Mechanism and Control of Continuous-State Coupled Elastic Actuation

Focusing on the physical interaction between people and machines within safety constraints in versatile situations, this paper proposes a new, efficient, coupled elastic actuation (CEA) to provide future human-machine systems with an intrinsically programmable stiffness capacity to shape the output force corresponding to the deviation between human motions and the set positions of the system. As a possible CEA system, a prototype of a two degrees of freedom (2DOF) continuous-state coupled elastic actuator (CCEA) is designed to provide a compromise between performance and safety. Using a pair of antagonistic four-bar linkages, the inherent stiffness of the system can be adjusted dynamically. In addition, the optimal control in a simple various stiffness model is used to illustrate how to find the optimal stiffness and force trajectories. Using the optimal control results, the shortest distance T.-H. Huang · H.-P. Huang (B) Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan e-mail: [email protected] T.-H. Huang e-mail: [email protected] J.-Y. Kuan Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA e-mail: [email protected] control is proposed to control the stiffness and force trajectory of the CCEA. Compared to stateof-the-art variable stiffness actuators, the CCEA system is unique in that it can achieve near-zero mechanical stiffness efficiently and the shortest distance control provides an easy way to control various stiffness mechanisms. Finally, a CCEA exoskeleton is built for elbow rehabilitation. Simulations and experiments are conducted to show the desired properties of the proposed CCEA system and the performance of the shortest distance control.