JPH0599611A - Laser length measuring apparatus - Google Patents

Abstract

PURPOSE:To eliminate the influence of micro vibration of atmosphere so as to enable measurement with high accuracy by surrounding the optical path between groups of reflecting mirrors with a hollow body. CONSTITUTION:A phase discrimination integrator 15 compares signals of detectors 6, 13 to each other, thereby judging and integrating the code and magnitude of their phases. In this case, the wavelength of light serving as a reference unit for measurement should be stabilized. Because an optical path is common to all of light rays except between a semi-transparent mirror 17 and a total reflection mirror 18, the fluctuation of atmosphere acts equally on any of laser light reflected by the mirrors 17 and 18, so that its effects are canceled out. Also, an actuator 19 is isolated from atmosphere between the mirrors 17 and 18 so that its optical path is not affected by the fluctuation of atmosphere. When a multilayer piezoelectric element is used as the actuator 19 the stroke of movement is shortened; then either the mirror 17 or 18 is fixed and the amount of movement of the other is measured; this process is repeated whereby the actuator 19 can be moved as much as desired.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser length measuring device, and more particularly to a laser length measuring device capable of eliminating a length measuring error due to atmospheric fluctuation.

[0002]

2. Description of the Related Art In recent years, a laser interference length measuring method has been widely used as a highly accurate length measuring means, and there are many commercially available devices.

An example of the above-described conventional laser length measuring device will be described below with reference to the drawings. FIG. 3 shows the configuration of a conventional laser length measuring device. In the figure, 1 is a dual frequency laser, 2 is a beam splitter, 3 is a polarization beam splitter, 4 is a total reflection mirror, 5 and 6 are detectors, 7 is a subtractor, 8 is an amplifier, 9 is a stabilizing circuit, Reference numeral 10 is a polarization beam splitter, 11 is a fixed corner cube mirror, 12 is a moving corner cube mirror, 13 is a detector, 14 is an amplifier, and 15 is a phase discrimination amplifier.

The operation of the laser length measuring device constructed as above will be described below. First, the two-frequency laser 1 emits two-wavelength lasers having slightly different wavelengths. Next, the laser light of these two wavelengths is split into two directions by the beam splitter 2. One of the laser beams is further divided into two directions by the polarization beam splitter 3 and enters the detectors 5 and 6, respectively. 2 for detectors 5 and 6
The beat signal generated by the interference of the high frequency laser lights is detected. The phases of these signals are different from each other by 180 degrees, the two are compared by the subtractor 7, and the result is stabilized by the stabilizing circuit 9.
Is fed back to the dual frequency laser 1. Further, the signal from the detector 6 is introduced into the phase discrimination integrator 15 through the amplifier 8. On the other hand, the other laser light split by the beam splitter 2 is split into a single wavelength laser light by the polarization beam splitter 10, one of which is reflected by a fixed corner cube mirror 11 and the other of which is reflected by a moving corner cube mirror 12. After that, they are combined again by the polarization beam splitter 10 and enter the detector 13. The detector 13 detects a beat signal shifted by the phase due to the difference in optical path length between the fixed corner cube mirror 11 and the moving corner cube mirror 12, and this signal is taken into the phase discriminator 15 through the amplifier 14. The phase discrimination integrator 15 compares the signal from the detector 6 with the signal from the detector 13 to determine the sign and magnitude of the phase and integrate them to calculate the amount of movement of the moving corner cube 12. In the above-described method, the reference unit for length measurement is the wavelength of light, and if the wavelength varies, the accuracy of length measurement is degraded, so it is important to stabilize the wavelength.

[0005]

However, in the above-mentioned structure, the wavelength fluctuates due to fluctuations in the atmosphere, which causes a measurement error. For macroscopic fluctuations, there are devices that monitor atmospheric pressure, temperature, humidity, etc. to compensate for measurement errors. However, for microscopic fluctuations, the atmospheric condition is measured at each position in the optical path. Since it is difficult to monitor in real time, there is a problem that sufficient correction cannot be performed.

In view of the above problems, the present invention provides a laser length measuring device capable of highly accurate length measurement excluding the effect of microscopic atmospheric fluctuations.

[0007]

In order to solve the above problems, a laser length measuring apparatus according to the present invention is a length measuring apparatus that uses interference of laser light, in which an optical path between reflecting mirror groups is surrounded by a hollow object. Preferably, the hollow body is a part of an actuator, or the reflecting mirrors face each other, and the reflecting mirror group is provided with independent actuators.

[0008]

According to the present invention, the optical path between the reflecting mirrors is surrounded by a hollow object, so that the atmospheric air in the optical path is separated from the atmospheric air in the vicinity of the laser length-measuring device and a microscopic view of the surrounding atmosphere is made. It prevents the measurement error from occurring due to the wavelength variation by preventing the dynamic variation from affecting the atmosphere in the optical path.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser length measuring apparatus according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a laser length measuring apparatus according to the first embodiment of the present invention. In the figure, the same parts as those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. In the figure, 16 is a beam splitter, 17 is a semi-transparent mirror, 18 is a total reflection mirror,
Reference numeral 19 is an actuator, and for example, a hollow laminated piezoelectric element or the like is suitable. The operation of the laser length measuring device configured as described above will be described below with reference to FIG. In FIG. 1, the same parts as those in FIG. 3 have the same operation, and therefore the description thereof will be omitted and only parts different from those of FIG. 3 will be described. First, the optical path of the laser light shown in FIG. 1 is a modification of what is called a common path (common optical path), and the optical path is common except between the semi-transparent mirror 17 and the total reflection mirror 18, and fluctuations of the atmosphere. Acts similarly on the reflected laser light from the semi-transparent mirror 17 and the reflected light from the total reflection mirror 18, so that the influence of atmospheric fluctuation is offset. Next, between the semi-transparent mirror 17 and the total reflection mirror 18 is isolated from the atmosphere by the actuator 19 in this embodiment, and even if the atmosphere fluctuates, the influence thereof does not affect the optical path inside the actuator 19. When the laminated piezoelectric element is used as the actuator 19, the movement stroke is short, but in this case, the semi-transparent mirror 17 is first used as a fixed mirror to measure the movement amount of the total reflection mirror 18, and then the total reflection after the movement. The semi-transparent mirror 17 is moved by using the mirror 18 as a fixed mirror, and the amount of movement is measured. By repeating this series of movements one after another, it is possible to move the actuator 19 as much as possible while measuring the position of each mirror.

As described above, according to the present embodiment, the influence of atmospheric fluctuation can be prevented by surrounding the optical path between the reflecting mirrors with the hollow actuator.

A second embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a laser length measuring apparatus showing a second embodiment of the present invention. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. The difference from the configuration of FIG. 1 is that the semi-transparent mirror 17 and the total reflection mirror 18 are provided with actuators 20 and 21, respectively.
The point is that a film 22 is surrounded between the semi-transparent mirror 17 and the total reflection mirror 18. The film 22 is made of a stretchable and air-impermeable material, and has a semi-transparent mirror 17 and a total reflection mirror 1.
The optical path between 8 is kept airtight. The operation of the laser length measuring device configured as described above will be described below.

Since the same parts as those in FIG. 3 have the same functions, description thereof will be omitted. In FIG. 2, since the film 22 is stretchable, it expands and contracts in accordance with the movements of the semi-transparent mirror 17 and the total reflection mirror 18, and its shape changes so that the internal pressure and the atmospheric pressure are balanced. Therefore, the refractive index of the gas inside does not change, and since the influence of the air flow of the outside air does not reach the inside surrounded by the film 22, the measurement error due to the change in the wavelength of the laser light does not occur. Further, the semi-transparent mirror 17 and the total reflection mirror 18 are provided with the actuator 2 respectively.
Since 0 and 21 are attached, the stroke can be made larger than that of the first embodiment. As described above, the film 22 is provided so as to surround the semi-transparent mirror 17 and the total reflection mirror 18, and the semi-transparent mirror 17 and the total reflection mirror 18 are provided with actuators. Can be obtained. The gas inside the film 21 may be air or a gas such as He. Further, in the first embodiment, the actuator is the laminated piezoelectric element, but a linear actuator or the like which can obtain the same effect may be used.

[0013]

As described above, according to the present invention, in the laser length measuring device, by enclosing the optical path between the reflecting mirror groups with a hollow object, it is possible to obtain a laser length measuring device which is insensitive to atmospheric fluctuations. ..

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a laser length measuring apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a laser length measuring device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a conventional laser length measuring device.

[Explanation of symbols]

 1 2 frequency laser 2, 16 beam splitter 3 polarizing beam splitter 5, 6, 13 detector 17 semi-transparent mirror 18 total reflection mirror 19, 20, 21 actuator 22 film

Claims (3)

[Claims] 1. A laser length measuring device using a laser light interference, wherein an optical path between reflecting mirror groups is surrounded by a hollow object. 2. The laser measuring device according to claim 1, wherein the hollow body is a part of an actuator. 3. The laser length measuring apparatus according to claim 1, wherein the reflecting mirrors are opposed to each other, and independent actuators are attached to the reflecting mirror groups.