JP2010044205A - Image-forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image-forming device which generates a transfer voltage without fail. <P>SOLUTION: The image-forming device includes: a photoreceptor 28 which carries on it a developer image, which is developed with a developer, by making use of electrification; a transfer roller 14 which transfers the developer image on a recording medium in response to the application of a transfer voltage Vt; an application means 55 which generates the transfer voltage Vt and applies the transfer voltage Vt to the transfer roller 14; and current-restricting means (40 and 60) which restrict a current Ir which is generated, due to the electrification of the photoreceptor 28, between the photoreceptor 28 and the application means 55. When the application means 55 is started up, the current-restricting means (40 and 60) increase the resistance between the photoreceptor 28 and the application means 55 compared with the ordinary one to decrease the current Ir caused by the electrification of the photoreceptor 28. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to activation of a transfer voltage thereof.

In a conventional image forming apparatus, a technique called constant current control is known as a method for appropriately controlling a transfer voltage in order to perform good image formation (prior art document 1). In Document 1, the high-voltage control device detects the transfer current flowing through the transfer roller, and controls the transfer voltage so that the current value falls within a predetermined range. In the image forming apparatus, if a transfer voltage is applied while the photoconductor is not charged, the photoconductor may be damaged. Therefore, the photoconductor is usually charged before the transfer voltage is generated.
JP 2008-76750 A

  However, in the image forming apparatus described in Document 1, when the transfer voltage is generated in a state where the photoconductor is positively charged before the transfer voltage is generated and the transfer voltage is applied to the transfer roller, the photoconductor Due to this charging, a current (hereinafter referred to as inflow current) flows into the transfer roller. For this reason, the high voltage (transfer voltage) generation circuit may not be able to start up properly due to the inflow current.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of reliably generating a transfer voltage.

  Utilizing charging, a photosensitive member carrying a developer image developed by a developer, a transfer roller for transferring the developer image to a recording medium in response to application of a transfer voltage, and generating the transfer voltage An application means for applying the transfer voltage to the transfer roller, and when the application means is activated, a current generated between the photoconductor and the application means due to the charging is applied to the photoconductor. Current limiting means for reducing the resistance between the applying means and the application means by increasing the resistance compared to the normal time.

  According to this configuration, when the application unit is activated, a current generated between the photoconductor and the application unit, for example, an inflow current from the photoconductor to the application unit can be reduced. Accordingly, it is possible to reliably start the applying unit and apply the transfer voltage to the transfer roller. Here, “normal time” means a case where the transfer current is under constant current control after activation of the applying means, or a case where the transfer voltage is under constant voltage control.

  According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the current limiting unit is connected between the transfer roller and the application unit, and a current flowing between the transfer roller and the application unit is generated. Current adjusting means for adjusting, and control means for controlling the current adjusting means so as to maximize the resistance value of the current adjusting means when the applying means is activated.

  According to this configuration, when the application unit is started, the resistance value of the current adjusting unit connected between the transfer roller and the application unit is maximized. The current generated between the applying means and the application means can be suitably reduced.

  According to a third aspect of the present invention, in the image forming apparatus of the second aspect of the present invention, the image forming apparatus further includes a detection unit for detecting a current flowing through the transfer roller, and the control unit is configured to The current adjusting means is controlled based on the detected current value.

  According to this configuration, the current adjusting unit can be used for constant current control of the transfer current after activation of the applying unit. Therefore, the current adjusting means can be used both as a means for reducing current caused by charging of the photosensitive member when the applying means is activated and a means for controlling the constant current after the applying means is activated.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the photoconductor includes a plurality of photoconductors, and the transfer roller and the current adjusting unit include the plurality of photoconductors. The application means is connected in common to the plurality of transfer rollers.

  According to this configuration, when the image forming apparatus is a color image forming apparatus including a plurality of photoconductors, one application unit may be activated. Therefore, the start-up control of the application unit is simplified as compared with the case where the application unit is individually provided for each transfer roller. That is, as long as the application means is activated against the current caused by charging of the photosensitive member corresponding to the first transfer roller, the trouble of activating the application means corresponding to the other transfer rollers can be saved. .

  According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the current limiting means includes a transfer roller contact / separation means for contacting / separating the transfer roller with respect to the photoconductor, and the transfer roller contact / separation means When the application unit is started, the transfer roller is separated from the photoconductor.

  According to this configuration, when the application unit is activated, the resistance between the photoconductor and the application unit can be significantly increased by separating the transfer roller from the charged photoconductor. For this reason, when the application unit is activated, the current caused by charging of the photosensitive member can be greatly reduced, and the application unit can be activated reliably.

  An image forming apparatus according to a sixth aspect of the present invention relates to a photoconductor on which an electrostatic latent image is formed, a charger that charges the photoconductor by discharging according to application of a charging voltage, and the photoconductor An exposure unit that irradiates light to form the electrostatic latent image on the surface of the photoreceptor, and an electrostatic latent image that is in contact with the photoreceptor and formed on the surface of the photoreceptor is developed with a developer. A developing roller for forming a developer image, a transfer roller for transferring the developer image to a recording medium in response to application of a transfer voltage, and generating the charging voltage and applying the charging voltage to the charger. A charging voltage applying means; a transfer voltage applying means for generating the transfer voltage; and applying the transfer voltage to the transfer roller; and controlling the light irradiation intensity of the exposure means, and the charging voltage applying means and the transfer voltage. Start of application means and voltage generation Control means for controlling, prior to activation of the transfer voltage application means, the control means activates the charging voltage application means to charge the photosensitive member by the charger, and the transfer voltage application means When charging the photoconductor prior to activation, control is performed to reduce the charge amount of the photoconductor for a predetermined period corresponding to the activation of the transfer voltage applying means.

  According to this configuration, when the photosensitive member is precharged, the charging amount of the photosensitive member is reduced for a predetermined period corresponding to the activation of the transfer voltage applying unit. Therefore, by activating the transfer voltage application unit in correspondence with the predetermined period, the transfer voltage application unit can be activated when the portion of the photoreceptor whose charge amount has decreased reaches the transfer roller. As a result, when the transfer voltage application unit is activated, the current caused by charging of the photosensitive member can be reduced, and the transfer voltage application unit can be activated reliably.

  Here, the “predetermined period corresponding to the activation of the transfer voltage applying unit” means that the portion of the photoconductor whose charge amount has decreased in the predetermined period reaches a position facing the transfer roller when the transfer voltage applying unit is activated. Means that

  According to a seventh aspect of the invention, in the image forming apparatus of the sixth aspect of the invention, the control means reduces the charging voltage from the normal charging voltage to such an extent that the developer does not adhere to the photoconductor for the predetermined period. The charging voltage application means is controlled, or the light irradiation intensity is reduced from the normal printing irradiation intensity to such an extent that the developer does not adhere to the photoconductor, and the light is applied to the photoconductor for the predetermined period. The exposure means is controlled so as to irradiate the light.

  According to this configuration, the charging voltage is reduced to such an extent that the developer does not adhere to the photosensitive member for a predetermined period corresponding to the activation of the transfer voltage applying unit. Alternatively, the photoconductor is irradiated with light whose irradiation intensity has been reduced to such an extent that the developer does not adhere to the photoconductor for a predetermined period corresponding to the activation of the transfer voltage applying means. For this reason, the charge amount of the photosensitive member is suitably reduced for a predetermined period corresponding to the activation of the transfer voltage applying unit, and even when the developing roller is pressed against the photosensitive member and a predetermined developing bias is applied, Unnecessary developer (toner) is prevented from adhering to the photoreceptor. The “normal charging voltage” is applied by the charging voltage applying means after the application means is started and the transfer current is controlled at a constant current or when the transfer voltage is controlled at a constant voltage. Means the charging voltage. Further, “normal printing irradiation intensity” means the intensity of light irradiated by the exposure means when an electrostatic latent image is formed on the surface of the photoreceptor based on image data.

  According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth aspect of the present invention, the image forming apparatus further includes a contact / separation unit that contacts and separates the developing roller with respect to the photoconductor in accordance with the control of the control unit. The charging voltage applying means is controlled to turn off the generation of the charging voltage for the predetermined period, or the light irradiation intensity is set to be equal to or higher than the normal printing irradiation intensity, and the light is applied to the photoconductor for the predetermined period. The exposure unit is controlled to irradiate and the developing roller is separated from the photoconductor by the contact / separation unit at least for a certain period after the predetermined period.

  According to this configuration, the charging voltage is turned off for a predetermined period corresponding to the activation of the transfer voltage applying unit, or light having a normal printing irradiation intensity or higher is applied for the predetermined period corresponding to the activation of the transfer voltage applying unit. Irradiate the body. The developing roller is separated from the photosensitive member by the contact / separation means at least for a fixed period after a predetermined period corresponding to the activation of the transfer voltage application means. Therefore, the charge amount of the photoconductor is greatly reduced for a predetermined period corresponding to the activation of the transfer voltage applying means. Even when the surface potential of the photosensitive member decreases below the developing bias in a predetermined period, the developing roller is moved away from the photosensitive member at least during a period (a fixed period) in which the portion of the photosensitive member having the reduced surface potential contacts the developing roller. By separating them, unnecessary developer (toner) adhesion to the photoreceptor is avoided.

  According to the image forming apparatus of the present invention, it is possible to reliably generate a transfer voltage.

<Embodiment 1>
Next, Embodiment 1 of the present invention will be described with reference to FIGS.
1. Overall Configuration of Printer FIG. 1 is a side sectional view showing a schematic configuration of a color laser printer 1 which is an example of an image forming apparatus of the present invention. In the following description, the right side in FIG. The image forming apparatus is not limited to a color laser printer, and may be, for example, a monochrome laser printer or a color or monochrome LED printer. Further, it may be a multi-function machine having a copy function and a facsimile function.

  In the following description, for convenience of explanation, when a configuration corresponding to four colors is shown as a representative, only a member number is attached unless there is a particular situation. For example, when described as the transfer roller 14, it means four transfer rollers (14K, 14Y, 14M, 14C) corresponding to four colors (black, yellow, magenta, cyan).

  A color laser printer (hereinafter simply referred to as a “printer”) 1 includes a main body casing 2, and a lower portion of the main body casing 2 is provided with a supply tray 4 on which paper 3 (an example of a recording medium) is stacked. ing. A pickup roller 5 is provided above the front end of the supply tray 4, and a pair of registration rollers 8 is provided above the pickup roller 5.

  The sheet 3 at the top of the supply tray 4 is separated by the rotation of the pickup roller 5 and sent to the registration roller 8. The registration roller 8 corrects the skew of the sheet 3 and then sends the sheet 3 onto the belt unit 11 of the image forming unit 10.

The image forming unit 10 includes a belt unit 11, a scanner unit 19, a process unit 20, a fixing unit 31, a circuit board 34, and the like.
The belt unit 11 has a configuration in which a belt 13 is stretched between a pair of front and rear belt support rollers 12. Then, the belt support roller 12 on the rear side is rotationally driven, whereby the belt 13 circulates in the counterclockwise direction in the figure, and the paper 3 placed on the upper surface of the belt 13 is conveyed backward.

  Further, on the inner side of the belt 13, transfer rollers 14 are provided at positions facing each photosensitive drum 28 of the process unit 20, which will be described later, across the belt 13. The transfer roller 14 is configured by covering a metal roller shaft with a conductive rubber material. Further, the transfer roller 14 is urged against a photosensitive drum (an example of a photosensitive member) 28, and sandwiches the paper 3 conveyed on the belt 13 between the photosensitive drum 28.

The scanner unit 19 irradiates the surface of the corresponding photosensitive drum 28 with laser light L for each color emitted from a laser diode (an example of an exposure unit) 33.
The process unit 20 corresponds to a frame 21 that can be pulled out from the main casing 2 and, for example, four colors that can be attached to and detached from the frame 21 (black, yellow, magenta, and cyan in order from the upstream side in the conveyance direction of the paper 3). Four developing cartridges (22K, 22Y, 22M, 22C) are provided. A photosensitive drum 28 and a charger 29 are provided below the frame 21 corresponding to each developing cartridge 22.

  Each developing cartridge 22 includes a toner storage chamber 23, and a supply roller 24, a developing roller 25, and a layer thickness regulating blade 26 on the lower side thereof. Each toner storage chamber 23 stores positively chargeable toner (an example of a developer) of each color.

  The toner discharged from the toner storage chamber 23 is supplied to the developing roller 25 by the rotation of the supply roller 24, and is positively frictionally charged between the supply roller 24 and the developing roller 25. Further, the toner supplied onto the developing roller 25 enters between the layer thickness regulating blade 26 and the developing roller 25 as the developing roller 25 to which the developing bias is applied rotates, and here, the toner is further sufficiently rubbed. It is charged and carried on the developing roller 25 as a thin layer having a constant thickness.

The photosensitive drum 28 includes a grounded metal drum body, and the surface layer thereof is covered with a positively chargeable photosensitive layer made of polycarbonate or the like.
The charger 29 is of a scorotron type, and is provided between the discharge wire 29a and the discharge wire 29a and the photosensitive drum 28, which are disposed to face the photosensitive drum 28 with a predetermined interval therebetween. And a grid 29b for controlling the amount of discharge to the drum 28. In the charger 29, a high voltage is applied to the discharge wire 29a to cause corona discharge of the discharge wire 29a, thereby making the current flowing from the discharge wire 29a to the grid 29b constant, that is, by making the grid voltage constant, The surface of the drum 28 can be uniformly charged to a positive polarity.

  At the time of image formation, the photosensitive drum 28 is rotationally driven in the clockwise direction in the drawing, and accordingly, the surface of the photosensitive drum 28 is uniformly positively charged by the charger 29. The positively charged portion is exposed by high-speed scanning of laser light from the scanner unit 19, and an electrostatic latent image corresponding to the image to be formed on the paper 3 is formed on the surface of the photosensitive drum 28.

  Next, the electrostatic latent toner formed on the surface of the photosensitive drum 28 when the positively charged toner carried on the developing roller 25 contacts the photosensitive drum 28 by the rotation of the developing roller 25. Supplied to the image. Thereby, the electrostatic latent image on the photosensitive drum 28 is visualized, and the surface of the photosensitive drum 28 is based on the difference between the developing bias applied to the developing roller 25 and the surface potential of the photosensitive drum 28. A toner image (developer image) on which toner is attached is carried only on an exposed portion having a potential lower than the developing bias.

  Thereafter, the toner image carried on the surface of each photosensitive drum 28 is transferred from the sheet 3 conveyed by the belt 13 to each transfer position between the photosensitive drum 28 and the transfer roller 14 (paper nip portion of the transfer roller 14). Are sequentially transferred onto the paper 3 by a negative transfer voltage applied to the transfer roller 14. The sheet 3 having the toner image transferred thereon is then conveyed to the fixing device 31.

  The fixing device 31 includes a heating roller 31A having a heat source and a pressure roller 31B that presses the paper 3 toward the heating roller 31A, and heat-fixes the toner image transferred onto the paper 3 on the paper surface. Then, the sheet 3 on which the toner image is thermally fixed by the fixing device 31 is conveyed upward and discharged onto a discharge tray 32 provided on the upper surface of the main body casing 2.

2. Electrical Configuration Next, an electrical configuration related to the present invention of the printer 1 will be described with reference to FIG. FIG. 2 shows a schematic block diagram of the electric circuit 50 mounted on the circuit board 34 and a configuration related to the electric circuit 50.

  The electric circuit 50 includes a CPU (an example of a control unit in the present invention) 60, a charging voltage application circuit (an example of a charging voltage application unit) 51 connected to the CPU 60, an LD (laser diode) driving circuit 52, and a developing bias application circuit 53. , A motor drive circuit 54, a transfer voltage application circuit (an application means, an example of a transfer voltage application means) 55, a transfer current detection circuit (an example of a detection means) 56, a ROM 61 and a RAM 62.

  The CPU 60 controls the entire printer. The ROM 61 stores an operation program for the entire printer, and the RAM 62 stores image data used for printing processing.

  The charging voltage application circuit 51 generates a charging voltage Vcgw applied to the discharge wire 29a of the charger 29 and a grid voltage Vcgg applied to the grid 29b of the charger 29. Here, the normal voltage of the charging voltage Vcgw (corresponding to “normal charging voltage”) is, for example, 5.5 kV to 8 kV, and the normal voltage of the grid voltage Vcgg (corresponding to “normal charging voltage”) is, for example, about 700V.

  The LD drive circuit 52 generates an LD drive current Id to be supplied to the laser diode 33 under the control of the CPU 60 in order to irradiate the surface of the photosensitive drum 28 with a laser beam L having a predetermined intensity from the laser diode 33. Here, the LD drive current (LD drive current corresponding to the “normal print irradiation intensity”) Id corresponding to the normal laser light L having a predetermined intensity is, for example, about 30 mA.

  The development bias application circuit 53 generates a development bias Vdev to be applied to the development roller 25. The development bias Vdev is, for example, 300V to 500V.

  The motor drive circuit (an example of the developing roller contacting / separating unit) 54 is connected to a motor (an example of the developing roller contacting / separating unit) 25 a provided for pressing and separating the developing roller 25 with respect to the photosensitive drum 28. During the printing operation of the printer 1, the motor driving circuit 54 drives the motor 25 a according to the control of the CPU 60 and presses the developing roller 25 against the photosensitive drum 28 in order to adhere toner to the photosensitive drum 28. The motor drive circuit (an example of a transfer roller contact / separation unit) 54 is connected to a motor (an example of a transfer roller contact / separation unit) 35 provided for press-contacting / separating the transfer roller 14 with respect to the photosensitive drum 28. During the printing operation of the printer 1, the motor driving circuit 54 drives the motor 35 according to the control of the CPU 60 and presses the transfer roller 14 against the photosensitive drum 28 in order to transfer the toner image onto the paper 3.

  The transfer voltage application circuit 55 generates a transfer voltage Vt to be applied to the transfer roller 14 under the control of the CPU 60. The transfer voltage Vt is about −7 kV, for example. The transfer current detection circuit 56 detects a transfer current It generated by applying the transfer voltage Vt. The CPU 60 performs constant current control in which the transfer current It is set to a predetermined current value in accordance with a detection signal (feedback signal) from the transfer current detection circuit 56. When the transfer voltage application circuit 55 is activated, an inflow current flows from the previously charged photosensitive drum 28 to the transfer voltage application circuit 55 via the transfer roller 14 (“photosensitive member and application means due to charging” in the present invention). Example of “Current Generated Between” and “Ir” flows, the transfer current detection circuit 56 also detects the inflow current Ir.

3. Inflow Current Inflow Reduction Means Next, inflow current reduction means to the transfer voltage application circuit 55 according to the first embodiment will be described with reference to FIGS.

  In the first embodiment, when the transfer voltage application circuit 55 is activated, an inflow current Ir flowing from the photosensitive drum 28 to the transfer voltage application circuit 55 due to charging is caused between the photosensitive drum 28 and the transfer voltage application circuit 55. The resistance is reduced by increasing the resistance compared to normal. Here, “normal time” means a case where the transfer current It is controlled at a constant current after the transfer voltage application circuit 55 is started.

3-1. Example 1 (Inflow current reduction example 1 using a current adjustment circuit)
FIG. 3 is a schematic circuit diagram showing a first embodiment in which the inflow current Ir is reduced by the current adjustment circuit. FIG. 4 is a flowchart showing the control processing procedure. FIG. 3 shows a configuration corresponding to four colors. Since the configuration related to each color is the same, the configuration related to black (K) will be described as a representative.

  As shown in FIG. 3, the transfer voltage application circuit 55 is provided in common for each transfer roller (14K, 14Y, 14M, 14C). Between the transfer voltage application circuit 55 and the transfer roller 14K, there is provided a current adjustment circuit (an example of a current limiting unit and a current adjustment unit) 40K that limits the inflow current Ir when the transfer voltage application circuit 55 is activated. Yes. The current adjustment circuit 40K adjusts the value of the transfer current It during application of the transfer voltage Vt to the transfer roller 14K after the transfer voltage application circuit 55 is activated.

  The CPU 60 includes a PWM (pulse width modulation) signal generation unit 63 and an ADC (analog-digital converter) unit 64. The PWM signal generation unit 63 generates PWM signals (PWM_K, PWM_Y, PWM_M, PWM_C). The ADC unit 64 receives the detection signals (FB_0, FB_K, FB_Y, FB_M, and FB_C) of the transfer current detection circuit 56 and converts them into digital signals.

  The transfer current detection circuit 56 includes a current detection resistor 41K, first voltage detection resistors 42K and 43K, and second voltage detection resistors 44 and 45. The first voltage detection resistors 42K and 43K divide the voltage at one end (current adjustment circuit 40K side) of the current detection resistor 41K to generate a detection signal FB_K. The second voltage detection resistors 44 and 45 divide the voltage at the other end (the transfer voltage application circuit 55 side) of the current detection resistor 41K to generate a detection signal FB_0. The CPU 60 detects the transfer current It from the difference (voltage value) between the detection signal FB_K and the detection signal FB_0 and the resistance value of the current detection resistor 41K.

  The current adjustment circuit 40K includes, for example, a variable DC voltage source VS, a resistor R1, a photocoupler PC, and a transistor Tr. The variable DC voltage source VS is configured by a smoothing circuit including a resistor and a capacitor, for example. The variable DC voltage source VS receives the PWM signal PWM_K from the CPU 60, and generates a DC voltage corresponding to the pulse width of the PWM signal PWM_K. The generated DC voltage is applied to the photodiode of the photocoupler PC via the resistor R1. The photodiode emits light in response to a current that flows based on a DC voltage. A collector current of the phototransistor is generated according to the light emission amount of the photodiode, and the collector current is supplied to the base of the transistor Tr. The transistor Tr controls the transfer current It, which is the collector current of the transistor Tr, according to the collector current of the phototransistor supplied to the base. That is, the CPU 60 controls the current adjustment circuit 40K by the PWM signal PWM_K to control the transfer current It.

  Next, the transfer voltage application process in the first embodiment will be described with reference to the flowchart of FIG. The CPU 60 starts a transfer voltage application process in accordance with a predetermined print command.

  In step S100 of the flowchart of FIG. 4, the CPU 60 first sets the transfer output resistance to the maximum. Here, for example, the pulse width of the PWM signal PWM_K is set to zero, and the light emission by the photodiode of the photocoupler PC of the current adjustment circuit 40K is turned off. At this time, the transistor Tr of the current adjustment circuit 40K is turned off, and the resistance value with respect to the inflow current Ir of the current adjustment circuit 40K is maximized.

  Next, in step S110, the transfer voltage application circuit (transfer high voltage power supply) 55 is activated. At this time, since the transistor Tr is turned off, an inflow current Ir that flows from the photosensitive drum 28K to the transfer voltage application circuit 55 via the transfer roller 14K even if the photosensitive drum 28K is charged before that time. Is greatly reduced. As a result, the transfer voltage application circuit 55 is preferably activated without being affected by the inflow current Ir.

  Next, in step S120, the system waits for a predetermined time, for example, 20 ms. In step S130, the CPU 60 determines whether or not the application of the transfer voltage Vt has been completed. If it is determined that the application of the transfer voltage Vt has been completed (step S130: YES), the operation of the transfer voltage application circuit 55 is stopped in step S140.

  On the other hand, if it is determined in step S130 that the application of the transfer voltage Vt has not been completed, the transfer current It is measured based on the detection signal FB_K and the detection signal FB_0 in step S135, and is measured in step S150. It is determined whether the transfer current It is equal to or less than the target minimum value. When it is determined that the transfer current It is equal to or less than the target minimum value (step S150: YES), in step S155, the transfer output resistance is decreased in order to increase the transfer current It. Specifically, the pulse width of the PWM signal PWM_K is increased from the present time, and the collector current of the transistor Tr, that is, the transfer current It is increased. Then, the process proceeds to step S130.

  On the other hand, if it is determined in step S150 that the measured transfer current It is not less than the target minimum value, it is determined in step S160 whether the transfer current It is greater than or equal to the target maximum value. If it is determined that the transfer current It is greater than or equal to the target maximum value (step S160: YES), in step S165, the transfer output resistance is increased in order to reduce the transfer current It. Specifically, the pulse width of the PWM signal PWM_K is decreased from the present time, and the collector current of the transistor Tr, that is, the transfer current It is decreased. Then, the process proceeds to step S130. On the other hand, if it is determined in step S160 that the transfer current It is not equal to or greater than the target maximum value, the process proceeds to step S130 assuming that the transfer current It is within the predetermined range.

  As described above, in the first embodiment, when the transfer voltage application circuit 55 is activated, the inflow current Ir flowing from the photosensitive drum 28 to the transfer voltage application circuit 55 due to charging is changed to the transistor Tr of the current adjustment circuit 40K. By turning off, the inflow current Ir is significantly reduced. Therefore, even when the photosensitive drum 28K is charged in advance, the transfer voltage application circuit 55 is preferably activated without being affected by the inflow current Ir.

  At that time, the current adjustment circuit 40K is used both as a means for reducing the inflow current Ir when the transfer voltage application circuit 55 is started and a means for constant current control after the transfer voltage application circuit 55 is started. Therefore, it is structurally advantageous.

  Further, since the transfer voltage application circuit 55 is shared by the respective transfer rollers 14, the transfer voltage application circuit 55 is compared with the case where the transfer voltage application circuit 55 is individually provided for each transfer roller 14. Start-up control is simplified. That is, for example, as long as the transfer voltage application circuit 55 is activated against the inflow current Ir corresponding to the first transfer roller 14K, it corresponds to the other transfer rollers (14Y, 14M, 14C). This saves the trouble of starting up the transfer voltage application circuit 55.

3-2. Example 2 (Inflow current reduction example 2 by current adjustment circuit)
FIG. 5 is a schematic circuit diagram showing a second embodiment in which the inflow current Ir is reduced by the current adjustment circuit. The second embodiment shows an example in which a resistor 46K, which is a transfer current detection circuit 56, is provided on the photosensitive drum 28K side.

  With this configuration, the configuration of the transfer current detection circuit 56 can be simplified, and the transfer current It can be easily detected.

3-3. Example 3 (Inflow current reduction example 3 by current adjustment circuit)
FIG. 6 is a schematic circuit diagram showing a third embodiment in which the inflow current Ir is reduced by the current adjustment circuit. Example 3 shows an example in which a transfer voltage application circuit (55K, 55Y, 55M, 55C) is provided for each transfer roller (14K, 14Y, 14M, 14C). A transfer voltage application circuit 55K is connected to the transfer roller 14K. Next, a current adjustment circuit 40K is connected to the transfer voltage application circuit 55K, and a resistor 47K that is a transfer current detection circuit 56 is connected to the current adjustment circuit 40K.

  In this example, the transfer voltage application circuit 55 is not shared, but the configuration of the transfer current detection circuit 56 can be simplified and the transfer current It can be easily detected.

3-4. Example 4 (Inflow current reduction due to transfer roller separation)
FIG. 7 is a schematic explanatory view showing a structure related to the separation of the transfer roller 14. FIG. 8 is a flowchart showing the control processing procedure.

  As shown in FIG. 7, the printer 1 includes a transfer roller (14K, 14Y, 14M, 14C) and a transfer roller (14K, 14Y, 14M, 14C). And a shaft (an example of a transfer roller contacting / separating means) 36 connected to the motor 35. The rotation of the motor 35 is controlled by the control of the motor drive circuit 54 by the CPU 60, whereby the shaft 36 moves. With the movement of the shaft 36, the transfer rollers (14K, 14Y, 14M, 14C) are moved so as to be separated and pressed against the belt 13.

  In the fourth embodiment, a motor 35 and a shaft 36 are used in place of the current adjustment circuit 40 of the first to third embodiments as means for reducing the inflow current Ir when the transfer voltage application circuit 55 is started. That is, a printing operation is started in accordance with a printing command, charging voltages (Vcgw and Vcgg) are applied to the charger 29, and the photosensitive drum 28 is charged. At this time, for example, when an inflow current Ir of a predetermined value or more is detected by the transfer current detection circuit 56, the CPU 60 drives the motor 35 via the motor drive circuit 54 to transfer the transfer rollers (14K, 14Y, 14M, 14C). ) Is separated from the belt 13. Thereafter, the CPU 60 activates the transfer voltage application circuit 55.

  As described above, in the fourth embodiment, when the transfer voltage application circuit 55 is activated, the resistance between the photosensitive drum 28 and the transfer voltage application circuit 55 is reduced by moving the transfer roller 14 away from the belt 13 at a normal time. Increase significantly compared to. Therefore, the inflow current Ir can be suitably reduced, and the transfer voltage application circuit 55 can be reliably started.

<Embodiment 2>
Next, a method for reducing the inflow current Ir to the transfer voltage application circuit 55 according to the second embodiment will be described with reference to FIGS. In the second embodiment, when the photosensitive drum 28 is charged prior to the activation of the transfer voltage application circuit 55, the CPU 60 reduces the charge amount of the photosensitive drum 28 for a predetermined period corresponding to the activation of the transfer voltage application circuit 55. By performing the control, the inflow current Ir at the start of the transfer voltage application circuit 55 is reduced.

  That is, in order to reliably start the transfer voltage application circuit 55, the first embodiment has shown means for reducing the inflow current Ir on the side where the inflow current Ir flows, but in the second embodiment, the inflow current Ir is reduced. Means for reducing the generation of inflow current Ir on the generation side will be described.

4). Inflow current generation reduction means 4-1. Example 1 of Embodiment 2 (Example 1 due to decrease in charging voltage)
FIG. 8 is a flowchart showing a processing procedure according to the first embodiment for reducing the generation of the inflow current Ir. FIG. 9 is a schematic time chart relating to the processing. In Example 1 of Embodiment 2, the charging voltages (Vcgw and Vcgg) are decreased from the normal voltage for a predetermined period corresponding to the activation of the transfer voltage application circuit 55. A decrease in the charging voltages (Vcgw and Vcgg) reduces the amount of charge on the surface of the photosensitive drum when the transfer voltage application circuit 55 is started, and decreases the charged potential on the surface of the photosensitive drum. Thereby, the generation of the inflow current Ir is reduced.

  The CPU 60 starts the process of FIG. 8 according to the print command, and drives the main motor (not shown) in step S210 of FIG. 8 to start the operations of the photosensitive drum 28, the developing roller 25, and the belt unit 11. Next, in step S220, the charging voltage application circuit 51 is activated, the normal charging voltage Vcgw is applied to the discharge wire 29a of the charger 29, and the normal grid voltage Vcgg is applied to the grid 29b of the charger 29 (FIG. 9 time t0).

  Next, in step S230, it is determined whether or not the inflow current Ir detected by the transfer current detection circuit 56 is greater than or equal to a predetermined value. Here, the predetermined value is a value determined depending on the material of the photoconductor and the circuit configuration, and means a value that is small enough to suitably start the transfer current detection circuit 56. If it is determined that the inflow current Ir is not equal to or greater than the predetermined value (step S230: NO), the inflow current Ir is small, so that the process proceeds to step S250 to activate the transfer voltage application circuit 55 as it is.

  On the other hand, if it is determined in step S230 that the inflow current Ir is greater than or equal to a predetermined value (corresponding to time t1 in FIG. 9), in step S240, the CPU 60 causes the charging voltage application circuit 51 to determine the charging voltage Vcgw and the grid. The voltage Vcgg is generated at a value lower than normal during the predetermined period K1 (see FIG. 9).

  When the charging voltage Vcgw and the grid voltage Vcgg are lowered, the developer is lowered from the normal voltage to such an extent that the developer does not adhere to the photosensitive drum 28. In other words, the voltage is lowered from the normal voltage to such an extent that the charged potential on the surface of the photosensitive drum does not become equal to or lower than the developing bias Vdev and the desired precharging of the photosensitive drum 28 is obtained.

  Next, in step S250, the sheet 3 is picked up by the pickup roller 5, and the conveyance of the sheet 3 is started. In step S260, the charging voltage application circuit 51 is operated so that the charging voltage Vcgw and the grid voltage Vcgg have normal voltage values (corresponding to time t2 in FIG. 9).

  The charging voltage Vcgw and the grid voltage Vcgg are returned to the normal voltage, and the time when the portion of the photosensitive drum 28 charged by the normal voltage reaches the position where it contacts the developing roller 25 (see arrow Y2 in FIG. 9). At time t3 of 9, the developing bias Vdev is applied to the developing roller 25.

  Next, in step S270, the CPU 60 activates the transfer voltage application circuit 55 and causes the transfer voltage application circuit 55 to apply the transfer voltage Vt to the transfer roller 14 (corresponding to time t4 in FIG. 9). Then, the constant current control of the transfer current It is performed after time t4 in FIG. Here, a time t4 in FIG. 9 is a time when the portion of the photosensitive drum 28 charged by the charging voltage Vcgw and the grid voltage Vcgg having a voltage lower than normal is opposed to the transfer roller 14 for a predetermined period K1. is there. Preferably, time t4 in FIG. 9 is a time at which the portion of the photosensitive drum 28 charged at the intermediate time point of the predetermined period K1 contacts the transfer roller 14 via the belt 13 (see arrow Y1 in FIG. 9). As described above, the predetermined period K1 is a period corresponding to the activation of the transfer voltage application circuit 55 in consideration of the rotational speed of the photosensitive drum 28.

  Usually, the charging current (discharge current) is reduced by reducing the charging voltage Vcgw and the grid voltage Vcgg. As a result, the charge amount on the corresponding photosensitive drum surface is also reduced, and the charged potential on the photosensitive drum surface is reduced. Therefore, at the time t4 in FIG. 9 when the portion of the photosensitive drum 28 charged by the charging voltage Vcgw and the grid voltage Vcgg lower than normal contacts the transfer roller 14 via the belt 13, the photosensitive drum 28 is charged. The resulting inflow current Ir from the photosensitive drum 28 to the transfer voltage application circuit 55 is reduced. By starting the transfer voltage application circuit 55 at this time, the transfer voltage application circuit 55 can be reliably started.

4-2. Example 2 of Embodiment 2 (Example 1 by laser light irradiation)
FIG. 10 is a flowchart showing a processing procedure according to the second embodiment for reducing the generation of the inflow current Ir. FIG. 11 is a schematic time chart relating to the processing. The same steps as those in FIG. 8 are denoted by the same step numbers, and the description thereof is omitted.

  In Example 2 of the second embodiment, a laser having an output lower than the normal LD output (corresponding to the normal print irradiation intensity) is applied to the normally charged photosensitive drum 28 for a predetermined period corresponding to the activation of the transfer voltage application circuit 55. By irradiating the light L, the amount of charge on the surface of the photosensitive drum when the transfer voltage application circuit 55 is activated is decreased, and the charged potential on the surface of the photosensitive drum is decreased. Thereby, the generation of the inflow current Ir is reduced. Here, the normal LD output is an LD output when an electrostatic latent image is formed on the surface of the photoreceptor based on image data.

  That is, when it is determined in step S230 in FIG. 10 that the inflow current Ir is greater than or equal to a predetermined value (step S230: YES), in step S240A, the CPU 60 controls the LD drive circuit 52 to perform time t1 in FIG. During a predetermined period K2 of time t2, a drive current Id having a value lower than that in the normal printing operation is generated and supplied to the laser diode 33 (see FIG. 11). Accordingly, prior to the normal printing operation, the laser diode 33 irradiates the photosensitive drum 28 with the laser beam L having an output lower than the normal LD output in order to reduce the charge amount on the surface of the photosensitive drum. .

  When the LD output (LD irradiation intensity) is reduced, the normal output is reduced to such an extent that the developer does not adhere to the photosensitive drum 28. In other words, it is reduced from the normal LD output to such an extent that the charging potential on the surface of the photosensitive drum does not become the developing bias Vdev or less and a desired preliminary charging of the photosensitive drum 28 is obtained. When the irradiation of the laser beam is completed, the charging voltage Vcgw and the grid voltage Vcgg are returned to the normal voltage, and the time when the portion of the photosensitive drum 28 charged by the normal voltage reaches the position where it contacts the developing roller 25 is reached. At a time t3 in FIG. 11, a developing bias Vdev is applied to the developing roller 25.

  In step S260A, the CPU 60 irradiates the laser diode 33 with the laser light L of the normal LD output for the normal printing operation. Next, in step S270, the CPU 60 activates the transfer voltage application circuit 55 and causes the transfer voltage application circuit 55 to apply the transfer voltage Vt to the transfer roller 14 (corresponding to time t4 in FIG. 11). Here, at time t4 in FIG. 11, the portion of the photosensitive drum 28 that has been exposed for a predetermined period K2 by the laser beam L that is lower than the normal LD output comes into contact with the transfer roller 14 via the belt 13. It is time. Preferably, time t4 in FIG. 11 is a time when a portion exposed at an intermediate time point in the predetermined period K2 contacts the transfer roller 14 (see arrow Y3 in FIG. 11). Here, the predetermined period K2 is a period corresponding to the activation of the transfer voltage application circuit 55 in consideration of the rotational speed of the photosensitive drum 28.

  As described above, also in Example 2 of the second embodiment, the photosensitive drum 28 that is normally charged for a predetermined period K2 corresponding to the activation of the transfer voltage application circuit 55 with the output laser light L that is lower than the normal LD output. , The inflow current Ir can be reduced when the transfer voltage application circuit 55 is activated. As a result, the influence of the inflow current Ir when the transfer voltage application circuit 55 is activated is reduced, and the transfer voltage application circuit 55 can be activated reliably.

4-3. Example 3 of Embodiment 2 (Example 2 due to decrease in charging voltage)
FIG. 12 is a flowchart illustrating a processing procedure according to the third example of the second embodiment for reducing the generation of the inflow current Ir. FIG. 13 is a schematic time chart relating to the processing. The same steps as those in FIG. 8 are denoted by the same step numbers, and the description thereof is omitted.

  In Example 3 of the second embodiment, the charging voltage generation is turned off for a predetermined period corresponding to the activation of the transfer voltage application circuit 55, whereby the charge amount on the surface of the photosensitive drum when the transfer voltage application circuit 55 is activated is reduced. At the same time, the charging potential on the surface of the photosensitive drum is decreased. Thereby, the generation of the inflow current Ir is reduced.

  That is, when it is determined in step S230 in FIG. 12 that the inflow current Ir is equal to or greater than a predetermined value (step S230: YES, corresponding to time t1 in FIG. 13), in step S245, the CPU 60 causes the charging voltage application circuit 51 to Generation of the charging voltage Vcgw and the grid voltage Vcgg is stopped for a predetermined period K3 (see FIG. 13).

  Next, in step S246, the CPU 60 causes at least the uncharged portion to pass through the developing roller 25 so that the uncharged portion of the photosensitive drum 28 that has not been charged by turning off the charging voltage Vcgw and the grid voltage Vcgg does not come into contact with the developing roller 25. During this time (corresponding to the “certain period” in the present invention), the developing roller 25 is separated from the photosensitive drum 28. Specifically, the CPU 60 drives the motor 25 a to separate the developing roller 25 from the photosensitive drum 28. This is because the toner is not unnecessarily adhered to an uncharged portion (portion where the potential is lower than the developing bias) of the photosensitive drum 28.

  In FIG. 13, the charging voltage Vcgw and the grid voltage Vcgg are returned to the normal voltage, and the time of FIG. 13 is the time when the portion of the photosensitive drum 28 charged by the normal voltage reaches the position where it contacts the developing roller 25. An example is shown in which the developing roller 25 is pressed against the photosensitive drum 28 at t3.

  Next, in step S270, the CPU 60 activates the transfer voltage application circuit 55 and causes the transfer voltage application circuit 55 to apply the transfer voltage Vt to the transfer roller 14 (corresponding to time t4 in FIG. 13). Here, time t4 in FIG. 13 is a time when the non-charged portion of the photosensitive drum 28 is in contact with the transfer roller 14. Preferably, time t4 in FIG. 13 is a time at which the non-charged portion of the photosensitive drum 28 contacts the transfer roller 14 via the belt 13 at an intermediate point in the predetermined period K3 (see arrow Y4 in FIG. 13). Here, the predetermined period K3 is a period corresponding to the activation of the transfer voltage application circuit 55 in consideration of the rotational speed of the photosensitive drum 28.

  Thus, in Example 3 of Embodiment 2, the charging voltage Vcgw and the grid voltage Vcgg are turned off for a predetermined period K3 corresponding to the activation of the transfer voltage application circuit 55, whereby the transfer voltage application circuit 55 is activated. Sometimes the inflow current Ir can be further reduced. As a result, the influence of the inflow current Ir when the transfer voltage application circuit 55 is activated is reduced, and the transfer voltage application circuit 55 can be activated more reliably. At this time, since the developing roller 25 is separated from the photosensitive drum 28 at least while the non-charged portion passes the developing roller 25, adhesion of toner to the non-charged portion of the photosensitive drum 28 is avoided.

4-4. Example 4 of Embodiment 2 (Example 2 by laser light irradiation)
FIG. 14 is a flowchart illustrating a processing procedure according to the fourth example of the second embodiment for reducing the generation of the inflow current Ir. FIG. 15 is a schematic time chart relating to the processing. The same steps as those in FIG. 8 are denoted by the same step numbers, and the description thereof is omitted.

  In Example 4 of the second embodiment, the normally charged photosensitive drum 28 is irradiated with laser light L having a normal LD output (normal print irradiation intensity) for a predetermined period corresponding to the activation of the transfer voltage application circuit 55. In addition, the amount of charge on the surface of the photosensitive drum when the transfer voltage application circuit 55 is activated is decreased, and the charged potential on the surface of the photosensitive drum is decreased. Thereby, the generation of the inflow current Ir is reduced.

  That is, when it is determined in step S230 in FIG. 14 that the inflow current Ir is greater than or equal to a predetermined value (step S230: YES), in step S245A, the CPU 60 controls the LD drive circuit 52 to perform time t1 in FIG. A drive current Id during a normal printing operation is generated and supplied to the laser diode 33 during a predetermined period K4 from time t2 (see FIG. 15). In response thereto, the laser diode 33 irradiates the photosensitive drum 28 with the laser light L of the normal LD output for a predetermined period K4 prior to the normal printing operation. Here, the output intensity of the laser beam L is not limited to the normal printing irradiation intensity, but may be any value that is equal to or higher than the normal printing irradiation intensity.

  Next, in step S246, as in FIG. 12, the CPU 60 drives the motor 25a via the motor drive circuit 54 to prevent toner from unnecessarily adhering to the uncharged portion of the photosensitive drum 28, and at least the photosensitive drum 28. The developing roller 25 is separated from the photosensitive drum 28 while the portion irradiated with the laser beam passes through the developing roller 25 (corresponding to the “certain period” in the present invention).

  In FIG. 15, there is an example in which the developing roller 25 is pressed against the photosensitive drum 28 at time t <b> 3 in FIG. 15, which is a time after the laser light irradiation portion of the photosensitive drum 28 has passed the position where it contacts the developing roller 25. Indicated.

  Next, in step S270, the CPU 60 activates the transfer voltage application circuit 55 and causes the transfer voltage application circuit 55 to apply the transfer voltage Vt to the transfer roller 14 (corresponding to time t4 in FIG. 15). Here, time t4 in FIG. 15 is the time when the laser light irradiation portion of the photosensitive drum 28 reaches the paper nip portion of the transfer roller 14. Preferably, the time t4 in FIG. 15 is a time when the laser light irradiation portion of the photosensitive drum 28 at the intermediate point in the predetermined period K4 contacts the transfer roller 14 via the belt 13 (see arrow Y5 in FIG. 15). Here, the predetermined period K4 is a period corresponding to the activation of the transfer voltage application circuit 55 in consideration of the rotational speed of the photosensitive drum 28.

  As described above, in Example 4 of Embodiment 2, laser light irradiation is performed by irradiating the photosensitive drum 28 with the laser light L of normal LD output for a predetermined period K4 corresponding to the activation of the transfer voltage application circuit 55. The charged potential of the portion can be greatly reduced. Therefore, the inflow current Ir can be further reduced when the transfer voltage application circuit 55 is activated. As a result, the influence of the inflow current Ir when the transfer voltage application circuit 55 is activated is reduced, and the transfer voltage application circuit 55 can be activated more reliably. At this time, since the developing roller 25 is separated from the photosensitive drum 28 at least while the laser light irradiation portion of the photosensitive drum 28 passes through the developing roller 25, the toner adheres to the laser light irradiation portion of the photosensitive drum 28. To be avoided.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.

  (1) In the first embodiment, the current adjustment circuit 40 may be configured by a digital potentiometer, and the resistance value may be changed by the CPU 60 to control the transfer current and the transfer current.

  (2) In the second embodiment, the predetermined periods (K1, K2, K3, and K4) may be determined according to the printing conditions, and the length of each predetermined period is arbitrary. The predetermined period may be a period corresponding to the timing at which the transfer voltage application circuit 55 is activated in consideration of the rotational speed of the photosensitive drum 28 and the like. That is, the start time of the predetermined period is such that the portion of the photosensitive drum 28 whose charge amount has been reduced by the process of the predetermined period has reached the position facing the transfer roller 14 at the start timing of the transfer voltage application circuit 55. And its length need only be determined.

  (3) In each embodiment, an example in which the photosensitive drum (photosensitive member) 28 is positively charged has been described. However, the present invention can also be applied to a case where the photosensitive member is negatively charged. That is, the current generated between the photosensitive member and the applying unit due to the charging of the photosensitive member is not limited to the inflow current Ir flowing into the transfer voltage applying circuit (applying unit) 55 from the photosensitive drum 28 side.

1 is a side sectional view showing a schematic configuration of an image forming apparatus according to the present invention. Schematic block diagram of an electric circuit provided in the image forming apparatus The schematic circuit diagram which shows Example 1 which reduces inflow of inflow current in Embodiment 1 of the present invention. The flowchart which shows the process sequence of Example 1. Schematic circuit diagram showing a second embodiment for reducing inflow of inflow current Schematic circuit diagram showing a third embodiment for reducing inflow of inflow current Schematic configuration diagram showing a fourth embodiment for reducing the inflow of inflow current The flowchart which shows the process sequence of Example 1 which reduces generation | occurrence | production of inflow current in Embodiment 2 of this invention. Time chart showing transition of signals according to Example 1 of Embodiment 2 The flowchart which shows the process sequence of Example 2 which reduces generation | occurrence | production of inflow current. Time chart showing transition of signal according to example 2 of embodiment 2 The flowchart which shows the process sequence of Example 3 which reduces generation | occurrence | production of inflow current. Time chart showing transition of signals according to Example 3 of Embodiment 2 The flowchart which shows the process sequence of Example 4 which reduces generation | occurrence | production of inflow current. Time chart showing transition of signal according to example 4 of embodiment 2

Explanation of symbols

1. Laser printer (image forming device)
14 ... transfer roller 25 ... developing roller 28 ... photosensitive drum (photoconductor)
29 ... Charger 33 ... Laser diode (exposure means)
40 ... Current adjusting circuit (current limiting means, current adjusting means)
51. Charging voltage application circuit (charging voltage application means)
54 ... Motor drive circuit (transfer roller contact / separation means, contact / separation means)
55. Transfer voltage application circuit (application means, transfer voltage application means)
56. Transfer current detection circuit (detection means)
60 ... CPU (current limiting means, control means)

Claims (8)

A photosensitive member that carries a developer image developed by a developer using charging;
A transfer roller for transferring the developer image to a recording medium in response to application of a transfer voltage;
Applying means for generating the transfer voltage and applying the transfer voltage to the transfer roller;
When starting up the application unit, the current generated between the photoconductor and the application unit due to the charging increases the resistance between the photoconductor and the application unit compared to the normal time. Current limiting means to reduce by causing,
An image forming apparatus. The image forming apparatus according to claim 1.
The current limiting means includes
A current adjusting unit that is connected between the transfer roller and the applying unit and adjusts a current flowing between the transfer roller and the applying unit;
Control means for controlling the current adjustment means so as to maximize the resistance value of the current adjustment means when the application means is activated;
including. The image forming apparatus according to claim 2.
It further comprises detection means for detecting the current flowing through the transfer roller,
The control means controls the current adjusting means based on a current value detected by the detecting means after the application means is activated. The image forming apparatus according to any one of claims 1 to 3,
The photoreceptor includes a plurality of photoreceptors,
The transfer roller and the current adjusting means are provided corresponding to each of the plurality of photoconductors,
The application unit is connected in common to the plurality of transfer rollers. The image forming apparatus according to claim 1.
The current limiting means includes transfer roller contact / separation means for contacting / separating the transfer roller with respect to the photosensitive member,
The transfer roller contacting / separating means places the transfer roller away from the photoconductor when the applying means is activated. A photoreceptor on which an electrostatic latent image is formed;
A charger for charging the photosensitive member by discharging according to application of a charging voltage;
Exposure means for irradiating light on the photoconductor based on image data to form the electrostatic latent image on the surface of the photoconductor;
A developing roller that abuts against the photoreceptor and develops an electrostatic latent image formed on the surface of the photoreceptor with a developer to form a developer image;
A transfer roller for transferring the developer image to a recording medium in response to application of a transfer voltage;
Charging voltage application means for generating the charging voltage and applying the charging voltage to the charger;
Transfer voltage applying means for generating the transfer voltage and applying the transfer voltage to the transfer roller;
A control means for controlling the light irradiation intensity of the exposure means, and for controlling the activation and voltage generation of the charging voltage application means and the transfer voltage application means,
The control means includes
Prior to activation of the transfer voltage application means, the charging voltage application means is activated to charge the photosensitive member by the charger,
An image forming apparatus that, when charging the photosensitive member prior to activation of the transfer voltage applying unit, performs control to reduce the charge amount of the photosensitive member for a predetermined period corresponding to activation of the transfer voltage applying unit. The image forming apparatus according to claim 6.
The control means includes
Controlling the charging voltage application means so as to reduce the charging voltage from the normal charging voltage to such an extent that the developer does not adhere to the photoconductor for the predetermined period; or
The exposure unit is controlled so that the light irradiation intensity is lowered from the normal printing irradiation intensity to such an extent that the developer does not adhere to the photoconductor, and the photoconductor is irradiated with the light for the predetermined period. To do. The image forming apparatus according to claim 6.
In accordance with the control of the control means, further comprising contact / separation means for contacting and separating the developing roller with respect to the photoconductor,
The control means includes
Controlling the charging voltage application means to turn off the generation of the charging voltage for the predetermined period; or
While controlling the exposure means to irradiate the photoconductor with the light for the predetermined period, with the light irradiation intensity equal to or higher than the normal printing irradiation intensity,
The developing roller is separated from the photoconductor by the contact / separation means at least for a certain period after the predetermined period.

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