1 research outputs found
Optimally Controlling the Timing of Energy Transfer in Elastic Joints: Experimental Validation of the Bi-Stiffness Actuation Concept
Elastic actuation taps into elastic elements' energy storage for dynamic
motions beyond rigid actuation. While Series Elastic Actuators (SEA) and
Variable Stiffness Actuators (VSA) are highly sophisticated, they do not fully
provide control over energy transfer timing. To overcome this problem on the
basic system level, the Bi-Stiffness Actuation (BSA) concept was recently
proposed. Theoretically, it allows for full link decoupling, while
simultaneously being able to lock the spring in the drive train via a
switch-and-hold mechanism. Thus, the user would be in full control of the
potential energy storage and release timing. In this work, we introduce an
initial proof-of-concept of Bi-Stiffness-Actuation in the form of a 1-DoF
physical prototype, which is implemented using a modular testbed. We present a
hybrid system model, as well as the mechatronic implementation of the actuator.
We corroborate the feasibility of the concept by conducting a series of
hardware experiments using an open-loop control signal obtained by trajectory
optimization. Here, we compare the performance of the prototype with a
comparable SEA implementation. We show that BSA outperforms SEA 1) in terms of
maximum velocity at low final times and 2) in terms of the movement strategy
itself: The clutch mechanism allows the BSA to generate consistent launch
sequences while the SEA has to rely on lengthy and possibly dangerous
oscillatory swing-up motions. Furthermore, we demonstrate that providing full
control authority over the energy transfer timing and link decoupling allows
the user to synchronously release both elastic joint and gravitational energy.
This facilitates the optimal exploitation of elastic and gravitational
potentials in a synergistic manner.Comment: 8 pages, 9 figures. Submitted to IEEE Robotics and Automation Letter