Virtual Pendulum Model for Stable Bipedal Walking Control
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Solution Overview
Problem
Bipedal robots struggle with balance stabilization and unnatural walking motions due to limitations in existing simplified models like the linear inverted pendulum model and spring-loaded inverted pendulum model, which fail to accurately represent human walking dynamics and are prone to falling under external forces.
Innovation Solution
A virtual pendulum model is introduced for a bipedal robot, featuring a virtual body with legs connected at a pivot point above the center of mass, utilizing ground reaction forces to stabilize posture and ankle torque to compensate for energy loss during walking, with kinematic equations defining the robot's motion and posture angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the linear inverted pendulum model is used to simplify the robot, then the high-order dynamic interpretation is improved, but the walking motion becomes unnatural compared to human motions
Solution Approach 1:
The patent changes the key parameter of the pendulum model by positioning the pivot point above the center of mass rather than at the center of mass. This parameter change transforms the model from LIPM to VIPM, enabling natural walking motions while maintaining analytical tractability for control design.
2Use of energy by moving object
If the spring loaded inverted pendulum model is used to model the robot, then the energy conservation interpretation is improved, but the robot loses balance and falls over when external force is applied
Solution Approach 1:
The patent inverts the traditional pendulum configuration by placing the pivot point above the center of mass. This inversion creates a restoring moment that naturally stabilizes the body posture, allowing the robot to maintain balance under external forces while still considering energy dynamics.
3Device complexity
If the point mass model is used to simplify the robot, then the model simplicity is improved, but the balance stabilization of the upper body cannot be appropriately described
Solution Approach 1:
The patent segments the robot model into distinct components: a point mass representing the body, and massless legs with specific geometric constraints. This segmentation allows the model to remain simple while capturing the essential dynamics of upper body balance stabilization through the virtual pivot point configuration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables stable limit-cycle walking trajectories and natural posture stabilization, effectively addressing the limitations of previous models by mimicking human walking dynamics and maintaining balance without additional control mechanisms.
Implementation Method 1
a ground reaction force, which acts on the two legs, acts towards the VPP, thereby providing a restoring moment with respect to the CoM such that stabilization of the posture of the body naturally occurs
Implementation Method 2
provides the ankle torque to compensate for kinetic energy of the robot model lost by an impact when a leg ('leading leg') positioned at a front side in the double stance phase steps on the ground
Data Source
AI summary
A method for modeling a robot simplified for stable walking control of a bipedal robot provides a robot model that is simplified as a virtual pendulum model including a virtual body, two virtual legs connected to the body at a virtual pivot point (VPP) that is set at a position higher than the center of mass (CoM) of the body, and virtual feet connected to the two legs, respectively, to step on the ground. A ground reaction force, which acts on the two legs, acts towards the VPP, thereby providing a restoring moment with respect to the CoM such that stabilization of the posture of the body naturally occurs.