Quadruped Gait Control with Toe-Slip Detection for Soft Sand
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Solution Overview
Problem
Legged robots face challenges in maintaining stable walking performance on soft surfaces like deep sand and silt due to slipping and traction loss, which disrupt stance and swing control algorithms.
Innovation Solution
Implementing algorithms to constrain toe force ratios, modify swing trajectories, and detect toe slips to prevent overextension, ensuring stable locomotion by lifting the leg into a swing state when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional sticking contact mode is assumed for legged locomotion, then gait control algorithms can be simplified, but the model becomes invalid when operating on granular media like deep sand
Solution Approach 1:
The patent implements dynamic adaptation of contact mode between sticking and sliding based on real-time detection of toe slip conditions. The system transitions from a static sticking contact assumption to a dynamic contact model that responds to granular media conditions, allowing the quadruped to maintain reliable locomotion control across varying terrain hardness and granularity.
Solution Approach 2:
The patent employs force sensors and estimators to detect contact forces and toe slip conditions, providing feedback to the control system. This feedback mechanism enables the system to identify when the sticking contact assumption fails and switch to appropriate sliding contact control strategies, ensuring model validity remains high despite terrain variations.
2Reliability
If the coefficient of friction is reduced to prevent slipping, then traction loss is minimized, but the quadruped may overextend its leg beyond the threshold in stance
Solution Approach 1:
The patent uses force sensors to monitor contact forces and detect when the knee joint approaches its extension threshold. This feedback enables real-time adjustment of the coefficient of friction and leg position control, preventing both slipping and overextension by adapting to actual mechanical conditions during stance phase.
Solution Approach 2:
The system dynamically adjusts the coefficient of friction based on real-time detection of toe slip conditions and knee joint position. When the knee approaches its extension threshold, the system transitions from low-friction sliding contact to higher-friction sticking contact, preventing overextension while maintaining traction stability throughout the stance phase.
3Reliability
If the quadruped impacts the ground harder than nominal at touchdown, then slipping is reduced, but the knee joint may extend beyond the threshold causing loss of traction
Solution Approach 1:
The patent modifies swing trajectories to control touchdown velocity and impact force before the stance phase begins. By pre-adjusting the swing path and impact parameters, the system achieves optimal contact forces that prevent slipping without causing excessive knee extension, balancing traction and joint safety in advance.
Solution Approach 2:
The system dynamically adjusts swing trajectory and impact velocity based on real-time detection of toe slip conditions and knee joint position. When the knee approaches its extension threshold, the system reduces impact force and modifies the swing path to prevent overextension, while maintaining sufficient impact to prevent slipping during normal operation.
4Adaptability or versatility
If contact sensors are used to detect soft terrain characteristics, then locomotion control can be optimized, but the device complexity increases
Solution Approach 1:
The patent employs force sensors that serve multiple functions: detecting contact forces, measuring normal and tangential forces, and identifying toe slip conditions. This multi-functionality reduces the need for separate dedicated sensors for each measurement, thereby reducing overall device complexity while maintaining comprehensive terrain adaptation capability.
Solution Approach 2:
The system uses observer or estimator algorithms to detect contact forces and terrain characteristics using existing sensor data, rather than requiring additional dedicated force sensors. This self-service approach leverages available sensor information to infer terrain properties and contact conditions, reducing hardware complexity while maintaining adaptability.
Data Source
AI summary
The present invention pertains to a method for a quadruped robot to navigate through granular media, such as deep sand and for providing improvements in the walking performance over various types of granular media. In particular, the present invention proposes reducing the assumed coefficient of friction about the ground, impacting the ground harder than nominal in the vertical direction at touchdown, and forcing a toe lift off into swing if a knee joint extends beyond a threshold stance to help increase the robustness of a quadruped robot's locomotive abilities on challenging terrains and provide an improvement in the field of biomechanics and robotic navigation.