A method for measuring the minimum turning diameter of a car based on the principle of triangle positioning.

Abstract

This invention relates to a method for measuring the minimum turning diameter of a car using the principle of triangle positioning. The system used in the measurement method includes cylindrical stakes and a gimbal, a laser scanning rangefinder with a 360° field of view, and a level. The method includes the following steps: (1) The cylindrical stakes are evenly distributed on a certain circumference, which become the corner points of the inscribed regular polygon of the circumference and are used as distance measurement references; (2) The car is in the lowest forward gear, the steering wheel is turned to the limit position and remains unchanged, and the car travels one revolution. According to the principle of triangle positioning, the distance from each sampled point to the detectable cylindrical stake is measured using the laser scanning rangefinder to locate the point, and the coordinates of the sampled points are selected and calculated; (3) The least squares method is used to fit the coordinates of all the sampled points to a circle to obtain the minimum turning trajectory circle and its diameter. The measurement method of this invention realizes automation and intelligence, which not only ensures the test quality but also improves the measurement efficiency.

Description

Technical Field

[0001] This invention belongs to the field of vehicle testing, specifically relating to a method for measuring the minimum turning diameter of a car using the principle of triangle positioning. Background Technology

[0002] The minimum turning diameter of a vehicle refers to the diameter of the circle traced by the center plane of the outer steering wheel on the supporting plane when the steering wheel is turned to its limit and the vehicle is turning at its lowest stable speed. It largely characterizes a vehicle's ability to navigate narrow, winding terrain or bypass seemingly insurmountable obstacles. As a crucial geometric parameter for vehicle passability, a smaller minimum turning diameter generally indicates better maneuverability.

[0003] To verify whether a vehicle's minimum turning diameter meets the specified requirements and to ensure that the vehicle has the ability to pass through narrow, winding areas or bypass insurmountable obstacles, it is necessary to measure the vehicle's minimum turning diameter. Currently, the minimum turning diameter, minimum turning lane circle diameter, and overhang value of a vehicle are often tested using the water-spraying method. This involves the tester pouring water onto the ground from various points on the vehicle body, such as the farthest point from the turning center, the closest point, the center of the tire tread, and the outermost point of the rear of the vehicle, using a handheld water bottle to mark the trajectory for measurement. However, this method is cumbersome, time-consuming, and labor-intensive, and is easily affected by high temperatures, wind, rain, and other weather conditions.

[0004] Other methods include patent applications (patent numbers 2014206205744 and 2015102234342), patents (patent numbers 2017104454577 and 2017107692257), and patents (patent numbers 2017107692257), patents (patent numbers 2017107692257), patents (patent numbers 2017107692257), etc., but they are still relatively cumbersome to operate. Furthermore, all of the above methods require manually measuring the diameter of the trajectory circle formed on the ground using a steel tape measure, making automation and intelligence difficult to achieve, and thus no longer suitable for the development trend of automotive testing in the digital age. Summary of the Invention

[0005] The purpose of this invention is to provide a method for measuring the minimum turning diameter of a car using the principle of triangle positioning.

[0006] The technical solution to achieve the objective of this invention is as follows: a method for measuring the minimum turning diameter of a car using the principle of triangle positioning. The measurement method employs a measurement system comprising multiple cylindrical posts of identical dimensions and a vehicle-mounted component. The vehicle-mounted component includes a gimbal with a 360° field of view scanning range, a laser scanning rangefinder mounted on the gimbal, a level mounted on the laser scanning rangefinder, and a connecting mechanism connecting the gimbal and the vehicle body. The method includes the following steps:

[0007] Step (1): Distribute multiple cylindrical stakes evenly on a circle in a flat and open area to form the corner points of the inscribed regular polygon, which are used as distance measurement references; connect the vehicle-mounted part of the measurement system to the vehicle body;

[0008] Step (2): The car is in the lowest forward gear, the steering wheel is turned to the limit position and remains unchanged. After driving one revolution, according to the principle of triangle positioning, the distance from each sampling instant measured point to the detectable cylindrical pole is measured by laser scanning rangefinder to locate the point, and the coordinates of the measured points are selected and calculated.

[0009] Step (3): Use the least squares method to perform circle fitting on the coordinates of all measured points obtained during the car's turn, thereby obtaining the minimum turning trajectory circle and its diameter.

[0010] Furthermore, the diameter of the cylindrical stake in step (1) should be large enough to ensure that it can be detected by the laser scanning rangefinder at various distances under a specific angular resolution, and the height of the cylindrical stake should be higher than that of the wheel to ensure that it can be detected by the laser scanning rangefinder.

[0011] Furthermore, the number of cylindrical piles in step (1) is greater than or equal to 6.

[0012] Furthermore, the connecting mechanism in step (1) includes a gooseneck tube and a suction cup;

[0013] One end of the gooseneck tube is connected to the gimbal, and the other end is connected to the suction cup. The shape of the gooseneck tube is variable and its strength is sufficient to support the gimbal, level and laser scanning rangefinder after changing into a certain shape.

[0014] The suction cup can be either air-type or permanent magnet type.

[0015] Furthermore, in step (1), the vehicle body and the vehicle body are connected at the farthest point from the steering center, the closest point, the top of the center of the tire surface, and the outermost point of the rear of the vehicle.

[0016] Furthermore, the specific steps for calculating the coordinates of the measured point using the triangle positioning principle in step (2) are as follows:

[0017] Let n be the number of cylindrical piles, and let P1, P2, ..., P be the center of each cylindrical pile, i.e., the reference points.i ,…,P n The tires are evenly distributed on a certain circumference. When the steering wheel is turned to its limit and the car is turning at a relatively low and stable speed, the center of the outer tire tread traces a circle on a flat surface. The center of this circle is point O, and the radius is R. At a certain instant, the center of the tire tread is at point Q. i And at this moment, the laser scanning plane just passes through the reference point P. i After a period of time i Then it passes through the adjacent reference point P i+1 Because the car is turning, the center of the tire tread becomes point Q. i+1 When the laser scanning frequency is high, considering the low turning speed of the car, time t i Very short, ignore point Q i and point Q i+1 The positional deviation between them is considered to coincide at point Q'. i Based on the known reference point P i and point P i+1 The coordinates and laser detection distance Q' i P i and Q' i P i+1 Find the measured point Q' i The coordinates.

[0018] Furthermore, "based on the known reference point P" i and point P i+1 The coordinates and laser detection distance Q' i P i and Q' i P i+1 Find the measured point Q' i The coordinates are specifically:

[0019] Let the radius of the cylindrical pile be r0, and the radius of the circumcircle of the regular polygon formed by n ≥ 6 reference points be R0, with the center at point O0. Establish a reference coordinate system O0XY, then the coordinates P of each reference point are... i (x i ,y i ), 1≤i≤n is represented as:

[0020]

[0021] Using the distance data detected by the laser scanning rangefinder at corresponding moments on the cylindrical pile, and based on the principle of triangulation—that is, when the coordinates of two reference points and the orientation of the measured point relative to these two reference points are known—the measured point and the two reference points with known coordinates form a triangle. The distances from the measured point to the two reference points are measured, and the coordinates Q of each measured point are obtained using the following formula. i ′(x Qi′ ,yQi′ ):

[0022]

[0023] Furthermore, in step (2), when screening and calculating the coordinates of the measured points, it is necessary to determine whether the starting sequence number of the detected cylindrical piles changes within adjacent scanning cycles. The criteria for this determination are as follows:

[0024] The time difference between the time corresponding to the first effective ranging value within the effective field of view and the time corresponding to the nearest smaller ranging value outside the effective field of view within an adjacent scanning cycle remains unchanged when it becomes smaller; otherwise, it changes. In this case, the coordinates of the center of each cylindrical pile need to be rotated counterclockwise by an angle of 2π / n around the center of the reference circle.

[0025] Furthermore, step (3) is as follows:

[0026] Let the equation of the theoretical trajectory circular curve be:

[0027] R 2 =(xA) 2 +(yB) 2

[0028] =>R 2 =x 2 -2Ax+A 2 +y 2 -2Bx+B 2

[0029] Let a = -2A, b = -2B, c = A 2 +B 2 -R 2 ,but

[0030]

[0031] coordinates of all measured points denoted as sample set (X) i ,Y i )i∈N * The distance from each point to the center of the theoretical trajectory circle is d. i Using the least squares method to limit the objective function to the square of the difference between the square of the distance from the noise point to the center of the theoretical trajectory circle and the square of the radius, the objective function is:

[0032]

[0033] Find the partial derivatives and set them to zero to find the extrema of the objective function, i.e.

[0034]

[0035] make

[0036]

[0037] achievable

[0038]

[0039] Therefore, the fitted estimate of the minimum turning diameter D = 2 × R can be obtained.

[0040] Furthermore, to measure the width of the turning channel, the fitted estimates D1 and D2 of the outer and inner circles of the turning channel are measured, and the width of the turning channel B = (D1-D2) / 2 can be obtained.

[0041] Compared with the prior art, the significant advantages of this invention are:

[0042] The measurement method of this invention is simple, convenient, accurate, efficient, automatic, fast, flexible and reliable. It can measure not only the minimum turning diameter, but also the minimum turning channel circle diameter and the external swing value. At the same time, it realizes automation and intelligence, which is conducive to ensuring test quality and improving measurement efficiency. Attached Figure Description

[0043] Figure 1 This is a simplified assembly diagram of the vehicle-mounted portion of the measurement system used in this invention.

[0044] Figure 2 This is a schematic diagram of the gimbal structure of the present invention.

[0045] Figure 3 This is a schematic diagram of the arrangement of cylindrical piles.

[0046] Figure 4 This is a schematic diagram illustrating the principle of testing the minimum turning diameter of a car.

[0047] Figure 5 A schematic diagram for determining whether the starting sequence number of the cylindrical pile changes in adjacent scanning cycles;

[0048] Explanation of reference numerals in the attached figures:

[0049] 1-Level, 2-Laser scanning rangefinder, 3-Gimbal, 4-Gooseneck tube, 5-Suction cup. Detailed Implementation

[0050] The present invention will now be described in further detail with reference to the accompanying drawings.

[0051] The method for measuring the minimum turning diameter of a car provided by the present invention includes: a cylindrical pole and a vehicle-mounted part, the vehicle-mounted part including a laser scanning rangefinder 2, a level 1, a gimbal 3, a gooseneck tube 4 and a suction cup 5.

[0052] The cylindrical stakes, in multiple units, have the same diameter and length. The diameter should be large enough to ensure detection by the laser rangefinder at various distances with a specific angular resolution. The length should be a certain distance above the wheel to ensure detection by the laser rangefinder. The cylindrical stakes, evenly distributed on a circle in a flat, open area, become the corner points of an inscribed regular polygon (greater than or equal to 6) within that circle, serving as distance measurement references. The structural and arrangement diagrams of the cylindrical stakes are shown below. Figure 3 As shown.

[0053] The laser scanning rangefinder 2 has a certain rangefinding accuracy, scanning frequency, angular resolution, and a scanning range with a 360° field of view. It is used to measure the distance from each instantaneous measured point to the detectable cylindrical pile.

[0054] The level 1 is installed on the laser scanning rangefinder and is used to determine and correct the horizontal position of the laser scanning rangefinder.

[0055] The gimbal 3 is used to mount and fix the laser scanning rangefinder, serving a balancing and stabilizing function. A simplified diagram of the gimbal structure is shown below. Figure 2 As shown.

[0056] The gooseneck tube 4 is connected to the gimbal at one end and has a certain length, rigidity and strength. It can be bent into a specific shape in space and maintain that shape. After bending, it has a certain supporting force and is used to support the gimbal, level and laser scanning rangefinder. The bending force is controllable so as to adjust the position and attitude of the laser scanning rangefinder at each measured point.

[0057] The suction cup 5, connected to the other end of the gooseneck tube 4, can be of any form, such as air or permanent magnet, and is used to fix the vehicle-mounted component near the various test points on the vehicle body. A simplified assembly diagram of the vehicle-mounted component is shown below. Figure 1 As shown. The measurement point can be the point on the vehicle body furthest from the steering center, the point closest to the steering center, the point above the center of the tire surface, or the outermost point of the rear of the vehicle.

[0058] In the above-described scheme of this invention, a suction cup 5 fixed to the car body, a gooseneck tube 4 connected to the suction cup, a gimbal 3 connected to the other end of the gooseneck tube 4, a laser scanning rangefinder 2 installed and fixed on the gimbal 3, a level 1 installed and fixed on the laser scanning rangefinder 2, and several cylindrical poles set around the test site as references are used for positioning based on the principle of triangle positioning. The laser scanning rangefinder measures the distance from each instantaneous sampling point (i.e., the center of the laser scanning rangefinder) to the detectable cylindrical poles for positioning. Then, the least squares method is used to perform circle fitting on the coordinates of all the measured points obtained when the car turns around once, thereby obtaining the minimum turning trajectory circle and its diameter.

[0059] A schematic diagram illustrating the principle of the minimum turning diameter test for automobiles is shown below. Figure 4 As shown, let n be the number of cylindrical piles, and let their centers be reference points P1, P2, ..., Pn. i ,…,P n The tires are evenly distributed on a certain circumference. When the steering wheel is turned to its limit and the car is turning at a relatively low and stable speed, the center of the outer tire tread traces a circle on a flat surface. The center of this circle is point O, and the radius is R. At a certain instant, the center of the tire tread is at point Q. i And at this moment, the laser scanning plane just passes through P. i Point, after a period of time t i Then it passes through the adjacent reference point P i+1 Because the car is turning, the center of the tire tread becomes point Q. i+1 Considering the low turning speed of the car, especially when the laser scanning frequency is high (at least ≥10Hz), time t i It's very short, click Q. i and point Q i+1 The positional deviations between them are very small, and they can be considered to coincide at point Q'. i Therefore, based on the known reference point P i and point P i+1 The coordinates and laser detection distance Q' i P i and Q' i P i+1 Find the measured point Q' i The coordinates of the measured points (two distance equations, two unknowns, the point is inside the reference circle) can be obtained. Similarly, the coordinates of each measured point can be obtained using laser ranging data from adjacent reference points within a short time. The estimated trajectory circle and its radius can then be obtained through fitting. To ensure that each measured point can be located, the laser scanning rangefinder should be able to detect no fewer than two reference points in each scanning cycle.

[0060] Let the radius of the cylindrical pile be r0, and the radius of the circumcircle of the regular polygon formed by n (n≥6) reference points be R0, with the center at point O0. Establish a reference coordinate system O0XY, then the coordinates P of each reference point are... i (x i ,y i (1≤i≤n) can be expressed as

[0061]

[0062] Using the distance data of the cylindrical stake detected by the laser scanning rangefinder at corresponding times, and based on the principle of triangle positioning—that is, when the coordinates of two reference points and the orientation of the measured point relative to the two reference points are known—the measured point and the two reference points with known coordinates can form a triangle. Accurate positioning can be achieved by measuring the distance from the measured point to the two reference points. The coordinates of each measured point can be obtained using the following formula.

[0063]

[0064] Because the laser rangefinder rotates with the car's steering center while its scanning beam rotates, the sequence number and number of cylindrical stakes that can be detected may change in different scanning cycles. Although the laser rangefinder only measures a series of times and corresponding distance data, the distance values ​​outside the effective field of view (i.e., the part obscured by the car body) are small, the distance values ​​within the effective field of view are mostly invalid or particularly large, and only a few are valid values—that is, the distance from the laser rangefinder to the cylindrical stake. Based on this, it can be determined whether the starting sequence number of the cylindrical stakes detected by the laser rangefinder changes in each scanning cycle. When the time difference between the time corresponding to the first valid distance value within the effective field of view and the time corresponding to the nearest smaller distance value outside the effective field of view in an adjacent scanning cycle becomes smaller (i.e., when...), the starting sequence number of the cylindrical stakes detected by the laser rangefinder changes in each scanning cycle. Figure 5 If the situation shown does not change, then it will change. In this case, the coordinates of the center of each cylindrical pile need to be rotated counterclockwise by an angle of 2π / n around the center of the reference circle.

[0065] After obtaining the coordinates of all measured points during the car's turn, the coordinates of these measured points are fitted with a circle using the least squares method to obtain the minimum turning trajectory circle and its diameter.

[0066] Let the equation of the theoretical trajectory circular curve be:

[0067] R 2 =(xA) 2 +(yB) 2

[0068] =>R 2 =x 2 -2Ax+A 2 +y 2 -2Bx+B 2

[0069] Let a = -2A, b = -2B, c = A 2 +B 2 -R 2 ,but

[0070]

[0071] coordinates of all measured points denoted as sample set (X) i ,Y i )i∈N * The distance from each point to the center of the theoretical trajectory circle is d. i Using the least squares method to limit the objective function to the square of the difference between the square of the distance from the noise point to the center of the theoretical trajectory circle and the square of the radius, the objective function is:

[0072]

[0073] Find the partial derivatives and set them to zero to find the extrema of the objective function, i.e.

[0074]

[0075] make

[0076]

[0077] achievable

[0078]

[0079] Therefore, the fitted estimate of the minimum turning diameter D = 2 × R can be obtained. Similarly, the fitted estimates D1 and D2 of the outer circle and inner circle of the turning channel can be obtained respectively, and then the width of the turning channel B = (D1-D2) / 2 can be obtained.

Claims

1. A method for measuring the minimum turning diameter of a car using the principle of triangle positioning, characterized in that, The measurement method employs a measurement system comprising multiple cylindrical stakes of identical dimensions and a vehicle-mounted component. The vehicle-mounted component includes a pan-tilt unit (PTZ), a laser scanning rangefinder with a 360° field of view, a level mounted on the PTG, and a connecting mechanism linking the PTG and the vehicle body. The method includes the following steps: Step (1): Distribute multiple cylindrical stakes evenly on a circle in a flat and open area to form the corner points of the inscribed regular polygon, which are used as distance measurement references; connect the vehicle-mounted part of the measurement system to the vehicle body. Step (2): With the car in the lowest forward gear and the steering wheel turned to the limit position and kept there, drive one revolution. Based on the principle of triangle positioning, use a laser scanning rangefinder to measure the distance from each sampling instant to the detectable cylindrical pole for positioning, and then filter and calculate the coordinates of the measured points. Step (3): Use the least squares method to perform circle fitting on the coordinates of all measured points obtained during the car's turn, thereby obtaining the minimum turning trajectory circle and its diameter; The specific steps for calculating the coordinates of the measured point using the triangle positioning principle in step (2) are as follows: Let n be the number of cylindrical piles, and let P1, P2, …, P be the center of each cylindrical pile, i.e., the reference point. i , …, P n The tires are evenly distributed on a certain circumference. When the steering wheel is turned to its limit and the car is turning at a relatively low and stable speed, the center of the outer tire tread traces a circle on a flat surface. The center of this circle is point O, and the radius is R. At a certain instant, the center of the tire tread is at point Q. i And at this moment, the laser scanning plane just passes through the reference point P. i After a period of time i Then it passes through the adjacent reference point P i+1 Because the car is turning, the center of the tire tread becomes point Q. i+1 When the laser scanning frequency is high, considering the low turning speed of the car, time t i Very short, ignore point Q i and point Q i+1 The positional deviation between them is considered to coincide at point Q'. i Based on the known reference point P i and point P i+1 The coordinates and laser detection distance Q' i P i and Q' i P i+1 Find the measured point Q' i The coordinates; "Based on the known reference point P" i and point P i+1 The coordinates and laser detection distance Q' i P i and Q' i P i+1 Find the measured point Q' i The coordinates are specifically: Let the radius of the cylindrical pile be r0, and the radius of the circumcircle of the regular polygon formed by n ≥ 6 reference points be R0, with the center at point O0. Establish a reference coordinate system O0XY, then the coordinates P of each reference point are... i (x i ,y i ), 1≤i≤n is represented as: ， Using the distance data detected by the laser scanning rangefinder at corresponding moments on the cylindrical pile, and based on the principle of triangulation—that is, when the coordinates of two reference points and the orientation of the measured point relative to these two reference points are known—the measured point and the two reference points with known coordinates form a triangle. The distances from the measured point to the two reference points are measured, and the coordinates of each measured point are obtained using the following formula. : ， In step (2), when screening and calculating the coordinates of the measured points, it is necessary to determine whether the starting sequence number of the detected cylindrical piles changes within adjacent scanning cycles. The criteria for this determination are as follows: When the time difference between the first effective ranging value in the effective field of view and the nearest smaller ranging value outside the effective field of view in adjacent scanning cycles becomes smaller, the time difference remains unchanged; otherwise, the time difference changes. In this case, the coordinates of the center of each cylindrical pile need to be rotated counterclockwise by 2π / n around the center of the reference circle. Step (3) is as follows: Let the equation of the theoretical trajectory circular curve be: ， make , , ,but ， coordinates of all measured points denoted as sample set The distance from each point to the center of the theoretical trajectory circle is Using the least squares method to limit the objective function to the square of the difference between the square of the distance from the noise point to the center of the theoretical trajectory circle and the square of the radius, the objective function is: ， Find the partial derivatives and set them to zero to find the extrema of the objective function, i.e. ， make ， get ， This yields the minimum turning diameter. Fitted estimates .

2. The measurement method according to claim 1, characterized in that, In step (1), the diameter of the cylindrical stake should be large enough to ensure that it can be detected by the laser scanning rangefinder at various distances with a specific angular resolution. The height of the cylindrical stake should be higher than that of the wheel to ensure that it can be detected by the laser scanning rangefinder.

3. The measurement method according to claim 2, characterized in that, The number of cylindrical piles in step (1) is greater than or equal to 6.

4. The measurement method according to claim 3, characterized in that, The connecting mechanism in step (1) includes a gooseneck tube and a suction cup; One end of the gooseneck tube is connected to the gimbal, and the other end is connected to the suction cup. The shape of the gooseneck tube is variable and its strength is sufficient to support the gimbal, level and laser scanning rangefinder after changing into a certain shape. The suction cup can be either air-type or permanent magnet type.

5. The measurement method according to claim 4, characterized in that, Connect the vehicle body and the vehicle body at the farthest point from the steering center, the closest point, the top of the center of the tire surface, and the outermost point of the rear of the vehicle in step (1).

6. The measurement method according to claim 5, characterized in that, Used to measure the width of a turning lane, and to measure the fitted estimates of the outer and inner circles of the turning lane. and Then, the width of the turning lane can be obtained. .

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