JPS61148419A - Scanning rotary polygon mirror - Google Patents

Abstract

PURPOSE:To rotate a rotary polygon mirror accurately even in an extremely slow rotation area and to make a scan by rotating the rotating shaft on which the polygon mirror is fitted with an air jet, and braking the rotation with an eddy current from a good conductor disk and a fixed magnet. CONSTITUTION:The polygon mirror 21 is fitted on the rotating shaft 22. A rotary magnet 24 is fitted atop of the rotating shaft 22 and supported with the reaction force of the fixed magnet 25 to form a magnetic bearing. Further, a casing 28 is provided with a jet supply hole 35 to supply compressed air, which is injected from a jet injection hole 35 in the tangential direction of the rotating shaft 22 to rotate the rotating shaft 22. The compressed air is supplied to an air supply flow 32 to support the rotating shaft 22 by an air bearing. The rotating speed of the rotating shaft 22 is detected by a current controller 38 to control the rotating with the eddy current generated by the good conductor disk 29 fitted on the rotating shaft 22 and the electromagnet 30 of the casing 28. Thus, the rotating shaft is rotated with the air jet, so the rotating shaft rotates at a uniform speed to control the rotating speed with the eddy current, so that the shaft rotates with high precision even in the slow rotation range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a scanning rotating polygon mirror that scans a light beam by rotating the polygon mirror.

[Background of the invention]

The scanning rotating polygon mirror is a device that scans the laser beam in laser printers that print characters and symbols using laser light, and laser readers that read images using laser light, and is an important device that can be said to be the heart of these devices. It is.

Conventionally, many efforts have been made to increase the rotational speed of the scanning rotating polygon mirror as much as possible from the viewpoint of increasing the printing speed and reading speed. .

FIG. 1 shows a conventional scanning rotating polygon mirror for scanning at high speed. The polygon mirror 1 is attached to a rotation shaft 2 by a nut 3.A rotor 4 of an electric motor is fixed to the zero rotation shaft 2, and a one rotation magnet 5 is attached.The zero rotation magnet 5 is magnetized in the axial direction. This is one of the thrust bearings that supports the rotating shaft 2 by the repulsive force with the fixed magnet 6. Fixed magnet 6
fits into the holder 7 and is supported by a spring 8. The other end of the spring 8 is fixed to the casing 9. A stator 10 of an electric motor is fixed to the casing 9, and rotational force is applied to the rotor 4. As a result, the rotating shaft 2 is rotated. A plurality of pivots 11 protrude in the radial direction from the casing 9, and pads 12 of a hydrodynamic air bearing are attached to the tips of the pivots 11. When the rotating shaft 2 rotates at a high speed of about 10' rpm, dynamic air pressure is generated between the rotating shaft 2 and the pad 12, and this pressure holds the rotating shaft 2 in the radial direction.

The rotation of the rotation axis is I x 10' to 5 x 10'r
When high-speed rotation of pm is required, the moment of inertia around the axis acts greatly and the degree of one rotation is maintained extremely high.

However, recently, as the applications of scanning rotating polygon mirrors have diversified, there has been a demand for extremely low rotation speed of about 10"rpm and high rotational accuracy with a rotational fluctuation error of 0.01% or less. For scanning at low rotational speeds, conventional high-speed rotating scanning polygon mirrors have the following drawbacks and are currently completely unusable: (1) The rotation axis The electric motor used to drive the motor rotates the rotating shaft by rotating the magnetic field.
As the speed decreases, the rotational error of the magnetic field increases and the effect of the inertia of the rotational axis weakens, so the rotational uniformity decreases rapidly. occurs and loses its function as a scanning rotating polygon mirror.

(2) At low speed rotation, no dynamic pressure is generated between the pad of the hydrodynamic air bearing and the rotating shaft, so the rotating shaft cannot be supported in the radial direction. That is, since it does not act as a bearing, the shaft cannot rotate once.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a scanning rotating polygon mirror that can perform accurate scanning with extremely little rotational fluctuation error even in a low rotational speed range.

[Summary of the invention]

To achieve this objective, the scanning rotating polygon mirror of the present invention stops the rotational drive by the rotating magnetic field of the electric motor and uses an air jet to apply continuous and uniform rotational force to the rotating shaft. Furthermore, in order to keep the number of rotations constant and uniform, a disk of good conductor is attached to the rotating shaft, and a magnetic field is applied to it using an electromagnet, generating an eddy current and applying a uniform braking force. I made it possible to do so. Since the current to the electromagnet is adjusted by detecting the rotation of the rotating shaft, the rotational speed of the rotating body is highly consistent.

In addition, the hydrodynamic air bearing, which is the radial bearing of the rotating shaft, is stopped, and the air source of the air jet used to drive the rotating shaft is used to support the rotating shaft in the radial direction with the hydrostatic air bearing. A magnetic bearing was used as the bearing.

As a result, the rotating shaft can be supported even when rotating at a low speed of about 10" rpm, and air consumption can be halved.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a scanning rotating polygon mirror of the present invention. The polygon mirror 21 is attached to a rotating shaft 22 with a nut 23, and a rotating magnet 24 as a magnetic bearing is attached to the tip of the rotating shaft 22. A fixed magnet 25 that supports the rotating magnet 24 with repulsive force is housed in a holder 26.

It is supported by a spring 27. The other end of the spring is fixed to the casing 28. There is solid contact between the holder 26 and the casing 28, or a grease or the like is provided between the holder 26 and the casing 28 so that damping force due to frictional force or viscous force moves.

A disk 29 made of highly conductive aluminum or copper is fixed to the rotating shaft 22. The casing 28 has an electromagnet 3o
is attached so that a portion of the disc 29 is sandwiched between the two magnetic poles.

A hydrostatic air bearing 31 is arranged within the casing 28 .

As will be described later, compressed air led from an air source (not shown) for driving the rotating shaft 22 enters the bearing through the air supply hole 32, is ejected from the throttle 33, and rotates the rotating shaft 22 in the radial direction. Support.

An air jet ejection device 34 is fixed within the casing 28 . When the compressed air led from the air source is supplied from the jet supply hole 35, it is ejected from the jet ejection hole 36 which is oriented tangentially to the rotation axis to apply extremely uniform rotational force to the rotation axis.

There is a rotation detector 37 between the rotating shaft and the casing,
The rotational speed of the rotating shaft is accurately detected.

The current control device 38 receives the value of the rotational speed indicated by the rotation detector and supplies an appropriate current to the electromagnet to apply a brake on the single rotation shaft, thereby maintaining rotation with extremely little rotational fluctuation.

FIG. 3 is an axial cross-sectional view of an air jet blowing device for generating the rotational force of the scanning rotating polygon mirror of the present invention. Air introduced from the jet supply hole 35 in the direction of the arrow is directed from the jet ejection hole 36 toward the rotating shaft.

The arrow indicates that the water ejects almost tangentially. Since sufficiently regulated air is blown onto the rotating shaft, which has a smooth surface, the driving force of the rotating shaft is uniform regardless of the number of rotations. Of course, the rotational driving force is uniform even in a low rotational speed range of about 10''rp+a.

In this way, the air jet blows out low-speed rotation with little speed fluctuation error, which could never be achieved with conventional electric motors.

〔Effect of the invention〕

As explained above, in the scanning rotating polygon mirror of the present invention, the rotating shaft is driven by an air jet with a uniform rotational force that does not fluctuate,
Furthermore, since feedback rotation control is performed that detects the rotation of the rotating shaft and applies braking using eddy current, it is possible to perform high-precision rotation with almost no rotation fluctuations even in the extremely low rotation speed range, making it possible to perform high-performance scanning rotation for low-speed rotation. I was able to provide a mirror.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view of a conventional scanning rotating polygon mirror, FIG. 2 is a longitudinal sectional view of a scanning rotating polygon mirror according to an embodiment of the present invention, and FIG.
The figure is a plan sectional view of an air jet ejection device which is a part of the scanning rotating polygon mirror of the present invention. 21... Polygon mirror, 22... Rotating shaft, 24... Rotating magnet, 25... Fixed magnet, 29... Disc, 30...
- Electromagnet, 31... Static pressure air bearing, 34... Air jet ejection device, 37... Rotation detector, 38... Current control device.

Claims (1)

[Claims] 1. A scanning rotary polygon mirror characterized in that a rotating shaft on which the polygon mirror is attached is rotated by an air jet. 2. The scanning rotary polygon according to claim 1, wherein in the scanning rotary polygon mirror, rotation can be braked by generating an overcurrent from an electromagnet fixed to a well-conducting disc attached to the rotating shaft. mirror. 3. The scanning rotating polygon mirror according to claim 2, wherein the scanning rotating polygon mirror is capable of detecting the rotation of the rotating shaft and controlling the control force due to overcurrent. 4. The scanning rotating polygon mirror according to any one of claims 1 to 3, wherein the rotating shaft of the scanning rotating polygon mirror is supported in the radial direction by a static pressure air bearing. 5. The scanning rotating polygon mirror according to any one of claims 1 to 3, wherein the rotating shaft is supported in the axial direction by a repulsion type magnetic bearing.