EtherCAT® Motion Controller

In the landscape of modern industrial automation, the demand for connectivity, data throughput and synchronization has influenced the development of various fieldbuses. As manufacturers adopt Industry 4.0 standards, the network connecting the control system to the machine hardware is a relevant consideration. For engineers and system architects, the EtherCAT motion controller represents a widely used solution for general connectivity, offering determinism and flexibility that differs from traditional Ethernet and older serial buses.

While proprietary high-performance protocols like Aerotech’s HyperWire^® use fiber-optic transmission to achieve higher bandwidth and synchronization for demanding precision motion control applications, EtherCAT serves as a standard for integrating a broad range of third-party devices. This guide explores the architecture and implementation of EtherCAT, providing technical context for automation strategies.

What is an EtherCAT motion controller?

An EtherCAT motion controller is a centralized or distributed control device that uses the EtherCAT (Ethernet for Control Automation Technology) protocol to communicate with servo drives, I/O modules and sensors. Unlike standard TCP/IP Ethernet, which is non-deterministic, EtherCAT is designed for real-time industrial automation applications.

At its core, the EtherCAT motion controller acts as the "MainDevice." It generates trajectory points for the motion profile and transmits them to the "SubDevices" (drives) over standard Ethernet cabling.

The "Processing on the Fly" Principle

EtherCAT communication uses a method known as "processing on the fly." The EtherCAT motion controller sends a single Ethernet frame containing data for multiple devices on the network. As this frame passes through each node (drive or I/O module), the following happens:

• The device reads the data addressed to it.

• The device inserts its own feedback data into the frame.

• The frame continues to the next device immediately.

This mechanism manages bandwidth by reducing the overhead associated with small data packets. While this method supports data transfer efficiency, synchronization between axes is managed separately through EtherCAT’s Distributed Clocks mechanism, which compensates for propagation delays.

EtherCAT Communication Structure

EtherCAT communication involves a hardware component located within the drives known as the Fieldbus Memory Management Unit (FMMU). This component functions by mapping logical addresses from the controller directly to the drive's physical memory space. The controller, or MainDevice, interacts with the network as a single memory block, writing command positions to specific logical addresses. On the drive – or SubDevice – side, the FMMU hardware directs data to the appropriate register. This process allows the drive's processor to maintain its servo loop operation without interruption for data packet parsing.

What are the different types of EtherCAT motion controllers?

Controllers can be categorized based on their hardware architecture and their specific industrial functions.

PC-Based Software Controllers

Systems often use a PC as the EtherCAT controller. In this configuration, the MainDevice functionality is implemented via EtherCAT software running on a real-time operating system (RTOS) or a dedicated core of a PC. This configuration allows for path planning and integration with HMI (Human Machine Interface) software.

Standalone Hardware Controllers

Dedicated industrial controllers equipped with an EtherCAT port are an alternative to PC-based systems. These devices are used in environments where a PC may not be suitable or where a DIN-rail mounted solution is preferred.

EtherCAT CNC Controller

An EtherCAT CNC controller is a subtype designed to handle G-code execution for machining tasks. These controllers manage multi-axis motion for applications like milling or cutting, using the protocol’s capability to handle I/O and motor feedback.

Does EtherCAT require special hardware?

EtherCAT implementation involves specific hardware requirements for the MainDevice and SubDevices.

The EtherCAT MainDevice

The EtherCAT MainDevice functionality typically operates on a standard Ethernet port (NIC) without requiring specialized plug-in cards. The network management relies on the EtherCAT software stack.

The EtherCAT SubDevices

SubDevices, such as motor drives or sensors, require a specific ESC chip. This hardware facilitates the "processing on the fly" method by allowing devices to read and write data without the delays associated with software stacks at the node level.

Do I need a special switch?

EtherCAT networks typically avoid standard Ethernet switches to prevent unpredictable latency. Devices are generally connected in a line or daisy-chain topology. For star topologies, a specialized EtherCAT junction is used instead of a standard switch.

What is the difference between a full EtherCAT motion device and a fiber-optic motion bus?

The primary distinction between a full EtherCAT motion device and a fiber-optic motion bus lies in the physical transmission medium and the resulting data throughput. EtherCAT motion devices typically rely on standard Ethernet cables operating at 100 Mbps, which serves as a standard for interconnecting a wide variety of industrial devices. In contrast, fiber-optic buses like Aerotech’s HyperWire use glass optical fiber to transmit data, achieving a bandwidth of 2 Gbps. This increase in bandwidth supports extensive data collection and higher frequency control signals, exceeding the capacity limits of standard Ethernet connections.

Beyond data speed, the choice of bus impacts the precision and reliability of the control system. While EtherCAT uses distributed clocks to manage synchronization for general automation, specialized solutions like HyperWire provide virtually zero jitter for multi-axis applications requiring nanometer-level synchronization. Additionally, because HyperWire uses optical transmission, it is immune to electrical noise, maintaining signal integrity in industrial environments where copper-based standards may be susceptible to interference.

How do I know if I should use an EtherCAT motion controller?

Implementing an EtherCAT-based system involves evaluating connectivity needs against performance requirements.

High Node Count and Connectivity

For systems integrating many axes or I/O points over large distances, an EtherCAT MainDevice supports up to 65,535 devices on a single segment. This capacity is relevant for large-scale factory automation.

Multi-Vendor Ecosystem

EtherCAT is an open protocol, allowing for the integration of components from different vendors. An EtherCAT motion controller can facilitate communication between motors, sensors and I/O blocks from various manufacturers.

Bandwidth and Synchronization Considerations

EtherCAT typically operates at cycle rates between 1 kHz - 4 kHz with a bandwidth of 100 Mbps. Applications requiring higher bandwidth – such as extensive data collection at 200 kHz or high-precision control – may benefit from proprietary buses like HyperWire, which operate at a cycle rate of 100kHz and bandwidth of 2 Gbps. Additionally, while EtherCAT uses Distributed Clocks for synchronization, fiber-optic solutions like HyperWire offer lower jitter, which can be a factor in high-performance multi-axis applications.

Will an EtherCAT motion controller be compatible with my setup?

Compatibility considerations are relevant for projects involving legacy equipment or mixed technologies.

Integration with Other Technologies

An EtherCAT motion controller can function as a gateway. Many controllers support bridge modules for communicating with protocols like PROFINET, EtherNet/IP^® or Modbus TCP, allowing the EtherCAT communication network to share data with a plant-wide PLC.

Hybrid Systems: Automation1 and EtherCAT

EtherCAT can be used in conjunction with precision controllers like Aerotech’s Automation1. In this configuration, the Automation1 motion controller acts as an EtherCAT Controller SubDevice generating high performance trajectories communicated over HyperWire within a larger EtherCAT network. This setup uses EtherCAT for auxiliary functions or third-party devices while reserving the fiber-optic bus for precision-dependent axes.

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