JPH04261564A - Supporting device for laser beam scanner - Google Patents

Abstract

PURPOSE:To decrease the deviation in scanning lines by supporting the axial line parallel with the scanning line on a recording medium on which a laser beam scans on the laser beam scanner as a supporting axis. CONSTITUTION:The photosensitive body 14 is mounted to a supporting member 15 and positioning is executed with prescribed accuracy by this supporting member 15 and a body side plate. Since the revolving shaft (a)of this photosensitive body 14 and the scanning line(b) need to be parallel, the axial line (c) connecting the centers of front and rear through-holes 11 a, 11b provided on the front side plate 9 and the rear side plate 1, respectively, are provided in parallel with the revolving shaft (a)of the photosensitive body 14. A housing 6 is rotatable around the axial center (c) in the state of axially fitting the laser beam scanner to the body by using a stepped screw 12 and, therefore, the rear surface of the housing 6 is fixed via an elastic member 17, such as rubber, to a frame 16 spanned between the side plates 9 and 10.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam scanning device applied to digital copying machines, laser printers, laser facsimile machines, and the like.

0002

[Prior Art] Digital copying machines, laser printers, and laser facsimile machines have electrophotographic plotters as image recording units, and image formation using image signals is achieved by irradiating a photoreceptor with a modulated laser beam. It's becoming mainstream. In such a device, a laser beam is repeatedly scanned (main scan) while being focused approximately on a certain straight line in space by the action of a rotating polygon mirror and an imaging lens. On the other hand, the photoreceptor of a plotter, which is a recording medium, moves at a constant speed in a direction perpendicular to the scanning line while the beam repeats main scanning on the surface of the photoreceptor (sub-scanning). As a result, the beam will raster scan over the photoreceptor surface. What greatly influences the quality of the image recorded at this time is the relative positional relationship between the scanning line and the photoreceptor. In particular, misalignment of scanning lines in the sub-scanning direction results in a striped pattern in the image, which is most disliked. Therefore, a proposal was made to prevent the scanning line from shifting in the sub-scanning direction, for example, in 1983.
This is disclosed in Japanese Patent No.-153259. With regard to the attachment of the optical frame that supports the beam scanning device and the main body frame of the plotter, this invention adopts a structure in which the optical frame is rotatably supported and fixed on an axis parallel to the rotation axis of the photoreceptor.

0003

[Problem to be Solved by the Invention] However, if no consideration is given to the positional relationship between the photoreceptor and the optical frame, simply supporting the photoreceptor on an axis parallel to the rotation axis will not be enough to suppress the deviation of the scanning line. Not enough. In order to keep the displacement small, it is necessary to make the rotation angle of the optical frame relatively small, and it is necessary to design the optical frame to extremely rigidly regulate the positional relationship between the optical frame and the photoreceptor. Therefore, for example, inconveniences arise, such as the inability to use elastic members for vibration isolation. Furthermore, if the optical frame is made of resin or the like, when it is rigidly fixed, the position of the optical element may be shifted due to deformation due to the screw tightening at multiple points, which may increase the beam spot diameter and deteriorate the image quality. The present invention has been made based on this background, and provides a laser that can suppress image quality deterioration due to external vibrations even if the rigidity of the housing in which optical elements are integrally incorporated is relatively small. An object of the present invention is to provide a beam scanning device.

0004

[Means for Solving the Problems] The above object is to provide a support device for a laser beam scanning device that modulates a laser beam light source in accordance with an image signal to expose and scan a recording medium, in a plane perpendicular to the laser beam irradiation optical axis. This is achieved by using an axis parallel to the scanning line on the recording medium scanned by the laser beam as the support axis.

[0005]

[Operation] When the laser beam scanning device is misaligned due to external vibrations, etc., it supports the axis that is in a plane perpendicular to the laser beam irradiation optical axis and parallel to the scanning line on the recording medium scanned by the laser beam. Rotates as an axis.

[0006]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. FIG. 3 is an exploded perspective view of a laser beam scanning device according to one embodiment. The laser light source unit 1 holds a semiconductor laser and a collimating lens in a predetermined positional relationship, and generates a parallel beam when supplied with power and an image signal. The cylinder lens 2 forms a linear image of the light beam in the sub-scanning direction on the deflection surface. The deflector 3 is made of a rotating polygon mirror and deflects the beam in the main scanning direction at a constant angular velocity. The imaging lens 4 forms an image of the incident beam on a predetermined scanning line with a predetermined spot diameter. To achieve this, the lens has an fθ characteristic that converts constant angular velocity scanning into constant velocity scanning in the main scanning direction, and a surface tilt correction function that sets the deflection plane and the imaging plane in a conjugate relationship in the sub-scanning direction. There is. This causes scanning line blur (pitch unevenness) due to manufacturing errors in the rotating polygon mirror.
is sufficiently corrected for practical use, and the scanning line does not substantially deviate in the sub-scanning direction. The mirror 5 is provided to fold the optical path of the beam and configure the device according to the practical size and arrangement of the device, and is used in many devices, although it is not essential. The housing 6 is provided primarily for the purpose of holding these optical elements in a predetermined positional relationship and positional accuracy.
By attaching the cover 7 and the dustproof glass 8, a sealed state is obtained, and exposure to dust and laser can be avoided. The position of the scanning line is determined by the arrangement of the mirror 5, and in this embodiment, the mirror 5 is arranged so that the axis c and the scanning line are parallel to each other as shown in the figure. The housing 6 is designed to have sufficient rigidity for the above purpose. Each optical element built into the housing 6 is fixed to a mounting reference, and their relative positional relationship is maintained during manufacturing. However, since vibrations occur due to various causes when the device is in operation, it is quite difficult to maintain the relative positional relationship. Increasing the rigidity of all structural members has its limits as an office machine, such as weight, so a certain degree of flexural vibration must be tolerated.

FIG. 1 is a perspective view showing a state in which the laser beam scanning device is attached to an image forming apparatus, and FIG. 2 is a longitudinal sectional view taken along a cutting line XX passing through the axis c in the same state in which the laser beam scanning device is attached. Positioning through holes 11a and 11b are formed in the front side plate 9 and rear side plate 10 of the image forming apparatus main body, and a stepped screw 12 having a stepped portion serving as a positioning pin is inserted therethrough to connect the housing 6. Since the housing 6 is formed with a positioning guide hole 13 that is screwed into the stepped screw 12 with high accuracy, the housing 6 is connected to the main body side plates (front side plate 9, rear side plate 1).
0) with high accuracy. Also, since the stepped screw 12 is provided with a spring washer 18,
Fixed by a constant pressing load. The photoreceptor 14 is attached to a support member 15 in the same manner as in a conventional copying machine, and is positioned with a predetermined accuracy by the support member 15 and the main body side plate. Since the rotation axis a of the photoreceptor 14 and the scanning line b must be parallel, the axis c connecting the centers of the front and rear through holes 11a and 11b provided in the front side plate 9 and the rear side plate 10, respectively.
is provided parallel to the rotation axis a of the photoreceptor 14. When the laser beam scanning device is pivotally attached to the main body using the stepped screw 12, the housing 6 is rotatable around the axis c, so the lower surface of the housing 6 is placed on the frame 16 passed between the side plates 9 and 10. It is fixed via an elastic member 17 such as rubber. Therefore, even if the housing 6 vibrates due to external vibrations, as long as the elasticity value of the elastic member 17 is greater than or equal to a predetermined value, the housing 6 can be regarded as a rigid body in terms of the vibration mode. That is, the flexural vibration within the housing 6 can be ignored compared to the rotational displacement vibration about the axis c. Therefore, it is sufficient to suppress the deviation of the scanning line in the sub-scanning direction caused by rotational fluctuations between the housing 6 and the main body about the axis c.

FIG. 4 shows the irradiation optical axis of the laser beam and the photoreceptor 1.
4. FIG. 5 is a diagram showing the positional relationship between the laser beam irradiation point and the tangent on the circumferential surface of the photoreceptor 14 when the laser beam scanning device has misaligned. FIG. 6 is the scanning line b FIG. 3 is a diagram showing a state in which the laser beam scanning device is misaligned when the axis c and the axis c coincide with each other. Hereinafter, a description will be given of fluctuations in the irradiation position of the laser beam on the circumferential surface of the photoreceptor 14 when the housing 6 rotates about the axis c as a fulcrum. A straight line connecting the reflection point R of the laser beam on the mirror 5 and the focal point Q0 on the scanning line b (laser beam irradiation optical axis)
A straight line perpendicular to RQ0 and the scanning line b0 (a tangent to the laser beam irradiation optical axis RQ0 on the circumferential surface of the photoreceptor 14) S0 intersects the axis c at point P, and the arrangement of the through holes 11a, 11b and the support member 15, mirror Set the inclination angle in step 5. As shown in FIG. 5, when the housing 6 rotates by an angle Δθ around the axis c (fulcrum P in FIGS. 4 to 6) due to external vibration, etc., a point that pinches the focal point Q0 on the laser beam irradiation optical axis RQ0 A0, B0 and focus Q0 move to A1, B1 and Q1, respectively. Assuming that the position of the photoreceptor 14 is fixed, the irradiation position of the laser beam on the circumferential surface of the photoreceptor 14 due to rotation of the housing 6 moves from the focal point Q0 to the point C1, and if the angle Δθ is sufficiently small, the irradiation point C1 is moved. A line that passes through and is perpendicular to the paper surface becomes a new scanning line b1. Therefore, when the distance Q0 C1 becomes large, problems such as striped patterns appearing in the image as described above occur. Therefore, if the position of the photoconductor 14 is moved to a corrected position where its circumferential surface is aligned with the straight line S1 shown in FIG. No misalignment of scanning lines occurs. However, in the former case, it is impossible to predict the correction position S1 in advance, and it is also difficult in practice to correct the positional deviation of the scanning line after it has occurred. Further, the latter method is not practical because it is subject to many restrictions on the method of attaching the laser beam scanning device. In this embodiment, the light image at the irradiation point C1 is out of focus by the distance Q1 C1;
With a normal device having a resolution of about 400 dpi, it is easy to set the depth of focus to a depth that does not cause image blur. Although a drum-shaped photoreceptor is used in this embodiment, a belt-shaped photoreceptor or any other shape of photoreceptor may be used.

[0009]

As explained above, according to the present invention, the laser beam is emitted by using the supporting axis as the axis that is in the plane perpendicular to the laser beam irradiation optical axis and parallel to the scanning line on the recording medium scanned by the laser beam. Since it is supported on the beam scanning device, even if the laser beam scanning device is misaligned due to external vibrations, the deviation of the scanning line can be sufficiently minimized, and even if the housing is of low rigidity, it can be protected against mechanical disturbances such as external vibrations. image quality deterioration can be minimized.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view of main parts of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of the same.

FIG. 3 is an exploded perspective view of the laser beam scanning device.

FIG. 4 is an explanatory diagram showing the positional relationship between the irradiation optical axis of a laser beam and a photoreceptor.

FIG. 5 is an explanatory diagram showing the positional relationship between a laser beam irradiation point and a tangent on the circumferential surface of a photoreceptor when a positional shift occurs in the laser beam scanning device.

FIG. 6 is an explanatory diagram showing a state in which the laser beam scanning device is misaligned when the scanning line and the axis line are aligned.

[Explanation of symbols]

1 Laser light source unit 2 Cylinder lens 3 Deflector 4 Imaging lens 6 Housing 9 Front plate 10 Rear side plate 11a, 11b Through hole 13 Positioning guide hole 14 Photoreceptor

Claims (1)

[Claims] Claim 1: A support device for a laser beam scanning device that exposes and scans a recording medium by modulating a laser beam light source in accordance with an image signal, the device being located within a plane perpendicular to the laser beam irradiation optical axis and scanned by the laser beam. A support device for a laser beam scanning device, characterized in that the support axis is an axis parallel to a scanning line on a recording medium.