JPH06160069A - Precision positioning device - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a precision positioning device in which an Abbe error and a thermal expansion error are reduced by shortening a distance between a point to be positioned and an actual scale reading position. [Structure] In a precision positioning device in which a linear encoder 9 detects the position of a work 7 mounted on a movable body 3 which is supported by a bearing 2 and moves linearly, a scale portion 9A of the linear encoder is provided on the work 7. Since the position is detected at a position close to the point P to be positioned, the position measurement error caused by the Abbe error and the thermal expansion of the work 7 is reduced, and the positioning accuracy is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a precision positioning device used in a disc writing device or the like.

[0002]

2. Description of the Related Art For example, a positioning device (positioner) for allowing a writing portion (head) of a disk writing device to access a target information track generally includes a motor which is a thrust generating mechanism, a bearing which is a supporting mechanism, A carriage equipped with a head and a position detector for detecting the position of the carriage and feedback-controlling the drive of the motor based on the position information to precisely position the head at a predetermined position are provided. An example of a conventional precision positioning device of this type is shown in FIG.

This is a linear type precision positioning device for linearly moving a disk writing unit. A movable body 3 supported by a gas bearing (air slide) 2 on a base 1 is axially moved by a linear motor 4. It is designed to be driven.
A disk writing unit 8 is attached to the tip of the movable body 3 via a work 7 extending in the axial direction. A linear encoder 9 is mounted as a position detector.
The scale portion 9A is attached to a position near the work 7 on the upper surface of the movable body 3, and is read by the detector 9B attached to the upper portion of the gas bearing 2. The reading position of the detector 9B of this linear encoder is separated from the point P to be positioned at the tip of the work 7 by a distance d.

[0004]

However, in the above-mentioned conventional precision positioning device, the reading position O of the detector 9B of the linear encoder is separated from the point P to be positioned at the tip of the work 7 by the distance d. However, since the point P to be positioned and the actual scale reading position O are considerably separated, there is a problem in that positioning error occurs. One of the errors is called an Abbe measurement error, which occurs when the movable body 3 supported in a non-contact manner by the gas bearing 2 changes its posture during movement and tilts from the straight direction. The other error is due to the temperature change of the work 7 from the scale reading position O to the point P to be positioned, and is caused by thermal expansion.

Incidentally, the Abbe's measurement error is as shown in FIG.
As shown in, the error caused by the distance between the mounting position of the scale S and the target point P to be measured is d. If the distance is d and the angle change of the stage is α, the error amount ε
₁ is given by ε ₁ = α × d.

For example, if α = 1 second and d = 100 mm,
The Abbe error is 0.5 μm. In order to reduce this error, it is necessary to bring the mounting position of the scale S and the target point P to be measured as close to each other as possible and to use a stage having a high posture accuracy. In FIG. 5, L is the true movement amount, and 1 is the measured value by the scale. Therefore, the present invention has been made by paying attention to the above conventional problems,
An object of the present invention is to provide a precision positioning device in which the Abbe error and the thermal expansion error are reduced by making the distance between the point P to be positioned and the actual scale reading position O as short as possible.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a precision positioning device for detecting the position of a workpiece mounted on a movable body which is supported by a bearing and linearly moves, by a linear encoder,
The scale portion of the linear encoder is arranged on the work.

[0008]

[Function] Since the linear encoder which is the position detector is arranged at a position close to the point to be positioned, that is, the work,
Positioning error due to Abbe's error and thermal expansion of the work is reduced, and positioning accuracy is improved.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 show an embodiment of the present invention, in which the same or corresponding parts as in the conventional case are designated by the same reference numerals.
A gas bearing (air slide) 2 is fixed to the upper surface of the base 1. The gas bearing 2 is a static pressure air bearing, and regardless of the type, it may be a multi-hole bearing, a porous bearing, a surface-throttle bearing, or the like, but a porous type is preferable in terms of high accuracy and high rigidity. preferable. Gas bearing 2 consisting of the static pressure air bearing
In addition, a movable body 3, which is a prismatic movable shaft, is horizontally supported. The rear part of the movable body 3 is connected to a mover (not shown) of the linear motor 4 mounted on the upper surface of the base 1. The linear motor 4 of this embodiment uses a linear DC brushless motor (LDM) that is capable of smooth high-speed traveling and has almost no mechanical vibration, but is not limited to this. The work 7 has a mounting flange 7 at the tip of the movable body 3.
It is attached at a. At the tip of the work 7 (which is the position of the point P to be positioned), the disk writing unit 8
Is attached. The type of the linear encoder 9 used for positioning the linear displacement of the linear motor 4 is not limited. For example, an optical linear encoder that outputs a digital signal, a magnetic linear encoder, or a high-resolution laser linear encoder that uses a semiconductor laser to detect interference of reflected diffracted light may be used.

The scale portion 9A of the linear encoder 9
Are attached to the upper surface of the work 7. The scale portion 9A may be integrally molded with the work 7, may be fixed by adhesion, or a commercially available plate scale may be attached using a dedicated jig. The detector 9B of the linear encoder 9 is fixed to the upper surface of the gas bearing 2 and is attached to the tip of a mounting arm 10 extending in the direction of the disk writing unit 8, and the reading position O of the detector 9B and the workpiece 7 are attached.
The distance d from the point P to be positioned at the tip of is set to be extremely short.

Next, the operation will be described. When the movable body 3 and thus the work 7 and the disk writing portion 8 are moved in the axial direction by the operation of the linear motor 4, the amount of movement is detected by the linear encoder 9 which is a traveling direction position sensor. The movement of the movable body 3 and the work 7 is controlled by feeding back the detection signal to the drive command signal of the linear motor 4 to accurately position the disc writing unit 8 at a predetermined position.
The linear encoder 9 has its reading position O arranged at a position close to the point P to be positioned and made the distance d between them extremely short. Therefore, the linear encoder 9 is caused by the Abbe error ε ₁ = α × d and the thermal expansion of the work 7. Position measurement error
High positioning accuracy can be obtained.

The precision positioning device of the above embodiment is
Although it has been described as applied to the disk writing device, it goes without saying that it can also be applied to other linear drive devices.

[0013]

As described above, according to the present invention,
In a precision positioning device that uses a linear encoder to detect the position of a workpiece mounted on a movable body that is supported by a bearing and moves in a straight line, since the scale part of the linear encoder is arranged on the workpiece, the point to be positioned and the reading of the linear encoder The distance from the position is shortened, the position measurement error caused by the Abbe error and the thermal expansion of the work is reduced, and the positioning accuracy is improved.

[Brief description of drawings]

FIG. 1 is a side view of an embodiment of the present invention.

FIG. 2 is a plan view of what is shown in FIG.

FIG. 3 is a rear view of what is shown in FIG.

FIG. 4 is a side view of a conventional precision positioning device.

FIG. 5 is a perspective view illustrating an Abbe error.

[Explanation of symbols]

 2 Bearing 3 Movable body 7 Work piece 9 Linear encoder 9A Scale part of linear encoder P Point to be positioned

Claims (1)

[Claims] 1. A precision positioning device for detecting the position of a work mounted on a movable body which is supported by a bearing and moves linearly in a linear encoder, wherein a scale portion of the linear encoder is arranged on the work. Precision positioning device.