Time Warping for Floating-Base Robot Motion Feasibility
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Solution Overview
Problem
Existing methods for controlling floating-base humanoid robots struggle to accurately replicate human-like motions while maintaining balance and avoiding collisions, as they often require modifying human motions to fit the robot's kinematics and dynamics, which can result in unbalanced or collision-prone movements.
Innovation Solution
The use of 'time warping' to modify the timeline of human motions, allowing the robot to perform the same poses at different times, thereby changing velocity and acceleration profiles to make infeasible motions feasible, using a generalized motion feasibility index that considers friction constraints and center-of-pressure constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If human motions are modified to fit the robot's kinematics and dynamics, then the robot can maintain balance, but the motions no longer appear human-like and may collide with obstacles
Solution Approach 1:
The patent applies parameter changes by modifying the temporal parameters of human motions through time warping. Instead of altering spatial parameters (which would change the poses and risk collision), the system warps the time dimension to adjust velocity and acceleration profiles, making infeasible motions feasible while preserving the original human-like poses and trajectories
Solution Approach 2:
The patent transitions from modifying motions in spatial dimensions to modifying them in the temporal dimension. By applying time warping functions that transform the time parameter t to a warped time parameter τ(t), the system achieves feasible robot motions without altering the spatial configuration of poses, thus avoiding collisions while maintaining balance
2Manufacturing precision
If human motions are not modified, then the motions remain human-like, but the robot cannot perform them due to kinematic and dynamic differences
Solution Approach 1:
The system changes the temporal parameters of the motion by applying time warping functions. This allows the robot to perform the exact same poses as humans while adjusting the timing, velocity, and acceleration to match the robot's dynamic capabilities, ensuring both motion accuracy and balance maintenance
Solution Approach 2:
The patent makes the motion timeline dynamic by applying time warping that adapts the execution speed of poses based on the robot's dynamic constraints. The warping function dynamically adjusts the timing of each pose to ensure feasibility while maintaining the overall motion pattern, enabling the robot to replicate human motions within its dynamic capabilities
3Manufacturing precision
If the robot tries to replicate human motions exactly, then human-like appearance is achieved, but the robot loses balance and falls over
Solution Approach 1:
The patent resolves this contradiction by changing the temporal parameters through time warping. The warping function adjusts the velocity and acceleration profiles of the motion while keeping the poses identical to human motions. This allows the robot to achieve human-like appearance through accurate pose replication while maintaining balance stability through dynamically feasible timing adjustments
Data Source
AI summary
A control method, and a robot controller implementing the method, is provided that adapts human motions to floating-base humanoid robots with time warping techniques. The method of modifying a set of reference motions modifies the timeline of a reference motion so as to speed up or slow down one or more of the motions or motion segments. Through the use of time warping, the velocity and acceleration profiles of the motion are changed to turn an infeasible motion into a feasible one. The optimal time warping is obtained through a generalized motion feasibility index that quantifies the feasibility of a motion considering the friction constraint as well as the center-of-pressure (CoP) constraint. Due to the use of the motion feasibility index, the proposed motion adaptation method taught herein can be applied to motions on arbitrary terrains or with any number of links in contact with the environment.