JPH02293810A - Optical deflector and rotary polygon mirror used therein - Google Patents

Abstract

PURPOSE:To prevent the degradation in the accuracy of the reflecting surfaces of the polygon mirror by thermal expansion while adopting the constitution to fix the polygon mirror by using screws to the seat of a revolving shaft by providing mounting holes in which external threads pass and spaces which are not used as the mounting holes on approximately the concentrical region of the rotary polygon mirror. CONSTITUTION:For example, 8 pieces of small holes 12 are formed at equal angular intervals on the approximate circle around the center of the polygon mirror 1 on the outer side of a hole 11. These holes maintain the coaxiality with the hole 11. Of 8 pieces of the small holes 12, the four small holes 12a existing at every other point are used as the mounting holes with internal threads cut in which the screws 4 pass. The spaces not used as the mounting holes are provided together with the mounting holes 12a on the polygon mirror 1. The form of suppressing the strains occurring in the difference in the degree of thermal expansion and to relieve stresses is, therefore, attained, even when the polygon mirror 1 expands thermally. The accuracy of the reflecting surfaces of the polygon mirror 1 is maintained as constant as possible and the fluctuation in the scanning position of a beam is suppressed as far as possible.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a light deflection device for scanning a light beam from a light source onto a wave irradiation body, and more particularly to a light deflection device using a rotating polygon mirror. [Prior Art] In recent years, laser beam printers (LBP), which record a desired image by forming a static IM latent image on a photoconductor by flickering a laser beam, and film-like printers have been developed. This is a configuration of a conventional optical deflection device, that is, a laser scanner device, which has been widely used to record an image by scanning a flickering laser beam on a photoreceptor, similar to LBP, using silver halide photography. Example is the third
It is shown in the figure. In the figure, a laser driver 101 that receives an image signal blinks a solid-state laser element 102 at a predetermined timing.
The laser beam emitted from the collimator lens system 1
It is converted into parallel light by 03 and enters the multifaceted surface [9104] which rotates in the eight directions of arrows. And this multifaceted m l
The laser beam reflected by O4 passes through f/θ lens group 1.
05, a spot image is formed on the scanned surface (the surface of the photoreceptor drum) 106. In such a configuration, the polyhedral m l O 4 is typically
It is made of aluminum (82) as the main raw material, and a metal vapor deposition film is formed on the reflective surface to prevent oxidation, thereby satisfying various properties such as strength, workability, and weight. Furthermore, in such laser scanner devices, highly accurate balance adjustment is required for the polygon mirror and the rotation axis to prevent the reflecting surface from swinging when the polygon mirror rotates, causing the beam scanning position to change for each reflecting surface. It has been subjected. For this purpose, multiple screw insertion holes (approximately 2 to 6) are provided at equal angular intervals on the polygon mirror, and the male screws are passed through these holes and screwed into the multiple female screw holes provided on the seat of the rotating shaft. As a result, the polygon mirror is held between the screw head of the male screw and the seat so that the positional relationship between the rotating shaft and the polygon mirror does not shift due to rotational acceleration or deceleration. This fixing method using screws has excellent strength and has the advantage of not causing misalignment between the rotating shaft seat and the rotating mirror even when using a large polygon mirror or rotating the polygon mirror at high speeds such as 2000 rpm. are doing.

[Problem to be solved by the invention]

However, the pressure required to fix the polygon mirror to the seat of the rotating shaft is applied to the polygon mirror centering on the heads of the male screws, which are distributed at equal angular intervals and tightened. Therefore, when the polygon mirror expands #I due to the temperature rise caused by the operation of the device, the part of the polygon mirror that is pressurized by the screw head and the part of the polygon mirror between the screw heads where no pressure is applied to the left. However, the disadvantage is that the difference in the degree of expansion causes distortion, which significantly deteriorates the accuracy of the highly precisely finished reflective surface. As described above, when distortion occurs in a polygon mirror due to thermal expansion, even if the rotation is perfectly balanced, the scanning position of the beam shifts for each reflective surface of the polygon mirror, and the quality of the image obtained is significantly reduced. I will do it. In order to correct the uneven pressure caused by screw fastening mentioned above, it is possible to insert a spacer between the screw head and the polygon mirror to relieve the pressure from the screw head, but if the spacer's wall thickness is about the same as that of the polygon mirror, Without it, it is not possible to obtain uniform pressure. Therefore, the thickness of the spacer increases the size of the device and increases the rotational moment of the polygon mirror, which increases the power consumed to rotate the polygon mirror and eventually causes heat generation in the motor section. Furthermore, the center of gravity of the rotation axis that supports the polygon mirror becomes high, making the rotational balance unstable and hindering the high-speed rotation of the polygon mirror. Therefore, in view of the above-mentioned problems, it is an object of the present invention to provide an optical deflection device which uses a screw to fix a polygon mirror to a seat on a rotating shaft, while preventing deterioration of the precision of the reflective surface of the polygon chain due to thermal expansion. and to provide a rotating polygon mirror used therein. [Means for Solving the Problems] In order to achieve the above object, the present invention includes a rotating polygon mirror held by a seat provided on a rotating shaft and a plurality of male screws.
A mounting hole through which the male screw passes and a space that is not used as a mounting hole are provided on a substantially concentric area centered on the center of the polygon mirror. The above-mentioned space is typically a hole with the same diameter as the mounting hole or a different diameter, and the mounting hole and the above-mentioned space are provided at equal angular intervals, the same number are provided, or they are provided alternately. Further, the mounting hole and the space may be provided on the same diameter, or may be provided on substantially concentric areas but on different diameters. [Operation J] In the present invention having the above configuration, the polygon mirror is provided with a space that is not used as a mounting hole along with a mounting hole.
Even when the polygon mirror thermally expands, it suppresses the distortion caused by the difference in the degree of thermal expansion and relieves stress, and the accuracy of the polygon mirror's reflection surface is kept as constant as possible, reducing variations in the beam scanning position. It can be suppressed as much as possible. [Example] Fig. 1 shows a first example of Honmen Akira. In the same figure,
1 is a polygon mirror with 8 reflecting surfaces 1a, 2 is a rotation axis for fixing the polygon ML on the seat 2a and rotating it, and 3 is a rotation balance when the polygon 1 and the rotation axis 2 are fixed. Balance ring for attaching the balance weight for
4 is four male screws. A hole l1 is formed in the center of the polygon mirror 1 to fit the rotating shaft 2, and has the function of aligning the center of rotation of the rotating shaft 2 and the polygon mirror l. Outside the hole l1, eight small holes l2 are formed at equal angular intervals on a substantially circle centered on the center of the polygon jQ l, and these are coaxial with the hole l1 (the central axis of the hole is parallel to ). % of 8 small holes 12
The four small holes 12a located every other place are used as mounting holes with internal threads through which the screws 4 pass. The seat 2a of the rotating shaft 2 for receiving the polygon mirror 1 has a highly accurate flat surface, and female threads l3 are cut in four places at equal angular intervals at positions with the same diameter as the small holes 12 formed in the polygon mirror l. ing. Balance ring 3. The outer diameter is approximately the same as the outer diameter of the seat 2a provided on the rotating shaft 2, and four small holes 14 are bored at equal angular intervals at the same diameter positions as the female threads 13 cut on the rotating shaft 2. , in the center there is a hole l with the same diameter as the hole 11 of the polygon mirror l.
5 is open. Furthermore, keeping the coaxiality with the center hole 15, a circular full 1 hole is made for attaching the Joki balance weight.
The assembly of the above-mentioned components provided with 6 is carried out as follows. First, the multifaceted ill is fitted onto the rotating shaft 2,
Next, after fitting the balance ring 3 onto it, insert the four male screws 4 from the top of the balance ring 3 into the small hole l4 and the mounting hole 1.
2a and finally screwed into the female thread l3 provided on the seat 2a of the rotating shaft 2. As a result, the multifaceted flexure 1 is clamped between the head 4a of the male screw 4 and the seat 2a of the rotating shaft 2, and is fixed to the rotating shaft 2. The balance ring 3 has the function of somewhat relieving the pressure from the male screw 4 applied to the polygon mirror l. In the above configuration, the polygon mirror l is securely fixed between the head 4a of the male screw 4 and the seat 2a of the rotating shaft 2 so that the positional relationship between the rotating shaft 2 and the polygon at does not shift due to acceleration and deceleration of rotation. ing. Furthermore, in the above multiface [1], between the mounting holes 12a,
Since the hole 12 which is not used as a mounting hole is formed, when the multifaceted ML thermally expands, the pressure is not applied as much as the part pressurized by the screw head, and the degree of expansion is large and the effect of strain is the largest. This means that the receiving part has been removed. Therefore, deterioration in the accuracy of the highly precisely finished reflective surface 1a is suppressed, and variations in the scanning position of the beam are suppressed as much as possible. In the above embodiment, the mounting screw hole and the non-mounting hole are formed on the same diameter of the multifaceted fal with the same diameter dimensions, but the method of opening the non-mounting hole or space is optimal for each deflection device. It can take any form. In other words, the degree and amount of distortion of the polygonal boundary due to thermal expansion varies depending on the material and thickness of the polygon mirror, the position of the mounting screw hole, the size of the screw, the screw tightening torque, etc., so consider these factors. The accuracy of the polygonal mirror reflection surface should be kept as constant as possible. Other examples of how to make holes are shown in Figures 2(a) and (b). In the second embodiment shown in FIG. 2(a), holes 22 of different diameters are formed at equal angular intervals on the same diameter as the mounting screw hole 22a for fixing the polygon mirror l. In the third embodiment shown in FIG. 2(b), holes 32 having the same diameter as the mounting screw hole 32a for fixing the polygon mirror 1 are formed at equiangular intervals on a diameter different from the screw hole 32a. It has been done. [Effects of the Invention] As explained above, according to the present invention, the part that is most affected by distortion when the polygon mirror is thermally expanded is removed, so that the construction of the optical deflection device is improved. Even if the jJ temperature changes, variations in the beam scanning position are minimized, making it possible to obtain high-quality output images.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the first embodiment of the present invention, and FIGS. 2(a) and (b) are diagrams showing polygon mirrors of the second and third embodiments, respectively. The figure shows a conventional optical deflection device. l...Rotating polygon tQ. 2...Rotating shaft, 2a...Rotating shaft seat, 3...Balance ring, 4...Male thread, 4a - - - -
*Screw head. 12a. 22a, 32a...Mounting hole,
l2, 22, 32...Hole that is not a mounting hole, l3...
...Female thread of rotating shaft, l4...Balance ring hole

Claims (1)

[Claims] 1. In an optical deflection device that uses a rotating polygon mirror to scan a light beam from a light source onto an irradiated object, the rotating polygon mirror is held between a seat provided on a rotating shaft and a plurality of male screws, An optical deflection device characterized in that a mounting hole through which the male screw passes and a space not used as a mounting hole are provided on a substantially concentric circle region centered on the center of the polygon mirror. 2. The light deflection device according to claim 1, wherein the mounting hole and a space not used as the mounting hole are provided at equal angular intervals. 3. The light deflection device according to claim 1, wherein the space not used as the mounting hole is a hole. 4. The light deflection device according to claim 1, wherein the same number of the mounting holes and spaces not used as the mounting holes are provided. 5. The light deflection device according to claim 1, wherein the mounting holes and spaces not used as the mounting holes are provided alternately. 6. The optical deflection device according to claim 3, wherein the mounting hole and the hole not used as the mounting hole have substantially the same diameter. 7. The optical deflection device according to claim 3, wherein the mounting hole and the hole not used as the mounting hole have different diameters. 8. In a rotating polygon mirror having a plurality of reflective surfaces, a mounting hole for a male screw to pass through and a space that is not used as a mounting hole are provided on a substantially concentric area centered on the center of the polygon mirror. Features a rotating polygon mirror.