JP2017015925A - Image forming apparatus, control method of the same, and computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately specify, from a timing of exposure by an exposure part, a transit time required for an electrostatic latent image formed through the exposure to reach a transfer position.SOLUTION: An image forming apparatus comprises a control part that: causes a charging part to charge a surface of a photoreceptor; causes an exposure part to expose the surface of the photoreceptor charged by the charging part to form an electrostatic latent image; after the start of exposure of the surface of the photoreceptor, specifies a change timing at which a transfer current or a transfer voltage changes on the basis of a signal output from a detection part while an output voltage is output to a transfer body by a voltage output part; and specifies, on the basis of an exposure timing at which the exposure part exposes the surface of the photoreceptor and the change timing at which the transfer current or transfer voltage changes, a transit time required for the electrostatic latent image to reach a transfer position between the photoreceptor and transfer body from the exposure timing.SELECTED DRAWING: Figure 5

Description

  The technology disclosed in this specification relates to an image forming apparatus.

  There is known an image forming apparatus including a photoconductor, a charging unit, an exposure unit, a developing unit, a transfer body, and a voltage output unit (see Patent Document 1). In this image forming apparatus, the charging unit charges the surface of the photoconductor that is rotationally driven, the exposure unit exposes the surface of the charged photoconductor to form an electrostatic latent image, and the developing unit uses the static image. The developer image is formed by supplying the developer to the electrostatic latent image, and the voltage output unit outputs the output voltage to the transfer member, so that the developer image reaches the transfer position between the photosensitive member and the transfer member. Is transferred to a sheet or the like passing through the transfer position.

JP 2010-61003 A

  In the above-described image forming apparatus, for example, from the exposure timing at which the exposure unit exposes the surface of the photoconductor due to fluctuations in the rotation speed of the photoconductor, changes in the positional relationship between the photoconductor, the exposure unit, and the transfer body, The movement time until the electrostatic latent image formed by exposure reaches the transfer position (hereinafter, simply referred to as the movement time of the electrostatic latent image) may vary. In the conventional image forming apparatus, since the image forming operation is executed on the assumption that the moving time of the electrostatic latent image is always constant, the moving time of the electrostatic latent image varies, for example, development on a sheet. There is a possibility that the position where the agent image is transferred varies. As described above, the conventional image forming apparatus does not consider the variation in the movement time of the electrostatic latent image, and has not been provided with means for accurately specifying the movement time of the electrostatic latent image.

  The present specification discloses a technique capable of solving at least a part of the problems described above.

  The technology disclosed in this specification can be implemented as the following forms.

  The image forming apparatus disclosed in the present specification includes a rotationally driven photoconductor, a charging unit, an exposure unit, a developing unit, a transfer body arranged to face the surface of the photoconductor, and the transfer A voltage output unit that outputs an output voltage to the body, and a transfer current that flows through the transfer body according to the output of the output voltage or a signal according to the transfer voltage applied to the transfer body according to the output of the output voltage. An output detection unit; and a control unit, wherein the control unit causes the charging unit to charge the surface of the photoconductor, and causes the exposure unit to expose the surface of the photoconductor charged by the charging unit. Based on the signal output from the detection unit in a state where the output voltage is output to the transfer body by the voltage output unit after the start of exposure of the surface of the photoreceptor, The transfer current or the transfer voltage changes The electrostatic latent image is determined based on the exposure timing based on the exposure timing at which the surface of the photoconductor is exposed by the exposure unit and the change timing of the transfer current or the transfer voltage. The moving time until reaching the transfer position between the transfer body and the transfer body is specified.

  When there is a non-exposed area on the surface of the photoconductor that is not exposed at the transfer position, and when there is an electrostatic latent image (exposed area) exposed by the exposure unit, the surface of the photoconductor Since the potential difference between the transfer body and the transfer body is different, the transfer current flowing through the transfer body or the transfer voltage applied to the transfer body in a state where the output voltage is output to the transfer body is different. Therefore, the timing at which the electrostatic latent image reaches the transfer position can be specified based on the timing at which the transfer current or transfer voltage changes. Therefore, according to this image forming apparatus, the electrostatic latent image reaches the transfer position from the exposure timing based on the exposure timing at which the surface of the photoconductor is exposed by the exposure unit and the change timing at which the transfer current or transfer voltage changes. The travel time until it is determined. As a result, even if fluctuations in the rotational speed of the photosensitive member or fluctuations in the positional relationship between the photosensitive member, the exposure unit, and the transfer member occur, the movement time from the exposure timing until the electrostatic latent image reaches the transfer position is reduced. It can be specified with high accuracy.

  The technology disclosed in this specification can be realized in various forms, for example, forms of an image forming apparatus, a control method and a computer program for the image forming apparatus, a recording medium on which the computer program is recorded, and the like. Can be realized.

Explanatory drawing which shows schematic structure of the printer 100 in one Embodiment. Explanatory drawing showing a part of the process unit 220 and the electrical configuration of the printer 100 Explanatory drawing which shows the photosensitive drum 222 and the transfer roller 225 seen from the conveyance direction of the sheet W. Explanatory drawing which shows the flow from the exposure by the exposure part 210 until the electrostatic latent image R1 formed by the exposure reaches the transfer position X2. Flow chart showing the flow of time specification processing Flow chart showing the flow of timing identification processing Time chart showing the relationship between the exposure timing of the exposure unit 210 and the change timing of the transfer current It Explanatory drawing which shows the relationship between the toner image R2 transcribe | transferred on the sheet | seat W, and the target electric current value of constant current control. Flow chart showing the flow of print processing

  FIG. 1 shows a schematic configuration of a printer 100 according to an embodiment. FIG. 1 shows XYZ axes orthogonal to each other for specifying the direction. In this specification, for convenience, the X-axis positive direction is referred to as the forward direction, the X-axis negative direction is referred to as the rear direction, the Y-axis positive direction is referred to as the right direction, the Y-axis negative direction is referred to as the left direction, and Z Although the positive axial direction is referred to as the upward direction and the negative Z-axis direction is referred to as the downward direction, the printer 100 may actually be installed in an orientation different from such an orientation. The same applies to FIG.

  The printer 100 forms an image on a sheet W such as a recording sheet or an OHP sheet by using toners (developers) of four colors of black (K), yellow (Y), magenta (M), and cyan (C), for example. This is a direct transfer tandem type electrophotographic image forming apparatus. In the following description, when each component of the printer 100 is distinguished for each toner color, the letters K, Y, M, and C, which represent the above-described colors, are added to the end of the component codes. In other cases, these characters are omitted as appropriate. Moreover, in each figure, the code | symbol of the component of the same structure provided corresponding to each color shall be attached | subjected typically to the component corresponding to a certain color, and it abbreviate | omits suitably about the component corresponding to another color.

  As shown in FIG. 1, the printer 100 includes a sheet supply unit 120, a sheet conveyance unit 130, and an image forming unit 200.

  The sheet supply unit 120 includes a tray 121 and a pickup roller 122. The tray 121 is a container that can store a plurality of sheets W. The pickup roller 122 takes out the sheets W stored in the tray 121 one by one and sends them out toward the sheet conveying unit 130.

  The sheet conveyance unit 130 includes a conveyance roller pair 131, a registration roller pair 132, a belt 133, a driven roller 134, a drive roller 135, and a discharge roller pair 136. The conveyance roller pair 131 conveys the sheet W supplied from the sheet supply unit 120 toward the registration roller pair 132. The registration roller pair 132 corrects the skew of the sheet W sent from the conveyance roller pair 131 and conveys the sheet W toward the belt 133. The belt 133 is an endless belt that spans between the driving roller 135 and the driven roller 134 and rotates as the driving roller 135 rotates. Along with the rotation of the belt 133, a surface (hereinafter referred to as “stretching surface”) of the belt 133 that faces a plurality of photosensitive drums 222 (to be described later) is a direction in which the plurality of photosensitive drums 222 are arranged (front-rear direction). Direction). Along with the movement of the tensioning surface of the belt 133, the sheet W conveyed to the belt 133 is conveyed toward the fixing unit 230 described later. The discharge roller pair 136 discharges the sheet W that has passed through the fixing unit 230 to the outside of the printer 100.

  The image forming unit 200 includes an exposure unit 210, four process units 220 (220K, 220Y, 220M, and 220C) corresponding to each color, and a fixing unit 230.

  The exposure unit 210 includes a laser light source corresponding to each color and a rotating polygon mirror (none of which are shown). For each color, a light beam L emitted from a laser light source is deflected by a rotating polygon mirror that is rotationally driven by a motor (not shown), and is irradiated toward the photosensitive drum 222. As a result, each photosensitive drum 222 is exposed, and an electrostatic latent image is formed on the surface of the photosensitive drum 222. Hereinafter, a position on the surface of the photosensitive drum 222 to which the light beam L from the exposure unit 210 is irradiated is referred to as an irradiation position X1 of the light beam L.

  The four process units 220 are arranged side by side in the conveyance direction of the sheet W by the belt 133 (X-axis negative direction, substantially horizontal direction in the present embodiment). The configuration of the black process unit 220K will be described below. The configuration of the process units 220 of other colors is the same.

  The process unit 220K includes a charging unit 221, a photosensitive drum 222, a toner box 223, a developing roller 224, and a transfer roller 225. FIG. 2 shows an electrical configuration of the charging unit 221, the photosensitive drum 222, the developing roller 224, the transfer roller 225, and the printer 100. As shown in FIG. 2, the photosensitive drum 222 has a cylindrical shape that is parallel to the stretched surface of the belt 133 and extends in a direction (left-right direction) substantially perpendicular to the conveyance direction of the sheet W by the belt 133. And is rotatably supported by a cartridge (not shown) of the process unit 220K. Specifically, as shown in FIG. 2, the photosensitive drum 222 includes a conductive drum body 226 and a cylindrical photosensitive layer 227 formed on the outer peripheral surface of the drum body 226. The controller 300 is rotationally driven. The drum body 226 is grounded. The photosensitive drum 222 is an example of a photosensitive member.

  The charging unit 221 is disposed so as to face the surface of the photosensitive drum 222 and uniformly charges the surface of the photosensitive drum 222. The developing roller 224 supplies the toner in the toner box 223 onto the photosensitive drum 222, thereby developing the above-described electrostatic latent image formed on the photosensitive drum 222 by the exposure unit 210 to form a toner image. The developing roller 224 is an example of a developing unit. The transfer roller 225 is disposed so as to face the surface of the photosensitive drum 222 with the stretched surface of the belt 133 interposed therebetween.

  The transfer roller 225 includes a shaft body 225A having conductivity and a cylindrical elastic layer 225B having elasticity formed on the outer peripheral surface of the shaft body 225A. The transfer roller 225 transfers the toner image formed on the photosensitive drum 222 onto the sheet W that is placed on the stretched surface of the belt 133 and conveyed. The transfer roller 225 is an example of a transfer body. Hereinafter, a position where the photosensitive drum 222 and the transfer roller 225 face each other is referred to as a transfer position X2. The photosensitive drum 222 and the transfer roller 225 are disposed so as to press each other in the vertical direction. Therefore, a nip portion P where the photosensitive drum 222 and the transfer roller 225 press each other is formed at the transfer position X2. Specifically, FIG. 3 shows the photosensitive drum 222 and the transfer roller 225 as viewed from the sheet W conveyance direction. As shown in FIG. 3, the length of the transfer roller 225 is shorter than the length of the photosensitive drum 222 in the rotation axis direction (left-right direction) of the photosensitive drum 222, and both ends of the transfer roller 225 are longer than both ends of the photosensitive drum 222. Located inside. That is, the nip portion P is located in a facing area E2 where the lower surface of the surface portion E1 excluding both end portions protruding outward from the transfer roller 225 and the upper surface of the outer peripheral surface of the transfer roller 225 are opposed to each other. Is formed. In other words, the nip portion P has a predetermined width in the conveyance direction of the sheet W, and substantially the same width as the transfer roller 225 in the rotation axis direction of the photosensitive drum 222. The surface portion E1 is a portion of the outer peripheral surface of the photosensitive drum 222 that passes through the facing area E2 as the photosensitive drum 222 rotates, and the facing area E2 transfers the toner image on the photosensitive drum 222 to the transfer roller. It can be said that this is a transferable region which is the maximum region that can be transferred to the 225 side.

  In this embodiment, a black process unit 220K, a yellow process unit 220Y, a magenta process unit 220M, and a cyan process unit 220C are arranged in order from the upstream side to the downstream side in the conveyance direction of the sheet W. Therefore, a black toner image, a yellow toner image, a magenta toner image, and a cyan toner image are sequentially transferred onto the conveyed sheet W in a superimposed manner.

  The fixing unit 230 fixes the toner image on the sheet W by heating the toner image transferred to the sheet W while applying pressure. As a result, an image is formed on the sheet W.

  The printer 100 further includes an arrangement mechanism 148. The toner box 223 and the developing roller 224 for each color are provided to be displaceable between a supply position and a separation position. The supply position is a position where the developing roller 224 is close to the photosensitive drum 222 and toner can be supplied from the developing roller 224 to the photosensitive drum 222 as in the process unit 220K shown in FIG. The separation position is a position farther from the photosensitive drum 222 than the supply position, like the process units 220Y to 220C shown in FIG. Therefore, when the developing roller 224 and the like are at the supply position, toner is more easily supplied from the developing roller 224 to the photosensitive drum 222 than when the developing roller 224 and the like are at the separation position. The arrangement mechanism 148 individually displaces each toner box 223 and the developing roller 224 between the supply position and the separation position in accordance with an instruction from the control unit 300.

  FIG. 2 shows an electrical configuration of the printer 100. The printer 100 includes a display unit 150, an operation unit 152, a communication interface 154, a control unit 300, and an application unit 400 in addition to the above-described sheet supply unit 120, sheet conveyance unit 130, image forming unit 200, and arrangement mechanism 148. And comprising.

  The display unit 150 is configured by a liquid crystal display, for example, and displays various types of information in response to instructions from the control unit 300. The operation unit 152 includes various buttons and the like that accept user operations. The communication interface 154 is hardware that enables communication with an external device. The communication interface 154 is, for example, a network interface, a serial communication interface, a parallel communication interface, or the like.

  The control unit 300 includes a CPU 310, a ROM 320, a RAM 330, a nonvolatile memory 340, and an ASIC (Application Specific Integrated Circuit) 350. The ROM 320 stores a control program for controlling the printer 100, various settings, initial values, and the like. The RAM 330 is used as a work area when the CPU 310 executes various programs and as a temporary storage area for data. The non-volatile memory 340 is a rewritable memory such as NVRAM, flash memory, HDD, or EEPROM. The ASIC 350 is a hardware circuit dedicated to image processing, for example. The CPU 310 controls each component of the printer 100 according to a control program read from the ROM 320 and signals sent from various sensors.

  The application unit 400 includes a charging voltage application unit 410, a development voltage application unit 420, a transfer voltage application unit 430, a current sensor 440, and a voltage sensor 450.

  The charging voltage application unit 410 performs a charging application operation of applying a charging voltage VW (for example, +5 kV to +7 kV) having the same polarity as the toner in the toner box 223 to the charging unit 221 in accordance with an instruction from the control unit 300. The development voltage application unit 420 performs a development application operation in which a development voltage VD (for example, +400 V to +450 V) having the same polarity as the toner is applied to the development roller 224 in accordance with an instruction from the control unit 300. The transfer voltage application unit 430 performs a transfer application operation of outputting an output voltage (for example, −1200 V) having a polarity opposite to that of the toner to the transfer roller 225 in accordance with an instruction from the control unit 300. The transfer voltage application unit 430 is an example of a voltage output unit.

  The current sensor 440 is connected between the transfer voltage application unit 430 and the transfer roller 225, and outputs a current detection signal SG1 corresponding to the transfer current It flowing through the transfer roller 225. The controller 300 can acquire the value of the transfer current It from the current detection signal SG1. The voltage sensor 450 is connected in parallel to the transfer roller 225, and outputs a voltage detection signal SG2 corresponding to the transfer voltage Vt applied to the transfer roller 225. The controller 300 can acquire the value of the transfer voltage Vt from the voltage detection signal SG2. The current sensor 440 and the voltage sensor 450 are examples of a detection unit.

  FIG. 4 shows a flow from the exposure by the exposure unit 210 until the electrostatic latent image R1 formed by the exposure reaches the transfer position X2. Specifically, at the exposure start timing T1, the exposure unit 210 starts exposure on the charged surface of the rotationally driven photosensitive drum 222, and at the exposure end timing T2, the exposure unit 210 starts the exposure of the surface of the photosensitive drum 222. The exposure to is terminated. An electrostatic latent image R1 is formed on the surface of the photosensitive drum 222 during the period from the exposure start timing T1 to the exposure end timing T2. Thereafter, the electrostatic latent image R <b> 1 moves from the irradiation position X <b> 1 with the rotation of the photosensitive drum 222 and passes between the photosensitive drum 222 and the developing roller 224. At the leading edge arrival timing T3, the leading edge of the electrostatic latent image R1 in the rotation direction of the photosensitive drum 222 reaches the nip portion P, and at the trailing edge arrival timing T4, the trailing edge of the electrostatic latent image R1 in the rotation direction of the photosensitive drum 222. Reaches the nip P.

  Here, from the exposure timing at which the exposure unit 210 exposes the surface of the photosensitive drum 222 (for example, T1, T2), the timing at which the electrostatic latent image R1 formed by the exposure reaches the transfer position X2 (for example, T3, T4). The moving time of the electrostatic latent image may vary, and there are various factors that cause variations in the moving time of the electrostatic latent image. For example, when the photosensitive drum 222 is replaced, the rotational speed of the photosensitive drum 222 may be different due to a difference in solids of the photosensitive drum 222 before and after replacement. If the rotational speed of the photosensitive drum 222 is different, the time required for the electrostatic latent image R1 to move from the irradiation position X1 to the transfer position X2 (for example, T3-T1, T4-T2) is different. It varies. Further, the positional relationship among the exposure unit 210, the photosensitive drum 222, and the transfer roller 225 may change. When the positional relationship of the exposure unit 210 and the like changes, the distance between the irradiation position X1 and the transfer position X2 in the rotation direction of the photosensitive drum 222 changes. For example, in FIG. 2, when the position of the transfer roller 225 is shifted counterclockwise in the rotation direction of the photosensitive drum 222, the distance between the irradiation position X1 and the transfer position X2 in the rotation direction is shortened. Thus, when the distance between the irradiation position X1 and the transfer position X2 changes, the moving time of the electrostatic latent image varies even if the rotational speed and diameter of the photosensitive drum 222 do not change.

  As described above, the moving time of the electrostatic latent image that may vary can be specified by the following method. Of the surface of the photosensitive drum 222, the surface potential of the exposed area where the electrostatic latent image R1 is formed is different from the surface potential of the non-exposed area where the exposure is not performed. For this reason, when there is a non-exposed area at the transfer position X2 (nip portion P) as in the state of timings T1 to T3 in FIG. 4, and at the transfer position X2 as in the state of timing 4 in FIG. The potential difference between the photosensitive drum 222 and the transfer roller 225 is different from when the electrostatic latent image R1 (exposure area) is present. When the potential difference is different, the transfer voltage It applied to the transfer roller 225 or the transfer voltage Vt applied to the transfer roller 225 in a state where the output voltage is output to the transfer roller 225 by the transfer voltage application unit 430 is different. Therefore, the timing (T3, T4 in FIG. 4) at which the electrostatic latent image R1 reaches the transfer position X2 can be specified based on the timing at which the transfer current It or the transfer voltage Vt changes after exposure by the exposure unit 210. . In the present embodiment, as described below, the moving time of the electrostatic latent image is specified based on the exposure timing at which the surface of the photosensitive drum 222 is exposed by the exposure unit 210 and the change timing at which the transfer current It changes. The

  The operation of the control unit 300 for specifying the moving time of the electrostatic latent image will be described with reference to FIGS.

  For example, when the printer 100 is turned on, the control unit 300 executes the time specifying process shown in FIG. In S110, the control unit 300 determines whether the printer 100 satisfies a predetermined execution condition. The predetermined execution condition is, for example, that there is no sheet W at the transfer position X2, and more specifically, after the printer 100 is activated or the photosensitive drum 222 is replaced, the operation unit 152 or the communication interface 154 is used. Is a period before the print command is received. In S110, when the control unit 300 determines that the printer 100 does not satisfy the predetermined execution condition (NO), the control unit 300 waits as it is and when the printer 100 determines that the predetermined execution condition is satisfied (YES), for example, in the RAM 330. The stored process number N is initialized to 1 (S120). The process number N is an identification number of each of the four color process units 220, and the numbers 1 to 4 are associated in this order from the process unit 220K to the process unit 220C. Therefore, only the process unit 220 having the process number N is set as a target for specifying the moving time of the electrostatic latent image by the process of S120.

  In the time specifying process of FIG. 5 of the above embodiment, for the two process units 220 in which the photosensitive drums 222 are not adjacent to each other, the processes from S130 to S220 may be executed at the same time. For example, for the process unit 220K and the process unit 220M, the processes from S130 to S220 may be executed at the same time.

  Next, in S130, the control unit 300 causes the placement mechanism 148 to place only the development roller 224 provided in the process unit 220 of the process number N among the four development rollers 224 at the supply position, and perform other development. The roller 224 is disposed at a separated position (S130). Thereafter, the control unit 300 causes the charging voltage application unit 410 to start the charging application operation, so that only the charging unit 221 provided in the process unit 220 of the process number N charges the surface of the photosensitive drum 222. (S140), the sheet supply unit 120 and the sheet conveyance unit 130 are caused to start rotating the photosensitive drum 222 and the driving roller 135 (S150). However, at this time, the sheet conveyance unit 130 is not caused to execute the removal of the sheet W from the tray 121 by the pickup roller 122.

  After starting the rotational drive of the photosensitive drum 222 and the like, the control unit 300 causes the transfer voltage application unit 430 to start the transfer application operation for only the transfer roller 225 provided in the process unit 220 of the process number N, and the current sensor 440. Based on the current detection signal SG1 output from, execution of constant current control for controlling the output voltage output from the transfer voltage applying unit 430 so that the transfer current It approaches a predetermined target current value is started (S160). . Next, the control unit 300 causes only the exposure unit 210 provided in the process unit 220 of the process number N to start exposure of the surface of the photosensitive drum 222 (S170, see T1 in FIG. 4). At this time, the exposure unit 210 exposes at least the facing region E2 of the photosensitive drum 222 in the entire rotation axis direction (left-right direction) of the photosensitive drum 222.

  After the start of exposure, the control unit 300 executes the timing specifying process shown in FIG. 6 (S180). As shown in FIG. 6, the control unit 300 causes a timer (not shown) to start counting time (S310), and determines whether or not a predetermined time ΔT1 has elapsed from the exposure start timing T1 based on the time counted by the timer. (S320). As shown in FIG. 7, the specified time ΔT1 is half the exposure time from the exposure start timing T1 to the exposure end timing T2 (= (T2−T1) / 2). An intermediate timing between the exposure start timing T1 and the exposure end timing T2 is that the central portion of the electrostatic latent image R1 in the rotation direction of the photosensitive drum 222 (hereinafter simply referred to as the central portion of the electrostatic latent image R1) is exposed. This timing is formed by exposure of the portion 210, and is hereinafter referred to as exposure timing TC1 of the electrostatic latent image R1. In S320, when it is determined that the specified time ΔT1 has not elapsed (NO), the control unit 300 stands by, and when it is determined that the specified time ΔT1 has elapsed (YES), the time counted by the timer is cleared to zero. (S330).

  Next, the control unit 300 stops the above-described constant current control and applies it to the transfer voltage application unit 430 regardless of the current detection signal SG1 output from the current sensor 440, that is, regardless of the fluctuation of the transfer current It. The control value is set to a fixed value (S340). The control unit 300 determines whether or not the exposure unit 210 has exposed an area equal to or larger than the width of the nip P in the rotation direction of the photosensitive drum 222 (S350). For example, the control unit 300 can make the determination in S350 based on whether or not the total time of the current count time of the timer and the specified time ΔT1 has reached the time corresponding to the width of the nip portion P. In S350, when the control unit 300 determines that an area larger than the width of the nip portion P is not exposed (NO), the exposure unit 210 causes the exposure to continue and exposes an area larger than the width of the nip portion P. If it is determined (YES), the exposure unit 210 ends the exposure (S360, see T2 in FIG. 4). Thereby, formation of the electrostatic latent image R1 is completed. The width of the electrostatic latent image R1 in the rotation axis direction of the photosensitive drum 222 is the same width as that of the facing region E2, and the width of the electrostatic latent image R1 in the rotation direction of the photosensitive drum 222 is equal to or larger than the width of the nip portion P. .

  After the exposure is completed, the control unit 300 determines whether the magnitude relationship between the transfer current It and the threshold value TH has been reversed based on the current detection signal SG1 from the current sensor 440 (S370). The threshold value TH is, for example, the value of the transfer current It when there is a non-exposed region at the transfer position X2 (nip portion P) (see T1 and T2 in FIG. 4), and the electrostatic latent image R1 (exposure) at the transfer position X2. This is an intermediate value from the value of the transfer current It when there is a region (see T3 and T4 in FIG. 4). As shown in FIG. 7, when the electrostatic latent image R1 has not reached the nip portion P (see T1 to T2 in FIG. 4), the transfer current It is equal to or greater than the threshold value TH, and the electrostatic latent image R1 is in the nip portion. When reaching P (see T3 in FIG. 4), the transfer current It starts to decrease, and at timing T5, the transfer current It falls below the threshold value TH, so that the magnitude relationship between the transfer current It and the threshold value TH is reversed. . Hereinafter, the timing T5 is referred to as a first change timing T5. In S370, when the control unit 300 determines that the magnitude relationship between the transfer current It and the threshold value TH is not reversed (NO), the control unit 300 waits as it is and determines that the magnitude relationship between the transfer current It and the threshold value TH is inverted. If YES (YES), the count time of the timer at that time is stored in the RAM 330, for example, as the first inversion time ΔT2 (S380).

  After determining that the magnitude relationship between the transfer current It and the threshold value TH has been inverted in S370 (YES), the control unit 300 determines again whether the magnitude relationship between the transfer current It and the threshold value TH has been inverted (step S370). S390). As shown in FIG. 7, when the electrostatic latent image R1 passes through the nip portion P (see TC2 in FIG. 7), the transfer current It is below the threshold value TH, but the electrostatic latent image R1 is not in the nip portion. When starting to pass through P (see T4 in FIG. 4), the transfer current It starts to increase, and at time T6, the transfer current It exceeds the threshold value TH, thereby inverting the magnitude relationship between the transfer current It and the threshold value TH. Hereinafter, the timing T6 is referred to as a second change timing T6. In S390, when the control unit 300 determines that the magnitude relationship between the transfer current It and the threshold value TH is not reversed (NO), the control unit 300 stands by and determines that the magnitude relationship between the transfer current It and the threshold value TH is inverted. If YES (YES), the timer finishes counting time (S400), the count time of the timer at that time is stored as, for example, the RAM 330 as the second inversion time ΔT3 (S410), and this timing specifying process is terminated. The process proceeds to S190 of 5.

  In S190, the control unit 300 specifies the moving time of the electrostatic latent image R1 based on the specified time ΔT1, the first inversion time ΔT2, and the second inversion time ΔT3 stored in the RAM 330. Specifically, the control unit 300 calculates an average time ΔT4 (= (ΔT2 + ΔT3) / 2) of the first inversion time ΔT2 and the second inversion time ΔT3. As shown in FIG. 7, the average time ΔT4 is the time from the exposure timing TC1 of the electrostatic latent image R1 to the timing TC2 when the central portion of the electrostatic latent image R1 reaches the transfer position X2. This corresponds to the movement time of the electrostatic latent image R1. The control unit 300 stores the average time ΔT4 in, for example, the RAM 330 as the moving time of the electrostatic latent image R1.

  Thereafter, the control unit 300 causes the transfer voltage application unit 430 to end the transfer application operation (S200), and causes the sheet supply unit 120 and the sheet conveyance unit 130 to end the rotational driving of the photosensitive drum 222 and the like (S210). The charging operation by the unit 221 is terminated (S220). Next, the control unit 300 determines whether or not the process number N has reached the process number M (S230). The process number M is the total number of process units 220 provided in the printer 100, and is 4 in the present embodiment. That is, the control unit 300 determines whether or not the movement time of the electrostatic latent image R1 has been specified for all the process units 220 in S230. In S230, when the control unit 300 determines that the process number N has not reached the process number M (NO), the control unit 300 adds 1 to the process number N (S240) and executes the processes from S130 to S220. The moving time of the electrostatic latent image R1 is specified for the (N + 1) th process unit 220. In S230, when the control unit 300 determines that the process number N has reached the process number M (YES), since the moving time of the electrostatic latent image R1 has been specified for all the process units 220, this time specifying process is performed. finish.

  FIG. 8 shows the relationship between the toner image R2 transferred to the sheet W and the target current value for constant current control. As shown in FIG. 8, each region formed by dividing the region FX that can be transferred onto the sheet W evenly in the moving direction of the sheet W is divided into unit regions F (F1, F2, F3, F4,... The area on the image corresponding to each unit area F is called a line area. The unit region F and the line region are, for example, one or a plurality of pixel lines. The ratio of the area occupied by the transfer portion (R21, R22, R23, R24,...) Of the toner image R2 in each unit area F, in other words, the ratio of the number of exposed pixels to the total number of pixels in each line area. Is called the exposure rate. The exposure pixel is a pixel to be exposed by the exposure unit 210. In the toner image R2, the unit areas F1, the unit areas F2 and F3, and the unit area F4 have different exposure rates.

  Here, if the transfer current It is made constant regardless of the exposure rate, the following problem occurs. That is, for example, when the transfer current It is set to a value suitable for the transfer of the toner images in the unit areas F2 and F3, the toner images in the unit areas F1 and F4 having a lower exposure rate than the unit areas F2 and F3 are transferred. The toner may be scattered due to an excessive transfer current It flowing to the transfer position X2. On the other hand, when the transfer current It is set to a value suitable for the transfer of the toner images in the unit areas F1 and F4, when transferring the toner images in the unit areas F2 and F3 having a higher exposure rate than the unit areas F1 and F4, The toner may not be sufficiently transferred to the sheet W due to a shortage of the transfer current It flowing to the transfer position X2.

  Therefore, the unit area F with a higher exposure rate has a larger amount of toner supplied by the developing roller 224. Therefore, if the target current value of the transfer current It is increased by this amount, excessive transfer, insufficient transfer, etc. Generation | occurrence | production can be suppressed and a high quality image can be formed. For this purpose, it is preferable to accurately specify the moving time of the electrostatic latent image corresponding to the transfer portion of the toner image R2 transferred to the unit region F for each unit region F. This is because if the movement time of the electrostatic latent image is deviated, for example, when the electrostatic latent image corresponding to the unit region F1 reaches the transfer position X2, the transfer with respect to the exposure rate of other unit regions F such as the unit region F2 is performed. This is because the target current value of the current It may be set. On the other hand, in the present embodiment, as described below, transfer is performed in accordance with the exposure rate of each unit region F by using the accurate movement time of the electrostatic latent image specified by the time specifying process. The target current value of the current It is appropriately changed.

  The operation of the control unit 300 for the printer 100 to form an image on the sheet W will be described with reference to FIG.

  For example, when the printer 100 is turned on, the control unit 300 executes a printing process shown in FIG. In S510, the control unit 300 determines whether or not the operation unit 152 or the communication interface 154 has received a print command. If the control unit 300 determines that the print command has not been received (NO), the control unit 300 waits and accepts the print command. If it is determined (YES), if color printing is designated by the print command, the arrangement mechanism 148 causes the development rollers 224 for all colors to be arranged at the supply position (S520). Hereinafter, it is assumed that color printing is designated. Thereafter, the control unit 300 causes the charging voltage application unit 410 to start the charging application operation, thereby causing the charging unit 221 for all colors to start a charging operation for charging the surface of the photosensitive drum 222 for all colors (S530). Then, the photosensitive drum 222, the driving roller 135, and the fixing unit 230 are started to rotate by the sheet feeding unit 120 and the sheet conveying unit 130, and the sheet from the tray 121 by the pickup roller 122 is caused to be fed to the sheet conveying unit 130 at a predetermined timing. W extraction is executed (S540).

  After starting to rotate the photosensitive drum 222 and the like, the control unit 300 causes the transfer voltage application unit 430 to start the transfer application operation for the transfer rollers 225 for all colors, and starts executing constant current control (S550). Next, the control unit 300 causes the exposure unit 210 of all colors to sequentially start the exposure of the surface of the photosensitive drum 222 for each line area corresponding to each unit area F (see S560 in FIG. 4 T1), and causes the timer to Time counting is started (S570). For each line area, the controller 300 calculates an exposure rate based on the dot pattern data of the line area (S580), determines a current value of the transfer current It according to the exposure ratio, and associates the line area with the line area. For example, the data is stored in the RAM 330 (S590). Specifically, the current value of the transfer current It when the electrostatic latent image (toner image) formed in the line area reaches the transfer position X2 is absolute for the line area corresponding to the unit area F with a high exposure rate. The value is set to a large value (that is, the output voltage from the transfer voltage application unit 430 is a low value). The electrostatic latent image formed here is an example of a second electrostatic latent image. Thereafter, the control unit 300 performs, for each line area, when the movement time ΔT4 of the electrostatic latent image specified by the time specifying process has elapsed from the exposure start timing of the line area (see T1 in FIG. 7). The current value associated with the region is set as the target current value in the constant current control (S600). As a result, the leading edge of the electrostatic latent image on the next line area is moved to the transfer position X2 from the time when the leading edge of the electrostatic latent image (toner image) on each line area reaches the transfer position X2. Current control is executed with the target current value associated with the line area during the period before the arrival. Thus, as shown in FIG. 8, when the toner image portion R21 of the unit area F1 is transferred to the sheet W, the target current value is set to It1, and the toner image parts R21, R23 of the unit areas F2, F3 are set to the sheet. When transferring to W, the target current value is set to It2 larger than It1, and when the toner image portion R24 of the unit area F4 is transferred to the sheet W, the target current value is larger than It1 and from it2. It is set to a small It3.

  The control unit 300 determines whether or not the transfer of all the line regions has been completed for all the process units 220 (S610), and determines that the transfer of all the line regions has not been completed for all of the process units 220. In the case (NO), the processes from S560 to S600 are executed for the remaining line areas. In S610, when the control unit 300 determines that the transfer of all the line areas has been completed for all the process units 220 (YES), the control unit 300 ends the operations of the charging unit 221, the photosensitive drum 222, the fixing unit 230, and the like. (S620), the printing process is terminated.

  According to this embodiment, based on the exposure timing (T1, T2) at which the surface of the photosensitive drum 222 is exposed by the exposure unit 210 and the change timing (T5, T6) at which the transfer current It changes, the exposure timing TC1 The moving time until the electrostatic latent image R1 reaches the transfer position X2 is specified. As a result, the moving time of the electrostatic latent image R1 can be accurately identified even if fluctuations in the rotational speed of the photosensitive drum 222 or fluctuations in the positional relationship among the photosensitive drum 222, the exposure unit 210, and the transfer roller 225 occur. Can do.

  Further, in order to specify the change timing (T5, T6) based on whether or not the magnitude relationship between the transfer current It and the threshold value TH is reversed, for example, the change rate is a change rate per unit time of the transfer current It. Compared with the case where change timing is specified based on it, change timing can be specified with a simple configuration.

  Further, when specifying the change timing (T5, T6), the constant current control is stopped, and the control value given to the transfer voltage application unit 430 is set to a fixed value regardless of the fluctuation of the transfer current It (S340). As a result, when the change timing is specified, the difference in transfer current It between when the electrostatic latent image R1 is not at the transfer position X2 and when it is present is larger than in the configuration in which constant current control is executed. The moving time of the electrostatic latent image can be specified with higher accuracy.

  Further, when forming the electrostatic latent image R1 for specifying the moving time of the electrostatic latent image, the exposure unit 210 exposes the entire surface portion E1 of the photosensitive drum 222 in the rotation axis direction of the photosensitive drum 222. The As a result, the difference in transfer current It between when the electrostatic latent image R1 is not at the transfer position X2 and when the electrostatic latent image R1 is present is larger than when only a part of the rotation axis direction is exposed to the surface portion E1. Therefore, the moving time of the electrostatic latent image can be specified with higher accuracy.

  Furthermore, when forming the electrostatic latent image R 1, the exposure unit 210 exposes a region that is equal to or larger than the width of the nip P in the rotation direction of the photosensitive drum 222. As a result, the difference in the transfer current It between when the electrostatic latent image R1 is not at the transfer position X2 and when the electrostatic latent image R1 is not present is larger than when only the area less than the width of the nip portion P is exposed in the rotational direction. Therefore, the moving time of the electrostatic latent image can be specified with higher accuracy.

  Further, when the electrostatic latent image R1 passes between the photosensitive drum 222 and the developing roller 224, the developing roller 224 is disposed at the supply position (S130). As a result, the electrostatic latent image R1 is passed between the photosensitive drum 222 and the developing roller 224 as compared with the case where the developing roller 224 is in the separated position. Since a large amount of toner is supplied to R1, the difference in transfer current It between when the electrostatic latent image R1 is not at the transfer position X2 and when it is present increases, so that the movement time of the electrostatic latent image can be made more accurate. Can be identified. Even if the developing voltage VD is not applied to the developing roller 224, if the developing roller 224 is disposed at the supply position so that toner is supplied to the toner image R2, the developing roller during the process of S130. It is not necessary to apply the development voltage VD to 224.

  According to this embodiment, the control unit 300 uses the moving time of the electrostatic latent image specified by the time specifying process of FIG. 5 to form the photosensitive drum 222 when forming an image on the sheet W based on the image data. The transfer current It can be changed at an appropriate timing even when the rotation speed of the photosensitive drum 222, the positional relationship among the photosensitive drum 222, the exposure unit 210, and the transfer roller 225 changes (see FIG. 8).

  Further, since the transfer current It is changed to a larger value as the ratio of the exposure rate is larger (S600 in FIG. 9), the transfer current It is set as compared with the case where the transfer current It is constant regardless of the exposure rate. A high-quality image can be formed by changing the value to an appropriate value according to the amount of toner.

  Further, in the time specifying process of FIG. 5, the processes from S130 to S220 of FIG. 5 are executed for the four process units 220 at different times. Thereby, the movement time of the electrostatic latent image can be accurately identified for each process unit 220 while suppressing the electrical influence between the two process units 220 adjacent to each other.

  The technology disclosed in the present specification is not limited to the above-described embodiment, and can be modified into various forms without departing from the gist thereof. For example, the following modifications are possible.

  In the above-described embodiment, the control unit 300 performs the process of setting the control value given to the transfer voltage application unit 430 (S340 in FIG. 6) before the exposure start (S170 in FIG. 5) or at the end of the exposure (FIG. 6 may be executed after S360).

  In S580 of FIG. 9 in the above embodiment, the control unit 300 calculates the ratio of the exposed pixels to the total number of pixels for each of the plurality of pixel lines constituting the line region, and averages the ratios of the plurality of pixel lines. May be the exposure rate of the line region.

  In the above embodiment, the control unit 300 may change the threshold value TH used in S370 and S390 according to the ambient temperature and humidity of the printer 100, and the secular change of the photosensitive drum 222 and the transfer roller 225.

  In the embodiment described above, the control unit 300 determines that the transfer voltage Vt is a predetermined target voltage based on the voltage detection signal SG2 output from the voltage sensor 450 instead of the constant current control in S160 of FIG. 5 and S550 of FIG. The execution of the constant voltage control for controlling the transfer current It output from the transfer voltage applying unit 430 so as to approach the value may be started, and the constant voltage control may be stopped in S340 of FIG.

  In the timing specifying process of FIG. 6 of the above embodiment, the control unit 300 sequentially calculates the rate of change of the transfer current It using, for example, an AD converter, and determines whether or not the rate of change is equal to or greater than a threshold value. Thus, the change timing of the transfer current It may be specified.

  In the time specifying process of FIG. 5 in the above embodiment, the control unit 300 may use the time from the exposure start timing T1 to the first change timing T5 as the movement time of the electrostatic latent image, or from the exposure end timing T2. The time until the second change timing T6 may be the moving time of the electrostatic latent image.

  In the above embodiment, the control unit 300 may determine the transfer start position of the toner image with respect to the sheet W, for example, using the moving time of the electrostatic latent image specified by the time specifying process of FIG.

  In S <b> 130 of FIG. 5, the developing roller 224 may be disposed at a separated position while the electrostatic latent image R <b> 1 passes between the photosensitive drum 222 and the developing roller 224. With such a configuration, since the toner in the toner box 223 is suppressed from being supplied to the photosensitive drum 222 side, it is possible to specify the moving time of the electrostatic latent image while suppressing toner consumption. .

  The configuration of the printer 100 of the above embodiment is merely an example, and various modifications can be made. For example, in the above-described embodiment, the printer 100 performs printing using toners of four colors of black, yellow, magenta, and cyan. However, the type and number of toner colors used for printing are not limited thereto. . In the above embodiment, the printer 100 is a tandem printer that performs printing using the photosensitive drum 222 provided for each color. However, the printer 100 performs printing using one photosensitive drum that is common to each color. A rotary type printer (also called a four-cycle method when the number of colors is four) may be used. Moreover, in the said embodiment, although the exposure part 210 is a structure provided with a laser light source and a rotary polygon mirror, another structure may be sufficient like the structure provided with the linear LED light source corresponding to a scanning line.

  The image forming apparatus is not limited to a single printer, but may be a copier, a facsimile machine, or a multifunction machine. The present invention can also be applied to these copying machines and the like. In addition, the image forming apparatus is not limited to a configuration in which development is performed using positive polarity toner, but may be configured to perform development using negative polarity toner. In the case of the latter configuration, the polarity of each voltage or the like is opposite to that of the above embodiment.

  In the above-described embodiment, the photosensitive drum 222 as a roller body is illustrated as the photosensitive body. However, the photosensitive body is not limited to this, and may be a belt body such as a photosensitive belt.

  In the above-described embodiment, the charging unit 221 may be a scorotron type having a grid electrode or a corotron type having no grid electrode. Further, a contact type having a charging roller in contact with the surface of the photosensitive drum 222 may be used.

  In the above-described embodiment, the transfer body 225 is exemplified as the transfer body, but the transfer body is not limited to this, and may be a belt body such as an intermediate transfer belt.

  In the above-described embodiment, the arrangement mechanism 148 has a configuration in which the toner box 223 and the developing roller 224 of each color are arranged at the supply position and the separation position. However, the arrangement is not limited to this, and for example, the toner box 223 of each color is displaced. The developing roller 224 for each color is provided so as to be displaceable between the supply position and the separation position, and the arrangement mechanism 148 is configured to arrange the development roller 224 for each color at the supply position and the separation position. Also good.

  In addition, the processing executed by one CPU 310 in the above embodiment may be executed by a combination of a plurality of CPUs, one or more ASICs, one or more CPUs, and one or more ASICs. In such a case, the execution subject of the above process is an example of a control unit. The control unit 300 is a collective term for hardware used for controlling the printer 100, such as the CPU 310, and is not necessarily a single piece of hardware existing in the printer 100.

  In the present application, “the transfer voltage has a large value” means that the transfer voltage has the same polarity and a larger absolute value. That is, “the transfer voltage is a large value” means that the transfer voltage is a high value when the transfer voltage is positive, and the transfer voltage is a low value when the transfer voltage is negative. It means to become.

DESCRIPTION OF SYMBOLS 100: Printer 120: Sheet supply part 121: Tray 122: Pickup roller 130: Sheet conveyance part 148: Arrangement mechanism 210: Exposure part 220: Process part 221: Charging part 222: Photosensitive drum 224: Development roller 225: Transfer roller 300: Control unit 430: Transfer voltage application unit 440: Current sensor 450: Voltage sensor E1: Surface portion E2: Opposite area It: Transfer current P: Nip part R1: Electrostatic latent image R2: Toner image SG1: Current detection signal SG2: Voltage Detection signal T1: Exposure start timing ΔT2: First inversion time T2: Exposure end timing T3: Tip arrival timing ΔT3: Second inversion time T5: First change timing T6: Second change timing TH: Threshold Vt: Transfer voltage W: Sheet X2: Transfer position

Claims (12)

A rotationally driven photoreceptor;
A charging part;
An exposure unit;
A developing section;
A transfer member disposed opposite to the surface of the photoreceptor;
A voltage output unit for outputting an output voltage to the transfer body;
A detection unit that outputs a signal corresponding to a transfer voltage applied to the transfer body in response to a transfer current flowing in the transfer body in accordance with an output of the output voltage or an output of the output voltage;
A control unit,
The controller is
Charging the surface of the photoreceptor to the charging unit;
The exposure unit is exposed to the surface of the photoreceptor charged by the charging unit to form an electrostatic latent image,
After the start of exposure of the surface of the photoconductor, the transfer current or the transfer voltage changes based on the signal output from the detection unit in a state where the output voltage is output to the transfer body by the voltage output unit. Identify the change timing
Based on the exposure timing at which the surface of the photoconductor is exposed by the exposure unit and the change timing of the transfer current or the transfer voltage, the electrostatic latent image is transferred between the photoconductor and the transfer body from the exposure timing. An image forming apparatus for specifying a moving time until the transfer position is reached. The image forming apparatus according to claim 1.
The controller is
An image forming apparatus that determines whether or not a magnitude relationship between the transfer current or the transfer voltage and a threshold value is reversed, and identifies a timing at which the magnitude relationship is reversed as the change timing. The image forming apparatus according to claim 1, wherein:
The controller is
When an image is formed on a sheet passing through the transfer position, constant current control is performed to control the voltage output unit based on the signal output from the detection unit so that the transfer current approaches a target current value. ,
An image forming apparatus that sets a control value given to the voltage output unit to a fixed value when specifying the change timing. The image forming apparatus according to claim 1, wherein:
The controller is
When forming an image on a sheet passing through the transfer position, constant voltage control is performed to control the voltage output unit so that the transfer voltage approaches a target voltage value based on the signal output from the detection unit. ,
An image forming apparatus that sets a control value given to the voltage output unit to a fixed value when specifying the change timing. The image forming apparatus according to any one of claims 1 to 4, wherein:
The controller is
The exposure unit exposes the entire surface of the surface of the photoconductor that passes through a facing area where the photoconductor and the transfer body face each other in the entire rotation axis direction of the photoconductor. An image forming apparatus for forming an electrostatic latent image. The image forming apparatus according to any one of claims 1 to 5, wherein:
At the transfer position, a nip portion is formed where the photoconductor and the transfer body are pressed against each other,
The controller is
An image forming apparatus in which the electrostatic latent image is formed by exposing the exposure unit to an area that is equal to or larger than the width of the nip portion in the rotation direction of the photoconductor. The image forming apparatus according to claim 1, further comprising:
An arrangement mechanism for disposing the developing unit at a supply position where the developer can be supplied to the photoconductor and a distant position farther from the photoconductor than the supply position;
The controller is
An image forming apparatus in which the developing unit is placed in the separated position by the arrangement mechanism while the electrostatic latent image passes between the photosensitive member and the developing unit. The image forming apparatus according to any one of claims 1 to 7,
The controller is
After forming the travel time, when forming an image on the sheet based on the image data,
The exposure unit exposes the surface of the photoreceptor charged by the charging unit based on the image data to form a second electrostatic latent image,
Causing the developing unit to supply developer to the second electrostatic latent image;
An image forming apparatus that controls the voltage output unit so that the transfer current or the transfer voltage changes when the movement time elapses from an exposure timing based on the image data. The image forming apparatus according to claim 8.
The controller is
The larger the proportion of the area occupied by the second electrostatic latent image in the predetermined unit area on the surface of the photoconductor, the greater the ratio of the transfer current when the moving time has elapsed from the exposure timing based on the image data, or the An image forming apparatus that controls the voltage output unit so that a transfer voltage becomes a large value. The image forming apparatus according to any one of claims 1 to 9,
A plurality of process units including at least the photoconductor, the exposure unit, the transfer body, the voltage output unit, and the detection unit;
The controller is
An image in which the formation of the electrostatic latent image by exposure of the surface of the photoconductor and the specification of the change timing are performed at least at different times with respect to the two process units adjacent to each other. Forming equipment. A rotationally driven photoreceptor;
A charging part;
An exposure unit;
A developing section;
A transfer member disposed opposite to the surface of the photoreceptor;
A voltage output unit for outputting an output voltage to the transfer body;
And a detection unit that outputs a signal corresponding to a transfer current flowing through the transfer body in accordance with an output of the output voltage or a transfer voltage applied to the transfer body in accordance with an output of the output voltage. A control method,
Charging the surface of the photoreceptor with the charging unit;
Exposing the surface of the photoconductor charged by the charging unit to the exposure unit to form an electrostatic latent image;
After the start of exposure of the surface of the photoconductor, the transfer current or the transfer voltage changes based on the signal output from the detection unit in a state where the output voltage is output to the transfer body by the voltage output unit. Identifying the change timing to perform,
Based on the exposure timing at which the surface of the photoconductor is exposed by the exposure unit and the change timing of the transfer current or the transfer voltage, the electrostatic latent image is transferred between the photoconductor and the transfer body from the exposure timing. And a step of specifying a moving time until the intermediate transfer position is reached. A rotationally driven photoreceptor;
A charging part;
An exposure unit;
A developing section;
A transfer member disposed opposite to the surface of the photoreceptor;
A voltage output unit for outputting an output voltage to the transfer body;
An image forming apparatus comprising: a detection unit that outputs a transfer current flowing through the transfer body according to the output of the output voltage or a signal according to a transfer voltage applied to the transfer body according to the output of the output voltage. ,
A process of charging the surface of the photosensitive member to the charging unit;
A process of exposing the surface of the photoreceptor charged by the charging unit to the exposure unit to form an electrostatic latent image;
After the start of exposure of the surface of the photoconductor, the transfer current or the transfer voltage changes based on the signal output from the detection unit in a state where the output voltage is output to the transfer body by the voltage output unit. Processing to identify the change timing to be
Based on the exposure timing at which the surface of the photoconductor is exposed by the exposure unit and the change timing of the transfer current or the transfer voltage, the electrostatic latent image is transferred between the photoconductor and the transfer body from the exposure timing. And a computer program for executing a process for specifying a movement time until the transfer position is reached.

Images