JP2997765B2 - High sensitivity space positioning method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention locates an object by radiating light from a low coherence light source into a Michelson interferometer and detecting a white interference fringe formed by the measuring light and the reference light. The present invention relates to a high-sensitivity space positioning method.

[0002]

2. Description of the Related Art In recent years, not only in the precision machinery industry and the semiconductor-related industry, but also in the biotechnology industry and the medical field, it is indispensable for high-precision control of various devices, precision machining of parts, and precision measurement. As a spatial positioning measurement technique, a positioning method utilizing white interference by laser light having a wide spectrum width, that is, laser light from a low coherence light source has been developed and has been used in a wide range of fields.

In the above-described positioning method using white light interference, with the advancement of laser technology, a pulse laser having a large peak value is used, or a continuous wave laser having a large output is used to reduce these laser beams with a low reflectance. When applied to the surface of an object and the spatial position of the object is determined precisely, but the reflectance is extremely low and the background light is large,
Since a detection signal with a sufficient SN ratio cannot be obtained, a method of increasing the detection time and improving the SN ratio of the detection signal is employed.

[0004]

However, as described above, if the detection time is long, even a single point measurement requires a long time, and not only cannot be applied to a site where the measurement environment is relatively poor, but also It is impossible to apply to two-dimensional measurement such as shape measurement, and the positioning accuracy of space is poor.

In the above positioning method using white light interference, laser light having a wide spectrum width output from a single laser light source is used, or light of different wavelengths output from a plurality of laser light sources is used. However, when a single laser light source is used, many high-order interference fringes are formed, and it is difficult to identify zero-order white interference fringes. In addition, when using a plurality of laser light sources having different wavelengths, it is necessary to stabilize the light sources in order to synchronize two or more laser light sources. It was difficult to carry out stably.

[0006] The present invention has been proposed in view of the above,
By making it possible to accurately detect the peak of the white interference fringe, high sensitivity, high accuracy, even for objects with extremely low reflectance,
Moreover, it is an object of the present invention to provide a highly sensitive spatial positioning method capable of stably determining the spatial position of an object.

[0007]

In order to achieve the above object, according to the present invention, light from a low coherence light source is incident on a Michelson interferometer, and white interference fringes formed by measurement light and reference light are provided. In the high-sensitivity spatial positioning method for detecting and positioning an object, the reference light is reflected by a reference light reflecting portion having a phase modulating means for randomly modulating the phase of the reference light, and the reference light and the measurement are performed. Obtain a white interference fringe signal that is randomly modulated by forming white interference fringes with light.On the other hand, the light of a coherence light source for interferometric measurement is converted to a normal Michelson type using a plane reflector as a reference light reflector. The interference measurement signal obtained based on the interference fringes when the light is incident on the interferometer is incorporated in advance, and the white interference fringe signal and the random number of the reference light reflecting portion that contributed to the formation of the white interference fringe signal are obtained. Correlation with the reference random signal according to the column, the noise component is removed from the white interference fringe signal by the filtering effect by the correlation, and the above-described interference measurement signal is applied to the signal from which the noise component has been removed, so that the correlation peak is obtained. The method is characterized in that a position is identified with high sensitivity, and an object is positioned based on the position data.

FIG. 1 is a view schematically showing an optical system for carrying out the high-sensitivity spatial positioning method of the present invention. In the figure, a laser beam having a spectrum width of about 100 nm emitted from a low coherent laser light source 1 is incident on a Michelson interferometer, is split by a beam splitter 4 into a measuring beam 21 and a reference beam 22, Is reflected by the measured object 5.

The reference light 22 is reflected by a composite reflector 7 provided on a stage for scanning interference fringes. Unlike a conventional interferometer, the composite reflector 7 has a reference light reflecting surface. Use several small flat mirrors and measure several μm
It is configured to have random steps before and after, and has a number of cell structures with different depths of view. When scanning the composite reflecting mirror 7, the reference light 22 reflected by the composite reflecting mirror 7 and the measuring light 21 reflected by the object 5 to be measured 5
Are mixed by the beam splitter 4, and as a result, pseudo-random white interference fringes are formed corresponding to the positions where the optical path lengths coincide. That is, white interference fringes are formed at random spatial positions with the scanning of the composite reflecting mirror 7.
This white interference fringe is converted into an electric signal by the photoelectric detector 8,
As shown in FIG. 2A, a pseudo-randomly modulated white interference fringe signal 23 a having different intervals and different signal magnitudes is input to the computer 9.

[0010] The random step structure of the reference light reflecting surface in the composite reflecting mirror 7 follows the M sequence. Here, the M-sequence refers to a binary sequence having the largest cycle among binary sequences obtained by performing appropriate exclusive OR feedback on n shift registers. The white interference fringe signal 23a obtained by making the step of the composite reflecting mirror 7 follow the M sequence is the sum of signals whose phases are pseudo-randomly delayed according to the M sequence.

In a stage prior to the measurement, of the laser light emitted from the low coherent laser light source 1, the measurement light is reflected by the reference object 6, which is a temporarily moved object having a high reflectance, and the reference light is a complex type light. When the light is reflected by the reflecting mirror 7, the interference fringes formed based on the reflected light become random-modulated white interference fringes having a good SN ratio, and the white interference fringes are also converted into electric signals by the photoelectric detector 8. The data is input to the computer 9 and used in the processing of the computer 9 to correct an error unique to the optical system. For example, it is used for correcting an error of the light intensity distribution of the composite reflecting mirror 7.

Further, prior to the measurement, of the laser light emitted from the coherent laser light source 2 for interferometric measurement, the measurement light is reflected by the temporarily moved reference object 6 and the reference light is reflected by the plane reflecting mirror 11. , The interference fringes formed on the basis of the reflected light are also converted into electric signals by the photoelectric detector 8 and become an interference measurement signal 23b as shown in FIG. You.

The computer 9 calculates the white interference fringe signal 23
a, a reference random signal 24 (FIG. 2) according to the M-sequence of the composite reflector 7 that contributed to the formation of the white interference fringe signal 23a.
(B)), and the positioning of the measured object 5 is performed by the following procedure using the interference measurement signal 23b.

First, the computer 9 generates a white interference fringe signal 23a.
And the reference random signal 24. When referring to this correlation, in general, when two random signals are correlated, the correlation is shown only when the same random signal is at the same position, and when different random signals or even the same random signal are shifted. The correlation becomes very small. For this reason, as shown in FIG. 3, when the correlation between the white interference fringe signal 23a and the reference random signal 24 is obtained, only the component modulated by the same signal as the reference random signal 24 is obtained as shown in FIG. And noise components having no correlation mixed into the white interference fringe signal 23a are suppressed. That is, the white interference fringe signal 23a is a signal having a clear waveform from which noise components have been removed by the filtering effect due to correlation. The computer 9 applies the interference measurement signal 23b to the signal from which the noise component has been removed, identifies the position where the correlation peaks with high sensitivity, and positions the measured object 5 from the position data. .

As described above, in this embodiment, the noise component is removed from the white interference fringe signal 23a, which has been pseudo-randomly phase-modulated, by a filtering effect by correlation.
Since the measured object 5 is positioned based on the signal from which the noise component has been removed, even if the measured object 5 has a low reflectivity and the reflected light is extremely weak light, the background in the measuring environment can also be measured. Even when the light is strong, the position where the correlation peaks can be identified with high sensitivity and instantly and stably, and therefore, the object 5 to be measured can be positioned with high resolution and high sensitivity. It is extremely effective for on-line measurement and position control of equipment required at production sites in various fields. For example, it is possible to detect the shape of a free-form surface, which is a mirror surface formed by ultra-high-end processing, and the spatial position of an internal interface such as a living body with high sensitivity, and can be applied to precision measurement of two-dimensional shapes. In addition, the accuracy of spatial positioning for various types of measurement and control can be greatly improved.

In the above description, the composite reflecting mirror 7 is used as a phase modulating means for randomly modulating the phase of the reference light 22.
Is used, but other phase modulation means may be used. For example, as shown in FIG. 4, a phase modulation means 60 formed by combining a light shielding mask 61 in which slit-shaped openings 61a... Are arranged in accordance with the M sequence and a plane mirror 62 may be used. As shown in FIG. 5, a dispersion element 71 and a cylindrical lens 72 are provided.
A phase modulating means 70 combining a liquid crystal spatial phase modulator 73 and a liquid crystal spatial phase modulator 73 may be used.

The phase modulating means 70 shown in FIG.
2 is extracted and separated for each wavelength by a dispersive element 71, and is incident on a different position of a liquid crystal spatial phase modulator 73 for each wavelength via a cylindrical lens 72, and the voltage applied to the liquid crystal spatial phase modulator 73 is changed. In other words, a different phase difference is given for each wavelength by changing the voltage applied to the liquid crystal, and all the wavelengths are superimposed again to realize an arbitrary delay.

[0018]

As described above, according to the high-sensitivity spatial positioning method of the present invention, a noise component is removed from a pseudorandomly phase-modulated white interference fringe signal by a filtering effect by correlation, and the noise component is removed. Since the object is positioned based on the signal from which the light is removed, even if the reflectivity of the object is low and the reflected light is extremely weak, or if the background light in the measurement environment is strong, Even with this, the position where the correlation peaks can be identified with high sensitivity and instantly and stably, and therefore, the object can be positioned with high resolution and high sensitivity, which is required in production sites in various fields. This is extremely effective for online measurement and device position control. For example, it is possible to detect the shape of a free-form surface, which is a mirror surface formed by ultra-high-end processing, and the spatial position of an internal interface such as a living body with high sensitivity, and can be applied to precision measurement of two-dimensional shapes. In addition, the accuracy of spatial positioning for various types of measurement and control can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an optical system for implementing a high-sensitivity spatial positioning method of the present invention.

FIG. 2 is a diagram showing various signals input to a computer.

FIG. 3 is an explanatory diagram of a correlation process between a white interference fringe signal and a reference random signal.

FIG. 4 is a diagram showing another example of the phase modulation means.

FIG. 5 is a diagram showing another example of the phase modulation means.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Low coherent laser light source 2 Coherent laser light source for interference measurement 3 Beam mixer 4 Beam splitter 5 Object to be measured (reference object) 6 Reference object 7 Composite reflector 8 Photoelectric detector 9 Computer 11 Planar reflector 21 Measurement light 22 Reference light 23a White interference fringe signal 23b Interferometric signal 24 Reference random signal 60, 70 Phase modulation means

────────────────────────────────────────────────── (5) References JP-A-5-19225 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 11/00-11/30 102 G01B 9 / 02

Claims (4)

(57) [Claims] 1. A high-sensitivity spatial positioning method in which light from a low coherence light source is incident on a Michelson-type interferometer, and a white interference fringe formed by measurement light and reference light is detected to position an object. The reference light is reflected by a reference light reflecting portion having a phase modulation means for randomly modulating the phase of the reference light, and white interference fringes are randomly modulated by forming white interference fringes with the reference light and the measurement light. The fringe signal is obtained, and the light from the coherence light source for interferometric measurement is incident on an ordinary Michelson-type interferometer that uses a plane reflecting mirror for the reference light reflector. A long signal is taken in advance, and the white interference fringe signal is correlated with a reference random signal according to a random sequence of a reference light reflecting portion that has contributed to the formation of the white interference fringe signal. The noise component is removed from the white interference fringe signal by the filtering effect, and the above-mentioned interference measurement signal is applied to the signal from which the noise component has been removed, whereby the peak position of the correlation is identified with high sensitivity, and based on the position data, A high-sensitivity spatial positioning method, comprising: 2. The high-sensitivity spatial positioning method according to claim 1, wherein the reference light reflecting section having the phase modulating means is a complex reflecting mirror having a number of steps according to the M sequence. 3. The reference light reflecting section having the phase modulating means is a combination of a light blocking mask in which slit-shaped openings are arranged in accordance with the M sequence and a plane mirror. High sensitivity space positioning method. 4. The high-sensitivity spatial positioning method according to claim 1, wherein the reference light reflecting section having the phase modulating means is a combination of a dispersion element and a liquid crystal spatial phase modulator.