Design, modeling and implementation of a biphasic media variable stiffness actuator

Nowadays, an increasing number of industrial processes are expected to have robots interacting safely with humans and the environment. Compliance control of robotic systems strongly addresses these scenarios. This thesis develops a variable stiffness actuator (VSA) whose position and stiffness can be controlled independently. Actuator’s stiffness is controlled by changing pressure of control fluid into distribution lines. The used control fluid is biphasic, composed of separated gas and liquid fractions with predefined ratio. Firstly, an approach for the mathematical model is introduced and a model-based control method is implemented to track the desired position and stiffness. Results from force loaded and unloaded simulations proved the feasibility of these methods. Based on the previous outcome, a compliant revolute joint mechanism was modeled and implemented in order to use it as a test bench for the VSA. The mechanism is able to track position and stiffness accurately; however, better mechanical design and manufacturing methods are suggested in order to avoid excessive friction. Later on, a momentum-based collision detection and reaction algorithm is proposed, simulated and tested on the mechanism. Experimental results confirm that this method can be used to attain a higher level of safety in the system. Finally, a compliant cable-driven revolute joint using biphasic media variable stiffness actuators is modeled and simulated. This cable-driven mechanism is characterized by a wide range of stiffness and high-power output.