Concentric Helical Actuator Design and Characterization

Abstract In the fields of traditional robotics, bio-inspired robotics, and mechanism design, the two fundamental types of actuators are rotational and prismatic actuators. The dominant rotational actuator is the electric motor (less common rotational actuators include hydraulic and pneumatic motors). Within prismatic actuators, hydraulic and pneumatic pistons as well as screw based linear actuators vie for dominance. One implementational drawback of most versions of these three actuators is that they cannot rigidly contract to less than half of their original length. This is not typically a problem in traditional robotics or mechanism design, but it can be a problem for bio-inspired robotics and other novel robots that attempt very large changes in volume while maintaining some rigidity. This paper will describe the design and simulation of a novel concentric helical actuator that can achieve a contraction/extension ratio larger than 1:3 (200% strain). The mechanical advantage between the input torque and the output linear force of the actuator changes as a function of the actuator position. For a given force, the motor torque is the largest when the actuator is fully contracted. This actuator can produce 1N of linear force for every 30Nmm of motor torque, which makes it useful for light weight robot applications. This concentric helical actuator can serve as a useful mechanism in bio-inspired and novel robotics.