JP2004102276A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of obtaining high-grade images with high accuracy in the image registration positions of respective colors at a low cost by decreasing the number of BD (Beam Detect) sensors. <P>SOLUTION: The image forming device is provided with a plurality of light emitting elements for generating light beams for scanning a plurality of image carriers, an optical system including a single polyhedral mirror for deflecting generated light beams onto the image carriers and a detecting means which is provided corresponding to at least one of the light beams and for receiving the light beams by which the polyhedral mirror is scanned and generating first synchronizing signals for recording the images. The device generates second synchronizing signals for forming the images by the light beam not provided with the detecting means by delaying the first synchronizing signals outputted from the detecting means in accordance with the information relating to the errors of the respective surfaces. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an image forming apparatus using an electrophotographic process, and more particularly to a color image forming apparatus that forms different color images using a plurality of laser beams.

2. Description of the Related Art In an image forming apparatus using a conventional 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 polygon), and scans a photosensitive member. In this way, image formation is performed. Photoconductors are often in the form of drums and are called photosensitive drums. When this method is applied to a color laser printer, different colors such as yellow (Y), magenta (M), cyan (C), A color image is formed on a sheet-like medium by superimposing a plurality of images (four colors of black (BK)). There are the following configurations for achieving this superposition technique.

As one configuration, a first color image signal is scanned on a photosensitive drum to form a latent image, a developer is adhered for visualization, transferred to a recording sheet, and then the photosensitive drum is cleaned and again. The second color image signal is scanned on the same photosensitive drum to form a latent image, and the same process as in the first is performed. However, a developer of the second color is used. This is repeated for the third color image signal and the fourth color image signal. In this manner, one image is recorded by superimposing images developed a plurality of times on the same recording paper.

In another configuration, the same number of photosensitive drums are provided for a plurality of image signals, and latent images are formed on the photosensitive drums corresponding to the respective color image signals on a one-to-one basis. Visualization development is performed with the agent, and the image is sequentially transferred to recording paper. In this case, it is common to prepare one laser, one scanner, one BD (Beam @ Detect) sensor for detecting the image writing timing of the laser, and one photosensitive drum for one image signal. Therefore, when there are a plurality of image signals to be superimposed, the same number of lasers, scanners, photosensitive drums and BD sensors as the image signals are required.

The first configuration performs a series of electrophotographic processes of charging, exposure, development, transfer, and cleaning on a first color image signal, and then performs the same process again on a second color image signal. The processing must be performed in time series for the third color image signal and the fourth color image signal. Therefore, there is a drawback that one print time is very long.

The second configuration has an advantage that printing can be performed in a shorter time than the first configuration. However, as described above, the same number of lasers, scanners, photosensitive drums, and BD sensors as the number of color image signals must be prepared, which has the disadvantage that the apparatus becomes large and expensive.

に お い て In either configuration, since the images of the respective colors are superimposed, so-called color misregistration, which occurs when the image positions of the respective colors do not match, is likely to occur. In particular, the latter configuration has a problem that registration for each color is difficult to achieve because each color image is formed using different scanners and photosensitive drums. Therefore, registration is performed for each color. For example, a resist detection pattern image is formed on an intermediate transfer belt (Intermediate Transfer Belt: abbreviated as ITB) or an electrostatic transfer belt (Electrostatic Transport Belt: abbreviated as ETB), and is read by a resist detection sensor. Means for performing correction by feeding back to an image writing position or the like is used.

The resist detection sensor irradiates a resist detection image pattern formed on the ITB or ETB with a light source, reads the reflected light with a light receiving sensor that focuses the reflected light, and reads the time of the signal of the light receiving sensor when the resist detection pattern passes. The electrical processing is performed using the actual intensity change as the displacement information.

Usually, to shorten the printing time of the laser printer, it is done by increasing the rotation speed of the scanner. The conventional scanner rotation speed of a laser printer is usually high speed rotation of 20,000 rpm or more. Further, the mirror used in the scanner is a polygon mirror, which is a polygon mirror. Since the error in the deflection angle causes the position variation on the photosensitive drum due to the optical path length of the laser beam, the scanner has a very low inclination error on each surface. It is necessary that the vibration be small and that the vibration due to the high-speed rotation be small. Therefore, the motor becomes large in order to obtain a stable high-speed rotation of the polygon mirror, and the mirror surface must be limited in tilting error, so that a precision processing technique is required in the scanner manufacturing process. For this reason, the production yield is low and the cost is very high.

装置 An apparatus prepared with a plurality of scanners as described above becomes large and expensive.

In order to reduce the cost, a common scanner is used for a plurality of colors (Japanese Patent Laid-Open No. 58-95361). Only one in which a BD sensor is provided (JP-A-4-313776) has been devised. To briefly explain JP-A-4-313776, a plurality of light sources are configured so that the photosensitive member is simultaneously scanned by different surfaces of the polygon, and the other light sources other than the light source provided with the BD sensor are the rotational positions of the polygon. Since the phase difference (angle difference) is known in advance, it can be estimated from the BD signal of the light source provided with the BD sensor.
JP-A-58-95361 JP-A-04-313776

Among the above proposals, in Japanese Patent Application Laid-Open No. 58-95361, the polygon mirror and the scanner motor are shared by one. However, since the BD sensor must be prepared for each color, an increase in cost is inevitable.

(4) In Japanese Patent Application Laid-Open No. 4-313776, the cost can be reduced because only one BD sensor is used. However, regarding the BD of the light source without a BD sensor, it is assumed that the rotational phase difference of the polygon, that is, the surface division 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.

An example in which a common scanner is used for a plurality of colors will be described with reference to FIGS. In FIG. 15, a BD sensor 106 exists on the scanning path of LD1 (101). Assuming that the BD signal from the normal BD sensor 106 is BD1, an image is formed at a correct position by writing the image after a predetermined timing (for example, tc) from BD1 as shown by 1601 and 1602 in FIG. On the other hand, if the BD sensor 106 is also present on the scanning path of the LD2 (102), an image is output tc after BD2 (the BD signal from the BD sensor 701 is BD2) as shown by 1603 and 1604 in FIG. By doing so, an image is formed at a correct position.

If the two lasers 101 and 102 are completely symmetrical positions and the polygon mirror 103 is also a square having an ideal angle of 90 degrees, the BD sensors 106 and 701 output BD signals at exactly the same timing. This means that only one of the BD sensors needs to be used.

However, in reality, it is impossible to make the surface division accuracy of each mirror surface of the polygon mirror all the same, and there always exists an error α as shown in FIG. (Α is usually an angle of tens to hundreds of seconds)
The following describes how the BD cycle becomes when such a polygon mirror is used.

The position of each surface of the polygon 103 as shown in FIG. 15 is defined as (1) to (4), and the period of the BD signal when the laser beam output from the laser 101 is reflected by the polygon 103 and enters the BD sensor 106 Is measured every time. FIG. 13 is a plot of the BD cycle. In FIG. 13, t1-2 indicates the time from the detection of the BD on the (1) surface of the polygon to the detection of the BD on the (2) surface. The same applies to t2-3, t3-4, and t4-1. Meaning. Δt1 indicates the difference between t1-2 and the average BD cycle (４ of one rotation), and the same applies to t2, t3, and t4. FIG. 14 shows this state with time on the horizontal axis. On the basis of the BD detected on the (1) surface of the polygon, the upper side is the BD cycle of an ideal polygon mirror, and the lower side is the actual BD cycle of the polygon mirror. At t1-2, the period is shorter than the ideal BD period by Δt1. At t2-3, the period is longer by Δt2 than the ideal BD period. The errors accumulate to be Δt1 + Δt2. (Δt1 is negative, Δt2 is positive) In this way, when the polygon makes one round, errors accumulate and become Δt1 + Δt2 + Δt3 + Δt4. This will be equal to zero. The above is the characteristic of the BD cycle when an actual polygon mirror is used.

(4) Normally, the BD is always detected on each surface of the polygon every time. Therefore, the error of each surface of the polygon is not affected, and the writing position of the image is not shifted. However, as shown in FIG. 15, a configuration in which two lasers are simultaneously scanned by one polygon, only one laser is provided with a BD sensor, and the BD detection of the other laser is detected from a BD signal of a certain laser having a BD sensor. , The deviation of the BD period for each surface as shown in FIG. 13 and FIG. 14 influences, and the scanning surface of the laser with BD and the scanning surface of the laser without BD are different. The writing timing of the image does not match, and it appears as a writing position shift. In order to avoid this, the surface division error of the polygon may be increased to the limit. However, in order to increase the surface division error of the polygon mirror, advanced precision processing technology is indispensable. This results in poor production yields and is very expensive.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is an object of the present invention to reduce the number of BD sensors, reduce costs, and provide high-precision, high-accuracy image registration positions for each color. To provide a simple image forming apparatus.

The image forming apparatus of the present invention includes a plurality of image carriers, a plurality of light emitting elements for generating a light beam for scanning the image carrier, and a light beam generated by the plurality of light emitting elements. A single polygonal mirror that deflects onto the body, and is provided corresponding to at least one of the light beams, receives a light beam scanned by the polygonal mirror, and on the image carrier by the light beam An optical system including detection means for generating a first synchronization signal for recording an image, storage means for storing information on an error of each surface of the polygon mirror, and a first synchronization signal output from the detection means And generating means for generating a second synchronizing signal for forming an image with a light beam not provided with the detecting means by delaying based on the value of the storage unit.

As described above, according to the present invention, it is possible to reduce the number of deflection scanning means (polygon mirror) and laser beam detection means (BD sensor), thereby reducing costs and providing an image forming apparatus with no image shift. can do.

Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings.

FIG. 3 is a cross-sectional view showing a configuration of a color laser printer (hereinafter, referred to as a laser printer) which is an image forming apparatus according to the present embodiment. 201 is a laser printer and 202 is a host computer. This embodiment is an example of a four-drum type color laser printer. The present color laser printer is provided with an image forming section for four colors to form a color image in which images of four colors (yellow: Y, magenta: M, cyan: C, black: BK) are superimposed.

The image forming section includes toner cartridges 207 to 210 having photosensitive drums 301 to 304 as image carriers, and a laser diode (corresponding to a laser beam generating element in the claims) for generating a laser beam as a light source for image exposure. It comprises scanner units 205 and 206. Of these, one toner cartridge is provided for each of the four colors.

The scanner units 205 and 206 are characterized in that they are one common in yellow and magenta, and one common in cyan and black. The scanner units 205 and 206 will be described later in detail.

(4) When image data is received from the host computer 202, the video data is expanded into bitmap data by the video controller 203 in the laser printer 201, and a video signal for image formation is generated. The video controller 203 and the engine controller 204 perform serial communication and transmit and receive information. The video signal is transmitted to the engine controller 204, and the engine controller 204 drives the laser diodes (not shown) in the scanner units 205 and 206 according to the video signal, and drives the laser diodes (not shown) on the photosensitive drums 301 to 304 in the toner cartridges 207 to 210. To form an image. The photosensitive drums 301 to 304 are used for forming black, 301, 302, magenta, and 304 yellow images, respectively.

The photosensitive drum is in contact with the intermediate transfer belt 211, and a color image is formed by transferring the images formed on the photosensitive drums of the respective colors onto the intermediate transfer belt 211 and superimposing them sequentially.

As for each color image, first, a yellow (Y) image is transferred to the intermediate transfer belt 211, and then magenta (M), cyan (C), and black (BK) are transferred thereon to form a color image. You.

(4) On the other hand, the photosensitive drum 301 is rotated 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, and a laser beam modulated by a video signal generated by a video controller scans the surface, thereby forming an invisible electrostatic latent image. Is done. The electrostatic latent image is visualized as a toner image by the developing device 309.

The recording paper in the cassette 314 is fed to the registration roller 319 by the paper feeding roller 316, and the recording paper is conveyed in synchronization with the image on the intermediate transfer belt 211 by the driving timing of the registration roller 319. Then, the color image is transferred from the intermediate transfer belt ITB211 to the recording paper by the transfer roller 318. (Secondary transfer) The recording paper on which the image has been transferred is fixed by the fixing device 313 by heat and pressure, and then discharged to a paper discharge tray 317 above the printer.

There is also a registration detection sensor 212 that monitors the registration position of the image on the intermediate transfer belt 211. This sensor reads the position of each color image formed on the intermediate transfer belt 211 and feeds back the data to the video controller 203 or the engine controller 204 to adjust the image registration position of each color and prevent color misregistration. It is for.

FIG. 1 is a diagram showing details of the scanner units 205 and 206 in FIG.

Since # 205 and 206 have the same configuration, the configuration of one of the scanner units 205 will be described.

In FIG. 1, reference numerals 101 and 102 denote laser diodes, which scan the photosensitive drums 301 and 302 with a video signal generated by the engine controller 204. For convenience, 101 is referred to as a first laser diode (LD1), and 102 is referred to as a second laser diode (LD2). Reference numeral 103 denotes a polygon mirror (corresponding to a deflection scanning means in the claims), which is rotated by a motor (not shown) at a constant speed in the direction of arrow A in the figure and scans while reflecting beams from the laser diodes LD1 and LD2. The motor is controlled to rotate at a constant speed by an acceleration signal and a deceleration signal of a speed control signal from the engine controller 204 and rotates.

# 106 is an optical sensor that is on the scanning path of the laser diode LD1 and generates a signal when a laser beam is incident to generate a horizontal synchronizing signal, and is referred to as a BD (BeamDetect) sensor. Note that the BD sensor exists 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 return mirror 104, and scans the photosensitive drum 301 from right to left.

In practice, the laser beam passes through various lens groups (not shown) for focusing on the photosensitive drum or for converting the laser beam from diffused light to parallel light.

Normally, the video controller transmits a video signal to the engine controller a predetermined time after detecting the output signal of the BD sensor 106. As a result, the writing position of the main scanning of the image by the laser beam on the photosensitive drum always coincides.

(4) On the other hand, the laser diode LD2 also forms an electrostatic latent image on the photosensitive drum 302 in the same manner as the laser diode LD1.

(4) Regarding the detection of BD, since the BD sensor does not exist on the scanning path of the laser diode 102, the BD signal for the laser diode LD2 is generated by the engine controller 204. In the following description, the laser-side horizontal synchronizing signal having no BD sensor is referred to as a pseudo / BD signal. Details of the generation method will be described later.

In this manner, a black (BK) color image is formed on the photosensitive drum 301 by the laser diode LD1 having the BD sensor 106 and cyan is formed by the laser diode LD2 on the side not having the BD sensor 106. The color image (C) is formed on the photosensitive drum 302. The black (BK) side has a BD sensor, and the cyan (C) side does not have a BD sensor. Conversely, the black (BK) side may not have a BD sensor, and the cyan (C) side may have a BD sensor.

In the scanner unit 206 having the same configuration as the scanner unit 205, a magenta (M) image is formed on the photosensitive drum 303 and a yellow (Y) image is formed on the photosensitive drum 304, respectively. This is because the yellow (Y) side has no BD sensor, and the magenta (M) side has a BD sensor. Conversely, the magenta (M) side may not have a BD sensor, and the yellow (Y) side may have a BD sensor.

The above is a series of processes of image formation.

Next, the configuration of the pseudo BD generation method will be described with reference to the block diagram of FIG.

The engine controller 204 includes an ASIC 402 and a CPU 403, and the ASIC 402 and the CPU 403 are connected to an address data bus. The ASIC 402 includes a circuit for generating a pseudo / BD signal, and generates a laser control signal A (206) and a laser control signal B (207) for controlling laser emission in order to detect main-scanning write start position timing. ing. First, the / BD signal 401, which is a horizontal synchronization signal from the BD sensor, is connected to the ASIC 404 and the video controller 203 provided in the engine controller 204. The ASIC 402 receives the / BD 401, calculates a BD cycle, and the CPU 403 calculates a correction value of the pseudo / BD signal from the BD cycle, and inputs the correction value to the ASIC through the address data bus. Then, the ASIC 402 generates the pseudo / BD 404. The video controller 203 receives the / BD 401 output from the BD sensor 106 and the pseudo / BD signal 404 generated by the ASIC 402. At a predetermined timing after the detection by the BD sensor 106, the video data VDO 1 and VDO 2 are output from the video controller 203 to the LD 1 (101) and the LD 2 (102) of the scanner 205. An image is formed on the intermediate transfer belt 211 by the image data VDO1 and VDO2, and is printed on a recording sheet.

Further, in order to prevent color misregistration, the registration detection sensor 212 reads the positions of the color image on the side with the BD sensor and the color image on the side without the BD sensor formed on the intermediate transfer belt 211, and adjusts the image registration position. .

Next, a method of calculating a correction value for each of the four surfaces and a method of generating a pseudo BD will be described with reference to the timing chart of FIG. 5 and the relationship diagram of polygons, lasers, and BD sensors of FIG.

周期 The period of the surface A of the / BD signal 401 for each surface of the polygon 103 measured by the ASIC 402 is xa, the period of the surface B is xb, the period of the surface C is xc, and the period of the surface D is xd. The smallest cycle of the four cycles is subtracted from the BD cycle for each surface, and the resulting value is used as a correction value. Because, when the / BD signal side uses the A plane, the pseudo / BD signal side uses the B plane, and when the / BD signal side uses the B plane, the pseudo / BD signal side uses the C plane. When the / BD signal side uses the C plane, the pseudo / BD signal side uses the D plane, and when the / BD signal side uses the D plane, the pseudo / BD signal side uses the C plane. This is because the correction value is determined based on the correspondence between the / BD signal side and the pseudo / BD signal side using the A surface. Since the correction value depends on the polygon and hardly changes with time, the writing from the / BD signal is constant. In addition, the reference plane is determined by determining the polygon surface of the BD cycle having the minimum cycle value as the correction value 0.

Therefore, if the shortest BD cycle is xb,
The correction value of the B side of the pseudo / BD signal corresponding to the A side of the / BD signal side is
(Period of A side of BD signal)-(Shortest BD period)
= Xa-xb
The correction value is xa-xb
The correction value of the C-plane of the pseudo / BD signal corresponding to the B-plane on the / BD signal side is
(Period of surface B of BD signal)-(Shortest BD period)
= Xb-xb
The correction value is 0
The correction value of the D surface of the pseudo / BD signal corresponding to the C surface of the / BD signal side is
(Period of C-plane of BD signal)-(Shortest BD period)
= Xc-xb
The correction value is xc-xb
The correction value of plane A of the pseudo / BD signal corresponding to plane D on the side of / BD signal is
(Period of BD surface of BD signal)-(Shortest BD period)
= Xd-xa
The correction value is xd-xa

Since the correction value of the pseudo-BD signal of the / BD signal on the A-side (the pseudo- / BD signal on the B-side) is xa-xb, a pseudo- / BD signal that is delayed by (xa-xb) clock from the / BD signal is generated. Output.

Since the correction value of the pseudo / BD signal of the / BD signal on the B surface (the pseudo / BD signal on the C surface) is 0, the / BD signal itself is output as a pseudo BD.

Since the correction value of the pseudo BD signal of the / BD signal of the C plane (the pseudo / BD signal of the D plane) is xc-xb, a pseudo / BD signal that is delayed by (xc-xb) clocks from the / BD signal is generated. Output.

Since the correction value of the / BD signal on the D side (pseudo / BD signal on the A side) is xd-xa, a pseudo / BD signal delayed by (xd-xa) clock from the / BD signal is generated. Output.

In the case of the / BD signal 401, the pseudo / BD signal 404 as shown in FIG.

Next, a circuit configuration will be described with reference to FIG. 7 of a circuit block diagram inside the ASIC 402.

First, the pseudo BD control is performed by using the / BD signal 401 output from the BD sensor 106 of the scanner unit 205 and the signal line of the address data bus ADDRESSDATABUS723 of the CPU 403 and the ASIC 402 to start the pseudo BD control in the 2-bit counter 701. Is started, and the 2-bit counter 701 is repeatedly operated in the order of 00 → 01 → 11 → 10 → 00 so as to know which surface of the polygon 103 is irradiated with the laser. Assuming that the counter value (DATA) is 00 when the surface is A, the surface is B when the counter value is 01, the surface is C when the counter value is 11, and the surface is D when the counter value is 10. Then, as shown in the timing chart for determining the polygon surface position of the ASIC internal circuit shown in FIG. 4, when measuring the BD period of the surface A, the sella 703 becomes High level, and the BD period of the surface B is measured. When SEL 704 is at the high level, when measuring the BD cycle of the C plane, sel 705 is at the HIGH level, and when measuring the BD cycle of the D plane, sel 706 is at the HIGH level. Become. Next, the BD cycle is counted by the clk 722 with the 17-bit counter of 707, and when sela 703, selb 704, selc 705, and sell 706 are selected, the count value DATA of the BD cycle of the surface of each polygon 103 is 708, 709, 710, 711. Is added 32 times. Then, in order to calculate the average value of one cycle by dividing the BD cycle added by 32 times by 32, the added count values DATA01, DATA10, DATA11, and DATA10 are shifted downward by 5 bits (712), and are shifted to the upper 5 bits. Remove bits. The count value is stored in 17-bit registers 713, 714, 715, and 716. When it is detected that the BD cycle of each polygon 103 has been added 32 times by using the 5-bit counter 717, a Porend 718 of a BD cycle addition end signal is output. The 17-bit registers 713, 714, 715, and 716 have the average value of the BD cycle, and when the output 718 is output, the CPU 403 uses the ADDRESSDATABUS 723 to output the average value xa, xb, xc, of the 32 BD cycles. xd can be read by the CPU. In addition, since the CPU 403 can also read the edge 718 using the ADDRESSDATABUS 723, when detecting that the edge 718 is output, the CPU 403 reads the average values xa, xb, xc, and xd of the BD cycle.

Next, the CPU 403 inputs the correction values xas, xbs, xcs, and xds corresponding to the respective polygon surfaces to the 8-bit registrars 718, 719, 720, and 721 of the ASIC 402 from the ADDRESS DATABUS 723. One of the correction values is selected by cella 703, selb 704, selc 705, and sell 706, and the pseudo / BD 404 is output to the video controller 203 by the 8-bit counter 722 from the correction values xas ', xbs', xcs ', and xds'. In this embodiment, the correction value is calculated from the average of 32 BD periods of each surface of the polygon 103, but the number is not limited to this. For example, when the BD cycle of each surface is added every 64 times, the lower 6 bits may be shifted and the upper 5 bits may be deleted.

The above is the description of the circuit block diagram inside the ASIC.

{Operations of the CPU 403 will be described with reference to the flowchart of FIG.

指示 An instruction to rotate the scanner motor is issued to the ASIC 402 (S601).

Next, the CPU 403 instructs the ASIC 402 to start BD cycle measurement (S602). Then, the ASIC 402 measures the BD period of each surface of the polygon (S603), and calculates the average value of the BD period of each surface of the polygon. When each of the BD periods is measured, the ASIC 402 outputs a BD period measurement end bit “porend” to the CPU 403.

(4) When the BD cycle measurement end bit porend becomes true (S604), the CPU 403 reads the average values xa, xb, xc, and xd of the BD cycle of each surface of the polygon measured by the ASIC 402 (S605). This is the n-th reading.

Next, if the number of readings is three or more, the correction value calculation in S608 is performed. If the number of readings is two or less, the process returns to S602 to measure the BD cycle again.

If the number of readings is three or more, the CPU 403 calculates a correction value from the BD cycle of each surface of the polygon (S608).

Next, the CPU 403 calculates the correction values xas (n), xbs (n), xcs (n), xds (n) calculated from the BD cycle measured at the (n) th time and the (n−1) th time. Correction values xas (n-1), xbs (n-1), xcs calculated from the BD period of each surface of the polygon measured at the previous (n-1) th time calculated from the BD period of each surface of the measured polygon (N−1), xds (n−1) and correction values xas (n−2), xbs (n−2) calculated from the BD cycle of each surface of the polygon measured two times before (n−2) , Xcs (n−2) and xds (n−2) are compared as shown below (S609), and if all are less than α, the correction values xas (n), xbs (n), xcs (n) , Xds (n) are set in the correction register of the ASIC (S610). If at least one is not equal to or less than α, the process returns to step S602 to instruct the start of the BD cycle measurement. α is an arbitrary value.

| Xas (n) -xas (n-1) | ≦ α
| Xbs (n) -xbs (n-1) | ≦ α
| Xcs (n) -xc (n-1) | ≦ α
| Xds (n) -xd (n-1) | ≦ α
| Xas (n-1) -xas (n-2) | ≦ α
| Xbs (n-1) -xbs (n-2) | ≦ α
| Xcs (n−1) −xcs (n−2) | ≦ α
| Xds (n-1) -xds (n-2) | ≦ α
| Xas (n−2) −xas (n) | ≦ α
| Xbs (n−2) −xbs (n) | ≦ α
| Xcs (n−2) −xcs (n) | ≦ α
| Xds (n−2) −xds (n) | ≦ α

Then, the ASIC 402 outputs a pseudo / BD signal 404.

The above is a series of operations of the CPU.

As described above, in the scanning optical system of one polygon and two stations, the BD cycle for each polygon surface is measured, and a BD signal (pseudo BD signal) on the side without a BD sensor is generated from the BD cycle. In addition, it is possible to eliminate polygon division errors.

A description will be given of the “pseudo BD generation method” that is the second embodiment.

FIG. 8 shows a scanner unit according to the second embodiment. The difference from the first embodiment is that LD2 (702) is on the opposite side of LD1 (101) and polygon 103. The laser beam from the laser diode LD1 irradiates the polygon mirror 103 simultaneously from the right side of the figure, and the laser beam from the laser diode LD2 irradiates the polygon mirror 103 from the left side of the figure. Otherwise, the configuration is the same as that of the first embodiment. In this configuration, a method of calculating a correction value for each of the four surfaces and a method of generating a pseudo BD will be described with reference to a timing chart of FIG. 9 and a relationship diagram of polygons, lasers, and BD sensors of FIG. Here, an example of a four-sided polygon is shown. The number of faces of the polygon does not matter.

The combined cycle of the A and B faces of the / BD signal 401 for each face of the polygon 103 measured by the ASIC 402 is xa_b, the combined cycle of the B and C faces is xb_c, and the combined cycle of the C and D faces is xc_d , D-plane and A-plane are xd_a. The smallest cycle of the four cycles is subtracted from the BD cycle for each surface, and the resulting value is used as a correction value.

If the shortest BD cycle is xa_b,
The correction value of the C-plane of the pseudo / BD signal corresponding to the A-plane on the / BD signal side is:
(Period of A / B plane of BD signal)-(shortest BD period)
= Xa_b-xa_b
The correction value is 0
The correction value of the surface D of the pseudo / BD signal corresponding to the surface B on the side of the / BD signal is
(Period of B / C plane of / BD signal)-(shortest BD period)
= Xb_c-xa_b
The correction value is xb_c-xa_b
The correction value of plane A of the pseudo / BD signal corresponding to plane C of the / BD signal is
(Period of C / D plane of / BD signal)-(shortest BD period)
= Xc_d-xa_b
The correction value is xc_d-xa_b
The correction value of the B side of the pseudo / BD signal corresponding to the D side of the / BD signal side is
(Period of D / A plane of / BD signal)-(shortest BD period)
= Xd_a-xa_b
The correction value is xd_a-xa_b

擬 似 Since the correction value of the pseudo / BD signal of the / BD signal on the A plane (the pseudo / BD signal on the C plane) is 0, the / BD signal itself is output as the pseudo / BD.

Since the correction value of the pseudo-BD signal of the / BD signal on the B plane (the pseudo / BD signal on the D plane) is xb_c-xa_b, a pseudo / BD signal delayed by (xb_c-xa_b) clocks from the / BD signal is generated, Output.

Since the correction value of the pseudo BD signal of the / BD signal on the C plane (the pseudo / BD signal on the A plane) is xc_d-xa_b, a pseudo / BD signal delayed by (xc_d-xa_b) clocks from the / BD signal is generated. Output.

Since the correction value of the / BD signal of the D plane (pseudo / BD signal of the B plane) is xd_a-xa_b, a pseudo / BD signal delayed by (xd_a-xa_b) clocks from the / BD signal is generated. Output.

In the case of the / BD signal 401, the pseudo / BD signal 904 is as shown in FIG.

As described above, in the scanning optical system of one polygon and two stations, the laser position is provided on the side opposite to the laser on the side of the BD sensor and the polygon, and the BD period for each surface of the polygon is measured. By generating a BD signal (pseudo BD signal) on the side without a BD sensor from the BD cycle, it is possible to eliminate a polygon division error. Further, the station on the side with the BD sensor and the station on the side without the BD sensor use the same polygon surface for reflecting the laser, so that polygon surface accuracy is not required. Peel off.

A description will be given of the “pseudo BD generation method” according to the third embodiment.

FIG. 18 is a cross-sectional view showing a configuration of a color laser printer (hereinafter, referred to as a laser printer) which is an image forming apparatus according to the present embodiment. FIG. 17 is a diagram showing details of the scanner unit 905 in FIG. The main difference from the first embodiment is that the number of scanner units is one, and an image of four colors is formed using one polygon 809.

The image forming section includes toner cartridges 207 to 210 having photosensitive drums 301 to 304 as image carriers, and a laser diode (corresponding to a laser beam generating element in the claims) for generating a laser beam as a light source for image exposure. And a scanner unit 905. Of these, one toner cartridge is provided for each of the four colors.

ス キ ャ ナ Further, the scanner unit 905 is characterized in that the scanner unit 905 is common to yellow, magenta, cyan, and black.

Next, differences of the scanner unit 905 from the first embodiment will be described in detail.

In FIG. 17, reference numerals 801, 802, 803, and 804 denote laser diodes, which scan the photosensitive drums 805, 806, 807, and 808 based on video signals generated by the engine controller 204. For convenience, 801 is referred to as a first laser diode (LD1), 802 is referred to as a second laser diode (LD2), 803 is referred to as a third laser diode (LD3), and 804 is referred to as a fourth laser diode (LD4). Reference numeral 809 denotes a polygon mirror (corresponding to a rotating polygon mirror in the claims), which is rotated by a motor (not shown) at a constant speed in the direction of arrow A in the figure to reflect beams from the laser diodes LD1, LD2, LD3, and LD4. Scan while scanning. The motor is controlled to rotate at a constant speed by an acceleration signal and a deceleration signal of a speed control signal from the engine controller 204 and rotates.

The BD sensor 106 is only on the scanning path of the laser diode LD1, and is not present on the scanning paths of the other laser diodes LD2, LD3, and LD4.

The laser beam emitted from the laser diode LD1 is scanned while being reflected by the polygon mirror 809, further reflected by the return mirror 810, and scans the photosensitive drum 805 from right to left. On the other hand, the laser diode LD2 also forms an electrostatic latent image on the photosensitive drum 806 in the same manner as the laser diode LD1. Also, the LD3 forms an electrostatic latent image on the photosensitive drum 807 similarly to the laser diode LD1. Also, the LD 4 forms an electrostatic latent image on the photosensitive drum 808 in the same manner as the laser diode LD 1.

Note that regarding the detection of BD, the engine controller 204 generates a BD signal for the laser diode LD2, a BD signal for the laser diode LD3, and a BD signal for LD4. Details of the generation method will be described later.

In this way, a black (BK) color image is formed on the photosensitive drum 805 by the laser diode LD1 having the BD sensor 106, and cyan (C) is formed by the laser diode LD2 having no BD sensor 106. A color image is formed on the photosensitive drum 806, a magenta (M) color image by the laser diode LD3 is formed on the photosensitive drum 807, and a yellow (Y) color image by the laser diode LD4 is formed on the photosensitive drum 808. The black (BK) side has a BD sensor, and the cyan (C) side, the magenta (M) side, and the yellow (Y) side do not have a BD sensor. The black (BK) side does not have a BD sensor, but may have a BD sensor on the cyan (C) side, the magenta (M) side, or the yellow (Y) side.

The above is a series of processes of image formation.

構成 The configuration of the pseudo BD generation method is the same as in the first and second embodiments.

FIG. 21 shows a circuit block diagram of the ASIC 402. As shown in FIG. The difference from the first embodiment is that there are three pseudo BDs: a pseudo BD for cyan (C) 1901, a pseudo BD for magenta (M) 1902, and a pseudo BD for yellow (Y) 1903.

Next, a method of calculating a correction value for each of the four surfaces and a method of generating a pseudo BD will be described with reference to a timing chart of FIG. 20 and a relation diagram of polygons, lasers, and BD sensors of FIG.

The period of the surface A of the / BD signal 401 for each surface of the polygon 809 measured by the ASIC 402 is xa, the period of the surface B is xb, the period of the surface C is xc, and the period of the surface D is xd. The smallest cycle of the four cycles is subtracted from the BD cycle for each surface, and the resulting value is used as a correction value.

This is because when the / BD signal side for black (BK) uses the A surface, the pseudo / BD signal side for yellow (Y) is the B surface, the pseudo / BD signal side for the magenta (M) is the C surface, and the cyan / BD signal side is cyan. For the pseudo / BD signal side for (C), use the D surface,
When the black (BK) / BD signal side uses the B surface, the yellow (Y) pseudo / BD signal side has the C surface, the magenta (M) pseudo / BD signal side has the D surface, and the cyan (C) ) For pseudo / BD signal side uses A side,
When the black (BK) / BD signal side uses the C surface, the yellow (Y) pseudo / BD signal side has the D surface, the magenta (M) pseudo / BD signal side has the A surface, and the cyan (C) Use the side B for the pseudo / BD signal side for
When the black (BK) / BD signal side uses the D surface, the yellow (Y) pseudo / BD signal side has the A surface, the magenta (M) pseudo / BD signal side has the B surface, and the cyan (C) Use the C plane for the pseudo / BD signal side for
This is because the correction value is determined from the correspondence between the / BD signal side and the pseudo / BD signal side.

補正 Also, since the correction value depends on the polygon and hardly changes over time, the writing from the / BD signal is constant. In addition, the reference plane is determined by determining the polygon surface of the BD cycle having the minimum cycle value as the correction value 0.

A method of calculating the correction value of the pseudo BD signal 1903 for yellow (Y) will be described below.

If the shortest BD cycle is xb,
The correction value of surface B of pseudo / BD signal 1903 for yellow (Y) corresponding to surface A on the side of / BD signal 401 is
(Period of A side of BD signal)-(Shortest BD period)
= Xa-xb
The correction value is xa-xb
The correction value of the C side of the pseudo / BD signal 1903 for yellow (Y) corresponding to the B side of the / BD signal 401 is
(Period of surface B of BD signal)-(Shortest BD period)
= Xb-xb
The correction value is 0
The correction value of the D surface of the pseudo / BD signal 1903 for yellow (Y) corresponding to the C surface on the side of the / BD signal 401 is
(Period of C-plane of BD signal)-(Shortest BD period)
= Xc-xb
The correction value is xc-xb
The correction value of the A side of the pseudo / BD signal 1903 for yellow (Y) corresponding to the D side of the / BD signal 401 is
(Period of BD surface of BD signal)-(Shortest BD period)
= Xd-xa
The correction value is xd-xa

Therefore, the pseudo / BD signal 1903 for yellow (Y) is as follows.

Since the correction value of the yellow (Y) pseudo / BD signal of the / BD signal 401 on the A side is xa-xb, the yellow (Y) pseudo / BD signal 1903 delayed by (xa-xb) clocks from the / BD signal 401. Is generated and output.

Since the correction value of the yellow (Y) pseudo / BD signal 1903 of the / BD signal 401 on the B side is 0, the / BD signal 401 itself generates and outputs the yellow (Y) pseudo / BD signal 1903.

The pseudo / BD signal 1903 for yellow (Y) of the / BD signal 401 on the C plane has a correction value of xc-xb, so the pseudo / BD signal for yellow (Y) delayed by (xc-xb) clocks from the / BD signal 401. 1903 is generated and output.

Since the correction value for the yellow (Y) pseudo / BD signal 1903 of the / BD signal 401 on the D side is xd-xa, the yellow (Y) pseudo / BD signal delayed by (xd-xa) clocks from the / BD signal 401 1903 is generated and output.

As shown in FIG. 20, in the case of the / BD signal 401, the pseudo / BD signal 1903 for yellow (Y) is used.

The method of calculating the correction value of the pseudo / BD signal 1902 for magenta (M) will be described below.

The time difference between the plane B of the pseudo / BD signal 1903 for yellow (Y) and the plane C of the pseudo / BD 1902 for magenta (M) is
0,
The correction value of the surface A of the / BD signal 401 and the surface B of the pseudo / BD signal 1903 for yellow (Y) is
xa-xb,
The correction value of the C-plane of the magenta (M) pseudo / BD signal 1902 corresponding to the A-plane on the side of the / BD signal 401 is
0 + xa-xb
= Xa-xb
The time difference between the plane C of the pseudo / BD signal 1903 for yellow (Y) and the plane D of the pseudo / BD 1902 for magenta (M) is
xc-xb,
The correction value of the surface B of the / BD signal 401 and the surface C of the pseudo / BD signal 1903 for yellow (Y) is
Since it is 0,
The correction value of the D side of the magenta (M) pseudo / BD signal 1902 corresponding to the B side of the / BD signal 401 is
xc-xb + 0
= Xc-xb
The time difference between the surface D of the pseudo / BD signal 1903 for yellow (Y) and the surface A of the pseudo / BD 1902 for magenta (M) is
xd-xb,
The correction value of the C surface of the / BD signal 401 and the D surface of the pseudo / BD signal 1903 for yellow (Y) is
xc−xb,
The correction value of the A side of the magenta (M) pseudo / BD signal 1902 corresponding to the C side on the side of the / BD signal 401 is
xc-xb + xd-xb
= Xc + xd-2xb
The time difference between the surface A of the pseudo / BD signal 1903 for yellow (Y) and the surface B of the pseudo / BD 1902 for magenta (M) is
xa-xb,
The correction value of the D surface of the / BD signal 401 and the A surface of the pseudo / BD signal 1903 for yellow (Y) is
xd-xb,
The correction value of the B-side of the magenta (M) pseudo / BD signal 1902 corresponding to the D-side of the / BD signal 401 is
xa-xb + xd-xb
= Xa + xd-2xb

Therefore, the pseudo / BD signal 1902 for magenta (M) is as follows.

Since the correction value of the magenta (M) pseudo / BD signal 1902 of the / BD signal 401 on the A side is xa-xb, the magenta (M) pseudo / BD signal delayed by (xa-xb) clocks from the / BD signal 401. 1902 is generated and output.

Since the correction value of the magenta (M) pseudo / BD signal 1902 of the / BD signal 401 on the B side is xc-xb, the magenta (M) pseudo / BD 1902 delayed by (xc-xb) clocks from the / BD signal 401 is obtained. Generate and output.

Since the correction value of the magenta (M) pseudo / BD signal 1902 of the / BD signal 401 on the C plane is xc + xd−2xb, the magenta (M) pseudo / BD signal delayed by (xc + xd−2xb) clocks from the / BD signal 401 1902 is generated and output.

Since the correction value of the magenta (M) pseudo / BD signal 1902 of the / BD signal 401 on the D surface is xa + xd-2xb, the magenta (M) pseudo / BD signal delayed by (xa + xd-2xb) clocks from the / BD signal 401 1902 is generated and output.

As shown in FIG. 20, in the case of the / BD signal 401, the pseudo / BD signal 1902 for magenta (M) is obtained.

A method of calculating the correction value of the pseudo / BD signal 1901 for cyan (C) will be described below.

The time difference between the plane C of the pseudo / BD 1902 for magenta (M) and the plane D of the pseudo / BD signal 1901 for cyan (C) is
xc-xb,
The correction values of the A surface of the / BD signal 401 and the C surface of the magenta (M) pseudo / BD 1902 are
xa-xb,
The correction value of the D side of the pseudo / BD signal 1901 for cyan (C) corresponding to the A side on the side of the / BD signal 401 is
xc-xb + xa-xb
= Xa + xc-2xb
The time difference between the plane D of the pseudo / BD 1902 for magenta (M) and the plane A of the pseudo / BD signal 1901 for cyan (C) is
xd-xb,
The correction value of the B surface of the / BD signal 401 and the D surface of the magenta (M) pseudo / BD 1902 is
xc−xb,
The correction value for the A side of the pseudo / BD signal 1901 for cyan (C) corresponding to the B side on the side of the / BD signal 401 is
xd-xb + xc-xb
= Xc + xd-2xb
The time difference between the surface A of the pseudo / BD 1902 for magenta (M) and the surface B of the pseudo / BD signal 1901 for cyan (C) is
xa-xb,
/ BD signal 401 and the magenta (M) pseudo / BD 1902 A surface correction value is
xc + xd-2xb, so
The correction value of the B surface of the pseudo / BD signal 1901 for cyan (C) corresponding to the C surface on the side of the / BD signal 401 is
xa-xb + xc + xd-2xb
= Xa + xc + xd-3xb
The time difference between the plane B of the pseudo / BD 1902 for magenta (M) and the plane C of the pseudo / BD signal 1901 for cyan (C) is
0,
The correction values of the D side of the / BD signal 401 and the B side of the magenta (M) pseudo / BD 1902 are
xa + xd-2xb, so
The correction value for the C-plane of the pseudo / BD signal 1901 for cyan (C) corresponding to the D-plane on the side of the / BD signal 401 is
0 + xa + xd-2xb
= Xa + xd-2xb

Therefore, the pseudo / BD signal 1901 for cyan (C) is as follows.
Since the correction value of the cyan (C) pseudo / BD signal 1901 of the / BD signal 401 on the A side is xa + xc−2xb, the cyan (C) pseudo / BD signal delayed by (xa + xc−2xb) clocks from the / BD signal 401 1901 is generated and output.

The pseudo / BD signal 1901 for cyan (C) of the / BD signal 401 on the B side has a correction value of xc + xd−2xb. Therefore, the pseudo / BD signal for cyan (C) delayed from the / BD signal 401 by (xc + xd−2xb) clocks. 1901 is generated and output.

Since the pseudo- / BD signal 1901 for cyan (C) of the / BD signal 401 on the C plane has a correction value of xa + xc + xd-3xb, the pseudo- / BD signal for cyan (C) is delayed by (xa + xc + xd-3xb) clocks from the / BD signal 401. 1901 is generated and output.

The pseudo / BD signal 1901 for cyan (C) of the / BD signal 401 on the D plane has a correction value of xa + xd−2xb, and therefore the pseudo / BD signal for cyan (C) delayed by (xa + xd−2xb) clocks from the / BD signal 401. 1901 is generated and output.

As shown in FIG. 20, in the case of the / BD signal 401, the pseudo / BD signal 1901 for cyan (C) is obtained.

As described above, in the scanning optical system of one polygon and four stations, similarly to the scanning optical system of one polygon and two stations, the BD cycle for each surface of the polygon is measured, and from the BD cycle, the side having no BD sensor is measured. By generating the BD signal (pseudo BD signal), it is possible to eliminate polygon surface division errors.

FIG. 2 is a perspective view of a scanner unit used in the first embodiment. 1 is a block diagram illustrating a configuration of a first embodiment. Sectional view showing the structure of the first embodiment. Timing chart for determining polygon surface position of ASIC internal circuit Timing chart for explaining the operation of the first embodiment Operation flowchart of the CPU according to the first embodiment Circuit block diagram of ASIC according to first and second embodiments FIG. 2 is a perspective view of a scanner unit used in the first embodiment. Timing chart for explaining the operation of the first embodiment FIG. 6 is a diagram showing the relationship between the polygon, laser, and BD sensor according to the first embodiment. FIG. 7 is a diagram showing the relationship between polygons, lasers, and BD sensors according to the second embodiment Figure of polygon mirror explaining conventional example Plot diagram of BD period illustrating a conventional example Timing chart of BD cycle illustrating a conventional example Diagram of a scanner unit illustrating a conventional example Timing chart explaining a conventional example FIG. 14 is a perspective view of a scanner unit used in the third embodiment. Sectional view showing the structure of the third embodiment. FIG. 7 is a diagram illustrating a relationship between a polygon, a laser, and a BD sensor according to the third embodiment. Timing chart for explaining the operation of the third embodiment Circuit block diagram of ASIC of Embodiment 3

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 101 Laser diode 102 Laser diode 103 Boligon mirror 106 BD sensor 203 Video controller 204 Engine controller 211 Intermediate transfer belt 212 Registration detection sensor 301 Photosensitive drum 302 Photosensitive drum

Claims (12)

A plurality of image carriers,
A plurality of light emitting elements for generating light beams for scanning the image carrier; a single polygon mirror for deflecting the light beams generated by the plurality of light emitting elements onto the image carrier; and the light beam. Detecting means for receiving a light beam scanned by the polygon mirror and generating a first synchronizing signal for recording an image on the image carrier by the light beam. An optical system including:
Storage means for storing information relating to the error of each surface of the polygon mirror,
Generating a second synchronization signal for forming an image with a light beam not provided with the detection unit by delaying the first synchronization signal output from the detection unit based on the value of the storage unit; And an image forming apparatus. The image forming apparatus according to claim 1, wherein the storage unit stores a delay amount for each surface of the polygon mirror. 3. The image forming apparatus according to claim 2, further comprising a calculating unit that calculates the delay amount by measuring an interval between the first synchronization signals generated by the detecting unit. There is a light beam that scans n planes before the plane corresponding to the detection means,
4. The image forming apparatus according to claim 3, wherein the calculating unit calculates the delay amount by measuring an interval between the first synchronization signals n planes after the first synchronization signal. 5. 4. The image forming apparatus according to claim 3, wherein the calculation unit calculates the delay amount by calculating a difference between a synchronization signal interval on each surface and a minimum value of the interval. 4. The image forming apparatus according to claim 3, wherein the calculation unit executes the measurement operation a plurality of times, and calculates the delay amount based on an average value of the measurement values. 5. 8. The image forming apparatus according to claim 7, wherein when the difference between the maximum value and the minimum value calculated by the calculation unit is larger than a predetermined value, the calculation by the calculation unit is performed again. 8. The image forming apparatus according to claim 1, wherein the image forming apparatus has a plurality of the optical systems, and forms a color image by superimposing images of a plurality of colors. Having four image carriers and two optical systems,
9. The image forming apparatus according to claim 8, wherein each of the optical systems forms an image for two colors. Having four image carriers and one optical system;
9. The image forming apparatus according to claim 8, wherein the optical system forms an image for four colors. 9. The image forming apparatus according to claim 8, further comprising detecting means corresponding to a light beam for forming a black toner image. 9. The image forming apparatus according to claim 8, wherein a detecting unit corresponding to a light beam for forming a yellow toner image is not provided.

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