CN116753894A - Parallel robot complex component profile contact type on-site measurement system and method - Google Patents
Parallel robot complex component profile contact type on-site measurement system and method Download PDFInfo
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Abstract
The invention discloses a parallel robot complex member profile contact type on-site measurement system and method, belongs to the technical field of complex member on-site measurement, and relates to a parallel robot complex member profile contact type on-site measurement system and method. The measuring system consists of a parallel robot, a support frame, a contact displacement sensor, a sensor connecting mechanism and a profiling clamp assembly. The measuring method adopts a complex component profile contact type on-site measuring system to establish a workpiece coordinate system of a component to be measured; and extracting point location features according to the component CAD model, and planning a parallel robot measurement track. And acquiring the motion track of the tail end of the parallel robot and the surface distance change of the complex component by using a contact displacement sensor, and realizing fitting reconstruction by overlapping the actually measured displacement change on the tail end track of the parallel robot to acquire the spatial point position data of the surface of the complex component, thereby realizing the profile measurement of the complex component to be measured. The method effectively avoids errors caused by secondary clamping and effectively improves the machining efficiency and precision of the parts.
Description
Technical Field
The invention belongs to the technical field of complex component on-site measurement, and particularly relates to a parallel robot complex component profile contact on-site measurement system and method.
Background
In the important industrial fields of national economy such as aerospace, energy power, automobiles and ships, a large number of key complex components exist, such as radomes, and the like, the high-efficiency manufacturing significance of the key complex components is great. In the processing process of the key complex components, accurate geometric shape description of the components is required to be obtained in place so as to guide the subsequent processing technology, thereby ensuring the processing quality and efficiency of the components.
The existing measuring method is mainly divided into contact type measurement and non-contact type measurement. The conventional contact type measuring method, such as a three-coordinate measuring machine, can obtain the component profile point position data with higher precision, but the complex component is required to be clamped for the second time, so that errors are introduced, and the in-situ automatic and efficient measurement of the complex component cannot be realized. The non-contact measuring method represented by optical measurement, such as a three-dimensional laser scanner, has the advantages of rapid scanning precision and high efficiency, is widely applied to large-scale surface type measurement, has lower measuring precision, often needs to paste mark points on the surface of a measured object, is difficult to meet the cleanliness requirement of the complex component, is limited by the depth of field constraint of equipment, and cannot realize the full profile measurement of the complex component. Along with the rapid development of the robot technology, the advantages of strong stability and small error of the parallel robot are combined, the parallel robot is integrated with the contact displacement sensor, and an effective method is provided for in-situ high-precision and high-efficiency measurement of the complex component profile. Therefore, the parallel robot complex component profile contact type in-situ measurement system is established in the processing environment, and has important significance for improving the processing quality and efficiency of complex components.
In the prior art document 1, namely A sampling-based motion planning method for active visual measurement with an industrial robot, a measuring system based on an industrial robot is proposed, and image capturing and point cloud reconstruction are carried out on a component through a camera fixed at the tail end of the robot, so that characteristic measurement of a target component is realized, however, the accumulated error of the industrial robot is larger, and the measuring system is easily influenced by the color, the smoothness and the like of the component, so that the measuring system has a certain limitation;
in the prior art document 2"An adaptive computer-aided path planning to eliminate errors of contact probes on free-form surfaces using a-DOF parallel robot CMM and a turn-table, the four-degree-of-freedom parallel device is combined with the trigger type measuring head integrated measuring system, and the characteristics of small accumulated error, good dynamic performance and high precision of the contact type measuring method of the parallel device are combined, so that the detection precision of the system is effectively improved. However, the trigger gauge head has low measurement efficiency, and it is difficult to realize efficient measurement of complex components.
Disclosure of Invention
The invention provides a parallel robot complex component profile contact type on-site measurement system for overcoming the defects of the prior art, and the on-site high-precision and high-efficiency measurement of complex components is realized. The system establishes an in-situ measurement system in a processing environment through a contact type measuring device consisting of a parallel robot, a one-dimensional contact type displacement sensor, a sensor connecting mechanism and a component profiling clamp, and performs contact type scanning measurement on complex component profiles by combining measurement track planning under the condition that stations are unchanged in the processing process, so that errors caused by secondary clamping can be effectively avoided, and further processing precision and efficiency are effectively improved.
The technical scheme of the invention relates to a complex component profile contact type on-site measurement system of a parallel robot, which is characterized by comprising the parallel robot, a support frame, a one-dimensional contact type displacement sensor, a sensor connecting mechanism and a profiling clamp assembly.
The parallel robot 2 is adopted to provide a motion track required by measurement for a contact type measurement system, and the parallel robot 2 is composed of a static platform, a driving arm, a driven arm and a terminal moving platform after simplification; the whole parallel robot 2 is arranged on the parallel robot support frame 1;
the sensor connecting mechanism is composed of a robot tail end transfer plate 9, a lengthened measuring rod 3 and a displacement sensor mounting plate 7, wherein the robot tail end transfer plate 9 is fixedly connected below a moving platform of the parallel robot 2, threads are formed at two ends of the lengthened measuring rod 3, one end of the lengthened measuring rod is fixedly connected in the robot tail end transfer plate 9 through the threads, the other end of the lengthened measuring rod is connected with the displacement sensor mounting plate 7, the sensor mounting plate 7 is of a 45-degree L-shaped structure, and a displacement one-dimensional contact type displacement sensor 8 is fixedly arranged on one side of the L-shaped structure of the displacement sensor mounting plate 7 through a screwing nut; the accurate control of the measuring track of the measuring head of the contact type displacement sensor is realized by controlling the motion of the movable platform at the tail end of the parallel robot; by controlling the parallel robot to move in cartesian space and the fourth axis to rotate, three-dimensional profile measurement of the complex member can be achieved.
The profiling clamp assembly consists of left and right profiling clamping plates 10 and 12, a bottom supporting plate 5, a locking bolt 11 and a cross connecting beam; the cross connecting beam is formed by fixedly connecting left and right connecting cross beams 6 and front and rear cross connecting beams 13; a conical mounting hole is formed in the middle of the bottom supporting plate 5, the bottom supporting plate 5 is horizontally arranged on the ground, and the center of the bottom supporting plate is concentric with the lengthened measuring rod 3; the cross connecting beam is fixed in the parallel robot support frame 1; the left and right profiling splints 10 and 12 are fixed on left and right connecting beams 6 in the cross connecting beam, the tested workpiece 4 is arranged in the left and right profiling splints 10 and 12 which are horizontally arranged, and the bottom of the tested workpiece 4 is arranged in a conical mounting hole of the supporting plate 5 to realize centering and supporting fixation of the tested workpiece; symmetrically distributed mounting holes are formed in the front side and the rear side of the left profiling clamp plate 10 and the right profiling clamp plate 12, and the left side and the right side of the left profiling clamp plate and the right profiling clamp plate are driven to be far away or close by rotating the locking bolt 11, so that the clamping force of the left profiling clamp plate 10 and the right profiling clamp plate 12 on the workpiece 4 to be tested is changed;
the method is characterized in that a complex member profile contact type on-site measurement system is adopted in the measurement method, the relative pose of a base coordinate system of the parallel robot and a measuring head of a displacement sensor is calibrated, and a complex member workpiece coordinate system to be measured is established; then extracting point location features according to the CAD model of the complex component, and planning a parallel robot measurement track; acquiring the motion track of the tail end of the parallel robot and the surface distance change of the complex component by using a contact displacement sensor, and realizing the acquisition of the spatial point position data of the surface of the complex component by superposing the actually measured displacement change on the tail end track of the parallel robot; and finally, fitting and reconstructing multi-position point location data of the complex component, thereby realizing the profile measurement of the complex component to be measured. The method comprises the following specific operation steps:
step 1, establishing a coordinate system of a complex component workpiece to be tested
Adopting a complex component profile contact type on-site measurement system, taking a parallel robot base coordinate system as a global measurement coordinate system, establishing a complex component workpiece coordinate system to be measured, and solving a conversion relation between the coordinate systems through a parallel robot forward kinematics equation and a coordinate transformation theory;
firstly, according to a simplified geometric model of a Delta parallel robot, taking the center of a static platform of the parallel robot as a coordinate origin, X W The shaft passes through the center point of the axis of the rotating shaft of the driving arm 1, Z W The axis is forward and vertical to the static platform upwards, and Y is determined according to the right hand rule W The axis is forward, and a parallel robot base coordinate system { O } is established W -X W Y W Z W And taking the same as a global measurement coordinate system. The center of the tail end movable platform of the parallel robot is taken as the origin of coordinates, and the upward direction of the plane perpendicular to the tail end movable platform is Z E The axis is forward, and the tail end moving platform winds Z W Axial rotation angle θ 4 Time base coordinate system x=0 W The axial forward direction is X E The axis is forward, Y is determined according to the right hand rule E The axis is forward, and a parallel robot tail end coordinate system { O } is established E -X E Y E Z E }；
According to the forward kinematics equation of the parallel robot, solving the { O { coordinate system of the end of the parallel robot by the forward kinematics principle of the parallel robot E -X E Y E Z E { O } to parallel robot base coordinate system W -X W Y W Z W Conversion relation between }:
wherein f represents the forward kinematics equation of the parallel robot, θ 1 ,θ 2 ,θ 3 Inputting driving angle theta for driving arm of parallel robot 4 Z is a base coordinate system around which a terminal moving platform of the parallel robot winds W Input angle of rotation in axial direction, angular displacement direction accords with right hand rule, x E ,y E ,z E The offset of the center of the movable platform at the tail end of the parallel robot relative to the origin of the base coordinate system of the parallel robot, W T E the coordinate transformation matrix is formed by connecting the end coordinate system of the parallel robot to the base coordinate system of the parallel robot.
Taking the center of a sensor measuring head in a zero state of a contact displacement sensor as an origin of a sensor coordinate system, and taking the direction of a sensor axis away from the measuring head as a sensor coordinate system Z T The axis is forward, and the robot end coordinate system Y is connected in parallel E The axial forward direction is the coordinate system Y of the sensor T The axis is forward, X is determined according to the right hand rule T The axis is forward, and a contact displacement sensor coordinate system { O }, is established T -X T Y T Z T }. Based on the sensor installation size, solving a sensor coordinate system { O ] in a zero state through coordinate transformation T -X T Y T Z T To the parallel robot end coordinate system { O } E -X E Y E Z E Conversion relation:
wherein ,dx 、h z X is that the center of a sensor probe is opposite to the center of a movable platform at the tail end of a parallel robot under a robot base coordinate system W 、Z W Offset distance in direction, theta T Robot end coordinate system Z with sensor axis relatively parallel E The included angle of the positive direction of the shaft, E T T for displacing sensor coordinate system to parallel robot end coordinate systemIs a coordinate transformation matrix of (a).
According to the transformation matrix from the end coordinate system of the parallel robot to the base coordinate system of the parallel robot W T E And a conversion matrix from the displacement sensor coordinate system to the parallel robot end coordinate system E T T Obtaining a coordinate system { O from the contact displacement sensor T -X T Y T Z T { O } to parallel robot base coordinate system W -X W Y W Z W Conversion matrix between }:
W T T ＝ W T E E T T (3)
taking a revolving body housing complex component as an example, taking the top circumference center of the complex component to be measured as the origin of a workpiece coordinate system, and taking the direction perpendicular to the plane where the circular ring is positioned and pointing to the parallel robot as the workpiece coordinate system Z M The axis is forward, and the robot base coordinate system Y is connected in parallel W The axial forward direction is the coordinate system Y of the workpiece M The axis is forward, X is determined according to the right hand rule M The axis is forward, and a workpiece coordinate system { O } is established M -X M Y M Z M }. Single-point measurement is carried out on the circumference of the inner side of the top end of the workpiece through a displacement sensor, and the space coordinate p of the measuring point under the parallel robot base coordinate system is recorded j And (j is more than or equal to 3), fitting the measuring point data by adopting a least square method, and obtaining the center coordinates of the circumference of the inner side of the top end of the workpiece under the parallel robot base coordinate system. Solving a conversion matrix from a workpiece coordinate system to a parallel robot base coordinate system:
wherein ,(xM ,y M ,z M ) Is the coordinate of the circle center of the circumference at the top of the workpiece under the parallel robot base coordinate system, theta M For the object coordinate system Z M Axial forward and parallel robot base coordinate system Z W The positive included angle of the shaft.
Step 2, planning a parallel robot measurement track
And solving the offset curved surface based on the radius of the tip of the probe of the sensor, generating a corresponding measuring head track curve, and solving the measuring track of the robot based on the conversion relation between the workpiece coordinate system and the robot base coordinate system.
And taking the radius R of the ball head at the tip end of the probe of the contact displacement sensor as the offset distance, and solving an offset curved surface Sr along the normal direction of the normal line of the measured curved surface S based on the three-dimensional model of the workpiece to be measured. Based on CAD model of workpiece to be measured, according to workpiece Y M O M Z M In-plane bus equation according to Z M The positions of measuring points on the calculation curve are distributed in the negative direction at equal intervals, and all the positions of the measurement curve are determined by adopting a parallel section method. Then based on Y M O M Z M Measuring point positions of the section curves of the workpiece on the plane, and calculating measuring point paths of each layer of measuring curves under a workpiece coordinate system according to a CAD model of the workpiece to be measured M p i ；
According to the conversion relation between the workpiece coordinate system and the parallel robot base coordinate system, converting the measuring point path under the workpiece coordinate system into the parallel robot base coordinate system, and solving the measuring head track under the parallel robot base coordinate system:
( W p Ti ,1) T ＝ W T M ( M p i ,1) T (5)
wherein ,W p Ti the motion trail of the measuring head under the base coordinate system of the parallel robot is that i is the measuring point serial number;
further, according to inverse kinematics of the parallel robots, solving input driving angles of all measuring points corresponding to the parallel robots, and verifying whether the input driving angles of the driving arms at the positions of the corresponding measuring points meet the driving angle range of the robots;
step 3, obtaining actual space point position data of the surface of the complex component
According to the motion trail of the measuring head under the base coordinate system of the parallel robot obtained by solving W p Ti The parallel robot is controlled to perform full-feature contact type scanning measurement on the workpiece, and the displacement sensor records and outputs the displacement fluctuation delta d of the measuring head at each measuring point i Conversion matrix from sensor coordinate system to parallel robot base coordinate system W T T The sensor measures oneThe dimensional displacement is converted into a parallel robot base coordinate system and is decomposed into three-dimensional components, and the displacement of the measuring head is further overlapped to the motion trail of the parallel robot to obtain the actual motion trail of the measuring head under the parallel robot base coordinate system:
wherein ,W p Ri the actual motion trail of the measuring head under the parallel robot base coordinate system is [ ] W Δd xi , W Δd yi , W Δd zi ) T ＝ W R T ·(0,0,Δd i ) T For the sensor to measure a representation of the offset in the parallel robot base coordinate system, W R T is that W T T Is used to rotate the matrix. And finally obtaining the actual space point position data of the complex component surface under the parallel robot base coordinates.
Step 4, fitting and reconstructing multi-part point location data of complex component
According to the actual motion trail of the measuring head under the parallel robot base coordinate system obtained in the step 3 W p Ri Fitting the surface point location data of the complex component to be measured by a least square method, reconstructing the profile of the complex component, and finally obtaining the profile of the complex component;
fitting the complex component surface measurement point data through a least square method, solving a complex component reconstruction curved surface U ', obtaining a complex component actual molded surface, comparing the offset of the reconstructed curved surface U' obtained by the curved surface reconstruction with the offset of the original CAD model curved surface U, and solving the actual component deviation; the maximum deviation between the theoretical curved surface and the actual measured curved surface is the maximum deviation distance D in the normal direction of a point on the actual measured curved surface U'Umax ：
D U'Umax ＝max(|| W P Ri - W P Ti ||) (7)
W P Ri For actually measuring points on the curved surface, i.e. measuring points obtained by actual measurement, W P Ti and (5) planning the obtained theoretical measuring points for points on the theoretical curved surface.
The invention has the remarkable effects and benefits that the system combines the advantages of high precision, good space accessibility and the like of the parallel robot, integrates the parallel robot and the contact displacement sensor, effectively solves the problems that the full-characteristic measurement of the complex component cannot be realized due to the interference of the space position in a scanning type measuring method, the secondary clamping error is introduced by a three-coordinate measuring system and the like, and combines the measurement planning to carry out the contact scanning measurement on the profile of the complex component under the condition that the station of the complex component is kept unchanged in the processing process, thereby realizing the measurement and reconstruction of the profile of the complex component. The in-situ measurement system and the in-situ measurement method can be widely applied to high-precision in-situ measurement of complex component profiles such as an aircraft radome, effectively avoid errors caused by repeated carrying, secondary clamping and other processes, and can improve the processing precision and efficiency.
The profiling clamp assembly and sensor connecting mechanism in the in-situ measurement system design has the advantages of simple structure, convenient installation and adjustment and high measurement precision.
Drawings
FIG. 1-an overall flow chart for in-situ measurement of complex component profile contact for a parallel robot.
Fig. 2 a) is a structural diagram of a complex component profile contact type in-situ measurement system of a parallel robot, and fig. 2 b) is a structural diagram of a cross connecting beam. Wherein, the support frame of the 1-parallel robot; 2-parallel robot; 3-lengthening the measuring rod; 4-a workpiece to be measured; 5-a bottom support plate; 6-left and right connecting beams; 10-left profiling splints; 11-locking bolts; 12-right profiling splints and 13-front and back groined connecting beams.
FIG. 3-schematic diagram of a parallel robot complex component profile contact type in-situ measurement system displacement sensor connection, in which: 2-parallel robot; 3-lengthening the measuring rod; 7-a displacement sensor mounting plate; 8-a one-dimensional contact displacement sensor; 9-robot end adapter plate.
Fig. 4-schematic diagram of coordinate transformation relationship between the base coordinate system of the parallel robot and the end coordinate system of the parallel robot and the displacement sensor coordinate system, in which: { O W -X W Y W Z W Connected in parallelRobot base coordinate System { O E -X E Y E Z E Terminal coordinate system of } parallel robot, { O T -X T Y T Z T -a touch displacement sensor coordinate system.
FIG. 5-schematic view of a displacement sensor for measuring a curved surface inside a workpiece tip, wherein: { O M -X M Y M Z M -complex component workpiece coordinate system, S-workpiece inner curved surface, sr-gauge head center offset curved surface. R-contact displacement sensor probe tip ball head radius (mm).
FIG. 6-schematic diagram of measuring head motion track planning of complex component to be measured, wherein, FIG. a) measuring graph, b) measuring point path graph, c) measuring motion path graph; M p i is the motion track of the measuring head, wherein the i-measuring point is the serial number.
FIG. 7-Delta parallel robot simplified geometric model diagram. Wherein, θ 1 ,θ 2 ,θ 3 Inputting driving angle theta for driving arm of parallel robot 4 Z is a base coordinate system around which a terminal moving platform of the parallel robot winds W Input angle of rotation in the axial direction.
FIG. 8 a) -first measurement curve sensor readings, b) -schematic drawing of the actual movement trajectory of the stylus.
FIG. 9 a) -schematic view of a reconstruction of the profile of the complex component to be measured, FIG. 9 b) is an enlarged partial view of 9 a)
Detailed Description
The following describes the embodiments of the present invention in detail with reference to the technical scheme and the accompanying drawings.
The structure diagram of the complex component profile contact type on-site measuring system of the parallel robot is shown in fig. 2 and 3, and the measuring system consists of the parallel robot, a supporting frame, a sensor connecting structure, a contact type displacement sensor and a profiling clamp assembly. The parallel robot 2 is a Delta type parallel robot BAT1300-A6 of the Yifei company, and is composed of a static platform, a driving arm, a driven arm and a tail end moving platform after simplification, as shown in figure 7. The repeated positioning precision is 80 mu m, the 4 degrees of freedom are provided, the load is 6kg, and the allowable range of the driving angle input by the driving arm is theta 1 、θ 2 、θ 3 ∈[-π/6,π/2]An allowable range of an input angle rotating counterclockwise around the Z-axis direction of the base coordinate system is theta 4 ∈[0,2π]。
The one-dimensional contact type displacement sensor 8 adopts a Ma Bosi H50 displacement sensor, the measuring range is 10mm, the measuring precision is 0.5 mu m, the sensor is fixed on the lower side of the sensor connecting device 7 by screwing a nut, and as shown in figure 3, the accurate control of the measuring track of the measuring head of the contact type displacement sensor is realized by controlling the movement of the movable platform at the tail end of the parallel robot.
The sensor connecting mechanism is composed of a robot tail end transfer plate 9, a lengthened measuring rod 3 and a displacement sensor mounting plate 7 respectively, as shown in figure 3, the robot tail end transfer plate 9 is fixedly connected below a movable platform of the parallel robot 2, and the robot tail end transfer plate 9 and the displacement sensor mounting plate 7 are connected through threads at two ends of the lengthened measuring rod 3. The displacement sensor mounting plate 7 is of a 45-degree L-shaped structure, and the three-dimensional profile measurement of the complex component can be realized by controlling the parallel robot to move in a Cartesian space and the fourth axis to rotate.
The profiling clamp assembly consists of left and right profiling clamping plates 10 and 12, a bottom supporting plate 5, a locking bolt 11 and a cross connecting beam. The cross connecting beam is formed by fixedly connecting left and right connecting cross beams 6 with front and rear cross connecting beams 13. The middle of the bottom supporting plate 5 is provided with a conical mounting hole, the bottom supporting plate 5 is horizontally arranged on the ground, and the center of the bottom supporting plate is concentric with the lengthened measuring rod 3. The cross connecting beam is fixed in the parallel robot support frame 1; the left and right profiling splints 10, 12 are fixed on the left and right connecting beams 6 in the cross connecting beam. The tested workpiece 4 is arranged in left and right profiling splints 10 and 12 which are horizontally arranged, the bottom of the tested workpiece 4 is arranged in a conical mounting hole of the supporting plate 5, and the centering and supporting fixation of the tested workpiece are realized; symmetrically distributed mounting holes are formed in the front side and the rear side of the left profiling clamp plate 10 and the right profiling clamp plate 12, and the left side and the right side of the left profiling clamp plate and the right profiling clamp plate are driven to be far away or close by rotating the locking bolt 11, so that the clamping force of the left profiling clamp plate 10 and the right profiling clamp plate 12 on the workpiece 4 to be tested is changed;
the method is characterized in that a complex component profile contact type on-site measurement system is adopted in the method, and a to-be-measured component is clamped through a profiling clamp assembly, so that the clamping and positioning of the to-be-measured complex component are realized. And (3) establishing a workpiece coordinate system of the complex component to be tested by calibrating the relative pose of the base coordinate system of the parallel robot and the measuring head of the displacement sensor. Extracting point location features according to the CAD model of the complex component, and planning a parallel robot measurement track; and further, the change of the motion trail of the tail end of the parallel robot and the surface distance of the complex component is obtained based on the contact displacement sensor. And the space point position data acquisition of the surface of the complex component is realized by superposing the actually measured displacement change on the tail end track of the parallel robot. And finally, fitting and reconstructing multi-position point location data of the complex component, thereby realizing the profile measurement of the complex component to be measured. The method comprises the following specific operation steps:
step 1, establishing a coordinate system of a complex component workpiece to be tested
Establishing a parallel robot base coordinate system { O } by taking the parallel robot base coordinate system as a global measurement coordinate system W -X W Y W Z W { O } parallel robot end coordinate system E -X E Y E Z E Coordinate system { O } of contact displacement sensor T -X T Y T Z T And as shown in fig. 4.
Taking the circle center of the circumference of the top of the complex workpiece to be measured as the origin of a workpiece coordinate system, and taking the direction which is perpendicular to the plane where the circular ring is positioned and points to the parallel robot as the workpiece coordinate system Z M The axis is forward, in the robot base coordinate system Y W The axial forward direction is the coordinate system Y of the workpiece M The axis is forward, X is determined according to the right hand rule M The axis is forward, and a workpiece coordinate system { O } is established M -X M Y M Z M }. Single-point measurement is carried out on the circumference of the inner side of the top end of the workpiece through a displacement sensor, and the space coordinate p of the measuring point under the parallel robot base coordinate system is recorded j J=1, 2,3 is the measurement point number, p as shown in fig. 5 (a) j The method comprises the following steps of:
p is obtained by least square method j Fitting the measurement point data, and calculating to obtain the center coordinates (x) of the inner circumference of the top end of the workpiece under the parallel robot base coordinate system M ,y M ,z M ) The method comprises the following steps:
(x M ,y M ,z M )＝(0.021,-0.032,-1015.922) T
and obtaining the origin coordinates of the coordinate system of the workpiece.
Coordinate system Z of complex component workpiece to be measured M Axis forward direction and base coordinate system Z W Angle theta of axial forward direction M =0, the transformation matrix from the object coordinate system to the robot base coordinate system is calculated by equation (4):
step 2, planning a parallel robot measurement track
Selecting the radius R=0.5 mm of the ball head at the tip end of the probe of the contact displacement sensor, and solving the offset curved surface Sr along the normal direction of the normal line of the curved surface S to be measured based on the three-dimensional model of the workpiece to be measured, as shown in fig. 5 (b).
By using the bus equation of the workpiece to be measuredFor example, consider the collision condition between the working space of the displacement sensor and the workpiece to be measured, so as to obtain the workpiece Z to be measured M The axis origin is based, and 20 node positions are distributed at equal intervals in the negative direction, and the interval is 40mm. Based on the CAD model of the workpiece to be measured, the position of each layer of measurement curve is determined by adopting a parallel section method, and 20 layers are added, as shown in fig. 6 (a). Based on the object coordinate system Y M O M Z M Plane distribution of the measuring point positions of the inner side surface section curves of the workpiece, and calculation of the measuring point paths of each layer of measuring curves under the workpiece coordinate system M p i As shown in fig. 6 (b).
Taking the first measurement curve as an example, the measuring point path under the coordinate system of the workpiece is calculated as follows:
converting the path of the measuring point under the workpiece coordinate system into the parallel robot base coordinate system according to the conversion relation between the workpiece coordinate system and the parallel robot base coordinate system, taking the first measuring curve as an example, calculating the measuring head movement track under the parallel robot base coordinate system by using the movement track of the measuring head of the displacement sensor as shown in fig. 6 (c) W p Ti The method comprises the following steps:
when planning the measuring track of the parallel robot, verifying whether the driving angle input by the driving arm at the position of the corresponding measuring point meets the driving angle range of the robot, and if so, indicating that the control robot can reach the point; if the requirements are not met, it is stated that the control robot cannot reach the point position, and further adjustment of the robot-member relative position is required.
According to the simplified geometric model of the Delta type parallel robot BAT1300-A6 of the wingfei company, as shown in fig. 7, the driving arm input driving angle allowable range of the model parallel robot is as follows: θ 1 、θ 2 、θ 3 ∈[-π/6,π/2]The end moving platform is around the base coordinate system Z W The allowable range of the input angle rotating anticlockwise along the axial direction is theta 4 ∈[0,2π]。
Taking a first measurement curve as an example according to the installation size of the sensor, wherein the origin of the coordinate system of the end of the parallel robot relative to the center of the measuring head of the sensor is X in the robot base coordinate system W 、Z W Distance d in the direction x ＝15.6mm、h z 133.64mm and the positive Z-axis included angle theta of the sensor axis relative to the end coordinate system of the parallel robot T Pi/4, calculating from equation (2) to obtain the sensor probe center coordinate system { O } T -X T Y T Z T To the parallel robot end coordinate system { O } E -X E Y E Z E The coordinates of } are converted into:
taking the first measuring point of the first measuring curve as an example, the measuring head coordinate of the displacement sensor under the base coordinate system of the parallel robot is W p T1 ＝(324.521,-0.032,-1015.922) T Calculated by the formulas (1) and (2):
the input driving angles of the driving arm are obtained by calculation according to inverse kinematics of the parallel robot and are respectively as follows: θ 1 ＝-0.0327，θ 2 ＝0.6667，θ 3 =0.6666, all conform to θ 1 、θ 2 、θ 3 ∈[-π/6,π/2]，θ 4 =0, conform to θ 4 ∈[0,2π]The control of the parallel robot to move to the position meets the requirements, and other measuring point position verification methods are the same as the control of the parallel robot.
Step 3, obtaining actual space point position data of the surface of the complex component
The parallel robot drives a displacement sensor to perform contact scanning measurement on the workpiece, and the displacement sensor records and outputs the displacement fluctuation delta d of the measuring head at each measuring point of each layer of measuring curve i The first layer measurement profile sensor readings are shown in fig. 8 (a).
Taking the first measuring point of the first measuring curve as an example, the measuring head coordinate of the displacement sensor under the base coordinate system of the parallel robot is W p T1 ＝(324.521,-0.032,-1015.922) T Measuring head actual measurement displacement variation delta d 1 ＝0.56mm。
Conversion matrix from parallel robot end coordinate system to robot base coordinate system W T E And a conversion matrix from the sensor probe center coordinate system to the parallel robot end coordinate system E Τ T Calculating a conversion matrix from the coordinate system of the contact displacement sensor at the first measuring point of the first measuring curve to the robot base coordinate system according to the formula (3) W T T The method comprises the following steps:
conversion matrix from sensor coordinate system to parallel robot base coordinate system W T T The displacement measured by the sensor is converted into a parallel robot base coordinate system, and the displacement of the measuring head is further overlapped to the motion track of the parallel robot, as shown in fig. 8 (b). And (3) calculating to obtain the actual motion trail of the measuring head under the base coordinate system of the parallel robot by the formula (6).
The calculation method of other measurement points is the same as the above.
Step 4, fitting and reconstructing multi-part point location data of complex component
According to the actual motion trail of the measuring head under the parallel robot base coordinate system obtained in the step 3 W p Ri Fitting the complex component surface point location data to be measured through a least square method, solving a complex component reconstruction curved surface U 'to obtain a complex component profile, comparing the offset of the reconstructed curved surface U' obtained by the curved surface reconstruction with the offset of the original CAD model curved surface U, and solving the actual component deviation, as shown in figure 9; calculating the maximum deviation between the theoretical curved surface and the actual measured curved surface according to the formula (7):
D U'Umax ＝2.82mm
the parallel robot complex component profile contact type on-site measurement system and method are established in a processing environment, and under the condition that stations are unchanged in the processing process, the complex component profile is subjected to contact type scanning measurement in combination with measurement planning, so that the influence of the processes of part conveying, repeated clamping and the like on the part processing precision and efficiency is greatly reduced, the processing precision and efficiency are further effectively improved, and the parallel robot complex component profile contact type on-site measurement system and method have wide application prospects in the field of complex component on-site measurement.
Claims (2)
1. The parallel robot complex component profile contact type on-site measurement system is characterized by comprising a parallel robot, a support frame, a one-dimensional contact type displacement sensor, a sensor connecting mechanism and a profiling clamp assembly;
the parallel robot (2) is composed of a static platform, a driving arm, a driven arm and a tail end moving platform after being simplified; a parallel robot (2) is adopted to provide a motion track required by measurement for a contact type measurement system, and the whole parallel robot (2) is arranged on a parallel robot support frame (1);
the sensor connecting mechanism consists of a robot tail end rotating piece plate (9), an extension measuring bar (3) and a displacement sensor mounting plate (7); the robot tail end adapter plate (9) is fixedly connected below the movable platform of the parallel robot (2), threads are formed at two ends of the lengthened measuring rod (3), one end of the lengthened measuring rod is fixedly connected in the robot tail end adapter plate (9) through the threads, the other end of the lengthened measuring rod is connected with the displacement sensor mounting plate (7), and the sensor mounting plate (7) is of a 45-degree L-shaped structure;
the displacement one-dimensional contact type displacement sensor (8) is fixedly arranged on one side of an L-shaped structure of the displacement sensor mounting plate (7) through a screwing nut; the accurate control of the measuring track of the measuring head of the contact type displacement sensor is realized by controlling the motion of the movable platform at the tail end of the parallel robot; the measurement of the three-dimensional profile of the complex component is realized by controlling the parallel robot to move in a Cartesian space and the fourth axis to rotate;
the profiling clamp assembly consists of left and right profiling clamp plates (10, 12), a bottom supporting plate (5), a locking bolt (11) and a cross connecting beam; the cross connecting beam is formed by fixedly connecting left and right connecting cross beams (6) with front and rear cross connecting beams (13); a conical mounting hole is formed in the middle of the bottom supporting plate (5), the bottom supporting plate (5) is horizontally arranged on the ground, and the center of the bottom supporting plate is concentric with the lengthened measuring rod (3); the front and rear groined connecting beams are fixed in the parallel robot support frame (1); the left profiling clamp plates (10) and the right profiling clamp plates (12) are fixed on a left connecting beam (6) and a right connecting beam (6) in the cross connecting beam, a workpiece to be tested (4) is arranged in the left profiling clamp plates (10) and the right profiling clamp plates (12) which are horizontally arranged, and the bottom of the workpiece to be tested (4) is arranged in a conical mounting hole of the supporting plate (5) so as to realize centering and supporting fixation of the workpiece to be tested; mounting hole sites which are symmetrically distributed are machined on the front side and the rear side of the left profiling clamp plates and the right profiling clamp plates (10 and 12), and the left side and the right side of the left profiling clamp plates and the right profiling clamp plates are driven to be far away or close by rotating the locking bolt (11), so that the clamping force of the left profiling clamp plates and the right profiling clamp plates (10 and 12) on a workpiece (4) to be tested is changed.
2. The method is characterized in that a complex component profile contact type on-site measurement system is adopted in the measurement method, a base coordinate system of the parallel robot and a relative pose of a measuring head of a displacement sensor are calibrated, and a complex component workpiece coordinate system to be measured is established; then extracting point location features according to the CAD model of the complex component, and planning a parallel robot measurement track; acquiring the motion track of the tail end of the parallel robot and the surface distance change of the complex component by using a contact displacement sensor, and realizing the acquisition of the spatial point position data of the surface of the complex component by superposing the actually measured displacement change on the tail end track of the parallel robot; finally, fitting and reconstructing multi-position point location data of the complex component, thereby realizing the profile measurement of the complex component to be measured; the method comprises the following specific operation steps:
step 1, establishing a coordinate system of a complex component workpiece to be tested
Adopting a complex component profile contact type on-site measurement system, taking a parallel robot base coordinate system as a global measurement coordinate system, establishing a complex component workpiece coordinate system to be measured, and solving a conversion relation between the coordinate systems through a parallel robot forward kinematics equation and a coordinate transformation theory;
firstly, according to a simplified geometric model of a Delta parallel robot, taking the center of a static platform of the parallel robot as a coordinate origin, X W The shaft passes through the center point of the axis of the driving arm rotating shaft and Z W The axis is forward and vertical to the static platform upwards, and Y is determined according to the right hand rule W The axis is forward, and a parallel robot base coordinate system { O } is established W -X W Y W Z W -taking it as global measurement coordinate system; the center of the tail end movable platform of the parallel robot is taken as the origin of coordinates, and the upward direction of the plane perpendicular to the tail end movable platform is Z E Axial forward and end moving platformAround Z W Axial rotation angle θ 4 Time base coordinate system x=0 W The axial forward direction is X E The axis is forward, Y is determined according to the right hand rule E The axis is forward, and a parallel robot tail end coordinate system { O } is established E -X E Y E Z E }；
According to the forward kinematics equation of the parallel robot, solving the { O { coordinate system of the end of the parallel robot by the forward kinematics principle of the parallel robot E -X E Y E Z E { O } to parallel robot base coordinate system W -X W Y W Z W Conversion relation between }:
wherein f represents the forward kinematics equation of the parallel robot, θ 1 ,θ 2 ,θ 3 Inputting driving angle theta for driving arm of parallel robot 4 Z is a base coordinate system around which a terminal moving platform of the parallel robot winds W Input angle of rotation in axial direction, angular displacement direction accords with right hand rule, x E ,y E ,z E The offset of the center of the movable platform at the tail end of the parallel robot relative to the origin of the base coordinate system of the parallel robot, W T E the coordinate transformation matrix is from the end coordinate system of the parallel robot to the base coordinate system of the parallel robot;
taking the center of a sensor measuring head in a zero state of a contact displacement sensor as an origin of a sensor coordinate system, and taking the direction of a sensor axis away from the measuring head as a sensor coordinate system Z T The axis is forward, and the robot end coordinate system Y is connected in parallel E The axial forward direction is the coordinate system Y of the sensor T The axis is forward, X is determined according to the right hand rule T The axis is forward, and a contact displacement sensor coordinate system { O }, is established T -X T Y T Z T -a }; based on the sensor installation size, solving a sensor coordinate system { O ] in a zero state through coordinate transformation T -X T Y T Z T To the parallel robot end coordinate system { O } E -X E Y E Z E Transfer of }Relationship exchange:
wherein ,dx 、h z X is that the center of a sensor probe is opposite to the center of a movable platform at the tail end of a parallel robot under a robot base coordinate system W 、Z W Offset distance in direction, theta T Robot end coordinate system Z with sensor axis relatively parallel E The included angle of the positive direction of the shaft, E T T the coordinate transformation matrix is a coordinate system from a displacement sensor coordinate system to a parallel robot terminal coordinate system;
according to the transformation matrix from the end coordinate system of the parallel robot to the base coordinate system of the parallel robot W T E And a conversion matrix from the displacement sensor coordinate system to the parallel robot end coordinate system E T T Obtaining a coordinate system { O from the contact displacement sensor T -X T Y T Z T { O } to parallel robot base coordinate system W -X W Y W Z W Conversion matrix between }:
W T T ＝ W T E E T T (3)
taking a revolving body housing complex component as an example, taking the top circumference center of the complex component to be measured as the origin of a workpiece coordinate system, and taking the direction perpendicular to the plane where the circular ring is positioned and pointing to the parallel robot as the workpiece coordinate system Z M The axis is forward, and the robot base coordinate system Y is connected in parallel W The axial forward direction is the coordinate system Y of the workpiece M The axis is forward, X is determined according to the right hand rule M The axis is forward, and a workpiece coordinate system { O } is established M -X M Y M Z M -a }; single-point measurement is carried out on the circumference of the inner side of the top end of the workpiece through a displacement sensor, and the space coordinate p of the measuring point under the parallel robot base coordinate system is recorded j (j is more than or equal to 3), fitting measuring point data by a least square method to obtain the center coordinates of the circumference of the inner side of the top end of the workpiece under the parallel robot base coordinate system; solving for a coordinate system from a workpiece coordinate system to a parallel robot base coordinate systemConversion matrix:
wherein ,(xM ,y M ,z M ) Is the coordinate of the circle center of the circumference at the top of the workpiece under the parallel robot base coordinate system, theta M For the object coordinate system Z M Axial forward and parallel robot base coordinate system Z W An axial forward included angle;
step 2, planning a parallel robot measurement track
Solving an offset curved surface based on the radius of the tip of the probe of the sensor, generating a corresponding measuring head track curve, and solving a robot measurement track based on the conversion relation between a workpiece coordinate system and a robot base coordinate system;
taking the radius R of the ball head at the tip end of the probe of the contact displacement sensor as the offset distance, and solving an offset curved surface Sr along the normal direction of the normal line of the measured curved surface S based on the three-dimensional model of the workpiece to be measured; based on CAD model of workpiece to be measured, according to workpiece Y M O M Z M In-plane bus equation according to Z M The measuring point positions on the calculation curves are distributed in the negative direction at equal intervals, and all the measuring curve positions are determined by adopting a parallel section method; then based on Y M O M Z M Measuring point positions of the section curves of the workpiece on the plane, and calculating measuring point paths of each layer of measuring curves under a workpiece coordinate system according to a CAD model of the workpiece to be measured M p i ；
According to the conversion relation between the workpiece coordinate system and the parallel robot base coordinate system, converting the measuring point path under the workpiece coordinate system into the parallel robot base coordinate system, and solving the measuring head track under the parallel robot base coordinate system:
( W p Ti ,1) T ＝ W T M ( M p i ,1) T (5)
wherein ,W p Ti the motion trail of the measuring head under the base coordinate system of the parallel robot is that i is the measuring point serial number;
further, according to inverse kinematics of the parallel robots, solving input driving angles of all measuring points corresponding to the parallel robots, and verifying whether the input driving angles of the driving arms at the positions of the corresponding measuring points meet the driving angle range of the robots;
step 3, obtaining actual space point position data of the surface of the complex component
According to the motion trail of the measuring head under the base coordinate system of the parallel robot obtained by solving W p Ti The parallel robot is controlled to perform full-feature contact type scanning measurement on the workpiece, and the displacement sensor records and outputs the displacement fluctuation delta d of the measuring head at each measuring point i Conversion matrix from sensor coordinate system to parallel robot base coordinate system W T T Converting the one-dimensional displacement measured by the sensor into a parallel robot base coordinate system, decomposing the one-dimensional displacement into three-dimensional components, and further superposing the displacement of the measuring head onto the motion track of the parallel robot to obtain the actual motion track of the measuring head under the parallel robot base coordinate system:
wherein ,W p Ri the actual motion trail of the measuring head under the parallel robot base coordinate system is [ ] W Δd xi , W Δd yi , W Δd zi ) T ＝ W R T ·(0,0,Δd i ) T For the sensor to measure a representation of the offset in the parallel robot base coordinate system, W R T is that W T T Is a rotation matrix of (a); finally obtaining actual space point position data of the complex component surface under the base coordinates of the parallel robot;
step 4, fitting and reconstructing multi-part point location data of complex component
According to the actual motion trail of the measuring head under the parallel robot base coordinate system obtained in the step 3 W p Ri Fitting the surface point location data of the complex component to be measured by a least square method, reconstructing the profile of the complex component, and finally obtaining the profile of the complex component;
simulating the surface measurement point data of the complex component by using a least square methodCombining, solving a complex component reconstruction curved surface U ', obtaining a complex component actual molded surface, comparing the offset of the reconstructed curved surface U' obtained by the curved surface reconstruction with the offset of the original CAD model curved surface U, and solving the actual component deviation; the maximum deviation between the theoretical curved surface and the actual measured curved surface is the maximum deviation distance D in the normal direction of a point on the actual measured curved surface U'Umax ：
D U'Umax ＝max(|| W P Ri - W P Ti ||) (7)
W P Ri To actually measure a point on a curved surface i.e. a measured point actually measured, W P Ti and planning to obtain theoretical measuring points for points on the theoretical curved surface.
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