JP4492360B2 - Image forming apparatus - Google Patents

Description

The present invention provides an optical scanning device that divides an optical path emitted from a single light source having two-dimensionally arranged light emitting points into a plurality of scanned surfaces, and scans each scanned surface with a plurality of light beams. relates full-color image forming apparatus that implements a location, further detail, in accordance with the image forming mode, when the write resolution is changed, by appropriately selecting the mode switching parameters, extended image forming process speed in the monochrome image forming mode It relates to an image forming equipment which can.

  Conventionally, higher performance of laser printers and digital multifunction peripherals is desired, and image forming apparatuses have been increased in speed and resolution. For example, as a means for improving the performance of an optical scanning device in which a light beam emitted from a laser light source is deflected by a deflector such as a polygon mirror and scanned on a photosensitive member, a polygon mirror is increased in speed, and a multi-beam of a light source is used. However, there is a limit to improving these performances, and it has been difficult to achieve both high speed and high resolution. For this reason, there has been a trade-off between output performance such as high resolution output in the low speed mode and high speed output at the low resolution.

  However, in recent years, multi-beam light sources capable of emitting 30-class light beams have been put into practical use by the development of surface-emitting laser technology capable of two-dimensionally arranging light emitting points, and both high speed and high resolution can be achieved, for example, 2400 dpi. An optical scanning device capable of handling 100 sheets of output per minute has been proposed (see, for example, Patent Document 1).

  On the other hand, for the purpose of improving the productivity of full-color images, a so-called tandem type image forming apparatus has been developed in which a plurality of image forming units are arranged in series to form a full-color image in one pass. This is because the four transfer members are independently exposed and developed by the image data of yellow (Y), magenta (M), cyan (C), and black (K) sent from the data control unit, and then the intermediate transfer belt. The primary transfer is sequentially performed on the intermediate transfer belt, and the multiple transfer images created on the intermediate transfer belt are collectively transferred onto the sheet at the secondary transfer position, and finally fixed on the sheet by a fixing device.

  As the optical scanning device used in this tandem type image forming apparatus, the same number of optical scanning devices as the image forming unit are arranged in parallel, and the one in which a plurality of photosensitive members are exposed by a single optical scanning device (hereinafter referred to as the optical scanning device). In order to reduce the size of the image forming apparatus, the 1BOX type in which the scanning optical system optical paths of a plurality of colors can share the same space is advantageous.

  Various 1BOX type optical scanning devices have been proposed, but many use a single deflector, which scans bidirectionally on opposing deflection surfaces (see, for example, Patent Document 2) and a single deflection. The one that scans all the light beams in the same direction on the surface (see, for example, Patent Document 3) is typical.

  In the 1BOX type optical scanning device that scans in the same direction on a single deflection surface, the scanning optical system can be shared by a plurality of beams in addition to the deflector, so that the variation difference between the plurality of beams is reduced and the color on the image is reduced. There is an advantage that the registration can be maintained with high accuracy. There has also been proposed a configuration in which a light source is configured by a laser array arranged in a single row, and the configuration from the light source to the scanning optical system is shared (for example, see Patent Document 4).

  By the way, as a light source of a 1BOX type optical scanning device that is small and suitable for cost reduction, it is considered to apply a multi-beam of a two-dimensional arrangement excellent in high-speed and high resolution suitability. FIG. 12 is an example of an optical scanning device previously filed by the present applicant.

  The light source 100 is a surface emitting laser that emits 32 light beams, and is configured as four groups of eight. A light beam emitted from a single light source 100 is reflected and deflected by the same deflecting surface 102A of a single deflector 102, passes through a common lens 104, and then selectively reflected by the plane mirror 106. The optical path is divided, and a plurality of photosensitive members 108 are scanned with eight light beams.

Here, the relationship between the number of scanning beams and the output speed (image forming process speed) of the image forming apparatus will be described. When all 32 light beams are guided to the same photoconductor 108 for simultaneous scanning,
Optical scanning device parameters (1)
Focal length of imaging optical system: 332 mm
Reflective surface of polygon mirror: 6 surfaces Writing resolution: 2400 dpi
As an example,
Optical scanning device specifications ... (1)
Image forming process speed: 460 mm / s
Number of revolutions of polygon motor: 13,583 rpm
Video rate: 89.2MHz
When this parameter is selected, it is possible to output 100 sheets / min class applicable to high-speed machines.

On the other hand, when 32 light beams are divided into four and each photoconductor is scanned with eight light beams,
Optical scanning device specifications (2)
Image forming process speed: 220 mm / s
Number of revolutions of polygon motor: 25,984 rpm
Video rate: 170.7MHz
With this configuration, image output at 45 sheets / minute is possible. This corresponds to the output speed of a medium-speed machine. If a full-color image can be output at this speed, it is sufficient for office use, including use as a printer.

  Furthermore, since color machines installed in offices have a high frequency of monochrome image output, many color machines with a monochrome image formation speed increased with respect to the full color image formation speed have been put into practical use.

  However, in the case of the optical scanning device specification (2) described above, if the output speed is increased while the number of light beams that scan the single photosensitive member 108 is increased, the rotational speed of the polygon motor, the video rate (image) The modulation frequency of writing) exceeds the limit. In other words, the respective limit values considering reliability are approximately 30,000 rpm and 200 MHz, so when eight beams are applied to the above parameter (1), the output speed is limited to about 250 mm / s, A significant improvement in image output speed cannot be expected.

Possible measures to improve the image output speed include increasing the number of writing light beams (increasing the number of light-emitting points), shortening the focal length of the imaging optical system, and increasing the number of polygon mirror surfaces. There are problems that the optical system is enlarged by expanding the beam width, the degree of freedom of the optical path layout is reduced by using a single optical path, and the load on the polygon motor is increased (reducing reliability) due to the large diameter of the polygon mirror.
JP 2001-215423 A JP 2001-264655 A JP 2001-4948 A JP-A-6-286226

Therefore, in view of the above problems, the present invention divides an optical path of a light beam emitted from a single light source in which light emitting points are two-dimensionally arranged and leads it to a plurality of scanned surfaces. mounting a plurality of optical scanning devices 1BOX types of scanning with a light beam, a small, yet low-cost, excellent in Rutotomoni quality stability can achieve high productivity in the monochrome image forming mode, and further, by mode switching the transition time and purpose thereof is to provide an image forming apparatus that can minimize.

To achieve the above object, an image forming apparatus according to claim 1 according to the present invention, a plurality of the by the optical path splitting a light beam emitted from a single light source emitting points are two-dimensionally arranged It led to the scanning surface, comprising a respective surface to be scanned optical scanning device for scanning a plurality of light beams and a mode switching means for switching between the full-color image forming mode and the monochrome image forming mode, a light source in the main scanning direction with 1 row and emission point group arranged in regular intervals at a predetermined angle is constituted by the same number sequence and said surface to be scanned at a distance in the sub-scanning direction for the farthest from the optical axis of the light source The light emission point group is a black color light emission point group, and in the monochrome image formation mode, the black color light emission point group in the sub-scanning direction with respect to the position of the light emission point group in the full color image formation mode. Closest to the optical axis The light source is rotated in a direction in which the light emitting point group corresponding to the black color is separated from the optical axis around the light spot, and the light emitting point on the side farthest from the rotation center is turned off to reduce the number of light beams. It is characterized by being configured to reduce the writing resolution by decreasing and to increase the image forming process speed as compared with the full color image forming mode .

According to a second aspect of the present invention, there is provided an image forming apparatus according to the present invention, wherein a light beam emitted from a single light source having two-dimensionally arranged light emitting points is divided into optical paths and guided to a plurality of scanned surfaces. An optical scanning device that scans the scanning surface with a plurality of light beams, and mode switching means that switches between a full-color image forming mode and a monochrome image forming mode, and the light source is at a predetermined angle with respect to the main scanning direction. A group of light emitting points arranged in a row and at equal intervals is arranged in the same number as the scanned surface at a distance in the sub-scanning direction, and the light emitting point group is located at the center of the light emitting point group in the main scanning direction or at the center. It is configured to be rotatable around the nearest light emission point, and there is a light emission point group having the rotation center and a light emission point group corresponding to black on the opposite side across the optical axis. In formation mode The light source is rotated in a direction in which the light emission point group corresponding to the black color moves upstream in the main scanning direction with respect to the position of the light point group, and the light emission points at both ends of the light emission point group corresponding to the black color Is turned off to reduce the number of light beams, thereby reducing the writing resolution and increasing the image forming process speed as compared to the full-color image forming mode .

Here, the light emission point arrangement necessary for mode switching will be described. FIG. 4 is an explanatory diagram showing the arrangement of the light emitting points of the light source in the optical scanning device.

The light emitting points arranged in a line in the main scanning direction are arranged for four colors at a distance S2 in the sub scanning direction. Since the light emitting points corresponding to the respective colors are arranged in one row in the oblique horizontal direction, when the light source is rotated, the light emitting point pitch in the sub-scanning direction changes, and the writing density on the surface to be scanned changes. If the light emission points of the respective colors are arranged in a matrix, the light beam width in the main scanning direction can be narrowed, but the rotation results in uneven pitches between the columns. Therefore, it is necessary to arrange the light emitting points corresponding to the respective colors in a line.

In the first aspect of the present invention, the light emitting point group farthest from the optical axis of the light source is the black light emitting point group. In the monochrome image forming mode, the position of the light emitting point group in the full color image forming mode is set. The light emission point pitch is changed by rotating the light source around the light emission point group that is closest to the optical axis in the sub-scanning direction among the light emission point groups that correspond to the black color, by rotating the light source in the direction away from the optical axis. Then, the light emitting point farthest from the rotation center is turned off to reduce the number of light beams, thereby reducing the writing resolution and increasing the image forming process speed as compared with the full color image forming mode.

In the invention according to claim 2, the light source is configured to be rotatable around the light emitting point in the main scanning direction of the light emitting point group or the light emitting point closest to the center, and the light emitting point group having the rotation center. In the monochrome image formation mode, the black light emission point group is main-scanned with respect to the position of the light emission point group in the full color image formation mode. Rotate the light source in the direction to move upstream in the direction to change the light emission point pitch, turn off the light emission points at both ends of the black color light emission point group, and reduce the number of light beams to reduce the writing resolution The image forming process speed is increased as compared with the full color image forming mode.

Here, when shifting to a lower resolution by rotating the light source, the pitch (light flux width) of the light emitting points is widened, so that the space occupied by the light flux group is enlarged in the middle of the optical path, and the 1BOX type optical scanning that spatially divides the optical path. In the apparatus, there is a concern that an image quality defect may occur due to a light beam sneaking into an adjacent color optical path.

However, in the first and second aspects of the invention, since the light emitting point (light beam) whose optical path moves to the adjacent color side by turning the light emitting point group is turned off, the light to the adjacent color optical path is turned off. Beam wraparound can be avoided.

FIG. 6 is an explanatory diagram showing a change in the emission point occupation width H in the sub-scanning direction due to the rotation of the light source . When the number of light beams is 8, when switching the resolution from 2400 dpi to 1200 dpi, if the light source is rotated without changing the number of the light beams, the occupied width H of the light emitting point is doubled .

On the other hand, if the two ends are extinguished and an image is formed with six light beams at the time of shifting to the low resolution, the enlargement ratio of the occupied width H occupied by the six light beams (light emission point group) Is suppressed to an increase of about 43%.

As described above, by appropriately combining the resolution and the change in the number of scanning beams, it becomes possible to cope with a plurality of modes without concern about image quality defects, and the application range of the optical scanning apparatus and the image forming apparatus can be substantially expanded. .

Note that the monochrome image forming mode for reducing the writing resolution is a low resolution mode of 1200 dpi or higher, and the full color image forming mode for not reducing the writing resolution is a high resolution mode of 2400 dpi or higher.

Applications of resolution in the full-color image forming mode are high image quality by improving the degree of freedom in image quality design, and color registration correction by image data address correction. In particular, in color registration correction, if image data address correction is performed at a low resolution, a secondary failure called image streak occurs, and data correction in units of 10 μm by 2400 dpi is essential.

On the other hand, in the monochrome image forming mode, since color registration correction is not performed, the address correction resolution of image data is unnecessary. In addition, the reproducibility of the oblique line in the graphic image output is recognized as a difference between 600 dpi and 1200 dpi, but hardly recognized between 1200 dpi and 2400 dpi.

Therefore, the target image quality can be achieved by setting the image quality to 1200 dpi or higher in the monochrome image formation mode and to 2400 dpi or higher in the full-color image formation mode.

As described above, in the optical scanning device using the multi-beam light source by the surface emitting laser, the image in the monochrome image forming mode with high productivity demand without the performance trade-off such as the conventional switching of 600 dpi and 1200 dpi. An improvement in the forming process speed can be realized.

The image forming apparatus according to claim 3 is the image forming apparatus according to claim 1 or 2, wherein the mode switching unit includes:
(PS2 / PS1) × (dpi2 / dpi1) = (L2 / L1) (1)
PS: image forming process speed, dpi: writing resolution, L: number of light beams
The parameter is changed so as to satisfy the following relationship.

Here, the operation of the third aspect of the invention will be described. The resolution of the image forming apparatus is determined by the image forming process speed, the number of light beams, and the number of rotations of the polygon motor. Therefore, when the resolution and the number of light beams are determined, the rotation speed of the polygon motor is determined by the image forming process speed determined by the productivity of the image forming apparatus.

For example, in the above-described optical scanning device specification (2), when the image forming process speed in the monochrome image forming mode is 1.5 times (330 mm / s) and the resolution is 1200 dpi, the rotation speed of the polygon motor is 19,488 rpm. . This is advantageous in terms of reliability, noise, and vibration because the rotational speed is lower than the rotational speed 25,984 rpm in the full-color image forming mode, but requires a transition time by switching the rotational speed of the polygon motor. There is.

Furthermore, there is a problem that it is difficult to optimize the rotational characteristics of the polygon motor at two rotational speeds. If the rotational characteristics cannot be optimized, rotational characteristics such as jitter and hunting may become unstable. Therefore, if the parameters are switched according to the above equation (1), the mode can be switched without changing the rotational speed of the polygon motor.

According to a fourth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to third aspects, wherein the exposure amount of the optical scanning device is changed according to switching of the mode switching unit. It is characterized by switching.

When the image forming mode is switched, the exposure energy per unit area changes. Therefore, in the invention described in claim 4, this can be corrected by changing the amount of light emitted from the optical scanning device (switching the exposure amount).

Other and to perform the synchronization detection by matching or closest emitting point in the rotational center, as it can be a light beam whose optical path change due to rotation is minimized and the synchronization detection beam, without causing a reference variation by rotation You can Therefore, it is possible to prevent the image position from shifting.

As described above, according to the present invention, an image forming apparatus equipped with a 1BOX type optical scanning device achieves high image quality stability and high productivity in a monochrome image forming mode while being small and low cost. it is possible.

  The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings. 1 is a schematic side view showing a configuration of an image forming apparatus 10 according to the present invention, FIG. 2 is a schematic perspective view of an optical scanning apparatus 12 according to the present invention, and FIG. 3 is a sub-view of the optical scanning apparatus 12 according to the present invention. It is an optical path expansion | deployment figure in a scanning direction. The image forming apparatus 10 is a tandem type image forming apparatus in which four image forming units 14 are arranged in series in the vertical direction.

  As shown in FIGS. 2 and 3, a plurality of light beams emitted from a multi-beam light source 20 composed of a surface emitting laser in which light emitting points are two-dimensionally arranged are converted into parallel light by a collimator lens 22 and collimated. The beam shape is shaped by the aperture 24 arranged at the focal position of the meter lens 22. The light beam that has passed through the aperture 24 is converted into a convergent beam by the cylindrical lens 26 and is linearly imaged on the deflection surface 28A of the polygon mirror 28.

  The light beam deflected by the deflecting surface 28A of the polygon mirror 28 composed of six surfaces is given constant velocity scanning characteristics by a pair of fθ lenses (first imaging elements) 30, and then the splitter mirror 32. The optical path is divided in two directions (up and down directions). Each of the two light beams that have undergone the optical path splitting is selectively reflected by the folding mirror 34, so that the optical paths are split again at the optical path splitting position N.

  The four groups of light beams obtained by the division of the optical path are reflected and imaged by a cylindrical mirror 36 (second imaging element) disposed independently on each optical path, and scan on the photosensitive member 16. As shown in FIG. 3, the four groups of light beams are crossed after passing through the deflection surface 28A by the cylindrical lens 26, and the gap between the optical paths is widened after this intersection.

  The deflecting surface 28A and the photoconductor 16 are in a conjugate imaging relationship, and constitute an optical system that corrects the surface tilt of the polygon mirror 28. Further, FIG. 3 shows a state in which four light beams are emitted from the multi-beam light source 20, but this is because the light emitting point groups arranged in a line in the main scanning direction are spaced apart in the sub scanning direction. Each light emitting point group of light beams arranged in the same number as the photosensitive member is representative, and there are a plurality of adjacent light beams.

  Thus, the optical scanning device 12 deflects and reflects a plurality of light beams incident from the multi-beam light source 20 by the deflecting surface 28A of the single polygon mirror 28 having six surfaces, and the splitter mirror 32 and the folding mirror 34. The optical path is divided by, for example, the four photoconductors 16 to be scanned and exposed. This light beam is a light beam modulated by an image signal.

  Accordingly, the photosensitive member 16 charged by a charger (not shown) is exposed by this light beam, and a latent image is formed on the surface thereof. The latent image formed on the photosensitive member 16 is converted into a visible image by the developing unit 18 and then primarily transferred onto the intermediate transfer belt 40. Then, the multiple transfer images sequentially primary transferred by the four (each color) image forming units 14 are secondarily transferred onto the paper P sent out from the paper tray 42 at the secondary transfer point A, and the fixing device 44. As a result, a fixed image is formed and discharged onto the discharge tray 46 (see FIG. 1).

  Here, as shown in FIG. 4, the multi-beam light source 20 of the optical scanning device 12 has a group of light emitting points arranged in a line in the main scanning direction (indicated by arrow T) in the sub-scanning direction (indicated by arrow S). For example, eight light emitting points 50 extending in the main scanning direction are arranged in a line within a range of a distance S1 in the sub scanning direction. Is arranged. A similar group is arranged in four groups with a distance S2 in the sub-scanning direction. The four groups correspond to the yellow (Y), magenta (M), cyan (C), and black (K) image forming units 14 in full-color image formation.

  Note that “8”, which is the number of light emitting points 50 arranged in the main scanning direction, is used in an office and outputs a 2400 dpi image in a medium-speed image forming apparatus that requires both compactness, low cost, and productivity. It is the number necessary to do. Therefore, the number of light beams is not limited to eight. However, when the number of light beams is increased, the number of signal processing increases, and in the optical system, the beam width is widened in the main scanning direction. There arises a problem that the optical components constituting the system, in particular, the polygon mirror 28 is enlarged.

  In addition, each group is arranged in a line, as will be described later, even when the multi-beam light source 20 (surface emitting laser 52) rotates, the light emitting point pitch in the sub-scanning direction for each color is kept uniform. Because. For example, if one group is composed of two rows, the adjacent pitches are partially unequal due to the rotation of the multi-beam light source 20 (surface emitting laser 52).

  In the image forming apparatus 10 configured as described above, a first embodiment according to the present invention will be described next. FIG. 5 is an explanatory diagram showing a state in which the multi-beam light source 20 is rotated around the light emitting point 50KL at the left end of black (K) which is the fourth group. Each light emitting point 50 is arranged around the optical axis 48 of the scanning optical system.

  The black dots shown in FIG. 5 indicate the emission point arrangement in the full color image formation mode (high resolution mode), and the white dots indicate the emission point arrangement in the monochrome image formation mode (low resolution mode). Is rotated in the clockwise direction (arrow B direction) in the figure to switch the mode. As described above, the center of rotation is the light emitting point 50KL at the left end of the fourth group of black (K). The reason for selecting the light emitting point 50KL is to avoid the wraparound to the adjacent color optical path due to the rotation. This is to minimize the optical path position variation and the rotation angle caused by mode switching.

  For example, when rotating in the direction not having the adjacent color optical path around the light emitting point 50KR at the right end of black (K) which is the fourth group, it must pass through the horizontal state and rotate further, and the mode switching The optical path position is greatly different between before and after. That is, there is no adjacent color optical path outside the black (K) which is the fourth group, and even if there is no wraparound, the optical system must be unnecessarily enlarged, and the distance from the optical axis 48 also increases. Therefore, image formation characteristics are also deteriorated due to aberration, which is not desirable.

  Therefore, the light emission point group farthest from the optical axis 48 is set as a light emission point group corresponding to black (K), and in the monochrome image forming mode, the light axis 48 is centered on the light emission point closest to the optical axis 48 in the light emission point group. It is necessary to rotate away from the direction.

  Further, due to this rotation, in the yellow (Y) that is the first group, the two light emitting points 50YR on the right end side enter the optical path of the magenta (M) that is the adjacent second group, and image formation is performed in this state. Then, the image information of yellow (Y) is formed with magenta (M). Therefore, it is effective to turn off some of the light beams (light emission points 50) in order to avoid the wraparound to the adjacent color optical path due to rotation. That is, as shown in FIG. 6, by turning off the light emitting point 50R far from the center of rotation while the light emitting point 50 is rotated, the common range of the optical path position can be expanded before and after mode switching, and the optical characteristics change. Can be suppressed.

A numerical example of mode switching considering the above is shown below.
Full-color image formation mode Image data address correction: ON
Image forming process speed: 220 mm / s
Writing resolution: 2400 dpi
Polygon mirror: 6 surfaces Number of writing beams: 8 Polygon motor rotation speed: 25,984 rpm
Video rate: 170.7MHz

Monochrome image formation mode Image data address correction: OFF
Image forming process speed: 330 mm / s
Writing resolution: 1200 dpi
Polygon mirror: 6 surfaces Number of writing beams: 6 Polygon motor rotation speed: 25,984 rpm
Video rate: 85.4MHz

Here, the rotational speed of the polygon motor before and after the mode switching is constant. this is,
(PS2 / PS1) × (dpi2 / dpi1) = (L 2 / L 1 ) (1)
This is because mode switching that satisfies the relationship of PS: image forming process speed, dpi: writing resolution, and L: number of light beams is performed.

  If all parameters do not satisfy equation (1), it is necessary to change the number of revolutions of the polygon motor. However, by selecting parameters as close to equation (1) as possible, the change time can be shortened. . In addition, since the rotational speeds used in a plurality of modes are thereby approached, it is easy to optimize the rotational characteristics of the polygon motor, and the rotational characteristics such as jitter and hunting can be stabilized.

  Further, since the exposure amount (exposure energy) per unit area changes by changing the parameter, it is necessary to change the exposure amount (exposure energy) of the optical scanning device 12, that is, the amount of light emitted from the multi-beam light source 20. In the monochrome image forming mode in the above-described embodiment, it is sufficient to emit four times as much light as the full color image forming mode.

  Next, color registration correction by address correction of image data will be described. FIG. 7 is an explanatory diagram of registration correction by address correction of image data. If the optical scanning device 12 or the image forming apparatus 10 has mechanical distortion, the output image is distorted even if normal image data is transmitted. FIG. 7A shows a case where skew has occurred.

  In the conventional image forming apparatus, this distortion is detected, and the output image is corrected by adjusting the attitude of the mirror inside the optical scanning apparatus, for example. Such mechanical correction requires an adjustment mechanism and takes a long time for the adjustment. Therefore, there is a problem that the adjustment mode must be entered after the image forming apparatus is stopped. Therefore, it has been conventionally considered to reversely correct image data in advance and transfer the data to the optical scanning device.

  However, in this case, if the image output resolution is low (for example, 600 dpi), the correction step is noticeable and an image streak occurs. However, when the multi-beam light source 20 using the surface emitting laser 52 is put into practical use and the image forming apparatus 10 at 2400 dpi is put into practical use, it is possible to correct image data in units of 10 μm, and the image streak problem is solved. It became so. FIG. 7B shows the concept of image data correction at 2400 dpi. The distortion of the output image is detected, the pixel position is reversely corrected, and the corrected image is transmitted to the optical scanning device 12. Indicates that it will be output.

  Further, here, for the sake of convenience of explanation, the concept of correction in a single color has been described. However, the tandem image forming apparatus 10 reads a multicolor test patch on the intermediate transfer belt 40 to detect a color registration shift, By appropriately correcting the image data of each color, it is possible to output a full color image without color registration deviation. The concept of data correction in this case is also as shown in FIG.

  FIG. 8 is a schematic cross-sectional view in the main scanning direction showing the internal structure of the light source unit including the multi-beam light source 20 that rotates the light emitting point 50. The multi-beam light source 20 is configured by mounting and sealing a surface emitting laser 52 in a package 54 and mounted on a laser driving substrate 56. Then, as shown in FIG. 9, the surface of the package 54 is abutted against the three protrusions 60 provided on the bracket 58 and is positioned by a screw 64 via a spacer 62. .

  A cylindrical portion 58A is provided at the tip of the bracket 58, and the inner peripheral surface of the ball bearing 66 is press-fitted into the outer peripheral surface thereof. A positioning member 68 is press-fitted into the outer peripheral surface of the ball bearing 66. A collimator lens 22 is attached to the end of the bracket 58 via a collimator holder 70 so as to be adjustable in the optical axis direction. With this configuration, the bracket 58, that is, the multi-beam light source 20 attached to the bracket 58 can be rotated with respect to the positioning member 68.

  In the assembly process of the light source unit, the positioning member 68 is attached to the jig with the screw 64 temporarily fixed so that the light emitting point 50 serving as the rotation center does not move when the bracket 58 rotates. The laser driving substrate 56 on which the multi-beam light source 20 is mounted is adjusted and fixed.

  Then, such a light source unit is fixed to the housing 72 of the optical scanning device 12 with a screw 74. In this attachment step, the relative positions of the housing 72 and the light source unit in the X direction and the Y direction may be adjusted and fixed by the screw 74 so that the optical path of the light beam after the aperture 24 passes through a desired position. .

  Next, a configuration for rotating the multi-beam light source 20 will be described. FIG. 10 is an explanatory view showing the rotation mechanism of the multi-beam light source 20, and each part attached to the casing 72 of the optical scanning device 12 is viewed from the back side with the multi-beam light source 20 and the laser drive substrate 56 removed. The multi-beam light source 20 and the laser drive substrate 56 are indicated by a two-dot chain line.

  As shown in FIG. 10, the bracket 58 is rotatably attached to the positioning member 68, and the flange portion 76 provided integrally with the bracket 58 is connected to the stepping motor 80 by the tension coil spring 78. It is in contact with the tip of the shaft 82. Accordingly, when the stepping motor 80 rotates, the rotational motion is converted into a linear motion by a screw (not shown) provided in the shaft 82, the tip of the shaft 82 enters and exits, and the bracket 58 rotates (turns). It is.

  In addition, it is desirable to use a light beam (light emission point 50) that coincides with or is closest to the rotation center of the light emission point group for synchronous detection for controlling the writing position of the optical scanning device 12. According to this, since the optical path does not change on the optical system that performs synchronization detection, it is not necessary to correct the writing position each time the mode is switched.

  Next, a second embodiment according to the present invention will be described. As shown in FIG. 11, in the second embodiment, the light emitting point sequence of magenta (M), which is the second group having adjacent light emitting point groups on both sides, is rotated, and the central portion in the main scanning direction is The rotation center is different from the first embodiment.

  In this second embodiment, as shown in the drawing, the spread of the light flux width in the sub-scanning direction due to the rotation of the light emitting point group is distributed within the gap D between the adjacent colors on both sides, thereby avoiding the wraparound to the adjacent color optical path. Like to do. However, since the gap D between adjacent colors is very small, the light emitting points 50ML and 50R, for example, magenta (M) at the time of mode switching, the light emitting points 50ML and 50MR are turned off. It becomes more effective than

  Further, the second embodiment has an advantage that the position of black (K) on the multi-beam light source 20 can be arbitrarily selected because the light emitting points 50L and 50R at both ends may be turned off. For example, in the case of the image forming apparatus 10 shown in FIG. 1, in order to minimize the image output time (time from the start of the image forming operation to the discharge of the fixed image) in the monochrome image forming mode, the black (K) image formation is performed. It is necessary to make the path the shortest. Therefore, the arrangement of the black (K) image forming unit 14 is limited to the bottom of the four.

  In this case, the light emitting point 50 on the multi-beam light source 20 in the optical scanning device 12 corresponding to black (K) is set to the third group (cyan (C) in FIG. 11) sandwiched between the light emitting point groups on both sides. Therefore, the rotation method according to the second embodiment is effective. A light emitting point closest to the center in the main scanning direction may be used as the rotation center. According to this, in the adjustment of the multi-beam light source 20, the position fluctuation due to the rotation of the predetermined light emitting point can be minimized, and the adjustment is relatively easy to execute.

Schematic side view showing configuration of image forming apparatus Schematic perspective view of optical scanning device Optical path development in the sub-scanning direction of the optical scanning device Explanatory drawing which shows the light emission point arrangement | positioning of the light source in an optical scanning device Explanatory drawing which shows the light source of 1st Example based on this invention. Explanatory drawing which shows the change of the light emission point occupation width of a subscanning direction by rotation of a light emission point Illustration of registration correction by address correction of image data Schematic sectional view in the main scanning direction showing the internal structure of the light source unit Schematic perspective view showing the internal structure of the light source unit Schematic rear view showing the rotation mechanism of the light emitting point Explanatory drawing which shows the light source of 2nd Example which concerns on this invention. Schematic perspective view showing an example of an optical scanning device

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Optical scanning apparatus 14 Image forming part 16 Photoconductor (scanned surface)
18 Developing Device 20 Multi-beam Light Source 44 Fixing Device 48 Optical Axis 50 Light-Emitting Point 76 Saddle 80 Stepping Motor

Claims (4)

The light beam emitted from a single light source emitting points are arranged two-dimensionally by an optical path splitting leads to a plurality of the scanning surface, a light scanning device for scanning each surface to be scanned by a plurality of light beams,
Mode switching means for switching between a full-color image formation mode and a monochrome image formation mode;
Equipped with a,
Said light source, with one row and emission point group arranged in regular intervals at a predetermined angle against the main scanning direction is the is constituted by the same number sequence and the scan surface at a distance in the sub-scanning direction, the The light emitting point group farthest from the optical axis of the light source is the black light emitting point group,
In the monochrome image forming mode, with respect to the position of the light emitting point group in the full color image forming mode, the black light emitting point group is centered on the light emitting point closest to the optical axis in the sub-scanning direction. The light emitting point group corresponding to the color is rotated away from the optical axis, and the writing resolution is lowered by rotating the light source and turning off the light emitting point farthest from the rotation center to reduce the number of light beams. An image forming apparatus configured to increase an image forming process speed as compared with a full-color image forming mode . An optical scanning device that divides a light beam emitted from a single light source having two-dimensionally arranged light emitting points into a plurality of scanned surfaces and scans each scanned surface with a plurality of light beams;
Mode switching means for switching between a full-color image formation mode and a monochrome image formation mode;
With
The light source is configured by arranging the same number of light emitting point groups arranged at equal intervals with a predetermined angle with respect to the main scanning direction as the scanning surface with a distance in the sub scanning direction. It is configured to be rotatable around the center in the main scanning direction of any of the groups or the light emitting point closest to the center, and corresponds to the black color on the opposite side across the optical axis from the light emitting point group having the center of rotation. There is a luminous point cloud,
In the monochrome image formation mode, the light source is rotated in the direction in which the light emission point group corresponding to the black color moves upstream in the main scanning direction with respect to the position of the light emission point group in the full color image formation mode, and the black It is configured to reduce the writing resolution by turning off the light emitting points at both ends in the color-corresponding light emitting point group to reduce the number of light beams and increase the image forming process speed compared to the full color image forming mode. An image forming apparatus. The mode switching means is
(PS2 / PS1) × (dpi2 / dpi1) = (L2 / L1)
PS: image forming process speed, dpi: writing resolution, L: number of light beams
The image forming apparatus according to claim 1 , wherein the parameters are changed so as to satisfy the following relationship . The image forming apparatus according to claim 1 , wherein an exposure amount of the optical scanning device is switched in accordance with switching of the mode switching unit .

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