Force Threshold Position Controller for Legged Robot Stability
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Solution Overview
Problem
Legged robots face challenges in navigating uneven terrain due to poor performance when rapidly walking over such surfaces, necessitating a system and method to enhance their mobility and stability.
Innovation Solution
A force threshold-based position (FTP) controller is developed to operate independently on each leg, using force feedback to adjust the walking pattern and maintain a minimum ground reaction force, allowing the robot to stabilize and propel itself effectively on irregular terrain without relying on inertial information or complex coordination between legs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional position control methods are used, then the robot can maintain simple control logic, but the robot exhibits poor performance when rapidly walking over uneven terrain
Solution Approach 1:
The patent implements force feedback control where the robot measures ground reaction forces through compliant actuators and uses this feedback to adjust leg positioning and body orientation in real-time. This closed-loop feedback mechanism enables the robot to adapt to uneven terrain by continuously monitoring and responding to contact forces, significantly improving reliability on irregular surfaces while maintaining manageable control complexity through decentralized leg-level control.
2Adaptability or versatility
If force feedback control is implemented, then the robot can maintain stability and propel effectively on irregular terrain, but the control system becomes more complex
Solution Approach 1:
The control system is segmented into independent leg-level controllers that operate autonomously based on local force feedback measurements. Each leg controller processes ground reaction forces and adjusts its own positioning without requiring complex whole-body coordination, thereby achieving high terrain adaptability while keeping individual controller complexity low. This decentralized segmentation allows the robot to handle irregular terrain effectively.
Solution Approach 2:
The patent applies local quality control where each leg operates with its own force threshold-based position (FTP) controller that adapts to local terrain conditions independently. This localized control approach enables the robot to respond to specific terrain features at each contact point, achieving high adaptability to irregular surfaces while avoiding the complexity of centralized whole-body control through independent local decision-making at each leg.
3Measurement precision
If the robot uses compliant actuators to measure foot forces, then the robot can detect ground contact and force magnitude, but the measurement system becomes more complex
Solution Approach 1:
The compliant actuators serve dual functions: they provide the mechanical force needed for leg movement and simultaneously measure ground reaction forces through their inherent compliance characteristics. This self-service approach eliminates the need for separate force sensors, achieving precise foot force measurement while keeping the measurement system complexity low by reusing the actuator's mechanical properties for both actuation and sensing.
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 FTP controller enables legged robots to maintain stability and propel themselves efficiently on both flat and uneven terrain, overcoming the limitations of traditional position control methods by incorporating force feedback, thus improving their ability to traverse complex environments.
Implementation Method 1
each including a joint that is biased by a spring to a zero position. When the foot of a leg contacts the ground and applies a force to the ground, the joint moves (e.g., rotates) from the zero position against the force of the spring.
Data Source
AI summary
In one embodiment, a walking robot includes a robot body, multiple legs attached to and extending from the body, at least one leg including a pivot joint having an initial zero position and a foot that is adapted to contact a ground surface, wherein force applied to the foot because of contact with the ground causes the leg to pivot about the pivot joint, and an angular position sensor associated with the pivot joint and configured to measure a pivot angle through which the leg has pivoted about the pivot joint, the angle being related to the force applied to the foot.