JPS6238365A - Velocity measuring instrument using laser beam - Google Patents

Abstract

PURPOSE:To measure the velocity of the body to be measured correctly by adjusting the positions of the optical system and the body to be measured based on the reflecting light of two laser beams irradiated on the measuring face in the velocity measuring instrument using laser beam by dual beam mode. CONSTITUTION:A laser beam is divided into two parallel beams by a beam splitter 2 and irradiated on the body 6 to be measured through a condensing lens 3. In this case, a beam 20 is reflected by the body 6 to be measured and inputted into a photoelectric transducer 12 by being reflected with a half-mirror 5 passing through the condensing lens 3. A beam 21 is reflected by the body 6 to be measured similarly as well and inputted to a photoelectric transducer 11. The position of the body 6 to be measured is then adjusted so as to make the output difference minimum by inputting the output of two photoelectric transducers 11, 12 to a differential convertor 13. After this adjustment, the reflecting beam from the body 6 to be measured is received to a photoelectric transducer 9 via reflection lens 7, condensing lens 8 in the dual beam mode and then the velocity is measured by a signal processor 10. The velocity of the body to be measured can therefore be measured with high accuracy due to the position of the body to be measured being adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a laser speed measuring device using a laser beam, and more particularly to a so-called dual beam mode laser speed measuring device.

[Prior art and its problems]

BACKGROUND ART Conventionally, devices for measuring particle velocity using laser light have been proposed, focusing on the characteristics of laser light that is excellent in coherence and monochromaticity, and in recent years, dual-beam laser velocimeters have been widely used. A dual-beam mode laser velocimeter intersects laser beams with the same polarization plane at one point to form interference fringes, and the scattered light generated when the object to be measured passes through the intersection area has a periodic pattern corresponding to the interference fringes. It is used to measure the velocity of an object because it has a change in intensity. By the way, in such a laser speed measurement device, when the object to be measured is a flat surface, it is necessary to irradiate two laser beams perpendicularly to the surface of the object to be measured to form interference fringes along the detection surface. It is difficult to set the optical system correctly in this way, so it is difficult to determine whether it is set correctly.
The drawback was that it took time and effort to adjust the optical system.

[Purpose of the invention]

The present invention solves these problems with conventional laser speed measuring devices, and adjusts the relative position between the optical system and the object to be measured based on the reflected light of the laser beam irradiated onto the measurement surface. By doing so, it is possible to provide a speed measuring device that can accurately match the angles between two laser beams and a measuring surface.

[Structure and effects of the invention]

The present invention has a laser light source, a beam splitter that separates the laser light into two laser beams, and a focusing lens that focuses the two laser beams, and uses a dual beam mode to adjust the frequency of the intensity change of the scattered light. This is a laser speed measurement device that measures speed based on a first laser beam, which is inserted into a passage path of a laser beam, transmits the laser beam, and separates the reflected lights of the two laser beams. Second
a first optical means; The first optical means converts the reflected light output of the second optical means into electrical signals corresponding to the respective optical intensities. Second
a photoelectric converter; The device is characterized in that it includes a differential amplifier that amplifies the output difference of the second photoelectric converter, and a display section that displays the output of the differential amplifier.

As described above, the optical system adjustment device according to the present invention can be easily added to a dual beam mode laser velocity measuring device. According to the present invention, since the difference in intensity between the reflected lights of the two laser beams is always displayed on the display unit,
The arrangement of the optical system and the position of the object to be measured can be adjusted so that the indicated value becomes smaller. If the indicated value becomes zero, the object to be measured is located in the area where the two laser beams intersect, that is, the area where interference fringes are formed, and the two laser beams and the surface of the object to be measured are located. It is known that the position is exactly vertical. Therefore, if the speed of the object to be measured is measured in the dual beam mode after performing such position adjustment, accurate measurement becomes possible.

[Explanation of Examples]

FIG. 1 is a block diagram showing an embodiment of a laser velocity measuring device according to the present invention. In this figure, a laser light source 1 is a single frequency laser light source and provides a laser output to a beam splinter 2. The beam splitter 2 separates the laser light into two parallel laser beams having the same signal intensity and plane of polarization, and these laser beams are applied to the focusing lens 3. A half mirror 4.degree. 5 is provided between the beam splitter 2 and the focusing lens 3 to transmit the laser beam directed from the beam splitter 2 toward the focusing lens 3. The optical system of the speed measuring device and the object to be measured 6 are arranged at the focal position of the focusing lens 3 so that the wall surface of the object whose speed is to be detected is perpendicular to the two laser beams. A reflecting mirror 7 is provided between the two laser beams between the beam splitter 2 and the focusing lens 3 to reflect the scattered light. A condenser lens 8 that condenses the scattered light is located at a position facing the condenser lens 3 via the reflector 7.
is provided, and a photoelectric converter 9 is provided at the focal position of the condenser lens 8. The photoelectric converter 9 converts scattered light into an electrical signal, and is made of, for example, an avalanche type photodiode, and provides the photoelectrically converted electrical signal to the signal processing device 1o. The signal processing device 10 detects the object to be measured 6 by measuring the frequency of the output signal of the photoelectric converter 9.
It calculates and outputs the speed of Now, in the present invention, two more photoelectric converters 11 and 12 are provided at positions for receiving reflected light from the half mirrors 4 and 5 provided between the beam splitter 2 and the focusing lens 3. Photoelectric converter 11.1
Reference numeral 2 detects the level of reflected light intensity, and its output is given to the differential amplifier 13 as a DC signal. The differential amplifier 13 amplifies the potential difference between these output levels and provides the amplified output to the voltmeter 14.

Next, the operation of the laser speed measuring device of this embodiment will be explained. The laser beam oscillated from the laser light source 1 is split into two parallel laser beams 20 and 21 by the beam splitter 2.
The light beams are separated into two and are irradiated onto the surface of the object to be measured 6 through the focusing lens 3. Here, if the surface of the object to be measured 6 is flat, the reflected light of one of the laser beams 20 is reflected at an angle equal to the angle formed with the surface, and is applied to the focusing lens 3 again. Similarly, the other laser beam 21
is applied to the object to be measured 6 through the focusing lens 3, and its reflected light is transmitted to the focusing lens 3 again.

If the angle between the laser beam 20 and the surface of the object to be measured 6 is 01 as shown in the figure, the angle between the reflected light and the object to be measured 6 is also equal to θ1.

Similarly, if the angle between the laser beam 21 and the surface of the object to be measured 6 is 02, the angle between the reflected light and the object to be measured 6 is also equal to θ2. Half mirrors 4 and 5 provide these reflected lights to photoelectric converters 11 and 12, respectively. Signals having a level corresponding to the reflected light intensity are obtained from the photoelectric converters 11 and 12, and the DC output thereof is amplified by the differential amplifier 13 and displayed by the voltmeter 14. Here, the object to be measured 6 is rotated about the irradiation point as shown by arrow A in FIG. 1, and the position where the value of the voltmeter 14 is minimum is found. When this is the minimum, the difference in intensity between the reflected lights of the two laser beams 20 and 21 is the minimum. Next, the object to be measured 6 is directed in the direction of arrow B, that is, the laser beam 20.
21 and find the position where the value of the voltmeter 14 becomes zero.

The two laser beams 20 and 21 intersect on the surface of the object to be measured 6 and form an angle θ1. When θ2 is equal, the reflected light of the laser beam 20 is the laser beam 21
The laser beam passes through a line equal to
given to. In this case, the laser beam 21 is reflected by the surface of the object to be measured 6, passes along the same line as the laser beam 20, and is reflected perpendicularly to the laser beam 20 by the half mirror 4, so that the maximum amount of light is transmitted to the photoelectric converter. 11 and is converted into an electrical signal. Since these electrical signal outputs are equal when θ1 and 02 are equal, the voltage difference between them is also O. If the object to be measured 6 is placed at a position where the display on the voltmeter 14 becomes zero in this way, the surface of the object to be measured 6 will be perpendicular to the two laser beams 20 and 21 and will be in the intersection area. be arranged to be located. Therefore, it is extremely easy to adjust the optical system to such an arrangement, and it becomes possible to accurately measure the speed of the object to be measured 6 using the dual beam mode laser speed measuring device.

In this example, all the optical systems were arranged so as to have a predetermined positional relationship directly with respect to the object to be measured.
A polarization-preserving optical fiber is provided between the laser light source 1 and the beam splitter 2, and a polarization-preserving optical fiber is provided between the half mirrors 4 and 5 and the photoelectric converters 11 and 12, and between the condenser lens 8 and the photoelectric converter. It is also possible to configure the optical system and the signal processing system to be separated from each other by connecting them to the device 9 through optical fibers.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a laser velocity measuring device according to the present invention. 1--------Laser light source 2--Beam splitter 3--11111 Focusing lens 4. 5---
−・Half mirror−6−−−−−・Object to be measured 7−
...-Reflection@8--Condensing lens 9, 11
, 12------One photoelectric converter 10------
- Signal processing device 13...--Differential amplifier 14
・－・・・・・・－Voltmeter

Claims (2)

[Claims] (1) It has a laser light source, a beam splitter that separates the laser light into two laser beams, and a focusing lens that focuses the two laser beams, and uses a dual beam mode to change the frequency of the intensity of scattered light. A laser speed measuring device that measures speed based on the following: first and second optical means inserted into the passage path of the laser beam to transmit the laser beam and separate reflected lights of the two laser beams, respectively. and first and second photoelectric converters that convert reflected light outputs of the first and second optical means into electrical signals corresponding to the light intensities thereof, respectively; and of the first and second photoelectric converters. A laser speed measuring device comprising: a differential amplifier that amplifies an output difference; and a display section that displays the output of the differential amplifier. (2) The laser speed measuring device according to claim 1, wherein the first and second optical means are half mirrors.