Robot Force Control Using Velocity-Based Equivalent Mass Matrices
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Solution Overview
Problem
Existing robot control systems face challenges in stable control, particularly when the determinant of the Jacobian matrix becomes zero in singular postures, leading to interference between position and force control axes and vibration amplification.
Innovation Solution
The robot control system acquires the velocity of the robot along the force control axis and selects either a first equivalent mass matrix for zero velocity or a second equivalent mass matrix for non-zero velocity to generate a control signal, thereby reducing interference and stabilizing control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single equivalent mass matrix is used for all velocity conditions, then the control system structure is simple, but control stability deteriorates when the robot is in singular postures or experiences velocity transitions
Solution Approach 1:
The patent applies dynamics by switching between different equivalent mass matrices based on the robot's velocity state. When velocity is zero, one equivalent mass matrix is used; when velocity is non-zero, another equivalent mass matrix is used. This dynamic adaptation to velocity conditions resolves the contradiction by maintaining control stability across different operating states while avoiding the complexity of a single universal matrix that would fail in singular postures.
Solution Approach 2:
The patent changes the parameter of the equivalent mass matrix based on velocity conditions. By selecting different equivalent mass matrices corresponding to different velocity states (zero or non-zero), the system optimizes control performance for each state. This parameter change approach allows the control system to maintain stability in singular postures and during velocity transitions without requiring an overly complex unified structure.
2Adaptability or versatility
If the determinant of the Jacobian matrix becomes zero in singular postures, then the robot can reach extreme positions, but interference between position and force control axes increases and vibration is amplified
Solution Approach 1:
The patent converts the harmful effect of singular postures into a manageable condition by detecting when the determinant of the Jacobian matrix approaches zero and switching to an equivalent mass matrix appropriate for zero velocity. This transforms the potential source of vibration and interference into a controlled transition point, allowing the robot to reach extreme positions while maintaining stability through velocity-based matrix selection.
Solution Approach 2:
The equivalent mass matrix acts as an intermediary between the robot's motion state and the control output. By introducing velocity-based equivalent mass matrix selection, the system mediates the relationship between position and force control axes, preventing direct interference when the Jacobian determinant is zero. This intermediary mechanism allows extreme positioning while filtering out harmful vibrations and inter-axis interference.
Data Source
AI summary
A robot control system includes circuitry configured to: acquire velocity of a robot in a working space in which the robot processes a workpiece based on a force control axis and a position control axis, the velocity being along the force control axis; select an equivalent mass matrix representing a relationship between acceleration and force in the working space, based on the acquired velocity, from a first equivalent mass matrix corresponding to the velocity being zero and a second equivalent mass matrix corresponding to the velocity not being zero; and generate a control signal for controlling the robot based on the selected equivalent mass matrix.