KR20070034360A - Image Forming Apparatus and Image Forming Method for Correcting Light Fluctuation - Google Patents

Abstract

Provided is an image forming apparatus for correcting a light amount deviation. The image forming apparatus includes a photosensitive unit which is arranged in a sub-scanning direction with a photosensitive member on which an electrostatic latent image is formed and which has a different optical power to the photosensitive member, and an optical power as the loss of the amount of light reaching the photosensitive member increases. And a controller configured to scan the laser light having a large size and to scan the laser lights overlapping to form a main-scan line. There is also provided an image forming method for correcting the light amount deviation.

Image forming apparatus, optical scanning unit, multi beam, light intensity deviation

Description

Image forming apparatus for correcting variation of laser beam and method using the same}

1 is a graph showing a light amount distribution in a photoconductor according to the prior art.

2 is a schematic diagram showing an image forming apparatus according to an embodiment of the present invention.

3 is a schematic view showing a light scanning unit of FIG.

4 is a block diagram of the image forming apparatus of FIG. 1.

5 is a diagram illustrating creating a line buffer for dividing and storing binary data.

6 is a diagram showing the pulse signal and dot size of the laser diode for correcting the light amount deviation.

7A-7C are diagrams sequentially illustrating main-scanning lines scanned onto the photoreceptor surface through the line buffer of FIG. 6.

8 is a flowchart illustrating an image forming method according to another exemplary embodiment of the present invention.

** Explanation of symbols in main part of drawing **

135: photosensitive member

200: Gwangjusa Unit

211, 212: laser diode

320: control unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and an image forming method, and more particularly, to an image forming apparatus and an image forming method for correcting a variation in the amount of light reaching the surface of a photosensitive member.

Image forming apparatuses, such as laser printers and digital copiers, charge the photoreceptor surface with negative charges and then, by inputting image data, the laser diode scans a laser beam on the photoreceptor surface to neutralize the charged area. After forming an electrostatic latent image, the toner is developed, transferred, and fixed in order to form an image.

The laser scanning unit scans the laser light on the surface of the photoconductor. Laser light emitted from the laser diode of the optical scanning unit is incident to the rotating polygon mirror. As the polygon mirror rotates, the deflected laser light is scanned in a direction perpendicular to the moving direction (sub-scanning direction) of the photoconductor (main-scanning direction). Since the laser light is modulated corresponding to the image to be printed, an electrostatic latent image is formed on the surface of the photosensitive member.

The laser diode may always be said to emit laser light having a constant amount of light, but the amount of laser light reaching the surface of the photoconductor is not constant. This is mainly because a large portion of the incident and reflection is performed while the laser light reaches the photosensitive member, and a large portion of the loss occurs.

1 is a graph showing a light amount distribution in a photoconductor according to the prior art.

Referring to FIG. 1, the amount of light is maximized at the center portion of the photoconductor along the main-scanning direction, and at the vicinity of both edges, the amount of light is relatively smaller than at the center portion. In this case, both edge portions having a small amount of light are printed relatively blurred than a central portion having a large amount of light, which causes a problem of degrading print quality.

In Korean Patent Laid-Open Publication No. 2005-0048907, a light quantity deviation is corrected by adjusting a driving voltage of a laser diode under the title of "A device and method for controlling a laser diode output through optical power compensation." That is, the output voltage of the laser diode is measured, and a control voltage is generated by proportionally integrating the error voltage between the reference voltage and the output voltage. The control voltage generates a driving voltage of the laser diode compensated for the light amount deviation.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide an image forming apparatus and an image forming method for correcting a variation in amount of light scanned on a surface of a photosensitive member through a plurality of laser lights having different optical powers in order to solve the above problems.

Another object of the present invention is to provide an image forming apparatus and an image forming method in which a variation in dot size is minimized to correct an amount of light variation.

An image forming apparatus according to an aspect of the present invention for solving the above technical problem is a light scanning unit for scanning a photosensitive member on which an electrostatic latent image is formed and a plurality of laser lights arranged in a sub-scanning direction and having different optical powers to the photosensitive member. And a controller configured to scan the laser light having a larger optical power as the loss of the amount of light reaching the photosensitive member is larger, and to superimpose the laser lights to form a main-scan line.

Preferably, the photoreceptor moves in the sub-scanning direction by one corresponding to the main-scanning line.

Further, preferably, the laser light is modulated by a pulse width modulation (PWM) signal.

In the image forming method of forming an image by forming an electrostatic latent image on the photosensitive member according to another aspect of the present invention for solving the above technical problem, the main-scan line is divided in accordance with the deviation of the amount of light reaching the photosensitive member, By scanning a plurality of laser lights having different optical powers arranged in a sub-scanning direction overlapping the photosensitive member, the main-scanning line is formed in the photosensitive member, and the optical power increases as the amount of light reaching the photosensitive member increases. Scan a large laser light.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present embodiment is not limited to the embodiment disclosed below and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosure may be made thorough and complete, and to fully convey the spirit of the invention to those skilled in the art. Like numbers refer to like elements throughout.

2 is a schematic diagram showing an image forming apparatus according to an embodiment of the present invention.

Referring to FIG. 2, the image forming apparatus 100 may include a paper feeding unit 110, a developing unit 130, a transfer unit 140, a fixing unit 170, a discharge unit 180, and a light scanning unit 200. Include.

The paper feeding unit 110 includes a paper feeding cassette 112 and a pickup roller 114. When the image formation starts, the print medium P is picked up from the paper feeding cassette 112 by the pickup roller 114 to the developing unit 130. Supplied to the side.

The developing unit 130 develops toner on the photosensitive member 135 on which the electrostatic latent image is formed. The transfer unit 140 transfers the toner image developed on the photosensitive member 135 to the print medium P. FIG. The print medium P on which the toner image is formed is fixed by heat and pressure while passing through the fixing unit 170. The print medium P on which image formation is completed is discharged to the outside through the discharge unit 180.

The construction and operation of the paper feeding unit 110, the developing unit 130, the transfer unit 140, the fixing unit 170 and the discharge unit 180 is well known to those skilled in the art and will not be described in detail below.

The optical scanning unit 200 scans a plurality of laser lights arranged in the sub-scanning direction to form an electrostatic latent image on the surface of the photosensitive member 135 of the developing unit 130.

3 is a schematic view showing a light scanning unit of FIG.

Referring to FIG. 3, the optical scanning unit 200 includes a first laser diode 211, a second laser diode 212, a first incident optical system 221, a second incident optical system 222, and a polygon mirror 240. , A synchronization detecting unit 230 and a scanning optical system 250.

The two laser diodes 211 and 212 are independently modulated by the laser driving circuits 331 and 332 to emit laser light. The laser light by the two laser diodes 211, 212 is arranged parallel to the sub-scanning direction, which is the moving direction of the photosensitive member 135.

Since the laser diodes 211 and 212 are arranged so that the two laser lights emitted are parallel to the sub-scanning direction, the photoconductor 135 is performed once a scan is made in the main-scanning direction as the polygon mirror 240 rotates. Two main-scanning lines by two laser lights are formed on the surface of).

On the other hand, the two laser diodes 211 and 212 arranged in the sub-scanning direction have different optical powers. In this embodiment, the optical power of the first laser diode 211 is greater than the optical power of the second laser diode 212. The difference in the optical power may be a degree corresponding to the variation in the amount of light occurring on the surface of the photosensitive member 135.

The first and second incident optical systems 221 and 222 are collimator lenses that make the laser light emitted from the laser diodes 211 and 212 convergent or parallel light with respect to the optical axis, and the collimator. And a slit for limiting laser light passing through the lens, and a cylindrical lens for imaging the laser light passing through the slit in a horizontal linear direction.

The laser lights passing through the first and second incident optical systems 221 and 222 are deflected by the polygon mirror 240. The polygon mirror 240 is rotated by the polygon mirror motor 345 of FIG. 4. The incident laser light is deflected continuously with its angle changing as the polygon mirror 240 rotates. In general, one scan in the main-scan direction corresponds to one surface of the polygon mirror 240.

Laser light deflected by the polygon mirror 240 is scanned through the scanning optical system 250 to the surface of the photoreceptor 135. The scanning optical system 250 has a constant refractive index with respect to the optical axis and passes through the afceta lens 252 and the afceta lens 252 which focus on the photoreceptor 135 by correcting aberration of light deflected by the polygon mirror 240. And a reflecting mirror 254 that reflects one laser light to the photosensitive member 135 side.

The synchronization detecting unit 230 detects a position to start scanning by synchronizing the laser light in the main-scanning direction. That is, the synchronization detecting unit 230 detects a path of the laser light and operates as a synchronization means for finding a time point to start scanning to the surface of the photoreceptor 135. In general, the synchronization detecting unit 230 includes an optical sensor (unsigned) installed outside the scanning area to detect the laser light. When the synchronization detector 230 detects the laser light, the laser light starts scanning on the surface of the photoreceptor 135 after a predetermined time elapses.

4 is a block diagram of the image forming apparatus of FIG. 1.

Referring to FIG. 4, the memory unit 315 temporarily stores a line buffer, which will be described later, and stores a look-up table for converting line data stored in the line buffer into a dot size for printing. do.

The controller 320 controls the overall operation of the image forming apparatus 100 and stores the line data for driving the first laser diode 211 and the second laser diode 212 from a line buffer to be described later. Accept each from. The lookup table then converts each to the actual dot size to print. The dot size information is generally 8 bits, and has a value from 0 to 255.

In addition, the information about the converted dot size is transmitted to the first pulse width modulation (PWM) 321 and the second PWM unit 322. The PWM units 321 and 322 generate a PWM signal from the information about the dot size received from the controller 320.

The laser driving circuits 331 and 332 modulate the laser light emitted from the laser diodes 211 and 212 according to the PWM signals transmitted from the PWM units 321 and 322. That is, the laser driving circuits 331 and 332 turn on and off the laser diodes 211 and 212 according to the PWM signal. As the laser diodes 211 and 212 are turned on and off, an electrostatic latent image corresponding to the PWM signal is formed on the surface of the photosensitive member 135.

The synchronization detecting unit 230 detects the synchronization signal of the laser light as described above. The polygon mirror motor 345 rotates the polygon mirror 240, and the polygon mirror control unit 340 controls the polygon mirror motor 345.

The photosensitive member motor 355 rotates the photosensitive member 135, and the photosensitive member controller 350 controls the photosensitive member motor 355. In particular, the photoconductor controller 350 controls the photoconductor motor 355 to move the photoconductor 135 only by one main-scan line so that two laser lights arranged in the sub-scanning direction overlap each other. do.

That is, once scanning is performed, two main-scan lines are formed on the surface of the photosensitive member 135 in parallel in the sub-scanning direction by two laser lights. The photosensitive member 135 moves only as much as one main-scan line. Therefore, in the second scan, the surface of the photosensitive member 135 overlaps the newly scanned main-scan line with at least one of the two main-scan lines. That is, one main-scan line is formed by overlapping through two laser lights and scanning twice.

The image data processor 310 converts image data input from a host computer (not shown), a scanner (not shown), or the like into binary data. In addition, the binary data is divided according to the amount of light deviation to generate a line buffer and store it in the memory unit 315.

5 is a diagram illustrating creating a line buffer for dividing and storing binary data.

Referring to FIG. 5, the binary data converted from the input image data has a form in which main-scan line data (lines 1, 2, ...) with respect to the main-scan direction are arranged in the sub-scan direction. Have

The image data processor 310 may scan first line data (line 1-1, line 2-1,...) To be scanned by the first laser diode 211 for each main-scan line according to the light amount deviation of the photosensitive member 135. And second line data (lines 1-2, 2-2, ...) to be scanned by the second laser diode 212 to generate a line buffer.

The 'dummy' of FIG. 5 is a temporary line buffer without any data and does not generate any signal that modulates the laser diodes 211 and 212. This is because complete main-scan line data is formed when the first line data and the second line data overlap each other and are scanned.

The optical power of the first laser diode 211 is greater than the optical power of the second laser diode 212. Therefore, the first line data (lines 1-1, 2-1, ...) related to the first laser diode 211 is a portion in which the photosensitive member lacks light quantity (generally, both side edges of the photosensitive member 135). In the portions D1 and D3, the second line data (lines 1-2, 2-2, ...) relating to the second laser diode 212 is a portion having a relatively constant light amount (generally, a photosensitive member ( 135) to the center portion D2).

That is, according to the present invention, a plurality of laser lights are arranged in the sub-scanning direction, and the laser light having a relatively large optical power is scanned in a portion where the amount of light loss is large. As the optical power increases, the loss of the amount of light can be compensated for, and thus the amount of light deviation can be corrected.

6 is a diagram showing the pulse signal and dot size of the laser diode for correcting the light amount deviation.

Referring to FIG. 6, one period of the video clock VCLK corresponds to one bit of binary data, that is, one dot.

For the sake of simplicity, it is assumed that the amount of light at both corners of the photosensitive member 135 is only 50%, and the optical power of the first laser diode is 133% of the optical power of the second laser diode. In this case, even if the input dot size is 64, the amount of light at both edges is 50%, so that the dots actually scanned on the photosensitive member 135 have brightness corresponding to the size of 32.

According to the related art, in order to correct the light amount deviation, the dot size deviation may be reduced by increasing the driving voltage or pulse width at both corner portions to 200%. However, according to the present invention, since the optical power of the second laser light to be scanned at both corners is 133%, the same brightness can be obtained even by increasing the driving voltage or the pulse width by only 150%. That is, according to the present invention, the pulse widths on the left and right sides can be reduced by increasing the optical power, thereby minimizing the variation in dot size for correcting the variation in the amount of light.

The first PWM signal PWM1 is modulated from the first line data line 1-1, and the second PWM signal PWM2 is modulated from the second line data line 1-2. One main-scan line (line 1) is the sum of the first line data (line 1-1) of the first laser diode 211 and the second line data (line 1-2) of the second laser diode 212. Is formed. Therefore, when the first PWM signal PWM1 and the second PWM signal PWMM are overlapped in one line, the main-scan line is completed.

The PWM signals PWM1 and PWM2 are converted into dot sizes by the controller 320 through the line data lines 1-1 and 1-2, respectively, and then modulated by the PWM units 321 and 322, respectively. It is a signal. The first PWM signal PWM1 modulates the first laser diode 211, and the second PWM signal PWM2 modulates the second laser diode 212.

7A-7C are diagrams sequentially illustrating main-scanning lines scanned onto the photoreceptor surface through the line buffer of FIG. 5.

Referring to FIG. 7A, firstly, the first laser light and the second laser light are scanned on the photosensitive member 135 to form two main-scan lines L1 and L2 in the sub-scanning direction. At this time, a dummy line is formed in the first main-scan line L1, and line data for line 1-2 is scanned in the second main-scan line L2.

FIG. 7B shows a case where the first laser light and the second laser light are scanned secondly after the photosensitive member 135 is moved once in the sub-scanning direction. The first laser light is scanned superimposed on the second main-scan line L2, and the second laser light is scanned on the third main-scan line L3. Since the first laser light scans the line data for line 1-1, the second main-scan line L2 eventually forms 'line 1' (see FIG. 5) of the line data. In the third main-scanning line L3, line data relating to the line 2-2 is scanned.

FIG. 7C shows a case where the first laser light and the second laser light are scanned for the third time after the photoreceptor 135 is moved once more in the sub-scanning direction. The first laser light is scanned superimposed on the third main-scan line L3, and the second laser light is scanned on the fourth main-scan line L4. Since the first laser light scans the line data for the line 2-1, the third main-scan line L3 forms 'line 2' of the binary data. In the fourth main-scanning line L4, line data relating to the line 3-2 is scanned.

As described above, in the present invention, a plurality of laser lights having different optical powers are arranged in the sub-scanning direction, and are superposedly scanned to form one main-scan line, thereby completing the electrostatic latent image. Among the laser lights, laser light having a large optical power is scanned in a portion having a large amount of light loss to correct a light amount deviation.

8 is a flowchart illustrating an image forming method according to another exemplary embodiment of the present invention.

Referring to FIG. 8, the image data processing unit 310 converts input image data into binary data (S110).

The binary data is divided into main-scan lines (line 1, line 2, ...) according to the amount of light deviation to generate a line buffer (S110). At this time, the line buffer is divided so that laser light having a large optical power is scanned at a portion having a large amount of light loss.

The control unit 320 converts the dot size through the line data stored in the line buffer, modulates a PWM signal corresponding to each laser diode, and scans the laser light (S120).

After one scan is finished, the photosensitive member 135 is moved in the sub-scanning direction by one main-scanning line (S130).

The entire line has not been scanned, and then laser light is scanned through the line buffer (S140). In this case, two laser lights are superimposed to form one main-scan line.

In the above embodiments, the light amount deviation is corrected through two laser lights. However, it is preferable to arrange three or more laser lights having different optical powers in parallel in the sub-scanning direction to correct the light amount deviation. Would fall into the category of technical ideas.

In addition, although the above embodiments exemplify PWM modulation of laser light, pulse amplitude modulation (PAM) modulation of laser light is also within the scope of the technical idea of the present invention.

That is, the terms and expressions used herein are used for descriptive purposes only and do not have any limitation, and the use of such terms and expressions is not intended to exclude the equivalents of the components or parts thereof shown and described. Of course, various modifications are possible within the scope of the claimed invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

As described above, according to the present invention, a plurality of laser lights having different optical powers are arranged in the sub-scanning direction, and laser light having a large optical power is scanned in a portion having a large amount of light loss to correct the light amount variation. In addition, it is also possible to minimize the deviation of the dot size for correcting the deviation of the amount of light through the laser light of different optical power.

According to the present invention, the size of the dots formed on the print medium can be made uniform by the light amount deviation correction, and the print quality is improved.

Claims (5)

A photosensitive member on which an electrostatic latent image is formed; A light scanning unit which scans a plurality of laser lights arranged in a sub-scanning direction and having different optical powers to the photosensitive member; And And a controller configured to scan the laser light having a larger optical power as the loss of the amount of light reaching the photosensitive member is larger, and to superimpose the laser lights to form a main-scan line. The method of claim 1, And the photosensitive member moves in the sub-scanning direction by one corresponding to the main-scanning line. The method of claim 1, And the laser light is modulated by a pulse width modulation (PWM) signal. An image forming method of forming an image by forming an electrostatic latent image on a photosensitive member, Split the main-scan line according to the deviation of the amount of light reaching the photosensitive member, Scanning a plurality of laser lights having different optical powers arranged in the sub-scanning direction to overlap the photoconductor to form the main-scan line on the photoconductor, and the greater the loss of the amount of light reaching the photoconductor, the higher the optical power. An image forming method characterized by scanning a large laser light. The method of claim 4, wherein And the photosensitive member moves in the sub-scanning direction by one corresponding to the main-scanning line.

Images