Robot coordinate system calibration system based on orthogonal ranging

Abstract

The utility model discloses a robot coordinate system calibration system based on orthogonal ranging. Three positioners are adopted and installed in a user workpiece coordinate system where the robot can reach, and the three-dimensional coordinates of the positioners are known. A reflector is installed at the tail end of the robot, the reflector is moved to a detection area of the positioner, and three built-in orthogonal distance measuring sensors automatically obtain center coordinates of the reflector and feed back the center coordinates to the controller. And the controller obtains the position and angle deviation of the user workpiece coordinate system in the robot base coordinate system through data processing. According to the calibration system, when the reflector moves to the working area of the positioner, careful calibration is not needed, the distance measuring sensor automatically detects the deviation and automatically compensates and corrects the deviation, the precision is far higher than that of manual reading, and the calibration system is easy and convenient to operate, high in speed and high in efficiency. The positioner is small in size, free of limitation on the installation position, high in universality, capable of being suitable for any robot working airspace and high in cost performance.

Description

Technical Field

[0001] The utility model relates to a robot coordinate system calibration system, in particular to a robot user workpiece coordinate system calibration system based on orthogonal ranging. Background Art

[0002] Industrial robot systems have multiple coordinate systems, each of which plays a different and important role and is indispensable.

[0003] (1) Base coordinate system: This is a coordinate system constructed with the center of the robot base as the origin. Its X, Y, and Z axis values ​​are the offset values ​​of the robot terminal (TCP) relative to the origin. The base coordinate system is also the basic coordinate system of the robot and the basis of all other coordinate systems.

[0004] (2) Tool coordinate system: This is a coordinate system constructed with the tool center point (TCP) of the robot as the origin. The X, Y, and Z axis values ​​are the offset values ​​of the TCP relative to the origin. The tool coordinate system is used to facilitate the adjustment of the robot to the desired posture. Second, when changing tools, only the TCP calibration needs to be recalibrated, without recalibrating the robot.

[0005] (3) User workpiece coordinate system: Its origin position and direction are set by the user. The functions of user workpiece coordinate system are: first, it is convenient for customers to move the robot according to the coordinate system they set; second, when the user workbench and the robot move relative to each other, only the workpiece coordinate system needs to be updated, and there is no need to re-teach the robot trajectory.

[0006] Therefore, after the robot's own accuracy calibration meets the standard, the user's workpiece coordinate system must also be calibrated. Only then can the robot know the location of the user's workpiece coordinate system and accurately operate the user's workpiece. Conversely, if the user's workpiece coordinate system calibration is not accurate enough, even if the robot's own accuracy is very high, the robot's operation accuracy cannot be guaranteed, which may still lead to work failure or even scrapping.

[0007] At present, the calibration of workpiece coordinate systems by robot users at home and abroad mainly adopts manual teaching method. The process is as follows:

[0008] First, on the user's workpiece or fixture, set the X, Y, and Z axes at any angle at any position within the robot's motion range. The origin is located on the workpiece grasped by the robot. The direction of the coordinate system is arbitrarily defined according to customer needs, and the three axes are determined by the right-hand rule.

[0009] Then, select three visible teach points in the user workpiece coordinate system that the robot TCP can touch: the first teach point is the origin of the user coordinate system; the second teach point is on the X-axis, and the line connecting the first and second teach points is the X-axis, with the pointing direction being the positive X direction; the third teach point is in the positive direction area of ​​the Y-axis.

[0010] After that, the robot arm (TCP) is moved to these three points one after another, and the values ​​of the robot encoder are recorded to calculate the vectors and angles between adjacent points, thereby calculating the position and posture of the user workpiece coordinate system, thereby realizing the calibration of the user workpiece coordinate system.

[0011] However, this method of manually teaching and calibrating the user workpiece coordinate system has insurmountable drawbacks:

[0012] Poor accuracy: When moving the TCP to the three corner positions, theoretically, accurate alignment is achieved only when the TCP contacts the corners. However, once the robot TCP contacts a corner, the tool will inevitably deform, resulting in positioning deviation. If there is a gap between the two, this also results in positioning deviation. Therefore, positioning deviation is inevitable, leading to poor calibration accuracy.

[0013] Low efficiency: To minimize positioning deviation, operators need to observe the relative distance and status between the TCP and the corner points with their eyes and make repeated adjustments. This results in slow speed and low efficiency.

[0014] Unreliable: Long periods of repeated observation and adjustment are labor-intensive and physically and mentally exhausting, and the calibration structure is highly unreliable! Especially when multiple robots are working simultaneously in the user's workpiece coordinate system, the coordinate system calibration workload is enormous and time-consuming, making the problem even more prominent and serious.

[0015] Therefore, the current industrial robot application scenarios urgently need a user workpiece coordinate system calibration system that can balance accuracy and efficiency, greatly improve the coordinate system calibration accuracy, significantly improve the calibration efficiency, reduce the labor intensity of operators, and meet modern production needs. Summary of the Invention

[0016] This utility model addresses the current lack of high-precision rapid calibration systems for user workpiece coordinate systems in the industrial robot field. By doing so, it proposes a robot coordinate system calibration system based on orthogonal ranging. This calibration system utilizes three positioners, installed within the user workpiece coordinate system at locations within reach of the robot, whose three-dimensional coordinates are known. A reflector is mounted at the end of the robot. By teaching the desired reflector to reach the positioner's detection area, the positioner's three orthogonal ranging sensors automatically acquire the reflector's center coordinates and feed them back to the controller. The controller processes this data to determine the position and angular deviation of the user workpiece coordinate system within the robot's base coordinate system, thereby calibrating the user workpiece coordinate system. This calibration system eliminates the need for careful calibration when controlling the reflector's movement into the positioner's working area. The three orthogonal ranging sensors automatically detect these deviations and automatically compensate and correct them. This system not only significantly exceeds manual reading accuracy but also offers ease of operation, speed, and efficiency, enabling high-precision and rapid calibration of the user workpiece coordinate system. Furthermore, the positioner is compact, can be installed in any desired location, and is highly versatile, adapting to any robot's working area and offering a high cost-effectiveness.

[0017] The utility model is realized through the following technical solutions:

[0018] The utility model provides a robot coordinate system calibration system based on orthogonal ranging. The calibration system consists of three parts: a positioner, a reflector and a controller. The positioner has three orthogonal ranging sensors built in, wherein:

[0019] The positioner is an integrated small positioning and measuring instrument, there are three of them, which are installed in the user's workpiece coordinate system and at a place where the robot TCP can reach. Its position can be arbitrary and not limited, and does not have to be at the origin or on the coordinate axis. Its three-dimensional coordinates are known, and the direction of the positioner coordinate axis is parallel to the axis of the user's workpiece coordinate system;

[0020] The distance sensor is a non-contact absolute distance sensor. Each locator has three built-in distance sensors, and the three distance sensors are orthogonal to each other at the same point. This intersection is the origin of the locator's coordinate system, and the measuring axes of the three distance sensors are the three coordinate axes of the locator.

[0021] The front end of the reflector is square, and the rear end is mounted on the robot end flange via a connecting rod. The center point of the square at the front end can be used to represent the tool center (TCP) of the robot end. The size of the square at the front end of the reflector depends on the range of the ranging sensor. The reflector is made of light alloy to reduce weight.

[0022] The controller is a portable industrial computer that provides energy for the three positioners and obtains measurement data from the ranging sensors of the three positioners. It also processes the obtained data to obtain the origin coordinate position and coordinate axis inclination angle of the user workpiece coordinate system in the robot base coordinate system, and transmits them to the robot controller to realize coordinate system calibration.

[0023] The robot coordinate system calibration system based on orthogonal ranging of the present utility model is also characterized in that the locator adopts a U-shaped structure, two of the three ranging sensors are independently installed on the locator base, and the third ranging sensor is placed inside the base. This can ensure that the reflector can be moved from multiple angles and orientations to near the center position of the locator coordinate system, significantly improving the adaptability and convenience of user operation.

[0024] The present invention provides a robot TCP calibration method applicable to the above-mentioned robot coordinate system calibration system based on orthogonal ranging, which is as follows:

[0025] (1) First, fix the reflector to the end of the robot and move it with it;

[0026] (2) A locator is reliably fixed at a certain position in the robot's workspace and connected to the controller;

[0027] (3) Power on the controller and input the robot's DH model parameters;

[0028] (4) Move the reflector to a position near the origin of the locator coordinate system and stop. Ensure that the front surface of the reflector is facing the three ranging sensors of the locator. At this time, the locator obtains the readings of the three ranging sensors when the reflector stops and sends them to the controller. The controller also obtains the angle values ​​of the encoders of each axis of the robot at this time.

[0029] (6) Move the reflector out of the positioner's workspace, rotate the reflector 90 degrees, and return to a position near the origin of the positioner's coordinate system and stop. Similarly, ensure that the front end of the reflector is facing the three distance sensors of the positioner. At this time, the positioner obtains the readings of the three distance sensors when the reflector stops and sends them to the controller; the controller also obtains the angle values ​​of the encoders of each axis of the robot at this time;

[0030] (7) Move the reflector out of the positioner's workspace again, rotate it 90 degrees, and return to a position near the origin of the positioner's coordinate system and stop. Similarly, ensure that the front end of the reflector is facing the three distance sensors of the positioner. At this time, the positioner obtains the readings of the three distance sensors when the reflector stops and sends them to the controller; the controller also obtains the angle values ​​of the encoders of each axis of the robot at this time;

[0031] (8) The controller uses the readings of the three ranging sensors and the angle values ​​of each axis of the robot obtained by the above process when the reflector stops three times to obtain the three-dimensional coordinates of the center of the reflector (i.e., TCP) relative to the robot base coordinate system through inverse calculation, thereby realizing TCP calibration.

[0032] The present invention provides a robot user workpiece coordinate system calibration method applicable to the above-mentioned robot coordinate system calibration system based on orthogonal ranging, which is specifically as follows:

[0033] (1) Place the reflector at the end of the robot and perform TCP calibration in advance;

[0034] (2) Install the three positioners in the workpiece coordinate system and at a location that the robot TCP can reach. Their positions can be arbitrary and unrestricted, and do not have to be at the origin or on the coordinate axis. Their three-dimensional coordinates need to be known and determined, and the direction of the positioner coordinate axis must be parallel to the axis of the user's workpiece coordinate system.

[0035] (3) Move the reflector to the position near the origin of the coordinate system of the three positioners in turn. It is necessary to ensure that the front surface of the cube of the reflector is facing the three ranging sensors of the positioner. At this time, the positioner obtains the readings of the three ranging sensors when the reflector stops and sends them to the controller. The controller also obtains the angle value of the encoder of each axis of the robot at this time.

[0036] (4) The controller calculates the three-dimensional coordinates of the reflector's three stopping points in the user workpiece coordinate system based on the three-dimensional coordinates of the three positioners in the user workpiece coordinate system and the distance sensor readings when the reflector stops three times;

[0037] (5) The controller calculates the three-dimensional coordinates of the reflector's three stopping points in the robot's base coordinate system based on the encoder angle values ​​of each axis of the robot and the robot's own DH model parameters when the reflector stops three times;

[0038] (6) Based on the three-dimensional coordinates of the reflector's three stopping points in the robot base coordinate system and the user workpiece coordinate system, the controller can obtain the origin coordinates and coordinate axis deflection angles of the user workpiece coordinate system in the robot base coordinate system through conventional matrix inverse operations, thereby realizing the calibration of the user workpiece coordinate system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of the working principle of the user workpiece coordinate system calibration system of the utility model;

[0040] Figure 2 This is a schematic diagram of the principle of the positioner composition of the user workpiece coordinate system calibration system of the present invention;

[0041] Figure 3This is a schematic diagram of the reflector structure of the user workpiece coordinate system calibration system of the present invention;

[0042] Figure 4 This is a schematic diagram of the composition principle of the U-shaped positioner of the user workpiece coordinate system calibration system of the utility model;

[0043] Figure 5 This is a schematic diagram of the principle of the TCP calibration method of the user workpiece coordinate system calibration system of the present invention;

[0044] Figure 6 This is a schematic diagram of the principle of the TCP calibration method of the user workpiece coordinate system calibration system of the present invention;

[0045] In the figure, 1-locator, 2-reflector, 3-controller, 4-robot, 5-robot controller, 6-distance sensor. DETAILED DESCRIPTION

[0046] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art further understand the present invention, but are not intended to limit the present invention in any way. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the scope of the present invention. These modifications and improvements are all within the scope of protection of the present invention.

[0047] The utility model is realized through the following technical solutions:

[0048] The utility model provides a robot coordinate system calibration system based on orthogonal ranging. The calibration system comprises three parts: a locator, a reflector and a controller. The locator has three orthogonal ranging sensors built in. Figure 1 and 2 As shown, where:

[0049] The positioner 1 is a small, integrated positioning and measuring device. There are three of them, 1a, 1b, and 1c, installed within the user's workpiece coordinate system OwXwYwZw, within the reach of the robot 4's TCP. The position of the positioner 1 can be arbitrary and unrestricted, not necessarily at the origin or on the coordinate axes. Its three-dimensional coordinates are known: (xw1, yw1, zw1), (xw2, yw2, zw2), and (xw3, yw3, zw3). The directions of the coordinate axes OpXpYpZp of the positioner 1 are parallel to the directions of the user's workpiece coordinate axes OwXwYwZw.

[0050] The distance sensor 6 is a non-contact absolute distance sensor, such as a laser distance sensor, an eddy current distance sensor, an ultrasonic distance sensor, etc. Each locator 1 is equipped with three distance sensors 6x, 6y, and 6z. The three distance sensors 6x, 6y, and 6z are mutually orthogonal at the same point. This intersection is the origin Op of the coordinate system OpXpYpZp of the locator 1. The measuring axes of the three distance sensors 6x, 6y, and 6z are the three coordinate axes XpYpZp of the locator.

[0051] The front end of the reflector 2 is square, and the rear end is mounted on the end flange of the robot through a connecting rod. Figure 3 As shown; the center point of the square at the front end 2a of the reflector 2 can be used to represent the end tool center (TCP) of the robot 4; the size of the cube at the front end 2a of the reflector depends on the range of the ranging sensor 6. For example, if the range of the ranging sensor 6 is 10mm, the side length of the square at the front end 2a of the reflector can be 12-14mm; the material of the reflector 2 is a light alloy, such as aluminum alloy, to reduce weight;

[0052] The controller 3 is a portable industrial computer. On the one hand, it provides energy for the three positioners 1a, 1b and 1c and obtains the measurement data of the distance sensors 6x, 6y and 6z from the three positioners 1a, 1b and 1c; on the other hand, it processes the obtained data to obtain the user workpiece coordinate system OwXwYwZw in the robot's base coordinate system O R X R Y R Z R The origin coordinate position (Xw, Yw, Zw) and the coordinate axis inclination angles α and β are transmitted to the robot controller 5 to realize the coordinate system calibration.

[0053] The robot coordinate system calibration system based on orthogonal ranging of the present invention is also characterized in that the positioner 1 adopts a U-shaped structure, such as Figure 4 As shown, two of the three ranging sensors 6x, 6y and 6z, 6x and 6y, are independently installed on the base of the locator 1, and the third ranging sensor 6z is placed inside the base. This ensures that the reflector 2 can be moved from multiple angles and orientations to near the center position of the coordinate system of the locator 1, significantly improving the adaptability and convenience of user operation.

[0054] The present invention provides a robot TCP calibration method applicable to the above-mentioned robot coordinate system calibration system based on orthogonal ranging, such as Figure 5 As shown, the details are as follows:

[0055] (1) First, fix the reflector 2 to the end of the robot 4 and move it together;

[0056] (2) A positioner 1 is securely fixed at a certain position in the workspace of the robot 4 and connected to the controller 3;

[0057] (3) Controller 3 is powered on and the DH model parameters of robot 4 are input;

[0058] (4) Move the reflector 2 to a position near the origin of the coordinate system of the locator 1 and stop. It is necessary to ensure that the front end of the cube surface of the reflector 2 is facing the three distance sensors 6x, 6y and 6z in the locator 1. At this time, the locator 1 obtains the readings Lx1, Ly1 and Lz1 of the three distance sensors 6x, 6y and 6z when the reflector 2 stops, and sends them to the controller 3; the controller 3 also obtains the angle value {θ11, θ12, θ13, θ14, θ15, θ16} of the encoder of each axis of the robot 4 at this time;

[0059] (6) Move the reflector 2 out of the working space of the locator 1, rotate the reflector 2 90 degrees, and return to the position near the origin of the coordinate system of the locator 1a and stop. Similarly, ensure that the front end of the cube surface of the reflector 2 is facing the three distance sensors 6x, 6y and 6z in the locator 1a. At this time, the locator 1 obtains the readings Lx2, Ly2 and Lz2 of the three distance sensors 6x, 6y and 6z when the reflector 2 stops, and sends them to the controller 3; the controller 3 also obtains the angle value {θ21, θ22, θ23, θ24, θ25, θ26} of the encoder of each axis of the robot 4 at this time;

[0060] (7) Move the reflector 2 out of the working space of the positioner 1 again, rotate the reflector 2 90 degrees, and return to the position near the origin of the coordinate system of the positioner 1 and stop. Similarly, ensure that the front end of the cube surface of the reflector 2 is facing the three distance sensors 6x, 6y and 6z in the positioner 1. At this time, the positioner 1 obtains the readings Lx3, Ly3 and Lz3 of the three distance sensors 6x, 6y and 6z when the reflector 2 stops, and sends them to the controller 3; the controller 3 also obtains the angle value {θ31, θ32, θ33, θ34, θ35, θ36} of the encoder of each axis of the robot 4 at this time;

[0061] (8) The controller 3 uses the above process to obtain the readings of the three distance measuring sensors 6x, 6y and 6z when the reflector 2 stops three times {Lx1, Ly1, Lz1, Lx2, Ly2, Lz2 ， Lx3, Ly3, Lz3} and the angle values ​​of each axis of robot 4 {θ11, θ12, θ13, θ14, θ15, θ16; θ21, θ22, θ23, θ24, θ25, θ26; θ31, θ32, θ33, θ34, θ35, θ36}, the center of the front end cube of reflector 2 (i.e., TCP) relative to the base coordinate system O of robot 4 is obtained by inverse calculation R X R YR Z R The origin coordinate position (Xw, Yw, Zw) is obtained, thereby achieving TCP calibration.

[0062] The utility model provides a robot user workpiece coordinate system calibration method applicable to the above-mentioned robot coordinate system calibration system based on orthogonal ranging, such as Figure 6 As shown, the details are as follows:

[0063] (1) Place the reflector 2 at the end of the robot 4 and perform TCP calibration in advance;

[0064] (2) The three positioners 1a, 1b and 1c are installed in the workpiece coordinate system OwXwYwZw and at a location where the TCP of the robot 4 can reach. Their positions can be arbitrary and not limited, and do not have to be on the origin and coordinate axis. Their three-dimensional coordinates {(x W a, y W a,z W a),(x W b, y W b, z W b), (x W c, y W c, z W c)} It needs to be known and determined, and the direction of the locator coordinate axis OpXpYpZp is parallel to the direction of the user workpiece coordinate axis OwXwYwZw;

[0065] (3) Move the reflector 2 to the positions near the coordinate origins Owa, Owb and Owc of the three locators 1a, 1b and 1c respectively. It is necessary to ensure that the front end of the cube surface of the reflector 2 faces the three distance sensors 6x, 6y and 6z inside the locators 1a, 1b and 1c. At this time, the three locators 1a, 1b and 1c respectively obtain the readings of the three distance sensors 6x, 6y and 6z when the reflector 2 stops {Lxa, Lya, Lza, Lxb, Lyb, Lzb, Lxc, Lyc, Lzc} and send them to the controller 3; the controller 3 also obtains the angle values ​​of the encoders of each axis of the robot 4 at this time {θa1, θa2, θa3, θa4, θa5, θa6; θb1, θb2, θb3, θb4, θb5, θb6; θc1, θc2, θc3, θc4, θc5, θc6};

[0066] (4) The controller 3 calculates the three-dimensional coordinates {(x W a, y W a, z W a),(x W b, y W b, z Wb), (x W c, y W c, z W c)} and the readings of the distance measuring sensors 6x, 6y and 6z {Lxa, Lya, Lza, Lxb, Lyb, Lzb, Lxc, Lyc, Lzc} when the reflector 2 stops three times, and the three-dimensional coordinates {(xp W a, yp W a, zp W a)、(xp W b, yp W b, zp W b) (xp W c, yp W c, zp W c)};

[0067] (5) The controller 3 calculates the three-dimensional coordinates of the three stopping points of the reflector 2 in the robot base coordinate system OrXrYrZr {(xpra, ypra, zpra), (xprb, yprb, zprb), (xprc, yprc, zprc)} according to the encoder angle values ​​of each axis of the robot 4 {θa1, θa2, θa3, θa4, θa5, θa6; θb1, θb2, θb3, θb4, θb5, θb6; θc1, θc2, θc3, θc4, θc5, θc6} when the reflector 2 stops three times;

[0068] (6) Based on the three-dimensional coordinates of the three stopping points of the reflector 2 in the base coordinate system OrXrYrZr of the robot 4 and the user workpiece coordinate system OwXwYwZw, the controller 3 can obtain the origin coordinates (Xw, Yw, Zw) and the coordinate axis deflection angles (αw, βw, γw) of the user workpiece coordinate system OwXwYwZw in the robot base coordinate system OrXrYrZr through conventional matrix inverse operations, thereby realizing the calibration of the user workpiece coordinate system.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] (1) The robot coordinate system calibration system based on orthogonal ranging proposed in this utility model adopts a non-contact ranging sensor to measure the position of the reflector. The center coordinate position of the reflector can be accurately obtained without human visual observation and repeated adjustment, which significantly improves the calibration work efficiency and reduces production costs.

[0071] (2) The robot coordinate system calibration system based on orthogonal ranging proposed in this utility model adopts a non-contact ranging sensor to measure the position deviation of the reflector and automatically compensates and corrects it, thereby effectively overcoming the influence of positioning error and greatly improving the three-dimensional coordinate measurement accuracy.

[0072] (3) The robot coordinate system calibration system based on orthogonal ranging proposed in this utility model adopts an integrated small-size positioner, which is directly fixed in the user's workpiece coordinate system. It has good rigidity, small deformation, and can work stably and reliably for a long time.

[0073] (4) The robot coordinate system calibration system based on orthogonal ranging proposed in this utility model uses a universal ranging sensor to realize the positioner function, which has a simple structure and low cost. The controller uses a universal portable industrial computer, which is easy to maintain and reduces daily maintenance costs.

[0074] (5) The robot coordinate system calibration system based on orthogonal ranging proposed by the utility model has no requirements or restrictions on the installation position of the locator. It does not need to be installed on the origin and coordinate axis of the user's workpiece coordinate system. It has strong versatility and good adaptability.

[0075] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A robot coordinate system calibration system based on orthogonal ranging, the calibration system comprising a positioner, a reflector, and a controller. The positioner has three built-in orthogonal ranging sensors, wherein: The positioner is an integrated small positioning and measuring instrument, there are three of them, which are installed in the user's workpiece coordinate system and at a place where the robot TCP can reach. Its position can be arbitrary and not limited, and does not have to be at the origin or on the coordinate axis. Its three-dimensional coordinates are known, and the direction of the positioner coordinate axis is parallel to the axis of the user's workpiece coordinate system; The distance sensor is a non-contact absolute distance sensor. Each locator has three built-in distance sensors, and the three distance sensors are orthogonal to each other at the same point. This intersection is the origin of the locator's coordinate system, and the measuring axes of the three distance sensors are the three coordinate axes of the locator. The front end of the reflector is square, and the rear end is mounted on the robot end flange via a connecting rod. The center point of the square at the front end represents the tool center (TCP) of the robot end. The size of the square at the front end of the reflector depends on the range of the ranging sensor. The reflector is made of light alloy to reduce weight. The controller is a portable industrial computer that provides energy for the three positioners and obtains measurement data from the ranging sensors of the three positioners. It also processes the obtained data to obtain the origin coordinate position and coordinate axis inclination angle of the user workpiece coordinate system in the robot base coordinate system, and transmits them to the robot controller to realize coordinate system calibration.

2. The robot coordinate system calibration system based on orthogonal odometry according to claim 1, further characterized by: The locator adopts a U-shaped structure. Two of the three ranging sensors are independently installed on the locator base, and the third ranging sensor is placed inside the base to ensure that the reflector can be moved from multiple angles and orientations to near the center position of the locator coordinate system.

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