Device and method for controlling timing for starting image formation, and an image forming apparatus using such device and method

A device and method for controlling timing for starting image formation, and image forming apparatus using such device and method are described. A detector outputs a synchronization detection signal when a light beam enters the detector. The timing for starting image formation is determined based on timing when a counter value, which is counted from timing when the synchronization detection signal is detected, reaches a reference counter value. The reference counter value may be determined according to an operation mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority to Japanese patent application No. 2005-318659 filed on Nov. 1, 2005, in the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The following disclosure relates generally to a device, apparatus, method, system, computer program and product, each capable of forming an image using a light beam.

DESCRIPTION OF THE RELATED ART

In an image forming apparatus, an optical writing device is provided, which modulates a light beam according to image data, and scans the modulated light beam in the main scanning direction to form an image on an image carrier. In order to improve quality of the image, timing at which the modulated light beam starts irradiating in the main scanning direction, i.e., timing for starting image formation, is usually controlled using a detector that detects the light beam. For example, the detector may be provided outside of an image formation area. The detector detects the light beam before the light beam enters the image forming area, and outputs a synchronization detection signal to a writing controller. Based on the synchronization detection signal, the writing controller instructs the optical writing device to start irradiating the modulated light beam. Accordingly, the detection accuracy of the detector is one of the factors that contribute high image quality. For this reason, various approaches are taken to increase the detection accuracy of the detector. For example, an imaging apparatus described in the Japanese Patent Application Publication No. 2004-58404 measures a time period it takes for a light beam to travel between two sensors, and determines whether a synchronization detection signal is output normally by comparing the measured time period with a reference time period.

However, the imaging apparatus described in the Japanese Patent Application Publication No. 2004-58404 does not explicitly address a case in which timing when the synchronization detection signal is detected by the writing controller is delayed relatively to timing when the light beam is detected by the detector. As shown inFIG. 1, theoretically, the detector outputs a synchronization detection signal DETP1having a square waveform at timing T1when the detector detects the light beam, for example, using a light receiving element such as a photodiode. However, in reality, the detector outputs a synchronization detection signal DETP2having a sine waveform due to the electric characteristics of the detector. Accordingly, the writing controller may detect the synchronization detection signal DETP2at timing T2after the timing T1. Thus, the delay time period Δt, which is the difference between the timing T1and the timing T2, needs to be considered when determining timing for starting image formation.

Further, the position at which the image formation is started in the image forming area, i.e., the image formation start position, may vary depending on various image forming conditions including, for example, the process speed of the image forming apparatus or the resolution of the image. In order to further improve the image quality, the timing for starting image formation may need to be changed depending on various image forming conditions to compensate the fluctuations in the image formation start position.

BRIEF SUMMARY OF THE INVENTION

Example embodiments of the present invention include an apparatus, method, system, computer program and product, each capable of controlling timing for starting image formation.

In one example, an optical writing device is provided, which includes an exposure device and a writing controller. The exposure device irradiates a light beam and scans the light beam in a main scanning direction to form an image in an image forming area. The exposure device includes a first detector provided outside of the image forming area, which outputs a first synchronization detection signal when the light beam enters the first detector. The writing controller outputs an image forming start signal for instructing the exposure device to start image formation in the image forming area. The writing controller includes a counter, which counts a time period in the main scanning direction in synchronization with a reference clock signal to generate a counter value, initializes the counter value when the first synchronization detection signal is detected by the writing controller, and causes the writing controller to output the image forming start signal when the counter value is equal to or greater than a reference counter value.

In another example, a method for controlling timing for starting image formation is provided. An optical writing device, which outputs a synchronization detection signal, is provided. A counter value, which is a time period in a main scanning direction, is counted from timing when the first synchronization detection signal is detected. When the counter value becomes equal to or greater than a reference counter value, an image forming start signal is output, which causes the optical writing device to start image formation.

In addition to the above-described device and method, the present invention may be implemented in various other ways.

DETAILED DESCRIPTION OF THE INVENTION

In describing the example embodiments illustrated in the drawings, specific terminology is employed for clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views,FIG. 2illustrates an optical writing device100and its surroundings when the optical writing device100is incorporated in an image forming apparatus, according to an example embodiment of the present invention.

In this example, the image forming apparatus is implemented as a tandem-type color image forming apparatus. The image forming apparatus ofFIG. 1includes the optical writing device100, four image forming devices20Y,20M,20C, and20K, a transfer belt2, a first transfer roller3, a second transfer roller4, a sheet tray5, a fixing device13, a first mark detector14, and a second mark detector15.

In addition to the devices shown inFIG. 2, the image forming apparatus ofFIG. 2may include other devices, for example, an operation panel400shown inFIG. 5, an image reader such as a scanner, an image processor, a sheet transfer device, etc. Referring toFIG. 5, the operation panel400includes a liquid crystal touch panel420, “Settings” key401, “COPY” key402, “DOCUMENT SERVER” key403, “PRINT” key404, “SEND” key405, ten key406, Clear and Stop (C/S) key407, Start key408, “SAVE” key409, and “RESET” key410.

Alternatively, one or more devices shown inFIG. 2may not be provided. For example, the first mark detector14or the second mark detector15may not be provided.

The image forming devices20Y,20M,20C, and20K are arranged side by side along the transfer belt2to respectively form a yellow (Y) toner image, magenta (M) toner image, cyan (C) toner image, and black (K) toner image. Since the image forming devices20Y,20M,20C, and20K are substantially similar in structure and operation, the structure and operation of the image forming device20Y are described below as an example.

The image forming device20Y includes a photoconductor6Y, a charger7Y, a developer9Y, a cleaning device10Y, and a transfer device12Y. The charger7Y uniformly charges a surface of the photoconductor6Y. An exposure device8exposes a light beam11Y onto the charged surface of the photoconductor6Y to form an electrostatic latent image of yellow color on the surface of the photoconductor6Y. The developer9Y develops the electrostatic latent image into a toner image. The transfer device12Y transfers the toner image to a transfer position, which is a nip formed between the transfer belt2and the photoconductor6Y. At the transfer position, the toner image is transferred from the surface of the photoconductor6Y to a recording sheet1being carried by the transfer belt2. The cleaning device10Y removes a residual toner remained on the surface of the photoconductor6Y after the toner image is transferred. The toner images of magenta, cyan, and black are respectively formed and transferred one above the other onto the recording sheet1in a substantially similar manner.

The transfer belt2is supported by the first and second transfer rollers3and4, and is rotated in the direction indicated by the arrow ofFIG. 2by the transfer rollers3and4. In this example, one of the transfer rollers3and4is a drive roller. The sheet tray5, which stores a plurality of recording sheets, is provided below the transfer belt2. One of the plurality of recording sheets, such as the recording sheet1, is transferred toward the transfer belt2, and carried by the transfer belt2to sequentially receive the toner images of yellow, magenta, cyan, and black.

The transfer sheet having the respective color images thereon, i.e., a full-color image, is further transferred to the fixing device13. The fixing device13fixes the full-color image onto the recording sheet1with a heat and a pressure. The recording sheet1is then discharged from the image forming apparatus.

The optical wiring device100is capable of generating the light beams11Y,11M,11C, and11K according to image data. In one example, the image data is obtained by the image reader such as the scanner, and stored in an image memory. When forming an image, the optical writing device100reads out the image data from the image memory. The optical writing device100includes the exposure device8, a filter41, and a writing controller42. The exposure device8irradiates the yellow light beam11Y to the image forming device20Y, the magenta light beam11M to the image forming device20M, the cyan light beam11C to the image forming device20C and the black light beam11K to the image forming device20K, as described below referring toFIG. 3. The exposure device8further outputs a synchronization detection signal for each color as described below referring toFIG. 4. The filter41applies filtering to the synchronization detection signal output by the exposure device8. The writing controller42controls operation of the exposure device8, for example, by outputting an image forming start signal.

Referring toFIG. 3, the exposure device8includes a first laser diode (LD)16K, a second LD17Y, a third LD27C, a fourth LD28M, a first cylinder lens18K, a second cylinder lens19Y, a third cylinder lens29C, a fourth cylinder lens30M, a first reflective mirror20K, a second reflective mirror21Y, a polygon mirror22, a first f-theta lens23KC, a second f-theta lens24YM, a first mirror25K, a second mirror26Y, a third mirror31C, a fourth mirror32M, a first cylinder mirror33KC, a second cylinder mirror34YM, a third cylinder mirror37KC, a fourth cylinder mirror38YM, a first sensor35KC, a second sensor36YM, a third sensor39KC, and a fourth sensor40YM.

In operation, the first LD16K, which is driven by an LD driver of the writing controller42, irradiates the light beam11K toward an upper surface of the polygon mirror22through the first cylinder lens18K and the first reflective mirror20K. The polygon mirror22is rotatably driven by a mirror driver of the writing controller42. With the rotation of the polygon mirror22, the light beam11K is scanned through the first f-theta lens23KC and the first mirror25K toward the photoconductor6K (FIG. 2).

Similarly, the third LD27C, which is driven by the LD driver, irradiates the light beam11C toward a lower surface of the polygon mirror22through the third cylinder lens29C. With the rotation of the polygon mirror22, the light beam11C is scanned through the first f-theta lens23KC and the third mirror31C toward the photoconductor6C (FIG. 2).

Similarly, the second LD17Y, which is driven by the LD driver, irradiates the light beam11Y toward an upper surface of the polygon mirror22through the second cylinder lens19Y and the second reflective mirror21Y. With the rotation of the polygon mirror22, the light beam11Y is scanned through the second f-theta lens24YM and the second mirror26Y toward the photoconductor6Y (FIG. 2).

Similarly, the fourth LD28M, which is driven by the LD driver, irradiates the light beam11M toward a lower surface of the polygon mirror22through the fourth cylinder lens30M. With the rotation of the polygon mirror22, the light beam11M is scanned through the second f-theta lens24YM and the fourth mirror32M toward the photoconductor6M (FIG. 2).

Further, in this example, the first sensor35KC and the first cylinder mirror33KC are provided at a first position, which is located outside of the image forming area of the black and cyan color images. The third sensor39KC and the third cylinder mirror37KC are provided at a third position, which is located outside of the image forming area of the black and cyan color images. As shown inFIG. 3, the light beams11K and11C are scanned in the direction from the first position to the third position.

In operation, the first sensor35KC detects the light beams11K and11C deflected from the polygon mirror22through the first cylinder mirror33KC to obtain first detection timing before the light beam11K enters the image forming area and first detection timing before the light beam11C enters the image forming area. The third sensor39KC detects the light beams11K and11C deflected from the polygon mirror22through the third cylinder mirror37KC to obtain second detection timing after the light beam11K leaves the image forming area and second detecting timing after the light beam11C leaves the image forming area. For example, a first synchronization detection signal output by the first sensor35KC may be divided into a first synchronization detection signal for the black color and a first synchronization detection signal for the cyan color, in a substantially similar manner as described in the U.S. Pat. No. 6,587,137, patented on Jul. 1, 2003, the entire contents of which are hereby incorporated by reference. Similarly, a second synchronization detection signal output by the third sensor39KC may be divided into a second synchronization detection signal for the black color and a second synchronization detection signal for the cyan color.

As described below referring toFIG. 4, in one example, timing for starting image formation of the cyan or black color may be controlled based on the first detection timing, or the first synchronization detection signal, obtained by the first sensor35KC. Further, the timing for starting image formation of the cyan or black color may be controlled based on the difference time period between the first detection timing obtained by the first sensor35KC and the second detection timing obtained by the third sensor39KC, using the desired two-point detection method.

The second sensor36YM and the second cylinder mirror34YM are provided at a second position, which is located outside of the image forming area of the yellow and magenta color images. The fourth sensor40YM and the fourth cylinder mirror38YM are provided at a fourth position, which is located outside of the image forming area of the yellow and magenta color images. As shown inFIG. 3, the light beams11Y and11M are scanned in the direction from the second position to the fourth position.

In operation, the second sensor36YM detects the light beams11Y and11M deflected from the polygon mirror22through the second cylinder mirror34YM to obtain first detecting timing before the light beam11Y enters the image forming area and second detecting timing before the light beam11M starts scanning the image forming area. The fourth sensor40YM detects the light beams11Y and11M deflected from the polygon mirror22through the fourth cylinder mirror38YM to obtain second detection timing after the light beam11Y leaves the image forming area and second detection timing after the light beam11M leaves the image forming area. For example, a first synchronization detection signal output by the second sensor36YM may be divided into a first synchronization detection signal for the yellow color and a first synchronization detection signal for the magenta color, in a substantially similar manner as described in the U.S. Pat. No. 6,587,137, patented on Jul. 1, 2003, the entire contents of which are hereby incorporated by reference. Similarly, a second synchronization detection signal output by the fourth sensor40YM may be divided into a second synchronization detection signal for the yellow color and a second synchronization detection signal for the magenta color.

As described below referring toFIG. 4, in one example, timing for starting image formation of the yellow or magenta color may be controlled based on the first detection timing, or the first synchronization detection signal, obtained by the second sensor36YM. Further, timing for starting image formation of the yellow or magenta color may be controlled based on the difference time period between the first detection timing obtained by the second sensor36YM and the second detection timing obtained by the fourth sensor40YM, using the desired two-point detection method.

Referring now toFIG. 4, an example structure of the optical writing device100shown inFIG. 2is explained in more detail. The optical writing device100includes the exposure device8(FIG. 3), the filter41(FIG. 2), the writing controller42(FIG. 2), an input/output interface (I/O IF)44, a multiplexer (MUX)45, an analog/digital converter (A/D)46, a demultiplexer (DMUX)48, a first low pass filter (LPF) circuit49, a second LPF circuit50, a controller47, a first edge detector51, a second edge detector52, a register53, a central processing unit (CPU)54, a read only memory (ROM)55, and a random access memory (RAM)56. Further, the optical writing device100is electrically connected to the first mark detector14(FIG. 2), the second mark detector15(FIG. 2), and the operation panel400(FIG. 5), through the I/O I/F44. The optical writing device100may be connected to other devices in the image forming apparatus ofFIG. 2.

In addition to the LD driver and the mirror driver described above referring toFIG. 3, the writing controller42may include a modulator60, a clock generator61, a main scanning counter59, and a register62. The clock generator61generates a reference clock signal. The main scanning counter59counts a time period in the main scanning direction in synchronization with the reference clock signal to generate a counter value. The modulator60modulates a light beam according to image data. The register62may store a plurality of reference counter values, which may be used by the optical writing device100as described below. The register62may additionally store a reference time period, which may be used by the optical writing device100for correcting the color registration error.

In this example, the writing controller42outputs an image forming start signal, which causes the LD16K,17Y,27C, and28M to respectively start image formation of the black color, yellow color, cyan color, and magenta color. The timing for outputting the image forming start signal for the black or cyan color is determined based on at least one of the synchronization detection signals output by the sensors35KC and37KC. The timing for outputting the image forming start signal for the yellow or magenta color is determined based on at least one of the synchronization detection signals output by the sensors36YM and40YM.

As an example, operation of determining an image forming start signal for the yellow color is explained referring toFIGS. 4 and 6. The second sensor36YM, which may be implemented by a light receiving element such as a photodiode, detects the light beam11Y when the light beam11Y enters the second sensor36YM at timing T1(FIG. 6). However, due to the electric characteristics of the second sensor36YM and/or the filter41coupled to the second sensor36YM, the second sensor36YM may output a first synchronization detection signal DETP (FIG. 6) having the sine waveform. In this example, the filter41is provided between the second sensor36YM and the writing controller42to pass a low frequency component of the DETP signal as illustrated inFIG. 6.

The writing controller42may detect the DETP signal at timing T2(FIG. 6) after the timing T1when the level of the DETP signal reaches below a threshold Th. For example, the writing controller42outputs a high level signal when the level of the DETP signal is equal to or greater than the threshold Th. The writing controller42outputs a low level signal when the level of the DETP signal is less than the threshold Th. When the low level signal is output, the writing controller42outputs a reset signal RSTS (FIG. 6).

When the reset signal RSTS is output, the main scanning counter59resets the counter value to 0 (FIG. 6), and starts counting a time period in the main scanning direction in synchronization with the reference clock signal generated by the clock generator61.

When the counter value of the main scanning counter59reaches a reference counter value M0, the writing controller42activates an image forming start signal IFSS (FIG. 6) by changing the level of the image forming start signal IFSS from high to low. When the image forming start signal IFSS is activated, the exposure device8starts image formation of the yellow color in the image forming area.

In this example, the reference counter value M0may be previously read out from the register62. For example, the plurality of reference counter values stored in the register62may correspond to a plurality of operation modes of the image forming apparatus ofFIG. 2. The writing controller42may select the reference counter value from the plurality of reference counter values according to an operation mode in which the image forming apparatus ofFIG. 2is currently operating. Alternatively, the writing controller42may select the reference counter value, which corresponds to the default operation mode of the image forming apparatus ofFIG. 2. Alternatively, the writing controller42may select the reference counter value according to an instruction received through the I/O I/F44, for example, from the operation panel400or the CPU54.

Since the timing for starting image formation is counted from the timing T2, the timing for starting image formation is not negatively affected by the delay time period Δt, which is the difference between the timing T1and the timing T2. Accordingly, the detection accuracy of the second sensor36YM may increase.

The detection accuracy of any one of the other sensors35KC,39KC, and40YM may increase in a substantially similar manner.

In one example, the detection accuracy of the sensor, which outputs the first synchronization detection signal, may be increased. For example, the first sensor35KC and the second sensor36YM may be selected. Accordingly, timing for starting image formation may be controlled based on the first synchronization detection signal.

In another example, the detection accuracy of each sensor may be increased. With the increased detection accuracy of each sensor, the registration in the main scanning direction or the magnification error may be corrected with higher accuracy, for example, using the two-point detection method. The writing controller42obtains a difference time period between the timing when the first synchronization detection signal is detected and the timing when the second synchronization detection signal is detected. The writing controller42compares the obtained difference time period with a reference difference time period, which may be obtained from the register62. Based on the comparison result, the writing controller42may control a writing clock signal using the modulator60.

However, in order to facilitate the color registration process, the delay time period Δt, which is the difference between the timing T1and the timing T2, may be set substantially equal for all four colors. For example, one or more parameters related to the delay time period Δt, such as the characteristics of each sensor, the characteristics of a filter coupled to each sensor, or the value of a threshold Th, may be set equal for all four colors.

In addition or in alternative to using the single point or two-point detection method, the registration in the main scanning direction, the registration in the sub-scanning direction, the magnification error, or the skew, may be corrected with higher accuracy, using the detection result output by the first mark detector14and/or the second mark detector15. In operation, the mark detectors14and15each detect a pattern formed on the surface of the transfer belt2, for example, by receiving light beams deflected from the surface of the transfer belt2. Upon detection, the mark detectors14and15input the voltages of the light beams to the MUX45through the I/O IF44. The MUX45outputs one of the detected voltages through a sensor channel, which is selected by the controller47, as a data signal. The A/D converter46converts the data signal from analog to digital, and outputs the digital data signal to the DMUX48. The DMUX48outputs the digital data signal to a selected one of the LPF circuits49and50. The selected one of the LPF circuit49and50attenuates a high frequency component of the digital data signal according to a cut frequency, and passes a low frequency component to the corresponding one of the edge detectors51and52. The selected one of the edge detectors51and52compares the data signal with a threshold Th1, and obtains the detected position of the pattern based on the comparison result. The detected position may be stored in the register53. From the detected position, the CPU54may further calculate the amount of registration in the main scanning direction, the amount of registration in the sub scanning direction, the amount of skew, and/or the magnification error, for example, as described in the U.S. Patent Application Publication No. 2004/041896, published on Mar. 4, 2004, the entire contents of which are hereby incorporated by reference. Any one of the values obtained by the CPU54may be sent to the writing controller42through the I/O I/F44via an address bus57and a data bus58. Using the obtained values, the writing controller42may adjust operation of the exposure device8.

Further, in this example, the timing for starting image formation may be adjusted depending on various image forming conditions to compensate the fluctuations in the first image formation position.

In one example, various image forming conditions may be organized into a plurality set of image forming parameters as illustrated inFIG. 7. The plurality set of image forming parameters may be stored in the form of table in the ROM55(FIG. 4). The image forming parameters may include, for example, the resolution of an image expressed in dots per inch (dpi), the process speed of the image forming apparatus expressed in mm/s, the rotational speed of the polygon mirror22expressed in the revolution per minute (rpm), the frequency of the clock signal used for image formation expressed in MHz, etc. As shown inFIG. 5, each set of image forming parameters shown inFIG. 7corresponds to one of the operation modes operable by the image forming apparatus shown inFIG. 2, including, for example, the high-speed mode, heavy-paper mode, and high-quality mode.

As shown inFIG. 5, a user may select one of the operation modes by touching the liquid crystal touch panel420. Further, in this example, the reference counter value M, which determines the timing for starting image formation, is stored in a corresponding manner with the set of image forming parameters. By referring to the table shown inFIG. 7, the CPU54may instruct the writing controller42to adjust the timing for starting image formation according to the operation mode through the I/O I/F44.

When the high-speed mode is selected, the image forming apparatus ofFIG. 2operates with the image resolution of 600 dpi by 600 dpi, the process speed of V0 mm/s, the mirror speed of N0 rpm, and the clock frequency of f0 MHz. With this set of image forming parameters, the reference counter value M is set to M0.

When the heavy-paper mode is selected, the image forming apparatus shown inFIG. 2operates with the image resolution of 600 dpi by 600 dpi, the process speed of V0/2 mm/s, the mirror speed of N0/2, and the clock frequency of f0/2 MHz. With this set of image forming parameters, the reference counter value M is set to M1. Since the clock frequency of the heavy-paper mode is half the clock frequency f0 of the high-speed mode, the image forming start position of the heavy-paper mode is shifted toward one end of the image forming area relative to the image forming start position of the high-speed mode. Accordingly, the reference counter value M1should be greater than the reference counter value M0by a predetermined number of image pixels.

The number of image pixels may be determined based on the difference in a number of clocks counted during the delay time period Δt. For example, referring toFIG. 6, when the high-speed mode is selected, two clocks are counted during the delay time period Δt. When the heavy-paper mode is selected, the number of clocks is reduced from two to one as the clock frequency of the heavy-paper mode is reduced by half. Accordingly, the image forming start position is shifted by one image pixel toward one end of the image forming area. To compensate this, the reference counter value M1needs to be greater than the reference counter value M0by one: M1=M0+1.

When the high-quality mode is selected, the image forming apparatus shown inFIG. 2operates with the image resolution of 1200 dpi by 1200 dpi, the process speed of V0/4 mm/s, the mirror speed of N0/2, and the clock frequency of f0. With this set of image forming parameters, the reference counter value M is set to M2. Since the resolution of the high-quality mode is twice the resolution of the high-speed mode, the size of the image pixel of the high-quality mode becomes half the size of the image pixel of the high-speed mode. For this reason, the reference counter value of the high-quality mode becomes twice the reference counter value of the high-speed mode.

Further, the image forming start position of the high-quality mode may be shifted relative to the image forming start position of the high-speed mode by a predetermined number of image pixels.

The number of image pixels may be determined based on the difference in the size of image pixels formed during the delay time period Δt. For example, referring toFIG. 6, when the high-speed mode is selected, two clocks are counted during the delay time period Δt. When the high-quality mode is selected, two clocks are counted during the delay time period Δt. However, since the pixel size of the high-quality mode is half the pixel size of the high-speed mode, the image forming start position is shifted by two 1200 dpi image pixels (or one 600 dpi image pixel) toward one end of the image forming area. To compensate this, the reference counter value M2needs to be greater than the twice of the counter value M0by two: M2=M0*2+2.

Referring now toFIG. 8, operation of controlling a reference counter value M according to an operation mode is explained according to an example embodiment of the present invention. The operation shown inFIG. 8is performed by the CPU54. For example, when a user selects one of the operation modes displayed by the operation panel400ofFIG. 5, the CPU54loads a computer program stored in the ROM onto the RAM.

In this example, the image forming apparatus shown inFIG. 2is designed to operate in the high-speed mode by default. As illustrated inFIG. 5, the “HIGH-SPEED MODE” key431is initially selected by default. However, the user may select the “SETTINGS” key401to change the default operation mode.

At S1, the CPU54determines whether the high-speed mode has been selected.

When the high-speed mode has been selected (“YES” at S1), the operation proceeds to S2. Otherwise (“NO” at S1), the operation proceeds to S3.

At S3, the CPU54determines whether the heavy-paper mode has been selected. The heavy-paper mode may be selected by pressing the “HEAVY-PAPER MODE” key432. When the heavy-paper mode has been selected (“YES” at S3), the operation proceeds to S4. Otherwise (“NO” at S3), the operation proceeds to S5.

At S2, the CPU54sets the reference counter value M to M0, and the operation ends. In one example, the CPU54may obtain the set of image forming parameters from the ROM55, and instruct the exposure device8to operate according to the image forming parameters. However, since the reference counter value M0is set by default, S2may not be performed when the mode is not changed.

At S4, the CPU54sets the reference counter value M to M1, and the operation ends. In one example, the CPU54may obtain the set of image forming parameters from the ROM55, and instruct the writing controller42to operate according to the obtained set of image forming parameters. In another example, the CPU54may calculate the reference counter value M1from the default reference counter value M0, using the equation: M1=M0+1.

At S5, the CPU54sets the reference counter value M to M2, and the operation ends. In one example, the CPU54may obtain the set of image forming parameters from the ROM55, and instruct the writing controller42to operate according to the obtained set of image forming parameters. In another example, the CPU54may calculate the reference counter value M2from the default reference counter value M0, using the equation: M2=M0*2+2.

The operation shown inFIG. 8may be performed in various other ways. For example, the steps illustrated inFIG. 8may be performed in different order. Further, the operation shown inFIG. 8is preferably performed after completing the operation of correcting the color registration or magnification described above referring toFIG. 4. In this manner, the operation of correcting can be performed in the high-speed mode, thus increasing the process speed of the image forming apparatus ofFIG. 2. Since timing for starting image formation can be set for two other operation modes based on the default operation mode, the operation of correcting the color registration is not necessary for the other two operation modes.

Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced in ways other than those specifically described herein.

In another example, the optical writing device described above may be incorporated in any kind of image forming apparatus, for example, an image forming apparatus having a revolver-type image forming device, an image forming apparatus having an intermediate transfer device, etc.

Further, as described above, any one of the above-described and other methods of the present invention may be embodied in the form of a computer program stored in any kind of storage medium. Examples of storage mediums include, but are not limited to, flexible disk, hard disk, optical discs, magneto-optical discs, magnetic tapes, involatile memory cards, ROM (read-only-memory), etc. Further, the register or the memory described above in this specification may be replaced by any desired storage device or medium.

Alternatively, any one of the above-described and other methods of the present invention may be implemented by ASIC, prepared by interconnecting an appropriate network of conventional component circuits or by a combination thereof with one or more conventional general purpose microprocessors and/or signal processors programmed accordingly.