TechTalks from event: Technical session talks from ICRA 2012

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Bipedal Robot Control

  • Switching Control Design for Accommodating Large Step-Down Disturbances in Bipedal Robot Walking Authors: Park, Hae Won; Sreenath, Koushil; Ramezani, Alireza; Grizzle, J.W
    This paper presents a feedback controller that allows MABEL, a kneed, planar bipedal robot, with 1 m-long legs, to accommodate an abrupt 20 cm decrease in ground height. The robot is provided information on neither where the step down occurs, nor by how much. After the robot has stepped off a raised platform, however, the height of the platform can be estimated from the lengths of the legs and the angles of the robot’s joints. A real-time control strategy is implemented that uses this on-line estimate of step-down height to switch from a baseline controller, that is designed for flat-ground walking, to a second controller, that is designed to attenuate torso oscillation resulting from the step-down disturbance. After one step, the baseline controller is re-applied. The control strategy is developed on a simplified model of the robot and then verified on a more realistic model before being evaluated experimentally. The paper concludes with experimental results showing MABEL (blindly) stepping off a 20 cm high platform.
  • Design and Experimental Implementation of a Compliant Hybrid Zero Dynamics Controller with Active Force Control for Running on MABEL Authors: Sreenath, Koushil; Park, Hae Won; Grizzle, J.W
    This paper presents a control design based on the method of virtual constraints and hybrid zero dynamics to achieve stable running on MABEL, a planar biped with compliance. In particular, a time-invariant feedback controller is designed such that the closed-loop system not only respects the natural compliance of the open-loop system, but also enables active force control within the compliant hybrid zero dynamics and results in exponentially stable running gaits. The compliant-hybrid-zero-dynamics-based controller with active force control is implemented experimentally and shown to realize stable running gaits on MABEL at an average speed of 1.95 m/s (4.4 mph) and a peak speed of 3.06 m/s (6.8 mph). The obtained gait has flight phases upto 39% of the gait, and an estimated ground clearance of 7.5-10 cm.
  • Walking Control Strategy for Biped Robots Based on Central Pattern Generator Authors: Liu, Chengju; Chen, Qijun
    This paper deals with the walking control of biped robots inspired by biological concept of central pattern generator (CPG). A control architecture is proposed with a trajectory generator and a motion engine. The trajectory generator consists of a CoG (center of gravity) trajectory generator and a foot trajectory modulator. The CoG generator generates adaptive CoG trajectories online and the foot trajectories can be modulated based on the generated CoG trajectories. A biped platform NAO is used to validate the proposed locomotion control system. The experimental results confirm the effectiveness of the proposed control architecture.
  • On the Lyapunov Stability of Quasistatic Planar Biped Robots Authors: Varkonyi, Peter L.; Gontier, David; Burdick, Joel
    We investigate the local motion of a planar rigid body with unilateral constraints in the neighborhood of a two-contact frictional equilibrium configuration on a slope. A new sufficient condition of Lyapunov stability is developed in the presence of arbitrary external forces. Additionally, we construct an example, which is stable against perturbations by infinitesimal forces, but does not possess Lyapunov stability against infinitesimal displacements or impulses. The great difference between previous stability criteria and ours leads to further questions about the nature of the exact stability condition.
  • Humanoid Robot Safe Fall Using Aldebaran NAO Authors: Yun, Seung-kook; Goswami, Ambarish
    Although the fall of a humanoid robot is rare in controlled environments, it cannot be avoided in the real world where the robot may physically interact with the environment. Our earlier work introduced the strategy of direction changing fall, in which the robot attempts to reduce the chance of human injury by changing its default fall direction in realtime and falling in a safer direction. The current paper reports further theoretical developments culminating in a successful hardware implementation of this fall strategy conducted on the Aldebaran NAO robot[3]. This includes new algorithms for humanoid kinematics and Jacobians involving coupled joints and a complete estimation of the body frame attitude using an additional inertial measurement unit. Simulations and experiments are smoothly handled by our platform independent humanoid control software called Locomote. We report experiment scenarios where we demonstrate the effectiveness of the proposed strategies in changing the fall direction.
  • Control Design to Achieve Dynamic Walking on a Bipedal Robot with Compliance Authors: Lim, Bokman; Lee, Minhyung; Kim, Joohyung; Lee, Jusuk; Park, Jaeho; Seo, Keehong; Roh, Kyungshik
    We propose a control framework for dynamic bipedal locomotion with compliant joints. A novel 3D dynamic walking is achieved by utilizing natural dynamics of the system. It is done by 1) driving robot joints directly with the posture-based state machine and 2) controlling tendon-driven compliant actuators. To enlarge gait's basin attraction for stable walking, we also adaptively plan step-to-step motion and compensate stance/swing motion. Final joint input is described by a superposition of state machine control torques and compensation torques of balancers. Various walking styles are easily generated by composing straight and turning gait-primitives and such walking is effectively able to adapt on various environments. Our proposed method is applied to a torque controlled robot platform, Roboray. Experimental results show that gaits are able to traverse inclined and rough terrains with bounded variations, and the result gaits are human-like comparing the conventional knee bent walkers.