Self-calibration device for laser radar with multiple transmitters
By setting a right-angled groove on the edge of the lidar cover, self-calibration is achieved by reflecting the laser signal, which solves the problem of transmitter and receiver misalignment in lidar and realizes real-time accuracy calibration and cost optimization.
Patent Information
- Application Number
- CN202423300739.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-28
- Publication Date
- 2026-01-30
- Estimated Expiration
- 2034-12-28
AI Technical Summary
The laser transmitters and receivers stacked in a lidar system may experience transmission and reception path misalignment due to mechanical wear or environmental vibration during long-term use. Existing calibration methods are complex and add additional equipment costs.
Right-angled grooves are set on both sides of the light-transmitting cover of the lidar. The laser emitted by the laser emitter returns to the receiver after two reflections. The accuracy error is judged by measuring the laser signal transmission time and the angle is adjusted to achieve self-calibration.
It enables real-time calibration of lidar in any environment, avoiding simulation analysis and the use of additional targets, thus reducing calibration complexity and cost.
Smart Images
Figure CN223857401U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to optical communication technical field, in particular to a kind of self-calibration device for multi-transmitter laser radar. BACKGROUND
[0002] As a kind of measuring equipment, precision is a very important index, for the laser transmitter and laser receiver stacked in laser radar, since the laser transmitter and laser receiver stacked are rotated by motor, in normal state, the laser transmitter and laser receiver stacked are respectively located on two straight lines, in long time use process, the laser transmitter and laser receiver respectively located on two straight lines can be slightly displaced due to long-term wear of motor, thermal expansion and contraction of mechanical parts or vibration interference of external environment, etc., laser transmitter and laser receiver, the emission and receiving path of laser beam can be offset, in turn, affect the detection precision of laser radar.
[0003] In prior art, the commonly used correction method is to simulate and analyze the structure of laser radar before shipment, generates a set of compensation data according to the data obtained by simulation analysis, and selects the established compensation data according to the current state in actual work, but this method cannot correct the measurement value in real time. Another method is to add specific target within the scanning field of view of laser radar, and correct the measurement value by continuously measuring the scanning target. Another method is to emit laser in one way in optical path, and irradiate on target in laser radar, to correct the measurement value. But the above two methods need to add additional device, which increases the cost, and is inconvenient to operate.
[0004] Therefore, it is urgent to overcome the defects of the prior art in the technical field. CONTENT OF UTILITY MODEL
[0005] The utility model solves the technical problem that the emission precision and receiving precision of the laser transmitter and laser receiver stacked in laser radar can change in long time use process, and the current calibration method is complex, and additional device for calibration is not conducive to cost control.
[0006] The utility model adopts the following technical solutions:
[0007] In one aspect, the utility model provides a kind of self-calibration device for multiple laser emitter's laser radar, comprising: multiple laser emitter 1, laser receiver 2 and light tunnel cover 3;Multiple laser emitter 1 is stacked, and multiple laser receiver 2 is stacked, the laser emitter 1 and the laser receiver 2 in each group are placed side by side, multiple laser emitter 1 is located in same straight line, and multiple laser receiver 2 is also located in same straight line, and the light tunnel cover 3 is covered in the outside of the laser emitter 1 and the laser receiver 2;
[0008] Multiple right-angle grooves 30 are symmetrically provided at the two side edges of the light tunnel cover 3, the right-angle grooves 30 are correspondingly provided with one of the laser emitter 1 and the laser receiver 2, the right-angle grooves 30 receive laser from the corresponding laser emitter 1, and return to the corresponding laser receiver 2 after twice reflection.
[0009] Preferably, multiple right-angle grooves 30 are arranged in oblique lines;Or, multiple right-angle grooves 30 are arranged in straight lines.
[0010] Among them, the interval between adjacent right-angle grooves 30 is equal.
[0011] Preferably, the first group of laser emitter 1 and laser receiver 2 are taken as the starting position, and one right-angle groove 30 is correspondingly provided every interval of preset group number of laser emitter 1 and laser receiver 2.
[0012] Preferably, the right-angle groove 30 is plated with reflective film or equipped with reflective prism.
[0013] Preferably, the light tunnel cover 3 is arc-shaped, one side facing the laser emitter 1 is concave, and the other side facing the measured object is convex.
[0014] Preferably, the concave surface of the light tunnel cover 3 receives laser emitted by the laser emitter 1, and the convex surface of the light tunnel cover 3 receives return laser emitted by the measured object.
[0015] Preferably, the laser emitter 1 emits laser to the first right-angle surface 300 of the right-angle groove 30, the first right-angle surface 300 reflects the received laser to the second right-angle surface 301, and the second right-angle surface 301 reflects the received laser to the laser receiver 2.
[0016] Preferably, the laser emitter 1 and the laser receiver 2 can adjust the emission and reception angle with the light tunnel cover 3 as the reference object, and the adjustment range is from one end edge of the light tunnel cover 3 to the opposite edge.
[0017] Preferably, the distance between the laser emitter 1 and the light tunnel cover 3 is 3cm to 5cm.
[0018] Preferably, the laser transmitter 1 and the laser receiver 2 are located at positions that can ensure that, after the laser transmitter 1 emits laser towards the right-angle groove 30 of the light-through cover 3, the reflected light path of the laser after being reflected by the right-angle groove 30 is parallel to the emitting light path, so that the laser signal can be received by the laser receiver 2.
[0019] Compared with the prior art, the self-calibration device for the laser radar has the beneficial effects that: by arranging the right-angle groove 30 at the two side edges of the light-through cover 3 of the laser radar, the laser transmitter 1 emits laser towards one side of the right-angle groove 30 without blocking the normal scanning field of view of the laser radar, the laser is received by the laser receiver 2 after being reflected in the right-angle groove 30, the accuracy error of the laser transmitter 1 and the laser receiver 2 and the offset of the stacked laser transmitter 1 and the laser receiver 2 are judged according to the time of laser signal transmission, and the accuracy error of the laser radar can be obtained in real time in any environment by using the calibration device, without obtaining compensation data according to simulation analysis or additionally increasing a target object for calibration to correct the measurement value. BRIEF DESCRIPTION OF DRAWINGS
[0020] In order to more clearly illustrate the technical scheme of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating laborious work on the basis of these drawings.
[0021] Figure 1 is a top view of a self-calibration device for a multi-transmitter laser radar provided by the embodiments of the present application;
[0022] Figure 2 is a schematic view of the stacked arrangement of the laser transmitter and the laser receiver of the self-calibration device for the multi-transmitter laser radar provided by the embodiments of the present application;
[0023] Figure 3 is a schematic view of the right-angle groove of the self-calibration device for the multi-transmitter laser radar provided by the embodiments of the present application;
[0024] Figure 4 is a schematic view of the right-angle groove arranged in an oblique line of the self-calibration device for the multi-transmitter laser radar provided by the embodiments of the present application;
[0025] Figure 5 is a schematic view of the right-angle groove arranged in a straight line of the self-calibration device for the multi-transmitter laser radar provided by the embodiments of the present application;
[0026] Figure 6is a schematic diagram of laser transmitter and laser receiver deflection of a self-calibration device for a multi-transmitter laser radar provided by the embodiment of the utility model;
[0027] Figure 7 is a schematic diagram of other structures inside the laser radar of a self-calibration device for a multi-transmitter laser radar provided by the embodiment of the utility model.
[0028] In the drawings, the reference signs are:
[0029] 1-laser transmitter, 2-laser receiver, 3-light transmission cover, 30-right-angle groove, 300-first right-angle surface, 301-second right-angle surface. DETAILED DESCRIPTION
[0030] In order to make the purpose, technical scheme and advantages of the utility model more clear and obvious, the utility model is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the utility model and not to limit the utility model.
[0031] Unless otherwise required by the context, the term "comprising" is to be interpreted as open inclusion, that is, "including but not limited to". In the description of the specification, the terms "one embodiment", "some embodiments", "exemplary embodiments", "example", "specific example" or "some examples" are intended to mean that the specific features, structures, materials or characteristics related to the embodiment or example are included in at least one embodiment or example of the present disclosure. The illustrative representation of the above terms does not necessarily mean the same embodiment or example. In addition, the specific features, structures, materials or characteristics described can be included in any one or more embodiments or examples in any appropriate manner, that is, although they are carried in the embodiment or example of the above terms due to the order of appearance and position, etc., but they are not limited to be carried by one embodiment or example in a combined manner.
[0032] In the description of the utility model, it is understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present disclosure and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present disclosure.
[0033] In the description of the utility model, the terms "first", "second" are only used for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include one or more features. In the description of the embodiments of the present disclosure, unless otherwise stated, the meaning of "multiple" is two or more. In addition, for example, in the description, the same type of nouns will also be described as two independent individuals by adding "A", "B" at the end, in which case the features limited by "A", "B" are only used for the purpose of distinguishing the same type of individual description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features.
[0034] In describing some embodiments, "coupled", "coupled", and "connected" and their derivatives can be used. For example, the term "connected" can be used to describe some embodiments to indicate that two or more components have direct physical or electrical contact with each other. For another example, the term "coupled" can be used to describe some embodiments to indicate that two or more components have direct physical or electrical contact. However, the term "connected" or "coupled" can also refer to two or more components that do not have direct contact with each other, but still cooperate or interact with each other, such as "optical coupling", "wireless connection", etc. The embodiments disclosed herein are not necessarily limited to the content of the utility model.
[0035] In the description of the utility model, the expression "A and / or B" (where A and B are used to represent specific feature content) can be used, and the corresponding expression includes the following three combinations: only A, only B, and the combination of A and B.
[0036] In the description of the utility model, "about", "approximately" or "approximately" includes the value described and the average value within the acceptable deviation range of the specific value, wherein the acceptable deviation range is determined by considering the measurement being discussed and the error related to the measurement of the specific quantity (i.e. the limitation of the measurement system) by those skilled in the art.
[0037] In addition, the technical features involved in each embodiment of the utility model described below can be combined with each other as long as there is no conflict.
[0038] Embodiment 1:
[0039] The utility model embodiment 1 provides a kind of self-calibration device for multiple laser emitter's laser radar, as shown in Figure Figure 1 As shown in Figure Figure 2As shown, a plurality of the laser transmitter 1 is stacked, a plurality of the laser receiver 2 is stacked, the laser transmitter 1 and the laser receiver 2 in each group are placed side by side, a plurality of the laser transmitter 1 is located on the same straight line, a plurality of the laser receiver 2 is also located on the same straight line, and the light-through cover 3 is covered outside the laser transmitter 1 and the laser receiver 2; wherein the light-through cover 3 has the functions of protecting the internal optical and circuit components of the laser radar, isolating stray light, etc., and the distance between the laser transmitter 1 and the light-through cover 3 is 3-5 cm. A plurality of right-angled grooves 30 is symmetrically arranged at the two side edges of the light-through cover 3, the right-angled grooves 30 are correspondingly arranged with the laser transmitter 1 and the laser receiver 2 in one group, the right-angled grooves 30 receive laser from the corresponding laser transmitter 1, and the laser returns to the corresponding laser receiver 2 after being reflected twice. Specifically, the positions of the laser transmitter 1 and the laser receiver 2 can ensure that after the laser transmitter 1 emits laser towards the right-angled groove 30 of the light-through cover 3, the reflected light path of the laser reflected by the right-angled groove 30 is parallel to the emitting light path, so that the laser signal can be received by the laser receiver 2.
[0040] wherein, for the laser transmitter 1, the laser receiver 2 and the right-angled groove 30, Figure 3 As shown, the laser transmitter 1 emits laser to the first right-angled face 300 of the right-angled groove 30, the first right-angled face 300 reflects the received laser to the second right-angled face 301, and the second right-angled face 301 reflects the received laser to the laser receiver 2.
[0041] By arranging the right-angled groove 30 at the two side edges of the light-through cover 3 of the laser radar, without blocking the normal scanning field of view of the laser radar, the laser transmitter 1 emits laser to one side of the right-angled groove 30, the laser is received by the laser receiver 2 after being reflected in the right-angled groove 30, and whether there is an error in the accuracy of the laser transmitter 1 and the laser receiver 2 and whether there is a deviation in the stacked laser transmitter 1 and the laser receiver 2 is determined according to the time of laser signal transmission. The calibration device provided by the utility model can obtain the accuracy error of the laser radar in real time in any environment, without obtaining compensation data according to simulation analysis or additionally increasing a target object for calibration to correct the measurement value.
[0042] In addition to measuring the detection accuracy of the lidar, the right-angled groove 30 can also be used to determine the lidar's scanning range. The laser emitter 1 and the laser receiver 2 can adjust their emission and reception angles with the light-transmitting cover 3 as a reference, with the adjustment range from one edge of the light-transmitting cover 3 to the opposite edge. Specifically, the laser emitter 1 and the laser receiver 2 are driven to rotate by a motor, and the laser emitter 1, the laser receiver 2, and the motor are all connected to a controller. When the laser emitter 1 and the laser receiver 2 rotate to one side of the light-transmitting cover 3, if the laser emitter 1 emits a laser signal towards the right-angled groove 30 closest to the edge of the light-transmitting cover 3, and the laser receiver 2 receives the reflected laser signal, the controller controls the motor to drive the laser emitter 1 and the laser receiver 2 to rotate in the opposite direction, thereby realizing the lidar's reciprocating scanning detection in the horizontal direction.
[0043] For the light-transmitting cover 3, the light-transmitting cover 3 is arc-shaped, with a concave surface facing the laser emitter 1 and a convex surface facing the object being measured; the non-edge area of the concave surface of the light-transmitting cover 3 receives the laser emitted by the laser emitter 1, and the non-edge area of the convex surface of the light-transmitting cover 3 receives the reflected laser emitted by the object being measured.
[0044] In one embodiment, such as Figure 4 As shown, the plurality of right-angled grooves 30 are arranged in an oblique pattern; or, as... Figure 5 As shown, the multiple right-angled grooves 30 are arranged in a straight line; the interval between adjacent right-angled grooves 30 is equal. In both cases, starting with the first group of laser emitters 1 and laser receivers 2, a right-angled groove 30 is provided for every preset number of laser emitters 1 and laser receivers 2. The preset number of groups can be 1, 2, 3, etc., and can be designed according to actual needs. Since the purpose of the light-transmitting cover 3 is to protect the internal optical and circuit components of the lidar and isolate stray light, etc., and it is not specifically used to reflect laser signals, the right-angled grooves 30 are coated with a reflective film or equipped with a reflective prism.
[0045] When the laser radar is out of the factory, the device is least affected by the outside world at this time, and before the laser radar is used out of the factory, the time interval between the laser signal emitted by the laser emitter 1 at the right-angle groove 30 and the laser signal received by the laser receiver 2 is recorded as the first time interval t1, which is the time interval between the laser signal emitted by the laser emitter 1 at the right-angle groove 30 and the laser signal received by the laser receiver 2 in each group of laser emitters 1 and laser receivers 2 when the laser emitter 1 and the laser receiver 2 are normally rotated. During the use of the laser radar, the time interval between the laser signal emitted by the laser emitter 1 at the right-angle groove 30 and the laser signal received by the laser receiver 2 is recorded again as the second time interval t2. The difference between the first time interval t1 and the second time interval t2 is the measurement accuracy compensation value AT of the laser radar in the current use environment. Since the right-angle grooves 30 are arranged at intervals with respect to the multiple groups of laser emitters 1 and laser receivers 2, for the laser emitters 1 and the laser receivers 2 that are not correspondingly provided with the right-angle grooves 30, the measurement accuracy compensation value is the average of the measurement accuracy compensation values of the two groups before and after, for example, there are three groups of laser emitters 1 and laser receivers 2, the first group and the third group are correspondingly provided with the right-angle grooves 30, the measurement accuracy compensation value of the first group is AT1, and the measurement accuracy compensation value of the third group is AT2. Then the measurement accuracy compensation value AT3 of the second group is (AT1+AT2) / 2.
[0046] When the laser radar is used after it is out of the factory, the laser emitter 1 emits a laser signal to the measured object through the light shield 3, and the third time interval t3 between the emission of the laser signal by the laser emitter 1 and the reception of the reflected signal from the measured object by the laser receiver 2 is recorded. According to the aforementioned measured accuracy compensation value AT, the true time of the received signal of the measured object measured by the laser radar is the third time interval t3 plus the first compensation value AT.
[0047] For the measurement accuracy compensation value AT, Figure 4 and Figure 5 the measurement methods of the two right-angle groove 30 arrangement forms shown in the above two figures are the same, but since the laser emitters 1 and the laser receivers 2 are stacked, after a long time of use, a deflection as shown in Figure 6 may occur (the case shown in the figure is only one of the possible cases in a variety of deflection cases, and is only used for illustration, and does not represent only this case). The controller can also judge the deflection degree of the laser emitter 1 and the laser receiver 2 according to the transmission time interval of the laser signal. Here, the time interval between the reception of the laser signal by the previous group of laser receivers 2 and the emission of the laser signal by the next group of laser emitters 1 is taken as the fourth time interval t4.
[0048] As shown in Figure 6 , taking 32 groups of laser emitters 1 and laser receivers 2 as an example, first of all, Figure 5The straight angle grooves 30 shown are arranged in a straight line as an illustration, and 16 straight angle grooves 30 are arranged in total, with the first straight angle groove 30 corresponding to the first group of laser emitters 1 and laser receivers 2, the second straight angle groove 30 corresponding to the third group of laser emitters 1 and laser receivers 2, and so on. In actual application scenarios, one straight angle groove 30 can also be arranged corresponding to every 2 or 3 groups of laser emitters 1 and laser receivers 2 according to actual needs, without limitation (the same below). Under normal circumstances, 16 groups of laser emitters 1 and laser receivers 2 will simultaneously emit laser signals to the 16 straight angle grooves 30, and the 16 laser receivers 2 will simultaneously receive the reflected laser signals, that is, the fourth time interval t4 is 0. If the laser emitters 1 and laser receivers 2 are deflected, for example Figure 6 , the time at which the deflected laser emitters 1 emit laser signals is different from that at which the non-deflected laser emitters 1 emit laser signals, and the time at which the laser receivers 2 receive laser signals is also different from that at which the non-deflected laser receivers 2 receive signals, that is, the fourth time interval t4 is a positive or negative value.
[0049] In the embodiment shown in Figure 4 , the straight angle grooves 30 are arranged in a diagonal line as an illustration. Under normal circumstances, 16 groups of laser emitters 1 and laser receivers 2 will sequentially emit laser signals to the straight angle grooves 30 and receive laser signals. Since the spacing between the straight angle grooves 30 is equal, the fourth time interval t4 is a fixed value. If the laser emitters 1 and laser receivers 2 are deflected, for example Figure 6 , the fourth time interval t4 will change to a non-fixed value. According to the size of each calculated fourth time interval t4, the deflection of the laser emitters 1 and laser receivers 2 can be determined.
[0050] Embodiment 2:
[0051] The embodiment of the utility model provides a kind of self-calibration device for multiple laser emitters, based on embodiment 1, the embodiment further provides a specific implementation scheme for the device in actual use.
[0052] As shown in Figure 7 , in the embodiment, the laser radar includes laser emitters 1, laser receivers 2, waveform extraction unit 4, analog-digital converter 5, digital processor 6, light transmission mask 3 and measured object 7.
[0053] Before factory, laser emitters 1 emit laser beams to straight angle grooves, laser beams are reflected twice through straight angle grooves, and are reflected back to laser radar in parallel with the emission laser beams, and are received by laser receivers 2, and the reflection of light transmission mask 3 is extracted by waveform extraction unit 4, and is converted into digital signal by analog-digital converter 5, and the time interval between emission signal and straight angle groove reflection signal is recorded as first time interval t1.
[0054] After factory, laser emitter 1 emits laser beam to right angle groove, laser beam is reflected twice through right angle groove, is reflected back to laser receiver 2 in parallel with the emission laser beam, is received by laser receiver 2, is extracted by wave extraction unit 4 the reflection of light shield 3, is converted into digital signal by analog-digital converter 5, records the time interval second time interval t2 between emission signal and right angle groove reflection signal.
[0055] The difference of first time interval t1 and second time interval t2 is calculated as compensation amount.
[0056] When laser radar works normally, laser emitter 1 sends emission signal to measured object 7, and laser receiver 22 receives the reflection signal reflected back from measured object 7, and records the time interval third time interval t3 between emission signal and reflection signal of measured object 7.
[0057] The real time of laser radar testing measured object 7 is T', so the real time of laser radar testing measured object 7 is T'=t3+△T.
[0058] The above only is the preferred embodiment of the present application, and does not limit the present application, and any modification, equivalent replacement and improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims
1. A self-calibration apparatus for a multi-transmitter lidar, the apparatus comprising: The utility model relates to a kind of laser detection device, including: Multiple laser emitters (1), laser receivers (2) and light transmission cover (3);Multiple laser emitters (1) are stacked, multiple laser receivers (2) are stacked, the laser emitter (1) and the laser receiver (2) in each group are placed side by side, multiple laser emitters (1) are located in the same straight line, multiple laser receivers (2) are also located in the same straight line, and the light transmission cover (3) is covered outside the laser emitter (1) and the laser receiver (2); Multiple right-angle grooves (30) are symmetrically arranged at both side edges of the light transmission cover (3), the right-angle groove (30) is correspondingly arranged with one of the laser emitters (1) and the laser receivers (2), the right-angle groove (30) receives laser from the corresponding laser emitter (1), and the reflected light returns to the corresponding laser receiver (2) after two reflections.
2. The self-calibration apparatus for a multi-transmitter lidar according to claim 1, wherein, Multiple right-angle grooves (30) are arranged in diagonal lines, or multiple right-angle grooves (30) are arranged in straight lines. Wherein, the interval between adjacent right-angle grooves (30) is equal.
3. The self-calibration apparatus for a multi-transmitter lidar according to claim 2, wherein, With the first group of laser emitters (1) and laser receivers (2) as the starting position, one right-angle groove (30) is correspondingly arranged every interval of a preset number of laser emitters (1) and laser receivers (2).
4. The self-calibration apparatus for a multi-transmitter lidar according to claim 2, wherein, The right-angle groove (30) is coated with a reflective film or equipped with a reflective prism.
5. The self-calibration apparatus for a multi-transmitter lidar according to claim 1, wherein, The light transmission cover (3) is arc-shaped, one side facing the laser emitter (1) is concave, and the other side facing the measured object is convex.
6. The self-calibration apparatus for a multi-transmitter lidar according to claim 5, wherein, The concave surface of the light transmission cover (3) receives laser emitted by the laser emitter (1), and the convex surface of the light transmission cover (3) receives return laser emitted by the measured object.
7. The self-calibration device for a multi-transmitter lidar according to any of claims 1-6, characterized in that, The laser emitter (1) emits laser to the first right-angle surface (300) of the right-angle groove (30), the first right-angle surface (300) reflects the received laser to the second right-angle surface (301), and the second right-angle surface (301) reflects the received laser to the laser receiver (2).
8. The self-calibration device for a multi-transmitter lidar of any of claims 1-6, wherein, The laser emitter (1) and the laser receiver (2) can adjust the emission and reception angles with the light transmission cover (3) as the reference, and the adjustment range is from one end edge of the light transmission cover (3) to the opposite edge.
9. The self-calibration apparatus for a multi-transmitter lidar of any of claims 1-6, wherein, The distance between the laser emitter (1) and the light transmission cover (3) is 3-5 cm.
10. The self-calibration apparatus for a multi-transmitter lidar of any of claims 1-6, wherein, The positions of the laser emitter (1) and the laser receiver (2) can ensure that, after the laser emitter (1) emits laser to the right-angle groove (30) of the light transmission cover (3), the reflected light path of the reflected laser is parallel to the emission light path, so that the laser signal can be received by the laser receiver (2).