IEEE Robotics & Automation Magazine - June 2021 - 22

The results indicate the possibility of effectively shifting
the stable stiffness range so that the system meets the stiffness
requirements throughout the given task while minimizing the
overall stiffness. By being able to render various controller
stiffnesses, the manipulator can handle a wider range of tasks
that require different amounts of stiffness. PC is especially
important when the robot moves in unstructured environments
or manipulates objects with unknown kinematics and
dynamics, as passive compliance aids robustness in unforeseen
situations.
In addition to stiffness reduction, we have verified the
relaxed torque requirements by using the proposed structure
as compared to the previous approach. The torque requirements
are computed through the calculation of restoring the
joint torques based on the optimized Kpc
from (3). From the
potential energy stored in the springs, we have seen the possibility
of energy reduction, which could be verified through
further investigative experiments with batteries.
The benefits of implementing tendon-driven series elastic
actuators include a weight separation between the actuators
and manipulators and thus the usage of low-capacity motors
that drive the low-inertia manipulators. Additionally, for high
frequencies, the overall impedance of the system reduces to
that of the physical springs, making the system a zero-delay
low-pass filter. Introduction of the proposed structure with
NPC and CTR opens up a new possibility of reducing the
motor capacity and dropping the weight, size, and cost of the
motors even further. This can be advantageous in the field of
prostheses and exoskeletons. Furthermore, in such remote
systems, where battery life is crucial, energy efficiency is an
important factor to consider.
For future work, we hope to extend the current study by
●
conducting experiments in mobile environments, where the
battery lifespan is crucial, and seeking the feasibility and efficacy
of the proposed structure in terms of robustness and
energy efficiency
●
extending the optimization methodology to include other
design parameters, such as link lengths, actuation pulley
radii, routing strategies, and so on
●
further investigating the optimization of coupled PC to
check the feasibility of fully nonlinear and fully coupled
PC components.
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22 * IEEE ROBOTICS & AUTOMATION MAGAZINE * JUNE 2021
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Mincheol Kim, Department of Mechanical Engineering, University
of Texas at Austin, Austin, Texas, 78712, USA. Email:
mincheol@utexas.edu.
Ashish D. Deshpande, Department of Mechanical Engineering,
University of Texas at Austin, Austin, Texas, 78712, USA.
Email: ashish@austin.utexas.edu.
https://www.maxongroup.com/maxon/view/catalog/
IEEE Robotics & Automation Magazine - June 2021

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