Annularly-distributed multi-reflector laser triangulation distance measuring sensor

Abstract

The invention discloses a novel annularly-distributed multi-reflector laser triangulation distance measuring sensor which adopts a plurality of plane reflectors which are annularly or conically distributed. Light spots formed by irradiating laser to the surface of a measured target enter the lens after being reflected by the plurality of plane reflectors, are imaged on the image surface of the camera after passing through the lens, and form a series of annularly distributed image spots. And the diameter of the circular ring corresponds to the measured distance of the target, so that laser ranging can be realized. When the laser directivity is changed, the position of the circular ring is also changed, but the diameter of the circular ring is not changed, so that the influence of the laser directivity change can be thoroughly overcome in principle. According to the method, the laser directivity problem can be thoroughly solved, the distance measurement precision is remarkably improved, the cost of the multiple plane reflectors is far lower than that of an annular reflector, the precision is determined by a support and is easy to guarantee, and the method has wider practicability and universality.

Description

Technical Field

[0001] The present invention relates to a distance measuring sensor, in particular to a laser triangulation distance measuring sensor which can overcome the change of laser directivity and has a plurality of annularly distributed plane reflectors. Background Art

[0002] There are generally four principles for laser ranging methods: laser time of flight (ToF), laser phase difference, laser triangulation and laser confocal method. The time of flight method uses the flight time of the laser pulse to measure the target distance. It is only suitable for long-distance measurement and has low accuracy when measuring close distances. The phase difference method uses the continuous fluctuation phase difference of the laser to measure the target distance. It is suitable for terminal distance measurement, but the accuracy is still very low. The laser triangulation method is a method based on the principle of laser triangulation to measure the target distance. It has excellent characteristics such as high accuracy and large range, making it the preferred method for short-distance high-precision ranging. The laser confocal method uses the principle of laser dispersion to measure the target distance. It is characterized by extremely high absolute accuracy, but the range is also extremely small, and its application is obviously limited.

[0003] For laser triangulation ranging sensors, the laser beam is its working medium and also the ranging reference. When the laser beam directivity changes, it will cause the position of the measuring spot imaging to change, thus causing measurement errors. Especially for the case of using semiconductor lasers, its directivity has both jitter and drift, which will affect the repeatability and stability of the ranging mutual inductor.

[0004] Some scholars have expanded the classic laser triangulation ranging structure and established two symmetrical structures on the left and right to measure the object to be measured from two directions. This solution can weaken the influence of the change in the directivity of the laser beam, but it cannot completely eliminate it. In particular, when two different optoelectronic devices are used on the left and right, the compensation effect will be greatly reduced. At the same time, this symmetrical structure system is complex, expensive, difficult to implement, and difficult to promote and apply.

[0005] The applicant has also proposed a laser triangulation ranging sensor with an annular reflector, which reflects the laser spot on the surface of the target in a 360° circle, and then forms an image on the image plane of the camera through the lens, forming an imaging ring. The diameter of the imaging ring corresponds to the measured distance of the target, so laser ranging can be achieved. When the laser directivity changes, the position of the imaging ring also changes, but the diameter of the imaging ring does not change. In principle, the influence of the change in laser directivity can be completely overcome, and the ranging accuracy can be significantly improved. However, the annular reflector is difficult to manufacture, the cost is high, and the assembly precision requirements are high. It is difficult to implement, the precision is not easy to guarantee, and the cost performance is not high, which limits the practical application of the technical solution. Summary of the invention

[0006] Aiming at the defects and shortcomings of the existing laser triangulation ranging sensor that is sensitive to the change of laser directivity, the present invention proposes a ring-shaped or conical distribution of multiple reflectors of the laser triangulation ranging sensor. The light spot formed by the laser irradiating the surface of the measured target enters the lens after being reflected by multiple ring-shaped plane reflectors, and is imaged on the image plane of the camera through the lens, forming a series of circular image spots distributed in a ring. The diameter of the ring formed by the center of this series of image spots is in a corresponding relationship with the measured distance of the target, thereby realizing laser triangulation ranging. When the laser directivity changes, the position of the ring also changes, but the diameter of the ring does not change, thereby completely overcoming the influence of the change of laser directivity in principle. This method can not only completely solve the problem of laser directivity and significantly improve the ranging accuracy, but also the cost of multiple plane reflectors is much lower than that of the ring reflector, and the installation accuracy is determined by the bracket and is easy to ensure. The overall structure of the sensor is axisymmetric, with wider practicality and versatility.

[0007] The present invention is achieved through the following technical solutions: The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the sensor comprises a camera, a lens, a laser, a focusing lens, a filter, a reflector, a bracket, a housing, and a socket, wherein: The camera is an industrial-grade area array camera, located at the top of the sensor, fixed on the housing, and responsible for converting the reflection signal of the laser spot into an image digital signal; The lens is an industrial-grade lens, which is directly mounted on the camera and is responsible for imaging the light spot signal reflected by the reflector onto the image plane of the camera; The laser is an industrial-grade semiconductor laser, located at a distance below the lens, and installed at the center of the bracket so that the optical axis of the laser is coaxial with the optical axis of the lens, and is used to generate a laser beam and project it to the focusing lens; The focusing mirror is a focusing collimating mirror group, which is also installed at the center of the bracket and the front end of the laser. Its optical axis is coaxial with the laser and the lens optical axis. The focusing mirror keeps a certain distance from the laser and is responsible for focusing the divergent laser beam generated by the laser, projecting it onto the surface of the target to be measured and forming a laser spot. It also has a certain collimation function. The filter is a narrow-band filter, the central wavelength of which is consistent with the central wavelength of the laser, and can filter out interference from ambient light of other wavelengths; The reflector is a plane reflector, which has multiple pieces, close to the bracket, with the lens optical axis as the symmetry axis, and distributed in a ring or cone shape, which can reflect the laser spot from all directions of 360° and project it to the lens; The bracket is directly fixed in the housing and is used to simultaneously position the laser, focusing mirror and multiple reflectors to ensure that the laser, focusing mirror and all reflectors are coaxial, and has a hollow structure so that the reflected light beam can pass through and enter the lens; The housing is made of metal material, which can fix all the internal components and parts on one hand, and can also be used for installation, positioning and fixing of the entire sensor on the other hand; The socket is a universal industrial-grade socket, which is arranged on the sealing cover and is used for power supply and data transmission.

[0008] The working process of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is as follows: the divergent laser beam emitted by the laser is converged by the focusing mirror to form a focused laser beam, which is projected onto the surface of the target to be measured and forms a measuring light spot. The measuring light spot enters the lens after being reflected by multiple annularly distributed plane reflectors, and then is imaged on the image plane of the camera through the lens, forming a series of image spots distributed in a circular ring. When the distance to the target to be measured changes, the diameter of the ring formed by the center of these image spots also changes accordingly, thereby achieving ranging. When the laser directivity changes, the center position of the ring formed by the center of these image spots also changes accordingly, but the diameter of the ring does not change, thereby overcoming the influence of laser directivity drift.

[0009] The special feature of the annular distributed multi-reflector laser triangulation ranging sensor of the present invention is that the bracket adopts an integrated axisymmetric structure and is hollow inside, which is used to fix the laser and the focusing lens, ensuring that the optical axes of the laser and the focusing lens are coaxial with the optical axis of the lens; the base is a spoke-type hollow structure, ensuring that the reflected light of the reflector can pass through the bracket and enter the lens.

[0010] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the cross-section of the bracket is an equilateral polygon structure, which is used to fix multiple plane reflectors to form an annular distribution; the axial cross-section of the bracket is rectangular or trapezoidal, depending on different ranges and accuracies.

[0011] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the symmetry error of the polygonal structure of the bracket cross section should be high enough, generally not less than 1 / 5 of the ranging accuracy, so as to meet the requirements of ranging accuracy.

[0012] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the reflectors are high-reflectivity plane reflectors, which are generally not less than 90%; there are multiple reflectors, and their number is the same as the number of sides of the polygonal cross-section of the bracket.

[0013] The special feature of the annularly distributed multi-reflector laser triangulation distance measurement sensor of the present invention is that the distance between the annularly distributed multi-reflector and the lens should be greater than the closest measurement distance.

[0014] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the length of the annularly distributed multi-reflector should meet the requirement of the farthest measuring distance and should be greater than half of the difference between the farthest distance and the shortest distance.

[0015] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the housing is made of metal material, thereby ensuring the overall stability and reliability of the sensor.

[0016] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the shell adopts an integrated structure with a hollow interior for fixing all components, thereby ensuring the position accuracy and stability of all components and reducing the overall weight of the sensor.

[0017] The present invention proposes a processing method based on the above-mentioned annularly distributed multi-reflector laser triangulation ranging sensor, which is specifically as follows: (1) Turn on the laser to generate a laser beam that is projected onto the surface of the target to be measured, forming a laser spot. The laser spot is reflected by multiple plane mirrors and enters the lens, forming multiple image spots on the camera imaging surface. (2) Collect images from a camera and send them to a computer for processing; (3) Process each image spot separately and extract the corresponding centroid point and its coordinates; (4) Using the coordinates of the centroids of multiple image spots to perform circle fitting, the coordinates of the center of the circle and the radius are obtained; (5) Using the saved calibration curve data, calculate the corresponding distance value of the measured target. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the sensor composition of the present invention; Figure 2 It is a schematic diagram of the support structure of the present invention; Figure 3 It is a schematic diagram of the shell structure of the present invention; Figure 4 It is a schematic diagram of the data processing principle of the present invention.

[0019] In the figure, 1-camera, 2-lens, 3-laser, 4-focusing lens, 5-filter, 6-reflector, 7-bracket, 8-housing, 9-socket, 10-target to be measured. DETAILED DESCRIPTION

[0020] The following is a detailed description of an embodiment of the present invention in conjunction with the accompanying drawings. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and a specific operation process, but the protection scope of the present invention is not limited to the following embodiment.

[0021] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the sensor comprises a camera 1, a lens 2, a laser 3, a focusing lens 4, a filter 5, a reflector 6, a bracket 7, a housing 8, and a socket 9. Figure 1 As shown, where: The camera 1 is an industrial-grade area array camera, located at the top of the sensor, fixed on the housing 9, and responsible for converting the laser spot signal into an image digital signal; The lens 2 is an industrial-grade lens, which is directly mounted on the camera 1 and is responsible for imaging the laser signal reflected by the reflector 6 onto the image plane of the camera 1; The laser 3 is an industrial-grade semiconductor laser, which is installed at the center of the bracket 7 so that the optical axis of the laser 3 is coaxial with the optical axis of the lens 2, and is used to generate a laser beam and project it to the focusing lens 4; The focusing mirror 4 is a focusing collimating lens group, which is also installed at the center of the bracket 7 and the front end of the laser 3. Its optical axis is coaxial with the optical axis of the laser 3 and the lens 2. The focusing mirror 4 is kept at a distance from the laser 3 and is responsible for focusing the divergent laser beam generated by the laser 3, projecting it onto the surface of the target 10 to form a laser spot, and at the same time has a certain collimation function; The filter 5 is a narrow-band filter, the center wavelength of which is consistent with the center wavelength of the laser 3, and can filter out interference from ambient light of other wavelengths; The reflector 6 is a plane reflector, and there are a plurality of plane reflectors, for example, 8 plane reflectors 6; the reflector 6 is close to the bracket 7, with the optical axis of the lens 2 as the axis of symmetry, and is distributed in a ring or cone shape, and can reflect the laser spot from all directions of 360° and project it to the lens 2; The bracket 7 is directly fixed in the housing 8, and is used to simultaneously position the laser 3, the focusing mirror 4 and the multiple reflectors 6, ensuring that the laser 3, the focusing mirror 4 and all the reflectors 6 are coaxial, and has a hollow structure so that the reflected light beam can pass through and enter the lens 2; The housing 8 is made of metal material, which can fix all the internal components and parts on one hand, and can also be used for installation, positioning and fixing of the entire sensor on the other hand; The socket 9 is a universal industrial-grade socket, which is placed on the sealing cover and is used for power supply and data transmission.

[0022] The working process of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is as follows: the divergent laser beam emitted by the laser 3 is converged by the focusing mirror 4 to form a focused laser beam, which is projected onto the surface of the target 10 to be measured after passing through the filter 5 and forms a measuring light spot. The measuring light spot enters the lens 2 after being reflected by the multiple plane reflectors 6 distributed in an annular manner, and is imaged on the image plane of the camera 1 through the lens 2 to form a series of annularly distributed image spots. When the distance to the target 10 to be measured changes, the diameter of the ring formed by the center of these image spots also changes accordingly, thereby achieving ranging. When the laser directivity changes, the center position of the ring formed by the center of these image spots also changes accordingly, but the diameter of the ring does not change, thereby overcoming the influence of the laser directivity drift.

[0023] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the bracket 7 adopts an integrated axisymmetric structure, such as Figure 2 As shown, the interior is hollow and is used to fix the laser 3 and the focusing lens 4, ensuring that the optical axes of the laser 3 and the focusing lens 4 are coaxial with the optical axis of the lens 2; the base is a spoke-type hollow structure, ensuring that the reflected light of the reflector 6 can pass through the bracket 7 and enter the lens 2.

[0024] The special feature of the annular distribution multi-reflector laser triangulation ranging sensor of the present invention is that the cross section of the bracket 7 is an equilateral polygon structure, which is used to fix multiple plane reflectors 6 to form an annular distribution; the axial cross section of the bracket 7 is a rectangular row or a trapezoid, depending on different ranges and accuracies; for example Figure 2 The bracket 7 shown has an equilateral octagonal cross section, and can be used to mount eight plane reflectors with a trapezoidal axial cross section.

[0025] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the symmetry error of the polygonal structure of the bracket 7 should be high enough, generally not less than 1 / 5 of the ranging accuracy, so as to meet the requirements of ranging accuracy.

[0026] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the reflector 6 is a high-reflectivity plane reflector, which is generally not less than 90%, such as an aluminum-plated reflector; there are a plurality of reflectors 6, and the number of the reflectors 6 is the same as the number of sides of the cross-sectional polygon of the bracket 7; for example Figure 2 The bracket shown in the figure is octagonal and can be used to fix eight plane mirrors.

[0027] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the distance between the annularly distributed multi-reflector 6 and the lens 2 should be greater than the closest measuring distance; for example, if the closest measuring distance of the lens 2 is 100 mm, the distance between the reflector 6 and the lens 2 should be preferably greater than 110 mm.

[0028] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the length of the annularly distributed multi-reflector 2 should meet the requirements of the farthest measuring distance and should be greater than half of the difference between the farthest distance and the closest distance; for example, for the lens 2, the closest measuring distance is 100mm, the range is 50mm, and the farthest measuring distance is 150mm, then the length of the reflector 6 should be greater than 75mm.

[0029] The special feature of the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention is that the housing 8 is made of metal materials, such as aluminum alloy, stainless steel, etc., which ensures the overall stability and reliability of the sensor.

[0030] The special feature of the annular distributed multi-reflector laser triangulation ranging sensor of the present invention is that the housing 8 adopts an integrated structure with a hollow interior for fixing all components, thereby ensuring the position accuracy and stability of all components and reducing the overall weight of the sensor.

[0031] The present invention proposes a processing method based on the above-mentioned annularly distributed multi-reflector laser triangulation ranging sensor, which is specifically as follows: (1) Turn on the laser 3, generate a laser beam and project it onto the surface of the target 10 to form a laser spot. After being reflected by multiple plane reflectors 6, the laser spot enters the lens 2 and forms multiple image spots on the imaging surface of the camera 1; Figure 4 As shown, there are eight annularly distributed image spots; (2) Collect images from a camera and send them to a computer for processing, such as Figure 4 As shown; (3) Process each image spot separately and extract the corresponding centroid point and its coordinates; Figure 4 As shown, eight image spots can be used to obtain eight centroid points and their coordinates P1(x1,y1), P2(x2,y2),…,P8(x8,y8); (4) Using the coordinates of multiple image spot centroids P1(x1,y1), P2(x2,y2),…,P8(x8,y8) to perform circle fitting, we can obtain the circle center point Pc and its coordinates Pc(xc,yc) and radius R. (5) Using the saved calibration curve data f(x), calculate the corresponding distance value of the measured target, that is, D = f(R).

[0032] Compared with the prior art, the annularly distributed multi-reflector laser triangulation ranging sensor of the present invention has the following beneficial effects: (1) The annularly distributed multi-reflector laser triangulation ranging sensor of the present invention reflects the laser spot through a plurality of annularly distributed plane reflectors to form a series of image spots distributed in a circular ring, and uses the diameter of the circular ring to measure the distance of the measured target. Its measurement accuracy is much higher than the ranging accuracy of a single imaging point, and the improvement is several orders of magnitude. (2) The ring-distributed multi-reflector laser triangulation ranging sensor of the present invention. The laser spot is reflected by multiple ring-distributed plane reflectors to form a series of image spots distributed in a circular ring. When the laser directivity changes, the position of the circular ring also changes, but the diameter of the circular ring does not change. Therefore, the influence of the change in laser directivity can be completely overcome in principle. (3) The annularly distributed multi-reflector laser triangulation ranging sensor of the present invention reflects the laser spot through a plurality of annularly distributed plane reflectors to form a series of image spots distributed in a circular ring. When the measured target is a step or other condition that partially blocks the reflected light, individual image spots will also disappear due to the blockage, but it will not affect the fitting and diameter calculation of the entire circular ring, thereby effectively overcoming the reflected light blocking phenomenon. At the same time, no matter which direction the local blockage occurs, it will not affect the ranging function, thus completely getting rid of the direction dependence problem of traditional laser triangulation ranging. (4) The annular distributed multi-reflector laser triangulation ranging sensor of the present invention can be constructed using a general industrial-grade lens and camera, which is low-cost and easy to integrate. The customized displacement parts are annular reflectors, which can reduce costs through batch customization, thereby providing a good foundation for the promotion and application of this method. (5) The annular reflective structure laser triangulation ranging sensor of the present invention has an axisymmetric overall structure and a lateral dimension that is significantly smaller than that of a conventional laser triangulation ranging sensor, and thus has wider applicability and versatility.

[0033] (6) The annular reflective structure laser triangulation ranging sensor of the present invention uses a plurality of plane reflectors to replace the annular reflector, which is simple and easy to manufacture and has low cost, thus having outstanding cost performance and promotion value.

[0034] (7) The ring-shaped reflective structure laser triangulation ranging sensor of the present invention adopts a special bracket to fix a plurality of ring-shaped planar reflectors, the number and angle of which are adjustable and controllable, which is flexible and convenient.

[0035] It can be seen that the technical solution of the present invention has very outstanding advantages compared with the traditional laser triangulation ranging sensor.

Claims

1. A ring-distributed multi-reflector laser triangulation ranging sensor, characterized in that: The sensor includes a camera, a lens, a laser, a focusing lens, a filter, a reflector, a bracket, a housing, and a socket, wherein: The camera is an industrial-grade area array camera, located at the top of the sensor housing, responsible for converting the laser spot reflection signal into an image signal; The lens is an industrial-grade lens, which is installed on the camera and is responsible for imaging the laser signal reflected by the reflector onto the image plane of the camera; The laser is an industrial-grade semiconductor laser, located at a distance below the lens, and installed at the center of the bracket so that the optical axis of the laser is coaxial with the optical axis of the lens, and is used to generate a laser beam and project it to the focusing lens; The focusing lens is a focusing collimating lens group, whose optical axis is coaxial with the laser and the lens optical axis, located at the front end of the laser, responsible for focusing the divergent laser beam generated by the laser, projecting it onto the surface of the target to be measured and forming a laser spot, and at the same time having a certain collimation function; The filter is a narrow-band filter, the central wavelength of which is consistent with the central wavelength of the laser, and can filter out interference from ambient light of other wavelengths; The reflector is a plane reflector, which has multiple pieces, close to the bracket, with the lens optical axis as the symmetry axis, and distributed in a ring or cone shape, which can reflect the laser spot from all directions of 360° and project it to the lens; The bracket is directly fixed in the housing and is used to simultaneously position the laser, focusing mirror and multiple reflectors to ensure that the laser, focusing mirror and all reflectors are coaxial, and has a hollow structure so that the reflected light beam can pass through and enter the lens; The housing is made of metal material, which can fix all the internal components and parts on one hand, and can also be used for installation, positioning and fixing of the entire sensor on the other hand; The socket is a universal industrial-grade socket, which is arranged on the sealing cover and is used for power supply and data transmission.

2. The annularly distributed multi-reflector laser triangulation ranging sensor according to claim 1 is further characterized by: The bracket adopts an integrated axisymmetric structure with a hollow interior for fixing the laser and focusing lens, ensuring that the optical axes of the laser and focusing lens are coaxial with the optical axis of the lens; the base is a spoke-type hollow structure to ensure that the reflected light of the annular reflector can pass through the bracket and enter the lens.

3. The annularly distributed multi-reflector laser triangulation ranging sensor according to claim 1 is further characterized by: The cross section of the bracket is an equilateral polygon structure, which is used to fix multiple plane reflectors to form a ring distribution; the axial cross section of the bracket is a rectangular or trapezoidal structure to ensure the best precision performance.

4. The annularly distributed multi-reflector laser triangulation ranging sensor according to claim 1 is further characterized by: The symmetry error of the polygonal structure of the bracket cross section should be high enough, generally not less than 1 / 5 of the ranging accuracy, so as to meet the requirements of ranging accuracy.

5. The annularly distributed multi-reflector laser triangulation ranging sensor according to claim 1 is further characterized by: The reflector is a high reflectivity plane reflector, which is generally not less than 90%; there are multiple reflectors, and the number of reflectors is the same as the number of sides of the polygonal cross section of the bracket.

6. The annularly distributed multi-reflector laser triangulation ranging sensor according to claim 1 is further characterized by: The distance between the plane reflector and the lens should be greater than the closest measuring distance.

7. The annularly distributed multi-reflector laser triangulation ranging sensor according to claim 1 is further characterized by: The length of the plane reflector should meet the requirement of the farthest measuring distance and should be greater than half of the difference between the farthest distance and the shortest distance.

8. A processing method of the annularly distributed multi-reflector laser triangulation ranging sensor according to claim 1, which is specifically as follows: (1) Turn on the laser to generate a laser beam that is projected onto the surface of the target to be measured, forming a laser spot. The laser spot is reflected by multiple plane mirrors and enters the lens, forming multiple image spots on the camera imaging surface. (2) Collect an image from a camera and send it to a computer for subsequent processing; (3) Process each image spot separately and extract the corresponding centroid point and its coordinates; (4) Using the coordinates of the centroids of multiple image spots to perform circle fitting, the coordinates of the center of the circle and the radius are obtained; (5) Using the saved calibration curve data, calculate the corresponding distance value of the measured target.

Images