JP5304838B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain a scan start position from being shifted or dispersed on a medium to be scanned, and to provide an image of high quality. <P>SOLUTION: The image forming device includes a laser oscillation means for oscillating a laser beam, based on a pixel clock generated by N-dividing a high-frequency clock, a laser beam deflection means for deflecting a laser beam to scan the medium to be scanned thereon by the laser beam, and a synchronization detecting means for synchronization-detecting the laser beam deflected by the laser beam deflection means. The image forming device further includes a pixel clock changing means capable of changing the number of division in every one-pixel block, and a scanning width is partially extended or contracted partially by the pixel clock changing means. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that controls and modulates the light output of a semiconductor laser used as a light source in a laser printer, a digital copying machine, or the like.

  In recent years, semiconductor lasers have been widely used as light sources for optical writing means in image forming apparatuses, optical disks, and the like because of their small size and the convenience of being able to directly perform high-speed modulation with a drive current.

  However, since the relationship between the light output intensity of the semiconductor laser and the drive current is closely dependent on the temperature, when controlling the light output intensity of the semiconductor laser, heat from the semiconductor laser and other circuit configurations is an obstacle. There was a problem.

  Therefore, as a method for eliminating the influence of the temperature dependency of the semiconductor laser, it is considered to change the drive current value in accordance with the light output intensity of the semiconductor laser.

  Prior art employing such a method includes a semiconductor laser control device disclosed in Japanese Patent Application Laid-Open No. 05-075199, a semiconductor laser drive control circuit disclosed in Japanese Patent Application Laid-Open No. 05-235446, and Japanese Patent Application Laid-Open No. 09. There is a semiconductor laser control device disclosed in Japanese Patent No. 321376.

  Each of the above prior arts constitutes a photoelectric negative feedback loop that controls the semiconductor laser at high speed by constantly comparing the light receiving current of the light receiving element that monitors the light output of the semiconductor laser and the light emission command current, and the light emission command The semiconductor laser is modulated at high speed by adding a current proportional to the current to the semiconductor laser in addition to the output current of the photoelectric negative feedback loop. By doing so, it is possible to suppress the temperature characteristics and the droop characteristics of the semiconductor laser and perform high-speed modulation.

  However, in each of the above prior arts, the linearity of the light reception current output characteristic with respect to the light input of the light receiving element is significantly deteriorated when the light output of the semiconductor laser becomes small due to the characteristic of the light receiving element that monitors the light output of the semiconductor laser. Come. For this reason, the control accuracy in the case of a low light output is deteriorated, and the light output may be larger than a predetermined light output. If such a situation occurs, the laser printer or the like will have an adverse effect such as soiling.

  Further, in each of the above prior arts, since the light output from the semiconductor laser is always controlled, the light output cannot be completely turned off to operate the control system normally. This results in offset light.

  In addition, each of the above conventional techniques requires a circuit for setting a driving current for adding a driving current to the semiconductor laser, which causes a circuit scale restriction when improving the function of a light modulation IC such as a laser printer. become.

  Furthermore, in each of the above prior arts, there is one light receiving element that individually detects the light output from each semiconductor laser. Therefore, when detecting the outputs of a plurality of lasers as in a semiconductor laser array, one light receiving element is used. Means are required for separating and detecting the light output of each semiconductor laser from the signal obtained by the element.

  In addition, the pixel clock frequency setting method using a direct synthesizer as described in Japanese Patent Laid-Open No. 11-167081 can change the frequency at high speed by changing LUT data, but the frequency is variable. Since the step and the output frequency change speed are closely intertwined with the control speed of the PLL to be connected next and the low-pass filter, there are restrictions on the overall configuration design.

  Further, in the technique disclosed in the above Japanese Patent Laid-Open No. 11-167081, the frequency increment depends on the master clock frequency and the number of bits of the LUT, so that the circuit scale is increased for fine setting, or Therefore, it is necessary to increase the master clock speed, and it is difficult to realize one chip.

  Further, in the method of adding a phase error to a PLL as described in Japanese Patent Laid-Open No. 05-207234, a frequency error of the pixel clock occurs unless the additional signal of the phase error is made very stable. This is a major limitation when integrating a digital circuit and an analog circuit into one chip.

(Schematic configuration of a conventional image forming apparatus)
Here, FIG. 22 shows a schematic configuration of an image forming apparatus according to the prior art.

  Referring to FIG. 22, in the image forming apparatus according to the present technology, the laser beam emitted from the semiconductor laser unit 2208 and reflected by the polygon mirror 2201 is scanned through the scanning lens 2202 when the polygon mirror 2201 rotates. A light spot is formed on the photosensitive member 2203 as a medium, and the photosensitive member 2203 is exposed to form an electrostatic latent image.

  The semiconductor laser unit 2208 controls the emission time of the semiconductor laser in accordance with the image data generated by the image processing unit 2204 and the image clock whose phase is set by the phase synchronization circuit 2207. As a result, the electrostatic latent image on the scanned medium is controlled. Further, the phase synchronization circuit 2207 sets the clock generated by the clock generation circuit 2206 to a phase synchronized with the photodetector that detects the light of the semiconductor laser scanned by the polygon mirror 2201.

  As described above, the laser driving circuit 2205, the phase synchronization circuit 2207, and the clock generation circuit 2206 are high in positional accuracy and interval accuracy of the electrostatic latent image formed on the scanned medium in the image forming apparatus using the laser scanning optical system. It is indispensable. For this reason, in the image forming apparatus, the same frequency as that of the image clock is required in a number of paths, causing a problem of EMI of the image forming apparatus. In addition, such a circuit configuration requires a large number of parts, leading to an increase in cost. Furthermore, as the printing speed increases, it becomes very difficult to operate the image data transfer clock at the same timing in all systems, and the image data transfer must be transferred in parallel with a slow clock. Also occurred.

  In addition, with the increase in the speed and density of laser printers, a method for achieving high speed and high density by recording using not only light from one light source but also light from a plurality of light sources is being adopted. In such a case, there are a case where a plurality of semiconductor lasers are used as a light source and a case where a semiconductor laser array in which a plurality of light emitting points are arrayed monolithically on one chip is used. This is called a multi-beam optical system, and is preferably selected from a system viewpoint.

  However, conventionally, since a light receiving element is common to all semiconductor lasers for a semiconductor laser array, it is described in Japanese Patent Laid-Open Nos. 05-075199, 05-235446, 09-321376, and the like. However, when the semiconductor laser array is used as a result, there is a problem that the cost is high.

  Further, as described in JP-A-05-075199, JP-A-05-235446, JP-A-09-321376, etc., in order to remove the influence of temperature characteristics, droop characteristics, etc. of the semiconductor laser However, there is a problem in that offset light is generated because continuous control is performed at the same time. In addition, these conventional techniques have a problem that a current setting circuit or the like is required and the circuit scale becomes large. Further, when a semiconductor laser array is used, a means for separating and detecting each light output is required.

  Further, the beam profile of a semiconductor laser is usually approximated to a Gaussian distribution, and an electrostatic latent image in an electrophotographic system is formed according to the Gaussian distribution. For this reason, the electrostatic latent image is not binary, and a portion having an analog distribution is generated as the resolution increases. This is problematic in that it is easily affected by external fluctuation factors such as fluctuations in development bias, and image density fluctuations are likely to occur.

  In addition, the pixel clock frequency setting method using a direct synthesizer as described in Japanese Patent Laid-Open No. 11-167081 can change the frequency step at high speed by changing the LUT data. The output frequency change speed is closely intertwined with the control speed of the PLL and the low-pass filter that are connected to the subsequent stage in terms of circuit, and thus involves restrictions on the overall configuration design. Further, since the frequency increment depends on the master clock frequency and the number of bits of the LUT, it is necessary to increase the circuit scale or to increase the master clock speed in order to make fine settings. It will be difficult to achieve this.

  Further, in the method of adding a phase error to a PLL as described in Japanese Patent Laid-Open No. 05-207234, a frequency error of the pixel clock occurs unless the additional signal of the phase error is made very stable. This is a major limitation when integrating a digital circuit and an analog circuit into one chip.

  In general, the scanning optical system has an incident angle and a reflection angle of a scanning light beam with respect to a polygon mirror, a scanning lens, etc., which vary depending on each scanning position. It depends on the scanning position. This causes a variation in the amount of irradiation light called shading.

  The difference in the amount of irradiation light depending on the scanning position causes density unevenness on the image and causes deterioration in image quality. Therefore, correction is required when high quality image quality is required.

  Further, in the case of a multi-beam optical system, if there is a difference in the oscillation wavelength of each light source, an exposure position shift occurs in the case of an optical system in which the chromatic aberration of the scanning lens is not corrected. As a result, the scanning width when the light spot corresponding to each light emitting source scans the scanned medium varies depending on the light emitting source and causes deterioration in image quality. Need to be corrected. As the light source here, for example, when a light source unit is configured by combining a plurality of semiconductor lasers, it indicates each semiconductor laser. For example, when a semiconductor laser array is used as a light source, it indicates a light emitting point. Further, when the light source unit is configured by combining a plurality of semiconductor laser arrays, the same problem arises and needs to be dealt with.

  In the case of a semiconductor laser array in which a plurality of light emitting points are monolithically arrayed on one chip, the position of the light emitting points may be shifted due to chip processing errors. As a result, an exposure position shift occurs, and the scanning position when the light spot corresponding to each light emitting point scans the scanned medium is shifted for each light emitting point, which causes deterioration in image quality. Furthermore, when a light source unit is configured by combining a plurality of semiconductor lasers, an exposure position shift occurs due to an assembly error during the assembly, and scanning when a light spot corresponding to each semiconductor laser scans the scanned medium. The position shifts for each semiconductor laser. This is also a factor of image quality degradation. Further, the same can be said when a light source unit is configured by combining semiconductor laser arrays.

  In addition, the variation in the distance from the rotation axis between the plurality of deflecting reflecting surfaces (the variation in the inscribed circle radius) caused by processing errors of a deflector such as a polygon scanner is a light spot that scans the surface to be scanned. Unevenness of scanning speed of (scanning beam) is generated.

  After detecting the synchronous light, a writing signal is emitted at a predetermined timing, the semiconductor laser starts to emit light, and data for one scan is sent to each light emitting source, and the latent image is formed on the scanned medium by repeating the process. As shown in FIG. At this time, due to the above factors in the deflector such as a polygon scanner, unevenness (variation) in the scanning length of each scanning line appears, and as with the writing magnification error, it is noticeable mainly at the edge of the image, and the variation in the writing end edge Appears as fluctuations at the edge of the image.

  Further, when the scanning start side and the scanning end side are compared, the timing of the light emission start can be adjusted by synchronization detection, so that the image including the scan length deviation due to the variation in the inscribed circle radius is shifted in the main scanning direction. As a result, errors on the scanning start side (synchronization side) accumulate on the scanning end side (anti-synchronization side), and fluctuations in the image end portion appear more greatly. (Fluctuation of the image occurs not only at the end edge but also at the middle image height, but the influence of the deflector on the image increases as the distance from the edge increases, and the deterioration of the image quality is conspicuous.) Image quality deterioration needs to be corrected when high quality image quality is required. This phenomenon occurs regardless of whether the light source unit is configured by combining a plurality of semiconductor lasers, a semiconductor laser array, or a combination of the two.

  In addition, it is desirable to minimize the magnification error at each position of the output image. For this reason, the scanning optical system needs to reduce the evaluation value of the deviation from the ideal scanning position called magnification error. Become. Furthermore, it is necessary to reduce an evaluation value obtained by time differentiation of a magnification error generally called linearity. In general, it is desirable that both magnification error and linearity be within ± 1%. If a higher image quality is desired, it needs to be ± 0.5% or less, and if a print-like image quality is desired, it needs to be ± 0.1% or less.

  In the case of a tandem type image forming apparatus, if the magnifications of the latent images formed on the respective scanned media are different, when the latent images are finally superimposed, the image appears as a color shift. In order to prevent this phenomenon, it is necessary to reduce the magnification error of the latent image on each scanned medium. In the case of the tandem method, the variation in scanning width is caused by the above factors, as well as the processing variation of each component for guiding each light beam to each scanned medium, the assembly arrangement error, etc. Of course, it is necessary to correct the influence of them.

  In addition, the light emitting point interval of the semiconductor laser array has a limit that can be approached due to the influence of thermal crosstalk and electrical crosstalk. In addition, it is disadvantageous in terms of cost to make several kinds of light emitting point intervals of the semiconductor laser array. However, various scanning optical systems have been developed depending on the writing density and scanning width, and the magnification of the scanning optical system is also various. Therefore, in order to obtain an arbitrary scanning pitch on the surface to be scanned, the semiconductor laser array is used by tilting the semiconductor laser array so that the pitch of the light emitting points is apparently desired in the sub-scanning direction. However, when the semiconductor laser array is tilted, the scanning start position on the surface to be scanned of the light beam emitted from each light emitting point is shifted. Even in the case of not tilting, the scanning start position on the surface to be scanned is shifted in the same manner as described above due to the positional shift of the light emitting point caused by the processing error at the time of manufacturing the semiconductor laser array. Since this becomes a factor of image quality deterioration, it is necessary to correct the scanning start position.

  Further, when a light source unit of a multi-beam optical system is configured by combining a plurality of semiconductor lasers, there is a problem that the scanning start position is shifted as in the above case, which also causes deterioration in image quality. It is necessary to correct the position.

  In the optical system design, in order to improve the quality of the output image, the performance of the optical system (reduction in curvature of field, reduction in magnification error, reduction in scanning line bending, etc.) has been achieved. There is a limit to the number of constituent elements of the optical system, the surface configuration, and the material. In order to achieve higher performance, it is necessary to increase the number of optical elements, introduce specially shaped surfaces, and use expensive optical materials, increasing the cost of optical systems, improving design difficulty, and improving processing difficulty. The problem arises. Therefore, this system reduces the design difficulty, reduces the difficulty of processing by configuring the optical system without using specially shaped surfaces, and configures the optical system without using expensive optical materials. It is necessary to reduce the cost.

  Therefore, the present invention has been made in view of the above-described problems, and an image forming apparatus that can provide a high-quality image by suppressing a shift or variation in a scanning start position on a scanned medium. The purpose is to provide.

  In order to achieve the above object, the present invention employs the following configuration.

According to the present invention, laser light oscillation means having two or more light emitting points that oscillate laser light based on a pixel clock generated by dividing a high-frequency clock by N, and a scanned medium are scanned by the laser light. A laser beam deflecting unit for deflecting the laser beam, a scanning optical system for imaging the laser beam deflected by the laser beam deflecting unit on a scanned medium, and the beam deflected by the laser beam deflecting unit Synchronous detection means for synchronously detecting laser light, and changing the pixel clock frequency division number so that the pixel clock is shortened when the scanning width is shortened, and the pixel clock is lengthened when the scanning width is increased. And a pixel clock changing unit .

  ADVANTAGE OF THE INVENTION According to this invention, the shift | offset | difference and dispersion | variation of the scanning start position on a to-be-scanned medium can be suppressed, and a quality image can be provided.

Relationship between an example of an optical modulation pulse that is not corrected according to the first embodiment of the present invention and an example of an exposure energy distribution, and an example of an optical modulation pulse that is corrected according to the first embodiment of the present invention and an exposure It is a graph which shows the relationship with an energy distribution example. 2 is a graph showing a relationship between an example of a light modulation pulse and an example of exposure energy distribution when the width of each light modulation pulse shown in FIG. 1 is shortened. It is a graph which shows the relationship between the pattern example of the light modulation pulse which is not correct | amended by the 1st Embodiment of this invention, and the exposure energy distribution example for every pattern. It is a graph which shows the relationship between the pattern example of the light modulation pulse by which correction | amendment by the 1st Embodiment of this invention was performed, and the example of exposure energy distribution for every pattern. It is a block diagram which shows the structural example of the pulse modulation apparatus 500 which produces | generates the modulation data for producing | generating the optical modulation pulse train by the 1st Embodiment of this invention. It is a figure which shows the example of the modulation data for producing | generating the optical modulation pulse (3) shown in FIG. It is a figure which shows the example of the modulation data for producing | generating the optical modulation pulse (3) shown in FIG. It is a block diagram which shows the structural example of the semiconductor laser control apparatus 800 for controlling a semiconductor laser according to the modulation data output from the pulse modulation apparatus 500 by the 1st Embodiment of this invention. (A) is a circuit diagram showing a first configuration example of the pixel clock generation circuit 900-1 according to the first embodiment of the present invention, (b) is a pixel clock generation circuit according to the first embodiment of the present invention. It is a circuit diagram which shows the 2nd structural example of 900-2. FIG. 6A is a block diagram illustrating a third configuration example of the pixel clock generation circuit 1000-1 according to the first embodiment of the present invention. FIG. 6B is a block diagram illustrating a fourth configuration example of the pixel clock generation circuit 1000-2 according to the first embodiment of the present invention. 5 is a timing chart showing signals for the pixel clock generation circuit according to the first embodiment of the present invention to control the phase of the internal clock with respect to the pixel clock in accordance with the phase Data. It is a figure which shows the example of the modulation data (Modulation Data) output from LUT507 by the 1st Embodiment of this invention. It is a figure which shows the structure of the selection table which selects the pulse of 8 phases when dividing the VCLK signal by 8 in the case of using the modulation data shown in FIG. FIG. 5A is a diagram illustrating a first configuration example of a semiconductor laser output control circuit that controls a peak value of light output intensity and a bias current of a cathode common semiconductor laser in the first embodiment of the present invention. FIG. 6B is a diagram illustrating a second configuration example of the semiconductor laser output control circuit that controls the peak value of the light output intensity and the bias current of the cathode common semiconductor laser in the first embodiment of the present invention. FIG. 6 is a diagram showing a third configuration example of the semiconductor laser output control circuit that controls the peak value of the light output intensity and the bias current of the anode common semiconductor laser in the first embodiment of the present invention. FIG. 3 is a circuit diagram showing a first configuration example of a control timing generation circuit that generates timing for controlling a semiconductor laser in the first embodiment of the present invention. FIG. 3 is a circuit diagram showing a second configuration example of a control timing generation circuit that generates timing for controlling a semiconductor laser in the first embodiment of the present invention. 1 is a block diagram showing a configuration example when a pulse modulation device, a semiconductor laser control device, a pixel clock generation circuit, a semiconductor laser output control circuit, and a control timing generation circuit provided by the first embodiment of the present invention are integrated into a single chip. It is. When the pulse modulation device, the semiconductor laser control device, the pixel clock generation circuit, the semiconductor laser output control circuit, and the control timing generation circuit provided by the first embodiment of the present invention are integrated into a single chip, a predetermined rule is used. It is a figure which shows the structural example at the time of setting it as the structure which produces | generates an optical modulation pulse. A first example in which each function of the pulse modulation device, the semiconductor laser control device, the pixel clock generation circuit, the semiconductor laser output control circuit, and the control timing generation circuit provided by the first embodiment of the present invention is realized by a program code. It is a block diagram which shows the example of a structure. A second example in which each function of the pulse modulation device, the semiconductor laser control device, the pixel clock generation circuit, the semiconductor laser output control circuit, and the control timing generation circuit provided by the first embodiment of the present invention is realized by a program code. It is a block diagram which shows the example of a structure. It is a block diagram which shows schematic structure of the image forming apparatus by a prior art. It is a timing chart which shows the signal for driving the IC chip shown in FIG. It is a figure which shows the shift | offset | difference of the light emission point position at the time of using a semiconductor laser array inclining. (A) is before tilting, and (b) is when tilting. (A) is a graph which shows the ratio of the light quantity between the image heights of the light spot which scans on a to-be-scanned surface, (b) is when the scanning light quantity on the to-be-scanned surface between each image height becomes substantially equal. It is a graph which shows the example of correction applied to. (A) is a perspective view which shows the structure of the multiple beam scanning apparatus by the 1st Embodiment of this invention. (B) is a figure which shows the structure of the light source device 10 in (a). It is a perspective view which shows the structure of the 4 beam light source unit applied in the 1st Embodiment of this invention. It is a figure which shows typically the operation | movement which scans the light spot on a to-be-scanned surface. It is a figure for demonstrating the method to discriminate | determine by which surface of a deflection | deviation reflective surface deflection scanning is carried out. It is a figure which shows the relationship between the space | interval of the several light emission point in a main scanning cross section, and the space | interval of the some light spot on a to-be-scanned surface. 1 is a block diagram showing a configuration of an image forming apparatus having a tandem configuration applied in a first embodiment of the present invention. It is a figure which shows typically the overlapping condition of an image (scanning line). (A) is an image formed by the prior art, and (b) is an image formed by the first embodiment of the present invention.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

  However, in the embodiment described below, a multi-beam optical system is used as a basis. However, the present invention is not limited to this, and even when there is only one light source, it is possible to obtain the same or more effects. In particular, the number of light sources is not limited.

  Also, when a light source unit is configured by combining a plurality of light sources, when a light source unit is configured using a semiconductor laser array, or when a multi-beam optical system is configured by combining these, a plurality of light beams are simultaneously transmitted. Since the scanning medium is scanned, variations at the scanning end portion are easily noticeable, but the present invention functions more effectively especially in such a case.

[First Embodiment]
A first embodiment of the present invention will be described in detail with reference to the drawings.

(Multiple beam scanning device)
FIG. 26 is a diagram showing a configuration of a multiple beam (multi-beam) scanning apparatus according to the present embodiment.

  In FIG. 26A, the light source unit 10 includes a light source unit having a plurality of (two in the present embodiment) light emitting units, and a coupling lens for coupling divergent light beams emitted from the respective light emitting units. It shall be. This configuration will be exemplified below with reference to FIG. In addition, the coupling lens provided in the light source unit 10 converts the divergent light beam emitted from each light emitting unit into a light beam form suitable for the subsequent optical system (for example, a parallel light beam, a weak divergent light beam, a convergent light beam, or the like). Convert. This is called coupling.

  In this embodiment, each of the coupled light beams is emitted from the light source unit 10 as a “parallel light beam”, and is brought close to the deflection reflection surface of the rotary polygon mirror 4 serving as a deflector by the cylindrical lens 3 as a line image imaging system. The image is formed in a substantially linear shape long in the main scanning direction.

  The two light beams deflected by the deflecting / reflecting surface of the rotary polygon mirror 4 pass through the imaging lenses 5 and 6 while being deflected at a constant angular velocity as the rotary polygon mirror 4 rotates at a constant speed, and are reflected by the optical path bending mirror 7. The optical path is bent. Thereafter, the image forming lenses 5 and 6 are focused as a light spot on the photosensitive surface of the photosensitive member 8 which is the substance of the surface to be scanned, and two scanning lines on the surface to be scanned are scanned. The two light spots are formed at a desired interval (scanning pitch) in the sub-scanning direction.

  The relative positional relationship between the light emitting units of the light source unit is the subordinate of the imaging system (coupling lens, cylindrical lens 4 and imaging lenses 5 and 6 in this embodiment) located between the light source unit and the surface to be scanned. It is determined so as to realize a desired scanning line pitch in accordance with the combined magnification (: M) in the scanning direction.

・ Light source unit 10
As shown in FIG. 26B, the light source unit 10 separately couples divergent light beams from the two semiconductor lasers 11 and 12 with coupling lenses 13 and 14 corresponding to the semiconductor lasers 11 and 12, respectively. The beam is combined by using the beam combining prism 15 by collimating the beam into a parallel beam. The beam combining prism 15 has a polarization separation film 15A, and the light beam from the coupling lens 13 passes through the polarization separation film 15A.

  The light beam from the coupling lens 14 is rotated by 90 degrees from the original state by the half-wave plate 16 and the light beam is sequentially reflected by the surface of the beam combining prism 15 and the polarization separation film 15A. Ejected from.

  The optical axes (indicated by chain lines) of the coupling lenses 13 and 14 are parallel to each other, and are combined into a single optical axis AX by way of the beam combining prism 15 as shown in the figure.

  In the optical device 10 shown in FIG. 26B, the vertical direction (semiconductor laser alignment direction) in the figure is the sub-scanning direction. Here, the light emitting portions 11a and 12a of the semiconductor lasers 11 and 12 are displaced in the sub-scanning direction (opposite directions) with respect to the optical axes of the corresponding coupling lenses 13 and 14, respectively. For this reason, the light beams B1 and B2 combined by the beam combining prism 15 are emitted at an angle with respect to the combined optical axis AX in the sub-scanning direction.

  However, the light source unit in the present embodiment is not limited to the one shown in FIG. 26B, and a known appropriate one can also be used. For example, a semiconductor laser array in which a plurality of light emitting units are arranged in a monolithic array may be used, and a plurality of divergent light beams emitted from the light emitting units may be coupled by a common coupling lens. Further, the light source unit may be configured by using a plurality of semiconductor laser arrays.

(Semiconductor laser array)
The light emitting point interval of the semiconductor laser array has a limit that can be approached by the influence of thermal crosstalk and electrical crosstalk. This is normally up to about 14 μm. In addition, it is disadvantageous in terms of cost to make several kinds of light emitting point intervals of the semiconductor laser array.

  However, various scanning optical systems have been developed depending on the writing density and the scanning width, and the scanning optical system also supports various magnifications. Therefore, in order to obtain an arbitrary scanning pitch on the surface to be scanned, the semiconductor laser array is tilted and used. Thereby, the pitch of the light emitting points is apparently a desired pitch in the sub-scanning direction.

  An example of this is shown in FIG. In FIG. 24, description will be made using a semiconductor laser array having four light emitting points as an example. Referring to FIG. 24, by tilting the semiconductor laser array with the light emitting point interval P by the angle θ, the pitch becomes equal to Pcos θ in the sub-scanning direction as shown in FIG. By doing so, the scanning pitch in the sub-scanning direction can be set to any desired pitch.

  However, when the semiconductor laser array is tilted, as shown in FIG. 24 (b), the light emitting point position is shifted by the distance d in the main scanning direction, so that the light beam emitted from each light emitting point is on the surface to be scanned. The scanning start position at is also shifted. As a result, a deviation occurs on the surface to be scanned in accordance with the amount multiplied by the magnification of the entire optical system in the main scanning direction.

  Even in the case of not tilting, the scanning start position on the surface to be scanned is shifted in the same manner as described above due to the positional shift of the light emitting point caused by the processing error at the time of manufacturing the semiconductor laser array.

  As described above, the deviation of the position of the light emitting point in the main scanning direction causes the deterioration of the final image quality. Therefore, it is necessary to correct the scanning start position. Hereinafter, a light source unit to which the apparatus and method for performing the correction are applied will be described with a specific configuration example.

(4-beam light source unit)
A specific configuration example of a four-beam light source unit using a total of four general-purpose semiconductor lasers will be described with reference to FIG. FIG. 27 is a perspective view of the 4-beam light source unit.

  In FIG. 27, semiconductor lasers 101 and 102 are supported by being press-fitted into mating holes (not shown) formed in parallel on the back side of a support member 103 made of aluminum die cast at intervals of about 8 mm in the main scanning direction. And arranged in a row symmetrically with respect to the first injection axis. The collimating lenses 104 and 105 are aligned at the X position so that the divergent light beams of the respective semiconductor lasers become parallel light beams, and are aligned at the Y and Z positions so as to be in a predetermined beam emission direction. It is fixed by filling the gap between the U-shaped support portions 103-1 and 103-2 formed in pairs with the UV curing adhesive. Thereby, the first light source unit is configured.

  Similarly, the second light source unit is configured by pressing the semiconductor lasers 106 and 107 into the support member 108 and fixing the collimating lenses 119 and 109 with a UV curable adhesive.

  The first or second light source unit includes a cylindrical portion (103-6 or 108-6) whose center coincides with an emission axis (first or second emission axis) arranged symmetrically with respect to the x axis, and a base member. It fixes so that it may engage with a mating hole (110-1 or 110-2) from the back side of 110. FIG. The fixing is performed by contacting the three positioning points (103-3, 103-4, 103-5, or 108-3, 108-4, 108-5) with reference to the positioning portions (103-3, 103-5). −4, 103-5, or 108-3, 108-4, 108-5) by passing a screw from the front side of the base member 110.

  The base member 110 has a plate 111 provided with apertures corresponding to the semiconductor lasers 101, 102, 106, and 107, and beams emitted from the semiconductor lasers 106 and 107 close to the optical axis of the semiconductor lasers 101 and 102. The synthesis prism 112 is supported.

  The base member 110 configured as described above is held by the holder member 113 and attached to an optical housing (not shown) that houses the scanning optical means with the center of the cylindrical portion 113-1 aligned with the optical axis of the scanning optical means. By doing so, a plurality of beams are made incident on the scanning optical means. Further, the lever 113-3 is moved up and down by the adjusting screw 115 so as to be rotatable about the cylindrical portion 113-1. As a result, the scanning line is tilted due to an arrangement error of the scanning optical system, and the beam array can be tilted in accordance with the scanning line.

  A substrate 114 on which a drive circuit for each of the semiconductor lasers 101, 102, 106, and 107 is formed is fixed to a support pillar 113-2, and the leads of the semiconductor lasers 101, 102, 106, and 107 are soldered for circuit connection. .

  However, in this embodiment, a semiconductor laser array in which a plurality of light emitting units are arranged in a monolithic array may be applied to the semiconductor laser.

  In the light source unit having a plurality of light emitting units as described above, the oscillation wavelength of each light emitting unit (or light emitting point) is different. For this reason, a phenomenon occurs in which the magnification of each scanning light that scans the surface to be scanned differs due to the chromatic aberration of the imaging lenses 5 and 6 shown in FIG.

  Similarly to the case where the semiconductor laser array is tilted, the light emitting point position is shifted in the main scanning direction. As a result, the scanning start position of the light beam emitted from each light emitting point on the surface to be scanned is shifted. Since the deviation of the scanning start position in the main scanning direction becomes the cause of the final image quality degradation as in the case where the semiconductor laser array shown in FIG. 24 is tilted, it is necessary to correct the scanning start position. There is.

  In other words, the deviation of the position of the light emitting point can be changed to “the relative position of each light emitting point of the semiconductor laser with respect to an axis orthogonal to the deflection scanning plane (main scanning plane) is different”. In such a state, that is, when there is no relative position of each light emitting point on an axis orthogonal to the changed scanning plane, the scanning start position of the light spot on the scanned surface is shifted in the main scanning direction, The writing end portion becomes rattling.

  In the above example, the semiconductor laser array is tilted, but the light emitting point on the chip of the semiconductor laser array is misaligned due to processing errors, or a light source unit is configured by combining multiple light sources The same can be said when an assembly error occurs.

(Tandem image forming apparatus)
Next, an image forming apparatus having a tandem configuration will be described with reference to FIG.

  A light beam from a light source unit (not shown) is deflected by the deflecting / reflecting surface of the rotary polygon mirror 4 serving as a deflector, and travels toward the imaging lens while being deflected at a constant angular velocity as the rotary polygon mirror 4 rotates at a constant speed. . The luminous fluxes changed at this time correspond to the number of scanned media (in FIG. 31, a total of four of 8a1, 8a2, 8b1, and 8b2). In the example of FIG. 31, there are four scanned media, so there are four light beams (A, B, C, D). However, the four light beams may be a light beam obtained by combining light beams from a plurality of light sources, or may be a plurality of light beams oscillated from a semiconductor laser array.

  The deflected light beams are distributed, and the light beams A and B are guided to the lenses 6a1 and 6a2 by the corresponding optical path bending mirrors (7a1 and 7a2) after passing through the lens 5a, respectively, and the lenses 5a and 6a1. Alternatively, it is condensed as a light spot on the scanning medium by the action of 6a2, and the surface of the scanning medium (8a1, 8a2) is scanned. Similarly, after passing through the lens 5b, the light beams C and D are guided to the lenses 6b1 and 6b2 by the corresponding optical path bending mirrors (7b1 and 7b2), respectively, and by the action of the lens 5b and the lens 6b1 or 6b2. The light is condensed as a light spot on the scanned medium, and the surface of the scanned medium (8b1, 8b2) is scanned. In the image forming apparatus having the tandem configuration according to the present embodiment, the four light beams simultaneously scan the four scanned media in this way. Each scanned medium corresponds to each color of yellow, magenta, cyan, and black. Therefore, the image forming apparatus according to the present embodiment forms each color image on each scanned medium, and finally superimposes them as one image to form a color image.

  FIG. 32 shows a schematic diagram of the final image (scanning line) overlap. In order to clarify the explanation, the scanning lines of the respective colors are illustrated separately in the sub-scanning direction, but they are actually overlapped. When correction according to the present embodiment described below is not applied, as shown in FIG. 32A, the scanning width of each scanning line occurs as variation or color misregistration. The correction according to the present embodiment is for obtaining a high-quality image in which these are superimposed as shown in FIG.

  Further, even if the scanning width of the scanning line exactly matches, if an arbitrary position on the scanning line is deviated from a desired position, the image quality is deteriorated. In order to prevent this, it is necessary for each position (dot) of the scanning line to be accurately (desired) at a desired position. That is, it is necessary to correct the magnification error at each position on the image.

  Therefore, it is desirable to minimize the magnification error at each position of the output image. Therefore, the scanning optical system needs to reduce the evaluation value of the deviation from the ideal scanning position called magnification error. It becomes. Furthermore, it is necessary to reduce an evaluation value obtained by time differentiation of a magnification error generally called linearity.

  In general, it is desirable that both magnification error and linearity be within ± 1%. If a higher image quality is desired, it needs to be ± 0.5% or less, and if a print-quality image is desired, it needs to be ± 0.1% or less.

When the predetermined time is t, a satisfactory image can be obtained by configuring so as to satisfy the following Expression 1.
(h (t) −h ₀ (t)) / h ₀ (t) <0.01 (Formula 1)
h (t): scanning length at an arbitrary position A during time t h ₀ (t): ideal scanning length at an arbitrary position A during time t Linearity shortens the time t in the above equation 1 as much as possible That is, time-differentiated and expressed by the following equation.
Linearity: (dh (t) −dh ₀ (t)) / dh ₀ (t) (Formula 2)
In general, in a scanning optical system, the incident angle and reflection angle of a scanning light beam with respect to a polygon mirror, a scanning lens, and the like vary depending on each scanning position, so that the transmittance and the reflectance vary, and the amount of irradiation light beam that scans the surface to be scanned Varies depending on the scanning position. This causes a difference between the image heights of the irradiation light amount called shading as shown in FIG. The difference in the amount of irradiation light depending on the scanning position as shown in FIG. 25A causes density unevenness on the image and causes deterioration in image quality. Therefore, correction is performed when high quality image quality is required. There is a need.

  FIG. 25A is a graph showing the ratio of the amount of light between the image heights of the light spots scanned on the surface to be scanned. In FIG. 25A, the peak light quantity is 1, and the scanning light quantity at each image height is shown as a ratio to the light quantity.

  In the case of a multi-beam optical system having a plurality of light emitting points, there are various variations depending on the configuration, such as the location of the optical element through which each scanning light beam passes while traveling toward the scanned medium, the polarization direction of each scanning light beam being different However, regarding the ratio of the light quantity of each image height, there may be a slight difference in the light quantity even if the image height is the same as shown by the solid line and the alternate long and short dash line in FIG. Thus, if there is a difference in the scanning light amount of each scanning line at the same image height, for example, when the optical system is used in a color machine, the difference in the light amount appears remarkably in the image, causing deterioration in image quality. .

  Therefore, it is necessary to perform correction so that the amount of scanning light on the surface to be scanned between the image heights is substantially equal. As the correction amount, as shown in FIG. 25B, when the solid line is the scanning light amount on the surface to be scanned, the light emission of the light source is increased so that the light amount where the light amount is reduced is increased as indicated by the broken line. Control the output.

In FIG. 25B, when the light quantity at the lowest place is I (A) and the light quantity at the highest place is I (A + B), if the correction amount is Δ, the following expression 3 is satisfied. A relationship is established.
Δ = I (A + B) / I (A) (Formula 3)
Correction can be performed by causing the light source to emit light at a value obtained by multiplying the light emission output by the correction amount Δ satisfying Equation 3.

  The difference in scanning light amount between image heights basically differs depending on the scanning optical system, but there is no significant difference between the same optical systems (between units). Therefore, the difference in the amount of scanning light between the image heights can be stored in advance as data, and correction can be performed using the stored data (shading data).

  For example, in the circuit for controlling the peak value of the optical output intensity and the bias current of the semiconductor laser shown in FIG. 14B, the shading data is calculated data that is the output of the D / A 1401 based on the pixel data of each line. It changes like the wavy line of (b) of FIG. Thereby, the correction of the present embodiment is performed.

(Example of light modulation pulse and exposure energy distribution)
Hereinafter, the relationship between the light modulation pulse and the exposure energy distribution when the correction according to the first embodiment of the present invention is not performed and when the correction is performed will be described with reference to FIGS.

  In FIG. 1, (4) is an example of a light modulation pulse when correction according to the present embodiment is not performed. In addition, the exposure energy distribution when the beam profile has a Gaussian distribution in the optical system in which the semiconductor laser beam is collimated by the collimator lens and then imaged on the surface of the photoreceptor through the scanning optical system is shown in (2). Show. On the other hand, in the case of performing correction according to the present embodiment, the light modulation pulse has a pattern as shown in (3), and the exposure energy distribution by the same optical system when exposed with the pattern is as shown in (1).

  FIG. 2 is an example in which the width of the modulated light pulse (4) is narrower than that in FIG. 1, and the pattern of the light modulated pulse (3) when the correction according to the present embodiment is performed, and this Also shown is an exposure energy distribution (1) in the case of exposure with a pattern of light modulation pulses (3).

  Further, an example of the exposure energy distribution ((2) in FIG. 1 or FIG. 2) when the width of the light modulation pulse ((4) in FIG. 1 or FIG. 2) without correction according to the present embodiment is sequentially changed. 3 is an example of the exposure energy distribution ((1) in FIG. 1 or FIG. 2) when the exposure is performed by the light modulation pulse ((3) in FIG. 1 or FIG. 2) changed by the correction according to the present embodiment. ) Is shown in FIG.

  The light modulation pulse pattern according to the present embodiment shown in FIG. 4 is a combination of a thin first symmetrical light pulse train as shown in (3) of FIG. 2 and a second pulse that emits light at the center of the entire pulse. It is made up of more.

  Here, when narrowing the width of the exposure energy distribution, the interval between the first pulses is narrowed. In the case of widening, the interval between the first pulses is widened, and the second pulse suppresses the decrease in the light emission amount at the center of the exposure energy distribution.

  As can be seen from the above, by exposing with the light modulation pulse of this embodiment, a steep exposure energy distribution close to the case where the light beam diameter is reduced by about 20% can be obtained. Further, by correcting in this way, in the present embodiment, the surface potential distribution similar to that obtained when the beam diameter is made narrower can be obtained in the photoreceptor surface potential distribution. ) Can be obtained.

  In the present embodiment, the modulation of the laser beam has been described by taking the scanning optical system as an example. However, the object to be irradiated with the laser light is rotating (for example, an optical disc). Even this is an effective method.

(Configuration example of pulse modulator)
FIG. 5 shows a block diagram of a configuration example of a pulse modulation device (Pulse-Modulation-Unit) 500 that generates modulation data (Modulation Data) for generating an optical modulation pulse train as described above.

  Referring to FIG. 5, a pulse modulation apparatus 500 according to this configuration example includes a phase detector 501, a loop filter 502, a VCO 503, an 8 bit shift register 505, and a 1/8 (frequency divider circuit) constituting a PLL (Phase-Locked-Loop). ) 504, a flip-flop (FF) 506 to which image data and a clock signal are input, and an LUT (Look-up-up-up-) that outputs modulation data based on the image data and the VCLK signal input from the VCO 503 table) 507.

  In FIG. 5, a Clock signal is a clock for transferring image data. The image data is 8-bit data, is converted into data corresponding to the modulation pulse train by the LUT 507, and is loaded into the 8-bit-Shift-Register 505 in response to the Load signal. On the other hand, a VCLK signal having a frequency eight times that of the Clock signal is generated by the Phase-Detector 501, Loop-Filter 502, VCO 503 and 1/8 (frequency divider circuit) 504, and modulation data is generated in the LUT 507 in accordance with this VCLK signal. And output.

  In this way, the optical modulation pulse of (3) in FIG. 2 is generated by the modulation data as shown in FIG. 6, and the optical modulation pulse of (3) in FIG. 1 is modulated as shown in FIG. Generated by data.

  Further, by adopting a configuration in which the image data is converted by the LUT 507 in the present embodiment, even when the laser scanning optical system is changed, only the contents of the LUT 507 are changed, and the same circuit as shown in FIG. 1 or FIG. It is possible to freely select a light modulation pulse.

  In this configuration example, with the above configuration, a light modulation pulse with a high degree of freedom can be generated, and an image with good graininess can be obtained by the light modulation pulse generation according to this configuration.

(Configuration example of semiconductor laser controller)
FIG. 8 shows a configuration example of a semiconductor laser control device (LD-Control-Unit) 800 for controlling and modulating the semiconductor laser in accordance with the modulation data from the Pulse-Modulation-Unit 500 shown in FIG. .

  Referring to FIG. 8, the LD-Control-Unit 800 according to this configuration example includes the Pulse-Modulation-Unit 500 shown in FIG. 5, the control circuit 802 to which Modulation Data output from the Pulse-Modulation-Unit 500 is input, and the control. A modulation signal generation circuit 803 that outputs a modulation signal based on a control voltage output from the circuit 802 and Modulation Data output from the Pulse-Modulation-Unit 500, a differential amplifier 804, an LD drive transistor 808, and a semiconductor laser (LD) 806, light receiving element (PD) 807, resistor (RE) 808, variable resistor (REXT) 809, and capacitors (Hold-Capacitor) HC1 and HC2.

In this configuration, for example, in the case of optical output P ₀ , a voltage (via REXT 809) generated by the output current of the light receiving element (PD) 807 that receives the light of the semiconductor laser (LD) 806 detected through the XPD terminal. The control circuit 802 controls the light output P ₀ based on the result of the comparison between the photocurrent (converted into a voltage) and the VCONT voltage. The control result (voltage value) is held by the Hold-Capacitor HC1 connected to the XCH terminal.

On the other hand, when the optical output is P _1, the same control is performed, and the control result is held in the Hold-Capacitor HC2. Assuming that the characteristic of the optical output is a straight line with respect to the voltage between P ₁ and P ₀ (in fact, this linearity is accurately established by the IL characteristic of the semiconductor laser), and in multiple stages. Is to be modulated.

When Modulation Data is Dn (data changing at the VCLK speed), the semiconductor laser drive current is In, the Hold-Capacitor HC1, Hold-Capacitor HC2 voltages are V1, V2, and P ₁ = P _0/2 Equation 4 is established.
In = {(V0−V1) × Dn + V1} / RE (Formula 4)
Here, the control circuit 802 and the modulation signal generation circuit 803 are set so as to satisfy (−1 ≦ Dn ≦ 1).

  With this configuration, it is possible to generate the pattern of the optical modulation pulse of the semiconductor laser (LD) in accordance with the modulation data (Modulation Data) output from the Pulse-Modulation-Unit 500. In FIG. 1 and FIG. It becomes relatively easy to generate an exposure energy distribution. Thereby, in this embodiment, an image with good graininess can be obtained.

(First configuration example of pixel clock generation circuit)
In FIG. 5, a configuration example of a pulse modulation device that generates a VCLK signal having a frequency that is eight times the pixel clock from the pixel clock has been described, but the pixel clock itself is generally generated from the reference clock. Here, when the semiconductor laser 806 is used as a light source, the exposure (scanning) position due to chromatic aberration (so-called chromatic aberration of magnification) of the scanning optical system due to the oscillation wavelength jump of the semiconductor laser 806 and the difference of the oscillation wavelengths of the plurality of light emitting units Since a shift occurs, a pixel clock generation circuit that can finely adjust the pixel clock is required.

  For example, when the number of pixels in one scan is 14000, the pixel clock frequency is 60 MHz, and the pixel position accuracy at both ends of the scan is 1/4 pixel width, in order to enable this frequency setting with a single PLL, 60 MHz ÷ ( 14000 × 4) = 1.07 kHz, and the PLL must be controlled with a reference clock of about 1 kHz. As a result, the phase fluctuation amount of the PLL cannot be detected unless it is every 1 kHz, and the control bandwidth as the PLL is lowered. Furthermore, it becomes weak against disturbances, etc., and in order to improve the pixel position accuracy, the demand for the stability of the VCO 503 constituting the PLL becomes very high. In order to avoid this, a method using a double PLL may be considered. However, when such a circuit is separately provided, the jitter of the PLL circuit is accumulated twice, resulting in an increase in jitter. . In addition, the cost is high.

  FIG. 9A shows a configuration example of the pixel clock generation circuit 900-1 that solves this problem and simultaneously realizes VCLK signal generation and pixel clock generation.

  Referring to FIG. 9A, the pixel clock generation circuit 900-1 according to the present embodiment includes a phase frequency comparison circuit 901, a Loop-Filter 902, a VCO 903, a Programmable-Counter 904, a Load-Pulse-Generator 905, and a 1/8 frequency division. Circuits 906 and 907, Register 908, and Buffer 909 are included.

  In this configuration, the phase frequency comparison circuit 901 that compares the result of dividing the VCLK signal by N by the programmable-counter 904 with the reference clock, the loop-filter 902 that filters the result of the phase frequency comparison circuit 901, and the output of the loop-filter 902 A VCLK signal is generated by a PLL including a VCO 903 whose start frequency changes based on the voltage. Further, the division ratio N of Programmable-Counter 904 is set from the outside by setting the division ratio.

  In this configuration example, the VCLK signal is generated in this way, and data “0” is loaded into the 1/8 frequency divider circuit 906 by the VCLK signal and the phase synchronization pulse, so that the pixel clock phase-synchronized with the phase synchronization pulse is obtained. Are generated at a frequency 1/8 of the VCLK signal. This configuration example also includes a 1/8 frequency dividing circuit 908 that loads phase Data set in advance at the same timing and generates an internal clock having a phase difference from the pixel clock.

  The 1/8 frequency dividing circuit 907 in FIG. 9A is not necessary when the pixel clock is slow. Further, it is not necessary if the time delay until image data is transferred is not a problem. However, when the frequency of the pixel clock is high, when capturing image data from the outside synchronized with the output, there is a problem of delay time from the pixel clock output to image data input, and data cannot be captured correctly. Exists. In such a case, the configuration is avoided by making the phase of the image data capturing clock variable with respect to the output pixel clock based on the preset phase data as in this configuration example.

  Further, in this configuration example, the count (frequency division) of the 1/8 frequency dividing circuits 906 and 907 can be enabled / disabled by the Phase-Set signal. This is because in this configuration example, the rising edge of the Phase-Set signal is captured by the VCLK signal, and the count (frequency division) operation for one clock cycle of the VCLK signal is stopped. With this configuration, the phase of the pixel clock and the internal clock can be delayed in 1/8 clock steps.

  As described above, by executing the phase delay amount of 1/8 clock cycle at an interval determined during one scanning period or an interval close to the determined interval, the frequency of the pixel clock in one scanning period is equivalent. Can be fine-tuned. This is equivalent to the fact that the frequency variable step that can be set by the PLL can be set more finely.

(Second configuration example of pixel clock generation circuit)
Further, when the pixel clock frequency is finely adjusted by 1/8 clock, the pixel clock generation circuit is configured as shown in FIG. 9B, and the frequency dividing circuit 910 is loaded with “1” instead of “0”. Thus, by setting the frequency dividing number from 8 to 7, it can be solved by shortening by 1/8 clock.

  The second configuration example of the pixel clock generation circuit 900-2 illustrated in FIG. 9B is compared with the pixel clock generation circuit 900-1 illustrated in FIG. , 907 are replaced with frequency dividing circuits 910, 911, respectively, and a new register 912 is provided. Load data is set in the register 912 from the outside, and load data based on the set content is input to the frequency dividing circuit 910, and the frequency dividing number is determined in the frequency dividing circuit 910.

  At this time, when “7” is output from the register 912, it is shorter than when “8” is output, and when “9” is output, it is longer than when “8” is output. .

  As another method, the original pixel clock is shortened and set short, and the phase of the pixel clock and the internal clock is gradually increased at a predetermined interval in the scanning period or at an interval close to the predetermined interval. There is also a method for obtaining a desired image by performing fine adjustment by delaying the image by 1/8 clock.

  Here, when the light emitting part of the semiconductor laser (LD), which is a light source part, is a multi-beam optical system composed of a plurality of light emitting parts, if the emission wavelength of each light emitting part is different, the surface to be scanned is scanned and imaged Due to the chromatic aberration of the scanning optical system, there is a difference in the scanning width of the scanning light from each light emitting unit, causing image position deviation due to each scanning line and density unevenness in the highlight part, which causes image deterioration.

  In this configuration example, the difference in scanning width can be corrected by using the above-described phase shift, and writing can be performed at a desired target writing position. This is realized by shifting the light emitting portion whose scanning width is extended to be shorter, and shifting the light emitting portion whose scanning width is reduced to be longer. On the other hand, if the original image clock is shortened and set short in advance, it is possible to cope with this by changing the shift amount between the light emitting part where the scanning width is extended and the light emitting part where the scanning width is reduced. It is.

(Summary of Pixel Clock Generation Circuits According to First and Second Configuration Examples)
The demand for higher quality from the market is increasing year by year, and the required specifications for higher density and higher accuracy of the scanning optical system are becoming stricter. However, in the conventional method, in order to increase the performance of the scanning optical system, it is necessary to increase the number of components, use a special glass material, or introduce a special surface into the surface shape of the components. In terms of cost, the cost is high, and further, there is a problem that advanced machining technology is required on the machining side.

  In contrast, in the present embodiment, the scanning constant velocity, which is one of the required performance at the time of designing the optical system, is configured to allow a certain degree of deterioration and improve other performances. A high-density and high-precision optical system can be easily and inexpensively manufactured without increasing the number of sheets, using a special glass material, or introducing a special surface into the component surface shape. That is, by using the phase shift shown above, it is possible to correct the scanning isokineticity to about ± 10%, which is advantageous in optical system design, and accordingly, in terms of cost and optical element processing. Become.

  In addition, when the semiconductor laser array is tilted, as described above with reference to FIG. 24 (b), the light emitting point positions are shifted by the distance d in the main scanning direction. The scanning start position on the surface to be scanned is also shifted. In that case, the surface to be scanned is displaced by an amount multiplied by the magnification of the entire optical system in the main scanning direction.

This will be described in more detail with reference to FIG. FIG. 30 shows the relationship between the intervals between the plurality of light emitting points and the intervals between the plurality of light spots on the surface to be scanned in the main scanning section. Referring to FIG. 30, the light beam emitted at the interval d scans the surface to be scanned at the interval d ′ according to the magnification relationship according to the ratio between the coupling lens and the imaging lens focal length. In other words, the scanning light beam scans the surface to be scanned as a light spot by the condensing action of the imaging lens. At this time, the respective light spots are scanned with a gap d ′ in the main scanning direction as described above. Here, when the magnification of the entire optical system in the main scanning direction is β _m , the relationship of the following Expression 5 is established.
| D ′ | = | β _m · d | (Formula 5)
On the other hand, even when the tilt is not tilted, the scanning position on the surface to be scanned is shifted in the same manner as described above due to the positional shift of the light emitting point caused by the processing error in manufacturing the semiconductor laser array. Similarly to the case where the semiconductor laser array is tilted, the light source portion is configured by a plurality of semiconductor lasers, and the light emission point position is shifted in the main scanning direction. The scanning start position on the surface to be scanned is also shifted.

  The deviation of the scanning start position in the main scanning direction becomes a factor of final image quality degradation as in the case where the semiconductor laser array is tilted, and thus the scanning start position needs to be corrected.

  In other words, the deviation of the position of the light emitting point is when the relative position of each light emitting point of the semiconductor laser with respect to an axis orthogonal to the deflection scanning plane (main scanning plane) is different. In such a state, that is, when there is no relative position of each light emitting point on an axis orthogonal to the changed scanning plane, the scanning start position of the light spot on the scanned surface is shifted in the main scanning direction, The writing end portion becomes rattling.

  This phenomenon will be described with reference to FIG. FIG. 28 schematically shows the operation of scanning the light spot on the surface to be scanned.

  Referring to FIG. 28, by tilting the semiconductor laser array, the light spot scans the surface to be scanned at an interval d ′. In this operation, light is oscillated from the semiconductor laser array in accordance with the image modulation signal after a predetermined timing based on the detection signal from the synchronization detection optical system (scanning light detection means) arranged in front of the image area, An electrostatic latent image is formed on the scanning surface. At this time, the semiconductor laser array also takes the oscillation timing of other light emitting points based on the light beam that first traverses the synchronous detection optical system. For this reason, in this state, the writing start position of the light spot by each light emitting point is shifted in the image area, which causes image deterioration.

  Therefore, by using the pixel clock generation circuit according to the present embodiment described above, the phase is shifted so that the writing of the image information starts at the timing when the light beam for writing the image area finally reaches the image area. The start position of the electrostatic latent image formed on the surface to be scanned can be adjusted. Here, assuming that the interval d ′ is N / 8 clocks long, in the case of a semiconductor laser array having four light emitting points as shown in FIG. 28, the control signal for the scanning light that precedes is (3 × N) / 8 clocks can be shifted to match the last scanning light. Similarly, the second may be shifted by (2 × N) / 8 clock, and the third may be shifted by N / 8 clock.

  In the above example, the last scanning light is used as a reference. However, the present embodiment is not limited to this, and any reference may be used. However, in that case, the shift is made to be arbitrarily short or to be long.

  As described above, even when the semiconductor laser array is tilted, it is possible to align the image writing end portions.

  In general, when actually setting the frequency variable step of the PLL in detail, for example, the frequency division setting range of Programmable-Counter 905 in (a) or (b) of FIG. Although it is possible to lower the clock or raise the VCLK signal, lowering the reference clock makes it possible to detect the frequency fluctuation of the VCLK signal only in the reference clock cycle, and stabilizes the oscillation frequency of the VCO 903. It becomes a big technical issue.

  For example, when the number of pixels in one scan is set to 14000, the pixel clock frequency is set to 60 MHz, and the pixel position accuracy at both ends of the scan is set to a 1/4 pixel width, in order to enable this frequency setting with a single PLL, (60 MHz ÷ (14000 × 4) = 1.07 kHz), and the PLL must be controlled with a reference clock of about 1 kHz. As a result, the phase fluctuation amount of the PLL can be detected only every 1 kHz, and the control bandwidth as the PLL is lowered. Furthermore, it becomes weak against disturbances, etc., and in order to improve the pixel position accuracy, the demand for the stability of the VCO constituting the PLL becomes very high. In order to avoid this, there is a method using a double PLL or the like, but having such a circuit separately causes the jitter of the PLL circuit to be accumulated twice, causing an increase in jitter. In addition, the cost is high. On the other hand, increasing the VCLK signal requires a higher oscillation frequency from the VCO, which is also a technical problem.

  On the other hand, according to the present embodiment, the frequency can be set in a step exceeding that if the oscillation frequency of the VCO can be increased, and in a step exceeding that if the VCO can be stabilized. Further, it is possible to eliminate the discontinuity of the exposure energy amount by preventing the semiconductor laser from emitting light for 1/8 clock cycle in which the phase delay due to the Phase-Set signal is generated. It is also possible to configure so that the Phase-Set signal is set when the semiconductor laser does not emit light. It is also possible to configure so as to set at a slightly shifted position for each scan. It is also possible to configure so that only the first line of the page is set. Further, it may be configured to set at a predetermined (or arbitrary) time interval in the apparatus while the apparatus is powered on. In this case, the time interval may be measured by incorporating an internal clock of the apparatus, or may be measured by a method such as a time counter.

  By changing the phase delay amount at such timing, in this embodiment, the pixel clock phase can be changed without affecting the output image. In addition, the Phase-Set signal is increased or decreased at regular intervals at each scanning start timing (for example, 1/8 → 2/8 → 3/8 → 4/8 → 5/8 → 6/8). → 7/8 → 0) By changing, the position of each pixel can be controlled every 1/8 clock cycle.

  With the above configuration, a high-quality image can be obtained by finely adjusting the screen angle for image output. In addition, by configuring so that the timing of setting the phase change circuit can be arbitrarily changed, various cases can be handled.

(Third configuration example of the pixel clock generation circuit)
Next, a third configuration example of the pixel clock generation circuit according to the present embodiment will be described with reference to FIG.

  Referring to (a) of FIG. 10, the pixel clock generation circuit 1000-1 according to this configuration example has an N-Counter 1010 inside, and automatically generates a Phase-Set signal every N counts, and 1/8 pixel. The phase is delayed by the amount of the clock.

  In the case of this configuration example, the optical modulation pulse is not output for a time of 1/8 clock. Even in such a configuration, the exposure energy distribution (1) shown in FIG. 1 does not become discontinuous. This is because the light is extinguished only for a sufficiently short time with respect to the beam diameter of the semiconductor laser (PD). In addition, the fact that the timing at which light is extinguished is the separation of pixels also contributes to the above effect. Note that the count value N of the N-Counter 1010 can be set from the outside by serial data. By doing so, the frequency in steps that cannot be set by the PLL can be set by serial data, so that the frequency steps can be set finely equivalently.

(Fourth Configuration Example of Pixel Clock Generation Circuit)
Further, when a deflector such as a polygon scanner has a variation (variation of inscribed circle radius) with respect to the distance from the rotation axis (center) of the deflecting reflection surface, a light spot (on the surface to be scanned) ( This causes a variation in the scanning width of the scanning beam.

  In the operation during scanning, after detecting synchronous light, a writing signal is emitted at a predetermined timing, and the semiconductor laser starts to emit light. By reading this, data for each scanning is obtained for each light emitting source. Sent. By repeating this operation, an image is formed as a latent image on the scanned medium. At this time, due to the above factors in the deflector such as a polygon scanner, the unevenness (variation) of the scanning length of each scanning line appears, and as with the writing magnification error, it is noticeable mainly at the edge of the image, and the variation of the writing end edge Appears as fluctuations at the edge of the image.

  This variation in scan width can also be corrected by shifting the phase of the pixel clock and the internal clock (matching the writing end). However, the variation in the scanning width caused by the deflector occurs when the deflection reflection surface changes, and also periodically occurs according to the cycle of the deflection reflection surface. Therefore, it is necessary to determine which surface of the deflecting reflecting surface is deflected and scanned.

  As an example of the method, marking is performed on the upper surface of the deflector, and it is configured to recognize that the rotation has been performed once every time the mark is read. Further, an input signal is obtained by a synchronous detection system before the start of each scan. With these two types of information, it is possible to determine which surface is currently being scanned.

  This will be described with reference to FIG. 29. 1 / nCounter 2901 is reset by a mark detection signal from the deflector. After resetting, the counting of the synchronization pulse is started again, the 1, 2, 3,..., N planes are counted and reset again by the mark detection signal from the deflector. By repeating this, it is possible to determine on which surface of the deflector the deflection scanning is performed.

  FIG. 10B shows a fourth configuration example of the pixel clock generation circuit that generates a pixel clock after determining which surface is deflected and scanned by the operation shown in FIG. FIG. 10B is a circuit diagram showing a pixel clock generation circuit 1000-2 according to this configuration example.

  Referring to FIG. 10B, the pixel clock generation circuit 1000-2 according to the present configuration example is different from the pixel clock generation circuit 1000-1 described in FIG. -Counter 1012 is newly provided.

  In addition, since the scanning width is expanded and contracted by the deflecting / reflecting surface, information for each surface is stored as line information in an external memory or the like. Next, the count value setting circuit 1011 loads line information from the outside in accordance with an identification signal indicating which surface of the deflector output from the line-counter 1012 is used to scan the surface to be scanned. Determine how to shift the phase of the clock and internal clock. The number of reflection surfaces of the identified deflector is determined by the operation shown in FIG. The count value setting circuit 1011 loads line information based on data (identification information) from the line-counter 1012 and sets a count value. The N-Counter 1010 generates a Phase-Set signal based on the count value output from the count value setting circuit 1011 and shifts the phase of the signal generated in the subsequent stage. The above operation is not limited to the number of light sources, and is the same, and the same effect can be obtained even when the number of light sources is one or a plurality of light sources.

(Each signal of the pixel clock generation circuit according to the third or fourth configuration example)
FIG. 11 shows each signal for the pixel clock generation circuit 1000-1 or 1000-2 shown in FIG. 10A or 10B to control the phase of the internal clock with respect to the pixel clock in accordance with the phase Data. It is a timing chart which shows. In FIG. 11, from the top, VCLK signal, synchronization pulse, Reset signal, pixel clock, image data, Reset2 signal, and internal clock. Further, in FIG. 11, the operation is performed only when the Phase-Set signal is 'L'. With this configuration, the synchronization pulse is always valid when the Phase-Set signal is “L”, and the phase relationship between the internal clock and the image data is controlled. On the other hand, for example, by setting the Phase-Set signal to “L” only at the first timing of power-on, the initially set phase difference can be maintained.

(Modulation data example)
FIG. 12 is a diagram illustrating an example in which the number of bits of Modulation Data output from the LUT 507 is reduced as compared with the case of FIG. In this example, left and right independent pulses can be selected based on the center of one pixel. When this data is used, a selection table for selecting an 8-phase pulse when the VCLK signal is divided by 8 is set, as shown in FIG. 13, instead of the 8-bit-Shift-Register 505 in the configuration shown in FIG. This makes it possible to generate a pulse at an arbitrary position.

  With this configuration, the circuit scale of the LUT can be reduced in the configuration shown in FIG. For this reason, when obtaining the light modulation pulse as shown in FIGS. 2 and 4 at low cost, it can be used as an effective means.

(First Configuration Example of Semiconductor Laser Output Control Circuit)
FIG. 14A shows a first configuration example of a semiconductor laser output control circuit for driving a semiconductor laser whose cathode is common in the configuration for controlling the peak value of the light output intensity and the bias current of the semiconductor laser. FIG.

  In FIG. 14A, the light output of the semiconductor laser is detected by the light receiving element (PD) 1407 by Error-AmpA1, the detected result is converted into a voltage, compared with the reference voltage, and the control value is set to Hold-CapacitorHC3. The control to hold is performed. In this configuration example, the terminal voltage of RE 1408 is controlled by Error-AmpA2 so that the power supply voltage VCC is 80 mV. Further, the control result is held in the Hold-Capacitor HC4.

  Note that Error-Amp A1 is controlled at a timing delayed by a certain time after the LDON signal for emitting light from the semiconductor laser (LD) 1406 becomes active. Error-AmpA2 is controlled with a delay of a certain time from when the LDON signal becomes inactive so that the bias current when the semiconductor laser 1406 is turned off becomes a constant value.

  Thus, by starting control with a certain time delay from the LDON signal, the light reception current of the light receiving element 1407 by the light output from the semiconductor laser 1406, the voltage obtained by converting the light reception current, and the error An error due to a delay time in transmission of a signal to AmpA1 is prevented from occurring.

  The same applies to the bias current control timing. Further, the semiconductor laser 1406 is connected to the emitter of a bipolar transistor (LD driving transistor) 1405 so that the base voltage of the bipolar transistor 1405 is transmitted to the semiconductor laser 1406 as little as possible.

  As described above, in this configuration example, a predetermined optical output is obtained by setting the voltage between the terminals of the semiconductor laser 1406 to a predetermined voltage. With this configuration, the semiconductor laser can be modulated at high speed.

(Second configuration example of semiconductor laser output control circuit)
FIG. 14B shows a circuit diagram of a second configuration example of the semiconductor laser output control circuit according to the present embodiment. As described above, this configuration example is configured to perform shading correction when controlling the light output intensity of the semiconductor laser.

  Accordingly, the semiconductor laser output control circuit according to the present configuration example is newly provided with a D / A 1401 as compared with FIG. 14A, and data (shading data) for performing shading correction is added thereto. A value obtained by converting the input shading data into analog is added in the adder 1402 to the control value held in the Hold-Capacitor HD3.

  As a result, the voltage for controlling the LD 1406 becomes a value reflecting the correction by the shading data.

(Third configuration example of semiconductor laser output control circuit)
FIG. 15 shows a configuration example when an anode common semiconductor laser is used. In this configuration example, the semiconductor laser is connected to the collector of the transistor as compared with FIG. With such a configuration, it is possible to realize a circuit substantially similar to the cathode common semiconductor laser shown in FIG. As a result, the anode common semiconductor laser and the cathode common semiconductor laser can be used in the same IC.

(First configuration example of control timing generation circuit)
In addition, a first configuration example of a control timing generation circuit that generates timing for controlling the semiconductor laser in the present embodiment will be described with reference to a circuit diagram of FIG.

  Referring to FIG. 16, the control timing generation circuit according to the present configuration example rapidly charges the capacitor C1 when the LDON signal is “H” and the LDON signal is “L” in order to generate the timing for controlling the semiconductor laser. Sometimes the capacity of the capacitor C1 is discharged with a constant current. Thus, in this configuration example, the control is stopped when a thin pulse train comes.

  Therefore, with this configuration, it is possible to hold a control value for a narrow pulse train and improve control accuracy compared to a simple delay circuit + logic circuit configuration.

(Second configuration example of control timing generation circuit)
When the semiconductor laser is connected as shown in FIG. 14 or FIG. 15, when the terminal voltage of the light receiving element for detecting the light of the semiconductor laser is common to the anode, it changes with reference to GND, and the common cathode In the case of, the change is made with reference to VCC. Here, using such a property, the anode common semiconductor laser is connected when the terminal voltage of the light receiving element is VCC / 2 or less, and the cathode common semiconductor laser is connected otherwise. FIG. 17 shows a second configuration example of the control timing generation circuit when configured.

  By adopting the circuit configuration as shown in FIG. 17, in this configuration example, it is automatically determined whether it is an anode common semiconductor laser or a cathode common semiconductor laser, and the control direction according to FIG. 14 or FIG. A control timing generation circuit that can be changed to is realized. As a result, the same circuit (IC) can be used for both the anode common semiconductor laser and the cathode common semiconductor laser.

(First configuration example in which each function is integrated into a single chip IC)
FIG. 18 summarizes the matters described in the above description, and the pulse modulation device, the semiconductor laser control device, the pixel clock generation circuit, the semiconductor laser output control circuit, and the control timing generation circuit provided in the present embodiment are made into one chip IC. It is a figure which shows the structural example at the time of implement | achieving.

  In this configuration example, by providing two types of synchronization signals for the same pixel clock frequency, the anode common semiconductor laser and the cathode common semiconductor laser can be controlled independently. Further, in this configuration example, there are two channels of circuit units for controlling and modulating the semiconductor laser.

  In FIG. 18, Voltage-Reference 1801 is a reference power supply circuit for the entire IC, and supplies reference power to other circuit blocks.

  In FIG. 18, a PLL is configured by Phase-Detector 1802, VCO 1803, Clock-Driver 1804, 12BIT-Programmable-Counter 1805. Here, among the 12-bit data set in Counter-Register (12BIT) 1806, the lower 1 bit is set to delay the phase of the output clock (VCLK) signal of Clock-Driver 1804 by π, and the upper 11 bits are 12BIT. -The division ratio of Programmable-Counter 1805 is set.

  With such a configuration, the frequency of the CLK signal output from the VCO 1803 is F-REF × N / 2 (N: 12 BIT data).

  The AResetPulse-Generator 1808 outputs an ACLK signal in which either forward or inversion of the Areset and the CLK signal is selected in synchronization with IDETP1. Similarly, the BResetPulse-Generator 1809 outputs a BCLK signal in which either BReset or normal / inverted CLK signal is selected in synchronization with IDETP2. The ADivider-Drive 1810 or the BDivider-Driver 1811 divides by 4 according to the ACLK signal and AReset, or the BCLK signal and BReset, and outputs a pixel clock (APCLK signal or BPCLK signal) synchronized with ADETP or BDETP, respectively.

  In the IC chip configuration shown in FIG. 18, the pixel clock can be delayed by 1/8 phase in accordance with the rising edges of ADPhase and BDPhase in the timing chart as shown in FIG. As a result, the start position of the pixel clock can be delayed and controlled every 1/8 clock cycle for each line scan.

  Further, by providing M rising edges during the scanning period of one line, the pixel clock frequency can be equivalently changed to (FCLK × N / (N + M / 8)). Further, as shown in the timing chart of FIG. 23, by generating the ALDMASK signal and the BLDMASK signal, the pixel clock is delayed by 1/8 clock cycle, and the semiconductor laser is forcibly turned OFF during this period. With this configuration, the image density is prevented from changing abruptly.

  In such a configuration, the semiconductor laser is automatically turned off. However, if the density is reduced by 1/8 from the image data in advance, it is not necessary to forcibly turn off the semiconductor laser. As described above, when the image data is reduced by 1/8 in advance, the LDMASK signal can be invalidated by setting the MaskEN signal to High.

(Second configuration example in which each function is integrated into a single chip IC)
A configuration example of a circuit formed as a one-chip IC configured to generate a light modulation pulse in accordance with a predetermined rule is shown as a second configuration example in FIG.

(First configuration example when each function is realized by a program code)
In addition, by writing a program code into the Code-Area-Program-Counter 2005 by the serial interface 2001, an effective writing period of image data, density pattern generation for electrophotographic process control, detection of isolated point dots, and an image corresponding thereto It is also possible to configure the unit that performs the data conversion process to realize the above described items. An example of such a configuration is shown in FIG. In FIG. 20, the ALU 2003 executes an operation with the output clock of the Clock-Generator 2006 (8 times the pixel clock). The program code is set to have a predetermined program count value for each synchronization signal.

  As described above, the ALU 2003 that performs the process for outputting the transferred image data inputs the final result to the LD-Controller 2007, and the LD-Controller 2007 modulates the semiconductor laser according to this data. In FIG. 20, the speed conversion RAM 2002 functions as a buffer memory for absorbing the speed difference between the clock transferred to the IC and the write clock.

(Second configuration example when each function is realized by a program code)
Further, in FIG. 21, the ALU 2103 writes the calculation result to the Shift-Register 2109 and the data pattern corresponding to the light modulation pattern for one pixel once in 8 clock cycles of the Clock-Generator 2106, and the Shift-Register 2109 In this example, modulation data is input to the LD-Controller 2107 according to the clock.

  As described above, according to the present embodiment, it is possible to realize the correction of the scanning width of the image by shifting the phase of the pixel clock by performing the image forming clock, the image forming timing, and the semiconductor laser modulation control. In addition, the design difficulty of the optical system can be reduced, the processing difficulty by configuring the optical system without using a specially shaped surface can be reduced, and an expensive optical material It is possible to reduce the cost by configuring the optical system without using. Furthermore, in a multi-beam optical system, when there are differences in the oscillation wavelengths of each semiconductor laser when a plurality of light sources are combined, there are differences in the oscillation wavelengths of the respective emission points of the semiconductor laser array, When a plurality of the above are combined, the difference in scanning width due to the exposure position shift that occurs when the chromatic aberration of the scanning lens is not corrected can be corrected by shifting the phase of the pixel clock.

  Further, according to the present embodiment, it is possible to realize the correction of the scanning width of the image by shifting the phase of the pixel clock by performing the image forming clock, the image forming timing, and the semiconductor laser modulation control, and the optical System design difficulty can be reduced, processing difficulty can be reduced by configuring the optical system without using specially shaped surfaces, and optical without using expensive optical materials. Cost reduction can be achieved by configuring the system. Furthermore, the position of the light emitting point is shifted due to an error in processing of the chip of the semiconductor laser array, the positional deviation of the light emitting point caused by an assembly error when a multi-beam optical system is configured by combining a plurality of semiconductor lasers, and the semiconductor The difference in scanning width caused by the shift of the scanning start position on the surface to be scanned, which occurs when a light source unit is configured by combining a plurality of laser arrays, is corrected by shifting the phase of the pixel clock, and the writing start position ( In addition, a high-quality image can be obtained.

  Further, according to the present embodiment, it is possible to realize the correction of the scanning width of the image by shifting the phase of the pixel clock by performing the image forming clock, the image forming timing and the semiconductor laser modulation control, and the optical system. Design difficulty can be reduced, processing difficulty can be reduced by configuring the optical system without using special shape surface, and optical system without using expensive optical material It is possible to reduce the cost by configuring. Furthermore, the fluctuation of the image edge that appears due to a deflector such as a polygon scanner is corrected by shifting the phase of the pixel clock, and the writing end position is adjusted to obtain a high-quality image. Also, in an optical system using a semiconductor laser as a light source, variations in scanning length (difference in optical scanning width of each scanning line) caused by a deflector such as a polygon scanner, and accompanying image fluctuations appearing at the edge of the image A semiconductor laser control IC capable of correcting the above can be provided.

  Further, according to the present embodiment, it is possible to realize the correction of the scanning width of the image by shifting the phase of the pixel clock by performing the image forming clock, the image forming timing, and the semiconductor laser modulation control, and the optical System design difficulty can be reduced, processing difficulty can be reduced by configuring the optical system without using specially shaped surfaces, and optical without using expensive optical materials. Cost reduction can be achieved by configuring the system. Furthermore, in an image forming apparatus having a tandem configuration, by matching the magnifications of the latent images on the respective scanned media, it is possible to prevent image deterioration due to color misregistration due to a difference in scanning width when images are superimposed and formed.

  Further, according to the present embodiment, it is possible to realize the correction of the scanning width of the image by shifting the phase of the pixel clock by performing the image forming clock, the image forming timing, and the semiconductor laser modulation control, and the optical System design difficulty can be reduced, processing difficulty can be reduced by configuring the optical system without using specially shaped surfaces, and optical without using expensive optical materials. Cost reduction can be achieved by configuring the system. Further, the position error at each image position (each image height) of the image on the scanned medium is reduced, and high-quality image formation in which the image is formed at the target position at any position on the image is achieved. be able to.

  Furthermore, according to the present embodiment, the present invention relates to an image forming apparatus that forms an image by scanning a scanned medium with modulated light of a semiconductor laser based on an image signal. Semiconductor laser modulation control can be performed. Further, in the image forming apparatus that constitutes the light source unit by the multi-beam optical system, it is responsible for setting the phase difference between the output image (pixel) clock and the internal clock, so that the image data transfer circuit block connected to this IC Therefore, it is possible to provide an IC that controls the semiconductor laser simultaneously with high-speed image (pixel) clock generation.

  Furthermore, according to the present embodiment, the present invention relates to an image forming apparatus that forms an image by scanning a scanned medium with modulated light of a semiconductor laser based on an image signal. Semiconductor laser modulation control can be performed. Furthermore, the degree of freedom in setting the frequency of the high-frequency clock is improved, the image (pixel) clock can be synchronized with the writing position, and the present invention can provide an IC that controls the semiconductor laser simultaneously with the generation of a high-speed image (pixel) clock.

  Furthermore, according to the present embodiment, the present invention relates to an image forming apparatus that forms an image by scanning a scanned medium with modulated light of a semiconductor laser based on an image signal. Semiconductor laser modulation control can be performed. Furthermore, the degree of freedom in setting the frequency of the high-frequency clock is improved, and a high-speed light modulation pattern that can obtain an optimum exposure energy distribution from image data can be generated. An IC for controlling can be provided.

  Furthermore, according to the present embodiment, the present invention relates to an image forming apparatus that forms an image by scanning a scanned medium with modulated light of a semiconductor laser based on an image signal. Semiconductor laser modulation control can be performed. Furthermore, the speed can be increased, and the writing position of a plurality of light emitting points can be finely adjusted. According to the present invention, an IC that controls a semiconductor laser simultaneously with high-speed image (pixel) clock generation can be provided.

  Furthermore, according to the present embodiment, the present invention relates to an image forming apparatus that forms an image by scanning a scanned medium with modulated light of a semiconductor laser based on an image signal. Semiconductor laser modulation control can be performed. Furthermore, since the semiconductor laser modulation circuit can be installed in another place, the layout around the light source section can be easily performed, and the present invention can provide an IC that controls the semiconductor laser simultaneously with the generation of a high-speed image (pixel) clock.

  Furthermore, according to the present embodiment, it is possible to realize a high speed by integrating circuit portions having a high transmission speed, and according to the present invention, it is possible to provide an IC that controls a semiconductor laser simultaneously with a high-speed image (pixel) clock generation. Simultaneously with the generation of the image writing clock, the control of the semiconductor laser can be efficiently accommodated in one chip, and a small size, high speed and low cost can be realized.

DESCRIPTION OF SYMBOLS 3 Cylindrical lens 4 Rotating polygon mirror 5, 6 Imaging lens 7 Optical path bending mirror 8 Photoconductor 10 Optical apparatus 11, 12, 101, 102, 106, 107 Semiconductor laser 13, 14 Coupling lens 15, 112 Beam synthesis prism 15A Polarization Separation membrane 16 1/2 wavelength plate AX Synthetic optical axis 11a, 12a Light emitting portion 103, 108 Support member 104, 105, 119, 109 Collimator lens 103-1, 103-2 Support portion 103-6, 108-6, 113- DESCRIPTION OF SYMBOLS 1 Cylindrical part 110 Base member 110-1, 110-2 Mating hole 103-3, 103-4, 103-5, 108-3, 108-4, 108-5 Positioning part 111 Plate 113 provided with aperture 113 Holder Member 113-3 Lever 115 Adjustment screw 114 Substrate 113-2 Post 8a 1, 8a1, 8b1, 8b2 Scanned medium 5a, 6a1, 6a2, 6b1, 6b2 Lens 7a1, 7a2, 7b1, 7b2 Optical path bending mirror 500 Pulse-Modulation-Unit
501, 1802 Phase-Detector
502, 902 Loop-Filter
503, 903, 1803 VCO
504, 906, 907 1/8 frequency divider 505 8bit-Shift-Register
506 flip-flop 507 LUT
800 LD-Control-Unit
802 Control circuit 803 Modulation signal generation circuit 804 Differential amplifier 805, 1405 LD drive transistor 806, 1406 LD
807, 1407 PD
808, 1408 RE
809 REXT
901 Phase frequency comparison circuit 904 Programmable-Counter
905, 1005 Load-Pulse-Generator
908, 912, 2108 Register
909 Buffer
910, 911 Frequency dividing circuit 1008 Phase detection circuit 1010, 1011 N-Counter
1012 Count value setting circuit 1013 Line-Counter
1401 D / A
1402 Adder 1410 Delay
1411 NOR
1412 AND
1409 RPD
1801 Voltage-Reference
1804 Clock-Driver
1805 12bit-Programable-Counter
1806 Counter-Register (12BIT)
1807 Detect-Pulse-Selector
1808 AResetPulse-Generator
1809 BResetPulse-Generator
1810 ADivider-Driver
1811 BDivider-Driver
1812 Pulse-Select-Register (18BIT)
1813 ALatch
1814 AP1-Selector
1815 AP2-Selector
1816 ALD-Controller
1817 Start-up
1818 LD-Error
1819 BLatch
1820 BP1-Selector
1821 BP2-Selector
1822 BLD-Controller
2001 Serial I / F
2002 Speed conversion RAM
2003 AUL
2004 Working-Area
2005 Code-Area-Program-Counter
2006 Clock-Generator
2007 LD-Controller
2109 Shift-Register
A1, A2, A3, A4 Error-Amp
B1, B2, B3 Buffer
HC1, HC2, HD3, HD4 Hold-Capacitor
Q1-8, Q11-15 Transistor

JP 05-075199 A JP 05-235446 A JP 09-321376 A Japanese Patent Laid-Open No. 11-167081 JP 05-207234 A

Claims (5)

Laser light oscillation means comprising two or more light emitting points for oscillating laser light based on a pixel clock generated by dividing a high frequency clock by N;
Laser beam deflecting means for deflecting the laser beam so as to scan the scanned medium with the laser beam;
A scanning optical system that forms an image of the laser beam deflected by the laser beam deflecting unit on a scanned medium;
Synchronization detection means for synchronously detecting the laser light deflected by the laser light deflection means;
Pixel clock changing means for changing the frequency division number of the pixel clock so that the pixel clock is shortened when the scan width is shortened, and the pixel clock is lengthened when the scan width is lengthened. An image forming apparatus.   The image forming apparatus according to claim 1, wherein the pixel clock changing unit changes the frequency division number of the pixel clock from N to N + 1 or N−1. The pixel clock changing means is
2. The image formation according to claim 1, wherein a frequency division number is made larger than N at a first light emission point among the two or more light emission points, and a frequency division number is made smaller than N at a second light emission point. apparatus. The laser beam deflecting means is composed of a rotating polygon mirror,
Storage means for storing data set corresponding to the expansion and contraction of the scanning width for each surface of the rotary polygon mirror;
The image forming apparatus according to any one of claims 1, characterized in that to enable the division number change of the pixel clock by the pixel clock changing means based on the data 3. The laser beam oscillating means, an image forming apparatus according to any one of claims 1 to 4, characterized in that a semiconductor laser array.

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