Majid Namnabat - Department of Control Engineering, College of Technical Engineering, Saveh Branch, Islamic Azad University, Saveh, Iran.
Amir Hossein Zaeri - Department of Electrical Engineering, Shahinshahr Branch, Islamic Azad University, Isfahan, Iran.
Mohammad Vahedi - Department of Mechanical Engineering, College of Technical Engineering, Saveh Branch, Islamic Azad University, Saveh, Iran.

Control of the force exerted on an object is important for boosting system performance in robotics manipulators. Any undesired applied force may leave remarkable effects on the system, with the potential to damage the object. In addition, measuring external force is another challenge associated with such cases. Proposing an appropriate force estimation algorithm is a solution to overcome this deficiency. In this research, a control strategy is proposed to control the external force applied on the n-dof robotics. To eliminate force measurement in the controller, a force estimation strategy based on a disturbance observer is employed. Subsequently, a sliding-mode based control is implemented to cope with the force estimation error. The closed-loop stability of the system in the presence of estimated force is analytically considered. The proposed algorithm was implemented on piezoelectric actuators as the experimental setup. The experimental results confirm that by employing the proposed control scheme, precise force control is achievable. The force estimation algorithm can also suitably estimate external force.

Robotic Systems, force control, sliding mode control, Force Estimation