Mechanical Footstep Timing Using Capture Point Balance Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing robotic systems lack efficient mechanisms for determining the timing of footsteps, leading to instability and difficulty in maintaining balance, especially in the presence of disturbances.
Innovation Solution
Robotic systems determine mechanically-timed footsteps by calculating a capture point based on the center of mass position and velocity, using a linear inverted pendulum model to arrest momentum, and adjusting the timing of foot contact based on a threshold position relative to this capture point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional fixed-timing footstep control is used, then the control system is simple, but the robot cannot maintain balance under disturbances
Solution Approach 1:
The patent implements feedback control by continuously monitoring the robot's center of mass position and velocity, calculating the capture point based on this state information, and adjusting footstep timing accordingly. The capture point serves as a feedback target that dynamically adapts to disturbances, allowing the robot to maintain balance through real-time state correction rather than fixed predetermined timing.
Solution Approach 2:
The patent transitions from static fixed-timing control to dynamic adaptive control by making the footstep timing dependent on the robot's instantaneous mechanical state. The capture point calculation incorporates center of mass position and velocity to determine optimal foot placement timing, creating a dynamic control system that adapts to changing conditions and disturbances.
2Reliability
If mechanically-timed footsteps with capture point calculation are implemented, then balance and stability are enhanced, but the computational complexity increases
Solution Approach 1:
The patent replaces complex multi-variable optimization computations with a mechanically-inspired capture point model based on the linear inverted pendulum approximation. This mechanical analogy provides a computationally efficient method to calculate optimal foot placement timing by leveraging physical principles rather than solving complex optimization problems in real-time.
Solution Approach 2:
The patent changes the control parameter from fixed time intervals to dynamic capture point positions that are continuously updated based on center of mass state. This parameter transformation allows the system to achieve adaptive balance control while maintaining computational efficiency through the closed-form capture point calculation rather than iterative optimization.
3Adaptability or versatility
If fixed footstep timing is used, then the control algorithm is simple, but the robot cannot adapt to disturbances
Solution Approach 1:
The patent applies preliminary action by proactively positioning the capture point before disturbances occur or as they develop. The continuous calculation of the capture point based on center of mass trajectory allows the system to prepare optimal foot placement timing in advance, preventing balance loss rather than reacting after disturbance impact.
Data Source
AI summary
An example implementation for determining mechanically-timed footsteps may involve a robot having a first foot in contact with a ground surface and a second foot not in contact with the ground surface. The robot may determine a position of its center of mass and center of mass velocity, and based on these, determine a capture point for the robot. The robot may also determine a threshold position for the capture point, where the threshold position is based on a target trajectory for the capture point after the second foot contacts the ground surface. The robot may determine that the capture point has reached this threshold position and based on this determination, and cause the second foot to contact the ground surface.