Biped Robot Impedance Control via Torso Tilt Feedback
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Solution Overview
Problem
Biped walking robots face instability and difficulty in pose control due to fixed impedance control methods, which fail to adjust to varying ground conditions and torso tilts, leading to weak ground support and inaccurate torso tilt correction.
Innovation Solution
A method that measures the moment and tilt of a walking robot's foot and torso, adjusts impedance and ZMP variations to enhance stability, and concurrently controls foot and torso movements to maintain balance on uneven surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If impedance control method uses fixed impedance control gain, then control simplicity is maintained, but walking stability deteriorates on ground having various prominences and depressions
Solution Approach 1:
The patent implements dynamic impedance control by adjusting the impedance control gain based on the measured tilt angle of the torso. The gain is increased when the tilt angle exceeds a threshold value to enhance stabilizing torque during large tilts, and reduced when the tilt angle is within the threshold to prevent excessive stiffness during normal walking. This dynamic adjustment resolves the contradiction between control simplicity and walking stability on uneven terrain.
2Adaptability or versatility
If impedance control method lowers the stiffnesses of ankle joints, then adaptability to ground is improved, but supporting force by the ground becomes weak
Solution Approach 1:
The patent dynamically adjusts ankle joint stiffness based on torso tilt angle. When the tilt angle exceeds the threshold, the impedance control gain is increased to provide stronger supporting force. When the tilt angle is within the threshold, the gain is reduced to maintain adaptability to ground variations. This dynamic stiffness adjustment resolves the contradiction between adaptability and supporting force.
3Device complexity
If impedance control method measures and uses only the repulsive force from the ground, then measurement simplicity is maintained, but foot-to-ground adhesion becomes insufficient
Solution Approach 1:
The patent introduces the torso tilt angle as an intermediary parameter to enhance foot-to-ground adhesion. The tilt angle measurement from the pose sensor serves as additional information that, when combined with the repulsive force from F/T sensors, enables the impedance control to generate stronger stabilizing torque. This intermediary measurement resolves the contradiction between measurement simplicity and foot-to-ground adhesion.
4Device complexity
If impedance control method estimates the tilt of a torso through ZMP calculation, then calculation simplicity is maintained, but precision of tilt correction deteriorates
Solution Approach 1:
The patent implements direct feedback from pose sensors that measure the torso tilt angle directly, replacing the indirect ZMP-based estimation method. The measured tilt angle is fed back to the impedance controller, which adjusts the ankle joint torque based on this precise measurement. This direct feedback mechanism resolves the contradiction between calculation simplicity and precision of tilt correction.
Data Source
AI summary
Disclosed are a walking robot and a method of controlling the same, in which impedance control and torso tilt control are achieved complementarily such that impedance can be adjusted according to the tilt of a torso or the tilt of the torso can be adjusted according to the impedance. The method includes measuring a moment of a foot; measuring a tilt of a torso; adjusting the scale of the measured moment based on the tilt of the torso, and controlling the foot based on the scale-adjusted moment; and adjusting the scale of the measured tilt based on a ZMP variation amount of the foot, and controlling the tilt of the torso based on the scale-adjusted ZMP variation amount.