Flexible Joint Robot Position Control via Nonlinear Disturbance Observer
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Solution Overview
Problem
Existing linear disturbance observers for flexible joint robots limit performance and movement due to conservative controller design, causing instability and reduced efficiency, especially at singularities, and restrict the range of robot movements.
Innovation Solution
A nonlinear disturbance observer-based control system that converts control inputs from the Cartesian coordinate system to the rotating workspace coordinate system, using a Jacobian transposed matrix and a disturbance observer to estimate and remove mutual reaction forces between robot links, thereby eliminating singularity and maintaining constant performance regardless of robot posture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a linear disturbance observer is used for flexible joint robots, then the controller design can guarantee stability, but the controller performance varies according to robot movements and is limited to conservative design
Solution Approach 1:
The patent transforms the linear disturbance observer into a nonlinear disturbance observer by changing the mathematical parameters and structure of the observer. This allows the controller to adapt to varying robot postures and movements while maintaining stability, resolving the contradiction between guaranteed stability and consistent performance across different configurations.
Solution Approach 2:
The patent introduces dynamic adaptation mechanisms that allow the controller to adjust its behavior based on real-time robot state. The nonlinear disturbance observer dynamically estimates and compensates for disturbances varying with robot posture, enabling consistent performance across different configurations while maintaining stability.
2Reliability
If a linear disturbance observer is designed to avoid singularity, then stability is maintained, but the range of robot movement is limited
Solution Approach 1:
The patent changes the coordinate system parameters from Cartesian to rotating workspace coordinates, which fundamentally alters how singularities are handled. This transformation allows the robot to pass through singularities without loss of controllability or stability, thereby expanding the movement range while maintaining stability.
Solution Approach 2:
The patent introduces a new dimensional framework by using rotating workspace coordinates instead of traditional Cartesian coordinates. This dimensional change allows the system to navigate through singularities that would otherwise block movement, effectively expanding the operational workspace while maintaining stability.
3Reliability
If conservative controller design is used to guarantee stability, then reliability is ensured, but robot performance and task efficiency are reduced
Solution Approach 1:
The patent implements a feedback mechanism through the nonlinear disturbance observer that continuously estimates disturbances and feeds this information back to the controller. This active compensation allows the system to maintain stability without conservative limitations, thereby improving task efficiency and overall robot performance.
Solution Approach 2:
The patent performs preliminary disturbance estimation and compensation through the nonlinear observer before disturbances significantly impact system performance. This proactive approach allows the controller to maintain optimal performance and efficiency while ensuring stability, avoiding the need for conservative design limitations.
Data Source
AI summary
A system for controlling a flexible joint robot includes a control input dimension conversion part configured to receive a control input of a robot and convert the Cartesian coordinate system of the control input to the rotating workspace coordinate system; an entire flexible joint robot dynamics part configured to receive the control input and a disturbance and output a control output by multiplying the control input reflecting the disturbance by at least one determinant; and a disturbance observer configured to reflect the estimated disturbance in the control input by calculating an estimated disturbance obtained by estimating the disturbance, wherein the disturbance observer includes a mutual reaction force removal part including a determinant for removing mutual reaction force between joints of the robot; a low-pass filter; and an estimated-disturbance dimension conversion part.