Design and control of a novel actuator based on human muscle characteristics, the Muscle Actuator

grantor: University of TorontoOver the past two decades considerable progress has been made in developing conventional actuator technologies for robotics. Nevertheless, new actuation technologies are required for the emergence of high performance robots. While sophisticated control algorithms can be used to improve actuator performance, limitations are imposed by the mechanical and electrical hardware of such systems. Given the shortcomings, a radically different approach was pursued that consisted of developing a new linear electromagnetic actuator (linear motion), called the 'Muscle Actuator'. Extensive simulation studies revealed that the global characteristics of the human muscle (' force'/'length and force'/'velocity') are key to high performance applications. The human muscle is capable of an abrupt stop without oscillation, even after high speed movements which are characteristic of high performance drive applications. Following the simulation studies, the global characteristics of the human muscle were adapted and emulated in a linear electromagnetic actuator. Based on the proposed design, extensive simulations and experiments were carried out to measure the force/length and force/velocity characteristics of the muscle actuator, and study the behavior of the actuator when parameters such as activation level (input current) and applied load vary. The experimental results are in good agreement with the results obtained from mathematical models. The non-linear damping characteristic of the designed actuator was analyzed in detail because it is the most important characteristic in the context of high speed/high precision motion. Despite the open-loop stability of the muscle actuator, the stability of the muscle actuator in the closed loop was also investigated. Closed-loop control is useful in compensating for uncertainty in parameters, which is due either to the nonlinear values not being exactly known, or because they vary during operations. A controller was designed using the 'feedback linearization' technique, and it was proved that the closed-loop is stable under certain conditions. Moreover, a pair of muscle actuators was used to make a one-degree-of-freedom joint, and the complete interfaces for the one-degree-of-freedom joint setup were designed and built. This setup was used to study the performance of the designed controller and the joint stiffness modulation capability in an antagonistic configuration. The modulation allows the mechanism to have a variable, depending on task, stiffness when contact between the joint-link and the surroundings occur. Finally, as a starting point for future work, an optimized design of the linear muscle actuator and two possible configurations for the rotary muscle actuator were presented.Ph.D