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Compliant actuation for biologically inspired bipedal walking robots

Tuesday, 11 July, 2006 - 16:00
Campus: Brussels Humanities, Sciences & Engineering campus
auditorium P. Janssens
Ronald Van Ham
phd defence

This thesis deals with compliant actuators and their use in energy efficient
walking bipeds. Two types of actuators with adaptable compliance are
discussed: PPAM (Pleated Pneumatic Artificial Muscles) and MACCEPA
(Mechanically Adjustable Compliance and Controllable Equilibrium Position

The PPAM is a design made to overcome shortcomings associated with the
existing types of pneumatic muscles. The compressibility of air makes them
inherently compliant, which can be employed to reduce shocks. Their main
advantages are the high power to weight ratio, the adaptable compliance when
used in an antagonistic setup and the fact that they can be directly coupled to
the joint without a gearing mechanism. A second design of the PPAM concept,
which resulted in an extended life time, is used in the biped Lucy. This planar
biped is actuated with 12 PPAM’s, giving the ability to control the six pin
joints, both in equilibrium position and in compliance. The control strategy is
based on the generation of trajectories for each joint out of the objective
locomotion parameters. Ways to adapt the compliance in order to lower energy
consumption are studied.

The second type of compliant actuator, the MACCEPA, is entirely developed
during this thesis, and patented. It is an electrical actuator of which the
compliance and equilibrium position are fully independent and both are set
by a dedicated servo motor. The angle-torque characteristic is quasi linear up
to 60 degrees, which makes the MACCEPA comparable to a torsion spring,
which allows to modify equilibrium position and spring constant online.
Moreover, the concept can be implemented using standard off-the-shelf
components. This actuator was used to build the biped Veronica. This is a
planar biped, with 6 MACCEPA actuators, each powering one pin joint. The
strategy of using the compliance for energy efficient walking, as elaborated in
this PhD, is based on the concept of passive walkers. The compliant actuators
are used to modify the natural frequencies of the limbs online, in order to
achieve a smooth and stable walking motion. Since the developed passive
walking robot is not limited to one walking speed, but can be controlled while
still using natural motions, this concept is entitled Controlled Passive Walking.