Adaptable compliance or variable stiffness for robotic applications [From the Guest Editors]

Exciting new robots are being developed that will operate in a different environment from traditional industrial factories or research laboratories. Researchers are working worldwide to create robots that are integrated into our daily lives. For the advancement of these new robots, compliant, safe, and new actuators are one of the important issues turning energy into safe motion. The biological counterpart is the muscle tendon structure that has functional performance characteristics and a neuromechanical control system that has far more superior capabilities. The superior power to weight ratio, force to weight ratio, and sensing characteristics limit the development of machines that can match motion, safety, and energy efficiency of a human or other animal. One of the key differences of biological systems is their adaptable compliance or variable stiffness compared with the traditional stiff electrical drives used for the standard industrial robotic applications, which require accurate, reference-trajectory tracking.More and more applications such as robots in close human or robot proximity, legged autonomous robots, and rehabilitation devices and prostheses demand a different set of design specifications, for which the use of compliant actuators can be beneficial as compared with the traditional stiff actuation schemes.