JPS61221606A - Measuring instrument for fine displacement - Google Patents

Abstract

PURPOSE:To measure displacement with high precision by projecting laser beam upon a plane mirror and separating the laser beam spectrally into the 1st laser beam and the 2nd laser beam which is branched from it. CONSTITUTION:When a laser oscillator 2 oscillates to emit laser beam 1, the laser beam is separated spectrally by a half-mirror 5 into laser beams 3 and 4. One beam 4 causes the projection of laser beam 7a as shown by an arrow 8. The other beam 3 is transmitted through the half-mirror 5 to generate laser beam 17, which is passed through a polarizing plate 10 to reciprocate between the plane mirror 16 and a right-angled mirror 18 plural times as shown by an arrow 26. Then, the beam 17 passes through the 2nd lambda/4 plate 20 in the middle of the 7th movement to generate laser beam 19, which is joined with the beam 7a at the projection point of the half-mirror 22 to generate interference laser 21, which is photodetected by a detector 23. The body whose displacement is to be measured is displaced finely as shown by an arrow 27. Then, there is specific variation in the difference between optical paths before and after the displacement. Then, an arithmetic processing part 24 calculates the quantity of displacement automatically on the basis of an electrical signal outputted by the detector 23.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a minute displacement measuring device used for position detection in, for example, a minute positioning mechanism.

[Technical background of the invention and its problems]

Conventionally, a Michelson laser interferometer has been used as a mechanism for measuring minute displacements with high precision in a non-contact manner.

The resolution of this laser interferometer is approximately 0.0 mm, which is half the wavelength.
The limit is 3 μm. However, recently, in the field of precision machinery such as semiconductor manufacturing equipment and ultra-precision cutting machines-"/1
A displacement measuring device with a resolution of 0.000 μm is required. Therefore, improvements have been made to the Michelson laser interferometer. For example, the laser interference light intensity is sinusoidal.

This is divided in the intensity direction to improve the division ability. Alternatively, the moving speed can be calculated using the Doppler effect from changes in laser interference light.

Furthermore, the position is detected by integrating this.

However, since both methods further divide one wave of laser interference light, there is a risk that large errors may occur due to fluctuations in the air. On the other hand.

There is a method to amplify the optical path difference, but since two laser beams with phase angles perpendicular to each other are incident on the optical system, it is impossible to directly obtain interference as light intensity, and complex arithmetic processing is required. It has its drawbacks.

[Purpose of the invention]

The present invention has been made by paying attention to the above-mentioned circumstances.

The purpose of the present invention is to provide a minute displacement measuring device that can perform high-precision displacement measurement in real time.

[Summary of the invention]

A laser beam is projected from a laser oscillator onto the plane mirror whose displacement is to be measured, and the laser beam is split into a first laser beam directed toward the plane mirror and a second laser beam branched from the first laser beam. A laser beam is made to reciprocate in a zigzag manner multiple times between a plane mirror and a second optical means, and the first laser beam that has reciprocated multiple times and the second laser beam are combined by a third optical means. This is to obtain interference laser light.

[Embodiments of the invention]

An embodiment of the present invention will be described below in detail with reference to the drawings.

The figure shows a minute displacement measuring device of this embodiment. This minute displacement measuring device consists of a laser oscillator (2) that oscillates a laser beam (1) with stable amplitude and only a vertical phase component, and a laser oscillator (2) that oscillates a laser beam (1) that has a stable amplitude and only a vertical phase component, and a A half mirror (5) that splits the light into (3>, (4)), and a laser beam (4) that is split perpendicularly to the laser beam (1) by this half mirror (5) and then returns to the half mirror. -Right-angle mirror (6) that emits light toward (5)
Then, light comes out from this right angle mirror (6) and forms a half mirror (5).
) is reflected in the same direction as the laser beam (1), and the total reflection mirror (9) receives the laser beam (7) and reflects the laser beam (7) in the direction of the arrow (8). ) enters the laser beam (3) with the same optical axis and transmits only the vertical phase component; and the phase of the laser beam αυ having only the vertical phase component emitted from the polarizing plate section of The first λ/4 plate (13) and the λ/4 plate (1
3, the laser beam α is incident and reflected in the direction of the arrow (I! The laser beam α is reflected downward by the polarizing plate α.
η is reflected again toward the polarizing plate a1, and then the plane mirror αQ
A right-angle mirror (with a frame and A first λ/4 plate a is inserted between the plane mirror [e and the deflection plate α0, and is provided so that the last reciprocating optical path on the laser source side that has reciprocated multiple times intersects the laser beam. A second λ/4 plate (A) that changes the phase of the light αη to a laser beam (II) with only the vertical phase component.

The laser beam (7a) that passes through the polarizing plate part and is reflected by the total reflection mirror (9) at the laser beam exit point is reflected in the same optical axis direction as the laser beam (7b). ) and laser beam α1 to obtain the interference laser beam c11), a detector (c) that receives the interference laser beam 31) and photoelectrically converts it into an electric signal corresponding to the light intensity, and this detector (ha). ) and an arithmetic processing section 4) that calculates the amount of displacement of the plane mirror cL61 based on the output signal from the mirror cL61. Thus, the half mirror (5) is set so that its incident surface faces upward so that the laser beam (4) is perpendicularly above the laser beam (1). In addition, the right angle mirror (6) is a half mirror (
5), and has a pair of reflective surfaces orthogonal to each other. This right-angle mirror (6) has a surface on which the optical axis of the laser beam (1) and the optical axis of the laser beam (4) are placed, and the laser beam (7) emitted from the right-angle mirror (6) and this laser beam. The light (7) is set so that the surface on which the laser beam (7b) reflected by the half mirror (5) is placed is not the same surface. In addition, the total reflection mirror (9) is
Laser beam (7a) at the laser beam 0 emission point of half mirror ■
The angle is set so that the target is reached. On the other hand, the polarizing plate α [, the plane mirror αe and the right angle mirror Q8 are connected to the laser beam αD
It has a rectangular optically active surface whose longitudinal direction is along the direction in which the reciprocating optical paths are arranged. In addition, a polarizing plate (1
(1 is disposed with the entrance plane facing upward. On the other hand, the right-angle mirror α is disposed directly below this polarizing plate (11). , 4 converts the vertical phase component of the laser beam α into the horizontal component of the laser beam a? at both longitudinal ends of the polarizing plate α [and the plane mirror QlO, respectively, and converts the horizontal component of the laser beam (1?) into the horizontal component of the laser beam (a?). ) is inserted to convert the vertical component into a laser beam 19.Furthermore, the plane mirror (11 is used to convert the laser beam α on the first round trip optical path and the laser beam (α) on the final round trip optical path.
l? ) are respectively the first and second λ/4 plates (13
, It is set to pass through Kanchu. The reflective surface (16M) of the plane mirror haze is inclined by an angle θ with respect to the surface (c) perpendicular to the optical axis of the laser beam I. Therefore, the laser beam 17) does not pass through the polarizing plate 4.

Multiple times between the first and second λ/4 plates C13, ■.

It moves back and forth between the plane mirror α and the right angle mirror (18) via a polarizing plate.

Next, the operation of the minute displacement measuring device having the above configuration will be described.

First, a plane mirror ([Q] is fixed to a displacement measurement object (not shown). Next, a laser beam (1) is emitted from a laser oscillator (2).
) to oscillate. Then, the laser beam (1)
A mirror (5) separates the laser beam into (3>, (4)).

Then, one laser beam (4) passes through the right-angle mirror (6) and enters the half mirror (5) again as a laser beam (7). This laser beam (7) is converted into a laser beam (7b) by a no. 1-f mirror (5) and a total reflection mirror (9).
), the laser beam (7a) is directed in the direction of arrow (8).
Idemitsu. Also.

The other laser beam (31) enters the polarizing plate Ql after passing through the half 2 laser (5).At this time, the laser beam (31) enters the polarizing plate Ql.
3) has only a vertical phase component, so it is emitted from this polarizing plate as a laser beam aυ and enters the first λh plate α. However, this first λ/4 plate (at 13,
One phase of the laser beam αυ changes by λ/4, and the laser beam I
Idemitsu as. Then, the laser beam I with is passed through a plane mirror α
At e, it is reflected in the direction of the arrow (t9).Then, it passes through the first λ/4 plate 0 again and enters the polarizing plate section as the laser beam αD.Then, the phase of this O laser beam αη is Since it is in the horizontal direction, the light enters the right-angle mirror (Is), where the laser light value η is reflected upward.Then, the laser light aη entering the polarizing plate (10) is It is reflected and enters the plane mirror tte K.At this time, the laser beam dη does not pass through the first λ/4 plate (13).Thus, the laser beam αη passes through the polarizing plate (II) at right angles to the plane mirror U frame. It reciprocates between the mirror (II) multiple times (five times in the figure) in the direction of the arrow (c).Then, during the seventh reciprocation, the laser beam passes through the second λ/4 plate (2). As a result, the phase of the laser beam ση is converted from the horizontal direction to the vertical direction (lI).Then, the laser beam passes through the polarizing plate Ql and enters the half mirror (a. , the laser beam (tI is this half mirror
It merges with the laser beam (7a) at the light emission point (2), becomes interference laser beam Qυ, and is received by the detector @.

Here, it is assumed that the object to be displaced is slightly displaced in one direction of the arrow, which is the same direction as the laser beam I. in this case.

A predetermined optical path difference exists between the laser beams (7a) and (19), which causes interference fringes.Therefore, a change occurs in the predetermined optical path difference between before and after the displacement. .This amount of change ΔP is given by a linear equation, that is.

Δp = Δd Tsumashi, in this case 1
The resolution is about λ/4n, and the resolution improves significantly compared to a normal Michelson type inverter. Thus, in the calculation processing unit QA, the displacement amount Δd is automatically calculated based on the electric signal output from the detector (c) when the plane mirror αe is changing.

In this way, the minute displacement measuring device of this embodiment is as follows.

Resolution can be significantly improved, and measurement accuracy can be dramatically increased. In particular, the resolution can be set arbitrarily by setting the number of reciprocations. For example, it becomes possible to achieve a resolution of 1/1 oopm, which is required in ultra-precision machines. Furthermore, the influence of air fluctuations is reduced, improving the reliability and stability of measurements.

In addition, in the above example, 1/4. Although a laser beam is made to reciprocate between a plane mirror and a right-angle mirror using a λ plate and a polarizing plate, an ordinary total reflection mirror may be used in place of the polarizing plate. That is, as shown in FIG.
A total reflection mirror (to) is arranged in place of , and the laser beam transmitted through the half mirror (5) c3]) is reflected from the incident position and the laser beam reflected from the plane mirror αe. By drilling the 04 person light position (through hole -, (b), the first and second 1/4 λ plates α (2) in the above embodiment can be omitted.Furthermore, plane fi!, α
Instead of tilting e by the angle θ, as shown in Fig. 3, a plane mirror [e
The angle of incidence on the reflecting surface (16a) may be set to the angle θ. The incident angle θ may be adjusted by moving the knob on the laser oscillator (2) side. Furthermore, displacement detection on the detector side may be performed using a Doppler method or a method using sine wave division.

〔Effect of the invention〕

The minute displacement measuring device of the present invention can arbitrarily adjust the resolution, and can stably obtain high measurement accuracy. For example, it is possible to obtain a resolution of = 1/Zooμm, and when applied to ultra-precision equipment, it produces exceptional effects.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a minute displacement measuring device according to one embodiment of the present invention, and FIGS. 2 and 3 are a perspective view and a plan view, respectively, showing other embodiments of the present invention. (2): Laser oscillator. (5): Half mirror (first optical means). Haze: Plane mirror. U: right angle mirror (second optical means). □□□: Half mirror (third optical means). (To): Detector. Agent Patent attorney Kensuke Chika (and 1 other person) Figure 2

Claims (1)

[Claims] A plane mirror that is attached to an object to be measured with its reflecting surface substantially perpendicular to the direction of displacement of the object to be measured; a laser oscillator that projects a laser beam onto the plane mirror; and a laser oscillator that is disposed between the laser oscillator and the plane mirror. and a first optical means for splitting the laser beam projected from the laser oscillator into a first laser beam projected onto the plane mirror and a second laser beam having a different optical path from the first laser beam. a second optical means for reciprocating the first laser beam projected onto the plane mirror in a zigzag pattern a plurality of times between the second optical means and the plane mirror; a third optical means that combines the first laser beam that has reciprocated twice and the second laser beam that has been separated by the first optical means into an interference laser beam; and a third optical means that receives the interference laser beam. 1. A minute displacement measuring device, comprising: a detector that performs photoelectric conversion.