Beam-spot position compensation method, optical scanning device, and multi-color image forming device

Abstract

In a beam-spot position compensation method for use in an optical scanning device which scans a surface of a photosensitive medium by a light beam emitted by a light source, a plurality of sections are defined by dividing a scanning region on the scanned surface. An emission timing of the light beam for every section is adjusted so that a spacing between beam-spot positions corresponding to pixels of start and end of each section is changed by a predetermined amount. The sparseness or denseness of beam-spot position spacings of the plurality of sections in the whole scanning region is compensated.

1 . A beam-spot position compensation method for use in an optical scanning device which scans a surface of a photosensitive medium by a light beam emitted by a light source, the beam-spot position compensation method comprising the steps of: 
 defining a plurality of sections by dividing a scanning region on the scanned surface;    adjusting an emission timing of the light beam for every section so that a spacing between beam-spot positions corresponding to pixels of start and end of each section is changed by a predetermined amount; and    compensating the sparseness or denseness of beam-spot position spacings of the plurality of sections in the whole scanning region.    
   
   
       2 . The beam-spot position compensation method according to  claim 1  wherein spacings between beam-spot positions of respective pixels in each section are reduced or expanded to a spacing that is considered as being a substantially equal interval.  
   
   
       3 . The beam-spot position compensation method according to  claim 1  wherein the step of compensating the sparseness or denseness of beam-spot position spacings is performed such that a deviation of the spacing between the beam-spot positions corresponding to the pixels of the start and end of each section from a predetermined target value is set to be approximately 0.  
   
   
       4 . The beam-spot position compensation method according to  claim 1  wherein the scanning region on the scanned surface is divided into the plurality of sections which have different widths respectively.  
   
   
       5 . The beam-spot position compensation method according to  claim 1  wherein the emission timing of the light beam is adjusted by shifting a phase of a pixel clock signal based on phase data which specifies a transition timing of the pixel clock signal.  
   
   
       6 . The beam-spot position compensation method according to  claim 5  wherein the step of adjusting the emission timing is performed so that spacings of phase shift pixels with respect to each section are set to have substantially equal intervals.  
   
   
       7 . The beam-spot position compensation method according to  claim 1  wherein the number of sections which are defined by dividing an effective scanning region on the scanned surface is 15 or less.  
   
   
       8 . An optical scanning device which uses a beam-spot position compensation method, comprising: 
 a light source which emits a light beam;    an optical deflector which scans a surface of a photoconductor by the light beam emitted by the light source;    a scanning/focusing optical system which focuses the light beam; and    a beam-spot position compensation unit which compensates the sparseness or denseness of beam-spot position spacing on the scanned surface, the beam-spot position compensation unit being configured to define a plurality of sections by dividing a scanning region on the scanned surface; adjust an emission timing of the light beam for every section so that a spacing between beam-spot positions corresponding to pixels of start and end of each section is changed by a predetermined amount; and compensate the sparseness or denseness of beam-spot position spacings of the plurality of sections in the whole scanning region.    
   
   
       9 . A multi-color image forming device comprising: 
 a plurality of optical scanning devices according to  claim 8;     a plurality of developing units each of which develops a toner image from an electrostatic image using one of a plurality of color toners; and    a plurality of transferring units which transfer respective toner images from the plurality of developing units to a recording medium in an integrated manner to form a color image on the recording medium.    
   
   
       10 . The multi-color image forming device according to  claim 9  wherein a beam-spot position corresponding to each pixel of a reference color which is one of multiple colors is set to a target position, and beam-spot positions corresponding to each pixel of other colors are compensated based on the target position.  
   
   
       11 . The multi-color image forming device according to  claim 10  wherein the beam-spot position corresponding to each pixel of the reference color is not compensated.  
   
   
       12 . The multi-color image forming device according to  claim 10  wherein a target value with respect to the beam-spot position corresponding to each pixel of the reference color is set so that a fixed amount of the sparseness or denseness of spacings of beam-spot positions corresponding to the respective pixels is left, and the beam-spot position corresponding to each pixel of the reference color is compensated based on the target value.  
   
   
       13 . The multi-color image forming device according to  claim 12  wherein the compensation of the beam-spot positions for the multiple colors is carried out by performing the compensation so that the beam-spot position corresponding to each pixel of the reference color is set to be a predetermined target position, and performing the compensation of the beam-spot positions corresponding to each pixel of the other colors based on a difference between each of the beam-spot positions corresponding to each pixel of the other colors and the target position of the reference color after the compensation is performed.  
   
   
       14 . The multi-color image forming device according to  claim 9  wherein division positions of the plurality of sections in the scanning region are the same for each of the multiple colors.  
   
   
       15 . The multi-color image forming device according to  claim 9  wherein, when absolute values of maximums of beam-spot position compensation remainders for the respective sections in compensating the beam-spot position corresponding to each pixel of the reference color are set to a 1 , a 2 , . . . , an, respectively, the conditions: a 1 , a 2 , . . . , an<average (a 1 , a 2 , . . . , an)×2 where average (a 1 , a 2 , . . . , an) denotes an average of the maximums a 1 , a 2 , . . . , an, are met.  
   
   
       16 . The multi-color image forming device according to  claim 9  wherein at least one of the plurality of sections includes a position in a vicinity of a local extremum in image quantity characteristics of a beam-spot position deviation defined by a difference between the beam-spot position corresponding to each pixel of the reference color and each of the beam-spot positions corresponding to the other colors.  
   
   
       17 . The multi-color image forming device according to  claim 9  wherein at least one of the plurality of sections includes a position of a local extremum in image quantity characteristics of a beam-spot position deviation defined by a difference between the beam-spot position corresponding to each pixel of the reference color and each of the beam-spot positions corresponding to the other colors, and end positions that are in a vicinity of the position of the local extremum.  
   
   
       18 . An optical scanning device which scans a surface of a photoconductive medium by a light beam emitted by a light source unit and modulated based on a pixel clock pulse, the optical scanning device comprising: 
 a detection unit which detects a full magnification factor G of a main scanning region on the surface;    a light source drive unit which varies a period of the pixel clock pulse in each of a plurality of sections of the main scanning region in accordance with a transition timing specified by a phase data; and    a magnification-factor prediction unit which predicts, based on the full magnification factor G detected, a partial magnification factor gn in each section,    wherein the phase data is set up so that a difference of the predicated partial magnification factor gn in each section and the detected full magnification factor G is compensated.    
   
   
       19 . A multi-color image forming device which includes a plurality of image supporting mediums corresponding to a plurality of colors, an optical scanning device forming an electrostatic latent image on a uniformly charged surface of each of the image supporting mediums by irradiating a light beam emitted by one of a plurality of light source units and modulated based on a pixel clock pulse, a development unit developing a toner image from each of the electrostatic latent images on the image supporting mediums, and a transferring unit transferring each of the developed images on the image supporting mediums to a printing sheet in an integrated manner to form a color image thereon, the optical scanning device comprising: 
 a detection unit which detects a full magnification factor G of a main scanning region on the surface;    a light source drive unit which varies a period of the pixel clock pulse in each of a plurality of sections of the main scanning region in accordance with a transition timing specified by a phase data; and    a magnification-factor prediction unit which predicts a partial magnification factor gn in each section,    wherein the phase data is set up so that a difference of the predicated partial magnification factor gn in each section and the detected full magnification factor G is compensated.    
   
   
       20 . The multi-color image forming device according to  claim 19  wherein the magnification-factor prediction unit predicts the partial magnification factor based on the detected full magnification factor G.  
   
   
       21 . The multi-color image forming device according to  claim 20  wherein the optical scanning device is provided so that a width of the main scanning region of each of the developed images is adjustable.  
   
   
       22 . The multi-color image forming device according to  claim 20  wherein the optical scanning device is provided so that a difference in width of the main scanning region between two of the developed images for the plurality of colors is adjustable.  
   
   
       23 . The multi-color image forming device according to  claim 19  wherein the optical scanning unit is provided so that a difference in width of the main scanning region between two of the developed images for the plurality of colors is adjustable and a difference in inclination of a main scanning direction to a sub-scanning direction is adjustable, and the magnification prediction unit predicts the partial magnification factor based on a detected amount of inclination adjustment.  
   
   
       24 . The multi-color image forming device according to  claim 19  wherein the phase data is set up for each of a predetermined number of printing sheets.  
   
   
       25 . The multi-color image forming device according to  claim 19  wherein a toner patch used to detect the full magnification factor G is formed on the transferring unit between printing pages.  
   
   
       26 . The multi-color image forming device according to  claim 19  wherein an optical detection unit for detecting the light beam in order to detect the full magnification factor G is provided at each of a start edge and an end edge of the main scanning region, and the full magnification factor G is detected based on a scanning time between the light beam detections of the optical detection units.  
   
   
       27 . The multi-color image forming device according to  claim 19  wherein a phase of the pixel clock pulse is shifted in accordance with the phase data and the shifted phase is fixed to a given phase in each section.  
   
   
       28 . The multi-color image forming device according to  claim 27  wherein phase shift pixels whose phase is shifted in accordance with the phase data are arranged at equal intervals.  
   
   
       29 . The multi-color image forming device according to  claim 27  wherein phase shift pixels whose phase is shifted in accordance with the phase data are arranged at intervals of a spacing which is given by a predetermined function formula.  
   
   
       30 . The multi-color image forming device according to  claim 19  wherein compensation of the full magnification factor G is made possible by adjusting a reference value of the pixel clock pulse.  
   
   
       31 . The multi-color image forming device according to  claim 19  wherein compensation of the full magnification factor G is made possible by adjusting a scanning speed of the light beam on each of the image supporting mediums.  
   
   
       32 . A multi-color image forming device which includes a plurality of image supporting mediums corresponding to a plurality of colors, an optical scanning device forming an electrostatic latent image on a uniformly charged surface of each of the image supporting mediums by irradiating a light beam emitted by one of a plurality of light source units and modulated based on a pixel clock pulse, a development unit developing a toner image from each of the electrostatic latent images on the image supporting mediums, and a transferring unit transferring each of the developed images on the image supporting mediums to a printing sheet in an integrated manner to form a color image thereon, the optical scanning device comprising: 
 a light source drive unit which varies a period of the pixel clock pulse in each of a plurality of sections of a main scanning region for each color in accordance with a transition timing specified by a phase data; and    a phase data setting unit which sets up the phase data so that a difference in magnification factor of the main scanning region between two of the developed images is compensated.    
   
   
       33 . The multi-color image forming device according to  claim 32  further comprising a magnification-factor detection unit which detects a magnification factor of the main scanning region or a magnification factor difference, wherein the phase data setting unit is provided to set up the phase data based on a detection value of the magnification-factor detection unit.  
   
   
       34 . The multi-color image forming device according to  claim 33  wherein the magnification-factor detection unit detects a main-scanning magnification factor in the main scanning region or a main-scanning magnification-factor difference, so that a variance of a partial magnification factor in each section of the main scanning region is distributed by a predetermined weighting function based on a detection value of the main-scanning magnification factor.  
   
   
       35 . The multi-color image forming device according to  claim 33  wherein the magnification-factor detection unit detects a main-scanning magnification factor in the main scanning region or a main-scanning magnification-factor difference, and compensates the main-scanning magnification-factor difference by adjusting the reference value of the pixel clock.  
   
   
       36 . The multi-color image forming device according to  claim 33  wherein the magnification-factor detection unit includes an optical detection unit which detects a light beam emitted by at least one light source, at a plurality of positions along the main scanning direction.  
   
   
       37 . The multi-color image forming device according to  claim 33  wherein the magnification-factor detection unit detects the main-scanning magnification factor or the main-scanning magnification-factor difference from each developed color image.  
   
   
       38 . The multi-color image forming device according to  claim 37  wherein each developed color image is a detection pattern of each color which is formed in parallel at a plurality of positions along the scanning direction of the transferring unit, and the magnification factor difference is a difference in the main scanning magnification factor with respect to a reference color.  
   
   
       39 . The multi-color image forming device according to  claim 32  wherein each section is provided by dividing the main scanning region on the scanned surface into the plurality of sections.  
   
   
       40 . The multi-color image forming device according to  claim 32  further comprising an inclination variation unit which varies the scanning line inclination of the light beam in each image supporting medium, and the phase data setting unit is provided to set up or compensate the phase data based on an amount of variation of the inclination variation unit.  
   
   
       41 . The multi-color image forming device according to  claim 32  further comprising a resist deviation compensation unit which varies an optical writing timing in the main scanning direction, and the phase data setting unit is provided to set up the phase data corresponding to each irradiation position in the main scanning direction, regardless of the optical writing timing.  
   
   
       42 . The multi-color image forming device according to  claim 32  wherein the phase data setting unit is provided to select the phase transition timing so that the transition timings of the plurality of sections are at approximately equal intervals, so that the difference in magnification factor of the main scanning region is compensated.  
   
   
       43 . The multi-color image forming device according to  claim 32  wherein the phase data setting unit is provided to select the phase transition timing for each section by using a predetermined function formula, so that the difference in magnification factor of the main scanning region is compensated.  
   
   
       44 . The multi-color image forming device according to  claim 32  wherein the phase data setting unit is provided to switch the phase data corresponding to each pixel so that the phase data between the adjoining scanning lines at a position near a boundary between two of the plurality of sections are different from each other.  
   
   
       45 . The multi-color image forming device according to  claim 32  wherein the phase data setting unit is provided to switch the phase data corresponding to each pixel so that the phase data between two of the plurality of colors integrated at a position near a boundary between two of the plurality of sections by the transferring unit are different from each other.  
   
   
       46 . An optical scanning device which includes one or more optical deflectors deflecting one or more light beams from one or more light sources, and one or more scanning/focusing optical systems focusing each deflected light beam on each of one or more surfaces of photoconductive mediums as an optical spot thereon, and the optical scanning device performing optical scanning of each of the one or more surfaces of the photoconductive mediums, comprising: 
 a scanning line compensation unit compensating an inclination of a scanning line and/or a deflection of a scanning line on the one or more scanned surfaces; and    a position-error compensation unit compensating a position error in a main scanning direction of the optical spot resulting from the compensation of the scanning line compensation unit, wherein the scanning line compensation unit is provided to mechanically vary an optical path of the deflected light beam, in order to compensate the inclination of the scanning line and/or the deflection of the scanning line, and the position-error compensation unit is provided to compensate the position error of the main scanning direction of the optical spot by adjustment of a timing of application of an image signal.    
   
   
       47 . The optical scanning device according to  claim 46  wherein the scanning line compensation unit is provided to adjust a posture of one or more optical components among optical components provided on an optical path from the optical deflector to the scanned surface, in order to compensate the inclination of the scanning line.  
   
   
       48 . The optical scanning device according to  claim 47  wherein the scanning line compensation unit is provided to adjust a posture of one or more lenses among the optical components provided on the optical path from the optical deflector to the scanned surface, and vary the optical path of the light beam in order to compensate the inclination of the scanning line.  
   
   
       49 . The optical scanning device according to  claim 47  wherein the scanning line compensation unit is provided to adjust a posture of one or more reflection mirrors among the optical components provided on the optical path from the optical deflector to the scanned surface, and vary the optical path of the light beam in order to compensate the inclination of the scanning line.  
   
   
       50 . The optical scanning device according to  claim 49  wherein the scanning line compensation unit is provided to perform the adjustment of the posture of the one or more reflection mirrors so that characteristics of the position error in the main scanning direction of the optical spot to an image quantity have one local extremum.  
   
   
       51 . The optical scanning device according to  claim 46  wherein the scanning line compensation unit is provided to deflect one or more of the optical components provided on the optical path from the optical deflector to the scanned surface, and vary the optical path of the light beam in order to compensate the deflection of the scanning line.  
   
   
       52 . The optical scanning device according to  claim 51  wherein the scanning line compensation unit is provided to deflect one or more lenses among the optical components provided on the optical path from the optical deflector to the scanned surface in the main scanning direction, and vary the optical path of the light beam.  
   
   
       53 . The optical scanning device according to  claim 51  wherein the scanning line compensation unit is provided so that one or more reflection mirrors among the optical components prepared into the optical path length from the optical deflector to the scanned surface are deflected in the main scanning direction and the optical path of the light beam is varied.  
   
   
       54 . The optical scanning device according to  claim 53  wherein the scanning line compensation unit is provided to deflect one reflection mirror in the main scanning direction and vary the optical path of the light beam, so that there are the number (n+1) of local extremums of the position error of the main scanning direction of the optical spot to image quantity with respect to the number n (≧1) of local extremums in a surface configuration of the reflection mirror.  
   
   
       55 . The optical scanning device according to  claim 46  wherein an amount of compensation of the position error of the main scanning direction of the optical spot to the image quantity in the position-error compensation unit is determined corresponding to an amount of compensation of the inclination of the scanning line and/or an amount of compensation of the deflection of the scanning line by the scanning line compensation unit.  
   
   
       56 . The optical scanning device according to  claim 46  wherein the position-error compensation unit is provided to perform the adjustment of the timing of application of the image signal by phase shifting of the clock of the image signal, in order to compensate the position error of the main scanning direction of the optical spot.  
   
   
       57 . The optical scanning device according to  claim 46  wherein the position-error compensation unit is provided to perform the adjustment of the timing of application of the image signal by changing a frequency of the clock of the image signal, in order to compensate the position error of the main scanning direction of the optical spot.  
   
   
       58 . The optical scanning device according to  claim 46  wherein the position-error compensation unit is provided to perform the adjustment of the timing of application of the image signal so that a width of an effective optical scanning is equal to a predetermined width, in order to compensate the position error of the main scanning direction of the optical spot.  
   
   
       59 . The optical scanning device according to  claim 46  wherein the position-error compensation unit is provided to perform the adjustment of the timing of application of the image signal so that spacings of the optical spots in the main scanning direction are equal intervals, in order to compensate the position error of the main scanning direction of the optical spot.  
   
   
       60 . The optical scanning device according to  claim 46  wherein the position-error compensation unit is provided to perform the position-error compensation by dividing an effective light scanning region into a plurality of sections, and the adjustment of the timing of application of the image signal for compensating the position error of the main scanning direction of the optical spot is set up for each region, and the same adjustment is performed for each region.  
   
   
       61 . An image forming device which includes a plurality of image supporting mediums corresponding to a plurality of colors, an optical scanning device forming an electrostatic latent image on a uniformly charged surface of each of the image supporting mediums by irradiating a light beam emitted by one of a plurality of light source units and modulated based on a pixel clock pulse, a development unit developing a toner image from each of the electrostatic latent images on the image supporting mediums, and a transferring unit transferring each of the developed images on the image supporting mediums to a printing sheet in an integrated manner to form a color image thereon, the optical scanning device performing optical scanning of each of the one or more surfaces of image supporting mediums and comprising: 
 a scanning line compensation unit compensating an inclination of a scanning line and/or a deflection of a scanning line on the one or more scanned surfaces; and    a position-error compensation unit compensating a position error in a main scanning direction of the optical spot resulting from the compensation of the scanning line compensation unit, wherein the scanning line compensation unit is provided to mechanically vary an optical path of the deflected light beam, in order to compensate the inclination of the scanning line and/or the deflection of the scanning line, and the position-error compensation unit is provided to compensate the position error of the main scanning direction of the optical spot by adjustment of a timing of application of an image signal.    
   
   
       62 . The image forming device according to  claim 61  wherein the scanning line compensation unit is provided to adjust a posture of one or more optical components among optical components provided on an optical path from the optical deflector to the scanned surface, in order to compensate the inclination of the scanning line.