JP2018196942A - Image formation apparatus - Google Patents

Abstract

To provide an image formation apparatus which suppresses reduction in the exposure amount due to the reflectance reduction of a rotary polygon mirror.SOLUTION: A rotary polygon mirror 23 scans a laser beam on a photoreceptor drum 1. A BD sensor 24 generates a synchronous signal (BD signal) in the main-scanning direction by receiving the scanned laser beam at a prescribed position. A control circuit 26 identifies a pulse width tbd of the BD signal in exposure amount adjustment processing, causes a light source 21 to emit the laser beam by using a drive circuit 25 with the light emission amount according to the pulse width tbd, and adjusts the exposure amount of the photoreceptor drum 1 by the laser beam to a prescribed value.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus.

  An image forming apparatus such as a printer or a multi-function machine forms a latent electrostatic image by scanning a laser beam on a photosensitive member using a rotating polygon mirror, and develops the latent electrostatic image with toner. The image is transferred to the paper and the toner image on the paper is fixed. In some image forming apparatuses, when the scanning line pitch or the inclination of the scanning line is corrected, the irradiation light amount of the laser beam (that is, the exposure amount of the photosensitive member) does not change due to the correction of the scanning line pitch or the inclination of the scanning line. The amount of laser light emitted is adjusted (see, for example, Patent Document 1).

JP 2004-45840 A

  However, the above-described image forming apparatus does not require correction of the scanning line pitch or the inclination of the scanning line even when the reflectance is reduced and the exposure amount is reduced due to dirt or the like adhering to the rotary polygon mirror. If so, the light emission amount of the laser beam is not adjusted, and an appropriate exposure amount cannot be obtained.

  The present invention has been made in view of the above problems, and an object of the present invention is to obtain an image forming apparatus that suppresses a reduction in exposure caused by a decrease in reflectance of a rotary polygon mirror.

  An image forming apparatus according to the present invention receives a photosensitive drum, a light source of laser light, a rotating polygon mirror that scans the laser light on the photosensitive drum, and the laser light to be scanned at a predetermined position. A synchronization sensor that generates a synchronization signal in the main scanning direction, a drive circuit that drives the light source, and a control circuit that controls the light emission amount of the light source based on the synchronization signal using the drive circuit. . In the exposure amount adjustment process, the control circuit specifies a pulse width of the synchronization signal, and causes the light source to emit the laser light with the light emission amount according to the pulse width. The exposure amount of the photosensitive drum by the laser light is adjusted to a predetermined value.

  According to the present invention, it is possible to obtain an image forming apparatus that suppresses a decrease in exposure caused by a decrease in reflectance of a rotary polygon mirror.

  These and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

FIG. 1 is a side view showing a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a view showing an example of the configuration of the exposure apparatus 2 in FIG. 1 and its surroundings. FIG. 3 is a circuit diagram showing an example of the BD sensor 24 in FIG. FIG. 4 is a diagram for explaining the relationship between the intensity of the detection voltage V in the BD sensor 24 shown in FIG. 3 and the pulse width of the BD signal. FIG. 5 is a timing chart for explaining the operation of the exposure apparatus 2 shown in FIG.

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

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

  The image forming apparatus shown in FIG. 1 includes a photosensitive drum 1, an exposure device 2, a developing unit 3, a conveyance belt 4, a driving roller 5, a transfer roller 6, and a fixing device 7.

  The exposure device 2 irradiates the photosensitive drum 1 with laser light to form an electrostatic latent image.

  The developing unit 3 is mounted with a toner container filled with toner (here, black toner), and causes the toner supplied from the toner container to adhere to the electrostatic latent image on the photosensitive drum 1.

  The conveyance belt 4 circulates by the driving force from the driving roller 5 and conveys the printing paper to the photosensitive drum 1 between the photosensitive drum 1 and the transfer roller 6.

  The transfer roller 6 brings the conveyed printing paper into contact with the photosensitive drum 1 and transfers the toner image on the photosensitive drum 1 to the paper. The printing paper to which the toner image has been transferred is conveyed to the fixing device 7 and the toner image is fixed on the paper.

  FIG. 2 is a view showing an example of the configuration of the exposure apparatus 2 in FIG. 1 and its surroundings.

  The exposure apparatus 2 shown in FIG. 2 includes a light source 21, a collimator lens 22a, a correction lens 22b, a rotary polygon mirror 23, a motor 23a for rotating the rotary polygon mirror 23, a BD sensor 24, and the like.

  In FIG. 2, the light source 21 emits laser light. The light source 21 is a laser diode, for example. The collimator lens 22a is a lens that converts laser light emitted from the light source 21 into parallel light. The correction lens 22b is an f-θ lens and is a lens for making the moving speed of the irradiation position of the laser light constant.

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

  The BD sensor 24 is a sensor that receives laser light scanned by the rotary polygon mirror 23 at a predetermined position in order to generate a main scanning synchronization signal. When light is incident, the BD sensor 24 induces an output voltage corresponding to the amount of light in a pulse shape. The BD sensor 24 is disposed at a predetermined position on the line to which the laser light is scanned, and generates a synchronization signal (BD signal) in the main scanning direction by receiving the scanned laser light at the predetermined position.

  FIG. 3 is a circuit diagram showing an example of the BD sensor 24 in FIG.

  As shown in FIG. 3, a photodiode PD, a resistor R, a reference voltage circuit 41, and a comparator 42 are provided. The photodiode PD is a light receiving element that induces a detection voltage V corresponding to the amount of laser light irradiation described above. The reference voltage circuit 41 generates a reference voltage Vr. The comparator 42 compares the detection voltage V with the reference voltage Vr. When the detection voltage V exceeds the reference voltage Vr, the comparator 42 sets the output voltage Vo to a predetermined low level. Vo is set to a predetermined high level. This output voltage Vo becomes a BD signal.

  FIG. 4 is a diagram for explaining the relationship between the intensity of the detection voltage V in the BD sensor 24 shown in FIG. 3 and the pulse width of the BD signal.

  As the laser light spot passes, the detection voltage V of the photodiode PD rises smoothly as shown in FIG. 4, and then falls smoothly. Since the BD sensor 24 generates the pulsed BD signal by comparing the detection voltage V with the reference voltage Vr as described above, the amount of laser light irradiation changes, and the detection voltage is accordingly changed. When V changes, the pulse widths tbd1, tbd2, and tbd3 of the BD signal also change as shown in FIG.

  For example, when the peak voltage of the detection voltage V is lower than the reference value, the pulse width tbd is narrower than the pulse width tbd1 corresponding to the reference value.

  As shown in FIG. 2, the image forming apparatus includes a drive circuit 25 and a control circuit 26.

  The drive circuit 25 is a circuit that drives the light source 21. The control circuit 26 is a circuit that causes the drive circuit 25 to drive the light source 21. The control circuit 26 uses the drive circuit 25 to control the light emission amount of the light source 21 based on the pulse width of the BD signal.

  In particular, in the exposure adjustment process, the control circuit 26 specifies the pulse width of the BD signal, causes the light source 21 to emit laser light with the light emission amount corresponding to the pulse width, and causes the laser light to be emitted. The exposure amount of the photosensitive drum 1 by light is adjusted to a predetermined value.

  The control circuit 26 executes the exposure amount adjustment process when a predetermined condition is satisfied. Here, the “predetermined condition” is, for example, that the number of printed sheets after the previous exposure adjustment processing has reached a predetermined threshold. Further, the control circuit 26 may change the above-described threshold according to the pulse width of the BD signal when the number of printed sheets after the previous exposure adjustment processing reaches a predetermined threshold. That is, in this case, the changed threshold value is applied to the next exposure amount adjustment process. For example, the threshold value is set smaller as the difference between the pulse width of the BD signal at the previous exposure amount adjustment processing and the pulse width of the BD signal at the current exposure amount adjustment processing is larger.

  Next, the operation of the image forming apparatus will be described. FIG. 5 is a timing chart for explaining the operation of the exposure apparatus 2 shown in FIG.

  As shown in FIG. 2, the control circuit 26 supplies the light control signal, the light amount level signal, and the light emission signal to the drive circuit 25, and controls the light emission of the light source 21.

  The light control signal specifies a period during which automatic light amount control of the light source 21 is permitted. Here, a period in which the light control signal is at a low level is a period in which automatic light amount control of the light source 21 is permitted. In the automatic light amount control, a part of the laser light from the light source 21 is received by a photodiode (not shown) in the light source 21, and the light emission amount of the light source 21 is adjusted according to the received light amount. Here, for example, the drive circuit 25 performs automatic light amount control in order to set the initial light amount when the light source 21 is activated.

  The light level signal is a signal that specifies the light emission amount of the light source 21. The drive circuit 25 emits light by applying a voltage corresponding to the level of the light amount level signal to the laser diode of the light source 21.

  The light emission signal is a signal that designates the light emission period of the light source 21. Here, the drive circuit 25 causes the light source 21 to emit light during a period in which the light emission signal is at a high level.

  In addition, the mirror surface on which the laser light is incident in the rotating polygon mirror 23 changes at a constant period. Therefore, as shown in FIG. 5, in the non-imaging period, the time when the pulse of the BD signal is detected from the time when the predetermined time has elapsed from the time when the laser light is incident on the nth surface of the rotary polygon mirror 23. Until this period, the control circuit 26 sets the light emission signal to a high level so that a pulse of the BD signal can be obtained.

  When the control circuit 26 detects the pulse of the BD signal, the control circuit 26 measures the pulse width tbd (here, the time from the falling pulse edge to the rising pulse edge) of the BD signal, and immediately corresponds to the measured pulse width tbd. The level of the light level signal to be specified is specified, and the light level signal is set to that level. Thereby, the drive circuit 25 adjusts the irradiation light amount (that is, the exposure amount) of the laser light to a predetermined value.

  For example, in FIG. 5, at the time T1 of the trailing edge of the pulse of the BD signal, the control circuit 26 changes the light amount level signal to the level P1 corresponding to the pulse width tbd of the pulse. At time T2 of the end edge of the pulse, the control circuit 26 changes the light amount level signal to the level P3 corresponding to the pulse width tbd of the pulse.

  That is, when the reflectivity of the mirror surface of the rotary polygon mirror 23 decreases due to dirt or the like, the amount of laser light irradiation decreases and the pulse width tbd of the BD signal becomes narrow, so the control circuit 26 increases the level of the light level signal. The amount of light emitted from the light source 21 is increased.

  Further, when the control circuit 26 detects the pulse of the BD signal, the light emission signal is once set to the low level, and then the image forming period is specified based on the pulse edge of the BD signal (here, the elapsed time from the rising pulse edge). In the image forming period, the light control signal is set to a high level, and the light emission signal is set to a level corresponding to the value of the image data corresponding to the image position corresponding to each timing.

  At this time, since the electrostatic latent image is formed by the laser beam scanned on the n-th surface of the rotating polygon mirror 23, as described above, it corresponds to the reflectance of the n-th surface of the rotating polygon mirror 23. Then, with the exposure amount adjusted to a predetermined value, an electrostatic latent image is formed by the laser light scanned on the nth surface of the rotary polygon mirror 23.

  When an electrostatic latent image is formed by laser light using the laser light scanned on the next surface (that is, the (n + 1) th surface) of the rotating polygon mirror 23, the rotating polygon mirror 23 is similarly configured. An electrostatic latent image is formed by the laser light in a state where the exposure amount is adjusted to a predetermined value corresponding to the reflectance of the (n + 1) plane.

  Therefore, even when the reflectances of the plurality of mirror surfaces of the rotary polygon mirror 23 are different from each other, the light emission amount of the laser light is set according to each mirror surface, and the exposure amount is adjusted to be constant.

  When the laser light emission amount is changed according to the gradation value of the image data, the maximum value (upper limit value) of the laser light emission amount is adjusted as described above, and a plurality of gradation levels are obtained. Are respectively adjusted to be constant.

  As described above, according to the first embodiment, the rotary polygon mirror 23 scans the laser beam on the photosensitive drum 1. The BD sensor 24 generates a synchronization signal (BD signal) in the main scanning direction by receiving laser light to be scanned at a predetermined position. Then, in the exposure adjustment process, the control circuit 26 specifies the pulse width tbd of the BD signal and causes the light source 21 to emit laser light with the light emission amount corresponding to the pulse width tbd. Then, the exposure amount of the photosensitive drum 1 by the laser beam is adjusted to a predetermined value.

  Thereby, the reduction of the exposure amount resulting from the reflectance fall of the rotary polygon mirror 23 is suppressed. As a result, deterioration of image quality is suppressed.

Embodiment 2. FIG.

  In the second embodiment, the control circuit 26 stores a set value corresponding to the above-mentioned laser light emission amount for each of the plurality of mirror surfaces of the rotary polygon mirror 23 in a predetermined storage device (non-volatile memory or the like) (not shown). The light source 21 is caused to emit light with a light emission amount corresponding to a set value for a surface that reflects the laser light among the plurality of mirror surfaces. That is, the setting value indicating the level of the light level signal for each mirror surface is stored in the storage device, and the control circuit 26 sets the light level signal for each mirror surface to a level corresponding to the setting value of the mirror surface. Then, the drive circuit 25 causes the light source 21 to emit laser light.

  In the second embodiment, the control circuit 26 specifies the pulse width tbd of the BD signal for each of the plurality of mirror surfaces of the rotary polygon mirror 23, and the light emission amount (that is, the light amount) corresponding to the pulse width tbd. The level signal level) is specified, and the drive circuit 25 is used to cause the light source 21 to emit laser light with the specified light emission amount, and the exposure amount of the photosensitive drum 1 by the laser light is adjusted to a predetermined value and specified. The set value stored in the above-described storage device is updated with the set value corresponding to the emitted light amount.

  Since the other configuration and operation of the image forming apparatus according to the second embodiment are the same as those of the first embodiment, the description thereof is omitted.

  As described above, according to the second embodiment, for each mirror surface of the rotary polygon mirror 23, the set value of the amount of laser light is stored and updated as appropriate. The measurement of the pulse width tbd and the update of the set value for each mirror surface are performed only at predetermined timings (when the power is turned on, at the start of printing, every predetermined driving time of the rotary polygon mirror 23, etc.), and at other timings It may not be performed. Further, the pulse width tbd is periodically measured, and the difference between the measured pulse width tbd and the reference value (here, the pulse width when the current set value is set) exceeds a predetermined threshold value. The set value may be updated.

  Various changes and modifications to the above-described embodiment will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. That is, such changes and modifications are intended to be included within the scope of the claims.

  For example, in the above-described embodiment, the control circuit 26 stores the pulse width of the BD signal in the initial stage (at the time of shipment, first use after shipment, etc.) in the above-described storage device, and then measures the BD measured thereafter. You may make it set the light emission amount of the light source 21 using the drive circuit 25 so that the pulse width of a signal may become the initial pulse width memorize | stored in the memory | storage device. Thereby, the exposure amount after time is maintained at the initial exposure amount.

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

1 Photosensitive drum 21 Light source 23 Rotating polygon mirror 24 BD sensor (an example of a synchronous sensor)
25 Drive circuit 26 Control circuit

Claims (5)

A photosensitive drum;
A laser light source;
A rotating polygon mirror that scans the laser beam on the photosensitive drum;
A synchronization sensor that generates a synchronization signal in the main scanning direction by receiving the scanned laser beam at a predetermined position;
A drive circuit for driving the light source;
A control circuit that controls the light emission amount of the light source based on the synchronization signal using the drive circuit;
In the exposure amount adjustment process, the control circuit specifies a pulse width of the synchronization signal, emits the laser light to the light source using the drive circuit with a light emission amount according to the pulse width, and Adjusting the exposure amount of the photosensitive drum by laser light to a predetermined value;
An image forming apparatus.   The control circuit stores (a) a setting value corresponding to the light emission amount for each of the plurality of mirror surfaces of the rotary polygon mirror in a predetermined storage device, and reflects the laser light among the plurality of mirror surfaces. The light source emits the laser beam with a light emission amount corresponding to the set value for a surface, (b) for each of a plurality of mirror surfaces of the rotary polygon mirror, a pulse width of the synchronization signal is specified, and the pulse width The light emission amount according to the laser light is specified, and the laser light is emitted to the light source using the drive circuit with the specified light emission amount, and the exposure amount of the photosensitive drum by the laser light is adjusted to a predetermined value. The image forming apparatus according to claim 1, wherein the setting value stored in the storage device is updated with a setting value corresponding to the specified light emission amount. The control circuit executes the exposure adjustment process when a predetermined condition is satisfied,
The predetermined condition is that the number of printed sheets after the previous exposure amount adjustment processing has reached a predetermined threshold;
The image forming apparatus according to claim 1.   4. The control circuit according to claim 3, wherein the control circuit changes the threshold value according to a pulse width of the synchronization signal when the number of printed sheets after the previous exposure amount adjustment processing reaches a predetermined threshold value. Image forming apparatus. The control circuit executes the exposure adjustment process when a predetermined condition is satisfied,
The predetermined condition is that a difference between a pulse width of the synchronization signal and a reference value exceeds a predetermined threshold;
The image forming apparatus according to claim 1.

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