JPH0141205B2 - - 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 in the axial direction perpendicular to the two-dimensional axis is measured using the specle pattern and light as reference from a light source. CONSTITUTION:Light from the light source 1 enters a polarized beam splitter 21. The light reflected here irradiates a target 4. The light reflected on the target 4 passes through the first PBS1 and enters an x axis light receiver 71 and a y axis light receiver 72. Then, the x-axis displacement and the y-axis displacement of the target 4 are measured from a specle pattern formed on the light receiving surface of these receivers. Light passing through the first PBS from the light source 1 enters the fifth PBS25 as reference light. An interference fringe is created on a Z-axis light receiver 73 by a reflected light from the target 4 whose plane of polarization differs by 90 deg. from each other and the Z-axis displacement of the target 4 is measured.

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 a device of this kind with a simple structure that can measure various three-dimensional mechanical quantities of an object to be measured with high precision and high resolution without contacting the object. be.

The device according to the present invention irradiates coherent light from a light source onto a movable diffusing surface on which a mechanical quantity to be measured is given, and measures a two-dimensional mechanical quantity using the speckle pattern obtained therefrom. At the same time, this speckle pattern is irradiated with light from a light source as a reference light, and the resulting pattern is used to measure mechanical quantities such as displacement in the axial direction orthogonal to the two-dimensional axis of the movable diffuser plate. The feature of the structure lies in the fact that it is made as follows.

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.
PBS, 25 is the fifth PBS. 1st, 2nd,
The third PBS, 21, 22, 23 serves to split the incoming light beam into two directions, and the fourth
The PBS 24 serves to convert beams coming from two directions into a one-way beam. Also, the fifth PBS2
5 is installed so as to have a positional relationship rotated by 45 degrees with respect to the fourth PBS, and its role is to cause two types of light to interfere and create stripes. 31 and 32 are lenses with focal lengths of f ₁ and f ₂ respectively, and 30 is lens 3
1 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 having a diameter of d. 4 is a target having a diffusing surface 40, which is connected from the lens 32 to
(l is preferably about 0 to _2f2 ), and this includes, for example, x, y, z as shown in the figure.
A three-dimensional measured mechanical quantity of direction is given. 51 is a λ/
4 plates, 61 and 62 are mirrors, the first PBS21
The light from light source 1 divided by
It is installed so that it is incident on 4. Here, the mirror 61 is inclined by θ ₁ =45° with respect to the optical axis Cl, whereas the mirror 62 is inclined by θ ₂ =45° with respect to the optical axis Cl.
It is tilted by = 45° + Δ ₀ . 52 is mirror 61
A λ/2 plate installed between and the first PBS21,
53 is a λ/4 plate provided between the first PBS 21 and the second PBS, and 54 is the λ/4 plate provided between the second PBS 22 and the third PBS.
This is a λ/4 plate installed between the PBS23 and the PBS23.

71 is an x-axis receiver that receives one of the lights divided by the third PBS 23, and 72 is a y-axis receiver that receives the other light that is split by the third PBS. An image sensor such as a CCD, which is configured by arranging elements in an array, is used. It is assumed that in each of the light receivers 71 and 72, the arrangement directions of the light receiving elements are orthogonal to each other. 73 is a light receiver that receives the light emitted from the fifth PBS. As this light receiver 73, an image sensor such as a CCD is used.

FIG. 2 is a block diagram showing an electrical circuit in the apparatus shown in FIG. In this figure, 7
0 is each light receiver 71 configured with a CCD, for example.
A clock oscillator for driving 72 and 73 applies, for example, a clock signal of frequency fc to each photoreceiver. 81, 82, 83 are each light receiver 71, 72, 7
Mixers 91, 92, and 93 input the output frequency signals fx, fy, and fz from 3 and mix them with the reference frequency signal _fR . The low-pass filters 41, 42, and 43 are counters that count the frequency signals from the low-pass filters 91, 92, and 93, respectively, and 6 is the count signal fox, foy, and foz from each of the counters 41, 42, and 43.
This is an arithmetic circuit that inputs
For example, a microprocessor is used. Reference numeral 60 denotes a display device, for example, a CRT, which displays the calculation results of the calculation circuit 6.

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 plane created by the incident light ray and the normal line to the incident plane is reflected, The light passes through the plate 51 and is irradiated onto the diffusing surface 40 of the target 4 as parallel light. The parallel light irradiated onto the diffusing surface 40 of the target 4 undergoes random phase modulation and is reflected by the unevenness of this diffusing surface, and this reflected light is
Returns through the λ/4 plate 51, the lens 32, the aperture of the aperture plate 30, and the lens 31, and returns to the first PBS 21.
incident on . Here, the lens 31, the aperture plate 30,
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 therethrough. 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 reflected light from the diffusing surface 40 of the target 4, which has passed through this point, passes through the λ/4 plate 53 and becomes circularly polarized light, which is transmitted to the second PBS 22.
The light is split into two, one passes through the λ/4 plate 54, becomes circularly polarized light, is split at the third PBS 23, and enters an x-axis light receiver 71 and a y-axis light receiver 72, respectively. A speckle pattern is then created on these light-receiving surfaces.

FIG. 3 shows an x-axis light receiver 71 and a y-axis light receiver 72.
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 the target 4 moves in the arrow x direction, and moves in the y-axis direction when the target 4 moves in the arrow y direction. The x-axis light receiver 71 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 72 detects the displacement in the y-axis direction of the speckle pattern shown in FIG. 3 irradiated onto this light-receiving surface.

On the other hand, the diffusion surface 40 incident on the fourth PBS 24
The reflected light from the 5th PBS passes through as is.
25. Also, from light source 1 to the first PBS
Among the light incident on the PBS 21, the P wave component is transmitted through this, passes through the λ/2 plate 52, the plane of polarization is rotated by 90 degrees, passes through the mirrors 61 and 62, and is transmitted to the fourth PBS 24.
The light is reflected there and enters the fifth PBS 25 as a reference light. The fifth PBS25 is the fourth
It is rotated 45 degrees with respect to PBS24,
Here, targets 4 whose polarization planes differ by 90° from each other
Of the reflected light from the light source 1 and the reference light from the light source 1,
As shown in Figure 5, the 45° component is transmitted, and the z
Interference fringes are created on the shaft light receiver 73. Note that a polarizing plate may be used as the fifth PBS 25.

FIG. 4 is a diagram showing an example of a pattern obtained on the z-axis photoreceiver 73, in which Michelson interference fringes are superimposed on a speckle pattern. This pattern moves in the z direction as the target 4 moves in the z direction. Z-axis receiver 7
3, the displacement in the z-axis direction of the pattern shown in FIG. 4 irradiated onto this light-receiving surface is grasped.

Here, if the distance between the lenses 31 and 32 is f ₁ + f ₂ and the target 4 is irradiated with a plane wave, a so-called pure movement state will occur, and in this state, the light receiving surface of each light receiver will be exposed to light. The average speckle diameter of the speckle pattern is (f ₁ λ)/(πd)
is given by Therefore, the distance from the lens 31 to each light receiver and the distance l between the lens 32 and the target 4 are independent of the pure movement state and the speckle diameter.

Each of the light receivers 71, 72, 73 is driven by applying a clock signal of frequency fc from a clock oscillator 70 to one end.
From fc=fc/N (where N is the receiver 71, 72,
Frequency signal whose fundamental frequency is 73 bits)
fx, fy, fz are output.

FIG. 6 is an explanatory diagram showing frequency spectra of frequency signals fx, fy, and fz obtained from each of the light receivers 71, 72, and 73. The frequency spectrum of this signal has a peak at an integer multiple of the fundamental frequency fo,
The peak is greatest where the interval between the interference fringes is equal to 1/(integer) of the total width of each light receiver, and moves as the 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 fx from the light receiver 71 shifts in frequency by Δfmx that is proportional to the moving speed dx/dt. Similarly, if the target 4 moves by Y in the y direction, m of the frequency signal fy from the photoreceiver 72
The peak Pm corresponding to the next harmonic is its moving speed
The frequency is shifted by fmy which is proportional to dY/dt.
The same applies to the frequency signal from the light receiver 73. That is, by measuring the phases of Δfmx, Δfmy, and Δfmz, the amounts of displacement in x, y, and z can be measured.

For example, in the circuit shown in FIG.
2,83 is the m-th harmonic output from each receiver
By mixing Pm and its neighboring frequency f _R , that is, by performing heterodyne detection, and passing each output through low-pass filters 91, 92, and 93, a frequency signal fox,
Obtain foy and foz, respectively.

fox=mfo-f _R ±Δfmx foy=mfo-f _R ±Δfmy foz=mfo-f _R ±Δfmz Each counter 41, 42, 43 counts these frequency signals, respectively. The arithmetic circuit 6 receives signals fox, foy, and from each counter 41, 42, and 43.
By inputting foz and performing predetermined calculations, such as calculations including integration, the displacement amounts X, Y, and Z of the target 4 in the directions of the arrows x, y, and z can be determined. Furthermore, since the polarities of Δfmx, Δfmy, and Δfmz change between positive and negative depending on the moving direction of the target 4, the moving direction can also be determined at the same time.

The device configured in this manner can simultaneously measure three-dimensional displacement using a beam from one light source, and the overall configuration can be simplified. Furthermore, since the signals obtained from each light receiver are frequency signals, calculation processing is easy and various mechanical quantities can be measured with high resolution.

FIG. 7 is a configuration explanatory diagram showing another embodiment of the apparatus according to the present invention. In this example, the first
In the device shown in the figure, the third PBS 23 and the λ/4 plate 54 are omitted, and the light separated from the second PBS 22 is received by the light receiver 70.
As shown in FIG. 8, the light receiving surface of this light receiver 70 is constructed by arranging two light receivers 71 and 72 orthogonally to each other.

According to this embodiment, a speckle pattern as shown in FIG. 3 is created on the light receiving surface of the light receiver 70, and the light receiver 71 detects the movement of this speckle pattern in the x direction, and the movement in the y direction. The receiver 72
is detected.

In each of the above embodiments, if the light source 1 has sufficient optical power, the second PBS 22, third PBS 23, λ/4 plates 53, 54, etc. may be half mirrors. Furthermore, the mirrors 61 and 62 may be prisms or cube corners. Furthermore, a retroreflective material may be attached to the diffusion surface 40 of the target 4 to increase the detection sensitivity. In addition, here, as each receiver,
Although it is assumed that an image sensor such as a CCD is used, a pattern detector such as a combination of 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 4 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 4. can be measured.

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 a device according to the present invention, FIG. 2 is a configuration block diagram showing an electrical circuit, and FIGS. 3 and 4 show an x-axis light receiver (y Fig. 5 is an explanatory diagram showing an example of the speckle pattern created on the light-receiving surface of the optical receiver) and the z-axis optical receiver; FIG. 7 is an explanatory diagram showing the frequency spectrum of the obtained signal, FIG. 7 is a configuration explanatory diagram showing another embodiment of the device according to the present invention, and FIG. 8 is an illustration of the light receiving surface of the light receiver used in the device shown in FIG. It is a configuration explanatory diagram. 1... Light source, 21, 22, 23, 24, 25... Polarizing beam splitter, 11, 12, 31, 32...
Lens, 30...Aperture plate, 4...Target, 40...
Diffusion surface, 51, 53, 54...λ/4 plate, 52...
λ/2 plate, 61, 62...Mirror, 71, 72, 7
3... Light receiver.

Claims (1)

[Scope of Claims] 1. A light source 1 that emits coherent light; a target 4 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 onto the target via a λ/4 plate 51, and also directs reflected and scattered light from the target through the λ/4 plate. an optical system that guides the reflected and diffused light from the target that has passed through the first polarized beam splitter and the λ/4 plate 53 into two directions; a polarizing beam splitter 22, which receives one of the lights split by the second polarizing beam splitter, and detects the movement of the speckle pattern obtained on the light receiving surface in the x-axis direction and the y-axis direction. Axial light receiving means 71 and y-axis light receiving means 72
and a light direction matching means 24 for guiding the other light split by the second polarizing beam splitter 22 and combining that light and light guided from another direction into light in one direction; The other light split by one polarizing beam splitter is passed through a λ/4 plate 52 to two mirrors 61 and 62 installed at a predetermined angle with respect to the optical axis of the light from the light source. an optical system that guides the light to the fourth polarized beam splitter 24; a polarizing means 25 for interfering the two types of light that have become unidirectional in the light direction matching means 24; and a polarizing means 25 for causing the light that has passed through the polarizing means 25 to interfere. and a z-axis light receiving means 73 for receiving light and detecting movement of interference fringes obtained on the light receiving surface.