Articulated Robot Wrist Control for Singularity Speed Limits
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Solution Overview
Problem
Articulated robots face challenges in maintaining the position, moving speed, and attitude angles of end effectors while preventing abrupt changes in wrist shaft speeds, often requiring trade-offs that compromise welding or painting quality due to excessive bulging or deviation from predetermined paths.
Innovation Solution
A control unit and method that dynamically adjust the angles and speeds of drive shafts to maintain the position and moving speed of the wrist end within allowable ranges, while reducing variations in attitude angles, by recalculating angles and speeds to avoid singularity regions and adjust weightings of attitude components, allowing for continuous operation without pre-computation phase peak loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the end effector is made to move at constant speed when joint angle θ5 is substantially 0 degree, then the moving speed of the end effector is maintained, but the joint angles θ4 and θ6 rapidly change causing the wrist shafts to exceed allowable speed ranges
Solution Approach 1:
The control device dynamically adjusts the moving speed of the end effector based on real-time calculation of wrist shaft speeds. When a wrist shaft exceeds its allowable speed range, the system automatically reduces the end effector's speed to bring the wrist shaft speeds back within acceptable limits, creating a dynamic speed adjustment mechanism that adapts to changing operational conditions
Solution Approach 2:
The control device implements a feedback mechanism where it continuously monitors the speeds of wrist shafts J4 and J6, compares them against allowable ranges, and adjusts the end effector's moving speed accordingly. This closed-loop control ensures that wrist shaft speeds remain within safe operational limits while maintaining optimal end effector performance
2Manufacturing precision
If the speed of wrist shafts is reduced to maintain path accuracy, then the accuracy of the path is maintained, but the productivity decreases due to lower operating speeds
Solution Approach 1:
The control device applies speed adjustment selectively rather than uniformly. It identifies specific sections of the movement path where wrist shaft speeds would exceed allowable ranges and reduces speed only in those localized areas, while maintaining higher speeds in safe zones, thereby minimizing the impact on overall productivity while ensuring path accuracy where needed
3Reliability
If the end effector moves along a predetermined path while maintaining wrist shaft speeds within allowable range, then the reliability is improved, but the position and attitude angles cannot be simultaneously satisfied
Solution Approach 1:
The control device continuously calculates the required wrist shaft speeds based on the desired end effector position and attitude, and continuously adjusts the end effector's moving speed to ensure wrist shafts remain within allowable ranges. This continuous adjustment maintains the predetermined path trajectory while ensuring reliable operation, avoiding abrupt changes or discontinuities in the movement
Data Source
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Figure 5
AI summary
In order to suppress fluctuations in specific components of posture angle in a target coordinate system while maintaining the position of the leading edge of the wrist, the velocity of movement of the leading edge of the wrist, and the permissible velocity of the shaft during velocity suppression, an articulated robot which moves while calculating the position in interpolated points on a teaching path, the posture and the angles in each axis is provided, wherein a judgment is made as to whether the velocity of the wrist shaft exceeds a permissible limit, and if the permissible limit is exceeded, a plurality of candidates for angle of the wrist shaft that maintain the velocity within permissible limits are calculated, and the candidate with the minimum fluctuation in the specific component of the posture angle of the weld line coordinate system is selected from said plurality of candidates and made to serve as the angle of the wrist shaft, the angles of other shafts that correspond to this angle are recalculated and made to serve as the subsequent interpolation point, and the articulated robot is driven.