EtherCAT Network Optimization for the NexBot STD031-001 SCARA Robot

Related Products

Tools Required

• EtherCAT Master Configuration Software
• Network Analysis Software (Optional)

Article

The NexBot Robotics STD031-001 SCARA Robot is engineered for high-speed, high-precision tasks, achieving a repeatability of ±0.01 mm. This level of precision is heavily dependent on the integrity and performance of its underlying control network. This robot utilizes the EtherCAT protocol for its real-time communication between the controller and the servo drives for each of its four axes. Proper configuration of the EtherCAT network is critical to minimize latency and jitter, ensuring that the robot performs according to its specifications.

This bulletin outlines key considerations and best practices for optimizing the EtherCAT network for your NXB-ROB-STD031-001 robot.

Understanding EtherCAT in the STD031-001

EtherCAT (Ethernet for Control Automation Technology) is a high-performance, deterministic Ethernet-based fieldbus system. Its unique 'processing-on-the-fly' principle allows for extremely short cycle times and precise synchronization. For the STD031-001, this means that position commands from the controller are delivered to the J1, J2, J3, and J4 axis drives with minimal delay and that feedback from the motor encoders is returned in a highly synchronized manner. A poorly configured network can introduce communication jitter, leading to degraded path accuracy and reduced overall throughput.

Network Topology and Cabling

A stable physical layer is the foundation of a reliable network. While EtherCAT is flexible, following these guidelines is recommended for industrial environments.

• Topology: For a single STD031-001 robot, a simple line topology is standard. The EtherCAT master port on the controller connects to the 'IN' port of the first servo drive, and the 'OUT' port of that drive connects to the 'IN' port of the next, and so on. This daisy-chain configuration is efficient and easy to implement.
• Cabling: Always use high-quality, shielded industrial Ethernet cables specifically rated for EtherCAT applications, such as the NXB-CBL-NET522-008. Poorly shielded or damaged cables are a primary source of intermittent communication errors. Ensure connectors are securely seated and that cable bend radii are respected to avoid signal degradation.
• Grounding: Ensure proper grounding and shielding practices are followed for the entire system, including the robot, controller, and cabinet, to mitigate the effects of electromagnetic interference (EMI).

Master Controller Configuration

The majority of performance tuning occurs within the EtherCAT master configuration software.

Cycle Time

The cycle time determines how frequently the master sends new process data to all slave devices (the servo drives).

• Recommendation: The STD031-001 is designed to operate optimally with a cycle time between 1 ms and 4 ms. A faster cycle time (e.g., 1 ms) provides higher-resolution control but places a greater load on the master controller.
• Tuning: Start with a conservative cycle time (e.g., 4 ms) and verify system stability. If the application requires faster response, incrementally decrease the cycle time and monitor the controller's CPU load and network diagnostic counters. If you observe late frames or a CPU load exceeding 80%, the cycle time is too aggressive.

Distributed Clocks (DC)

Distributed Clocks is a critical EtherCAT feature for achieving the high level of axis synchronization required by the STD031-001. When DC is enabled, all slave devices on the network synchronize their internal clocks to a master clock, typically within a sub-microsecond range.

• Enable DC: Always enable Distributed Clocks for multi-axis coordinated motion. Disabling this feature will result in a noticeable degradation of path-following accuracy and may cause vibration during high-speed movements.
• Synchronization: The master controller's SyncManager (SM) and Frame Control Unit (FCL) events should be configured to align with the DC clock, ensuring that PDOs are processed at precisely the right moment. Consult your controller's documentation for specific settings related to 'Sync0' and 'Sync1' events.

Process Data Object (PDO) Mapping

PDOs contain the application data exchanged during each cycle, such as target position, velocity, and actual encoder position.

• Efficiency: Only map the PDOs that are strictly necessary for your application. Including superfluous data (e.g., diagnostic parameters that do not need to be read every cycle) in the real-time cyclic frame increases network load unnecessarily. Use acyclic communication channels (SoE/SDO over EtherCAT) for non-time-critical parameter access.
• Verification: After configuring your PDO map, verify that the total size of the EtherCAT frame does not exceed the MTU (Maximum Transmission Unit) and that it can be transmitted and processed within the selected cycle time.

Verifying Network Health

Regularly monitor the EtherCAT network's health, especially after making configuration changes.

• Working Counters: The most important diagnostic tool is the EtherCAT Working Counter (WKC). A correct WKC value indicates that all slave devices correctly received and processed the datagram. A persistent mismatch in the WKC points to a communication fault (e.g., a faulty cable, connector, or slave device).
• Lost Frames/CRC Errors: Monitor the master's diagnostic interface for lost frames or CRC (Cyclic Redundancy Check) errors. These errors often indicate physical layer problems, such as EMI or a damaged cable.

By carefully managing the physical network, optimizing master settings, and enabling key features like Distributed Clocks, you can ensure your NexBot Robotics STD031-001 SCARA Robot operates with the maximum speed, precision, and reliability for which it was designed.

Keywords