JPH08101014A - Displacement/speed measuring instrument - Google Patents

Abstract

PURPOSE: To easily measure the displacement and speed of an object to be measured with high accuracy by offsetting errors caused when a polarizing plane maintaining optical fiber is given bending, impact, or vibration, by simultaneously transmitting measuring light rays and reference light rays through the optical fiber. CONSTITUTION: First and second laser beams having different angles of polarizing planes and frequencies are propagated through a polarizing plane-maintaining optical fiber 12 while maintaining the relation between the polarizing planes after being emitted from a light source 10, and separated from each other through a beam splitter 36 in a measuring head 14, and the first laser beam is projected on an object 15 to be measured. The second laser beam is reflected by a reference reflection mirror 38, reversely propagated through the optical fiber 12 together with reflected light from the object 15, and transmitted to a measuring means 16 after being reflected by a half mirror 26. The measuring means 16 only transduces the component which is polarized in a prescribed direction through a polarizing filter 40 into electric signals. The electric signals are processed 44 by an optical heterodyne method and the speed and displacement of the object 15 are measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement / speed measuring device for measuring the displacement and speed of an object to be measured without contact.

[0002]

2. Description of the Related Art There is a measuring instrument utilizing an optical heterodyne method as a technique for non-contactly measuring the displacement and velocity of an object to be measured such as a vibrating body. The basic principle of the optical heterodyne method is to use a beat signal (beat) generated when light beams having slightly different frequencies are made to interfere with each other. By mixing two lights that have passed through different optical paths and photoelectrically converting the generated beat signal,
The phase Φ of the signal is given by the following equation.

Φ = 2πL12 / λ where λ is the wavelength of the beat signal, and L12 represents the optical path difference between the original two lights. From this equation, when the phase change amount ΔΦ of the beat signal is measured, the change amount ΔL12 of the optical path difference is obtained, and the moving speed of the measured object that appears as the temporal change amount of the optical path difference is obtained from the measurement of the frequency of the beat signal. can get.

In a conventional measuring instrument using such an optical heterodyne method, an optical fiber is connected between a measuring instrument main body for performing various calculations and controls and a measuring head including an optical system element to measure an object to be measured. There is a device in which a measuring head is placed in the vicinity of to measure. Since such a measuring device uses a beat signal, two laser beams having different frequencies by a predetermined amount, that is, a reference beam and a measuring beam are used. These two
The two optical signals are supplied from the measuring instrument body to the measuring head through separate optical fibers, and the measuring light reflected by the object to be measured and the reference light reflected at a predetermined position are transmitted through separate optical fibers. And can be processed by the optical heterodyne measurement method to measure velocity and displacement.

[0004]

However, in the conventional optical heterodyne measuring instrument, the measuring light and the reference light are transmitted to the measuring head through separate optical fibers, and the measuring head returns them to the main body through the separate optical fibers. Therefore, when the optical fiber is bent or vibration is applied, the glass inside the optical fiber deforms and the refractive index changes due to the stress of the glass crystal, which changes the propagation speed of the light and causes a measurement error. Will be done. For this reason, in order to realize high measurement accuracy, it is necessary to make the characteristics of a plurality of optical fibers uniform and be careful not to apply bending or vibration, and there is a problem that the work is complicated and the cost is high.

Therefore, an object of the present invention is to provide a displacement / velocity measuring device which can easily obtain highly accurate measurement results.

DISCLOSURE OF THE INVENTION The displacement / velocity measuring apparatus of the present invention has a first laser beam which is linearly polarized light and a polarization plane which is different from the polarization plane of the first laser beam by a certain angle. A light source that outputs a second laser beam having a frequency shifted from the frequency by a predetermined frequency from a common output terminal, one polarization-maintaining optical fiber that receives the first and second laser beams at one end, and the polarization-maintaining optical fiber. It is connected to the other end, irradiates the object to be measured with the first laser beam, returns the first reflected beam to the polarization-maintaining optical fiber, and returns the second reflected beam obtained by reflecting the second laser beam at a predetermined position. A measuring head for returning to the polarization plane optical fiber, and detecting the first and second reflected light rays from one end of the polarization plane preserving optical fiber,
A measuring means for measuring the displacement of the speed and the position of the object to be measured from the detection output.

The measuring head of the displacement / velocity measuring apparatus of the present invention irradiates the first object to be measured with the first laser beam and a beam splitter for separating the second laser beam into different directions, and this beam splitter. A deflection means for deflecting the second laser beam from the splitter and irradiating the second object to be measured, and preserving polarization planes of the first and second reflected light beams reflected from the first and second object to be measured. It is characterized by returning to an optical fiber.

[0007]

1 is a block diagram schematically showing the construction of an embodiment of a velocity / displacement measuring apparatus of the present invention. This apparatus includes a light source unit 10, a polarization-maintaining optical fiber 12 connected to the light source unit 10, and a polarization-maintaining optical fiber 1.
2, a measuring head 14 connected to the other end of the measuring object 14, the measuring head 14 to the measuring head 14 and the polarization-maintaining optical fiber 1
And measuring means 16 for measuring the reflected light beam returned via 2. The light source unit 10 generates two laser beams. These two output laser beams differ in frequency by a predetermined frequency (for example, 80 MHz) and also differ in polarization plane by a predetermined angle (for example, 90 °). The output laser beam of the laser light source 20 is split by the polarization beam splitter 22 into two beams whose polarization planes are deviated by a predetermined angle (for example, 90 °). Beam splitter 22
One output light beam (first laser light beam) from the beam splitter 22 is output from the light source unit 10 via the half mirrors 24 and 26, and the other output light beam (second laser light beam) from the beam splitter 22 is an AOM (acousto-optic modulator). ) 28 undergoes a predetermined frequency shift, for example 80 MHz. The oscillator 30 generates a reference signal of 80 MHz, which is
It becomes equal to the frequency shift amount in the OM 28. AOM
The second laser beam output from 28 is output from a common output end together with the first laser beam via the reflectors 32 and 34 and the half mirrors 24 and 26.

The first and second laser beams output from the light source section 10 propagate through the polarization-maintaining optical fiber 12 while maintaining the relationship of polarization planes. These first and second laser beams are separated by the beam splitter 36 in the measuring head 14, the first laser beam is applied to the object 15 to be measured, and the reflected beams thereof travel in the same optical path.
Further, the second laser beam is reflected by the reference reflection mirror 38 provided at a predetermined position in the measuring head 14 and goes backward in the same optical path. The first reflected light beam from the object to be measured 15 and the second reflected light beam from the reference reflection mirror 38 go backward through the polarization-preserving optical fiber 12, are reflected by the half mirror 26, and are sent to the measuring means 16. These first and second
The reflected light beam is first applied to the polarization filter 40, and only the component in the predetermined polarization direction passes through. The light beam that has passed through the polarization filter 40 is converted into an electric signal by an optical / electrical converter (O / E) 42, and is processed by an optical heterodyne method by a measurement processing unit 44 to measure the velocity and displacement of an object to be measured. It Since the measurement processing unit 44 needs a signal having a beat frequency (80 MHz in the embodiment) by the heterodyne method, the output signal of the oscillator 30 is supplied to the measurement processing unit 44.

According to the measuring apparatus of FIG. 1, the first and second laser beams and the first and second reflected beams are configured to pass through the common polarization-maintaining optical fiber 12, so that even if the fibers are bent or vibrate. Even if is added, the influence is equally given to the propagating light beam, and therefore the error components cancel each other out when measured by the optical heterodyne method by the measuring means. Therefore, the trouble of handling is eliminated, and the cost is reduced because there is only one optical fiber.

FIG. 2 is a block diagram showing the configuration of an embodiment of the measurement processing unit 44 of FIG. The electric signal from the O / E 42 passes through the band pass filter BPF 50, and the buffer amplifier 5
2 and is supplied to the first mixer 54 via 2 and mixed with the output (70 MHz) of the first reference oscillator 56. The output of the first mixer 54 is supplied to the FM detector 58 and the phase detector 60. The output of the first reference oscillator 56 and the output of the second reference oscillator 62 are mixed by the second mixer 64, and the output of this mixer 64 is supplied to the other input end of the phase detector 60. From the FM detector 58 to the LPF (low pass filter)
What is obtained via 66 is the velocity signal of the measured object 15. Further, what is obtained from the phase detector 60 via the LPF 68 is a displacement signal of the measured object 15. Furthermore,
The output of the FM detector 58 is also supplied to the differentiator 70, where it is further differentiated to obtain the acceleration signal of the measured object 15. The velocity signal, the displacement signal, the acceleration signal, and the monitor signal output from the buffer amplifier 52 are supplied to a microprocessor (not shown) and appropriately processed. The configuration shown in FIG. 2 is well known to those skilled in the art as a measuring device using the optical heterodyne method. Although the second oscillator is included here, it may be supplied from the oscillator 30 of the light source unit as shown in FIG.

FIG. 3 is a simplified diagram showing the configuration of another embodiment of the measuring head 14. The first and second laser beams from the polarization-maintaining optical fiber 12 are split into two by the beam splitter 36, and the first laser beam is applied to the first measured object. On the other hand, the second laser beam
The second object to be measured is illuminated by the polarizer 39 such as a reflector. The light rays reflected by the first and second objects to be measured traverse the same optical path, and the measuring means 16 of the apparatus of FIG.
Is returned to. By using the measuring head having the configuration of FIG. 3, it is possible to measure the displacement of the separation distance between the two objects to be measured and the relative speed.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the embodiments described herein, and various modifications and changes can be made as necessary without departing from the gist of the present invention. It will be apparent to those skilled in the art that changes can be made.

[0013]

According to the present invention, since one polarization-maintaining single-mode optical fiber is used to simultaneously transmit both the measurement light beam and the reference light beam, bending, shock, vibration, etc. are applied to the optical fiber. However, the errors that occur are canceled out,
High measurement accuracy can be easily maintained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a velocity / displacement measuring device of the present invention.

FIG. 2 is a block diagram showing a configuration of an embodiment of a measurement processing unit in FIG.

3 is a block diagram showing the configuration of another embodiment of the measuring head of FIG. 1. FIG.

[Explanation of Codes] 10 Light Source Section 12 Polarization Preserving Optical Fiber 14 Measuring Head 16 Measuring Means

Claims (2)

[Claims] 1. A first laser beam that is linearly polarized light, and a second laser beam that has a plane of polarization that differs from the plane of polarization of the first laser beam by a certain angle and that has a frequency shifted from the frequency of the first laser beam by a predetermined frequency. A polarization-preserving optical fiber for receiving the first and second laser beams at one end, and a first polarization-maintaining optical fiber connected to the other end of the polarization-preserving optical fiber.
A measurement head which irradiates a laser beam on an object to be measured, returns the first reflected light beam to the polarization-maintaining optical fiber, and returns the second reflected light beam reflected from the second laser beam at a predetermined position to the polarization-polarized optical fiber. A measuring means connected to the one end of the polarization-maintaining optical fiber for detecting the first and second reflected light rays and measuring the displacement of the velocity and the position of the object to be measured from the detection output. Displacement / velocity measuring device. 2. The measuring head irradiates the first object to be measured with the first laser beam and separates the second laser beam into different directions; and a second beam splitter from the beam splitter. A deflection means for deflecting the laser beam and irradiating the second object to be measured, wherein the first and second reflected light beams reflected from the first and second object to be measured are returned to the polarization-preserving optical fiber. The displacement / velocity measuring device according to claim 1.