JPS59162405A - Optical-type mechanical-quantity measuring device - Google Patents

Abstract

PURPOSE:To make it possible to measure three-dimensional mechanical quantities highly accurately with high resolution without contact with a body to be measured, by forming reference light and light to be measured based on the output light from a light source. CONSTITUTION:Coherent light from a laser light source 1 is made to be parallel light through lenses 11 and 12, sequentially transmitted to polarization beam splitters PBSs 21-24, and divided into a vertical-component wave S and a horizontal-component wave P. The S wave from the PBS21 is projected on a diffusing surface 50 of a target 5 through a lambda/2 plate 42. Three-dimensional quantities to be measured are imparted to the target 5. A speckle pattern is formed on light receiving surfaces of X-axis and Y-axis sensors 8x and 8y, based on the reflected light from the diffusing surface 50 through the PBSs 21 and 22, a mirror 33, a lambda/4 plate 44, and the PBS23. Based on the light component in a (z) system, interference fringes with the reference light from a mirror 32 are formed on a receiving surface of a sensor 8z through a stop 62 and the PBS24. The movement of the interference fringes is detected, and the mechanical quantities in the directions of three-dimensional axes are 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.

The purpose of the present invention is to realize this type of device with a simple structure that can measure various three-dimensional mechanical quantities with high precision and high resolution without contacting the measured/magical object. It is something.

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 of interference fringes is used to move the movable diffuser plate in the axial direction perpendicular to the two-dimensional axis. Its structural feature lies in the fact that it measures quantities.

FIG. 1 is a configuration explanatory diagram showing an example of a device according to the present invention. In the figure, reference numeral 1 denotes a light source, for example, a He Ne laser light source is used, from which coherent light is emitted. 1
A lens 1.12 constitutes a beam expander BX that expands the light emitted from the light source 1 into parallel light. 2
1 is the first polarizing beam splitter (hereinafter abbreviated as PBS)
, 22 is the second PBS, 23 is the third PBS1, and 24 is the fourth PBS. Each PB8 U plays the role of splitting the incident light beam into two directions, and the light component (S
waves) and light components that vibrate in parallel (P waves). In the first PBS, the P wave passes through this PBS, is reflected by the mirror 31, passes through the λ/2 plate 41, is reflected by the mirror 32, enters the fourth PB 824, and becomes a two-system reference light.

Further, in the first PB 821, the S wave is reflected by this PBS, passes through the λ/4 plate 42, and is irradiated onto the diffusion surface 50 of the target 5. A three-dimensional mechanical quantity to be measured is given to this target 5- as shown in the figure.

The light (reflected light) diffused by the diffusion surface 50 of the target 5 is
After passing through the λ/4 plate 42 and returning to the PBS 21, the light passes through the lens 13 (focal point fo) and the λ/2 plate 43 and enters the PB 822, where the z-system light component (light traveling straight) and x and y thread light components (reflected light). The distribution of the light amount between the 2 system and the XY system can be adjusted by rotating the λ/2 plate 43. The XY system light component is reflected by the mirror 33, and the aperture p has a pinhole diameter of 0.8 ml, for example.
61, lens 14 (focal point f), //4 plates, 4 metal plates,
The light enters the PB823, where it is divided into an X system and a Y system, and speckle patterns are created on the light receiving surfaces of each of the X-axis sensor 8X and Y-axis sensor 8Y, and these are detected respectively.

The Z-system light component separated by the PB822 is passed through, for example, an aperture 62 with a pinhole diameter of 0.2III, a lens 15 (
It passes through the focal point f ), the PBS 24 and the polarizing plate 7, and is irradiated onto the two-axis sensor 8z, and interferes with the reference light coming from the mirror 32 side on its light receiving surface to form interference fringes, which are detected.

X-axis sensor 8X, Y-axis sensor 8Y and 2-axis sensor 8ZU
, consists of a large number of light-receiving elements arranged in an array, and image sensors such as CCDs can be used.
The arrangement directions of the light receiving elements of the X-axis sensor 8X and 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, 80 is, for example, C
Each sensor 8X, 8Y consists of a CD.

A clock oscillator that drives 8z, for example, the frequency fc
clock signals are applied to each sensor.

71.72.73 is a mixer which inputs the output frequency signal fx+fy+fz from each set 8X, 8Y, 8Z and mixes this with the reference frequency signal fR, 81°8
2.83 is a low-pass filter that passes a specific frequency signal in the output signal from the corresponding mixer;
91.92.93 are low pass filters 81.8 respectively
90 is a count signal fax from each counter 91, 92, 93,
This is an arithmetic circuit that inputs foy and foz, and for example, a microprocessor is used as this arithmetic circuit. 9
5 is a display device, for example a CRT is used, and an arithmetic circuit 9
Display the calculation result at 0.

FIG. 3 is a diagram showing an example of a speckle pattern created on the Hx-axis sensor 8X and the Y-axis sensor 8Y. In this figure, when the target 5 moves in the direction of the arrow X, the speckle pattern moves in the X-axis direction;
moves in the direction of the arrow X) moves in the y-axis direction. The X-axis sensor 8X detects the displacement in the X-axis direction of the speckle pattern shown in FIG. 3 formed on this light-receiving surface.

Further, the Y-axis sensor 8YU detects displacement in the Y-axis direction of a speckle pattern as shown in FIG. 3 formed on this light-receiving surface.

FIGS. 4 and 5 are diagrams showing an example of a pattern obtained on the two-axis sensor 8z, in which Michelson interference fringes are superimposed on a speckle pattern. This pattern shows that when target 5 moves in the two directions of arrows, Z
Move in the axial direction.

The two-axis sensor 8z detects the two-axis direction quality of the pattern shown in FIG. 4 illuminated on this light receiving surface.

Here, FIG. 4 shows the case where the diameter of the pinhole provided in the diaphragm 962 is 0.8111, and FIG. 5 shows the case where the diameter of the pinhole provided in the diaphragm 2 is 0.2. .

As described above, it is recognized that when the diameter of the pinhole provided in the aperture 62 is reduced, the speckle pattern becomes larger as a whole, and the stripes take on a shape close to a straight line. This means that the speckle diameter is (f・λ)/d (d: pinhole diameter, f
: Lens focal length, λ: Laser wavelength). Also, by reducing the pinhole diameter d, the high frequency components in the speckles are cut, and the spatial frequency of the fringes is not disturbed by the speckles. This is thought to be due to the fact that the Note that the smaller the diameter d of the pinhole, the better the interference fringes should be, but if d is reduced, the intensity of light decreases and the S/N ratio deteriorates. Therefore, it is necessary to appropriately select the value of the diameter d by taking all these factors into account. According to the device having the configuration shown in FIG. 1, d is Q, 2/m
Cheng Shu was the best choice.

FIG. 6 is a diagram showing the relationship between spatial frequency F and spectral intensity I. In this diagram, when the pinhole diameter is decreased, the 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 .

In the device according to the present invention, by selecting the diameter of the pinhole provided in the diaphragm 62 to a predetermined size, the interference fringes created on the light receiving surface of the two-axis sensor 8z are made clear, and the two-directional degree position of the target 5 is made clear. can be reliably detected.

In FIG. 2, each sensor 8X, 8Y, 8Z is driven by applying a clock signal of frequency fc from a clock oscillator 80 to one end, and each sensor Bx, By, Bz
Therefore, frequency signals fx, fy, whose fundamental frequency is fc=fc/N (where N is the number of bits of each sensor)
fz is output.

FIG. 7 is an explanatory diagram showing frequency spectra of frequency signals fx, fy, fz obtained from each sensor 8x, By, Bz. The frequency spectrum of this signal has a peak at a point that is an integer multiple of the fundamental frequency fo, and the peak is greatest where the interval between the interference fringes is equal to 1/(an integer) of the total width of each sensor. , moves as the target 5 moves. For example, if the target 5 moves by X amount in the X direction, the frequency signal f from the sensor 8X
For example, the peak Pm corresponding to the m-th harmonic of x is shifted in frequency by Δfmx which is proportional to the moving speed dX/dt.

Similarly, when the target 5 moves by Y in the X direction, the peak Pm corresponding to the m-th harmonic of the frequency signal fy from the sensor 8Y shifts in frequency by fmy, which is proportional to the moving speed dY/dt. The same applies to the frequency signal from the sensor 8z.

January If you measure the phase of Δfmx +Δfmy, Δfmz, it will be X.

The amount of displacement in y and z can be measured.

For example, in the circuit shown in Figure 2, the mixer 71.72°73
1d, the m-arrow harmonic Pm output from each sensor and its neighboring frequency fR are mixed, that is, heterodyne detection is performed, and each output is passed through a rotor filter 81, 82, 83.
By doing so, frequency signals fox, foy, and foz as shown in the following equations are obtained at the output terminals, respectively.

fax=mfo-fR±Δfmx'foy=mfo-fH±Δfmy foz=mfo-fR±Δfmz Each counter 91, 92.93U calculates and counts these frequency signals. Arithmetic circuit 90Vi, each counter 9
Signal fax+ foy, foz from 1.92.93
By inputting and performing predetermined calculations, for example calculations including integration, the displacement amounts x, y, and z of the target 5 in the directions of the arrows x+y+z can be found. Also Δfmx
, Δfmy, Δfmz, the polarity changes between positive and negative depending on the moving direction of the target 5, so that the moving direction can be determined at the same time.

The device configured in this manner can simultaneously measure three-dimensional displacement using a beam from a single light source, and the entire configuration can be fully opened. 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 PHs 122, 23, 24, etc. may be half mirrors. Further, the diffusion surface 50 of the target 5 may be provided with a retroreflector 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 the 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. can.

[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. 3 is an X-axis sensor in the device shown in FIG. An explanatory diagram showing an example of a speckle pattern created on a Y-axis sensor, Figures 4 and 5 are explanatory diagrams showing an example of a pattern created on a two-axis sensor, and Figure 6 shows spatial frequency and speckle intensity. FIG. 7 is an explanatory diagram showing the frequency spectra of signals obtained from each sensor. 1... Light source, 21.22.23, 24... Polarizing beam splitter, 31.32... Mirror, 5... Target, 6], , 62-... Aperture, 8x, By, Bz
=-x-axis, Y-axis, 2-axis sensor Fig. 3 Claw 4 Fig. 5 Claw Fig. 6

Claims (1)

[Claims] (1) Coherent light from a light source is irradiated onto the diffuse surface of the target where the mechanical quantity to be measured is given, and the reflected light is passed through a diaphragm with a pinhole, and a pattern is created by the light passing through this diaphragm. In addition to detecting the movement and measuring the mechanical quantities of the target in one-dimensional or two-dimensional directions, the reflected light is divided and the coherent light from the light source is added to the light that passes through the diaphragm 9 having a pinhole. The one-dimensional or V
An optical mechanical quantity measuring device configured to measure a mechanical quantity in an axial direction perpendicular to an axis in an i-two-dimensional direction.