Co-Design Strategies for Optimal Variable Stiffness Actuation

Robotic systems powered by variable stiffness actuators (VSAs) provide important benefits for applications that demand safety, performance, and energy-efficiency. Being multidisciplinary systems, performance of such devices cannot be fully exploited unless co-design techniques that account for their inherent design couplings are employed for their optimization. These co-design strategies enable a synergetic design of mechanical and control aspects of the system. We present application of two alternative co-design frameworks to robotic systems with VSA and demonstrate their effectiveness on a case study for optimal system design of a robotic prosthesis. Our results indicate that substantial reductions in required motor torques, leading to important performance gains in system weight and bandwidth can be achieved, compared with suboptimal designs where design couplings are not considered. Furthermore, we provide a critical evaluation of the trade-offs involved in utilizing simultaneous versus nested co-design frameworks to obtain system level optima. In particular, we contrast the ease of implementation and computational efficiency of the simultaneous framework with the modular structure of the nested framework that allows using discipline-specific optimization tools and provide guidance in selecting the appropriate method for a given design task. Finally, through an example, we provide evidence that the system level optimization results can guide design of novel and more efficient actuation concepts.