Legged Robot Balance Control via Two-Phase Disturbance Response
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Solution Overview
Problem
Humanoid robots struggle to maintain balance when subjected to unexpected force disturbances, which can lead to falls and potential harm to humans or damage to the robot.
Innovation Solution
A two-phase control strategy for legged robots, comprising a reflex phase to absorb the disturbance force by managing angular and linear momentum, and a recovery phase to return to a statically stable upright posture, utilizing control laws based on the rate of change of angular momentum and potential energy to maintain balance and recover posture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the robot uses a rigid resistance strategy against disturbance force, then the robot can maintain its posture, but the robot may fall due to excessive force accumulation
Solution Approach 1:
The robot employs a two-phase control strategy where the first phase (reflex phase) acts as a cushioning mechanism to absorb the initial impact of disturbance forces. By allowing controlled yielding and momentum change during this phase, the system prevents force accumulation that would otherwise cause falling, while the second phase (recovery phase) restores posture stability.
Solution Approach 2:
The control system dynamically switches between two phases: the reflex phase where the robot yields to disturbance forces by allowing momentum change, and the recovery phase where the robot restores its posture. This dynamic adaptation allows the robot to balance between force absorption and posture maintenance, resolving the contradiction between rigid resistance and stable posture.
2Force
If the robot yields to disturbance force during reflex phase, then the robot absorbs the disturbance, but the robot's position changes temporarily
Solution Approach 1:
The control strategy is segmented into two distinct phases: the reflex phase for disturbance absorption where position change is acceptable, and the recovery phase for posture restoration where the robot returns to its original position. This segmentation allows temporary position compromise for the sake of force absorption, with guaranteed recovery afterward.
Solution Approach 2:
During the reflex phase, the robot performs a preliminary action of yielding to the disturbance force to absorb its impact. This preliminary yielding prevents more severe instability later, and the subsequent recovery phase corrects the position, ensuring that the temporary position change serves a protective function.
3Stability of the object's composition
If the robot returns to original posture quickly, then the robot restores stability, but the robot may not fully absorb the disturbance energy
Solution Approach 1:
The control strategy implements periodic action through two distinct phases: the reflex phase where the robot absorbs disturbance energy by yielding, and the recovery phase where the robot restores its posture. This periodic alternation between energy absorption and posture restoration ensures that disturbance energy is fully absorbed before stability is restored, preventing residual oscillations.
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
The strategy effectively enables robots to withstand and recover from unexpected forces, ensuring balance and preventing falls, thereby enhancing safety in human-robot interactions.
Implementation Method 1
the control law is based on {dot over (H)}G, the rate of change of the robot's angular momentum at G, its center of mass (CoM)
Implementation Method 2
the control law is also based on {dot over (L)}x, the rate of change of the robot's linear momentum at its CoM
Implementation Method 3
during the recovery phase, the control law causes the robot to perform a movement that increases its potential energy
Data Source
AI summary
Systems and methods are presented that enable a legged robot to maintain its balance when subjected to an unexpected force. In the reflex phase, the robot withstands the immediate effect of the force by yielding to it. In one embodiment, during the reflex phase, the control system determines an instruction that will cause the robot to perform a movement that generates a negative rate of change of the robot's angular momentum at its centroid in a magnitude large enough to compensate for the destabilizing effect of the force. In the recovery phase, the robot recovers its posture after having moved during the reflex phase. In one embodiment, the robot returns to a statically stable upright posture that maximizes the robot's potential energy. In one embodiment, during the recovery phase, the control system determines an instruction that will cause the robot to perform a movement that increases its potential energy.