Mechanism and Structures: Humanoids and Quadrupeds - Bioinspired Approaches for Human-Centric Technologies - page 143

Fig. 5.10 Design of the CompAct Actuator unit
20:1). Each CompAct actuator unit weighs 0.52 Kg, with a maximum output torque
of 40 Nm, a peak output speed 10.7 rad/s and a nominal power 190 W.
To minimise dimensions while achieving high rotary stiffness, the compliant
module is formed as a mechanical structure consisting of a three spoke output
component (output pulley (Fig. 5.10 ), a circular input pulley and six linear springs).
The input pulley is fixed to the output shaft of the harmonic drive. The output link
(three spoke element) rotates with respect to the input pulley and is coupled to it by
six linear springs. More details on the SEA unit can be found in Tsagarakis
et al. ( 2009 ).
5.4.1.3 Leg Mechanical Design
COMAN's legs have an anthropomorphic kinematic structure with hips, a thigh
with integrated knee joints, a calf with integral ankle joints and a foot. The
design of leg is based on the “cCub” prototype developed in Tsagarakis
et al. ( 2011a ), although several joint modules were radically redesigned to
improve the assembly process, profile and compactness while incorporating an
additional passive compliance in the hip flexion joint. The hip joint is
constructed as a cantilever structure with a pitch-roll-yaw assembly providing a
large range of motion, Table 5.2 . The hip pitch motion is driven by the
compliant actuation module introduced before (peak torque of 55 Nm), while
the roll and yaw motion actuators are conventional stiff modules (Kollmorgen
Brushless DC motor combined with a 100:1 Harmonic reduction drive giving a
peak torque of 55 Nm). The hip roll motor is placed below the hip centre
transmitting its torque to the hip (around the hip centre) using a four bar
mechanism. This permits integration of the CompAct SEA module at the hip
pitch actuator without increasing the distance between the two hip centres. The
hip yaw motion is powered by an actuator enclosed inside the thigh structure.
The knee joint is directly driven by a CompAct compliant actuator (peak torque
of 55 Nm) at the centre of the knee joint, Fig. 5.11 . The ankle pitch motion is driven