A Soft Linear Actuator with Gentle Manipulation Mechanism

This paper proposes a soft linear actuator imitating a foxtail movement and introduces two applications. The proposed biomimetic soft linear actuator mainly consists of three parts: a soft core containing a vibration motor with silicone spikes on its surface, a tubular passage to guide the movement of the soft core, and a switching mechanism to change the direction of the movement of the soft core when an excessive tensile force is applied. When vibration is generated, the soft core moves along the tubular passage toward one direction depended on the leaning direction of the spikes; namely, it can be utilized as a linear actuator to manipulate an object if the core is wired onto it. By inserting a spring at the end of the wire, the leaning direction of the spikes can be changed reversely if the tensile force between the core and the object connected by wire-spring exceeds either the kinetic force toward movement direction generated by the core or the frictional force between the spikes and the tubular passage. Consequently, this characteristic endows the proposed soft linear actuator with a gentle and safe manipulation to handle the object. We present the two applications of gentle manipulation: an elbow manipulator mimicking a human bicep to lift its lower arm and a five-finger robot hand grasping a fragile object. By testing these two applications, we could substantiate the feasibility of the proposed soft linear actuator as a core element to realize safe human-robot interaction or cooperation.