Nonlinear PID control of a six-DOF parallel manipulator

A nonlinear proportional integral derivative (N-PID) algorithm in linkspace is proposed to realise high precision tracking control of a general six-DOF parallel manipulator. In practice, the performance of the controlled system is limited by how to pick out the differential signals of the noncontinuous measured signals with stochastic noise. Therefore, the developed N-PID controller uses two nonlinear tracking differentiators to yield high quality differential signals in the presence of disturbances and measurement noise. A nonlinear combination of proportional, integral and derivative action on the control error is used to synthesise the control law for enhanced performance in areas such as increased damping and reduced tracking error. Experimental results indicate that the nonlinear control method is easy for the engineer to implement and achieves a superior performance.