JPH05184099A - Polygon scanner motor equipped with bearing unit - Google Patents

Abstract

PURPOSE:To suppress vibration and noise by reducing the beating due to micro difference of natural vibration between two radial ball bearings having identical type, width, and inner/outer diameters. CONSTITUTION:A rotor 3 is disposed, through an air gap, on the outside of a stator 2 secured to a bracket 1 on the opposite side to a load and the rotor 3 is secured to a rotary shaft 5 being born on the bracket 1 rotatably through deep groove ball bearings 4a, 4b. The bearings 4a, 4b have identical type, width and inner/outer diameters but the numbers Nc, Nd of rollers 4c, 4d on the load side and the opposite side are 8 and 7, respectively. According to the constitution, significant difference appears between the natural vibrations of both bearings and the beating disappears.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polygon scanner motor for driving a polygon mirror used in laser beam printers, digital copying machines, facsimiles and the like.

[0002]

2. Description of the Related Art There are some conventional polygon scanner motors that use a magnetic disk drive spindle motor as a whole. For these, in addition to a normal inner rotor type motor, an outer rotor type motor is used. Is also frequently used. The outer rotor type motor is divided into a shaft rotating type and a shaft fixed type. The former is divided into one in which the rotor and the stator are located on the anti-load side of the bracket (for example, FIG. 1 of JP-A-2-223361) and one on the load side (the same, FIG. 2). The latter is one in which two bearings are located on one load side of the stator (for example, the first in Japanese Patent Application Laid-Open No. 2-311153).
FIG. 2) and one distributed to both sides of the stator (for example, FIG. 2 of JP-A-3-3645). These motors are provided with at least two radial ball bearings or angular ball bearings, and when the outer diameters are the same, the number of rolling elements is the same in terms of purchasing a commercial product and standardization.

[0003]

Since the polygon scanner motor rotates at a high speed of 15000 rpm to 20000 rpm, its problems of vibration and noise are great. They are,
(1) Wind noise of the polygon mirror, (2) race noise of rolling elements of the bearing, (3) electromagnetic noise and the like. As measures against these problems, installation of a mirror cover for (1), use of precision bearings for assembling to a motor and installation method for a motor (2)
Was solved by the relative positional accuracy between the rotor and the stator and electromagnetic techniques, but a beat noise of unknown cause remained. As a result of analyzing this, it was clarified that there was an extremely slight difference (around 1 Hz) between the natural frequencies of the two bearings, and the “beat” was based on this difference. It was found that this difference in natural frequency also depends on machining tolerances such as the inner diameter of the outer ring, which is relatively unimportant for precision bearings. When the beat is high, it reaches 35dbA at a distance of 1m, which is quite annoying in the office at midnight.

An object of the present invention is to provide a polygon scanner motor provided with a bearing device capable of reducing a beating noise due to a slight difference in natural frequency of two radial ball bearings having the same type, width and inner and outer diameters. It is in.

[0005]

A polygon scanner motor provided with a bearing device of the present invention group includes a stator supported by a bracket, a rotor arranged in the stator with a gap, and the rotor. In a polygon scanner motor comprising a plurality of radial ball bearings rotatably supported with respect to the bracket, at least two of the plurality of radial ball bearings have the same type, width and inner / outer diameter, and have the same number of rolling elements. It should be different. At this time, the radial ball bearing may be a deep groove ball bearing or an angular ball bearing.

[0006]

[Function] The type and width of the radial ball bearing used and the inner and outer diameters (basic numbers) are the same, and the design of the housing and shaft,
The natural frequency of both bearings changes significantly due to the difference in the number of rolling elements, and the "beat" does not occur, and the vibration and noise are reduced, while the advantage of ensuring the uniformity of work is maintained.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a half sectional view showing the rotation of an embodiment. The figure shows, as an example of a polygon scanner motor, a shaft-rotating outer rotor arranged on the anti-load side, and a rotor 3 is arranged outside a stator 2 fixed to the anti-load side of a bracket 1 with a gap. The rotor 3 is fixed to a rotary shaft 5 which is rotatably supported by the bracket 1 via two deep groove ball bearings 4a and 4b. A disk 7 for mounting a polygon mirror is provided on the load side of the rotary shaft 5 via a magnetic fluid seal 6.
Is fixed.

By the way, the basic numbers (type, width, inner and outer diameters) of the bearing numbers of the bearings 4a and 4b are the same, but the numbers Nc and Nd of the rolling elements 4c and 4d on the load side and the antiload side are:
8 and 7 respectively. Therefore, despite the same basic number, the natural frequencies due to the rotation of the bearings differ by 100 Hz or more, the beat is eliminated, and the noise due to the natural frequencies of both bearings becomes 25 db or less. Even if the numbers of rolling elements on the load side and the anti-load side were reversed, similar good results were obtained. The natural frequency changes depending on the number of rolling elements because the number of rolling elements is the fulcrum and the outer ring (or inner ring)
It is conceivable that the distance between the fulcrums will be shorter when the beam is considered to be a beam.

[0009]

The polygon scanner motor provided with the bearing device of the present invention has the same type and width of the radial ball bearing and the same inner and outer diameters but different number of rolling elements. It has the effect of drastically changing, eliminating the "beat" and reducing vibration and noise.

[Brief description of drawings]

FIG. 1 is a rotation-illustrated half-sectional view of an embodiment.

[Explanation of symbols] 1 bracket 2 stator 3 rotor 4a bearing 4b bearing 4c rolling element 4d rolling element 5 rotating shaft

Claims (3)

[Claims] 1. A stator supported by a bracket, a rotor disposed in the stator with a gap, and a plurality of radial ball bearings rotatably supporting the rotor with respect to the bracket. The polygon scanner motor according to claim 1, wherein at least two of the plurality of radial ball bearings have the same type, the same width and the same inner and outer diameters but different numbers of rolling elements. 2. A polygon scanner motor provided with the bearing device according to claim 1, wherein the radial ball bearing is a deep groove ball bearing. 3. A polygon scanner motor provided with the bearing device according to claim 1, wherein the radial ball bearing is an angular ball bearing.