JP2010023280A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner constituted so that the influence of reciprocity law failure is reduced, and failures such as uneven image density is improved, in the case of providing an image of high density and high image quality at a high speed. <P>SOLUTION: The optical scanner includes a control unit 100 which forms scan-lines adjacent to one another among all the scan-lines on a surface to be scanned with deflection scanning in a time difference manner, and also, which can perform an interlace scanning control to perform the following scanning while jumping over the scan line on the surface to be scanned in the case of forming the minimum resolution pixel in the sub scanning direction with n-scan lines. In the case of forming the image on the surface to be scanned by lighting the light sources equal to or less than n-1 and thinning the scan positions, the control unit 100 compares the number of scanning times for the image formation by the center part of a vertical cavity surface emitting laser used as the light source, with the number of scanning times for the image formation by the end part of the vertical cavity surface emitting laser, and then, sets the light emitting condition of the vertical cavity surface emitting laser in accordance with the comparison result. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical scanning device and an image forming apparatus, and more particularly to light emission control in an optical scanning device using a laser capable of surface emission.

  As is well known, in an image forming apparatus using an electrophotographic system, a semiconductor laser (LD) is used as a light source (hereinafter referred to as an LD light source for convenience) as an image information writing device for forming an electrostatic latent image on a latent image carrier. A configuration using an optical scanning device is sometimes used.

  In an image forming apparatus using beam scanning light from an LD light source, it is necessary to rotate a photoconductor used as a latent image carrier at high speed in order to obtain high resolution and high speed print output. In response to this, it is necessary to increase the rotation frequency of the polygon mirror, which is a scanning member used in the scanning exposure system for imaging the beam scanning light from the LD light source on the photosensitive member, and to increase the scanning frequency in the sub-scanning direction.

  However, the rotational speed of the polygon mirror is currently around 30,000 (rpm), and in order to obtain a rotational speed higher than this, there are difficult problems such as improvement of the bearing of the polygon mirror. In addition, when the rotational speed of the polygon mirror is increased, in addition to the structural problems with the bearings described above, there is a risk of increasing noise such as wind noise and increasing power consumption.

Therefore, conventionally, in order to solve these problems, in order to achieve high resolution and high-speed print output without increasing the number of rotations of the polygon mirror, a plurality of light sources are arranged in the sub-scanning direction and once in the main scanning direction. A multi-beam scanning exposure method is employed in which scanning with a plurality of beams is performed (for example, Patent Document 1).
According to this method, the polygon mirror rotation speed required in the case of only one beam light source becomes a two-beam light source, so that the rotation speed can be reduced to ½, which is impossible in the case of one beam. Scanning becomes possible, and even if exposure scanning with one beam is possible, there is a margin in rotation. As a result, the linear velocity of the photosensitive member can be increased, and the rotation speed of the polygon mirror can be increased accordingly, and high-speed printing can be performed.

  As a configuration for performing scanning exposure using a multi-beam, scanning is performed on a latent image forming surface of a photosensitive member which is a latent image carrier by combining a plurality of two-dimensionally arranged LD light sources as a light source. A configuration that enables high-speed output by increasing the number of beams (for example, Patent Document 2), or a surface emitting laser (VCSEL: Vertical Cavity) in which a plurality of light emitting units can be easily arranged on one semiconductor laser chip There exists a structure (for example, patent document 3) which uses Surface Emitting Laser-Diode) as a light source.

JP 2003-241403 A JP-A-2005-250319 JP 2004-287292 A

However, when performing multi-beam scanning exposure, as disclosed in Patent Document 1, there is a problem that the density and thickness of one dot (or one line) differ due to reciprocity failure. The reason is as follows.
When a plurality of LD light sources are arranged and the number thereof is N, N multi-beam lines are simultaneously exposed on the photoconductor when one main scanning direction exposure is performed on one surface of the rotating polygon mirror. . One beam usually has an elliptical beam shape, and the beams partially overlap each other, so when viewed at one point on the photoconductor, an extremely strong power is irradiated at one time, and the exposure energy is the same. Even so, at one point of the photoconductor, the same exposure energy is received once and the case where it is received twice. For this reason, even if the exposure energy is the same on the photosensitive member side, the photoelectric change with respect to the latent image formation is different, and the above-described dot density and thickness may not be uniform.

The reciprocity failure described above will be explained. Normally, assuming that exposure energy = light power (value per unit time, unit area) × exposure time, when exposure is repeated once and when exposure is repeated And the photoattenuation curve that affects the latent image formation characteristics due to the attenuation of the charged charge in the photoconductive layer on the photoconductor side differs, and specifically, when the exposure is repeated, the case of one exposure Unlike the case, the surface potential of each dot in the photoconductive layer after beam irradiation is different.
FIG. 23 is a light attenuation curve that affects the formation of an electrostatic latent image by exposure (a diagram showing the relationship between the surface potential of the photoconductor and the exposure energy. Usually, a change in the surface potential according to the exposure energy is obtained. .

  On the other hand, FIG. 24 shows a light attenuation curve when the above-described multi-beam exposure method is used. As shown in FIG. 24, when the exposure energy is the same, one exposure, that is, simultaneous exposure is performed. 24 (shown by a broken line in FIG. 24) and when exposure is performed in two steps, that is, when sequential exposure is performed (shown by a solid line in FIG. 24), the surface potential of the photoreceptor is lowered. On the other hand, regarding the absolute value of the potential on the surface of the photoreceptor, the potential decrease on the surface is more remarkable when the exposure is repeated. In this way, when forming dots (or lines) using multi-beams, if the photoreceptor has a strong reciprocity failure, dots (or lines) formed depending on whether multiple beams are exposed simultaneously or sequentially. The density and thickness are different, and a defective image called image unevenness is obtained.

  The image unevenness may be visually recognized as density unevenness such as banding or moire depending on the size of the frequency, which causes a problem that the image is identified as a defective image.

Here, regarding visibility, when the image data is considered as a distribution diagram of density, luminance, and the like, the distribution can be regarded as a wave. A pattern (wave) in which light and dark are alternately repeated can be considered and the repetition can be regarded as a frequency. This frequency is generally called a spatial frequency.
When this spatial frequency is low, the width of the light / dark pattern becomes wide, and conversely, when the spatial frequency is high, the width of the light / dark pattern becomes narrow. MTF (Modulation Transfer Function) represents the relationship between spatial frequency and contrast (light / dark ratio), and graphs the spatial frequency f, which means sharpness and fine structure reproducibility at the image edge, and the contrast sensitivity MTF of the visual system. The human visual characteristic is shown in FIG. The spatial frequency (VTF: cycle / degree) in this case is obtained by the following equation.
VTF (u) = 5.05 exp (-0.138 u) {1-exp (-0.1 u)}
From FIG. 25, it can be seen that image processing is necessary in consideration of the characteristic that the closer to the high frequency side, the less visible (visually) it is, and the lower frequency side is easier to visually recognize.

  On the other hand, in the configuration as disclosed in Patent Documents 1 and 2, that is, in the configuration using a plurality of light sources and using a multi-beam, a general-purpose LD can be used, so that the component cost is low, but the light source and the optical system, In particular, it is difficult to stably maintain the relative positional relationship with the coupling lens with a plurality of beams, and there is a possibility that the scanning line interval formed on the surface to be scanned by the multi-beams becomes non-uniform. Furthermore, in this method, it is necessary to use a large number of light sources. However, it is difficult to meet this requirement mechanically, and it is difficult to realize high density and ultra high speed.

  Although the case of using an edge-emitting type one-dimensional LD is also conceivable, in this case, the power consumption for blocking increases, and the optical characteristics may be deteriorated.

  Therefore, by using a surface emitting laser (vertical cavity surface emitting laser: VCSEL) as disclosed in Patent Document 3, two-dimensional integration is achieved, thereby reducing power consumption compared to an edge emitting laser. And many light sources may be integrated two-dimensionally. As a result, it is possible to increase the number of beams in the sub-scanning direction written in one scan.

However, when increasing the number of beams in the sub-scanning direction using a surface-emitting laser, for example, if 10 surface-emitting lasers are arranged and scanned in the sub-scanning direction at 1200 dpi, the minimum writing pixel of 1200 dpi is 25. When 4/1200 = 2.12 × 10 ⁻² (mm) is set and writing is performed with 10 surface emitting lasers, the sub-scanning frequency is 1 / (2.12 × 10 ⁻² ) [cycle / mm. ]. For this reason, since not only the moire image of the sub-scanning frequency and the image frequency but also the sub-scanning frequency unevenness is in the human visibility region, the written image itself may be directly recognized as moire.

  Furthermore, when scanning using multi-beams, if a configuration in which light sources are arranged, such as a surface emitting laser, there is a problem that the life of the light source deteriorates due to the influence of thermal interference between laser elements. For this reason, in the case of a surface emitting laser, the space between the light source elements cannot be reduced.

  In addition, when the interval between the elements is narrowed, the electrical wiring becomes difficult. On the other hand, in order to increase the element interval, the absolute value of the sub-scanning lateral magnification in the entire optical system is lowered in the sub-scanning direction. Treatment such as is necessary. However, if this value is lowered, light utilization efficiency will be reduced and higher output will be required. However, since it is difficult to increase output with surface emitting lasers, the above method cannot be used to improve the light source life. become. Surface emitting lasers are known to have poor optical response at low output, and there are still problems that must be solved when using surface emitting lasers to increase the number of beams. is there.

  The object of the present invention is to reduce the influence of reciprocity failure in consideration of the problems in the conventional optical scanning device, and to improve the problems such as uneven density of the image when obtaining a high-speed, high-density and high-quality image. It is an object of the present invention to provide an optical scanning device and an image forming apparatus having a configuration that can be used.

In order to achieve this object, the present invention has the following configuration.
(1) In an optical scanning device that performs writing scanning using a laser beam,
A light source using a two-dimensional array of surface emitting lasers;
A first optical system for guiding a plurality of beams from the light source to a deflecting unit;
A second optical system for guiding a plurality of beams from the deflecting means to a surface to be scanned,
When scanning lines adjacent to each other in all scanning lines on the scanning surface are formed by deflection scanning different in time and the minimum resolution pixel in the sub-scanning direction is formed by n scanning lines, A control unit capable of interlaced scanning control for performing the next scanning over the scanning line,
When the controller performs image formation on the surface to be scanned by turning on n-1 or less light sources and thinning the scanning position, the number of scans in which image formation is performed at the center of the surface emitting laser used for the light source And the number of scans in which an image is formed at the end, and the emission condition of the surface emitting laser is set according to the result.
(2) In the case where k surface-emitting lasers that are two-dimensionally arranged are used as the light source, the control unit,
When the distance between both ends of the scanning line formed by one scanning by the deflecting means is L1, and the distance between adjacent scanning lines on the surface to be scanned is L2,
L1> (k−1) × L2
The light scanning device according to (1), wherein the light emission condition satisfying the above relationship is set.
(3) The optical scanning device according to (2), wherein the control unit performs setting such that a scanning line interval formed by one deflection scan is not uniform by the k light emitting points.
(3) The control unit excludes the scanning line having the narrowest interval among the scanning line intervals formed by the one deflection scanning from both ends in the sub-scanning direction (2) or (3) ).
(5) The optical scanning device according to (1) or (2), wherein the control unit performs adjustment so that the number of times of normal scanning and the number of times of scanning of the end portion coincide with each other.
(6) The control unit sets the thinning position so that the emission positions of the surface emitting lasers during one scanning are adjacent when the number of times of image formation at the center of the surface emitting laser is smaller than the number of edge scanning times. The optical scanning device according to (1) or (2).
(7) The control unit sets the thinning position so that the emission position of the surface emitting laser during one scan is separated when the number of scans in which the image is formed at the center of the surface emitting laser is greater than the number of end scanning. The optical scanning device according to (1) or (2).
(8) An image forming apparatus using the optical scanning device according to any one of (1) to (7).
(9) Regarding the light beam diameter used in the optical scanning device,
Ws ≦ Wm (Wm: beam diameter in the main scanning direction, Ws: beam diameter in the sub-scanning direction)
The image forming apparatus as set forth in (8), characterized in that:

  According to the present invention, with the number of scans between the central portion and the end portion of the surface emitting laser as a reference, the thinning scan that enables the light emission conditions and the light amount stabilization in the interlaced scan that reduces the influence of reciprocity failure Since each of the light emission conditions is set, variation in the scanning position of the surface emitting laser can be reduced and density unevenness can be made inconspicuous.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing an image forming apparatus using an optical scanning device according to the present invention. The image forming apparatus shown in the figure includes a drum-shaped photosensitive member 1 that can rotate in a clockwise direction indicated by an arrow in the figure as a latent image carrier. Around the photosensitive member 1, a charging device 2, an optical scanning device 3, a developing device 4, a transfer device 5, and a cleaning device 6 are arranged for performing image forming processing along the rotation direction.

  The photosensitive member 1 is uniformly charged to, for example, negative polarity by the charging device 2, and an electrostatic latent image is formed by the scanning light from the optical scanning device 3. The electrostatic latent image is subjected to a visible image processing with toner contained in the developer supplied from the developing device 4 to become a toner image. The electrostatic latent image is statically applied to the transfer material P fed from a paper feeding device (not shown) by the transfer device 5. When the electrotransfer is performed, the toner image is heated and fixed by the fixing device 7.

  After the transfer, the transfer residual toner is removed by the cleaning device 6 and the residual charge is removed by the charge removal lamp 8. Then, the photosensitive member 1 is again charged uniformly by the charging device 2 for the next image forming process. Provided.

The image forming apparatus shown in FIG. 1 is based on the premise that a single color image is transferred onto a transfer material using a single photoconductor, but the image forming apparatus has a configuration in which a plurality of colors form an image. There is also.
FIG. 2 is a diagram illustrating a configuration for performing image formation of a plurality of colors. The image forming apparatus illustrated in FIG. 2 includes the photosensitive member 1 illustrated in FIG. 1 and each device disposed in the periphery thereof. This is a tandem type image forming apparatus in which an image forming unit is juxtaposed along a stretched surface of an intermediate transfer belt 10 used as an intermediate transfer member. In FIG. 2, Y (yellow), M (magenta), C (cyan), and K (black), which indicate the color of an image formed in the image forming unit, are attached to each photoconductor 1. Yes.

  In the image forming apparatus shown in FIG. 2, the intermediate transfer belt 10 is used as a member that sucks and conveys the transfer material, and is formed at each image forming unit in the process of moving the sucked transfer material toward each image forming unit. A color image is sequentially superimposed and transferred. The transfer material carrying the superimposed transferred toner image is heated and fixed by the fixing device 9.

The optical scanning device 3 used in the image forming apparatus shown in FIGS. 1 and 2 has the configuration shown in FIG. It should be noted that the light source may be indicated as LD in the member names listed below.
In FIG. 3, the light source 20 uses a two-dimensionally arranged semiconductor laser. The light beam emitted from the light source 20 is converted into a parallel light beam by the coupling lens 21, passes through the aperture 22, and becomes a light beam focused near the polygon mirror 24 in the sub-scanning direction by the cylindrical lens 23. Further, it is deflected by the polygon mirror 24, and forms an image on the image plane 28 through the dust-proof glass 27 by the deflector side scanning lens 25 and the image plane side scanning lens 26. A soundproof glass is provided between the deflector and the deflector side lens.

  The light source 20 and the coupling lens 21 are fixed to the same member made of aluminum. Here, there is a half mirror between the aperture 22 and the cylindrical lens 23 (the light intensity division ratio increases the ratio of the beam toward the photoconductor. For example, 9: 1, or 8: 2, or 7: 3. 29) is provided, and the reflected beam is guided to the photodiode through the imaging lens. In FIG. 3, reference numeral 30 denotes a soundproof glass.

  The semiconductor laser used as the light source 1 in the optical scanning device 3 shown in FIG. 3 is composed of a surface emitting laser (VCSEL), which is easy to two-dimensionally integrate and consumes more power than an edge emitting laser. Therefore, the advantage is that it is advantageous in that it can be integrated two-dimensionally with a larger number of light sources.

  In the surface emitting laser used for the light source 1 in the present embodiment, adjacent scanning lines in all scanning lines on the surface to be scanned are formed by deflection scanning different in time, and the n scanning lines are in the sub-scanning direction. When the minimum resolution pixel is formed, interlaced scanning control is performed in which the next scanning is performed by skipping the scanning line on the scanning surface.

Hereinafter, regarding the optical scanning, the writing method including the above-described interlaced scanning, the influence on the image with respect to the writing position, that is, the occurrence of the density unevenness of the image will be considered.
FIG. 4 is a scanning position pattern diagram when interlaced scanning is used. The spacing between elements is 10.6 μm, and the resolution (number of pixels per inch = 2.54 cm) is 2.54 ⁴ [um] / 10.6 [um] ≈2400 [dpi]. Forty lines are arranged in the sub-scanning direction, the scanning line is scanned between the scanning lines scanned in the first scanning, and the writing surface has a double resolution of 4800 dpi as the surface to be scanned. .

  Regarding the density unevenness in the case of performing the interlaced scanning, the result shown in FIG. 5 is obtained when the adjacent scanning and the scanning with the multi-beam using a plurality of LD arrays are compared.

FIG. 5A shows scanning using multi-beams by interlaced scanning, and FIG. 5B shows the case of adjacent scanning. From FIG. 5, it can be seen that interlaced scanning is a method of forming an image by increasing the interval between adjacent scanning lines and performing scanning a plurality of times as compared with adjacent scanning.
Next, when evaluating density unevenness in each writing method, the result shown in FIG. 6 is obtained. As an evaluation image, a 1200 dpi, 2-dot horizontal line image that is likely to have a latent image difference was evaluated. In FIG. 6, since scanning with multi-beams differs in writing resolution from 4800 dpi for 1200 dpi writing and surface emitting laser (hereinafter sometimes referred to as VCSEL for convenience), the evaluation images are the same. The light source was turned on. As can be seen from FIG. 6, the VCSEL emits 8 dots for multi-beam 2 dots.
When this evaluation image is exposed, as shown in FIG. 7, the number of scans differs depending on the writing method and the writing position of the light source (including the central portion or the end portion of the VCSEL, that is, scanning switching). Here, the vertical of each pattern is the sub-scanning position, and the horizontal is the scanning number. It is. In FIG. 7, interlaced scanning is displayed as interlaced scanning.
In FIG. 7, for example, in adjacent scanning, VCSEL normally lights up at the same time for 8 lines, but when it reaches the end, it extends over 2 scannings.
Similarly, the multi-LD (8chLD in FIG. 7) is normally turned on at the same time for two lines. However, when it reaches the end, lighting over two scans occurs.
This causes density unevenness due to reciprocity failure due to different scanning times. As described with reference to FIG. 25, this density unevenness also occurs at a period with high visual sensitivity.

However, when an image is formed by a plurality of scans with a wide scanning interval, such as interlaced scanning, since the image is formed by a plurality of scans with a low writing density, density unevenness generated at the LD end is reduced. ing. The comparison result is shown in FIG. This is a comparison of the difference between the amount of toner adhering to the vicinity where unevenness occurs and the amount of other toner adhering. The value is small = density unevenness is small, and interlaced scanning is the image with the least density unevenness. Was confirmed.
By the way, the above-described interlace scanning method is a method in which image unevenness is reduced by forming an image by scanning a plurality of times with a low writing density. However, the VCSEL has a large internal resistance of the element, and the response speed is slower than that of the conventional edge emitting LD.
When the response speed is slow, there is a possibility that the exposure amount at the time of a low pulse, that is, a low light amount may be insufficient when the exposure amount is controlled by pulse fluctuation. For example, when the LD is arranged so that the LD interval on the surface to be scanned is 10.6 μm pitch and written by interlaced scanning, the final LD scan interval is about 5 μm (resolution equivalent to 4800 dpi). When an image of 1200 dpi is formed by an LD device, one pixel is formed by 4LD, that is, one LD light amount has to be set to a low light amount that is 1/4 that of a normal multi-beam, and there is a possibility that the light amount is insufficient.

  In order to solve this problem, there is a method for securing the light amount by increasing the light amount at the light emitting point by lighting up other light emitting points without exposing at least one light emitting point in the LD forming one pixel. Possible (hereinafter referred to as thinning lighting).

FIG. 9 shows a scanning position pattern when thinning lighting is performed. In this case, 50% is set as the thinning degree and the lighting is performed.
When such thinning-out lighting is performed, the result shown in FIG. 10 is obtained as a result of image comparison with the case where this method is not adopted.

  Depending on the location of the light emitting point (including the end portion and not including the end portion), for example, a difference in writing as shown in FIG. 10 occurs in a 1200 dpi 2-dot line image. Here, the vertical of each pattern is the sub-scanning position, and the horizontal is the scanning number. It is.

  In the image comparison in which the result shown in FIG. 10 is obtained, the amount of toner attached to the line image at the writing position of these light emitting elements is compared and the difference is compared to obtain the result shown in FIG. . As is clear from FIG. 11, it is understood that the density is improved by performing scanning by thinning lighting.

  From the above consideration, when thinning is turned on, the number of light sources to be turned on is small and the amount of light from each light source is increased, so that the writing density is high and an image is formed by scanning a plurality of times, thereby increasing image unevenness. There is a possibility that a banding image is generated. Therefore, in order to solve these problems, it is possible to compare the number of scans for image formation at the center of the light source and the number of scans for image formation at the light source end, and to set and control the light emission conditions of the light source according to this result. This is important for eliminating image density unevenness and banding.

The present embodiment is characterized in that the following light emission control is executed on the basis of such consideration results. Before that, the characteristics of the light source used in the present embodiment will be described. A surface-emitting laser that can be used as a light source has a beam shape having a relationship of WS ≦ Wm where the beam diameter in the main scanning direction is Wm and the beam diameter in the sub-scanning direction is Ws. The reason is as follows.
In general, the beam shape of a laser beam is an elliptical shape in which the beam diameter in the main scanning direction is smaller than the beam diameter in the sub-scanning direction. On the other hand, the beam shape from the surface emitting laser is almost circular. For this reason, if the width of the opening in the main scanning direction is different from the width in the sub-scanning direction, there is a problem that the amount of light is insufficient and the speed cannot be increased.

  Therefore, the light source used in the present embodiment makes the difference between the width in the main scanning direction and the width in the sub scanning direction at the opening by making the beam diameter in the main scanning direction larger than the beam diameter in the sub scanning direction. In addition, the coupling efficiency (ratio of the optical power emitted from the light emitting point with respect to the optical power emitted from the aperture) can be increased. Furthermore, high resolution burning can be achieved by using a plurality of surface emitting lasers. In this case, since the interval between adjacent scanning lines is narrowed, the beam diameter in the sub-scanning direction can be made larger than the interval between adjacent scanning lines, thereby filling the image and obtaining an image without occurrence of unevenness.

Next, the light emission control executed in the present embodiment is as follows.
(A) Scanning lines that are adjacent to each other on all scanning lines on the surface to be scanned are formed by deflection scanning that is temporally different, and the minimum resolution pixel in the sub-scanning direction is formed by n scanning lines. When an image is formed on the surface to be scanned by skipping scanning lines on the surface and thinning the scanning position by turning on n-1 or less light sources in a state where the interlaced scanning is performed and the next scanning is performed. The number of scans for image formation at the center of the surface emitting laser used as the light source is compared with the number of scans for image formation at the end, and the emission conditions of the surface emitting laser are set according to the result.
(B) When k surface-emitting lasers that are two-dimensionally arranged are used as the light source, the distance between both ends of the scanning line formed by one scanning by the deflecting means is L1, and the entire scanning on the surface to be scanned Let L2 be the distance between adjacent lines.
L1> (k−1) × L2
The light emission conditions satisfying the above relationship are set.
(C) Setting is made so that the interval between scanning lines formed by one deflection scan is not uniform with k light emitting points.
(D) The scanning line having the narrowest interval among the scanning line intervals formed by one deflection scan is excluded from both ends in the sub-scanning direction.
(E) Adjustment is performed so that the number of normal scans coincides with the number of scans at the edge.
(F) When the number of scans in which the image is formed at the center of the surface emitting laser <the number of end scans, the thinning position is set so that the emission positions of the surface emitting lasers during one scan are adjacent.
(G) When the number of scans in which the image is formed at the center of the surface emitting laser is larger than the number of end scans, the thinning position is set so that the light emitting position of the surface emitting laser during one scan is separated.

  FIG. 12 is a block diagram showing a configuration of a control system for executing the setting control. In FIG. 12, the control system includes a control unit 100 as a main controller that executes an image forming sequence program of the image forming apparatus. An external PC (personal computer) 101 capable of outputting pixel information or a scanner 102 provided in the image forming apparatus is connected to the input side of the control unit 100 as a member related to the present embodiment, and a light source is connected to the output side. The drive unit 103A of the surface emitting laser 103 used as the is connected. Although not shown, the control unit 100 is provided with a memory that stores information such as image information and a thinning mode change pattern.

  When the writing information is input based on the reading information from the external PC 101 or the scanner 102, the control unit 100 executes the controls listed in (a) to (g) based on the above-described consideration results.

  FIG. 13 is a flowchart for explaining the operation of the control unit 100, and the control contents shown in FIG. 13 correspond to the contents listed in (a). In other words, when the embedded pattern is acquired, the thinning mode is set from the result of the above-described consideration, and when the pattern writing scanning number N1 at the center of the light source is acquired, the writing to the light source end is determined, When writing to the end of the light source is performed, the number of scans N2 with the light source is acquired and the number of scans is compared. If the comparison results of the number of scans are the same, a light emission signal is output to the drive unit (a member indicated by reference numeral 103 in FIG. 12). If they are not the same, the light emission mode is changed and the light emission signal is output.

  In the embodiment as described above, the inventor observed density unevenness at the time of writing including the light source end, and as shown in FIGS. It was confirmed that unevenness was reduced.

  According to this embodiment, an image can be formed using a stable amount of light by selectively controlling interlaced scanning and thinning scanning. In addition, density unevenness in the sub-scanning direction, which is a concern with surface-emitting lasers, can be reduced.

Next, the control contents listed in (b) to (d) will be described.
FIG. 16 is a diagram showing the scanning position when the scanning line spacing is non-uniform. The scanning conditions shown in FIG. 16 are a resolution of 4800 dpi, a light emitting point count of 40 channels, and a light emitting point spacing of 1 dot. The case where it arranges every other is shown.

  In FIG. 16, some light emitting point intervals are different from other light emitting point intervals. In other words, the 21st light emitting point is set at a non-uniform interval by shifting 2 dots with respect to the 1 dot interval of the other light emitting point intervals.

  By setting the non-uniform spacing, it is possible to arrange the light source in consideration of the thermal characteristics of the light source explained in the discussion, and furthermore, operation without inconsistent density unevenness by eliminating variations in scanning position without being affected by reciprocity failure. Is possible.

FIG. 17 shows an example of scanning when the scanning line intervals are non-uniform. In the figure, the pattern column is the sub-scanning position, and the horizontal line No. Is shown. In the figure, the description of the first surface scan, the second surface scan, and the third surface scan means the deflection scanning surface number. Also, in the figure, pattern 1 and pattern 2 show the case where non-uniform spacing is set in VCSEL interlaced scanning, pattern 3 shows the case where VCSEL adjacent scanning is set, and pattern 4 sets multi-beam scanning. Shows the case.
In the case of non-uniformity as shown in FIG. 17, the scanning line having the narrowest interval among the scanning line intervals formed by one deflection scan is not located at both ends in the sub-scanning direction, so that the parallel scanning is performed. The line spacing is not excessively wide, the optical characteristics are easily secured, the variation due to the scanning position can be reduced, and the density unevenness can be made inconspicuous. In particular, the interlaced scanning shown by the pattern 2 has a narrow interval (20th and 21st scanning line intervals), so that the parallel scanning line intervals do not become too wide, and it is easy to ensure optical characteristics. There is.
In such non-uniform control, the control unit 100 performs the process shown in FIG.
18 is different from the process shown in FIG. 13 in setting a thinning interval based on a difference in the number of scans. That is, in the relationship of the number of scans, the light emission interval is narrowed when N1 <N2, and the issue interval is widened when N1> N2, and the change of each scanning position by this processing is shown in FIG. As shown in

The result of observing the toner adhesion amount in the vicinity of the portion where the unevenness is generated by such processing and the toner adhesion amount in other locations is as shown in FIG.
What can be said from the results of FIG. 20 is that even if the number of scans differs depending on the setting of the thinning interval, an image with little density unevenness can be obtained by performing close writing.

  Further, when N1> N2 described above, for example, the write condition and the toner adhesion amount at that time when an image is basically formed by three scans and the number of scans at the light source end is two scans. The experimental results are as shown in FIGS. FIG. 21 shows an example of scanning for 1200 dpi and 2 dot lines in the writing method.

  21 and 22, even if the number of scans is different, density unevenness is controlled by controlling thinning-out lighting so that the light emission position in one scan is separated when the number of scans in which the image is formed in the center of the LD> the number of end scans. It can be confirmed that an image with a small amount can be formed.

1 is a schematic diagram illustrating an example of an image forming apparatus using an optical scanning device according to the present invention. FIG. 5 is a schematic diagram illustrating another example of the image forming apparatus illustrated in FIG. 1. It is a figure which shows the structure of the optical system used for the optical scanning device by this invention. It is a pattern figure which shows the scanning position by the interlaced scanning performed in the optical apparatus by this invention. It is a figure which shows the example of writing by the interlaced scanning shown in FIG. It is a pattern figure which shows the evaluation image regarding the density nonuniformity by a writing system. It is a dot pattern figure for demonstrating the example of operation by a writing system. FIG. 8 is a diagram for explaining a toner adhesion amount in the writing method illustrated in FIG. 7. It is a dot pattern diagram for explaining thinning scanning which is one of scanning methods. FIG. 10 is a dot pattern diagram for explaining a difference in the number of times of writing depending on whether or not thinning lighting is performed in the thinning scanning shown in FIG. 9. FIG. 11 is a diagram for explaining a difference in toner adhesion amount depending on whether or not thinning lighting is performed illustrated in FIG. 10. It is a block diagram for demonstrating the structure of the control system used for the optical scanning device by this invention. It is a flowchart for demonstrating the control procedure performed with the control system shown in FIG. It is a dot pattern diagram for demonstrating the example of writing by the procedure shown in FIG. It is a figure for demonstrating the difference in the toner adhesion amount by the writing by the case of the writing example shown in FIG. 14, and writing by general thinning-out scanning. FIG. 5 is a dot pattern diagram for explaining a writing state when scanning line intervals are made non-uniform. It is a figure which shows the dot pattern by the classified writing system. 18 is a flowchart for explaining a control procedure in the case of making the scanning line interval non-uniform in the writing example shown in FIG. 17. It is a dot pattern figure for demonstrating the write state by the control procedure shown in FIG. It is a figure for demonstrating the toner adhesion amount obtained by the writing by the control procedure shown in FIG. FIG. 18 is a dot pattern diagram for explaining a writing example for one of the writing examples shown in FIG. 17 when the number of scans is different. It is a figure for demonstrating the toner adhesion amount by the writing shown in FIG. FIG. 6 is a light attenuation curve diagram for explaining a light attenuation state by writing on the photosensitive member side. FIG. 24 is a light attenuation curve diagram for explaining a light attenuation state when a reciprocity failure occurs with respect to the light attenuation curve shown in FIG. 23. It is a figure which shows the relationship between the sensitivity for demonstrating the visual sensitivity with respect to image nonuniformity, and a spatial frequency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 3 Optical scanning device 100 Control part 101 External PC
102 Scanner 103 Surface Emitting Laser 103A Light Source Drive Unit

Claims (9)

In an optical scanning device that performs writing scanning using a laser beam,
A light source using a two-dimensional array of surface emitting lasers;
A first optical system for guiding a plurality of beams from the light source to a deflecting unit;
A second optical system for guiding a plurality of beams from the deflecting means to a surface to be scanned,
When scanning lines adjacent to each other in all scanning lines on the scanning surface are formed by deflection scanning different in time and the minimum resolution pixel in the sub-scanning direction is formed by n scanning lines, A control unit capable of interlaced scanning control for performing the next scanning over the scanning line,
When the controller performs image formation on the surface to be scanned by turning on n-1 or less light sources and thinning the scanning position, the number of scans in which image formation is performed at the center of the surface emitting laser used for the light source And the number of scans in which an image is formed at the end, and the emission condition of the surface emitting laser is set according to the result. In the case where k surface-emitting lasers that are two-dimensionally arranged are used as the light source, the control unit,
When the distance between both ends of the scanning line formed by one scanning by the deflecting means is L1, and the distance between adjacent scanning lines on the surface to be scanned is L2,
L1> (k−1) × L2
The light scanning apparatus according to claim 1, wherein a light emission condition satisfying the relationship is set.   The optical scanning device according to claim 2, wherein the control unit performs setting such that a scanning line interval formed by one deflection scan is non-uniform by the k light emitting points.   4. The light according to claim 2, wherein the control unit excludes a scanning line having the narrowest interval among scanning line intervals formed by the one deflection scanning from both ends in the sub-scanning direction. Scanning device.   3. The optical scanning device according to claim 1, wherein the control unit performs adjustment so that the number of normal scanning and the number of scanning of the end portion coincide with each other.   The control unit sets the thinning position so that the emission positions of the surface emitting lasers during one scan are adjacent when the number of scans formed at the center of the surface emitting laser is smaller than the number of edge scanning times. The optical scanning device according to claim 1 or 2.   The control unit sets the thinning position so that the emission position of the surface emitting laser during one scan is separated when the number of scans formed at the center of the surface emitting laser is greater than the number of end scanning. The optical scanning device according to claim 1 or 2.   An image forming apparatus using the optical scanning device according to claim 1. Regarding the light beam diameter used in the optical scanning device,
Ws ≦ Wm (Wm: beam diameter in the main scanning direction, Ws: beam diameter in the sub-scanning direction)
The image forming apparatus according to claim 8, wherein the following conditions are set.

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