| The clearance of the kinematic pair is a necessary condition to ensure the normal assembly and operation of the mechanism.At the same time,the deformation of the kinematic pair and the friction and wear caused by the relative movement of the kinematic pair elements during the operation of the mechanism will also further expand the size of the kinematic pair gap.However,due to the existence of the movement joint clearance,it will seriously affect the dynamic behavior and various performance indicators of the mechanism,causing the mechanism to produce vibration and shock and reduce the stability.Therefore,it is very meaningful to study the dynamic characteristics of the mechanism with the movement joint clearance.In this paper,a6-PSS("P" for moving joint,"S" for spherical hinge)parallel mechanism suitable for high speed and high acceleration is designed according to the requirements of a certain special test.Related theoretical studies have been carried out on the dynamics and wear characteristics of the hinge gap.The main contents of the full text are as follows:First of all,according to the requirements of a special test for a six-degree-of-freedom parallel mechanism in space,a 6-PSS parallel mechanism suitable for high speed and high acceleration is proposed.Based on the Jacobian matrix of the mechanism,the conditions for the mechanism to produce a singular configuration are obtained.Considering the singular conditions and motion interference conditions of the mechanism comprehensively,the design of the main parameters of the mechanism is completed through mechanism kinematics and Adams software,and the three-dimensional model of the mechanism is established.The operability index is used to quantitatively analyze the singularity of the mechanism in the case of single-degree-of-freedom motion and two-degree-of-freedom coupled motion.Secondly,a dynamic model of the 6-PSS mechanism with spherical hinge clearance is established.Firstly,establish the motion constraint equation of the mechanism based on the topological diagram of the mechanism,use the associative array method to describe the topological diagram of the mechanism and solve the constraint Jacobian matrix;on the basis of the constraint equation,establish the dynamic equation of the ideal mechanism;The classical RK method is used to solve the dynamic equation,and the dynamic equation of the ideal 6-PSS parallel mechanism is solved numerically by this method and compared with the Adams simulation result to verify the correctness of the model.Secondly,considering that there is a gap at the spherical hinge connecting the upper and lower platforms,a kinematic model with the spherical hinge gap is established based on the "contact-separation" two-state model;the LN normal contact force and the modified Coulomb tangential contact with a correction coefficient are used The force solving the interaction force generated by the contact of the kinematic pair;the clearance spherical hinge contact force is substituted for the clearance-free spherical hinge motion constraint,and the dynamic equation of the 6-PSS parallel mechanism with the spherical hinge clearance is established.Then,using the established dynamic model with spherical hinge gap,analyze the different gap influence factors,including gap size,movement speed,gap position and recovery coefficient,and analyze the dynamic behavior of the entire 6-PSS parallel mechanism with spherical hinge gap.The influence of different clearance factors on the dynamics of the mechanism is quantitatively evaluated through the root mean square error index of acceleration.Finally,in view of the problems of frequent alternating stress between the ball and the ball seat caused by the spherical joint clearance of the 6-PSS parallel mechanism during operation,the friction and wear of the motion pair will be accelerated,combined with the Archard wear formula,the mechanism is in different spherical joint clearances.The size and the depth of wear under the gap position are analyzed.The research in this paper can provide an important reference for the precision optimization design and control strategy of the 6-PSS parallel mechanism. |
PDF Full Text Request