Locomotion

Reactive Controller Framework (RCF)

While there is a lot of work addressing single aspects of the overall locomotion gait planning and control problem, solutions that take all these elements together in a systematic and coherent fashion are rare. In this contribution we present a reactive gait generation and control framework for a quadruped robot that has the following main goals:

  • Creation of stable omni-directional periodic gait;
  • Robustness against disturbances from uneven ground and external forces on the trunk;
  • Foot slip avoidance;
  • Reduction of impact forces at the feet.

To achieve these goals we make extensive use of kinematic and dynamic models of our hydraulic quadruped robot HyQ and exploit the high performance torque-control available at all the joints. The resulting control framework exhibits the following features (Barasuol, 2013):

  • Avoid trajectories that would penetrate the ground (avoid high ground reaction forces – GRF);
  • Avoid weak contact or loss of contact (avoid slippage);
  • Avoid undesired leg internal forces (avoid slippage and waste of energy);
  • Reduce disturbances between joint position and trunk attitude controllers;
  • Reduce disturbances at the trunk due to poor state estimation (avoid excessive GRF);
  • Increase the locomotion robustness with respect to unexpected terrain irregularities (avoid excessive GRF).

RCFweb

Planned walking over rough terrain

  • Α framework for quadrupedal locomotion over highly challenging terrain where the choice of appropriate footholds is crucial for the success of the behavior.
  • we developed a path planning approach that evaluates the geometry of the environment, computes desired body trajectories and selects locally optimal footholds along the planned path.
  • We exploit the active compliance of our system to smoothly interact with the environment, even when this is inaccurately perceived or dynamically changing, and update the planned path on-the-fly.
  • We leverage the full set of benefits that a high performance torque controlled quadruped robot can provide and demonstrate the flexibility and robustness of our approach on a set of experimental trials of increasing difficulty.
  • A. Winkler, C. Mastalli, I. Havoutis, M. Focchi, D. G. Caldwell, C. Semini, Planning and Execution of Dynamic Whole-Body Locomotion for a Hydraulic Quadruped on Challenging Terrain, IEEE International Conference on Robotics and Automation (ICRA), 2015 [full article]
  • C. Mastalli, A. Winkler, I. Havoutis, D. G. Caldwell, C. Semini, On-line and On-board Planning and Perception for Quadrupedal Locomotion, 2015 IEEE International Conference on Technologies for Practical Robot Applications (TEPRA), 2015 [full article]
  • A. Winkler, I. Havoutis, S. Bazeille, J. Ortiz, M. Focchi, R. Dillmann, D. G. Caldwell, C. Semini, "Path Planning with Force-Based Foothold Adaptation and Virtual Model Control for Torque Controlled Quadruped Robots," IEEE International Conference on Robotics and Automation (ICRA), 2014. [full article]

Local reflex generation in quadrupedal locomotion

Legged robots that dynamically locomote through rough terrain need to constantly handle unpredicted collisions (e.g. foot stumbling due to an obstacle) due to the unstructured nature of the environment. If these disturbances are strong enough they can cause errors in the robot's trunk that are di cult to control with a common feedback-based controller, imposing a serious risk to the overall system stability. The impulsive nature of such disturbances demands a very short reaction time, especially in case of dynamic gaits (trot, gallop, etc.). A quick reaction becomes increasingly crucial when the robot is deprived of reliable visual feedback (e.g. smoky areas or thick vegetation) or when an accurate map of the environment is not available. In this paper we propose a local elevator re ex which enables the robot to reactively overcome high obstacles. Thanks to this reflex capability the robot is able to step over a platform of 11cm height (14% of the leg length) without prior knowledge of the terrain. (Focchi, 2013)