JP2006289828A - Image forming apparatus and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a matter that use frequency of any one of two laser light emitting points increases and the intensity of laser light being emitted from that laser light emitting point falls off to possibly decrease the quantity of laser light. <P>SOLUTION: In a printer performing image formation by projecting two laser beams corresponding to black and magenta image signals to different reflective faces of one spinning polygon mirror of two light polariscopes and projecting laser beams corresponding to cyan and yellow image signals to different reflective faces of the other spinning polygon mirror, spinning speed ratio of one spinning polygon mirror is set equal to one half that of the other spinning polygon mirror (S3) when an image is formed using a full color image signal (S2). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for forming an image by an electrophotographic method and a control method thereof.

  In a printer apparatus that prints an image by an electrophotographic method, for example, used in a laser beam printer (LBP) or a digital copying machine, the laser is driven by a modulation signal corresponding to the image signal, and the light is modulated from the laser and emitted. An image is formed by a laser beam. At this time, the laser beam is deflected by a rotating polygon mirror, and is focused in a spot shape on the surface of a photosensitive recording medium (photosensitive drum) by a scanning optical element (imaging element) having fθ characteristics. The surface is scanned.

In such a printer apparatus using laser light, a color image forming apparatus having a plurality of (for example, four) deflection scanning apparatuses has been recently proposed (see Patent Document 1 and Patent Document 2). In recent years, there has been an increasing demand for an image forming apparatus capable of printing a color image while maintaining a printing speed equivalent to that of a monochrome black monochrome laser beam printer (see Patent Documents 3 to 5).
JP-A-6-183056 Japanese Patent Laid-Open No. 10-186254 JP-A-5-336331 JP-A-11-65212 JP 2000-280523 A

  Conventionally, in order to increase the formation speed of a black image, there is one in which the number of laser beams corresponding to black or one specific color is larger than the number of laser beams corresponding to other colors. In such a configuration, two rotating polygon mirrors are provided, and two laser beams corresponding to black or one specific color are incident on different reflecting surfaces of one rotating polygon mirror to deflect a total of four laser beams. A so-called two-polygon mirror type deflection scanning device is used. When such a deflection scanning device is used, the number of laser beams of one specific color is always two, whereas the number of laser beams of other colors is one each. When a full-color image including colors is formed, the number of laser beams corresponding to other colors is reduced. Accordingly, when the number of laser beams corresponding to the colors used for forming the color image is combined when forming a full-color image, it is necessary to reduce the number of laser beams of one specific color to ½. If the number of laser beams is reduced in this way, for example, one of the two laser emission points will be used more frequently, and the intensity of the laser beam emitted from that laser emission point will decrease. As a result, the amount of laser light may decrease. In this case, when forming an image of black or one specific color, density unevenness of the image occurs due to variations in the amount of laser light between a plurality of laser emission points.

  An object of the present invention is to solve the above-mentioned drawbacks of the conventional examples.

  A feature of the present invention is to provide an image forming apparatus and a control method therefor that can maintain good image forming characteristics by eliminating a factor of variation in the amount of emitted laser light.

  The above features are achieved by combinations of the features described in the independent claims, and the dependent claims merely define advantageous embodiments of the invention.

An image forming apparatus according to an aspect of the present invention has the following configuration. That is,
An image that includes a plurality of optical deflectors each having a single rotating polygonal mirror and that forms an image by injecting laser light corresponding to an image signal of a predetermined color into each of the different reflecting surfaces of the single rotating polygonal mirror. A forming device,
A first number of laser beams corresponding to the first and second color image signals are respectively incident on different reflecting surfaces of at least one of the plurality of optical polarizers, and the plurality of lights Image forming means for forming an image by making a second number of laser beams corresponding to the image signals of the third and fourth colors incident on different reflecting surfaces of other rotating polygon mirrors of the polarizer;
First and second drive motors for rotating and driving each of the one rotary polygon mirror and the other rotary polygon mirror;
At the time of image formation using the first to fourth color image signals, the ratio of the rotation speeds of the first and second drive motors is set to the first and second color image signals corresponding to the first and second color image signals. Drive control means for rotationally driving the first and second drive motors determined based on the number of 1 and the second number corresponding to the third and fourth color image signals;
It is characterized by having.

An image forming apparatus according to an aspect of the present invention has the following configuration. That is,
An image that includes a plurality of optical deflectors each having a single rotating polygonal mirror and that forms an image by injecting laser light corresponding to an image signal of a predetermined color into each of the different reflecting surfaces of the single rotating polygonal mirror. A forming device,
A first number of laser beams corresponding to the first and second color image signals are respectively incident on different reflecting surfaces of at least one of the plurality of optical polarizers, and the plurality of lights Image forming means for forming an image by making a second number of laser beams corresponding to the image signals of the third and fourth colors incident on different reflecting surfaces of other rotating polygon mirrors of the polarizer;
A driving motor for rotating each of the one rotating polygon mirror and the other rotating polygon mirror at the same rotation speed;
During image formation using the image signals of the first to fourth colors, irradiation with laser light corresponding to the image signals of the first and second colors is applied to the image signals of the third and fourth colors. Control means for performing control at a timing different from the irradiation timing with the corresponding laser beam;
It is characterized by having.

An image forming apparatus control method according to an aspect of the present invention includes the following steps. That is,
An image that includes a plurality of optical deflectors each having a single rotating polygonal mirror and that forms an image by injecting laser light corresponding to an image signal of a predetermined color into each of the different reflecting surfaces of the single rotating polygonal mirror. A method for controlling a forming apparatus, comprising:
A first number of laser beams corresponding to the first and second color image signals are respectively incident on different reflecting surfaces of at least one of the plurality of optical polarizers, and the plurality of lights An image forming step in which a second number of laser beams corresponding to the image signals of the third and fourth colors are incident on each of the different reflecting surfaces of the other rotating polygon mirrors of the polarizer to form an image;
During image formation using the image signals of the first to fourth colors, irradiation with laser light corresponding to the image signals of the first and second colors is applied to the image signals of the third and fourth colors. A control process for controlling to execute at a timing different from the irradiation timing with the corresponding laser beam;
It is characterized by having.

  The outline of the present invention does not enumerate all necessary features, and therefore, a sub-combination of these feature groups can also be an invention.

  According to the present invention, there is an effect that good image forming characteristics can be maintained without causing a variation in the amount of emitted laser light.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the invention according to the scope of claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention.

[Embodiment 1]
FIG. 1 is a schematic cross-sectional view for explaining an image forming unit of a color image forming apparatus (laser beam printer) according to an embodiment of the present invention.

  In the figure, the deflection scanning apparatus 100 has a plurality (two) of rotating polygon mirrors, and laser beams corresponding to two colors are incident on different reflecting surfaces of the respective rotating polygon mirrors, and the laser beams corresponding to the two colors are reflected to perform optical scanning. It is carried out. The configuration of the deflection scanning apparatus 100 will be described in detail with reference to FIG. Photosensitive drums 1BK, 1M, 1C, and 1Y as image carriers are provided at the emission destinations of the laser beams from the deflection scanning device 100, respectively. In the present embodiment, each light beam (laser beam) LBK (black laser beam), LM (magenta laser beam), LC (cyan laser beam), LY, each optically modulated based on image information. (Laser light for yellow) is emitted from the deflection scanning device 100, and irradiates the corresponding photosensitive drums 1BK, 1M, 1C, and 1Y surfaces to form an electrostatic latent image on the surface thereof. In the following description, members related to image formation of black, magenta, cyan, and yellow are indicated by adding BK, M, C, and Y after the respective reference symbols (numbers).

  The electrostatic latent images are formed on the surfaces of the photosensitive drums 1BK, 1M, 1C, and 1Y that are uniformly charged by the primary chargers 2BK, 2M, 2C, and 2Y, respectively. The electrostatic latent images on the photosensitive drums are visualized as black, magenta, cyan, and yellow images by the developing devices 4BK, 4M, 4C, and 4Y, respectively. The images visualized on the respective surfaces of the photosensitive drums 1BK, 1M, 1C, and 1Y in this way are transferred onto the transfer material P on the transfer belt 7 in order by the corresponding transfer rollers 5BK, 5M, 5C, and 5Y. A color image is formed by electrotransfer. Thereafter, the residual toner remaining on the respective surfaces of the photosensitive drums 1BK, 1M, 1C, and 1Y is removed by the corresponding cleaners 6BK, 6M, 6C, and 6Y to form the next color image. Again, the primary chargers 2BK, 2M, 2C, and 2Y are uniformly charged.

  The transfer material P is stacked and accommodated on the paper feed tray 8, and is sequentially fed one by one by the rotation of the paper feed roller 9. The transfer belt P is synchronized with the image writing timing by the registration roller 10 and is conveyed. 7 is sent out. The drive roller 11 feeds the transfer belt 7 with high accuracy and is connected to a drive motor (not shown) with little rotation unevenness. After the image is thus transferred, the transfer material P is sent to the fixing device 25, and the color image formed on the transfer material P is thermally fixed. Thereafter, the transfer material P is conveyed by the rotation of the paper discharge roller 26 and discharged outside the apparatus.

  2A and 2B are a schematic top view (A) and a cross-sectional view (B) illustrating the configuration of the deflection scanning apparatus 100 according to the first embodiment.

  In the deflection scanning device 100, the laser beams emitted from the black and magenta semiconductor lasers 101BK and 101M are respectively incident on different reflecting surfaces of the optical deflector 103a including the rotary polygon mirror 102a having four reflecting surfaces. . The laser beams emitted from the cyan and yellow semiconductor lasers 101C and 101Y are respectively incident on different reflecting surfaces of the optical deflector 103b provided with the rotating polygon mirror 102b and scanned in different directions. The laser beams scanned by the rotary polygon mirrors 102a and 102b are transmitted through the first scanning lenses 104BK, 104M, 104C and 104Y, respectively, and the directions thereof are changed by the folding members 105BK, 105M, 105C and 105Y, respectively. The light passes through the second scanning lenses 106BK, 106M, 106C, and 106Y and forms an image on the corresponding photosensitive drum. As described above, in the deflection scanning apparatus 100 according to the present embodiment, two sets of such optical member groups are arranged in parallel and accommodated in one housing 107, whereby laser light is guided onto four photosensitive drums. . Reference numerals 108 to 111 denote beam detectors (BD), which pass the laser beam outside the region where the scanning exposure to the photosensitive drum is performed in order to detect the scanning start timing of the laser beams for black, magenta, cyan, and yellow, respectively. Is detected.

  Here, the magenta laser light source 101M that scans using the rotating polygon mirror 102a that scans the laser light corresponding to black is commonly used from the semiconductor laser as the light source, similar to the laser light source 101BK for black. Two laser beams are emitted. For this, two semiconductor lasers each having one light emitting point may be provided, or a multi-laser beam having two light emitting points in one semiconductor laser may be used. On the other hand, each of the light sources 101C and 101Y for cyan and yellow emits one laser beam that is smaller than the number of laser beams for black and magenta.

  Next, an operation during image formation in the deflection scanning apparatus 100 according to the present embodiment will be described.

  When forming an image such as black or magenta, or a secondary color of black and magenta, or an image in which magenta is used for part of a black image, the black semiconductor laser 101BK or the magenta semiconductor laser is used. One or both of 101M are used, and two laser beams are used to form an image.

  When forming a full-color image using four colors of black, magenta, cyan, and yellow, two laser beams emitted from each of the black and magenta semiconductor lasers 101BK and 101M are used. An image is formed by using one laser beam emitted from each of the cyan and yellow semiconductor lasers 101C and 101Y. At that time, the rotational speed of the rotary polygon mirror 102a is driven to rotate at half the rotational speed of the cyan and yellow side rotary polygon mirror 102b.

  Accordingly, the laser beams corresponding to black and magenta are always emitted as two laser beams, regardless of the image forming mode, and image formation is performed. As a result, there is no difference in use frequency between the light emitting points of the black and magenta semiconductor lasers, and the possibility that only the light emitting point of one of the semiconductor lasers deteriorates is reduced. Therefore, the light emission point of one of the semiconductor lasers is further deteriorated, the amount of laser light emitted from the light emission point is reduced, and the problem of uneven density in the image does not occur.

  Except for black, magenta is most frequently used as a single color or a secondary color with black. As a result, the magenta semiconductor laser is disposed at a position where the same rotating polygonal mirror 102a as black is used. As a result, when forming not only black but also magenta single color or secondary image of black and magenta, since the number of magenta laser beams is two, the image forming speed can be further increased. it can. This is very effective when printing an image including a single black color, an emphasis character using magenta for the black single color, or an underline.

  Further, for example, in the deflection scanning apparatus 100 used in an image forming apparatus having an image formation speed of 20 sheets per minute with an A4 size and a resolution of 600 dpi (dots / inch), four reflective surfaces are provided as in the present embodiment. When the rotating polygon mirrors 102a and 102b are used, the process speed is about 99 mm / second. In that case, the rotational speed of the light deflector 103b on the cyan and yellow sides is 35079 rpm. On the other hand, the rotation speed of the optical deflector 103a on the black side using two laser beams each is 17539 rpm, which is half of that.

  In this way, the rotation speed of the optical deflector 103a that scans the black and magenta laser beams can be reduced to ½ of the rotation speed of the optical deflector 103b that scans cyan and yellow. For this reason, the vibration level caused by the dynamic imbalance of the black-side optical deflector 103a when forming a full-color image is (1/2) × (1/2) = compared to the cyan-side optical deflector 103b. 1/4. Similarly, the noise generated by the rotation of the rotating polygon mirror is dramatically reduced.

  Further, since the rotation speed of the black rotating polygon mirror 102a is low, the energy for driving the rotating polygon mirror 102a can be reduced, and the amount of heat generated by the motor driving the rotation can be reduced.

  In general, the frequency of the black monochrome mode is higher than that of the full color mode. For this reason, the durability of the bearing of the rotating polygon mirror 102a is stricter than the resistance of the cyan rotating polygon mirror 102b and the bearing, but the rotation speed of the rotating polygon mirror 102a in the full color mode can be reduced. As a result, the load on the bearing of the rotary polygon mirror 102a in the full color mode can be reduced, and the life of the bearing can be extended.

  If the frequency of image formation in the monochromatic mode is still high and there is a difference in the service life between the bearings of the two optical deflectors 103a and 103b, the bearing of the optical deflector 103a on the black side, which is frequently used, is polished. It is advisable to have a means for improving wear. For example, even when the same ball bearing is used, a means of using a ball bearing using a ceramic ball on the black side can be considered. In particular, since a hydrodynamic bearing is generally used for the bearing of a recent rotating polygon mirror, in that case, the bearing portion of the black rotating polygon mirror 102a has wear resistance such as Ni-P. High durability can be achieved by using plating.

  In the first embodiment, in order to simplify the description, the number of black and magenta laser beams is two each, and the number of cyan and yellow laser beams is one, respectively. In the above description, the rotation speed of the black rotating polygon mirror 102a is set to ½ of the rotation speed of the cyan rotating polygon mirror 102b. However, in general, any configuration is possible as long as the number of laser beams on the black and magenta sides is a, the number of laser beams on the cyan and yellow sides is b, and the relationship of a> b is satisfied.

  FIG. 3 is a diagram illustrating a configuration example when the deflection scanning apparatus 100 according to the present embodiment is used in an image forming apparatus having an A4 size and an image forming speed of 20 sheets per minute and a resolution of 600 dpi.

  In FIG. 3, each of the rotary polygon mirrors 102a and 102b has four surfaces and the process speed is 99 mm / second, and two optical deflectors 103a and 103a corresponding to the number of laser beams (a and b) are shown. The respective rotation speeds of 103b are shown.

  When a full-color image is formed, the rotation speed of the black-side rotary polygon mirror 102a is b / a. Further, when forming an image of black or magenta single color or its secondary color, the image forming speed varies depending on the rotation speed of the optical deflector 103a. For example, the image forming speed when scanning is performed at the same rotational speed as that of the optical deflector 103b at the time of forming a full-color image is a / b times that at the time of forming a full-color image, and the image forming speed of a mode that is frequently used. Can be increased.

  FIG. 4 is a block diagram for explaining the parts related to the control of the laser beam printer according to the first embodiment. The parts common to the parts described above are indicated by the same symbols, and the explanations thereof are omitted.

  The motor 402 is a motor that rotationally drives the rotary polygon mirror 102a of the optical polarizer 103a, and is rotationally driven by a motor driver 403 in accordance with a signal from the control unit 401. The motor 404 is a motor that rotationally drives the rotary polygon mirror 102b of the optical polarizer 103b, and is rotationally driven by a motor driver 405 in accordance with a signal from the control unit 401. The control unit 401 controls the operation of the entire printer, and includes a CPU 410, a ROM 411 that stores programs and data executed by the CPU 410, and a RAM 412 that is used as a work area for temporarily storing various data during control processing by the CPU 410. I have.

  FIG. 5 is a flowchart for explaining a control process executed by the control unit 401 of the laser beam printer according to the first embodiment. A program for executing this process is stored in the ROM 411 and is executed under the control of the CPU 410. Is done.

  This process is started by inputting print data and instructing the start of printing. First, in step S1, it is determined whether image formation (printing) is performed only with black or magenta. If so, the process proceeds to step S4, and the rotational speeds of the motors 402 and 404 are set to be the same. On the other hand, if it is determined in step S1 that the image is not formed with only black or magenta, the process proceeds to step S2 to determine whether or not the image is formed in full color (black and mixed colors of magenta and other colors). If not, the process proceeds to step S4 and the above-described processing is performed. If the color is full, the process proceeds to step S3, and the rotation speed of the motor 402 is set to half (1/2) of the rotation speed of the motor 404. Thus, the rotational driving of the rotary polygon mirrors 102a and 102b of the optical polarizers 103a and 103b is started according to the set rotational speed, and when the beam detect (BD) signal of each color is detected in step S5, the detected BD signal is converted into the detected BD signal. Corresponding color image signals are output to form an image on the photosensitive drum. In this way, the processing of steps S5 to S7 is repeatedly executed until image formation is performed for one page in step S7.

  As described above, in the full-color mode, two lines of images are formed by two scans of the cyan and yellow laser beams while the black and magenta laser beams perform one scan to form the image of two lines. . As a result, only one laser emission point of each of the black and magenta semiconductor lasers is used, so that a change in characteristics of each emission point does not occur, and image deterioration caused by the change can be prevented.

[Embodiment 2]
Next, a second embodiment of the present invention will be described. Since the hardware configuration of the image forming apparatus according to the second embodiment is basically the same as that of the first embodiment, the description thereof is omitted. The configuration of the deflection scanning apparatus 100 according to the second embodiment is also the same as that shown in FIGS. 2A and 2B, and a description thereof will be omitted.

  In the second embodiment, similarly to the first embodiment described above, the number of magenta laser beams to be scanned using the rotating polygon mirror 102a in common with the laser beam corresponding to black is set to two as in the case of black. Yes. Each of the other laser light sources 101C and 101Y for cyan and yellow emits one laser beam which is smaller than those on the black and magenta sides. The rotating polygon mirror 102a includes four reflecting surfaces that are an integral multiple (twice) of the number of laser beams. When forming an image in which black or magenta single color, a secondary color of black and magenta, or an image in which magenta is used for a part of a black image is formed at the time of image formation, the black semiconductor laser 101BK, magenta Either one or both of the semiconductor lasers 101M are used, and an image is formed using two laser beams.

  In the second embodiment, when a full color image using four colors of black, magenta, cyan, and yellow is formed, the black and magenta semiconductor lasers 101BK and 101M each emit two laser beams, and the rotating polygon mirror The surface to be scanned in 102a is skipped by one surface and reflected every two surfaces for scanning. On the other hand, each of the cyan and yellow semiconductor lasers 101C and 101Y emits one laser beam, and an image is formed using all the reflecting surfaces of the rotary polygon mirror 102b. At this time, the rotation speeds of the black rotating polygon mirror 102a and the cyan rotating polygon mirror 102b are the same.

  Therefore, the black and magenta side semiconductor lasers always emit two laser beams regardless of the image forming mode, so there is no difference in use frequency between the semiconductor lasers, and only one semiconductor laser is used. The possibility of deterioration is low. Therefore, the light amount is not reduced due to the deterioration of the semiconductor laser on one side, and the problem of uneven density on the image does not occur.

  Except for black, magenta is most frequently used as a single color or a secondary color with black. As a result, by arranging a magenta laser at a position where the rotating polygon mirror 102a used in common with black is used, when forming an image of not only black but also a magenta single color or a secondary color of black and magenta. However, the image forming speed can be increased compared with the full color mode. This is very effective when printing a single black color or an image in which a black single color includes a magenta emphasis character or an underline.

  Further, as an effect peculiar to the second embodiment, it is possible to substantially halve the periodic positional deviation of the scanning lines of the black and magenta laser beams in the sub-scanning direction. Thereby, defects such as density unevenness in the image can be reduced.

  FIG. 6 is a flowchart for explaining a control process executed by the control unit 401 of the laser beam printer according to the second embodiment. A program for executing this process is stored in the ROM 411 and executed under the control of the CPU 410. Is done.

  This process is started by inputting print data and instructing to start printing. First, in step S11, it is determined whether or not image formation (printing) is performed only with black or magenta. If so, the process proceeds to step S4 in FIG. 5 described above, and the rotational speeds of the motors 402 and 404 are set to be the same. On the other hand, if it is determined in step S11 that the image is not formed with only black or magenta, the process proceeds to step S12 to determine whether or not the image is formed in full color (black and mixed colors of magenta and other colors). Otherwise, the process proceeds to step S4 (FIG. 5) and the above-described processing is performed. However, when the color is full, the process proceeds to step S13, and the rotation speed of the motor 402 is set to be the same as the rotation speed of the motor 404. Thus, the rotational driving of the rotary polygon mirrors 102a and 102b of the optical polarizers 103a and 103b is started according to the set rotational speed, and the image output flag of the RAM 412 is turned on in step S14. In step S15, it is checked whether a black or magenta beam detect (BD) signal is detected. If not detected, the process proceeds to step S20. If detected, the process proceeds to step S16 to determine whether the image output flag is on. If it is on, the image output flag is turned off in step S17. In step S18, a black or magenta image signal corresponding to the detected BD signal is output, and the process proceeds to step S20. On the other hand, if the image output flag is not on in step S16, the image output flag is turned off in step S19, and the process proceeds to step S20 without outputting the image signal (execution of surface skipping).

  In step S20, it is checked whether or not a cyan or yellow beam detect (BD) signal has been detected. If not detected, the process returns to step S15. If detected, the process proceeds to step S21, and cyan or yellow corresponding to the detected BD signal is detected. The image signal is output and the process proceeds to step S22. In this manner, the processes of steps S15 to S21 are repeatedly executed until image formation for one page is performed in step S22.

  This mechanism will be described with reference to FIGS.

  FIG. 7 is a diagram for explaining the positional deviation in the sub-scanning direction for each black reflecting surface measured by the inventors of the present application. In the figure, the horizontal axis indicates the number of scanning planes, and the vertical axis indicates the amount of displacement.

  As shown in the figure, it can be seen that periodic positional deviation occurs every four surfaces, which is the number of surfaces of the rotary polygon mirror. This is thought to be due to the dynamic unbalance caused by the weight imbalance of the deflecting means including the rotating polygon mirror, in addition to the static tilting of the reflecting surface caused by the accuracy of the rotating polygon mirror and its mounting seat surface. It is done. In the case of a rotating polygon mirror having four reflecting surfaces, this appears as a periodic shift repeated every four surfaces. As a result of this shift, a periodic positional shift for each line in the sub-scanning direction is similarly generated on the image, resulting in a serious image defect.

  In recent years, as the image forming speed increases, it is difficult to avoid the vibration of each optical element with respect to the vibration characteristics having a very complicated mode shape. In particular, as in the present embodiment, in the deflection scanning apparatus 100 including two optical deflectors, the optical element may vibrate vigorously depending on the unbalance amount and state of the two optical deflectors.

  8A to 8E are diagrams for explaining the periodic positional deviation for each line in the sub-scanning direction. FIG. 8A shows SIN type 1, FIG. 8B shows SIN type 2, and FIG. C) shows an L type, (D) shows a step type, and (E) an M type.

  In the second embodiment, since every two surfaces are scanned by skipping one surface, the pattern of the surface skipping is 1 or 2 regardless of the type of periodic displacement in black and magenta. However, their probability of occurrence is all equal. As a result, as shown in FIG. 9, the positional deviation amount in the sub-scanning direction can be halved as an expected value (average of random variables).

  FIG. 9 shows the relationship between the cyclic misalignment type shown in FIGS. 8A to 8E and the misalignment in the sub-scanning direction, corresponding to the method of irradiating the rotary polygon mirror with laser light, and It is a figure explaining the relationship with an expected value.

  Here, the number of surfaces of the rotating polygon mirror 102a is set to an integral multiple of the number a of laser beams from the semiconductor lasers 101BK and 101M, and surface skipping is performed for each a surface. As a result, the same reflecting surface of the rotating polygon mirror 102a is always used, and the influence of the positional deviation in the sub-scanning direction due to the squareness error of the reflecting surface of the rotating polygon mirror 102a can be reduced.

  In the second embodiment, in order to simplify the description, the number of black and magenta laser beams is two, the number of cyan and yellow laser beams is one, and the reflecting surfaces of the rotary polygon mirrors 102a and 102b. In the above description, the number of surfaces is four, and the scanning by the black rotating polygon mirror 102a is skipped by one surface and scanned every two surfaces.

  However, in practice, as shown in FIG. 10, the number of laser beams of the black and magenta rotating polygon mirrors 102a is a, and the number of laser beams of the cyan and yellow rotating polygon mirrors 102b is b. Any configuration may be used as long as the number of reflecting surfaces of the polygon mirror 102b satisfies an integer multiple of a. In this case, the scanning with the black laser light is performed for each a-plane (skipping).

  In the flowchart of FIG. 6 described above, when the number of skips is “4”, the flag area is used as a 2-bit counter for counting the BD signal instead of the image output flag. After that, every time a carry signal is output from the 2-bit counter, an image signal corresponding to black or magenta may be output in step S18.

  Although the description is simplified in the flowcharts of FIGS. 5 and 6 described above, actually, in synchronization with the BD signal corresponding to the laser beam of each color, the image signal (PWM signal) corresponding to the color is used. Each corresponding semiconductor laser 101Bk, 101M, 101C, 101Y is driven to form an image.

  In the above-described embodiment, an example in which two optical deflectors each including a rotary polygon mirror have been described, but more optical deflectors may be provided.

  Further, the number of laser beams scanned simultaneously by one optical deflector is not limited to two, and may be more than that, and the number of reflecting surfaces of one rotary polygon mirror is not limited to four.

  In any case, as long as the principle shown in FIG. 3 or FIG. 10 can be applied, it is not limited to these numerical values.

1 is a schematic cross-sectional view for explaining an image forming unit of a color image forming apparatus (laser beam printer) according to an embodiment of the present invention. FIG. 2 is a schematic top view (A) and a cross-sectional view (B) illustrating a configuration of a deflection scanning apparatus according to the present embodiment. FIG. 6 is a diagram illustrating a configuration example when used in an image forming apparatus with an A4 size and an image forming speed of 20 sheets per minute and a resolution of 600 dpi. It is a block diagram for demonstrating the part regarding control of the laser beam printer which concerns on this Embodiment 1. FIG. 4 is a flowchart for explaining a control process executed by a control unit of the laser beam printer according to the first embodiment. It is a flowchart explaining the control processing performed by the control part of the laser beam printer which concerns on Embodiment 2 of this invention. It is a figure explaining the position shift of the subscanning direction for every black reflective surface which the present inventors measured. FIGS. 8A and 8B are diagrams illustrating periodic positional deviation for each line in the sub-scanning direction. FIG. 8A is a SIN type 1, FIG. 8B is a SIN type 2, FIG. 8C is an L type, and FIG. (E) M type is shown. Corresponding to the method of irradiating the rotary polygon mirror with laser light, the relationship between the periodic displacement type shown in FIGS. 8A to 8E and the displacement in the sub-scanning direction, and the expected value It is a figure explaining a relationship. It is a figure explaining the structural example at the time of applying Embodiment 2 of this invention to a more general example.

Claims (22)

An image that includes a plurality of optical deflectors each having a single rotating polygonal mirror and that forms an image by injecting laser light corresponding to an image signal of a predetermined color into each of the different reflecting surfaces of the single rotating polygonal mirror. A forming device,
A first number of laser beams corresponding to the first and second color image signals are respectively incident on different reflecting surfaces of at least one of the plurality of optical polarizers, and the plurality of lights Image forming means for forming an image by making a second number of laser beams corresponding to the image signals of the third and fourth colors incident on different reflecting surfaces of other rotating polygon mirrors of the polarizer;
First and second drive motors for rotating and driving each of the one rotary polygon mirror and the other rotary polygon mirror;
At the time of image formation using the first to fourth color image signals, the ratio of the rotation speeds of the first and second drive motors is set to the first and second color image signals corresponding to the first and second color image signals. Drive control means for rotationally driving the first and second drive motors determined based on the number of 1 and the second number corresponding to the third and fourth color image signals;
An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, wherein a is an integral multiple of b, where a is the first number and b is the second number.   The drive control means sets the rotation speed of the first drive motor to b / a times the rotation speed of the second drive motor during image formation using the image signals of the first to fourth colors. The image forming apparatus according to claim 2.   The image forming apparatus according to claim 1, wherein the first and second colors include black and magenta.   The bearing of at least any one of the plurality of optical polarizers has higher durability than the bearing of the other rotating polygon mirror. The image forming apparatus described in the item.   The image forming apparatus according to claim 5, wherein the high durability is achieved by plating the surface of the bearing. An image that includes a plurality of optical deflectors each having a single rotating polygonal mirror and that forms an image by injecting laser light corresponding to an image signal of a predetermined color into each of the different reflecting surfaces of the single rotating polygonal mirror. A forming device,
A first number of laser beams corresponding to the first and second color image signals are respectively incident on different reflecting surfaces of at least one of the plurality of optical polarizers, and the plurality of lights Image forming means for forming an image by making a second number of laser beams corresponding to the image signals of the third and fourth colors incident on different reflecting surfaces of other rotating polygon mirrors of the polarizer;
A driving motor for rotating each of the one rotating polygon mirror and the other rotating polygon mirror at the same rotation speed;
During image formation using the image signals of the first to fourth colors, irradiation with laser light corresponding to the image signals of the first and second colors is applied to the image signals of the third and fourth colors. Control means for performing control at a timing different from the irradiation timing with the corresponding laser beam;
An image forming apparatus comprising:   8. The image forming apparatus according to claim 7, wherein a is an integer multiple of b, where a is the first number and b is the second number.   In the image formation using the image signals of the first to fourth colors, the control unit converts the first number of laser beams corresponding to the image signals of the first and second colors to the one of the ones. 9. The image forming apparatus according to claim 8, wherein the image forming apparatus is controlled to irradiate each rotating a / b surface of the rotary polygon mirror.   The image forming apparatus according to claim 7, wherein the first and second colors include black and magenta.   11. The image forming apparatus according to claim 7, wherein the bearing of the one rotating polygon mirror has higher durability than the bearing of the other rotating polygon mirror. 11. An image that includes a plurality of optical deflectors each having a single rotating polygonal mirror and that forms an image by injecting laser light corresponding to an image signal of a predetermined color into each of the different reflecting surfaces of the single rotating polygonal mirror. A method for controlling a forming apparatus, comprising:
A first number of laser beams corresponding to the first and second color image signals are respectively incident on different reflecting surfaces of at least one of the plurality of optical polarizers, and the plurality of lights An image forming step in which a second number of laser beams corresponding to the image signals of the third and fourth colors are incident on each of the different reflecting surfaces of the other rotating polygon mirrors of the polarizer to form an image;
Ratio of rotational speeds of first and second drive motors that rotate each of the one rotary polygon mirror and the other rotary polygon mirror during image formation using the first to fourth color image signals. Is determined based on the first number corresponding to the first and second color image signals and the second number corresponding to the third and fourth color image signals, and A drive control step of rotationally driving the first and second drive motors;
A control method for an image forming apparatus, comprising:   13. The method of controlling an image forming apparatus according to claim 12, wherein a is an integer multiple of b, where a is the first number and b is the second number.   In the drive control step, at the time of image formation using the first to fourth color image signals, the rotation speed of the first drive motor is set to b / a times the rotation speed of the second drive motor. The method of controlling an image forming apparatus according to claim 13.   15. The control method for an image forming apparatus according to claim 12, wherein the first and second colors include black and magenta. An image that includes a plurality of optical deflectors each having a single rotating polygonal mirror and that forms an image by injecting laser light corresponding to an image signal of a predetermined color into each of the different reflecting surfaces of the single rotating polygonal mirror. A method for controlling a forming apparatus, comprising:
A first number of laser beams corresponding to the first and second color image signals are respectively incident on different reflecting surfaces of at least one of the plurality of optical polarizers, and the plurality of lights An image forming step in which a second number of laser beams corresponding to the image signals of the third and fourth colors are incident on each of the different reflecting surfaces of the other rotating polygon mirrors of the polarizer to form an image;
During image formation using the image signals of the first to fourth colors, irradiation with laser light corresponding to the image signals of the first and second colors is applied to the image signals of the third and fourth colors. A control process for controlling to execute at a timing different from the irradiation timing with the corresponding laser beam;
A control method for an image forming apparatus, comprising:   17. The method of controlling an image forming apparatus according to claim 16, wherein a is an integer multiple of b, where a is the first number and b is the second number.   In the control step, at the time of image formation using the first to fourth color image signals, the first number of laser beams corresponding to the first and second color image signals 18. The method of controlling an image forming apparatus according to claim 17, wherein the control is performed so that irradiation is performed for each rotating a / b surface of the rotary polygon mirror.   The method of controlling an image forming apparatus according to claim 16, wherein the first and second colors include black and magenta. An image that includes a plurality of optical deflectors each having a single rotating polygonal mirror and that forms an image by injecting laser light corresponding to an image signal of a predetermined color into each of the different reflecting surfaces of the single rotating polygonal mirror. A forming device,
A laser beam is configured to be emitted as a first color and a second color using the first optical deflector,
An image forming apparatus configured to emit b laser beams, which are fewer than a, respectively, as a third color and a fourth color using a second optical deflector.   When forming a monochromatic image, an image is formed using the a laser beams in the first color, and when forming a multicolor image, b laser beams are used for the first to fourth colors. The image forming apparatus according to claim 20, wherein the image is formed.   When forming a monochromatic image, an image is formed using the a number of laser beams in the first color, and when forming a multicolor image, a number of laser beams are used for the first and second colors. 21. The image forming apparatus according to claim 20, wherein an image is formed using b laser beams for each of the third to fourth colors.

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