JP2013041222A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of calculating a suitable transfer voltage value for image forming, capable of starting ATVC control from a start-up of a scanner, and capable of shortening a first printout time.SOLUTION: In the image forming apparatus, a speed control unit starts a rotary polygon mirror 106, a light source control unit makes a light source 104 emit light at predetermined time intervals and counting means measures the number of rotations of the rotary polygon mirror 106, and a speed control unit performs rotation control of the rotary polygon mirror 106 until the number of rotations of the rotary polygon mirror 106 reaches a predetermined number of rotations. The image forming apparatus includes transfer current detecting means 203d which starts detection of a current flowing in transfer means 110 until the number of rotations of the rotary polygon mirror 106 reaches the predetermined number of rotations after the speed control unit starts the rotary polygon mirror 106, and usability determination means 202A which determines whether or not to use a detection result of the transfer current detecting means 203d on the basis of a timing when an image carrier 102 scans a light flux.

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a semiconductor laser printer, and more particularly to an image forming apparatus that performs an operation of adjusting a transfer voltage applied to a transfer unit.

  Patent Document 1 discloses an image forming apparatus that sets a reference voltage (hereinafter referred to as “ATVC”) applied to a transfer unit during image formation during non-image formation.

  Patent Document 2 discloses an exposure means using a polygon mirror, a scanner motor, and a semiconductor laser for forming an electrostatic latent image on a photoconductor according to an image signal. The scanner motor has a large inertia and takes time to reach a stable rotational state. Therefore, in order to shorten the output time of the first sheet of paper (hereinafter referred to as “first printout time”), it is necessary to start driving the scanner motor at the same time as printing is instructed.

  In starting the scanner motor, the semiconductor laser is turned on, and the rotation speed of the scanner motor is detected by a light receiving sensor provided on the laser scan. The following control is described in order to shorten the lighting time of the semiconductor laser and realize the long life without extending the startup time of the scanner motor.

  In other words, after starting to drive the scanner motor, the semiconductor laser is forcibly turned on at regular intervals (hereinafter referred to as “flashing light emission”), and the semiconductor laser is forcibly turned on when the rotation speed of the scanner motor reaches a predetermined speed. To rotate the polygon mirror in a stable state. Thereafter, in order not to irradiate the photoconductor with the semiconductor laser, the light is turned on and off in accordance with the synchronization signal input to the light receiving sensor (hereinafter referred to as “unblanking light emission”).

Japanese Patent Laid-Open No. 5-6112 Japanese Patent Laid-Open No. 2002-244055

  A conventional ATVC control timing will be described with reference to FIG. 10 attached hereto.

  ATVC detects the current transfer current value and sets the transfer output voltage. By repeating this operation a plurality of times, an appropriate transfer output voltage is adjusted during image formation. On the other hand, in order to shorten the lighting time of the semiconductor laser and extend the life without extending the startup time of the scanner motor, the flashing light emission is performed when the scanner is started.

  Since the charged photoreceptor surface has a different potential between the photoreceptor surface irradiated with the semiconductor laser and the unexposed photoreceptor surface, the transfer current flowing on the contact surface between the photoreceptor and the transfer means (for example, transfer roller) is different. Therefore, conventionally, after changing from flashing light emission and forced light emission at the time of scanner activation to unblanking light emission, ATVC is started at a time when the photosensitive member surface exceeds at least the transfer position. As a result, the ATVC start is delayed and the first printout time becomes longer.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of calculating a transfer voltage value suitable for image formation, starting ATVC control from the time of scanner activation, and reducing the first printout time. That is.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention
An image carrier;
An exposure apparatus that scans and exposes the surface of the image carrier by deflecting a light beam from a light source with a rotary polygon mirror to form an electrostatic latent image on the image carrier;
A light source control unit for controlling ON / OFF of the light source;
Synchronization signal generating means for detecting a light beam from the light source deflected by the rotary polygon mirror and generating a synchronization signal for each scanning line;
Counting means for counting the number of rotations of the rotary polygon mirror by counting the period of the synchronization signal;
A speed control unit for controlling the rotation of the rotary polygon mirror so that the number of rotations counted by the counting unit becomes a predetermined number of rotations set in advance;
Developing means for attaching toner to the electrostatic latent image of the image carrier to form a toner image;
Transfer means for transferring the toner image to a recording medium or an intermediate transfer member;
A transfer voltage applying means for applying a voltage to the transfer means;
A transfer current detecting means for detecting a current flowing through the transfer means when the transfer voltage applying means applies a voltage to the transfer means;
With
The speed control unit activates the rotating polygon mirror, the light source control unit emits the light source at predetermined time intervals, the counting means measures the number of rotations of the rotating polygon mirror, In the image forming apparatus in which the speed control unit performs rotation control of the rotary polygon mirror until the rotation speed reaches a predetermined rotation speed.
The transfer current detection means starts detecting the current flowing through the transfer means until the rotational speed of the rotary polygon mirror reaches a predetermined rotational speed after the speed control unit activates the rotary polygon mirror, and the image An image forming apparatus comprising: a usability determining unit that determines whether or not to use a detection result of the transfer current detecting unit from a timing at which a light beam is scanned on a carrier.

  According to the present invention, a transfer voltage value suitable for image formation can be calculated, and ATVC control can be started from the time of scanner activation, and the first printout time can be shortened.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. 1 is a block diagram illustrating a configuration of an image forming apparatus according to the present invention. FIG. 2 is a configuration diagram of an engine controller and each control unit in the image forming apparatus of the present invention. It is a figure explaining one Example of the laser lighting timing at the time of scanner starting. It is a timing chart which shows ATVC control. It is a flowchart which shows ATVC control. It is a figure explaining the other Example of the laser lighting timing at the time of scanner starting. It is a figure explaining the relationship between laser lighting and a transfer roller position. It is a figure explaining the other Example of the laser lighting timing at the time of scanner starting. It is a timing chart which shows the conventional ATVC control.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
FIG. 1 is a schematic diagram illustrating the overall configuration of the image forming apparatus according to the present exemplary embodiment. In this embodiment, the image forming apparatus 100 is a laser beam printer and includes a process cartridge 101 that can be attached to and detached from the image forming apparatus main body 100A.

  The image forming apparatus 100 includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 102 as an image carrier. Around the photosensitive drum 102, a charging roller (charging means) 108 for uniformly charging the photosensitive drum 102, and an exposure device (exposing the electrostatic latent image) by exposing the charged photosensitive drum 102 to exposure. (Exposure means) 103 is arranged. Further, a developing roller (developing means) 109 is disposed around the photosensitive drum 102 for attaching toner to the electrostatic latent image formed on the photosensitive drum 102 to form a toner image. In this embodiment, the photosensitive drum 102, the charging roller 108, and the developing roller 109 are unitized as one unit to constitute the process cartridge 101.

  The exposure device 103 is a laser beam scanning device, and includes a semiconductor laser 104 as a light source and a polygon mirror 106 that is a rotating polygon mirror that is rotated by a scanner motor 105. Between the exposure device 103 and the photosensitive drum 102, a light beam (light beam) emitted from the semiconductor laser 104 is deflected by the polygon mirror 106, and a laser optical path L that scans and exposes the surface of the photosensitive drum 102 is formed. The exposure apparatus 103 further includes a light receiving sensor 107 that receives the light beam deflected by the polygon mirror 106. The light receiving sensor 107 constitutes synchronizing signal generating means for detecting a light beam from the semiconductor laser 104 as a light source and generating a synchronizing signal for each scanning line. Details will be described later.

  The toner image developed by the developing roller 109 is transferred to a predetermined recording sheet S as a recording medium by a transfer roller 110 as a transfer unit, and the sheet S on which the toner image is transferred is conveyed to a fixing device 111. The The fixing device 111 has a fixing heater 112 for fusing the toner transferred to the paper S by heat, and the toner on the paper is transferred to the paper while the paper S is conveyed by the fixing film 124 and the pressure roller 125. Heat and pressure fix to S.

  The recording paper S is stored in the paper feed cassette 113, and is sent out from the paper feed cassette 113 to the conveyance path by one rotation of the pickup roller 114. That is, when the paper picked up by the pickup roller 114 is a paper bundle, the feed roller 115 and the retard roller 116 forming a roller pair separate the paper into one and send it out to the conveyance path.

  The sheet S fed from the cassette 113 is conveyed to the transfer unit T by the intermediate roller 117 and the pre-transfer roller 118. In the transport path between the pre-transfer roller 118 and the transfer roller 110, image writing (recording / printing) on the photosensitive drum 102 and paper transport are synchronized, and the length of the fed paper S in the transport direction is measured. A top sensor 119 which is detection means for performing the above is disposed.

  Further, on the downstream side of the fixing device 111, a fixing sensor 120 for detecting the presence or absence of the paper S after fixing, a transport roller 121 for discharging the paper S after fixing to a paper discharge transport path, and a paper discharge paper are stacked. A paper discharge roller 122 that discharges paper to the paper discharge tray 123 is disposed.

  FIG. 2 is a circuit configuration block diagram of the image forming apparatus 100 according to the present exemplary embodiment.

  In FIG. 2, a printer controller 201 develops image code data sent from an external device such as a host computer (not shown) into bit data necessary for printer printing, and reads printer internal information and displays it. The engine controller 202 is a control unit that controls each unit of the printer engine, and performs printing operation control in accordance with instructions from the printer controller 201. At the same time, the printer internal information is notified to the printer controller 201.

  The engine controller 202 includes a CPU 202A and an ASIC (Application Specific Integrated Circuit) 202B, as will be understood with reference to FIG. 3, and includes the following control unit.

  The high voltage control unit 203 performs high voltage output control such as charging, development, and transfer according to instructions from the engine controller 202.

  The optical system control unit 204 controls driving / stopping of the scanner motor 104 and lighting of the laser beam in accordance with an instruction from the engine controller 202. That is, the optical system control unit 204 has a light source control unit 204a that controls ON / OFF of the semiconductor laser 104 that is a light source, and a rotation speed (speed) of the polygon mirror 106 that is set to a predetermined rotation speed (predetermined speed) set in advance. Are provided with a speed control unit 204b for controlling driving of the polygon mirror, that is, rotation control, and a counting means 204c for measuring the number of rotations of the polygon mirror.

  The fixing device control unit 205 controls the fixing device to drive / stop energization of the fixing heater in accordance with an instruction from the engine controller 202.

  The sensor input unit 206 notifies the engine controller 202 of detection results of the light receiving sensor 107, the top sensor 119, the fixing sensor 120, and the like.

  The paper transport control unit 207 drives / stops the motor / roller and the like for transporting the recording paper in accordance with an instruction from the engine controller 202. That is, the paper conveyance control unit 207 includes the paper feed roller 114, the feed retard roller pairs 115 and 116, the pre-transfer roller 118, the photosensitive member 102, the fixing film 124, the pressure roller 125, the conveyance roller 121, and the paper discharge roller in FIG. Control of driving / stopping 122 is performed.

  FIG. 3 is a configuration diagram of the engine controller 202 and each control unit in the image forming apparatus 100.

  The CPU 202A in the engine controller 202 transmits a PWM signal to the high-voltage output circuits 203a, 203b, and 203c of the charging roller 108, the developing roller 109, and the transfer roller 110 by the high-pressure control unit 203. A booster in each high voltage output circuit applies a high voltage corresponding to the input PWM signal to each high voltage output unit. When the duty ratio of the PWM signal transmitted from the CPU 202A changes, the high voltage applied to each high voltage output unit changes. A transfer current detection circuit 203d constituting transfer current detection means is connected to the transfer voltage output circuit 203c constituting transfer voltage application means, and converts the current flowing through the transfer roller 110 into voltage. This Analog signal is input to the CPU 202A and converted into a digital value by the A / D converter 202C in the CPU. The CPU 202A can know the current flowing through the transfer roller 110 from this digital value.

  The ASIC 202B in the engine controller 202 controls the rotation speed (number of rotations) of the scanner motor 104 and ON / OFF of the semiconductor laser 104 by the speed control unit 204b and the light source control unit 204a by the optical system control unit 204, respectively. . The CPU 202A can set the lighting method of the semiconductor laser 104 for the ASIC 202B. Examples of lighting methods include extinguishing, forced light emission, unblanking light emission, and VIDEO lighting according to a signal transmitted from the printer controller 201.

  FIG. 4 shows the laser lighting timing when the scanner motor is activated. In FIG. 3, when the CPU 202A sets the target rotation speed (rotation speed) of the scanner motor 105 to the ASIC 202B and instructs the DRIVE 202 to drive the scanner motor 105, the scanner motor 105 starts rotating. Further, the ASIC 202B is asynchronous with the output of the light receiving sensor 107, and repeats laser on / off at predetermined time intervals, that is, at intervals of laser lighting time = tp1 and laser extinguishing time = td1 to perform flashing light emission. At this time, it is assumed that the laser lighting time = tp1 is longer than the target signal cycle output from the light receiving sensor 107 when the scanner motor 105 rotates at the target rotation speed. Further, it is assumed that the laser turn-on time = tp1 and the laser turn-off time = td1 are shorter than the time necessary for the scanner motor 105 to reach the target rotation speed.

  The ASIC 202B monitors the synchronization signal for each scanning line output from the light receiving sensor 107 at the time of flashing light emission, that is, the signal cycle, and detects the rotation speed (rotation speed) of the scanner motor 105 by the counting means 204c. When the number of revolutions of the scanner motor 105 reaches a predetermined number of revolutions, the ASIC 202B constantly turns on the laser to accelerate or decelerate the scanner motor 105 and control it to reach the target number of revolutions. When the scanner motor 105 reaches the target rotational speed, the ASIC 202B performs unblanking light emission that turns on the laser only in the vicinity of the light receiving sensor 107.

  Next, the ATVC control when the scanner motor is activated in this embodiment will be described. FIG. 5 is an ATVC control timing chart when the scanner motor is activated. For the sake of simplicity, the state during the start-up of the scanner motor 105 is omitted.

  When the scanner motor 105 is started, the output of the charging voltage is started. When the charged area of the photosensitive drum 102 reaches the transfer portion T, the output of the transfer voltage is started and ATVC control is started. In addition, the semiconductor laser 104 starts flashing light emission at intervals of laser lighting time = tp1 and laser extinguishing time = td1. The region irradiated with laser by flashing emission reaches the transfer portion T after the time ts has elapsed. Since the transfer current decreases in the laser-irradiated region, the transfer current decreases between ab, cd, and ef.

  In ATVC control, since the transfer current detection result in the region not irradiated with laser is used, if the transfer current detection result in the region irradiated with laser is also used, the correct transfer current cannot be detected, and the accuracy of the ATVC control result is poor. turn into. Therefore, it is necessary to use only the transfer current detection result in the region not irradiated with the laser.

  Since the CPU 202A gives an instruction for forced light emission of the semiconductor laser 104, the CPU 202A can detect the timing at which the region irradiated with the laser reaches the transfer portion T after the forced light emission instruction. The CPU detects that the laser-irradiated region has reached the transfer portion T in a period such as ab, cd, ef, etc. after ts have elapsed after forced light emission. The CPU determines that the transfer current detection result during a period such as a to b, c to d, and e to f cannot be used, and does not feed back the detection result to the transfer voltage output. That is, the CPU 202A functions as an availability determination unit that determines whether to use the detection result of the transfer current detection unit 203d from the timing at which the photosensitive drum 102 is irradiated with laser.

  Further, the CPU 202A holds the set value of the transfer voltage output during the periods ab, cd, ef, and the like. When the CPU 202A detects that the laser-irradiated region has passed through the transfer portion T, the CPU 202A uses the transfer current detection result to resume feedback to the transfer voltage output and cancel the holding of the transfer voltage output set value. .

  With this control, the ATVC control can be started from the time of starting the scanner without using the region where the transfer current decreases due to the laser irradiation for the ATVC control.

  FIG. 6 is a flowchart showing ATVC control when the scanner is activated in this embodiment.

When printing is started, the photosensitive drum 102 and the scanner motor 105 are started to drive, the high voltage of the charging roller 108 is output, and the semiconductor laser 104 starts flashing light emission (S401). When the position of the photosensitive drum 102 to which a high voltage is applied by the charging roller 108 rotates and reaches the transfer roller 110, ATVC is started (S402). The transfer voltage of the transfer roller 110 is set (S403), and the transfer voltage is output (S404). A transfer current value flowing through the transfer roller 110 to which the transfer voltage is applied is detected (S405). When the transfer current value is detected, the CPU 202A determines whether the detected area is a laser irradiated area (S406). If the area where the transfer current is detected is not irradiated with laser, feedback is made to the transfer current set value based on the detected transfer current detection value in order to converge to a predetermined transfer current value (S407). These controls are repeated a predetermined number of times (S408). If the area where the transfer current is detected is an area irradiated with a laser, the transfer current detection value is not used (S409), and the transfer voltage setting value is not fed back to the transfer current setting value and held for a predetermined time ( S410). After a predetermined time has elapsed, ATVC is restarted and transfer current detection is performed. If the current value acquired in S405 is lower than the target current value, the transfer high voltage output value is increased in the next S407, and if it is higher than the target current value, the transfer high voltage output value is decreased in the next S407. To do. After a predetermined number of times performed in S408, a final transfer high-voltage output value obtained for a reference transfer high-voltage output value V _0.

  As described above, even when the photosensitive drum 102 is irradiated with laser when the scanner is activated, according to the present invention, the transfer current detection result in the region irradiated with the laser on the photosensitive drum 102 is not used. Hold the transfer voltage setting. The reference transfer voltage at the time of image formation can be calculated by executing ATVC control only in the photosensitive drum area not irradiated with the laser. Further, the reference transfer voltage can be calculated much faster than the conventional ATVC.

Example 2
Next, an image forming apparatus according to a second embodiment of the present invention will be described. In the second embodiment, a method for detecting the accuracy of the transfer current detected by the ATVC control more accurately than in the first embodiment will be described.

  1 (schematic diagram showing configuration), FIG. 2 (block diagram of circuit configuration), FIG. 3 (configuration diagram of engine controller and each control unit), FIG. 5 (ATVC control timing chart when scanner motor is activated), FIG. (The flowchart showing the ATVC control at the time of starting the scanner) is the same as that in the first embodiment, and a description thereof will be omitted.

  FIG. 7 shows the laser lighting timing when the scanner is activated in this embodiment. In the first embodiment, the laser lighting timing at the time of starting the scanner is asynchronous with the rotation cycle of the transfer roller 110, but in this embodiment, the laser lighting timing and the rotation cycle of the transfer roller 110 are synchronized.

When the CPU sets the target rotation speed of the scanner motor 105 to the ASIC and instructs the ASIC to drive the scanner motor 105, the scanner motor starts rotating. In addition, the ASIC is asynchronous with the output of the light receiving sensor 107, and repeats turning on / off of the laser at intervals of laser lighting time = tp2 and laser extinguishing time = td2 to perform flashing light emission. tp2 and td2 are synchronized with the transfer roller 110. When the peripheral length of the transfer roller 110 is Lt [mm] and the process speed is P [mm / s], it is expressed by the following equation. At this time, N and n = natural numbers and N> n.
tp = Lt / (P × 2 ^N ) [s] Formula 1
td = tp × ((2 ^N −2 ⁿ ) / 2 ⁿ ) [s] Equation 2

  Specific examples are shown below. FIG. 8A shows the relationship between the transfer roller 110 and the region of the photosensitive drum 102 irradiated with laser when N = 4 and n = 2. As shown in the drawing, among the areas f1 to f16 obtained by dividing the peripheral length of the transfer roller 110 into 16, the areas facing the photosensitive drum area irradiated with the laser from the transfer roller 110 are f1, f5, f9, and f13. . The area not irradiated with laser is evenly distributed over one rotation of the transfer roller 110. Therefore, by performing ATVC control in a region not irradiated with laser, the transfer current of substantially one turn of the transfer roller 110 can be detected, and the transfer voltage can be set with higher accuracy.

  As described above, according to the present invention, the laser lighting timing at the time of starting the scanner and the transfer roller cycle are synchronized. As a result, when ATVC control is performed when the scanner is activated, the transfer voltage can be set with higher accuracy, and the reference transfer voltage can be calculated earlier than the conventional ATVC control.

Example 3
An image forming apparatus according to a third embodiment of the present invention will be described. In the third embodiment, a method different from that of the second embodiment will be described for how to synchronize the laser lighting timing and the transfer roller cycle when the scanner is activated.

  1 (schematic diagram showing configuration), FIG. 2 (block diagram of circuit configuration), FIG. 3 (configuration diagram of engine controller and each control unit), FIG. 5 (ATVC control timing chart when scanner motor is activated), FIG. (A flowchart showing ATVC control when the scanner is activated) is the same as that of the first embodiment, and a description thereof will be omitted.

  FIG. 9 shows the laser lighting timing when the scanner is activated in this embodiment. In Example 2, the laser was turned on in an area obtained by dividing the circumferential length of the transfer roller by an even multiple, and the transfer current could not be detected in the laser-lit area. In this embodiment, a method will be described in which the transfer roller circumferential length is divided by a natural number multiple and the laser is selectively turned on according to the circumference of the transfer roller 110 to detect the transfer current in the entire transfer roller area.

When the CPU 202A sets the target rotational speed of the scanner motor 105 to the ASIC 202B and instructs the ASIC 202B to drive the scanner motor 105, the scanner motor starts rotating. Further, the ASIC 202B is asynchronous with the output of the light receiving sensor 107, and repeats laser on / off at intervals of laser lighting time = tp3 and laser off time = td3 to perform flashing light emission. tp3 and td3 are synchronized with the transfer roller 110. When the peripheral length of the transfer roller 110 is Lt [mm] and the process speed is P [mm / s], it is expressed by the following equation. At this time, M and m = natural numbers and (M−2) ≧ m.
tp = Lt / (P × M) [s] Equation 3
td = tp × m [s] Equation 4

  Specific examples are shown below. FIG. 8B shows a relationship in which the transfer roller faces the region of the photosensitive member irradiated with laser when M = 5 and m = 2. As shown in the figure, blinking light emission is performed in which the laser is turned on at intervals of td3 in the region of g1 to g5 in which the peripheral length of the transfer roller 110 is divided into five. By executing this flashing light emission for three rotations of the transfer roller, the opposing regions of the transfer roller 110 and the photosensitive region irradiated with the laser are g1 to g5. In the region not irradiated with laser, the entire region is the target for three rotations of the transfer roller. Therefore, by performing ATVC control over three or more rounds of the transfer roller, the transfer current for the entire area of the transfer roller can be detected, and the transfer voltage can be set with higher accuracy.

  As described above, according to the present invention, the laser lighting timing at the time of starting the scanner and the transfer roller cycle are synchronized with each other and the transfer roller circumferential length divided region is selectively applied over one or more rounds. Laser irradiation. As a result, when ATVC control is performed when the scanner is activated, transfer current detection and transfer voltage setting can be performed with higher accuracy, and a reference transfer voltage can be calculated earlier than conventional ATVC control.

  In each of the above embodiments, the present invention has been described as an image forming apparatus that directly transfers the toner image of the photosensitive drum 102 onto the paper S as a recording medium. However, the present invention is limited to the image forming apparatus having this configuration. It is not something. An intermediate transfer member such as an intermediate transfer belt as a recording medium other than the photosensitive drum is provided. The toner image on the photosensitive drum 102 is temporarily transferred to the intermediate transfer member, and then the toner image on the intermediate transfer member is transferred to a sheet. An intermediate transfer type image forming apparatus may be used. Since the configuration of such an image forming apparatus is well known to those skilled in the art, further detailed description is omitted.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 100A Image forming apparatus main body 101 Toner cartridge 102 Photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 103 Exposure apparatus 104 Semiconductor laser 105 Scanner motor 106 Polygon mirror 107 Light reception sensor (synchronization signal generation means)
108 Charging roller (charging device)
109 Developing roller (developing device)
110 Transfer roller (charging device)
DESCRIPTION OF SYMBOLS 201 Printer controller 202 Engine controller 203 High voltage | pressure control part 204 Optical system control part 205 Fixing control part 206 Sensor input part 207 Paper conveyance control part CPU Control means (usability determination means)

Claims (4)

An image carrier;
An exposure apparatus that scans and exposes the surface of the image carrier by deflecting a light beam from a light source with a rotary polygon mirror to form an electrostatic latent image on the image carrier;
A light source control unit for controlling ON / OFF of the light source;
Synchronization signal generating means for detecting a light beam from the light source deflected by the rotary polygon mirror and generating a synchronization signal for each scanning line;
Counting means for counting the number of rotations of the rotary polygon mirror by counting the period of the synchronization signal;
A speed control unit for controlling the rotation of the rotary polygon mirror so that the number of rotations counted by the counting unit becomes a predetermined number of rotations set in advance;
Developing means for attaching toner to the electrostatic latent image of the image carrier to form a toner image;
Transfer means for transferring the toner image to a recording medium or an intermediate transfer member;
A transfer voltage applying means for applying a voltage to the transfer means;
A transfer current detecting means for detecting a current flowing through the transfer means when the transfer voltage applying means applies a voltage to the transfer means;
With
The speed control unit activates the rotating polygon mirror, the light source control unit emits the light source at predetermined time intervals, the counting means measures the number of rotations of the rotating polygon mirror, In the image forming apparatus in which the speed control unit performs rotation control of the rotary polygon mirror until the rotation speed reaches a predetermined rotation speed.
The transfer current detection means starts detecting the current flowing through the transfer means until the rotational speed of the rotary polygon mirror reaches a predetermined rotational speed after the speed control unit activates the rotary polygon mirror, and the image An image forming apparatus comprising: a usability determining unit that determines whether to use a detection result of the transfer current detecting unit from a timing at which a light beam is scanned on a carrier. The transfer means is a transfer roller;
The light source control unit controls ON / OFF of the light source in synchronization with a rotation cycle of the transfer roller from when the rotary polygon mirror is activated until a predetermined rotation speed is reached. Item 2. The image forming apparatus according to Item 1.   The image forming apparatus according to claim 2, wherein ON / OFF of the light source is controlled for an area obtained by dividing the circumferential length of the transfer roller by an even multiple.   The circumference of the transfer roller is divided by a natural number multiple, the ON / OFF of the light source is selectively controlled according to the circumference of the transfer roller, and the transfer current is detected in the entire area of the transfer roller. The image forming apparatus according to claim 2.

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