JP4866057B2 - Optical device, image forming apparatus, and lighting position changing method - Google Patents

Description

  The present invention relates to an optical device used in a laser printer, a digital copying machine, and the like, an image forming apparatus having the optical device, and the like. The present invention relates to a method for changing a light beam lighting position (which is a lighting timing) output from a light emitting source when the light source is changed.

Documents disclosing means for correcting the main scanning magnification include Patent Documents 1 and 2. In these documents, in order to correct the main scanning magnification, a plurality of light beam detecting means for detecting a light beam on the main scanning line is used, and one of the light beam detecting means detects the light beam and then the other light. Means for correcting the main scanning magnification by measuring the number of counts of a predetermined clock until the beam detecting means detects the light beam, and correcting the write clock in comparison with a preset reference count number Is disclosed.
Japanese Patent No. 3315474 Japanese Patent No. 3548210

  In recent years, image forming apparatuses have been required to have high accuracy and high functionality, and have a function of changing a pixel clock frequency in order to correct a main scanning magnification or to correspond to a plurality of printing modes. Yes.

  In order to exhibit such a function, in the image forming apparatus, BD (Beam Detect) lighting for generating a line start signal for synchronizing the lines and automatic light amount adjustment of the light beam are performed. APC (Automatic Power Control) lights up. The lighting positions of these lighting are set by the count number obtained by counting the pixel clock with reference to the line start signal, and the BD lighting and the APC lighting are performed at the timing when the set value matches the pixel clock count number. FIG. 7 is a timing chart regarding the line start signal, the pixel clock, the BD lighting, the BD lighting signal indicating the start timing of the APC lighting, and the APC lighting signal. When the line start signal is inputted, the count value by the counter becomes 0 and the count is sequentially performed. When the count value becomes N, a BD lighting signal and an APC lighting signal are input.

  However, when the pixel clock frequency changes, such as when the main scanning magnification is corrected by a method such as Patent Documents 1 and 2, it is necessary to change these lighting positions.

  Conventionally, in order to reliably perform these lighting after changing the pixel clock frequency, before changing the pixel clock frequency, these lighting positions are set to positions corresponding to the changed pixel clock frequency, and then the pixel clock frequency is changed. I was going.

  However, when the pixel clock frequency is generated using a PLL (Phase Locked Loop) circuit, the target pixel clock frequency is not obtained immediately after the setting value of the PLL circuit is changed. It vibrates and converges to the target frequency after a predetermined time has elapsed. As an example, FIG. 8 shows a change example of the output frequency when the frequency of the pixel clock is changed from 50 MHz to 51 MHz. It can be seen that the frequency oscillates during the “unstable period” shown in FIG. At this time, in an unstable period until the frequency becomes stable, counting is performed with an unstable clock, and therefore BD lighting or APC lighting may be performed at an unexpected position.

  FIG. 9 shows a timing chart of signal input for BD lighting and APC lighting by counting with an unstable frequency pixel clock. While a clock faster than the target frequency is output, the counting speed is also increased. In this case, for example, as shown in (1) of FIG. 9, the light is lit from a position earlier than the target position. As a result, there is a possibility that the abnormal image is output in the effective image area. On the contrary, while a clock having a speed lower than the target frequency is being output, the counting speed is also slow. In this case, for example, as shown in (2) of FIG. 9, the lighting start position is delayed, and lighting is started from a position past the light beam detecting means. As a result, there is a possibility that the line start signal cannot be generated and the corresponding image cannot be output.

  The present invention has been made in view of such a background. Even when there is a period in which an unstable clock is output immediately after the pixel clock frequency is changed, the BD lighting or the APC lighting is appropriately performed. An object of the present invention is to provide an optical device or the like that changes the lighting position thereof.

An aspect of the present invention that achieves the above object includes a light emitting source that outputs a light beam by lighting control for controlling a lighting timing of the light emitting source, a deflecting unit that deflects the light beam in a main scanning direction, and the deflected light. In an optical device having a light beam detecting means for detecting a beam on a main scanning line and a clock generating means for generating a pixel clock for controlling the lighting of the light emitting source, light source driving data is created according to the pixel clock, Based on the light source driving data, the lighting position for controlling the lighting of the light source is changed from the end position of the effective image area to the detection position of the light beam detecting means in response to the pixel clock change request. when transitioning to, in an optical device including a lighting position changing means for changing the middle of both positions, and the turn-on position, the light beam by the light beam detecting means Characterized in that it is a turn-on position for detecting.
Immediately after changing the pixel clock frequency, the lighting position slightly fluctuates in an unstable state after changing the pixel clock frequency by changing the lighting position to a position with sufficient margin from the above situation. Even if it becomes, it becomes possible to perform appropriate lighting.

With the turn-on position or a lighting position for detecting the light beam by the light beam detecting means, a lighting position for performing automatic power adjustment of the light beam output from the light source, BD lighting and APC lighting can be appropriately performed even when the frequency of the pixel clock is changed.

  Another embodiment of the invention relates to an image forming apparatus having the optical device. Thereby, it is possible to provide an image forming apparatus capable of stably performing the lighting.

In another aspect of the present invention, light emission source drive data is created according to a pixel clock for lighting control that controls the lighting timing of the light emission source of the optical device used in the image forming apparatus, and the light emission source drive data is used as a basis. In addition, the lighting position of the light source is controlled from the end position of the effective image area to the detection position of the light beam detection means for detecting the light beam by the light beam detection means. It is characterized in that it is changed to the middle of both positions when changing.

  According to the present invention, the output frequency is unstable immediately after changing the frequency of the pixel clock by changing the lighting position to a position with a sufficient margin from the situation where lighting is performed at an unexpected position. Appropriate lighting can be performed even if the lighting position slightly moves back and forth.

  Hereinafter, the best mode for carrying out the optical apparatus and the image forming apparatus of the present invention will be described. In the description, the drawings submitted at the same time as this specification will be appropriately referred to. This optical device uses a laser diode (LD) as a light source, and functions as a writing control unit that forms an electrostatic latent image by irradiating the surface of the photosensitive drum with a laser beam. This writing control unit can be used not only for a monochrome monochrome image forming apparatus but also for a color image forming apparatus of a plurality of colors.

  FIG. 1 shows a schematic diagram of the configuration of the image forming apparatus. The charging device 101 charges the drum-shaped photoconductor 107. The charged photoconductor 107 is irradiated with light according to image data by the optical device 102 to form a latent image. The formed latent image is developed with toner by the developing unit 103. The developed image is transferred by the transfer unit 105 to a sheet material or the like sent from the paper supply unit 104. The image transferred to the sheet material or the like is thermally fixed by the fixing unit 106. Thereafter, the cleaning unit 108 cleans the photoreceptor 107 to remove excess toner.

  When forming a color image, an image is formed for each color component color (cyan (C), magenta (M), yellow (Y), black (Bk), etc.), and the image of each color is superimposed on the sheet material and transferred. By doing so, a color image is formed.

  FIG. 2 shows a schematic block diagram of hardware resources of the image forming apparatus. The image forming apparatus includes a scanner unit 201 that reads a document image, an AU (Analog) / D (Digital) conversion of the read signal, black offset correction, shading correction, and an IPU (Image Processing Unit) 202 that performs image processing. ASIC (Application Specific Integrated Circuit) 203 for controlling writing, an LD control unit 204 for controlling a semiconductor laser, a semiconductor LD 205 for forming electrostatic latent image data on a photosensitive drum, and the entire apparatus CPU (Central Processing Unit) 206 that executes control of the CPU, ROM (Read Only Memory) 207 as a recording medium that stores a control program to be read by the CPU 206, and RAM (Random Access Memory) temporarily used by the control program 208, an image memory 209 for storing the read image as image data, and exchange of data between the devices Local I / F 211 for interfacing between the internal system bus 212, and a system bus IPU202 performed, the user gives an instruction, and an operation panel 210 for displaying an image is formed. When an electrostatic latent image is formed on the photoconductor 107 from the image read by the scanner unit 201 and printed out by the printer unit, the CPU 206 performs sub-scanning position control of the paper, and the write control ASIC 203 is controlled. A line start signal in the main scanning direction is output. The write control ASIC 203 receives the image data from the IPU 202 based on the line start signal, and turns on the LD 205 by the LD control unit 204 based on the image data.

  FIG. 3 illustrates the configuration of the optical device 102. The optical device 102 will be described. Laser beam light is emitted from the semiconductor LD 205. The emitted light beam is scanned in one direction (main scanning direction) as the polygon mirror 301 rotates under the polygon control unit 302. The scanned light beam forms a latent image on the scanned medium (photosensitive member 107) via the Fθ lens 303. The scanned beam light is detected by traversing the light beam detecting means 304 on the extension of the scanned medium, and the detection signal is output. Using the output detection signal, the dot position deviation detection control unit 305 detects a position deviation in the main scanning direction, and outputs correction data for correcting the position deviation to the pixel clock generation unit 306. The pixel clock generation unit 306 generates a pixel clock based on the correction data. The IPU 202 performs image processing at a timing based on the generated pixel clock. In accordance with the output detection signal, the image data processed by the IPU 202, and the pixel clock generated by the pixel clock generation unit 306, LD drive data generation unit 307 generates LD drive data. Based on the generated LD drive data, the LD control unit 204 controls the lighting of the LD 205.

  Since an image generally covers a plurality of lines, the above process is performed for each line. Therefore, it is necessary to align the image writing position on each line. This is because if the writing position is shifted in each line, the line in the sub-scanning direction is bent or appears in a shifted form in the finally formed image. Therefore, as a method for aligning the image writing position, the light beam detector 304 is arranged on the main scanning line, and each line start signal is generated based on the detection signal output when the light beam is incident on the light beam detector 304. Then, image writing is performed.

  In the color image forming apparatus, the latent image formed by the optical device 102 needs to have the same main scanning magnification for each color. This is because, if the image width of each transferred color is shifted, it finally appears as a color shift.

  Since the main scanning magnification changes due to the influence of the environment and the temperature of the machine, it is necessary to control the main scanning magnification for each color. The main scanning magnification is controlled by changing the pixel clock by the pixel clock generation unit 306, and the pixel clock generation unit 509 is provided with a PLL circuit and has a phase variable function.

  Further, the light amount of the LD 205 changes due to the influence of the machine temperature and the like. When the light amount of the LD 205 changes, the latent image generated on the scanned medium also changes. Therefore, it is necessary to perform control so that the light amount of the LD 205 is kept constant at regular intervals. As this control method, automatic light amount adjustment (APC) is generally known in which the amount of light detected by a photodiode installed inside or outside the LD is fed back and controlled. APC is generally performed outside the effective image area. Therefore, APC lighting, which is LD lighting necessary for performing APC, is also performed outside the effective image area.

  Considering the safety of the light beam, it is desirable to turn off the LD 205 outside the image area. However, if the LD 205 is turned off outside the image area, the light beam does not enter the light beam detecting means 304 and the APC is not turned on in the same manner. Therefore, the LD is turned on at an appropriate position outside the image area. To control.

  Therefore, it is necessary to set the BD lighting position and the APC lighting position and control the LD 205 so that light irradiation is performed from a desired position on the main scanning line. Note that BD lighting starts when a BD lighting signal is output, and turns off when laser light is incident on the light beam detecting means 304. These positions are set based on the line start signal and the time elapsed from the reference, the pixel clock count counted from the reference, and the like.

  Considering the safety of the light beam and the life of the LD, it is desirable to start the BD lighting immediately before the light beam detecting means 504, and the LD light quantity needs to be kept as constant as possible in the image area. The APC lighting is preferably performed immediately before the line starts.

  The BD lighting and APC lighting signals are generated using the counter 308, the lighting position setting value 310 that can be input from the operation panel 210, and the comparator 309. The counter 302 counts the pixel clock generated by the pixel clock generation unit 306 and is reset by the line start signal. The counter value is compared with the lighting position set value 310 by the comparator 309, and when the counter value and the set value become equal, a lighting signal is output to the LD drive data generation unit 307.

  However, when there is a pixel clock change request from the CPU 206 to change the main scanning magnification and the pixel clock is changed, as described above, the pixel clock frequency output from the pixel clock generation unit 306 is not corrected until the pixel clock frequency is stabilized. There is a problem that BD lighting and APC lighting are not performed. A method for solving this problem will be described.

  This will be described with reference to the flowchart of FIG. In the image forming apparatus, when there is a pixel clock change request from the CPU 206 (S01), first, the BD lighting position and APC lighting position are changed (S02), and then the pixel clock is changed (S03). Resolve. Changing the BD lighting position and the APC lighting position means shifting these lighting positions to positions earlier than in the conventional case (see FIG. 9). After waiting until the pixel clock is stabilized, the BD lighting position and the APC lighting position are returned to the original positions (S04).

  FIG. 5 shows a timing chart showing the transition of the BD lighting position, and FIG. 6 shows a timing chart showing the transition of the APC lighting position. The numbers in FIGS. 5 and 6 correspond to the numbers in the flowchart of FIG. 4, and each signal indicates a lighting signal in the process of each flowchart.

  When there is a pixel clock change request, first, the BD lighting position and the APC lighting position are changed to an intermediate position from the end position of the effective image area to the light beam detection position (S02 in FIG. 5 and S02 in FIG. 6). Here, the “intermediate position” refers to the time when the image processing of the next main scanning line is performed after the completion of the image processing for one line of the main scanning after the beam light is irradiated to the end position of the effective image area. This is the intermediate timing between the two timings when the light beam detecting means 304 shifts to the timing for detecting the light beam applied to the line. This intermediate position is best performed at a position that bisects the interval between the above two timings, but the object of the present invention can be achieved even at a position slightly deviated from this position.

  While the clock whose pixel clock is faster than the target frequency is being output, the counting speed is increased, and conversely, when the clock having a lower speed than the target frequency is being output, the counting speed is also decreased. However, when each lighting position is changed to the above-described position, the interval from the designated lighting position to the effective image area and the light beam detection position becomes wider than the original position. At this time, the pixel clock frequency was changed, and until the output frequency was stabilized (see FIG. 8), counting was performed with a clock faster than the target frequency, and lighting was started at a position faster than the target lighting position. Even in this case, since there is a sufficient margin with respect to the effective image area, it does not light up in the image area and become an abnormal image. Also, when the pixel clock frequency is changed and the output frequency stabilizes (see Fig. 8), counting is performed with a clock slower than the target frequency, and lighting starts at a position later than the target lighting position. However, since there is a sufficient margin with respect to the light beam detection position, the light beam detection will not be disabled.

  Thereafter, after the pixel clock frequency is stabilized, each lighting position is returned to the original position (S04 in FIG. 5 and S04 in FIG. 6).

  Although it is not always necessary to return each lighting position after the pixel clock frequency is stabilized, if the BD lighting is performed at the position of S02 in FIG. 5, the lighting time increases compared to the case of S01 in FIG. Considering the safety of the LD, unnecessary lighting should be avoided as much as possible, and even when considering the life of the LD, it is ideal to make the lighting time as short as possible, so the BD lighting position is the pixel clock frequency. It is desirable to return it to its original position after it has stabilized. In addition, when APC lighting is performed at the position of S02 in FIG. 6, the output of the light beam adjusted by APC lighting decreases with the passage of time. Therefore, when APC lighting is performed at the position of S02 in FIG. 6, even if the light quantity is adjusted to be optimal for image formation by APC lighting, the APC lighting is performed at the position of S01 in FIG. This is longer than the case where it is performed, and there is a concern about deterioration of image quality. Therefore, it is desirable to return the APC lighting position to the original position after the pixel clock frequency is stabilized.

  By implementing this embodiment, the following effects can be obtained. In other words, by changing the BD lighting position and the APC lighting position to a position with a sufficient margin from the situation where the problem occurs, immediately after changing the pixel clock frequency, the output frequency is unstable and the lighting position is slightly moved back and forth. Even if it comes to do, it becomes possible to perform appropriate lighting. At this time, in consideration of returning to the original position, the position having a sufficient margin may be set to an intermediate position from the end position of the effective image area to the detection position of the light beam detection means.

  The above-described embodiment is the best mode for carrying out the present invention, but the present invention is not limited to this. Therefore, various modifications can be made without departing from the scope of the present invention.

  Development of laser printers, digital copying machines, and the like, which are image forming apparatuses equipped with the optical apparatus of the present invention, is desired.

1 is a schematic diagram of a configuration of an image forming apparatus. 1 is a schematic block diagram of hardware resources of an image forming apparatus. 2 shows the configuration of the optical device 102. 5 is a flowchart illustrating a method of changing a BD lighting position and an APC lighting position. The timing chart showing transition of BD lighting position is illustrated. 3 is a timing chart showing the transition of the APC lighting position. It is a timing chart regarding the BD lighting signal and APC lighting signal which show the start timing of a line start signal, a pixel clock, BD lighting, and APC lighting. A change example of the output frequency when the frequency of the pixel clock is changed from 50 MHz to 51 MHz is shown. A timing chart of signal input of BD lighting and APC lighting by performing counting with a pixel clock having an unstable frequency is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Charging part 102 Optical apparatus 103 Developing part 104 Paper feeding part 105 Transfer part 106 Fixing part 107 Photoconductor 108 Cleaning part 201 Scanner part 202 IPU
203 ASIC for write control
204 LD control unit 205 LD
206 CPU
207 ROM
208 RAM
209 Image memory 210 Operation panel 211 Local I / F
212 Internal system bus 301 Polygon mirror 302 Polygon control unit 303 Fθ lens 304 Light beam detection means 305 Dot position shift detection control unit 306 Pixel clock generation unit 307 LD drive data generation unit 308 Counter 309 Comparator 310 Lighting position setting value

Claims (4)

A light source that outputs a light beam by lighting control for controlling the lighting timing of the light source; and
Deflecting means for deflecting the light beam in the main scanning direction;
A light beam detecting means for detecting the deflected light beam on a main scanning line;
In an optical device having a clock generation means for generating a pixel clock for controlling lighting of the light emitting source,
In accordance with the pixel clock, light source drive data is created, and based on the light source drive data, the lighting position when performing the lighting control for controlling the lighting of the light source is an effective image according to the pixel clock change request. in the optical device and a lighting position changing means for changing in the middle of, the two positions when the transition from the position of the end of the region to the detection position of the light beam detecting means,
The optical device is characterized in that the lighting position is a lighting position for detecting a light beam by the light beam detecting means . A light source that outputs a light beam by lighting control for controlling the lighting timing of the light source; and
Deflecting means for deflecting the light beam in the main scanning direction;
A light beam detecting means for detecting the deflected light beam on a main scanning line;
In an optical device having a clock generation means for generating a pixel clock for controlling the lighting of the light emitting source,
In accordance with the pixel clock, light source drive data is created, and based on the light source drive data, the lighting position when performing the lighting control for controlling the lighting of the light source is an effective image according to the pixel clock change request. In an optical device comprising a lighting position changing means for changing to the middle of both positions when transitioning from the position of the end of the region to the detection position of the light beam detection means,
The lighting position and the optical science device you being a lighting position for performing automatic power adjustment of the light beam output from the light source. An image forming apparatus having an optical device according to claim 1 or 2. When light source drive data is created according to the pixel clock for lighting control that controls the lighting timing of the light source of the optical device used in the image forming apparatus, and lighting control of the light source is performed based on this light source drive data Between the two positions when the lighting position for detecting the light beam by the light beam detecting means is changed from the end position of the effective image area to the detection position of the light beam detecting means. The lighting position changing method characterized by making it change.

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