JPS62205310A - Polygon mirror - Google Patents

Abstract

PURPOSE:To reduce the windage torque of a mirror by cutting boundary corner parts between mirror surfaces of a polygon mirror and adjacent mirror surfaces without extending to effective reflecting surfaces of the mirror surfaces. CONSTITUTION:The boundary corner parts 9 between the respective mirror surfaces 8a of the polygon mirror 1 composed of a octagonal mirror are cut arcuately to a radius R from the center O of the rotating mirror 5 of the mirror 1. Then, this cutting range is so determined without affecting the effective reflecting surfaces of the respective mirror surfaces 8a, i.e. impeding the reflection of laser light. Consequently, the wind loss torque is reducible without decreasing the size and thickness of the mirror 1 and made less and less as the rotation of the mirror 1 is faster and faster.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a polygon mirror in an image forming apparatus such as a laser printer or a facsimile machine.

(Prior Art) Conventionally, a polygon mirror 1 used in a laser printer etc. has each mirror surface 2 of the polygon mirror as shown in FIGS. 5 and 6.
The boundary corners 3 between the edges a are formed in a sharply protruding shape. This polygon mirror 1 rotates with its central portion supported and fixed on a rotating shaft of a polygon mirror scanner (not shown), but during this rotation, a loss of rotational force occurs due to air resistance.

It is desirable to reduce the rotational force lost due to this air resistance (hereinafter referred to as windage torque) as much as possible. In the experimental formula, this windage torque is T L = CMρR04・tω2−−−−−−−−
(1) Here CM = 4.07/N"' (2≦N
≦16) R' = cos (360/2N) ω =-''-・2π A: Distance from the rotation axis to the mirror surface t: Mirror thickness N: Number of polygon surfaces n: Motor rotation speed ρ: Air density (1,205X10-'[:gts”/
cm']).

In order to reduce this windage torque, it is conceivable to reduce the dimension A and/or the thickness t in the above equation (1). However, with laser printers, as the angle of view becomes wider,
It is difficult to reduce the A dimension, and it is also not preferable to make the thickness t extremely thin in order to provide rigidity for maintaining the shape accuracy of the mirror.

(Purpose) The present invention solves the problems of conventional polygon mirrors by drawing a perpendicular line from the mirror's rotation axis ○ to the mirror surface, and calculating the distance from the intersection of this perpendicular line and the mirror surface to the axis center. It is an object of the present invention to provide a polygon mirror in which windage torque is reduced without reducing A and thickness t.

(composition) The present invention will be explained below based on illustrated embodiments.

In this embodiment, the present invention will be explained using an eight-sided mirror among polygon mirrors as an example.

In FIG. 1, a boundary corner 9 between mirror surfaces 8a of a polygon mirror 1 consisting of an eight-sided mirror is cut into an arc shape with a radius R from the center O of the rotation axis 5 of the polygon mirror 1. This cutting range is a range that does not interfere with the effective reflection surface of each mirror surface 8a, that is, a range that does not interfere with the reflection of laser light among the mirror surfaces. For example, A = 6 cm,
In the case of a polygon mirror set at t = 0.6 cm, cutting with a radius of 6.4 cm will not cut off the effective reflective surface of the mirror surface.

This process of cutting the boundary corners is performed before finishing the mirror surface.

The inventors conducted an experiment to compare the windage torque between the conventional polygon mirror shown in FIG. 5 and the polygon mirror in the above embodiment. The results of this experiment are shown in FIG.

In FIG. 7, the vertical axis represents the load torque, and the horizontal axis represents the rotation speed of the polygon mirror. Curve C represents the change in load torque with respect to the rotation speed of the polygon mirror of the present invention, and curve B represents the conventional polygon mirror. - shows the change in load 1 herk with respect to the rotational speed. This result shows that the higher the rotation speed of the polygon mirror of the present invention, the more the windage torque is reduced.

Next, other embodiments of the present invention will be described.

In FIG. 3, the upper and lower edges 6 of the outer diameter portion of the polygon mirror 11 are chamfered and have a streamlined shape when viewed from the front. The boundary corners 10 between the respective mirror surfaces 7a of the polygon mirror 11 are cut into an arc shape with a radius R around the rotating shaft 5. In this case, it goes without saying that the cutting range is the range excluding the effective reflective surface of the mirror surface.

Since the polygon mirror 11 has the upper and lower edges of its outer diameter portion chamfered, and the boundary corners between the mirror surfaces are cut, windage torque can be further reduced.

In the above two embodiments, an example is shown in which the boundary corner is cut in an arc shape with a radius R from the center of the rotation axis. The removed area may be cut out flatly. Furthermore, although the above two embodiments are 8-sided polygon mirrors, the present invention is not limited to 8-sided polygon mirrors as long as they are usable polygon mirrors.

(Effects of the Invention) The present invention cuts the boundary corner between a mirror surface of a polygon mirror and an adjacent mirror surface to an extent that does not reach the effective reflection surface of the mirror surface, so the size of the polygon mirror can be increased. Windage torque can be reduced without reducing the thickness and thickness.

[Brief explanation of drawings]

FIG. 1 is a plan view of a polygon mirror showing one embodiment of the present invention, FIG. 2 is a front view of the same as above, FIG. 3 is a plan view of a polygon mirror showing another embodiment of the present invention, and FIG. FIG. 5 is a front view of the conventional polygon mirror, FIG. 6 is a front view of the same as above, and FIG. 7 shows the results of investigating windage torque between the conventional polygon mirror and the polygon mirror of the present invention. It is a graph diagram. 1.11... Polygon mirror, 7a, 8a... Mirror surface, 9°10... Boundary corner. Figure 1 Figure from the lead map side Figure 7 Figure 05000 10000 (34H song%G diagram

Claims (1)

[Claims] A polygon mirror in which the boundary corner between a mirror surface and an adjacent mirror surface is cut to an extent that does not extend to the effective reflection surface of the mirror surface.