For complex robotic tasks (e.g., manipulation, locomotion), the lack of knowledge of precise interaction models, the difficulties to precisely measure the task associated physical quantities (e.g., position of contact points, interaction forces) in real-time, the finite sampling time of digital control loops and the non-collocation of sensors and transducers have negative effects on performance and stability of robots when using simple force or simple movement controllers. To cope with these issues, a new compact design for high performance actuators specifically adapted for integration in robotic mechanisms is presented. This design makes use of a mechanical differential as its central element. Results shown that differential coupling between an intrinsically high impedance transducer and an intrinsically low impedance mechanical spring provides the same benefits as serial coupling, but in a more compact and simple design. This new actuator, named Differential Elastic Actuator (DEA), provides interesting design implementations, especially for rotational actuators used for mobile robot locomotion.

This video shows the functionalities of a 3 serial DOF robotic arm. Each DOF is actuated with a patent pending differential elastic actuator (DEA) [1,2]. Compared to the abundantly studied series elastic actuator [3,4], DEA uses a differential coupling between a high impedance mechanical speed source and a low impedance mechanical spring. Possible implementations of a mechanical differential include the use of a standard gearbox, harmonic drive, cycloidal gearbox, bar mechanism, cable mechanism and all other mechanism that implement a differential function between three mechanical ports. For the implementation reported in this video, we used a harmonic drive for a very compact design. A passive torsion spring (thus the name elastic), with a known impedance characteristic corresponding to the spring stiffness, is used, with an electrical DC brushless motor. A non-turning sensor connected in series with the spring measures the torque output of the actuator.

Without a properly designed power management unit, power failures are to be expected on systems raining on batteries. Unfortunately, there is no low cost fully configurable unit that is available on the market for small mobile robots. This paper presents the design of a power management unit for a six legged pneumatic robot that runs at a top speed of 1.11 m/s. The system consists of a main unit that acts as a fast charger, a power supply and a monitor of the energy left available to the robot. This unit communicates with small circuit embedded on each NiMH battery, which gives their level and stores the battery's parameters so that the charger can adapt its charging algorithm to batteries of different capacity or chemistry. Furthermore, this power management unfit takes advantage of the controller area network (CAN) and the PIC18F brain to act as a monitoring, fully configurable, remotely controllable and autonomous node.