JP2015052727A - Optical scanning device and image forming device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanning device which realizes low cost and size reduction and is capable of forming good images, and to provide an image forming device having the same.SOLUTION: An optical scanning device includes; a first incident optical system for allowing a light beam to enter a first deflection surface of deflection means obliquely with respect to a reference plane; a second incident optical system for allowing a light beam to enter a second deflection surface obliquely with respect to the reference plane from the same side; a first image forming optical system for focusing light on a first scanning surface; and a second image forming optical system for focusing light on a second scanning surface. The first image forming optical system and the second image forming optical system each have a toric lens having a same shape that is asymmetric in a sub-scanning direction. At least one of the first image forming optical system and the second image forming optical system has reflective surfaces for reflecting the light beam in an optical path between the deflection means and the toric lens. Difference between the number of the reflective surfaces located in the optical path from the deflection means to the toric lens in the first image forming optical system and that in the second image forming optical system is an odd number.

Description

  The present invention relates to an optical scanning device and an image forming apparatus using the same, and is suitable for an image forming apparatus such as a laser beam printer (LBP) having an electrophotographic process, a digital copying machine, or a multifunction printer (multifunctional printer). It is.

  2. Description of the Related Art Conventionally, optical scanning devices and image forming apparatuses using the same have been required to reduce the number of parts and reduce the size of the devices, and various methods for achieving this have been proposed.

  In Patent Document 1, an opposed scanning system is employed, and a plurality of optical systems share the same rotating polygonal mirror by arranging lenses and mirrors substantially symmetrically with a rotating polygonal mirror as a deflecting unit interposed therebetween. The number of parts of the optical scanning device is reduced, and the size of the device is kept small. Further, in Patent Document 1, two upper and lower light beams are incident obliquely in the sub-scanning direction on different deflection surfaces of the rotary polygon mirror, and the imaging lens on the deflecting means side is shared by the two upper and lower light beams. The number of parts of the equipment is reduced.

  Such a plurality of imaging lenses in Patent Document 1 are toric lenses having a vertically symmetrical shape with a sufficiently wide width in the sub-scanning direction, and are symmetrical in the sub-scanning direction. An imaging optical element having the same shape can be used.

  In Patent Document 1, an optical path reflected downward from the first deflection surface with respect to the reference surface within the sub-scan section, and an optical path reflected downward from the second deflection surface with respect to the reference surface. Thus, there is only one reflecting surface in the optical path from the deflecting means to the imaging optical element (the difference in the number of reflecting surfaces is an even number). Here, the reference plane is a plane that is orthogonal to the deflection axis (rotation axis) of the deflection means (rotating polygon mirror) and bisects the deflection means in the sub-scanning direction.

  Further, in the sub-scan section, an image is reflected from the deflecting unit by an optical path reflected upward from the first deflection surface with respect to the reference surface and an optical path reflected from the second deflection surface to the same upper side with respect to the reference surface. The number of reflection surfaces in the optical path to the optical element is zero (the difference in the number of reflection surfaces is an even number).

  Patent Document 2 discloses an example in which a counter scanning system and an oblique incident optical system are employed, as in Patent Document 1. Furthermore, Patent Document 2 discloses an example in which a toric lens that is asymmetric in the vertical direction is used in order to reduce the height of the apparatus by setting the distance between the imaging lens and the light beam narrow.

  That is, when the scanning light is folded by the folding mirror, if a toric lens having a vertically-symmetrical shape having a sufficiently wide width in the sub-scanning direction as in Patent Document 1 is used, the luminous flux directed to the folding mirror causes vignetting by the lens. . Therefore, in Patent Document 2, as an imaging lens as an imaging optical element, a toric lens having an optical axis offset from the center of the outer shape of the lens and being asymmetric in the sub-scanning direction is used, thereby preventing vignetting of the light flux. It is out.

  Here, in Patent Document 2, an optical path reflected downward from the first deflection surface with respect to the reference surface in the sub-scan section, and reflected from the second deflection surface to the same lower side with respect to the reference surface. In the optical path, there are two reflecting surfaces in the optical path from the deflecting means to the imaging optical element (the difference in the number of reflecting surfaces is an even number). Further, in Patent Document 2, deflection is performed by an optical path reflected upward from the first deflection surface to the reference plane and an optical path reflected from the second deflection surface to the same upper side with respect to the reference plane in the sub-scan section. The number of reflecting surfaces in the optical path from the means to the imaging optical element is zero (the difference in the number of reflecting surfaces is an even number).

JP 2009-271384 A JP 2010-26055 A

  However, since the optical scanning device disclosed in Patent Document 1 uses a toric lens having a vertically symmetrical shape with a sufficiently wide width in the sub-scanning direction, the interval between the imaging lens and the light beam directed to the folding mirror is set to be narrow. I can't. As a result, in Patent Document 1, it is impossible to further reduce the size of the apparatus while avoiding vignetting.

  On the other hand, the optical scanning device of Patent Document 2 is directed to downsizing by using an eccentric toric lens that is asymmetric in the sub-scanning direction. However, the arrangement of the left and right optical systems arranged opposite to each other and how to route the optical path by mirrors Is substantially plane symmetric with respect to the rotating polygon mirror. For this reason, the left and right imaging optical systems that are reflected on the same side with respect to the reference plane cannot be made to have the same shape of the eccentric toric lens, and two types of toric lens shapes are required.

  An object of the present invention is to provide an optical scanning device that can achieve low cost and downsizing and can form a good image, and an image forming apparatus using the same.

  In order to achieve the above object, an optical scanning device according to the present invention includes a deflection unit that deflects a light beam in a main scanning direction by a first deflection surface and a second deflection surface different from the first deflection surface, When a plane perpendicular to the deflection axis of the deflection unit and bisecting the deflection unit in the sub-scanning direction is used as a reference plane, the first light flux from the first direction with respect to the reference plane in the sub-scanning section is A first incident optical system that obliquely impinges on the first deflecting surface; and a second light flux from the second direction on the same side as the first direction with respect to the reference surface in the sub-scan section. A second incident optical system that obliquely enters the deflecting surface, a first imaging optical system that condenses the first light beam deflected by the deflecting means on a first scanned surface, and the deflecting means. And a second imaging optical system for condensing the second light beam deflected by the second scanning surface, and the first imaging optical system. The imaging optical system and the second imaging optical system have a toric lens having the same shape and an asymmetric shape in the sub-scanning direction, and the first imaging optical system and the second imaging optical system. At least one of the optical systems has a reflecting surface that reflects a light beam in an optical path between the deflecting unit and the toric lens, and in the first imaging optical system and the second imaging optical system The difference in the number of reflecting surfaces in the optical path from the deflecting means to the toric lens is an odd number.

  Another optical scanning device according to the present invention includes a first deflecting surface and a second deflecting surface different from the first deflecting surface, deflecting means for deflecting a light beam in the main scanning direction, and deflection of the deflecting means. When a plane perpendicular to the axis and bisecting the deflection means in the sub-scanning direction is used as a reference plane, the first light beam is deflected from the first direction with respect to the reference plane in the sub-scanning section. A first incident optical system obliquely incident on the surface, and a second light beam from the second direction opposite to the first direction with respect to the reference surface in the sub-scanning cross section to the second deflection surface A second incident optical system for oblique incidence, a first imaging optical system for condensing the first light beam deflected by the deflecting unit on a first surface to be scanned, and the second by the deflecting unit. And a second imaging optical system for condensing the light beam on the second surface to be scanned, and the second imaging optical system and the second coupling optical system. The optical system has toric lenses that have the same shape and are asymmetric in the sub-scanning direction, and at least one of the first imaging optical system and the second imaging optical system includes the deflection unit. In the optical path from the deflecting means to the toric lens in the first imaging optical system and the second imaging optical system, having a reflecting surface for reflecting the light beam in the optical path between the toric lens The difference in the number of reflective surfaces is an even number including zero.

  According to the present invention, it is possible to provide an optical scanning apparatus that can achieve low cost and downsizing and can form a good image, and an image forming apparatus using the same.

(A) is principal part sectional drawing (sub-scanning sectional view) of the optical scanning apparatus concerning the 1st Embodiment of this invention in the sub-scanning direction, (b) is principal part sectional drawing (sub-scanning direction) of the sub-scanning direction of a comparative example. FIG. (A) is a principal part sectional view (main scanning sectional view) in the main scanning direction of the optical scanning device according to the first embodiment, and (b) is a principal part sectional view (secondary section) of the incident optical system in the first embodiment. FIG. (A) is a principal part sectional view (sub-scanning sectional view) of the imaging lens (eccentric lens) in the first embodiment, and (b) is a principal part sectional view (sub-clause) of the imaging lens (eccentric lens) in the comparative example. FIG. It is principal part sectional drawing (subscanning sectional drawing) of the subscanning direction of the optical scanning device concerning the 2nd Embodiment of this invention. 1 is a schematic view of a main part of an image forming apparatus equipped with an optical scanning device according to an embodiment of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<< First Embodiment >>
(Image forming device)
FIG. 5 is a schematic view of a main part of the color image forming apparatus according to the embodiment of the present invention. This embodiment is a tandem type color image forming apparatus that scans four beams with an optical scanning device and records image information on a photoconductor as an image carrier in parallel. In FIG. 5, 60 is a color image forming apparatus, and 100 is an optical scanning apparatus which will be described later. 21, 22, 23, and 24 are photosensitive drums as image carriers (photoconductors) that form images of different colors, 31, 32, 33, and 34 are each a developing device, and 51 is a conveyance belt.

  In FIG. 5, a developing device (not shown) that develops an electrostatic latent image formed on the photosensitive surface of the photoreceptor as a toner image, and the toner image developed by the developing device is a transfer material (recording material). And a fixing device for fixing the transferred toner image to the transfer material. In FIG. 5, the color image forming apparatus 60 receives color signals as R (red), G (green), and B (blue) code data from an external device 52 such as a personal computer.

  These color signals are converted into image data (dot data) of Y (yellow), M (magenta), C (cyan), and B (black) by a printer controller 53 in the apparatus. These image data are input to the optical scanning device 100. The light scanning device 100 emits light beams 41, 42, 43, and 44 that are modulated in accordance with each image data, and the light beams 41, 42, 43, and 44 are exposed to the photosensitive surfaces (first surfaces) of the photosensitive drums 21, 22, 23, and 24. The first to fourth scanned surfaces) are scanned in the main scanning direction.

  The color image forming apparatus in this embodiment scans four beams by the optical scanning device 100, and each corresponds to each color of Y (yellow), M (magenta), C (cyan), and B (black). In parallel, image signals (image information) are recorded on the surfaces of the photosensitive drums 21, 22, 23, and 24, and color images are printed at high speed.

  In the color image forming apparatus according to the present embodiment, the latent image of each color is formed on the corresponding photosensitive drums 21, 22, 23, and 24 by using the light beam based on each image data by the optical scanning device 100 as described above. doing. Thereafter, a single full color image is formed by multiple transfer onto a recording material.

  As the external device 52, for example, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 60 constitute a color digital copying machine.

(Optical scanning device)
FIG. 1A is a sectional view (sub-scanning sectional view) of a main part in the sub-scanning direction of the optical scanning device according to the first embodiment of the present invention, and FIG. 2A is a sectional view of the first embodiment of the present invention. It is principal part sectional drawing (main scanning sectional drawing) of the main scanning direction of the optical scanning device which concerns. FIG. 2B is a sectional view (sub-scanning sectional view) of the main part of the incident optical system in the sub-scanning direction. In FIG. 1A, scanned surfaces 10a, 10b, 10c, and 10d are photosensitive drums for forming yellow (Y), magenta (M), cyan (C), and black (Bk) images in order. A photosensitive drum surface), which is an optical scanning device for forming four color images.

1) Definition In the following description, the main scanning direction (Y direction) is a direction perpendicular to the deflection axis (rotation axis or oscillation axis) of the deflection means and the optical axis of the imaging optical system (the light beam is reflected by the rotating polygon mirror). Direction of deflection (deflection scanning). The sub-scanning direction (Z direction) is a direction parallel to the deflection axis (rotation axis or swing axis) of the deflection means. The main scanning section is a plane including the main scanning direction and the optical axis of the imaging optical system. The sub-scanning section (child line section) is a section perpendicular to the main scanning direction.

  The reference plane (reference plane G) is a plane that is orthogonal to the deflection axis (rotation axis or swing axis) of the deflection means (rotating polygon mirror) and bisects the deflection means in the sub-scanning direction.

2) Inclination of the optical scanning device with respect to the array surface of the plurality of scanned surfaces In the embodiment shown below, although not an essential matter, the optical scanning device is a plane including four scanned surfaces together with the reference surface G It is inclined with respect to the surface to be scanned). In other words, the rotational axis of the rotary polygon mirror is arranged so as to be inclined from the vertical direction with respect to the seat surface of the optical box and the plane including the four scanned surfaces. As shown in FIG. 1A, the tilting direction is set to a direction in which the sub-scanning oblique incident angle is tilted to the imaging optical path d side, which is the upward direction. Thereby, the space in the upper left part of Fig.1 (a) is securable.

  The present invention also holds when there is no inclination of the optical scanning device with respect to the array surface of the plurality of scanned surfaces (when the rotation axis of the rotary polygon mirror is perpendicular to the plane including the four scanned surfaces). However, in this embodiment, a case where there is an inclination is shown. In the present embodiment, while the optical path lengths of the imaging optical path c and the imaging optical path d whose sub-scanning oblique incident angles are opposite to each other are the same, the position of the rotary polygon mirror is approximately at the center on the four scanned surfaces. The deformation of the box due to the heat generated by the rotary polygon mirror can be made symmetrical, and the influence on the image can be reduced.

3) Incident optical system In FIG. 2A, the incident optical systems L1a, L1c and L1b, L1d are obliquely incident on different deflection surfaces from the same direction in the main scanning section. Further, as can be seen from FIG. 2B, the incident optical systems L1a and L1d are upward with respect to the reference plane G in the sub-scan section, and the incident optical systems L1b and L1c are downward with respect to the reference plane G in the sub-scan section. The light beam is obliquely incident on the deflecting surface 6 of the rotary polygon mirror 5 so as to have an angle. Hereinafter, the sub-scanning direction oblique incidence is referred to as an angle with respect to the reference plane G is referred to as the sub-scanning direction oblique incidence angle.

  Therefore, the four incident light beams from the four incident optical systems become four deflected reflected light beams by the rotary polygon mirror 5. Two of the four deflected and reflected light beams are deflected and reflected so as to be directed below the reference surface G, and the other two light beams facing each other across the rotary polygon mirror are directed above the reference surface G.

Reference numerals 1a, 1b, 1c, and 1d denote light source means, which are composed of a semiconductor laser having a light emitting portion (light emitting point). Reference numerals 2a, 2b, 2c, and 2d denote apertures (aperture stops) that form a light beam incident on the anamorphic collimator lenses 3a, 3b, 3c, and 3d in a desired optimum beam shape. The anamorphic collimator lens 3a converts the light beam emitted from the light source means 1a into a parallel light beam in the main scanning direction and condenses in the vicinity of the deflection surface 6 of the rotary polygon mirror 5 in the sub-scanning direction. An image is formed on the deflection surface 6 as a longitudinal line image in the main scanning direction. Each element of the aperture stops 2a, 2b, 2c, and 2d and the anamorphic collimator lenses 3a, 3b, 3c, and 3d is an incident optical system L1a, It constitutes one element of L1b, L1c, and L1d. The light beams emitted from the light source means 1a, 1b, 1c, and 1d are guided to the deflection surface (deflection reflection surface) 6 of the rotary polygon mirror 5 described later. The anamorphic collimator lenses 3a, 3b, 3c, and 3d may be constituted by a collimator lens and a cylinder lens having power only in the sub-scanning direction.

4) Optical deflector (deflecting means)
Reference numeral 5 denotes a rotating polygon mirror (polygon mirror) as an optical deflector (deflection means) including a plurality of deflection surfaces, which rotates at a constant speed in the direction of arrow A in the figure. Further, the number of rotary polygon mirrors 5 in this embodiment is equal to or less than the number of scanning system units, and the number is one.

5) Imaging optical system L2a, L2b, L2c, and L2d are imaging optical systems having a condensing function and fθ characteristics, and have positive power (refractive power) in the main scanning section, and in the sub-scanning section. And a positive power different from the positive power in the main scanning section.

5-1) Imaging optical system related to imaging optical path a In the imaging optical path a from the deflecting means to the scanned surface 10a, the imaging optical system L2a is composed of first and second imaging lenses 71 and 72. . The imaging optical system L2a images a light beam based on image information deflected and scanned by the rotary polygon mirror 5 as a deflecting unit onto a surface to be scanned (photosensitive drum surface) 10a in a spot in the main scanning section. The imaging lens 72 is formed of a toric lens that is asymmetrical in the sub-scanning direction in order to correct adverse effects on spot performance due to sub-scanning oblique incidence and to prevent interference with each scanning light or housing member.

  Further, the imaging optical system L2a performs surface tilt compensation of the deflection surface 6 by optically conjugating the deflection surface 6 of the rotary polygon mirror 5 and the photosensitive drum surface 10a in the sub-scan section. Yes. Reference numeral 8 in FIG. 1A denotes a plane mirror for bending the optical path of the light beam from the imaging lens 72 and does not affect the imaging performance. In the present embodiment, as will be described later, in the optical path between the deflecting means and the imaging lens 72 that is a toric lens, the imaging lens 72 can have the same shape as the imaging lens 72 in the other imaging optical path. The number of reflecting surfaces provided on the surface for reflecting the luminous flux is taken into consideration.

  In this embodiment, the light beam modulated and emitted from the semiconductor laser 1a according to the image information is incident on the deflecting surface 6 of the rotary polygon mirror 5 by the incident optical system L1a, and on the photosensitive drum surface 10a by the imaging optical system L2a. Is guided. Then, by rotating the rotary polygon mirror 5 in the direction of arrow A by a driving means (not shown), image information is recorded by optically scanning the photosensitive drum surface 10a in the main scanning direction. Further, the rotation speed of the rotary polygon mirror 5 is detected by a synchronization detection means (not shown), and the control means (not shown) controls the rotary polygon mirror 5 to rotate at a constant speed.

5-2) Imaging optical system concerning imaging optical path b Next, the imaging optical path b from the deflecting means to the scanned surface 10b will be described. The configuration and optical action of the imaging optical path b are the same as the imaging optical path a. Each optical element in the imaging optical path b functions in the same manner as the imaging optical path a. In FIG. 1A, the optical elements are denoted by the same reference numerals as the optical elements in the imaging optical path a. In the present embodiment, as will be described later, the number of reflecting surfaces is considered so that the plane mirror 8 on the incident surface side of the imaging lens 72 can have the same shape as the imaging lens 72 in the other imaging optical path. The imaging optical path b is different from the imaging optical path a in the arrangement with respect to the rotating polygon mirror and the way of returning the scanning light reflected and deflected by the rotating polygon mirror.

  As can be seen from FIG. 2A, in the main scanning section, the imaging optical system L2b of the imaging optical path b faces the imaging optical system L2a of the imaging optical path a around the rotary polygon mirror 5. Has been placed.

5-3) Imaging optical system for imaging optical paths c and d Imaging optical paths c and d from the deflecting means to the scanned surfaces 10c and 10d are in the optical path to the imaging lens 72 via the imaging lens 71. The plane mirror 8 is not provided, but the plane mirror 8 that bends the optical path along the optical path from the imaging lens 72 to the scanned surfaces 10c and 10d is provided.

5-4) Imaging lens 72 as an eccentric toric lens
Here, the imaging lens 72 of the present embodiment is a toric lens having an asymmetric shape in the sub-scanning direction. FIG. 3A is a cross-sectional view of the imaging lens 72 in the sub-scanning direction. A dotted line in FIG. 3A represents an optical axis for defining the lens surface shape of the imaging lens 72. As can be seen from the figure, the optical axis of the lens surface shape is offset from the center of the outer shape of the lens, so that the lens thickness is vertically asymmetric in the sub-scanning direction. A toric lens having a shape in which the optical axis of the lens surface is shifted in the sub-scanning direction with respect to the center of the lens outer shape is referred to as an eccentric toric lens.

  Here, for easy understanding, the thick side of the imaging lens 72 that is vertically asymmetric in the sub-scanning direction is defined as the outer edge Z1, and the thinner side is defined as the outer edge Z2. The distance from the optical axis to the outer edge Z1 is set to 2.72 mm, and the distance from the optical axis to the outer edge Z2 is set to 5.28 mm.

(Positional relationship between the light beams U and L with respect to the reference plane G)
Here, as described above, the plane perpendicular to the deflection axis (rotation axis) of the deflection means (rotating polygon mirror) and bisecting the deflection means in the sub-scanning direction is the reference plane (surface G in FIG. 1A). To do. At this time, U is a light beam that enters the optical deflector and is reflected by the optical deflector, and is a light beam that is farther from the reference plane G than the principal ray, and L is closer to the reference plane G than the principal ray. Side light flux.

  Unlike an imaging lens that is vertically symmetric in the sub-scanning direction, in the imaging lens 72 that is asymmetrical in the sub-scanning direction, the upper and lower luminous fluxes pass in the sub-scanning direction of the corresponding imaging lens 72 in the sub-scanning direction. Otherwise, high imaging performance cannot be obtained. For this reason, in this embodiment, the imaging optical path is set so that the light beam L is incident on the thick side Z1 of the imaging lens 72.

  In the first imaging light path L2a and the second imaging light path L2b respectively directed to the scanned surfaces 10a and 10b in FIG. 1A, the light beams U and L reflected by the deflecting means are folded back by the folding mirror 8. Then, it enters an imaging lens 72 as an imaging optical element as shown in the figure.

(Conditions that the respective imaging optical elements in the first imaging optical path a, the second imaging optical path b, the third imaging optical path c, and the fourth imaging optical path d can have the same shape)
The imaging optical elements (imaging lenses) in the first imaging optical path a, the second imaging optical path b, the third imaging optical path c, and the fourth imaging optical path d have optical characteristics (lens characteristics) in the main scanning direction. ) Is generally asymmetric with respect to the optical axis, and cannot be used with both ends in the main scanning direction interchanged. For this reason, the condition that the imaging optical elements can have the same shape is that when one of the imaging optical elements is rotated in the sub-scan section, the incident surface is on the light beam incident side and overlaps the other. In other words, the relationship between U and L incident on the incident surface coincides with the originally required relationship between U and L when the two imaging optical elements rotate in the sub-scan section.

(When the first incident optical system and the fourth incident optical system that cause the light source beam to enter different deflection surfaces are on the same side with respect to the reference surface G)
A comparison of the sub-scanning cross section shown in FIG. 1B prior to the description of the present embodiment regarding whether or not the respective imaging optical elements in the first imaging optical path a and the fourth imaging optical path d can have the same shape. An example will be described. In this comparative example, two incident optical systems that allow light source light beams to enter different deflection surfaces are provided on the same side with respect to the reference surface G. The number of mirrors (the number of reflecting surfaces) provided in the optical path from the rotary polygon mirror to the imaging lens 72 is one. Further, the number of mirrors provided in the optical path from the rotating polygon mirror to the imaging lens 73 is also the same as that of one, and the difference in the number of reflection surfaces is set to zero (even number).

  In the comparative example, assuming that the imaging lens as the imaging optical element can have the same shape, regarding the left imaging lens 73, the right imaging lens 72 in FIG. The relationship is such that they are rotated clockwise in the drawing. At this time, the relationship between L and U does not match the originally required relationship between U and L. That is, in the right imaging lens 72, U is above L, and when rotated clockwise, U is below L. The relationship between U and L that is originally required is shown in FIG. U is above L relative to 1 (b).

  Therefore, the left imaging lens 73 cannot have the same shape as the right imaging lens 72. As a result, in order to correct the scanning light beam deflected by the deflecting means to have good imaging performance, an imaging lens (eccentric toric lens) having a shape reversed in the sub-scanning direction as shown in FIG. 3B. 72 and an imaging lens (eccentric toric lens) 73 are required.

  In contrast to such a comparative example, in the present embodiment shown in FIG. 1A, the first incident optical system and the fourth incident optical system are on the same side with respect to the reference plane G as follows. Take a simple structure. That is, the number of mirrors from the rotary polygon mirror to the imaging lens 72 is one for the imaging optical path to the scanned surface 10a, and the number of mirrors from the rotary polygon mirror to the imaging lens 72 for the imaging optical path to the scanned surface 10d. Is set to 0, and the difference in the number of reflection surfaces is set to an odd number.

  The thick side of the imaging lens 72 that is vertically asymmetric in the sub-scanning direction is indicated by Z1, and the imaging lens 72 of the imaging lens 72 in both the first imaging optical path and the fourth imaging optical path is shown in FIG. The outer end Z1 side is set to be the L side of the light beam.

  Here, in this embodiment, it is confirmed whether or not the imaging lenses as the imaging optical elements can have the same shape. Regarding the imaging lens 72 of the imaging optical path to the scanned surface 10d, the imaging lens 72 of the imaging optical path to the scanned surface 10a is counterclockwise in the plane of FIG. It becomes the relationship which rotates and arranges.

  At this time, the relationship between L and U matches the originally required relationship between U and L. That is, in the imaging lens 72 on the imaging optical path to the scanned surface 10a, U is above L, and when rotated counterclockwise, U is maintained above L. The relationship between U and L that is originally required for the imaging lens 72 in the imaging optical path to the scanned surface 10d is that U is higher than L as shown in FIG.

  Therefore, the imaging lens 72 of the imaging optical path to the scanned surface 10d can have the same shape as the imaging lens 72 of the imaging optical path to the scanned surface 10a.

(When the first incident optical system and the second incident optical system that cause the light source light beam to be incident on different deflection surfaces are on the opposite side with respect to the reference surface G)
In FIG. 1A, the number of mirrors (the number of reflecting surfaces) provided in the optical path from the rotary polygon mirror to the imaging lens 72 with respect to the imaging optical path a to the scanned surface 10a is one. Further, the number of mirrors provided in the optical path from the rotary polygon mirror to the imaging lens 72 with respect to the imaging optical path b to the scanned surface 10b is also one, and the difference in the number of reflection surfaces is set to an even number including zero. Yes.

  Here, in this embodiment, it is confirmed whether or not the imaging lenses as the imaging optical elements can have the same shape. Regarding the imaging lens 72 of the imaging optical path to the scanned surface 10b, the imaging lens 72 of the imaging optical path to the scanned surface 10a is clockwise in the plane of FIG. It becomes the relationship which rotates and arranges.

  At this time, the relationship between L and U matches the originally required relationship between U and L. That is, in the imaging lens 72 on the imaging optical path to the scanning surface 10a, U is above L, and when rotated clockwise, U is below L. The relationship between U and L that is originally required for the imaging lens 72 in the imaging optical path to the scanned surface 10b is such that U is lower than L as shown in FIG. Therefore, the imaging lens 72 of the imaging optical path to the scanned surface 10b can have the same shape as the imaging lens 72 of the imaging optical path to the scanned surface 10a.

(When the first incident optical system and the third incident optical system that cause the light source beam to enter the same deflection surface are on the opposite side of the reference surface G)
In FIG. 1A, the number of mirrors (the number of reflecting surfaces) provided in the optical path from the rotary polygon mirror to the imaging lens 72 with respect to the imaging optical path a to the scanned surface 10a is one. Further, the number of mirrors provided in the optical path from the rotary polygon mirror to the imaging lens 72 with respect to the imaging optical path c to the scanned surface 10c is zero, and the difference in the number of reflection surfaces is set to an odd number.

  Here, in this embodiment, it is confirmed whether or not the imaging lenses as the imaging optical elements can have the same shape. Regarding the imaging lens 72 of the imaging optical path to the scanned surface 10c, the imaging lens 72 of the imaging optical path to the scanned surface 10a is clockwise in the plane of FIG. It becomes the relationship which rotates and arranges.

  At this time, the relationship between L and U matches the originally required relationship between U and L. That is, in the imaging lens 72 on the imaging optical path to the scanning surface 10a, U is above L, and when rotated clockwise, U is below L. The relationship between U and L, which is originally required for the imaging lens 72 in the imaging optical path to the scanned surface 10c, is U below L as shown in FIG.

  Therefore, the imaging lens 72 of the imaging optical path to the scanned surface 10c can have the same shape as the imaging lens 72 of the imaging optical path to the scanned surface 10a.

  As described above, according to the present embodiment, the imaging lenses 72 of the imaging optical paths to the scanned surfaces 10a, 10b, 10c, and 10d can all be made the same shape.

(Specific values in the imaging optical paths a and b)
Here, the specification values in the imaging optical path a to the scanning surface 10a of this embodiment are shown in Table 1A, and the specification values in the imaging optical path b to the scanning surface 10b of this embodiment are shown in Table 1B. . The optical arrangements in Tables 1A and 1B represent the origin of each surface and the direction of the optical axis without considering folding by the mirror 8 for easy understanding. Table 2A shows the surface shape of each optical surface in the imaging optical path a of this embodiment, and Table 2B shows the surface shape of each optical surface in the imaging optical path b of this embodiment.

  As shown in Tables 1A and 1B, with respect to the reference plane G (perpendicular to the deflecting surface 6 of the optical deflector 5 and passing through the reference point C0), the incident light beams on the deflecting surface 6 are −3 °, respectively. Deflection scanning is performed with an inclination of + 3 °. That is, the incident optical systems L1a and L1b that enter the optical deflector are arranged so as to be inclined with respect to the reference plane G in + 3 ° and −3 ° sub-scanning directions, respectively. If this oblique incident angle is too large, it will be difficult to correct the collapse of the spot due to the twist of wavefront aberration, while if it is too small, it will be difficult to separate the light beams. Desirably, it should be set in the range of 2 ° to 5 °.

  In the present embodiment, an infrared light source having a light beam oscillation wavelength λ of λ = 790 nm is used as the light source means 1. The proportionality coefficient κ (Y = κθ) between the image height Y and the deflection reflection angle θ is κ = (rad / mm).

In Tables 1A and 1B, the aspheric shape of each optical surface is defined by the following expression. The incident surface of the anamorphic lens 3 of this embodiment is a diffractive surface on which a diffraction grating is formed on a plane, and the exit surface is an anamorphic refractive surface having different radii of curvature in the main scanning direction and the sub-scanning direction. The anamorphic lens 3 is formed by injection molding using a plastic material, and is a temperature compensation optical system that compensates for changes in refractive power due to environmental fluctuations with changes in diffraction power due to wavelength changes of the semiconductor laser. The above-described diffraction surface is defined by the phase function expressed below.
φ = 2πm / λ (C ₃ Z ² + C ₅ Y ² )
Here, φ is a phase function, and m is a diffraction order. In this embodiment, first-order diffracted light (m = 1) is used. λ is a design wavelength, and in this embodiment, λ = 790 nm. Further, the exit surface of the anamorphic lens 3 of this embodiment, the entrance surface of 72 of the imaging lens 71, and the generatrix shape of the exit surface are configured as aspherical shapes that can be expressed as functions up to the 12th order.

  The optical surfaces of the anamorphic lens 3 and the imaging lenses 71 and 72 are respectively represented by the origins and optical axes x shown in Tables 1A and 1B, the reference axis y in the main scanning direction, the reference axis z in the sub-scanning direction, 2A, defined from the following aspheric expression expressed in Table 2B. For example, on the lens entrance surface of the imaging lens 71, (X, Y, Z) = (13.500, −0.2, 0.000) is set as the aspherical origin, and the lens entrance surface of the imaging lens 72 is used. Then, (X, Y, Z) = (56.700, −0.2, 1.638) is set as the origin of the aspherical expression.

  The surface shape of each lens surface is the main scanning when the optical axis X passing through the origin of each optical surface shown in Table 1A and Table 1B and the axis perpendicular to the optical axis in the main scanning cross section is the Y axis. The bus direction corresponding to the direction is represented by the following expression.

(Where R is the radius of curvature of the bus, and K, B ₂ , B ₄ , B ₆ , B ₈ , B ₁₀ , B ₁₂ are aspherical coefficients)
Further, a sub-line direction corresponding to the sub-scanning direction is defined by the following expression when defined as the reference axis Z in the sub-scanning direction shown in Tables 1A and 1B.

  S is a child line shape defined in a plane perpendicular to the main scanning section including the normal line of the bus bar at each position in the bus bar direction. Here, the radius of curvature (sub-curvature radius of curvature) r ′ in the sub-scanning direction at a position Y away from the optical axis in the main scanning direction is expressed by the following equation.

(Where r ₀ is the radius of curvature on the optical axis, E ₂ , E ₄ , E ₆ , E ₈ , E ₁₀ , E ₁₂ , E ₁₄ , E ₁₆ , is a coefficient)
Mj_k is a coefficient representing the aspherical surface in the child line direction. For example, Mj_1 is a first-order term of Z and represents the tilt of the surface in the sub-scanning direction (child line tilt). Mj_4 is a fourth-order term of Z and represents an aspherical surface in the sub-scanning direction. In this embodiment, the first-order term of Z and the fourth-order term of Z are not used.

  Each coefficient shown in Tables 2A and 2B has subscripts u and l. The upper side and the lower side mean, respectively, and the side where the light source unit 1 is located is defined as the lower side and the side opposite to the side where the light source unit 1 is located is defined as the upper side with respect to each lens surface vertex of the imaging optical system. Coefficients without the subscripts U and l are coefficients common to the Upper side and the Lower side.

  In the present embodiment, the function of the surface shape is defined by the above definition formula, but the scope of the right of the present invention is not limited thereto.

  As can be seen from the aspherical coefficients in Tables 2A and 2B, the imaging lens 71 used in the imaging optical path a and the imaging lens 71 used in the imaging optical path b are lenses having lens surfaces having the same shape. Further, as can be seen from FIG. 1A, the imaging lens 71 used in the imaging optical path a and the imaging lens 71 used in the imaging optical path b are lenses having the same shape including the outer shape.

  Further, as can be seen from the aspherical coefficients in Tables 2A and 2B, the imaging lens 72 used in the imaging optical path a and the imaging lens 72 used in the imaging optical path b are lenses having lens surfaces having the same shape. is there. Further, as can be seen from FIG. 1A, the imaging lens 72 used in the imaging optical path a and the imaging lens 72 used in the imaging optical path b are lenses having the same shape including the outer shape.

  Here, FIG. 3A shows a sub-scanning cross-sectional shape including the outer shape of the imaging lens 72 of the present embodiment. FIG. 3A is a sub-scan sectional view for explaining the shape including the outer shape of the imaging lens 72, and the imaging lens 74 is an explanatory diagram for explaining the outer shape of the imaging lens 72. As can be seen from FIG. 3A, the imaging lens 72 is obtained by cutting the lens surface on the side where the scanning light does not pass within the width of the imaging lens 74 in the sub-scanning direction. This is an eccentric toric lens whose axis is offset.

  Further, as can be seen from the figure, the two imaging lenses 72 are arranged so as to rotate about the Y axis in accordance with the respective optical paths, and the positional relationship with the deflected reflected light beam incident on the imaging lens 72. However, the two optical paths are optically substantially equivalent.

  In the present embodiment, since the two imaging lenses 72 having the same shape are arranged in the respective optical paths so as to be rotated about the Y axis in this way, molding can be performed with only one type of lens molding die. And the manufacturing cost of the optical scanning device is reduced. Further, since it can be configured with only one type of lens, it is possible to suppress the complexity of mold management, molding management, and assembly management, and to achieve a reduction in manufacturing cost and an increase in yield of the optical scanning device.

(Comparison with the case where the imaging optical element is rotationally symmetrical about the deflection axis)
By the way, conventionally, there has been considered a method in which the imaging lens is rotationally symmetrically arranged around the rotation axis of the rotary polygon mirror with respect to the optical system arranged oppositely. However, resin toric lenses generally have a technique in which resin is poured into the mold from one of the longitudinal sides, resulting in left-right asymmetry due to left-right asymmetric lens internal distortion and thermal stress during molding. Birefringence and GI may occur.

  For this reason, in the method in which the imaging lens is rotationally symmetrically arranged around the rotation axis of the rotary polygon mirror with respect to the opposed optical system, imaging is performed between the opposed optical systems due to the left-right asymmetry of the lens. The problem that performance will mutually differ will arise. Further, in the method of rotationally symmetric arrangement about the rotation axis center of the conventional rotary polygon mirror, the shape of the imaging lens 72 on the left and right in the main scanning direction is inverted, so that the imaging lenses having the same shape in the opposed optical paths are arranged. It is impossible to obtain good imaging performance using 72.

  On the other hand, in the present embodiment, the two imaging lenses 72 are aligned with their respective optical paths and rotated around the Y axis, and the arrangement of the optical system and the number of mirrors are set optimally. Thus, the above-mentioned problem is solved while achieving good imaging performance on the entire scanning surface.

(Effect of this embodiment)
According to the present embodiment, the imaging lens 72 can be configured with one type of eccentric toric lens for a plurality of optical paths in the optical scanning device. Therefore, it is possible to provide a scanning optical system that can achieve low cost and compactness and that can form a good image, and an image forming apparatus using the scanning optical system. Furthermore, in the present embodiment, the imaging lens 72 is made of a resin lens, and a molding die having the same shape is used, so that the cost of the lens can be further reduced.

  In this embodiment, the imaging lens 71 (which is on the deflection means side and also serves as two imaging optical paths) is not set to the same shape as the imaging lens 72, but the imaging lens 71 used in the imaging optical path a; The imaging lens 71 used in the imaging optical path b can be set to a lens having the same shape including the outer shape.

  Further, in the present embodiment, the imaging optical path c and imaging optical path d toward the scanned surfaces 10c and 10d at both ends are opposed to each other in the main scanning section, and the sub-scanning oblique incident angle is set to the upside down direction and rotated. The number of mirrors from the polygon mirror to the imaging lens 72 is set to zero. By doing so, light can be guided to the scanned surfaces 10c and 10d farthest from the rotary polygon mirror with the minimum number of mirrors.

  In the present embodiment, the imaging lens 72 is arranged on the rotary polygon mirror side of the final mirror 8 in all imaging optical paths. With this configuration, the thickness in the height direction of the optical scanning device can be suppressed as compared with the case where the imaging lens is disposed between the final mirror and the surface to be scanned.

<< Second Embodiment >>
In this embodiment, the arrangement and the number of mirrors 8 in the imaging optical path c in the first embodiment are changed, and other optical elements and specification values are the same. FIG. 4 is a cross-sectional view of the main part in the sub-scanning direction of the present embodiment. In this embodiment, as shown in FIG. 4, the number of mirrors from the rotary polygon mirror 5 to the imaging lens 72 is one, the imaging optical path a and the imaging optical path b are one, the imaging optical path c is two, and the imaging optical path. d is set to zero.

  In the present embodiment, the number of mirrors from the rotary polygon mirror 5 to the imaging lens 72 in the imaging optical path c and the imaging optical path b, which are two imaging optical paths whose sub-scanning oblique incident angles are set in the same direction in the vertical direction. Difference (difference in the number of reflecting surfaces) is set to an odd number. In addition, in the imaging optical path c and the imaging optical path d, which are two imaging optical paths that are arranged opposite to each other in the main scanning section and whose sub-scanning oblique incident angle is set in the upside down direction, the rotating polygon mirror 5 The difference in the number of mirrors up to the imaging lens 72 (difference in the number of reflecting surfaces) is set to an even number.

  Further, in the present embodiment, as shown in FIG. 4, the imaging optical path c toward the scanning surface 10c is bent to the lower right, thereby obtaining the effect of further reducing the right side height of the optical scanning device. As a result, the height of the paper discharge unit (not shown) at the upper right side that greatly affects the height of the printer body can be lowered, and the effect of reducing the height of the printer body is obtained.

(Modification)
As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

(Modification 1)
Regarding the incident optical system in the above-described embodiment, the light source means 1 uses a semiconductor laser having one light emitting point. However, the present invention is not limited to this, and for example, the light source means 1 is composed of a monolithic multi-beam laser having a plurality of light emitting points. Also good. Further, beam combining means for combining a plurality of light beams from a plurality of light source means may be arranged in the incident optical system.

(Modification 2)
In the embodiment described above, the number of mirrors (the number of reflecting surfaces) from the rotary polygon mirror 5 to each imaging lens 72 is the same as that in the first embodiment, the imaging optical paths a and b are one, and the imaging optical paths c and d. In the second embodiment, the imaging optical paths a and b are 1, the imaging optical path c is 2, and the imaging optical path d is 0. The present invention is not limited to this. For example, the imaging optical path a can be set to 1, the imaging optical path b can be set to 3, the imaging optical path c can be set to 2, and the imaging optical path d can be set to 0.

(Modification 3)
In the above-described embodiment, the imaging lens 72 is a resin lens. However, the present invention is not limited to this, and the imaging lens 72 may be formed of a glass lens that is decentered with respect to the optical axis.

(Modification 4)
In the embodiment described above, the folding mirror is used as the reflecting surface that reflects the light beam. However, the present invention is not limited to this, and any reflecting optical element (for example, a reflecting prism) can be used.

6 .. Deflection surface, 72 .. Imaging optical element (eccentric toric lens), 10 a, 10 b, 10 c, 10 d... Scanned surface (photosensitive drum surface), L 1 a, L 1 b, L 1 c, L 1 d. , L2a, L2b, L2c, L2d .. Imaging optical system

Claims (10)

Deflecting means for deflecting a light beam in the main scanning direction by a first deflecting surface and a second deflecting surface different from the first deflecting surface;
When a plane perpendicular to the deflection axis of the deflection unit and bisecting the deflection unit in the sub-scanning direction is used as a reference plane, the first light flux from the first direction with respect to the reference plane in the sub-scanning cross section. A first incident optical system that obliquely enters the first deflection surface;
A second incident optical system that obliquely enters the second light flux from the second direction on the same side as the first direction with respect to the reference surface within the sub-scanning section;
A first imaging optical system for condensing the first light beam deflected by the deflecting means on a first surface to be scanned;
A second imaging optical system for condensing the second light beam deflected by the deflecting means on a second scanned surface;
Have
The first imaging optical system and the second imaging optical system have toric lenses having the same shape and asymmetric shape in the sub-scanning direction,
At least one of the first imaging optical system and the second imaging optical system has a reflecting surface that reflects a light beam in an optical path between the deflecting means and the toric lens, and the first An optical scanning device characterized in that the difference in the number of reflecting surfaces in the optical path from the deflecting means to the toric lens in the imaging optical system and the second imaging optical system is an odd number. Deflecting means for deflecting a light beam in the main scanning direction by a first deflecting surface and a second deflecting surface different from the first deflecting surface;
When a plane perpendicular to the deflection axis of the deflection unit and bisecting the deflection unit in the sub-scanning direction is used as a reference plane, the first light flux from the first direction with respect to the reference plane in the sub-scanning cross section. A first incident optical system that obliquely enters the first deflection surface;
A second incident optical system that obliquely enters the second light beam from the second direction opposite to the first direction with respect to the reference surface within the sub-scanning section;
A first imaging optical system for condensing the first light beam deflected by the deflecting means on a first surface to be scanned;
A second imaging optical system for condensing the second light flux on a second scanned surface by the deflecting means;
Have
The first imaging optical system and the second imaging optical system have toric lenses having the same shape and asymmetric shape in the sub-scanning direction,
At least one of the first imaging optical system and the second imaging optical system has a reflecting surface that reflects a light beam in an optical path between the deflecting means and the toric lens, and the first An optical scanning device characterized in that the difference in the number of reflection surfaces in the optical path from the deflecting means to the toric lens in the imaging optical system and the second imaging optical system is an even number including zero. A third incident optical system that obliquely makes a third light flux incident on the first deflection surface from a third direction opposite to the first direction with respect to the reference surface within a sub-scanning section;
A fourth incident optical system that obliquely makes a fourth light beam incident on the second deflection surface from a fourth direction opposite to the second direction with respect to the reference surface within a sub-scanning section;
A third imaging optical system for condensing the third light beam deflected in the main scanning direction by the deflecting unit on a third surface to be scanned;
A fourth imaging optical system for condensing the fourth light beam deflected in the main scanning direction by the deflecting unit on a fourth surface to be scanned;
Have
At least one of the first imaging optical system and the second imaging optical system has a reflecting surface that bends an optical path, and the third imaging optical system and the fourth imaging optical system. At least one of them has a reflective surface that bends the optical path;
The first imaging optical system, the second imaging optical system, the third imaging optical system, and the fourth imaging optical system have the same shape as each imaging optical element. The toric lens having an asymmetric shape in the sub-scanning direction,
The difference in the number of reflecting surfaces in the optical path from the deflecting means to the toric lens in the first imaging optical system and the third imaging optical system is an odd number, and the first imaging optical system 2. The optical scanning device according to claim 1, wherein a difference in the number of reflecting surfaces in an optical path from the deflecting unit to the toric lens in the fourth imaging optical system is an even number including zero.   4. The optical scanning device according to claim 1, wherein the toric lens is an eccentric toric lens in which an optical axis and an outer center are shifted in a sub-scanning section. 5. The first imaging optical system and the third imaging optical system include a second imaging optical element that is also used on the deflecting unit side, and the imaging optical element that is also used as the third imaging optical system and the third imaging optical element. Having at least one reflecting surface in the optical path between the surface to be scanned and
The second imaging optical system and the fourth imaging optical system include an imaging optical element that is also used as the deflecting unit, and the imaging optical element that is also used as the fourth imaging optical element. The optical scanning device according to claim 3, wherein at least one of the reflecting surfaces is provided in an optical path between the surfaces.   The first scanned surface is closer to the deflection means than the third scanned surface, and the second scanned surface is closer to the deflection means than the fourth scanned surface. The optical scanning device according to claim 3, wherein the optical scanning device is provided.   7. The optical scanning device according to claim 1, wherein the reference surface is inclined with respect to the array surface of the surface to be scanned.   8. The optical scanning device according to claim 1, a developing device that develops an electrostatic latent image formed on a photosensitive member by a light beam scanned by the optical scanning device as a toner image, and development. An image forming apparatus comprising: a transfer device that transfers the transferred toner image onto a transfer material; and a fixing device that fixes the transferred toner image onto the transfer material.   An optical scanning device according to claim 1, and a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the optical scanning device. An image forming apparatus.   The image forming apparatus according to claim 8, wherein images having different colors are formed on the first scanned surface and the second scanned surface.