Dynamic Modellingand Control of a 3-DOF Planar Parallel Robotic (XYθ_Z Motion) Platform

摘要

This study addresses the dynamic modelling and control of a novel three degrees of freedom (3-DOF) planar parallel robotic motion platform in the presence of parameter uncertainties and external disturbances. The proposed planar parallel motion platform is a guide way free manipulator and has two legs both with a revolute-prismatic-revolute (RPR) configuration located in the same plane connecting a moving platform. Of the two, one leg comprises of only one active prismatic joint, while the other leg consists of an active prismatic and an active rotary joint. The dynamic model has been derived using Euler-Lagrangian energy based formulation method. The proposed controller is based on computer torque control integrated with a disturbance observer. The disturbance vector comprising of disturbances due to parameter uncertainties, payload variations, frictional effects and further disturbances is estimated using a nonlinear disturbance observer incorporated with an extended Kalman filter (EKF). The observer uses only position and orientation measurements. Simulations with a typical trajectory are presented and compared with traditional controllers such as proportional integral derivative (PID) controller and computed torque controller, and the results show that superior tracking performance is achieved in the presence of parameter uncertainties and external disturbances.