Research On Error Compensation Of 3-TPS Hybrid Robot

As a new product of modern processing technology,hybrid robot not only inherits the advantages of serial and p arallel robots,but also avoids the disadvantages of the other two kinds of robots in varying degrees.Hybrid robot has compact structure,good rigidity,large loadcarrying capacity,high accuracy,good dynamic characteristics,large workspace and high modularity.However,due to the complex structure of parallel mechanism of hybrid robot,there are many geometric error sources which have strong non-linear characteristics on accuracy.Compared with mature traditional industrial robots,hybrid robots still have the problem of low motion accuracy.In this paper,based on the 3-TPS hybrid robot developed by Northeastern University,the influence factors of each error are analyzed,and the kinematics calibration and error compensation are studied.The main contents of the thesis are as follows:(1)The establishment of motion control algorithm for hybrid robots.According to the structural characteristics of 3-TPS hybrid robot,the coordinate system is established.The forward and inverse kinematics formulas are derived from parallel mechanism and series constraint mechanism respectively.The forward kinematics solution of parallel mechanism is solved by iteration method,and the workspace is solved by numerical method.The kinematics model is transformed into an available motion control algorithm for hybrid robots,and the trajectory motion of the robot can be programmed on the built hardware and software platform.(2)Actuator error analysis and traj ectory error estimation.The main error sources affecting the actuator position of 3-TPS hybrid robot are analyzed,and the error model is established.The error transfer functions of each error source are deduced according to the principle of error independent action.The influence of structural errors on the actuator position and posture of 3TPS hybrid robot is simulated.The error sensitive source is analyzed by calculating the error sensitivity.Then,aiming at the trajectory error of the hybrid robot,two methods of calculating the tracking error and contour error are put forward.The contour error estimation algorithm suitable for 3-TPS hybrid robot is explored from the plane and space trajectories respectively.The generalized error contour estimation algorithm is proposed for general trajectories,and the actual motion of typical trajectories is used to estimate the contour error.The method deals with the feedback data of the driving rod encoder,compares the tracking error with the contour error,and draws a conclusion that the contour error can better reflect the trajectory error.(3)Error compensation scheme and algorithm design of hybrid robot.The error compensation schemes for 3-TPS hybrid robots are studied.On the one hand,the calibration schemes are formulated for geometric errors.On the other hand,the error compensation schemes based on control system are explored.The error compensation schemes are carried out by modifying NC instructions and using series feedback servo system.Then,aiming at the kinematics calibration scheme,the inverse kinematics calibration model based on the complete pose is established.The experimental pose is selected,and the parameter identification algorithm based on the combination of non-linear programming and genetic algorithm is designed to identify the structural parameters in the control model.The identification algorithm program is adjusted by using the selected position and attitude theory data,and the effectiveness of the algorithm is verified by simulation.(4)Calibration and error compensation experiment of hybrid robot based on laser tracker.The experimental scheme of driving rod length measurement and pose measurement is worked out.The measuring experimental platform is built by using the absolute laser tracker measuring system and the accurate data of actual pose and rod length corresponding to each point of the experimental cube are collected and processed.The experimental errors are analyzed.22 actual structural parameters are obtained and corrected by parameter identification algorithm.The kinematics model is built,and the error compensation effect is verified by using a number of measurement points.The validity of the calibration model and parameter identification algorithm applied to 3-TPS hybrid robot is verified.