JPH02293811A - Optical deflector - Google Patents

Abstract

PURPOSE:To prevent the degradation in the accuracy of the reflecting surfaces of a rotary polygon mirror by thermal expansion while adopting the constitution to fix the polygon mirror to the seat of a revolving shaft by using screws by screwing the polygon mirror to the thread parts formed to an annular member and the seat of the revolving shaft by passing screws to the polygon mirror. CONSTITUTION:The polygon mirror 1 is fitted to the revolving shaft 2 and after a balance ring 3 is fitted thereon 4, pieces of the external threads 4 are passed into small holes 14 and mounting holes 12 from above the balance ring 3 and are finally screwed in internal threads 13 provided on the seat 2a of the revolving shaft 2. Consequently, the polygon mirror 1 is held between the head 4a of the make screws 4 and the seat 2a of the revolving shaft 2 thus fixed to the revolving shaft 2. The generation of strains is minimized in this way even if the polygon mirror 1 is thermally expanded by a temp. rise and the fluctuation in the scanning position of a beam by the degraded accuracy of the reflecting surface 1a of the polygon mirror 1 is minimized.

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 (LBPs) that record a desired image by scanning a laser beam and forming a static latent image on a photoreceptor by flickering the laser beam, and film-like photoreceptors have been developed. A device that records an image using silver halide photography by scanning a blinking laser beam on the surface of the laser beam, similar to the LBP, is widely used. An example configuration is shown in Figure 5. In the figure, a laser driver 10l that receives an image signal blinks a solid-state laser element 102 at a predetermined timing, and the laser beam emitted from this solid-state laser element 102 is transmitted to a collimator lens system 103.
The light is converted into parallel light by , and is incident on a polygonal surface 1m104 that rotates in the eight directions of the arrows. And this polygon mirror 1 04
The laser beam reflected by the f/theta lens group 105 forms a spot image on the surface to be scanned (the surface of the photoreceptor drum) 106. In such a configuration, the polygon m 1 0 4 is typically
It is composed of a metal whose main material is aluminum (AI2), and the reflective surface is coated with gold to prevent oxidation. A vapor deposited film is formed, which satisfies 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. In addition, the polygon mirror has multiple screw insertion holes (about 2 to 6) at equal angular intervals, and the male screws are passed through these holes and inserted into the multiple female screw holes provided on the seat of the rotating shaft. A polygon mirror is supported between the screw head of the male screw and the above seat so that the positional relationship between the rotation axis and the polygon mirror does not shift due to acceleration and deceleration of rotation. 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 for fixing 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. ing. Therefore, when the polygon mirror thermally expands 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. The disadvantage is that the degree of expansion differs, causing distortion, and the precision of the highly-finished reflective surface is significantly degraded. In this way, when distortion occurs in a polygon mirror due to thermal expansion, the scanning position of the beam shifts for each reflective surface of the polygon mirror even if the rotation is perfectly balanced, and the quality of the image obtained is significantly reduced. I will do it. In particular, in equipment that requires high-speed rotation, energy loss such as high-frequency iron loss and wind loss increases in the motor section that generates the rotational driving force, and the amount of heat generated in the motor section becomes extremely large. A major problem is the degradation of image quality due to distortion due to thermal expansion of the polygon mirror. Therefore, in view of the above-mentioned problems, the object of the present invention is to fix a multi-sided bracket to a rotating shaft seat using a screw. It is an object of the present invention to provide an optical deflection device having a structure that prevents the accuracy of the reflecting surface of a polygon mirror from deteriorating due to thermal expansion.

[1,000 Steps to Solve the Problems] In the present invention to achieve the above object, a rotating polygon mirror for scanning a light beam from a light source onto an irradiated object such as a photoreceptor is mounted on a rotating shaft. It is held by a tab-shaped member such as a disk, and is fixed to the rotating shaft by passing a screw through the annular member and the polygon mirror and screwing it into the female thread formed in the seat of the rotating shaft. The annular member may be a disk having approximately the same outer diameter as the seat of the rotating shaft, or the thickness of the seat may be approximately the same as the thickness of the annular member. Further, it is preferable that the elastic modulus of the material of the seat of the rotating shaft and the material of the annular member is larger than the elastic modulus of the material of the polygon mirror. [Function] In the configuration of the above basic invention, the polygon mirror can be supported with a relatively uniform pressure distribution by the annular member and the seat of the rotating shaft, so even if the polygon mirror thermally expands due to temperature rise, distortion will not occur. The occurrence of this phenomenon is minimized, and variations in the beam scanning position due to a decrease in the precision of the reflecting surface of the polygon mirror are suppressed as much as possible [Embodiment 1 Figure 1 shows an embodiment of the present invention. In the same figure, ■ is 8
A polygon mirror made of aluminum (Aβ) alloy having a reflective surface 1a, 2 a rotation axis for fixing the polygon 1 on the seat 2a and rotating it, 3 a rotation axis when the polygon Pal and the rotation axis 2 are fixed. It is a balance ring for attaching the balance way 1 for rotational balancing, and has approximately the same outer diameter as the seat 2a,
4 is a male screw. The rotating shaft 2 and balance ring 3 are made of mild steel, and have chemical nickel plating applied to their surfaces. A hole 1l for fitting the rotating shaft 2 is formed in the center of the polygonal boundary 1, and has the function of aligning the rotational centers of the rotating shaft 2 and the polygonal mirror 1. On the outside of the hole 11, four mounting holes l2 are formed at equal angular intervals on a substantially circle centered on the center of the multifaceted fat. ) is maintained. The seat 2a of the rotating shaft 2 for receiving the polygonal mirror l has a highly accurate flat surface, and four internal threads l3 are cut at equal angular intervals at positions with the same diameter as the small holes l2 formed in the polygonal fal. There is. The balance ring 3 is finished to have an outer diameter that is approximately the same as the outer diameter of the seat 2a provided on the rotating shaft 2, and has four small holes l4 at equal angular intervals at the same diameter positions as the female threads l3 cut on the rotating shaft 2. At the same time, a hole 1 with the same diameter as the hole 11 of the polygon mirror 1 is provided in the center.
5 is open. Furthermore, a circular groove 1 is provided for attaching the balance weight while maintaining coaxiality with the center hole l5.
The assembly of the above-mentioned components provided with 6 is carried out as follows. First, the polygon mirror 1 is fitted onto the rotating shaft 2, and then the balance ring 3 is fitted onto it, and then the four male screws 4 are inserted from the top of the balance ring 3 into the small hole l4 and the mounting hole 12.
and finally a female screw l3 provided on the seat 2a of the rotating shaft 2.
Screw it together. As a result, the polygon mirror 1 is supported by 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. In the above configuration, the multifaceted fil is securely fixed between the male screw 40 heads 4a and the seat 2a of the rotating shaft 2 so that the positional relationship between the rotating shaft 2 and the multifaceted boundary 1 does not shift due to acceleration and deceleration of rotation. There is. Next, we will change the material of the balance ring 3 from the above example to the multifaceted F.
Figures 2 and 3 show the pressure distribution between the polygon mirrors and the comparison with an example made of Aff alloy, which is the same material as D1. In Figures 2 and 3, the tightening torque for screw 4 is 12
kg" cm, the wall thickness of the balance ring 3 was set to 5 mm, and the wall thickness of the polygon L was set to 7 mm.
(made of mild steel) shows the pressure distribution between the balance ring 3 and the polygon mirror 1, and FIG. 2(b) shows the pressure distribution between the polygon mirror l and the seat 2a. ) shows the balance ring made of 82 alloy and the opening of the polygon mirror, and (b) shows the pressure distribution between the polygon mirror and the seat. This pressure distribution was determined using a pressure-sensitive film that uses microcapsules. This indicates that the pressure is low. In FIG. 2(a), the balance ring 3 is made of a material with a high elastic modulus, that is, it is difficult to deform under stress, so it hardly deforms even when pressure is applied by the screw 4. It can be seen that the entire balance ring 3 applies pressure uniformly to the polygon mirror 1. In Figure 2(b),
It can be seen that the pressure is evenly distributed on the surface of seat 2a. On the other hand, in the example shown in Fig. 3, the balance ring is made of the same material as polygon mirror 1 and has an elastic modulus of approximately 7000 kg/m11.
Since it is made of 1" AR alloy, the balance ring is distorted by the pressure from the M3 screw 4, and the pressure received from the screw head 4a is not divided to the left within the balance ring with a wall thickness of 5 mm, and is multifaceted. Therefore, a distributed pressure is applied from the balance ring to the multiface Ml, as shown in Fig. 3(a), which is stronger at the screw head 4a and weaker there. The pressure (Fig. 3 (a)) is transmitted to the surface of the seat 2a while being divided within the multifaceted ml (Fig. 3 (b)). In Fig. 3, the elastic modulus of the material of the balance ring 3 is If the elastic modulus is lower than the elastic modulus of the material of the multifaceted ml, the balance ring will become more easily distorted, and the unevenness of pressure will become even more pronounced.Furthermore, for comparison, the multifaceted ml will be directly attached to the head of the screw without using a balance ring. Figure 4 shows a conventional example in which the
Figure 4(a) shows the pressure distribution between the screw head and the polygon opening.
bl represents the pressure distribution between the polygon mirror and the seat. It can be seen that the pressure distribution is significantly uneven compared to Figures 2 and 3. In Fig. 4(a), high pressure is applied only where the polygon mirror and the screw head are in contact, and as shown in Fig. 4(b).
Even through the polygon mirror, the uneven pressure distribution is transmitted to the seat without being corrected. Next, we will show the results of measurements using interference fringes to determine how the flatness of the reflecting surface 1a changes when the polygon mirror 1 is raised 30 degrees from room temperature. In the polygon mirror fixing method shown in FIG. 2 of the above embodiment, even when the temperature was raised by 30 degrees, the flatness was only about 1.4 times worse than at room temperature, whereas in the example shown in FIG. 5@, in the conventional example shown in Figure 4, distortion occurred to approximately 3.1 times. By the way, in order to obtain the same pressure distribution as shown in Fig. 2 using A2 alloy, which is the same material as the polygon L, the thickness of the balance ring had to be increased to about 13 mm, but the thickness of the balance ring had to be increased to about 12 kg. - When tightening the screw with a torque of cm, the pressure broke internally within the balance ring, and the pressure against the multifaceted AT did not increase as much as the mild steel balance ring 3. In the above embodiment, it is preferable in terms of strength that the thickness of the seat 2a provided on the rotating shaft 2 and the thickness of the balance ring 3 are approximately the same. In addition, the elastic modulus of the seat 2a and the balance ring 3 must be at least the same as the elastic modulus of the polygon mirror l, but it is better to make the elastic modulus of the seat 2a and the balance ring 3 twice or more.
The wall thickness can be made thinner, making it possible to make the device more compact. As an example, let's take multifaceted armor l as An (elastic modulus = 6500 kg/m
If the balance ring 3 and seat 2a are made of stainless steel (SUS) (modulus of elasticity = 2 1 000 kg/mm)
) or iron (elastic modulus = 21 000 kg/mm"). [Effect 1 of the invention As explained above, according to the present invention, it is possible to press the polygon mirror with relatively uniform pressure. This makes it possible to minimize deterioration in the accuracy of the reflective surface of the polygon mirror even if the temperature rises due to motor heat generation during operation, etc. Therefore, variations in the beam scanning position are minimized, making it possible to produce high-quality output images, etc. It becomes possible to obtain.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining an embodiment of the present invention, Fig. 2 is a diagram showing the pressure distribution on the front and back surfaces of the polygon mirror in the polygon mirror fixing method according to this embodiment, and Fig. 3 is a diagram for explaining a similar method according to another example. FIG. 4 is a diagram showing the pressure distribution on the front and back surfaces of a polygon mirror, FIG. 4 is a diagram showing the pressure distribution on the front and back surfaces of a similar polygon mirror according to a conventional example, and FIG. 5 is a diagram illustrating a conventional optical deflection device. l...Multi-sided m. ta... Reflective surface, 2...
··Axis of rotation. 2a...Seat, 3...Balance ring, 4...Male thread, 4a...Screw head,
l2...Mounting hole. 13.--Female thread, l4.
...Small hole, 16...Groove

Claims (1)

[Claims] 1. In an optical deflection device using a rotating polygon mirror for scanning a light beam from a light source onto an irradiated object, the polygon mirror is held between a seat provided on a rotating shaft and an annular member, and An optical deflection device characterized in that a polygon mirror is fixed to a rotating shaft by passing a screw through the annular member and the polygon mirror and screwing it into a female screw portion formed in a seat of the rotating shaft. 2. The optical deflection device according to claim 1, wherein the annular member is a disc having substantially the same outer diameter as the seat. 3. The optical deflection device according to claim 1, wherein the elastic modulus of the material constituting the seat of the rotating shaft and the annular member is greater than the elastic modulus of the material of the polygon mirror. 4. The optical deflection device according to claim 3, wherein the elastic modulus of the material constituting the seat of the rotating shaft and the annular member is at least twice the elastic modulus of the material of the polygon mirror. 5. The optical deflection device according to claim 1, wherein the thickness of the seat provided on the rotating shaft and the thickness of the annular member are substantially the same. 6. The optical deflection device according to claim 1, wherein the polygon mirror is made of aluminum alloy, and the rotating shaft and the annular member are made of mild steel.