Patent Publication Number: US-2023152427-A1

Title: Laser radar receiving system

Description:
TECHNICAL FIELD 
     The present application relates a laser radar, in particular a receiving system of the laser radar. 
     BACKGROUND 
     Laser radar is an active distance detection device using photoelectric detection technology, which is widely used in unmanned driving, unmanned aerial vehicles, robots and other fields. 
     At present, all laser radars basically have a range, including the longest range (upper limit) and the shortest range (lower limit). General laser radar has a near blind area. For example, the target within a certain distance from laser radar cannot be detected. There are many reasons for the existence of the near blind area. For example, when a parallel beam of light hits the rough surface of the target, the surface will reflect the light in all directions. Therefore, due to the inconsistency of the normal directions of each point, the parallel incident rays would be reflected randomly in different directions. Moreover, the existing laser radar is provided with an emitting channel. When the target is near the laser radar, part of the light reflected back from the diffuse reflection of the target is blocked by the transmitting channel, and this part of the light cannot be projected to the receiving tube, so it is difficult to guarantee the measurement range of the two-dimensional or three-dimensional information of the target. Therefore, the existing laser radar has a blind area for short-range detection. 
     How to further expand the short-range measurement range of the existing laser radar has been one of the key issues in the laser radar research field. 
     DESCRIPTION OF THE INVENTION 
     In order to solve the problem in the prior art that the laser radar has a blind area for short-range detection due to the blocking of the emitting channel, resulting in the fact that the nearest measurement range of the laser radar is still not close enough, the present application relates a laser radar receiving system, in which the laser radar includes a first reflector mirror, an emitting channel, an emission system and a basic receiving system. The laser beam emitted by the emission system is reflected by the first reflector mirror, and then reaches the target through the emitting channel. The laser beam reflected from the target passes through the emitting channel, and then is reflected by the first reflector mirror and finally received by the basic receiving system, in which the laser radar receiving system further includes a reflecting element, 
     The space outside the emitting channel includes an area which the laser beam diffusely reflected from the target cannot reach due to the blocking of the emitting channel, and the reflecting element is disposed outside the area and used for reflecting the laser beam diffusely reflected from the target to the basic receiving system. 
     Further, the laser radar further includes a window cover, inside which the first reflector mirror, the transmitting channel and the reflecting element are arranged, and outside which the transmitting system and the basic receiving system are arranged. The space outside the transmitting channel inside the window cover includes a first area, a second area and a third area. The first area is an area which the laser beam diffusely reflected from the target cannot reach due to the blocking of the transmitting channel, the second area is the area which the laser beam emitted from the emitting channel is reflected back into the window cover through the window cover, the third area is located between the first area and the second area, and the reflecting element is disposed in the third area, and is used for reflecting the laser beam diffusely reflected from the target back into the third area to the basic receiving system. 
     Further, the spatial size of the first area is negatively correlated with the distance between the target and the laser radar. 
     Further, the reflecting element is a reflector mirror. The emitting channel has an opaque hollow cylindrical structure. 
     Further, the emission system includes a laser tube for emitting laser beams and a second reflector mirror, and the laser beams emitted by the laser tube are reflected by the second reflector mirror and the first reflector mirror in turn, and then pass through the emitting channel to the target conveyed outside the window cover. The basic receiving system includes a third reflector mirror and a receiving tube, and the laser beam diffusely reflected by the target passes through the transmitting channel, and then is reflected to the receiving tube by the first reflector mirror and the second reflector mirror in turn. 
     Further, the reflecting surface of the first reflector mirror and the reflecting surface of the reflecting element are opposite to and parallel to the reflecting surface of the third reflector mirror. 
     Further, the central axis of the transmitting channel intersects with the center of the first reflector mirror, the optical axis of the receiving tube intersects with the center of the third reflector mirror at an angle of 45°, the optical axis of the laser tube intersects with the center of the second reflector mirror at an angle of 45°, and the optical axis of the laser tube is parallel to the optical axis of the receiving tube. 
     Further, the transmitting system further includes a transmitting objective lens, and the basic receiving system further includes a receiving objective lens, in which the center of the first reflector mirror, the center of the second reflector mirror, the center of the third reflector mirror, the central axis of the transmitting objective lens and the central axis of the receiving objective lens are on the same straight line. 
     Further, the transmitting objective lens and the receiving objective lens are convex lenses. 
     Further, the center of the reflective element is not on the straight line. 
     Compared with the prior art, the application has the following advantages: 
     1. The laser radar receiving system provided by the present application can reflect the laser beam projected by the target outside the light receiving blind area caused by the emitting channel into the receiving tube through the reflecting element outside the light receiving blind area caused by the emitting channel, so as to comprehensively collect the diffuse reflection light of the near target, improve the information collection rate of the near target, and further expand the near measurement range of the existing laser radar. 
     2. In addition, for the laser radar with window cover, the laser radar receiving system provided by the present application further sets the reflection element outside the stray light interference area caused by the window cover to avoid the interference of stray light diffusely reflected by the window cover, thus improving the measurement accuracy and further expanding the measurement range of the radar. 
    
    
     
       BRIEF INTRODUCTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of the optical path of the laser radar of the application. 
     
    
    
     REFERENCE NUMBER 
       11 —Window cover,  111 —first area,  112 —second area,  113 —third area,  12 —first reflector mirror,  121 —first reflector mirror&#39;s reflecting surface,  131 —side wall,  1311 —outer side wall,  1312 —inner side wall,  141 —laser tube,  142 —second reflector mirror,  143 —transmitting objective lens,  151 —third reflector mirror,  152 —receiving tube,  153 —receiving objective lens,  16 —reflecting element. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The advantages of the present application will be explained in detail with reference to the drawing and preferred embodiments. 
     As shown in  FIG.  1   , the present application provides a laser radar receiving system, in which the laser radar includes a first reflector mirror  12 , an emitting channel, an emission system and a basic receiving system. The laser beam emitted by the emission system is reflected by the first reflector mirror  12 , and then reaches a target through the emitting channel. The laser beam reflected from the target passes through the emitting channel, and then is reflected by the first reflector mirror and finally received by the basic receiving system. The laser radar receiving system further includes a reflecting element  16 . The space outside the emitting channel includes an area which the laser beam diffusely reflected from the target cannot reach due to the blocking of the emitting channel, i.e., a light receiving blind area, and the reflecting element  16  is disposed outside the light receiving blind area, and is used for reflecting the laser beam diffusely reflected from the target outside the light receiving blind area to the basic receiving system. Therefore, the laser beam projected by the target outside the light receiving blind area can be reflected into the receiving tube  152 , so as to comprehensively collect the diffuse reflection light of the close-range target, improve the information collection rate of the short-range target, and further expand the short-range measurement range of the radar. For example, the existing laser radar will have different nearest measurement ranges according to the specific environmental requirements. In other words, there will be a near range measurement blind area. The application can further expand the near range measurement by adding the reflective element  16 . For example, the shortest range of a laser radar in a specific use environment is 0.8 m, which means the target within 0.8 m of the laser radar cannot be measured. However, by adding the reflecting element  16 , the laser radar receiving system of the present application can further extend the nearest measuring range from 0.8 m to 0.3 m, which means that the target within 0.3 m from the laser radar cannot be measured, thus further expanding the short measuring range of the laser radar. Preferably, the nearest range of the laser radar using the laser radar receiving system of the present application is 0.1 m. The laser radar receiving system can be applied to various laser radars, including but not limited to triangulation ranging laser radar, pulse ranging laser radar based on time flight, and phase ranging laser radar; or coaxial laser radar and non-coaxial laser radar; or mechanical laser radar or solid-state laser radar. Preferably, the reflective element  16  is a reflector mirror, in which the reflector mirror is circular, rectangular, triangular or in other shapes. 
     When a parallel laser beam hits the rough surface of the target, the surface will reflect the beam in all directions. Therefore, although the incident rays are parallel to each other, the normal directions of each point are inconsistent, resulting in irregular reflection of the reflected beam in different directions, which is called diffuse reflection. Moreover, the window cover  11  of the existing laser radar is provided with an emitting channel. Generally speaking, the emitting channel is an opaque hollow cylindrical structure, such as an opaque cylindrical structure or a square one. The emitting channel has a side wall  131 , which is circular to form the cylindrical shape. The side wall  131  has an outer side wall  1311  and an inner side wall  1312 , in which the outer side wall  1311  refers to the side wall near one end of the window cover  11 , and the inner side wall  1312  refers to the side wall away from the window cover  11 . As the light propagates linearly, when the distance between the target and the laser radar is short, and the received laser beam is diffusely reflected by the target, the laser beam reflected back into the window cover  11  cannot reach some areas outside the emitting channel due to the blocking of the opaque emitting channel, especially the blocking of the outer end side wall  1311 . This means there is a light receiving blind area and it cannot be further reflected by the first reflector mirror  12  to the basic receiving system. Therefore, two-dimensional or three-dimensional information of near-range objects cannot be obtained. This is one of the reasons why the existing laser radar has a blind area for near-range detection. By adding the reflecting element  16 , the radar receiving system of the present application can shorten the blind area of short-range detection, and further expand the short-range measurement range of laser radar. 
     According to an embodiment of the present application, the laser radar further includes a window cover  11 , in which the first reflector mirror  12 , the transmitting channel and the reflecting element  16  are arranged, and the transmitting system and the basic receiving system are arranged outside the window cover  11 . The space outside the transmitting channel in the window cover  11  includes a first area  111 , a second area  112  and a third area  113 . The first area  111  is an area which the laser beam diffusely reflected from the target cannot reach due to the blocking of the emitting channel, the second area  112  is an area which the laser beam emitted from the emitting channel reflects back into the window cover  11  through the window cover  11 , and the third area  113  is located between the first area  111  and the second area  112 . That is, the third area  113  is a space other than the first area  111  and the second area  112  outside the emitting channel in the window cover  11 . The reflecting element  16  is disposed in the third area  113  for reflecting the laser beam diffusely reflected from the target back into the third area  113  to the basic receiving system. It can not only avoid the blind area of short-distance detection, but also avoid the interference of stray light, so as to improve the measurement accuracy and further expand the measurement range. 
     The laser beam emitted by the emission system is reflected by the first reflector mirror  12 , reaches the target through the emitting channel, and forms a spot on the target. In addition, when the laser radar has a window cover  11 , the laser beam emitted by the laser radar will pass through the inner and outer walls of the window cover  11 . As the inner and outer walls are not ideal smooth surfaces, the surfaces of the inner and outer walls of the window cover  11  will diffusely reflect the laser beam emitted by the laser radar, which means the stray light will be formed. Because of the blocking of the emitting channel in the window cover  11 , specifically, the blocking of the outer end side wall  1311  of the emitting channel, and the linear propagation of light, the laser beam diffusely reflected from the inner and outer walls of the window cover  11  can only fill the second area  112  (i.e. the stray light interference area), and the basic receiving system cannot distinguish the effective echo signal reflected from the near effective target after receiving the stray light signal, thus resulting in the blind area of short distance measurement or lower measurement accuracy. The stray light will superimpose and interfere with the useful return light signal, thus affecting the measurement accuracy. If it is a long-distance return signal, the signal is weak, while the stray light signal always exists in equal quantity, which will cause greater interference to the long-distance return signal, and even cause the circuit to be unable to distinguish the long-distance signal, thus affecting the measurement range. In the present application, the reflective element  16  is added and disposed outside the second area  112 , so that the stray light interference caused by the window cover  11  can be avoided. Preferably, the reflecting element  16  is disposed in the third area  113 , that is, the third area  113  is an area outside the emitting channel, which is neither the first area  111  nor the second area  112 , so that the laser beam of the present application can simultaneously avoid the light receiving blind area caused by the emitting channel and the stray light interference area caused by the window cover  11 , thus comprehensively collecting the diffuse reflection light of the near-range target, improving the information collection rate of the near-range target, and further expanding the measurement range of the radar and improving the measurement accuracy. 
     The spatial size of the first area  111  is negatively correlated with the distance between the target and the laser radar. Specifically, the first area  111  in  FIG.  1    is larger when the distance between the target and the laser radar is shorter, and vice versa. The spatial size of the second area  112  is positively related to the distance between the emitting channel and the window cover  11 . The second area  112  is larger when the distance between the emitting channel and the window cover  11  is longer, and vice versa. However, for a specific laser radar, the distance between the emitting channel and the window cover is fixed, so the second area  112  is a fixed area. Therefore, only the actual size of the first area  111  changes with the distance between the target and the laser radar. 
     Preferably, the optical axis of the transmitting system and that of the basic receiving system are coaxial or non-coaxial. The optical axis of the emission system refers to the central axis of the laser beam emitted from the laser tube  141  between the laser tube  141  and the second reflector mirror  142 . The optical axis of the basic receiving system refers to the central axis of the laser beam received by the receiving tube  152  between the third reflector mirror  151  and the receiving tube  152 . Typically, the optical axis of the transmitting system and the optical axis of the basic receiving system are not coaxial, but the optical axes may be parallel or vertical. 
     When the optical axis of the transmitting system is parallel to that of the basic receiving system, for example, the transmitting system includes a laser tube  141  and a second reflector mirror  142  for emitting laser beams, the laser tube  141  is preferably a laser diode. The laser beam emitted by the laser tube  141  is reflected by the second reflector mirror  142  and the first reflector mirror  12  in turn, and then passes through the emitting channel to the target that is transmitted outside the window cover  11 . Preferably, the laser radar is a mechanical laser radar, which further includes a motor, and the first reflector mirror  12  and the emitting channel are driven by the motor together. Preferably, the first reflector mirror  12  and the emitting channel can rotate in all directions. The basic receiving system includes a third reflector mirror  151  and a receiving tube  152 . The laser beam diffusely reflected by the target passes through the transmitting channel, and then is reflected to the receiving tube  152  by the first reflector mirror  12  and the second reflector mirror  142  in turn. Preferably, the reflecting surface  121  of the first mirror and the reflecting surface of the reflecting element  16  are opposite to and parallel to the reflecting surface of the third reflector mirror  151 . Preferably, the central axis of the emitting channel intersects the center of the first reflector mirror  12 , the optical axis of the receiving tube  152  intersects the center of the third reflector mirror  151  at an angle of 45°, the optical axis of the laser tube  141  intersects the center of the second reflector mirror  142  at an angle of 45°, and the optical axis of the laser tube  141  is parallel to that of the receiving tube  152 . Preferably, the transmitting system outside the window cover  11  further includes a transmitting objective lens  143  for collimating the diffused laser beams, and the basic receiving system further includes a receiving objective lens  153  for converging the parallel laser beams. Preferably, the transmitting objective lens  143  and the receiving objective lens  153  are convex lenses. Preferably, the convex lenses are lenticular lenses, plano-convex lenses, concave-convex (or positive meniscus) lenses, etc. The transmitting objective lens  143  and the receiving objective lens  153  are spherical mirrors or aspherical mirrors. Preferably, the center of the first reflector mirror  12 , the center of the second reflector mirror  142 , the center of the third reflector mirror  151 , the central axis of the transmitting objective lens  143 , and the central axis of the receiving objective lens  153  are on the same straight line, and the center of the reflecting element  16  is not on the straight line, as shown in  FIG.  1   . 
     According to the above embodiments of the present application, the principle of the optical path of the laser beam is that the laser beam emitted from the laser tube  141  is reflected by the second reflector mirror  142 , collimated into a parallel beam by the emission objective lens  143 , reflected by the first reflector mirror  12 , passes through the emitting channel, passes through the window cover  11 , and is finally projected onto the target to form a spot. Part of the laser beam from the emitting channel is reflected or diffusely reflected back into the window cover  11  by the window cover  11 , and is projected into the second area  112  in the window cover  11 , that is, the stray light interference area. The parallel laser beam projected on the target is reflected and diffusely reflected on the surface of the target, and part of the laser beam is reflected back to the emitting channel by the target. This part of the laser beam reflected back to the emitting channel is first reflected by the first reflector mirror  12 , then passes through the receiving objective lens  153  and converges, is reflected by the third reflector mirror  151 , and finally received by the receiving tube  152 . Part of the laser beam is diffusely reflected by the target to the area outside the emitting channel, and the area outside the emitting channel that cannot be reached due to the blocking of the emitting channel is the first area  111 . In order to diffuse the laser signal of the target outside the emitting channel to the laser tube  141 , and avoid the stray light that will reduce the measurement accuracy, the laser radar receiving system of the present application adds the reflecting element  16 , and the reflecting element  16  is located in the third area  113  between the first area  111  and the second area  112 , so that it can simultaneously achieve the functions of further expanding the short-distance measurement range and avoiding the stray light interference to improve the measurement accuracy. 
     To sum up, the laser radar receiving system of the present application can achieve the technical effects of further expanding the short-distance measurement range and avoiding the stray light interference to improve the measurement accuracy by adding the reflecting element  16  and setting the reflecting element  16  in the area outside the short-distance receiving blind area and the stray light interference area (as shown in the third area  113  in  FIG.  1   ). 
     The above specific embodiments have been described in detail, but they are only part of the examples, and the application is not limited to the embodiments. For those skilled in the art, any equivalent modifications and substitutions made to the present application are also within the scope of the present application. Therefore, all equivalent changes and modifications made without departing from the spirit and scope of the present application should be covered within the scope of the present application.