JPH0141204B2 - - Google Patents

Abstract

PURPOSE:To achieve a three-dimensional measurement by measuring a two- dimensional mechanical quantity utilizing a specle pattern while the mechanical quantity is measured in the axial direction perpendicular to the two-dimensional axis using return light from a light diffusion surface and light from the light source. CONSTITUTION:Light from the light source 1 is expanded with a light expander BX and enters a first polarized beam splitter 21 as parallel light. Here, light having one vibration component is reflected to irradiate a target 3. Light reflected on the target 3 enters an X-axis light receiver 55 and a y-axis light receiver 56 passing through a first PBS21 to create specle patterns. The two-dimensional mechanical quantity of the target 3 is measured from the specle patterns created with these light receivers 55 and 56. The second PBS22 is set turned by 45 deg. with respect to the first PBS21 and the third and fourth PBSs 23 and 24 are set turned by 45 deg. with respect to the first and second PBSs 21 and 22. Thus, the displacement in the direction Z of the target 3 is measured from outputs of light detectors 51-54 respectively.

Description

[Detailed description of the invention]

The present invention relates to an optical mechanical quantity measuring device that uses optical interference to determine mechanical quantities such as displacement amount, displacement speed, and vibration frequency. An object of the present invention is to realize this type of device with a simple structure that can measure various three-dimensional mechanical quantities of an object with high precision without contacting the object. The device according to the present invention irradiates coherent light from a light source onto a light diffusing surface of a target to which a mechanical quantity to be measured is applied, and measures a two-dimensional mechanical quantity using the speckle pattern obtained therefrom. In addition, the return light from the light diffusing surface and the light from the light source are separated by 90 degrees out of phase through several beam splitters.
The structure is characterized in that the mechanical quantity in the axial direction orthogonal to the two-dimensional axis of the target is measured by calculating four types of optical signals. FIG. 1 is a configuration explanatory diagram showing an example of a device according to the present invention. In the figure, 1 is a light source, for example
A HeNe laser light source is used, which emits coherent light. 11 and 12 are lenses, and light source 1
It constitutes a beam expander BX that expands the light emitted from the beam into parallel light. 21 is a first polarizing beam splitter (hereinafter abbreviated as PBS), 22 is a second PBS, 23 is a third PBS, and 24 is a fourth PBS.
In PBS, these split the incoming light beam into two directions. 25 is a beam splitter (hereinafter abbreviated as BS) that splits the return light from the target 3 that is incident through the first PBS 21 into two directions, and 26 is a beam splitter that splits the light from the first BS further into two directions. 2 of
It's BS. The second PBS 22 is the first PBS 21
The third and fourth PBSs 23 and 24 are arranged with their optical axes rotated by 45 degrees with respect to the second PBS 23 and 24.
The optical axis is rotated by 45° with respect to the PBS. 31 and 32 have focal lengths of f ₁ and 32, respectively.
The f ₂ lens 33 is a diaphragm plate installed between the lenses 31 and 32 at a distance of f ₁ from the lens 31 and f ₂ from the lens 32, and is provided with a through hole with a diameter of d. There is. The target 3 has a light diffusing surface 30, and is installed at a distance l (l is preferably about ₀ to 2f2) from a lens 32, and has three directions in the x, y, and z directions as shown in the figure. A measured mechanical quantity of dimension is given. 41 and 42 are fixed mirrors for changing the optical path, and the light beam from the light source 1 divided by the first PBS is made to enter the second PBS 22. Note that a prism or the like may be used instead of this fixed mirror. 51, 52, 53, and 54 are photodetectors, for example, phototransistors,
Photodiodes, photovoltaic cells, etc. are used. The photodetectors 51 and 52 each receive the light divided by the third PBS 23, and the photodetectors 53 and 54
receives the divided light at the fourth PBS 24.
55 is an x-axis light receiver that receives one of the lights divided by the second BS 26, and 56 is a y-axis receiver that receives the other light.
These axial light receivers use image sensors such as CCDs, which are constructed by arranging a large number of light receiving elements in an array. Note that the arrangement directions of the respective light receiving elements are arranged so as to be orthogonal to each other. 61 is a λ/
The fourth plate 62 is a λ/4 plate installed between the first PBS 21 and the mirror 41. FIG. 2 is a block diagram showing an electrical circuit in the apparatus shown in FIG. In this figure, 7
1 is a difference calculation circuit that obtains the difference between the output signals of the photodetector 51 and the photodetector 52; 72 is a difference calculation circuit that obtains the difference between the output signals of the photodetector 53 and the photodetector 54; 8
1, 82, 83, and 84 are mixers, and 50 is an image sensor 55 composed of, for example, a CCD.
A clock oscillator driving the clock 56 outputs a clock signal of frequency fc. 73 is mixer 81,
Each difference calculation circuit 71, 72 is applied via 82.
adders 85 and 86 are low-pass filters that pass specific frequency signals in the output signals from the corresponding mixers;
1, 92, 93, and 94 are counters, and 90 is an arithmetic circuit into which count signals from each counter are input. As this arithmetic circuit, for example, a microprocessor is used. Reference numeral 95 denotes a display device, for example, a CRT, which displays the calculation results of the calculation circuit 90. The operation of the device configured as described above is as follows. Light with a wavelength λ emitted from the light source 1 is expanded by the beam expander BX, becomes parallel light, and enters the first PBS 21. Here, the light component (S wave) that vibrates in the direction perpendicular to the incident surface created by the incident light ray and the normal line to the incident surface is reflected here, and the lens 3
1. Parallel light is irradiated onto the diffusing surface 30 of the target 3 through the through hole of the aperture plate 33, the lens 32, and the λ/4 plate 61. Diffusion surface 30 of target 3
The parallel light irradiated onto the surface undergoes random phase modulation and is reflected by the unevenness of this diffusing surface, and this reflected light is reflected again by the λ/4 plate 61, the lens 32, and the diaphragm plate 33.
through the hole, returning through the lens 31 to the first PBS
21. Here, the lens 31, the aperture plate 3
3. The lens 32 functions as a low-pass filter that realizes a state of pure speckle movement and lowers the spatial frequency of light passing through it. first
The light re-entering the PBS 21 is a light component (P wave) whose vibration direction is parallel to the plane of incidence, and passes through the first PBS 21 . The return light from the diffusion surface 30 of the target 3 that has passed through this point is reflected by the first
Divided into two at BS25, one is the second PBS22
The other beam is further divided into two at the second BS 26, and is incident on the x-axis photodetector 55 and the y-axis photodetector 56, respectively. A speckle pattern is then created on these light-receiving surfaces. FIG. 3 shows an x-axis light receiver 55 and a y-axis light receiver 56.
FIG. 3 is a diagram showing an example of a speckle pattern obtained above. In this figure, the speckle pattern moves in the x-axis direction when target 3 moves in the direction of arrow x, and moves in the y-axis direction when target 4 moves in the direction of arrow y. The x-axis light receiver 55 detects the displacement in the x-axis direction of the speckle pattern shown in FIG. 3 irradiated onto this light-receiving surface. Further, the y-axis light receiver 56 detects the displacement in the y-axis direction of the speckle pattern shown in FIG. 3 irradiated onto this light-receiving surface. Here, if the distance between the lenses 31 and 32 is f ₁ + f ₂ and the target 3 is irradiated with a plane wave, a so-called pure movement state will occur, and in this state, the light received by each of the light receivers 55 and 56 will be The average speckle diameter of the speckle pattern obtained on the surface is
It is given by (f ₁ λ)/(πd). Therefore, the distance from the lens 31 to each of the light receivers 55, 56 and the distance l between the lens 32 and the target 3 are independent of the pure movement state and the speckle diameter. Each of the light receivers 55 and 56 is driven by applying a clock signal of frequency fc from the clock oscillator 50 to one end, and from each of the light receivers 55 and 56 f ₀ =f _c /
Frequency signals f _x and f _y whose fundamental frequency is N (where N is the number of bits of the light receivers 55 and 56) are output. FIG. 4 is an explanatory diagram showing the frequency spectra of the frequency signals f _x and f _y obtained from each of the light receivers 55 and 56. The power spectrum of this signal has a peak at a point that is an integer multiple of the fundamental frequency f ₀ , and the peak is greatest where the distance between the interference frames is equal to 1/(integer) of the total width of each photoreceiver. and moves as target 4 moves. For example, if the target 4 moves by X in the x direction, the peak Pm corresponding to, for example, the _m -th harmonic of the frequency signal _f do. In the same way,
When the target 4 moves by Y in the y direction, the peak Pm corresponding to the m-th harmonic of the frequency signal _fy from the light receiver 72 shifts in frequency by _Δfny proportional to the moving speed dY/dt. In FIG. 2, mixers 83 and 84 mix, or heterodyne detect, the m-th harmonic Pm output from each light receiver and its neighboring frequency f _R , and pass each output through low-pass filters 85 and 86. As a result, frequency signals f _0x and f _0y as shown in the following equations are obtained at the output terminals, respectively. f _0x = mf ₀ −f _R ±Δf _nx f _0y = mf ₀ −f _R ±Δf _ny Each of the counters 93 and 94 counts these frequency signals, respectively. The arithmetic circuit 90 inputs the signals f _0x and f _0y from the counters 93 and 94 and calculates the displacement amount X, Y of the target 3 in the directions of the arrows x and y by performing a predetermined calculation, for example, an integral calculation. You can know. Furthermore, since the polarities of Δf _ny and Δf _ny change between positive and negative depending on the moving direction of the target 3, the moving direction can also be determined at the same time. Returning to FIG. 1, the light from the light source 1 that has passed through the first PBS 21 passes through the λ/4 plate 62, the mirrors 41, 42
It enters the second PBS 22 through the beam and becomes a reference beam.
Further, the return light from the target 3 is incident on the second PBS 22 via the first BS. Here, the electric field of the reference light is E _R (E _R sinωt＋E _R
cosωt), and the return light from the reflective surface 30 of the target 3 is E _T sin(ωt+), then the vector diagram of the electric field of the light incident on the third PBS 23 is as shown by the solid line in Figure 5A, and , the vector diagram of the electric field of the light incident on the fourth PBS 24 is as shown by the solid line in Figure 5 (b). However, ω is the angular frequency of the light, is 2π/λ・Z, and λ is the wavelength, Z is the displacement amount of the target 3 in the optical axis direction.The return light from the target 3 is transmitted to the second PBS2.
2 is rotated by 45 degrees with respect to the first PBS 21, so the electric field is

[Formula] becomes. Further, each photodetector 51,
The electric fields of the light incident on 52, 53, and 54 are as shown by the broken lines in FIG. 5A and 5B, respectively. Therefore, if the optical power detected by each photodetector 51 to 54 is PD ₁ to PD ₄ , these are (1) to
Each can be expressed by equation (4). In equations (1) to (4),

[Equation] Then, Equations (1) to (4) become signals expressed by Equations (5) to (8), each having a phase shift of 90°. PD ₁ = A + Bcos ... (5) PD ₂ = A - Bcos ... (6) PD ₃ = A - Bsin ... (7) PD ₄ = A + Bsin ... (8) In the circuit shown in Figure 2, difference calculation The circuit 71 inputs the signals expressed by equations (5) and (6) from the photodetectors 51 and 52, calculates the difference between the two signals, and outputs a signal of 2Bcos at its output terminal. do. Similarly, the difference calculation circuit 72 inputs each signal expressed by equations (7) and (8), calculates the difference between both signals, and outputs a signal −2Bsin at its output terminal. do. The adder circuit 73 adds 2Bsin(ωct-) to its output terminal by adding the signals applied through the mixers 81 and 82, respectively.
Obtain a frequency signal of Here ωc is mixer 8
The carrier frequency of the carrier signal added to 1 and 82 is shown. Counter 91 counts the frequency signal from addition circuit 73, and counter 92 counts the frequency of the carrier signal. By calculating the difference between the count values from each counter 91 and 92, the calculation circuit 90 can determine the phase amount = 2π/λ·Z corresponding to the displacement amount of the target 3 in the direction of the arrow z. Note that as the arithmetic processing circuit for the output signals from each of the photodetectors 51 to 54, a circuit other than the one shown in the block diagram of FIG. 2 may be used. In addition, in FIG. 2, the photodetector 52 is omitted and there are three photodetectors, and the circuit of this part is as follows.
An arithmetic processing circuit as shown in FIG. 6 may also be used. That is, the difference between FIG. 6 and FIG. 2 is that by calculating the difference between the signals expressed by equations (5) and (7) from the photodetectors 51 and 53,
By obtaining a signal Bsin(+π/4) and calculating the difference between the signals expressed by equations (5) and (8) from the photodetectors 51 and 54, −√2Bsin(−
π/4) is obtained, and the amount of phase difference is calculated. In the above embodiment, a retroreflective material may be attached to the diffusion surface 30 of the target 3 to increase the detection sensitivity. In addition, here, as the light receivers 55 and 56, CCD
Although it is assumed that an image sensor such as the above is used, a pattern detector such as a combination of these and a spatial filter may also be used. In addition, although we have explained here the case of measuring the displacement amount and movement speed of the target 3 in the x, y, and z directions, it is also possible to measure various three-dimensional mechanical quantities such as the vibration frequency, rotation speed, or shape change of the target 3. can do. As explained above, according to the device according to the present invention, various mechanical quantities such as three-dimensional displacement of a target can be measured with high resolution without contacting the target to which the mechanical quantity to be measured is given. .

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing an example of the device according to the present invention, FIG. 2 is a configuration block diagram showing an electrical circuit, and FIG. 3 is a configuration diagram showing an example of a device according to the present invention. Figure 4 is an explanatory diagram showing an example of the speckle pattern obtained. Figure 4 is an explanatory diagram showing the frequency spectrum of the signal obtained from the x-axis optical receiver (y-axis optical receiver). Figure 5 is an explanatory diagram showing the frequency spectrum of the signal obtained from the x-axis optical receiver (y-axis optical receiver). FIG. 6 is an explanatory diagram showing the electric field of the light incident on each photodetector and the electric field of the light incident on each photodetector. FIG. 6 is a block diagram showing the main part configuration of another example of the electric circuit. 1... Light source, 21-24... Polarizing beam splitter, 11, 12, 31, 32... Lens, 33
... Aperture plate, 3 ... Target, 30 ... Diffusion surface, 41, 42 ... Mirror, 51 to 54 ... Photodetector, 55, 56 ... Light receiver, 61, 62 ...
λ/4 plate.

Claims (1)

[Scope of Claims] 1. A light source 1 that emits coherent light; a target 3 to which mechanical quantities to be measured in the x, y, and z-axis directions are given; and a first target that divides the light from the light source into two directions. A polarizing beam splitter 21 irradiates one of the lights split by this polarizing beam splitter to the target via a λ/4 plate 61, and returns light from the target to the λ/4 plate.
the first polarizing beam splitter 2 through four plates;
1; a first light splitting means 25 for splitting the return light from the target that has passed through the first polarizing beam splitter into two directions; A second light splitting means 26 that further splits one light into two directions.
and receiving each light split by the second light splitting means,
The x-axis light receiving means 5 detects the movement of the speckle pattern obtained on each light receiving surface in the x-axis direction and the y-axis direction.
5 and y-axis light receiving means 56, and a second polarizing beam splitter 22 to which the other light split by the first light splitting means 25 is guided.
and an optical system that guides the other light split by the first polarizing beam splitter to the second polarizing beam splitter 22 via the λ/4 plate 62, and the second polarizing beam splitter. third and fourth polarizing beam splitters 23 and 24 that further split each of the lights split by 22 into two directions; the third and fourth polarizing beam splitters 23,
The phase difference of each optical signal is determined by inputting the signals from the light detecting means 51 to 54 and performing predetermined calculations including difference calculations. An optical mechanical quantity measuring device, comprising: calculating means for determining the amount φ, and calculating from this the amount of movement of the target in the z-axis direction.