JPH0444922B2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field 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. be.

(Prior Art) Conventionally, there have been methods for determining two-dimensional mechanical quantities using optical signals, but there have been no methods for measuring three-dimensional mechanical quantities with high precision and high resolution.

(Objective of the present invention) An object of the present invention is to provide a device of this kind with a simple structure that can measure various three-dimensional mechanical quantities with high precision and high resolution without contacting the object to be measured. This is what we are trying to achieve.

Another object of the present invention is to provide a mechanical quantity measuring device in which the optical system can be easily adjusted depending on the type of target to which the mechanical quantity to be measured is applied.

(Summary of the present invention) The apparatus according to the present invention irradiates coherent light from a light source onto a movable diffusing surface to which a mechanical quantity to be measured is given, and a speckle pattern obtained from the movable diffuser surface is A two-dimensional mechanical quantity is measured using the light passing through the first pinhole and a second pinhole with a smaller diameter.
The light from the light source is used as a reference light to irradiate the light passing through the pinhole of Its structural feature lies in the fact that it measures quantities.

(Example) The first 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.
It's PBS. Each PBS has two incoming light beams.
A light component that vibrates in the direction perpendicular to the incident plane (S wave) and a light component that vibrates parallel to the incident plane (P wave), which is created by the incident light ray and the normal line to the incident plane.
Divided into. In the first PBS, the P wave
It passes through the PBS, is reflected by the mirror 31, passes through the λ/2 plate 41, is reflected by the mirror 32, and is transferred to the fourth PBS.
24, it becomes a Z-system reference light. Also, the first
At PBS21, the S wave is reflected by this PBS,
The diffusion surface 5 of the target 5 passes through the λ/4 plate 42.
irradiated to 0. The target 5 is provided with three-dimensional mechanical quantities X, Y, and Z to be measured as shown in the figure.

The diffused light (reflected light) of target 5 is λ/
After passing through the fourth plate 42 and returning to the PBS 21, the lens 13 (focal point f ₀ ) and the first pinhole 6
0, and a λ/2 plate 4 having a second pinhole 40 installed close to the aperture 6.
3 respectively, enter PBS22, and here,
The light passing through the second pinhole 40 passes through the first pinhole 60 as a Z-system light component (light traveling straight).
The light that passes through is the X, Y system light component (reflected light)
Each can be divided as follows. Note that the diameter of the pinhole 60 provided in the aperture 6 is the same as that of the λ/2 plate 43.
The diameter of the pinhole 40 is selected to be larger than the diameter of the pinhole 40 provided therein. The XY system light components are mirror 33
reflected by lens 14 (focal point f), λ/4 plate 44
The light enters the PBS 23, where it is divided into an X system and a Y system, and speckle patterns are created on the light receiving surfaces of each X-axis sensor 8X and Y-axis sensor 8Y, and these are detected respectively.

The Z-based light components separated in PBS22 are:
The light is irradiated onto the Z-axis sensor 8Z through the lens 15 (focal point f), the PBS 24, and the polarizing plate 7, and interferes with the reference light coming from the mirror 32 side on its light-receiving surface to create interference fringes, which are detected. .

The X-axis sensor 8X, Y-axis sensor 8Y, and Z-axis sensor 8Z are configured by arranging a large number of light receiving elements in an array, and image sensors such as CCD can be used. The arrangement directions of the light receiving elements of the Y-axis sensor 8Y are arranged to be orthogonal to each other.

FIG. 2 is a block diagram showing an electrical circuit in the apparatus shown in FIG. In this figure, 8
0 is each sensor 8X composed of, for example, a CCD,
A clock oscillator that drives 8Y and 8Z applies a clock signal of, for example, frequency fe to each sensor. 71, 72, 73 are the respective sensors 8X, 8Y, 8
Mixers 81, 82, and 83 input the output frequency signals fx, fy, and fz from Z and mix them with the reference frequency signal f _R , respectively. Low-pass filters 91, 92, and 93 are counters that count the frequency signals from the low-pass filters 81, 82, and 83, respectively; 90 is a count signal fox, foy, and
This is an arithmetic circuit that inputs foz, and for example, a microprocessor is used as this arithmetic circuit. 9
Reference numeral 5 denotes a display device, for example, a CRT, which displays the calculation results of the calculation circuit 90.

The speckle pattern created on the X-axis sensor 8X and Y-axis sensor 8Y moves in the X-axis direction when the target 5 moves in the arrow X direction, and in the y direction when the target 5 moves in the arrow y direction. Move in the axial direction. The X-axis sensor 8X detects the displacement of the speckle pattern created on this light-receiving surface in the X-axis direction. Further, the Y-axis sensor 8Y detects displacement in the Y-axis direction of the speckle pattern created on this light-receiving surface.

The pattern obtained on the z-axis sensor 8Z resembles a speckle pattern overlaid with Michelson interference fringes. This pattern moves in one direction as the target 5 moves in the direction of arrow z. The Z-axis sensor 8Z detects the unidirectional displacement of the pattern formed on this light-receiving surface.

Figure 3 shows the spatial frequency F and the spectral intensity I.
FIG. In this diagram,
When the pinhole diameter is decreased, this characteristic curve changes in the direction of arrow a, and when the pinhole diameter is increased, the characteristic curve changes in the direction of arrow b.

In the device according to the present invention, the diameter of the first pinhole 60 provided in the diaphragm 6 is increased to allow high spatial frequency components in the speckle to pass through.
PBS22 is used to separate the XY system side. In addition, the diameter of the second pinhole 40 provided in the λ/2 plate 43 is made smaller to allow low spatial frequency components in the speckle to pass (high frequency components are cut).
This component is used on the Z diameter side through PBS22. That is, the first pinhole 6
The light that has passed through the second pinhole 40 has its polarization plane rotated by 90 degrees by the λ/2 plate, so it is reversed by the PBS 22 and heads towards the X, Y system side, and the light that has passed through the second pinhole 40 has its polarization plane rotated. Since there is nothing wrong with that, I pass PBS22 and head towards the Z system side. Here, the diameter of the first pinhole 60 is smaller than the diameter of the second pinhole 40.
It is desirable that it be about 10 times larger. By this,
The reduction in light intensity is suppressed to improve the S/N ratio, the interference fringes formed on the light receiving surface of the Z-axis sensor 8Z are made clear, and the displacement of the target 5 in the Z direction can be reliably detected.

In Figure 2, each sensor 8X, 8Y, 8Z
is driven by applying a clock signal of frequency fc from the clock oscillator 80 to one end, and from each sensor 8X, 8Y, 8Z, fc=fc/N (however,
Frequency signals fx, fy, and fz whose fundamental frequency is N is the number of bits of each sensor are output.

FIG. 4 is an explanatory diagram showing frequency spectra of frequency signals fx, fy, fz obtained from each sensor 8X, 8Y, 8Z. The frequency spectrum of this signal has a peak at an integer multiple of the fundamental frequency f ₀ ,
The peak is greatest where the interval between the interference fringes is equal to 1/(integer) of the total width of each sensor, and moves as the target 5 moves. For example, if the target 5 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 sensor 8X shifts in frequency by _Δfnx proportional to the moving speed dX/dt.
Similarly, if the target 5 moves by Y in the y direction, the peak pm corresponding to the m-th harmonic of the frequency signal fy from the sensor 8Y will be equal to the moving speed dY/
Shift the frequency by fmy which is proportional to dt. The same applies to the frequency signal from the sensor 8Z. In other words, if we measure the phases of Δ _fnx , Δ _fny , and Δ _fnz , x,
The amount of displacement in y and z can be measured.

For example, in the circuit shown in FIG.
2,73 is the m-th harmonic output from each sensor
By mixing Pm and its neighboring frequency f _R , that is, by performing heterodyne detection, and passing each output through low-pass filters 81, 82, and 83, a frequency signal fox,
Obtain roy and foz, respectively.

fox=mfo-f _R ±Δ _fnx foy=mfo-f _R ±Δ _fny foz=mfo-f _R ±Δ _fnz Each of the counters 91, 92, and 93 counts these frequency signals, respectively. The arithmetic circuit 90 receives signals fox, foy, and from each counter 91, 92, and 93.
By inputting foz and performing predetermined calculations, such as calculations including integration, the displacement amounts X, Y, and Z of the target 5 in the directions of the arrows x, y, and z can be determined. In addition, Δ _fnx , Δ _fny , and Δ _fnz are the target 5
Since the polarity changes between positive and negative depending on the direction of movement, the direction of movement can 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 sensor are frequency signals, calculation processing is easy and various mechanical quantities can be measured with high resolution.

In the above embodiment, if the light source 1 has sufficient optical power, the PBS22, 23, 24
etc. may be used as a half mirror. Further, the diffusion surface 50 of the target 5 may be provided with retroreflectors or other necessary patterns to increase the detection sensitivity. In addition, although we have explained here the case of measuring the displacement amount and movement speed of the target 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 5. 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. .

Further, in the present invention, the aperture 6 having the first pinhole and the λ/2 plate 43 having the second pinhole 40 are connected to the first polarizing beam splitter 21 and the second polarizing beam splitter. Since the diaphragm 6 and the λ/2 plate 43 are arranged between the vines 22 and the iris 22, it is possible to easily arrange the diaphragm 6 and the λ/2 plate 43 while simultaneously adjusting them with respect to the optical axis. There is an advantage that even when replacing according to the type, it can be done at the same installation position.

[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, FIG. 3 is a diagram showing the relationship between spatial frequency and spectral intensity, and FIG. The figure is an explanatory diagram showing the frequency spectrum of signals obtained from each sensor. 1... Light source, 21, 22, 23, 24... Polarizing beam splitter, 31, 32... Mirror, 5...
...Target, 6,43...Aperture, 60,40...
...Pinhole, 8X, 8Y, 8Z...X axis, Y
axis, Z-axis sensor.

Claims (1)

[Scope of Claims] 1. A light source 1 that emits coherent light; a target 5 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. One of the lights split by the first polarizing beam splitter is irradiated to the target via the λ/4 plate 42, and the reflected and scattered light from the target is irradiated to the λ/4 plate. an optical system that guides the light to the first polarizing beam splitter 21 through the four plates 42; an aperture 6 having a first pinhole 60 that passes the light passing through the first polarizing beam splitter 21; A second pinhole 40 having a diameter smaller than the diameter of the first pinhole 60 is installed close to the aperture 6 and passes the light passing through the first polarizing beam splitter 21. The light passing through the plate 43 and the first and second pinholes is
A second polarizing beam splitter 22 that splits the beam in the direction
and an x-axis light receiving means 8x and a y-axis bearing that receive one of the lights split by the second polarizing beam splitter 22 and detect movement in the x-axis direction and y-axis direction of the speckle pattern obtained on the light receiving surface. an optical means 8y; a light direction matching means 24 for converting the light guided from the other direction of the other light split by the second polarizing beam splitter 22 into light in one direction; optical systems 31 and 32 that guide the other light split by the polarizing beam splitter 21 to the light direction matching means 24 as light from the other direction via the λ/2 plate 41; A polarizing means 7 for interfering two types of light in one direction; and a z-axis light receiving means 8z for detecting the movement of interference fringes obtained on the light receiving surface that receives the light that has passed through the polarizing means 7. Optical mechanical quantity measuring device equipped with