Optimal gait planning for humanoids with 3D structure walking on slippery surfaces

Design and Research of a Walking Robot with Two Parallel Mechanisms

In this paper, a new type of biped mobile robot is designed. Each leg of the robot is a 6 degree-of-freedom (DOF) parallel mechanism, and each leg has three relatively fixed landing points. The leg’s structure gives the robot better performance on large carrying capacity, strong environmental adaptability and fast moving speed simultaneously. At the same time, it helps the robot move more steadily and change direction more simply. Based on the structural features of the leg, the inverse kinematics model of the biped robot is established and a unified formula is obtained. According to an analysis of robot’s workspace, gait planning is completed and simulated. Finally, the special case that the robot can keep the upper body horizontal while walking on a slopy surface is validated.

Robust Control of Semi-passive Biped Dynamic Locomotion based on a Discrete Control Lyapunov Function

This paper focuses on robust control of a simplest passive model, which is established on a DCLF (discrete control Lyapunov function) -based control system, and presents gait transition method based on the study of purely passive walker. Firstly, the DCLF is introduced to stabilize walking process between steps exponentially by modulating the length of next step. Next, the swing leg trajectory from mid-stance position to foot-strike can be planned. Then the control law is calculated to resist external disturbance. Besides, an impulse is added just before foot-strike to realize a periodic walking pattern on flat or uphill ground. With walking terrain varying, the robot can transit to an adaptive walking gait in a few steps. With different push or pull disturbances acting on hip joint and the robot gait transiting on a continuously slope-changing downhill, the effectiveness of the presented DCLF-based method is verified using simulation experiments. The ability to walk on a changing environment is also presented by simulation results. The insights of this paper can help to develop a robust control method and adaptive walking of dynamic passive locomotion robots.

Control Synergies for Rapid Stabilization and Enlarged Region of Attraction for a Model of Hopping

Inspired by biological control synergies, wherein fixed groups of muscles are activated in a coordinated fashion to perform tasks in a stable way, we present an analogous control approach for the stabilization of legged robots and apply it to a model of running. Our approach is based on the step-to-step notion of stability, also known as orbital stability, using an orbital control Lyapunov function. We map both the robot state at a suitably chosen Poincaré section (an instant in the locomotion cycle such as the mid-flight phase) and control actions (e.g., foot placement angle, thrust force, braking force) at the current step, to the robot state at the Poincaré section at the next step. This map is used to find the control action that leads to a steady state (nominal) gait. Next, we define a quadratic Lyapunov function at the Poincaré section. For a range of initial conditions, we find control actions that would minimize an energy metric while ensuring that the Lyapunov function decays exponentially fast between successive steps. For the model of running, we find that the optimization reveals three distinct control synergies depending on the initial conditions: (1) foot placement angle is used when total energy is the same as that of the steady state (nominal) gait; (2) foot placement angle and thrust force are used when total energy is less than the nominal; and (3) foot placement angle and braking force are used when total energy is more than the nominal.

Simultaneous Prevention of Rotational and Translational Slip for a Humanoid Robot

Slip often occurs in humanoid robot walking, especially when the robot walks on a low friction floor or walks fast. Unexpected slip may cause the robot to fall and then sustain damage. In real environments, rotational and translational slip phenomena can happen during biped walking. Previous studies have mainly focused on solving these problems independently. In this paper, we propose strategies for simultaneous rotational and translational slip prevention based on a three mass model, which takes into account the effect of the swing leg. The rotational slip is prevented through a bionic walking pattern generator which mimics the yaw moment compensation mechanism of a human. The translational slip is eliminated through a novel reaction force ratio reduction control with the compensation of CoM (center of mass) acceleration. The effectiveness of the presented strategies is validated by simulations and experiments with an actual humanoid robot.