JP2017019119A - Image forming device and control method for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device in a simple configuration capable of suppressing image failure.SOLUTION: An image forming device comprises: a photoreceptor; one or more light sources; deflection means for deflecting light emitted by the light source; detection means for detecting the light deflected to a predetermined direction by the deflection means and outputting a signal indicating detection timing of the light; and switching means for switching intensity of light emitted by the light source. The switching means makes a light intensity in a time period including time when the detection means detects the light, in a time period when the light deflected by the deflection means does not expose the photoreceptor, greater than that in a time period when the light deflected by the deflection means exposes the photoreceptor.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer.

  In an electrophotographic image forming apparatus, an electrostatic latent image is formed on a photosensitive member by scanning and exposing the charged photosensitive member with light, and an image is formed by developing the electrostatic latent image with toner. doing. Specifically, the light from the light source is reflected by a rotating polygon mirror, and thereby the main scanning of the photoreceptor is performed. The photoreceptor is rotated so that the surface thereof moves in the sub-scanning direction orthogonal to the main scanning direction during image formation. An electrostatic latent image is formed on the photosensitive member by repeatedly performing main scanning while rotating the photosensitive member. The light reflected by the rotary polygon mirror in a predetermined direction is configured to enter the synchronization sensor. This synchronization sensor outputs a synchronization signal indicating the timing of receiving light (hereinafter referred to as synchronization timing). The image forming apparatus determines the writing timing of main scanning based on this synchronization signal, and performs APC (Auto Power Control) control of the light source.

  In recent years, the sensitivity of photoconductors has been increased, and the light intensity necessary for exposing the photoconductor has been decreasing. However, when the light emission intensity of the light source is reduced, the amount of light incident on the synchronization sensor is also reduced, and the synchronization sensor may not be able to detect the synchronization timing correctly. If the synchronization timing cannot be detected correctly, it may cause image defects. For this reason, in Patent Document 1, the reflectance of the region that reflects toward the synchronization sensor among the reflection surfaces of the rotary polygon mirror is made higher than the reflectance of the region that reflects toward the photoconductor, A configuration for increasing the intensity of incident light is disclosed.

JP-A-5-107488

  In the configuration of Patent Document 1, it is necessary to form a rotating polygon mirror using materials having different reflectances, which increases the processing cost of the rotating polygon mirror. In addition, irregular reflection occurs at the boundary of different reflectances, and the irregularly reflected light may expose the photoconductor to cause image defects.

  The present invention provides an image forming apparatus that suppresses image defects with a simple configuration and a method for controlling the image forming apparatus.

  According to one aspect of the present invention, an image forming apparatus detects a photoconductor, one or more light sources, deflection means for deflecting light emitted from the light sources, and light deflected in a predetermined direction by the deflection means. And detecting means for outputting a signal indicating the detection timing of the light, and switching means for switching the light intensity of the light emitted from the light source, wherein the switching means includes the light deflected by the deflecting means as the light The light intensity of a period including the time when the detection means detects light in the period when the photoconductor is not exposed is greater than the light intensity of the period when the light deflected by the deflecting means exposes the photoconductor. It is characterized by strengthening.

  According to the present invention, image defects can be suppressed with a simple configuration.

The figure which shows the exposure structure by one Embodiment. The figure which shows the control structure by one Embodiment. The timing chart of the light intensity setting by one Embodiment. 6 is a flowchart of image forming processing according to an embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In addition, the following embodiment is an illustration and does not limit this invention to the content of embodiment. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

  FIG. 1 shows an exposure configuration of the image forming apparatus of this embodiment. The exposure unit 9 includes a light source unit 107. The light source unit 107 includes one or more light sources, and light emitted from each light source is shaped into a parallel beam by the collimator lens 134 and shaped into a parallel beam. The light that has passed through the collimator lens 134 is reflected by the reflecting surface of the rotary polygon mirror 133. The light reflected by the rotary polygon mirror 133 passes through the fθ lens 132 and forms a light spot on the surface of the photoreceptor 8. By rotating the rotary polygon mirror 133, the light spot formed on the photoconductor 8 moves in the main scanning direction, whereby the surface of the photoconductor 8 is scanned and exposed. Thus, the rotating polygon mirror 133 functions as a deflecting unit that deflects the light emitted from the light source. The photosensitive member 8 is rotated in the direction of arrow R in the figure at the time of image formation, and an electrostatic latent image is formed on the photosensitive member 8 by repeatedly scanning with a light spot while rotating the photosensitive member 8. Is done. The fθ lens 132 is designed so that the light spot from the light source unit 107 moves at a constant speed on the surface of the photoreceptor 8.

  The reflection mirror 131 reflects light reflected in a predetermined direction upstream of the main scanning start position S of the photoconductor 8 toward the synchronization sensor 121. When receiving the light reflected by the reflection mirror 131, the synchronization sensor 121 outputs a synchronization signal (hereinafter referred to as a BD signal) indicating the detection timing. In this embodiment, the synchronization sensor 121 receives a light, sets the output signal to a low level, and outputs a high level signal at other times. The control drive circuit 130 uses the timing when the BD signal becomes low level as a synchronization timing, determines the main scanning write timing based on this synchronization timing, and adjusts the light emission intensity of each light source of the light source unit 107 (APC control). Etc. to drive the light source unit 107.

  FIG. 2 is a block diagram showing a control configuration according to the present embodiment. The laser driver 12 and the control unit 19 shown in FIG. 2 are provided in the control drive circuit 130 shown in FIG. The control unit 19 includes a CPU 27, a memory 28, a timing signal generator 25, and an image signal generator 26. The CPU 27 controls the operation of the timing signal generator 25 by reading and executing a program stored in the memory 28. The memory 28 is composed of, for example, a ROM and a RAM. The ROM stores, for example, a program for controlling various operations of the image forming apparatus. The RAM is used as a work area for executing various processes executed by the CPU 27 and a storage area for temporarily storing data such as variables and setting information.

  The timing signal generator 25 generates a CTRL signal that is a control signal indicating APC control and writing timing in the main scanning direction, and outputs the CTRL signal to the laser driver 12. The timing signal generator 25 outputs a rotation control signal to the motor driver 15 that drives the rotary polygon mirror 133. Further, the timing signal generator 25 notifies the laser driver 12 of the emission intensity of each light source of the light source unit 107 by controlling the duty of the light intensity reference voltage (PWM signal). That is, the timing signal generator 25 functions as a switching unit that switches the light emission intensity of the light source according to the light intensity reference voltage.

  The image signal generator 26 generates an image signal based on image data received from an external device (scanner device or computer) and outputs the image signal to the laser driver 12. The laser driver 12 modulates the drive current set by the APC control with an image signal and outputs the modulated drive current to each light source of the light source unit 107. Thereby, each light source emits light according to the gradation of the image.

  FIG. 3 is a timing chart regarding the light intensity setting. In the present embodiment, the light source unit 107 includes two light sources, for example, laser diodes, and scans the photosensitive member 8 with two light beams. Hereinafter, in order to distinguish between the two light sources, one is called a first light source and the other is called a second light source. As shown in FIG. 3, the timing at which the BD signal goes low from the timing at which scanning of one scanning line ends (the timing at which the line END signal in the drawing becomes low) (the timing at which light enters the synchronization sensor 121). ) Until the timing signal generator 25 outputs the PWM signal 1. The timing signal generator 25 outputs the PWM signal 2 in other periods. Here, the light intensity indicated by the PWM signal 1 is stronger than the light intensity indicated by the PWM signal 2. The light intensity indicated by the PWM signal 1 is set to a level at which the synchronization sensor 121 can detect the incident light without error, and the light intensity indicated by the PWM signal 2 is set to a level sufficient to expose the photoconductor 8. When the synchronization sensor 121 detects light, APC control is performed for each of the two light sources. After the APC control is finished, image formation is performed using the first light source and the second light source (VIDEO section in FIG. 3). When the scanning of one scanning line is completed, the timing signal generator 25 outputs the PWM signal 1. In FIG. 3, while the timing signal generator 25 outputs the PWM signal 1, only the first light source emits light to detect the BD signal. However, the light source used for detecting the synchronization timing can be switched every time a certain time or synchronization timing (timing when the BD signal goes low) is detected a certain number of times. Thereby, the lifetime of a light source can be lengthened. In this case, the control unit 19 functions as a selection unit that selects a light source used for detecting the BD signal. Note that the selection unit changes the light source used for detecting the BD signal, for example, every time a certain time or the number of times the BD signal is detected becomes a certain number.

  FIG. 4 is a flowchart of the image forming process according to the present embodiment. In the flowchart of FIG. 4, the light source used for detecting the synchronization timing is switched alternately. In the following description, “detecting a BD signal” means that the BD signal has become low, that is, the synchronization sensor 121 has detected light. The control unit 19 determines whether or not the number of times of detection of the BD signal in S11, more specifically, the number of times that the BD signal has become low, is an even number at the start of image formation. If the number is even, the control unit 19 determines in S12 that the next BD signal is detected by the light emitted from the first light source. On the other hand, if it is an odd number, the control unit 19 determines in S13 that the next BD signal is detected by the light emitted from the second light source. The controller 19 outputs the PWM signal 1 to the laser driver 12 in S14, causes the light source for detecting the BD signal to emit light in S15, and waits until the BD signal is detected. When the BD signal is detected, the control unit 19 outputs the PWM signal 2 to the laser driver 12 in S16, and makes the light intensity smaller than the light intensity for detecting the BD signal. Thereafter, the controller 19 performs APC control of both light sources in S17, and then performs scanning / exposure of one line in the main scanning direction in S18. After the scanning / exposure for one line is completed, the control unit 19 determines whether image formation is completed in S19. If not completed, the control unit 19 repeats the processing from S11, and if completed, ends the processing.

  As described above, the light intensity of the laser diode is increased after the scanning of one line of the photosensitive member 8 is completed until the BD signal is detected. This prevents erroneous detection of the synchronization timing and thus prevents image defects. Note that the period during which the light intensity is increased may be a period in which the exposure of the photoconductor 8 is not performed and includes a period in which light from the light source is incident on the synchronization sensor 121. That is, it is not necessary to increase the light intensity immediately after the scanning of one line of the photoconductor 8 is completed, and it is not necessary to decrease the light intensity immediately after detecting the BD signal. Further, when a plurality of light sources are provided, the light source used for detection of the synchronization timing is switched at a certain number of times or every certain time. With this configuration, the life of the light source can be extended.

[Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  8: Photoconductor, 107: Light source unit, 133: Rotating polygon mirror, 121: Sensor for synchronization, 25: Timing signal generator

Claims (6)

A photoreceptor,
One or more light sources;
Deflection means for deflecting light emitted by the light source;
Detecting means for detecting light deflected in a predetermined direction by the deflecting means and outputting a signal indicating a detection timing of the light;
Switching means for switching light intensity of light emitted from the light source;
With
The switching means deflects the light intensity of the period including the time when the detection means detects light in the period when the light deflected by the deflection means does not expose the photoconductor by the deflection means. An image forming apparatus characterized in that light is made stronger than light intensity during a period of exposing the photosensitive member.   The switching means, after completing the exposure of one scanning line in the photoconductor, includes a light intensity in a period including a time when the detecting means detects light, and a light intensity in a period in which the photoconductor is exposed. The image forming apparatus according to claim 1, wherein the image forming apparatus is stronger. Having multiple light sources,
The image forming apparatus according to claim 1, further comprising a selection unit that selects a light source that emits light to be detected by the detection unit.   The said selection means changes the light source which inject | emits the light made to detect by the said detection means, whenever the detection frequency of the light by the said detection means reaches a fixed number of times. Image forming apparatus.   5. The image forming apparatus according to claim 1, further comprising a determination unit that determines a timing for starting exposure of one scanning line on the photoconductor based on the detection timing. 6. . An image forming apparatus control method comprising:
Deflecting the light emitted by the light source by the deflecting means;
A detecting step in which the detecting means detects light deflected in a predetermined direction by the deflecting means;
Exposing the photoreceptor with light deflected by the deflecting means, and
The light intensity of a period including the time when the light deflected by the deflecting means does not expose the photoconductor and including the time when the detecting means detects the light, and the light deflected by the deflecting means is the photoconductor. The control method is characterized in that the intensity of light is made stronger than the light intensity during the exposure period.

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