EtherCAT Master (aka MainDevice) and Motion Controller: Key Functionalities and Differences

Introduction

EtherCAT (Ethernet for Control Automation Technology) is a high-performance, Ethernet-based fieldbus system designed for real-time industrial automation. The system comprises two key components: the EtherCAT Master (now called MainDevice) and the EtherCAT Motion Controller. This document provides an in-depth analysis of the functionalities and differences between these two critical components of the EtherCAT network.
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Overview of EtherCAT Technology

EtherCAT is a high-speed communication protocol used in industrial environments. It enables real-time control and data exchange among devices like servo/stepper drives, IO hardware, sensors, vision, etc. EtherCAT's efficiency lies in its use of a unique frame-passing technique, allowing for fast and efficient data exchange.
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Key Functionalities

EtherCAT Master

• Network Initialization and Configuration: The EtherCAT master initializes and configures the EtherCAT network. This involves detecting all the EtherCAT slaves (devices) on the network, understanding their capabilities, and configuring them to operate as required. This process includes assigning addresses to the slaves and setting up the communication parameters.
• Managing Communication: The master controls the data exchange within the EtherCAT network. It sends Ethernet frame(s) that pass through each slave device. Each slave reads from and writes data to the frame as it passes, enabling highly efficient and fast data processing.
• Synchronization: One of the key features of EtherCAT is its precise synchronization capability. The master ensures that all the slaves on the network are synchronized with each other, often with very high precision. This is crucial in applications requiring coordinated motion control and precise timing.
• Error Handling and Diagnostics: The master continuously monitors the network for errors or faults in the slaves or the network itself. This includes managing retries or reconfigurations in case of communication failures.
• Network Topology Management: The master manages the topology of the EtherCAT network, which can be linear, tree, or a combination of these. It handles the addition or removal of slaves and adapts the communication processes accordingly.
• Safety Protocol Management: In safety-critical applications, the EtherCAT master manages the safety protocols, ensuring the communication and control processes adhere to the required safety standards.
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EtherCAT Motion Controller

• Motion Libraries: Typically include via software API to offer a wide range of predefined functions for common motion control tasks such as point-to-point movement, linear and circular interpolation, coordinated motion, gearing, camming, and more.
• Complex Motion Profiles: Enable easy implementation of complex motion profiles, which would be time-consuming and error-prone if coded from scratch. This includes advanced trajectories, speed profiles, and acceleration/deceleration patterns.
• Real-Time Control: Designed to handle real-time data processing, ensuring minimal jitter and latency. This is essential for applications that require real-time control and fast response times.
• High-Level Abstraction: By abstracting the low-level details of motion control, these libraries allow engineers to focus on the broader aspects of system design and application logic rather than the intricacies of motor control.
• Multi-Axis Motion Control: The ability to control multiple axes of motion simultaneously. This is crucial for coordinating complex movements in machinery like CNC machines, robotic arms, or conveyor systems.
• Programmable Motion Profiles: These controllers allow the programming of complex motion trajectories and patterns. Users can define each axis's acceleration, velocity, deceleration, and position and synchronize these parameters across multiple axes.
• Synchronization and Coordination: The ability to synchronize motion with external events or signals. This is essential in applications where the timing of the motion needs to be matched with other processes.
• PID Control: Proportional-integral-derivative (PID) control algorithms are used to maintain the desired motion parameters (like position, speed, and acceleration) accurately, compensating for disturbances and system variances. In EtherCAT, most drives run in position operating mode where the PID loop is closed inside the servo drives.
• I/O Control and Integration: Managing digital and analog inputs and outputs to interact with sensors, switches, and other peripheral devices. This includes reading sensor inputs to adjust motion parameters or triggering external events based on motion states.
• Conditional Logic Processing: Implementing conditional logic based on I/O states or internal variables. This allows the controller to make decisions and alter motion or outputs based on real-time conditions.
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EtherCAT and the RMP

The EtherCAT Master / MainDevice is tightly integrated with the RMP Motion Controller.  The EtherCAT network receives motion/IO control and targeting updates from the RMP every sample/network cycle.  It is crucial in applications requiring precise and coordinated motion control, such as robotics and CNC machines.
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Differences Between EtherCAT Master (MainDevice) and EtherCAT Motion Controller

An EtherCAT Master/Main Device is the central command and control unit in an EtherCAT network, a high-speed communication system used in industrial automation. The primary role of the EtherCAT Master is to manage and coordinate the data flow within the network. It initiates communication with all connected EtherCAT devices, known as slaves, and controls the overall data exchange process. The master is typically implemented on a PC or an industrial controller equipped with specialized software to handle the EtherCAT protocol. Its responsibilities include network initialization, device configuration, and error management. The master ensures that data packets are correctly and efficiently distributed to and from each device in the network, maintaining the system's overall performance and stability. 

On the other hand, an EtherCAT Motion Controller is dedicated to controlling and managing a specific type of EtherCAT slave device focused on controlling and managing motion-related tasks in automated systems. Unlike the EtherCAT Master, the RMP, through one of our RapidCode APIs, can precisely control motion, io, user limits, safety, and more.

The motion controller plays a critical role in ensuring that complex motion sequences are executed accurately and synchronously, which is essential in applications like robotics, CNC machines, and conveyor systems.
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Integration and Compatibility

Integrating an EtherCAT Master and Motion Controllers in a network requires careful consideration of compatibility, especially regarding the real-time requirements and the specific motion control needs of the application. It is essential to ensure that the Master's capabilities align with the Motion Controller's requirements for seamless operation.
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Conclusion

You want to use the RMP EtherCAT motion controller as it is a combination of the EtherCAT master stack (MainDevice) and also has full motion controller capabilities discussed in this article. Playing the role of a Master/MainDevice, RMP can seamlessly discover, establish, and maintain the network. We currently support over 50 manufacturers for seamless EtherCAT device integration. 

RMP also comes with software tools and motion libraries that make development simpler for OEMs. This way, OEMs can focus on their software development without having to invest in creating machine-specific motion and IO libraries.

Please click on the links below to learn more:

Knowledge Base

Software API
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Note on naming convention: The EtherCAT Technology Group has since renamed the Master and Slave keywords. “Since ETG does not intend to offend, we will use the terms MainDevice (abbreviated MDevice) and SubordinateDevice (abbreviated SubDevice). In our (new) documents, we will thus replace 'Master' with 'MainDevice' or 'MDevice' and 'Slave' with 'SubDevice' and will show the terms MainDevice and SubordinateDevice in the list of abbreviations. Source ethercat.org - section 1.5.