Calibration of Stewart-Gough Parallel Robot with Minimum Sensor and Position Control in Joint Space

Abstract

The Stewart-Gough Platform (SGP) is defined as a 6-DOF parallel robot. It consists of two rigid plates; moving platform (MP) in top and base platform (BP) in bottom and also six actuating links that connect them to each other and provide up to six DOF for the MP with respect to the BP. SGP's impressive features are high load carrying capacity, low inertia, high stiffness, better repetition and precise positioning. This paper focuses on the accuracy enhancement of a six DOF SGP robot through kinematic calibration. In this method minimum number of sensors have been used for SGP kinematic calibration. This method is presented with details and is implemented on an experimental robot. The assumption of the methodology is that the orientation of MP can be measured by two inclinometers. Calibration involves of a nonlinear function optimization with 36 unknown parameters. Nonlinear least square scheme is used for the optimization. Experimental studies reveal that the proposed method is effective in enhancing the SGP accuracy. The main contribution of this work is implementation of the proposed method on an experimental robot and achievement acceptable results by position control of SGP in joint space. The robot position is controlled in the joint space; results show that calibrated robot follows command signal more accurate than before the calibration.