The spring loaded inverted pendulum (SLIP) model has been extensively shown to be fundamental for legged locomotion. However, the way this low-order template model dynamics is anchored in high-dimensional articulated multibody systems describing compliantly actuated robots (and animals) is not obvious and has not been shown so far. In this paper, an articulated leg mechanism and a corresponding quadrupedal robot design are introduced, for which the natural oscillation dynamics is structurally equivalent to the SLIP. On the basis of this property, computationally simple and robust control methods are proposed, which implement the gaits of pronking, trotting, and dynamic walking in the real robotic system. Experiments with a compliantly actuated quadruped featuring only low performance electrical drives validate the effectiveness of the proposed approach.
Legged locomotion requires highly dynamic and efficient actuation as well as robust environment interaction. In the past years soft robots with elastic actuation have been investigated and their fitness for cyclic tasks and safe and robust environment interaction has been shown. To evaluate the benefits and drawbacks of series elastic actuation, variable impedance actuation as well as multi-articular elastic coupling in legged locomotion, we developed a two legged human size test-bed. These modular robotic legs give the possibility to evaluate and directly compare different elastic actuation concepts on a single system. Hopping and bipedal modal motion experiments where performed to proof the concept.
In this paper we consider the control of robots that feature visco-elastic actuators with adjustable physical damping. Considering the link variables of the robot as output, the corresponding system dynamics has a relative degree of 3. We present a novel control approach that allows to realize a torque interface on the link side, while preserving the intrinsic viscoelastic structure and the inertial properties of the system. By means of this joint torque interface one can implement link-side position tracking and impedance tasks. For this case, we provide a stability and passivity analysis. The control approach has been verified by experiments with a visco-elastic joint testbed.
This paper presents a methodology for controlling dynamic bipedal walking in a compliantly actuated humanoid robotic system. The approach is such that it exploits the natural leg dynamics of the single and double support phase of the gait. The present approach avoids to close a torque control loop at joint level. While simulation implementations of torque based walking for series elastic actuator (SEA) humanoids display very promising results, several robustness issues very often appear in the experiments. Therefore we introduce here a minimalistic controller, which is based on feedback of control input collocated variables, with the only exception of zero joint torque control. Reshaping of the intrinsic elasticities by control is completely avoided. In order to achieve a coordinated movement of swing and stance leg during single support phase, an appropriate one-dimensional manifold of the motor positions is designed. This constrained behavior is experimentally shown to be compatible with the intrinsic mechanical oscillation mode of the double support phase. The feasibility of this methodology is experimentally validated on a human-scale, anthropomorphic bipedal robotic system with SEA actuation.
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