A parallel robot complex component profile contact in-situ measurement system and method

Abstract

The application relates to a complex component profile contact in-situ measurement system and method of a parallel robot, and belongs to the technical field of complex component in-situ measurement, and relates to a complex component profile contact in-situ measurement system and method of a parallel robot. The measurement system is composed of a parallel robot, a support frame, a contact displacement sensor, a sensor connecting mechanism and a profiling clamp assembly. The measurement method adopts the complex component profile contact in-situ measurement system, establishes a workpiece coordinate system of a component to be measured, extracts point features according to a component CAD model and plans a parallel robot measurement track. The contact displacement sensor is used to obtain the distance change between the end motion track of the parallel robot and the surface of the complex component, the measured displacement change is superposed on the end track of the parallel robot, the spatial point data of the surface of the complex component are obtained for fitting and reconstruction, and the profile measurement of the measured complex component is realized. The method effectively avoids the error caused by secondary clamping and effectively improves the machining efficiency and precision of the parts.

Description

Technical Field

[0001] This invention belongs to the field of in-situ measurement technology for complex components, and specifically relates to an in-situ measurement system and method for the profile contact of complex components of a parallel robot. Background Technology

[0002] In key industrial sectors of the national economy, such as aerospace, energy and power, and automobiles and ships, there are numerous critical and complex components, such as radomes. Achieving efficient manufacturing of these critical and complex components is of great significance. During the processing of such components, it is necessary to obtain accurate geometric descriptions of the components in-situ to guide subsequent processing techniques, thereby ensuring the processing quality and efficiency of these components.

[0003] Existing measurement methods are mainly divided into contact measurement and non-contact measurement. Conventional contact measurement methods, such as coordinate measuring machines (CMMs), can obtain high-precision component profile point data, but complex components require secondary clamping, introducing errors and failing to achieve in-situ automatic and efficient measurement of complex components. Non-contact measurement methods, represented by optical measurement, such as 3D laser scanners, offer fast scanning accuracy and high efficiency, and are widely used in large-scale surface measurement. However, their measurement accuracy is relatively low, and they often require marking points on the surface of the measured object, making it difficult to meet the cleanliness requirements of such complex components. Furthermore, limitations imposed by the equipment's depth of field prevent the measurement of the entire profile of complex components. With the rapid development of robotics technology, combining the advantages of parallel robots—high stability and low error—integrating parallel robots with contact displacement sensors provides an effective method for high-precision and efficient in-situ measurement of complex component profiles. Therefore, establishing a parallel robot contact-based in-situ measurement system for complex component profiles in a processing environment is of great significance for improving the processing quality and efficiency of complex components.

[0004] Existing technical document 1, "A sampling-based motion planning method for active visual measurement with an industrial robot", proposes a measurement system based on an industrial robot. It uses a camera fixed at the end of the robot to capture images of components and reconstruct point clouds to achieve feature measurement of the target components. However, industrial robots have large cumulative errors, and the measurement system is easily affected by the color and smoothness of the components, so it has certain limitations.

[0005] Existing technical document 2, "An adaptive computer-aided path planning to eliminate errors of contact probes on free-form surfaces using a 4-DOF parallel robotCMM and a turn-table," proposes an integrated measurement system using a four-DOF parallel device combined with a trigger-type probe. This system effectively improves detection accuracy by combining the low cumulative error and good dynamic performance of the parallel device with the high precision of the contact measurement method. However, the trigger-type probe has low measurement efficiency, making it difficult to achieve efficient measurement of complex components. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a parallel robot-based contact-type in-situ measurement system for complex component profiles, achieving high-precision and efficient in-situ measurement of complex components. This system establishes an in-situ measurement system within the machining environment using a contact-type measurement device comprised of a parallel robot, a one-dimensional contact displacement sensor, a sensor connection mechanism, and a component contouring fixture. While maintaining a constant workstation position during machining, it performs contact-type scanning measurement of the complex component profile using a planned measurement trajectory. This effectively avoids errors introduced by secondary clamping, thereby significantly improving machining accuracy and efficiency.

[0007] The technical solution described in this invention is a parallel robot complex component profile contact-type in-situ measurement system, characterized in that the in-situ measurement system consists of a parallel robot and support frame, a one-dimensional contact displacement sensor, a sensor connection mechanism, and a contouring fixture assembly.

[0008] Parallel robot 2 is used to provide the motion trajectory required for the contact measurement system. The simplified parallel robot 2 consists of a static platform, an active arm, a driven arm, and an end effector platform. The entire parallel robot 2 is mounted on the parallel robot support frame 1.

[0009] The sensor connection mechanism consists of a robot end effector plate 9, an extended measuring rod 3, and a displacement sensor mounting plate 7. The robot end effector plate 9 is fixedly connected to the lower part of the moving platform of the parallel robot 2. The extended measuring rod 3 has threads processed at both ends. One end is fixedly connected to the robot end effector plate 9 by the threads, and the other end is connected to the displacement sensor mounting plate 7. The sensor mounting plate 7 has a 45° L-shaped structure. The one-dimensional contact displacement sensor 8 is fixedly installed on one side of the L-shaped structure of the displacement sensor mounting plate 7 by tightening the nut. By controlling the movement of the moving platform of the parallel robot end effector, the precise control of the measurement trajectory of the contact displacement sensor probe can be achieved. By controlling the movement of the parallel robot in Cartesian space and the rotation of the fourth axis, the three-dimensional profile measurement of complex components can be realized.

[0010] The contouring clamp assembly consists of left and right contouring clamps 10 and 12, a bottom support plate 5, locking bolts 11, and a grid connecting beam. The grid connecting beam is formed by left and right connecting beams 6 and front and rear grid-shaped connecting beams 13. The bottom support plate 5 has a tapered mounting hole in the middle and is horizontally mounted on the ground, its center concentric with the extended measuring rod 3. The grid connecting beam is fixed in the parallel robot support frame 1. The left and right contouring clamps 10 and 12 are fixed in the left side of the grid connecting beam. The workpiece 4 to be measured is installed on the right connecting crossbeam 6 and in the horizontally arranged left and right contour clamps 10 and 12. The bottom of the workpiece 4 is installed in the conical mounting hole of the support plate 5 to achieve centering and support fixation of the workpiece. The left and right contour clamps 10 and 12 have symmetrically distributed mounting holes on their front and rear sides. By rotating the locking bolt 11, the left and right contour clamps are driven to move away from or towards each other, thereby changing the clamping force of the left and right contour clamps 10 and 12 on the workpiece 4.

[0011] A method for in-situ contact-based measurement of complex component profiles using a parallel robot is characterized by employing a complex component profile contact-based in-situ measurement system. This involves calibrating the relative pose of the parallel robot's base coordinate system and the probe of a displacement sensor to establish the workpiece coordinate system of the complex component under test. Then, point features are extracted based on the CAD model of the complex component, and the measurement trajectory of the parallel robot is planned. The distance change between the parallel robot's end effector trajectory and the surface of the complex component is acquired using a contact-based displacement sensor. By superimposing the measured displacement change onto the end effector trajectory, spatial point data of the complex component surface is obtained. Finally, the point data from multiple locations of the complex component are fitted and reconstructed to achieve the profile measurement of the complex component. The specific operation steps of the method are as follows:

[0012] Step 1: Establish the coordinate system of the complex component to be tested.

[0013] A contact-type in-situ measurement system for complex component profiles is adopted. The base coordinate system of the parallel robot is used as the global measurement coordinate system to establish the workpiece coordinate system of the complex component to be measured. The transformation relationship between the coordinate systems is solved by the forward kinematic equations of the parallel robot and coordinate transformation theory.

[0014] First, based on the simplified geometric model of the Delta parallel robot, with the center of the static platform of the parallel robot as the origin of the coordinate system, X... W The axis passes through the center point of the axis of the drive arm 1, Z. W The positive axis is perpendicular to the static platform and points upwards. Y is determined according to the right-hand rule. W Establish the parallel robot base coordinate system {O} in the positive axis direction. W -X W Y W Z WThis is used as the global measurement coordinate system. The origin is the center of the moving platform at the end effector of the parallel robot, and the Z-axis is perpendicular to the plane of the moving platform and pointing upwards. E Positive axis, end-effector moving platform rotates around Z W When the rotation angle θ4 in the axial direction is 0, the base coordinate system X W The positive direction of the axis is X E Positive axis, determine Y according to the right-hand rule E Establish the coordinate system {O} of the parallel robot end effector in the positive axis direction. E -X E Y E Z E};

[0015] Based on the forward kinematics equations of a parallel robot, and using the principles of forward kinematics for parallel robots, the solution is obtained from the coordinate system {O} of the parallel robot's end effector. E -X E Y E Z E} to the parallel robot base coordinate system {O W -X W Y W Z W The conversion relationship between}

[0016]

[0017] Where f represents the forward kinematics equation of the parallel robot, θ1, θ2, θ3 are the input driving angles of the parallel robot's active arm, and θ4 is the angle of the parallel robot's end effector platform about its base coordinate system Z. W The input angle of rotation along the axis, the direction of angular displacement follows the right-hand rule, x E ,y E ,z E This represents the offset of the center of the end effector platform of the parallel robot relative to the origin of the parallel robot's base coordinate system. W T E This is the coordinate transformation matrix from the end-effector coordinate system to the base coordinate system of the parallel robot.

[0018] With the center of the sensor probe in the zero-position state of the contact displacement sensor as the origin of the sensor coordinate system, and the direction of the sensor axis away from the probe as the Z-axis of the sensor coordinate system. T Positive axis, with the Y-axis of the parallel robot end effector coordinate system E The positive axis is the sensor coordinate system Y. T Positive axis, X is determined according to the right-hand rule. T Establish the coordinate system {O} of the contact displacement sensor in the positive axis direction. T -X T Y T Z TBased on the sensor installation dimensions, the sensor coordinate system {O} in the zero-position state is solved through coordinate transformation. T -X T Y T Z T} to the parallel robot end-effector coordinate system {O E -X E Y E Z E The transformation relationship of}:

[0019]

[0020] Where, d x h z The sensor probe center relative to the center of the parallel robot end effector platform in the robot's base coordinate system is X. W Z W Offset distance in direction, θ T The sensor axis is relative to the Z coordinate system of the parallel robot end effector. E The angle along the positive axis, E T T This is the coordinate transformation matrix from the displacement sensor coordinate system to the parallel robot end effector coordinate system.

[0021] According to the transformation matrix from the parallel robot end-effector coordinate system to the parallel robot base coordinate system W T E Transformation matrix from the displacement sensor coordinate system to the parallel robot end effector coordinate system E T T The coordinate system {O} of the contact displacement sensor is obtained. T -X T Y T Z T} to the parallel robot base coordinate system {O W -X W Y W Z W Transformation matrix between}

[0022] W T T = W T E E T T (3)

[0023] Taking a complex component like a rotating shell as an example, the center of the top circumference of the complex component under test is taken as the origin of the workpiece coordinate system, and the direction perpendicular to the plane containing the ring and pointing to the parallel robot is taken as the Z-axis of the workpiece coordinate system. M Positive axis, with the parallel robot base coordinate system Y W The positive axis is the workpiece coordinate system Y. MPositive axis, X is determined according to the right-hand rule. M Establish the workpiece coordinate system {O} in the positive axis direction. M -X M Y M Z M A single-point measurement is performed on the inner circumference of the top of the workpiece using a displacement sensor, and the spatial coordinates p of the measuring point in the parallel robot's base coordinate system are recorded. j (j≥3), the least squares method is used to fit the measurement point data to obtain the coordinates of the center of the inner circumference of the workpiece top in the parallel robot base coordinate system. The transformation matrix from the workpiece coordinate system to the parallel robot base coordinate system is then solved:

[0024]

[0025] Among them, (x M ,y M ,z M Let θ be the coordinate of the center of the top circumference of the workpiece in the parallel robot's base coordinate system. M For the workpiece coordinate system Z M Positive axis and parallel robot base coordinate system Z W The positive angle of the axis.

[0026] Step 2: Plan the measurement trajectory of the parallel robot

[0027] The offset surface is solved based on the radius of the sensor probe tip, and the corresponding probe trajectory curve is generated. The robot measurement trajectory is solved based on the transformation relationship between the workpiece coordinate system and the robot base coordinate system.

[0028] Using the radius R of the ball head at the probe tip of the contact displacement sensor as the offset distance, and based on the three-dimensional model of the workpiece, the offset surface Sr is solved along the normal direction of the measured surface S. Based on the CAD model of the workpiece, and according to the workpiece Y... M O M Z M The equation of the generatrix in the plane, according to Z M The positions of measuring points on the curve are calculated using an equidistant distribution in the negative direction, and the positions of all measured curves are determined using the parallel section method. Then, based on Y... M O M Z M The measurement point positions of the workpiece cross-sectional curve on the plane are calculated based on the CAD model of the workpiece, and the measurement point path of each layer of the measurement curve in the workpiece coordinate system is calculated. M p i ;

[0029] Based on the transformation relationship between the workpiece coordinate system and the parallel robot base coordinate system, the measurement point path in the workpiece coordinate system is transformed to the parallel robot base coordinate system, and the probe trajectory in the parallel robot base coordinate system is solved:

[0030] ( Wp Ti ,1) T = W T M ( M p i ,1) T (5)

[0031] in, W p Ti The probe's motion trajectory is shown in the parallel robot's base coordinate system, where i is the measurement point number.

[0032] Furthermore, based on the inverse kinematics of the parallel robot, the input drive angle of the parallel robot corresponding to all measurement points is solved to verify whether the input drive angle of the active arm at the corresponding measurement point position meets the robot drive angle range.

[0033] Step 3: Obtain actual spatial point data on the surface of complex components.

[0034] Based on the obtained probe motion trajectory in the parallel robot base coordinate system W p Ti The system controls a parallel robot to perform full-feature contact scanning measurement of the workpiece. Displacement sensors record and output the displacement change Δd of the probe at each measurement point. i Based on the transformation matrix from the sensor coordinate system to the parallel robot base coordinate system W T T The one-dimensional displacement measured by the sensor is transformed into the parallel robot's base coordinate system and decomposed into three-dimensional components. The probe displacement is then superimposed onto the parallel robot's motion trajectory to obtain the actual motion trajectory of the probe in the parallel robot's base coordinate system.

[0035]

[0036] in, W p Ri For the actual motion trajectory of the probe in the base coordinate system of the parallel robot, W Δd xi , W Δd yi , W Δd zi ) T = W R T ·(0,0,Δd i ) T This represents the offset measured by the sensor in the base coordinate system of the parallel robot. W R T for W T T The rotation matrix is ​​obtained. Finally, the actual spatial position data of the complex component surface in the parallel robot's base coordinate system are obtained.

[0037] Step 4: Fitting and reconstructing multi-point data of complex components

[0038] Based on the actual motion trajectory of the probe in the parallel robot base coordinate system obtained in step 3 W p Ri That is, the surface point data of the complex component being measured is fitted by the least squares method to reconstruct the surface of the complex component and finally obtain the profile of the complex component.

[0039] The surface measurement data of complex components are fitted using the least squares method to solve for the reconstructed surface U' of the complex component, obtaining the actual surface of the complex component. The offset between the reconstructed surface U' and the original CAD model surface U is compared to determine the deviation of the actual component. The maximum deviation between the theoretical surface and the actual measured surface is the maximum deviation distance D along the normal vector direction of a point on the actual measured surface. U'Umax :

[0040] D U'Umax =max(|| W P Ri - W P Ti ||) (7)

[0041] W P Ri These are the points on the actual measured surface, i.e., the measured points obtained from the actual measurements. W P Ti These are points on the theoretical surface, i.e., theoretical measurement points obtained through planning.

[0042] The significant effect and benefit of this invention is that the system combines the advantages of parallel robots, such as high precision and good spatial accessibility, with a contact displacement sensor. This effectively overcomes the problems of scanning measurement methods being unable to achieve full feature measurement of complex components due to spatial position interference, and the secondary clamping errors introduced by coordinate measuring machines. While keeping the complex component's workstation position unchanged during processing, the system performs contact scanning measurement of its profile based on measurement planning, achieving profile measurement and reconstruction of complex components. This in-situ measurement system and method can be widely applied to high-precision in-situ measurement of complex component profiles such as aircraft radar radomes, effectively avoiding errors introduced by repeated handling and secondary clamping, thus improving processing accuracy and efficiency.

[0043] The in-situ measurement system design of this invention features a simple structure for the contouring fixture assembly and sensor connection mechanism, which are easy to install and adjust, and offer high measurement accuracy. Attached Figure Description

[0044] Figure 1 —A flowchart of the overall process for in-situ measurement of complex component profiles of a parallel robot.

[0045] Figure 2 a) is a structural diagram of a parallel robot complex component profile contact-type in-situ measurement system. Figure 2 b) is a structural diagram of the grid-shaped connecting beam. Wherein, 1-parallel robot support frame; 2-parallel robot; 3-extended measuring rod; 4-workpiece to be measured; 5-bottom support plate; 6-left and right connecting beams; 10-left contour clamping plate; 11-locking bolt; 12-right contour clamping plate; 13-front and rear grid-shaped connecting beams.

[0046] Figure 3 —A schematic diagram of displacement sensor connection for a contact-type in-situ measurement system for complex component profiles of a parallel robot. In the diagram: 2-parallel robot; 3-extended measuring rod; 7-displacement sensor mounting plate; 8-one-dimensional contact displacement sensor; 9-robot end effector plate.

[0047] Figure 4 —A schematic diagram illustrating the coordinate transformation relationship between the parallel robot's base coordinate system, the parallel robot's end effector coordinate system, and the displacement sensor coordinate system. In the diagram: {O W -X W Y W Z W}- Parallel robot base coordinate system, {O E -X E Y E Z E}- Parallel robot end-effector coordinate system, {O T -X T Y T Z T - Coordinate system of contact displacement sensor.

[0048] Figure 5 —A schematic diagram of a displacement sensor measuring the inner curved surface at the top of a workpiece. In the diagram: {O M -X M Y M Z M} - Coordinate system of complex components, S - Inner curved surface of the workpiece, Sr - Offset curved surface of the probe center. R - Radius of the ball tip of the contact displacement sensor probe (mm).

[0049] Figure 6 —A schematic diagram of the probe motion trajectory planning for the complex component to be measured, wherein, a) measurement curve, b) measurement point path, and c) measurement motion path; M p i Let i represent the trajectory of the probe, where i is the number of the measuring point.

[0050] Figure 7—Simplified geometric model of the Delta parallel robot. Where θ1, θ2, and θ3 are the input drive angles of the parallel robot's active arm, and θ4 is the angle of the parallel robot's end effector platform around its base coordinate system Z. W The input angle of rotation in the axial direction.

[0051] Figure 8 a) — Sensor reading of the first measurement curve, b) — Schematic diagram of the actual movement trajectory of the probe.

[0052] Figure 9 a) — Schematic diagram of the reconstructed profile of the complex component to be tested. Figure 9 b) is a magnified view of 9a). Detailed Implementation

[0053] The specific embodiments of the present invention will now be described in detail with reference to the technical solution and accompanying drawings.

[0054] A structural diagram of a parallel robot complex component profile contact in-situ measurement system according to this embodiment is shown below. Figure 2 , 3 As shown, the measurement system consists of a parallel robot and support frame, sensor connection structure, contact displacement sensor, and contouring fixture assembly. The parallel robot 2 is the Delta-type parallel robot BAT1300-A6 from Yifei Company, simplified to a static platform, active arm, driven arm, and end effector platform, as shown in the attached diagram. Figure 7 As shown. Its repeatability is 80μm, it has 4 degrees of freedom, a load capacity of 6kg, and the allowable range of input drive angles for the active arm is θ1, θ2, θ3∈[-π / 6,π / 2]. The allowable range of input angles for counterclockwise rotation around the Z-axis of its base coordinate system is θ4∈[0,2π].

[0055] The one-dimensional contact displacement sensor 8 uses a Marposs H50 displacement sensor with a range of 10mm and a measurement accuracy of 0.5μm. It is fixed to the lower side of the sensor connection device 7 by tightening a nut, as shown in the attached figure. Figure 3 As shown, precise control of the measurement trajectory of the contact displacement sensor probe is achieved by controlling the movement of the end effector platform of the parallel robot.

[0056] The sensor connection mechanism consists of a robot end effector plate 9, an extended measuring rod 3, and a displacement sensor mounting plate 7, as shown in the attached diagram. Figure 3 As shown, the robot end effector plate 9 is fixedly connected to the lower part of the moving platform of the parallel robot 2. The robot end effector plate 9 and the displacement sensor mounting plate 7 are connected by threads at both ends of the extended measuring rod 3. The displacement sensor mounting plate 7 has a 45° L-shaped structure. By controlling the parallel robot to move in Cartesian space and rotate along the fourth axis, the three-dimensional profile measurement of complex components can be realized.

[0057] The contouring clamp assembly consists of left and right contouring clamps 10 and 12, a bottom support plate 5, locking bolts 11, and a grid connecting beam. The grid connecting beam is formed by left and right connecting crossbeams 6 and front and rear grid-shaped connecting beams 13 fixedly connected together. The bottom support plate 5 has a tapered mounting hole machined in the middle and is horizontally mounted on the ground, its center concentric with the extended measuring rod 3. The grid connecting beam is fixed in the parallel robot support frame 1; the left and right contouring clamps 10 and 12 are fixed to the left and right connecting crossbeams 6 within the grid connecting beam. The workpiece 4 to be measured is installed in the horizontally arranged left and right contour clamps 10 and 12. The bottom of the workpiece 4 to be measured is installed in the conical mounting hole of the support plate 5 to achieve centering and support fixation of the workpiece to be measured. The left and right contour clamps 10 and 12 have symmetrically distributed mounting holes on their front and rear sides. By rotating the locking bolt 11, the left and right contour clamps are driven to move away from or towards each other, thereby changing the clamping force of the left and right contour clamps 10 and 12 on the workpiece 4 to be measured.

[0058] A method for in-situ contact-based measurement of complex component profiles using a parallel robot is characterized by employing a complex component profile contact-based in-situ measurement system. The method uses a contour-following fixture assembly to clamp and position the component under test. A workpiece coordinate system for the complex component is established by calibrating the relative pose of the parallel robot's base coordinate system and the displacement sensor probe. Point features are extracted from the complex component's CAD model, and the parallel robot's measurement trajectory is planned. Then, the distance change between the parallel robot's end effector trajectory and the complex component's surface is acquired based on the contact displacement sensor. By superimposing the measured displacement change onto the parallel robot's end effector trajectory, spatial point data on the complex component's surface is obtained. Finally, the point data from multiple locations on the complex component are fitted and reconstructed to achieve the profile measurement of the complex component. The specific operation steps of the method are as follows:

[0059] Step 1: Establish the coordinate system of the complex component to be tested.

[0060] Using the parallel robot's base coordinate system as the global measurement coordinate system, establish the parallel robot's base coordinate system {O}. W -X W Y W Z W}、 Parallel robot end-effector coordinate system {O E -X E Y E Z E}、Coordinate system of contact displacement sensor {O T -X T Y T Z T},like Figure 4 As shown.

[0061] The origin of the workpiece coordinate system is the center of the top circumference of the complex workpiece to be tested, and the direction perpendicular to the plane containing the ring and pointing towards the parallel robot is the Z-axis of the workpiece coordinate system. M Positive axis, with the robot's base coordinate system Y W The positive axis is the workpiece coordinate system Y. M Positive axis, X is determined according to the right-hand rule. M Establish the workpiece coordinate system {O} in the positive axis direction. M -X M Y M Z M A single-point measurement is performed on the inner circumference of the top of the workpiece using a displacement sensor, and the spatial coordinates p of the measuring point in the parallel robot's base coordinate system are recorded. j j = 1, 2, 3 are the measurement point numbers, such as Figure 5 As shown in (a), p j They are respectively:

[0062]

[0063] p is obtained by least squares method j The measurement data was fitted to calculate the coordinates (x, y) of the center of the inner circumference of the top of the workpiece in the parallel robot base coordinate system. M ,y M ,z M )for:

[0064] (x M ,y M ,z M = (0.021, -0.032, -1015.922) T

[0065] This gives us the coordinates of the origin of the workpiece coordinate system.

[0066] The coordinate system of the complex component under test (Z) M Positive axis and base coordinate system Z W Positive angle θ M =0, the transformation matrix from the workpiece coordinate system to the robot base coordinate system is calculated by formula (4):

[0067]

[0068] Step 2: Plan the measurement trajectory of the parallel robot

[0069] Selecting a contact displacement sensor with a probe tip ball radius R = 0.5 mm, and based on the three-dimensional model of the workpiece to be measured, solving for the offset surface Sr along the normal direction of the measured surface S, as follows: Figure 5 As shown in (b).

[0070] Using the generatrix equation of the workpiece to be tested For example, considering the collision between the displacement sensor's working space and the workpiece under test, let the Z-axis of the workpiece under test be taken as an example. M Based on the origin of the axis, 20 node positions are evenly distributed in the negative direction, with a spacing of 40mm. Based on the CAD model of the workpiece to be measured, the parallel section method is used to determine the position of the measurement curve in each layer, for a total of 20 layers. Figure 6 As shown in (a). Based on the workpiece coordinate system Y... M O M Z M The planar distribution of measurement points for the inner surface cross-section curve of the workpiece is performed, and the measurement point path for each layer of the measurement curve in the workpiece coordinate system is calculated. M p i ,like Figure 6 As shown in (b).

[0071] Taking the first measurement curve as an example, the path of the measuring point in the workpiece coordinate system is calculated as follows:

[0072]

[0073] Based on the transformation relationship between the workpiece coordinate system and the parallel robot base coordinate system, the measurement point path in the workpiece coordinate system is transformed to the parallel robot base coordinate system. Taking the first measurement curve as an example, the motion trajectory of the displacement sensor probe is as follows: Figure 6 As shown in (c), calculate the probe's motion trajectory in the parallel robot's base coordinate system. W p Ti for:

[0074]

[0075] When planning the measurement trajectory of a parallel robot, it is necessary to verify whether the input drive angle of the active arm at the corresponding measurement point meets the robot drive angle range. If it does, it means that the robot can reach the point. If it does not meet the requirements, it means that the robot cannot reach the point and the relative position of the robot and the component needs to be further adjusted.

[0076] Based on the simplified geometric model of Yifei Company's Delta-type parallel robot BAT1300-A6, such as Figure 7 As shown, the allowable range of input drive angles for the active arm of this parallel robot is: θ1, θ2, θ3 ∈ [-π / 6, π / 2], and the end effector platform revolves around its base coordinate system Z. W The allowable range of the input angle for counterclockwise rotation along the axis is θ4∈[0,2π].

[0077] Based on the sensor installation dimensions, taking the first measurement curve as an example, the center of the sensor probe is at a position relative to the origin of the parallel robot's end effector coordinate system in the robot's base coordinate system (X). W Z W Distance d in the direction x=15.6mm, h z =133.64mm, the angle θ between the sensor axis and the positive Z-axis of the parallel robot's end effector coordinate system. T =π / 4, the coordinate system {O} of the sensor probe center is calculated using formula (2). T -X T Y T Z T} to the parallel robot end-effector coordinate system {O E -X E Y E Z E The coordinates of} are converted to:

[0078]

[0079] Taking the first measuring point of the first measurement curve as an example, the coordinates of the displacement sensor probe in the parallel robot's base coordinate system are: W p T1 =(324.521,-0.032,-1015.922) T The results are obtained from formulas (1) and (2):

[0080]

[0081] Based on the inverse kinematics calculation of the parallel robot, the input driving angles of the active arm are: θ1 = -0.0327, θ2 = 0.6667, θ3 = 0.6666, all of which satisfy θ1, θ2, θ3 ∈ [-π / 6, π / 2], and θ4 = 0, which satisfies θ4 ∈ [0, 2π]. This indicates that the parallel robot can be controlled to move to this position, which meets the requirements. The verification methods for the positions of other measurement points are the same.

[0082] Step 3: Obtain actual spatial point data on the surface of complex components.

[0083] The parallel robot drives the displacement sensor to perform contact scanning measurement on the workpiece. The displacement sensor records and outputs the displacement change Δd of the probe at each measuring point on each layer of the measurement curve. i The first layer measurement curve sensor readings are as follows: Figure 8 As shown in (a).

[0084] Taking the first measuring point of the first measurement curve as an example, the coordinates of the displacement sensor probe in the parallel robot's base coordinate system are: W p T1 =(324.521,-0.032,-1015.922) T The measured displacement change of the probe is Δd1 = 0.56 mm.

[0085] Based on the transformation matrix from the end-effector coordinate system to the robot base coordinate systemW T E Transformation matrix from the sensor probe center coordinate system to the parallel robot end effector coordinate system E T T The transformation matrix between the contact displacement sensor coordinate system and the robot base coordinate system at the first measuring point of the first measurement curve is calculated using formula (3). W T T for:

[0086]

[0087] Based on the transformation matrix from the sensor coordinate system to the parallel robot base coordinate system W T T The displacement measured by the sensor is transformed into the coordinate system of the parallel robot, and the displacement of the probe is further superimposed on the motion trajectory of the parallel robot, such as... Figure 8 As shown in (b), the actual motion trajectory of the probe in the base coordinate system of the parallel robot is calculated using formula (6).

[0088]

[0089] The calculation method for other measurement points is the same.

[0090] Step 4: Fitting and reconstructing multi-point data of complex components

[0091] Based on the actual motion trajectory of the probe in the parallel robot base coordinate system obtained in step 3 W p Ri This involves using the least squares method to fit the surface measurement data of the complex component to the least squares method, solving for the reconstructed surface U' of the complex component, obtaining the component's profile, and comparing the offset between the reconstructed surface U' and the original CAD model surface U to determine the actual component deviation. Figure 9 As shown; the maximum deviation between the theoretical surface and the actual measured surface is calculated using formula (7):

[0092] D U'Umax =2.82mm

[0093] A parallel robot contact-based in-situ measurement system and method for complex component profiles is proposed. The in-situ measurement system is established in the machining environment. While keeping the workstation unchanged during the machining process, the system performs contact scanning measurement on the profile of complex components in conjunction with measurement planning. This significantly reduces the impact of part handling and repetitive clamping processes on the machining accuracy and efficiency, thereby effectively improving machining accuracy and efficiency. It has broad application prospects in the field of in-situ measurement of complex components.

Claims

1. A contact-based in-situ measurement method for complex component profiles of parallel robots, characterized in that, This measurement method employs a contact-based in-situ measurement system for complex component profiles. The complex component profile contact-type in-situ measurement system consists of a parallel robot and support frame, a one-dimensional contact displacement sensor, a sensor connection mechanism, and a contouring fixture assembly; The parallel robot (2) is simplified to consist of a static platform, an active arm, a driven arm, and an end effector platform. The parallel robot (2) is used to provide the motion trajectory required for the contact measurement system. The entire parallel robot (2) is mounted on the parallel robot support frame (1). The sensor connection mechanism consists of a robot end-effector plate (9), an extended measuring rod (3), and a displacement sensor mounting plate (7). The robot end-effector plate (9) is fixedly connected to the lower part of the parallel robot (2) moving platform. The extended measuring rod (3) has threads at both ends. One end is fixedly connected to the robot end-effector plate (9) by the threads, and the other end is connected to the displacement sensor mounting plate (7). The sensor mounting plate (7) has a 45° L-shaped structure. The one-dimensional contact displacement sensor (8) is fixedly installed on one side of the L-shaped structure of the displacement sensor mounting plate (7) by tightening the nut; the precise control of the measurement trajectory of the contact displacement sensor probe is realized by controlling the movement of the end moving platform of the parallel robot; the measurement of the three-dimensional profile of complex components is realized by controlling the movement of the parallel robot in Cartesian space and the rotation of the fourth axis. The contouring clamp assembly consists of left and right contouring clamps (10, 12), a bottom support plate (5), locking bolts (11), and a grid connecting beam; wherein, the grid connecting beam is formed by the left and right connecting beams (6) and the front and rear grid-shaped connecting beams (13) fixedly connected; the bottom support plate (5) has a tapered mounting hole in the middle, and the bottom support plate (5) is horizontally installed on the ground, with its center concentric with the extended measuring rod (3); the front and rear grid-shaped connecting beams are fixed in the parallel robot support frame (1); the left and right contouring clamps (10, 12) are fixed to the grid connecting beams. On the left and right connecting beams (6), the workpiece (4) to be measured is installed in the horizontally set left and right contour clamps (10, 12). The bottom of the workpiece (4) to be measured is installed in the conical mounting hole of the support plate (5) to achieve centering and support fixation of the workpiece to be measured. There are symmetrically distributed mounting holes on the front and rear sides of the left and right contour clamps (10, 12). By rotating the locking bolt (11), the left and right contour clamps are driven to move away from or closer to each other, thereby changing the clamping force of the left and right contour clamps (10, 12) on the workpiece (4) to be measured. The method includes the following steps: First, the relative pose of the parallel robot's base coordinate system and the displacement sensor probe is calibrated to establish the workpiece coordinate system of the complex component to be measured. Then, point features are extracted based on the CAD model of the complex component, and the measurement trajectory of the parallel robot is planned. The distance change between the parallel robot's end effector trajectory and the surface of the complex component is obtained using a contact displacement sensor. By superimposing the measured displacement change onto the end effector trajectory of the parallel robot, spatial point data of the complex component surface is acquired. Finally, the point data of multiple parts of the complex component are fitted and reconstructed to achieve the profile measurement of the complex component. The specific operation steps of the method are as follows: Step 1: Establish the coordinate system of the complex component to be tested. A contact-type in-situ measurement system for complex component profiles is adopted. The base coordinate system of the parallel robot is used as the global measurement coordinate system to establish the workpiece coordinate system of the complex component to be measured. The transformation relationship between the coordinate systems is solved by the forward kinematic equations of the parallel robot and coordinate transformation theory. First, based on the simplified geometric model of the Delta parallel robot, with the center of the static platform of the parallel robot as the origin of the coordinate system, The shaft passes through the center point of the drive arm's pivot axis. The positive axis is perpendicular to the stationary platform and points upwards, determined according to the right-hand rule. Establish the parallel robot's base coordinate system along the positive axis. This is used as the global measurement coordinate system; with the center of the parallel robot's end effector platform as the origin, and perpendicular to the plane of the end effector platform upwards as... Positive axis, end-effector moving platform rotates Axial rotation angle Time base coordinate system Positive axis The positive direction of the axis is determined by the right-hand rule. Establish the coordinate system of the parallel robot end effector along the positive axis. ; Based on the forward kinematics equations of a parallel robot, and using the principles of forward kinematics for parallel robots, the solution is obtained from the coordinate system of the parallel robot's end effector. To the parallel robot base coordinate system The conversion relationship between them: (1) in, This represents the forward kinematics equations of a parallel robot. Input the drive angle for the parallel robot's active arm. For the parallel robot end effector platform to revolve around its base coordinate system The input angle of rotation along the axis, and the direction of the angular displacement conforms to the right-hand rule. This represents the offset of the center of the end effector platform of the parallel robot relative to the origin of the parallel robot's base coordinate system. This is the coordinate transformation matrix from the end-effector coordinate system to the base coordinate system of the parallel robot; With the center of the sensor probe in the zero-position state of the contact displacement sensor as the origin of the sensor coordinate system, and the direction of the sensor axis away from the probe as the sensor coordinate system... Positive axis, with the parallel robot end effector coordinate system The positive axis is the sensor coordinate system. The positive direction of the axis is determined by the right-hand rule. Establish the coordinate system of the contact displacement sensor along the positive axis. Based on the sensor installation dimensions, the sensor coordinate system in the zero-position state is solved through coordinate transformation. To the end-effector coordinate system of the parallel robot Conversion relationship: (2) in, , The sensor probe center relative to the center of the parallel robot end effector platform in the robot's base coordinate system , Offset distance in direction, The sensor axes are relative to the coordinate system of the parallel robot end effector. The angle along the positive axis, This is the coordinate transformation matrix from the displacement sensor coordinate system to the parallel robot end effector coordinate system; According to the transformation matrix from the parallel robot end-effector coordinate system to the parallel robot base coordinate system Transformation matrix from the displacement sensor coordinate system to the parallel robot end effector coordinate system The coordinate system of the contact displacement sensor is obtained. To the parallel robot base coordinate system Transformation matrix between: (3) Taking a complex component like a rotating shell as an example, the origin of the workpiece coordinate system is the center of the top circumference of the complex component under test, and the direction perpendicular to the plane containing the ring and pointing towards the parallel robot is the workpiece coordinate system. Positive axis, with parallel robot base coordinate system The positive axis is the workpiece coordinate system. The positive direction of the axis is determined by the right-hand rule. Establish the workpiece coordinate system along the positive axis. A single-point measurement is performed on the inner circumference of the top of the workpiece using a displacement sensor, and the spatial coordinates of the measurement point in the parallel robot's base coordinate system are recorded. The least squares method is used to fit the measurement point data to obtain the coordinates of the center of the inner circumference of the top of the workpiece in the parallel robot base coordinate system; the transformation matrix from the workpiece coordinate system to the parallel robot base coordinate system is then solved. (4) in, Let be the coordinates of the center of the top circumference of the workpiece in the parallel robot's base coordinate system. Workpiece coordinate system Positive axis and parallel robot base coordinate system Positive angle of the axis; Step 2: Plan the measurement trajectory of the parallel robot The offset surface is solved based on the radius of the sensor probe tip to generate the corresponding probe trajectory curve, and the robot measurement trajectory is solved based on the transformation relationship between the workpiece coordinate system and the robot base coordinate system. Using the radius R of the ball head at the tip of the contact displacement sensor as the offset distance, the offset surface Sr is solved along the normal direction of the measured surface S based on the three-dimensional model of the workpiece; based on the CAD model of the workpiece, according to the workpiece... The equation of the generatrix in the plane, according to The positions of measuring points on the curves are calculated using an equidistant distribution in the negative direction, and the positions of all measured curves are determined using the parallel section method; then, based on... The measurement point positions of the workpiece cross-sectional curve on the plane are calculated based on the CAD model of the workpiece, and the measurement point path of each layer of the measurement curve in the workpiece coordinate system is calculated. ; Based on the transformation relationship between the workpiece coordinate system and the parallel robot base coordinate system, the measurement point path in the workpiece coordinate system is transformed to the parallel robot base coordinate system, and the probe trajectory in the parallel robot base coordinate system is solved: (5) in, The probe's motion trajectory is shown in the parallel robot's base coordinate system, where i is the measurement point number. Furthermore, based on the inverse kinematics of the parallel robot, the input drive angle of the parallel robot corresponding to all measurement points is solved to verify whether the input drive angle of the active arm at the corresponding measurement point position meets the robot drive angle range. Step 3: Obtain actual spatial point data on the surface of complex components. Based on the obtained probe motion trajectory in the parallel robot base coordinate system The system controls a parallel robot to perform full-feature contact scanning measurement of the workpiece, and displacement sensors record and output the displacement change of the probe at each measuring point. Based on the transformation matrix from the sensor coordinate system to the parallel robot base coordinate system The one-dimensional displacement measured by the sensor is transformed into the parallel robot's base coordinate system and decomposed into three-dimensional components. The probe displacement is then superimposed onto the parallel robot's motion trajectory to obtain the actual motion trajectory of the probe in the parallel robot's base coordinate system. (6) in, This represents the actual motion trajectory of the probe in the base coordinate system of the parallel robot. This represents the offset measured by the sensor in the base coordinate system of the parallel robot. for The rotation matrix is ​​obtained; finally, the actual spatial position data of the complex component surface in the parallel robot base coordinate system is obtained. Step 4: Fitting and reconstructing multi-point data of complex components Based on the actual motion trajectory of the probe in the parallel robot base coordinate system obtained in step 3 That is, the surface point data of the complex component being measured is fitted by the least squares method to reconstruct the surface of the complex component and finally obtain the profile of the complex component. By fitting the surface measurement data of complex components using the least squares method, the reconstructed surface U' of the complex component is solved, obtaining the actual surface of the complex component. The offset between the reconstructed surface U' and the original CAD model surface U is compared to determine the actual component deviation. The maximum deviation between the theoretical surface and the actual measured surface is the maximum deviation distance along the normal vector direction of a point on the actual measured surface. : (7) These are the points on the actual measured surface, i.e., the points measured in the actual measurement. These are the points on the theoretical surface, i.e., the theoretical measurement points obtained through planning.

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