JP5446168B2 - Light beam scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a light beam scanning device, a facsimile machine provided with the light beam scanning device, a printer, a copying machine, and a multifunction machine having the functions thereof.

In an image forming apparatus that forms an image on a recording medium including paper using an electrophotographic method, an electrostatic charge formed on a photoreceptor is exposed by a laser beam (laser beam) generated from a semiconductor laser light source. An electrostatic latent image is formed and developed with a developer to form an image.
Conventionally, there are many semiconductor laser light sources that irradiate one to four, and at most about eight laser beams from one semiconductor element, and one pixel is formed by the laser beam from one light source.

In recent years, surface emitting laser light sources (for example, VCSELs) that can emit about 40 laser beams from one chip have been put into practical use. An image forming apparatus that performs high-speed image formation has been proposed.
In this surface emitting laser light source, one pixel is formed by laser beams from a plurality of light sources.
This is because the output of the laser beam from the surface emitting laser light source is smaller than the laser beam from the conventional semiconductor laser light source (the output is weak). This is because it may not be obtained, and in order to obtain a sufficient amount of light necessary for development, it is suitable to irradiate laser beams from a plurality of light sources for forming one pixel.
For this reason, if there is a difference in oscillation wavelength between laser beams irradiated in one pixel, the beam spot position of each laser beam is shifted from a desired position due to the influence of the optical system having wavelength dependency. There is a possibility that the shape of the pixel (one dot) is broken and the image quality is deteriorated.

Conventionally, in an image forming apparatus that performs writing with a plurality of light sources, in order to correct the wavelength difference between the light sources, the spot position of the laser beam due to the wavelength difference between the light sources is corrected by correcting the phase of the pixel clock in the data area. There was a light beam scanning device for correction (see, for example, Patent Document 1).
JP 2007-203739 A

However, in a surface-emitting laser light source, when one pixel is constituted by a plurality of laser beams, generally, each laser beam irradiated in one pixel is emitted based on a common pixel clock. Therefore, each laser by phase control of the pixel clock is used. There was a problem that correction of the spot position of the beam could not be performed.
Further, as in the conventional light beam scanning apparatus described above, by performing drive control of a plurality of laser beams constituting one pixel, the spot position (irradiation position) of each laser beam in the sub-scanning direction is corrected. However, there is a problem that the spot position in the main scanning direction cannot be corrected.
The present invention has been made in view of the above points. When one pixel is formed by irradiation light generated by emitting a plurality of laser beams based on a common pixel clock, the main scanning direction is determined by the wavelength difference of each laser beam. The purpose of this is to prevent the irradiation position from shifting.

To achieve the above object, the present invention has a plurality of light sources, a light beam generating means for generating a light beam from each of the light sources, and lighting of each light source of the light beam generating means based on image data. A lighting control means for controlling, an image data processing means for generating and transferring the image data to the lighting control means, and a single pixel by condensing a plurality of light beam spots from the light sources on the surface to be scanned In the light beam scanning apparatus comprising the optical means for scanning, the position detecting means for detecting the spot position of each light beam constituting the one pixel, and the respective spot positions detected by the position detecting means. a shift amount calculation means for calculating a shift amount of the spot of each of the other light beam with respect to the light beam spot to be a reference among the respective light beams Te, depending on the deviation amount calculating means Based on the deviation amount storage means for storing the calculated deviation amount, and the deviation amount stored in the deviation amount storage means, the light source start time of the light beam serving as the reference is compared with the light source start time of each other light beam. Correction of the lighting start time of each light source, correction of the phase of each other light beam spot with respect to the phase of the reference light beam spot, and other correction with respect to the reference light beam spot width. Determination means for determining whether to correct the spot width of each light beam, and the image data processing means turns on the light source of the reference light beam based on the determination result of the determination means Correction of the lighting start time of each light source of each other light beam with respect to the start time, correction of the phase of each spot of the other light beam with respect to the phase of the spot of the light beam serving as the reference, and the reference Light beam spot By one of the correction of the other spot width of the light beam to wide, corrects the image data so that other spot of the light beam with respect to the light beam spot becomes the reference is not shifted, respectively A light beam scanning device is provided.

Further, the correction of the image data of the image data processing means, and compensation of the lighting start time of each light source in each of the other light beam to the lighting start time of the light beam of the light source serving as the reference, the above reference Any one of correction of the phase of the spot of each other light beam with respect to the phase of the spot of the light beam and correction of the spot width of each of the other light beams with respect to the spot width of the light beam serving as the reference Or it is good to correct | amend all combining .

Further, the correction of the image data by the image data processing means may be executed for each image print job.
The position detecting means may be a photodetector that detects the scanning position of the spot of the light beam.
Furthermore, an image forming apparatus equipped with the light beam scanning device as described above is also provided.

  When the light beam scanning apparatus and the image forming apparatus according to the present invention form one pixel with irradiation light generated by emitting a plurality of laser beams based on a common pixel clock, the irradiation in the main scanning direction is performed according to the wavelength difference of each laser beam. The position can be prevented from shifting.

Hereinafter, the best mode for carrying out the present invention will be specifically described with reference to the drawings.
〔Example〕
FIG. 2 is a block diagram showing a functional configuration of the image forming apparatus according to the embodiment of the present invention.
The image forming apparatus 100 includes an optical device 101 including optical elements such as a semiconductor laser light source and a polygon mirror, an image forming unit 102 including, for example, a drum-shaped photoconductor, a charging device, a developing device, and an intermediate transfer belt. This is a color copying machine including a transfer unit 103.
The optical device 101 deflects a light beam emitted from a light source such as a semiconductor laser light source (not shown) by a polygon mirror 110 and makes it incident on scanning lenses 111a and 111b such as an fθ lens.

The number of the light beams corresponding to the image of each color of black (K), yellow (Y), cyan (C), and magenta (M) is generated and reflected after passing through the scanning lenses 111a and 111b, respectively. Reflected by mirrors 112k to 112m.
For example, the black light beam passes through the scanning lens 111a, is reflected by the reflection mirror 112k, and enters the WTL lens 113k. The same applies to the light beams of yellow, cyan, and magenta, and the description thereof is omitted.
The WTL lenses 113k to 113m reshape the incident light beams, respectively, then deflect the light beams to the reflection mirrors 114k to 114m, and the light beams are further reflected by the reflection mirrors 115k to 115m, respectively, for exposure. The photosensitive members 120k to 120m are irradiated in the form of images as light beams K to M used in the above.

Since the light beams K to M are irradiated onto the photoconductors 120k to 120m using a plurality of optical elements as described above, timing synchronization is performed in the main scanning direction and the sub-scanning direction with respect to the photoconductors 120k to 120m. Has been done.
Hereinafter, the main scanning direction with respect to the photoreceptors 120k to 120m is defined as the scanning direction of the light beam, and the sub-scanning direction is defined as the direction orthogonal to the main scanning direction, that is, the direction in which the photoreceptors 120k to 120m rotate. To do.
The photoreceptors 120k to 120m include a photoconductive layer including at least a charge generation layer and a charge transport layer on a conductive drum such as aluminum.
The photoconductive layers are disposed corresponding to the photoreceptors 120k to 120m, respectively, and surface charges are applied by chargers 122k to 122m including a corotron, a scorotron, a charging roller, or the like.

The electrostatic charges imparted on the photoreceptors 120k to 120m by the chargers 122k to 122m are imagewise exposed by the light beams K to M, respectively, so that electrostatic charges are electrostatically formed on the scanned surfaces of the chargers 122k to 122m. A latent image is formed.
The electrostatic latent images formed on the scanned surfaces of the photosensitive members 120k to 120m are respectively developed by developing units 121k to 121m including a developing sleeve, a developer supply roller, a regulating blade, and the like. A developer image is formed on the surface to be scanned.
The developers carried on the scanned surfaces of the photoconductors 120k to 120m are transferred onto the intermediate transfer belt 130 that moves in the direction indicated by the arrows by the conveying rollers 131a to 131c. 132k to 132m are primary transfer rollers for the photoconductors 120k to 120m, respectively.

The intermediate transfer belt 130 is conveyed to the secondary transfer unit while carrying the C, M, Y, and K developers transferred from the scanned surfaces of the photoreceptors 120k to 120m.
The secondary transfer unit includes a secondary transfer belt 133 and conveying rollers 134a and 134b.
The secondary transfer belt 133 is conveyed in the direction of the arrow C by the conveyance rollers 134a and 134b.
An image receiving material P such as high-quality paper or a plastic sheet is supplied to the secondary transfer unit from an image receiving material storage unit T such as a paper feed cassette by a conveying roller 135.
The secondary transfer unit applies a secondary transfer bias to transfer the multicolor developer image carried on the intermediate transfer belt 130 onto the image receiving material P held by suction on the secondary transfer belt 133.

The image receiving material P is supplied to the fixing device 136 along with the conveyance of the secondary transfer belt 133.
The fixing device 136 includes a fixing member 137 such as a fixing roller containing silicone rubber, fluorine rubber, etc., pressurizes and heats the image receiving material P and the multicolor developer image, and receives the image by the paper discharge roller 138. The material P is discharged as a printed matter P ′ to the outside of the image forming apparatus 100.
After the transfer of the multicolor developer image, the intermediate transfer belt 130 is supplied to the next image forming process after the transfer residual developer is removed by a cleaning unit 139 including a cleaning blade.
A sub-scanning detection device (not shown) is provided near the end point in the main scanning direction of each of the photoconductors 120k to 120m, and detects a deviation in the sub-scanning direction.

FIG. 1 is a functional block diagram showing a configuration of the writing unit shown in FIG.
Since this writing unit is common to each of the photoconductors 120k to 120m, the photoconductor 120 and the scanning lens 111 will be described.
The writing unit includes a semiconductor laser unit 3 including a semiconductor laser light source that generates a light beam.
The semiconductor laser unit 3 is a light beam generating unit that has a plurality of light sources and generates a light beam from each of the light sources.
The semiconductor laser driving unit 2 is a lighting control unit that controls lighting of each light source of the semiconductor laser unit 3 based on the image data supplied from the image processing unit 1.

The image processing unit 1 is an image data processing unit that generates image data and transfers it to the semiconductor laser driving unit 2.
The laser beam emitted from the semiconductor laser unit 3 is deflected and scanned (scanned) by the rotating polygon mirror 110 to form a light spot on the photosensitive member 120 that is a scanned medium via the scanning lens (fθ lens) 111. Then, the photosensitive member 120 is exposed to form an electrostatic latent image. The polygon mirror 110 and the scanning lens 111 are optical means for condensing a plurality of light beam spots from each light source on the surface to be scanned on the photoconductor 120 to form one pixel and scanning.
The phase synchronization unit 4 sets the modulation signal generated by the clock generation unit 5 to a phase synchronized with the photodetector (PD) 123 that detects the light beam of the semiconductor laser deflected and scanned by the polygon mirror 110.

That is, the phase synchronization unit 4 generates a pixel clock (image clock) synchronized in phase based on the output signal of the PD 123 for each line, and supplies the pixel clock to the image processing unit 1 and the semiconductor laser driving unit 2. To do. Note that the pixel clock is supplied from the phase synchronization unit 4 to the semiconductor laser driving unit 2 through the image processing unit 1.
The writing unit follows the image data generated by the image processing unit 1 and the pixel clock whose phase is set for each line by the phase synchronization unit 4, and each light source of the semiconductor laser unit 3 via the semiconductor laser driving unit 2. By controlling the light emission time, the electrostatic latent image formed on the photoconductor 120 that is the medium to be scanned is controlled.
The light beam detector (BD) 124 is position detecting means for detecting the spot position of each light beam constituting one pixel.

Based on the spot position of each light beam detected by the BD 124, the main scanning position information calculation unit 6 shifts the spot of each light beam with respect to the reference light beam spot among the light beams ( This shift amount is a shift amount calculation means for calculating main scanning position information, which is information of a position shift, a spot width shift, and a phase shift.
The main scanning position information storage unit 7 stores the main scanning position information calculated by the main scanning position information calculation unit 6 and supplies it to the image processing unit 1.
Then, the image processing unit 1 supplies image data supplied to the semiconductor laser driving unit 2 so that the spots of the other light beams are not shifted from the spots of the reference light beam based on the main scanning position information. The process which correct | amends is also performed.
The image processing unit 1, the phase synchronization unit 4, the clock generation unit 5, and the main scanning position information calculation unit 6 are realized by a CPU, and the main scanning position information storage unit 7 is realized by a RAM, for example. .

FIG. 3 is a diagram showing a partial configuration of the light beam emitting section of the semiconductor laser unit 3 of FIG.
The semiconductor laser unit 3 is, for example, a VCSEL (Vertical-Cavity Surface-Emitting).
As shown in FIG. 3, for example, assuming a VCSEL having a 3 × 4 beam, each of the twelve light sources Da to Dl is equally spaced (the distance between the center points of the light sources is a). The VCSEL is inclined at a predetermined angle in the main scanning direction, and one pixel 10 is formed by spots of light beams from four light sources.
For example, in the case where one pixel having a diameter of 1200 dpi is formed by the light sources Da to Dd, the light sources De to Dh, and the light sources Di to Dl, sub-centers of the respective center points of the light sources Da to Dd, the light sources De to Dh, and the light sources Di to Dl. The VCSEL is inclined so that the interval in the scanning direction is 4800 dpi.

  In this way, when one pixel is composed of spots of light beams from a plurality of light sources, the physical positions of the spot positions of the light beams in one pixel are generated in the main scanning direction. By changing the lighting start time (lighting start timing) of each light beam, the light beam spots from each light source in one pixel are positioned at the same position in the main scanning direction.

FIG. 4 is a diagram illustrating an example of a waveform diagram of image data generated by the image processing unit illustrated in FIG. 1.
Based on the pixel clock from the phase synchronization unit 4 as shown in (a) of the figure, the image processing unit 1 determines the emission start times of the light sources Da to Dd as shown in (b) of the figure. Image data in which the peaks of the waveform indicating the light emission time are respectively set to 11a to 11d is created.
The peak of each waveform is determined by determining the light emission start time based on the pixel clock for the light source Da that generates the reference light beam, and setting the light emission time dt peak 11a. Based on this, the light beam spot of the light source Da is set. Waveform peaks 11b to 11d indicating the light emission start times and the light emission times of the other light sources Db to Dd are set so as to be aligned with the irradiation position and the irradiation width. In the figure, at corresponds to the scanning time of the interval a shown in FIG.

However, at this time, if there is a wavelength difference in the oscillation wavelength of each light beam constituting one pixel, the spot position of each light beam may be shifted due to the wavelength characteristics of the optical system up to the photosensitive member 120 to be scanned, The spot shape may be different from the desired shape.
In addition, the oscillation wavelength of each light source varies depending on the characteristics of the element, but the wavelength may change due to a temperature change or the like.
Normally, when one pixel is formed by light beam spots from a plurality of light sources, the light beam spots of the respective light sources are made to be in a straight line with respect to the conveying direction of the image receiving material P. If the center position of the spot position of each light beam shifts, one pixel will have a non-uniform dot shape.

FIG. 5 is an explanatory diagram of a non-uniform dot shape.
For example, the center position a of the light beam spot sp from the light source Db, the center position c of the light beam spot sp from the light source Dc, and the light source Dd with respect to the center position a of the light beam spot sp from the light source Da. If the center position d of the spot sp of the light beam is shifted as shown in the figure and the spot width (irradiation width) of each spot sp does not become the same, the dot of the pixel 10 constituted by these four spots sp For example, if the shape does not become a circle and one pixel has a non-uniform dot shape, the image quality of the entire image formed by such pixels may be deteriorated.

Therefore, in this image processing apparatus, the dot shape is kept uniform by improving the wavelength difference of the light beam of each light source in one pixel, and the image quality is improved.
First, the spot position of each light beam constituting one pixel is detected, and the main spot of each other light beam with respect to the reference light beam spot in each light beam is detected based on the detected spot position. Processing for calculating the main scanning position information of the deviation amount in the scanning direction and the deviation amount of the spot width in the main scanning direction will be described.
Processing when a CCD is used as the BD 124 will be described.

FIG. 6 is an explanatory diagram of processing for calculating main scanning position information of a light beam spot using a CCD.
As shown in FIG. 6A, the CCD 125 observes the spot positions of the spots spa to spd of the light beams of the light sources Da to Dd constituting one pixel. In the figure, wa to wd indicate the widths of the spots spa to spd of the light beams of the light sources Da to Dd, and a to d indicate the center positions of the spots of the light beams Da to Dd. , Z1 is the amount of deviation between the center position of the spot spa and the center position of the spot spb, z2 is the amount of deviation between the center position of the spot spb and the center position of the spot spc, and z3 is the center position of the spot spc and the spot spd. The amount of deviation of the center position of each is shown.

Next, the main scanning position information calculation unit 6 takes the line profile of the beam intensity of each spot obtained by the CCD 125, and obtains the main scanning position information of the spot position and beam width of each light beam in the main scanning direction.
FIG. 6B shows an example of a waveform of a change in beam intensity of each light beam measured by the CCD 125. In FIG. 6B, the shapes of the waveforms are shown so as not to overlap each other, and the beam intensity of each waveform shows a change width of the same value with respect to the lower side of the waveform. The main scanning position information calculation unit 6 calculates the deviation amount of the light beams from the other light sources Db to Dd with respect to the light beam from the reference light source Da from the obtained waveform of the change in the beam intensity of each light beam. calculate.
The shift amount z1 of the main scanning position of the light beams from the light sources Da and Db is the main scanning position (corresponding to the center position a of the spot) at which the beam intensity of the light beam from the light source Da becomes the maximum value, and from the light source Db. It is obtained from the difference from the main scanning position (corresponding to the center position b of the spot) where the beam intensity of the light beam becomes the maximum value.

The amount z2 of the main scanning position of the light beam from the light sources Db and Dc is the maximum at the main scanning position where the beam intensity of the light beam from the light source Db is maximum and the beam intensity of the light beam from the light source Dc. It is obtained from the difference from the main scanning position (corresponding to the center position c of the spot).
Further, the deviation z3 of the main scanning position of the light beam from the light sources Dc and Dd is the main scanning position where the beam intensity of the light beam from the light source Dc is maximum and the beam intensity of the light beam from the light source Dd is the maximum. It is obtained from the difference from the main scanning position (corresponding to the center position d of the spot).
Also, the spot widths wa, wb, wc, wd of each spot can be obtained based on the main scanning position of each waveform.
The main scanning position information calculation unit 6 stores the main scanning position information of the spot position and beam width of each light beam obtained as described above in the main scanning position information storage unit 7.
Then, the image processing unit 1 corrects the image data based on the main scanning position information stored in the main scanning position information storage unit 7.

Next, processing when a synchronization detection plate is used as the BD 124 will be described.
The synchronization detection plate is a photodiode that detects the scanning position of the light beam, and the amount of deviation between the spots can be obtained based on a synchronization signal generated by scanning the synchronization detection plate.
Therefore, when this synchronization detection plate is used, in the correction process of the image data in the image processing unit 1, only the correction of the spot position is performed without correcting the spot width and the phase.
FIG. 7 is an explanatory diagram of processing for calculating the amount of deviation of the spot of the light beam using the synchronization detection plate.

As shown in FIG. 7A, the synchronization detection plate 126 includes a light receiving portion 127 inside, and only the light sources Da to Dd constituting one pixel are turned on for each light receiving portion 127. Light beam spots spa to spd are made incident.
Then, the light receiving unit 127 outputs a voltage value that is lowered according to the amount of incident light of each of the spots spa to spd.

For example, a change in voltage value over time shown in the waveform diagram of FIG.
First, the light receiving unit 127 outputs the voltage value V0 before the incidence of the light beam. Here, when the spot spd of the light beam of the light source Dd is detected, the voltage value is reduced from V0 to Vd according to the incident light quantity of the spot spd and output, and when the spot spc of the light beam of the light source Dc is detected, the spot spc. The voltage value is further reduced from Vd to Vc in accordance with the amount of incident light. Further, when the spot spb of the light beam of the light source Db is detected, the voltage value is further reduced from Vc to Vb in accordance with the incident light quantity of the spot spb, and when the spot spa of the light beam of the light source Da is detected, the spot The voltage value is further reduced from Vb to Va according to the amount of incident light of spa and output.

In the figure, td-in to ta-in indicate times when the light receiving unit 127 starts detecting the light beam spots spd to spa, respectively. Td-out to ta-out are respectively the light receiving unit 127 of the light beam. The time when the detection of the spots spd to spa is finished is shown.
Then, in the main scanning position information calculation unit 6, ta = (ta−in) − (tb− in FIG. 7B), based on the change in voltage value output from the light receiving unit 127 and the elapsed time as described above. in) and the amount of deviation of the spot position between the spots spa and spb is obtained based on the time ta obtained by the calculation and the movement distance (movement speed) of the light beam per unit time in the main scanning direction. . Similarly, the amount of deviation of the spot position between the spots spa and spc is obtained from tb, and the amount of deviation of the spot position between the spots spa and spd is obtained from tc, and each deviation amount is used as the main scanning position information. The information is stored in the information storage unit 7.

Then, the image processing unit 1 corrects the image data based on the main scanning position information stored in the main scanning position information storage unit 7.
In this way, if a synchronization detection plate is used as a means for detecting the beam spot positions of a plurality of light sources constituting one pixel, it is not necessary to add a new measuring means, thereby suppressing an increase in cost. Can do.

Next, image data correction processing in the image processing unit 1 will be described.
First, a process for correcting a deviation in the main scanning direction of the spot position of each light beam by correcting the lighting start time of each light source constituting one pixel will be described.
FIG. 8 is a waveform diagram for explanation when the lighting start time of each light source is corrected.

For example, when the light beam of the light source Da is set as a reference light beam, the shift amount of the main scanning position information described above with respect to the peak 12a of the waveform indicating the lighting start time and lighting time (dt) of the light source Da. For example, for the light source Db, the position of the peak 12b before correction is corrected to a peak 12b 'at a position corresponding to the shift amount, and for the light source Dc, the position of the peak 12c before correction is corrected according to the shift amount. For the light source Dd, the position of the peak 12d before correction is corrected to the peak 12d 'at the position corresponding to the amount of deviation. In this case, the lighting times (dt) in each mountain are all kept the same.
As described above, the light output from each of the light sources Da to Dd is performed by moving the writing timing (corresponding to the lighting start time) of the image data of the other light sources Db to Dd back and forth with the image data signal of the light source Da as a reference. Correction is made so that the spot positions of the beams are aligned in the main scanning direction.

Normally, the lighting start time of each light beam uses a common synchronization detection signal for each light beam in one pixel, and the physical time as shown in FIG. In consideration of a typical light beam spot position interval a, they are set to be the same position in the main scanning direction on the image.
Therefore, the writing position is corrected to the interval of each light beam spot in consideration of the deviation of the spot position of the actual light beam by correcting the image data as described above, and the irradiation position of each spot is set to one pixel. Correct so that there is no deviation in the configuration.
In this correction process, the pixel clock unit, that is, one dot is used as the minimum correction amount.
In this way, since the data lighting start time of each light source is controlled as means for correcting the main scanning positions of the beam spots of a plurality of light sources constituting one pixel, correction can be performed in units of pixel clocks. it can.

Next, a description will be given of a process for correcting the deviation of the spot position of each light beam in the main scanning direction by correcting the phase of the light beam spot of each light source constituting one pixel.
FIG. 9 is a waveform diagram for explanation when correcting the phase of the spot of the light beam of each light source.

  For example, the light beam of the light source Da is determined as a reference light beam, and a peak 13a whose lighting time is set to a time dt 'shorter than one period of the pixel clock is arranged in the center with respect to one period of the pixel clock. When set, for the light source Db, for example, for the light source Db, the phase of the peak 13b before correction is set as the amount of deviation with respect to the peak 13a of the waveform of the light source Da. The light source Dc is corrected to shift to the phase of the peak 13b ′ according to the spot width, and the light source Dc is corrected to shift the phase of the peak 13c before correction to the phase of the peak 13c ′ according to the shift amount. Corrects so that the phase of the peak 13d before correction is shifted to the phase of the peak 13d 'according to the shift amount and the spot width. In this case, the lighting time (dt ′) in each mountain is kept the same.

Accordingly, the lighting signal of the image data to the light source Da serving as a reference is arranged in the center within the range of one cycle of the pixel clock, whereas the lighting signal of the image data to the light sources Db and Dd is within the range of the pixel clock. The lighting signal of the image data of the light source Dc is arranged on the left side within the range of the pixel clock. Therefore, the main scanning position of the light beam spot can be corrected at a timing of one cycle or less of the pixel clock.
In this way, the image processing unit 1 corrects the phase of each other light beam spot with respect to the phase of the light beam spot serving as a reference.
In this way, by controlling the lighting phase of the image data, the irradiation range of the spot of each light beam can be made uniform, and the spot position of the light beam can be corrected with high accuracy.

Next, processing for correcting the deviation of the spot position of each light beam in the main scanning direction by correcting the spot width of each light beam constituting one pixel will be described.
FIG. 10 is a waveform diagram for explanation when correcting the spot width of the light beam of each light source.
For example, the light beam of the light source Da is determined as a reference light beam, and a peak 14a whose lighting time is set to a time dt1 shorter than one cycle of the pixel clock is set so that the phase is arranged in the center with respect to one cycle of the pixel clock. In this case, with respect to the peak 14a of the waveform of the light source Da, based on the shift amount and spot width of the main scanning position information described above, for example, for the light source Db, the width of the peak 14b before correction is set to the shift amount and spot. The light source Dc is corrected so as to be expanded to the width dt2 of the peak 14b ′ according to the width, and the width of the peak 14c before correction is corrected to be reduced to the width dt3 of the peak 14c ′ according to the shift amount and the spot width. The light source Dd is corrected so that the width of the peak 14d before correction is reduced to the width dt4 of the peak 14d ′ according to the shift amount and the spot width. In this case, the case of dt2>dt1>dt3> dt4 is shown.

Therefore, by correcting the spot width of each light beam with respect to the reference light beam spot width as described above, the spot width in the main scanning direction of the light beam of the light source Db is larger than the actual spot width. The spot width in the main scanning direction of the light beam of the light source Da is widened, while the spot width in the main scanning direction of the light beams of the light sources Dc and Dd is made narrower than the actual spot width to make the main beam of the light beam of the light source Da. It can be aligned with the spot width in the scanning direction.
In this way, the spot shape in the main scanning direction of each light beam due to the difference in wavelength can be corrected.

Next, one of the three types of image data correction processing described above may be selected based on main scanning position information stored in the main scanning position information storage unit 7.
FIG. 11 is a functional block diagram showing another configuration of the writing unit shown in FIG. 2, and parts common to FIG.
In this writing unit, the newly provided correction method determination unit 8 determines the lighting start time of the light source of the reference light beam based on the main scanning position information stored in the main scanning position information storage unit 7. Correction of the lighting start time of each light source of each other light beam, correction of the phase of each other light beam spot relative to the phase of the reference light beam spot, and the spot width of the reference light beam On the other hand, it is determined whether to correct the spot width of each other light beam, and the determination result is notified to the image processing unit 1.

For example, from the stored main scanning position information, the left or right side of the reference light beam spot, or the amount of deviation is greater than or less than the pixel clock width, or the main scanning direction beam width of the reference beam It is determined whether the beam width is wide or narrow, and an optimal correction method is determined.
Then, the image processing unit 1 corrects the lighting start times of the light sources of the other light beams with respect to the lighting start times of the light sources of the reference light beams based on the determination result of the correction method determination unit 8. Correction of the phase of each other light beam spot with respect to the phase of the reference light beam spot, and correction of the spot width of each other light beam with respect to the reference light beam spot width. In any case, the process of correcting the image data is performed so that the spots of the other light beams are not shifted from the spots of the reference light beam.
In this manner, since the optimum correction method can be selected and executed based on the main scanning position information stored in the main scanning position information storage unit 7, automatic correction can be performed.

  Furthermore, if the image processing unit 1 corrects image data by combining all or any two of the above-described correction processes, an appropriate correction is made according to the deviation of the spot position of the actual light beam. And more accurate correction can be performed.

  Furthermore, the image processing unit 1 corrects the beam spot position of each light source on the scanned surface for each image print job if the above-described image data correction processing is executed for each image print job. The deviation of the beam spot position due to the temperature rise due to the printing operation can be corrected.

Conventionally, correction of the spot position of the light beam in the main scanning direction has been performed by correcting the phase and frequency of the pixel clock.
However, when one pixel is constituted by a plurality of light sources as in the VCSEL, the pixel clock for each light source in the same pixel is common, and in the conventional correction method for controlling the pixel clock, each light beam in one pixel is The spot position and spot width cannot be corrected individually.
Therefore, in the image forming apparatus of this embodiment, by correcting the image data output for each light source as described above, the main light beam from each light source is used even between light sources using a common pixel clock. Correction can be made so that spot positions in the scanning direction are aligned, and image deterioration can be reduced.

  The light beam scanning device and the image forming apparatus according to the present invention can be applied to a facsimile machine, a printer, a copying machine, and a multifunction machine having a plurality of functions including image reading, copying, printing, and communication.

FIG. 3 is a functional block diagram illustrating a configuration of a writing unit illustrated in FIG. 2. 1 is a block diagram illustrating a functional configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the structure of a part of light beam emission part of the semiconductor laser unit of FIG. It is a figure which shows an example of the waveform diagram of the image data which the image process part shown in FIG. 1 produces | generates. It is explanatory drawing of a non-uniform dot shape.

It is explanatory drawing of the process which calculates the main scanning position information of the spot of a light beam using CCD. It is explanatory drawing of the process which calculates the deviation | shift amount of the spot of a light beam using a synchronous detection board. It is a wave form diagram with which it uses for description when the lighting start time of each light source is correct | amended. It is a wave form diagram with which it uses for description in the case of correct | amending the phase of the spot of the light beam of each light source. It is a wave form diagram with which it uses for description in the case of correct | amending the spot width of the light beam of each light source. FIG. 4 is a functional block diagram illustrating another configuration of the writing unit illustrated in FIG. 2.

Explanation of symbols

1: Image processing unit 2: Semiconductor laser drive unit 3: Semiconductor laser unit 4: Phase synchronization unit 5: Clock generation unit 6: Main scanning position information calculation unit 7: Main scanning position information storage unit 8: Correction method determination unit 10: Pixel 100: Image forming apparatus 101: Optical apparatus 102: Image forming section 103: Transfer section 110: Polygon mirror 111, 111a, 111b: Scan lens 112k to 112m, 114k to 114m, 115k to 115m: Reflection mirror 113k to 113m: WTL Lenses 120, 120k to 120m: Photoconductors 121k to 121m: Developers 122k to 122m: Chargers 123: PD 124: BD 125: CCD 126: Synchronization detection plate 127: Light receiving unit 130: Intermediate transfer belt 131a to 131c: Carrying Rollers 132k to 132m: primary transfer roller 133: secondary transfer belt 134a, 134b: transport roller 135: transport roller 136: fixing device 137: fixing member 138: paper discharge roller 139: cleaning unit T: image receiving material storage unit P: Image receiving material P ': printed matter

Claims (5)

A light beam generating means for generating a light beam from each of the light sources; a lighting control means for controlling lighting of each light source of the light beam generating means based on image data; and Image data processing means for generating and transferring to the lighting control means; and optical means for condensing a plurality of light beam spots from each of the light sources on the surface to be scanned to constitute one pixel and scan it. In the light beam scanning device,
Position detecting means for detecting a spot position of each light beam constituting the one pixel;
A deviation amount calculating means for calculating a deviation amount of each light beam spot with respect to a light beam spot serving as a reference among the light beams based on each spot position detected by the position detecting means ;
Deviation amount storage means for storing the deviation amount calculated by the deviation amount calculation means;
Based on the deviation amount stored in the deviation amount storage means, the correction of the lighting start time of each light source of the other light beams with respect to the lighting start time of the light source of the reference light beam, and the reference Either correction of the phase of each other light beam spot with respect to the phase of the light beam spot, or correction of the spot width of each other light beam with respect to the reference light beam spot width. And a judging means for judging
The image data processing means corrects the lighting start time of each light source of each other light beam with respect to the lighting start time of the light source of the reference light beam based on the determination result of the determining means, and the reference Either the correction of the phase of each other light beam spot with respect to the phase of the light beam spot, or the correction of the spot width of each other light beam with respect to the reference light beam spot width. the light beam scanning apparatus characterized by other spots of the light beam to the light beam spot becomes the reference was made to correct the image data so as not to shift respectively.   2. The light beam scanning apparatus according to claim 1, wherein the correction of the image data of the image data processing means is performed by starting the lighting of each light source of each of the other light beams with respect to the lighting start time of the light source of the reference light beam. Correction of time, correction of the phase of the spot of each other light beam with respect to the phase of the spot of the reference light beam, and spot of each other light beam with respect to the spot width of the reference light beam A light beam scanning apparatus which performs correction by combining any two or all of the width correction. 3. The light beam scanning apparatus according to claim 1 , wherein the correction of the image data by the image data processing unit is executed for each image print job. In the light beam scanning apparatus according to any one of claims 1 to 3, wherein the position detecting means, a light beam scanning apparatus which is a photodetector for detecting the scanning position of the spot of the light beam. Image forming apparatus characterized by mounting the optical beam scanning apparatus according to any one of claims 1 to 4.

Images