Trajectory Control Device for Articulated Robot Oscillation Suppression
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Solution Overview
Problem
Existing trajectory control methods for articulated robots, such as those used in arc welding, face challenges in achieving high accuracy due to low natural frequency, phase delay, and differences in servo control characteristics among axes, leading to inaccurate weaving motions.
Innovation Solution
A trajectory control device that calculates and compensates for coupling torque between joint axes using a dynamics model, incorporating filtering processes with high-frequency cutoff characteristics to reduce oscillations and align phase and gain characteristics, ensuring accurate motion control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If velocity feedforward control is applied to improve response characteristic, then trajectory accuracy should improve, but oscillation occurs due to low natural frequency
Solution Approach 1:
The patent implements dynamic characteristics calculation units that adaptively adjust filter cutoff frequencies based on the robot's current posture and operating conditions. This allows the system to optimize the balance between trajectory tracking accuracy and oscillation suppression in real-time, rather than using fixed parameters
Solution Approach 2:
The system changes control parameters (filter cutoff frequencies, feedforward gains) dynamically based on the robot's state. The first and second dynamic characteristics calculation units compute optimal parameters that prevent oscillation while maintaining trajectory accuracy, adapting to varying natural frequencies during motion
2Manufacturing precision
If nonlinear compensation control is implemented to decouple axes, then trajectory accuracy should improve, but phase shift reduces effectiveness
Solution Approach 1:
The patent incorporates feedback mechanisms where the actual joint angles and velocities are measured and used to update the dynamic characteristics calculation. This feedback loop compensates for phase delays by continuously adjusting the compensation torques based on actual system response
Solution Approach 2:
The system calculates coupling torque compensation command values in advance based on predicted trajectory requirements. The first dynamic characteristics calculation unit pre-computes necessary compensation before execution, reducing the impact of phase delays during actual motion
3Device complexity
If servo control is performed at each axis independently, then control simplicity is maintained, but trajectory error occurs due to different response characteristics among axes
Solution Approach 1:
The patent merges independent axis controls by introducing coupling torque compensation that accounts for interactions between axes. The dynamics model combines information from all joint axes to calculate compensation torques, effectively coordinating the axes while maintaining individual servo control structures
Solution Approach 2:
The coupling torque compensation command values act as intermediaries between independent axis controllers. These compensation values mediate the interactions between axes, allowing each axis to be controlled independently while still achieving coordinated trajectory accuracy through the compensation mechanism
Data Source
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AI summary
In a trajectory control device (10) for an articulated robot, a first dynamic characteristic calculation unit (300) is provided with a high-frequency cutoff characteristic having a cutoff frequency which is lower than the natural oscillation frequency of the robot, performs filtering processing with respect to a joint-angle command value (θc), and outputs a processed joint-angle target value (θd). A second dynamic characteristic calculation unit (400) is provided with a high-frequency cutoff characteristic having a cutoff frequency which is lower than that of the first dynamic characteristic calculation unit (300), performs filtering processing with respect to the output from a coupling-torque compensation command value calculation unit (200), and outputs a processed coupling-torque compensation value (cd).