A Study On End Precision Control Of A 3-PTT Parallel Mechanism

With the continuous development of social science and technology,new demands are driving the expansion of the application field and scope of robots.The emergence of parallel robots perfectly compensates for the shortcomings of small load and low accuracy of series robots.Based on the advantages of parallel robots,their application in light industry,commerce,agriculture and other fields can well meet the development needs of the industry.Parallel robots have great potential research value,among which the research on end effector accuracy is of great significance in improving the motion and control accuracy of parallel mechanisms.It can provide technical support for the development and application of robots,improve their work accuracy and stability,and thus improve production efficiency and product quality.In order to reduce the end error of parallel mechanisms and expand their applications,this paper studies the end accuracy control theory of a 3-PTT parallel mechanism.Firstly,the kinematics model of 3-PTT parallel mechanism is established,and the degrees of freedom of the mechanism are analyzed according to the modified Kutzbach Grubler formula and screw theory,and the forward and inverse kinematics model of3-PTT parallel mechanism is solved.Through the joint simulation of ADAMS/MATLAB,the kinematics analysis of the mechanism is carried out to verify the correctness of the forward and inverse position solution model.Further solve the Jacobian matrix of the parallel mechanism and analyze its singularity.Solve the workspace of the mechanism through the limit boundary search method,providing theoretical support for motion control and error compensation of the mechanism.Secondly,analyze the error sources of the 3-PTT parallel mechanism and establish a static error model of the mechanism using the total differential method.Afterwards,position error analysis was conducted on the 90 randomly obtained position points in three different scenarios.The average position error was then taken for each scenario,and the effects of structural parameter error,slider zero length error,and structural parameter and slider zero length error on the end position error of the mechanism were obtained.This provides a theoretical basis for compensating the position error of the mechanism.At the same time,a terminal precision control strategy based on Jacobian and RBF networks is proposed.The end correction position obtained by RBF and the slider correction position obtained by Jacobian are used to obtain a kinematics model that can simulate the actual movement of the mechanism.Then,the overall control plan of the experiment was determined,and the roles of various software and hardware components in the control system were summarized;Introduce the important components of the mechanical body in the experimental platform and conduct finite element analysis on them.Design the hardware configuration scheme of the parallel mechanism control system,connect the software and hardware platforms,and build the experimental platform.Finally,set up a comparative experiment to measure the return error of the lead screw and compensate for it.When measuring the end position of the mechanism,in order to reduce the contingency of the experiment,repeat the measurement for 7 times,and take the mean value of the measurement results instead of the measured value.The measured values were substituted into the control model for verification,and the results showed that the positional errors of the end axial(X-axis)and radial(Y-axis)were reduced by more than 90% in the experiment,and the positional errors of the vertical direction(Z-axis)were reduced by more than 80%.The control method proposed in this paper is effective.