2 research outputs found
Exploiting the Natural Dynamics of Series Elastic Robots by Actuator-Centered Sequential Linear Programming
Series elastic robots are best able to follow trajectories which obey the
limitations of their actuators, since they cannot instantly change their joint
forces. In fact, the performance of series elastic actuators can surpass that
of ideal force source actuators by storing and releasing energy. In this paper,
we formulate the trajectory optimization problem for series elastic robots in a
novel way based on sequential linear programming. Our framework is unique in
the separation of the actuator dynamics from the rest of the dynamics, and in
the use of a tunable pseudo-mass parameter that improves the discretization
accuracy of our approach. The actuator dynamics are truly linear, which allows
them to be excluded from trust-region mechanics. This causes our algorithm to
have similar run times with and without the actuator dynamics. We demonstrate
our optimization algorithm by tuning high performance behaviors for a
single-leg robot in simulation and on hardware for a single degree-of-freedom
actuator testbed. The results show that compliance allows for faster motions
and takes a similar amount of computation time
Investigations of a Robotic Testbed with Viscoelastic Liquid Cooled Actuators
We design, build, and thoroughly test a new type of actuator dubbed
viscoelastic liquid cooled actuator (VLCA) for robotic applications. VLCAs
excel in the following five critical axes of performance: energy efficiency,
torque density, impact resistence, joint position and force controllability. We
first study the design objectives and choices of the VLCA to enhance the
performance on the needed criteria. We follow by an investigation on
viscoelastic materials in terms of their damping, viscous and hysteresis
properties as well as parameters related to the long- term performance. As part
of the actuator design, we configure a disturbance observer to provide
high-fidelity force control to enable a wide range of impedance control
capabilities. We proceed to design a robotic system capable to lift payloads of
32.5 kg, which is three times larger than its own weight. In addition, we
experiment with Cartesian trajectory control up to 2 Hz with a vertical range
of motion of 32 cm while carrying a payload of 10 kg. Finally, we perform
experiments on impedance control and mechanical robustness by studying the
response of the robotics testbed to hammering impacts and external force
interactions.Comment: 11 pages, 10 figure