Dynamic Characteristics Analysis Of3-RPR Planar Parallel Mechanism With Joint Clearance

As the gradually development and improvement of technology, high reliability and high accuracy has become the direction and an very important symbol of modern machinery. More and more factors are being considered in mechanical system. The design, manufacturing, assembly and frictional wear will produce clearance. Kinematic pair clearance has great influence on the performance of machine. The exit of clearance will reduce the accuracy and stability of mechanical system significantly. The exiting of clearance is common phenomenon in mechanical systems. This dissertation researches the dynamic characteristics of3-RPR planar parallel mechanism with joint clearance.Mathematical model of kinematic pair clearance and contact force are established in3-RPR planar parallel mechanism with joint clearance. Contact force are embedded into the mechanical system through mathematical methods.Establish the virtual prototype model of3-RPR planar parallel mechanism with joint clearance through Pro/E and ADAMS. Three-dimensional solid model established by Pro/E is imported into ADAMS, then define the material, vice constraints, contact force and so on. Verify the correctness of the model and analysis the influence of clearance radius, damping, friction coefficient, stiffness coefficient and gravity. The result show that clearance has little impact on the position but great influence on the velocity and acceleration of platform. The contact frequency can be reduced through decreasing clearance radius, increase friction and damping coefficient, as a result, mechanical system stabilize faster.Based on the simulation result, dynamic parameters such as contact force and slip velocity can be extracted. Calculate the dynamic irregular wear of shaft and bearing then add the wear depth to corresponding contact points of contour curve. Embed new contour curve into model and start a new simulation to analysis the impact of irregular wear to dynamic characteristics of3-RPR planar parallel mechanism with joint clearance. Irregular wear clearance has little influence on position but huge impact on velocity and acceleration of mechanism. After irregular wear, contact force is greater and mechanism system is more unstable.