Until recently, the main actuation approach for humanoid
the use of stiff position/velocity units coupled with highly geared,
non-backdrivable transmissions. These humanoids are precise and highly
repeatable, when performing locomotion and manipulation tasks within
well-defined environments under anticipated physical interactions.
However, it has become clear that the ability of these robots to cope
with disturbances and adapt to unpredicted physical interactions is
severely limited. To address this performance deficiency several
experimental compliant actuation systems have been developed during the
past ten-fifteen years. The incorporation of physical elasticity in the
actuation poses many mechatronic challenges including the design
complexity, the physical realization, and the sizing of the actuator
passive elasticity particularly in multi degree of freedom robots such
I will report on the fundamental principles of the compliant actuation including a comprehensive description of the different mechanical configurations schemes which can be used to realize them. Following this, I will introduce ongoing work towards the development of intrinsic and actively controlled compliant humanoid robots that can cope with physical contacts and adapt to disturbances and physical interactions. Details on the actuation mechatronics, dimensioning of the joint passive elasticity and motion control will be presented. To further enhance the capabilities of current actuation, new mechatronic actuation modules with combined inherent physical principles are being explored to form the future motion units of the next generation of robots. These include various units combing passive variable compliance and semi-active damping configurations. Details on these developments will be also reported.