ServoSEA concept: Cheap, miniature series-elastic actuators for orthotic, prosthetic and robotic hands

Abstract

For interactive humanoids, rehabilitation robots, and orthotic and prosthetic devices, the human-robot interaction is an essential but challenging element. Compliant Series-Elastic Actuators (SEAs) are ideal to power such devices due to their low impedance and smoothness of generated forces. In this paper we present the ServoSEA, which is a miniature Series-Elastic Actuator (SEA) based on cheap RC servos, and which is useful for actuation of orthotic, prosthetic or robotic hands. RC servos are complete packages that come with rotary motor and sensor and have an integrated control board to control the output angle. In the ServoSEA, a small rotational spring is attached to the output shaft and the internal rotary sensor is relocated to measure the spring deflection. These small modifications immediately make the integrated control board behave as a series-elastic torque controller. Here we present several design alternatives and report on the performance of our implementation that will be used in the active SCRIPT wrist and hand orthosis. The performance measurements showed that feedforward control of the example implementation of the ServoSEA results in acceptable, though not perfect, force tracking behavior. It is clear that although the ServoSEA concept is universal, final performance strongly depends on the quality of the original RC servo.

Optimal Design of a Nonlinear Series Elastic Actuator for the Prosthetic Knee Joint Based on the Conjugate Cylindrical Cam

“…The inverse of equation ( 18) is the curvature of the cam. Therefore, to ensure the radius of curvature of the theoretical cylindrical cam profile is higher than the cam roller, the constraints are given as ρ 1i > r cc , ρ 2i > r cc (19) where ρ 1i and ρ 2i represent the ith discrete radii of curvature of the cam profile 1 and 2; r cc represents the radius of the cam roller. In this paper, the minimum r cc is given as 0.005m.…”

“…Some researchers took advantage of different drive components or add additional mechanisms to improve the actuation performance of SEAs. For example, Ates et al used RC servos to develop a miniature SEA for the hand orthosis [19], and Zheng et al proposed a pneumatic SEA capable of supporting a 75kg individual [20], [21]. In addition, Garcia et al combined the SEA with the magneto-rheological damper to achieve a 20% reduction in the energy wasted in braking the knee during its extension in the leg stance phase [22], and Rouse et al developed a clutchable SEA which can reduce the overall energy consumption of the actuator [23], [24].…”

Proprioception-Based Grasping for Unknown Objects Using a Series-Elastic-Actuated Gripper

“…1) SEA Module: Similar to the design from Ates et al [21], we developed a simple and compact SEA module ( Fig. 1).…”