JP4630685B2 - Color image forming apparatus and control method thereof - Google Patents

Description

  The present invention relates to a color image forming apparatus using an electrophotographic process for forming different color images using a plurality of laser beams, and more particularly to reduction of color misregistration (color alignment) between the plurality of colors.

  Conventionally, in an image forming apparatus using an electrophotographic method, a laser beam modulated by an image signal is reflected by a scanner having a rotating polygon mirror (hereinafter sometimes abbreviated as a polygon mirror or a polygon) and scanned on a photosensitive member. Thus, image formation is performed. A drum-shaped photosensitive member is often used and is called a photosensitive drum. When this method is applied to a color laser printer, a color image is recorded by superimposing a plurality of images of different colors (for example, four colors of yellow (Y), magenta (M), cyan (C), and black (BK)). It is formed on paper (sheet-like medium). There are the following methods for achieving this superposition technique.

  As a first method, a first color image signal is scanned on a photosensitive drum to form a latent image, a developer is attached for visualization, the developer is transferred to recording paper, and then the photosensitive drum is cleaned, The second color image signal is scanned on the same photosensitive drum again to form a latent image, and the first step is performed. However, the developer of the second color is used. The same process is repeated for the third color image signal and the fourth color image signal. In this way, one image is recorded by superimposing images developed multiple times on the same recording paper.

  As a second method, the same number of photosensitive drums are provided for a plurality of image signals, a latent image is formed on the photosensitive drum corresponding to each color image signal, and developers of different colors are provided. Therefore, there are some which perform visual development and transfer them sequentially onto recording paper. In this case, one laser, one scanner, one BD (Beam Detect) sensor for detecting the image writing timing of the laser, and one photosensitive drum are generally prepared for one image signal. Therefore, when there are a plurality of image signals to be superimposed, the same number of lasers as the image signals, the same number of scanners, and the same number of photosensitive drums are necessary.

  In the first method, a series of electrophotographic processes of charging-exposure-development-transfer-cleaning is performed on the first color image signal, and then the same process is performed again on the second color image signal. The third color image signal and the fourth color image signal must be performed in time series. Therefore, there is a problem that the printing time for one sheet is long.

  The second method has an advantage that printing can be performed in a short time as compared with the first method. However, as described above, the same number of color image signals as lasers, scanners, and photosensitive drums must be prepared. However, there is a problem that the apparatus becomes large and expensive.

  In either method, since the images of the respective colors are superimposed, so-called color misregistration, which occurs when the image positions of the respective colors are not aligned, is likely to occur. Particularly in the second method, since each color image is formed using different scanners and photosensitive drums, there is a problem that registration for each color is difficult. Therefore, registration for each color is performed. For example, a resist detection pattern image is formed on an intermediate transfer belt (abbreviation of ITB: Intermediate Transfer Belt) or an electrostatic transfer belt (ETB: abbreviation of Electrostatic Transportation Belt), and this is read by a resist detection sensor. Means for correcting by feeding back to the writing position control or the like is used.

  The resist detection sensor reads the resist detection image pattern formed on the ITB or ETB with a light source, reads the reflected light with a light reception sensor, and the time of the signal of the light reception sensor when the resist detection pattern passes Electrical processing is performed by using a typical intensity change as positional deviation information.

  Usually, the printing time of a laser printer is shortened by increasing the rotation speed of the scanner. A conventional scanner rotation speed of a laser printer is usually a high speed rotation of 20000 rpm or more. Furthermore, the mirror used in the scanner is a polygon mirror, a polygon mirror, and the error in deflection angle causes position fluctuations on the photosensitive drum due to the optical path length of the laser beam. It is necessary that the amount of vibration is small, and that vibration due to high-speed rotation is small. Therefore, the motor becomes large in order to obtain a stable high-speed rotation of the polygon mirror, and the mirror manufacturing process is required for the scanner manufacturing process because it is necessary to limit the tilting error on each mirror surface. For this reason, the yield of manufacture is bad and it has become very expensive. An apparatus having a plurality of scanners as described above becomes large and expensive.

  Therefore, in order to reduce the cost, a common scanner is used for a plurality of colors (Patent Document 1). Furthermore, a scanner is used in common, and a BD is used for only one light source among a plurality of light sources. A sensor provided with a sensor (Patent Document 2) has been proposed.

  To briefly describe Patent Document 2, a plurality of light sources are configured such that a photoconductor is simultaneously scanned by different surfaces of a polygon, and light sources other than the light source provided with the BD sensor are polygon rotational phase differences ( Since the angle difference is known in advance, it can be estimated from the BD signal of the light source provided with the BD sensor.

  Furthermore, there has been proposed a multi-beam image forming apparatus having a plurality of light sources for irradiating a plurality of lasers on one surface of a polygon. In this multi-beam type image forming apparatus, a plurality of laser beams from a plurality of lasers are scanned by a polygon mirror and irradiated onto a charged surface of a photosensitive member, whereby images of a plurality of lines are simultaneously formed on the photosensitive member. Is written to. When the BD signal detects a plurality of laser beams, the plurality of laser beams are modulated by the image signal in synchronization with the BD signal, and image writing for a plurality of lines is simultaneously performed. Accordingly, since the image signal written to the photosensitive member, that is, the amount of information increases at the same time, the number of polygon rotations can be reduced, and image formation can be performed at high speed and stably. In this configuration, as disclosed in Patent Document 1, it is necessary to share one polygon mirror and one scanner motor, and to prepare a BD sensor for each color, which increases the cost.

  On the other hand, Patent Document 2 proposes a configuration in which one BD sensor is provided, and cost reduction can be realized. However, regarding the BD of a light source without a BD sensor, it is assumed that the rotational phase difference of the polygon, that is, the surface accuracy is accurate. That is, since the rotational phase difference is known in advance, the scanning position of the laser without the BD sensor is known from the BD signal of the laser with the BD sensor.

In general, an image forming apparatus includes a video controller that develops image data from a host computer into bitmap data and forms a video signal for image formation, and an engine controller that controls an image forming unit other than the video controller. . The video controller and the engine controller transmit and receive information through serial communication, and exchange signals such as image data, a horizontal synchronization signal (hereinafter referred to as a BD signal), and a vertical synchronization signal (hereinafter referred to as a TOP signal). In particular, an in-line color image forming apparatus including an image forming unit such as a photosensitive drum for each color includes a BD signal independent of each color. Regarding the vertical synchronization signal, in addition to a method in which a TOP signal is independently provided for each color, there is a method in which the vertical synchronization timing of the color is generated by counting the BD signal of each color from a certain reference TOP signal. is there. In the case of the latter method, the video controller counts the BD signal of each color by a predetermined value on the basis of the timing when the TOP signal is turned on, so that the video controller generates the writing start timing of each color in the vertical direction.
Japanese Patent Publication No. 4-51829 JP-A-4-313776

Ma Ruchibimu method, for example, in the case of two-beam method, image writing is common to start from the count by the BD signal Zen'irodai 1 line beam. However, depending on the phase relationship between the TOP signal and the BD signal, there is a possibility that the position of the first line beam in the sub-scanning direction is shifted by one line or more for the first color and the second color, and the deviation is between the first polygon and the second polygon. However, there is a problem that the image quality is deteriorated due to an increase in color shift and a further increase in color misregistration.

  The present invention has been made under such circumstances. In a color image forming apparatus having a configuration in which a multi-beam method is used for speeding up and the number of rotating polygon mirrors is reduced for cost reduction. An object of the present invention is to provide a high-quality image with little color misregistration in the sub-scanning direction.

  In order to solve the above problems, in the present invention, a color image forming apparatus is configured as described in (1) below.

(1) a video controller that outputs a video signal based on the image data when image data is received from an external device, and an engine controller that forms an image based on the video signal output from the video controller; Are the laser light emitting units for the respective colors for forming the images of the respective colors, each including a laser light emitting unit for each color having a first light source and a second light source for irradiating a laser beam, and different in the same rotating polygon mirror Color image formation that performs deflection scanning of the first laser beam and the second laser beam irradiated from the first light source and the second light source in the laser light emitting unit of each color on the surface, and forms an image based on the deflection scanning The engine controller is attached to the left and right in a direction orthogonal to the moving direction of the belt. And a first detection means and a second detection means for detecting the position of the position detection image formed on the belt, and a reference color position detection image as a reference position, and further, the belt Positions by the first light source and the second light source in laser light emitting units of other colors different from the reference color so that the first detection unit and the second detection unit can detect the first side by side in a direction orthogonal to the moving direction of Forming means for forming one detection image using the first laser beam and forming the other image using the second laser beam; a position of the reference color position detection image; and the first laser beam. Based on which of the difference between the position detection image position by the difference between the position of the reference color position detection image and the position of the position detection image by the second laser beam is close to a predetermined value, Other Laser beam selection means for selecting whether to start light emission from the first laser beam or the second laser beam at the image writing position in the moving direction of the belt of the color, and data from the engine controller to the video controller A serial communication line for transmitting by serial communication, and the notification of the selection result by the laser beam selection means to the video controller is performed by serial communication via the serial communication line. A color image forming apparatus.

  According to the present invention, in a color image forming apparatus having a configuration in which a multi-beam method is used for speeding up and the number of rotary polygon mirrors is reduced for cost reduction, high quality with little color misregistration in the sub-scanning direction is achieved. Images can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  A “color laser printer” that is Embodiment 1 will be described. This embodiment is an example of a four-drum type color laser printer.

  FIG. 2 is a block diagram showing a schematic configuration of the present embodiment, in which 201 is a laser printer and 202 is a host computer. In the present embodiment, a two-beam laser scanning method is adopted for the laser optical system in order to realize a high-speed apparatus. This two-beam laser scan will be described in detail later. The color laser printer includes a four-color image forming unit (also referred to as an image forming station) to form a color image in which images of four colors (yellow Y, magenta M, cyan C, and black BK) are superimposed. Yes. The image forming unit includes toner cartridges 207 to 210 having a photosensitive drum as an image carrier, and scanner units 205 and 206 having laser diodes for generating a laser beam as a light source for image exposure. Among these, the toner cartridge has one for each of the four colors. However, the scanner unit is characterized in that there are two in total, one common for yellow and magenta, and one common for cyan and black.

  When the image data from the host computer 202 is received, the video controller 203 in the laser printer 201 develops the image data into bitmap data and generates a video signal for image formation. The video controller 203 and the engine controller 204 perform serial communication to transmit and receive information. The video signal is transmitted to the engine controller 204. The engine controller 204 drives laser diodes (not shown) in the scanner units 205 and 206 in accordance with the video signal, and photosensitive drums (not shown) in the toner cartridges 207 to 210. An image is formed on each of them. The photosensitive drum is in contact with the intermediate transfer belt ITB 211, and images formed on the photosensitive drums of the respective colors are transferred onto the ITB 211 and sequentially superimposed to form a color image. There is also a registration detection sensor that monitors the registration position of the image on the ITB 211.

  FIG. 3 is a sectional view showing the structure of the color laser printer 201. The same components as those in FIG. 2 are denoted by the same reference numerals. The video controller and engine controller described in FIG. 2 are not shown. Reference numerals 301 to 304 denote photosensitive drums, each of which is used to form a black image 301, 302 cyan, 303 magenta, and 304 yellow.

  FIG. 1 is a diagram showing details of the scanner units 205 and 206 in FIG. 3, and a common scanner is used for a plurality of colors. For convenience, the configuration of the scanner unit 205 will be described, but the same applies to 206. In FIG. 1, reference numerals 101 and 102 denote laser diodes (hereinafter sometimes abbreviated as lasers), which are driven and controlled by a control signal from an engine controller (not shown). For convenience, 101 is referred to as LD1, and 102 is referred to as LD2. Reference numeral 103 denotes a polygon mirror, which is rotated at a constant speed in the direction of the arrow in the drawing by a scanner motor (not shown), and scans while reflecting the beams from the laser diodes LD1 and LD2. In this embodiment, the beam from the laser diode LD1 is irradiated to the polygon mirror 103 simultaneously from the right side of the drawing, and the beam from the laser diode LD2 is simultaneously irradiated from the left side of the drawing.

  An optical sensor 106 is on the scanning path of the laser diode LD1 and generates a signal when a laser beam is incident, and is called a BD (Beam Detect) sensor. This BD sensor is only on the scanning path of the laser diode LD1, and does not exist on the scanning path of the other laser diode LD2. The laser beam emitted from the laser diode LD1 is scanned while being reflected by the polygon mirror 103, further reflected by the folding mirror 104, and scanned on the photosensitive drum 301 from right to left. In practice, the laser beam passes through various lenses for focusing on the photosensitive drum or for converting the laser beam from diffused light to parallel light, but the description is omitted. The laser diode LD1 generates a laser beam modulated by a video signal generated by a video controller (not shown), and the laser beam scans on the photosensitive drum 301. On the other hand, the photosensitive drum 301 is rotated in the direction of the arrow shown in FIG. 1 at a constant speed by a drum motor (not shown). The surface of the photosensitive drum 301 is uniformly charged by the charging roller 305 shown in FIG. 3, and the surface is scanned with a laser beam modulated by a video signal generated by a video controller. An electrostatic latent image is formed. The electrostatic latent image is visualized as a toner image by the developing device 309 in FIG.

  Usually, the video controller transmits a video signal to the engine controller a predetermined time after detecting the output signal of the BD sensor. By doing so, the image writing position by the laser beam on the photosensitive drum always coincides.

  On the other hand, the laser diode LD2 also forms an electrostatic latent image on the photosensitive drum 302 in the same manner as LD1. Since BD detection does not exist on the scanning path of the laser diode 102, a video signal is transmitted to the engine controller after a predetermined time from the BD signal of the LD1. By doing so, the image writing position by the laser beam on the photosensitive drum always coincides. In this way, a black (BK) color image is formed on the photosensitive drum 301 by the laser diode LD1, and a cyan (C) color image is formed on the photosensitive drum 302 by the laser diode LD2. The scanner unit 205 in FIG. 3 has been described above, but the same applies to the scanner unit 206. That is, magenta (M) and yellow (Y) color images are formed on the photosensitive drum 303 and the photosensitive drum 304, respectively.

  Each color image is sequentially transferred (primary transfer) so as to overlap on the ITB 211 conveyed at a constant speed. That is, first, a yellow (Y) image is transferred to the ITB, and then transferred onto magenta (M), cyan (C), and black (BK) in this order to form a color image. The color image formed on the ITB 211 is conveyed by the ITB 211. On the other hand, the sheet in the cassette 314 is picked up by the pick-up roller 316 at the position of the transfer roller 318 so that the timing exactly matches the image on the ITB 211. The color image is pressed by the transfer roller 318 and transferred from the ITB 211 to the sheet. The sheet on which the image has been transferred is fixed by the fixing device 313 by heat and pressure, and is then discharged to the upper portion of the printer, the discharge tray 317. The above is a series of image forming processes.

  Reference numeral 212 in FIG. 3 denotes the position of the registration detection sensor. This sensor is for reading an image of each color formed on the ITB 211 and feeding back the data to the video controller or engine controller to adjust the image registration position of each color and prevent color misregistration.

  FIG. 4 is a block diagram showing a part of the interface between the engine controller 204 and the video controller 203. S401 is a TOP signal representing a vertical synchronizing signal, S402 is a BD1 signal representing a black (BK) horizontal synchronizing signal, and S403 is a BD3 signal representing a magenta (M) horizontal synchronizing signal. S <b> 404 is a C image writing beam selection signal LDselect1 signal that selects whether the cyan (C) image writing is performed using the first line beam or the second line beam and is output to the video controller 203. S405 is an M image writing beam selection signal LDselect2 signal that is output to the video controller 203 by selecting whether the first line beam or the second line beam is used to write the magenta (M) image. Further, S406 is a Y image writing beam selection signal LDselect3 signal that is selected to perform yellow (Y) image writing using the first line beam or the second line beam and is output to the video controller 203. Normally, there are image data signals and various timing signals between the engine controller 204 and the video controller 203, but these signals are omitted in this block diagram. Here, the configuration in which image writing information is transmitted using a signal line for each color has been described, but via a serial communication circuit using a status / command signal normally used for communication between the engine controller 204 and the video controller 203. There is no problem as a configuration.

  In the present embodiment, the BD signal output from the engine controller 204 to the video controller 203 does not have yellow (Y) or cyan (C) BD signals. Regarding cyan (C) BD detection, since there is no BD sensor on the scanning path of the laser diode, a video signal is synchronized with the pseudo BD2 signal made from BD1 after a predetermined time from the BD1 signal of black (BK). It transmits to the engine controller 204. As for yellow (Y) BD detection, since there is no BD sensor on the scanning path of the laser diode, video is synchronized with the pseudo BD4 signal made from BD3 after a predetermined time from the BD3 signal of magenta (M). A signal is transmitted to the engine controller 204. By doing so, the image writing position by the laser beam on the photosensitive drum always coincides between the image forming station with the BD sensor and the image forming station without the BD sensor.

  A method for generating the vertical synchronization timing by the video controller 203 will be described with reference to the timing chart of FIG. The TOP signal S501 is a signal that is output from the engine controller 204 to the video controller 203 prior to the writing of all the image data of yellow, magenta, cyan, and black. For yellow (Y), the video controller 203 generates a yellow (Y) vertical writing timing S502 by counting a predetermined value with reference to the timing when the TOP signal S501 becomes LOW. To do. From that timing, yellow (Y) image data is sent to the engine controller 204 in synchronization with a pseudo BD4 signal (an internal signal generated by the video controller 203 from the BD3 signal). As a result, image writing can be performed at a predetermined timing in the vertical direction with respect to yellow (Y). On the other hand, with respect to magenta (M), the video controller 203 generates a writing timing of the magenta vertical method by counting a predetermined value with reference to the timing when the TOP signal S501 becomes LOW. From that timing, image data of magenta (M) is sent to the engine controller 204 in synchronization with the BD3 signal (internal signal generated by the video controller 203 from the BD1 signal). Thereby, image writing can be performed at a predetermined timing in the vertical direction with respect to magenta (M). Since the same applies to cyan and black, the description thereof is omitted here.

  At this time, the count value n from the TOP signal S501 to the start of writing of each color may be obtained from the result of registration detection performed before the printing operation. According to this method, the influence of expansion / contraction of mechanical parts due to variations in mechanical tolerances of individual printers and temperature rises can be absorbed, and the writing position for each color can be adjusted with higher accuracy.

Next, an image correction method in the sub-scanning direction in the present embodiment will be described.
The image correction method proposed in this embodiment is based on the resist detection means disclosed in Japanese Patent Application Laid-Open No. 2003-090973. FIG. 6 shows the intermediate transfer belt 211 extracted. In the same figure, 212a and 212b are registration detection sensors. The two sensors are used for correcting the main scanning magnification or performing registration detection in the sub-scanning direction at two locations. I won't go into details about that. This sensor is widely used in an in-line type color laser printer that forms four color images on four independent photosensitive drums and superimposes the four color images to form a color image. In order to detect the registration position of the toner image in the sub-scanning direction, a horizontal line of one line is drawn on the intermediate transfer belt 211 by a laser, and the timing at which the horizontal line image is detected by the registration detection sensor may be checked. The registration position of the image in the sub-scanning direction can be detected depending on whether it is detected earlier or later than the predetermined timing. Such registration detection is performed before the printing operation, and is performed to prevent color misregistration by matching the writing positions of the laser diodes LD1 and LD3 with the BD sensor and the writing positions of the laser diodes LD2 and LD4 without the BD sensor. .

  Also, it is possible to prevent color misregistration caused by matching the positions of the remaining colors, that is, yellow (Y), cyan (C), and magenta (M) with respect to the position of a certain reference color, for example, black (K).

  Next, a method for selecting the remaining three colors of the image writing beam based on the detection of the registration position and black (BK) will be described.

  FIG. 7 shows lines S711 to S714 drawn with only the first line beam on the ITB 211 for each color of yellow (Y), magenta (M), cyan (C), and black (BK), and for the second line. It is a figure explaining line S721-S724 drawn only by the beam as a horizontal line for each line at the registration detection position of ITB211 as a resist detection pattern one line at a time. For example, the lines 601 and 602 in FIG. 6 are drawn only by the first line beam, and the lines 603 and 604 are drawn only by the second line beam. The registration detection sensor 212 is used to measure the timing for detecting these resist detection image patterns.

  The registration check pattern is basically drawn on the ITB or ETB belt at the same time for all colors. In this embodiment, the order of the patterns of the colors detected by the registration detection sensor 212 is black (BK) → cyan (C) → magenta (M) → yellow (Y) because of the rotational direction of the ITB 211 belt. Yes. Further, here, in order to detect the shift amount of the pattern of each color, the line drawn by the beam for the first line of the black (BK) laser LD1 is used as a reference.

First, the time from the detection timing of the image pattern (S701, S711) drawn by the first line beam of the black (BK) laser LD1 to the predetermined writing timing (S702) of the cyan (C) laser LD2 is expressed as t _C. In this case, the timing t _C1 until the detection of the image pattern (S712) of the first line beam of the LD2 from the result of the registration detection, and the timing t _C2 until the detection of the image pattern (S722) of the second line beam. Which is closer to t _C.

If t _C1 + (t _C2 −t _C1 ) / 2 <t _C , the LD2 is written from the second line beam, so that the color shift in the sub-scanning direction can be reduced.
If t _C1 + (t _C2 −t _C1 ) / 2> t _C , the LD2 is written from the first line beam, so that the color shift in the sub-scanning direction can be reduced.

  In the case of the image pattern as shown in FIG. 7, the LD 2 can write out with the second line beam, thereby reducing the color shift in the sub-scanning direction. At this time, the C image writing beam selection signal LDselect1 in FIG. 4 is set to “1”.

Next, the time from the detection timing of the pattern (S701, S711) drawn by the beam for the first line of the black (BK) laser LD1 to the predetermined writing timing (S703) of the magenta (M) laser LD3 is t _M In this case, the timing t _M1 until the detection of the image pattern (S713) of the first line beam of LD3 from the result of the registration detection, and the timing t _M2 until the detection of the image pattern (S723) of the second line beam. which is to determine whether closer to the t _M of.
If t _M1 + (t _M2 -t _M1 ) / 2 <t _M , writing of LD3 is performed from the second line beam, thereby reducing color shift in the sub-scanning direction.
If t _M1 + (t _M2 −t _M1 ) / 2> t _M , writing of LD3 is performed from the first line beam, so that color misregistration in the sub-scanning direction can also be reduced.

  In the case of the image pattern as shown in FIG. 7, the LD 3 can write out with the second line beam, thereby reducing the color shift in the sub-scanning direction. At this time, the M image writing beam selection signal LD select 2 signal of FIG. 4 is set to “1”.

When the time from the detection timing of the pattern (S701, S711) drawn by the beam for the first line of the black (BK) laser LD1 to the predetermined writing timing (S704) of the yellow (Y) laser LD4 is t _Y From the result of the registration detection, which of timing t _Y1 until detection of the image pattern (S714) of the first line beam of LD3 and timing t _Y2 until detection of the image pattern (S724) of the second line beam is greater. or to determine the close to t _Y.
If t _Y1 + (t _Y2 −t _Y1 ) / 2 <t _Y , writing of the LD 4 is performed from the second line beam, thereby reducing color shift in the sub-scanning direction.
Further, if t _Y1 + (t _Y2 −t _Y1 ) / 2> t _Y , the LD 4 is written from the first line beam, so that the color shift in the sub-scanning direction can be similarly reduced.

In the case of the image pattern as shown in FIG. 7, the LD 4 can reduce the color shift in the sub-scanning direction by writing with the first line beam. At this time, the Y image writing beam selection signal LD select 3 signal of FIG. 4 is set to “0”.
The discrimination of the image writing beam using the registration detection means as described above may be performed at the time of shipment, or may always be performed at the timing of registration detection when the power source of the printer main body is activated.

  Next, a sequence diagram for explaining a video signal transmitted from the video controller 203 to the engine controller 204 when the LD select signal for selecting the image writing beam is “0” or “1” is shown in FIG. Shown in a) and (b). Here, VIDEO 1 is a video signal for transmitting image data of the first line beam, and VIDEO 2 is a video signal for transmitting image data of the second line beam. For ease of explanation, the image data is numbered as VDATA1, VDATA2,... From the image writing timing. When the LD select signal selected from the result of the registration detection is set to “0”, as shown in FIG. 8A, VDATA1, which is image writing data, is transmitted through the VIDEO1 signal, and the first line beam To form an image on the ITB or ETB belt. When the LD select signal is set to “1”, VDATA1, which is image writing data, is transmitted through the VIDEO2 signal as shown in FIG. 8B, and is transmitted from the second line beam to the ITB or ETB belt. An image is formed.

  By using the above-described method, by selecting whether to write the image of yellow (Y), magenta (M), or cyan (C) with the first line beam or the second line beam, It is possible to correct the deviation of the writing position for each image forming station and reduce the color deviation in the sub-scanning direction.

  In the present embodiment, black (BK) and cyan (C) scanned by the first polygon, magenta (M) scanned by the second polygon, and yellow are further scanned using the selected writing beam. A method for correcting the color misregistration in the sub-scanning direction caused by the rotational phase difference of the polygon with respect to (Y) will be described.

  In order to minimize the amount of color misregistration of the four colors of yellow (Y), magenta (M), cyan (C), and black (BK), the sub-scanning directions of black (BK) and cyan (C) It is necessary to correct the color misregistration so that the amount of misregistration between the center position of the color misregistration and the center position of the color misregistration in the sub-scanning direction of yellow (Y) and magenta (M) is minimized.

  This method will be described with reference to FIG. Here, the image writing beam is already selected for all colors by the above-described method, and the following correction is performed using the image writing beam.

  For the first scanner, assuming that the color shift from the cyan (C) position S905 is ΔBKC with reference to the black (BK) position S903, the position S904 of “black (BK) position S903 + ΔBKC / 2” is set to the first scanner. Set as the reference position for the scanner. Next, regarding the second scanner, if the color shift from the yellow (Y) position S910 with respect to the magenta (M) position S908 is ΔMY, the “magenta (M) position S908 + ΔMY / 2” position S909 is obtained. It can be the reference position of the second scanner.

  Here, the deviation S911 between them is calculated again so that the reference position of the first scanner and the reference position of the second scanner are at the same position in the sub-scanning direction. Since the color misregistration amount of one line or more has already been corrected by the above-described correction method based on the image writing beam selection, S911 has a color misregistration amount of less than one line. This can be corrected by changing the surface phase of the scanner described below.

  FIG. 10 shows a correction method when the color misregistration amount of both is equivalent to 1/2 line. In this embodiment, since a laser beam having two light emitting sources is used, when the color misregistration amount is ½ line, as shown in FIG. 10, ¼ BD with respect to the polygon surface of the first image forming station. What is necessary is just to control by the phase shifted only by period S1002. Therefore, a reference signal having a phase delayed by 90 degrees from the reference signal for the PLL control of the first scanner motor may be used as the reference signal for the PLL control of the second scanner motor. By doing this, the black (BK) and cyan (C) sub-scanning center positions scanned by the first scanner and the yellow (Y) and magenta (M) sub-scans scanned by the second scanner are used. An image is formed at the center position in the direction without color misregistration. By this method, the color misregistration between the four colors in the sub-scanning direction can be accurately corrected.

  FIG. 11 shows a block diagram of the scanner motor control circuit in this embodiment.

  The rotation reference signal generator 1101 generates rotation reference signals having different phases in the BD cycle, and outputs rotation reference signals S1103 and S1104 to the first motor PLL control unit 1102 and the second motor PLL control unit 1103. The first motor PLL control unit 1102 controls the first scanner motor 1104 based on the FG signal S1101 of the FG generator 1105 and the rotation reference signal S1103. At that time, PLL control is performed so that the rotation reference signal S1103 and the BD signal S1105 of the BD sensor 1108 are in phase. The second motor PLL control unit 1103 controls the second scanner motor 1106 based on the FG signal S1102 of the FG generator 1107 and the rotation reference signal S1104. At that time, PLL control is performed so that the rotation reference signal S1104 and the BD signal S1106 of the BD sensor 1109 are in phase.

  FIG. 12 is a timing chart showing an example of the rotation reference signal. There are eight types of rotation reference signals with the same BD period and different phases. In accordance with the color misregistration in the sub-scanning direction of black (BK) and cyan (C) scanned by the first scanner and magenta (M) and yellow (Y) scanned by the second scanner, S1201, Any rotation reference signal of S1202, S1203, S1204, S1205, S1206, S1207, and S1208 is used as the rotation reference signal of the first and second scanner motors.

  In this embodiment, an example is shown in which eight rotation reference signals having phases different by 45 degrees are provided. In this case, color misregistration correction can be performed in units of 1/4 line. Here, the example of eight rotation reference signals is shown, but this number is not limited to eight. If a large number of rotation reference signals having different phases are provided, the unit of color misregistration correction can be reduced. . In the present embodiment, a method of correcting the color misregistration amount based on the information of the registration detection image pattern on the left side is shown. However, the color misregistration amount may be corrected based on the average position of the left and right registration detection image patterns in the sub-scanning direction.

  In addition, an example of one horizontal line as an image pattern for resist detection is shown. However, any pattern can be used as long as it can detect a color shift in the sub-scanning direction, and the resist detection image pattern is not limited.

  Here, in this embodiment, a method of providing the image writing beam selection signal for three colors (Y, M, and C) other than the reference color black (BK) is shown. However, any reference color may be used, and the color is not limited to black (BK). Also, the line thickness when drawing the image pattern for resist detection and the image pattern for resist detection are not limited to the method described in the present embodiment. As long as the timing of the image pattern drawn separately with respect to the reference pattern is measured by the registration test and can be compared with a predetermined timing, anything can be used.

  As described above, according to this embodiment, in the color image forming apparatus configured to use the multi-beam method for speeding up and reduce the number of rotating polygon mirrors for cost reduction, It is possible to provide a high-quality image with little color misregistration.

A “color laser printer” that is Embodiment 2 will be described.
In this embodiment, a method of performing PLL control of the scanner motor using the BD signal from the BD sensor without having the FG generator in the scanner motor will be described.

  Since the configuration of the present embodiment is the same as that of the first embodiment except for the control circuit section of the scanner motor, the description of the first embodiment is cited. In addition, the method for selecting an image writing beam that can minimize the color shift of the sub-scanning method among the first line beam and the second line beam is the same as the method described in the first embodiment. The description of Example 1 is incorporated.

  FIG. 13 is a block diagram of the control circuit of the scanner motor of this embodiment. In this embodiment, there is no FG generator in the scanner motor.

  The rotation reference signal generation unit 1301 generates rotation reference signals having the same cycle as the BD cycle but different phases, and sends rotation reference signals S1303 and S1304 to the first motor PLL control unit 1302 and the second motor PLL control unit 1303. Output. The first motor PLL control unit 1302 controls the first scanner motor 1304 based on the BD signal S1305 of the BD sensor 1308 and the rotation reference signal S1303. At that time, PLL control is performed so that the rotation reference signal S1303 and the BD signal S1301 of the BD sensor 1305 are in phase. The second motor PLL control unit 1303 controls the second scanner motor 1306 based on the BD signal S1302 of the BD sensor 1307 and the rotation reference signal S1304. At that time, PLL control is performed so that the rotation reference signal S1304 and the BD signal S1302 of the BD sensor 1307 are in phase.

  According to the present embodiment, by using the output of the existing BD sensor as the rotation position detection signal of the scanner motor without using the FG signal, the FG signal generation unit can be deleted, and the cost can be reduced. it can.

A “color laser printer” that is Embodiment 3 will be described.
In this embodiment, as a technique for writing an image and transmitting the beam selection from the engine controller to the video controller, it is not a technique using an independent signal line as in the first and second embodiments, but communication between the engine controller and the video controller in advance. A method using the serial communication circuit used will be described.

  The first and second polygons may be PLL-controlled to correct the deviation in the sub-scanning direction of the colors scanned by the respective polygons as in the first embodiment or as in the second embodiment. But you can.

  FIG. 14 is a block diagram showing a part of the interface between the engine controller 204 and the video controller 203 of this embodiment. S401 is a TOP signal representing a vertical synchronizing signal, S402 is a BD1 signal representing a black (BK) horizontal synchronizing signal, and S403 is a BD3 signal representing a magenta (M) horizontal synchronizing signal. The difference from the previous embodiments is that data for selecting an image writing beam for each color is transmitted as serial data using a command line and a status line. The video controller 203 transmits serial data to the engine controller 204 via the command line S1401 in synchronization with the serial clock signal S1403. The engine controller 203 that has received the command returns serial data to the video controller 204 via the status line 1402. As described above, in general, various information communication between the engine controller 204 and the video controller 203 is performed using the command line and the status line. Here, the configuration in which the command line and the status line are provided independently is shown, but it can also be realized by, for example, alternately switching and transmitting the command and the status with one signal line.

  According to the present embodiment, the selection information of the image writing beam is also included in the serial data, so that data transmission can be performed without increasing the number of signal lines. In the multi-beam optical system, even if the number of beams is further increased, the cost such as the number of pins of the connector, the wire material, and the number of ports of the IC does not need to be increased.

Detailed view of scanner unit in Examples 1, 2, and 3 The block diagram which shows schematic structure of Example 1, 2, 3 Sectional drawing which shows the structure of Example 1, 2, 3 A block block diagram showing a part of the interface between the engine controller 204 and the video controller 203 in the first embodiment. Timing chart for explaining generation of vertical synchronization timing in the first embodiment The figure which shows intermediate transfer belt ITB in Examples 1, 2, and 3 and its periphery Explanatory drawing of selection of image writing beam in Examples 1, 2, and 3. Timing chart for explaining image control in Embodiment 1 FIG. 6 is a diagram for explaining a technique for correcting color misregistration in the sub-scanning direction caused by a polygon rotation phase difference in the first embodiment. Timing chart when changing the surface phase of the scanner in the first embodiment FIG. 2 is a block diagram illustrating a configuration of a scanner motor control circuit according to the first embodiment. Timing chart showing rotation reference signal in embodiment 1 Block diagram showing a configuration of a scanner motor control circuit in the second embodiment FIG. 9 is a block diagram illustrating a part of an interface between an engine controller and a video controller according to a third embodiment.

Explanation of symbols

101 LD1
102 LD2
103 Bolgon mirror 201 Laser printer 205 Scanner unit (BK-C)
206 Scanner unit (MY)
211 ITB
212 Registration sensor 301 Photosensitive drum (BK)
302 Photosensitive drum (C)
303 Photosensitive drum (M)
304 Photosensitive drum (Y)

Claims (2)

A video controller that outputs a video signal based on the image data when image data is received from an external device; and an engine controller that forms an image based on the video signal output from the video controller. Each color laser light emitting unit for forming an image of each color, each comprising a laser light emitting unit of each color having a first light source and a second light source for irradiating a laser beam, on the different surfaces of the same rotary polygon mirror A color image forming apparatus that performs deflection scanning of a first laser beam and a second laser beam emitted from the first light source and the second light source in each color laser light emitting unit, and forms an image based on the deflection scanning. And
The engine controller
First detection means and second detection means for detecting the position of the position detection image provided on the left and right sides in a direction perpendicular to the moving direction of the belt, and formed on the belt;
A reference color position detection image is formed as a reference position, and the reference color is arranged so that it can be detected by the first detection means and the second detection means arranged side by side in a direction perpendicular to the moving direction of the belt. One of the position detection images by the first light source and the second light source in the laser light emitting unit of another color different from the above is formed using the first laser beam, and the other is formed using the second laser beam. Forming means;
The difference between the position of the position detection image of the reference color and the position of the position detection image of the first laser beam, the position of the position detection image of the reference color and the position detection image of the second laser beam Based on which of the difference from the position and which is close to a predetermined value, light emission is started from the first laser beam or the second laser beam at the image writing position of the other color in the moving direction of the belt. Laser beam selection means for selecting
A serial communication line for transmitting data from the engine controller to the video controller by serial communication,
The color image forming apparatus , wherein the result of selection by the laser beam selection means is notified to the video controller by serial communication via the serial communication line . A video controller that outputs a video signal based on the image data when image data is received from an external device; and an engine controller that forms an image based on the video signal output from the video controller. Each color laser light emitting unit for forming an image of each color, each comprising a laser light emitting unit of each color having a first light source and a second light source for irradiating a laser beam, on the different surfaces of the same rotary polygon mirror Control of a color image forming apparatus that performs deflection scanning of the first laser beam and the second laser beam emitted from the first light source and the second light source in each color laser light emitting unit and forms an image based on the deflection scanning. A method,
In the step of performing image formation by the engine controller,
A detection step for detecting by the first detection means and the second detection means the position of the position detection image provided on the left and right in the direction orthogonal to the moving direction of the belt and formed on the belt;
A reference color position detection image is formed as a reference position, and the reference color is arranged so that it can be detected by the first detection means and the second detection means arranged side by side in a direction perpendicular to the moving direction of the belt. One of the position detection images by the first light source and the second light source in the laser light emitting unit of another color different from the above is formed using the first laser beam, and the other is formed using the second laser beam. Forming process;
The difference between the position of the position detection image of the reference color and the position of the position detection image of the first laser beam, the position of the position detection image of the reference color and the position detection image of the second laser beam Based on which of the difference from the position and which is close to a predetermined value, light emission is started from the first laser beam or the second laser beam at the image writing position of the other color in the moving direction of the belt. A laser beam selection process for selecting
A step of transmitting data from the engine controller to the video controller by serial communication via a serial communication line,
A method for controlling a color image forming apparatus , wherein the selection result in the laser beam selection step is notified to the video controller by serial communication via the serial communication line .

Images