JP2008170640A - Image forming apparatus and laser light-amount controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce image density unevenness in a sub-scanning direction. <P>SOLUTION: An image forming apparatus includes: an image processing part for binarizing image data output to a laser exposure device scanning and exposing a photoreceptor drum in accordance with a processing condition for image density reproduction; and a light amount setting part 205 for setting an emission light amount of laser light output from the laser exposure device based on a detected variation amount and a processing condition set on a screen processing part by detecting the variation amount of a mutual spacing of a scanning line of the laser amount scanning and exposing the surface of the photoreceptor drum. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine and a printer using an electrophotographic system.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, when a charged photosensitive drum is scanned and exposed with a laser beam, the scanning pitch of the laser beam in the sub-scanning direction needs to be uniform. For this reason, the photosensitive drum is positioned at a predetermined position so that the laser beam irradiation position on the surface of the photosensitive drum is determined at a predetermined position, and a laser exposure apparatus is also fixedly installed. However, the image forming apparatus is provided with a driving source such as a motor for rotating the photosensitive drum and a conveying system for conveying the recording paper, and vibrations from these driving sources are easily transmitted to the entire image forming apparatus. . Also, the rotational speed of the photosensitive drum may vary due to some factor. If the relative position between the laser exposure device and the photosensitive drum fluctuates due to such vibrations or fluctuations in the rotational speed of the photosensitive drum, density unevenness in the sub-scanning direction (recording paper conveyance direction) will appear on the image. May occur.

  Therefore, in order to suppress the occurrence of density unevenness due to vibration or the like, for example, an optical unit on which a laser exposure apparatus is mounted is attached to the image forming apparatus main body via a vibration isolator (for example, see Patent Document 1), or a polygon mirror. On the other hand, a technique for applying a vibration having a phase opposite to the frequency and frequency of vibration of the polygon mirror and substantially equal to the vibration amount is disclosed (for example, see Patent Document 2).

JP 2001-194849 A (page 3-4) JP 2001-38955 A (page 4-6)

  An object of the present invention is to reduce image density unevenness in the sub-scanning direction.

  For this purpose, the image forming apparatus according to the present invention includes a photoconductor, a laser exposure unit that outputs one or more laser beams for scanning and exposing the surface of the photoconductor, and image data output to the laser exposure unit. A binarization processing unit that binarizes in accordance with processing conditions for reproducing image density, a scanning line interval detection unit that detects a variation amount of an interval between scanning lines of laser light that scans and exposes the surface of the photoreceptor, and a scanning line A light amount setting unit for setting the light emission amount of the laser light output from the laser exposure unit based on the fluctuation amount detected by the interval detection unit and the processing conditions set by the binarization processing unit It is characterized by.

Here, the binarization processing unit binarizes the image data in accordance with the processing conditions set to reproduce the halftone in a pseudo manner, and the light amount setting unit sets the light amount of the laser light corresponding to the processing conditions. It can be characterized by. The binarization processing unit may be characterized in that the image data is binarized according to a processing condition set corresponding to an image attribute included in the image data. Further, the binarization processing unit binarizes the image data using a predetermined screen angle set corresponding to the image attribute included in the image data, and the light amount setting unit corresponds to the screen angle of the laser light. It can be characterized by setting the amount of light.
Further, the scanning line interval detection unit can detect the fluctuation amount based on the irradiation position of the laser light from the laser exposure unit on the surface of the photosensitive member in the sub-scanning direction. Furthermore, the scanning line interval detection unit is characterized in that it detects the amount of variation based on the irradiation position of the laser beam from the laser exposure unit on the surface of the photosensitive member in the sub-scanning direction and the variation in the rotational speed of the photosensitive member. can do.

In addition, the image forming apparatus of the present invention reproduces the image density of the photoconductor, the laser exposure unit that outputs one or more laser beams for scanning exposure on the surface of the photoconductor, and the image data output to the laser exposure unit. A binarization processing unit that binarizes in accordance with the processing conditions for this, and a light amount setting for setting the light emission amount of the laser light output from the laser exposure unit corresponding to the interval between the scanning lines of the laser light on the photosensitive member surface And the light amount setting unit sets the light emission amount of the laser light set corresponding to the interval between the scanning lines to a different light emission amount according to the processing conditions set by the binarization processing unit. It is characterized by.
Here, a light amount information storage for storing information defining the relationship between the interval between the scanning lines and the light emission amount of the laser light set corresponding to this interval for each processing condition set in the binarization processing unit A light quantity setting unit that acquires information on the processing conditions set by the binarization processing unit from the light quantity information storage unit, and sets the light emission amount of the laser light based on the acquired information. It can be.

  Further, the present invention is regarded as a laser light amount control device, and the laser light amount control device of the present invention uses a binarization condition for reproducing a halftone in a pseudo manner from image data in which a predetermined density gradation number is set. A binarization processing unit that generates binarized image data based on the image, and a laser exposure unit that scans and exposes a photosensitive member with laser light that is turned on based on the image data generated by the binarization processing unit A scanning line interval detecting unit for detecting a variation amount of the interval between the scanning lines on the surface of the photosensitive member of the laser beam scanned and exposed from the laser exposure unit, a variation amount detected by the scanning line interval detecting unit, and a binary value And a light amount setting unit that sets a light emission amount of laser light that is scanned and exposed from the laser exposure unit based on the binarization condition set by the conversion processing unit.

Here, in correspondence with the binarization condition set by the binarization processing unit, a light amount setting function for calculating the correction amount of the emitted light amount of the laser light from the variation amount detected by the scanning line interval detection unit is stored. A function storage unit that acquires a light amount setting function corresponding to the binarization condition set by the binarization processing unit from the function storage unit, and uses the acquired light amount setting function to perform laser processing. It is possible to set a light emission amount of light. In addition, the light amount setting unit is configured to apply a plurality of binarizations when a plurality of binarization conditions in the binarization processing unit are applied to each pixel of image data output on the same scanning line. Based on any of the conditions, the amount of emitted laser light can be set.
Further, the scanning line interval detection unit can detect the fluctuation amount based on the irradiation position of the laser light from the laser exposure unit on the surface of the photosensitive member in the sub-scanning direction. Further, the scanning line interval detection unit can detect a variation amount based on a variation in the rotation speed of the photosensitive member.

According to the first aspect of the present invention, image density unevenness in the sub-scanning direction can be reduced as compared with the case where the present invention is not adopted.
According to claim 2 of the present invention, it is possible to provide a halftone image with reduced image density unevenness in the sub-scanning direction as compared with the case where the present invention is not adopted.
According to claim 3 of the present invention, image density unevenness in the sub-scanning direction of images having different image attributes such as different image objects can be reduced as compared with the case where the present invention is not adopted.

According to claim 4 of the present invention, image density unevenness in the sub-scanning direction can be reduced corresponding to the screen angle used in the binarization process, compared to the case where the present invention is not adopted. .
Further, according to the fifth aspect of the present invention, it is possible to detect the fluctuation amount of the interval between the scanning lines generated based on the vibration.
According to the sixth aspect of the present invention, it is possible to detect the amount of change in the interval between the scanning lines that is generated based on the vibration and the change in the rotational speed of the photosensitive member.

According to the seventh aspect of the present invention, image density unevenness in the sub-scanning direction can be reduced as compared with the case where the present invention is not adopted.
Further, according to the eighth aspect of the present invention, it is possible to provide a halftone image with reduced image density unevenness in the sub-scanning direction as compared with the case where the present invention is not adopted.

According to claim 9 of the present invention, image density unevenness in the sub-scanning direction can be reduced as compared with the case where the present invention is not adopted.
According to the tenth aspect of the present invention, it is possible to provide a halftone image with reduced image density unevenness in the sub-scanning direction as compared with the case where the present invention is not adopted.
According to the eleventh aspect of the present invention, the image density in the sub-scanning direction is also improved when a plurality of pixels having different image attributes are formed on one scanning line as compared with the case where the present invention is not adopted. An image with reduced unevenness can be provided.
According to the twelfth aspect of the present invention, it is possible to detect the fluctuation amount of the interval between the scanning lines generated based on the vibration.
Further, according to the thirteenth aspect of the present invention, it is possible to detect a variation amount of the interval between the scanning lines generated based on the variation of the rotation speed of the photosensitive member.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus to which the exemplary embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a digital color printer, for example, and is an image that performs predetermined image processing on image data input from an external device such as a personal computer (PC) 3 or an image reading device 4. The image processing unit 10 as an example of a processing unit, the control unit 80 as an example of a control unit that controls the operation of the entire image forming apparatus 1, and a hard disk (Hard Disk Drive) in which a processing program or the like is recorded are realized. The main storage unit 85 includes an image forming unit 90 as an example of an image forming unit that forms an image corresponding to the image data of each color component.

  The image forming unit 90 includes a photosensitive drum 31 as an image carrier that rotates in the direction of arrow A, a charging roll 32 that uniformly charges the photosensitive drum 31 around the photosensitive drum 31, and an image processing unit. A laser exposure unit (ROS: Raster Output Scanner) 25, yellow (Y), magenta (M) as an example of a laser exposure unit that emits laser light L modulated according to image data from 10 to the photosensitive drum 31. Developer units 33Y, 33M, 33C, and 33K containing toners of cyan, (C), and black (K) are mounted on the photosensitive drum 31. The rotary developer 33 rotates about the rotation shaft 33a. A drum cleaner 34 that removes residual toner and a static elimination lamp 35 that neutralizes the photosensitive drum 31 before charging by the charging roll 32 are included. Here, the photoconductor drum 31, the charging roll 32, the drum cleaner 34, and the charge removal lamp 35 are integrally configured as a photoconductor unit 30 and are detachably disposed on the main body of the image forming apparatus 1.

  Further, the image forming unit 90 is provided with an intermediate transfer belt 41 disposed so as to contact the surface of the photosensitive drum 31. The intermediate transfer belt 41 includes a drive roll 46 for rotating the intermediate transfer belt 41, a tension roll 47 for keeping the tension applied to the intermediate transfer belt 41 constant, idler rolls 48a to 48c that are driven to rotate, and secondary to be described later. It is stretched by a backup roll 49 for transfer, and is configured to rotate in the direction of arrow B.

  At the primary transfer portion T1 where the intermediate transfer belt 41 is in contact with the photosensitive drum 31, a primary transfer roll 42 is disposed on the back side of the intermediate transfer belt 41 so as to be in pressure contact with the photosensitive drum 31 via the intermediate transfer belt 41. Has been. Further, the secondary transfer portion T2 of the intermediate transfer belt 41 facing the conveyance path of the paper P is disposed on the toner holding surface side (outer peripheral surface side) of the intermediate transfer belt 41 so as to be able to contact with and separate from the intermediate transfer belt 41. Further, a secondary transfer roll 50 and a backup roll 49 which is disposed on the back surface side (inner peripheral surface side) of the intermediate transfer belt 41 and serves as a counter electrode of the secondary transfer roll 50 are disposed. Further, on the downstream side of the secondary transfer portion T2 in the intermediate transfer belt 41, a belt cleaner 55 that can be brought into contact with and separated from the intermediate transfer belt 41 is disposed at a position facing the idler roll 48a with the intermediate transfer belt 41 interposed therebetween. It is installed.

In the image forming unit 90 of the present embodiment, when the laser exposure device 25 receives the pulse width modulated image data from the image processing unit 10, the laser exposure device 25 causes the light amount correction unit 20 described later to perform the laser light L. Are emitted in real time, and laser light L that is turned on in accordance with image data is emitted to the photosensitive drum 31.
Prior to that, the photosensitive drum 31 starts to rotate at a predetermined speed in the direction of arrow A, and the surface of the photosensitive drum 31 is charged to a predetermined potential by the charging roll 32. Then, laser light L is emitted from the laser exposure device 25 to the surface of the photosensitive drum 31, whereby an electrostatic latent image is formed on the photosensitive drum 31. At this time, if the electrostatic latent image formed on the photosensitive drum 31 corresponds to yellow (Y) image information, the electrostatic latent image is developed by the developing device 33Y containing Y toner. A Y toner image is formed on the photosensitive drum 31. The Y toner image formed on the photosensitive drum 31 is transferred to the intermediate transfer belt by the primary transfer bias applied to the primary transfer roll 42 at the primary transfer portion T1 where the photosensitive drum 31 and the intermediate transfer belt 41 face each other. 41 is transferred. On the other hand, the toner remaining on the photosensitive drum 31 after the primary transfer is removed by the drum cleaner 34.

When a single color image (for example, a black and white image) is formed, the secondary transfer process is immediately performed on the toner image primarily transferred to the intermediate transfer belt 41.
On the other hand, when a color image composed of toner images of a plurality of colors is formed, the toner image formation on the photosensitive drum 31 and the primary transfer process for the toner image are repeated for the number of colors. Thereafter, a secondary transfer process is performed. For example, when a full color image is formed by superimposing four color toner images, Y, M, C, and K toner images are sequentially formed on the photosensitive drum 31, and these toner images are sequentially transferred to the intermediate transfer belt. 41 is primarily transferred. The intermediate transfer belt 41 rotates and moves at the same peripheral speed as that of the photosensitive drum 31 while holding the primary-transferred toner image. On the intermediate transfer belt 41, Y, M, C, and K are sequentially added every rotation. The toner images are superimposed. At this time, the secondary transfer roll 50 and the belt cleaner 55 are set at positions separated from the intermediate transfer belt 41.

In the secondary transfer process, the paper P is fed by the pickup roll 72 to the paper tray 71 as the one-color or multi-color toner image primarily transferred onto the intermediate transfer belt 41 is conveyed to the secondary transfer portion T2. And is conveyed one by one to the position of the registration roll 74 by the conveyance roll 73. In synchronization therewith, the secondary transfer roll 50 is set at a position in contact with the intermediate transfer belt 41.
Subsequently, the sheet P is supplied to the secondary transfer unit T2 so as to match the timing at which the toner image on the intermediate transfer belt 41 reaches the secondary transfer unit T2. The paper P is sandwiched between the next transfer roll 50. At this time, in the secondary transfer portion T 2, a transfer electric field formed between the secondary transfer roll 50 and the backup roll 49 by the secondary transfer bias applied to the backup roll 49 is applied to the intermediate transfer belt 41. The toner images held on the sheet P are collectively transferred to the sheet P in a secondary transfer. Thereafter, the sheet P on which the toner image is transferred is conveyed to the fixing device 60 by the conveyance guide 76 and the sheet conveyance belt 77. The fixing device 60 fixes the toner image on the paper P by heating and pressing. Further, the transfer residual toner adhering to the intermediate transfer belt 41 after the secondary transfer is removed by the belt cleaner 55 in contact with the intermediate transfer belt 41 after the completion of the secondary transfer.

  The image processing unit 10 temporarily stores image data received by the input interface 11 that receives input of image data from an external device such as a personal computer (PC) 3 or an image reading device 4 such as a scanner. An input buffer 12, a PDL analysis unit 13 that generates intermediate data by analyzing image data in a PDL (Page Description Language) format, and the intermediate data generated by the PDL analysis unit 13 is expressed as an array of pixels. The rendering processing unit 14 that develops (renders) the image data for printing (raster image data), the intermediate buffer 15 that is used as a work area during the rendering process in the rendering processing unit 14, and prints the rendered image data Color system image data suitable for processing ( YMCK), a color conversion processing unit 16 for performing color conversion, a screen processing unit 17 for performing screen processing on the color-converted image data, and an image data storage unit 18 for storing image data screen-processed by the screen processing unit 17. A pulse width modulation unit 19 is provided for reading the image data stored in the image data storage unit 18 and converting it into a signal pulse having an on-time length corresponding to the image data.

The input interface 11 receives a print job including image data and a drawing command from an image reading device 4 such as a personal computer (PC) 3 or a scanner. Then, the image data is output to the input buffer 12, and the drawing command is output to the PDL analysis unit 13. Here, the image data includes, for example, pixel data belonging to, for example, the sRGB color space represented by 8 bits (1 byte) for each RGB, and the type of image object (font) that is one of the image attributes included in the image data. For example, 2-bit tag data representing objects, graphic objects, image objects, etc.).
The input buffer 12 temporarily stores the image data input from the input interface 11 and outputs it to the PDL analysis unit 13.

The PDL analysis unit 13 acquires image data from the input buffer 12 according to the drawing command, and generates, for example, intermediate data for one print page from the acquired image data. Then, the generated intermediate data is output to the rendering processing unit 14.
At that time, the PDL analysis unit 13 recognizes the object type from the tag data indicating the object type included in the image data received by the input interface 11 and generates a signal (object signal) indicating the object type. . Then, the PDL analysis unit 13 transmits the generated object signal to the light amount correction unit 20 (see the subsequent stage) of the image forming unit 90.
The rendering processing unit 14 performs a rendering process on the intermediate data acquired from the PDL analysis unit 13 according to the drawing command. The rendered raster image data (image data in which pixel groups are arranged) is output to the color conversion processing unit 16.

  The color conversion processing unit 16 converts the input raster image data into color system image data (YMCK) suitable for printing processing in the image forming unit 90 and outputs it to the screen processing unit 17. The color conversion processing unit 16 performs color conversion processing using a color conversion table called DLUT (Direct Look-Up Table). In this case, the color conversion processing unit 16 has a different DLUT for each type of object (font object, graphic object, image object, etc.). Then, the type of the object is specified based on the tag data included in the raster image data from the rendering processing unit 14, and optimum color conversion corresponding to the type of the object is performed.

The screen processing unit 17 performs screen processing on multi-value (8 bits each) raster image data for each color component (YMCK) input from the color conversion processing unit 16. Thereby, binarized image data (1-bit image data) is generated. That is, the screen processing unit 17 is an example of a binarization processing unit, and raster image data, which is multi-value image information having a predetermined density gradation number, is simulated according to the size of colored dots called halftone dots. Then, binarized image data representing the density of the halftone image is generated.
The screen processing unit 17 includes various parameters (screen pattern, screen line width, screen pitch, screen angle, etc .: hereinafter referred to as “screen parameters”) as image processing attributes. Are provided for each type of image object (font object, graphic object, image object, etc.). Then, based on the tag data included in the raster image data from the rendering processing unit 14, the type of the image object (also simply referred to as “object”) is specified, and the screen parameters set corresponding to the type of the object are used. Screen processing optimal for each object. Then, the screen processing unit 17 temporarily stores the generated image data in the image data storage unit 18.

  The pulse width modulation unit 19 reads out the image data stored in the image data storage unit 18 for each color component in the order of image formation in the image forming unit 90, and converts the image data into a signal pulse having an on-time length according to the image data. Convert. Then, image data for each color component as a signal pulse subjected to pulse width modulation by the pulse width modulation unit 19 is output to the laser exposure device 25 in the order of image formation.

Next, the laser exposure apparatus 25 will be described.
FIG. 2 is a diagram showing a configuration of the laser exposure device 25 and a state in which the laser exposure device 25 scans and exposes the photosensitive drum 31. The laser exposure device 25 includes a light source 251 made of a semiconductor laser, a collimator lens 252 and a cylinder lens 253, for example, a rotating polygon mirror (polygon mirror) 254 formed of a regular octahedron, an fθ lens 255, a folding mirror 256, a reflection mirror 257, and An SOS sensor (light receiving element) 258 and a laser driver 259 are included. The laser exposure apparatus 25 is disposed in the housing 260 and constitutes an integrated optical unit.

In the laser exposure device 25, the divergent laser light L emitted from the light source 251 is converted into parallel light by the collimator lens 252, and deflected and reflected by the polygon mirror 254 by the cylinder lens 253 having a refractive power only in the sub-scanning direction. A line image is formed in the vicinity of the surface 254a as a long line image in the main scanning direction. The laser beam L is reflected by the deflecting / reflecting surface 254a of the polygon mirror 254 that rotates at a constant speed at a high speed, and is scanned counterclockwise (in the direction of the arrow C) at an equal angular velocity.
After passing through the fθ lens 255, the direction of the laser light L is changed toward the surface of the photosensitive drum 31 by the folding mirror 256, and the surface of the photosensitive drum 31 is scanned and exposed in the direction of arrow D. Here, the fθ lens 255 has a function of equalizing the scanning speed of the light spot of the laser light L on the surface of the photosensitive drum 31.
Further, the above-described line image is formed in the vicinity of the deflecting / reflecting surface 254a of the polygon mirror 254, and the fθ lens 255 causes a light spot on the surface of the photosensitive drum 31 with the deflecting / reflecting surface 254a as an object point in the sub scanning direction. Since the image is formed, this scanning optical system has a function of correcting the surface tilt of the deflecting / reflecting surface 254a.

  The laser light L enters the SOS sensor 258 via the reflection mirror 257 prior to scanning exposure on the surface of the photosensitive drum 31. That is, every time the laser beam L scans the surface of the photosensitive drum 31, the first laser beam L of each scanning line is incident on the SOS sensor 258. The SOS sensor 258 detects the irradiation timing for each scanning line on the surface of the photosensitive drum 31, and generates a signal (SOS signal) indicating the irradiation start timing.

The light source 251 is connected to a laser driver 259 that generates a laser drive signal for controlling ON / OFF of the semiconductor laser in accordance with image data output from the image processing unit 10. The laser driver 259 outputs a laser drive signal to the light source 251, so that the light source 251 emits laser light L corresponding to the image data from the image processing unit 10.
At that time, the laser driver 259 is connected to the SOS sensor 258 and inputs the SOS signal generated by the SOS sensor 258. In the laser driver 259, timing for starting output of a laser drive signal to the semiconductor laser of the light source 251 is set based on the SOS signal from the SOS sensor 258.

  In the image forming apparatus 1 of the present embodiment, the position of the laser beam L emitted from the light source 251 of the laser exposure apparatus 25 on the surface of the photosensitive drum 31 is detected, and the sub-scan corresponding to the position of the sub-scanning direction is detected. A sub-scanning position detection sensor 110 that generates a position signal is provided. The sub-scanning position detection sensor 110 is disposed between the laser exposure device 25 and the photosensitive drum 31. For example, as shown in FIG. 3 (a diagram for explaining the arrangement position of the sub-scanning position detection sensor 110), the laser light L scans and exposes the surface of the photosensitive drum 31 so as not to affect image formation. In the region where the image is formed, the surface of the photoconductive drum 31 is disposed in the vicinity of the surface of the photoconductive drum 31 in a region closer to the end in the axial direction than the region where the image is formed on the surface of the photoconductive drum 31 (image forming region). Then, the sub-scanning position detection sensor 110 detects the position in the sub-scanning direction for each line scan of the laser beam L for image formation. The sub-scanning position signal generated by the sub-scanning position detection sensor 110 is output to the control unit 80 in real time.

  In the image forming apparatus 1 of the present embodiment, the rotary encoder 120 that detects the rotational speed of the photosensitive drum 31 when the laser exposure device 25 scans and exposes the photosensitive drum 31 includes the rotary shaft of the photosensitive drum 31. It is arranged coaxially with 31a. The rotary encoder 120 is configured to transmit a data signal relating to the rotational speed of the photosensitive drum 31 detected by the rotary encoder 120 to the control unit 80 during scanning exposure of the laser light L.

  By the way, the image forming apparatus 1 is provided with drive sources such as a motor for rotating the photosensitive drum 31 and a transport system for transporting the paper P. Vibrations from these drive sources are generated by the laser exposure device 25 and the like. It is transmitted to the photosensitive drum 31. Further, the photosensitive drum 31 also has rotational speed unevenness due to fluctuations in the voltage supplied to the rotationally driven motor, fluctuations in the driving load, electrical noise entering the motor driving signal, and the like. Due to such vibration and uneven rotation speed of the photosensitive drum 31, the scanning pitch (adjacent in the sub-scanning direction (rotating direction of the photosensitive drum 31) of the laser light L emitted from the laser exposure device 25 during the image forming operation. In some cases, non-uniformity called “scanning pitch unevenness” may occur in the interval between the scanning lines.

When such scanning pitch unevenness occurs, stripe density unevenness (this is referred to as “banding”) occurs in the sub-scanning direction, that is, the conveyance direction of the paper P, on the image formed by the image forming unit 90. This leads to a decrease in image quality. For example, in a region where the scanning pitch is narrower than a predetermined value, the pixel interval is close, so the density is high, and in a region where the scanning pitch is wider than the predetermined value, the pixel interval is separated, so the density is low and the image is dark and light Inconvenience occurs.
In such a case, in the configuration in which the screen processing unit 17 is provided in the image processing unit 10 and the gradation control is performed on the image data by the screen processing as in the image forming apparatus 1 of the present embodiment, the setting is performed by the screen processing unit 17. Depending on the setting value of the screen parameter such as the screen angle, for example, a difference occurs in the degree of banding caused by the scanning pitch unevenness.

Here, FIG. 4 is a diagram illustrating a state in which banding occurs due to a change in pixel interval in the sub-scanning direction due to uneven rotation speed of the photosensitive drum 31. In FIG. 4, when the screen angle is set to (a) 90 °, (b) 72 °, (c) 45 °, (d) 18 °, and (e) 0 °, (A) the pixel interval changes. 1B, a state where the pixel interval is approximately halved, and a state where the pixel interval is approximately doubled.
As shown in FIG. 4, as the screen angle is larger, the banding is less noticeable to human eyes with respect to the change in the pixel interval, and as the screen angle is smaller, the banding is more prominent with respect to the change in the pixel interval. Yes.

Further, FIG. 5 shows that the pixel interval in the sub-scanning direction changes due to vibration transmitted to the laser exposure device 25 and the photosensitive drum 31 or due to the rotational speed unevenness of the photosensitive drum 31 being added to such vibration. It is the figure which showed the state which banding generate | occur | produced. In FIG. 5, as in FIG. 4, when the screen angles are set to (a) 90 °, (b) 72 °, (c) 45 °, (d) 18 °, (e) 0 °, (B) A state in which the pixel interval is not changed, and (B) a state in which the pixel interval is approximately halved and a state in which the pixel interval is approximately doubled are alternately and periodically repeated.
As shown in FIG. 5, in this case as well, as in the case of FIG. 4, as the screen angle is larger, banding is less conspicuous for human eyes against changes in the pixel interval. Banding shows a conspicuous tendency against the change of the interval.
That is, as the screen angle increases, the banding appearance for human eyes tends to be less sensitive to changes in the pixel spacing in the sub-scanning direction. This is expressed as “low banding sensitivity” in this specification. On the other hand, the smaller the screen angle, the more sensitive the banding looks to the human eye with respect to changes in the pixel spacing in the sub-scanning direction. This is expressed as “high banding sensitivity” in this specification. Therefore, even if the pixel interval in the sub-scanning direction changes in the same manner, the degree of occurrence of banding varies depending on the setting value of the screen parameter such as the screen angle set by the screen processing unit 17. 4 and 5 have been described using line screen processing as an example, but the same applies to the case of using dot screen processing.

  Therefore, in the image forming apparatus 1 of the present embodiment, the sub-scanning position detection sensor 110 detects the position of the laser light L on the surface of the photosensitive drum 31 in real time for each scanning line. At the same time, the rotational speed of the photosensitive drum 31 is detected by the rotary encoder 120. Then, based on the position of the laser beam L on the surface of the photosensitive drum 31 in the sub-scanning direction and the rotational speed of the photosensitive drum 31, the amount of change in the scanning pitch is calculated. Further, based on the calculated variation amount of the scanning pitch, a process for correcting the light emission amount of the semiconductor laser is performed so as to reduce the density unevenness of the stripe pattern caused by the scanning pitch unevenness in the screen processed image. At this time, the light amount correction amount of the semiconductor laser is determined corresponding to the screen parameter set in the screen processing unit 17 of the image processing unit 10. Thereby, the irradiation position (pixel position) in the sub-scanning direction on the photosensitive drum 31 to which the laser beam L is supposed to be irradiated, and the irradiation position (pixel position) in the sub-scanning direction where the laser beam L is actually irradiated. The banding is adjusted so that it is not noticeable to the human eye.

  That is, to the laser exposure device 25 of the present embodiment, a light amount correction unit 20 that corrects the light amount of the semiconductor laser of the light source 251 is connected as an example of a light amount setting unit (laser light amount control device). Then, the light amount correction unit 20 calculates the variation amount of the scanning pitch based on the position of the laser light L on the surface of the photosensitive drum 31 in the sub-scanning direction and the rotational speed of the photosensitive drum 31. Based on the calculated fluctuation amount of the scanning pitch, the light amount of the semiconductor laser of the light source 251 is corrected. At this time, the correction parameter used for correcting the light quantity of the semiconductor laser is set corresponding to the screen parameter set in the screen processing unit 17.

For example, as described above, the screen processing unit 17 according to the present embodiment converts screen parameters (screen line width, screen pitch, screen angle, etc.) as binarization processing conditions into object types (font object, graphic object, For each image object). Then, the type of the object is specified based on the tag data included in the raster image data from the rendering processing unit 14, and the optimum screen size is set for each object using the screen parameters set in accordance with the type of the object. Screen processing is performed.
Based on the object signal received from the PDL analysis unit 13, the light amount correction unit 20 of the present embodiment identifies the screen parameter set corresponding to the object type by the screen processing unit 17, and uses the screen parameter as the screen parameter. The light quantity of the semiconductor laser of the light source 251 is corrected for each pixel using the corresponding correction parameter.

Next, the light amount correction unit 20 of the present embodiment will be described.
FIG. 6 is a diagram illustrating a functional configuration of the light amount correction unit 20 of the present embodiment. As shown in FIG. 6, the light amount correction unit 20 includes an object information acquisition unit 201 that acquires an object signal from the PDL analysis unit 13, a sub-scanning position signal generated by the sub-scanning position detection sensor 110, and a rotary encoder. The pixel position information acquisition unit 202 that acquires the data signal relating to the rotation speed of the photosensitive drum 31 detected at 120 from the control unit 80, the sub-scanning position signal acquired by the pixel position information acquisition unit 202, and the photosensitive drum 31. And the pixel position in the sub-scanning direction on the photosensitive drum 31 to which the laser beam L is supposed to be irradiated and the pixel position in the sub-scanning direction where the laser beam L is actually irradiated are The pixel position fluctuation amount calculation unit 2 as an example of the scanning line interval detection unit that calculates the fluctuation amount of the scanning pitch by obtaining the pixel position fluctuation amount that is the distance of 3. Correction parameter storage unit 204 as an example of a function storage unit that stores a correction parameter as a light amount setting function used when correcting the light amount of the semiconductor laser set corresponding to the screen parameter, correction parameter storage unit 204 Is provided with a light amount setting unit 205 that sets a light amount corresponding to the variation amount of the scanning pitch calculated by the pixel position variation amount calculation unit 203 using the correction parameter stored in the above.

FIG. 7 is a block diagram showing an internal configuration of the light amount correction unit 20 of the present embodiment. As shown in FIG. 7, the light amount correction unit 20 performs digital calculation processing according to a predetermined processing program when performing pixel amount variation amount calculation processing in the sub-scanning direction and semiconductor laser light amount correction amount calculation processing. CPU 211 to be executed, RAM 212 used as a working memory for CPU 211, ROM 213 for storing processing programs executed by CPU 211, SRAM, flash memory, etc. that can be rewritten and can retain data even when power supply is interrupted A non-volatile memory 214 and an interface unit 215 for controlling input / output of signals to / from each unit such as the control unit 80 connected to the light amount correction unit 20, the image processing unit 10, and the laser exposure device 25 are provided.
The main storage unit 85 (see FIG. 1) stores a processing program executed by the light amount correction unit 20, and the light amount correction unit 20 reads this processing program when the image forming apparatus 1 is started up. Various processes in the light amount correction unit 20 are executed.

When the pixel position in the sub-scanning direction due to the laser light L changes in the direction in which the scanning pitch is made smaller than the prescribed scanning pitch, the light amount correction unit 20 according to the present embodiment Based on the correction parameter set corresponding to the screen parameter, the light amount is corrected for each pixel so as to reduce the light amount of the semiconductor laser of the light source 251 in accordance with the variation amount of the pixel position. As a result, the light spot diameter of the scanning line is reduced, and the generation of a stripe-patterned high density portion in the sub-scanning direction caused by the dense scanning pitch between the scanning lines is suppressed.
On the other hand, the light amount correction unit 20 responds to the screen parameters in the screen processing unit 17 when the pixel position in the sub-scanning direction by the laser light L fluctuates in a direction in which the scanning pitch is larger than the specified scanning pitch. On the basis of the correction parameters set in this manner, the light amount is corrected for each pixel so as to increase the light amount of the semiconductor laser of the light source 251 in accordance with the variation amount of the pixel position. As a result, the light spot diameter of the scanning line is increased, and therefore, the generation of the stripe-patterned low density portion in the sub-scanning direction caused by the sparse scanning pitch between the scanning lines is suppressed.

FIG. 8 is a flowchart showing an example of a processing procedure in the light amount correction unit 20 of the present embodiment. As shown in FIG. 8, in the light quantity correction unit 20, first, the object information acquisition unit 201 acquires an object signal representing the type of object from the PDL analysis unit 13 of the image processing unit 10 (S <b> 101). Then, the acquired object signal is sent to the light amount setting unit 205.
At the same time, in the pixel position information acquisition unit 202, the image data corresponding to the object signal acquired in step 101 is subjected to pulse width modulation by the pulse width modulation unit 19 and output as laser light L from the laser exposure device 25. At this time, the sub-scanning position signal generated by the sub-scanning position detection sensor 110 and the data signal relating to the rotational speed of the photosensitive drum 31 detected by the rotary encoder 120 at that time are acquired from the control unit 80 (S102). ). Then, the acquired sub-scanning position signal and a data signal related to the rotational speed of the photosensitive drum 31 are sent to the pixel position variation calculation unit 203.

The pixel position fluctuation amount calculation unit 203 performs a predetermined calculation based on the acquired sub-scanning position signal and the data signal related to the rotational speed of the photosensitive drum 31. Then, a pixel position variation amount which is a distance between a pixel position in the sub-scanning direction on the photosensitive drum 31 to be irradiated with the laser light L and a pixel position in the sub-scanning direction where the laser light L is actually irradiated is calculated. Then, the fluctuation amount of the scanning pitch is calculated (S103). Then, the calculated fluctuation amount of the scanning pitch in the sub-scanning direction is sent to the light amount setting unit 205.
The light amount setting unit 205 specifies the type of the object set in the image data from the object signal acquired by the object information acquisition unit 201 in step 101. Then, the correction parameter corresponding to the specified object type is acquired from the correction parameter storage unit 204 (S104). The screen processing unit 17 of the image processing unit 10 sets screen parameters corresponding to the type of object when executing the screen processing. The type of object determined in step 104 is the screen processing unit. 17 is the same as the object type set in step 17.

  Here, FIG. 9 is a diagram illustrating an example of the correction parameter as the light amount setting function stored in the correction parameter storage unit 204. FIG. 9 shows correction parameters provided corresponding to the screen angle by line screen processing as an example of the screen parameters. With the correction parameters shown in FIG. 9, as shown in FIGS. 4 and 5, in the line screen processing, for the human eye, the larger the screen angle, the lower the banding sensitivity to the change in the pixel interval in the sub-scanning direction. In consideration of the characteristic that the banding sensitivity tends to be higher with respect to the change of the pixel interval as the angle is smaller, the light amount correction amount with respect to the variation amount of the scanning pitch is set to be larger as the screen angle is smaller.

  On the other hand, when dot screen processing is performed in the screen processing unit 17, correction parameters different from those in the case of line screen processing are set. In the dot screen processing, gradation control using a two-dimensional dot screen having two orthogonal direction components is performed, unlike gradation control by one-dimensional line screen processing having one direction component. Therefore, unlike the banding sensitivity characteristic by one direction component shown in FIGS. 4 and 5, two orthogonal direction components simultaneously act on the banding sensitivity characteristic. That is, for example, in a dot screen having a screen angle of 72 °, a banding sensitivity characteristic at a screen angle of 72 ° and a banding sensitivity characteristic at a screen angle of −18 ° orthogonal to this appear synergistically. Similarly, in a dot screen having a screen angle of 45 °, a banding sensitivity characteristic at a screen angle of 45 ° and a banding sensitivity characteristic at a screen angle of −45 ° orthogonal to this appear synergistically. Therefore, in the dot screen processing, as shown in FIG. 10 (a diagram for explaining the banding sensitivity characteristic with respect to the screen angle in the dot screen), the banding sensitivity with respect to the change in the pixel interval in the sub-scanning direction is the lowest at the screen angle of 45 °. As the screen angle becomes smaller than 45 °, and the screen angle becomes larger than 45 °, the banding sensitivity to the change in the pixel interval in the sub-scanning direction tends to increase. Therefore, when dot screen processing is used in the screen processing unit 17 of the image processing unit 10, a correction parameter corresponding to the banding sensitivity characteristic related to the screen angle of such a dot screen is set.

  In the correction parameter storage unit 204 of the present embodiment, the correction parameter as the light amount setting function is stored. However, instead of the light amount setting function, the variation amount of the scanning pitch is associated with the screen parameter. The corresponding light quantity correction amount of the semiconductor laser can also be stored as a table. As described above, the correction parameter storage unit 204 may take any format as long as it is information that defines the relationship between the variation amount of the scanning pitch and the light amount correction amount of the semiconductor laser in correspondence with the screen parameter.

  Next, returning to the processing flow of FIG. 8, the light amount setting unit 205 is calculated by the pixel position variation calculation unit 203 in step 103 using the correction parameter acquired from the correction parameter storage unit 204 in step 104. A light amount correction amount corresponding to the variation amount of the scanning pitch in the sub-scanning direction is calculated for each pixel (S105). Then, based on the calculated light amount correction amount, a light amount value set by the semiconductor laser of the light source 251 of the laser exposure device 25 is calculated, and a light amount setting signal for each pixel for setting the light amount of the calculated setting value. Is generated. Then, the generated light quantity setting signal is transmitted to the laser driver 259 (S106). Upon receiving the light amount setting signal, the laser driver 259 sends the light amount setting signal to the light source 251 together with the laser drive signal corresponding to the image data.

  Here, a plurality of different image objects may be mixed on one scanning line. In that case, the light amount value set for each pixel varies depending on the above processing. However, it may be difficult to control the amount of laser light L scanned at a high speed with a plurality of set values on one scanning line because of the data processing speed. Therefore, when a plurality of different image objects are mixed on one scanning line, the light amount setting unit 205 of the present embodiment uses a correction parameter corresponding to the screen angle having the lowest banding sensitivity in step 105. A light amount correction amount is calculated for each pixel. As a result, the banding suppression effect for image objects using a screen angle with high banding sensitivity is reduced, but the occurrence of image defects due to fluctuations in the light quantity of the entire scan line is suppressed, and the deterioration of the image quality of the entire image is suppressed. is doing. In this case, in step 105, the light amount correction amount can be calculated for each pixel using the correction parameter corresponding to the screen angle having the highest banding sensitivity.

As described above, in the image forming apparatus 1 of the present embodiment, sub-scanning of the laser light L emitted from the laser exposure device 25 using the correction parameters set corresponding to the screen parameters in the screen processing unit 17. The light quantity of the semiconductor laser of the light source 251 is adjusted in real time in accordance with the scanning pitch in the direction. As a result, even when the relative position between the laser beam L and the photosensitive drum 31 varies due to vibration in the image forming apparatus 1 or uneven rotation speed of the photosensitive drum 31, the image forming apparatus 1 forms the image. Banding that occurs on screened images is reduced to an inconspicuous level.
In the light amount setting unit 205 of the present embodiment, the sub-scanning position signal generated by the sub-scanning position detection sensor 110 and the data signal regarding the rotational speed of the photosensitive drum 31 detected by the rotary encoder 120 are output. Using this, the fluctuation amount of the scanning pitch is calculated. However, for example, depending on the configuration of the image forming apparatus 1, the variation amount of the scanning pitch can be calculated using only the sub-scanning position signal generated by the sub-scanning position detection sensor 110. It is also possible to calculate the amount of variation in the scanning pitch using only the data signal relating to the rotational speed of the photosensitive drum 31 detected by the rotary encoder 120.

  Subsequently, the sub-scanning position detection sensor 110 of the present embodiment will be described. FIG. 11 is a diagram illustrating a PSD (Position Sensitive Detector) as an example of the sub-scanning position detection sensor 110. As shown in FIG. 11A, in the PSD, the longitudinal direction of the detection surface is arranged along the sub-scanning direction. Then, the PSD changes the output voltage V according to the position (a, b, c) of the laser light L that passes through the detection surface of the PSD, as shown in FIG. Therefore, the position of the laser light L in the sub-scanning direction can be detected by detecting the output voltage V of PSD.

  FIG. 12 is a diagram for explaining detection of the position in the sub-scanning direction of the laser light L when PSD is used as the sub-scanning position detection sensor 110. As shown in FIG. 12A, when the relative position between the laser exposure device 25 and the photosensitive drum 31 changes due to vibration in the image forming apparatus 1, sub-scanning of the laser light L is performed. The direction position fluctuates. Then, as shown in FIG. 12B, the output voltage V from the sub-scanning position detection sensor (PSD) 110 also changes in accordance with the vibration waveform. In that case, the period of the vibration waveform is sufficiently long with respect to the scanning pitch of the laser light L. Therefore, the output voltage V from the sub-scanning position detection sensor 110 detected for one scanning line of the laser beam L, that is, the position in the sub-scanning direction can be regarded as the position in the sub-scanning direction on the next scanning line of the scanning line. it can. Therefore, when the next scanning of the scanning line whose sub-scanning direction position is detected by the sub-scanning position detection sensor 110, the control unit 80 sets the detected sub-scanning direction position to the sub-scanning direction position on the next scanning line. Detect as.

  As described above, when the light amount correction unit 20 corrects the light amount of the semiconductor laser of the light source 251, the light amount correction unit 20 uses the sub-scanning direction position detected in the scanning line immediately before the scanning line whose light amount is corrected. It is possible to provide a time margin for calculating the light amount correction amount at. Therefore, it is possible to correct the light amount with high accuracy for each scanning line. Further, if the detection of the position in the sub-scanning direction and the correction of the light amount of the semiconductor laser are performed simultaneously on the same scanning line, the light amount of the semiconductor laser may change between the head and the rear end of one scanning line. On the other hand, if the position in the sub-scanning direction detected in the immediately preceding scanning line is used, the light quantity for each scanning line can be set constant. Thereby, it is possible to suppress the occurrence of density unevenness in the main scanning direction by changing the image density in the scanning line.

Next, the arrangement position of the sub-scanning position detection sensor 110 in the axial direction of the photosensitive drum 31 will be described. As described above, the sub-scanning position detection sensor 110 is located between the laser exposure device 25 and the photosensitive drum 31, for example, in a region where the laser beam L scans and exposes the surface of the photosensitive drum 31, and forms an image. It is disposed in the vicinity of the surface of the photosensitive drum 31 in a region closer to the axial end than the region (see FIG. 3). One of the sub-scanning position detection sensors 110 is preferably arranged in such an area and in an upstream end area of the scanning line.
As described above, every time the laser beam L scans the surface of the photosensitive drum 31, the first laser beam L of each scanning line is incident on the SOS sensor 258, and the laser driver 259 receives the laser drive signal from the light source 251. An SOS signal that is a reference for the timing of starting output is generated. Therefore, if the sub-scanning position detection sensor 110 can detect the position of each scanning line in the sub-scanning direction at the same time as the first laser light L of each scanning line is incident on the SOS sensor 258, the light quantity correction unit 20 performs the following operation. It is possible to provide a large time margin for calculating the light amount correction amount of the semiconductor laser in the scanning line.

FIG. 13 is a diagram showing the relationship between the timing at which the sub-scanning position detection sensor 110 detects the position of each scanning line in the sub-scanning direction and the light amount calculation time in the light amount correction unit 20. FIG. 13A shows a case where one is arranged on the downstream end (EOS) side of the scanning line, that is, near the end point of the scanning line. In this configuration, the time from when the sub-scanning position detection sensor 110 detects the position in the sub-scanning direction until the next scanning is started is t1, and the time that can be calculated by the light quantity correction unit 20 is short. Therefore, it is insufficient for setting the light amount with high accuracy for each scanning line.
On the other hand, FIG. 13B shows a case where one is arranged on the upstream end (SOS) side of the scanning line, that is, in the vicinity of the starting point of the scanning line. In this configuration, the time from when the sub-scanning position detection sensor 110 detects the position in the sub-scanning direction until the start of the next scanning is t2, and the time that can be calculated by the light quantity correction unit 20 is 1 on the EOS side. Compared to the case where two are arranged, the time for one line scanning is increased. For this reason, it is possible to set the light amount with high accuracy for each scanning line.

  FIG. 13C shows a case where the scanning lines are arranged on the SOS side and the EOS side, respectively. In this configuration, the sub-scanning position detection sensor 110 on the SOS side can secure a sufficient calculation time in the light amount correction unit 20 and can detect a change in the sub-scanning direction position within one line scan. Become. Therefore, it is possible to set the light amount for each scanning line with higher accuracy.

By the way, in the image forming apparatus 1 of the present embodiment, the case where the PSD is used as the sub-scanning position detection sensor 110 has been described. However, the sub-scanning position detection sensor 110 is not limited to this, and any detection means can be used as long as it can detect the sub-scanning direction position of each scanning line.
14 and 15 are diagrams showing another configuration example of the sub-scanning position detection sensor 110. FIG. In FIG. 14, as the sub-scanning position detection sensor 110, a photodiode formed in a triangular shape having a length in the main scanning direction along the sub-scanning direction is used (FIG. 14A). With such a configuration, the output time of the signal from the sub-scanning position detection sensor 110 differs according to the position (a, b, c) of the laser light L passing through the photodiode as shown in FIG. Thus, signals with different output waveforms can be obtained. Thereby, the sub-scanning direction position of each scanning line can be detected.
As the sub-scanning position detection sensor 110 using a photodiode, the photodiode itself has a shape having the same length in the main scanning direction along the sub-scanning direction, such as a square, and the main scanning along the sub-scanning direction. The surface of the photodiode can be covered with a mask having an opening formed in a triangular shape whose length in the scanning direction becomes longer.

  Further, in FIG. 15, a line CCD (Charge Coupled Devices) arranged in a line along the sub-scanning direction is used as the sub-scanning position detection sensor 110 (FIG. 15A). With such a configuration, as shown in FIG. 15B, output signals having different output timings from the sub-scanning position detection sensor 110 are obtained according to the positions (a, b, c) of the laser light L passing through the line CCD. It is done. Thereby, the sub-scanning direction position of each scanning line can be detected.

On the other hand, the sub-scanning position detection sensor 110 may be disposed in an integrally coupled state with the photosensitive drum 31 in order to accurately detect the position in the sub-scanning direction of each scanning line on the surface of the photosensitive drum 31. Necessary. That is, the photosensitive drum 31 and the sub-scanning position detection sensor 110 need to be arranged so that both vibrate in the same manner when receiving vibration from the main body of the image forming apparatus 1.
Therefore, in the present embodiment, the sub-scanning position detection sensor 110 is integrally installed on the photoconductor unit 30 as an example of a photoconductor support member that rotatably supports the photoconductor drum 31. Since the photoconductor unit 30 is integrated with the photoconductor drum 31, the sub-scanning position detection sensor 110 can be moved in the same manner as the photoconductor drum 31.

  Further, the sub-scanning position detection sensor 110 can be integrally installed on a positioning member (not shown) in which the photosensitive drum 31 is positioned with respect to the main body of the image forming apparatus 1. The positioning member determines the position of the photosensitive drum 31 in the main body of the image forming apparatus 1 and sets a position reference with respect to all process elements such as the laser exposure device 25 and the intermediate transfer belt 41. Therefore, the positioning member is coupled in a state of being in close contact with the photosensitive drum 31. As a result, the positioning member moves in the same manner as the photosensitive drum 31 with respect to the vibration of the image forming apparatus 1 main body. Therefore, the sub-scanning position detection sensor 110 can be moved in the same manner as the photosensitive drum 31 by installing the sub-scanning position detection sensor 110 integrally with the positioning member.

In the image forming apparatus 1 of the present embodiment, a semiconductor laser that emits one beam is used as the light source 251, and the sub-scanning position detection sensor 110 applies the one-beam laser light L on the surface of the photosensitive drum 31. The position is detected for each scanning line. In addition to such a configuration, a laser array light source that simultaneously emits a plurality of beams is used as the light source 251 in order to cope with an increase in the speed and resolution of the image forming apparatus, and the sub-scanning position detection sensor 110 converts the plurality of beams The position of the laser beam L on the surface of the photosensitive drum 31 in the sub-scanning direction can be detected for each scanning line. Similarly, the amount of light from the laser array light source can be adjusted in real time.
In the configuration using a semiconductor laser that emits one beam as the light source 251, the sub-scanning position detection sensor 110 sets the position of the laser beam L of one beam in the sub-scanning direction on the surface of the photosensitive drum 31 for each of a plurality of scanning lines. It can also be set to detect as an average value. Similarly, it is also possible to adjust the light quantity from the light source 251 in real time using the average value of fluctuation amounts at a plurality of scanning pitches.

As described above, in the image forming apparatus 1 according to the present embodiment, the laser exposure device 25 uses the correction parameters set corresponding to the screen parameters that are the binarization processing conditions in the screen processing unit 17. The light quantity of the semiconductor laser of the light source 251 is adjusted in real time in accordance with the scanning pitch of the emitted laser light L in the sub-scanning direction.
As a result, even when the relative position between the laser beam L and the photosensitive drum 31 varies due to vibration in the image forming apparatus 1 or uneven rotation speed of the photosensitive drum 31, the image forming apparatus 1 forms the image. The banding generated on the screen-processed image can be reduced to an inconspicuous level, and a high-quality image can be provided.

1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. It is the figure which showed the structure of the laser exposure apparatus, and the state which a laser exposure apparatus scans and exposes a photosensitive drum. It is a figure explaining the arrangement position of a sub-scanning position detection sensor. FIG. 6 is a diagram illustrating a state in which banding occurs due to a change in pixel interval in the sub-scanning direction due to uneven rotation speed of the photosensitive drum. A diagram showing a state in which banding occurs due to a change in the pixel interval in the sub-scanning direction due to vibration transmitted to the laser exposure device or the photosensitive drum, or due to addition of uneven rotation speed of the photosensitive drum to such vibration. It is. It is a figure explaining the functional structure of a light quantity correction | amendment part. It is a block diagram which shows the internal structure of a light quantity correction | amendment part. It is the flowchart which showed an example of the procedure of the process in a light quantity correction | amendment part. It is the figure which showed an example of the correction parameter memorize | stored in the correction parameter memory | storage part. It is a figure explaining the banding sensitivity characteristic with respect to the screen angle in a dot screen. It is a figure explaining PSD as an example of a sub-scanning position detection sensor. It is a figure explaining the detection of the subscanning direction position of the laser beam at the time of using PSD as a subscanning position detection sensor. It is the figure which showed the relationship between the timing which detects the subscanning direction position of each scanning line by a subscanning position detection sensor, and the light quantity calculation possible time in a light quantity correction | amendment part. It is the figure which showed the other structural example of the subscanning position detection sensor. It is the figure which showed the other structural example of the subscanning position detection sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Image processing part, 20 ... Light quantity correction part, 25 ... Laser exposure apparatus, 30 ... Photoconductor unit, 31 ... Photoconductor drum, 80 ... Control part, 110 ... Sub scanning position detection sensor, 201 ... object information acquisition unit, 202 ... pixel position information acquisition unit, 203 ... pixel position variation calculation unit, 204 ... correction parameter storage unit, 205 ... light quantity setting unit, 251 ... light source, 259 ... laser driver

Claims (13)

A photoreceptor,
A laser exposure unit that outputs one or a plurality of laser beams for scanning and exposing the surface of the photoreceptor;
A binarization processing unit that binarizes image data output to the laser exposure unit according to processing conditions for image density reproduction;
A scanning line interval detection unit for detecting a fluctuation amount of an interval between the scanning lines of the laser beam for scanning exposure on the surface of the photosensitive member;
Based on the fluctuation amount detected by the scanning line interval detection unit and the processing condition set by the binarization processing unit, a light emission amount of the laser light output from the laser exposure unit is set. An image forming apparatus comprising: a light amount setting unit. The binarization processing unit binarizes the image data in accordance with the processing conditions set to reproduce a halftone in a pseudo manner,
The image forming apparatus according to claim 1, wherein the light amount setting unit sets the light amount of the laser light in accordance with the processing condition.   The image forming apparatus according to claim 1, wherein the binarization processing unit binarizes the image data in accordance with the processing conditions set corresponding to an image attribute included in the image data. The binarization processing unit binarizes the image data using a predetermined screen angle set corresponding to an image attribute included in the image data,
The image forming apparatus according to claim 1, wherein the light amount setting unit sets a light amount of the laser light corresponding to the screen angle.   2. The scanning line interval detection unit detects the variation amount based on an irradiation position of the laser light from the laser exposure unit on the surface of the photosensitive member in a sub-scanning direction. Image forming apparatus.   The scanning line interval detection unit detects the amount of variation based on the irradiation position of the laser light from the laser exposure unit on the surface of the photosensitive member in the sub-scanning direction and the variation in the rotational speed of the photosensitive member. The image forming apparatus according to claim 1. A photoreceptor,
A laser exposure unit that outputs one or a plurality of laser beams for scanning and exposing the surface of the photoreceptor;
A binarization processing unit that binarizes image data output to the laser exposure unit according to processing conditions for image density reproduction;
A light amount setting unit that sets the light emission amount of the laser light output from the laser exposure unit in correspondence with the interval between scanning lines of the laser light on the surface of the photoconductor,
The light amount setting unit sets the light emission amount of the laser light set corresponding to the interval between the scanning lines to a different light emission amount according to the processing condition set by the binarization processing unit. An image forming apparatus. Information on the amount of light stored for each of the processing conditions set by the binarization processing unit, information defining the relationship between the interval between the scanning lines and the light emission amount of the laser light set corresponding to the interval A storage unit;
The light amount setting unit acquires the information related to the processing condition set by the binarization processing unit from the light amount information storage unit, and sets the light emission amount of the laser light based on the acquired information. The image forming apparatus according to claim 7. A binarization processing unit that generates binarized image data based on a binarization condition for reproducing a halftone in a pseudo manner from image data in which a predetermined density gradation number is set;
A laser exposure unit that scans and exposes a photosensitive member with laser light that is turned on based on the image data generated by the binarization processing unit;
A scanning line interval detection unit for detecting a variation amount of an interval between scanning lines on the surface of the photosensitive body of the laser beam scanned and exposed from the laser exposure unit;
Based on the fluctuation amount detected by the scanning line interval detection unit and the binarization condition set by the binarization processing unit, the light emission amount of the laser light scanned and exposed from the laser exposure unit A laser light amount control device comprising: a light amount setting unit for setting A light amount setting function for calculating a correction amount of the light emission amount of the laser light from the variation amount detected by the scanning line interval detection unit corresponding to the binarization condition set by the binarization processing unit. A function storage unit for storing
The light amount setting unit acquires the light amount setting function corresponding to the binarization condition set by the binarization processing unit from the function storage unit, and uses the acquired light amount setting function to generate the laser light. 10. The laser light quantity control device according to claim 9, wherein the quantity of emitted light is set.   In the case where a plurality of the binarization conditions in the binarization processing unit are applied to each pixel of the image data output on the same scanning line, the light amount setting unit 10. The laser light quantity control device according to claim 9, wherein a light emission quantity of the laser light is set based on any of the binarization conditions.   The scanning line interval detection unit detects the variation amount based on an irradiation position of the laser light from the laser exposure unit on the surface of the photosensitive member in a sub-scanning direction. Laser light quantity control device.   The laser light amount control apparatus according to claim 9, wherein the scanning line interval detection unit detects the amount of change based on a change in rotation speed of the photoconductor.

Images