Non-contact four-wheel aligner

Abstract

The invention belongs to the technical field of automobile detection, and particularly relates to a non-contact four-wheel aligner which comprises an integral steel structure, a steering wheel gradienter, an electrical signal processing module and a PLC (programmable logic controller) control system. Centering and positioning mechanisms are installed at the positions, corresponding to the front roller sets and the rear roller sets, of the top of the whole steel structure, XDP visual processing units are arranged on the centering and positioning mechanisms, the installation positions of the two front roller sets and the two rear roller sets on the whole steel structure are different, and other structures are the same. The front roller set comprises a floating mechanism and a roller mechanism installed on the floating mechanism, and the floating mechanism and the roller mechanism provide supporting and floating for four tires of the vehicle. The detection accuracy can be improved, the defects in the prior art are effectively overcome, and the performance of the four-wheel aligner is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of vehicle detection, and particularly relates to a non-contact four-wheel aligner. Background Art

[0002] In the field of vehicle repair and maintenance, the four-wheel aligner plays a crucial role in ensuring the smoothness of vehicle driving and the stability of operation. It can effectively improve the driving performance and safety of the vehicle by inspecting and adjusting parameters such as the toe-in and camber of the wheels.

[0003] Currently, four-wheel aligners can be divided into contact type and non-contact type according to the measurement structure and measurement method. The contact measurement mode uses a probe-type differential transformer and requires corresponding fixtures to be installed on the tire side to measure the change in the end face height of the wheel; the non-contact measurement mode uses a laser sensor and can perform non-contact measurement without installing other auxiliary facilities.

[0004] Among them, as an advanced detection device, the non-contact four-wheel aligner captures images of the wheels through a camera and uses image processing algorithms to analyze the images to obtain wheel alignment parameters. It can even generate a three-dimensional wheel model for measurement through a combination of a stereo camera, laser projection, and multi-level image processing algorithms, avoiding errors such as fixture error and scale board error caused by mechanical installation and providing more accurate positioning data.

[0005] However, there are many problems with the existing non-contact aligners in terms of the centering mechanism. The common cylinder centering method can achieve centering, but during testing, it continuously outputs the clamping force on the tire, putting the tire in a stress state and seriously affecting the measurement accuracy; the method of clamping the vehicle body for centering avoids the clamping stress on the tire, but due to the irregular state of the vehicle body, it cannot guarantee the centering accuracy of the tire. The electronic control centering scheme uses a swinging method to straighten the vehicle body through an electronic control system when the roller group rotates, which not only takes a long time but also is difficult to guarantee the accuracy of the vehicle body at the center line position.

[0006] These problems limit the performance improvement and wide application of non-contact four-wheel aligners, and there is an urgent need for a new, efficient, and accurate centering mechanism to solve them. Summary of the Invention

[0007] The purpose of the present invention is to provide a non-contact four-wheel aligner that can improve the detection accuracy, effectively solve the drawbacks of the existing technology, and greatly improve the performance of the four-wheel aligner.

[0008] The specific technical solutions adopted by the present invention are as follows:

[0009] A non-contact four-wheel aligner, comprising an integral steel structure, a steering wheel level, an electrical signal processing module and a PLC control system. Two front roller groups and two rear roller groups are symmetrically arranged on the integral steel structure. A centering and positioning mechanism is installed at the top of the integral steel structure at a position corresponding to each of the front roller groups and the rear roller groups. An XDP vision processing unit is provided on the centering and positioning mechanism;

[0010] Except for the different installation positions on the integral steel structure, the structures of the two front roller groups and the two rear roller groups are the same. The front roller group includes a floating mechanism and a roller mechanism installed on the floating mechanism. The floating mechanism and the roller mechanism provide support and floating for the four tires of the vehicle;

[0011] The four centering and positioning mechanisms are used to keep the geometric center line of the vehicle parallel to the geometric center line of the equipment before measuring the geometric dimensions of the vehicle chassis. The centering and positioning mechanism includes a mounting frame installed on the top of the integral steel structure. A slide rail is provided on the side of the mounting frame. A lead screw is movably provided on the mounting frame. A servo motor is provided at the bottom of the mounting frame. The servo motor drives the lead screw to rotate through gear transmission. A slider is threadedly connected to the lead screw. The slider slides horizontally on the slide rail. A centering stop wheel is installed on the slider;

[0012] When performing four-wheel alignment detection on a vehicle, the steering wheel level is installed on the steering wheel of the vehicle to be detected. The steering wheel level is wirelessly communicatively connected to the electrical signal processing module and the PLC control system. The steering wheel level is used to obtain the steering wheel deflection angle value and send it to the electrical signal processing module and the PLC control system;

[0013] The XDP vision processing unit includes an assembly piece installed on the mounting frame. An assembly plate is provided at the top of the assembly piece. Two cameras and a laser sensor are installed on the assembly plate. Each camera takes multiple images of the corresponding tire area during four-wheel alignment of the vehicle. The laser sensor emits several laser beams to the tire, and after reflection, the laser reflection data is obtained. The XDP vision processing unit sends the multiple tire area images and the laser reflection data to the electrical signal processing module and the PLC control system. The electrical signal processing module and the PLC control system perform algorithm fitting on the multiple tire area images and the laser reflection data; and complete the output of the detection result.

[0014] The floating mechanism includes a vertical shaft movably installed on the integral steel structure. A rotary encoder is installed at the lower end of the vertical shaft. An encoder floating assembly is provided at the upper end of the vertical shaft. A bottom plate is connected to the encoder floating assembly. Universal ball bearings are provided at the top corner positions of the bottom plate. A floating plate is installed on the universal ball bearings;

[0015] The drum mechanism includes a bracket installed on the floating plate. An active wheel and a driven wheel are provided on the bracket, and a braking system is installed on the bracket. The braking system is used to lock the active wheel.

[0016] A floating locking mechanism is further provided on the bottom plate. The floating locking mechanism includes a floating cylinder whose root is movably installed on the bottom plate. The end of the floating cylinder is movably connected with a crank arm. The end of the crank arm rotates around a fixed shaft. The end of the crank arm is connected with a clamping arm. Another clamping arm is also sleeved on the fixed shaft. The roots of the two clamping arms are meshed with each other through gears. An irregular groove is formed in the middle of the floating plate. The ends of the two clamping arms are adapted to the irregular groove.

[0017] The steering wheel level includes a device body. A support frame is arranged on the outer side of the device body. A horizontal measuring device is installed above the support frame. A roller is arranged at the rear side of the support frame for steering wheel positioning. A pneumatic spring is arranged above the support frame. A rubber head is bonded to the outer end of the pneumatic spring.

[0018] The steps of the algorithm fitting are as follows:

[0019] S1: According to the instructions of the synchronizer of the PLC control system, four XDP vision processing units synchronously acquire the tire area image and laser reflection data at the current moment. The electrical signal processing module performs image preprocessing according to the sampling, extracts the sub-pixel center line of the laser reflection data in the image, and calculates the hub edge feature points.

[0020] S2: Calculate the hub diameter and tire height according to the tire parameters, and convert them to the pixel coordinate system as conditional parameters. Combine the RANSAC ellipse fitting based on the edge feature points to locate the hub edge in the image. Obtain the outer edge ellipse of the tire according to the tire height pixel information. The area between the two concentric ellipses is the tire tread area. Filter the center line outside the tread area to obtain the center line information of the tire in this image.

[0021] S3: According to the pixel coordinates of the center line of the camera and the external parameters of the camera, perform operations such as coded feature point matching, filtering, and restoration to obtain the point cloud information of the tire, and convert the tire point cloud to the test platform coordinate system according to the calibration transformation matrix T.

[0022] S4: Establish a three-dimensional elliptical ring model according to the tire parameters, perform template matching on the tire point cloud based on the non-linear optimization method, and make the three-dimensional distance between the tire three-dimensional points and the three-dimensional of this model reach the minimum through the designed objective function. Finally, obtain the toe-in direction angle, camber angle, and wheel center of the tire.

[0023] When in the tire area image in S1, it includes the following steps:

[0024] S11: Denoising processing, smoothing the image to remove random noise in the image;

[0025] S12: Grayscale processing, converting the color image into a grayscale image to reduce the amount of data and facilitate subsequent processing.

[0026] In the above S11, let the original image be I(x, y), and the image after Gaussian filtering be Ig(x, y). Then the calculation formula for Gaussian filtering is:

[0027]

[0028] where G(m, n) is the Gaussian kernel function, and M and N are the half-widths of the convolution kernel.

[0029] In the above S12, grayscale processing can adopt the weighted average method. Let the red, green, and blue channels of the color image be R(x, y), G(x, y), and B(x, y) respectively, and the grayscale image be Hgray(x, y). Then the grayscale formula is:

[0030] Hgray(x, y) = 0.299R(x, y) + 0.587G(x, y) + 0.114B(x, y)

[0031] where 0.299, 0.587, and 0.114 are the color channel weighting coefficients.

[0032] In the above S3, the point cloud information of the tire is restored using the principle of triangulation. Let the optical centers of the upper and lower cameras be O1 and O2 respectively, and the pixel coordinates of the feature points in the images of the two cameras be (u1, v1) and (u2, v2) respectively. Then the calculation formula for the three-dimensional coordinates (X, Y, Z) of the point cloud is:

[0033]

[0034] where b is the baseline distance between the two cameras, f is the focal length of the camera, and c x and c y are the principal point coordinates of the camera.

[0035] The three-dimensional elliptical torus model constructed in the above S4 is defined as:

[0036] Let an ellipse with the center O on the XOY plane r where one of its axes passes through the X-axis and has a length of 2r, and the distance from O r to the origin O is R. The torus formed by rotating the ellipse around the Z-axis with O as the control point for one circle is the three-dimensional elliptical torus, and its three-dimensional elliptical torus model formula is:

[0037]

[0038] Among them, v is the angular parameter of the ellipse itself. When it is on the left side, 0 ≤ v ≤ π; when it is on the right side, -π ≤ v ≤ 0, and 0 ≤ u ≤ 2π, -5 ≤ k ≤ 5. And u is the angular parameter of rotation around the Z-axis, R is the distance from the center of the toroidal body to the origin, r is the length of the minor semi-axis of the ellipse, and e k is the deformation coefficient.

[0039] The objective function is as follows:

[0040] f min (C x , C y , C z , α, γ, R, r, k) = ∑ i ‖y i - y‖

[0041] Among them, C x , C y , C z respectively represent the X, Y, and Z coordinates of the wheel center of the tire in three-dimensional space, α represents the toe-in direction angle of the tire, γ represents the camber angle of the tire, y i represents the coordinates of the corresponding point of the tire point cloud model, and y represents the actual coordinates of the tire point cloud.

[0042] The technical effects achieved by the present invention are as follows:

[0043] The present invention uses a servo motor as the power source, and precisely pushes the vehicle to be detected to the center by means of a sliding plate and centering idler wheels, greatly improving the detection accuracy. After centering, the centering positioning device does not completely retract and does not contact the test tire of the vehicle, which not only avoids interfering with the measurement but also is efficient and fast. It redefines the non-contact four-wheel aligner, effectively solves the drawbacks of the prior art, greatly improves the performance of the four-wheel aligner, and provides more reliable and efficient equipment support for vehicle maintenance. Brief Description of the Drawings

[0044] Figure 1 is the overall structural schematic diagram of the present invention;

[0045] Figure 2 is the structural schematic diagram of the centering positioning mechanism in the present invention;

[0046] Figure 3 is the structural schematic diagram of the camera and laser emitter in the present invention;

[0047] Figure 4 is the overall front view of the steering wheel level in the present invention;

[0048] Figure 5 is the side view of the steering wheel level in the present invention;

[0049] Figure 6It is a schematic structural diagram among the universal ball bearing, the encoder floating assembly and the universal ball bearing in the present invention;

[0050] Figure 7 It is a schematic structural diagram among the bracket, the driving wheel and the braking system in the present invention;

[0051] Figure 8 It is a schematic structural diagram among the floating cylinder, the clamping arm and the crank arm in the present invention;

[0052] Figure 9 It is a flow chart of algorithm fitting in the present invention.

[0053] In the attached drawings, the list of components represented by each reference numeral is as follows:

[0054] 1. Overall steel structure; 2. Front roller group; 3. Rear roller group; 4. Centering and positioning mechanism; 5. Steering wheel level; 6. XDP vision processing unit; 201. Vertical shaft; 202. Rotary encoder; 203. Base plate; 204. Universal ball bearing; 205. Floating plate; 206. Bracket; 207. Driving wheel; 208. Driven wheel; 209. Braking system; 210. Floating cylinder; 211. Crank arm; 212. Fixed shaft; 213. Clamping arm; 214. Encoder floating assembly; 401. Mounting frame; 402. Slide rail; 403. Lead screw; 404. Servo motor; 405. Slide block; 406. Centering stop wheel; 501. Device main body; 502. Support frame; 503. Horizontal measuring device; 504. Roller; 505. Pneumatic spring; 506. Rubber head; 601. Assembly piece; 602. Assembly plate; 603. Camera; 604. Laser sensor. Detailed implementation manners

[0055] In order to make the purpose and advantages of the present invention clearer, the present invention will be specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific implementation manners of the present invention, and does not strictly limit the scope of protection specifically claimed by the present invention.

[0056] As Figures 1 - 9 shown, a non-contact four-wheel aligner includes an overall steel structure 1, a steering wheel level 5, an electrical signal processing module and a PLC control system. Two front roller groups 2 and two rear roller groups 3 are symmetrically arranged on the overall steel structure 1. A centering and positioning mechanism 4 is installed at the top of the overall steel structure 1 and at positions corresponding to each front roller group 2 and rear roller group 3. An XDP vision processing unit 6 is provided on the centering and positioning mechanism 4. The motor drive drives the two front roller groups 2 and the two rear roller groups 3 to rotate;

[0057] The two front roller groups 2 and the two rear roller groups 3 have the same structure except for their different installation positions on the overall steel structure 1. The front roller group 2 includes a floating mechanism and a roller mechanism installed on the floating mechanism. The floating mechanism and the roller mechanism provide support and floating for the four tires of the vehicle;

[0058] The four centering and positioning mechanisms 4 are used to keep the geometric center line of the vehicle parallel to the geometric center line of the equipment before measuring the geometric dimensions of the vehicle chassis. The centering and positioning mechanism 4 includes a mounting frame 401 installed on the top of the overall steel structure 1. A slide rail 402 is provided on the side of the mounting frame 401. A lead screw 403 is movably installed on the mounting frame 401. A servo motor 404 is provided at the bottom of the mounting frame 401. The servo motor 404 drives the lead screw 403 to rotate through gear transmission. A slider 405 is threadedly connected to the lead screw 403. The slider 405 slides horizontally on the slide rail 402. A centering wheel 406 is installed on the slider 405;

[0059] When centering multiple tires is required, the servo motor 404 is used to drive the lead screw 403 at the output end of the servo motor 404. Through the sliding connection between the slider 405 and the mounting frame 401 and the threaded connection between the slider 405 and the lead screw 403, the slider 405 can drive the centering wheel 406 to move towards the tire, thereby pushing the outer side of the wheel to synchronously center the vehicle left and right. After the vehicle is centered, the slider 405 and the centering wheel 406 disengage from the wheel to ensure that the wheel is in a free state. The centering and positioning mechanism 4 is controlled by the servo motor 404, achieving accurate control of the centering position and high-speed operation speed. The four centering and positioning mechanisms 4 are completely independent and have no mechanical connection. A centering wheel 406 is installed on the slider 405 to quickly center the tire. After the vehicle is centered, the slider 405 and the centering wheel 406 disengage from the wheel to ensure that the wheel is in a free state. The centering and positioning mechanism 4 is controlled by the servo motor 404, achieving accurate control of the centering position and high-speed operation speed. The four centering and positioning mechanisms 4 are completely independent and have no mechanical connection;

[0060] When performing four-wheel alignment detection on the vehicle, the steering wheel level 5 is installed on the steering wheel of the vehicle to be detected. The steering wheel level 5 is wirelessly communicatively connected to the electrical signal processing module and the PLC control system. The steering wheel level 5 is used to obtain the steering wheel deflection angle value and send it to the electrical signal processing module and the PLC control system;

[0061] The XDP vision processing unit 6 includes an assembly piece 601 mounted on a mounting bracket 401. At the top of the assembly piece 601, there is an assembly plate 602. Two cameras 603 and a laser sensor 604 are mounted on the assembly plate 602. Each camera 603 takes multiple images of the corresponding tire areas during vehicle four-wheel alignment. The laser sensor 604 emits several laser beams towards the tires, and after reflection, laser reflection data is obtained. The XDP vision processing unit 6 sends the multiple tire area images and the laser reflection data to the electrical signal processing module and the PLC control system. The electrical signal processing module and the PLC control system perform algorithm fitting on the multiple tire area images and the laser reflection data, and finally output the detection results.

[0062] The floating mechanism includes a vertical shaft 201 movably installed on the overall steel structure 1. A rotary encoder 202 is installed at the lower end of the vertical shaft 201. An encoder floating component 214 is provided at the upper end of the vertical shaft 201. A bottom plate 203 is connected to the encoder floating component 214. Universal ball bearings 204 are provided at the top corner positions of the bottom plate 203, and a floating plate 205 is installed on the universal ball bearings 204.

[0063] The rotation torque angle of the front wheel is measured by the rotary encoder 202.

[0064] The roller mechanism includes a bracket 206 installed on the floating plate 205. A driving wheel 207 and a driven wheel 208 are provided on the bracket 206. A braking system 209 is installed on the bracket 206, and the braking system 209 is used to lock the driving wheel 207.

[0065] A floating locking mechanism is also provided on the bottom plate 203. The floating locking mechanism includes a floating cylinder 210 whose root is movably installed on the bottom plate 203. The end of the floating cylinder 210 is movably connected to a crank arm 211. The end of the crank arm 211 rotates around a fixed shaft 212. The end of the crank arm 211 is connected to a clamping arm 213. Another clamping arm 213 is also sleeved on the fixed shaft 212. The roots of the two clamping arms 213 are meshed with each other through gears. An irregular groove is formed in the middle of the floating plate 205, and the ends of the two clamping arms 213 are adapted to the irregular groove.

[0066] When clamping the floating plate 205, the floating cylinder 210 can be driven to drive the crank arm 211 to rotate. Since the stroke rod of the floating cylinder 210 is rotatably connected to the bottom plate 203 itself and through the meshing of gears, the clamping arms 213 are driven to move towards the position close to the irregular groove, so as to engage with the irregular groove and clamp the floating plate 205.

[0067] The steering wheel level 5 includes a device main body 501. A support frame 502 is arranged on the outer side of the device main body 501. A horizontal measuring device 503 is installed above the support frame 502. A roller 504 is arranged at the rear side of the support frame 502 for steering wheel positioning. A pneumatic spring 505 is arranged above the support frame 502. A rubber head 506 is bonded to the outer end of the pneumatic spring 505;

[0068] The steering wheel level 5 communicates with the four-wheel alignment table by radio, and can communicate with the control system of the four-wheel aligner. The steering wheel deflection value is wirelessly transmitted to the industrial control computer of the four-wheel alignment table for toe adjustment compensation to ensure that the steering wheel is in a horizontal position when the vehicle is driving straight;

[0069] When the device main body 501 is assembled on the steering wheel, the horizontal rotation amplitude of the steering wheel can be detected when the steering wheel rotates.

[0070] Refer to the appendix Figure 9 , and the steps of algorithm fitting are as follows:

[0071] S1: According to the instructions of the synchronizer of the control storage terminal, multiple test devices synchronously acquire tire area images at the current moment. The sensor calculation unit performs image preprocessing on the collected data, extracts the sub-pixel center line of the laser line in the image, and calculates the hub edge feature points;

[0072] When obtaining the tire area image in S1, the following steps are included:

[0073] S11: Denoising processing, using the Gaussian filtering algorithm to smooth the image and remove the random noise in the image. The convolution kernel size and standard deviation of the Gaussian filtering are adjusted according to the specific noise situation of the image;

[0074] In S11, let the original image be I(x, y), and the image after Gaussian filtering be Ig(x, y). Then the calculation formula of Gaussian filtering is:

[0075]

[0076] Among them, G(m, n) is the Gaussian kernel function, and M and N are the half widths of the convolution kernel.

[0077] S12: Grayscale processing, converting the color image into a grayscale image to reduce the amount of data and facilitate subsequent processing.

[0078] In S12, grayscale processing can adopt the weighted average method. Let the red, green, and blue channels of the color image be R(x, y), G(x, y), and B(x, y) respectively, and the grayscale image be Hgray(x, y). Then the grayscale formula is:

[0079] Hgray(x,y) = 0.299R(x,y) + 0.587G(x,y) + 0.114B(x,y)2

[0080] Among them, 0.299, 0.587, and 0.114 are color channel weighting coefficients.

[0081] Use the edge detection algorithm to detect the edge information in the image, and obtain the edge image. Edge detection includes steps such as Gaussian smoothing, gradient calculation, non-maximum suppression, and double-threshold processing. Then, screen out the edge points related to the wheel hub in the edge image as the wheel hub edge feature points. The screening can be carried out by analyzing the characteristics of the position, direction, and continuity of the edge points;

[0082] S2: Calculate the wheel hub diameter and tire height according to the tire parameters, and convert them to the pixel coordinate system as conditional parameters. Combine the RANSAC ellipse fitting based on the edge feature points to locate the wheel hub edge in the image. According to the pixel information of the tire height, obtain the outer edge ellipse of the tire. The area between the two concentric ellipses is the tire tread area. Filter the center line outside the tread area to obtain the center line information of the tire in this image. Select a part of the points from the feature points to fit the ellipse model, and then calculate the distance from other points to this model. Consider the points with a distance less than the set threshold as inliers. Repeat this process multiple times, and select the model with the largest number of inliers as the final fitting result;

[0083] S3: Based on the center line pixel coordinates of the upper and lower cameras 603 and the external parameters of the camera 603, perform operations such as feature point matching, filtering, and restoration based on coding to obtain the point cloud information of the tire, and convert the tire point cloud to the test platform coordinate system according to the calibration transformation matrix T;

[0084] In S3, use the principle of triangulation to restore the point cloud information of the tire. Let the optical centers of the upper and lower cameras 603 be O1 and O2 respectively, and the pixel coordinates of the feature point in the images of the two cameras 603 be (u1, v1) and (u2, v2) respectively. Then the calculation formula for the three-dimensional coordinates (X, Y, Z) of the point cloud is:

[0085]

[0086] Among them, b is the baseline distance between the two cameras 603, f is the focal length of the camera 603, c x and c y are the principal point coordinates of the camera 603.

[0087] S4: Establish a three-dimensional elliptical torus model according to the tire parameters, perform template matching on the tire point cloud based on nonlinear optimization, and make the three-dimensional distance between the tire three-dimensional points and this model reach the minimum through the designed objective function, and finally obtain the toe angle, camber angle, and wheel center of the tire;

[0088] The three-dimensional elliptical torus model constructed in S4 is defined as follows:

[0089] Let there be an ellipse on the coordinate XOY plane with the center at O r , where one axis passes through the X-axis and has a length of 2r, and the distance from O r to the origin O is R. The toroidal surface formed by rotating the ellipse around the Z-axis with O as the control point for one full circle is the three-dimensional elliptical torus, and its three-dimensional elliptical torus model formula is:

[0090]

[0091] where v is the angular parameter of the ellipse itself. When it is on the left side, 0 ≤ v ≤ π; when it is on the right side, -π ≤ v ≤ 0, and 0 ≤ u ≤ 2π, -5 ≤ k ≤ 5. And u is the angular parameter for rotation around the Z-axis, R is the distance from the center of the torus to the origin, r is the length of the minor semi-axis of the ellipse, and e k is the deformation coefficient.

[0092] The objective function is:

[0093] f min (C x , C y , C z , α, γ, R, r, k) = ∑ i ‖y i - y‖^5

[0094] where C x , C y , C z respectively represent the X, Y, and Z coordinates of the wheel center of the tire in three-dimensional space, α represents the toe-in direction angle of the tire, γ represents the camber angle of the tire, y i represents the coordinates of the corresponding point of the tire point cloud model, and y represents the actual coordinates of the tire point cloud.

[0095] In order to minimize the influence on the test structure and improve the measurement accuracy, software technology algorithms are used to eliminate the influence of tire deformation and letters. A filter is set up in the software to process the measurement data for a fixed number of rotation cycles. Compensate for the edge runout of the tire and remove the periodic runout at the tire edge. The software judges abnormal runout data based on the average trend of the tire state.

[0096] The toe-in value and camber value after the filtering operation can more realistically reflect the actual position state of the tire. Through algorithm fitting, the actual model and spatial coordinates of the tire are obtained.

[0097] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. The structures, devices, and operation methods not specifically described and explained in the present invention are implemented according to the conventional means in the art without special explanation and limitation.

Claims

1. A non-contact four-wheel aligner, characterized in that, It includes an overall steel structure (1), a steering wheel level (5), an electrical signal processing module and a PLC control system. Two front roller groups (2) and two rear roller groups (3) are symmetrically arranged on the overall steel structure (1). At the position corresponding to each of the front roller groups (2) and the rear roller groups (3) on the top of the overall steel structure (1), a centering and positioning mechanism (4) is installed, and an XDP vision processing unit (6) is provided on the centering and positioning mechanism (4). Except for the different installation positions of the two front roller groups (2) and the two rear roller groups (3) on the overall steel structure (1), the rest of the structures are the same. The front roller group (2) includes a floating mechanism and a roller mechanism installed on the floating mechanism. The floating mechanism and the roller mechanism provide support and floating for the four tires of the vehicle. The four centering and positioning mechanisms (4) are used to keep the geometric center line of the vehicle parallel to the geometric center line of the equipment before measuring the geometric dimensions of the vehicle chassis. The centering and positioning mechanism (4) includes a mounting frame (401) installed on the top of the overall steel structure (1). A slide rail (402) is provided on the side of the mounting frame (401). A lead screw (403) is movably provided on the mounting frame (401). A servo motor (404) is provided at the bottom of the mounting frame (401). The servo motor (404) drives the lead screw (403) to rotate through gear transmission. A slider (405) is threadedly connected to the lead screw (403). The slider (405) slides horizontally on the slide rail (402). A centering stop wheel (406) is installed on the slider (405). When performing four-wheel alignment detection on the vehicle, the steering wheel level (5) is installed on the steering wheel of the vehicle to be detected. The steering wheel level (5) is wirelessly communicatively connected to the electrical signal processing module and the PLC control system. The steering wheel level (5) is used to obtain the steering wheel deflection angle value and send it to the electrical signal processing module and the PLC control system. The XDP vision processing unit (6) includes an assembly piece (601) installed on the mounting frame (401). An assembly plate (602) is provided at the top of the assembly piece (601). Two cameras (603) and a laser sensor (604) are installed on the assembly plate (602). Each camera (603) takes multiple images of the corresponding tire area during vehicle four-wheel alignment. The laser sensor (604) emits several laser beams to the tire, and after reflection, the laser reflection data is obtained. The XDP vision processing unit (6) sends the multiple tire area images and the laser reflection data to the electrical signal processing module and the PLC control system. The electrical signal processing module and the PLC control system perform algorithm fitting on the multiple tire area images and the laser reflection data, and finally output the detection result.

2. The non-contact four-wheel aligner according to claim 1, characterized in that: The floating mechanism includes a vertical shaft (201) movably installed on the overall steel structure (1). A rotary encoder (202) is installed at the lower end of the vertical shaft (201). An encoder floating assembly (214) is provided at the upper end of the vertical shaft (201). A bottom plate (203) is connected to the encoder floating assembly (214). Universal ball bearings (204) are provided at the top corner positions of the bottom plate (203). A floating plate (205) is installed on the universal ball bearings (204). The roller mechanism includes a bracket (206) installed on the floating plate (205). A driving wheel (207) and a driven wheel (208) are provided on the bracket (206). A braking system (209) is installed on the bracket (206). The braking system (209) is used to lock the driving wheel (207).

3. The non-contact four-wheel aligner according to claim 2, characterized in that: A floating locking mechanism is further provided on the bottom plate (203). The floating locking mechanism includes a floating cylinder (210) whose root is movably installed on the bottom plate (203). The end of the floating cylinder (210) is movably connected to a crank arm (211). The end of the crank arm (211) rotates around a fixed shaft (212). A clamping arm (213) is connected to the end of the crank arm (211). Another clamping arm (213) is also sleeved on the fixed shaft (212). The roots of the two clamping arms (213) are meshed with each other through gears. A special-shaped groove is formed in the middle of the floating plate (205). The ends of the two clamping arms (213) are adapted to the special-shaped groove.

4. The non-contact four-wheel aligner according to claim 2, characterized in that: The steering wheel level (5) includes a device main body (501). A support frame (502) is arranged on the outer side of the device main body (501). A horizontal measurement device (503) is installed above the support frame (502). A roller (504) is arranged at the rear side of the support frame (502) for steering wheel positioning. A pneumatic spring (505) is arranged above the support frame (502). A rubber head (506) is bonded to the outer end of the pneumatic spring (505).

5. The non-contact four-wheel aligner according to claim 1, wherein: The steps of the algorithm fitting are as follows: S1: According to the instructions of the synchronizer of the PLC control system, four XDP vision processing units (6) synchronously acquire the tire area image and laser reflection data at the current moment. The electrical signal processing module preprocesses the image, extracts the sub-pixel center line of the laser reflection data in the image, and calculates the hub edge feature points. S2: Calculate the hub diameter and tire height according to the tire parameters, and convert them to the pixel coordinate system as conditional parameters. Combine the RANSAC ellipse fitting based on the edge feature points to locate the hub edge in the image. Obtain the outer edge ellipse of the tire according to the pixel information of the tire height. The area between the two concentric ellipses is the tire tread area. Filter the center line outside the tread area to obtain the center line information of the tire in this image. S3: Perform operations of coded feature point matching, filtering, and restoration according to the center line pixel coordinates of the camera (603) and the external parameters of the camera (603) to obtain the point cloud information of the tire, and convert the tire point cloud to the test platform coordinate system according to the calibration transformation matrix T. S4: Establish a three-dimensional elliptical torus model based on the tire parameters. Perform template matching on the tire point cloud in a non-linear optimization manner. Minimize the three-dimensional distance between the tire three-dimensional points and the three-dimensional model through the designed objective function, and finally obtain the toe angle, camber angle, and wheel center of the tire.

6. The non-contact four-wheel aligner according to claim 5, characterized in that: In step S1 when obtaining the tire area image, it includes the following steps: S11: Denoising processing, perform smoothing processing on the image to remove random noise in the image; S12: Grayscale processing, convert the color image into a grayscale image to reduce the data volume and facilitate subsequent processing; In step S11, assuming the original image is I(x, y) and the image after Gaussian filtering is Ig(x, y), the calculation formula for Gaussian filtering is: where G(m, n) is the Gaussian kernel function, and M and N are the half-widths of the convolution kernel; In step S12, grayscale processing can adopt the weighted average method. Assuming the red, green, and blue channels of the color image are R(x, y), G(x, y), and B(x, y) respectively, and the grayscale image is Hgray(x, y), the grayscale formula is: Hgray(x, y) = 0.299R(x, y) + 0.587G(x, y) + 0.114B(x, y) (2) where 0.299, 0.587, and 0.114 are the color channel weighting coefficients.

7. The non-contact four-wheel aligner according to claim 5, characterized in that: In step S3, use the principle of triangulation to restore the point cloud information of the tire. Assuming the optical centers of the upper and lower cameras (603) are O1 and O2 respectively, and the pixel coordinates of the feature points in the images of the two cameras (603) are (u1, v1) and (u2, v2) respectively, the calculation formula for the three-dimensional coordinates (X, Y, Z) of the point cloud is: where b is the baseline distance between the two cameras (603), f is the focal length of the camera (603), and c x and c y are the principal point coordinates of the camera (603).

8. The non-contact four-wheel aligner according to claim 5, characterized in that: The three-dimensional elliptical torus model constructed in step S4 is defined as: Let there be an ellipse on the coordinate XOY plane with the center at O r , where one of its axes passes through the X-axis and has a length of 2r, and the distance from O r to the origin O is R. The torus formed by rotating it around the Z-axis with O as the control point for one full circle is the three-dimensional elliptical torus, and its three-dimensional elliptical torus model formula is: Among them, v is the angular parameter of the ellipse itself. When it is on the left side, 0 ≤ v ≤ π; when it is on the right side, -π ≤ v ≤ 0, and 0 ≤ u ≤ 2π, -5 ≤ k ≤ 5. And u is the angular parameter of rotation around the Z-axis, R is the distance from the center of the torus to the origin, r is the length of the minor semi-axis of the ellipse, and e k is the deformation coefficient.

9. The non-contact four-wheel aligner according to claim 5, characterized in that: The objective function is: f min (C x ,C y ,C z ,α,γ,R,r,k)=∑ i ‖y i -y‖ (5) Among them, C x , C y , C z respectively represent the X, Y, and Z coordinates of the wheel center of the tire in three-dimensional space, α represents the toe-in direction angle of the tire, γ represents the camber angle of the tire, y i represents the coordinates of the corresponding point of the tire point cloud model, while y represents the actual coordinates of the tire point cloud.

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