JP2005326541A - Image forming apparatus and color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve first printout time and throughput by eliminating a pseudo BD (Beam Detect) control in the case of a monochrome mode. <P>SOLUTION: The image forming apparatus, which has the monochrome mode and a color mode, can switch the two modes and produces BDs of other colors in pseudo from a real BD of one color (black) with one BD sensor, is constituted so that the psuedo-DB control is not performed in the case of the monochrome mode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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.

  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 a polygon) and scanned on a photosensitive member. Thus, image formation is performed. A drum-shaped photoreceptor is often used and is called a photosensitive drum. When this method is applied to a color laser printer, for example, yellow (Y), magenta (M), cyan (C), A color image is formed on a sheet-like medium by superimposing four color images of black (BK). Configurations for achieving this superposition technique include the following.

  As one configuration, a first color image signal is scanned on the photosensitive drum to form a latent image, a developer is attached for visualization, this is transferred to recording paper, 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 the first 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.

  In another configuration, 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 development of different colors is performed. Visualization development is carried out with the agent, and it is sequentially transferred onto the 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, scanners, photosensitive drums and BD sensors as the image signals are required.

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

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

  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 are not aligned, is likely to occur. In particular, the latter configuration has a problem that registration of each color is difficult because each color image is formed using different scanners and photosensitive drums. Therefore, registration for each color is performed. For example, a resist detection pattern image is formed on an intermediate transfer belt (abbreviated as ITB) or an electrostatic transfer belt (abbreviated as ETB) and 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 reads a resist detection image pattern formed on the ITB or ETB with a light source and 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 sensor is used for only one light source among a plurality of light sources. Has been devised (Patent Document 2). 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 other light sources other than the light source provided with a 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.
Japanese Patent Publication No. 4-51829 JP-A-4-313776

  Among the above proposals, in Patent Document 1, the polygon mirror and the scanner motor are shared by one. However, since it is necessary to prepare a BD sensor for each color, an increase in cost is inevitable.

  Moreover, in patent document 2, since the BD sensor is made into one, cost reduction is realizable. However, regarding the BD of the light source without the 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). If the BD signal from the normal BD sensor 106 is BD1, an image is formed at a correct position by writing an image from BD1 after a predetermined timing (eg, tc) as indicated 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 after tc from BD2 (BD signal from the BD sensor 701 is set to BD2) as shown in 1603 and 1604 of FIG. By doing so, an image is formed at a correct position.

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

  However, in reality, it is impossible to make the surface division accuracy of each mirror surface of a polygon mirror the same, and there is always an error α as shown in FIG. 12 (α is usually about several tens to several hundreds of seconds). angle).

  Next, the BD cycle when such a polygon mirror is used will be introduced.

  The position of each surface of the polygon 103 as shown in FIG. 15 is (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 each time. FIG. 13 is a plot of the BD period. In FIG. 13, t1-2 indicates the time from when the BD is detected on the (1) surface of the polygon until the BD is detected on the (2) surface, and the same applies to t2-3, t3-4, and t4-1. Meaning. Δt1 indicates a difference between t1-2 and an average BD cycle (one quarter of one rotation), and Δt2, Δt3, and Δt4 have the same meaning. 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 for an ideal polygon mirror, and the lower is the BD cycle for an actual polygon mirror. The period t1-2 is shorter than the ideal BD period by Δt1. The period t2-3 is longer by Δt2 than the ideal BD period. The error accumulates to Δt1 + Δt2. (Δt1 is negative and Δt2 is positive) In this way, when the polygon makes one revolution, errors accumulate and become Δt1 + Δt2 + Δt3 + Δt4. This is equal to zero. The above is the characteristic of the BD cycle when an actual polygon mirror is used.

  Usually, since BD is always detected on each surface of the polygon, the error of each surface of the polygon is not affected, and the image writing position does not shift. However, as shown in FIG. 15, two lasers are simultaneously scanned with one polygon, a BD sensor is disposed only on one laser, and the BD detection of the other laser is detected from the BD signal of the laser with the BD sensor. , The deviation of the BD period for each surface as shown in FIG. 13 and FIG. 14 affects, and the scanning surface of the laser with BD differs from the scanning surface of the laser without BD. The image writing timing of the other is not suitable and appears as a writing position shift. In order to avoid this, it is only necessary to raise the polygon surface division error 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 manufacturing yield and is very expensive.

  In order to solve the above problem, a pseudo BD generation circuit that pseudo-generates a BD signal for a laser without a BD sensor including correction of surface division error of each surface of the polygon is provided, and the pseudo BD is formed before image formation. It has also been proposed to perform control to generate a pseudo BD signal by a generation circuit (Japanese Patent Laid-Open No. 2004-102276).

  If this method is adopted, although a slight circuit addition is required, a pseudo BD can be generated with high accuracy, so that it is possible to achieve a cost reduction without causing a positional deviation in writing.

  However, this method also has the following problems.

  That is, since pseudo BD generation control is performed before image formation, the time from the start of printing to the end, that is, the first printout time is delayed.

  Since a color laser printer normally forms a color image by superimposing four color images, four lasers are required, and a BD signal or a pseudo BD signal is required for each laser.

  However, when printing a black-and-white text document or the like, the so-called monochrome mode often has a mode in which an image is formed only with a black color.

  In this monochrome mode, only the black laser needs to be used, and other color lasers need not be used.

  An object of the present invention is to shorten the first printout time in the monochrome mode by not performing the pseudo BD control in the monochrome mode in the image forming apparatus that performs the pseudo BD generation control.

  According to the present application, means for solving the above problems are configured as follows.

A plurality of laser beam generating means as light sources for image formation;
A rotating polygon mirror that horizontally scans the laser beam by reflecting the laser beam output from the laser beam generating means simultaneously on different surfaces and rotating the laser beam at a constant speed;
A laser scanning unit that is on a laser beam scanning path of one laser beam generating unit, and that includes a laser beam detecting unit that generates a horizontal synchronization signal that serves as a reference for image writing timing when a laser beam is input;
A plurality of image carriers scanned by the laser beam;
In the image forming apparatus having a pseudo horizontal synchronization signal generating unit that generates a pseudo horizontal synchronization signal that serves as a reference for image writing timing for the laser beam generating unit without the laser beam detecting unit from the horizontal synchronization signal.
The pseudo horizontal synchronizing signal is not generated when an image is formed only by a laser beam generating unit having a laser beam detecting unit.

The pseudo horizontal synchronizing signal generating means
Measure the time interval of the horizontal synchronization signal between each surface of the rotary polygon mirror, determine the minimum value from the measurement results,
Subtracting the minimum value from the time interval to calculate the delay time for each surface,
A pseudo horizontal synchronization signal is generated after the delay time from the generation of the horizontal synchronization signal.

  The laser scanning means has two laser beam generating means, and the two laser beam generating means are configured to irradiate the rotary polygon mirror with laser beams from the same direction.

  Further, apart from the above configuration, the laser scanning unit includes two laser beam generation units, and the two laser beam generation units irradiate the rotary polygon mirror with laser beams from opposite directions. And

  Furthermore, the laser scanning means has a plurality of laser scanning means, and the laser beam generating means serves as an image forming light source for each color of yellow, magenta, cyan, and black, and superimposes the images of the respective colors to form a color image on a sheet-like medium. In the color image forming apparatus to be formed, the laser beam detecting means is on the black laser beam scanning path and does not generate a pseudo horizontal synchronizing signal when an image of only black is formed.

According to each configuration described above, since it is not necessary to perform pseudo BD generation control in the monochrome mode,
It is possible to shorten the first printout time in the monochrome mode, and it is possible to provide an image forming apparatus with excellent usability that does not cause the user to wait for a long time until the end of printing.

According to the present invention,
A plurality of laser beam generating means as light sources for image formation;
A rotating polygon mirror that horizontally scans the laser beam by reflecting the laser beam output from the laser beam generating means simultaneously on different surfaces and rotating the laser beam at a constant speed;
A laser scanning unit that is on a laser beam scanning path of one laser beam generating unit, and that includes a laser beam detecting unit that generates a horizontal synchronization signal that serves as a reference for image writing timing when a laser beam is input;
A plurality of image carriers scanned by the laser beam;
In the image forming apparatus having a pseudo horizontal synchronization signal generating unit that generates a pseudo horizontal synchronization signal that serves as a reference of image writing timing for the laser beam generating unit without the laser beam detecting unit from the horizontal synchronization signal.
At the time of image formation only by the laser beam generating means having the laser beam detecting means, the pseudo horizontal synchronizing signal is not generated.
The pseudo horizontal synchronizing signal generating means
Measure the time interval of the horizontal synchronization signal between each surface of the rotary polygon mirror, from the measurement results, find the minimum value,
Subtracting the minimum value from the time interval to calculate the delay time for each surface,
The pseudo horizontal synchronization signal is generated after the delay time from the generation of the horizontal synchronization signal.

Further, the laser scanning means has two laser beam generating means, and the two laser beam generating means are characterized by irradiating the rotary polygon mirror with the laser beam from the same direction,
Further, apart from the above configuration, the laser scanning unit includes two laser beam generation units, and the two laser beam generation units irradiate the rotary polygon mirror with laser beams from opposite directions. It was.

In addition, the laser scanning means includes a plurality of laser scanning means, and the laser beam generating means serves as an image forming light source for each color of yellow, magenta, cyan, and black, and superimposes the images of the respective colors to form a color image on a sheet-like medium. In the color image forming apparatus to be formed, the laser beam detecting means is on the black laser beam scanning path, and is configured so as not to generate a pseudo horizontal synchronizing signal at the time of black only image formation.
In the monochrome mode, it is possible to shorten the first printout time without performing pseudo BD generation control, and to provide an image forming apparatus with excellent usability that does not cause the user to wait for a long time until the end of printing.

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

(First embodiment)
Example 1 of the present invention will be described below.

  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. Reference numeral 201 denotes a laser printer, and 202 denotes a host computer. This embodiment is an example of a four-drum type color laser printer. This color laser printer includes an image forming unit 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 unit includes toner cartridges 207 to 210 having photosensitive drums 301 to 304 as image carriers, and a laser diode (corresponding to the laser beam generating element in the claims) that generates a laser beam as a light source for image exposure. It consists of scanner units 205 and 206. The toner cartridge has one for each of the four colors.

  The scanner units 205 and 206 are characterized by two common ones for yellow and magenta and one common for cyan and black. The scanner units 205 and 206 will be described in detail later.

  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, and the engine controller 204 drives laser diodes (not shown) in the scanner units 205 and 206 in accordance with the video signal, and on the photosensitive drums 301 to 304 in the toner cartridges 207 to 210. An image is formed respectively. Each of the photosensitive drums 301 to 304 is used to form an image of 301 for black, 302 for cyan, 303 for magenta, and 304 for yellow.

  The photosensitive drum is in contact with the intermediate transfer belt 211, and an image formed on the photosensitive drum of each color is transferred onto the intermediate transfer belt 211 and sequentially superimposed, thereby forming a color image.

  For each color image, a yellow (Y) image is first transferred to the intermediate transfer belt 211, and then transferred onto magenta (M), cyan (C), and black (BK) in this order to form a color image. The

  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 a charging roller 305, and a laser beam modulated by a video signal created by a video controller is scanned on the surface to form 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 at the driving timing of the registration roller 319. The color image is transferred from the intermediate transfer belt ITB 211 to the recording paper by the transfer roller 318 (secondary transfer). The recording paper onto which the image has been transferred is fixed by the fixing device 313 by heat and pressure, and then discharged onto the upper portion of the printer, the paper discharge tray 317.

  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 for each color to prevent color misregistration. 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 scanner unit 205 will be described.

  In FIG. 1, reference numerals 101 and 102 denote laser diodes, which scan the photosensitive drums 301 and 302 by 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). A polygon mirror 103 is rotated at a constant speed in the direction of arrow A in the figure by a motor (not shown), and scans while reflecting the beams from the laser diodes LD1 and LD2. The motor is controlled to rotate at a constant speed by the acceleration signal and deceleration signal of the speed control signal from the engine controller 204 and rotates.

  An optical sensor 106 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 called a BD (BeamDetect) sensor. The 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 lens groups (not shown) in order to focus on the photosensitive drum or to convert the laser beam from diffused light to parallel light.

  Usually, the video controller transmits a video signal to the engine controller after a predetermined time from detecting the output signal of the BD sensor 106. As a result, the main scanning start position of the image 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 the laser diode LD1.

  Regarding the detection of BD, since the BD sensor does not exist on the scanning path of the laser diode 102, the engine controller 204 generates the BD signal for the laser diode LD2. In the following description, the horizontal synchronization signal on the laser side that does not have the BD sensor will be referred to as a pseudo / BD signal. Details of the generation method will be described later.

  In this way, a black (BK) color image by the laser diode LD1 on the side having the BD sensor 106 is formed on the photosensitive drum 301, and cyan by the laser diode LD2 on the side not having the BD sensor 106. A color image (C) is formed on the photosensitive drum 302. The black (BK) side has a BD sensor, and the cyan (C) side has no BD sensor.

  With respect to the scanner unit 206 having the same configuration as the scanner unit 205, magenta (M) and yellow (Y) color images are formed on the photosensitive drum 303 and the photosensitive drum 304, respectively. The yellow (Y) side does not have a 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 image forming processes.

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

  An ASIC 402 and a CPU 403 are provided in the engine controller 204, and the ASIC 402 and the CPU 403 are connected by 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 position timing. ing. First, the / BD signal 401 which is a horizontal synchronizing 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 the BD period, and the CPU 403 calculates a correction value of the pseudo / BD signal from the BD period, and inputs the correction value to the ASIC through the address data bus. Then, the ASIC 402 generates a 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. Also, the image data VDO1 and VDO2 are output from the video controller 203 to the LD1 (101) and LD2 (102) of the scanner 205 at a predetermined timing after the detection by the BD sensor 106. With the image data VDO1 and VDO2, an image is formed on the intermediate transfer belt 211 and printed on a recording sheet.

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

  Next, the correction value calculation method and the pseudo BD generation method for each of the four surfaces will be described with reference to the timing chart of FIG. 5 and the relational diagram of the polygon, laser, and BD sensor of FIG.

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

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

  Since the correction value of the pseudo / BD signal of the A-side / BD signal (B-side pseudo / BD signal) is xa-xb, a pseudo / BD signal delayed by (xa-xb) from the / BD signal is generated and output. To do.

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

  Since the correction value of the pseudo / BD signal of the C-side / BD signal (D-side pseudo / BD signal) is xc-xb, a pseudo / BD signal delayed by (xc-xb) from the / BD signal is generated and output. To do.

  Since the correction value of the pseudo / BD signal of the D-side / BD signal (A-side pseudo / BD signal) is xd-xa, a pseudo / BD signal delayed by (xd-xa) from the / BD signal is generated and output. To do.

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

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

  First, the pseudo-BD control is performed using the / BD signal 401 output from the BD sensor 106 of the scanner unit 205 to the 2-bit counter 701 and the signal line of the CPU 403 and the address data bus ADDRESSDATABUS 723 of the ASIC 402 to start the pseudo BD control. The signal positive 702 for starting the operation is input, and the 2-bit counter 701 is repeatedly operated from 00 → 01 → 11 → 10 → 00 so that it can be seen which surface of the polygon 103 is irradiated with the laser. When each counter value (DATA) is 00, it is assumed that it is the A plane. When it is 01, it is the B plane, when it is 11, it is the C plane. 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 cycle from the A surface to the B surface, the seala 703 becomes the high level, and from the B surface to the C surface. When measuring the BD period, the sel 704 is at the high level, and when measuring the BD period from the C plane to the D plane, the sel 705 is at the high level, and the BD period from the D plane to the A plane is set. When measuring, the sell 706 becomes a high level.

  Next, the BD period is counted by clk 722 by a 17-bit counter 707, and when sela 703, selb 704, select 705, and sell 706 are selected, the BD period count value DATA of each surface of each polygon 103 is set to 708, 709, 710, 711. It is added 32 times. Then, in order to divide the BD cycle added 32 times by 32 and calculate the average value of one cycle, the added count values DATA01, DATA10, DATA11, DATA10 are shifted to the lower 5 bits (712), and the upper 5 Delete the bit. The count value is stored in the 17-bit registers 713, 714, 715, and 716. When the 5-bit counter 717 is used to detect that the BD cycle of each polygon 103 has been added 32 times, a BD cycle addition end signal 718 is output. The 17-bit registers 713, 714, 715, and 716 have an average value of the BD period, and when the parent 718 is output, the CPU 403 uses the ADDRESS DATABUS 723 and the BD period average values xa, xb, xc, and xd for 32 times. Can be read by the CPU. Further, since the CPU 403 can also read the parent 718 using the ADDRESS DATABUS 723, the CPU 403 reads the average values xa, xb, xc, and xd of the BD period when detecting that the parent 718 is output.

  Next, the CPU 403 inputs correction values xas, xbs, xcs, and xds corresponding to the respective polygon planes from the ADDRESS DATABUS 723 to the 8-bit register 718, 719, 720, 721 of the ASIC 402. One of the correction values is selected by “sela” 703, “selb” 704, “selc” 705, and “seld” 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 cycles of each surface of the polygon 103, but this number is not limited to this. For example, when the BD period of each surface is added every 64 times, the upper 5 bits may be deleted by shifting to the lower 6 bits.

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

  The series of operations of the CPU 403 will be described with reference to the flowchart of FIG.

  An instruction to rotate the scanner motor is given 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 the average value of the BD period of each surface of the polygon is calculated. When each of the BD periods is measured, the ASIC 402 outputs a BD period measurement end bit prior to the CPU 403.

  When the BD cycle measurement end bit "poorend" becomes true (S604), the CPU 403 reads the BD cycle average values xa, xb, xc, and xd of the polygon surfaces measured by the ASIC 402 (S605). This is the nth reading.

  Next, if the number of readings is 3 times or more, the correction value calculation of S608 is performed, and if it is 2 times or less, the process returns to S602 to measure the BD cycle again.

  If the read count is 3 times 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), and xcs calculated from the BD cycle of each surface of the polygon measured the previous (n−1) th time calculated from the BD cycle 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 period of each face of the polygon measured the previous (n-2) times. , Xcs (n-2), xds (n-2) are compared as shown below (S609), and if all are less than or equal to α, correction values xas (n), xbs (n), xcs (n) , Xds (n) are set in the ASIC correction register (S610). If even one is not less than α, the process returns to S602 to instruct to start 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 pseudo / BD signal 404 is output from the ASIC 402.

  The above is a series of operations of the CPU.

  The above is the description of the method for generating the pseudo BD signal.

  This pseudo BD generation control is performed only in the color mode, and is not performed in the mono mode.

  This will be described with reference to FIGS. 17, 18, and 19. FIG.

  FIG. 17 is a color mode timing chart, and FIG. 18 is a mono mode timing chart.

  The horizontal axis indicates the passage of time from the start of printing, and the vertical axis lists items that the printer sequentially processes from the start of printing.

  FIG. 19 is a flowchart including both a color mode and a mono mode.

  S1 in FIG. 19 is the start of printing, and corresponds to the time t0 in FIGS.

  When printing is started, the scanner motor is first activated (S2). At the same time, the fixing device is started up (S3). Thereafter, it is determined whether or not the scanner motor has reached a predetermined rotational speed (S4). Usually, the fact that the scanner motor has reached a predetermined number of revolutions is called scanner ready. When a predetermined time elapses when the scanner is not ready (S15), it is determined that the scanner has started up abnormally, and scanner startup abnormal processing is performed (S16). In the scanner startup abnormality process, usually, the printing operation is immediately stopped, and the fact that there is a failure is displayed on the display panel provided in the printer, or is notified to the host computer connected to the printer.

  When the scanner is ready, it is next determined whether the print mode is the color mode or the monochrome mode (S5 in FIG. 19, t2 in FIGS. 17 and 18).

  After this, color mode and mono mode control are separated. First, the color mode will be described, and then the mono mode will be described.

  In the color mode, pseudo BD generation control is started (S10). This control is as described above. Thereafter, pseudo BD ready is detected (S11). The pseudo BD ready means that the difference between the correction values measured at the above-mentioned n to n + 2 times is within α. When a predetermined time elapses that is not pseudo-BD ready (S13), the pseudo-BD error is determined, and pseudo-BD error processing is performed. As the pseudo BD error processing, the correction value when the pseudo BD control was performed last time is stored in the storage means, and the value is used, or a predetermined value, for example, zero is used as the correction value. Pseudo BD generation control may be performed. This is a method of notifying the display panel or the host computer of a warning without immediately stopping the printing operation because an image can be formed although the accuracy is lowered even if the pseudo BD cannot be generated correctly. In this embodiment, the processing is the same as that of the scanner startup abnormality.

  When the pseudo BD ready is reached, the high-voltage power supply is turned on (t3). The start-up of the high-voltage power supply means controlling the voltage and current of each of the high-voltage power supplies for charging, transfer, and development necessary for the electrophotographic process so that they become target values. When the startup of the high-voltage power supply is completed (t4 in FIG. 17), image formation and primary transfer of four colors of yellow (Y), magenta (M), cyan (C), and black (K) are performed (S12). This is a process in which an electrostatic latent image is formed on four drums with four lasers, visualized with four color toners, and an image is superimposed on the ITB. When this process ends (t9), secondary transfer is performed to transfer the toner image on the ITB to the recording medium (S7, t10). Thereafter, the recording medium on which the toner image is transferred is fixed as a permanent image by a fixing device controlled to a target temperature (S8, t12). When the fixing is finished (t13), the recording medium is discharged onto the paper discharge tray (t14 to t15), and the printing is finished (S17).

  On the other hand, in the mono mode, the above-described pseudo BD control is not performed, and only black (K) image formation and primary transfer are performed (S6, t8 in FIG. 18). In FIG. 18, the primary transfer of Y, M, and C is shown in parentheses at timings t5, t6, and t7. This is only described for comparison with the color mode, and no actual control is performed. After the primary transfer of only black (K) is completed (t9 in FIG. 18), the same control as in the color mode, that is, secondary transfer (S7, t10 to t11), fixing (S8, t12 to t13), and paper discharge (S9, t14 to t15) is performed, and the printing is finished (S17).

  The first printout time is the time from the start of printing until the recording medium is discharged. In the color mode, the time is from t0 to t15 in FIG. 17, and in the mono mode, the time is from t0 to t15 in FIG. As can be seen by comparing FIG. 17 and FIG. 18, in the mono mode, the time from t2 to t3 required for the pseudo BD control is lost. Accordingly, the first printout time in the mono mode is shortened.

  In the present embodiment, an example of four polygons is shown. However, it is not limited to four sides.

  It is also effective for polygons having 6 faces, 8 faces, and more faces.

(Second embodiment)
FIG. 8 shows a scanner unit according to the second embodiment. The difference from the first embodiment is that LD2 (802) is opposite to LD1 (101) and polygon 103. The laser beam from the laser diode LD1 is applied to the polygon mirror 103 simultaneously from the right side of the drawing, and the laser beam from the laser diode LD2 is applied simultaneously from the left side of the drawing. Other than that, the configuration is the same as that of the first embodiment. In this configuration, the correction value calculation method and pseudo BD generation method for each of the four surfaces will be described with reference to the timing chart of FIG. 9 and the relational diagram of the polygon, laser, and BD sensor of FIG. Again, an example of a four-sided polygon is shown.

The combined period of the A surface and the B surface of the / BD signal 401 for each surface of the polygon 103 measured by the ASIC 402 is xa_b, the combined period of the B surface and the C surface is xb_c, and the combined period of the C surface and the D surface is xc_d. , The combined period of the D and A planes is xd_a. The smallest period among these four periods is subtracted from the BD period for each surface, and the value is used as a correction value.
If the shortest BD period is xa_b,
The correction value of the C surface of the pseudo / BD signal corresponding to the A surface on the / BD signal side is
(/ Band signal combined with A and B sides)-(shortest BD cycle)
= Xa_b-xa_b
The correction value is 0.
The correction value of the D surface of the pseudo / BD signal corresponding to the B surface on the / BD signal side is
(/ B signal signal combined with B and C surfaces)-(shortest BD cycle)
= Xb_c-xa_b
The correction value is xb_c-xa_b.
The correction value of the A surface of the pseudo / BD signal corresponding to the C surface on the / BD signal side is
(/ B signal signal combined with C and D planes)-(shortest BD period)
= Xc_d-xa_b
The correction value is xc_d-xa_b.
The correction value of the B surface of the pseudo / BD signal corresponding to the D surface on the / BD signal side is
(/ The period when the D and A planes of the BD signal are combined) − (the shortest BD period)
= Xd_a-xa_b
The correction value is xd_a-xa_b.

  Since the correction value of the pseudo / BD signal of the A-side / BD signal (C-side pseudo / BD signal) is 0, the / BD signal itself is output as pseudo / BD.

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

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

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

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

  As described above, in the scanning optical system of one polygon and two stations, the BD period for each surface of the polygon is measured with a configuration in which the laser position is provided on the side opposite to the polygon on the side where the BD sensor is located. By generating a BD signal (pseudo BD signal) on the side where there is no BD sensor from the BD cycle, it is possible to eliminate the polygon surface division error.

The pseudo BD control described above is not performed in the mono mode as in the first embodiment.
The control flowchart of the present embodiment is the same as that of the first embodiment and is as shown in FIG.

  Further, the timing chart is the same as that of the first embodiment, as shown in FIGS.

  Even in the configuration of the optical system as in the present embodiment, the first printout time in the mono mode can be shortened.

The perspective view of the scanner unit used in Example 1 Block diagram showing the configuration of the first embodiment Sectional drawing which shows the structure of Example 1 Timing chart for determining the polygon surface position of the ASIC internal circuit FIG. 4 is a timing chart for explaining the operation of the first embodiment, and a relational diagram between a polygon, a laser, and a BD sensor. Operation Flowchart of CPU of Embodiment 1 ASIC circuit block diagram The perspective view of the scanner unit used in Example 1 FIG. 4 is a timing chart for explaining the operation of the first embodiment, and a relational diagram between a polygon, a laser, and a BD sensor. Relationship diagram between polygon, laser, and BD sensor of Example 1 Relationship diagram between polygon, laser, and BD sensor of Example 2 Polygon mirror diagram illustrating a conventional example Plot diagram of BD period explaining a conventional example BD cycle timing chart explaining a conventional example Diagram of a scanner unit explaining a conventional example Timing chart explaining a conventional example Timing chart explaining first printout time in color mode Timing chart explaining the first printout time in mono mode Flow chart explaining control of color mode and mono mode

Explanation of symbols

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 313 Fixing device

Claims (5)

A plurality of laser beam generating means as an image forming light source and the laser beam outputted from the laser beam generating means are simultaneously reflected on different surfaces and rotated at a constant speed to horizontally scan the laser beam. One rotating polygon mirror,
A laser scanning unit that is on a laser beam scanning path of one laser beam generating unit, and that includes a laser beam detecting unit that generates a horizontal synchronization signal that serves as a reference for image writing timing when a laser beam is input;
A plurality of image carriers scanned by the laser beam;
In the image forming apparatus having a pseudo horizontal synchronization signal generating unit that generates a pseudo horizontal synchronization signal that serves as a reference of image writing timing for the laser beam generating unit without the laser beam detecting unit from the horizontal synchronization signal.
An image forming apparatus characterized in that the pseudo horizontal synchronizing signal is not generated when an image is formed only by a laser beam generating means having a laser beam detecting means. The pseudo horizontal synchronizing signal generating means is
Measure the time interval of the horizontal synchronization signal between each surface of the rotary polygon mirror, determine the minimum value from the measurement results,
Subtracting the minimum value from the time interval to calculate the delay time for each surface,
The image forming apparatus according to claim 1, wherein a pseudo horizontal synchronization signal is generated after the delay time from the generation of the horizontal synchronization signal.   3. The image forming apparatus according to claim 1, wherein the laser scanning unit includes two laser beam generating units, and the two laser beam generating units irradiate the rotary polygon mirror with laser beams from the same direction. apparatus.   3. The image according to claim 1, wherein the laser scanning unit includes two laser beam generation units, and the two laser beam generation units irradiate the rotary polygon mirror with laser beams from opposite directions. Forming equipment.   Image forming for forming a color image on a sheet-like medium by superimposing the images of each color as a light source for image formation for each color of yellow, magenta, cyan, and black. 6. The color image forming apparatus according to claim 1, wherein the laser beam detecting means is on a black laser beam scanning path and does not generate a pseudo horizontal synchronizing signal when an image of only black is formed. apparatus.

Images