JP2017087650A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problems in which radiation noise deteriorates when multi-beam is simultaneously turned on in an image formation apparatus which performs image formation using multi-beam, and if a conventional method for improving this problem is used, the pixel shift occurs and high quality image formation cannot be performed.SOLUTION: In an image formation apparatus for forming an image on a photoreceptor by a beam from each of a plurality of lasers in accordance with a multi-beam method, the following control is executed. Namely, it is determined whether the emission timings of beams emitted from the plurality of lasers respectively and forming the respective dots are the same. When it is determined that the emission timings of the beams are the same, the timing being the center of the respective dots to be formed is not changed for the beam, and the emission timings from the respective lasers are changed to be different from each other.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus, and more particularly to control of a laser beam for forming an image on a recording medium according to, for example, an electrophotographic system.

  In recent printers employing an electrophotographic system, a multi-beam system having a plurality of light emitting sources has become the mainstream in order to cope with an increase in printing speed. In the multi-beam method, when turning on / off the beam light according to the input image signal, if a plurality of laser light sources are turned on at the same time, the output of the image signal is larger than when a single laser light source is turned on. Of current required. For this reason, there is a problem that the electromagnetic field radiated on the transmission path connecting the printer controller and the optical driver also increases. In order to solve this problem, when forming an image using a multi-beam laser conventionally, if the timing of light emission of each laser beam at the image writing position is the same, a part of the image signal is delayed. A method of shifting the light emission timing is used.

  FIG. 7 is a time chart showing the emission timing of the laser beam according to the conventional example. FIG. 7 shows an example in which two light beams are generated by image signals VD01 and VD02 sent from the image signal generator to the laser driver. As shown in FIG. 7, when the on timing of the image signal VD01 indicated by the solid line and the image signal VD02 indicated by the two-dot chain line overlap, the on timing of the image signal VD02 is delayed as indicated by the solid line, A method of shifting from the timing is taken.

  As described above, conventionally, some image signals are delayed so that a plurality of lasers are not simultaneously turned on, and the radiated electromagnetic field is reduced (for example, see Patent Document 1).

JP 2002-172816 A

  However, in the above conventional example, the on / off timing of some of the image signals is delayed, and this shifts from the originally formed dot range, so that pixel shift occurs and a high-quality image cannot be formed. There was a problem.

  The present invention has been made in view of the above conventional example, and provides an image forming apparatus capable of reducing radiation noise without causing pixel shift even when image formation is performed using a plurality of lasers. The purpose is that.

  In order to achieve the above object, the image forming apparatus of the present invention has the following configuration.

  That is, the first light emitting means for irradiating the photosensitive member with light to form an image, and the light emission starts at a timing delayed from the light emission start of the first light emitting means, and the light emission by the first light emitting means is completed. And a second light emitting unit that terminates by performing light emission of the same amount of light emission from the start of light emission to the end of light emission of the first light emitting unit.

  Therefore, according to the present invention, even when an image is formed using a plurality of lasers, there is an effect that radiation noise can be reduced without causing pixel shift.

1 is a perspective view showing a main part of an image forming apparatus that forms an image according to an electrophotographic system that is a typical embodiment of the present invention. 2 is a block diagram illustrating a control configuration of the image forming apparatus. FIG. It is the block diagram which showed the detail of the internal structure of the image signal transmitted from the image signal generation part at the time of using 2 beam laser, and an optical control part. It is a timing chart of the image signal and drive signal at the time of light emission pattern change. It is a flowchart which shows the light emission pattern change procedure. It is a figure which shows the concept of an image writing position adjustment value. It is a time chart which shows the light emission timing of the laser beam according to a prior art example.

  Hereinafter, preferred embodiments of the present invention will be described more specifically and in detail with reference to the accompanying drawings.

  In this specification, “recording” (sometimes referred to as “printing”) is not limited to the case of forming significant information such as characters and graphics, but may be significant. Furthermore, it also represents a case where an image, a pattern, a pattern, or the like is widely formed on a recording medium or a medium is processed regardless of whether or not it is manifested so that a human can perceive it visually.

  The “recording medium” includes not only paper used in general recording apparatuses but also widely includes cloth, plastic film, metal plate, glass, ceramics, wood, leather, and the like.

<Outline of Image Forming Apparatus (FIGS. 1-2)>
FIG. 1 is a perspective view showing a main part of an image forming apparatus (LBP) for forming an image in accordance with an electrophotographic system which is a typical embodiment of the present invention.

  As shown in FIG. 1, the main part of the image forming apparatus includes a scanner unit 9 and a photosensitive drum 8. In the scanner unit 9, the laser light emitted from the laser diode 107 is shaped by the collimator lens 134, shaped into a parallel beam, reflected by the rotating polygon mirror 133, and deflected and scanned. The laser beam deflected and scanned passes through the fθ lens 132 and forms an image on the surface of the photosensitive drum 8 rotating in the direction of the arrow to form a dot-like spot. The main scanning direction indicated by the arrow (the rotation axis of the photosensitive drum 8) The scanning line is formed by moving in a direction parallel to the direction, and the photosensitive drum 8 is exposed.

  On the other hand, a reflection mirror 131 is provided at a position where a laser beam at a position upstream of the scanning start position S of the scanning line on the photosensitive drum 8 with respect to the main scanning direction is incident. The laser light incident on the reflection mirror 131 is incident on the BD sensor 121. The BD sensor 121 detects that a laser beam has entered, and outputs a timing signal corresponding thereto. Based on the BD signal that is the output from the BD sensor 121, the start timing of the laser beam scanning is determined. That is, the BD signal becomes a synchronization signal in the main scanning direction.

  In addition, after the laser beam scans the photosensitive drum 8 and before the next photosensitive drum 8 is scanned, automatic light amount control (APC) of the laser light amount is executed, and the light emission level of the laser diode 107 (for the next scanning) (Emission intensity) is adjusted.

  During the image forming operation, the scanner unit 9 emits a laser beam at a light emission level (intensity) that allows toner to adhere to the image formable area (effective area of the photosensitive drum 8) on the surface of the photosensitive drum 8 based on the image data. Irradiate.

  A drive current based on the operation of the laser drive circuit 130 flows through the light emitting element in the laser diode 107, and emits laser light with an intensity corresponding to the drive current. A control signal indicating the start of the image area (writing start timing) of the APC and photosensitive drum 8 is sent to the laser drive circuit 130 in synchronization with the BD signal, and image formation is started at the writing start timing. Further, the laser light is turned on / off at a timing synchronized with a reference clock for image formation based on the image signal.

  FIG. 2 is a block diagram illustrating a control configuration of the image forming apparatus.

  As shown in FIG. 2, 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 includes a ROM and a RAM. The ROM stores a program for controlling various operations of the image forming apparatus. The RAM stores a work area, variables, setting information, etc. for executing various processes executed by the CPU 27. Is used as a storage area for temporarily storing the data. In the case of a multi-beam laser, the writing position by the laser beam is shifted due to the distance between the laser elements. Therefore, the shift of the writing position generated on the photosensitive drum 8 is measured, and the correction value of the writing position is stored in the memory 28. Then, the CPU 27 reads the correction value and determines whether the writing position is simultaneous.

  The timing signal generator 25 generates a control signal (CTRL signal) for APC and image area (writing start timing). The timing signal generator 25 inputs the CTRL signal to the laser driver 12 of the optical control unit 11 and inputs the rotation control signal to the motor driver 15 that drives the polygon motor 13.

  The image signal generator 26 inputs image data received from an external device (a scanner device or a personal computer (PC)) to the laser driver 12 as an image signal based on the BD signal. This input is made to the image area according to the main scanning timing and the sub scanning timing generated by the timing signal generator 25. The laser driver 12 modulates the drive current set by the APC with an image signal and outputs the modulated current to the laser diode 107. As a result, the laser diode 107 outputs laser light having a lighting time corresponding to the gradation indicated by the image data.

  As described above, the control unit 19 drives the laser diode 107 via the laser driver 12. The laser diode 107 incorporates a photodiode (described later), and the laser driver 12 receives laser light and executes APC.

  FIG. 3 is a block diagram showing details of the image signal transmitted from the image signal generation unit and the internal configuration of the optical control unit when a two-beam laser is used.

  The image signal generator 26 shown in FIG. 3 shows a case where the image signal is output and transmitted as LVDS (low voltage differential signal), but the signal transmission method is not limited to LVDS, and other transmission methods may be used. It may be used. In the example of FIG. 3, the image signal generator 26 outputs the light emission timing of each laser according to the image data as the image signals (VD01, VD02), and is the time from on to off of the output image signal. Luminous time is determined.

  The laser driver 12 emits a laser in accordance with the image signal input from the image signal generator 26. The amount of light at this time is adjusted in the laser driver 12, and a drive current (ILD1, ILD2) corresponding to the amount of light is adjusted to a laser diode. 107 is supplied.

  In this embodiment, in order to form a light emission pattern with no image positional deviation, the above-described light emission time and light amount are adjusted as follows.

  FIG. 4 is a timing chart showing image signals (VD01, VD02) output to the laser driver and drive currents (ILD1, ILD2) supplied to the laser diode. 4A shows on / off timings of the image signals VD01 and VD02 input from the image signal generator 26 to the laser driver 12. FIG. On the other hand, (b) shows the time and amount of current through which the drive currents ILD1 and ILD2 flow from the laser driver 12 to the laser diode 107.

  FIG. 4A shows the on / off timing of the image signals VD01 and VD02 for each dot of the pixel. In this embodiment, when the image signal VD01 and the on-timing are simultaneous as indicated by the two-dot chain line, the light emission time without shifting the dot center as indicated by the solid line in the on-off timing of the image signal VD02. Is variable from the center of the dot to be equal to the left and right. This prevents the on / off timing of the image signal VD02 from overlapping with that of the image signal VD01. The on / off timing of the image signal VD02 is adjusted within one dot.

  FIG. 4B shows the on / off timing of the drive currents ILD1 and ILD2 for each pixel dot corresponding to FIG. 4A. As shown in FIG. 4A, when the image signal VD01 and the image signal VD02 are simultaneously turned on, the timing of turning on / off the image signal VD02 is varied to adjust the laser light quantity. The amount of laser light is determined according to the light emission time determined by the on / off timing of the image signal. For example, the light emission pattern is determined so that the density of one dot does not differ, such that the light amount is doubled when the light emission time is halved.

  For example, as shown in FIG. 4B, if the pulse width of the drive current ILD1 is T and the current value is H, the pulse width of the drive current ILD2 is T / 2 and the current value is 2H. It is adjusted to. In this way, the input energy by the drive currents ILD1 and ILD2 can be made the same.

  FIG. 5 is a flowchart showing a laser emission pattern changing procedure executed by the CPU 27 when a two-beam laser is used. Since a two-beam laser is used, in the following description, one of the two lasers is referred to as laser 1 and the other is referred to as laser 2.

  First, in step S1, when the CPU 27 receives an image formation request from an external device such as a scanner device or a PC, the CPU 27 reads the image writing position adjustment value of each laser from the memory 28. The adjustment value of the image writing position is measured in advance and is already stored in the memory 28 when the image forming apparatus is powered on.

  FIG. 6 is a conceptual diagram of the image writing position adjustment value.

  In the case of a multi-beam laser diode, the distance between the laser 1 and the laser 2 and the drum surface is different for each apparatus, and the writing timing (light emission) for adjusting the distance difference so that the laser light reaches the drum surface simultaneously. (Timing) adjustment value is set.

  When the writing position adjustment value is an integer multiple of the pixel 1-dot period (for example, 600 dpi), the laser writing timing (light emission timing) matches as shown in FIG. On the other hand, when the adjustment value is not an integer multiple of the one-dot period of the pixel, the laser writing timing does not match as shown in FIG.

  Therefore, next, in step S2 of FIG. 5, the CPU 27 checks whether or not the adjustment value of the read position of the read image of each laser is an integral multiple of one dot period. Here, if the adjustment value is an integer multiple, the writing start timing is the same. If it is determined that the adjustment value is an integer multiple of a one-dot period, the process proceeds to step S3; Proceed to S5.

  In step S3, the setting of the light emission time within one dot of the laser 2 is changed, and in step S4, the light amount setting value is changed to a light amount corresponding to the set light emission time. Thereafter, the process proceeds to step S5.

  In step S5, in accordance with the value changed in steps S3 to S4, and when it is determined that the adjustment value is not an integral multiple of a one-dot period, the set value is not changed, and an image forming mode in which image formation is performed. Start operation with.

  In step S6, the polygon motor 13 is rotated. In step S7, the process waits until the polygon motor 13 reaches a steady rotational speed at which image formation is possible. The process proceeds to step S8. In step S8, APC emission by the laser 1 is started. Next, in step S9, the process waits for detection of the BD signal. When the BD signal is detected, the process proceeds to step S10.

  In step S10, the laser 1 is turned off. In step S11, the laser 2 emits APC light. When the adjustment value of the light amount of the laser 2 is an integral multiple of a one-dot period, the light amount setting is changed, so that APC light emission is performed with the changed light amount. After the APC is emitted for a certain period of time, the laser 2 is turned off in step S12.

  In step S13, after the light amounts of the laser 1 and the laser 2 are adjusted by APC, an image signal corresponding to the light emission time is received. In step S14, each laser emits light in the VIDEO mode used for image formation in accordance with the received image signal, and image formation is performed in step S15.

  Therefore, according to the embodiment described above, it is determined whether or not the writing timing of the multi-laser is the same, and if the writing is the same, the light emission time within one dot is changed, and the light amount corresponding to the changed set time And the light emission patterns of the plurality of lasers are made different from each other. Accordingly, it is possible to prevent a plurality of lasers from being simultaneously turned on, reduce radiation noise, and form a high-quality image without pixel shift.

  In the embodiment described above, an example in which image formation is performed using a two-beam laser has been described. However, the present invention is not limited thereto. For example, the present invention can also be applied to a multi-beam type image forming apparatus using three or more lasers.

  In the above-described embodiment, a single-function image forming apparatus has been described as an example, but the present invention is not limited thereto. For example, a multifunction printer (copier) including an ADF unit that automatically feeds recording paper to the image forming apparatus described above and an image reading apparatus may be used, or a multifunction machine in which a facsimile function is added to the copier. .

8 Photosensitive drum, 12 Laser driver, 13 Polygon motor,
15 Motor driver, 19 Control unit 107 Laser diode,
121 BD sensor, 133 polygon mirror

Claims (5)

A first light emitting means for irradiating the photosensitive member with light to form an image;
Light emission is started at a timing delayed from the light emission start of the first light emission means, and light emission of the same light emission amount from the light emission start of the first light emission means to the light emission end by the time of light emission completion of the first light emission means. An image forming apparatus comprising: a second light emitting unit that finishes when the image forming process is completed.   During the period from the start of light emission to the end of light emission of the second light emitting means, the first light emitting means and the second light emitting means emit light for forming unit dots of an image formed on the photoconductor. The image forming apparatus according to claim 1. First setting means for setting a light emission timing of the second light emitting means;
And second setting means for setting a light emission amount of the second light emitting means,
The first setting means sets the light emission timing so that the light emission start timing and the light emission end timing of the second light emission means are different from those of the first light emission means,
The second setting means is configured to cause the light emission amount per unit dot to be the same as the light emission amount of the first light emission means based on the light emission timing by the first setting means. The image forming apparatus according to claim 1, wherein the amount of light emission is set. Each of the first light emitting means and the second light emitting means has a laser diode,
4. The image forming apparatus according to claim 1, wherein a drive current supplied to the laser diode is changed in accordance with a light emission amount of the second light emitting unit by the second setting unit. 5. . A storage means for storing an adjustment value for adjusting a light emission timing of the first light emission means and the second light emission means;
When the adjustment value stored in the storage means is an integral multiple of a period in which each dot is formed by the first light emitting means and the second light emitting means, the first setting means is configured to perform the second light emission. 5. The image forming apparatus according to claim 1, wherein the light emission timing of the means is set to be different from the light emission timing of the first light emission means.

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