Most of industrial robots work as an open chain that called serial robots. They have some problem in implementation such as accuracy, flexibility etc. In this case, we should use parallel robots. However, they have singularity problem in their workspace. To solve this problem, redundancy is a common solution. In this thesis, we benefit from a 3-DOF robot with a redundant actuator, which works like a human shoulder. At first, we derived a dynamic model of the hydraulic actuator in order to design a controller. To achieve a force control routine for actuators, a lag controller has designed. In order to achieve a good performance in position control, a control structure that consists of gravity compensation, H_∞ robust controller, and controller that compensate error of parameter estimation, has proposed. Simulation result illustrates acceptable response in terms of accuracy and robustness. The proposed closed loop system has a significant tracking performance, despite the presence of disturbance and measurement noise.