JP2005338630A - Light beam scanning method, system, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform planar scanning by imposing less load to an optical system for beam shaping, highly precisely coping with multi-beam system, easily widening the beam width and allowing a unit including the optical system such as a lens to be miniaturized when writing with a multibeam. <P>SOLUTION: An optical scanning mirror 100 has four mirrors. Each mirror has two mirror faces 104 and 105, and the mirror face is separated by two blanking parts 106. On the mirror face, an inclination to a rotation center axis 102 toward a terminal 104b from a start end 104a is continuously changed to constitute a face twisted by regarding a circumference 103 as a reference. A beam emission cycle is controlled so that a dot interval formed on a scanning face is a substantially regular interval to a mirror rotation angle. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for scanning a surface to be scanned with a laser light beam or the like, and more particularly, to a novel optical scanning mirror, a light beam scanning method, an apparatus, and an image forming apparatus for such optical scanning. An optical scanning mirror, an optical scanning method, and an optical beam scanning device according to the present invention include an electrophotographic or thermal recording printer, an image forming apparatus such as a copying machine, a print substrate, a film for printing, or CTP in the printing field. The present invention can be widely applied to an image setter or plotter device for making a printing plate, and a use for forming an image by exposing a silver salt film.

  As this type of prior art, for example, a rotating mirror having a side surface with a free curved surface that is a straight envelope surface whose inclination angle with respect to the central axis of the columnar body changes continuously, and a rotating mirror thereof, There is a scanning optical device used (for example, see Patent Document 1).

  The rotating mirror is intended to avoid windage loss during rotation, and the light incident direction on the mirror surface is a direction closer to the imaging target surface than the mirror surface and deviates from the vertical to the mirror rotation axis. The direction. Moreover, since this rotary mirror may be anything as long as it is a free-form surface, a mirror shape having an elliptical cross section is also employed.

  However, when such a mirror having a shape with a large change in diameter is used, the distance from the optical system for collimating the light source and irradiation light to the mirror surface, and the beam shaping optical system or the object to be covered from the mirror surface. Since the distance to the scanning surface changes, when the incident light is not completely parallel light, the shape of the reflected light beam from the mirror changes, and the load on the correction optical system becomes very large. Furthermore, since the beam diameter and the focal position of the reflected light from the mirror surface change greatly, the correction optical system inserted between the mirror surface and the surface to be scanned becomes complicated and expensive. Furthermore, since light is incident on the mirror from the surface to be scanned with respect to the mirror, an arrangement space for the incident optical system on the mirror is required. In particular, in the case of multi-beam support, the scanning system becomes large.

  Although the above-mentioned prior art is limited to a single beam configuration, light is applied to a curved surface whose angle changes slightly, and image formation is performed using the reflected light. Therefore, mirror processing errors, assembly errors, etc. Deviation is accumulated. However, in the above prior art, no correction is made for these deviations, so that a reduction in image quality becomes a problem. Further, since multi-beam scanning is not taken into consideration, no countermeasures (image correction, etc.) such as misalignment with the image formed by the adjacent beam that can occur in such a configuration are taken.

  As another conventional technique, based on a modulation signal corresponding to each of the plurality of beams, a light source that emits a plurality of beams, a scanning unit that scans the plurality of beams to form an image on a scanned medium, The modulation means for modulating the plurality of beams in synchronization with a plurality of clock signals capable of changing at least one partial oscillation frequency during one scanning period by the scanning means, and the clock generation means for outputting the plurality of clock signals And a frequency change timing control means for controlling the timing of changing the oscillation frequency of the plurality of clock signals by outputting a frequency change timing control signal to the clock generating means, and the frequency change timing control means includes the frequency change timing control means, Required for scanning in the scanning direction offset distance on the scanned medium by the scanning means generated between a plurality of beams There is an image forming apparatus that controls the oscillation frequency change timing of the clock signal corresponding to the offset beam of the plurality of clock signals so that the frequency change timing is offset by approximately the same time as the interval (for example, see Patent Document 2). reference).

  According to the above prior art, the plurality of beams generated from the light source are scanned by the scanning unit so as to form an image on the scanned medium, thereby forming an image on the scanned medium. In the modulation means, the modulation signal corresponding to each of the plurality of beams is synchronized with the plurality of clock signals output from the clock generation means capable of changing at least one partial oscillation frequency during one scanning period by the scanning means corresponding to each of the plurality of beams. Thus, a plurality of beams are modulated. That is, the scanning frequency can be corrected by the scanning means by forming an image with a plurality of beams whose oscillation frequency is swept during one scan and modulated in synchronization with a plurality of clock signals output from the clock generating means. .

  However, in the above apparatus, since the interval in the sub-scanning direction of a plurality of beams is as short as 1 to several dots, the interval of tens of dots or hundreds of dots or more as in the proposed invention is the purpose of correcting the beam position.・ Meaning is different. Further, since the writing means has a plurality of arrays in the main scanning direction and the sub-scanning direction, the configuration of the writing means is completely different.

  As another conventional technique, the actual image position on the medium is sequentially driven from a light source having a large shift amount with respect to a predetermined position, and image formation is performed by changing the writing timing of a plurality of light sources, thereby correcting the shift 1 There is an apparatus that forms two images (see, for example, Patent Document 3). However, since this apparatus is adopted in the drum scanning system, it cannot be applied to the planar scanning system as it is. In the drum scanning method, the joint drawing method with the drawing area by the adjacent light source is performed by writing one line in the main scanning direction, whereas in the plane scanning method, the drawing is performed by sequentially moving in the sub-scanning direction. Is made. For this reason, the correction method is completely different.

  The present applicant has previously proposed an optical scanning mirror, an optical scanning method using the mirror, an optical scanning device equipped with the mirror, and an image forming apparatus (Japanese Patent Application No. 2002-362722). ). The optical scanning mirror has the following characteristics.

  That is, it has a rotation center axis, and has a mirror surface along a circumference of a predetermined radius around the rotation center axis in a plane perpendicular to the rotation center axis, and the mirror surface extends from one end to the other end. This is a surface twisted with reference to the circumference, in which the inclination with respect to the rotation center axis continuously changes (see FIG. 1).

  The above-described technology relates to an optical scanning mirror having unprecedented features, but since no correction is made for various misalignments of an image formed on a medium, there is a problem in that image quality is deteriorated. Become.

  As another prior art, with respect to an apparatus having a writing unit for outputting a plurality of beams, correction of an image formed on a medium corresponding to each of the plurality of beams, in particular, image data conversion of a deviation in the main scanning direction. Alternatively, there is a method and an apparatus that perform correction by performing image data transfer control (see, for example, Patent Document 4). Since this prior art is the same as Patent Document 3 and the scanning method is a drum scanning method, the correction method is different from the scanning method proposed here.

  Furthermore, as another conventional technique, with respect to an apparatus having writing means for outputting a plurality of beams, correction of an image formed on a medium corresponding to each of the plurality of beams, in particular, an image in the sub-scanning direction is corrected. There is a method and an apparatus that perform correction by performing data conversion or image data transfer control (see, for example, Patent Document 5). Since this prior art is the same as Patent Document 3 and the scanning method is a drum scanning method, the correction method is different from the scanning method proposed here.

Japanese Patent Laid-Open No. 11-142864 JP 2002-341279 A Japanese Patent No. 3067942 JP 2002-264373 A JP 2002-264291 A

  In order to use the above-mentioned mirror to support multi-beams, a configuration in which a plurality of mirrors are mounted on the same axis is adopted. In this case, the effects of machining errors and assembly errors of individually machined mirrors are affected. The accuracy may be reduced.

The present invention has been made in view of the above problems,
The object of the present invention is that the burden on the optical system for beam shaping is small, multi-beam compatibility can be realized with high accuracy, widening is easy, and when multi-beam writing is used, an optical system such as a lens is included. Provides a light scanning method and a light beam scanning device that use a mirror that can realize a high-quality image formation and that can perform planar scanning, and an image forming device including the light scanning device. There is to do.

  The present invention has a rotation center axis and has at least one mirror surface in the direction of the rotation center axis along a circumference of a predetermined radius centered on the rotation center axis in a plane perpendicular to the rotation center axis. (Hereinafter referred to as the rotation axis direction mirror), and the surface of the rotation axis direction mirror is a surface twisted with respect to the circumference, the inclination of the rotation axis continuously changing from one end to the other end. In the light beam scanning device using a certain light scanning mirror, the most important feature is that the beam irradiation period is controlled so that the interval between dots formed on the scanning surface is substantially equal to the mirror rotation angle. To do.

  In the present invention, the position where the effective incident light hits the mirror is on the circumference around the rotation center axis in a plane perpendicular to the rotation center axis of the mirror. Accordingly, since the distance between the mirror surface and the light incident system is always constant, the beam shape of the reflected light from the mirror surface does not change greatly during scanning. Therefore, it is possible to greatly reduce the load required for correcting the beam shape on the optical system. Also, the focal position correction is very simple compared to the prior art because there is no significant change in the reflected light from the mirror. However, effective incident light refers to light actually used for scanning.

  In cutting and molding, metals such as aluminum and stainless steel are usually used, but a mirror in which a metal layer is formed on the surface of a resin part made by molding can also be used.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention relates to a light beam scanning method, an apparatus, and an image formability apparatus using the optical scanning mirror shown in the examples of FIGS. 1 and 2, and in particular, correction of an image formed on a scanning surface. With the goal.

  First, the optical scanning mirror used in the present invention will be described. 1 and 2A are front views, FIG. 1B is a right side view, and FIG. 1C is a bottom view.

  The optical scanning mirror 100 has at least one mirror (one in the example of FIG. 1 and four in the example of FIG. 2) in the direction of the rotation center axis on the outer peripheral surface of the disk-shaped rotating body 101, and Each mirror is formed by forming two mirror surfaces 104 and 105 in the circumferential direction of the mirror. The mirror surfaces 104 and 105 are separated by two blanking portions 106 provided on the outer peripheral surface of the rotating body 101. Near the center in the width direction of the mirror surfaces 104 and 105, there is a place in a plane perpendicular to the rotation center axis 102 of the rotator 101 that coincides with a circumference 103 having a predetermined radius centered on the rotation center axis. The surface is twisted with the circumference 103 as a reference. Accordingly, there is a portion equidistant from the rotation center axis 102 of the rotating body 101 in the vicinity of the centers of the mirror surfaces 104 and 105.

  The mirror surfaces 104 and 105 will be further described. The mirror surface 104 continuously changes in inclination with respect to the rotation center axis 102 from the start end (scan start position) 104a to the end end (scan end position) 104b. The inclination of the mirror surface 104 is 0 ° at the central position 104c in the length direction, the direction of the inclination is reversed at the central position 104c, and the inclination is the maximum reverse angle (± α °) at the start end 104a and the end 104b. Become. Referring to FIG. 1 (a), the mirror surface is inclined in a direction that can be seen from the front side on the start side, and in a direction that cannot be seen on the end side. The mirror surface is also a twisted surface with the same circumference as the reference, the tilt angle is 0 ° at the center position, and the tilt direction reverses at that position, and the start end (scan start position) and end end (scan end) Position), the inclination is the maximum reverse angle (± α °).

  As will be described later, the light beam lighting timing on the mirror surface is irradiated with the light beam on the mirror surface while rotating the optical scanning mirror around the rotation center axis, and parallel to the rotation center axis by the reflected light beam. When a flat surface is scanned, the mirror surface is irradiated with a light beam so that the interval between images formed on the surface to be scanned and the rotation angle of the optical scanning mirror are directly proportional.

  If the mirror surface is irradiated with a beam at such timing, a correction optical system such as an f-θ lens is provided between the optical scanning mirror and the surface to be scanned by rotating the optical scanning mirror at a constant speed. Therefore, the surface to be scanned can be scanned at a constant speed.

As an example of the scanning method and apparatus using the optical scanning mirror of the present invention, a configuration in which a single beam is irradiated onto one optical scanning mirror as in the example of FIG. 3 or a plurality of beams as in the example of FIG. It is possible to irradiate one optical scanning mirror.
In this embodiment, there are notches (blanking portions) 106 at two positions on the surface of the optical scanning mirror, and this is a one-way scanning mirror that starts scanning again from the origin direction after passing through the blanking portion. A bi-directional scanning type mirror that does not have a portion and in which the tilt angle of the mirror surface is reversed again is also an object of the present invention. However, in the case of an optical scanning mirror having a blanking portion, it is necessary to control the phase so as not to irradiate the blanking portion with a light beam as in the example of FIG.

  As the present optical scanning device, for example, a collimating lens, a condensing lens, and a focus correcting lens are provided only at the front stage of the optical scanning mirror, at the rear stage of the mirror, or at the front and rear stages of the mirror as in the example of FIG. By including a lens, a beam shaping lens, and other correction optical systems 205 and 251, scanning accuracy can be further increased.

  However, as shown in the example of FIG. 7, various problems occur in the drawing result. Hereinafter, various correction methods of the present invention will be described.

  7A and 7B show examples of scanning methods. (A) is an example of unidirectional scanning, and (b) is an example of bidirectional scanning. However, in the figure, in order to make the scanning direction easy to understand, the inclination of the scanning locus is emphasized. Actually, the inclination of the image in the main scanning direction is very small. In this example, a scanning example using a plurality of beams is shown, but the beam interval may be short or long depending on the apparatus configuration.

  The example of FIG. 7F shows a problem that occurs in an image formed by a single light beam. That is, this is an example where the dot pitch in the main scanning direction (a direction substantially perpendicular to the moving direction of the scanning target) is not equal. Excluding the influence of some vibrations, this can be attributed to the processing of the mirror surface for optical scanning or to the design of the tilt angle. What is caused by processing results in irregular dot pitch variations, whereas what is caused by the surface tilt design of the optical scanning mirror is often a dot pitch having a certain rule. Regarding the surface tilt design of the optical scanning mirror, for example, there is a problem when the rotation angle of the optical scanning mirror and the tilt angle of the mirror surface are made linear as shown in the example of FIG.

  The pre-correction scanning trajectory shown in FIG. 8 has a trajectory having a non-linear interval with respect to the rotation angle of the scanning mirror. However, as a condition, an optical correction system (lens or the like) is not inserted either before or after the optical scanning mirror, and the writing cycle is set at an equal interval as shown in FIG. 9 before the correction. is there.

  When writing is performed on the optical scanning mirror thus made at the timing shown in FIG. 9, the scanning interval can be made linear with respect to the rotation angle of the mirror, as shown in FIG. it can. As described above, the mirror surface tilt angle can be corrected by controlling the writing cycle.

  FIG. 10A shows a scanning result and a result after correction, and FIG. 10B shows an example of data transfer control before and after correction. The data before correction shows the same tendency even if it is repeatedly performed. As described above, when the same result is shown every time, scanning can be performed at substantially equal intervals by performing writing at a timing in which the amount of deviation is corrected in advance. For example, even when the maximum / minimum difference in dot pitch before correction is 2 μm as shown in FIG. 10A, the data transmission period can be controlled to 0.4 μm. As described above, it is effective to correct the data communication cycle based on the drawing result.

  FIG. 11 shows an example of a correction method when there is a variation in the dot pitch in the sub-scanning direction. When there is an error of about 10% with respect to the ideal value as in the pre-correction data in FIG. 11A, for example, if an optical scanning mirror having four mirror surfaces is used as shown in FIG. By irradiating the light beam only at the optimal timing, instead of scanning every time the mirror surface passes, the pitch variation in the sub-scanning direction can be greatly reduced. However, the sub-scanning direction pitch variation before correction in this case is limited to the case where the same tendency is always observed at every writing.

  FIG. 12 is also a method for reducing the pitch variation in the sub-scanning direction, and controls the rotational speed of the optical scanning mirror according to the encoder output signal cycle representing the amount of movement of the scanning surface. In this example, the rotation speed of the mirror for optical scanning is changed by shifting the phase for each pulse of the encoder output, but the rotation speed of the mirror is controlled based on the result of multiple pulses by dividing the encoder output. Also good. In general, when the encoder output cycle is long, the movement of the scanning surface is slow, and when it is short, the movement of the scanning surface is fast. Therefore, if the scanning surface moving speed is slow, the mirror rotating speed is also slowed down, and if the scanning surface moving speed is fast, the mirror rotating speed is also fastened. By performing such control, it is possible to reduce pitch variation in the sub-scanning direction.

  More specifically, the relationship between the pulse period of the encoder and the rotation speed of the mirror is stored in the control system in the form of an expression or a reference table, and necessary mirror rotation speed information or a motor for driving the mirror as appropriate. This is done by obtaining a supply signal to the driver.

  FIG. 13 shows an example of a method for correcting the problem shown in FIG. That is, a method for reducing variation in the writing start position in the main scanning direction is shown. The optical scanning mirror used in the present invention scans in a direction substantially orthogonal to the rotational direction in accordance with the rotational phase of the mirror. Therefore, it is possible to grasp the scanning position in the main scanning direction by grasping the rotation phase of the mirror. Therefore, an image can be written from a desired position by previously grasping the relationship between the rotation angle of the mirror and the scanning position of the light beam. The relationship between the rotation angle of the mirror and the scanning position may be stored in the control system as an approximate expression or a conversion table, and the light beam irradiation timing to the mirror may be obtained according to the rotation angle information of the mirror.

  FIG. 14 shows an example of scanning with a plurality of beams by using an optical scanning mirror having a plurality of mirrors in the rotation axis direction. The mirror has one main body, but has a plurality of mirrors in a direction parallel to the rotation axis, and each mirror has the same number of at least one mirror surface in the circumferential direction.

  FIG. 15 shows a configuration having a plurality of optical scanning mirrors on the same axis, (a) shows an example in which a plurality of mirrors having only one mirror in the direction of the rotation axis are mounted, and (b) shows the direction of the rotation axis. An example in which a plurality of optical scanning mirrors having a plurality of mirrors are mounted coaxially will be described. Further, FIG. 16 shows an example in which a plurality of optical scanning mirrors are driven by individual rotation axes.

  The examples in FIGS. 14 to 16 are configured to scan with a plurality of beams, but each beam is equipped with at least one of the above correction methods, and each beam forms a good image. Is possible. However, in such a scanning method using a plurality of beams, an image deviation from the scanning result using adjacent beams as shown in FIGS. 7C to 7E and 7H occurs.

  FIG. 17 shows an example of a method for solving the problem of FIG. That is, the problem is that each image formed by a plurality of beams is displaced in the main scanning direction and the sub-scanning direction, and the image quality is remarkably deteriorated. When the original image data shown in FIG. 17 (a) is scanned in the image layout as shown in the left figure of FIG. 17 (b), the positional deviation from the image by the adjacent beam as shown in the right figure of FIG. 17 (b). When data occurs, data as shown in the left figure of FIG. 17C in which the pixel arrangement of the original image is rearranged in advance in a direction that cancels each deviation in the main and sub scanning directions is prepared, and the data after the rearrangement is used. By scanning, it is possible to form a good image with no joints as shown in the right diagram of FIG. It should be noted that the shift smaller than the pixel pitch can be eliminated by adjusting the scanning timing partially or entirely.

  Furthermore, as shown in FIG. 20, each light source unit position is made a system that can be displaced minutely independently, and by moving the optical unit in a direction that cancels the deviation amount on the scanning surface, each image by a plurality of beams is obtained. Can be reduced. Displacement means can be realized by using a piezo or a voice coil motor. In addition, as shown in FIG. 21, the scanning position correction can also be performed by slightly shifting the transfer timing of the image data. FIG. 21A shows an example in which the data transfer timing is changed in units of pixels, and FIG. 21B shows an example in which a deviation less than the dot pitch is corrected. In FIG. 21B, a high-frequency clock is prepared so that fine timing adjustment can be performed. In this case, a method of preparing clocks with various frequencies or mounting a clock source capable of output is used.

  FIG. 18 shows an example of a method for solving the problems of FIGS. 7 (e) and (h). That is, the problem is that there are variations in dot pitches in the main scanning direction of a plurality of beams as shown in FIG. 7E, and variations in dot pitches in the sub-scanning direction of a plurality of beams as shown in FIG. 7H. Will occur.

  For example, as a cause of variations in the dot pitch in the main scanning direction, except for lack of smoothness of the scanning surface, the amount of displacement of the mirror surface tilt with respect to the rotation angle of each optical scanning mirror differs, and the data corresponding to each mirror The case where there is variation in transfer timing is mainly considered. As a countermeasure, the data transfer frequency corresponding to each mirror is adjusted and controlled by itself so that the dot pitch in the main scanning direction on the scanning plane of each of the plurality of beams is substantially equal to the range in which the image quality does not deteriorate. . However, this adjustment has a condition that the mirror surface for scanning the next line of the arbitrary mirror does not reach the beam irradiation position from the light source until all mirrors have scanned the same line.

  Also, as the cause of dot pitch variation in the sub-scanning direction, the mirror circumference (surface length) caused by the processing error of the mirror diameter, excluding mounting misalignment of multiple light scanning mirrors and insufficient optical system position accuracy, etc. ) And each rotation speed variation when each optical scanning mirror is rotated by an independent axis by a drive system corresponding to each axis. In this way, especially when the processing accuracy of the optical scanning mirror is low, scanning in the sub-scanning direction is achieved by controlling a plurality of mirrors with individual axes and drive systems and controlling the rotation speed to be suitable for each optical scanning mirror. By adjusting the interval, it is possible to correct within a range that does not deteriorate the image quality. However, changing the rotation speed of the optical scanning mirror in this way also affects the data transfer cycle in the main scanning direction.

  Therefore, as shown in FIG. 18, when there are variations in the dot pitch in the main and sub-scanning directions for each beam in the scanning result of a plurality of beams (this figure shows adjacent beams (N−1 and N + 1) with respect to the Nth beam). The dot pitches in the main scanning direction and the sub-scanning direction before the correction are represented), and first, the scanning pitch correction in the sub-scanning direction is performed. This is dealt with by adjusting the rotational speed of each optical scanning mirror as described above. Thereafter, scanning pitch correction in the main scanning direction is performed. This is preferably performed by the methods of claims 1 and 2.

  However, the point to be noted in this case is that it is more preferable to introduce conversion of the image data arrangement in addition to the control of the data transfer clock because the dot pitch displacement amount on the scanning surface becomes non-linear compared to a normal polygon mirror. . It is also effective to use an optical scanning mirror that has been processed so that the rotational angle displacement amount of the optical scanning mirror and the scanning interval on the scanning surface are linear. Furthermore, it is more desirable to add correction using an optical system.

FIG. 19 shows an example of a method for solving the problem shown in FIG. 7 (d), which is a significant deterioration in image quality caused by different scanning directions of a plurality of beams.

  In this way, although the scanning directions are rarely different, the beam spacing is actually farther away, so even if there is a slight angle shift, there will be a large shift at the joint with the image by the adjacent beam, and the image quality will deteriorate due to the step. Cannot be ignored.

  Therefore, as shown in FIG. 19, a beam having a large angular deviation can be made inconspicuous by narrowing the scanning width in the main scanning direction and widening the scanning width of the adjacent beam. However, in order to use such a method, it is necessary to scan from each beam by changing the pixel arrangement of the original image data.

  FIG. 22 shows a multi-color image forming apparatus that forms a color image by superimposing colors. If the images of each color shift, the original image color cannot be reproduced, and the detail image is blurred and lacks in definition, resulting in a blurred picture. End up. Therefore, for example, when a large shift occurs as shown in FIG. 22A when image formation with four colors is performed, the pixel alignment of the original image is changed to each shift amount as shown in FIG. By using it for scanning according to the above, it becomes possible to obtain an image with little deviation as shown in FIG.

  The light beam scanning method and apparatus according to the present invention described above are used for image forming apparatuses such as electrophotographic and thermal recording printers and copiers, printing plates and printing plates for printing films such as film for printing and CTP in the printing field. It is suitable as a light beam scanning device in an image setter or a plotter device, and can also be applied to applications in which a silver salt film is exposed to form an image.

  As such an application example, an example of an electrophotographic image forming apparatus will be described with reference to FIG. In FIG. 23, reference numeral 400 denotes a light beam scanning device according to the present invention. This light beam scanning device 400 is, for example, a light beam scanning device having the configuration shown in FIGS. 14 to 16 and the correction optical systems 250 and 251 shown in FIG. It is the structure provided correspondingly. However, a configuration in which one of the correction optical systems 250 and 251 is omitted depending on the shape of each of the plurality of mirrors in the rotation axis direction is possible. Reference numeral 401 denotes a photosensitive drum (image carrier) that provides a surface to be scanned of the light beam scanning device 400.

  The light beam scanning device 400 scans the surface (surface to be scanned) of the photosensitive drum 401 in the axial direction of the drum with a plurality of laser beams modulated by the image signal. The photosensitive drum 401 is driven to rotate in the direction of the arrow in the figure, and the surface charged by the charging unit 402 is scanned with a laser beam by the light beam scanning device 400 to form an electrostatic latent image. The electrostatic latent image is visualized as a toner image by the developing unit 403, and the toner image is transferred to the recording paper 405 by the transfer unit 404. The transferred toner image is fixed on the recording paper 405 by the fixing unit 406. Residual toner is removed by a cleaning unit 407 on the surface portion of the photosensitive drum 401 that has passed through the transfer unit 404.

  Since the light beam scanning apparatus 400 can perform high-speed scanning with a plurality of beams, high-speed image formation is possible. Further, since the light beam scanning device 400 can be made compact and inexpensive compared to a configuration using a plurality of polygon mirrors, a compact and inexpensive image forming apparatus can be realized.

  Note that the conveyance mechanism for the recording paper 405, the driving mechanism for the photosensitive drum 401, the control means such as the developing unit 403, and the transfer unit 404 may be the same as those in the conventional image forming apparatus, and are omitted in the drawing. A configuration in which a belt-like photoconductor is used as the image carrier instead of the photoconductor drum 401 is also possible. It is also possible to adopt a configuration in which the toner image is once transferred to a transfer medium, and the toner image is transferred from the transfer medium to recording paper.

  As another application example, an example of an image forming apparatus targeting a medium such as a printing plate including a CTP plate or a mask film for producing a printing plate will be described with reference to FIG.

  The image forming apparatus shown in FIG. 24 is an example of the present invention. The medium used in this apparatus may be any medium as long as it can form an image in a photosensitive mode or a heat-sensitive mode by light irradiation such as laser light, and before or after image formation, or both before and after depending on the type of medium. However, some process steps such as cleaning and development are required, and these media are also targeted. Specifically, various types of printing plates and mask films for making plates are also included. The energy irradiation device in the figure is a light beam scanning device including a mirror and an optical lens (not shown) of the present invention. An image can be formed by scanning light while moving the medium.

  As another application example, an example of an image forming apparatus equipped with a writing device for a printing plate such as a CTP plate and having a printing function using ink will be described with reference to FIG.

  The image forming apparatus shown in FIG. 25 is an example of the present invention. These examples are apparatuses having printing functions such as lithographic printing such as offset printing machines and stencil printing machines, and plate making functions. First, a plate is produced by light irradiation, and then printing on a recording sheet is performed using the produced plate. However, a plate that includes a resin or the like that adheres to the drum surface in accordance with image information and removes the resin after printing is included in the plate.

  FIG. 25A is an example in which plate-making is performed on a roll-shaped plate by a light beam scanning device, and printing is performed on recording paper with a single color ink, and FIG. This is an example of a four-color offset printing machine that performs plate making using a light beam scanning device installed on each cylinder and then prints a full-color image on a recording sheet. In both cases, an ink image is formed on the medium on the plate cylinder, the ink image is transferred from the plate to the blanket, and finally the ink image is transferred from the blanket to the recording paper.

The 1st example of the mirror for optical scanning used for this invention is shown. The 2nd example of the mirror for optical scanning used for this invention is shown. The 1st example of the scanning apparatus by the mirror for optical scanning of this invention is shown. The 2nd example of the scanning device by the mirror for optical scanning of this invention is shown. The timing which controls a beam irradiation period is shown. The 3rd example of the scanning device by the mirror for optical scanning of this invention is shown. Various problems that occur in the drawing results are shown. An example is shown in which the rotation angle of the optical scanning mirror and the tilt angle of the mirror surface are linear. An example of correcting the mirror surface tilt angle by controlling the writing cycle will be shown. The values before and after correction of the dot pitch in the main scanning direction and before and after correction of the data transfer clock are shown. The values before and after correcting the dot pitch in the sub-scanning direction and before and after correcting the mirror scanning are shown. A method for reducing pitch variation in the sub-scanning direction will be described. A method for reducing variations in the writing start position in the main scanning direction will be described. An example of scanning with a plurality of beams using an optical scanning mirror is shown. A configuration having a plurality of optical scanning mirrors on the same axis is shown. An example in which a plurality of optical scanning mirrors are driven by individual rotation axes will be described. A method for eliminating the positional deviation of beam irradiation will be described. A method for eliminating variations in dot pitch in the scanning direction will be described. A method for eliminating variations in main scanning scan angle between light sources will be described. An example in which the amount of deviation on the scanning surface is reduced by moving the optical system will be described. An example in which scanning position correction is performed by shifting the transfer timing of image data is shown. A method for obtaining a color image with little deviation will be described. 1 shows a first example of an image forming apparatus. 2 shows a second example of an image forming apparatus. 3 shows a third example of an image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Optical scanning mirror 101 Rotating body 102 Rotation center axis 103 Circumference 104, 105 Mirror surface 106 Blanking part 107 Rotation axis hole

Claims (20)

  Having a rotation center axis, and having at least one mirror surface in the rotation center axis direction along a circumference of a predetermined radius centered on the rotation center axis in a plane perpendicular to the rotation center axis (hereinafter referred to as “rotation center axis direction”). Rotation axis direction mirror), and the surface of the rotation axis direction mirror is a surface that is twisted with respect to the circumference, the inclination of the rotation axis continuously changing from one end to the other end. In a light beam scanning apparatus using a mirror, a light beam scanning method is characterized in that the beam irradiation period is controlled so that the interval between dots formed on the scanning surface is substantially equal to the mirror rotation angle.   2. The light beam scanning method according to claim 1, wherein the dot interval trajectory data on the scan surface is measured in advance so that the dot intervals formed on the scan surface are substantially equal to the mirror rotation angle. A light beam scanning method characterized by controlling a data transmission cycle to a light source possessed by the light beam scanning device.   2. The light beam scanning method according to claim 1, wherein the mirror is rotated under the condition that the scanning density in the sub-scanning direction is higher than the image density, and the mirror is lighted at a timing at which the moving amount of the scanning surface becomes an interval corresponding to the image density. A light beam scanning method characterized by irradiating and scanning a beam.   4. The light beam scanning method according to claim 3, wherein the mirror rotation speed is controlled based on an encoder output signal representing a moving amount of the scanning surface.   2. The light beam scanning method according to claim 1, wherein the scanning start time in the main scanning direction is controlled from the mirror rotation angle information so that the line head positions formed on the scanning surface are substantially the same. A light beam scanning method.   6. The method according to claim 1, wherein a mirror having a plurality of mirror surfaces in a rotation axis direction (hereinafter referred to as a plurality of rotation axis direction mirrors) is used as the optical scanning mirror. A method of scanning a light beam, comprising: scanning the surface to be scanned with a plurality of light beams reflected by the mirror surfaces of the plurality of mirrors in the rotation axis direction.   A plurality of light beams reflected by the mirror surfaces of the plurality of light scanning mirrors using the method according to claim 1, wherein the light scanning mirrors are simultaneously rotated on the same axis. A method of scanning the light beam by scanning the surface to be scanned.   6. The method according to claim 1, wherein a plurality of the optical scanning mirrors are used, each mirror is simultaneously rotated on a separate axis, and the plurality of optical scanning mirrors are mirrored. A method of scanning a light beam, comprising: scanning the surface to be scanned with a plurality of light beams reflected by the surface.   The light beam scanning apparatus using the method according to claim 6, wherein a deviation amount in a main scanning direction and a sub scanning direction generated at a boundary between an image by an adjacent light beam and an image by an attention light beam is determined. Accordingly, after rearranging the image data to be transmitted to the light beam scanning device, the light beam scanning device forms an image with the light beam scanning device.   9. A light beam scanning apparatus using the method according to claim 6, wherein the image data drawing timing is set so that dot intervals in the main scanning direction formed by a plurality of beams are substantially the same. A light beam scanning device characterized by changing each beam.   In the light beam scanning device using the method according to any one of claims 6 to 8, according to the difference between the scanning angle of the adjacent light beam on the scanning surface and the scanning angle of the light beam of interest on the scanning surface, A light beam scanning apparatus characterized in that the number of dots formed by each light beam in the main scanning direction is changed.   The light beam scanning apparatus using the method according to claim 6, wherein a deviation amount in a main scanning direction and a sub scanning direction generated at a boundary between an image by an adjacent light beam and an image by an attention light beam is determined. Accordingly, the optical beam scanning apparatus is characterized in that the optical system is moved in a direction to cancel the deviation.   The light beam scanning apparatus using the method according to claim 6, wherein a deviation amount in a main scanning direction and a sub scanning direction generated at a boundary between an image by an adjacent light beam and an image by an attention light beam is determined. In response, the light beam scanning device transmits image data at a timing to cancel the deviation.   2. A multi-color image forming apparatus using the light beam scanning method according to claim 1, wherein an image forming position of a target color is controlled with reference to an image forming position of an arbitrary color.   9. A light beam scanning apparatus using the light beam scanning method according to claim 8, wherein the intervals between the sub-scanning directions of all the beams are made substantially equal by adjusting the rotational speed of each mirror individually. Light beam scanning device.   A light beam scanning apparatus comprising a light beam irradiation mechanism on which the light beam scanning method according to claim 1 is mounted.   An image forming apparatus comprising the light beam scanning device according to claim 16.   18. The image forming apparatus according to claim 17, wherein the image carrier, means for charging the surface of the image carrier, and light modulated by an image signal using the charged surface of the image carrier as a scanning surface. An image forming apparatus comprising: a light beam scanning device for forming an electrostatic latent image by scanning with a beam; and means for visualizing the electrostatic latent image formed on the image carrier. .   18. The image forming apparatus according to claim 17, wherein an image is formed on the medium by scanning the medium, means for conveying the medium, and a light beam modulated by an image signal with respect to the medium in the conveyed state. An image forming apparatus comprising: a light beam scanning device.   20. An image forming apparatus comprising: the image forming apparatus according to claim 19; means for forming an ink image on the medium; and means for transferring the ink image to a recording sheet.

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