JP2005351945A - Mirror for optical scanning, method of optical scanning, optical scanner and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the work load of an optical system while forming a beam, multi-beams are realized in a highly precise manner, the width of the beams is easily expanded, the size of a unit including the optical system is made small and plane scanning can be conducted. <P>SOLUTION: An optical scanning mirror 100 is provided with four mirrors in the direction of an axis of rotation 102 of a rotating body 101 and each mirror has two mirror surfaces 104 and 105. The mirror faces are separated by two blanking sections 106, the tilt with respect to the axis of rotation 102 continuously varies from a starting end (a scanning starting position) 104a to an end (a scanning completion position) 104b and a twisted face is constituted using an inner circumference 103 as a reference. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  As another prior art, there is an optical deflecting device that includes a cylindrical mirror whose outer surface is a reflecting surface, and in which the central axis of the cylinder and the rotation axis of the mirror do not match (see, for example, Patent Document 2).

  However, in this apparatus, since the diameter from the rotation axis to the mirror surface constantly changes in the mirror rotation state, the distance from the optical system having a light source or a collimating function to the mirror surface, and the mirror, The distance from the surface to the beam shaping optical system or the surface to be scanned changes. Therefore, a great load is applied to the optical system necessary for beam shape and focus correction, resulting in an expensive apparatus.

  When the cylindrical mirror is rotated at a high speed, vibration noise is likely to be generated, and the scanning speed is limited in terms of the rotational speed. In the case of unidirectional scanning, the time for half rotation for returning the beam to the scanning start position is wasted, which also hinders the speeding up of scanning. Further, in the configuration in which the cylindrical mirror is rotated around the eccentric axis, scanning can be performed only in a direction perpendicular to the rotational axis of the cylindrical mirror. Therefore, when scanning with a plurality of beams, the rotation of the plurality of axes is synchronized. A mechanism is required separately.

  Polygon mirrors (rotating polygon mirrors) are widely used as optical scanning means in image forming apparatuses and the like. A configuration using a plurality of polygon mirrors and scanning with a plurality of beams is also known (see, for example, Patent Document 3).

  However, the method of performing optical scanning using a polygon mirror generally increases the size of the entire apparatus including the optical system. Further, since the polygon mirror can only scan in the direction orthogonal to the rotation axis thereof, it is not easy to mount a large number of beams at a high density, and a mechanism for synchronizing the rotation of a plurality of polygon mirrors is indispensable.

  Therefore, 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. 15).

Japanese Patent Laid-Open No. 11-142864 Japanese Examined Patent Publication No. 6-105331 Japanese Patent Laid-Open No. 6-208066

  In order to support multi-beams using the above-mentioned mirrors, 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 adopted. The accuracy may decrease.

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. An optical scanning mirror that is small in size and capable of plane scanning, an optical scanning method and an optical scanning device that use the mirror, and an image forming apparatus that includes the optical scanning device are provided. .

  The present invention has a rotation center axis, and has a plurality of mirror surfaces in a 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, Each of the mirror surfaces is characterized by being a twisted surface with respect to the circumference, the inclination of which is continuously changed from one end to the other end with respect to the rotation center axis.

  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. The effective incident light refers to light that is actually used for scanning.

  In the present invention, for example, when manufacturing with a processing machine, since a plurality of mirrors are processed on the same member under the same conditions with the processing machine, there is little processing variation of each mirror, and the optical scanning apparatus after processing This makes it possible to greatly reduce the labor required for individual mirror position adjustment. In addition, the superiority does not change even when the mirror is manufactured by molding. In the above-described processing 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. FIG. 1 shows a first embodiment of an optical scanning mirror according to the present invention. 1A is a front view, FIG. 1B is a right side view, and FIG. 1C is a bottom view.

  The optical scanning mirror 100 has a plurality of mirrors (four in this example) in the direction of the rotation center axis on the outer peripheral surface of the disk-shaped rotator 101, and each mirror has two mirror surfaces 104, 105 is formed. 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, the centers of the mirror surfaces 104 and 105 are equidistant from the rotation center axis 102 of the rotating body 101.

  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. 1A, the mirror surface 104 is tilted in a direction that can be seen from the front on the start end 104a side, and is tilted in a direction that cannot be seen on the end 104b side. The mirror surface 105 is also a twisted surface with the same circumference 103 as a reference. The tilt angle is 0 ° at the center position 105c, and the tilt direction is reversed with respect to that position, and a start end (scanning start position) 105a. The inclination is the maximum reverse angle (± α °) at the end (scan end position) 105b.

  The rate of change of the tilt of the mirror surfaces 104 and 105 is reflected by irradiating the mirror surfaces 104 and 105 with a light beam while rotating the optical scanning mirror 100 about the rotation center axis 102, as will be described later. When a plane parallel to the rotation center axis 102 is scanned with the light beam, the amount of movement of the reflected light beam on the surface to be scanned and the rotation angle of the light scanning mirror 100 are directly proportional to each other. The rate of change of slope is set. In order to obtain such a change rate of inclination, a correction optical system such as an f-θ lens is provided between the optical scanning mirror 100 and the surface to be scanned by rotating the optical scanning mirror 100 at a constant speed. The scanning surface can be scanned at a constant speed.

  The shape of the mirror can be variously configured as shown in FIGS. 2A to 2D in addition to FIG. FIGS. 2A and 2C are examples in which the scanning directions of the adjacent mirrors in the plurality of rotation axis direction mirrors are the same, and FIGS. 2B and 2D are the scanning of the adjacent mirrors in the rotation axis direction plural mirrors. An example in which the direction is the reverse direction is shown.

  2A and 2B are mirrors up to the boundary between adjacent mirrors in the direction of the central axis of rotation, whereas FIGS. 2C and 2D are configurations in which the boundary is not a scanning mirror. . From the viewpoint of the processing method, as shown in FIGS. 2 (c) and 2 (d), it is easier and less troublesome if only the necessary part is a mirror, but the method of use is not much different.

  Although the number of mirrors in the rotation center axis direction is four in this example, this number is obtained from the scannable width of each mirror and the required scan width, and an arbitrary number can be formed.

  In this optical scanning mirror 100, a rotating shaft hole 107 for mounting on a motor rotating shaft or the like is formed in the rotating body 101. When a plurality of optical scanning mirrors 100 are inserted and used on the same motor rotation shaft or the like, it is convenient that the rotation shaft hole 107 is provided. However, as means for precisely aligning the centers of the optical scanning mirror 100 and the motor rotation shaft, for example, in place of the rotation shaft hole 107, for example, FIG. 3 (a) or FIG. 3 (b) (FIG. 1 (b) As shown in FIG. 4 (c), it is possible to form a concave portion (or convex portion) for centering on the side surface of the rotating body 101. As shown in FIG. In addition to this, it is possible to form a concave portion (or convex portion) or the like for precise alignment. FIG. 4D shows an example in which two mirrors of FIG. 4C are actually mounted on the rotation center axis.

  The shape of the concave portion or the convex portion may be any shape, but at least the concave portion or the convex portion of the adjacent optical scanning mirror needs to be fitted. However, if it is used instead of a shaft, a shape other than a circle is desirable, and a polygon having a clear corner such as a quadrangle or a hexagon is more desirable.

  Further, as shown in FIG. 4 (e), centering can be performed in a configuration in which notches and grooves are provided on the outer peripheral surface.

  Furthermore, as shown in FIG. 4 (f), a plurality of optical scanning mirrors can be aligned by providing a hole in addition to the rotation center axis and inserting a pin or a rod-like jig into the hole. Become.

  The optical scanning mirror provided with the concave portion or convex portion, hole, notch or the like for centering as described above is also included in the present invention.

  The distance between each mirror in the rotational axis direction and the distance from the scanned surface so that the scanning range of the scanned surface by each laser beam deflected by the adjacent mirrors in the rotational axis direction partially overlaps, and The angle of mirror twist, the diameter of the optical scanning mirror, the length of the mirror surface, etc. are determined.

  The mirror surfaces 104 and 105 may be surfaces having a curved cross-sectional shape as shown in FIG. Such a mirror surface having a cross-sectional shape is easier to grind with a rotary blade than a mirror surface having a planar cross-sectional shape.

  Although not shown, the thickness of the rotating body 101 can be made larger than the width of the mirror surfaces 104 and 105 so that the outer peripheral surface of the rotating body 101 remains outside the mirror surfaces 104 and 105. Three or more mirror surfaces similar to the mirror surfaces 104 and 105 can be formed on the outer peripheral surface of the rotating body 101 along the same circumference.

  It is possible to form only one mirror surface similar to the mirror surfaces 104 and 105 on the outer peripheral surface of the rotating body 101. The overall shape of the rotating body 101 may be a columnar shape or a cylindrical shape. The mirror on the outer peripheral surface does not have to be twisted based on the center and may be asymmetrical. The optical scanning mirrors having the respective modified configurations as described above are also included in the present invention.

  If such an optical scanning mirror of the present invention is used, high-speed unidirectional scanning can be performed with a simple and compact device configuration, and high-density mounting of multiple beams can be easily realized. Hereinafter, an optical scanning apparatus for carrying out an optical scanning method using the optical scanning mirror of the present invention will be described.

  A first embodiment of an optical scanning device according to the present invention using the optical scanning mirror 100 shown in FIG. 1 is shown in FIGS. FIG. 6 shows a configuration viewed from the front side of the optical scanning mirror 100, and FIG. 7 shows a configuration viewed from the side of the optical scanning mirror 100.

  The optical scanning mirror 100 is inserted into the rotating shaft 201 of the motor 200, and is driven to rotate at a constant speed in the direction of the arrow shown in FIG. Since the optical scanning mirror 100 has a substantially symmetric shape around its rotation center axis, it is difficult to generate vibration and noise even if it is rotated at a high speed. Therefore, the optical scanning mirror 100 can be rotated at high speed without any problem, which is advantageous for increasing the scanning speed.

  Reference numeral 202 denotes a laser unit as a scanning light source. The laser beam 203 emitted from the laser unit 202 is incident on the mirror surfaces 104 and 105. The optical axis of the laser beam 203 and the centers of the mirror surfaces 104 and 105 (circumference 103 shown in FIG. 1A). Adapted to. The centers of the mirror surfaces 104 and 105, that is, the irradiation center of the laser beam 203 are equidistant from the rotation center axis of the optical scanning mirror 100. Reference numeral 205 denotes a surface to be scanned that is scanned by the laser light beam 204 reflected by the mirror surfaces 104 and 105, and is a surface parallel to the rotation center axis of the optical scanning mirror 100. There are also means for controlling the laser unit 202 and the motor 201, which are omitted in the drawing.

  The scanning operation is as follows. When the start end 104 a of the mirror 104 comes to the incident position of the laser beam 203, the reflected laser beam 204 is deflected by the largest angle in a direction parallel to the rotation center axis of the optical scanning mirror 100, and is on the surface to be scanned 205. Go to position 207. As the optical scanning mirror 100 rotates, the deflection angle of the laser beam 204 gradually decreases. When the center position 104c of the mirror surface 104 reaches the incident position of the laser beam 203, the deflection angle of the laser beam 204 is minimized. , To a position 208 on the scanned surface 205. As the optical scanning mirror 100 rotates, the deflection angle of the laser light beam 204 increases in the opposite direction. When the end 104b of the mirror surface 104 comes to the incident position of the laser light beam 203, the laser light beam 204 is placed on the surface to be scanned 207. Go to position 209. Thus, the scanned surface 205 is scanned from the position 207 to the position 209 in the direction of the arrow 210 parallel to the rotation center axis by the reflected laser light beam 204.

  When the optical scanning mirror 100 further rotates, the laser light beam 203 is similarly deflected by the mirror surface 105, and the scanned surface 205 is scanned from the position 207 to the position 209 in the direction of the arrow 210 by the reflected laser light beam 204. That is, the scanning surface 205 is scanned twice in the same direction (one-way scanning) during the period in which the optical scanning mirror 100 rotates once from the angle shown in FIG. Thus, according to the optical scanning device of the present embodiment, there is no wasted time for returning the beam to the scanning start position, and high-speed unidirectional scanning can be performed.

  The rate of change in inclination from the start end to the end of the mirror surfaces 104 and 105 of the optical scanning mirror 100 is determined as described above, and the optical scanning mirror 100 rotates at a constant speed. Scanning can be performed at a constant speed without providing a correction optical system such as an f-θ lens for scanning at a constant speed.

  In the optical scanning device of this embodiment, if the scanned surface 205 and the optical scanning mirror 100 are relatively moved in a direction orthogonal to the scanning direction by the reflected laser light beam 204, two-dimensional scanning of the scanned surface 205 is performed. It is clear that this is possible. In addition, if N mirror surfaces similar to the mirror surfaces 104 and 105 are formed on the optical scanning mirror 100, it is obvious that N-way scanning can be performed N times by one rotation of the optical scanning mirror 100. If the rotation speed of the optical scanning mirror 100 is the same, higher-speed scanning is possible. Naturally, the optical scanning device having such a configuration is also included in the present invention.

  The drive control of the laser unit 202 will be described with reference to the timing chart of FIG.

  As the optical scanning mirror 100 rotates, the mirror surfaces 104 and 105 or the blanking unit 106 pass through the incident position of the laser light beam 203 at a timing as shown in FIG. Since the blanking unit 106 does not perform effective scanning, a blanking signal as shown in FIG. 8B is supplied to the laser unit 202 by a control unit (not shown) so as not to generate excessive reflected light, and the blanking unit 106 performs blanking. In the period of the ranking unit 106 and a few periods before and after it, the laser light beam 203 is not output or is reduced to an extremely low power level. During such a period other than the blanking period, the laser unit 202 emits a laser beam 203 whose intensity is modulated in accordance with, for example, an image signal supplied from a control unit (not shown), and this is deflected by the mirror surface 104 or the mirror surface 105. As a result, the surface to be scanned 205 is scanned with a laser beam having power according to the image signal.

  FIG. 9 shows a second embodiment of the optical scanning device according to the present invention. The optical scanning device of the second embodiment has the same configuration as that of the first embodiment except that correction optical systems 250 and 251 are added.

  In general, since the laser beam 203 is emitted through a circular aperture provided inside or outside the laser unit 202, the laser beam 203 has a substantially circular intensity distribution. On the other hand, since the mirror surfaces 104 and 105 are substantially arc-shaped surfaces, the intensity distribution of the laser beam 204 reflected by the mirror surfaces 104 and 105 is orthogonal to the rotation center axis of the optical scanning mirror 100 due to the influence of the curvature. It spreads in the direction (circumferential direction). As a result, the spot shape of the laser light beam 204 applied to the scanned surface 205 is a non-circular shape extending in the direction orthogonal to the scanning direction, but it is generally desirable that the spot shape is close to a circular shape.

  In this embodiment, the correction optical system 250 corrects the intensity distribution shape of the laser light beam 203 after passing through the correction optical system 250 so that the width direction is wider than the length direction of the mirror surfaces 104 and 105. By this correction, the spot shape on the non-scanning surface 205 is corrected to a substantially circular shape. It is possible to obtain the same effect by correcting the intensity distribution shape of the laser beam 204 reflected by the mirror surfaces 104 and 105 with the correction optical system 251, and such a configuration is also included in the present invention.

  The center of the mirror surfaces 104 and 105, that is, the laser beam irradiation center position is ideally equidistant from the rotation center axis of the optical scanning mirror 100. However, for processing accuracy, some variation in the distance is avoided. I can't. The influence of this variation in distance appears as meandering of the scanning locus on the scanned surface 205. Generally, it is desirable that the amount of meandering is small. In the present embodiment, the correction optical system 251 reduces the meandering amount of the scanning locus by suppressing the shake of the laser light beam 204 that has passed through the correcting optical system 251 in the direction orthogonal to the scanning direction. If the variation in the distance between the centers of the mirror surfaces 104 and 105 and the rotation center axis is acceptable, meander correction by the correction optical system 251 is not necessary.

  Depending on the purpose of scanning, it may be desirable to intentionally change the distance between the centers of the mirror surfaces 104 and 105 and the rotation center axis to meander the scanning locus. Such an optical scanning mirror and an optical scanning device are also included in the present invention.

  A third embodiment of the optical scanning device according to the present invention will be described with reference to FIG. In this optical scanning device, a laser unit 202 b is provided separately from the laser unit 202, and two laser units 202 and 202 b irradiate laser light beams 203 and 203 b from opposite directions and are deflected by mirror surfaces 104 and 105. The scanning surface 205 is simultaneously unidirectionally scanned by the laser light beams 204 and 204b, and the rest is the same as in the first embodiment. However, with respect to the laser light beam 203b, since the start ends of the mirror surfaces 104 and 105 are the scan end position and the end is the scan start position, the scanning directions of the laser light beams 204 and 204b are opposite to each other. Thus, since the present embodiment is configured to simultaneously scan with two laser beams, higher speed scanning is possible.

  Also in this embodiment, a correction optical system similar to the correction optical systems 250 and 251 (FIG. 9) in the second embodiment can be provided, and such a configuration is also included in the present invention. Further, when the optical scanning mirror 100 is provided with a larger number of mirror surfaces, the laser light beams are simultaneously irradiated onto the three or more mirror surfaces, and the simultaneous scanning with the three or more laser light beams is performed. A configuration is also possible, and an optical scanning device having such a configuration is also included in the present invention.

  A fourth embodiment of the optical scanning device of the present invention will be described with reference to FIG. In this embodiment, two (generally a plurality of) optical scanning mirrors 100 shown in FIG. 1 are inserted into the rotating shaft 201 of the common motor 200, and each optical scanning mirror is not shown. A laser unit is arranged corresponding to the plurality of mirrors 100 in the rotation axis direction. The scanning operation by each set of the optical scanning mirror 100 and the laser unit is the same as in the first and second embodiments. The distance between the optical scanning mirrors 100 and the distance from the scanned surface 205 are such that the scanning range of the scanned surface 205 by the laser beam deflected by the adjacent optical scanning mirrors 100 partially overlaps. It has been decided.

  It should be noted that the intervals between the respective optical scanning mirrors are preferably arranged in accordance with the intervals of the plurality of mirrors in the rotation axis direction of the respective optical scanning mirrors as well as the above-described overlap.

  With such a configuration, the surface to be scanned 205 can be scanned at a high speed with a wide scanning width by a plurality of laser light beams. Since the scanning direction by the optical scanning mirror 100 of the present invention is a direction parallel to the rotation center axis, a large number of optical scanning mirrors 100 can be easily arranged densely as in this embodiment, and therefore A wide scanning width and high-speed scanning can be easily realized. Since all the optical scanning mirrors 100 are attached to the rotation shaft 201 of the common motor 201, no special means for synchronizing the rotation of the optical scanning mirror 100 is necessary.

  Since a part of the scanning range by the adjacent optical scanning mirrors 100 overlaps, for example, in the case of image formation, it is possible to easily ensure the continuity of the images on each scanning line on the scanned surface 205. it can. In particular, since the scanning with the laser light beam deflected by each optical scanning mirror 100 is a unidirectional scanning in the same direction, the start and end of modulation by the image signal of the laser light beam emitted from each laser unit 201 or the like Blanking timing adjustment becomes easy.

  Although not shown, in the fourth embodiment, two lasers for irradiating laser light beams from the opposite directions corresponding to the respective optical scanning mirrors 100 as in the third embodiment (FIG. 10). Obviously, if the unit is arranged, a faster two-dimensional scan is possible. Naturally, the optical scanning device having such a configuration is also included in the present invention. In the fourth embodiment, a correction optical system similar to the correction optical systems 250 and 251 (FIG. 9) in the second embodiment may be provided corresponding to each optical scanning mirror 100. The optical scanning device having such a configuration is also included in the present invention.

  FIG. 3B shows a second embodiment of the optical scanning mirror according to the present invention. In FIG. 3B, this optical scanning mirror 300 has a predetermined radius centered on the rotation center axis in a plane perpendicular to the rotation center axis 302 on the outer peripheral surface of the disk-shaped rotation body 301 as a whole. These are formed by forming two mirror surfaces 304 and 305 along the circumference 303. The centers of the mirror surfaces 304 and 305 (irradiation center position of the laser light beam) coincide with the circumference 303, and therefore the centers of the mirror surfaces 304 and 305 are equidistant from the center of the rotation center axis 302 of the rotating body 301.

  The mirror surfaces 304 and 305 are continuously twisted with respect to the circumference 303 as a whole, with the inclination with respect to the rotation center axis 302 continuously changing. There is no portion corresponding to the blanking section 106 (FIG. 1A) in the first embodiment, and the two mirror surfaces 304 and 305 form one surface whose inclination changes continuously.

  The inclination of the mirror surface 304 is 0 ° at the center position 304c, the direction of the inclination is reversed at the center position 304c, and the inclination is the maximum reverse angle (± α °) at the start end 304a and the end end 304b. Referring to FIG. 3B, the mirror surface 304 is inclined so as not to be seen from the front on the start end 304a side, and is inclined so as to be seen from the front on the end 304b side. Similarly, the mirror surface 305 has an inclination angle of 0 ° at the center position 305c, and the direction of the inclination is reversed with respect to the position. The inclination is the maximum reverse angle (± α °). Similar to the mirror surfaces 104 and 105 of the first embodiment, the rate of change in the inclination of the mirror surfaces 304 and 305 is to be scanned parallel to the rotation center axis 302 when the optical scanning mirror 300 is rotated at a constant speed. The scanning of the surface is determined to be constant speed scanning.

  Since this optical scanning mirror 300 is used by being rotated, a rotating shaft concave portion and a convex portion 307 for mounting on a motor rotation center shaft or the like are formed on the rotating body 301.

  Since the optical scanning mirror 300 of this embodiment does not have a discontinuous surface like the blanking portion 106 as compared with the optical scanning mirror 100 of the first embodiment, it is generally easy to process. The mirror surfaces 304 and 305 may have a curved cross-sectional shape in the width direction (see FIG. 5). Such a mirror surface having a cross-sectional shape is generally easier to process than a mirror surface having a plane cross-section.

  Although not shown, the thickness of the rotator 301 can be made larger than the width of the mirror surfaces 304 and 305 so that the outer peripheral surface of the rotator 301 remains outside the mirror surfaces 304 and 305. Three or more mirror surfaces similar to the mirror surfaces 304 and 305 can be formed on the outer peripheral surface of the rotating body 301 along the same circumference. Further, the overall shape of the rotating body 101 may be a columnar shape or a cylindrical shape. The optical scanning mirrors having the respective modified configurations as described above are also included in the present invention.

  Further, a configuration in which a blanking portion similar to that of the first embodiment is provided between the start end 304a of the mirror surface 304 and the end 305b of the mirror surface 305, or, more general, continuous N (≧ 2). A configuration in which a blanking portion is provided between the first and last mirror surfaces of each mirror surface is also possible, and this is also included in the present invention.

  Although not shown in the drawings, the present invention naturally includes an optical scanning device in which the optical scanning mirror 100 in each of the above-described embodiments of the optical scanning device and its modifications is replaced with the optical scanning mirror 300 of this embodiment. .

  When the optical scanning mirror 300 of the present embodiment is used, every time the mirror is rotated once, one reciprocating scan is performed. Referring to FIG. 7, when the start end 304 a of the mirror surface 304 comes to the laser light beam incident position, the laser light beam is deflected toward the position 207 on the surface to be scanned 205, for example. When the optical scanning mirror 300 further rotates in the direction of the arrow in FIG. 3B, the laser light beam is swung to the right in FIG. 7, and when the end 304b of the mirror surface 304 comes to the laser light beam incident position, the laser light is emitted. The beam is swung to position 209. In this way, scanning is performed from position 207 to position 209 in half rotation (forward scanning). When the optical scanning mirror 300 further rotates, the laser light beam is deflected in the reverse direction by the mirror surface 305, and the laser light beam is swung to the position 207 when the end 305 b of the mirror surface 305 comes to the laser light beam irradiation position. That is, scanning is performed from position 209 to position 207 in the subsequent half rotation (reverse scanning). Since the change rate of the inclination of each mirror surface of the optical scanning mirror 300 is set as described above, the scanning is a constant speed scanning. If the number of mirror surfaces of the optical scanning mirror 300 is three, one reciprocal half of scanning is performed per rotation. If there are four mirror surfaces, two reciprocal scans are performed in one rotation.

  As shown in FIG. 11, when a plurality of optical scanning mirrors 300 are arranged in the same direction, it is clear that the forward scanning direction and the backward scanning direction by the adjacent optical scanning mirrors 300 are the same. It is.

  The optical scanning device of the present invention described above is an image forming apparatus for making a printing plate such as an image forming apparatus such as an electrophotographic printer or a thermal recording printer, a copying machine, a printing board or a film for printing or CTP in the printing field. Alternatively, it is suitable as an optical scanning device in a plotter device, and can also be applied to applications in which an image is formed by exposing a silver salt film.

  As such an application example, an example of an electrophotographic image forming apparatus will be described with reference to FIG.

  In FIG. 12, reference numeral 400 denotes an optical scanning device according to the present invention. In the optical scanning device 400, for example, the optical scanning device having the configuration shown in FIG. 11 is provided with the correction optical systems 250 and 251 shown in FIG. 9 corresponding to the plurality of mirrors in the rotation axis direction of each optical scanning mirror. It is a configuration. 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 optical scanning device 400.

  The optical 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 optical 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 optical scanning device 400 can perform high-speed scanning with a plurality of beams, high-speed image formation is possible. Further, since the optical scanning device 400 can be configured to be 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 for 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. 13 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 before and after depending on the type of medium. In both cases, some process steps including cleaning and development are required, but 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 an optical 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. 14 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. 14A is an example in which plate-making is performed on a roll-shaped plate by an optical scanning device, and printing is performed on a recording sheet with a single color ink, and FIG. This is an example of a four-color offset printing machine that performs plate making with an optical scanning device installed in each, 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.

1 shows a first embodiment of an optical scanning mirror according to the present invention. The other example of a shape of the mirror for optical scanning is shown. An example of an optical scanning mirror provided with a concave or convex part for centering, a hole, a notch or the like is shown. It is a continuation of FIG. The mirror surface which has a curved cross-sectional shape is shown. 1 shows a first embodiment (front side) of an optical scanning device according to the present invention. 1 shows a first embodiment (side surface side) of an optical scanning device according to the present invention. The control timing in a 1st Example is shown. 2 shows a second embodiment of an optical scanning device according to the present invention. 3 shows a third embodiment of the optical scanning device according to the present invention. 4 shows a fourth embodiment of an optical scanning device according to the present invention. 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. The previously proposed optical scanning mirror is shown.

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 (23)

  A rotation center axis, and a plurality of mirror surfaces 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). A plurality of mirrors), and each mirror surface is a surface twisted with respect to the circumference, the inclination of which is continuously changed from one end to the other end with respect to the rotation center axis. mirror.   2. The optical scanning mirror according to claim 1, wherein when a light beam is irradiated on each mirror surface of the plurality of mirrors in the rotation axis direction, the rotation angle of the optical scanning mirror and the light reflected by the mirror surface An optical scanning mirror characterized in that the inclination of the mirror surface changes from one end to the other end so that the amount by which the beam moves on a plane parallel to the rotation center axis is in direct proportion.   3. The light according to claim 1, wherein each surface of the plurality of mirrors in the rotation axis direction has an inclination that increases from a central position toward both ends, and the direction of the inclination is reversed at the central position. Scanning mirror.   4. The optical scanning mirror according to claim 1, wherein each of the plurality of mirrors in the rotation axis direction has a plurality of the mirror surfaces along the circumference (hereinafter, a plurality of mirrors in the circumferential direction). .   Each of the plurality of mirrors in the rotation axis direction has a blanking portion that separates the surfaces of the plurality of circumferential direction mirrors, and the inclinations at the ends of the two mirror surfaces adjacent to each other through the blanking portion are opposite to each other. The optical scanning mirror according to claim 4, wherein the optical scanning mirror is provided.   5. The optical scanning mirror according to claim 4, wherein in each of the plurality of mirrors in the rotation axis direction, the surfaces of the plurality of mirrors in the circumferential direction are formed as one continuous surface whose inclination changes continuously as a whole. .   The optical scanning mirror according to claim 1, wherein each mirror surface of the plurality of mirrors in the rotation axis direction has a curved cross-sectional shape.   2. The optical scanning mirror according to claim 1, wherein the optical scanning mirror has at least one hole or notch on a side surface of the mirror.   In the optical scanning mirror, at least one concave portion is provided on one side of the mirror side surface, the same number of convex portions are provided at the same position on the opposite side surface, and the concave portion and the convex portion are fitted to each other. The optical scanning mirror according to claim 1.   10. The optical scanning mirror according to claim 1, wherein the optical scanning mirror is rotated about its rotation center axis, and is perpendicular to the rotation center axis on the circumference of each mirror surface of the plurality of mirrors in the rotation axis direction. An optical scanning method comprising irradiating a light beam from a direction parallel to a flat surface and scanning a surface to be scanned parallel to the rotation center axis with the light beam reflected by each mirror surface.   The optical scanning mirror according to claim 4, wherein the optical scanning mirror is rotated about its rotation center axis, and a plurality of light beams are arranged on the surfaces of the plurality of circumferential direction mirrors in each of the plurality of mirrors in the rotation axis direction of the optical scanning mirror. Simultaneously irradiate a beam from a direction parallel to a plane perpendicular to the rotation center axis, and scan the surface to be scanned parallel to the rotation center axis with a plurality of light beams reflected by the plurality of mirror surfaces in each circumferential direction. An optical scanning method characterized by:   The light beam having an intensity distribution shape spreading in the width direction from the length direction is irradiated on the mirror surface of each of the plurality of mirrors in the rotation axis direction of the optical scanning mirror. Optical scanning method.   11. The surface to be scanned is scanned with a plurality of light beams reflected by the mirror surfaces of the plurality of light scanning mirrors by simultaneously rotating a plurality of the light scanning mirrors on the same axis. , 11 or 12 Optical scanning method   14. The optical scanning method according to claim 13, wherein in the adjacent optical scanning mirrors, the scanning ranges of the light beams reflected by the plurality of mirrors in the rotation axis direction of the respective optical scanning mirrors are partially overlapped. .   11. The optical scanning method according to claim 10, wherein in the plurality of mirrors in the rotation axis direction of the optical scanning mirror, a scanning range by a light beam reflected by a mirror surface of an adjacent mirror is partially overlapped.   The optical scanning method according to any one of claims 10 to 15, wherein the optical scanning mirror is rotated at a constant speed to scan the surface to be scanned at a constant speed.   10. The optical scanning mirror according to claim 1, driving means for rotating the optical scanning mirror around its rotation center axis, and a plurality of rotation axis direction mirrors included in the optical scanning mirror And a means for irradiating each mirror surface with a light beam, and scanning the surface to be scanned parallel to the rotation center axis with the light beam reflected by each mirror surface.   The optical scanning device according to claim 17, wherein the optical scanning method according to claim 11 is mounted.   An optical system in which an optical system is disposed between a mirror surface of a plurality of mirrors in the rotation axis direction of the optical scanning mirror and a light source, and an fθ lens is provided between the mirror surface of the plurality of mirrors in the rotation axis direction and the surface to be scanned. The optical scanning device according to claim 17, wherein a system is arranged.   20. The optical scanning device according to claim 19, wherein an optical system including a condensing lens is disposed between a mirror surface of a plurality of mirrors in the rotation axis direction of the optical scanning mirror and a surface to be scanned. .   An electrostatic latent image is formed by scanning an image carrier, means for charging the surface of the image carrier, and scanning with a light beam modulated by an image signal, using the charged surface of the image carrier as a scanning surface. 21. An image forming apparatus comprising: the optical scanning device according to claim 17; and means for visualizing an electrostatic latent image formed on the image carrier. apparatus.   21. The method according to claim 17, further comprising: a medium; means for conveying the medium; and scanning the light beam modulated by the image signal with respect to the medium in a conveying state to form an image on the medium. An image forming apparatus comprising the optical scanning device described above.   23. An image forming apparatus comprising: the image forming apparatus according to claim 22; means for forming an ink image on the medium; and means for transferring the ink image to a recording sheet.

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