Abstract: Disclosed are a frequency modulation apparatus and a frequency modulation method for generating an image clock that is used for turning on/off a laser beam that scans an image bearing member, such as a photosensitive drum. The frequency modulation apparatus divides, into a plurality of segments for each pixel, a main scan line on an image bearing member, and calculates auxiliary clock periods based on a reference clock period and variable-magnification coefficients corresponding to the segments. Then, the frequency modulation apparatus generates image clocks for the respective segments based on an initial predesignated period value and the obtained auxiliary clock periods. Furthermore, the frequency modulation apparatus includes a detecting device for detecting a difference between a reference value stored in a memory and an actual laser irradiation location, and corrects a shift in the laser irradiation location in accordance with the detection results obtained by the detecting device.

Abstract: A high-frequency clock generating circuit generates a plurality of high-frequency clock signals having different phases. A modulation-signal generating circuit generates a pulse modulation signal based on transition timing data including data pertaining to a turn-on timing at which a state of a light source is changed from a turn-off state to a turn-on state and a turn-off timing at which the state of the light source is changed from the turn-on state to the turn-off state by inputting any one of the high-frequency clock signals for a predetermined period including the turn-on timing and the turn-off timing.

Abstract: An image forming apparatus for forming color images may include at least two or more colors, having a function of magnification correction of image size by one page unit, the image forming apparatus including: an image carrier; a polygonal mirror rotator independently provided for each color; and a controller which simultaneously conducts first control for changing rotation speed of the polygonal mirror rotator in order for changing image size in a sub-scanning direction perpendicular to a main scanning direction, and second control for correcting a correction amount for color registration error depending on magnification correction of image size, and for adjusting a rotating phase of the polygonal mirror rotator depending on the corrected correction amount for color registration error.

Abstract: An optical writing device includes a scanning unit that scans an optical beam in a main scanning direction while shifting a scanning position in a sub-scanning direction by a predetermined pitch, a clock frequency changing unit that changes a frequency of a write clock at a position in the main scanning direction, an image data processing unit that processes image data according to change in the frequency of the write clock, and a correcting unit that adds, when a pixel is removed from the image data, removed pixel to pixels corresponding to the next write clock.

Abstract: An image forming apparatus that is operable at a plurality of image forming speeds and can be constructed at low costs without adding circuits or the like. A conversion circuit converts image data into lighting patterns for turning on/off laser light on a basis of each of units of auxiliary pixels formed by dividing a pixel as an image forming element. A shift register sequentially stores lighting patterns for pixels pixel from the conversion circuit, and sequentially outputs them to a laser drive circuit. In monochrome printing, the rotational speed of a polygon motor is set to perform a printing operation. In color printing, the difference between an image forming speed for the monochrome printing and an image forming speed for the color printing is calculated, and based on the difference, the amount of insertion of pixel pieces using the shift register is determined for a printing operation.

Abstract: An image forming apparatus includes a light source, a deflector, beam detectors, a clock generator, a measurement mechanism, a frequency corrector, and a phase corrector. The light source illuminates in response to image data. The deflector deflects an optical beam into a scanning beam. The beam detectors including first and second beam detectors detect the scanning beam. The clock generator generates writing clock signals. The measurement mechanism measures a count number of the writing clock signals generated during a period between the scanning beam is detected by the first and second beam detectors. The frequency corrector corrects a frequency of the writing clock signals such that the count number measured becomes substantially equivalent to a predetermined number. The phase corrector varies a phase of the writing clock signals such that the count number is substantially constant before and after the phase of the writing clock signals is varied.

Abstract: A color image forming apparatus for forming a color image on a recording medium, includes: an image carrier; a polygon mirror; a signal forming device for forming a pseudo main scanning reference signal having a fixed cycle; and a controller for controlling image formation on a predetermined surface of the recording medium on the basis of the pseudo main scanning reference signal formed by the signal forming device and a main scanning reference signal which is formed by detecting a light beam that is scanned by the polygon mirror.

Abstract: An image forming apparatus that includes: a laser beam source; plural photoconductive members corresponding to plural colors; a modulation drive unit for performing pulse width modulation for each of colors by an image clock having a cycle of a pixel length; a single piece of polygon mirror whose reflection surfaces are disposed in a rotation direction thereof with a plurality of different inclination angles with colors; a beam detector that is disposed adjacent to the photoconductive member; and an image clock/data switching unit configured to generate the image clock of a frequency varying with the colors for making the same a color-based image magnification, and switch the image clocks generated for each of the colors in synchronization with a detection signal coming from the beam detector.

Abstract: A frequency modulation apparatus capable of reducing a peak level of a radiation noise of a characteristic frequency band due to an image clock. This frequency modulation apparatus is used in an image formation apparatus having an image bearing body to be scanned by a laser beam, and comprises an auxiliary clock calculating portion for calculating an auxiliary clock period based on a reference clock period and a modulation coefficient, and an image clock generating portion for generating the image clock in which a frequency is different at least in one portion and other portions of an image area on a main scan line to be scanned by the laser beam on said image bearing body based on the initial period value set in advance and said auxiliary clock period, and said image clock generating means perform a frequency modulation so that the frequency of said image clock changes within a predetermined fluctuation.

Abstract: An image forming apparatus includes a light source which illuminates in response to image data, and a deflector to deflect an optical beam output from the light source into a scanning beam running along a main scanning line across an image forming area in a main scanning direction. There are plurality of beam detectors to detect the scanning beam at a plurality of different positions along the main scanning line, the plurality of beam detectors including first and second beam detectors detecting the scanning beam at positions in front-end and rear-end sides, respectively, in the main scanning direction.

Abstract: A pixel clock generation circuit is disclosed, including a high frequency clock generation unit configured to generate high frequency clock, a clock modulation data generation unit configured to generate clock modulation data based on pixel clock phase data indicating timing of a transition in pixel clock. The pixel clock generation circuit further includes a modulation clock generation unit configured to modulate the frequency and phase of the high frequency clock based on the modulation data thereby to generate modulated pixel clock.

Abstract: An image forming apparatus that is capable of carrying out image formation on a recording medium such as plain paper without increasing the FCOT (First Copy Out Time) and is also capable of carrying out optimal image formation on a recording medium, such as thick paper, for which the processing speed is reduced with no registration misalignment between the leading ends of toner images and the leading end of the recording medium. An image is primarily transferred onto a rotatively driven image carrier, and the image on the image carrier is secondarily transferred onto a recording medium. An image writing reference position signal for starting image formation is issued based on the circumference of the image carrier which is the length of the image carrier in the direction of rotation thereof or based on a detected reference position on the image carrier.

Abstract: An image forming apparatus includes an intermediate transfer member position detection unit configured to detect a position of the intermediate transfer member to output an image forming operation start signal, a pattern detection unit configured to detect a registration correction pattern formed on the intermediate transfer member based on the image forming operation start signal, a misregistration variation detection unit configured to read the registration correction pattern detected by the pattern detection unit based on the image forming operation start signal and to generate a reference clock signal based on the read registration correction pattern, and a polygonal mirror drive motor control unit configured to adjust a rotation speed of the polygonal mirror drive motor based on the reference clock signal generated by the misregistration variation detection unit.

Abstract: A comparator compares a time interval between a first synchronization signal and a second synchronization signal with a target value, and outputs an error therebetween. A frequency calculator calculates a set value of a pixel clock frequency based on the error output from the comparator, and outputs a frequency specification signal for specifying a pixel clock frequency according to the calculated set value. A frequency divider divides a high frequency clock generated by a high frequency clock generator by a frequency division ratio based on the frequency specification signal output from the frequency calculator, and generates the pixel clock.

Abstract: Embodiments of the invention provide systems and methods for correcting scan position errors in an imaging system. In one embodiment of the present invention, the method includes determining an image beam velocity error as a function of a position within a scan line of an image, and using the image beam velocity error to determine a plurality of pixel clock frequencies to be respectively applied to a plurality of positions within the scan line.

Abstract: A system and method for spatially matching the output of two imaging stations in an electro-photographic device by using a second order polynomial curve and a third order polynomial curve to approximate the non-linearity errors between the two imaging stations and using the second order polynomial curve and the third order polynomial curve to modify the frequency of a pixel clock.

Abstract: An image processing apparatus which comprises a RAM acting as a shared memory for storing image data, and an image processing board, connected to the RAM through a PCI bus acting as a general-purpose bus, for performing raster conversion to the image data and performing a necessary image process to the converted data by using a line memory is provided. In this apparatus, in a case where the image processing board can not input or output the data from or to the PCI bus, it is controlled not to generate a sync signal used for a process in the image processing board, whereby a stable operation is possible in an image forming apparatus and an image processing method which include the image processing apparatus.

Abstract: In an electrophotographic (EP) device, methods and apparatus include determining a delay of one or more sensors (hsync) to accurately know when to start the process of scanning latent images. In one aspect, the sensor includes a leading and trailing edge defined along a direction of laser beam scan travel. Determining the delay includes learning a position of a laser beam on the sensor at a time when a controller connected to the sensor receives a signal from the sensor indicating the sensor is being sufficiently impinged upon by the laser beam. It also includes learning a latest possible position of the laser beam along the direction of laser scan travel where the laser beam can be turned on and still have the sensor assert a signal indicating it has been sufficiently impinged upon by the laser beam. Bi-directionally scanning EP devices are also disclosed, including controllers, photoconductors, sensors, etc.

Abstract: A transition detection circuit detects a transition of a state of a pixel clock, and outputs a detection signal according to a timing of the detected state transition. A control signal generation circuit generates a control signal according to the detection signal and phase data indicating a transition timing of the pixel clock. A pixel clock control circuit causes the state of the pixel clock to transit according to the control signal.

Abstract: A pixel clock generating apparatus includes a data offset circuit and a pixel generator. The data offset circuit defines multiple data blocks, each data block consisting of a predetermined number of successive clocks, and produces phase data for each data block. The phase data represents an amount and a direction of phase shift to be carried out for a certain clock in each data block. The pixel generator receives the phase data from the data offset circuit and generates a phase-shifted pixel clock a predetermined number of times in each data block based on the phase data.

Abstract: An optical scan device having an optical deflector reflecting a light beam from a light beam source so as to deflect the light beam and having a surface to be scanned on which information is written such that the light beam deflected by the deflector scans the surface is disclosed. Optical detectors are arranged at least in two locations, a start side of writing and an end side of writing, which locations are outside an effective writing area. A measuring part measures a scan time required by the light beam deflected by the optical deflector to scan a range between the optical detectors. A correcting part corrects each dot position of image data in the effective writing area to an arbitrary position based on a variation amount of the measured scan time.

Abstract: A high-quality image forming apparatus that is capable of accurately adjusting the size and position of an image during image formation on a second surface of a transfer material, even when there has been expansion/contraction of the transfer material due to thermal fixing after image formation on a first surface thereof, to thereby avoid image displacement during two-sided image formation and multiple image formation.

Abstract: An image forming apparatus that is capable of carrying out image formation on a recording medium such as plain paper without increasing the FCOT (First Copy Out Time) and is also capable of carrying out optimal image formation on a recording medium, such as thick paper, for which the processing speed is reduced with no registration misalignment between the leading ends of toner images and the leading end of the recording medium. An image is primarily transferred onto a rotatively driven image carrier, and the image on the image carrier is secondarily transferred onto a recording medium. An image writing reference position signal for starting image formation is issued based on the circumference of the image carrier which is the length of the image carrier in the direction of rotation thereof or based on a detected reference position on the image carrier.

Abstract: An electronic circuit is utilized to correct scan non-linearity of a raster output scanner. The circuit modulates a clock frequency to match a scan linearity error profile. Because it is a separate circuit, the exiting closed-loop clock generator does not need to be modified. The correction circuit synchronizes itself with the clock signal using a counter/subtractor phase detector, which ensures that the phase and frequency of the internal clock matches the phase and frequency of the master.

Abstract: A frequency modulation device for use in an image forming apparatus. The image formation apparatus includes an image carrier and a laser device for scanning the image carrier along a plurality of scan lines. Each scan line is divided into segments having segment boundaries in which the same segment boundary in adjacent scan lines are offset. The frequency modulation device generates frequency data for use in modulating the input image data, which is utilized by the laser device to scan the image carrier, which permits output of an electrophotograph of high image quality by suppressing segment boundaries caused by moiré fringes or color shifting to below a level at which such boundaries are not visually detectable.

Abstract: An optical scanning unit includes an optical deflector, a plurality of scanning optical systems, and a pixel-clock generating unit. A photodetector is arranged in at least two locations on a writing-start side and a writing-end side outside the writing area. The optical scanning unit measures a scanning time, and corrects respective dot positions of image data in the writing area to arbitrary positions based on an amount of fluctuation of the scanning time measured.

Abstract: Disclosed are a frequency modulation apparatus and a frequency modulation method for generating an image clock that is used for turning on/off a laser beam that scans an image bearing member, such as a photosensitive drum. The frequency modulation apparatus divides, into a plurality of segments for each pixel, a main scan line on an image bearing member, and calculates auxiliary clock periods based on a reference clock period and variable-magnification coefficients corresponding to the segments. Then, the frequency modulation apparatus generates image clocks for the respective segments based on an initial predesignated period value and the obtained auxiliary clock periods. Furthermore, the frequency modulation apparatus includes a detecting device for detecting a difference between a reference value stored in a memory and an actual laser irradiation location, and corrects a shift in the laser irradiation location in accordance with the detection results obtained by the detecting device.

Abstract: An apparatus for forming a pattern has a scanning-time setter, a time-error detector, a scanning-time corrector, a pulse data selector, and a control pulse signal generator. The scanning-time setter sets a “fine-section scanning-time” as a pass-time of the beam for each section of a series of fine sections. The time-error detector successively detects a time-error between the set fine-section scanning-time and an actually detected fine-section scanning-time for each fine section. The scanning-time corrector successively corrects the set fine-section scanning-time for each fine section on the basis of the time-error to successively generate a corrected fine-section scanning-time. The pulse data selector successively selects a set of pulse data, corresponding to the corrected fine-section scanning-time, from a series of sets of pulse data. The control-pulse signal generator successively generates a sequence of control-pulse signals in accordance with a selected set of pulse data.

Abstract: An optical scanning device includes a scanning optical system scans an image surface in a main scanning direction by focusing a deflected light beam onto the image surface as a beam spot, the scanning optical system providing an amount of linearity at an outer peripheral end of the image surface. An optical writing unit controls ON/OFF state of a light source in accordance with an image signal. A frequency dividing unit generates a secondary frequency of a pixel clock, which is equal to an initial frequency of the pixel clock divided by an integer. An electrical correction unit adjusts the secondary frequency of the pixel clock with respect to each of respective pixels included in the image signal, when the beam spot is located near the outer peripheral end of the image surface, so as to obtain uniform-velocity characteristics.

Abstract: There is described a signal controlling circuit particularly used in a printer or copier. The circuit includes a delay chain section to generate a plurality of delayed clock signals, a synchronized signal detecting section to detect a number of delay stages, a total delay time of which is equivalent to a single period of the reference clock signal, based on delayed clock signals synchronized with an index signal and are selected from the plurality of delayed clock signals, an index signal counting section to count index signals inputted into the index signal counting section, a phase shift calculating section to calculate a phase shift amount in respect to the reference clock signal, and a delayed clock selecting section to select a specific delayed clock signal out of the plurality of delayed clock signals in an alternative way, so as to output the specific delayed clock signal to an external section.

Abstract: The invention concerns an image-forming apparatus employing a clock-generating circuit, which generates dot clock pulses utilized for an image-writing section of the image-forming apparatus. The clock-generating circuit includes a digital-delay dot clock adjusting section to generate first dot clock pulses having a predetermined number of pulses within a predetermined time interval at a constant exposing range of the image-writing section, wherein each period of the first dot clock pulses is slightly increased or reduced by changing a selection for a plurality of delayed clock pulses, which are generated by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times; and a jitter suppressing section to suppress a jitter component included in the first dot clock pulses, wherein the jitter suppressing section divides the first dot clock pulses to generate second dot clock pulses, and then, multiplies the second dot clock pulses to generate the dot clock pulses.

Abstract: An apparatus for forming a pattern has a light source, a scanning unit, a memory, a pulse data selector, a control pulse signal generator, a control pulse signal generator, a writing pulse signal generator, and an optical modulator. The time-interval detector detects successively a time-interval that is a pass-time of the beam in each of a series of fine sections. The pulse data selector selects a set of pulse data, corresponding to the detected time-interval, from a series of sets of pulse data. The control pulse signal generator successively generates a sequence of control pulse signals in accordance with the selected set of pulse data.

Abstract: An apparatus for forming a pattern has a beam position detector, a fine-section scale corrector, a pulse data selector, and a control pulse signal generator. The beam position detector measures a position of the beam on a scanning-line. The fine-section scale corrector changes a scale of a series of fine-sections to a series of corrected fine-sections, in accordance with a scale-change rate, to change a scale of the pattern. The pulse data selector selects a set of pulse data, corresponding to a length of the corrected fine section that the beam passes, from a series of sets of pulse data. The control pulse signal generator successively generates a sequence of control pulse signals in accordance with the selected set of pulse data.

Abstract: High-resolution serial data can be obtained by using a costly, large-scale high-performance IC. A high resolution can be achieved without using any high-performance PLL or the like by a low-cost, simple system capable of generating a fundamental waveform on the basis of serial data synchronous with the leading and the trailing edges of a clock signal, of generating a delayed clock signals of a plurality of times by a delay device, and of superposing the fundamental waveform and the delayed clock signals.

Abstract: A system architecture for scanned non-linearity correction in a printer uses any raster output scanner having scanned non-linearity profile previously stored in memory from a test station installed with any pixel board. The pixel board includes a correction table register wherein the pixel board utilizes the scanned non-linearity profile of the raster output scanner to calculate the correction table register to correct for pixel misregistration.

Abstract: A pixel clock generation apparatus includes a detector detecting a time interval between two horizontal synchronization signals. A comparing part compares the time interval detected by the detector and a target value, and outputs the difference. A phase shift data generation part stores one or more lookup tables each storing a pattern of phase shift data for controlling a phase shift amount of a pixel clock, and reads and outputs the phase shift data from the lookup table based on the difference that is output from the comparing part. A high frequency clock generation part generates a high frequency clock. A pixel clock generation part generates the pixel clock whose phase is controlled in accordance with the phase shift data based on the high frequency clock.

Abstract: A pixel clock generating device includes a measurement unit that measures a scanning time required for scanning a length and outputs a measured value, a pixel clock generating unit that generates a pixel clock, and a reference clock generating unit that generates a reference clock having a frequency higher than the pixel clock. A phase of the pixel clock is controlled based on (i) the reference clock and (ii) a comparison result between the measured scanning time and a preset scanning time.

Abstract: An image is accurately recorded by a light beam on a PS plate wound on a drum which is rotating at a constant speed. A rotary encoder detects information of a recording position in a main scanning direction by the light beam that is emitted from an optical unit to the PS plate. Based on the detected information, a PLL circuit of a recording synchronizing signal generating unit generates an original clock. Pulses of the original clock are counted by a decimating counter, which outputs a decimating instruction to decimate a pulse from the original clock each time the count reaches a preset count. Based on the decimating instruction, a pulse is decimated from the original clock, and a decimated clock is frequency-divided at a fixed frequency-dividing ratio by a frequency divider, which outputs a pixel clock for recording the image.

Abstract: The present invention provides a pattern drawing device that enables drawing with reduced operational processing loading of the associated CPU. Thus, in a pattern drawing device for forming a plurality of tracks disposed concentrically on a substrate to produce a two-dimensional pattern, a basic pixel sequence is prepared and used repeatedly in forward (positive) and/or reverse (negative) order to produce symmetric portions of the two-dimensional pattern.

Abstract: There is described a duplex image-forming apparatus having a function of forming images onto both sides of a transfer material. The apparatus includes an image-forming section to respectively form an obverse-side image and a reverse-side image on a photoreceptor element by scanning a light beam, modulated with image signals based on pixel-clock signals and reflected from a polygon mirror rotating at an operating velocity based on polygon-clock signals; a transferring section to transfer said obverse-side image and said reverse-side image onto both surfaces of said recording sheet; a fixing section to fix the images onto both surfaces of said recording sheet; and a clock-frequency changing section to change a pixel-clock frequency, and a polygon-clock frequency, corresponding to a degree of shrinkage of said recording sheet caused by a fixing operation performed in said fixing section, at a transition time of an image-forming operation from one side to another side.

Abstract: In a pattern writing apparatus for writing a plurality of pattern blocks of LSI chips which are arrayed on a substrate, provided are a rasterization part (312) for rasterizing LSI data 931, an expansion/contraction rate calculation part 313 for obtaining the expansion/contraction rate of a substrate (9) on the basis of an image from a camera (15a), a data correction part (314) for correcting raster data (932) in accordance with the expansion/contraction rate and a data generation part (315) for generating writing data on the basis of the corrected data. From the writing data generated by the data generation part (315), an array of pattern blocks in which the width of a non-pattern region between adjacent ones of the pattern blocks is changed while the width of each pattern block is maintained is written on the substrate.

Abstract: It is intended to provide an image forming apparatus and image forming method capable of partial magnification corrections on various partial variations of magnification as well as constant and uniform positional shift regardless of any sections. A modulated image clock of a reference color (black) is generated from a clock generated at an image clock generating section 23 and an address is generated at an address generating circuit 36 basing on the modulated image clock. Output sections 30 for respective colors other than the reference color read out correction coefficients from correction coefficient memories 15 of respective colors following the address generated. Frequency modulator circuits 31 modulate image clocks in accordance with correction coefficients. PWM 33 outputs a driving pulse to a laser driver 6 basing on modulated image clocks synchronized with a reference signal 40 by synchronizer circuits 32 and inputted image data.

Abstract: In one embodiment, the present invention provides a scan line controller for use with a laser scanning device. The scan line controller includes a pulse width modulator system to receive a pulse code, including a first pulse width modulator to receive a first dot clock and a second pulse width modulator to receive a second dot clock, and to provide a video driver signal to a laser unit to provide a scan line from the video driver signal. The scan line controller further includes a space insertion/deletion unit configured to adjust a scan line length by inserting or deleting one or more delays into the first and the second dot clocks.

Abstract: A pixel clock pulse generating apparatus for use in an image forming apparatus includes high frequency clock pulse and pixel clock pulse generators. The high frequency clock pulse generator generates relatively high frequency clock pulses. The pixel clock pulse generator generates pixel clock pulses based on the phase data for instructing a transition time of pixel clock pulses and the high frequency clock pulses.

Abstract: The invention concerns a clock-generating circuit, which generates dot clock pulses for driving a light-emitting element employed in an optical-writing section of an image-forming apparatus and has a function of canceling f&thgr; property errors caused by a f&thgr; lens employed in the image-forming apparatus. The clock-generating circuit includes a digital-delay dot clock adjusting section to adjust timings of rising-edges or falling-edges of the dot clock pulses generated by changing a selection for a plurality of delayed-clock pulses, which are generated by delaying clock-pulses, outputted from a reference oscillator, in slightly different delay times; and a controlling section to control a selecting operation for the plurality of delayed clock pulses, performed in the digital-delay dot clock adjusting section, so as to compensate for f&thgr; property errors caused by the f&thgr; lens employed in the optical-writing section.

Abstract: An image forming apparatus that is capable of carrying out image formation on a recording medium such as plain paper without increasing the FCOT (First Copy Out Time) and is also capable of carrying out optimal image formation on a recording medium, such as thick paper, for which the processing speed is reduced with no registration misalignment between the leading ends of toner images and the leading end of the recording medium. An image is primarily transferred onto a rotatively driven image carrier, and the image on the image carrier is secondarily transferred onto a recording medium. An image writing reference position signal for starting image formation is issued based on the circumference of the image carrier which is the length of the image carrier in the direction of rotation thereof or based on a detected reference position on the image carrier.

Abstract: An optical scanning device includes a plurality of light sources, a drive circuit connected to the light sources to drive the light sources independently with from each other in a modulating manner, a deflector having a plurality of deflecting surfaces to deflect rays emitted from the light sources and scan imaging optical systems directing the deflected rays onto different scan surfaces respectively. The optical scanning device further includes synchronization detection means for receiving the rays before start writing onto the scan surface and outputting synchronization detection signals, delay time adjusting means for adjusting delay time, the delay time being a time period after outputting the synchronization detecting signal until starting the writing operation, and frequency adjustment means for adjusting driving frequencies of the light sources.

Abstract: Print data is resolved into pixels that each include a corresponding placement parameter. A nonlinear transfer function is applied to a width parameter for each pixel, and data is generated based on transformed width parameters and the corresponding placement parameters.

Abstract: A pixel clock generation apparatus includes a detector detecting a time interval between two horizontal synchronization signals. A comparing part compares the time interval detected by the detector and a target value, and outputs the difference. A phase shift data generation part stores one or more lookup tables each storing a pattern of phase shift data for controlling a phase shift amount of a pixel clock, and reads and outputs the phase shift data from the lookup table based on the difference that is output from the comparing part. A high frequency clock generation part generates a high frequency clock. A pixel clock generation part generates the pixel clock whose phase is controlled in accordance with the phase shift data based on the high frequency clock.

Abstract: In an image forming apparatus such as a digital copying machine using a multi-beam optical system, a printing area can be set in the unit equal to or smaller than a clock for image formation by use of a delay pulse for each light beam and the exposure position in the light beam scanning direction (main scanning direction) is always precisely controlled by selecting an optimum set value while the actual light beam position is being checked by use of a sensor.