JPS58225302A - Optical type mechanical quantity measuring apparatus - 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 given, 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 converted into three or four types of optical signals with a phase shift of 9σ through several beam splitters, and by calculating these optical signals, the target can be detected. A feature of the structure is that a mechanical quantity in an axial direction perpendicular to the two-dimensional axis is measured.

FIG. 1 is a configuration explanatory diagram showing an example of a device according to the present invention. In the figure, it; is a light source, for example, HeNe.
A laser light source is used, from which coherent light is emitted. Lenses 11 and 12 constitute a beam expander BX that expands the light emitted from the light source 1 into parallel light. 21Fi first polarized beam spa printer (PB
(abbreviated as S), 22 is the 2nd (7) PBS, 23#I
@, 1D PBS-, 24 is 1. in the 4th 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 entering through the first PBS 21 into two directions, 26Vi is a 20th BS that splits the light from the first BS further into two directions. be. 2f) PB 822 is the I-th P
The optical axes of the third and fourth PBSs 23 and 24 are arranged with their optical axes rotated by 45° relative to the second PBS. 31 and 32 are lenses each having a focal length of f1+f2, and 33 is between lenses 31 and 32;
The aperture plate is installed at a distance fl from 1 and f2 from the lens 32, and is provided with a through hole having a diameter d. The target 3 has a light diffusing surface 30, and is set away from the lens 32 by Jt (t is preferably θ to 2f), and includes three-dimensional measurement in the πmumZ direction as shown in the figure. A mechanical quantity is given. Reference numerals 41 and 42 are fixed mirrors for changing the optical path, which make the light beam split by the first PBS and then incident on the second PBS 22 from the light source 1. In addition,
A prism or the like may be used instead of this fixed mirror. 51.52° and 53.54 are photodetectors, for example, phototransistors, photodiodes, photovoltaic cells, etc. are used. Photodetector 51.52 is a third PBS
The photodetectors 53 and 54 receive the light divided by the fourth PBS 24, respectively. 55 is an X-axis light receiver that receives one of the lights divided by the second B526, and 56 is a V-axis light receiver that receives the other light, which are constructed by arranging a large number of light-receiving elements in a play shape. An image sensor such as COD is used. Note that the arrangement directions of the respective light receiving elements are arranged so as to be orthogonal to each other.

Installed between the 611m lens 32 and the target 3
The /4 plate 62 is a λ/4 plate installed between the first PB 821 and the mirror 41.

FIG. 2 is a block diagram showing an electrical circuit in the apparatus shown in FIG. In this figure, 71 is the photodetector 5
a difference calculation circuit that obtains the difference between the output signals of 1 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; 81, 82, 83, and 84 are mixers, respectively; and 50 drives an image sensor 55, 56 composed of, for example, a COD. A clock oscillator outputs a clock signal of frequency fc. 73 is mixer 81.82
tl-X adder that adds the signals from each difference calculation circuit 71 and 72 applied through tl; .92.93.94 is a counter, 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. , 95 is a display device, for example CR
T is used to display the calculation result in the calculation circuit 90.

The operation of the device configured as described above is as follows. The light with wavelength λ emitted from light source 1 is transmitted to beam expander B.
The light is expanded by X, becomes parallel light, and enters the first PBS 21. Here, the light component (S wave) that vibrates in the direction perpendicular to the incident plane created by the incident light ray and the normal line to the incident plane is reflected here, and is reflected by the lens 31, the aperture of the aperture plate 33, λ
The 6/4 plate tube 1 irradiates the diffusing surface 30 of the target 3 with parallel light. The parallel light irradiated onto the diffusing surface 30 of the target 3 undergoes random phase modulation due to the unevenness of this diffusing surface and is reflected, and this reflected light is reflected again by the λ/4 plate 6.
1. S/Z32. The light returns through the through hole of the aperture plate 33 and the lens 31, and enters the PBS 21 of B1. Here, the lens 31, the aperture plate 33, and the lens 32 function as a low-pass filter that realizes a state of pure movement of speckles and lowers the spatial frequency of light passing through ζ. The light re-entering the first PBS 21 is a light component (P wave) whose vibration direction is parallel to the incident surface, and the light re-enters the first PBS 21.
Pass through 1. Diffusion surface 3 of target 3 that passed here
The return light from 0 is split into two by the first B525, one enters the second PBS22, and the other enters the second BS22.
The light is further divided into two at 6, and enters an X-axis light receiver 55 and a V-axis light receiver 56, respectively. A speckle pattern is then created on these light-receiving surfaces.

FIG. 3 is a diagram showing an example of a speckle pattern obtained on the two-axis light receiver 55 and the V-axis light receiver 56. In this figure, the speckle pattern moves in two axes when the target 3 moves in the direction of the arrow X, and moves in the V-axis direction when the target 4 moves in the direction of the arrow ν. The X-axis light receiver 55 detects the biaxial displacement of the speckle pattern shown in FIG. 3 irradiated onto the light receiving surface.

Further, the V-axis light receiver 56 detects the displacement in the V-axis direction of the speckle pattern as shown in FIG. 3 irradiated onto this light-receiving surface.

Here, if the distances of the lenses 31 and 32 are f and +f2 and the target 3 is irradiated with a plane wave, a state of pure movement will be obtained, and in this state, each light receiver 55
．． The average speckle diameter of the speckle pattern obtained on the light receiving surface of 56 is given by (f, λ)/(πd). Therefore, the distance from the lens 31 to each light receiver 55,56, and the distance t between the lens 32 and the target 3
is unrelated to the pure movement state and the speckle diameter.

Each of the light receivers 55, 56 is driven by a clock signal having a frequency fc applied from the clock oscillator 50 to one end thereof. Frequency signals f□, f1. whose fundamental frequency is -fo (where N is the number of bits of the photoreceiver 55.56) are output.

FIG. 4 is an explanatory diagram showing the frequency spectra of frequency signals f and If obtained from each light receiver 55 and 56.

The power spectrum of this signal has a fundamental frequency f. There is a peak at a point that is an integer multiple of For example, if the target 4 moves by X in two directions, the peak Pm corresponding to the m-th harmonic of the frequency signal f2 from the light receiver 71 will have a frequency shift of 41 mg, which is proportional to the moving speed dX/dt. do. In the same way,
If the target 4 moves by Y in the V direction, the light receiver 72
The peak Pm corresponding to the m-th harmonic of the frequency signals from
Fi, the frequency is shifted by Δfmv proportional to its moving speed dY/dt.

In FIG. 2, mixers 83 and 84 perform mixing and smegging, that is, heterodyne detection, of m[harmonics Pm and their neighboring frequencies fR outputted from each light receiver, and pass each output through low-pass filters 85 and 86. As a result, the output term contains a frequency signal f as shown in the following equation. rye f(
Obtain Iy respectively.

fo, -mf, -1n±Δfme f 6 y −m fOl−fB±Δfmi/Each counter 93.94 counts these frequency signals, respectively. The arithmetic circuit 90 receives the signal f from each counter 93,94. , If, , and performs a predetermined calculation, for example, an integral calculation, the displacement amounts X and Y of the target 3 in the directions of the arrows ZeV can be determined. Also If If
Since the polarity of ml/@my changes from positive to negative depending on the direction of movement of target 3, the direction of movement can be determined at the same time.

Returning to FIG. 1, the light from the light source 1 that has passed through the first PB 821 is transmitted through the λ/4 plate 62. 2nd through mirror 41.42
The light enters the PBS 22 and becomes a reference light.

Furthermore, 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 ER(EHsinωt+EHc
oaa+t)+target 30If the return light from the reflecting surface 30 is ETsin(a+t+9i'), the vector diagram of the electric field of the light incident on the third PB823 is as shown by the solid line in FIG. 5(A), Also, the fourth P8
The vector diagram of the electric field of the light incident on 824 is as shown by the solid line in FIG. 5(b). However, ω is the angular frequency of light, ψld2π/λ・2, λ is the wavelength, and 2 is the target 3
is the amount of displacement in the optical axis direction.

Since the second PBS 22 is rotated by 45 degrees with respect to the first PBS 21, the electric field of the return light from the target 3 is ``・5ln(a+t+ψ) Toner b. Each photodetector 51
．． The electric field of the light incident on 52, 53, and 54 becomes as shown by the broken lines in FIGS. 5(a) and 5(b), respectively.

Therefore, if the optical power detected by each photodetector 51 to 54 is PD, to PD4, these are (1) to (4).
Each can be expressed by the formula.

Then, equations (1) to (4) become signals expressed by equations (5) to (8), each with a phase shift of 90°.

PD, = A + B cos tp =
(51PD2= A −B cos ψ−=・(61
P Ds = A B s in ψ"・"...(7
) PD4 = A + B sln 9)
-...(8) In the circuit shown in FIG.
By inputting each signal expressed by the formula and calculating the difference between the two signals, a signal of 2B cos ψ is outputted at the output terminal. Similarly, the difference calculation circuit 72 receives the signals expressed by equations (7) and (8), calculates the difference between the two signals, and outputs a signal -2Bsinψ at its output terminal. The adder circuits 73 each have a mixer 8
By adding each signal applied through 1.82, a frequency signal of 2Bsin(ωat-ψ) is obtained at its output. Here, ωC indicates the carrier frequency of the intermediate signal applied to the mixers 81 and 82°. The counter 91 counts the frequency signal from the adder circuit 73, and also counts the frequency of the counter 92 FiΦ signal. The arithmetic circuit 90 includes each counter 91 . , 92, arrow 2 of target 3 is calculated.
The phase amount ψ= corresponding to the amount of displacement in the direction can be determined as :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.

Furthermore, in FIG. 2, the photodetector 52 may be omitted to provide three photodetectors, and an arithmetic processing circuit as shown in FIG. 6 may be used as the circuit for this portion.

That is, the difference between FIG. 6 and FIG. 2 is that VTBsln(ψ+π/
4) and also obtain the signal (
By calculating the difference between the signals expressed by equations 5) and (8), a signal of -vT B 51n (ψ-π/4) is obtained, and the amount of phase difference ψ is calculated. .

In addition, in the above embodiment, the diffusion surface 3 of the target 3
0, a retroreflective material may be applied to increase the detection sensitivity. In addition, here, the light receiver 5
5.56, it is assumed that an image sensor such as a CCD is used, but a pattern detector such as a combination of these and a spatial filter may also be used. Although we have explained the case of measuring the moving speed, the frequency and rotation of target 3,
It is possible to measure various three-dimensional mechanical quantities such as the number of rotations or changes in shape.

As explained above, according to the device according to the present invention, various mechanical quantities such as three-dimensional displacement of the target can be measured with high resolution without contacting the target to which the mechanical quantity to be measured is given. .

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram showing an example of a device according to the present invention, FIG. 2 is a configuration block diagram showing an electrical circuit, and FIG.
An explanatory diagram showing an example of a speckle pattern created on the light-receiving surface of an axial receiver (V-axis receiver), FIG.
An explanatory diagram showing the frequency spectrum of the signal obtained from the y-axis optical receiver], Figure 5, Chichi No. 3. FIG. 6 is an explanatory diagram showing the electric fields of light incident on the fourth PBS and light incident on each photodetector, and 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, 51-54...Photodetector, 55
．． 56... Light receiver, 61.62... λ/4 plate

Claims (1)

[Claims] (1) Irradiate coherent light from a light source through a first polarizing beam splitter and a λ/4 (λ is wavelength) plate onto the diffusing surface of the target to which the mechanical quantity to be measured is applied.1. The movement of the pattern created by the returned light is detected and measured in each of the two-dimensional directions of the target, and the returned light and the reference light from the next light source, which is split by the polarizing beam splitter of the tIc1, are The amount of phase difference is determined by generating optical signals with a phase shift ratio of 3 or 4, each with a phase shift of 90°, through two or more polarizing beam splitters, and performing predetermined calculations including difference calculations on signals related to these optical signals. (ψ), and from this, a mechanical quantity in an axial direction perpendicular to the two-dimensional axis of the target is measured.