JPH0532739Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention relates to a vibration meter that uses the Doppler effect of light to measure vibrations of structures and machines without contact.

[Conventional technology]

Figure 2 is a configuration diagram of a vibration meter that measures the vibration of a vibrating object using the Doppler effect of light. In the figure, 1 is the vibrating object, 2 is a He-Ne laser, and 3a
4 is a beam splitter that splits the laser beam into two; 4 is a frequency shifter that acousto-optically shifts the frequency (wavelength) of one of the laser beams that has been split into two by the beam splitter 3a; and 5 is the frequency shift amount of frequency shifter 4. A driver 3b drives the frequency shifter 4 at an oscillation frequency corresponding to
6 is a condensing lens that collects the scattered light from the vibrating object 1, and 7 is the other half of the beam splitter 3a that does not pass through the frequency shifter 4, which is divided into two parts. 3c is a beam splitter that superimposes the scattered light from the moving object 1 that has been focused by the condenser lens 6 and the laser beam whose direction has been changed by the mirror 7; 8 is a beam splitter; A photodetector that converts the light of the ivy 3c into an electrical signal, 9 is an amplifier, 10
11 is an optical case that collects the components from the He-Ne laser 2 to the amplifier 9, 11 is a frequency tracker,
12 is a frequency-voltage converter (hereinafter referred to as an F/V converter).

As shown in Figure 2, the laser beam of frequency _O emitted from the He-Ne laser 2 is transmitted to the beam splitter 3.
One of the laser beams is split into two by a frequency shifter 4 and converted into a laser beam with a frequency _O + _S whose frequency is shifted by _S from the original laser frequency _O , and the laser beam is transmitted to the vibrating object 1 via the beam splitter 3b. The beam is irradiated parallel to the vibration direction.

The light scattered from the vibrating object 1 undergoes a Doppler shift depending on the vibration velocity v of the vibrating object 1. The scattered light that has undergone the Doppler shift is redirected by the beam splitter 3b and condensed by the condensing lens 6, and the other laser light that does not pass through the frequency shifter 4, which is split into two by the beam splitter 3a, is split into two by the beam splitter 3b.
The beam splitter 3c superimposes the light whose direction has been changed at ) There exists an alternating current signal (hereinafter referred to as a Doppler signal) with a Doppler frequency _d as shown in the equation.

_d = _s + 2v/λ ... (1) (where λ: wavelength of He-Ne laser) When the vibrating object 1 is vibrating sinusoidally at frequency _M and maximum vibration velocity v _O , its vibration velocity v is It can be expressed by equation (2).

v=v _O・sin (2π _M・t) ...(2) Therefore, the Doppler frequency _d in equation (1) is _d = _s + 2v ₀ /λ・sin (2π _M・t) ...(3) becomes.

Since the Doppler signal converted into an electrical signal by the photodetector 8 is weak, it is amplified by the amplifier 9, and then the Doppler frequency _d is detected by the frequency tracker 11, and the F/V
When converted into an analog voltage by the converter 12, the vibration velocity v of the vibrating object 1 is expressed as the AC signal in the second term of equation (3).
can be found.

This is a known fact.

[Problems to be solved by the invention] The conventional vibration meter described above has a length of 30 cm or more.
The optical case 10 is large in size to accommodate the components from the laser 2 to the amplifier 9, which poses problems such as inconvenience in handling and the inability to measure objects with only a narrow measurement space.

This invention was made to solve these problems, and the purpose is to obtain a non-contact vibrometer with a smaller and lighter optical case.

[Means for solving problems]

The vibrometer according to this invention uses two optical fiber cables to transmit and receive laser light, and only the transmitting and receiving optical system is provided in the optical case.

[Effect]

This idea uses an optical fiber cable to transmit and receive laser light, and by arranging only the transmitting and receiving optical system in the optical case, the optical case can be made smaller and lighter, making it easier to handle and measuring objects. You can spread things out.

〔Example〕

FIG. 1 is a block diagram of a vibration meter that utilizes the Doppler effect of laser light, showing one embodiment of this invention, and will be described below with reference to the drawings.

In the figure, 1, 2, 3a, 3c, 4-6, 8, 9,
Reference numerals 11 and 12 are the same as those of the above-mentioned conventional device. 13a
13b is an optical fiber cable for transmitting laser beams, 13b is an optical fiber cable for receiving scattered light, 14 is an optical connector connected to both ends of the optical fiber cables 13a and 13b, and 15 is an output laser beam of the transmitting optical fiber cable 13a. 16 is a hole-shaped mirror with a hole in the center that allows the irradiated laser beam to pass through and reflects the scattered light; 18 is a case that houses the collimator lens 15, hole-shaped mirror 16, and condensing lens 16. be.

In the vibration meter with the above configuration, the frequency shifter 4
However, the laser beam whose frequency has been shifted by _S from the original laser frequency _O is transmitted through the optical fiber cable 1 for transmission.
3a, the beam is transmitted to the case 17, and is turned into a parallel beam by the collimator lens 15. This parallel beam passes through the center of the perforated mirror 16 and is irradiated so as to be parallel to the vibration direction of the vibrating object 1.

Scattered light from the vibrating object 1 is reflected by the perforated mirror 16, condensed by the condensing lens 6 onto the receiving optical fiber cable 13b, and transmitted to the beam splitter 3c. The beam splitter 3c superimposes the laser beam having the original laser frequency _O and the above scattered light and guides it to the photodetector 8.

Thereafter, processing is performed in the same manner as in the conventional example, resulting in a vibrometer that measures the vibration velocity v of the vibrating object 1 shown in equation (3).

[Effect of idea]

As described above, according to this invention, the optical fiber cable 13 is used for transmitting and receiving laser light.
a, 13b, the case 17 can be made smaller and lighter by housing only the collimator lens 15 holes, the mirror 16, and the condenser lens 6, as well as separate optical fiber cables 1 for transmitting and receiving laser beams.
By using 3a and 13b, it is possible to provide a vibration meter that prevents interference between transmitted and received laser beams.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a vibration meter showing an embodiment of this invention, and FIG. 2 is a block diagram of a conventional vibration meter. In the figure, 13a and 13b are optical fiber cables,
14 is an optical connector, 15 is a collimator lens, 1
6 is a mirror with holes, and 17 is a case. In addition,
The same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of utility model claims] a laser that outputs a specific wavelength, a first beam splitter that splits the output beam of the laser into two, means for shifting the laser frequency of one of the two split laser beams by a specific frequency, and the frequency shifter. a first optical fiber cable for transmitting a laser beam transmitted from the first optical fiber cable; a collimator lens capable of parallelizing the output laser beam of the first optical fiber cable and irradiating the vibrating object parallel to its vibration direction; irradiate the laser beam from the collimator lens through the hole so as to be parallel to the vibration direction of the vibrating object, and reflect the scattered light that has undergone a Doppler shift in accordance with the vibration speed of the vibrating object in a predetermined direction. an optical case housing a hole-width mirror, a condensing lens for condensing the scattered light including the Doppler signal reflected by the hole-wielding mirror, and a second case for transmitting the scattered light including the Doppler signal received by the condensing lens. an optical fiber cable, and a second beam splitter that mixes the scattered light transmitted by the second optical fiber cable and the other laser beam that is not subjected to a frequency shift that is split by the first beam splitter. , a photodetector that electrically converts the mixed light, an amplifier that amplifies the output of the photodetector, a frequency tracker that detects a Doppler frequency from the output signal of the amplifier, and an output signal of the frequency tracker. A vibration meter comprising a frequency-voltage converter capable of outputting an analog voltage proportional to the vibration speed of a vibrating object from a Doppler frequency.