5 that the environment is a low temperature (Yes), the control unit 100 sets the grid voltage Vg to the second grid voltage Vg2, that is, the reference value VG, and sets the development voltage Vb to the second development voltage Vb2. Set (S6). If it is determined in step S2 that the elapsed time is less than the predetermined time (No), or if it is determined in step S5 that the environment is not a low temperature environment (No), the control unit 100 sets the grid voltage Vg to the reference value VG. Then, the development voltage Vb is set to the reference value VB (S7).

  After step S4, step S6, or step S7, the control unit 100 forms an image on one sheet of paper S based on the image formation command (S8). That is, the control unit 100 executes the above-described paper feed processing, exposure processing, development processing, transfer processing, fixing processing, and the like for one paper S. After step S8, the control unit 100 determines whether or not the voltage condition that the current grid voltage Vg is the reference value VG and the current development voltage Vb is the reference value VB is satisfied (S9). .

  If it is determined in step S9 that the voltage condition is not satisfied (No), the control unit 100 sets the corresponding voltage by a minute predetermined amount so that the voltage that has not reached the reference value gradually approaches the reference value. Control to decrease or increase is executed (S10). Specifically, for example, when the grid voltage Vg is set to the first grid voltage Vg1 and the development voltage Vb is set to the first development voltage Vb1 in the reduction process, the control unit 100 performs the grid voltage Vg in the process of step S10. Is set to a value obtained by adding a predetermined amount to the first grid voltage Vg1, and the developing voltage Vb is set to a value obtained by adding a predetermined amount to the first developing voltage Vb1. For example, when the grid voltage Vg is set to the reference value VG and the development voltage Vb is set to the second development voltage Vb2 in the development voltage increase process, the control unit 100 keeps the grid voltage Vg at the reference value VG. The development voltage Vb is set to a value obtained by subtracting a predetermined amount from the second development voltage Vb2.

  After step S10 or when it is determined in step S9 that the voltage condition has been satisfied (Yes), the control unit 100 specifies whether or not the image formation control has ended, specifically in the image formation command. It is determined whether image formation for the number of image formations has been completed (S11). If it is determined in step S11 that the image formation control has not ended (No), the control unit 100 returns to the process of step S8. As described above, when the control unit 100 repeatedly performs the processes in steps S8 to S11, the image formation can be performed with the grid voltage Vg or the development voltage Vb not set to the reference values VG and VB in the decrease process and the development voltage increase process. It is possible to gradually return to the reference values VG and VB as the number of finished sheets increases.

  If it is determined in step S11 that the image formation control has ended (Yes), the control unit 100 ends this control.

  Next, changes in each voltage due to the operation of the control unit 100 will be described with reference to a time chart shown in FIG. First, the operation of the control unit 100 when the elapsed time since the driving of the photosensitive drum 61 is less than a predetermined time will be described.

  As shown in FIG. 6, when the image forming command is received (time t1), the control unit 100 determines that the elapsed time since the driving of the photosensitive drum 61 is less than the predetermined time in the process of step S2. Then, the grid voltage Vg is set to the reference value VG, and the development voltage Vb is set to the reference value VB. Specifically, the control unit 100 starts applying the grid voltage Vg to the grid electrode 62B at time t1, and then applies the developing voltage Vb to the developing roller 71 at time t2. The time lag between the application of the grid voltage Vg and the application of the development voltage Vb is set to the time until a part of the surface of the photosensitive drum 61 whose surface potential has changed due to the change of the grid voltage Vg reaches the developing roller 71. Has been.

  Then, the control unit 100 keeps the voltages Vg and Vb at the reference values VG and VB even when it is time to start image formation (time t3). Here, the reference values VG and VB may be changed so as to be different values during image formation and during non-image formation.

  Next, the operation of the control unit 100 when the elapsed time after stopping the driving of the photosensitive drum 61 in a high temperature and high humidity environment is a predetermined time or more will be described.

  When the control unit 100 receives the image formation command (time t1), the control unit 100 determines Yes in steps S2 and S3, sets the grid voltage Vg to the first grid voltage Vg1 lower than the reference value VG, The development voltage Vb is set to a first development voltage Vb1 that is lower than the reference value VB. Here, since the decrease amount α of the first grid voltage Vg1 from the reference value VG is larger than the decrease amount β of the first development voltage Vb1 from the reference value VB, the voltage difference between the grid voltage Vg and the development voltage Vb ( Vg1−Vb1) is smaller than the voltage difference (VG−VB) when the elapsed time is less than the predetermined time. Here, there is a high possibility that the charge amount of the toner is low when the elapsed time is equal to or longer than a predetermined time or in an environment of high temperature and high humidity. If the voltage difference is large when the charge amount of the toner is reduced in this way, the polarity of the toner is reversed, and the phenomenon that the toner adheres to the non-exposed portion of the photosensitive drum 61 occurs. On the other hand, in the present embodiment, the voltage difference is reduced in a situation where the charge amount of the toner is low, so that adhesion of the toner to the non-exposed portion can be suppressed.

  Then, when it is time to start image formation (time t3), the control unit 100 repeats the processing of steps S8 to S11 according to the number of image formations, thereby changing the grid voltage Vg from the first grid voltage Vg1 to the reference value VG. The development voltage Vb is gradually increased from the first development voltage Vb1 toward the reference value VB (time t3 to t4). When the voltages Vg and Vb become the reference values VG and VB (time t4), the control unit 100 maintains the voltages Vg and Vb at the reference values VG and VB and continues image formation.

  Next, the operation of the control unit 100 when the elapsed time after the drive of the photosensitive drum 61 is stopped for a predetermined time or more in a low temperature environment will be described.

  Upon receiving the image formation command (time t1), the control unit 100 determines Yes in the process of step S2, No in the process of step S3, Yes in the process of step S5, and sets the grid voltage Vg to the second grid voltage Vg2. That is, the reference value VG is set, and the development voltage Vb is set to the second development voltage Vb2 higher than the reference value VB. Here, in a low-temperature environment, the electric potential at the exposed portion of the photosensitive drum 61 tends to increase due to the slow movement of charges. Therefore, the toner can be satisfactorily supplied to the high-potential exposed portion by making the development voltage Vb larger than the reference value VB in such a low temperature environment.

  Then, when it is time to start image formation (time t3), the control unit 100 repeats the processing of steps S8 to S11 according to the number of image formations, thereby maintaining the grid voltage Vg at the reference value VG. The development voltage Vb is gradually decreased from the second development voltage Vb2 toward the reference value VB (time t3 to t4). When the development voltage Vb reaches the reference value VB (time t4), the control unit 100 maintains the voltages Vg and Vb at the reference values VG and VB and continues image formation.

According to the above, the following effects can be obtained in the present embodiment.
When the elapsed time since the driving of the photosensitive drum 61 is stopped for a predetermined time or more and in a high-temperature and high-humidity environment, that is, when the charge amount of the toner is low, the grid voltage Vg is set. Therefore, toner adhesion to the non-exposed portion of the photosensitive drum 61 can be suppressed. At this time, even if the potential of the exposed portion of the photosensitive drum 61 decreases due to the decrease of the grid voltage Vg, the potential difference between the exposed portion and the developing roller 71 can be reduced by decreasing the developing voltage Vb. An increase in image density can be suppressed.

  Since the decrease amount β of the development voltage Vb is set according to the decrease amount α of the grid voltage Vg, it is possible to appropriately suppress an increase in image density in the decrease process.

  Since the decrease amount β of the development voltage Vb is set to a value smaller than the decrease amount α of the grid voltage Vg, it is possible to prevent the image density from being lowered by making the decrease amount of the development voltage Vb too large. .

  When it is determined that the elapsed time is equal to or longer than the predetermined time and the temperature is equal to or lower than the second temperature, the grid voltage Vg is set to a value larger than that during the lowering process, and the development voltage Vb is set equal to or longer than the predetermined time. Since the development voltage increase process is performed to increase the voltage when it is not determined to be low, it is possible to suppress the image density from being lowered by increasing the development voltage Vb even when the potential of the exposed portion is increased in a low temperature environment. it can.

  Considering that the charge amount of the toner gradually increases as the number of sheets on which image formation has been completed increases, the grid voltage Vg and the development voltage Vb, which have been lowered by the reduction process, are increased according to the increase in the number of sheets on which image formation has been completed. Thus, the reference values VG and VB are gradually returned to the reference values VG and VB, so that it is possible to satisfactorily suppress the adhesion of the toner to the non-exposed portion of the photosensitive drum 61 accompanying the increase in the toner charge amount.

  In addition, this invention is not limited to the said embodiment, It can utilize with various forms so that it may illustrate below.

  In the above-described embodiment, the grid voltage Vg or the development voltage Vb set to a value different from the reference values VG and VB is gradually returned to the reference values VG and VB according to the increase in the number of sheets for which image formation has been completed. However, the present invention is not limited to this. For example, when the number of completed images reaches a predetermined number, the grid voltage or the development voltage may be returned to the reference value all at once. Specifically, the control may be executed according to the flowchart shown in FIG.

  Since the flowchart shown in FIG. 7 is a partial modification of the flowchart shown in FIG. 5, the description of the same steps is omitted in the following description. In the flowchart shown in FIG. 7, new steps S21 and S22 are provided after the above-described steps S4 and S6, new steps S23 to S25 are provided instead of the above-described steps S9 and S10, and new steps are provided after the above-described step S11. Step S26 is provided.

  Steps S21 and S22 are processes for setting a flag F indicating 1 that the grid voltage Vg or the development voltage Vb is set to a value different from the reference values VG and VB. When the flag F is set to 1 in step S21 or step S22, the control unit 100 proceeds to the process of step S8. The flag F is stored in the storage unit 160.

  In step S <b> 23, the control unit 100 determines whether or not the flag F is “1”. If it is determined in step S23 that the flag F is 1 (Yes), the control unit 100 determines whether or not the number of sheets for which image formation has been completed is equal to or greater than a predetermined number (S24). Specifically, in step S24, the control unit 100 determines whether or not the number of images that have been formed is greater than or equal to a predetermined number, so that the operation of the image forming unit G after executing step S4 or step S6. It is determined whether the amount has reached a predetermined value. In other words, in step S24, the control unit 100 determines whether the operation amount of the image forming unit G from the start of the reduction process or the development voltage increase process has reached a predetermined value.

  If it is determined in step S24 that the number of completed images is equal to or greater than the predetermined number (Yes), the control unit 100 changes the grid voltage Vg to the reference value VG and changes the development voltage Vb to the reference value VB. (S25). When it is determined No in step S23, when it is determined No in step S24, or after step S25, the control unit 100 proceeds to the process of step S11. If it is determined Yes in step S11 or No in step S1, the control unit 100 returns the flag F to 0 (S26) and ends this control.

  In the above-described embodiment, the increase in the operation amount of the image forming unit is determined based on the increase in the number of sheets on which image formation has been completed. However, the present invention is not limited to this. The determination may be made based on an increase in the driving amount of the body drum 61 or the driving amount of the developing roller 71. The driving amount may be a driving time or the number of rotations.

  In the above-described embodiment, the elapsed time, temperature, and humidity are used as conditions for entering the reduction process. However, the present invention is not limited to this, and for example, only the elapsed time may be used as the condition, and either temperature or humidity may be used. One may be used as a condition. By adding temperature or humidity to the condition as in the above-described embodiment, it is possible to satisfactorily suppress the adhesion of toner to the non-exposed portion of the photosensitive drum 61.

  Also, as a condition for entering the reduction process, another condition may be determined instead of the elapsed time. For example, it may be determined whether or not the toner has been replaced, specifically, whether or not the process cartridge 5 that contains the toner has been replaced. When the toner is replaced, since the charge amount of the new toner is low, it is determined whether or not the charge amount of the toner is low by determining the replacement of the toner. Therefore, by executing the reduction process in such a case, the same effect as in the above embodiment can be obtained.

  Further, as a condition for entering the lowering process, it may be determined whether or not the photosensitive drum 61 has been replaced. When the photosensitive drum 61 is replaced and becomes a new one, a phenomenon that toner adheres to a non-exposed portion of the photosensitive drum 61 is likely to occur. Therefore, whether or not such a phenomenon occurs by performing the above-described determination. It will be judged. Therefore, by executing the reduction process in such a case, the same effect as in the above embodiment can be obtained.

  In the embodiment, it is determined whether or not the elapsed time counted by the timer 180 has reached a predetermined time or more. However, the present invention is not limited to this. For example, the temperature of the fixing device 8 detected by the fixing temperature sensor SE3 is determined. By determining whether or not the temperature is equal to or lower than the third temperature, it may be determined whether or not the elapsed time is equal to or longer than a predetermined time.

  In the embodiment, it is determined whether or not the elapsed time after the drive of the photosensitive drum 61 is longer than a predetermined time. However, the present invention is not limited to this. For example, the drive of the developing roller 71 is stopped. Then, it may be determined whether or not the elapsed time after that is a predetermined time or more.

  In the above-described embodiment, the grid voltage Vg is set to the reference value VG in the development voltage increase process, but the present invention is not limited to this, and the grid voltage in the development voltage increase process is larger than the grid voltage during the decrease process. Any value can be set.

  In the embodiment, the reference value VB of the development voltage Vb is set to the same value during non-image formation and during image formation, but the present invention is not limited to this. For example, as shown in FIG. 8, at the time of non-image formation before time t3, the reference value VB is set to a higher first value V1 and the reference value VB is set to the first value from the start of image formation. The reference value VB may be gradually decreased from V1, and thereafter, the reference value VB may be maintained at the second value V2 lower than the first value V1. In this case, the first development voltage Vb1 in the reduction process may be set to the same value as the second value V2, for example, and maintained constant both during non-image formation and image formation. Alternatively, the second development voltage Vb2 in the development voltage increase process may be set to a value higher than the first value V1, and gradually decreased toward the second value V2 from the start of image formation.

  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 above-described embodiment, the scorotron type charger 62 is exemplified as the charging unit. However, the present invention is not limited to this, and the charging unit may be, for example, a corotron type charger or is in contact with the photosensitive member. A charging roller may be used.

  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.

  In the above-described 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 apparatus that exposes a photoconductor with an LED, for example.

DESCRIPTION OF SYMBOLS 1 Laser printer 61 Photosensitive drum 62 Charging device 71 Developing roller 100 Control part

Claims (18)

An image forming unit having a photoconductor, a charging unit that charges the photoconductor, and a developing unit that supplies a developer to the photoconductor;
A control unit,
The controller is
Charging voltage application processing for applying a charging voltage to the charging unit;
A developing voltage application process for applying a developing voltage to the developing unit;
When it is determined that the elapsed time since the driving of the photosensitive member or the developing unit is stopped for a predetermined time or longer, the absolute value of the charging voltage and the developing voltage is not the same as the predetermined time or longer. And an image forming apparatus that performs a lowering process that lowers the image quality as compared with the case of determining. An exposure unit for exposing the photosensitive member;
The image forming apparatus according to claim 1, wherein the controller performs the reduction process during an exposure process in which the exposure unit exposes the photoconductor.   The image forming apparatus according to claim 1, wherein the control unit sets the amount of decrease in the development voltage to a value corresponding to the amount of decrease in the charging voltage in the decrease process.   The image forming apparatus according to claim 1, wherein the amount of decrease in the development voltage is smaller than the amount of decrease in the charging voltage. A humidity sensor,
The controller is
The reduction process is executed when it is determined that the elapsed time is equal to or longer than the predetermined time and the humidity detected by the humidity sensor is equal to or higher than a first humidity. 5. The image forming apparatus according to any one of 4 above. A temperature sensor,
The controller is
The lowering process is performed when it is determined that the elapsed time is equal to or longer than the predetermined time and the temperature detected by the temperature sensor is equal to or higher than a first temperature. The image forming apparatus according to claim 5. The controller is
When it is determined that the elapsed time is equal to or longer than the predetermined time and the temperature is equal to or lower than a second temperature lower than the first temperature, the absolute value of the charging voltage is larger than that during the lowering process. The image forming apparatus according to claim 6, wherein a developing voltage raising process is performed to raise the absolute value of the developing voltage more than when the elapsed time is determined not to be longer than the predetermined time. A temperature sensor,
The controller is
When it is determined that the elapsed time is equal to or longer than the predetermined time and the temperature is equal to or lower than the second temperature, the absolute value of the charging voltage is set to a value larger than that during the reduction process, and the absolute value of the developing voltage is set. 6. The image forming apparatus according to claim 1, wherein a developing voltage increase process is performed to increase a value as compared to a case where the elapsed time is determined not to be equal to or longer than the predetermined time.   In the reduction process, the control unit sets the absolute values of the charging voltage and the development voltage so that the elapsed time is not equal to or longer than the predetermined time as the operation amount of the image forming unit from the start of the reduction process increases. The image forming apparatus according to claim 1, wherein the image forming apparatus gradually increases toward a value for determination.   In the lowering process, the control unit sets the charging voltage and the development voltage to the charging time and the developing voltage when the operation amount of the image forming unit from the start of the lowering process reaches a predetermined value. 10. The image forming apparatus according to claim 1, wherein the image forming apparatus is changed to a value when it is determined that it is not. The image forming unit includes a fixing unit that thermally fixes a developer image on a recording sheet,
A fixing temperature sensor for detecting the temperature of the fixing unit;
11. The control unit according to claim 1, wherein the control unit determines that the elapsed time is equal to or longer than a predetermined time by determining that the temperature of the fixing unit is equal to or lower than a third temperature. 2. The image forming apparatus according to item 1.   The control unit determines an increase in the amount of operation of the image forming unit based on an increase in the number of images formed by the image forming unit, the driving amount of the photosensitive member, or the driving amount of the developing unit. The image forming apparatus according to claim 9 or 10. An image forming unit having a photoconductor, a charging unit that charges the photoconductor, and a developing unit that supplies a developer to the photoconductor;
A control unit;
A temperature sensor;
The controller is
Charging voltage application processing for applying a charging voltage to the charging unit;
A developing voltage application process for applying a developing voltage to the developing unit;
The charging voltage and the development voltage when the elapsed time since the drive of the photoconductor or the developing unit is stopped is a predetermined time or more and the temperature detected by the temperature sensor is the first temperature or more. A lowering process for lowering the absolute value of the time than when determining that the elapsed time is not equal to or longer than the predetermined time;
When it is determined that the elapsed time is equal to or longer than the predetermined time and the temperature is equal to or lower than a second temperature lower than the first temperature, the absolute value of the charging voltage is larger than that during the lowering process. And a development voltage increase process for increasing the absolute value of the development voltage more than when it is determined that the elapsed time is not equal to or longer than the predetermined time,
In the lowering process, the image forming apparatus is characterized in that the amount of decrease in the developing voltage is set to a value smaller than the amount of decrease in the charging voltage. An image forming unit having a photoconductor, a charging unit that charges the photoconductor, and a developing unit that supplies a developer to the photoconductor;
A control unit,
The controller is
Charging voltage application processing for applying a charging voltage to the charging unit;
A developing voltage application process for applying a developing voltage to the developing unit;
When it is determined that the charge amount of the developer in the developing unit is lower than a predetermined amount, the absolute values of the charge voltage and the development voltage are determined as the charge amount of the developer is not lower than the predetermined amount. An image forming apparatus that performs a reduction process that lowers more than the case. An image forming unit having a photoconductor, a charging unit that charges the photoconductor, and a developing unit that supplies a developer to the photoconductor;
A control unit,
The controller is
Charging voltage application processing for applying a charging voltage to the charging unit;
A developing voltage application process for applying a developing voltage to the developing unit;
A reduction process for lowering the absolute values of the charging voltage and the development voltage than when determining that the developer has not been replaced when it is determined that the developer has been replaced. Image forming apparatus. An image forming unit having a photoconductor, a charging unit that charges the photoconductor, and a developing unit that supplies a developer to the photoconductor;
A control unit,
The controller is
Charging voltage application processing for applying a charging voltage to the charging unit;
A developing voltage application process for applying a developing voltage to the developing unit;
A reduction process for lowering the absolute values of the charging voltage and the developing voltage than when determining that the photosensitive member has not been replaced when it is determined that the photosensitive member has been replaced. Image forming apparatus. A control method for controlling a charging voltage applied to a charging unit for charging a photoconductor and a developing voltage applied to a developing unit for supplying a developer to the photoconductor,
When it is determined that the elapsed time since the driving of the photosensitive member or the developing unit is stopped for a predetermined time or longer, the absolute value of the charging voltage and the developing voltage is not the same as the predetermined time or longer. The control method is characterized in that it is lower than the case where it is determined. A program for operating a control unit that controls a charging voltage applied to a charging unit that charges a photoconductor and a developing voltage applied to a developing unit that supplies developer to the photoconductor,
The control unit
Charging voltage application means for applying a charging voltage to the charging unit;
A developing voltage applying means for applying a developing voltage to the developing portion;
When it is determined that the elapsed time since the driving of the photosensitive member or the developing unit is stopped for a predetermined time or longer, the absolute value of the charging voltage and the developing voltage is not the same as the predetermined time or longer. A program that functions as a lowering means for lowering than the case of judging.

Images