Robot Admittance Control Under Jacobian Singularity Constraints
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Solution Overview
Problem
Existing admittance controllers for robots, such as humanoid robots, fail to account for the robot's own limitations and constraints, leading to abnormal operations, singularities, and potential harm to users due to excessive acceleration or velocity, especially in interactions with people.
Innovation Solution
Constrain position instructions using ill-condition numbers to avoid singularities and ensure velocity and force operability, and incorporate constraints on acceleration and velocity to account for hardware limitations, using a method that includes converting admittance controller transfer functions to discrete domains and integrating constraints into the control process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If admittance controller parameters are adjusted based on mass-spring-damping mathematical model, then desired dynamics characteristics and dynamic response effects are achieved, but robot's own limitations and constraints are ignored causing abnormal operations
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the relationship between admittance controller parameters and robot state constraints before actual operation. The constraint satisfaction determination module uses pre-established models to predict whether parameter adjustments will violate robot limitations, allowing the system to prevent abnormal operations before they occur rather than reacting after violations happen.
Solution Approach 2:
The patent implements feedback through the constraint satisfaction determination module that continuously monitors whether admittance controller parameter adjustments satisfy robot state constraints. When a parameter adjustment is proposed, the system checks it against pre-established constraints and provides feedback to block or modify adjustments that would cause abnormal operations, ensuring reliable operation while maintaining control flexibility.
2Speed
If admittance controller is designed by parameter adjustments on mass-spring-damping model, then dynamic response effects are improved, but constraints and restrictions on robot movement are not met
Solution Approach 1:
The system performs preliminary action by pre-establishing a database of robot state constraints and their relationships with admittance controller parameters. Before executing parameter adjustments for dynamic response, the constraint satisfaction determination module checks proposed changes against pre-defined movement constraints, ensuring that speed improvements do not violate robot operational boundaries.
Solution Approach 2:
The patent introduces an intermediary mechanism (the constraint satisfaction determination module) that mediates between the admittance controller's parameter adjustments and the robot's movement constraints. This intermediary translates controller parameter changes into predicted robot states and verifies them against constraints, allowing fast dynamic response while guaranteeing constraint satisfaction.
3Adaptability or versatility
If robot operates with high acceleration and velocity for compliance, then service capability in close contact scenarios is improved, but safety in human-robot interactions deteriorates due to excessive movements
Solution Approach 1:
The patent applies preliminary action by pre-defining safety constraints for robot acceleration and velocity in interaction scenarios. Before the robot executes compliant movements with high acceleration or velocity, the constraint satisfaction determination module checks whether these movements violate pre-established safety boundaries, preventing harmful effects on human users before they occur.
Solution Approach 2:
The system uses feedback by continuously monitoring robot state parameters (acceleration, velocity, position) against pre-established safety constraints during human-robot interactions. The constraint satisfaction determination module provides real-time feedback to block or adjust commands that would exceed safe movement limits, ensuring service adaptability while protecting human users from harm.
Data Source
AI summary
An admittance control method, a robot, and a storage medium are provided. The method includes: obtaining, based on a first admittance controller transfer function between force and position, a desired position of a robot in a current control cycle; determining a corresponding Jacobian matrix according to a configuration of the robot in the current control cycle, and calculating an ill condition number of the Jacobian matrix; and controlling the robot to move by inputting the obtained desired position in the current control cycle to a corresponding joint, in response to the ill condition number being less than a preset maximum ill condition number. In this manner, the configuration of the robot can be maintained within a reasonable rang of the ill condition number, and singularities caused by the admittance controller exceeding the work space can be avoided while the velocity reachability and force reachability of the robot can be ensured.