Research On Modeling And Motion Trajectory Of Non-spherical Wrist Live-working Robot

The use of live-working robot can effectively reduce the operating risk and labor intensity of maintenance personnel,which is one of the main means of future maintenance.However,there are many technical difficulties in the research of high-performance robots that can replace maintenance personnel,such as concise and accurate kinematics model,smooth and reasonable motion trajectory,reliable and fast inverse kinematics algorithm.In this paper,the following researches have been done on the non-spherical wrist live-working robot:1.The Modified D-H method is used to establish the coordinate system model with as few D-H parameters as possible,and then the corresponding forward kinematics equation is derived to obtain the concise expression of the position and orientation.In order to avoid setting the working point in the working dead zone during task planning,based on the forward kinematics equation,the Monte-Carlo method is used to solve the working space of the robot.In order to obtain accurate closed-form solutions,the algebraic solution method is used to derive 8 sets of inverse solutions expressed by the atan2(y,x)function,and the correctness of the expression is verified by the forward kinematics equation.2.Several trajectory generation algorithms are studied and compared,such as the the third-order polynomial algorithm,fifth-order polynomial algorithm,trapezoidal algorithm and Double-S speed curve algorithm.The results show that the trajectory generated by the algorithm can make the joint move fast and smoothly.Aiming at the problem that the trapezoidal interpolation strategy makes the position and orientation of robot’s terminal change unsmoothly,the simplified polynomial interpolation strategy is derived and used.The change curve of the generalized velocity proves that the simplified polynomial interpolation strategy can make the end of the robot move more smoothly.3.The non-spherical wrist live-working robot may encounter singularities during the operation of the Cartesian space trajectory.Therefore,the differential-vector method is used to construct the Jacobian matrix.The singular configuration of the robot is identified by the determinant of Jacobian matrix and verified by the singular value decomposition theory.To ensure the uniqueness of the inverse solution and obtain inverse solution of singular point,an algorithm of successive approximation to the desired position and orientation of robot’s terminal is researched.Through separately calculating the position difference and the posture difference,setting the dynamic factorα to adjust the iteration step length,and using the inverse solution output of the n –th interpolation point as the initial value of the iterative calculation of the inverse solution operation of the n+1-th interpolation point,the algorithm’s performance is improved.The test results show that the optimized algorithm is reliable and converges fast,can obtain singular point inverse solutions.