JPH067229B2 - Optical scanning device - Google Patents

Description

The present invention relates to an optical scanning device that can easily correct an image forming position shift on a recording medium caused by various manufacturing errors of a light source and a lens system.

"Prior Art" Conventionally, for example, as shown in FIG. 2, a light source 1 that oscillates a laser beam modulated according to input information, and a laser beam oscillated from the light source 1 is imaged as linearly focused light. An image forming lens system 2 including a collimator lens 22 and a plano-convex cylindrical lens 21, a rotary polygon mirror and other deflectors 3 arranged near the image forming position of the image forming lens system 2,
An fθ lens system 4 for converting the light beam reflected and deflected by the deflector 3 into a uniform velocity motion, a recording medium 5 such as a photosensitive drum for scanning the deflected beam from the deflector 3 on a bus line, Between the fθ lens system 4 and the recording medium 5 so that the deflection surface of the deflector 3 and the image forming position of the recording medium 5 can maintain a conjugate relationship with the combined system with the fθ lens system 4. A laser beam oscillated from the light source 1 is made incident on the deflector 3 as linear focused light parallel to the main scanning direction through the imaging lens system 2 and the deflection is performed. After being deflected and reflected by a predetermined angle by the rotation of the device 3, the fθ lens system 4 converts the motion into a constant velocity motion, and then the surface tilt correction lens system 6 corrects the surface tilt in the sub-scanning direction of the deflecting surface to record the recording medium 5. Optical dot corresponding to the input information on the bus Optical scanning apparatus for scanning and imaging the turn is already known.

In this type of apparatus, when processing errors such as surface accuracy and wall thickness accuracy of the various lens systems occur, the laser beam does not form an image on the photoconductor generatrix, and the image forming position shifts in the optical axis C direction. As a result, there is a problem in that a clear imaging spot cannot be obtained.

In order to solve such a drawback, in JP-A-57-144517, the image forming lens system 2 is configured to be movable in the direction of the optical axis C, and its moving means is, for example, as shown in FIG. 3A, an image forming lens. Moving stage 101 capable of moving the system 2 in the optical axis C direction
An adjusting screw 1 mounted on the moving stage 101 and connected to the moving stage 101.
The means for moving the imaging lens system 2 by moving the moving stage 101 along the sliding surface of the fixed base 103 by the rotation of 02 and holding the imaging lens system 2 as shown in FIG. 3B. Stand 11
The vertical reference plane 111 of 0 and the leaf spring 112 are sandwiched and fixed, and the washer 113 is interposed between the reference plane 111 and the imaging lens system 2, and the washer 113 is removed or additionally inserted to form an imaging lens. A means for making the system 2 movable in the optical axis C direction has been proposed. According to such technical means, a length corresponding to a deviation (ΔS) between the image forming position on the bus and the actual image forming position. By moving the imaging lens system 2 in the direction of the optical axis C by (ΔS / β, β: imaging magnification), the imaging position shift is corrected and an optimum image can be obtained.

[Problems to be Solved by the Invention] However, in the former case, since the imaging lens system 2 is configured to be movable using the screw 102, it is difficult to make fine adjustment due to the backlash of the screw 102 itself, and the latter. However, since the movement is adjusted by the washer 113, the movement amount cannot be continuously corrected, and in any case, it is not suitable as a correction means that requires fine adjustment on the order of 1/10 mm. .

Further, in the latter technical means, when the washer 113 is inserted and removed, the elastic force of the leaf spring 112 is changed or settled, and due to the variation of the pressing force, an eccentric load or backlash is easily generated in the imaging lens system 2. In some cases, it may be difficult to move in the direction of the optical axis C while maintaining the perpendicularity between the input / output surface of the lens system 2 and the optical axis C.

Also in the former technical means, the number of parts such as the fixed base 103, the moving stage 101, the supporting plate 104 for fixing the imaging lens system 2 on the moving stage 101, the adjusting screw 102 and the supporting base 105 is extremely large. In addition, the parallel movement of the imaging lens system 2 may be difficult due to the accumulation of processing errors and assembly errors of the various members.

Further, in the former technical means, since it is necessary to dispose the adjusting screw 102 for moving the close-up lens system 2 in the exit direction or the incident direction side of the imaging lens system 2, that portion is inevitably made dead space. , Leads to larger equipment.

Although the laser beam inevitably causes a beam waist at its focal position due to its characteristics, the width (2ω) of the beam waist is determined by the focal length (f) as shown in the following equation.
It changes according to the fluctuation of.

ω = (λ / πw) f 2w: Beam parallel incident width, λ: Wavelength Therefore, the imaging lens system 2 is moved to the optical axis C as in the prior art.
In the case of moving the image forming lens system 2 in the direction, the area of the image forming spot on the recording medium 5 also changes in accordance with the movement of the image forming lens system 2, and a thick or thin line image is formed.

In view of the above-mentioned drawbacks of the prior art, the present invention finely and continuously corrects the deviation amount of the image forming position on the recording medium 5 caused by the processing error and the assembly error of the light source and various lens systems. An object is to provide an optical scanning device configured as possible.

Another object of the present invention is to provide an optical scanning device capable of appropriately selecting a correction amount per unit in accordance with the image forming magnification β.

A further object of the present invention is to provide an optical scanning device having extremely high reproducibility, in which the amount of correction does not vary even if it is repeatedly corrected.

Still another object of the present invention is to provide an optical scanning device in which it is easy to provide a correction mechanism with a small number of parts and a small room for assembly error.

It is another object of the present invention to provide an optical scanning device capable of obtaining a uniform line image as a result of which the image forming spot area on the photoconductor hardly changes even after the above correction. .

[Means for Solving the Problems] In order to achieve the technical problem, the present invention is directed to a plano-convex cylindrical lens 21 or other components constituting the imaging lens system 2 as shown in FIGS. 1a to 1c. Has a rotating means for rotating the focusing lens in the sub-scanning direction, and a deviation in the sub-scanning direction between the lens incident surface vertex D position and the optical axis C, which occurs when the lens 21 is rotated, is slightly displaced. In order to suppress the amount, the technical means in which the rotation center A is formed at a predetermined position on the exit surface 21A side from the entrance surface vertex D position of the lens 21 is proposed.

In this case, the rotation center A does not necessarily have to be located on the optical axis C, and may be set at the upper end or the lower end of the exit surface 21A of the imaging lens system 2.

"Operation" According to such technical means, the plano-convex cylindrical lens 21
By rotating the other focusing lens in the sub-scanning direction, the image forming position S ′ moves in the direction closer to the recording medium 5 side along the optical axis C, and as a result, the recording medium 5 is moved.
It is possible to obtain the optimum image by correcting the image forming deviation of.

In this case, the cylindrical lens 21 is set to the optical axis C.
When arranged at a right angle to the cylindrical lens
When the lens 21 is rotated in either the front-back direction or the front-back direction, the image-forming position S ′ is moved in a direction closer to the recording medium 5 side. However, for example, due to the manufacturing tolerance of the cylindrical lens, the focal length is changed. The lens may be erected on the optical axis C according to the short lens and then rotated, or if the cylindrical lens 21 is tilted by a predetermined angle in advance, the lens is placed at a right angle position from the tilt angle position. The image forming position S ′ may be moved in a direction away from the recording medium 5 until the image forming position is reached, and may be moved closer when the image forming position S ′ exceeds the right angle position.

In the present technical means, the plano-convex cylindrical lens 21
Since it is sufficient to simply rotate the lens in the sub-scanning direction rather than moving it back and forth in the optical axis direction, it is possible to repeatedly rotate the lens as the supporting surface (supporting point) on the inclining surface side or the rotation center. As a result, since the support position is stable even if the above-mentioned rotation is repeated, the correction amount does not vary, and the reproducibility of correction can be made extremely high.

Further, similarly, since the correction is performed by the rotation, continuous adjustment is easier, the number of parts is smaller, and there is less room for assembly error as compared with the advancing / retreating structure.

Further, in the configuration in which the correction is performed by the rotation, since the focal length (f) of the laser beam hardly changes, the width of the beam waist (2ω), that is, the image forming spot area on the recording medium 5 is substantially ignored. It is as small as it gets, and it is possible to form a uniform line image.

Note that the present technical means positions the rotation center A position on the exit surface 21A side and, in the sub-scanning direction, between the optical axis C and the vertex D position of the lens entrance surface that occurs when the lens 21 rotates. The displacement is configured to be zero or suppressed to a minute deviation amount.

The reason for this is that the main surface of the plano-convex cylindrical lens 21 coincides with the apex of the front curvature surface, so that the sub-scanning direction between the lens incident surface apex D position and the optical axis C generated when the lens 21 rotates. If the deviation can be suppressed to zero or a minute deviation amount, there is little possibility that a problem will occur due to the deviation of the linear incident light on the deflecting surface from the optical axis C.

The correction amount is the exit surface of the plano-convex cylindrical lens 21.
It is determined by the tilt angle on the side of 21A, and is therefore
As shown in FIG. c, the rotation center position A is the intersection of the emission surface 21A and the optical axis C (FIG. 1a), and the optical axis C on the emission surface 21A side (first
b)), assuming that they are set at the lower end position of the lens on the exit surface 21A side (Fig. 1c) respectively, the correction amounts can be adjusted by a slight rotation in the order of Fig. 1a, Fig. 1b, and Fig. 1c. In addition, the deviation in the sub-scanning direction between the position D of the lens incident surface and the optical axis C, which occurs when the lens 21 rotates, can be suppressed to zero or a minute deviation amount.

Therefore, the correction amount per unit can be appropriately selected by determining the rotation center A position according to the imaging magnification β.

Incidentally, astigmatism occurs due to the rotation of the cylindrical lens 21, but since the light beam incident on the plano-concave cylindrical lens 21 is very small in the optical scanning device, the astigmatism caused by the lens is on the generatrix. It does not appear as a distortion of the spot image, so there is no practical problem.

[Embodiment] Hereinafter, a preferred embodiment of the present invention will be exemplarily described in detail with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely descriptions. It's just an example.

5 to 6 show an optical scanning device according to an embodiment of the present invention, in which 51 is a housing in which an upper cover 52 can be opened and closed,
The side of the bottom surface 51a of the housing 51 where the rotary polygon mirror 53 is mounted is turned inward to form a mounting passage 51d for the semiconductor laser 54 or the like sandwiched between the partition wall 51b and the side wall 51c.

In the mounting passage 51d, a housing 54 accommodating a semiconductor laser and a collimating lens and a cylindrical lens unit 20 are sequentially arranged from the opening end side, and the scanning beam 10 emitted from the semiconductor laser is converted into a linear spot light parallel to the main scanning direction. And then the reflection mirror 56 disposed on the exit side of the passage 51d.
The light is incident on the deflection surface 53a of the rotary polygon mirror 53 at a predetermined angle via.

The rotary polygon mirror 53 is connected to the synchronous motor 57, and the photosensitive drum
While rotating in synchronization with 58, the scanning beam 10 incident on the deflection surface 53a is swept in the main scanning direction and is incident on the fθ lens 59.

The swept scanning beam 10 is converted from a constant angular velocity motion to a constant velocity motion by the fθ lens 59, and then the first and second deflection mirrors 62 attached to the side plate 61 of the housing 51 and the upper cover 52. ， 63 through toroidal lens 64,
After entering the toric lens such as a cylindrical lens to correct the tilt of the rotary polygon mirror 53 in the sub-scanning direction,
The image is scanned on the generatrix of the photosensitive drum 58 located below the optical axis C of the toroidal lens 64.

On the other hand, a detection mirror 65 is arranged at the start end side of the beam scanning area on the exit side of the fθ lens 59,
The emitted scanning beam 10 before entering the photosensitive drum 58 is redirected by the detection mirror 65 and guided to the photodiode 66, and the scanning beam 10 is guided based on the horizontal synchronizing signal output from the photodiode 66. The emission timing of the scanning beam 10 of the semiconductor laser is controlled.

The scanning beam 10 of the semiconductor laser emitted based on the horizontal synchronizing signal is applied to the photosensitive drum 58 by the method described above.
By rotating the photosensitive drum 58 in the sub-scanning direction in synchronism with the rotation of the rotary polygon mirror 53 while being repeatedly scanned on the bus bar, a clear image corresponding to the input information on the photosensitive drum 58 without causing jitter or the like. Is formed.

4A and 4B show the configuration of the cylindrical lens unit 20 used in the optical scanning device,
An outer frame 23 fixed to 51 and a lens fixing frame 24 fitted in the cylindrical cavity portion 231 of the outer frame 23 and rotatable in the sub scanning direction.
And a plano-convex cylindrical lens 21 mounted on the L-shaped reference surface 241 of the fixed frame 24, and an adjusting screw 25 for rotating the lens 21 together with the fixed frame 24.

The outer frame 23 has a substantially cylindrical bottom surface, has opening windows 232 and 233 for entering and exiting the dome in a central position parallel to the optical axis, and obliquely above the exit side along the sub-scanning direction. A long hole 234 extending is bored, and a cylindrical cavity 231 having the same radius of curvature as the outer peripheral surface of the lens fixing frame 24 is formed.

The lens fixing frame 24 has a substantially semi-cylindrical shape, and an L-shaped reference surface 241 on which the cylindrical lens 21 can be positioned at a predetermined position.
And a screw hole 242 into which the adjusting screw 25 is screwed.

The cylindrical lens 21 has a vertical plane on the light emitting surface 21A side, and is fixed in contact with the L-shaped reference surface 241 of the lens fixing frame 24.

The adjusting screw 25 has a head portion 251 protruding above the elongated hole 234 of the outer frame 23, and is configured to be fixable at a predetermined position by a set screw 26 at an arbitrary position within the extension angle α range of the elongated hole 234, By rotating the adjusting screw 25, the lens fixing frame 24 and the cylindrical lens 21 can be integrally rotated in the sub-scanning direction.

According to this embodiment, by rotating the adjusting screw 25 along the long hole 234, the cylindrical lens can be easily and without causing a rotation error due to repeated operation.
21 can be rotated in the sub-scanning direction, and the effects of the present invention can be achieved smoothly.

Further, the amount of correction by the adjusting screw 25 can be freely determined by the extension angle α of the elongated hole 234.

[Advantages of the Invention] As described above, according to the present invention, the correction of the deviation amount of the image forming position on the recording medium caused by the processing error or the assembly error of the light source or various lens systems is finely and continuously corrected. Therefore, it is possible to further improve the sharpness of the image forming spot formed on the generatrix of the recording medium.

According to the present invention, the correction amount per unit can be freely determined by appropriately determining the rotational center position of the cylindrical lens and other focusing lenses according to the imaging magnification β of the optical scanning device, and as a result, the maintenance can be performed. Can be facilitated.

Further, according to the present invention, since the correction is performed by the rotation of the cylindrical lens, even if the correction is repeatedly performed, the correction amount does not vary, and it is possible to provide an optical scanning device having extremely high reproducibility.

Furthermore, according to the present invention, since the number of parts is small and there is little room for assembly error, it is possible to reduce manufacturing cost and maintenance cost.

Furthermore, according to the present invention, since the focal length of the cylindrical lens does not change even if the above correction is performed, the change of the image forming spot area on the photoconductor is minute, and as a result, a uniform line image is obtained. I can do things. And so on.

[Brief description of drawings]

FIGS. 1a to 1c are operation diagrams for explaining the principle of the present invention in which the rotational center position of the focusing lens is changed, and FIG. 2 is a schematic explanatory diagram showing an optical scanning device to which the present invention is applied, FIG. Figure 3B
Each of the drawings is a perspective view and a sectional view showing the structure of an imaging lens system according to the prior art, FIG. 4A is a front view showing the structure of a cylindrical unit according to an embodiment of the present invention, and FIG.
It is a B'line sectional view. 5 and 6 are a front sectional view and a plan sectional view showing an optical scanning device in which such a unit is assembled.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoichi Takei, 3-1,778 Osogi, Ome-shi, Tokyo Tomioka Optical Co., Ltd.

Claims (1)

[Claims] 1. An optical scanning device having an imaging lens system for causing a laser beam oscillated by a light source to enter a deflector as linear focused light, wherein a focusing lens forming the imaging lens system is rotated in a sub-scanning direction. The lens is configured to be movable, and its rotation center is incident on the lens in order to suppress the deviation in the sub-scanning direction between the apex position of the lens incident surface and the optical axis, which occurs when the lens is rotated, to a small deviation amount. An optical scanning device characterized in that it is formed at a predetermined position on the exit surface side from the surface vertex position.