JP2022173774A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can prevent a reduction in the life of a light source of an exposure unit, while accurately controlling the rotation speed of a polygon motor.SOLUTION: A controller 50 of an image forming apparatus controls the rotation speed of a rotor 64a based on an FG signal from when the rotor 64a starts rotating until when a period of the FG signal falls within a first range, when the period of the FG signal falls within the first range, executes switching control from a light-off state to a light-on state of an LD 61 for making a laser beam incident on a BD sensor 66 periodically at a first period and controls the rotation speed of the rotor 64a based on the BD signal, and when a period of the BD signal falls within a second range, executes switching control of the LD 61 for making the laser beam incident on the BD sensor 66 periodically at a second period longer than the first period and controls the rotation speed of the rotor 64a based on the BD signal.SELECTED DRAWING: Figure 9

Description

The present invention relates to an image forming apparatus such as an electrophotographic copier or an electrophotographic printer that forms an image on a sheet using an electrophotographic method.

2. Description of the Related Art When an image is formed by an electrophotographic image forming apparatus, an electrostatic latent image is formed on the surface of a photoreceptor by deflecting and scanning a light beam emitted from a light source by a polygon mirror in an exposure unit. After that, toner is attached to the electrostatic latent image formed on the surface of the photosensitive member to form a toner image, and the toner image is transferred to a sheet to form an image.

Here, Patent Document 1 describes the following configuration as a method for controlling the rotational speed of a polygon motor that rotationally drives a polygon mirror. The controller controls the rotation speed of the polygon motor based on the FG signal for a predetermined period after the polygon motor starts rotating. The FG signal is a signal output according to the magnetic flux change detected by the Hall element as the polygon motor rotates. After that, the controller controls the rotational speed of the polygon motor based on the BD signal output by the light receiving element receiving the light beam emitted from the light source.

The reason why the reference signal for controlling the rotational speed of the polygon motor is switched from the FG signal to the BD signal in Patent Document 1 is as follows. That is, the FG signal is a signal generated by a Hall element and tends to contain noise. On the other hand, a BD signal is a signal output by a light receiving element receiving a light beam, and has relatively little noise. Therefore, by switching from the FG signal to the BD signal as the reference signal for controlling the rotation speed of the polygon motor, the rotation speed control of the polygon motor can be performed with high accuracy.

JP 2018-10167 A

When adopting the configuration in which the reference signal for controlling the rotational speed of the polygon motor is switched from the FG signal to the BD signal as in the configuration of Patent Document 1, the following problems may occur. That is, in order for the controller to control the rotational speed of the polygon motor based on the BD signal, it is necessary to emit a light beam from the light source and cause the light receiving element to receive the light beam. As described above, the FG signal tends to contain a lot of noise, and the accuracy of rotational speed control based on the FG signal is relatively low. Therefore, until the rotation speed of the polygon motor is stabilized by the rotation speed control based on the BD signal, the controller controls the light source for making the light beam incident on the light receiving element so that the light beam is stably received by the light receiving element. It is necessary to quickly switch from the off state to the on state.

In this way, when the control unit continues the control of early switching of the light source from the off state to the on state for causing the light beam to enter the light receiving element until the rotation of the polygon motor is stopped, the lighting time of the light source is become longer. In this case, the life of the light source is shortened.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of controlling the rotation speed of a polygon motor with high accuracy while preventing the life of the light source of an exposure unit from being shortened.

A representative configuration of the image forming apparatus according to the present invention for achieving the above object is a photoreceptor and an exposure unit that irradiates a light beam on the surface of the photoreceptor to form an electrostatic latent image, A polygon that has a light source that emits a light beam and a plurality of reflecting surfaces, that deflects the light beam emitted from the light source by reflecting it on the reflecting surfaces while rotating, and scanning the light beam on the surface of the photoreceptor. A motor comprising a mirror, a rotor to which the polygon mirror is attached, and a magnet fixed to the rotor, for rotating the polygon mirror by rotating the rotor; a Hall element for outputting a first signal corresponding to the change in the magnetic flux; and a light receiving element for receiving the light beams deflected by the plurality of reflecting surfaces and outputting a second signal; a light source and a control section for controlling the motor, wherein the control section operates based on the first signal until the cycle of the first signal falls within a first range after the rotor starts rotating. controlling the rotation speed of the rotor, and switching control of the light source from the off state to the on state for causing the light beam to enter the light receiving element when the cycle of the first signal is within the first range; is periodically executed at a first period and the rotation speed of the rotor is controlled based on the second signal, and when the period of the second signal falls within a second range, light is emitted to the light receiving element. The switching control of the light source for making the beam incident is periodically executed in a second period longer than the first period, and the rotation speed of the rotor is controlled based on the second signal. and

According to the present invention, in an image forming apparatus, it is possible to control the rotation speed of a polygon motor with high accuracy while suppressing the shortening of the life of the light source of the exposure unit.

1 is a schematic cross-sectional view of an image forming apparatus; FIG. 1 is a perspective view of an optical scanning device; FIG. 3 is a circuit diagram showing the configuration of an LD and a laser driver; FIG. 3 is a block diagram showing the configuration of a motor control circuit; FIG. 4 is a flowchart of a startup sequence; 4 is a graph showing the rotation speed of the polygon motor in each mode; 4 is a timing chart showing LD lighting control during one cycle of a BD signal. 4 is a timing chart showing LD lighting control during one cycle of a BD signal. 4 is a timing chart showing LD lighting control during one cycle of a BD signal.

<Image forming apparatus>
Hereinafter, first, the overall configuration of an image forming apparatus according to an embodiment of the present invention will be described together with the operation during image formation with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative positions, etc. of the components described below are not intended to limit the scope of the present invention only to them, unless otherwise specified.

The image forming apparatus A is an intermediate tandem image forming apparatus that forms an image by transferring four color toners of yellow Y, magenta M, cyan C, and black K onto an intermediate transfer belt and then transferring the image onto a sheet. be. In the following description, although the subscripts Y, M, C, and K are attached to the members using the toners of the respective colors, the configurations and operations of the members are different except that the colors of the toners used are different. Since they are substantially the same, suffixes are omitted as appropriate unless they need to be distinguished.

FIG. 1 is a schematic cross-sectional view of the image forming apparatus A. As shown in FIG. As shown in FIG. 1, the image forming apparatus A includes an image forming section 100 that forms a toner image on a sheet S. As shown in FIG. The image forming section 100 includes photosensitive drums 1 (1Y, 1M, 1C, 1K) as photosensitive bodies, charging devices 2 (2Y, 2M, 2C, 2K), and developing devices 4 (4Y, 4M, 4C, 4K). . The image forming unit 100 also includes primary transfer devices 5 (5Y, 5M, 5C, 5K), optical scanning devices 60 (60Y, 60M, 60C, 60K), an intermediate transfer belt 6, a secondary transfer roller 7, and a secondary transfer facing device. A roller 8 is provided.

When the image forming apparatus A forms an image, first, an image forming job signal is input to the controller 50 shown in FIG. As a result, the sheet S stored in the sheet cassette 10 is sent to the registration roller 15 by the pickup roller 11 , the feeding roller 12 , and the conveying rollers 13 and 14 . After that, the registration rollers 15 convey the sheet S to the secondary transfer portion formed by the secondary transfer roller 7 and the secondary transfer counter roller 8 at a predetermined timing.

On the other hand, in the image forming section 100, first, the surface of the photosensitive drum 1Y is charged by the charging device 2Y. After that, the optical scanning device 60 irradiates the surface of the photosensitive drum 1Y with a laser beam LY in accordance with image data transmitted from an image reading unit (not shown) or an external device (not shown) to cause the surface of the photosensitive drum 1Y to stand still. Forms an electrostatic latent image. Thereafter, a yellow toner is attached to the electrostatic latent image formed on the surface of the photosensitive drum 1Y by the developing device 4Y to form a yellow toner image on the surface of the photosensitive drum 1Y. The toner image formed on the surface of the photosensitive drum 1Y is primarily transferred onto the intermediate transfer belt 6 by applying a primary transfer bias to the primary transfer device 5Y.

By a similar process, the photosensitive drums 1M, 1C, and 1K are also irradiated with laser beams LM, LC, and LK from the optical scanning devices 60M, 60C, and 60K according to the image data of each color, and electrostatic latent images are formed. . Then, toner images of magenta, cyan, and black are formed by developing devices 4M, 4C, and 4K. After that, by applying a primary transfer bias to the primary transfer devices 5M, 5C, and 5K, these toner images are superimposedly transferred onto the yellow toner image on the intermediate transfer belt 6 . As a result, a full-color toner image corresponding to the image data is formed on the surface of the intermediate transfer belt 6 .

After that, the intermediate transfer belt 6 receives a driving force from the secondary transfer opposing roller 8 and rotates, so that the full-color toner image is sent to the secondary transfer portion. Then, the full-color toner image on the intermediate transfer belt 6 is transferred to the sheet S by applying a secondary transfer bias to the secondary transfer roller 7 in the secondary transfer portion.

The sheet S onto which the toner image has been transferred is conveyed to the fixing device 16 and subjected to heat and pressure processing in the fixing device 16 , whereby the toner image on the sheet S is fixed to the sheet S. FIG. After that, the sheet S on which the toner image is fixed is discharged to the discharge tray 18 by the discharge rollers 17 .

<Optical scanning device>
Next, the configuration of the optical scanning device 60 (exposure unit) will be described.

FIG. 2 is a schematic diagram of the optical scanning device 60. As shown in FIG. Since the optical scanning devices 60Y to 60K all have the same configuration, the suffixes Y, M, C, and K are omitted in the following description. As shown in FIG. 2, the optical scanning device 60 includes a multi-beam LD 61 (light source) capable of simultaneously emitting a total of 16 laser beams (light beams), and collimating the laser beams emitted from the LD 61. It has a collimator lens 62 that The optical scanning device 60 also includes a polygon mirror 63 having a plurality of reflecting surfaces 63a and a polygon motor 64 (motor) that drives the polygon mirror 63 to rotate.

The optical scanning device 60 also includes an fθ lens 65 that forms an image of the laser beam deflected by the polygon mirror 63 on the surface of the photosensitive drum 1, and a BD signal (second signal) that receives the laser beam deflected by the polygon mirror 63. ) is provided. As will be described later, the BD signal is a signal that serves as a reference for the timing of writing an image in the main scanning direction onto the photosensitive drum 1 and is also a signal that is used to control the rotation speed of the polygon motor 64 .

The optical scanning device 60 also includes a motor control circuit 53 that drives the polygon motor 64 and a laser driver 52 that drives the LD 61 . Also provided is a FIFO memory 51 that stores an image signal and outputs the image signal to a laser driver 52 at a timing instructed by the controller 50 . The FIFO memory 51, laser driver 52, and motor control circuit 53 are controlled by a controller 50 (control section). That is, the controller 50 controls the polygon motor 64 by controlling the motor control circuit 53 , and controls the LD 61 by controlling the FIFO memory 51 and the laser driver 52 . Although the controller 50 is mounted on a control board (not shown) outside the optical scanning device 60 in this embodiment, it may be mounted on a board inside the optical scanning device 60 .

Next, basic operations of the optical scanning device 60 will be described. First, when exposure processing is started, 16 laser beams are emitted from the LD 61 . Next, the laser light emitted from the LD 61 is collimated by the collimator lens 62 and then enters the reflecting surface 63 a of the polygon mirror 63 . The laser beam incident on the reflecting surface 63a of the polygon mirror 63 is deflected while being reflected by the reflecting surface 63a as the polygon mirror 63 rotates.

Next, the laser light deflected by the reflecting surface 63 a of the polygon mirror 63 passes through the fθ lens 65 and then enters the BD sensor 66 . The BD sensor 66 outputs a BD signal upon receiving the laser light. The controller 50 controls the lighting of the LD 61 via the laser driver 52 by synchronizing the writing position of the image in the main scanning direction of each line based on the BD signal output from the BD sensor 66 . Specifically, after a predetermined time has passed since the BD signal was input, the controller 50 controls the FIFO memory 51 and the laser to form an electrostatic latent image on the surface of the photosensitive drum 1 according to the image signal. The LD 61 is lit (lights emitted) through the control of the driver 52 . As a result, the surface of the photosensitive drum 1 is irradiated with laser light according to the image signal, and an electrostatic latent image is formed on the surface of the photosensitive drum 1 .

In this manner, the optical scanning device 60 scans the surface of the photosensitive drum 1 with laser light to form an electrostatic latent image corresponding to image data. That is, when the polygon mirror 63 rotates to change the deflection angle of the laser beam, the spot image formed by the laser beam is scanned in the main scanning direction. Further, as the photosensitive drum 1 rotates, the spot image formed by the laser beam relatively moves in the sub-scanning direction.

A density sensor 67 arranged around the photosensitive drum 1 detects the toner density of the toner image formed on the surface of the photosensitive drum 1 and outputs the detection result to the controller 50 as a signal. The controller 50 calculates the sensitivity of the photosensitive drum 1 based on the toner density detected by the density sensor 67, and outputs reference voltages Vcont1 to Vcont16 to the laser driver 52 so as to obtain an appropriate amount of exposure.

<Laser driver>
Next, the configuration of the laser driver 52 will be described.

FIG. 3 is a circuit diagram showing the configuration of the LD 61 and laser driver 52. As shown in FIG. As shown in FIG. 3, the LD 61 includes a total of 16 laser diodes, LDs 61a to 61p, in a package. The laser driver 52 has a total of 16 laser drivers 52a-52p in the package. The laser drivers 52a to 52p all have the same configuration, and the signals input from the controller 50 and the FIFO memory 51 are different. Therefore, FIG. 3 shows the configuration of the laser driver 52a and omits the configurations of the laser drivers 52b to 52p.

Cathode terminals of the LDs 61a to 61p are grounded as a common terminal. Anode terminals of the LDs 61a-61p are connected to laser drivers 52a-52p, respectively, and drive currents are supplied from the laser drivers 52a-52p, respectively.

The laser drivers 52a-52p each include a resistor 42b, an error amplifier 43, an analog switch 44, a capacitor 45, a constant current source 46, PNP transistors 47a and 47b, an inverter 48 and a buffer 49.

A photodiode 41 is provided around the LDs 61a to 61p to detect the amount of light emitted from the LDs 61a to 61p. The photodiode 41 is arranged at a position capable of receiving at least part of the laser light emitted from each of the LDs 61a to 61p. The anode terminal of the photodiode 41 is grounded. A cathode terminal of the photodiode 41 is connected to a power supply voltage Vcc through a resistor 42a, and the cathode terminal becomes a monitor output when the power supply voltage Vcc is applied. In this embodiment, the power supply voltage Vcc is a DC voltage of 24V.

Also, the cathode terminal of the photodiode 41 is connected to the +input terminal of the error amplifier 43 of each of the laser drivers 52a to 52p. Reference voltages Vcont1 to Vcont16 output by the controller 50 are applied to the − input terminal of the error amplifier 43 . An output terminal of the error amplifier 43 is connected to the analog switch 44 . Control signals cont1 to cont16 are input from the controller 50 to control terminals for controlling the operation of the analog switch 44 .

The output of analog switch 44 is connected to one end of capacitor 45 . The output of the analog switch 44 is input to the constant current source 46 as a control signal for the constant current source 46 . The other end of capacitor 45 is grounded. The constant current source 46 outputs a current corresponding to the applied voltage to the emitter terminals of the PNP transistors 47a and 47b.

The collector terminal of the PNP transistor 47a serves as the output of the laser driver 52a and is connected to the anode terminal of the LD 61a. Image signals data1 to data16 are input from the FIFO memory 51 via the inverter 48 to the base terminal of the PNP transistor 47a.

A collector terminal of the PNP transistor 47b is connected to the resistor 42b. The other end of resistor 42b is grounded. Image signals data1 to data16 are input from the FIFO memory 51 via the buffer 49 to the base terminal of the PNP transistor 47b.

Next, an APC (:Auto Power Control) mode for adjusting the light amount of the LDs 61a to 61p will be described. Although the APC mode of the LD 61a will be described below, the same applies to the APC modes of the LDs 61b to 61p. Note that in the APC mode, the LDs 61a to 61p are not performed simultaneously, but sequentially.

When the APC mode of the LD 61a is started, the controller 50 outputs the control signal cont1 at high level and causes the FIFO memory 51 to output the image signal data1 at high level. At this time, since the controller 50 does not perform the APC mode of the LDs 61b to 61p, it outputs the control signals cont2 to cont16 at low level and causes the FIFO memory 51 to output the image signals data2 to data16 at low level.

When the image signal data1 is output high, the output of the inverter 48 becomes low, the PNP transistor 47a is turned on, and the PNP transistor 47b is turned off. When the PNP transistor 47a is turned on, the current supplied from the constant current source 46 lights the LD 61a.

As the light intensity of the LD 61a increases, the output current of the photodiode 41 increases and the voltage input to the error amplifier 43 decreases. The output of the photodiode 41 is compared with the reference voltage Vcont1 by the error amplifier 43, and the output voltage of the error amplifier 43 decreases. When the output voltage of the error amplifier 43 drops, the output current of the constant current source 46 drops and the light intensity of the LD 61a drops. By configuring the negative feedback circuit in this way, the light amount of the LD 61a is adjusted so that the output voltage of the photodiode 41 and the reference voltage Vcont1 are the same.

Next, operations of the LD 61 and the laser driver 52 during image formation will be described. In the following description, the operations of the LD 61a and the laser driver 52 during image formation will be described, but the operations of the LDs 61b to 61p during image formation are the same.

At the time of image formation, the controller 50 first outputs the control signal cont1 at low to cause the FIFO memory 51 to output the image signal data1. Since the control signal cont1 is low, the analog switch 44 is turned off and the voltage regulated in APC mode is held by the capacitor 45 . Since the voltage of the capacitor 45 is applied to the control terminal of the constant current source 46, the output of the constant current source 46 has the same current value as in the APC mode.

When the image signal data1 output from the FIFO memory 51 is high, the PNP transistor 47a is turned on and the LD 61a is lit. On the other hand, when the image signal data1 is low, the PNP transistor 47a is turned off and the LD 61a is extinguished. As a result, in the amount of light adjusted in the APC mode, lighting control of the LD 61a is performed based on the image signal data1, and exposure processing according to the image signal is performed.

When the image signal data1 is high, the PNP transistor 47b is turned off. When the image signal data1 is low, the PNP transistor 47b is turned on and current is supplied from the constant current source 46 to the resistor 42b. As a result, the current supplied from the constant current source 46 becomes constant without being affected by the on/off state of the image signal data1. High-speed driving of a constant current circuit, especially operation at several tens of MHz during image formation is generally difficult. However, by adopting such a configuration, the PNP transistors 47a and 47b are operated at high speed, and the constant current source 46 does not require high speed operation, thereby facilitating image formation.

<Motor control circuit>
Next, the configuration of the motor control circuit 53 will be described.

FIG. 4 is a block diagram showing the configuration of the motor control circuit 53. As shown in FIG. As shown in FIG. 4, the motor control circuit 53 has a switching circuit 94, a phase control circuit 91, speed control circuits 92 and 93, a control circuit 95, and a bridge circuit 96. The controller 50 controls the polygon motor 64 by controlling the switching circuit 94 , the phase control circuit 91 and the speed control circuits 92 and 93 .

The polygon motor 64 is a three-phase four-pole brushless DC motor. The polygon motor 64 has a rotor 64a, three field windings 64b1-64b3, and three Hall elements 64c1-64c3. A magnet 64a1 having two N poles and two S poles alternately arranged is fixed to the rotor 64a. A polygon mirror 63 is attached to the upper portion of the rotor 64a.

The rotor 64a is rotated by a rotating magnetic field generated by currents flowing through the field windings 64b1 to 64b3. When the rotor 64a rotates, the Hall elements 64c1 to 64c3 detect changes in the magnetic flux around the rotor 64a, and output the detection results to the control circuit 95 as FG signals. The control circuit 95 detects the magnetic pole position of the magnet 64a1 of the rotor 64a based on the FG signals output from the Hall elements 64c1 to 64c3, and supplies a drive signal to the bridge circuit 96 to generate a rotating magnetic field corresponding to the magnetic pole position. Output.

A power supply voltage Vcc is supplied to the bridge circuit 96 . The bridge circuit 96 supplies the field windings 64b1 to 64b3 with a voltage corresponding to the drive signal input from the control circuit 95. FIG. As a result, a current flows through the field windings 64b1 to 64b3, the rotor 64a is rotationally driven, and the polygon mirror 63 arranged above the rotor 64a is integrally rotationally driven with the rotor 64a.

The FG signal (first signal) output from the Hall element 64c1 is also input to the speed control circuit 93. FIG. The cycle of this FG signal is proportional to the rotation speed of the polygon motor 64 (rotor 64a). A reference clock signal having a period corresponding to the target rotation speed of the polygon motor 64 is input to the speed control circuit 93 from the controller 50 . The speed control circuit 93 generates an acceleration signal or a deceleration signal (hereinafter referred to as “acceleration/deceleration signal”) so that the period of the FG signal approaches the period of the reference clock signal, and outputs it to the switching circuit 94 . Note that the controller 50 outputs a start signal to the speed control circuit 93 when starting the rotation of the polygon motor 64 .

A BD signal output from the BD sensor 66 is also input to the controller 50 , the speed control circuit 92 and the phase control circuit 91 . The cycle of the BD signal is proportional to the rotation speed of the polygon motor 64. FIG. A reference clock signal having a period corresponding to the target rotational speed of the polygon motor 64 is input to the speed control circuit 92 from the controller 50 . The speed control circuit 92 generates an acceleration/deceleration signal so that the cycle of the BD signal approaches the cycle of the reference clock signal, and outputs the acceleration/deceleration signal to the switching circuit 94 .

The switching circuit 94 switches either the acceleration/deceleration signal input from the speed control circuit 93 or the acceleration/deceleration signal input from the speed control circuit 92 to the control circuit 95 according to the switching signal output from the controller 50 . output to The control circuit 95 outputs a driving signal corresponding to the acceleration/deceleration signal output from the switching circuit 94 to the bridge circuit 96 to control the voltage supplied from the bridge circuit 96 to the field windings 64b1 to 64b3. Specifically, the control circuit 95 outputs a drive signal for increasing the voltage supplied to the field windings 64b1 to 64b3 when an acceleration signal is input, and outputs a field winding signal when a deceleration signal is input. It outputs a drive signal for reducing the voltage supplied to the magnetic windings 64b1-64b3.

By controlling the voltage supplied to the polygon motor 64 so that the cycle of the FG signal or the BD signal corresponds to the target rotation speed, the rotation speed of the polygon motor 64 can be adjusted to match the target rotation speed. can be controlled to be Here, the speed control circuit 93 outputs the FG speed lock signal to the controller when the cycle of the FG signal falls within a predetermined range (within a first range) centered on the cycle corresponding to the target rotational speed. Output to 50. The speed control circuit 92 outputs a BD lock signal to the controller 50 when the cycle of the BD signal falls within a predetermined range (within a second range) centering on the cycle corresponding to the target rotational speed. do. The cycle range of the BD signal in which the speed control circuit 92 outputs the BD lock signal is narrower than the cycle range of the FG signal in which the speed control circuit 93 outputs the FG lock signal. This means that the rotation speed of the polygon motor 64 is more stable near the target rotation speed when the BD lock signal is output than when the FG lock signal is output.

The controller 50 also outputs a reference clock signal to the phase control circuit 91 in order to synchronize the image writing positions on the photosensitive drums 1 of each color. The phase control circuit 91 compares the phases of the reference clock signal and the BD signal, generates an acceleration/deceleration signal so that the phases of the two are the same, and outputs the acceleration/deceleration signal to the switching circuit 94 . The phase control circuit 91 outputs a phase lock signal to the controller 50 when the phase difference between the reference clock signal and the BD signal is within a predetermined range centered on when the phases of both are the same.

<Startup sequence>
Next, a start-up sequence executed to start the optical scanning device 60 at the start of the image forming operation will be described with reference to the flowchart shown in FIG. When the controller 50 receives the image forming job signal, it starts the activation sequence.

As shown in FIG. 5, the controller 50 first determines whether the input voltage applied from the power supply voltage Vcc and input to the controller 50 after being divided by the voltage dividing resistors 97 and 98 shown in FIG. 4 is less than the threshold. (S1). When the controller 50 determines that the input voltage is less than the threshold, the controller 50 terminates the startup sequence as an abnormality in the power supply voltage Vcc.

When the controller 50 determines that the input voltage is equal to or higher than the threshold value, the controller 50 outputs a start signal to the speed control circuit 93 and causes the switching circuit 94 to perform switching for outputting the acceleration/deceleration signal output from the speed control circuit 93 to the control circuit 95 . A signal is output (S2, S3). As a result, the switching circuit 94 outputs an acceleration/deceleration signal generated based on the FG signal from the speed control circuit 93 to the control circuit 95, and the rotational speed of the polygon motor 64 is controlled based on the FG signal. Hereinafter, the state in which the controller 50 controls the rotation speed of the polygon motor 64 based on the FG signal is referred to as "mode 1".

The controller 50 continues Mode 1 until the rotation speed of the polygon motor 64 approaches the target rotation speed and the speed control circuit 93 outputs the FG lock signal. Upon receiving the FG lock signal from the speed control circuit 93, the controller 50 instructs the laser driver 52 to turn on the LD 61a (S4, S5). As a result, a laser beam is emitted from the LD 61a, the laser beam is incident on the BD sensor 66, and the BD signal is output from the BD sensor 66. FIG.

Next, upon receiving the BD signal, the controller 50 outputs a switching signal to the switching circuit 94 to cause the control circuit 95 to output the acceleration/deceleration signal output from the speed control circuit 92 (S6, S7). As a result, the switching circuit 94 outputs an acceleration/deceleration signal generated based on the BD signal from the speed control circuit 92 to the control circuit 95, and the rotational speed of the polygon motor 64 is controlled based on the BD signal. Hereinafter, the state in which the controller 50 controls the rotation speed of the polygon motor 64 based on the BD signal before the BD lock signal is received is referred to as "mode 2".

The controller 50 continues Mode 2 until the rotation speed of the polygon motor 64 stabilizes at the target rotation speed and the speed control circuit 92 outputs the BD lock signal. Upon receiving the BD lock signal from the speed control circuit 92, the controller 50 determines whether or not the phase lock signal has been received from the phase control circuit 91 (S8, S9). A state in which the controller 50 controls the rotation speed of the polygon motor 64 based on the BD signal after receiving the BD lock signal and before receiving the phase lock signal is hereinafter referred to as "mode 3".

Next, when the phase of the BD signal approaches the phase of the reference clock signal, the controller 50 receives the phase lock signal from the phase control circuit 91 (S9). At this time, the rotation speed of the polygon motor 64 is stabilized at the target speed, and the writing positions on the photosensitive drums 1 of the respective colors are synchronized, and the image forming operation can be executed. In other words, the optical scanning device 60 is activated, so the controller 50 terminates the activation sequence.

The controller 50 controls the rotation speed of the polygon motor 64 based on the BD signal until the image forming operation is completed after the startup sequence is completed. Hereinafter, the state in which the controller 50 receives the BD lock signal and controls the rotation speed of the polygon motor 64 based on the BD signal after receiving the phase lock signal is referred to as "mode 4". If the rotational speed of the polygon motor 64 greatly deviates from the target rotational speed for some reason during the execution of mode 4, the controller 50 executes modes 2 and 3 again, and then returns to mode 4.

FIG. 6 is a graph showing the rotational speed of the polygon motor 64 in modes 1-4. As shown in FIG. 6, in mode 1, the polygon motor 64 starts rotating, and the controller 50 controls the rotational speed based on the FG signal. As a result, the rotation speed of the polygon motor 64 increases toward the target rotation speed of 32882 rpm. When the rotation speed of the polygon motor 64 reaches near the target rotation speed, the controller 50 receives the FG lock signal and shifts to mode 2. FIG.

Next, at the start of mode 2, the rotation speed of the polygon motor 64 becomes faster than the target rotation speed due to overshoot. Thereafter, when the controller 50 controls the speed of the polygon motor 64 based on the BD signal, the rotation speed of the polygon motor 64 stabilizes at the target rotation speed. At this timing, the controller 50 receives the BD lock signal and shifts to mode 3.

In mode 3, the rotation speed of the polygon motor 64 is stable at the target rotation speed, so the rotation speed of the polygon motor 64 does not change. The controller 50 transitions to mode 4 upon receipt of the phase lock signal. Even in mode 4, the rotation speed of the polygon motor 64 is stable at the target rotation speed, so the rotation speed of the polygon motor 64 does not change. In mode 4, the image forming operation is performed while the polygon motor 64 is stably rotating at the target rotational speed.

<LD lighting control>
Next, lighting control of the LD 61 in modes 2 and 4 will be described.

FIG. 7 is a timing chart showing lighting control of the LD 61 during one cycle of the BD signal in mode 2. FIG. As shown in FIG. 7, when the mode 2 is started, the controller 50 first outputs the control signal cont1 signal at high level, causes the FIFO memory 51 to output the image signal data1 at high level, and turns on the LD 61a. Next, when the BD sensor 66 receives the laser light emitted from the LD 61a, the BD signal is output and becomes low. The timing at which the BD signal becomes low is taken as a reference (0 μs).

Next, at 1 μs, the controller 50 outputs the control signal cont1 at low level, causes the FIFO memory 51 to output the image signal data1 at low level, and turns off the LD 61a. After that, the controller 50 controls the FIFO memory 51 so that the image signals data1 to data16 are output low until 260 μs. As a result, the LDs 61a-61p are extinguished from 1 μs to 260 μs.

Next, at 260 μs, the controller 50 outputs the control signal cont2 at high level, causes the FIFO memory 51 to output the image signal data2 at high level, and performs APC control of the LD 61b. Thereafter, at 264 μs, the controller 50 outputs the image signal data2 at low level, causes the FIFO memory 51 to output the image signal data2 at low level, and turns off the LD 61b. At the same time, the controller 50 outputs the control signal cont3 at high level, causes the FIFO memory 51 to output the image signal data3 at high level, and performs APC control of the LD 61c. The controller 50 repeats the same operation until 308 μs to sequentially perform APC control of the LDs 61b to 61p.

Next, at 335 μs, the controller 50 outputs the control signal cont1 at a high level so that the laser light deflected by the next reflecting surface 63 a of the polygon mirror 63 is incident on the BD sensor 66 , and the image is output from the FIFO memory 51 . The signal data1 is output at high. As a result, the LD 61a is switched from the off state to the on state. At this time, APC control of the LD 61a is performed. After that, at 365 μs, the BD sensor 66 receives the laser light and outputs a low BD signal. In this manner, lighting control of the LD 61 during one cycle of the BD signal is performed.

Here, mode 2 is the stage before the controller 50 receives the BD lock signal and the stage before the rotation speed of the polygon motor 64 stabilizes at the target rotation speed. Therefore, the controller 50 quickly switches the LD 61a for causing the laser light to enter the BD sensor 66 from the off state to the on state so that the BD sensor 66 can stably receive the laser light. Specifically, while the BD sensor 66 receives the laser beam at 365 μs, the LD 61 a is switched from the off state to the on state at 335 μs, which is 30 μs earlier.

In this way, if the control of early switching of the LD 61a from the off state to the on state for causing the laser light to enter the BD sensor 66 is continued even during image formation, the LD 61a during one cycle of the BD signal during image formation lighting control is the control shown in FIG. That is, as shown in FIG. 8, the controller 50 turns on or off the LDs 61a to 61p in order to irradiate the photosensitive drum 1 with laser light according to the image data in the period from 20 μs to 240 μs. Specifically, by outputting image signals data1 to data16 from the FIFO memory 51 to the laser driver 52, the LD61a to LD61p are turned on or off according to the image signals.

However, the receipt of the BD lock signal by the controller 50 means that the rotation speed of the polygon motor 64 has stabilized at the target rotation speed. Therefore, after receiving the BD signal, it is not necessary to turn on the LD 61a early in order to make the laser beam stably enter the BD sensor 66 as in the control shown in FIG. , the lighting time of the LD 61a increases, leading to a shortened life of the LD 61. Therefore, as will be described below, in the lighting control of the LD 61 in mode 4, the timing of switching control from the off state to the on state of the LD 61a for causing the laser light to enter the BD sensor 66 is shown in FIGS. Delay the control timing shown.

FIG. 9 is a timing chart showing lighting control of the LD 61 during one cycle of the BD signal in mode 4. FIG. As shown in FIG. 9, the lighting control of the LD 61 in mode 4 and the lighting control of the LD 61 shown in FIG. 8 are the same between 0 μm and 308 μs. In mode 4, the controller 50 outputs the control signal cont1 at HIGH at 360 μs, causing the FIFO memory 51 to output the image signal data1 at HIGH. As a result, the LD 61 a is switched from the off state to the on state so that the laser beam deflected by the next reflecting surface 63 a of the polygon mirror 63 is incident on the BD sensor 66 .

That is, in mode 4 in which the rotation speed of the polygon motor 64 is stable at a target rotation speed, the laser beam is made incident on the BD sensor 66 in contrast to mode 2 in which the rotation speed of the polygon motor 64 is relatively unstable. delay the lighting timing of the LD 61a. In other words, when the controller 50 receives the phase lock signal, the controller 50 controls switching from the off state to the on state of the LD 61a for causing the laser light to enter the BD sensor 66 in the cycle before receiving the BD lock signal ( It is periodically executed in a cycle (second cycle) longer than the first cycle). Note that the light-off state of the LD 61a referred to here is not limited to a state in which the LD 61a is completely turned off. The state in which is lit is also included.

By delaying the switching timing of the LD 61a from the off state to the on state for causing the laser light to enter the BD sensor 66 in this way, the lighting time of the LD 61a can be shortened, and the shortening of the life of the LD 61 can be suppressed. . Therefore, according to the configuration of the present embodiment, it is possible to suppress the shortening of the life of the LD 61 while controlling the rotation speed of the polygon motor 64 with high accuracy using the BD signal.

In this embodiment, after the controller 50 receives the phase lock signal, the configuration for lengthening the cycle of switching control from the off state to the on state of the LD 61a for causing the laser light to enter the BD sensor 66 has been described. , the present invention is not limited thereto. That is, as described above, when the controller 50 receives the BD lock signal, the rotation speed of the polygon motor 64 is stable at the target rotation speed. For this reason, the controller 50 may be configured to lengthen the switching control period of the LD 61a for causing the laser light to enter the BD sensor 66 with the reception of the BD lock signal as a trigger. That is, when the controller 50 receives the BD lock signal, the switching control of the LD 61a for causing the laser light to enter the BD sensor 66 from the off state to the on state is performed in a cycle longer than the cycle before receiving the BD lock signal. The same effect as described above can be obtained even with a configuration in which the process is executed periodically.

In the present embodiment, the configuration using the multi-beam LD 61 capable of emitting a plurality of laser beams as the light source of the optical scanning device 60 has been described, but the present invention is not limited to this. That is, as long as the light source of the optical scanning device 60 can emit at least one light beam, the same effects as described above can be obtained.

In the present embodiment, the image forming apparatus A is provided with a plurality of photosensitive drums 1 and optical scanning devices 60 and is capable of forming a full-color image. However, the present invention is not limited to this. That is, the present invention can also be applied to a monochrome image forming apparatus having one photosensitive drum 1 and one optical scanning device 60 .

1... Photosensitive drum (photosensitive body)
50... Controller (control unit)
60... Optical scanning device (exposure unit)
61... LD (light source)
63... Polygon mirror 63a... Reflective surface 64... Polygon motor (motor)
64a Rotor 64a1 Magnet 64c1 to 64c3 Hall element 66 BD sensor (light receiving element)
A... Image forming apparatus

Claims (5)

a photoreceptor;
An exposure unit that forms an electrostatic latent image by irradiating the surface of the photoreceptor with a light beam,
a light source that emits a light beam;
a polygon mirror having a plurality of reflective surfaces, which deflects a light beam emitted from the light source by reflecting it on the reflective surfaces while rotating, and scanning the light beam on the surface of the photoreceptor;
a motor comprising a rotor to which the polygon mirror is attached and a magnet fixed to the rotor, and rotating the polygon mirror by rotating the rotor;
a Hall element that detects a change in magnetic flux accompanying rotation of the rotor and outputs a first signal corresponding to the change in magnetic flux;
a light-receiving element that receives the light beams respectively deflected by the plurality of reflecting surfaces and outputs a second signal;
an exposure unit having
a control unit that controls the light source and the motor;
with
The control unit controls the rotation speed of the rotor based on the first signal until the period of the first signal falls within a first range after the rotor starts rotating, and When the period falls within the first range, switching control of the light source from the off state to the on state for causing the light beam to enter the light receiving element is periodically executed at the first period, and at the same time as the first period. The rotation speed of the rotor is controlled based on the two signals, and when the period of the second signal falls within the second range, the switching control of the light source for causing the light beam to enter the light receiving element is performed. An image forming apparatus, characterized in that the image forming apparatus periodically executes the process in a second period longer than the first period and controls the rotation speed of the rotor based on the second signal. When the period of the second signal falls within the second range and the phase of the second signal reaches a predetermined phase, the control unit sets the period for executing the switching control to the first period. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus switches from the cycle to the second cycle. 3. The image forming apparatus according to claim 1, wherein the control unit executes a mode for adjusting the amount of light of the light source when the light source is turned on by the switching control. 4. The apparatus according to any one of claims 1 to 3, wherein the control section controls timing for turning on the light source to form an electrostatic latent image on the surface of the photoreceptor based on the second signal. The image forming apparatus according to any one of items 1 to 3. 5. The image according to any one of claims 1 to 4, wherein the light source is capable of emitting a plurality of laser beams simultaneously, and part of the plurality of laser beams are received by the light receiving element. forming device.

Images