JPH0198903A - Laser length measuring method - Google Patents

Abstract

PURPOSE:To perform accurate positioning, etc., by fast feedback control even when a low-cost computation processing system is used by setting the angle between an optical axis and the movement axis of a moving mirror to a proper finite value previously. CONSTITUTION:This is a system which applies a Michelson type interferometer. Here, light from a two-frequency laser light source 10 is branched by a beam splitter 11 and light which is bent by 90 deg. causes interference on a receiver 17, so that a signal of a frequency difference is sent to a counter 23. Light which travels straight in the splitter 11 is branched by a beam splitter 12 and the respective light beams are reflected by a moving mirror 14 and a fixed mirror 13 to interfere on a receiver 18, so that they are sent to a counter 33. Then, when the signal of the frequency difference varying owing to a Doppler shift by the movement of the moving mirror 14 is denoted as DELTAf, a subtracter 19 outputs a signal corresponding to the DELTAf based upon those light beams. At this time, when the frequency is denoted as lambda, the angle D between the optical axis of incidence and the movement axis of the moving mirror 14 is set to the proper finite value previously and the number of effective digits of a numerical arithmetic expression I for calculating the movement distance is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of the Invention The present invention relates to a length measurement method using a laser beam, and more particularly to a laser length measurement method that applies the principle of a Michelson interferometer that utilizes laser beam interference.

Laser length measurement systems that apply 1 411 sets of Michelson interferometers are widely used. A laser beam emitted from a light source is split into two by a beam splitter, one of which is guided to a movable mirror and the other to a fixed mirror. The light reflected by both mirrors overlaps on the beam splitter and causes interference. Using this interference, the moving distance of the movable mirror can be measured based on the wavelength λ of the light.

, the circle that the mouth is about to cross 1. In the conventional length measurement system, as shown in Fig. 1, the movable mirror 4 moves in the direction of arrow A parallel to the optical axis (the direction in which light travels). . In FIG. 1, light of frequency f1 is perpendicularly incident on movable mirror 4. In FIG. The moving distance of the movable mirror 4 can be calculated based on the wavelength λ of the light.

Now, in data processing to calculate travel distance,
For example, in the case of -18-Ne laser light, the wavelength λ is O
o·6328 μm, the number of digits in numerical calculation becomes significantly large. For this reason, for example, positioning using high-speed feedpack control cannot be performed without installing a high-grade calculation processing system. Therefore, the cost tends to be high.

In order to solve these problems, the present invention has developed a low grade (
The object of the present invention is to provide a laser length measurement method that can accurately perform positioning through high-speed feedback control even when using a low-cost calculation processing system.

In order to achieve the object of the above, the gist of the present invention is the laser length measurement method set forth in claim 1.

4. To solve the problem - In the laser length measurement method according to the present invention, the angle between the optical axis, which is the traveling direction of the laser beam, and the moving axis, which is the moving direction of the movable mirror, is set to an appropriate value in advance. do. In this case, in the subsequent calculation process, it is necessary to convert the apparent movement distance m of the movable mirror<the optical axis direction) into the actual movement distance (the movement axis direction of the movable mirror). Specifically, the moving distance in the optical axis direction must be divided by the cosine function of the angle between the optical axis and the moving axis. In this division, by considering the wavelength λ of the laser beam in advance, it is possible to reduce the number of digits in the numerical calculation.

As described above, in the laser length measurement method according to the present invention, the key is to set the angle between the optical axis and the moving axis of the movable mirror to an appropriate finite value in advance. Keep the number small and simplify the process.

The laser length measurement method according to the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing the concept of the laser length measurement method according to the present invention. A beam splitter 11 is provided in the traveling direction of the two-frequency laser light generated from the two-frequency laser light source 10. A receiver 17 for detecting a frequency difference is arranged in the traveling direction of the light that has been split by the beam splitter 11 and changed its course at right angles. A counter 23 is provided at the next stage of the receiver 17, and the counter 23 is connected to the subtracter 19.

Another beam splitter 12 is installed in the traveling direction of the light that is split by the beam splitter 11 and travels straight. An optical filter 15 is provided in the traveling direction of the light that has been split by the beam splitter 12 and changed its course at right angles to cut off a light component having a frequency fl. A fixed mirror is fixed in the traveling direction of the light having a frequency of f2 that has passed through the optical filter 15.

An optical filter 16 is provided in the traveling direction of the light that is split by the beam splitter 12 and travels straight.

A movable mirror 14 is installed in the traveling direction of the light having the frequency fl that has passed through the optical filter 16.

This movable mirror 14 moves in the direction of arrow B.

As shown in FIG. 3, the reflective surface of the movable mirror 14 is perpendicular to the optical axis, and the movable mirror 14 moves in the direction of arrow B while always satisfying this relationship.

The moving axis is inclined at an angle with respect to the optical axis, and how to determine the angle will be explained later.

Note that the movable mirror 14 has a sufficient size so that it can receive light over the entire desired moving distance.

With respect to the optical axis from the two-frequency laser light source 10 to the movable mirror,
A receiver 18 is installed on the opposite side of the optical filter 15 and fixed mirror 13. Receiver 1°8 is counter 23
and further communicates with the subtractor 19.

The subtractor 19 is connected to a multiplier 20, which in turn is connected to a position indicator 21 and a feedback mechanism 22.

Next, the operation of the embodiment of the present invention shown in FIG. 2 will be described with reference to FIGS. 2 and 3.

Laser light consisting of two frequency components fl and f2 is generated from a two-frequency laser light source 10, and is split into two directions by a beam splitter 11.

Of the light traveling in two directions, the light whose path is bent at right angles by the beam splitter 11 heads toward the receiver 17 and interferes on the receiver. A signal corresponding to the frequency difference fl-f2 is sent from the receiver 17 to the counter 23.

The light that has passed straight through the beam splitter 11 is split into two directions by the beam splitter 12.

The light whose path is bent at a right angle by the beam splitter 12 is
The light passes through the optical filter 15 and becomes light having only the frequency component f2. This light is reflected by the fixed mirror 13 and directed toward the receiver 18.

The light that goes straight through the beam splitter 12 passes through the optical filter 1
6, becomes light with only frequency component 1, and moves to moving mirror 1.
It is reflected at 4. Here, as the moving mirror moves in the direction of the arrow, a Doppler shift occurs, the frequency of the reflected light becomes f1±Δf, and it returns in the direction of the beam splitter 12. This reflected light is bent at a right angle by the beam splitter 12, overlaps with the light of frequency f2 reflected from the fixed mirror, and is directed toward the receiver 18, where it interferes.

The signal corresponding to the frequency difference f, -f2±Δf is sent to receiver 1.
The signals from the counter 23 and the counter 33 are sent to the subtracter 19, and the result is Δf.
A signal corresponding to is output and sent to the next stage multiplier 20.

FIG. 3 shows the relationship between the movable mirror 14 and incident light (frequency -f1). The mirror surface and the optical axis are perpendicular. The movement axis of the movable mirror 14 and the optical axis form an angle X. The movable mirror 14 is indicated by arrow B.
If the mirror moves in the direction of 14', the moving distance of the moving mirror in the optical axis direction is L2, and the net moving distance is Ll.
It is. Ll can be calculated as shown in the following (Equation 1).

(Formula 1) %Formula% @In the case of e-Ne laser light, Ll is simplified as in (Formula 2) by setting λ = 0.6328 μm, for example, D = 37°721°. be done.

(Formula 2) %Formula% Therefore, the multiplier 20 only needs to perform the calculation of △f Xo,4. Also, by setting D=50.743°, L+
can be calculated as ΔfXO05.

For comparison, let's look at numerical calculations in the conventional example. When the optical axis and the movement axis are parallel as in the conventional example, (Equation 3
) The moving distance L2 is calculated as follows.

(Formula 3) %Formula%) (Formula 3) and the above △fXO,4 or 8fX0.5
By comparing , it can be seen that the number of digits of numerical calculation can be significantly reduced by the laser length measurement method according to the present invention.

The moving distance calculated by the multiplier 20 as described above is sent to the position display 21 and displayed as position information. The travel distance is also input to the feedback mechanism 22, and the well-known feedback control tll (high speed feedback control tI) is applied.
I) is performed.

Next, referring to FIG. 4, another embodiment of the present invention will be described.

FIG. 4 is a configuration diagram showing only the main parts when the laser length measurement method according to the present invention is applied to an XY table. A saddle 46 movable in the X direction is located on the bed 47, and an XY table 45 serving as a work stage is further installed above the saddle 46. The x-y table 45 is provided with an X-direction movable mirror 43 and a Y-direction movable mirror 1144 so that they can be installed at arbitrary angles with respect to the X and Y axes. The mirrors 43 and 44 that move in the X- and Y-axis directions are large enough to receive laser light within a desired range of movement of the X-Y table 45.

The configuration of the length measuring system is similar to that of the -121 embodiment shown in FIG. 2 described above, and is also the same in both the X and Y directions, so here a brief description will be given of its operation only in the X direction.

The length measurement system is a laser head 40. It is composed of an interferometer 48, a cube corner 41, an X-direction moving mirror 43, and a receiver 42. The cube corner 41 has an integral structure with an interferometer 48, and corresponds to the fixed mirror 13 in the embodiment shown in FIG. The beam splitter within interferometer 48 also serves as optical filter 14.15 in FIG. The light generated from the laser head 40 is transmitted to an interferometer 48.
The frequency components are separated by a polarizing beam splitter inside, and one frequency component is directed to a cube corner 41 fixed to an interferometer 48. The other frequency component travels to the X-direction moving mirror where it is reflected back to the interferometer 48. These two frequency beams travel to receiver 42 and interfere on the receiver.

When the X-Y table 45 moves in the X direction, the receiver 4
A Doppler shift occurs in the frequency difference detected at step 2, and this frequency difference becomes the measurement signal. This signal is sent to the next stage processing system (not shown) and the moving distance is calculated using the above equation (2).
Calculated using Furthermore, well-known high-speed feedback control is performed based on this moving distance to position the X-Y table. (Not shown) The X-direction movable mirror 43 is installed so that its mirror surface is parallel to the Y-axis and at an angle to the X-axis. An example of how to determine the angle is as described above. Laser head 40, interferometer 4
8. The cube corner 41 is set so that the beam heading toward the X-direction movable mirror 43 is incident perpendicularly to the mirror surface. The relationship between the incident light, the movable mirror, and its moving direction is the same as that shown in FIG. In FIG. 3, arrow B here corresponds to the X-axis direction.

In this example, the laser length measurement method of the present invention was applied to a table serving as a work stage, but it can also be applied to a spindle axis that moves in the Z-axis direction. The length method is not limited to the embodiments described above, and can be applied to position measurement in various machine tools, position determination by feedback control, and the like.

11 animals 11 In the laser length measurement method according to the present invention, by setting the angle between the optical axis and the moving axis of the moving mirror to an appropriate finite value in advance, the number of effective digits in numerical calculations for calculating the moving distance can be reduced. can be made smaller. Therefore, even if a relatively low-grade computer is used, the moving distance can be calculated efficiently in a short time, which is very advantageous for performing high-speed feedback control and the like. Therefore, according to the present invention, a laser length measurement system applicable to high-speed feedback control etc. can be provided at low cost.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the optical axis and the movable mirror in the prior art, and FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention.
FIG. 3 is a diagram showing the relationship between the optical axis and the movable mirror of the present invention, and FIG. 4 is a diagram showing only the main parts of another embodiment of the present invention. 4.4'...Moving mirror 10...Two-frequency laser light source 11.12...Beam splitter 13...Fixed mirror 14.14'...Moving mirror 15.16...Optical filter 17. 18.42...One receiver...Subtractor 20...Multiplier 21...Position indicator 22...Feedback mechanism 23.33...Counter 40...Laser head 41... Cube corner 43...X-direction movable mirror 44...Y-direction movable mirror 45...X-Y table 46...Saddle 47...Bed 48...Interferometer Fig. 1 Fig. 3

Claims (1)

[Claims] 1. In a laser length measurement method applying the principle of a Michelson interferometer, the wavelength of the laser beam is λ,
When the frequency difference or the signal corresponding to the frequency difference that changes due to Doppler shift occurring when the movable mirror moves by the moving distance L is Δf, the optical axis of the laser beam incident on the movable mirror and the moving axis of the movable mirror are The angle D formed by the movement distance L is set in advance to an appropriate finite value so as to reduce the number of effective digits of the numerical calculation △f×(1/2)×λ/cosD for calculating the moving distance L. Laser length measurement method. 2. Using a He-Ne laser beam with a wavelength λ of 0.63-28 μm as the laser beam, the angle D between the optical axis of the laser beam incident on the movable mirror and the moving axis of the movable mirror is 37
．． 721° or 50.743°, and the moving distance L of the movable mirror is calculated as 0.4×Δfμm or 0.5×Δfμm, the laser length measurement method according to claim 1. . 3. The laser length measurement method according to claim 1 or 2, characterized in that a movable mirror is installed on a work stage of a machine tool.