JPH081445U - Optical scanning unit - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an optical scanning unit that can be accurately assembled without causing a lens bending or a mounting position error when a plastic lens is used as a surface tilt correction lens of the optical scanning unit. The purpose is to do. [Structure] The present invention has a long rod-shaped plastic face tilt correction lens that is long in the longitudinal direction, and is fixed at both ends in the longitudinal direction. However, by making both ends free, even if a thermal expansion-contraction error occurs in the lens longitudinal direction, regardless of this, the heat of both ends is always made to coincide with the center position of the lens and the center position of the optical axis. It is intended to remove the strain by allowing expansion.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an optical scanning unit in which a lens housing for locating and fixing a surface tilt correction lens is arranged on the most downstream side in the beam passing direction facing a photoconductor, and particularly a plastic lens is used for the surface tilt correction lens. In this case, the present invention relates to an optical scanning unit that can be accurately assembled without causing a lens bending or a mounting position error.

[0002]

[Prior art]

 2. Description of the Related Art Conventionally, an optical scanning unit is known in which a laser beam modulated based on recorded information is scanned at a constant speed on a photoconductor through a deflector to form an electrostatic image corresponding to the recorded information on the photoconductor. In this type of unit, a cylindrical lens or toroidal lens extending in the beam scanning direction is arranged at the position facing the most downstream photosensitive member of various lens systems to correct the surface tilt of the deflector. , It is constructed so that a clear image is always formed on the photoconductor bus.

This kind of surface tilt correction lens must be arranged so as to maintain a synergistic relationship between the deflecting surface and the vicinity of the image forming position of the photoconductor, so that accuracy regulation in the optical axis direction is required. However, since the lens is located on the most downstream side of the scanning beam, the length in the lens longitudinal direction must be set to be approximately equal to the length on the photoconductor bus. It is extremely difficult to accurately position and fix such a lens having a considerable total length in a direction perpendicular to the optical axis direction without tilting in the longitudinal direction.

In particular, when a toroidal lens is used as the surface tilt correction lens, both the entrance surface and the exit surface are formed with a predetermined radius of curvature, so that the scanning beam generated when transmitting through the fθ lens system. However, when a lens having such a curvature is used, the position limiting surface on the unit side is formed into a curved surface in accordance with the curvature surface. Therefore, the manufacturing cost is high, it is difficult to perform the processing with high precision, and an assembly error is likely to occur.

Therefore, the applicant first formed the toroidal lens with a plastic lens, and on a plane extending in the longitudinal direction in a region deviating from the beam scanning region on either the incident surface side or the emission surface side thereof. We have proposed a prior application technology (actual application Sho 60-80976) in which a foot portion is formed and the upper surface (bottom surface) of the foot portion is brought into contact with a supporting surface on the unit side. The lens has a length approximately the same as the photoconductor bus length, and when a lens having such a considerable length is made of plastic, it cannot be ignored in the lens longitudinal direction due to its thermal expansion and contraction. Errors are likely to occur.

Particularly, in the toroidal lens, since the entrance surface and the exit surface are formed with concentric curvature radii, the error in the lens longitudinal direction appears as a positional deviation between the center position of the lens and the center position of the optical axis. Astigmatism that occurs during transmission of the fθ lens system cannot be corrected, and conversely, further aberration may occur during transmission of the lens or the error may be amplified.

[0007]

[Problems to be solved by the device]

 The technical problem to be solved by the present invention is to provide an optical scanning unit that can be accurately assembled without causing lens bending or mounting position error when a plastic lens is used as the surface tilt correction lens. The purpose is to do. The object of the present invention is to regulate the position of the lens in the longitudinal direction along with the direction of the optical axis so that the center line of the lens and the center line of the optical axis can be accurately positioned. The present invention is to provide an optical scanning unit in which there is no possibility of causing a problem. Especially, even when a toroidal lens is used as the surface tilt correction lens, the position regulating surface on the unit side can be easily processed and an assembly error, etc. The object is to provide an optical scanning unit that can be assembled with high accuracy without causing problems.

Another object of the present invention is that the surface tilt correction lens extending in the main scanning direction is not supported at both ends but its supporting (lens contact surface) surface is supported over the entire length in the longitudinal direction. (EN) Provided is an optical scanning unit which is configured as possible and, as a result, eliminates a problem in supporting both ends, for example, bending and twisting of a lens, which can always obtain a clear image on a photoconductor. It is in.

[0009]

[Means for Solving the Problems]

 In order to achieve the technical problem, the present invention is directed to, for example, as shown in FIGS. 1 and 3, a lens accommodating portion for positioning and fixing the surface tilt correction lens 2 on the most downstream side in the beam passing direction facing the photoconductor 3. In the optical scanning unit 1 in which 4 is formed, a plastic lens is used for the surface tilt correction lens 2, and a short side which is out of the beam scanning area of the lens entrance surface 2a or the exit surface 2b is provided on the surface tilt correction lens 2 side. The lens support surfaces (foot upper surfaces) 21 having a flat surface extending in the longitudinal direction on both sides in the direction, and the engaging recesses 23, 24 having a rectangular cross section provided at the central portions in the longitudinal direction of the support surfaces 21, 22. Alternatively, a plane provided in parallel with the convex surface and the supporting surfaces 21 and 22 outside the beam scanning region on the exit surface 2b or the incident surface 2a side of the lens, facing the supporting surfaces 21 and 22. Lens pressing surfaces (bottom surface) 26, 27 of the lens, while the lens supporting surfaces 21, 22 are in contact with the housing portion 4 side for housing the lens substantially in the longitudinal direction. 42 and 43, the engaging portions 44 and 45 that fit tightly into the engaging concave portions 23 and 24 or the convex portions at the center position in the longitudinal direction on the corresponding contact surfaces 42 and 43, and the lens pressing surfaces 26 and 27 are elastic. And a fixing portion (fixing portion member) 5 that presses the lens supporting surfaces 21 and 22 against the contact surfaces 42 and 43 by the fixing portion 5 via the lens pressing surfaces 26 and 27. It is characterized in that the engaging portions 44 and 45 are fitted into the engaging concave portions 23 and 24 or the convex portions while regulating the position in the direction, and the position in the longitudinal direction of the lens is regulated. We propose an optical scanning unit. In the present invention, the surface tilt correction lens is formed of a plastic lens, but it does not matter whether the lens is a cylindrical lens or a toroidal lens.

[0010]

[Action]

 The plastic lens has a larger thermal expansion than the glass lens, and the thermal expansion / contraction causes a non-negligible error in the lens longitudinal direction. If the lens is forcibly fixed in order to solve such a problem, the lens is likely to bend due to thermal expansion and contraction. In particular, since the surface tilt correction lens is formed in the shape of a rod that is long in the longitudinal direction, the above defects are more likely to increase. In order to eliminate distortions and the like caused by fixing the longitudinal plastic rod surface correction lens at both ends in the longitudinal direction, the present invention fixes the position only at the center and By making both ends free, even if there is a thermal expansion-contraction error in the lens longitudinal direction, regardless of this, the thermal expansion of both ends is always performed while the center position of the lens and the optical axis center position are aligned. This is a permissible removal of distortion.

That is, according to the present invention, the engaging portions 44 and 45 for restricting the position of the lens 2 in the longitudinal direction are formed on the center line CC ′ of the optical axis at the central position of the lens 2 in the longitudinal direction. In addition, the toroidal lens 2 that corrects the surface tilt is formed of a plastic lens, and even if there is a thermal expansion-contraction error in the lens longitudinal direction, the center position of the lens and the optical axis center position C are always irrelevant regardless of this. As a result, it is possible to smoothly correct the astigmatism that occurs when transmitting the fθ lens system 12 described above, and there is no risk of further aberration occurring when the lens 2 passes through. A clear image can be formed.

In this case, the surface tilt correction lens 2 housed in the lens housing section 4 is fixed by the fixing member 5 arranged so as to face the lens contact surfaces 42, 43. Since it is configured to be fixed by face-to-face support on a parallel surface via the lens, when the lens 2 is housed, the longitudinal direction of the lens 2 between the end surface on the longitudinal direction side of the lens 2 and the inner wall surface of the housing part is increased. It is possible to form the escape portion 46 capable of absorbing the positional deviation of the lens. As a result, even if the lens 2 is formed of a plastic lens, the thermal expansion / contraction error is absorbed and the positioning is fixed accurately and surely. You can do it.

Further, according to the present invention, the lens supporting surfaces (foot upper surfaces) 21, 22 and the contact surfaces 42, 43 with which the lens supporting surfaces 21, 22 come into contact with each other over substantially the entire longitudinal direction. Also, since the lens pressing surfaces 26, 27 elastically pressed by the fixing portion 5 are both planar and parallel, it is possible to perform accurate positioning without rattling or tilting, and as described above. The fixing member 5 is disposed on the side facing the lens contact surfaces 42 and 43, and the fixing member 5 is pressed to easily position and fix.

Furthermore, since the lens contact surfaces 42 and 43 are extended over the entire length in the longitudinal direction of the lens 2, there is no need to support the lens 2 by two-point support, and the entire length in the longitudinal direction is supported. Since the lens 2 is supported, it is possible to eliminate the possibility that the lens 2 is bent or twisted. Further, according to the present invention, since the lens contact surfaces 42, 43 and the engaging portions 44, 45 for restricting the position of the lens 2 in the longitudinal direction are both formed in the area deviated from the beam scanning area, The shape can be set to be a shape that is easy to process regardless of the shape of the lens 2 without any hindrance to scanning, and as a result, smooth light scanning can be performed with convenience in processing and assembly. I can.

[0015]

【Example】

 Hereinafter, a preferred embodiment of the present invention will be exemplarily described in detail with reference to FIGS. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the constituent parts described in this embodiment are not intended to limit the scope of the present invention thereto, but merely illustrative examples. Nothing more. First, the structure of the toroidal lens 2 applied to the present invention will be described with reference to FIG. The toroidal lens 2 is formed of a plastic lens, and the beam scanning area on the entrance surface 2a and the exit surface 2b side thereof is formed into a concentric arc shape having a center on the exit surface 2b side. Along with the correction function, the radius of curvature is set so as to correct the aberration generated when the scanning beam passes through the fθ lens system 12.

Further, on both side edges in the lateral direction outside the beam scanning region on the side of the entrance surface 2a of the lens 2, the beam axis center line CC ′ incident on the lens 2 is orthogonal to, that is, the longitudinal direction. A pair of feet are extended in parallel along the direction, and the upper surfaces 21 and 22 (unit contact surfaces) of the feet are flush with a virtual plane orthogonal to the top of the incident surface 2a. It is formed in a plane shape orthogonal to the beam axis center line CC ′.

Then, a pair of engaging recesses 23, 24 opening upward are formed on the foot upper surfaces 21, 22 at the center upper position in the longitudinal direction of the lens 2 which coincides with the beam axis center line CC ′. . On the other hand, foot lower surfaces 26 and 27 parallel to the foot upper surfaces 21 and 22 are formed on both ends in the lateral direction outside the beam scanning region on the lens 2 emission surface 2b side. The beam incident area sandwiched between the pair of foot upper surfaces 21 and 22 is set to be substantially the same as the width of the slit opening 13 of the unit 1 to be described later so that the laser beam B can be smoothly scanned. .

FIGS. 1 and 3 show the structure of an optical scanning unit 1 in which such a lens 2 is incorporated, FIG. 1 is an overall front sectional view, and FIG. 3 is a bottom view of an essential part. The frame body 10 is made of precision moldable plastic resin, and the scanning beam deflected by the rotary polygon mirror 11 spreads out in a substantially fan shape around the mounting position and the downstream side thereof is vertically erected. In addition to forming a space in which the second reflection mirror 15 can be attached, a slit port 13 extending in the main scanning direction is formed on the exit side of the reflection mirror 15, and further faces the photoconductor 33 immediately below the slit port 13. A lens housing portion 44 for fixing the toroidal lens 2 in a predetermined position is formed on the side where the lens is to be attached. In the figure, the upper cover 10a for opening the frame 10 is a cooling rib 10b formed on the bottom surface side.

Inside the frame 10, various scanning system members such as a semiconductor laser, a rotary polygon mirror 11, an f θ lens system 12 and the like, which are not shown, are arranged at predetermined positions, respectively. The laser beam incident on the rotary polygon mirror 11 through the lens system is incident on the fθ lens system 12 while being deflected by the rotary polygon mirror 11 in the main scanning direction, and after being converted to a constant velocity motion by the fθ lens system 12. , The first and second reflecting mirrors 14 and 15 are made incident on the toroidal lens 2 through the slit aperture 13 to correct the surface tilt and the aberration error, and scan the image on the photoconductor 3 via the filter 16. It is configured to be done. Reference numeral 17 is a photodiode for detecting the scanning start timing of the laser beam.

Next, the configuration of the lens housing portion 4 for positioning and fixing the toroidal lens 2 will be described in detail. The lens accommodating portion 4 has a substantially rectangular cross section, extends in the main scanning direction with the same width interval as the toroidal lens 2, and has a concave shape in which the opposite side of the photoconductor 3 is open. The housing portion 4 has stepped portions on both lower sides of the slit mouth 13 and has flat contact surfaces 42 and 43 on which the foot upper surfaces 21 and 22 of the toroidal lens 2 can contact, and the corresponding contact portions are formed. Engaging protrusions 44, 45 which can be fitted tightly into the engaging recesses 23, 24 on the lens 2 side are formed at the positions of the surfaces 42, 43 which coincide with the center line C-C 'of the beam axis.

Further, the entire length in the longitudinal direction of the lens housing portion 4 is slightly larger than the entire length in the longitudinal direction of the lens 2, and when the lens 2 is housed, a predetermined space is formed between both end surfaces of the lens 2 and the inner wall surface of the housing portion 4. 46 is set to be formable.

The filter 16 has a flat plate shape having a size capable of concealing the exit surface 2b side of the lens 2. The fixing member 5 is formed of a plate spring or other metal elastic member, and a slit hole 51 is formed at a position corresponding to the beam scanning region so that the beam can be scanned, and the lens bottom portion on both sides of the slit hole 51 is formed. A cushion material 52 made of a leaf spring, rubber, sponge material, or the like is attached at a position corresponding to the lower surfaces 26 and 27. If the cushion material 52 is brought into contact with the lower surface 26, 27 of the foot in the lens longitudinal direction, a more stable holding structure can be obtained by providing a plurality of the cushion materials 52 in the lens longitudinal direction.

Further, both ends of the fixing member 5 are bent in a rectangular shape, and a screw mounting hole 53 is formed in the bent portion, and the fixing member 5 is formed on both sides of the opening of the lens accommodating portion 4 via a screw 54. It is configured so that it can be fixed to the screw hole 17.

Next, a procedure for positioning and fixing the lens 2 according to the example will be described. The lens 2 is inserted from the opening side of the lens accommodating portion 4, and the engaging concave portions 23 and 24 are fitted to the incident surface side of the lens 2 while engaging the engaging protrusions 44 and 45 on the lens accommodating portion 4 side with the legs. After the upper surfaces 21 and 22 are placed on the housing portion side contact surfaces 44 and 45, the filter 16 is brought into contact with the lens foot lower surfaces 26 and 27, and then the fixing member 5 is attached via the screw 54 to the unit. By mounting the lens 2 on the lower surface, the lens 2 is pressed and held by the contact surfaces 44 and 45 through the cushion material 52 and the filter 16 and positioned and held at a predetermined position. Therefore, according to this embodiment, even if the lens 2 is repeatedly fixed, no positional deviation occurs, and the lens 2 can be fixed accurately and easily, and the above-described operational effects can be smoothly achieved. .

[0025]

[Effect of device]

 As described above, according to the present invention, even when the anti-tilt lens is formed of a rod-shaped plastic elongated in the longitudinal direction, the lens is fixed only in the center and both ends are free from expansion and contraction in the longitudinal direction. Therefore, even if there is a thermal expansion-contraction error in the lens longitudinal direction, regardless of this, the center position of the lens and the center position of the optical axis are always matched and the thermal expansion at both ends is allowed to eliminate distortion. Can be planned. That is, in order to regulate the position of the center of the lens in the optical axis direction by the lens contact surface and the thermal expansion of both ends by the engaging part and to control the center of the lens longitudinal direction, the lens center line and the optical axis center line are accurately measured. And it can be positioned reliably.

In particular, even when a toroidal lens is used as the surface tilt correction lens, since the lens contact surface and the engaging portion are set in an area outside the beam scanning area, the unit side and the lens The side position regulation surface can be easily processed, and it can be assembled with high accuracy without causing assembly errors.

Further, according to the present invention, since the lens is supported face-to-face by the fixing member arranged on the opposite side of the lens abutting face, more accurate positioning is possible, and at the emitting side of the lens. It can also be positioned and fixed integrally with the dustproof filter lens placed in, and as a result, it is possible to reduce the number of parts, downsize the device, and reduce the weight.

Further, according to the present invention, the support of the surface tilt correction lens extending in the main scanning direction is not fixed at both ends but is fixed at the center, and the support (position control) surface is made the entire length in the longitudinal direction. Since it is configured to be pressed and supported over time, it is possible to always obtain a clear image on the photoconductor, except for the problems in the above-mentioned both-ends support, for example, the possibility that the lens is bent or twisted. It has various remarkable effects.

[Brief description of drawings]

FIGS. 1 to 3 show the configuration of an optical scanning unit according to an embodiment of the present invention, and FIG. 1 is an overall front sectional view thereof.

FIG. 2 is a perspective view showing a configuration of a toroidal lens fixed to the unit.

FIG. 3 is a bottom view of a main part of the optical scanning unit shown in FIG. 1;

[Explanation of symbols]

 1: Optical scanning unit 2: Surface tilt correction lens 2a: Lens entrance surface 2b: Lens exit surface 3: Photoreceptor 4: Lens storage unit 5: Fixed unit 21, 22: Lens support surface 23, 24: Engagement concave or convex Portions 26 and 27: Lens pressing surfaces 42 and 43: Contact surfaces 44 and 45: Engaging portions

Claims (1)

[Scope of utility model registration request] 1. An optical scanning unit in which a lens housing portion for positioning and fixing a surface tilt correction lens is formed at the most downstream side in a beam passing direction facing a photoreceptor, wherein a plastic lens is used as the surface tilt correction lens, A flat lens support surface extending in the longitudinal direction on both sides in the short direction deviating from the beam scanning area of the entrance surface or the exit surface of the lens, and a central portion in the longitudinal direction of the support surface; And an engaging concave portion or a convex portion having a rectangular cross section provided at a position parallel to the support surface at a position facing the support surface deviating from the beam scanning area on the exit surface or the entrance surface side of the lens. A contact surface on which the lens support surface abuts over substantially the entire region in the longitudinal direction, and a contact surface on the storage portion side for accommodating the lens; An engaging portion that fits exactly into the engaging concave portion or the convex portion at the position, and a fixing portion that elastically presses the lens pressing surface are provided, and the fixing portion forms a lens supporting surface via the lens pressing surface. It is characterized in that the position is regulated in the lens longitudinal direction by fitting the engaging portion into the engaging concave portion or convex portion while controlling the position in the optical axis direction by pressing against the contact surface. Optical scanning unit