bots IN BRIEF
COMAN THE ROBOTARIAN
Most humanoid robots developed over the past few decades have
had stiff joints. That's a problem if they're ever going to interact with
people. Their unyielding arms and legs could cause an injury if they
accidentally whack someone, or if they lose balance and fall down.
Lately, there's been a growing interest in developing robotic joints with
variable stiffness which would improve their safety, but so far, few
groups have built a complete robot. Now, however, a team from the
Italian Institute of Technology (IIT) is approaching that goal with their
robot COMAN (COmpliant huMANoid).
Modeled after a four year old child, COMAN is 94.5 cm tall
(from foot to neck) and weighs 31. 2 kg. It features 25 degrees of
freedom and a combination of stiff and compliant joints. The compliant
joints ( 14 DOF) rely on a series of elastic actuators. These actuators
— a custom design created by the IIT team — are applied to the
flexion/extension of the arms and legs, and are both small and
modular which makes them ideal for multi-DOF robots like humanoids.
The researchers have also developed custom torque sensors for each
of the elastic joints, including a six-axis force/torque sensor for the
ankle joints.
So, what exactly does this compliance get you? The elastic
actuators literally add a spring to COMAN's step. In walking
experiments, the robot's hardware naturally absorbed the ground
reaction forces of each footstep "without additional control
enforcement, which is difficult to be realized by the stiff actuated
humanoids if no particular foot mechanism or active control is applied."
When the team implemented a stabilization control method, the robot steadied itself on a moving platform
and when it was knocked around.
COMAN's internal structure is made of titanium alloy, stainless steel, and aluminum alloy, covered by
an ABS plastic exoskeleton.
In the course of developing their own
compliant humanoid, the team also devised a
method for determining the optimal joint elasticity
which, until now, has largely been a time-consuming
trial and error process with scant documentation.
Their method provides a framework for other
researchers exploring compliant robots, and is
based on resonance analysis and energy storage
maximization criteria.
The IIT team — which includes Nikos G.
Tsagarakis, Stephen Morfey, Gustavo Medrano
Cerda, Zhibin Li, and Darwin G. Caldwell — is
among the first to build a compliant humanoid with
both arms and legs. If you're wondering why the
robot is headless, don’t worry. A head is in the
works. Plus, researchers have also completed a pair
of hands.
SERVO 06.2013 21
