JP2018063359A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology that reduces attachment of developer to an unexposed portion of a photoreceptor in an image forming apparatus of an electrophotographic system.SOLUTION: A printer 100, when rotating a photoreceptor drum 1 at a high speed to form an image, takes the difference between a voltage applied to a charger 2 and a voltage applied to a developing roller 41 as a first difference. The printer 100, when rotating the photoreceptor drum 1 at a low speed to form an image, takes the difference between a voltage applied to the charger 2 and a voltage applied to the developing roller 41 as a second difference smaller than the first difference in a low humidity state, and takes the difference between a voltage applied to the charger 2 and a voltage applied to the developing roller 41 as a third difference smaller than the second difference in a high humidity state.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus and an image forming method for forming an image by electrophotography.

  In an image forming apparatus that forms an image on a photoconductor by an electrophotographic method, the photoconductor has a first rotation speed and a second rotation speed that is lower than the first rotation speed. A technique for switching the rotational speed of a photoconductor according to the above conditions is known. For example, Patent Document 1 discloses an image forming apparatus that controls a photosensitive member so as to have different rotational speeds according to recording density. Patent Document 1 discloses a configuration in which the charging voltage is lowered when the rotation speed of the photoconductor is low compared to when the rotation speed of the photoconductor is high.

JP 2003-215892 A

  However, the conventional technique described above has the following problems. That is, when development is performed by bringing the photosensitive member and the developing roller into contact with each other, a part of the developer may adhere to an unexposed portion of the photosensitive member due to a decrease in the charge amount of the developer. This phenomenon becomes remarkable when the rotation speed of the photoconductor is slow, that is, when the developer on the developing roller is in contact with the photoconductor for a long time.

  The present invention has been made to solve the above-described problems of the prior art. That is, it is an object of the present invention to provide a technique for reducing the adhesion of developer to an unexposed portion of a photoreceptor in an electrophotographic image forming apparatus.

  An image forming apparatus for solving this problem includes a photosensitive member, a charger for charging the surface of the photosensitive member, and a developing roller that contacts the photosensitive member and supplies developer to the surface of the photosensitive member. And a humidity sensor and a control unit, wherein the control unit rotates the photosensitive member at a first speed to form an image, and applies an applied voltage of the charger and an applied voltage of the developing roller. When the image is formed by rotating the photoconductor at a second speed slower than the first speed, the humidity based on the signal from the humidity sensor is lower than a predetermined value. In this case, the difference between the applied voltage of the charger and the applied voltage of the developing roller is a second difference smaller than the first difference, and the humidity based on the signal from the humidity sensor is equal to or higher than the predetermined value. , The applied voltage of the charger and the mark of the developing roller The difference between the voltage, the smaller the third difference than the second difference, that perform particular voltage control, is characterized by.

  In the image forming apparatus disclosed in this specification, when the photosensitive member is printed at the second speed (low speed printing), the photosensitive member is printed at the first speed (high speed printing). , The difference between the applied voltage of the charger and the applied voltage of the developing roller is reduced. As a result, the so-called fogging in which the developer having a reduced charge amount on the developing roller adheres to the unexposed portion of the photoreceptor can be reduced.

  Further, in the image forming apparatus disclosed in the present specification, the difference is further reduced when the environment is a high humidity environment as compared with the case where the environment is a low humidity environment. As a result, the occurrence of fogging can be further suppressed in a high humidity environment where the charge amount of the developer tends to decrease. In other words, the image forming apparatus disclosed in the present specification determines the applied voltage of the charger and the applied voltage of the developing roller on the condition of humidity in addition to the rotational speed of the photosensitive member, and only the rotational speed of the photosensitive member. It can be expected that the adhesion of the developer to the unexposed part of the photoreceptor is further reduced as compared with the case where the above condition is satisfied.

  A control method, a computer program, and a computer-readable storage medium storing the computer program for realizing the functions of the apparatus are also novel and useful.

  According to the present invention, in an electrophotographic image forming apparatus, a technique for reducing the adhesion of a developer to an unexposed portion of a photoreceptor is realized.

1 is a cross-sectional view illustrating a schematic configuration of a printer according to an embodiment. It is sectional drawing which shows schematic structure of the process part of the printer concerning Embodiment. 1 is a block diagram illustrating an electrical configuration of a printer according to an embodiment. It is a figure which shows the relationship between a grid voltage and developing voltage in case an operation mode is mode A thru | or mode C in embodiment. It is a figure which shows the relationship between a grid voltage and developing voltage in case an operation mode is mode B in embodiment. 3 is a flowchart illustrating a procedure of print processing executed by the printer according to the embodiment. 6 is a flowchart illustrating a procedure of voltage setting processing executed by the printer according to the embodiment. It is a figure which shows the relationship between a grid voltage and a development voltage when the operation mode is the mode A thru | or mode C in an application form. It is a figure which shows the relationship between the threshold value of humidity and temperature in an applied form.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a printer capable of forming a color image.

  The printer 100 of this embodiment is a so-called tandem color laser printer, as schematically shown in FIG. The printer 100 includes process units 10Y, 10M, 10C, and 10K for each color of yellow (Y), magenta (M), cyan (C), and black (K). The process unit 10Y includes a photosensitive drum 1, a charger 2, and a developing unit 4. The other color process units 10M, 10C, and 10K have the same configuration. The printer 100 of this embodiment is arranged in the order of the process units 10Y, 10M, 10C, and 10K from the sheet conveyance direction, but the order is not limited to this.

  In addition, the printer 100 has an exposure unit 6 common to all the process units 10Y, 10M, 10C, and 10K above the process units 10Y, 10M, 10C, and 10K. Further, the printer 100 includes a transfer belt 7, a fixing device 8, a paper feed tray 91, and a paper discharge tray 92.

  Specifically, as shown in FIG. 2, the process unit 10 </ b> Y includes a charger 2, a developer 4, around the photosensitive drum 1 along the rotation direction of the photosensitive drum 1 (clockwise direction in FIG. 2). The light beam L from the exposure device 6 is irradiated on the surface of the photosensitive drum 1 at a position downstream of the charger 2 and upstream of the developing device 4 in the rotation direction of the photosensitive drum 1. The

  The photosensitive drum 1 includes a drum body 11 having conductivity and a cylindrical photosensitive layer 12 formed on the outer peripheral surface of the drum body 11. The drum body 11 is grounded. The photosensitive drum 1 is an example of a photosensitive member.

  The charger 2 is disposed so as not to contact the surface of the photosensitive drum 1 and to be parallel to the surface of the photosensitive drum 1. The charger 2 is a scorotron charger having a wire electrode 21 and a grid electrode 22. The wire electrode 21 is a linear metal, and is disposed along the axial direction of the photosensitive drum 1. The grid electrode 22 is a lattice-shaped metal, and is disposed between the wire electrode 21 and the photosensitive drum 1. The charger 2 generates a corona discharge when a positive wire voltage Vw is applied to the wire electrode 21 from the wire voltage application unit 25, and the surface of the photosensitive drum 1 is brought to a positive potential via the grid electrode 22. To charge.

  A grid circuit 23 is connected to the charger 2. The grid circuit 23 includes a Zener diode 231 as a constant voltage element and a resistor 232, the cathode side of the Zener diode 231 is connected to the grid electrode 22, and the anode side of the Zener diode 231 is grounded via the resistor 232. A connection point between the Zener diode 231 and the resistor 232 is connected to the controller 30. With this configuration, a grid voltage Vg is generated at the grid electrode 22 by the grid current that flows from the wire electrode 21 through the grid electrode 22 to the Zener diode 231 and the resistor 232. Here, the voltage Vp at the connection point between the Zener diode 231 and the resistor 232 shows a value proportional to the grid voltage Vg of the grid electrode 22. Therefore, the controller 30 detects the grid voltage Vg based on the voltage Vp at the connection point, and adjusts the wire voltage Vw so that the grid voltage Vg becomes a target value.

  The exposure device 6 (see FIG. 1) has a laser diode (not shown) and various optical members for irradiating the photosensitive drum 1 with a light beam emitted from the laser diode. The exposure device 6 includes, as various optical members, for example, a polygon mirror 61, an fθ lens 65, folding mirrors 66 and 67, and a toric lens 68. The polygon mirror 61 is rotated by the driving force of the polygon motor 62. In the exposure device 6, the light beam emitted from the laser diode is incident on the polygon mirror 61. The polygon mirror 61 has a regular hexagonal shape when viewed from above, and at the time of image formation, is rotated at a constant speed by a polygon motor 62 to reflect a light beam. The light beam is deflected with the rotation of the polygon mirror 61 and scanned on the photosensitive drum 1. As a result, the absolute value of the potential is lowered at the portion of the surface of the photosensitive drum 1 where the light beam is irradiated, and an electrostatic latent image is formed on the photosensitive drum 1.

  The developing device 4 holds toner charged to a positive polarity and supplies the toner to the surface of the photosensitive drum 1, a toner tank 42 for storing the toner, and toner stored in the toner tank 42. And a toner supply roller 43 that supplies the developing roller 41. The developing roller 41 is in contact with the photosensitive drum 1. The developing device 4 supplies a positive toner to the photosensitive drum 1 through the developing roller 41 by applying a positive developing voltage Vb from the developing voltage applying unit 45 to the developing roller 41, and The formed electrostatic latent image is developed. As a result, a toner image is formed on the photosensitive drum 1. The toner is an example of a developer.

  The developing device 4 is detachable from the printer 100, and the toner can be replenished by replacing the developing device 4. In addition, as long as the toner tank 42 is detachable from the developing device 4, only the toner tank 42 may be replaced. If the developing device 4 is a unit integrated with other members such as the photosensitive drum 1, the unit may be replaced.

  The transfer belt 7 includes a transfer roller 5 on the inner side of the contact position of the process units 10Y, 10M, 10C, and 10K with the respective photosensitive drums 1. The transfer roller 5 transfers the toner on the surface of the photosensitive drum 1 to a sheet conveyed on the transfer belt 7 or the transfer belt 7 by applying a negative transfer voltage Vt from the transfer voltage applying unit 55. .

  When the printer 100 receives the print command, the printer 100 pulls out the sheets stored in the paper feed tray 91 one by one and conveys them to the transfer belt 7. When the sheet passes between the photosensitive drum 1 and the transfer roller 5, the transfer roller 5 transfers the toner image formed on the photosensitive drum 1 to the sheet. Further, the printer 100 fixes the toner image transferred to the sheet to the sheet by the fixing device 8. Thereafter, the printer 100 discharges the sheet that has passed through the fixing device 8 to the discharge tray 92.

  When performing color printing, the printer 100 forms toner images of the respective colors in the process units 10M, 10C, and 10K of other colors and sequentially transfers them to the sheet. As a result, the toner images are superimposed on the sheet. Then, a color image is formed by fixing the superimposed toner images on the sheet.

  Next, the electrical configuration of the printer 100 will be described. As shown in FIG. 3, the printer 100 includes a CPU 31, ROM 32, RAM 33, NVRAM (nonvolatile RAM) 34, wire voltage application unit 25, development voltage application unit 45, transfer voltage application unit 55, Including a controller 30. The printer 100 includes process units 10Y, 10M, 10C, and 10K for each color, an exposure unit 6, a fixing unit 8, an operation panel 36, a communication interface 37, a humidity sensor 81, and a transport system 70. These are electrically connected to the controller 30.

  The ROM 32 stores various control programs for controlling the printer 100, various settings, initial values, and the like. The RAM 33 and the NVRAM 34 are used as a work area from which various control programs are read or as a storage area for temporarily storing data.

  The CPU 31 controls each component of the printer 100 while storing the processing result in the RAM 33 or the NVRAM 34 according to the control program read from the ROM 32. Note that the controller 30 in FIG. 3 is a general term that summarizes hardware used for controlling the printer 100 such as the CPU 31, and does not necessarily represent a single piece of hardware that actually exists in the printer 100. The CPU 31 is an example of a control unit. The controller 30 may be an example of a control unit.

  The wire voltage application unit 25 is connected to the wire electrode 21. The wire voltage application unit 25 applies a wire voltage Vw having the same polarity as the toner to the wire electrode 21 in accordance with an instruction from the CPU 31. In this embodiment, in order to set the grid voltage Vg to a target value, the wire voltage Vw is adjusted, for example, to +5 kV to +7 kV. The grid voltage Vg in this embodiment will be described later.

  The development voltage application unit 45 is connected to the development roller 41. The development voltage application unit 45 applies a development voltage Vb having the same polarity as the toner to the development roller 41 in accordance with an instruction from the CPU 31. The developing voltage Vb in this embodiment will be described later.

  The transfer voltage application unit 55 is connected to the transfer roller 5. The transfer voltage application unit 55 applies a transfer voltage Vt having a polarity opposite to that of the toner in accordance with an instruction from the CPU 31. In this embodiment, the target value of the transfer voltage Vt is set to, for example, -1200V. Note that the transfer roller 5 may perform current control for adjusting the transfer current amount flowing through the transfer roller 5 to a target current amount instead of voltage control.

  The operation panel 36 is provided on the exterior of the printer 100 and has various buttons for receiving input operations from the user, and a touch panel for displaying messages and setting contents. The communication interface 37 is hardware for communicating with an external device. Specific examples of the communication interface 37 include a wired LAN interface, a wireless LAN interface, a serial communication interface, a parallel communication interface, and a facsimile interface.

  The humidity sensor 81 outputs a different signal to the controller 30 according to the humidity value. The humidity sensor 81 is disposed at a position in the housing of the printer 100 for acquiring the humidity of the air around the process units 10Y, 10M, 10C, and 10K.

  The conveying system 70 is used for conveying a sheet, and includes various conveying units such as a paper feeding roller 71, a registration roller 72, and a transfer belt 7, and driving units thereof. The printer 100 has a high-speed conveyance mode and a half-speed conveyance mode that conveys a sheet at half the speed of the high-speed conveyance. Half-speed conveyance is automatically selected by the printer 100 when conveying a sheet such as thick paper that takes time to fix. It is also selected when silent printing is instructed by the user. Note that the half-speed transport only needs to be slower than the high-speed transport and does not necessarily need to be half the speed of the high-speed transport. When the half-speed conveyance is not performed, the printer 100 performs high-speed conveyance.

  When the sheet conveyance speed is changed, the printer 100 changes the rotation speed of the photosensitive drum 1 and the rotation speed of the developing roller 41 in accordance with the change. That is, when the sheet conveyance speed is decreased, the printer 100 decreases the rotation speed of the photosensitive drum 1 in accordance with the change, and further decreases the rotation speed of the developing roller 41 in accordance with the change in the rotation speed of the photosensitive drum 1. To do. The photosensitive drum 1 and the developing roller 41 are driven with a predetermined gear ratio by the same driving source. Thus, the printer 100 is configured so that the peripheral speed ratio between the photosensitive drum 1 and the developing roller 41 is the same even when the sheet conveyance speed is changed.

  Next, operation modes of the process units 10Y, 10M, 10C, and 10K will be described. The printer 100 has three modes of mode A, mode B, and mode C as 10Y, 10M, 10C, and 10K operation modes. This operation mode is set for each of the process units 10Y, 10M, 10C, and 10K, and the operation mode is determined by the printing amount for each of the process units 10Y, 10M, 10C, and 10K.

  Specifically, mode A is an operation mode in the case where the number of times of printing after the developing device 4 that is the toner container is replaced with a new one does not exceed the new product threshold value for determining whether or not the new product is in the new state. . That is, immediately after the developing device 4 is replaced, that is, when the toner is in a new state, the mode is A, and the printer 100 continues the mode A until the number of times of printing reaches the new product threshold. The new product threshold value may be set for each of the process units 10Y, 10M, 10C, and 10K, or may be common to all the process units 10Y, 10M, 10C, and 10K. In this embodiment, the new article threshold value is common to all the process units 10Y, 10M, 10C, and 10K, and the value is set to 300 times. As described above, the “new state” described in the present specification means a state in which the number of printings after the developing device 4 is replaced with a new one does not exceed the new product threshold value, and printing is performed once. It does not mean that the state is not.

  Mode B is an operation mode in which the number of times of printing after the developing device 4 is replaced with a new one is not less than the new product threshold and does not exceed the endurance threshold for determining whether or not it is in a deteriorated state. is there. That is, the printer 100 changes to the mode B when the developing device 4 is not in a new state, and thereafter continues the mode B until the number of printing times reaches the durability threshold. The durability threshold value may be set for each of the process units 10Y, 10M, 10C, and 10K, or may be common to all the process units 10Y, 10M, 10C, and 10K. In this embodiment, the endurance threshold is common to all the process units 10Y, 10M, 10C, and 10K, and the value is 8000 times.

  Mode C is an operation mode when the number of times of printing after the developing device 4 is replaced with a new one is equal to or greater than the durability threshold. That is, the printer 100 changes to the mode C when it can be determined that the toner accommodated in the developing device 4 has deteriorated, and then continues the mode C until the developing device 4 is replaced.

  The printer 100 determines the grid voltage Vg and the development voltage Vb according to the operation mode for each of the process units 10Y, 10M, 10C, and 10K. FIG. 4 shows the grid voltage Vg and the development voltage Vb when the operation mode is mode A to mode C. The absolute value of the development voltage Vb is smaller than the absolute value of the grid voltage Vg. FIG. 5 shows the grid voltage Vg and the development voltage Vb when the operation mode is mode B. 4 and 5, “high speed” means high speed conveyance, “half speed low humidity” means half speed conveyance and low humidity, and “half speed high humidity” means half speed conveyance and high humidity. . For example, the printer 100 determines that the humidity is high when the humidity is 70% or more, and determines that the humidity is low and low when the humidity is less than 70%.

  In the printer 100, development is performed with the developing roller 41 in contact with the photosensitive drum 1, and thus the toner charge amount may decrease due to the surface potential of the photosensitive drum 1. As a result, a so-called fog occurs in which a part of the toner having a relatively small amount of charge adheres to the unexposed portion of the photosensitive drum 1. The fog becomes prominent when the rotational speed of the photosensitive drum 1 is low, that is, when the time on which the toner on the developing roller 41 is in contact with the photosensitive drum 1 is long.

  Therefore, the printer 100 reduces the difference Vg−Vb between the grid voltage Vg and the development voltage Vb in the half-speed conveyance compared with the high-speed conveyance. As a result, the decrease in the charge amount of the toner on the developing roller 41 is suppressed, and the toner with a small charge amount is difficult to adhere to the unexposed portion of the photosensitive drum 1. Specifically, in the example of the printer 100 of this embodiment shown in FIG. 4, the relationship of the difference Vg−Vb between the high speed and the half speed low humidity or half speed high humidity in the yellow process unit 10Y corresponds.

  Further, the fog is likely to occur when the photosensitive drum 1 rotates at a low speed and the humidity is high. In other words, even when the humidity is high, the charge of the toner tends to decrease and fogging is likely to occur. Therefore, when the printer 100 is transported at half speed and is in a higher humidity state, the difference Vg−Vb between the grid voltage Vg and the development voltage Vb is further reduced so that the toner having a small charge amount is transferred to the photosensitive drum. 1 makes it difficult to adhere to the unexposed part. Specifically, in the example of the printer 100 of this embodiment shown in FIG. 4, the relationship of the difference Vg−Vb between the half-speed low humidity and the half-speed high humidity in the yellow process unit 10Y corresponds.

  Note that the grid voltage Vg and the development voltage Vb need not be changed for all colors during the half-speed conveyance. That is, the ease of fogging varies depending on the toner characteristics. It is assumed that the printer 100 according to the present embodiment is easy to generate fog in yellow and hardly generates fog in other colors. Therefore, as shown in FIG. 4, for colors other than yellow, the printer 100 does not change the grid voltage Vg and the development voltage Vb according to humidity. In other words, the printer 100 changes the grid voltage Vg and the development voltage Vb in accordance with the humidity on the condition that toner that easily generates fogging is used.

  Further, even when the toner charge amount is stable, that is, when the toner charge amount variation is small, the fog hardly occurs. Therefore, when the printer 100 is operating in the mode B, the grid voltage Vg and the development voltage Vb are not changed according to the humidity as shown in FIG. In other words, when the toner is new, the charge amount of the toner is difficult to increase and fogging is likely to occur. Even when the toner is at the end of its endurance, the toner charge amount is unlikely to rise and fog is likely to occur. Therefore, the printer 100 changes the grid voltage Vg and the development voltage Vb in accordance with the humidity on the condition that either one is new or the toner is deteriorated.

  Next, a printing process executed by the printer 100 to realize the above-described operation mode will be described with reference to a flowchart of FIG. The print processing is executed by the CPU 31 when a print job is received via the operation panel 36 or the communication interface 37.

  In the printing process, the CPU 31 first executes a voltage setting process for setting the grid voltage Vg and the developing voltage Vb based on the sheet conveyance mode and the operation mode (S001). Details of the voltage setting process will be described later.

  After S001, sheet feeding from the sheet feeding tray 91 is started by the conveying system 70, and the sheet is conveyed toward the process units 10Y, 10M, 10C, and 10K (S011). In S011, the CPU 31 determines whether it is high-speed conveyance or half-speed conveyance based on the silent printing instruction and the sheet type, and starts conveyance of the sheet according to the conveyance mode according to the determination result.

  Further, the CPU 31 causes the process units 10Y, 10M, 10C, and 10K to form toner images based on the print job (S012). The process of S011 and the process of S012 are executed in parallel, and whichever may be first or may be started simultaneously. The toner image formed in S012 is transferred to the sheet conveyed from the paper feed tray 91 in S011, and then subjected to heat fixing by the fixing device 8. Then, the CPU 31 discharges the sheet that has passed through the fixing device 8 to the discharge tray 92 by the conveyance system 70.

  After S012, the CPU 31 counts up the counter C (S013). The counter C is data prepared for each of the process units 10Y, 10M, 10C, and 10K, and stores the cumulative number of times printing has been performed since the developing device 4 has been replaced with a new one. That is, when a new developing device 4 is mounted, the counter C corresponding to the process unit in which the developing device 4 is mounted is reset to zero. Every time printing is performed, all counters C are counted up for color printing, and only counters C corresponding to the process unit 10K are counted up for monochrome printing. The counter C is stored in the NVRAM 34.

  After S013, the CPU 31 determines whether or not the next printing is necessary (S014). If the next printing is necessary (S014: YES), the CPU 31 proceeds to S011 and performs processing for the next printing. If the next printing is not necessary (S014: NO), the CPU 31 ends the printing process.

  Next, the voltage setting process in S001 will be described with reference to the flowchart of FIG. Since the grid voltage Vg and the development voltage Vb are set for each of the process units 10Y, 10M, 10C, and 10K, the voltage setting process is executed for each of the process units 10Y, 10M, 10C, and 10K.

  In the voltage setting process, the CPU 31 first determines whether or not it is in a new state (S101). Specifically, the determination as to whether or not the product is in the new state is made by reading the counter C from the NVRAM 34, and if the value does not exceed the new product threshold value, the product is in the new state.

  If it is not a new state (S101: NO), the CPU 31 determines whether or not it is in a durability deterioration state (S102). Specifically, the determination as to whether or not the state is the durability deterioration state is made the durability deterioration state if the value of the counter C is equal to or greater than the durability threshold value. S101 and S102 may be reversed.

  If it is not in the durability deterioration state (S102: NO), the CPU 31 determines whether or not half-speed conveyance is necessary (S111). That is, if it is not in a new state or in a state of durability deterioration, the operation mode is mode B. In mode B, as shown in FIG. 5, the grid voltage Vg and the development voltage Vb differ depending on whether or not half-speed conveyance is performed. Therefore, if half-speed conveyance is necessary (S111: YES), the CPU 31 sets the grid voltage Vg and the development voltage Vb for half-speed conveyance (S112). On the other hand, if half-speed conveyance is not necessary (S111: NO), the CPU 31 sets the grid voltage Vg and the development voltage Vb for high-speed conveyance (S113).

  When it is in a new state (S101: YES), or when it is in a durability deterioration state (S102: YES), the CPU 31 determines whether or not it is a specific color (S121). The specific color corresponds to a color that easily causes fogging, and yellow corresponds to this embodiment. That is, in the new state, the operation mode is mode A. In mode A, as shown in FIG. 4, for yellow, the grid voltage Vg and the development voltage Vb differ depending on the humidity in addition to the transport mode. In the degraded state, the operation mode is mode C. In mode C as well as mode A, for yellow, the grid voltage Vg and the development voltage Vb differ depending on the humidity in addition to the transport mode. On the other hand, if the color is other than yellow, the grid voltage Vg and the development voltage Vb are the same as those in the mode B. Therefore, if it is not a specific color (S121: NO), the process proceeds to S111, and the CPU 31 sets the grid voltage Vg and the development voltage Vb as in the mode B.

  If it is a specific color (S121: YES), the CPU 31 acquires the humidity based on the signal from the humidity sensor 81 (S122). Then, the CPU 31 determines whether or not half-speed conveyance is necessary (S131). If half-speed conveyance is not necessary (S131: NO), the CPU 31 sets the grid voltage Vg and the development voltage Vb for high-speed conveyance (S132).

  On the other hand, if half-speed conveyance is necessary (S131: YES), the CPU 31 determines whether or not it is in a high humidity state (S141). In S141, the CPU 31 determines that the humidity is high when the humidity acquired in S122 exceeds the threshold humidity (70% in this embodiment). If the humidity is high (S141: YES), the CPU 31 sets the grid voltage Vg and the development voltage Vb for the high-humidity and half-speed conveyance (S142). On the other hand, if not in the high humidity state (S141: NO), the CPU 31 sets the grid voltage Vg and the development voltage Vb for the low humidity state and half-speed conveyance (S143).

  After S112, after S113, after S132, after S142, or after S143, the CPU 31 ends the voltage setting process.

  In the printer 100, since the same grid voltage Vg and development voltage Vb are set in the mode A and the mode C, the printer 100 is in a new state (S101: YES), and is in a durability deterioration state (S102: YES). , The same processing is performed, but different grid voltage Vg and development voltage Vb may be set in mode A and mode C. In this case, a process for setting the grid voltage Vg and the developing voltage Vb separately may be provided for the new state (S101: YES) and the durability deterioration state (S102: YES).

  As described in detail above, the printer 100 performs development with the developing roller 41 in contact with the photosensitive drum 1. Compared with printing at high speed conveyance, printing at half speed conveyance is performed. Thus, the difference Vg−Vb between the grid voltage Vg and the development voltage Vb is reduced. As a result, a decrease in the charge amount of the toner on the developing roller 41 is suppressed, and fogging can be reduced. Further, when the printer 100 is in a high humidity environment, the difference Vg−Vb is further reduced as compared with the case of the low humidity environment. Thereby, generation | occurrence | production of fog can be suppressed more in the high-humidity environment where fog is likely to occur. In other words, the printer 100 determines the grid voltage Vg and the development voltage Vb on the basis of the humidity as well as the rotation speed of the photosensitive drum 1, and the fogging is compared with the case where only the sheet transport mode is a condition. A further reduction can be expected.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the present invention is not limited to a printer, and can be applied to any apparatus having an image forming function based on an electrophotographic method such as a copying machine or a FAX. Further, the numerical values of various voltages described in the embodiment are merely examples, and may be appropriately selected.

  The printer 100 according to the embodiment is a scorotron charger having the wire electrode 21 and the grid electrode 22, but is not limited thereto. For example, it may be a charger that has a charging roller to which a voltage is applied and charges the surface of the photosensitive drum 1 by bringing the charging roller into contact with the photosensitive drum 1.

  In the embodiment, each of the process units 10Y, 10M, 10C, and 10K includes the wire voltage application unit 25, the development voltage application unit 45, and the transfer voltage application unit 55. You may provide the voltage application part. For example, if the transfer voltages Vt of the process units 10Y, 10M, 10C, and 10K are common, the process units 10Y, 10M, 10C, and 10K may be provided with a common transfer voltage application unit 55.

  In the embodiment, the number of times of printing is counted as the amount of printing after the developing device 4 is replaced with a new one. However, the amount of printing is not limited to the number of times of printing. For example, the printing dots and the number of rotations of the developing roller 41 after the developing device 4 is replaced with a new one may be counted.

  In the embodiment, every time a print job is started, the CPU 31 sets the grid voltage Vg and the development voltage Vb. However, when the same type of sheet as the previous print job is continuously conveyed, the voltage of S001 is set. The setting process may be omitted. That is, the grid voltage Vg and the development voltage Vb may not be changed during continuous printing.

  In the embodiment, when the difference Vg−Vb between the grid voltage Vg and the development voltage Vb is changed, both the grid voltage Vg and the development voltage Vb are changed. However, as shown in FIG. Only the grid voltage Vg may be changed without changing the voltage Vb. Alternatively, only the development voltage Vb may be changed without changing the grid voltage Vg. Changing only one voltage simplifies the control of the other voltage. However, when the half-speed conveyance is performed, the exposure time per unit area of the surface of the photosensitive drum 1 becomes long, and the absolute value of the surface potential of the exposed portion tends to be smaller than that in the case of high-speed conveyance, and as a result, the density becomes high. easy. Therefore, the density change can be suppressed by reducing the developing voltage Vb as in the embodiment.

  In the embodiment, only yellow is a specific color that is likely to cause fogging, and the grid voltage Vg and the development voltage Vb are set according to humidity in addition to the transport mode. However, the specific color is limited to yellow. is not. For example, other colors may be specified colors. Further, the specific color is not limited to one color, and a plurality of specific colors may be used. Of course, all colors may be specified colors. In other words, the grid voltage Vg and the development voltage Vb may be set for all the process units 10Y, 10M, 10C, and 10K according to the humidity without determining whether the color is a specific color.

  In the embodiment, the grid voltage Vg and the development voltage Vb are set according to the humidity in the new state (mode A) or in the durability deterioration state (mode C). Instead, in all states, the grid voltage Vg and the developing voltage Vb may be set according to the humidity. Further, only one of the new state (mode A) and the durability deterioration state (mode C) may be determined.

  In the embodiment, the humidity threshold value indicating whether the humidity state is high is a fixed value (70% in this embodiment), but may be a variable value. For example, the printer 100 may be provided with a temperature sensor for detecting the temperature in the housing, and as shown in FIG. 9, the higher and lower the temperature, the lower the threshold value for humidity.

  In the embodiment, the grid voltage Vg and the development voltage Vb are set in two stages of low humidity and high humidity during half-speed conveyance, but may be divided into three or more stages. That is, the difference Vg−Vb between the grid voltage Vg and the development voltage Vb may be reduced as the humidity increases.

  The processing disclosed in the embodiments may be executed by a single CPU, a plurality of CPUs, hardware such as an ASIC, or a combination thereof. Further, the processing disclosed in the embodiment can be realized in various modes such as a recording medium or a method recording a program for executing the processing.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charger 41 Developing roller 81 Humidity sensor 30 Controller 100 Printer

Claims (10)

A photoreceptor,
A charger for charging the surface of the photoreceptor;
A developing roller that contacts the photoreceptor and supplies developer to the surface of the photoreceptor;
A humidity sensor,
A control unit;
With
The controller is
When the photosensitive member is rotated at a first speed to form an image,
The difference between the applied voltage of the charger and the applied voltage of the developing roller is the first difference,
When the image is formed by rotating the photoconductor at a second speed slower than the first speed,
When the humidity based on the signal from the humidity sensor is lower than a predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is a second difference smaller than the first difference,
When the humidity based on the signal from the humidity sensor is equal to or higher than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as a third difference smaller than the second difference.
An image forming apparatus. The image forming apparatus according to claim 1,
The controller is
When reducing the difference between the applied voltage of the charger and the applied voltage of the developing roller, both the absolute value of the applied voltage of the developing roller and the absolute value of the applied voltage of the charger are reduced.
An image forming apparatus. The image forming apparatus according to claim 1,
The controller is
When reducing the difference between the applied voltage of the charger and the applied voltage of the developing roller, the absolute value of the applied voltage of the charger is reduced without changing the applied voltage of the developing roller,
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
The charger is
A corona charger comprising a wire electrode and a grid electrode;
The controller is
As the applied voltage of the charger, the potential of the grid electrode is controlled.
An image forming apparatus. In the image forming apparatus according to any one of claims 1 to 4,
The peripheral speed ratio between the photoconductor and the developing roller is the same when the photoconductor is at the first speed and at the second speed.
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 5,
A plurality of the photoreceptors;
The charger and the developing roller corresponding to each of a plurality of the photoreceptors,
The controller is
When forming an image by rotating the photoconductor at the second speed, at least one of the plurality of photoconductors,
When the humidity based on the signal from the humidity sensor is lower than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is the second difference,
When the humidity based on the signal from the humidity sensor is not less than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is the third difference,
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 6,
A housing portion for housing the developer;
The controller is
Count the amount of printing since the container was replaced with a new one,
When forming an image by rotating the photosensitive member at the second speed, on the condition that the print amount count value does not exceed the first threshold value,
When the humidity based on the signal from the humidity sensor is lower than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is the second difference,
When the humidity based on the signal from the humidity sensor is not less than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is the third difference,
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 6,
A housing portion for housing the developer;
The controller is
Count the amount of printing since the container was replaced with a new one,
When forming an image by rotating the photoconductor at the second speed, further, provided that the print amount count value exceeds a second threshold value,
When the humidity based on the signal from the humidity sensor is lower than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is the second difference,
When the humidity based on the signal from the humidity sensor is not less than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is the third difference,
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 6,
A housing portion for housing the developer;
The controller is
Count the amount of printing since the container was replaced with a new one,
When an image is formed by rotating the photosensitive member at the second speed, the print amount count value does not exceed a first threshold value or exceeds a second threshold value that is greater than the first threshold value. On condition that
When the humidity based on the signal from the humidity sensor is lower than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is the second difference,
When the humidity based on the signal from the humidity sensor is not less than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is the third difference,
An image forming apparatus. A photoreceptor,
A charger for charging the surface of the photoreceptor;
A developing roller that contacts the photoreceptor and supplies developer to the surface of the photoreceptor;
In an image forming method of an image forming apparatus comprising:
An acquisition step for acquiring humidity;
A first step in which, when an image is formed by rotating the photosensitive member at a first speed, a difference between an applied voltage of the charger and an applied voltage of the developing roller is a first difference;
A determination step of determining whether or not the humidity acquired in the acquisition step is lower than a predetermined value when an image is formed by rotating the photoconductor at a second speed slower than the first speed; ,
When it is determined in the determination step that the humidity is lower than the predetermined value, a difference between the applied voltage of the charger and the applied voltage of the developing roller is set to a second difference that is smaller than the first difference. And the second step,
When it is determined in the determination step that the humidity is equal to or higher than the predetermined value, a difference between the applied voltage of the charger and the applied voltage of the developing roller is set as a third difference that is smaller than the second difference. The third step,
An image forming method for an image forming apparatus, comprising:

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