JPH0726811B2 - Optical precision measuring method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical precision length measuring method applied to dimension measurement of engine parts, turbine rotors and the like.

[Conventional technology]

In fields that require high-precision machining of machine parts, precision length measurement, that is, sub-micron length measurement, is required.
A two-wavelength interference laser length measurement method is known as such a method.

The basic configuration is, as shown in the system diagram of FIG. 6, a two-wavelength laser light source 1, a scanning reflecting mirror 2, a semitransparent mirror 3, a center mirror 4, a total reflecting mirror 5, a reference work 6, an object to be measured 7, a light. The intensity detector 8 and the signal processing unit 9 generate interference signals as shown in FIG. 7 by the interference of the two-wavelength laser light source 1, and the signal processing unit 9 generates the interference signal 2 of the reference work 6 and the DUT 7. The optical path difference is obtained from the phase difference of the reflected light from the point.

However, the surface of the DUT 7 is not a completely flat surface but has roughness, and as shown in FIG. 8, the light reflection position is not clear with respect to the shape of the surface roughness. When reflected at the peaks or valleys, the dimensional difference between the peaks and the valleys always causes an error, and the length is always measured.Therefore, conventionally, the contact type surface roughness meter was used to measure the roughness in advance for correction. ing.

[Problems to be solved by the invention]

However, such means have the following drawbacks.

(1) The light reflection position is unknown with respect to the surface roughness.

(2) The relationship between the surface roughness and the amount of reflected light is not quantitatively understood.

(3) It takes time because it is measured with a contact type surface roughness meter in advance.

(4) The contact type does not know the exact value for those with a small roughness pitch.

The present invention has been proposed in view of the above circumstances, and an object thereof is to propose an optical precision measurement method capable of accurately measuring an object to be measured with high accuracy in a non-contact manner.

[Means for solving problems]

Therefore, the present invention uses a two-wavelength laser light source to detect reflected light from a reference work and an object to be measured through a first light intensity detector and a second light intensity detector, respectively, and to detect both reflections. In the method for precisely measuring the object to be measured based on the phase difference of light, the surface roughness is obtained through a function generator based on the output of the light intensity detector that detects the reflected light of the object to be measured, The true measured value of the measured object by correcting the surface roughness by obtaining the difference between the measured value obtained by the phase difference and the surface roughness of the measured object obtained through the function generator. It is characterized by seeking.

[Work]

With such a configuration, the difference in the length measurement value by light between the reference work and the object to be measured (the former) is detected by the phase difference.
Function generator 9a-2 based on the output of the light intensity detector 8-2
The correction amount (the latter) is output via, and the true length measurement value is obtained by subtracting both.

〔Example〕

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall system diagram thereof, FIG. 2 is a partially enlarged view of a reflection surface of an object to be measured in FIG. 1, and FIG. 3 is a reflection surface of the object to be measured. Explanatory drawing showing the relationship between beam diameter and reflected light, FIG. 4 is a diagram showing the relationship between surface roughness and reflected light quantity in FIG. 3, and FIG.
The figure is a diagram showing the relationship between the surface roughness and the amount of reflected light.

First, in FIG. 1, the same symbols as in FIG. 6 indicate the same members and equipments as in FIG. 6, respectively. The difference from this device in FIG. 6 is that instead of the signal processing unit 9 in FIG. That is, the signal processing unit 9a including the phase detector 9a-1, the function generator 9a-2, and the subtractor 9a-3 is provided.

In such a device, the interference signal from the DUT 7 is detected by the light intensity detector 8-2 and input to the function generator 9a-2 and the phase detector 9a-1 in the signal processing 9a.

The phase detector 9a-1 detects a phase difference from the output of the light intensity detector 8-1, and the subtractor 9a-3 detects the phase difference and the output (roughness) obtained by the function generator 9a-2. Subtracted to find the true length measurement.

The reason is as follows. That is, in FIG. 2, since the laser beam diameter is larger than the roughness pitch of the surface of the object to be measured, the reflected light is reflected by the peaks of the surface and reflected by the valleys as shown in FIG. The vector sum with the light b is c = a + b, and conventionally, as shown in FIG.
Since the average value of c, that is, the "length measurement value with light" in the figure was obtained and the length of the object to be measured was measured based on this, it is 1/2 between the "true length measurement value". × A difference in surface roughness occurred.

This means that, as shown in FIG. 4, when a laser beam having a beam diameter smaller than the surface roughness pitch is projected on a reference work having a triangular wave-shaped standard roughness, the reflected light is caused by the peaks of the surface roughness. It becomes clear from the fact that it is only the reflected light and the reflected light from the valley.

On the other hand, a relationship between the surface roughness and the reflected light amount is statistically shown to be inversely proportional to the reflected light amount as shown in FIG.

Therefore, in the present invention, as shown in FIG. 2, a true length measurement value is obtained by subtracting "correction value = 1/2 surface roughness" from "length measurement value with light". Is performed in the signal processing 9a of FIG.

〔The invention's effect〕

According to such a method, since it is not necessary to measure the surface roughness with a contact type roughness meter in advance, the measuring time can be shortened and the correction can be performed accurately.

In short, according to the present invention, the two-wavelength laser light source is used to detect the reflected light from the reference work and the object to be measured through the first light intensity detector and the second light intensity detector, respectively. In the method for precisely measuring the measured object based on the phase difference of the reflected light, the surface roughness is obtained through the function generator based on the output of the light intensity detector that detects the reflected light of the measured object. , The true measurement of the object to be measured by correcting the surface roughness by obtaining the difference between the length measurement value obtained from the phase difference and the surface roughness of the object to be measured obtained through the function generator. The present invention is extremely useful industrially because an optical precision measuring method capable of accurately measuring an object to be measured with high accuracy in a non-contact manner can be obtained by obtaining a long value.

[Brief description of drawings]

FIG. 1 is an overall system diagram showing an embodiment of the present invention, FIG. 2 is a partially enlarged view of the reflection surface of the object to be measured in FIG. 1, and FIG. 3 is a beam diameter and reflected light on the reflection surface of the object to be measured. FIG. 4 is a diagram showing the relationship between the surface roughness and the amount of reflected light in FIG. 3, and FIG. 5 is a diagram showing the relationship between the surface roughness and the amount of reflected light. FIG. 6 is an overall system diagram showing a conventional optical precision measuring device,
FIG. 7 is a waveform diagram showing the output of the light intensity detector in FIG. 6, and FIG. 8 is a partially enlarged view of the reflection surface of the DUT in FIG. 1 ... Dual wavelength laser light source, 2 ... Scanning reflecting mirror, 3 ... Semi-transparent mirror, 4 ... Center mirror, 5 ... Total reflecting mirror, 6 ... Reference work, 7 ... DUT, 8 ... ... Light intensity detector, 9a ... Signal processing unit, 9a-1 ... Phase detector, 9a-2 ... Function generator, 9a-3 ... Subtractor

Claims (1)

[Claims] 1. A two-wavelength laser light source is used to detect reflected light from a reference work and an object to be measured through a first light intensity detector and a second light intensity detector, respectively, and the both reflected light is detected. In the method for precisely measuring the object to be measured based on the phase difference of, the surface roughness is obtained through the function generator based on the output of the light intensity detector that detects the reflected light of the object to be measured, The true measurement value of the measured object is obtained by correcting the surface roughness by obtaining the difference between the measured value obtained by the phase difference and the surface roughness of the measured object obtained through the function generator. An optical precision length measurement method characterized by that.