JP2505823Y2 - Laser displacement meter - Google Patents

Description

[Detailed Description of the Invention] <Industrial field of application> The present invention relates to an incremental laser displacement meter using laser interference, and in particular, by providing a laser displacement meter with an origin detection function, the integrated value of displacement can be calculated. It relates to a device that enables measurement to be continued even if it is lost.

<Prior Art> FIG. 3 is a block diagram showing the measurement principle of a conventional laser displacement meter. In FIG. 3, the semiconductor laser light source 1 is kept at a constant temperature in a constant temperature bath 2 and is driven by a high precision constant current 4 to stabilize the wavelength. The linearly polarized light emitted from the semiconductor laser light source 1 and collimated by the collimator lens 3 is split into two when it enters the beam splitter 5. One of the lights is reflected by the beam splitter 5, is reflected by the reference corner cube 7 via the 1/8 wavelength plate 6, and is again incident on the beam splitter 5 via the 1/8 wavelength plate 6. This light passes through the 1/8 wave plate 6 twice, so that there is 90 between the s-polarized component and the p-polarized component.
There is a phase difference of °. The other light passes through the beam splitter 5, is reflected by the corner cube 8 for measurement, and is incident on the beam splitter 5 again. This light is
Since it does not pass through the wave plate, there is no phase difference between the s-polarized component and the p-polarized component. The light from the reference corner cube 7 and the light from the measurement corner cube 8 are combined by the beam splitter 5 and are incident on the polarization beam splitter 9. The incident light is separated into an s-polarized component and a p-polarized component by the polarization beam splitter 9 and is incident on the detectors 10 and 11. Since the detectors 10 and 11 are given 90-degree phases for the p-wave and the s-wave, they are detected as sin and cos signals, and the detected two signals are electrically processed by the interference phase measurement unit 12. The moving distance Lm is output.

<Problems to be Solved by the Invention> However, the laser displacement meter described in the above-mentioned prior art is
Since it is an incremental type displacement meter, if the optical path is interrupted or the measurement corner cube is moved at the maximum moving speed or higher, the integrated value of displacement is lost and there is a problem that measurement cannot be performed.

The present invention has been made in view of the above-mentioned problems of the prior art, and makes it possible to detect the measurement origin by adding a high frequency superimposing function to the drive current of the semiconductor laser light source of the incremental displacement meter. The object of the present invention is to provide a laser displacement meter that can continue measurement even if the signal is lost.

<Means for Solving the Problems> The structure of the present invention for solving the above problems is a phase displacement type laser displacement meter using a frequency-stabilized LD light source and Michelson's interferometer. It is characterized in that it is provided with a white noise source capable of superimposing a high frequency on the driving of.

<Operation> According to the present invention, by adding a high-frequency superimposing function to the drive current of the semiconductor laser light source, it is possible to detect its own origin even though it is an incremental displacement meter.
It is possible to continue the measurement even if the accumulated displacement value is lost.

<Example> Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the laser displacement meter of the present invention. In FIG. 1, the same elements as those in FIG. 3 are designated by the same reference numerals, and duplicate description will be omitted. The difference between FIG. 1 and FIG. 3 is that a white noise source 13 that can perform high frequency superimposition is provided on the constant current source 4 that is the driving current source of the semiconductor laser light source 1, and the white noise source 13 is used as the constant current source when detecting the origin. This is the point where it was made to overlap with No. 4.

In such a configuration, the operation thereof is similar to that of the apparatus shown in FIG. 3, and therefore the description thereof will be omitted, but the operation of the laser displacement meter of the present invention during displacement measurement and origin detection will be described below.

Displacement measurement (no high frequency superimposition) Fig. 3 Changes in the interference phase (sin, cos) output from the detectors 10 and 11 when the optical path difference Lm is applied to the interference phase measurement unit 12 as in the device operation. Calculated by the following formula and traveled distance Lm
Is calculated.

= (2π / λ) ・ na ・ Lm ・ ・ ・ where na is the air refractive index.

When laser light is used, the coherence length is long, so the optical path difference
There is almost no change in the interference amplitude due to the change in Lm, and the locus becomes as shown in FIG. Therefore, the moving distance Lm can be obtained from the number of times the vector has rotated and the fraction.

At origin detection (with high-frequency superimposition) At origin detection, the white noise source 13 is superposed on the constant current source 4 at high frequency, whereby the spectral line width is widened and the coherence length is shortened. Therefore, the amplitude of the interference signal is
As shown in FIG. 2 (b), it greatly changes depending on the optical path difference Lm, and becomes the minimum at the point (origin) where the optical path difference Lm is 0. When this is expressed by a vector as in FIG. 2 (a), it becomes as shown in FIG. 2 (c), and the origin can be detected. That is, when the origin is detected, the white noise source 13 is turned on, the measuring corner cube 8 is moved to change the optical path difference Lm, and the amplitude obtained from the interference phase measuring unit 12 is minimized. ) Is the origin is the point where the maximum amplitude is the cos axis.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, by adding a high-frequency superimposing function to the drive current of the semiconductor laser light source, even though it is an incremental displacement sensor, Since the origin can be detected, it is possible to realize a laser displacement meter that can continue measurement even if the accumulated displacement value is lost.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a laser displacement meter of the present invention, FIG. 2 is a diagram showing the output of a detector used in the apparatus of FIG. 1, and FIG. 3 is a measurement principle of a conventional laser displacement meter. It is a block diagram which shows. 1 ... Semiconductor laser light source, 2 ... Constant temperature chamber, 3 ... Collimator lens, 4 ... Constant current source, 5 ... Beam splitter, 6 ... 1/8 wave plate, 7 ... Reference corner cube, 8 ...... Measuring corner cube, 9 …… Polarizing beam splitter, 10,11 …… Detector, 12 …… Interference phase measurement section, 13 …… White noise source.

Claims (1)

(57) [Scope of utility model registration request] 1. A phase-difference laser displacement meter using a frequency-stabilized LD light source and a Michelson interferometer, comprising a white noise source capable of superimposing a high frequency on the drive current of the frequency-stabilized light source. A laser displacement meter characterized in that.