JP5713820B2 - Exposure apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an exposure apparatus and an image forming apparatus.

  A laser scanning device scans a surface to be scanned with a laser beam emitted from a semiconductor laser using a scanning optical system. The amount of laser light incident on the surface to be scanned varies depending on the scanning position due to the characteristics of the optical system. Therefore, in order to make the light quantity of the laser light incident on the scanning target surface constant in the scanning direction, for example, the emitted light quantity of the semiconductor laser is corrected with a correction coefficient corresponding to the scanning position (see, for example, Patent Document 1).

JP 11-291548 A

  The apparatus as described above is incorporated in an image forming apparatus such as a laser printer, and is used to form an electrostatic latent image on a photosensitive drum.

  Therefore, a position detection sensor may be provided to obtain a synchronization signal in the main scanning direction. In that case, the position detection sensor is also scanned with laser light, and a synchronization signal is obtained from the output of the position detection sensor. An automatic output control (APC: Automatic Power Control) circuit may be provided for automatic control of the reference light quantity of the light source.

  In those cases, in each scan, a section for obtaining a synchronization signal by the position detection sensor (hereinafter referred to as a synchronization detection section) and / or a section for adjusting the light source light amount by the APC circuit (hereinafter referred to as an APC control section) is set. .

  In addition, at the end of the image area (section for forming an electrostatic latent image), the angle formed by the optical axis of the optical system and the traveling direction of the light beam increases. As a result, the amount of light attenuation increases, and the amount of light incident on an object such as a photosensitive drum decreases. In order to compensate for the light amount attenuation in the optical system and make the light amount incident on the object constant in the scanning direction, the light source light amount is corrected to be large at the end of the image area.

  Therefore, in each scan, when the image area is set after the synchronization detection section or the APC control section ends, the light amount set at the end of the image area and the light amount in the synchronization detection section or the APC control section For example, as shown in FIG. 6, the difference becomes large, and the light amount control may not be in time, and the light source light amount may be smaller than the required amount by the light amount correction (the light amount setting value in the figure).

  When the light source light quantity becomes smaller than the required amount in this way, the image density at the edge of the image area (toner density of the print image) becomes lower than the density at the center of the image area, leading to a decrease in print image quality.

  The present invention has been made in view of the above problems, and an object thereof is to obtain an exposure apparatus capable of obtaining a sufficient amount of light source required at the edge of an image area, and an image forming apparatus having the exposure apparatus. To do.

  In order to solve the above problems, the present invention is configured as follows.

An exposure apparatus according to the present invention includes a light source, a scanning device that scans light beams from the light source, a driver circuit that drives the light source, and a control signal generation unit that controls the light source by supplying a control signal to the driver circuit. The control signal generation unit supplies a control signal for setting the light quantity of the light source to the light quantity setting value for the light quantity correction to the driver circuit in a predetermined light quantity correction section within one scanning period by the scanning device. In the image area, a light beam for image formation is emitted from the light source. The time from the start timing of the light quantity correcting section to the start timing of the image area, the light amount of the light source is set to the time it takes to rise to a predetermined amount of light corresponding to a light quantity set value, the predetermined light amount Is the amount of light corresponding to the image density at which the color difference ΔE is 3 with respect to the image density obtained with the light amount setting value.

  Thereby, a sufficient amount of light source required at the end of the image area can be obtained sufficiently. Further, since the color difference ΔE is suppressed to 3 or less at the end of the image area, insufficient density is not visually recognized.

In addition to the above exposure apparatus, the exposure apparatus according to the present invention may be configured as follows. In this case, the exposure apparatus further includes a low-pass filter used for current control of the light source. When the ratio of the difference between the light amount setting value and the predetermined light amount with respect to the light amount setting value is K percent, the time constant of the low-pass filter is τ, and the time from the start timing of the light amount correction section to the start timing of the image area is T, The time from the start timing of the light amount correction section to the start timing of the image area satisfies the condition of Expression (1).
1-exp (−T / τ) ≧ (100−K) / 100 (1)

  The exposure apparatus according to the present invention may be as follows in addition to any of the exposure apparatuses described above. In this case, the exposure apparatus further includes an automatic output control circuit for adjusting the light amount of the light source. The automatic output control circuit adjusts the light amount of the light source outside the light amount correction section.

  The exposure apparatus according to the present invention may be as follows in addition to any of the exposure apparatuses described above. In this case, the control signal generator supplies a control signal for setting the light amount of the light source to the light amount setting value for each predetermined light amount correction unit interval in the light amount correction interval. The time from the start timing of the light quantity correction section to the start timing of the image area is longer than the light quantity correction unit section.

  In addition, an image forming apparatus according to the present invention forms an electrostatic latent image by irradiating a light beam on a photoconductor with any of the above exposure apparatuses.

  According to the present invention, in the exposure apparatus and the image forming apparatus having the exposure apparatus, a sufficient amount of light source required at the edge of the image area can be obtained sufficiently.

FIG. 1 is a side view showing a part of a mechanical internal configuration of an image forming apparatus having an exposure apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration example of the exposure apparatus in FIG. FIG. 3 is a circuit diagram showing a configuration example of the controller in FIG. FIG. 4 is a view for explaining light amount correction by the exposure apparatus shown in FIG. FIG. 5 is a diagram illustrating an example of the relationship between the light amount change rate from the reference light amount and the image density change amount at each light amount change rate. FIG. 6 is a diagram for explaining a shortage of light quantity at the edge of the image area.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a side view showing a part of a mechanical internal configuration of an image forming apparatus having an exposure apparatus according to an embodiment of the present invention. The image forming apparatus is an apparatus having an electrophotographic printing function, such as a printer, a facsimile machine, a copying machine, or a multifunction machine.

  The image forming apparatus of this embodiment has a tandem color developing device. The color developing device includes photosensitive drums 1a to 1d, exposure devices 2a to 2d, and developing units 3a to 3d. The photoconductor drums 1a to 1d are four-color photoconductors of cyan, magenta, yellow, and black. The exposure apparatuses 2a to 2d are apparatuses that form electrostatic latent images by irradiating the photosensitive drums 1a to 1d with laser light. The exposure apparatuses 2a to 2d include a laser diode that is a light source of laser light and optical elements (lenses, mirrors, polygon mirrors, etc.) that guide the laser light to the photosensitive drums 1a to 1d.

  Further, around the photosensitive drums 1a to 1d, a charger such as a scorotron, a cleaning device, a static eliminator and the like are arranged. The cleaning device removes residual toner on the photosensitive drums 1a to 1d after the primary transfer, and the static eliminator neutralizes the photosensitive drums 1a to 1d after the primary transfer.

  To the developing units 3a to 3d, toner cartridges filled with toners of four colors of cyan, magenta, yellow, and black are respectively mounted. The toner is supplied from the toner cartridge, and constitutes a developer together with the carrier. The developing units 3a to 3d form toner images by attaching the toner to the electrostatic latent images on the photosensitive drums 1a to 1d.

  The photosensitive drum 1a, the exposure device 2a, and the developing unit 3a develop magenta, and the photosensitive drum 1b, the exposure device 2b, and the developing unit 3b develop cyan, the photosensitive drum 1c, and exposure. Yellow development is performed by the apparatus 2c and the development unit 3c, and black development is performed by the photosensitive drum 1d, the exposure apparatus 2d, and the development unit 3d.

  The intermediate transfer belt 4 is an annular image carrier that contacts the photosensitive drums 1a to 1d and primarily transfers the toner images on the photosensitive drums 1a to 1d. The intermediate transfer belt 4 is stretched around the driving roller 5 and circulates in the direction from the contact position with the photosensitive drum 1d to the contact position with the photosensitive drum 1a by the driving force from the driving roller 5.

  The transfer roller 6 brings the conveyed paper into contact with the intermediate transfer belt 4 and secondarily transfers the toner image on the intermediate transfer belt 4 to the paper. The sheet on which the toner image has been transferred is conveyed to the fixing device 9 and the toner image is fixed on the sheet.

  The roller 7 has a cleaning brush, and the cleaning brush is brought into contact with the intermediate transfer belt 4 to remove the toner remaining on the intermediate transfer belt 4 after the transfer of the toner image onto the paper.

  The sensor 8 is a sensor used for toner density adjustment, and irradiates the intermediate transfer belt 4 with a light beam and detects the reflected light. When adjusting the toner density, the sensor 8 irradiates a predetermined region of the intermediate transfer belt 4 with a light beam, detects reflected light (measurement light) of the light beam, and outputs an electrical signal corresponding to the light amount.

  FIG. 2 is a view showing a configuration example of the exposure apparatuses 2a to 2d in FIG. Note that the exposure apparatus shown in FIG. 2 is an exposure apparatus 2a for the photosensitive drum 1a, and the exposure apparatuses 2b to 2d for the photosensitive drums 1b to 1d have the same configuration.

  In FIG. 2, a laser diode 21 is a light source that emits laser light.

  The optical system 22 is a group of various lenses arranged between the laser diode 21 and the polygon mirror 23 and / or between the polygon mirror 23 and the photosensitive drum 1a and the PD sensor 24. For the optical system 22, an fθ lens or the like is used.

  The polygon mirror 23 is an element having an axis perpendicular to the axis of the photosensitive drum 1a, a cross section perpendicular to the axis being a polygon, and a side surface being a mirror. The polygon mirror 23 rotates around its axis and scans the light emitted from the laser diode 21 along the axial direction (main scanning direction) of the photosensitive drum 1a.

  The PD sensor 24 is a sensor that receives light scanned by the polygon mirror 23 in order to generate a main scanning synchronization signal. When light is incident, the PD sensor 24 induces an output voltage corresponding to the amount of light. The PD sensor 24 is disposed at a predetermined position on a line where light is scanned, and is used to detect timing at which the light spot passes through the position.

  The controller 31 controls the light amount of the laser diode 21 based on the synchronization signal from the detection circuit 32. The detection circuit 32 is a circuit that generates a synchronization signal based on the output of the PD sensor 24.

  FIG. 3 is a circuit diagram showing a configuration example of the controller 31 in FIG.

  The controller 31 includes a control signal generation unit 41, D / A converters 42 and 45, a low-pass filter 43, a driver circuit 44, and an APC circuit 46. The laser diode LD in FIG. 3 is the laser diode 21 in FIG.

  The control signal generator 41 supplies a control signal to the driver circuit 44 to control the amount of light emitted from the laser diode LD. In this embodiment, the control signal generation unit 41 is a digital circuit that generates an image control signal and a light amount control signal. The image control signal is a control signal for forming an electrostatic latent image corresponding to an image to be printed on the photosensitive drum 1a. The light amount control signal is a control signal for performing light amount correction according to each position in the main scanning direction (that is, each timing in each scanning), and sets the light amount of the laser diode LD to the light amount setting value for light amount correction. It is a signal for.

  FIG. 4 is a view for explaining light amount correction by the exposure apparatus shown in FIG. In this embodiment, the control signal generation unit 41 sends a light amount control signal to the driver circuit via the D / A converter 42 and the low-pass filter 43 in a predetermined light amount correction section within one scanning period by the polygon mirror 23. 44. In this embodiment, the control signal generation unit 41 supplies an image control signal to the driver circuit 44 via the D / A converter 45 in a predetermined image area within one scanning period by the polygon mirror 23. This image area is set in the light amount correction section.

  The time from the start timing Tc of the light amount correction section to the start timing Ti of the image area is set to be longer than the time required for the light amount of the laser diode LD to rise to a predetermined light amount corresponding to the light amount setting value. Yes. The predetermined light amount is a light amount corresponding to an image density at which the color difference ΔE is 3 with respect to the image density obtained by the light amount setting value.

  In this embodiment, the control signal generation unit 41 outputs a light amount control signal for setting the light amount of the laser diode LD to the light amount setting value for each predetermined light amount correction unit interval in the light amount correction interval. To supply. The light quantity correction unit section is obtained by dividing the light quantity correction section into a predetermined number. Within each light quantity correction unit section, the light quantity setting value is constant as shown in FIG. The time from the start timing of the light quantity correction section to the start timing of the image area is longer than that of the light quantity correction unit section.

  The D / A converter 42 is a circuit that converts the light amount control signal from the control signal generation unit 41 into an analog signal. In the next stage of the D / A converter 42, a low-pass filter 43 used for current control of the laser diode LD is provided. The low-pass filter 43 includes a capacitor C and a resistor R, and has a time constant τ (= R × C).

  FIG. 5 shows the change rate of the light quantity from the reference light quantity and the change amount of the image density at each light quantity change rate (that is, the image density by the reference light quantity and the image density by the light quantity obtained by the product of the light quantity change rate and the reference light quantity). It is a figure which shows an example of a relationship with color difference (DELTA) E). The relationship shown in FIG. 5 is obtained in advance by experiments, for example. When the color difference ΔE is 3 or less, since the density change is not recognized visually, the upper limit K of the light quantity change rate for preventing the density change from being recognized visually is specified from the relationship shown in FIG. The In this embodiment, the time T from the start timing Tc of the light quantity correction section to the start timing Ti of the image area is an expression based on the upper limit value K (percentage) of the light quantity change rate, the time constant τ of the low-pass filter 43, and the like. Satisfy the condition (1).

  The driver circuit 44 is a circuit that drives the laser diode LD. The driver circuit 44 controls the light amount of the laser diode LD so that the light amount corresponds to the image control signal and the light amount control signal supplied via the low pass filter 43.

  The driver circuit 44 turns on / off the laser diode LD according to the output voltage of the D / A converter 45 (that is, the image control signal). By turning on / off the laser diode LD, an electrostatic latent image having a shape based on the image control signal is formed on the photosensitive drum 1a.

  In each scan, control is performed so that the laser diode LD is always lit during a period in which the spot of the laser beam is added on the PD sensor 24.

  The APC circuit 46 drives the laser diode LD with power corresponding to the reference voltage Vref. The APC circuit 46 detects the current Im conducted to the monitoring photodetector PDm as the voltage Vm across the detection resistor R, and controls the power of the laser diode LD so that the voltage Vm becomes equal to the reference voltage Vref.

  The APC circuit 46 measures the reference drive current value of the laser diode LD in the APC control section in each scan, and then maintains the reference drive current value in the scan period. Then, the driver circuit 44 performs light amount correction based on the light amount control signal using the reference drive current value as a reference. The APC circuit 46 performs light amount adjustment (that is, measurement of the reference drive current value) of the laser diode LD outside the light amount correction section described above, and does not perform light amount adjustment in the light amount correction section.

  Next, the operation of the image forming apparatus will be described.

  The exposure apparatuses 2a to 2d scan the laser beam in the main scanning direction for each line by the polygon mirror 23. The scanning position in the main scanning direction moves from the scanning start position by one scanning with the mirror surface with the polygon mirror 23, and passes over the PD sensor 24 and the photosensitive drum 1a (1b, 1c, 1d). To do. Then, the scanning position in the main scanning direction is moved again from the scanning start position by one scanning with the next mirror surface of the polygon mirror 23, and the PD sensor 24 and the photosensitive drums 1a (1b, 1c, 1d). ) Pass over.

  In each scanning, in the exposure apparatuses 2a to 2d, the synchronization signal is detected by the PD sensor 24 and the detection circuit 32 in the synchronization detection section, and the start timing Tc of the light amount correction section is specified from the detection timing of the synchronization signal. And before the start timing Tc of the light quantity correction section, the APC circuit 46 performs light quantity adjustment.

  Thereafter, at the start timing Tc of the light amount correction section, the control signal generation unit 41 starts supplying the light amount control signal to the driver circuit 44. The light quantity control signal is applied to the driver circuit 44 as an analog signal through the D / A converter 42 and the low-pass filter 43. This light quantity control signal as an analog signal has a voltage corresponding to the light quantity setting value specified by the control signal generation unit 41.

  The light amount setting value for the first light amount correction unit section is set to a higher value than the vicinity of the center of the image region in order to compensate for the light amount decrease at the edge of the image region due to the optical characteristics such as the polygon mirror 23 and the optical system 22. . As shown in FIG. 4, the light amount setting value for the first light amount correction unit section is higher than the light amount value of the laser diode LD in the non-light amount correction section including the APC control section and the synchronization detection section.

  Since the light amount correction is started at the start timing Tc of the light amount correction section, and the light amount setting value for the first light amount correction unit section is higher than the light amount value of the laser diode LD in the non-light amount correction section, the light amount of the laser diode LD As shown in FIG. 4, the curve rises with a curve (1-exp (−t / τ), where t is the time from Tc) governed by the time constant τ of the low-pass filter 43.

  The light amount setting value is the same as the light amount setting value for the first light amount correction unit section up to the light amount correction unit section including the start timing Ti of the image area, and the laser diode until the start timing Ti of the image area is reached. As shown in FIG. 4, the light amount of the LD reaches a light amount that is lower than the light amount setting value by an allowable light amount difference ΔQ. The allowable light amount difference ΔQ is a light amount change amount corresponding to an image density change where the color difference ΔE is 3, and is a product of the light amount setting value and the upper limit value K of the light amount change rate.

  For this reason, the shortage of light quantity at the edge of the image area is solved, and the lack of image density due to the lack of light quantity is also solved.

  As described above, according to the above embodiment, the control signal generation unit 41 provides the driver circuit 44 with the light amount control signal for setting the light amount of the laser diode LD to the light amount setting value for light amount correction in the light amount correction section. In addition, a light beam for image formation is emitted from the laser diode LD in the image area. The time T from the start timing Tc of the light quantity correction section to the start timing Ti of the image area is set to be longer than the time required for the light quantity of the laser diode LD to rise to a predetermined light quantity corresponding to the light quantity setting value. The predetermined light amount is a light amount corresponding to an image density at which the color difference ΔE is 3 with respect to the image density obtained with the light amount setting value.

  Thereby, a sufficient amount of light of the laser diode LD required at the end of the image area can be obtained. Further, since the color difference ΔE is suppressed to 3 or less at the end of the image area, insufficient density is not visually recognized.

  The above-described embodiments are preferred examples of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. is there.

  The present invention is applicable to, for example, an electrophotographic image forming apparatus.

1a to 1d photoconductor drum (example of photoconductor)
2a to 2d Exposure apparatus 21 Laser diode (an example of a light source)
23 Polygon mirror (an example of a scanning device)
41 control signal generator 43 low-pass filter 44 driver circuit 46 automatic output control circuit

Claims (5)

A light source;
A scanning device for scanning the light beam by the light source;
A driver circuit for driving the light source;
A control signal generator for controlling the light source by supplying a control signal to the driver circuit,
The control signal generation unit supplies the driver circuit with the control signal for setting the light amount of the light source to a light amount setting value for light amount correction in a predetermined light amount correction section within one scanning period by the scanning device. In addition, in a predetermined image area, a light beam for image formation is emitted from the light source,
Time from the start timing of the light amount correcting section to the start timing of the image area, is set between when the light amount of the light source is required to rise to a predetermined amount of light corresponding to the light quantity setting value,
The predetermined light amount is a light amount corresponding to an image density having a color difference of 3 with respect to an image density obtained by the light amount setting value;
An exposure apparatus characterized by the above. Further comprising a low pass filter used for current control of the light source,
The ratio of the difference between the light amount setting value and the predetermined light amount with respect to the light amount setting value is K percent, the time constant of the low-pass filter is τ, and from the start timing of the light amount correction section to the start timing of the image area. If the time is T, the time from the start timing of the light amount correction section to the start timing of the image area satisfies the condition of the formula (1).
The exposure apparatus according to claim 1.
1-exp (−T / τ) ≧ (100−K) / 100 (1) An automatic output control circuit for adjusting the light amount of the light source;
The automatic output control circuit performs light amount adjustment of the light source outside the light amount correction section;
The exposure apparatus according to claim 1 or 2, wherein The control signal generation unit supplies the driver circuit with the control signal for setting the light amount of the light source to the light amount setting value for each predetermined light amount correction unit interval in the light amount correction interval,
The time from the start timing of the light quantity correction section to the start timing of the image area is longer than the light quantity correction unit section;
The exposure apparatus according to any one of claims 1 to 3, wherein:   5. The image forming apparatus according to claim 1, wherein an electrostatic latent image is formed by irradiating the photosensitive member with the light beam.

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