Lidar test method

Abstract

A LiDAR test method according to the present invention comprises the steps of: providing a transmitter and a receiver; forming a transceiver by combining the transmitter and the receiver; performing an overlap test on the transceiver; and performing calibration on the transceiver. The step of forming the transceiver includes the steps of: fixing one of the transmitter or the receiver and then acquiring scan images of a test target while changing at least one of the position or orientation of the other; selecting optimal positions of the transmitter and the receiver on the basis of a plurality of the acquired scan images; fixing the transmitter and the receiver at the optimal positions and injecting a curable material; and curing the curable material using heat or light.

Description

Lidar testing methods

[0001] The present invention relates to a method for testing a Light Detection And Ranging (LiDAR) using a mirror.

[0002] LiDAR (Light Detection And Ranging) is a technology that uses laser pulse signals to detect the location, distance, direction of movement, and speed of objects. It is applied in various fields such as aerospace, autonomous vehicles, disaster prevention, atmospheric remote sensing, meteorological measurement, and water depth measurement. Because LiDAR has a wide measurement range, from short-distance measurement within 50 meters to long-distance measurement over 200 meters, and boasts much higher precision than existing measurement methods, its application and utilization fields are continuously expanding.

[0003] Ensuring the reliability of lidar requires testing during and after the manufacturing process. These tests include testing general performance metrics (e.g., detection range, range accuracy, range precision, angular resolution, field of view, frame frequency), performance metrics that impact operational safety (e.g., anti-interference, point cloud density), and performance variations caused by environmental factors.

[0004] Among these, testing detection distance and detection angle often faces significant spatial constraints depending on the required performance of the lidar. Manufacturing long-range lidar requires building a vast test space hundreds of meters across, and precisely controlling environmental conditions. This represents a significant technological, spatial, and economic cost.

[0005] As lidar performance rapidly advances, research and development is needed to improve space efficiency while simultaneously performing efficient and precise testing.

[0006] The purpose of the present invention is to provide a lidar testing method capable of performing efficient and precise testing while improving space efficiency.

[0007] A method according to the present invention comprises the steps of: providing a transmitter and a receiver; combining the transmitter and the receiver to form a transceiver; performing an overlap test on the transceiver; and performing a calibration on the transceiver; wherein the step of forming the transceiver comprises the steps of: fixing one of the transmitter and the receiver and then changing at least one of a position and a posture of the other one while acquiring a scan image of a test target; selecting an optimal position of the transmitter and the receiver based on a plurality of acquired scan images; fixing the transmitter and the receiver at the optimal position and injecting a curable material; and curing the curable material using heat or light.

[0008] The step of selecting the optimal position may include a step of calculating a sharpness score for each of the plurality of scanned images; and a step of determining the optimal position based on the sharpness score.

[0009] The step of performing the overlap test may include: setting a receiver of the transceiver to ON; setting a light source of a target disposed adjacent to the transceiver to ON; obtaining an Rx profile based on a first optical signal emitted from the light source and reflected by a mirror and received by the receiver; setting a transmitter of the transceiver and an optical sensor of the target to ON; obtaining a Tx profile based on a second optical signal emitted from the transmitter and reflected by the mirror and received by the optical sensor; and testing the transceiver based on an overlap degree of the Rx profile and the Tx profile.

[0010] The step of performing the calibration includes: a step of driving the transceiver to receive a lidar signal for a target; and a step of performing calibration for the transceiver based on the position information of the target obtained by the lidar signal and the actual position information of the target; wherein the lidar signal may be an optical signal obtained by light emitted from the transceiver, reflected by a mirror, and then incident on the target, and then sequentially reflected by the target and the mirror, and then incident on the transceiver.

[0011] Meanwhile, a method according to the present invention includes: a step of setting a receiver of a transceiver and a light source of a target to ON; a step of obtaining an Rx profile based on a first optical signal emitted from the light source and reflected by a mirror and received by the receiver; a step of setting a transmitter of the transceiver and a light sensor of the target to ON; a step of obtaining a Tx profile based on a second optical signal emitted from the transmitter and reflected by the mirror and received by the light sensor; and a step of determining whether the transceiver satisfies a criterion based on an overlap degree of the Rx profile and the Tx profile.

[0012] The mirror may include a first mirror arranged at a predetermined position in an area facing the transceiver or the target, and a second mirror arranged at a predetermined position in an area facing the first mirror, and the first optical signal may be an optical signal in which light emitted from the light source, reflected by the first mirror, and then incident on the second mirror, is sequentially reflected again by the second mirror and the first mirror, and is received by the receiver, and the second optical signal may be an optical signal in which light emitted from the transmitter, reflected by the first mirror, and then incident on the second mirror, is sequentially reflected again by the second mirror and the first mirror, and is received by the optical sensor.

[0013] The step of obtaining the Rx profile may include: a step of controlling a motion stage mounted on the transceiver to change at least one of a position and a posture of the receiver; and a step of generating the Rx profile based on an optical signal received at each of the changed positions or postures of the receiver.

[0014] The step of obtaining the Tx profile may include: a step of controlling a motion stage mounted on the transceiver to change at least one of a position and a posture of the transmitter; and a step of generating the Tx profile based on an optical signal received at each of the changed positions or postures of the transmitter.

[0015] The above-described judging step can determine whether the transceiver satisfies the criteria by comparing the difference between the peak value of the Rx profile and the peak value of the Tx profile with a preset threshold value.

[0016] The step of obtaining the above Tx profile may include a step of changing the path of light emitted from the transmitter and reflected by the mirror using an optical splitter; and a step of receiving the light whose path has been changed by the optical splitter through the optical sensor.

[0017] The above mirror includes a glass layer and a coating layer, and a wave front error (WFE) of the coating layer may be 10% or less of the wavelength of light emitted from the transmitter.

[0018] The above mirror can have a reflectivity of 98% or more.

[0019] The above mirror may have a diameter or side of 200 mm or more.

[0020] Meanwhile, a method according to the present invention includes a step of driving a transceiver to obtain a first lidar signal for a target; a step of performing calibration for the transceiver based on position information of the target obtained by the first lidar signal and actual position information of the target; wherein the first lidar signal may be an optical signal obtained by light emitted from the transceiver, reflected by a mirror, and then incident on the target, and then sequentially reflected by the target and the mirror, and then incident on the transceiver.

[0021] The actual distance of the target may be the sum of the distance between the transceiver and the mirror, and the distance between the mirror and the target.

[0022] The method may further include a step of tilting the mirror so that light incident from the transceiver is reflected and incident on the target.

[0023] The method may further include a step of tilting the target so that the path of light incident on the target from the mirror becomes perpendicular to the incident surface of the target.

[0024] The method may further include: a step of driving the transceiver to receive a second lidar signal for one or more target charts; and a step of performing calibration for the transceiver based on position information of the target chart obtained based on the second lidar signal and actual position information of the target chart.

[0025] The transceiver is disposed at a first position in an area facing the mirror, the target is disposed at a second position different from the first position in the area facing the mirror, and an angle formed by an optical path between the transceiver and the mirror and an optical path between the mirror and the target may be 90° or less.

[0026] The method may further include a step of controlling a rotating platform connected to the transceiver to change at least one of a position and an angle of the transceiver; and a step of tilting at least one of the mirror and the target in response to a change in the position or angle of the transceiver.

[0027] According to the lidar test method according to the present invention, the efficiency of the test space can be dramatically improved by using one or more mirrors.

[0028] Figure 1 is a flowchart illustrating a method according to one embodiment of the present invention.

[0029] Figure 2 is a conceptual diagram illustrating a method according to one embodiment of the present invention.

[0030] Figure 3 is a flowchart illustrating a transceiver formation step of a method according to the present invention.

[0031] FIG. 4 is a drawing showing a device used in the transceiver forming step of FIG. 3.

[0032] FIG. 5 illustrates a plurality of scan images obtained in the transceiver forming step of FIG. 3.

[0033] Figure 6 is a flowchart illustrating a first embodiment of an overlap test step of a method according to the present invention.

[0034] Figure 7 is a conceptual diagram specifically explaining the first embodiment of Figure 6.

[0035] Figure 8 is a flowchart illustrating a second embodiment of the overlap test step of the method according to the present invention.

[0036] Figure 9 is a conceptual diagram specifically explaining the second embodiment of Figure 8.

[0037] Figure 10 illustrates a structural design for changing the position and posture of a transceiver in the overlap test step of the method according to the present invention.

[0038] Fig. 11 is a photograph showing a profile obtained in the overlap test step of the method according to the present invention.

[0039] Figure 12 illustrates the configuration of a target used in the method according to the present invention.

[0040] Figure 13 is a drawing for explaining the light source structure and control method of the target used in the method according to the present invention.

[0041] Figure 14 illustrates the structure and arrangement of a target used in the method according to the present invention.

[0042] FIG. 15 illustrates various embodiments of the structure and arrangement of a target used in a method according to the present invention.

[0043] Figure 16 is a drawing for explaining a method for determining whether the criteria of the overlap test step of the method according to the present invention are met.

[0044] Figure 17 is a drawing for explaining the test environment and method of the calibration test step of the method according to the present invention.

[0045] Figure 18 is a flowchart specifying the calibration test step of the method according to the present invention.

[0046] Figure 19 illustrates the structure of a mirror used in the method according to the present invention.

[0047] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings so that a person having ordinary skill in the art to which the present invention pertains can easily practice the present invention.

[0048] FIG. 1 is a flowchart illustrating a method according to one embodiment of the present invention, and FIG. 2 is a conceptual diagram illustrating a method according to one embodiment of the present invention.

[0049] Referring to FIGS. 1 and 2 together, first, a transmitter (10) and a receiver (20) are provided (S100). LiDAR is basically composed of a transmitter (10) and a receiver (20), and a signal processing unit (not shown) processes an optical signal received through the receiver (20) to detect a target. The transmitter (10) emits a laser pulse of light of a predetermined wavelength (e.g., NIR (850-1100 nm) or SWIR (1400-1550 nm)), and the receiver (20) receives light that is incident on the target and then reflected from the target. The signal processing unit (not shown) can recognize information about the target by using the time it takes for the light to be reflected from the target and the speed of light, or by using the phase of the transmission / reception pulse, and can obtain various information such as distance.

[0050] Afterwards, the transmitter (10) and the receiver (20) are combined to form a transceiver (30) (S110). At this time, the transceiver can be formed through the FnA (Focus and Alignment) process. This is a process for finding the optimal position, or in other words, the optimal relative pose, of the transmitter (10) and the receiver (20). When combining the transmitter (10) and the receiver (20) to form the transceiver (30), it is necessary to find and fix the optimal position. Specifically, the transmitter (10) and the receiver (20) must be positioned and fixed in the most optimal position so that the receiver (20) can properly receive the light emitted and reflected from the transmitter (10).

[0051] If the transceiver (30) is formed with the transmitter (10) and receiver (20) fixed in the optimal position, an overlap test is performed on the transceiver (30) (S120). There are various methods for fixing the transmitter (10) and receiver (20), but a representative method is to fix the transmitter (10) and receiver (20), then inject a hardening material (e.g., epoxy) and harden it. There is a possibility that the position or posture of the transmitter (10) and receiver (20) may be slightly misaligned during this hardening process. The overlap test step (S120) is a step to determine whether performance deterioration has occurred due to such misalignment, and to check whether the optical paths of the transmitter (10) and receiver (20) overlap correctly at the target distance, etc. After the transceiver (30) is assembled, a pass / fail decision is made through an overlap test, and it is checked whether the distortion due to the curing process, etc., is within the allowable range in the transceiver forming step (S110). If the transceiver (30) is judged as failing (FAIL) in the overlap test step (S120), the transceiver (30) can be reassembled or discarded. A calibration test is performed on the transceiver (30) that is judged as passing (PASS) (S140).

[0052] The calibration test is a step for calibrating the detection range, range accuracy, range precision, angular resolution, field of view (FOV), etc. of the transceiver (30). For the calibration test, it is necessary to rotate the transceiver (30) at various angles. For this purpose, a step (S130) of coupling the transceiver (30) to a rotation platform (40) may be added. In the calibration step, a correction is performed so that the actual distance between the transceiver (30) and the target and the distance to the target obtained by driving the transceiver (30) are measured as the actual distance. The transceiver (30) is calibrated through the calibration test, thereby satisfying the required performance of the lidar.

[0053] FIG. 3 is a flowchart illustrating a transceiver forming step of a method according to the present invention, FIG. 4 is a drawing illustrating a device used in the transceiver forming step of FIG. 3, and FIG. 5 illustrates a plurality of scan images obtained in the transceiver forming step of FIG. 3.

[0054] As mentioned above, the FnA process is performed in the transceiver formation step. This is for alignment of the transmitter (10) and receiver (20).

[0055] Referring to FIGS. 3 and 4 together, after fixing the receiver (20), the position and / or posture of the transmitter (10) is changed (S111). Then, a scan image for a test target at each of the changed positions and / or postures of the transmitter (10) is acquired (S112). The scan image can be generated by an optical signal emitted from the transmitter (10), reflected by the test target, and received by the receiver (20). For example, a plurality of scan images are acquired by fixing the receiver (20) and rotating the transmitter (10) at a predetermined angle or moving it by a predetermined distance.

[0056] Conversely, a method of fixing the transmitter (10) and then changing the position and / or posture of the receiver (20) may also be used. Specifically, the transmitter (10) is fixed and then the position and / or posture of the receiver (20) is changed (S113). Then, a scan image of a test target at each of the changed positions and / or postures of the receiver (20) is acquired (S114). For example, a plurality of scan images are acquired while fixing the transmitter (10) and rotating the receiver (20) at a predetermined angle or moving it by a predetermined distance.

[0057] As illustrated in FIG. 4, the test target is fixed at a position spaced a predetermined distance from the transmitter (10) and the receiver (20), and can be implemented in various shapes such as a slit shape, a grid shape, etc. In addition, a motion stage that can move in the X, Y, Z, Yaw, Pitch, and Roll directions can be mounted to change the position and / or attitude of the transmitter (10) or the receiver (20). In other words, the motion stage is mounted on the transmitter (10) or the receiver (20), and the position and / or attitude of the transmitter (10) or the receiver (20) can be changed while controlling the movement and rotation of the motion stage.

[0058] Next, the optimal positions of the transmitter (10) and the receiver (20) are selected based on the scan images obtained by at least one of the two methods above (S115). The optimal positions can be selected in various ways. One method is to calculate a clarity score for each of a plurality of scan images using a predetermined formula, and determine the position and / or posture with the highest clarity score as the optimal position. In another method, the optimal position corresponding to the highest clarity can be output through the input of a plurality of scan images using an AI algorithm modeled by learning the scan images. In yet another method, a selection signal for the scan image with the highest clarity among the plurality of scan images can be received through user input, and the position where the scan image corresponding to the selection signal is generated can be determined as the optimal position.

[0059] Referring to the scan images illustrated in Fig. 5, it can be confirmed that the clarity of the scan image corresponding to pose[x] is the best in various ways. Accordingly, the positions of the transmitter (10) and receiver (20) in pose[x] can be selected as the optimal positions and the transmitter (10) and receiver (20) can be placed.

[0060] Once the optimal position is selected, the transmitter (10) and the receiver (20) are positioned or fixed in the optimal position, and then a curable material is injected (S116). The curable material includes a thermosetting material that is cured by heat and a photocurable material that is cured by light (e.g., ultraviolet rays). Thereafter, the curable material is cured by using heat or light (S117), thereby forming a transceiver (S118). Preferably, the curable material may be epoxy. That is, after the transmitter (10) and the receiver (20) are fixed in the optimal position, epoxy is injected, and ultraviolet rays (UV) are irradiated for a predetermined time to cure (pre-cure) the epoxy, thereby forming a transceiver. In addition, after performing the pre-cure in step S117, the main curing may be performed through an oven, thereby forming a transceiver (30). In particular, in this process, changes or distortions may occur in the relative positions of the transmitter (10) and receiver (20). Whether or not a change in position occurs when performing pre-curing at the optimal position and then performing main curing can be confirmed through an overlap test described later.

[0061] FIG. 6 is a flowchart illustrating a first embodiment of an overlap test step of a method according to the present invention, and FIG. 7 is a conceptual diagram specifically explaining the first embodiment of FIG. 6.

[0062] The overlap test is a test to check whether there is a change in position / alignment that may affect lidar performance due to the curing process that occurs when the transmitter (10) and receiver (20) are combined.

[0063] Referring to (a) of FIG. 7, a basic setting (SET1) for an overlap test according to the first embodiment is configured to mount a transceiver (30) on a motion stage, place the transceiver (30) and the target (50) adjacently, and place a mirror (60) at a predetermined position in an area facing the transceiver (30) and the target (50). The target (50) may include a light source that emits light and a light sensor that receives (detects) the light. In another embodiment, the target (50) may take the form of a general chart. Here, "place the transceiver (30) and the target (50) adjacently" does not mean that the transceiver (30) and the target (50) must be placed on the same line or at the same height, or must be placed within a specific distance. It is acceptable to position the mirrors (60) so that light emitted from either the transceiver (30) or the target (50) can be reflected by the mirror (60) and incident on the other of the transceiver (30) and the target (50).

[0064] In addition, the term "area facing the transceiver (30) and the target (50)" means an area where light emitted from either the transceiver (30) or the target (50) can reach, and it is sufficient for a mirror to be placed at any point (position) in the area.

[0065] First, the first embodiment of FIG. 6 improves test space efficiency by utilizing a single mirror (60). First, the receiver (20) of the transceiver (30) and the light source of the target (50) are driven (S123). Then, while controlling the motion stage, the position and / or posture of the receiver (20) is changed, and an Rx profile (first scan image) is acquired (S124).

[0066] Referring to (b) of FIG. 7, the Rx profile (first scan image) can be generated based on the first optical signal that is emitted from the light source of the target (50), reflected by the mirror (60), and then received by the receiver (20) of the transceiver (30). To explain step by step, the step of obtaining the Rx profile can include the step of controlling the motion stage mounted on the transceiver (30) to change at least one of the position and posture of the receiver (20), and the step of generating the Rx profile based on each optical signal received at the changed position or posture of the receiver (20). The path of the light at this time is the light source of the target (50) → mirror (60) → receiver (20) of the transceiver (30).

[0067] Thereafter, the receiver (20) of the transceiver (30) and the light source of the target (50) are turned OFF, and the transmitter (10) of the transceiver (30) and the light sensor of the target (50) are driven (S125). Similarly, while controlling the motion stage, the Tx profile (second scan image) is acquired while changing the position and / or posture of the transmitter (10) (S126).

[0068] Again, referring to (b) of FIG. 7, the Tx profile (second scan image) can be generated based on the second optical signal that is emitted from the transmitter (10) of the transceiver (30), reflected by the mirror (60), and then received by the optical sensor of the target (50). To explain step by step, the step of obtaining the Tx profile can include the step of controlling the motion stage mounted on the transceiver (30) to change at least one of the position and posture of the transmitter (10), and the step of generating the Tx profile based on each optical signal received by the optical sensor at the changed position or posture of the transmitter (10). The path of the light at this time becomes the transmitter (10) of the transceiver (30) → mirror (60) → optical sensor of the target (50).

[0069] Although FIG. 6 illustrates that steps S123 and S124 are performed before steps S125 and S126, in other embodiments, steps S125 and S126 may be performed before steps S123 and S124.

[0070] Finally, the degree of overlap between the Rx profile (first scan image) and the Tx profile (second scan image) is judged to determine whether the transceiver (30) passes or fails.

[0071] In the first embodiment of FIG. 6, space efficiency is improved by utilizing a mirror (60) for the overlap test. When performing an overlap test on a target located 100 m away, a test space large enough to cover that distance is required. For long-range lidar, an even larger test space may be required. However, using a single mirror (60) can reduce the length of the test space by approximately half. In other words, when performing an overlap test on a target located 100 m away, the same test results can be obtained by simply placing the mirror (60) at a location 50 m away.

[0072] FIG. 8 is a flowchart illustrating a second embodiment of an overlap test step of a method according to the present invention, and FIG. 9 is a conceptual diagram specifically explaining the second embodiment of FIG. 8.

[0073] First, the basic setting (SET2) for the overlap test according to the second embodiment is composed of mounting a transceiver (30) on a motion stage, arranging the transceiver (30) and the target (50) adjacently, arranging a first mirror (61) at a predetermined position in an area facing the transceiver (30) and the target (50), and arranging a second mirror (62) at a predetermined position in an area facing the first mirror (61). Similarly, “arranging the transceiver (30) and the target (50) adjacently” does not mean that the transceiver (30) and the target (50) must be arranged on the same line or at the same height, or must be arranged within a specific distance. It is acceptable to position the mirrors (60) so that light emitted from either the transceiver (30) or the target (50) can be reflected by the mirror (60) and incident on the other of the transceiver (30) and the target (50).

[0074] In addition, the term "area facing the transceiver (30) and the target (50)" means an area where light emitted from either the transceiver (30) or the target (50) can reach, and it is sufficient that the first mirror (61) is placed at any point (location) in the area. Similarly, the term "area facing the first mirror (61)" means an area where light reflected by the first mirror (61) can reach, and it is sufficient that the second mirror (62) is placed at any point (location) in the area. In other words, it should be understood that the expression "facing" is not limited to meaning a state where the two components face each other so as to be perpendicular to the optical path.

[0075] First, while the first embodiment of FIG. 6 improved test space efficiency by utilizing a single mirror (60), the second embodiment of FIG. 8 further improves test space efficiency by two times by utilizing two mirrors (61, 62). In the description of the second embodiment, since the operation is identical to that of the first embodiment and only the path of light is different, the same drawing numbers as those of FIG. 6 are used for the description.

[0076] First, the receiver (20) of the transceiver (30) and the light source of the target (50) are driven (S123). Then, while controlling the motion stage, the position and / or posture of the receiver (20) is changed, and an Rx profile (first scan image) is acquired (S124).

[0077] Referring to FIG. 9, the Rx profile (first scan image) can be generated based on an optical signal that is emitted from a light source of a target (50), reflected by a first mirror (61), then incident on a second mirror (62), reflected again from the second mirror (62), then incident on a first mirror (62), then reflected from the first mirror (62) and received by a receiver (20) of a transceiver (30).

[0078] To explain step by step, the step of obtaining the Rx profile may include a step of controlling a motion stage mounted on the transceiver (30) to change at least one of the position and posture of the receiver (20), and a step of generating the Rx profile based on each optical signal received at the changed position or posture of the receiver (20). At this time, the optical signal is a signal that is emitted from the light source of the target (50), reflected by two mirrors (61, 62), and then received by the receiver (20) of the transceiver (30). The path of the light at this time is the light source of the target (50) → the first mirror (61) → the second mirror (62) → the first mirror (61) → the receiver (20) of the transceiver (30).

[0079] Thereafter, the receiver (20) of the transceiver (30) and the light source of the target (50) are turned OFF, and the transmitter (10) of the transceiver (30) and the light sensor of the target (50) are driven (S125). Similarly, while controlling the motion stage, the Tx profile (second scan image) is acquired while changing the position and / or posture of the transmitter (10) (S126).

[0080] Meanwhile, increasing the number of mirrors in the same manner as described above allows overlap testing on targets at greater distances within a confined space. Therefore, the number of mirrors used in the present invention is not limited to one or two, and three or more mirrors may be used.

[0081] Again, referring to FIG. 9, the Tx profile (second scan image) can be generated based on an optical signal that is emitted from the transmitter (10) of the transceiver (30), reflected by the first mirror (61), then incident on the second mirror (62), then reflected again from the second mirror (62), then incident on the first mirror (62), then reflected from the first mirror (62) and received by the optical sensor of the target (50).

[0082] To explain step by step, the step of obtaining the Tx profile may include a step of controlling a motion stage mounted on the transceiver (30) to change at least one of the position and posture of the transmitter (10), and a step of generating the Tx profile based on each optical signal received by the optical sensor at the changed position or posture of the transmitter (10). At this time, the optical signal is a signal emitted from the transmitter (10) of the transceiver (30), reflected by two mirrors (61, 62), and then received by the optical sensor of the target (50). The path of the light at this time is the transmitter (10) of the transceiver (30) → first mirror (61) → second mirror (62) → first mirror (61) → optical sensor of the target (50).

[0083] In the second embodiment of FIG. 8, steps S123 and S124 are shown to be performed first and then steps S125 and S126 are performed. However, in other embodiments, steps S125 and S126 may be performed first and then steps S123 and S124 may be performed.

[0084] Finally, the degree of overlap between the Rx profile (first scan image) and the Tx profile (second scan image) is judged to determine whether the transceiver (30) passes or fails.

[0085] In the second embodiment of Fig. 8, space efficiency is significantly improved by using two mirrors (61, 62) for the overlap test. That is, when performing an overlap test on a target located at a distance of 100 m, the length of the test space can be reduced by a quarter by using two mirrors (60). That is, when performing an overlap test on a target located at a distance of 100 m, the overlap test can be performed simply by placing the first mirror (61) at a location 25 m away and placing the second mirror (62) at a location 25 m away from the first mirror (61).

[0086] FIG. 10 illustrates a structural design for changing the position and posture of a transceiver in the overlap test step of the method according to the present invention, which will be briefly described below. The transceiver (30) is placed on a motion stage (70) so that its posture and position can be changed in various ways. The motion stage (70) is a mechanical device that moves across one axis or more than six degrees of freedom (X, Y, Z, θ-X, θ-Y, θ-Z), and may include a linear slide for moving the transceiver (30) to a predefined length and a rotation / tilt stage for rotating the transceiver (30) in a 360° direction. Since the motion stage (70) guarantees precision in movement and rotation, it is possible to perform precise position / posture changes of the transceiver (30) by using it.

[0087] When scanning the Tx profile, since the optical sensor of the target (50) cannot scan the transmitter area at once, the motion stage (70) is used to check the entire profile of the transmitter (10). In addition, even when scanning the Rx profile, the entire profile of the receiver (20) can be checked by receiving light emitted from the light source of the target (50) while changing the position and / or posture using the motion stage (70). In particular, since the purpose of scanning the Rx profile is largely to check the limit point of the field of view of the receiver (20), the position is moved by a predetermined distance to find the limit point and the optical signal from the light source is received.

[0088] Fig. 11 is a photograph showing a profile obtained in the overlap test step of the method according to the present invention. Specifically, the graph shown in Fig. 11 is a Tx profile (P TX ) and Rx profile (P RX ), where the horizontal axis represents the angle of the vertical field of view (FOV), and the vertical axis represents the angle of the horizontal field of view (FOV).

[0089] Referring to FIG. 11, the Tx profile (P) is changed while changing the position and / or attitude of the transceiver (30) within a range of -20 to +20° in the X-axis and within a range of -0.3 to +0.2° in the Y-axis through the motion stage. TX ) and Rx profile (P RX ) can be obtained. As shown in Fig. 11, the Tx profile (P) on the same coordinate axis TX ) and Rx profile (P RX ) can be easily checked to determine the degree of overlap.

[0090] Here, the Tx profile (P TX ) and Rx profile (P RX ) is briefly explained about the target structure, arrangement, control method, etc. to effectively create it.

[0091] Fig. 12 illustrates the configuration of a target used in the method according to the present invention, and Fig. 13 is a drawing for explaining the light source structure and control method of the target used in the method according to the present invention.

[0092] A target (50) for an overlap test includes a light source (51) and a light sensor (52). The light source (51) can be implemented as an LED, a laser diode (LD), etc. In addition, depending on the type of light emitted, it can be a visible light emitting diode (VLED), an infrared LED (ILED), an ultraviolet LED (UV LED), etc. The light source can take on various forms, shapes, and operating methods. The light sensor (52) can be a photodiode, a photo-coupler, a photo-transistor, a CDS, etc., and detects light of various wavelengths.

[0093] As illustrated in Fig. 12, the light source (51) may have a +-shaped LED array, but is not limited thereto. The LEDs included in the light source (51) may take on various shapes, such as circular, oval, and polygonal, and the sizes of the LEDs may also be applied in various ways. Of course, other optical elements may constitute the light source (51) in addition to the LEDs. Even if the sensitivity of the receiver (20) is good, since high output is required, the amount of light emitted from the light source (51) needs to be somewhat large. To this end, multiple LEDs, rather than a single LED, may be arranged in various shapes.

[0094] Here, if the light source (51) is arranged in a + shape, a very advantageous effect can be achieved when scanning in the horizontal and vertical directions for the FOV test.

[0095] Referring to Fig. 13, when scanning in a horizontal direction, scanning can be performed with only the vertical LEDs in the +-shaped LED array illuminated. In this case, not only can the light recognition rate be improved, but the light quantity distribution can be made constant, and power consumption efficiency can also be improved. Similarly, when scanning in a vertical direction, the same technical effect can be achieved by performing scanning with only the horizontal LEDs in the +-shaped LED array illuminated.

[0096] A device for performing a method according to the present invention can perform light source control of a target when acquiring an Rx profile. That is, when scanning in a horizontal direction, the Rx profile can be acquired while changing the position and / or posture of the receiver (20) using a motion stage (70) in a state where only the vertical line of the light source (51) is illuminated (Fig. 13 (a)), and when scanning in a vertical direction, the Rx profile can be acquired while changing the position and / or posture of the receiver (20) using a motion stage (70) in a state where only the horizontal line of the light source (51) is illuminated (Fig. 13 (b)).

[0097] FIG. 14 illustrates the structure and arrangement of a target used in a method according to the present invention, and FIG. 15 illustrates various embodiments of the structure and arrangement of a target used in a method according to the present invention.

[0098] As illustrated in Fig. 14, an optical splitter (54) may be placed between the light source (51) and the light sensor (52). In addition, an aperture (53) may be further included to align the light path from the light source (51) or to control the emission and blocking of light.

[0099] When performing an overlap test, it is ideal for the optical paths of the light source (51) and the optical sensor (52) to be aligned. To this end, as illustrated in (a) of Fig. 15, the path of the light reflected from the mirror can be changed using an optical splitter (54) and directed toward the optical sensor (52). This allows the path of the light that should be reflected from the mirror and incident on the optical sensor (52) to be aligned with the path of the light emitted from the light source (51) to the mirror.

[0100] When adopting such a structure, the step of obtaining a Tx profile (S126 of FIGS. 6 and 8) may include a step of changing the path of light reflected by a mirror after being emitted from a transmitter (10) using an optical splitter (54), and a step of receiving the light whose path has been changed by the optical splitter (54) through an optical sensor (52).

[0101] That is, the light path (LP) from the light source (51) to the mirror and the light path (LP) from the mirror to the light sensor (52) are identical, but the light path can be made to face the light sensor (52) at the final stage using an optical splitter (54) so ​​that there is no physical (mechanical) interference between the light source (51) and the light sensor (52).

[0102] In another embodiment, as shown in (b) of FIG. 15, a light source (51) and a light sensor (52) may be placed in the optical path using a jig or the like.

[0103] Again, referring to FIGS. 6 and 8, when the Rx profile (first scan image) and the Tx profile (second scan image) are acquired (S124, S126), it is determined whether the transceiver (30) meets the criteria based on the degree of overlap between the two (S127), and if the degree of overlap is less than a preset value or ratio (S127-NO), it is determined as failed (S128). Conversely, if the degree of overlap is greater than or equal to the preset value or ratio (S127-YES), it is determined as passed (S129).

[0104] Rx Profile (P RX ) and Tx profile (P TX ) can be judged in various ways. Fig. 16 is a drawing for explaining a method for judging whether the criteria of the overlap test step of the method according to the present invention are met.

[0105] Briefly explaining each profile, Tx profile (P TX ) reflects the measurement value (voltage value) of the light sensor (51) of the target (50), and the value may be measured somewhat differently depending on the spatial area of ​​the transmitter (10). Areas with higher measurement values ​​(voltage values) are displayed brighter.

[0106] Rx Profile (P RX ) is obtained in the form of a Gaussian graph where the light source (51) of the target (50) and the field of view (FOV) of the receiver (20) of the transceiver (30) match, and the peak part of the Gaussian graph is a point representing the field of view (FOV) of the receiver (20), and when an image is generated with the full width at half maximum (FWHM) of the peak part as the width, a box-shaped scan image as shown in FIG. 16 is generated.

[0107] The graph in (a) of Fig. 16 shows the Rx profile (P RX ) and Tx profile (P TX ) has a high degree of overlap, and the graph in (b) of Fig. 16 shows the Rx profile (P RX ) and Tx profile (P TX ) can be confirmed to have a low degree of overlap.

[0108] The degree of overlap is determined by the Rx profile (P RX ) and Tx profile (P TX ) can be compared with a preset threshold value. For example, the Rx profile (P) at the same point (X / Y coordinate) on the graph RX ) and the peak value of the Tx profile (P TX) is greater than or equal to a threshold value (e.g., 8 μm), it is determined that the transceiver (30) does not meet the required standard, and if it is less than the threshold value, it is determined that the transceiver (30) meets the required standard.

[0109] In another embodiment, the Rx profile (P RX ) and Tx profile (P TX ) can be used to determine whether the criteria are met based on the area or ratio of the overlapping region. For example, the Rx profile (P RX ) and Tx profile (P TX ) can be processed to obtain an outline, and based on the area defined by the outline, the area or ratio of the overlapping area can be clearly calculated. If the area or ratio is greater than a preset threshold, it can be determined that the transceiver (30) satisfies the required standard, and if it is less than the preset threshold, it can be determined that the transceiver (30) does not meet the required standard.

[0110] In another embodiment, an AI algorithm modeled by learning a profile image can be used. The AI ​​algorithm can be an Rx profile (P RX ) and Tx profile (P TX ) as input value and the degree of overlap can be generated as output value. In some cases, the Rx profile (P RX ) and Tx profile (P TX ) can be designed so that the AI ​​algorithm can immediately output whether the required criteria are met by simply inputting it into the AI ​​algorithm.

[0111] FIG. 17 is a drawing for explaining a test environment and method of a calibration test step of a method according to the present invention, and FIG. 18 is a flowchart specifying the calibration test step of a method according to the present invention.

[0112] First, let's describe the test environment in detail. Figure 17 shows a top-down view of the test space, which is a rectangular space measuring 50 m long and 14 m wide, with a floor-to-ceiling height of 2.7 m. However, the test space is not necessarily limited to a rectangular space; its length, width, and height can also be varied.

[0113] The transceiver (230) to be calibrated can be placed at the first position of the test space, and it is advantageous to place the transceiver (230) near the corner in order to secure the maximum distance. In addition, one or more target charts (270) having various distances from the transceiver (230) are placed. In Fig. 17, a total of 17 target charts (#1 to #17) are illustrated as being placed, but the number of target charts may vary. Each target chart may have a different reflectivity. For example, target chart #11 placed at a distance of 35 m from the transceiver (230) has a reflectivity of 3%, and target chart #15 placed at a distance of 48 m is set to have a reflectivity of 65%. The distance and reflectivity of the target charts may be set in various ways.

[0114] To achieve the effect of expanding the test space within such a limited space, a mirror may also be utilized in calibration tests. That is, a mirror (260) may be placed at a predetermined position in an area facing the transceiver (230), and a target (250) may be placed at a predetermined position in an area facing the mirror (260). In the absence of a mirror (260), the maximum distance that can be measured in a test environment is only 48 m, but by placing a mirror (260), the measurement distance can be extended to a maximum of 96 m.

[0115] To recognize multiple target charts or targets placed in a test space, a rotating platform may be mounted on the transceiver (230). Furthermore, positional information on the target charts or targets can be acquired by changing the position using the rotating platform. Furthermore, a calibration test step is performed to verify that the preset actual distances of the target charts or targets are accurately measured, and corrections are performed to minimize the error range.

[0116] Hereinafter, the arrangement of each configuration for achieving the effect of expanding the test space by using the mirror (260) will be described. The transceiver (230) may be arranged at a first position in the area facing the mirror (260), and the target (250) may be arranged at a second position different from the first position in the area facing the mirror (260). At this time, it is preferable that the angle formed by the optical path between the transceiver (230) and the mirror (260), and the optical path formed between the mirror (260) and the target (250) is 90° or less. In order to secure maximum space efficiency, it is preferable that the transceiver (230) and the mirror (260) be as far apart as possible, and due to spatial constraints, the target (250) cannot be further away than the mirror (260). At this time, the target (250) may be in the form of a chart like other target charts, or may be in the form having a light source and a light sensor as described above. Meanwhile, the mirror (260) and the target (250) can be placed in an area that does not obstruct the optical path between the transmitter of the transceiver (230) and each target chart (270).

[0117] Referring to the flow chart of Fig. 18, the setting (SET3) for the calibration test step is the same as described above, so its description is omitted. In the calibration test step, a test using a target chart (270) and a test using a target (250) / mirror (260) can be performed.

[0118] A test (relatively long-distance) using a target (250) and a mirror (260) operates a transceiver (230) to receive a first lidar signal for the target (250) (S141). The first lidar signal may be an optical signal in which light emitted from the transceiver (230) is reflected by the mirror (260), then incident on the target (250), and then sequentially reflected by the target (250) and the mirror (260) before incident on the transceiver (230).

[0119] Then, the position information (measurement information) of the target (250) obtained by the first lidar signal is acquired (S141). Then, the actual position information of the target (250) is compared with the position information (measurement information) measured by the first lidar signal, and calibration is performed to minimize the difference (S145). At this time, the actual distance of the target (250) may be the sum of the distance between the transceiver (230) and the mirror (260), and the distance between the mirror (260) and the target (250).

[0120] At this time, the target (250) and the mirror (260) are provided to be tiltable, and it is preferable that the angle of the mirror (260) be tilted so that the light incident from the transmitter of the transceiver (230) is directed toward the target (250), and it is preferable that the angle of the target (250) be tilted so that the incident surface is perpendicular to the path of the light incident from the mirror (260). Thereby, the path of the light from the mirror (260) to the target (250) and the path of the light reflected by the target (250) and directed toward the mirror (260) can be matched.

[0121] To this end, the calibration test step may further include a step of tilting the mirror (260) so that the light incident from the transceiver (230) is reflected and incident on the target (250). In addition, the calibration test step may include a step of tilting the target (250) so that the path of the light incident on the target (250) from the mirror (260) becomes perpendicular to the incident surface of the target (250).

[0122] Additionally, the calibration test step may further include a step of controlling a rotating platform connected to the transceiver (250) to change at least one of the position and angle of the transceiver (250), and a step of tilting at least one of the mirror (260) and the target (250) in response to the change in the position or angle of the transceiver (250).

[0123] Meanwhile, a test (relatively short distance) using a target chart (270) operates a transceiver (230) to receive a second lidar signal for one or more target charts (270) (S143). The second lidar signal may be an optical signal that is emitted from the transceiver (230) and reflected by the target chart (270) and then incident on the transceiver (230).

[0124] Then, the position information (measurement information) of each target chart (270) acquired by the second lidar signal is acquired (S144). Then, calibration of the transceiver (230) is performed based on the actual position information of the target chart (270) and the position information (measurement information) measured by the second lidar signal (S145).

[0125] Fig. 19 illustrates the structure of a mirror used in the method according to the present invention. The mirror illustrated in Fig. 19 can be used in both the overlap test and the calibration test described above.

[0126] The mirror (260) includes a glass layer (261) and a coating layer (261). The coating layer (261) can be formed by coating various materials including metals (e.g., gold (Au), silver (Ag), aluminum (Al), dielectrics (YF3, ZnS, etc.)) on the glass layer (261). At this time, the reflectivity according to the wavelength can be determined depending on the coating material. The mirror (260) used in the present invention can have a reflectivity of 98% or more, preferably 99.99%.

[0127] Meanwhile, the coating layer (261) of the mirror (260) may have a wavefront error (WFE) of 10% or less of the wavelength of the light emitted from the transmitter. The wavefront error is a factor that deteriorates the performance of the optical system, reduces the resolution and clarity of the optical system, and causes distortion. However, by setting the wavefront error of the mirror (260) to 10% or less of the wavelength of the light emitted from the transmitter, the performance degradation mentioned above can be minimized.

[0128] For example, if the wavelength band of the lidar sensor is selected as 905 nm or 1550 nm, the wavefront error of the mirror (260) can be set to 90.5 nm or less or 150.5 nm or less. When using a wavelength of 905 nm, it has the advantage of being relatively less affected by moisture in the air because the absorption by water is relatively low. Conversely, when using a wavelength of 1550 nm, it has the advantage of being safer for the human body, having a long detection range, and having relatively less sunlight noise compared to a wavelength of 905 nm. The wavelength of the light emitted from the transmitter can be selected according to the required lidar performance, and the test efficiency can be improved by selecting an appropriate mirror (260) for each wavelength.

[0129] Meanwhile, referring to Fig. 9, the first mirror (61) has two reflection points, and considering this, it is preferable to make the diameter or side length of the mirror (260) 200 mm or more.

[0130] Although not shown in the drawing, the motion stage and / or rotation platform for changing the position / posture of the transceiver may be equipped with a visible light LED in a predetermined area on the front surface. This is to enable alignment while checking the optical path between the mirror and the target. Since the light emitted from the visible light LED is reflected by the mirror arranged on the opposite side, it is possible to immediately check whether the alignment of the transceiver and the mirror is proper. Meanwhile, since the height of the aperture equipped on the target is constant, it is possible to immediately check whether the alignment of the mirror and the target is proper by checking whether the light emitted from the visible light LED, reflected by the mirror, and then directed to the target is incident through the aperture.

[0131] Meanwhile, although not shown in the drawing, a test device for performing a test method according to the present invention may include a control unit, a receiving unit, an input unit, and a test unit.

[0132] The control unit determines whether each test (optimal position determination in the FnA process, overlap test, calibration test, etc.) passes or fails based on information (scan image, profile, lidar information, etc.) obtained at each step of the method according to the present invention, and controls various devices (motion stage, rotating platform, etc.) for driving, changing the position and / or attitude of the transceiver being tested, and can control tilting of the target or mirror, etc.

[0133] The receiving unit receives signals obtained from the test subject and signals obtained from the target, and the input unit receives user input for various settings for the test environment, various settings for objects (targets, target charts, etc.) placed in the test environment, and setting standards for the test.

[0134] The test section performs the overall operations described above related to the FnA process, overlap test, and calibration test.

[0135] Meanwhile, the method according to the present invention can be implemented as a computer program. The computer program according to the present invention is intended to execute various embodiments of the above-described testing method on a computer and can be recorded on a computer-readable recording medium. Furthermore, the computer program according to the present invention is intended to execute various embodiments of the above-described testing method on a computer and can be recorded on a computer-readable recording medium.

[0136] The method according to the present invention may be provided as a computer program product. The computer program product may be traded as a product between a seller and a buyer. The computer program product may be distributed in the form of a machine-readable storage medium (e.g., compact disc read-only memory (CD-ROM)), or may be distributed online (e.g., downloaded or uploaded) through an application store (e.g., Play Store™) or directly between two user devices (e.g., smartphones). In the case of online distribution, at least a portion of the computer program product may be temporarily stored or temporarily generated in a machine-readable storage medium, such as the memory of a manufacturer's server, an application store's server, or an intermediary server.

[0137] Meanwhile, the method according to the present invention can be performed by a computer, a computing device, etc. In addition, the method according to the present invention can be implemented in the form of program commands that can be executed through various computer means and recorded on a computer-readable medium. The computer-readable recording medium can include program commands, data files, data structures, etc., alone or in combination. The program commands recorded on the medium may be those specially designed and configured for the present invention or may be those known and available to those skilled in the art of computer software. Examples of the computer-readable recording medium include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical media such as CD-ROMs and DVDs, magneto-optical media such as floptical disks, and hardware devices specially configured to store and execute program commands such as ROMs, RAMs, and flash memories. Examples of program commands include not only machine language codes generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc. The above hardware device may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

[0138] In addition, although the above description focuses on examples, these are merely examples and do not limit the present invention. Those skilled in the art to which the present invention pertains will appreciate that various modifications and applications not exemplified above are possible without departing from the essential characteristics of the present invention. For example, each component specifically shown in the examples can be modified and implemented. In addition, differences related to such modifications and applications should be interpreted as being included within the scope of the present invention defined in the appended claims.

Claims

1. Step of providing a transmitter and a receiver; A step of forming a transceiver by combining the transmitter and the receiver; A step of performing an overlap test on the above transceiver; and A step of performing calibration for the above transceiver; The step of forming the above transceiver is: A step of obtaining a scan image of a test target while fixing one of the transmitter and the receiver and changing at least one of the position and posture of the other; A step of selecting the optimal positions of the transmitter and the receiver based on the acquired plurality of scan images; A step of fixing the transmitter and the receiver at the optimal position and injecting a curable material; and A method comprising a step of curing the curable material using heat or light.

2. In paragraph 1, The step of selecting the above optimal location is: A step of calculating a clarity score for each of the plurality of scanned images; and A method comprising: determining the optimal position based on the clarity score; 3. In paragraph 1, The steps for performing the above overlap test are: A step of setting the receiver of the above transceiver to ON and setting the light source of the target placed adjacent to the above transceiver to ON; A step of obtaining an Rx profile based on a first optical signal emitted from the light source, reflected by a mirror, and received by the receiver; A step of setting the transmitter of the transceiver and the optical sensor of the target to ON; A step of obtaining a Tx profile based on a second optical signal that is emitted from the transmitter, reflected by the mirror, and received by the optical sensor; and A method comprising: testing the transceiver based on the degree of overlap between the Rx profile and the Tx profile.

4. In paragraph 1, The steps for performing the above calibration are: A step of driving the transceiver to receive a lidar signal for a target; and A step of performing calibration for the transceiver based on the position information of the target obtained by the lidar signal and the actual position information of the target; The above lidar signal is, A method in which light emitted from the transceiver, reflected by a mirror, and then incident on the target is an optical signal sequentially reflected by the target and the mirror, and then incident on the transceiver.

5. Step of setting the receiver of the transceiver and the light source of the target to ON; A step of obtaining an Rx profile based on a first optical signal emitted from the light source, reflected by a mirror, and received by the receiver; A step of setting the transmitter of the transceiver and the optical sensor of the target to ON; A step of obtaining a Tx profile based on a second optical signal that is emitted from the transmitter, reflected by the mirror, and received by the optical sensor; and A method comprising: a step of determining whether the transceiver satisfies the criteria based on the degree of overlap between the Rx profile and the Tx profile.

6. In paragraph 5, The mirror includes a first mirror positioned at a predetermined position in an area facing the transceiver or the target, and a second mirror positioned at a predetermined position in an area facing the first mirror. The first optical signal is an optical signal that is emitted from the light source, reflected by the first mirror, and then incident on the second mirror, and then sequentially reflected by the second mirror and the first mirror and received by the receiver. The second optical signal is a method in which light emitted from the transmitter, reflected by the first mirror, and then incident on the second mirror is sequentially reflected by the second mirror and the first mirror and is received by the optical sensor.

7. In paragraph 5, The steps of obtaining the above Rx profile are: A step of controlling a motion stage mounted on the transceiver to change at least one of the position and attitude of the receiver; and A method comprising: generating the Rx profile based on the optical signal received at each changing position or posture of the receiver.

8. In paragraph 5, The step of obtaining the above Tx profile is: A step of controlling a motion stage mounted on the transceiver to change at least one of the position and attitude of the transmitter; and A method comprising: generating the Tx profile based on an optical signal received at each changing position or posture of the transmitter.

9. In paragraph 5, The above-mentioned judging step is a method for judging whether the transceiver satisfies the criteria by comparing the difference between the peak value of the Rx profile and the peak value of the Tx profile with a preset threshold value.

10. In paragraph 5, The step of obtaining the above Tx profile is: A step of changing the path of light reflected by the mirror after being emitted from the transmitter using an optical splitter; and A method comprising: a step of receiving light, the path of which has been changed by the optical splitter, through the optical sensor; 11. In paragraph 5, The above mirror includes a glass layer and a coating layer, A method wherein the wave front error (WFE) of the coating layer is less than or equal to 10% of the wavelength of light emitted from the transmitter.

12. In paragraph 5, The above mirror has a reflectivity of 98% or more.

13. In paragraph 5, The method wherein the above mirror has a diameter or side of 200 mm or more.

14. A step of driving a transceiver to acquire a first lidar signal for a target; A step of performing calibration for the transceiver based on the position information of the target obtained by the first lidar signal and the actual position information of the target; The above first lidar signal is, A method in which light emitted from the transceiver, reflected by a mirror, and then incident on the target is an optical signal sequentially reflected by the target and the mirror, and then incident on the transceiver.

15. In paragraph 14, A method wherein the actual distance of the target is the sum of the distance between the transceiver and the mirror and the distance between the mirror and the target.

16. In paragraph 14, A method further comprising the step of tilting the mirror so that light incident from the transceiver is reflected and incident on the target.

17. In paragraph 14, A method further comprising the step of tilting the target so that the path of light incident on the target from the mirror becomes perpendicular to the incident surface of the target.

18. In paragraph 14, A step of driving the transceiver to receive a second lidar signal for one or more target charts; and A method further comprising: a step of performing calibration for the transceiver based on the position information of the target chart obtained based on the second lidar signal and the actual position information of the target chart.

19. In paragraph 14, The above transceiver is placed at a first position in an area facing the mirror, The target is placed at a second position different from the first position in an area facing the mirror, A method wherein the angle formed by the optical path between the transceiver and the mirror and the optical path formed by the mirror and the target is 90° or less.

20. In paragraph 14, A step of controlling a rotating platform connected to the transceiver to change at least one of the position and angle of the transceiver; and A method further comprising: a step of tilting at least one of the mirror and the target in response to a change in the position or angle of the transceiver.

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