CN118731908A - An optical device for measuring solid motion velocity based on laser Doppler effect - Google Patents

Abstract

The present invention belongs to the field of laser measurement technology, and relates to a device for measuring the speed of solid motion. Specifically, it provides an optical device for measuring the speed of solid motion based on the laser Doppler effect, which is used to solve the problems of the high price of narrow-linewidth visible light lasers and the complex optical path structure in existing laser Doppler velocimeters. The present invention proposes a new optical path structure, using a narrow-linewidth non-visible light laser diode as a light source and a wide-linewidth visible light laser diode as an indicator light source to achieve Doppler frequency detection of the moving solid surface, and calculate the speed (rotation speed) and length of the solid motion according to the Doppler frequency; wherein the narrow-linewidth non-visible light laser diode has strong versatility and low cost, and the wide-linewidth visible light laser diode has even lower cost, thereby significantly reducing the cost of the velocimeter system, and the solid motion speed measurement optical device provided by the present invention has a simple structure and is easy to adjust.

Description

An optical device for measuring solid motion velocity based on laser Doppler effect

Technical Field

The invention belongs to the technical field of laser measurement, relates to a device for measuring solid motion speed, and specifically provides an optical device for measuring solid motion speed based on the laser Doppler effect.

Background Art

With the development of modern industrial technology, the requirements for system automation are also increasing. In industrial production, not only are there high requirements for the working stability of automated machines, but also for their measurement accuracy. For example, the length measurement of metal sheets, the speed measurement of non-woven fabrics, the speed and length measurement of wires and cables on industrial production lines all require high-precision instruments for monitoring and real-time measurement. Traditional measurement methods cannot meet the high-precision measurement requirements on industrial production lines with complex conditions such as high temperature and high speed. The laser Doppler effect-based velocimeter just makes up for this shortcoming. The laser Doppler velocimeter has the advantages of high accuracy, non-contact measurement, and a large measurement range, and is widely used in industrial production and other fields. However, most laser Doppler velocimeters use narrow linewidth (<1MHz) visible light lasers as light sources, but due to international factors, such lasers are expensive (20,000 to 40,000 yuan) and difficult to purchase, resulting in a high cost of velocimeters, which seriously limits the promotion and application of laser Doppler velocimeters.

Summary of the invention

The purpose of the present invention is to provide an optical device for measuring the velocity of solid motion based on the laser Doppler effect, so as to solve the problems of the existing laser Doppler velocimeter, such as the high price of the narrow line width visible light laser and the complex optical path structure. The present invention proposes a new optical path structure, using a narrow line width non-visible light laser diode as a light source and a wide line width visible light laser diode as an indicator light source, to achieve Doppler frequency detection of the moving solid surface, and to calculate the velocity (rotation speed) and length of the solid motion according to the Doppler frequency; wherein the narrow line width non-visible light laser diode has strong versatility and low cost, and the wide line width visible light laser diode has even lower cost, thereby significantly reducing the cost of the velocimeter system, and the solid motion velocity measurement optical device in the present invention has a simple structure and is easy to adjust.

To achieve the above object, the technical solution adopted by the present invention is:

An optical device for measuring solid motion velocity based on the laser Doppler effect, comprising: a narrow line width non-visible light laser diode 1, a wide line width visible light laser diode 2, an aspherical mirror 3, a beam splitter prism 4, a beam splitter 5, a collecting lens 6, and a photodetector 7; the characteristics are:

There are two aspherical mirrors 3, which are respectively arranged at the front ends of the narrow linewidth invisible light laser diode 1 and the wide linewidth visible light laser diode 2;

The laser emitted by the narrow line width non-visible light laser diode 1 is collimated by the aspheric mirror 3 and then divided into two beams by the beam splitter prism 4. One beam of light is irradiated to the surface of the object 8 to be measured through the beam splitter prism 4, and the other beam of light is reflected by the beam splitter prism 4 and then incident on the beam splitter 5, and then reflected by the beam splitter 5 to the surface of the object 8 to be measured. The two beams of light converge and interfere on the surface of the object 8 to be measured; the scattered light of the coherent light on the surface of the object 8 to be measured is collected by the collecting lens 6 and converged to the photoelectric detector 7;

The wide line width visible light laser diode 2 is arranged at a 90 degree position relative to the narrow line width invisible light laser diode 1 with the beam splitter prism 4 as a reference;

The laser emitted by the wide-linewidth visible light laser diode 2 is collimated by the aspheric mirror 3 and then divided into two beams by the beam splitter prism 4. One beam of light is incident on the beam splitter 5 through the beam splitter prism 4 and then reflected by the beam splitter 5 to the surface of the object to be measured 8. The other beam of light is reflected by the beam splitter prism 4 and irradiated to the surface of the object to be measured 8. The two beams of light also converge on the surface of the object to be measured 8 and overlap with the light spot formed by the laser emitted by the narrow-linewidth invisible light laser diode 1 on the surface of the object to be measured 8.

Furthermore, the narrow linewidth non-visible light laser diode 1 adopts a 1550nm DFB laser diode.

Furthermore, the wide-linewidth visible light laser diode 2 adopts a 685nm F-P laser diode.

Furthermore, the beam splitter prism 4 is a non-polarized beam splitter prism with a wavelength of 1200 nm to 1600 nm, and the beam splitting ratio is 50:50.

Furthermore, the beam splitter 5 uses a 1550nm polarization beam splitter.

Furthermore, the collecting lens 6 is a plano-convex lens with a focal length of 50 mm and a diameter of 20 mm, with its flat surface facing the object to be measured 8 and its convex surface facing the photodetector 7 .

In terms of working principle:

The present invention provides an optical device for measuring the motion speed of a solid based on the laser Doppler effect. A new optical path structure is creatively proposed. A narrow line width non-visible light laser diode 1 is used as a light source. The Doppler frequency of a moving solid can be detected through optical heterodyne technology, and then the motion speed and length of the solid can be obtained according to the Doppler frequency. The low-cost (2,000 to 5,000 yuan) and widely used narrow line width non-visible light laser diode is used to replace the expensive (20,000 to 40,000 yuan) and difficult to purchase narrow line width (<1MHz) visible light laser, which can significantly reduce the laser Doppler measurement cost. The system cost of the speed meter is reduced; and in order to solve the problem that the non-visible light source cannot be observed, the present invention uses a wide-linewidth visible light laser diode 2 with a lower cost (hundreds of yuan) as an indicator light source, and sets an indicator light source at a 90-degree position based on the dichroic prism on the narrow-linewidth non-visible light laser diode 1. The optical path formed by the dichroic prism 4 and the dichroic mirror 5 is cleverly used, so that the convergent light points of the light source and the indicator light source on the surface of the measured object 8 must coincide. Therefore, the non-visible light source can be indicated by the convergent light points of the indicator light source on the surface of the measured object 8, that is, the placement orientation of the measured object 8 is determined.

In summary, the beneficial effects of the present invention are:

The present invention provides an optical device for measuring the motion speed of a solid based on the laser Doppler effect. A new optical path structure is creatively proposed. A narrow linewidth non-visible light laser diode 1 is used as a light source, and a wide linewidth visible light laser diode 2 is used as an indicator light source. The Doppler frequency of a moving solid can be detected by optical heterodyne technology, and then the motion speed and length of the solid can be obtained according to the Doppler frequency. By replacing an expensive and difficult to purchase narrow linewidth visible light laser with a low-cost and widely used narrow linewidth non-visible light laser diode and a wide linewidth visible light laser diode, the system cost of the laser Doppler velocimeter can be significantly reduced. In addition, the laser Doppler velocimeter has the advantages of simple structure, convenient adjustment, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram showing the principle of an optical device for measuring solid motion velocity based on the laser Doppler effect provided by the present invention.

FIG. 2 is a schematic diagram of the structure of an optical device for measuring solid motion velocity based on the laser Doppler effect provided by the present invention.

DETAILED DESCRIPTION

In order to make the purpose, technical solution and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

Example 1

This embodiment provides an optical device for measuring the velocity of solid motion based on the laser Doppler effect, the principle of which is shown in FIG1 , and specifically comprises: a narrow line width non-visible light laser diode 1, a wide line width visible light laser diode 2, an aspherical mirror 3, a beam splitter prism 4, a beam splitter 5, a collecting lens 6, and a photodetector 7; wherein,

There are two aspherical mirrors 3, which are respectively arranged at the front ends of the narrow linewidth invisible light laser diode 1 and the wide linewidth visible light laser diode 2;

The laser emitted by the narrow line width non-visible light laser diode 1 is collimated by the aspheric mirror 3 and then divided into two beams by the beam splitter prism 4. One beam of light is irradiated to the surface of the object 8 to be measured through the beam splitter prism 4, and the other beam of light is reflected by the beam splitter prism 4 and then incident on the beam splitter 5, and then reflected by the beam splitter 5 to the surface of the object 8 to be measured. The two beams of light converge and interfere on the surface of the object 8 to be measured; the scattered light of the coherent light on the surface of the object 8 to be measured is collected by the collecting lens 6 and converged to the photoelectric detector 7;

The wide line width visible light laser diode 2 is arranged at a 90 degree position relative to the narrow line width invisible light laser diode 1 with the beam splitter prism 4 as a reference;

The laser emitted by the wide-linewidth visible light laser diode 2 is collimated by the aspheric mirror 3 and then divided into two beams by the beam splitter prism 4. One beam of light is incident on the beam splitter 5 through the beam splitter prism 4 and then reflected by the beam splitter 5 to the surface of the object to be measured 8. The other beam of light is reflected by the beam splitter prism 4 and irradiates the surface of the object to be measured 8. The two beams of light also converge on the surface of the object to be measured 8 and overlap with the light spot formed by the laser emitted by the narrow-linewidth invisible light laser diode 1 on the surface of the object to be measured 8, so as to indicate the invisible light and facilitate system debugging.

Specifically, in this embodiment, the narrow-linewidth non-visible light laser diode 1 adopts a 1550nm DFB laser diode, and the wide-linewidth visible light laser diode 2 adopts a 685nm F-P laser diode; the beam splitter prism 4 adopts a 1200nm-1600nm non-polarizing beam splitter prism with a splitting ratio of 50:50; the beam splitter 5 adopts a 1550nm polarizing beam splitter; the collecting lens 6 adopts a plano-convex lens with a focal length of 50mm and a diameter of 20mm, with its flat surface facing the object to be measured 8 and its convex surface facing the photodetector 7; by selecting the beam splitter prism 4 and the beam splitter 5 with a suitable wavelength near 1550nm, the collecting lens 6 can almost only receive 1550nm light, eliminating the influence of the 685nm indicator light on the system. On this basis, the actual object of the solid motion velocity measurement optical device based on the laser Doppler effect in this embodiment is shown in Figure 2. The 1550nm DFB laser diode and the 685nm F-P laser diode are respectively installed on the preset laser diode clamps, and temperature control modules 9 are respectively arranged under the clamps to ensure that the laser diodes work for a long time; the aspheric mirror, non-polarizing beam splitter prism, plano-convex lens, and polarizing beam splitter are also respectively fixed on the corresponding mounting parts. At the same time, slide rails are respectively arranged under the aspheric mirror to facilitate the laser collimation work. When the laser is working normally, the aspheric mirror is moved. When the spot size behind the aspheric mirror is basically consistent with the spot size on the surface of the object 8 to be measured, the laser collimation work is completed; and the plano-convex lens is arranged perpendicular to the scattered light of the coherent light on the surface of the object 8 to be measured to improve the utilization rate of the scattered light.

Furthermore, the straight-line distance from the center of the non-polarizing beam splitter prism to the center of the polarizing beam splitter is 35 mm, and the straight-line distance from the center of the non-polarizing beam splitter prism to the surface of the object 8 to be measured (where the two laser beams converge on the surface of the object 8 to be measured) is 400 mm. Thus, the angle θ of the two laser beams reaching the surface of the object 8 to be measured can be calculated, that is: Then θ≈5°;

Based on the above optical device, the Doppler frequency of moving solids can be detected by optical heterodyne technology. The current signal output by the photodetector is converted by A/D and frequency extracted by the subsequent signal processing system to obtain the Doppler frequency f _D . Then, the speed of the moving object is calculated according to the relationship between the Doppler frequency and the speed. The relationship is specifically:

Wherein, v is the velocity of the object being measured, _fD is the Doppler frequency, λ is the laser wavelength of the narrow linewidth non-visible light laser diode, and θ is the angle between the two beams of light converging on the surface of the object being measured;

By integrating the velocity, we can get the length of the measured object moving in a certain period of time. The solution formula for integrating the velocity within _t0 to get its length is:

In summary, the present invention provides an optical device for measuring solid motion speed based on the laser Doppler effect, which can detect the Doppler frequency of a moving solid through optical heterodyne technology, thereby measuring the solid motion speed and length.

The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and/or steps, can be combined in any way.

Claims (6)

1. A laser doppler effect based solid motion velocity measurement optical device comprising: a narrow linewidth invisible light laser diode (1), a wide linewidth visible light laser diode (2), an aspherical mirror (3), a beam splitting prism (4), a beam splitter (5), a collecting lens (6) and a photoelectric detector (7); the method is characterized in that:

the number of the aspherical mirrors (3) is two, and the aspherical mirrors are respectively arranged at the front ends of the narrow-linewidth invisible light laser diode (1) and the wide-linewidth visible light laser diode (2);

The laser emitted by the narrow linewidth invisible light laser diode (1) is collimated by the aspheric mirror (3) and then split into two beams by the beam splitting prism (4), one beam of light irradiates the surface of the object (8) to be detected through the beam splitting prism (4), the other beam of light is reflected by the beam splitting prism (4) and then enters the beam splitter (5) and then is reflected by the beam splitter (5) to the surface of the object (8) to be detected, and the two beams of light are converged and interfered on the surface of the object (8) to be detected; scattered light of coherent light on the surface of a measured object (8) is collected and converged into a photoelectric detector (7) through a collecting lens (6);

The wide-linewidth visible light laser diode (2) is arranged on a 90-degree azimuth of the narrow-linewidth invisible light laser diode (1) taking the beam-splitting prism (4) as a reference;

The laser emitted by the wide-linewidth visible light laser diode (2) is collimated by the aspheric mirror (3) and then is divided into two beams by the beam splitting prism (4), one beam of light is incident on the beam splitting prism (5) through the beam splitting prism (4) and then is reflected to the surface of the measured object (8) by the beam splitting prism (5), the other beam of light is reflected by the beam splitting prism (4) and then irradiates the surface of the measured object (8), and the two beams of light are converged on the surface of the measured object (8) and coincide with a light spot formed by the laser emitted by the narrow-linewidth invisible light laser diode (1) on the surface of the measured object (8).

2. The solid state movement velocity measurement optical device based on the laser doppler effect according to claim 1, characterized in that the narrow linewidth non-visible laser diode (1) employs a DFB laser diode of 1550 nm.

3. The solid motion velocity measurement optical device based on laser doppler effect according to claim 1, characterized in that the wide linewidth visible laser diode (2) adopts an F-P laser diode of 685 nm.

4. The solid motion velocity measurement optical apparatus based on the laser doppler effect according to claim 1, wherein the beam-splitting prism (4) adopts a non-polarized beam-splitting prism with a beam-splitting ratio of 50:50.

5. The solid motion velocity measurement optical device based on the laser doppler effect according to claim 1, characterized in that the spectroscope (5) employs a 1550nm polarizing beamsplitter.

6. The solid motion velocity measurement optical device based on the laser doppler effect according to claim 1, characterized in that the collecting lens (6) adopts a plano-convex lens with a focal length of 50mm and a diameter of 20mm, the plane of which faces the object (8) to be measured and the convex face of which faces the photodetector (7).