Comparison of elastic configurations for energy efficient legged locomotion

Energy efficient locomotion with the amazing agility of humans and other animals remains a challenge for legged robots. Many existing joint mechanisms for legged robots use a serial configuration which gives compliance, however this may be sub-optimal for energy efficiency. This paper investigates the energy efficiency of legged joints for stationary jumping for three configurations of the elastic and actuator elements: series, parallel and without an elastic element. The key result is that significant energy savings are possible with a parallel configuration over the series and nonelastic configurations for the range of typical animal and robot properties: mass, stance duty and toe jump height. While there are large regions where the series arrangement is more energy efficient, these are outside typical duty cycles and will be affected by significant impact losses. The results are obtained by optimizing a set of equations to find the minimum energy losses for stationary jumping. The scripts to generate the results are available as open source software

A novel energy efficient controllable stiffness joint

Achieving energy efficient legged locomotion is an important goal for the future of robot mobility. This paper presents a novel joint for legged locomotion that is energy efficient for two reasons. The first reason is the configuration of the elastic elements and actuator which we show analytically has lower energy losses than the typical arrangement. The second is that the joint stiffness, and hence stance duration, is controllable without requiring any energy from the actuator. Further, the joint stiffness can be changed significantly during the flight phase, from zero to highly rigid. Results obtained from a prototype hopper, demonstrate that the joint allows continuous and peak hopping via torque control. The results also demonstrate that the hopping frequency can be varied between 2.2Hz and 4.6Hz with associated stance duration of between 0.35 and 0.15 seconds