JP2006137200A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of improving the recording speed and/or the recording density in a monochromatic mode without including a mechanically or electrically movable part in a tandem type. <P>SOLUTION: By providing the number of optical beams to be outputted from an optical scanning device 5K for forming an image based on a monochromatic image signal larger than the number of optical beams to be outputted from the other optical scanning devices 5Y, 5M, 5C among optical scanning devices 5Y, 5M, 5C, 5K, and executing the optical scan in the optical scanning device 5K in a monochromatic mode using a larger number of, for example, two optical beams 32K, a higher speed can be achieved. At the time, the other optical scanning device 5Y, 5M, 5C side can be realized independently without including a mechanically or electrically movable part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a digital color copying machine, a color printer, and a color facsimile apparatus having a so-called tandem type structure having a plurality of optical scanning devices.

  Generally, in this type of color image forming apparatus, a color mode and a monochrome mode can be freely selected, and a color image and a monochrome image of, for example, black can be arbitrarily output by one machine.

  In such a color image forming apparatus, it is required that the recording speed can be improved so that a large amount of output images can be quickly processed in the monochrome mode. Here, in the case of a one-drum type color image forming apparatus using one photoconductor, in the full color mode, for Y (yellow), M (magenta), C (cyan), and K (black). However, in the monochrome mode, an image can be created by rotating the photosensitive member only once, so that the recording speed is substantially four times higher. However, for example, four photoconductors are used, and color images for Y, M, C, and K are formed on the respective photoconductors, and these color images are transported by a common sheet transport belt. In the case of a tandem type color image forming apparatus that is superimposed on paper, if no measures are taken, the recording speed in the monochromatic mode cannot be improved compared to the full color mode.

  For this reason, in order to increase the recording speed in the monochromatic mode than in the color mode, the rotational speed and pixel clock frequency of the rotating polygon mirror (polygon mirror = deflector) in the monochromatic mode are increased than in the color mode. There is a proposed example as described above (for example, see Japanese Patent Laid-Open No. 4-284468). However, in order to improve the recording speed as much as possible in the color mode, the rotation speed of the rotary polygon mirror and the pixel clock frequency are usually set close to the limit values. It is practically impossible to increase the pixel clock frequency any more, and in reality, it is not possible to improve the recording speed in the monochrome mode.

  For this reason, for example, according to Japanese Patent Application Laid-Open No. 10-307443, in a tandem type image forming apparatus, scanning is performed by increasing the number of light beams used in the monochrome mode than the number of light beams used in the color mode. It has been proposed to increase the recording speed without increasing the speed. According to this proposed example, the sheet conveying means, the plurality of photosensitive members arranged along the sheet conveying path, and the photosensitive members are provided in a one-to-one relationship, and the surface of each photosensitive member is irradiated with the light beam. An optical unit that performs optical scanning, and an optical path changing unit that is provided in at least one of optical paths from each optical unit to the photosensitive member and changes the optical path so that the light beam emitted from the optical unit reaches the other photosensitive member. , And is configured. According to this, for example, four light beams can be simultaneously scanned with respect to the black photosensitive member in the black single color mode as compared with the full color mode.

  However, the method disclosed in Japanese Patent Laid-Open No. 10-307443 has the following problems.

  First, the optical path changing means includes a mechanical movable part that needs to move with respect to the angle and position of the mirror in accordance with switching between the color mode and the monochrome mode. This is necessary for switching the photoconductor that the light beam performs optical scanning and for adjusting the optical path length in the case of switching. As a result, the configuration tends to be complicated. Incidentally, although it is possible to use electrical movement without mechanical movement, such as a liquid crystal shutter, as the optical path changing means, there is a lot of waste of light and the use efficiency is poor.

  Second, since a plurality of light beams for a single color mode are generated using light beams of a plurality of light units, the photosensitive member to be optically scanned is switched by the same light beam. It is necessary to greatly change the incident angle of the light beam to the light source. Originally, it is desired to adopt a beam incident angle that is almost perpendicular to all the photoconductors. However, it is difficult or impossible to set such a beam incident angle. Is possible. As a result, the light beam on the surface of the photoconductor is likely to become thick and blurred, and the image quality is likely to deteriorate.

  Thirdly, a plurality of light beams for the monochromatic mode are generated by using the light beams of the plurality of light units. Generally, the bending characteristic of the scanning line of the light beam for each light unit is different. In addition, since the directions of bending of the scanning lines are different from each other in the light beams, it is difficult to correct the bending of the scanning lines, and the image quality is likely to deteriorate. The bending of the scanning line becomes relatively large even at the point where the beam incident angle becomes large.

  Fourth, since a plurality of light beams for a single color mode are generated using light beams of a plurality of light units, and a movable optical path changing unit is essential, an existing color image forming apparatus Is practically impossible, requires significant design changes and must be newly manufactured.

  Fifth, since the optical path changing means must be moved in accordance with the switching between the color mode and the monochrome mode, for example, in the mixed mode such as the monochrome black mode → the color mode → the monochrome black mode →. It is necessary to wait for the optical path changing member to switch, resulting in a time lag and a decrease in the overall processing speed.

  Sixth, signal processing / control in the monochrome mode is complicated. That is, the image data distribution unit distributes the monochrome mode image signal to the black K optical unit and the other Y, M, and C optical units provided corresponding to the black photosensitive member. Actually, however, it is necessary to send an image signal for monochromatic black to the Y, M, and C dedicated optical units, and the writing order must be controlled, which complicates. .

  Therefore, the present invention provides an image forming apparatus that can improve the recording speed and / or recording density in the monochromatic mode without including any mechanical or electrical movable part, in an image forming apparatus having a tandem configuration. For the purpose.

  Another object of the present invention is to provide an image forming apparatus in which the setting of the incident angle of the light beam with respect to the irradiated surface is advantageous.

  It is another object of the present invention to provide an image forming apparatus in which the bending of the scanning line of the light beam on the irradiated surface is small.

  It is another object of the present invention to provide an image forming apparatus that can be easily applied to existing machines.

  It is another object of the present invention to provide an image forming apparatus capable of avoiding a decrease in processing speed due to mode switching without causing a time lag even in a mixed mode of a plurality of color modes and a single color mode.

  Another object of the present invention is to provide an image forming apparatus in which signal processing and control in the monochrome mode is relatively easy.

  According to the first aspect of the present invention, in the image forming apparatus provided with the optical scanning device that performs optical scanning based on the image signals of a plurality of colors, one of the optical scanning devices that forms an image based on the single color image signal. The number of light beams that can be output is made larger than the number of light beams that can be output by other optical scanning devices that form images based on image signals of other colors. The invention according to claim 2 is provided in a one-to-one relationship with each of the plurality of irradiated surfaces set for each color and each irradiated surface, and each of the irradiated surfaces is in accordance with an image signal of a corresponding color. In an image forming apparatus including an optical scanning device that performs optical scanning with a light beam, the number of light beams that can be output by one optical scanning device that forms an image based on a single-color image signal is calculated. The number of light beams that can be output by another optical scanning device that forms an image based on the color image signal is increased. According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, a multiple color mode for outputting an image based on a plurality of color image signals and a single color mode for outputting an image based on a single color image signal are provided. When the single color mode is selected, the corresponding irradiated surface is optically scanned by using one light beam with a number of light beams larger than the number of light beams that can be output by the other light scanning device. To do. According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, a multicolor mode for outputting an image based on a plurality of color image signals and a single color mode for outputting an image based on a single color image signal When a plurality of color modes are selected, a corresponding irradiated surface is formed using a light beam having the same number of light beams as the number of light beams output from the other light scanning device by the one light scanning device. Light scan. According to a fifth aspect of the present invention, in the image forming apparatus according to the first, second, third, or fourth aspect, a multiple color mode for outputting an image based on a plurality of color image signals and an image based on a single color image signal are output. A monochromatic mode is selectable, and beam number switching means is provided for switching the number of light beams used for optical scanning by the one optical scanning device in accordance with the selection between the multi-color mode and the monochromatic mode. According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the beam number switching means switches the number of light beams based on a mode switching signal corresponding to an attribute of an image signal to be image-formed.

  Therefore, the number of light beams that can be output by one optical scanning device itself that forms an image based on a single color image signal is larger than the number of light beams that can be output by another optical scanning device. Sometimes it is possible to increase the speed or density by performing optical scanning using more light beams in one optical scanning device, but at this time the other optical scanning device side is mechanically or electrically unrelated at all. This can be realized without including moving parts. As a result, even in the mixed mode of the multi-color mode and the single-color mode, since no movable part is included, a speed reduction due to mode switching can be avoided without causing a time lag. Further, since the optical scanning device and the irradiated surface always have a one-to-one correspondence, it is advantageous to set the incident angle of the light beam with respect to the irradiated surface, and the bending of the scanning line of the light beam on the irradiated surface is also advantageous. It will be small. At the same time, it is sufficient to handle only the dedicated color image signals in both the multi-color mode and the single-color mode, and signal processing and control are relatively easy. Furthermore, basically, it is only necessary to change the number of light beams of each optical scanning device, and therefore only the light source unit, and it can be easily applied to existing machines.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the third, fourth, fifth, or sixth aspect, the deflector that scans and deflects the light beam modulated according to the pixel clock with respect to the surface to be scanned by rotational driving. In addition, at the time of mode switching according to the selection between the multi-color mode and the single-color mode, at least one of the rotation speed of the deflector and the frequency of the pixel clock is changed and switched. Therefore, the recording speed in the monochrome mode can be further increased.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, a deflector that is rotationally driven to deflect and scan the light beam with respect to the surface to be scanned is provided for each optical scanning device. Prepare. Accordingly, an independent configuration can be provided for each optical scanning device.

  According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the number of deflectors that are rotationally driven to deflect and scan the light beam with respect to the surface to be scanned is the same as that of the optical scanning apparatus. Less than the number. Therefore, a configuration with a small number of parts sharing the deflector can be achieved.

  According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, one optical scanning device for a single color is for black. Therefore, it is possible to speed up or increase the density of image formation in the case of a black image that occupies most of document information and the like.

  According to the present invention, among the optical scanning devices, the number of light beams that can be output by one optical scanning device itself that forms an image based on a monochromatic image signal is greater than the number of light beams that can be output by another optical scanning device. Therefore, in the monochromatic mode, it is possible to achieve high speed or high density by performing optical scanning using more light beams in one optical scanning device. At this time, the other optical scanning device side has nothing to do with it. And can be realized without including mechanical or electrical movable parts. As a result, even in the mixed mode of the multi-color mode and the single-color mode, since no movable part is included, a speed reduction due to mode switching can be avoided without causing a time lag. Further, since the optical scanning device and the irradiated surface always have a one-to-one correspondence, it is advantageous to set the incident angle of the light beam with respect to the irradiated surface, and the bending of the scanning line of the light beam on the irradiated surface is also advantageous. Can be small. At the same time, it is sufficient to handle only dedicated color image signals in both the multi-color mode and the single-color mode, and signal processing and control can be made relatively easy. Furthermore, basically, it is only necessary to change the number of light beams of each optical scanning device, and therefore only the light source unit, and it can be easily applied to existing machines.

  According to the seventh aspect of the invention, the deflector for deflecting and scanning the light beam modulated in accordance with the pixel clock with respect to the surface to be scanned by rotational driving is provided, and the multicolor mode and the single color mode are selected. Since at least one of the number of rotations of the deflector and the frequency of the pixel clock is changed and switched at the time of switching the corresponding mode, it is possible to deal with it freely according to the switching of the conveyance speed and the recording density in the monochrome mode.

  According to the eighth aspect of the invention, since each optical scanning device is provided with a deflector that is rotationally driven and deflects and scans the light beam with respect to the surface to be scanned, the optical scanning device has an independent configuration. Can do.

  According to the ninth aspect of the present invention, since the number of deflectors that are driven to rotate and deflect and scan the light beam with respect to the surface to be scanned is smaller than the number of optical scanning devices, the number of components sharing the deflectors is small. It can be.

  According to the tenth aspect of the present invention, since one optical scanning device for a single color is for black, image formation in the case of a black image that occupies most of document information or the like can be speeded up or densified.

  An embodiment of the present invention will be described with reference to the drawings. This embodiment shows an application example to a tandem type full color laser printer.

[Overall schematic configuration and action]
A schematic configuration will be described with reference to FIG. First, on the lower side in the apparatus, a conveying belt 2 is provided that conveys transfer paper (not shown) that is disposed in the horizontal direction and is fed from the sheet feeding cassette 1. On the conveying belt 2, a photosensitive body 3Y for yellow Y, a photosensitive body 3M for magenta M, a photosensitive body 3C for cyan C, and a photosensitive body 3K for black K are sequentially arranged at equal intervals from the upstream side. Yes. Hereinafter, subscripts Y, M, C, and K are appropriately added to the reference numerals for distinction. These photoreceptors 3Y, 3M, 3C, and 3K are all formed to have the same diameter, and process members are sequentially disposed around the photoreceptors in accordance with an electrophotographic process. Taking the photoconductor 3Y as an example, a charging charger 4Y, an optical scanning device 5Y, a developing device 6Y, a transfer charger 7Y, a cleaning device 8Y, and the like are sequentially arranged. The same applies to the other photoconductors 3M, 3C, 3K. That is, in the present embodiment, the photoreceptors 3Y, 3M, 3C, and 3K are irradiated surfaces set for the respective colors, and a pair of optical scanning devices 5Y, 5M, 5C, and 5K is provided for each. 1 correspondence relationship.

  In addition, a registration roller 9 and a belt charging charger 10 are provided around the transport belt 2 on the upstream side of the photoconductor 5Y, and a belt separation charger 11 is provided on the downstream side of the photoconductor 5K. A static elimination charger 12, a cleaning device 13, and the like are provided in this order. Further, a fixing device 14 is provided on the downstream side of the belt separating charger 11 in the transport direction, and is connected to a paper discharge tray 15 by a paper discharge roller 16.

  In such a schematic configuration, for example, in the case of the full color mode (multiple color mode), each of the photoreceptors 3Y, 3M, 3C, and 3K is based on the image signals of the colors Y, M, C, and K, respectively. An electrostatic latent image is formed by optical scanning of the light beam by the optical scanning devices 5Y, 5M, 5C, and 5K. These electrostatic latent images are developed with the corresponding color toners to form toner images, which are superposed by being sequentially transferred onto transfer paper that is electrostatically attracted onto the transport belt 2 and transported. After being fixed as an image, it is discharged. In the black mode (monochromatic mode), the photoconductors 3Y, 3M, 3C and their process members are inactive, and only the photoconductor 3K is based on a black image signal (one scanning device). The electrostatic latent image is formed by optical scanning of the light beam by 5K. This electrostatic latent image is developed with black toner to become a toner image, and is transferred onto a transfer sheet that is electrostatically attracted onto the transport belt 2 and then transferred onto a transfer sheet, thereby being fixed as a black and white image. The paper is ejected.

[Configuration of optical scanning device]
As shown in FIG. 2, the optical scanning device 5 (5Y, 5M, 5C, 5K) basically has a light source unit 21 that emits a light beam by a laser beam for optical writing that is modulated and driven in accordance with an image signal. A collimating lens 22 for shaping the light beam into substantially parallel light, a polygon mirror 23 as a deflector rotated at high speed so as to deflect and scan the surface of the photosensitive member 3 in the main scanning direction, and light on the photosensitive member 3. The fθ lens 24 that is adjusted so as not to bend the scanning line in the beam and condenses the light beam, the folding mirrors 25 and 26 that appropriately fold the light beam, and the imaging state of the light beam are corrected in the same manner as the fθ lens 24. However, it is configured as a combination with a scanning lens 27 that irradiates the photosensitive member 3. Reference numeral 28 denotes a synchronization detection sensor that receives a light beam via a mirror 29 outside the effective image area.

  In reality, these four optical scanning devices 5Y, 5M, 5C, and 5K share one polygon mirror 23, and the scanning light path lengths for the respective photoreceptors 3Y, 3M, 3C, and 3K are all the same. As shown (see FIG. 1), the arrangement of the folding mirrors 25, 26, etc. is devised, and the folding mirror 30 is added at the final stage so that the light beams are applied to the photoreceptors 3Y, 3M, 3C, 3K. The optical housing 31 is set so as to be incident substantially perpendicularly and is generally flat. Here, since one polygon mirror 23 is shared by the four optical scanning devices 5Y, 5M, 5C, and 5K, the number of parts can be reduced and the light beams of the optical scanning devices 5Y, 5M, 5C, and 5K can be reduced. The deflection scanning speed is less likely to vary.

[Basic principle of this embodiment]
Here, in the present embodiment, when the number n of the light beams 32Y, 32M, and 32C that can be output from the light source units 21Y, 21M, and 21C of the optical scanning devices 5Y, 5M, and 5C is n = 1, The number m of the light beams 32K that can be output by the light source unit 21K of the scanning device 5K is m = 2 separated in the sub-scanning direction. In the full color mode under the configuration in which the number of light beams n and m that can be output is different, the number of the light beams 32K of the light source unit 21K is also different as shown in FIG. 4A. As described above, a full-color image is formed by performing optical scanning under the same conditions with the same number of light beams 32Y, 32M, and 32C of the light source units 21Y, 21M, and 21C.

  On the other hand, in the black mode (monochromatic mode), as shown in FIG. 4B, the number of light beams 32K of the light source unit 21K is set to two to perform simultaneous scanning in parallel. A black image is formed. The other light source units 21Y, 21M, and 21C are not driven. At this time, the two light beams 32K are set to a sub-scanning pitch corresponding to the recording density.

  As a result, simply, in the black mode (monochrome mode), optical scanning writing can be performed at a speed twice as high as that in the case of optical scanning with only one light beam 32K, and the conveyance speed can be doubled. Can do. When the speed of the transport belt 2 or the like is not changed in the full color mode, the pitch in the sub-scanning direction between the two light beams 32K is set to ½ in advance so that the full color mode is used. (For example, if it is 600 dpi in the full color mode, the density is 1200 dpi in the black mode).

  As described above, the number m of light beams that can be output by the optical scanning device 5K itself that forms an image based on the image signal for the black mode is larger than the number n of light beams that can be output by the other optical scanning devices 5Y, 5M, and 5C. Therefore, in the black mode, the optical scanning device 5K can perform high-speed scanning or high-density by performing optical scanning using a larger number of light beams, but at this time, the other optical scanning devices 5Y, 5M, and 5C side are completely different. It can be realized without including any mechanical or electrical movable parts. As a result, even in the mixed mode of the full color mode and the black mode, since no movable part is included, it is possible to avoid a speed reduction due to mode switching without causing a time lag. In addition, the optical scanning devices 5Y, 5M, 5C, and 5K and the photosensitive members 3Y, 3M, 3C, and 3K always have a one-to-one correspondence regardless of the selected mode and the number of light beams. It is advantageous to set the incident angle of the light beams 32Y, 32M, 32C, and 32K with respect to the bodies 3Y, 3M, 3C, and 3K, and the incident light is incident so as to be substantially perpendicular to the irradiation surface as shown in FIGS. And the bending of the scanning lines of the light beams 32Y, 32M, 32C, and 32K on the irradiated surface is small. At the same time, each of the optical scanning devices 5Y, 5M, 5C, and 5K only needs to handle an image signal for a dedicated color, both in the full color mode and in the black mode. It becomes easy. Furthermore, basically, the number of light beams n and m of each of the optical scanning devices 5Y, 5M, 5C, and 5K, and therefore only the light source units 21Y, 21M, and 21C may be changed as will be described later. Application is also possible easily.

[Schematic configuration of control system and control contents]
A schematic configuration of a control system for performing the above-described control is shown in a block diagram of FIG. A polygon motor drive circuit 35 for a polygon motor 34 for rotating the polygon mirror 23 is connected to a control circuit 33 having a microcomputer configuration such as a CPU. A control circuit 33 is connected to a semiconductor laser drive circuit 37 for driving the semiconductor laser 36 in each light source unit 21 via a video data control circuit 38 and a pixel clock generation circuit 39. Here, a print mode switching signal (mode selection signal) is input to the control circuit 33, a polygon motor rotation control signal is output from the control circuit 33 to the polygon motor drive circuit 35, and the pixel clock generation circuit 39. Is supplied with a clock frequency setting signal, a pixel clock is output from the pixel clock generation circuit 39 to the video data control circuit 38, and a pixel clock is output from the video data control circuit 38 to the semiconductor laser drive circuit 37. The video signal is output according to the above. Although not particularly illustrated, the control circuit 33 outputs a transport motor control signal for switching the transport speed (= photosensitive linear speed).

  Here, the rotation speed of the polygon motor 34 in the full color mode (multiple color mode) is R [rpm], the pixel clock frequency is F [MHz], the photosensitive member linear velocity is N [mm / s], and the recording density is D [ dpi]. The number of light beams that can be output from the light source unit 21K is m (m is an integer of 2 or more), and the number of light beams that can be output from the light source units 21Y, 21M, and 21C is n (n is m> n, and 1 It is an integer above.

  The operation control according to the mode will be described with reference to a schematic flowchart shown in FIG. Prior to the print operation, the print mode is read from the print mode switching signal. The print mode switching signal may be automatically set according to the attribute of the image signal to be imaged, such as black and white binary data. If the print mode is a multi-color mode (full color mode) with the photosensitive member linear velocity N [mm / s], the number of light beams from the single color light source (here, the semiconductor laser of the light source unit 21K) is set to the remaining plurality. The number is set to n which is the same as the number of color beams (here, the number of light beams n of the light source units 21Y, 21M, and 21C). Further, the rotation speed of the polygon motor 34 and therefore the polygon mirror 23 is set to R [rpm], the pixel clock frequency is set to F [MHz], and the image forming operation is performed in the state shown in FIG. To do.

On the other hand, if the printing mode is a photosensitive member linear velocity M [mm / s] (where M ≧ N) and the recording density is a single color mode (black mode) with D ′ [dpi], a single color light source (here, a light source) The number of light beams from the semiconductor laser of the unit 21K is set to the maximum number m. This process is executed as a function of the beam number switching means. Further, the rotation speed of the polygon motor 34 and therefore the polygon mirror 23 is set to R * (n / m) * (M / N) * (D ′ / D) [rpm], and the pixel clock frequency is set to F * (n / M) * (M / N) * (D ′ / D) ² [MHz], and the image forming operation is performed in the state as shown in FIG. As a result, the conveyance speed (= photosensitive linear velocity) can be increased up to m / n times without increasing the polygon mirror rotation speed and the pixel clock frequency (when the recording density is constant), and the monochrome mode (black mode) is used. The image forming operation can be performed at a higher speed than in the multi-color mode (full color mode).

[Configuration example of light source unit]
A configuration example of the light source units 21Y, 21M, and 21C is shown in FIG. 7, and a configuration example of the light source unit 21K is shown in FIG.

  The light source units 21Y, 21M, and 21C and the light source unit 21K are basically the same structural unit except that the number of semiconductor lasers 36 that are light sources is different. Here, a configuration example of the light source unit 21K will be described. Two general-purpose semiconductor lasers 36K mounted on the control board 40 are respectively inserted into fitting holes 41a formed on the back side of a support member 41 made of aluminum die cast and arranged in parallel at a slight interval in the main scanning direction. Press-fitted and supported. The two collimating lenses 42K provided in pairs with these two semiconductor lasers 36K are aligned in the optical axis direction so that the divergent light beams of the respective semiconductor lasers 36K become parallel light beams, and a predetermined beam The main scanning and sub-scanning directions are aligned so as to be emitted light, and an adhesive is filled and fixed in a gap between the support member 41 and the U-shaped support portion 41b formed in a pair with the fitting hole 41a. Such a support member 41 is attached to a flange 43 having a transmission hole 43a. In the flange 43, an aperture member 44 for shaping the beam shape is attached in front of the transmission hole 43a.

  Here, the two semiconductor lasers 36K and the collimating lens 42K are arranged symmetrically with respect to the emission axis a as shown in a cross-section in FIG. 9A, and the distance between the two semiconductor lasers 36K. The distance d between the two collimating lenses 42K with respect to D is set to be small (D> d) (that is, the optical axes of the two collimating lenses 42K are arranged eccentric to the exit axis a side and supported. It is fixed to the U-shaped support part 41b of the member 41 with an adhesive). Thereby, the light beam from each semiconductor laser 36K is emitted at an angle α in the crossing direction by the corresponding collimator lens 42K.

  Here, the flange 43 is closely fixed to a reference surface provided on the back surface of the holder 45 with the injection axis a being aligned with the center of the cylindrical portion 45 a serving as the rotation reference of the holder 45. The holder 45 contains a beam combining prism 46 useful for a light source unit for three beams or four beams, which will be described later.

  In addition, the optical housing 31 is provided with a bracket 47 that supports the optical unit 21 </ b> K in a cylindrical portion 45 a of the holder 45 so as to be freely adjustable. The bracket 47 is formed with a through hole 47a that penetrates the cylindrical portion 45a. The bracket 47 is compressed through a spring 48, and the presser member 49 is hooked on the collar portion 45b so as to contact and support the side wall by a compression force. Further, one end of the spring 48 is fitted into the hole of the pressing member 49 and the other end is locked to the locking member 50, thereby generating a clockwise torsional force and a rotation stopping portion 47 a formed on the bracket 47. Is abutted against the pitch adjusting screw 51, and the pitch adjusting screw 51 enables rotation adjustment around the optical axis a.

  Here, as shown in FIG. 9B, the two semiconductor lasers 36K are installed at an angle θ from the main scanning direction to the sub-scanning direction with the emission axis a as the rotation center. By adjusting with the adjusting screw 51, the beam spot interval (sub-scanning writing density) in the sub-scanning direction between the two light beams 32K on the photosensitive member 3K can be adjusted. Accordingly, it is possible to easily achieve high density in the single color mode (black mode).

  Such a light source unit 21K is substantially the same structural unit except that the number of semiconductor lasers 36 is different from that of the light source units 21Y, 21M, and 21C. Therefore, the same semiconductor as the light source units 21Y, 21M, and 21C is used for black. Only the light source unit 21K needs to be replaced and attached to the existing machine using the light source units having the number of lasers, and the configuration of the present embodiment can be easily changed.

[Variations]
a. Regarding the light source unit In this embodiment, the number m of light beams that can be output from the optical scanning device 5K is set to m = 2, and the number of beams n that can be output from the other optical scanning devices 5Y, 5M, and 5C is set to n = 1. However, m> n may be sufficient, for example, m = 3, n = 2 or 1, m = 4, n = 3, 2 or 1, and the like.

  Here, when the number of light beams is 3, the light source unit 21 is configured as shown in FIG. 10, for example. When the number of light beams is 4, the light source unit 21 is configured as shown in FIG. . Basically, the number of semiconductor lasers 36, the number of support members 41, and the shape of the aperture member 44 are different from the configuration of the light source unit 21K shown in FIG. Therefore, it can be replaced and attached as appropriate.

  Here, pitch adjustment in the light source unit 21 when the number of light beams is four will be described with reference to FIGS. In contrast to the case where the number of light beams is two, the two added semiconductor lasers 36 are combined by the beam combining prism 46 so that the emission axis thereof coincides with the emission axis a, and the four light beams are adjacent to each other. It is injected at. The beam combining prism 46 is fitted and fixed in the holder 45 before the flange 43 is attached. Under such a configuration, the beam spot interval (sub-scanning writing density) in the sub-scanning direction for the two added semiconductor lasers 36 can be adjusted in the same manner as described above. Here, since the two semiconductor lasers 36 and the added two semiconductor lasers 36 have the same spot interval L of the light beam, the tilt amount from the main scanning direction to the sub-scanning direction with the emission axis a as the rotation center. Are set differently, such as θ1 in the former and θ2 in the latter, as shown in FIG. 12, beam spots (LD1-L, LD1-R, LD1-R, LD2-L, LD2-R) can be adjusted to have a pitch P (sub-scanning writing density) at equal intervals in the sub-scanning direction.

b. Regarding the overall configuration of the tandem type In this embodiment, as the configuration of the full-color laser printer, a plurality of photoconductors 3Y, 3M, 3C, and 3K are arranged in parallel in the horizontal direction. For example, as shown in FIG. The configuration may be such that the individual photoconductors 3Y, 3M, 3C, 3K are arranged in parallel in the vertical direction. Alternatively, without directly transferring the photoconductors 3Y, 3M, 3C, and 3K onto the transfer paper, for example, as shown in FIG. 14, after each color toner image is once transferred onto the intermediate transfer belt 52, the image is transferred onto the transfer paper. It is also possible to have a configuration in which the transfer is performed. In these overall configurations including modifications, the order of arrangement of Y, M, C, and K is not limited to the illustrated example, and is not limited to the four combinations of Y, M, C, and K. It may be two or more and may be five or more. Furthermore, the monochrome mode is not necessarily limited to black, and any one color may be used depending on the application.

c. In this embodiment, one polygon mirror 23 is shared by four optical scanning devices 5Y, 5M, 5C, and 5K. For example, as shown in FIG. Polygon mirrors 23a and 23b may be provided so that the optical scanning devices 5Y and 5M share the polygon mirror 23a, and the optical scanning devices 5C and 5K share the polygon mirror 23b. Alternatively, as shown schematically in FIG. 13, polygon mirrors 23Y, 23M, 23C, and 23K may be individually provided for each of the optical scanning devices 5Y, 5M, 5C, and 5K. As the number of polygon mirrors increases, the overlapping of the optical path projection planes decreases, and the optical scanning devices 5Y, 5M, 5C, and 5K have independent configurations, so that the arrangement and the like can be easily designed. In addition, only the optical scanning device that forms an image with a single color can be a polygon motor that supports high speed.

1 is a schematic front view illustrating an overall configuration of a tandem full-color laser printer according to an embodiment of the present invention. It is a perspective view which shows the basic composition of an optical scanning device. It is a perspective view which shows the structure of the whole optical scanning device. It is a schematic diagram which shows schematically the basic principle of this Embodiment. It is a block diagram which shows schematic structure of a control system. It is a flowchart which shows the example of operation control according to a mode. It is a disassembled perspective view which shows the structural example of the light source unit of 1 light source. It is a disassembled perspective view which shows the structural example of the light source unit of 2 light sources. (A) is a horizontal sectional view showing a configuration of a light source unit of two light sources, and (b) is an explanatory view showing the pitch adjustment. It is a disassembled perspective view which shows the structural example of the light source unit of 3 light sources. It is a disassembled perspective view which shows the structural example of the light source unit of 4 light sources. It is explanatory drawing which shows spot spacing adjustment of 4 beams. It is a schematic front view which shows the modification of whole structure. It is a schematic front view which shows the other modification of a whole structure. It is a perspective view which shows the modification using two polygon mirrors.

Explanation of symbols

3 Scanned Surface 5K One Optical Scanning Device 5Y, 5M, 5C Other Optical Scanning Device 23 Deflector 32 Light Beam

Claims (10)

In an image forming apparatus including an optical scanning device that performs optical scanning based on image signals of a plurality of colors,
Among the optical scanning devices, the number of light beams that can be output from one optical scanning device that forms an image based on an image signal of a single color can be output from another optical scanning device that forms an image based on an image signal of another color. An image forming apparatus characterized by having more light beams. Optical scanning that is provided in a one-to-one relationship with each irradiated surface and a plurality of irradiated surfaces set for each color, and that scans each irradiated surface with a light beam corresponding to an image signal of a corresponding color An image forming apparatus comprising:
Among the optical scanning devices, the number of light beams that can be output from one optical scanning device that forms an image based on an image signal of a single color can be output from another optical scanning device that forms an image based on an image signal of another color. An image forming apparatus characterized by having more light beams.   A multi-color mode for outputting an image based on an image signal of a plurality of colors and a single-color mode for outputting an image based on a single-color image signal are freely selectable. 3. The image forming apparatus according to claim 1, wherein a corresponding irradiated surface is optically scanned using a light beam having a number of light beams larger than the number of light beams that can be output by the optical scanning device.   A multi-color mode for outputting an image based on a plurality of color image signals and a single-color mode for outputting an image based on a single-color image signal are freely selectable. 4. The image forming apparatus according to claim 1, wherein the corresponding irradiated surface is optically scanned using a light beam having the same number of light beams as that output by another optical scanning device.   A multi-color mode for outputting an image based on a multi-color image signal and a single-color mode for outputting an image based on a mono-color image signal are freely selectable, and the one color mode is selected according to the selection between the multi-color mode and the single color mode. 5. The image forming apparatus according to claim 1, further comprising beam number switching means for switching the number of light beams used for optical scanning.   6. The image forming apparatus according to claim 5, wherein the beam number switching means switches the number of light beams based on a mode switching signal corresponding to an attribute of an image signal to form an image.   A deflector that deflects and scans a light beam modulated in accordance with a pixel clock by rotational driving with respect to the surface to be scanned, and the number of rotations of the deflector when the mode is switched according to the selection between the multi-color mode and the single-color mode. 7. The image forming apparatus according to claim 3, wherein at least one of the pixel clock frequency and the pixel clock frequency is changed and switched.   8. The image forming apparatus according to claim 1, further comprising a deflector that is driven to rotate and deflects and scans the light beam with respect to the surface to be scanned.   8. The image forming apparatus according to claim 1, wherein the number of deflectors that are rotationally driven to deflect and scan the light beam with respect to the surface to be scanned is smaller than the number of optical scanning devices.   The image forming apparatus according to claim 1, wherein one optical scanning device for a single color is for black.

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