Guaranteeing Isochronous Control of Networked Motion Control Systems Using Phase Offset Adjustment.

Area of Science:

• Robotics and Automation
• Real-Time Systems
• Embedded Systems Engineering

Background:

• Networked motion control systems require isochronous command transfer for precision.
• Real-time Ethernet (RTE) offers deterministic communication but faces challenges from software unpredictability.
• Software jitter in motion controllers leads to deviations in control message intervals and imprecise motion.

Purpose of the Study:

• To present a simple, efficient heuristic for guaranteeing end-to-end isochronous control with minimal jitter.
• To address the challenge of unpredictable software behavior in achieving precise motion control over RTE networks.

Main Methods:

• A heuristic approach adjusting the phase offset of control message transmission times based on motion control task behavior.
• Pre-runtime analysis to determine a safe and reliable phase offset.
• Customizing an open-source integrated development environment (IDE) to apply the phase offset in runtime code.
• Constructing an EtherCAT-based motion control system testbed for experimental validation.

Main Results:

• The proposed heuristic effectively guarantees isochronous control with very small jitter.
• Demonstrated high effectiveness even on low-end embedded controllers using open-source software.
• Validated across various control periods and numbers of motor drives.

Conclusions:

• The heuristic provides a robust solution for achieving precise isochronous control in networked motion systems.
• The approach is practical and effective for real-time Ethernet applications, even with resource-constrained embedded controllers.
• Phase offset adjustment is a viable strategy to mitigate software-induced timing variations in motion control.