IMU-Based Active Safe Control of a Variable Stiffness Soft Actuator

Using soft pneumatic actuators is a feasible solution in the dynamic unstructed environment, thanks to their light weight and inherent compliance. It is commonly agreed that the passive compliance and adaptivity of soft robots make them much safer. However, under some special circumstances where stringent safety is requested (e.g., surgical operation), the passive compliance is far from meeting the demands. Therefore, active compliance control is still required to guarantee their operating safety. In this letter, a novel soft actuator is presented, whose stiffness is tunable in multiple ways, and more than a 10-fold stiffness enhancement is achievable, making it able to carry heavy loads while maintaining excellent dexterity and compliance. Meanwhile, we first proposed an active safe control strategy based on inertial measurement units. Through calibrating the load weight (i.e., weight of the end tools) and measuring vibration of soft structures, the collision can be detected in real time and the corresponding safe reaction is then adopted. We have validated its effectiveness on human body, the strategy still works at the speed of 200 mm/s with sharp tools. Furthermore, our control strategy can be applied to other soft or continuum robots, making them safer and more practical in actual applications.