Modular EtherCAT Concept

Introduction

A modular approach to machine design has many benefits, including flexibility, scalability, and improved efficiency. Modular machines are split into sub-sections with each sub-section containing all the mechanical and electrical devices, motors, sensors, etc. as well as corresponding application code, to work together to provide a functional segment in the manufacturing workflow. The advantages to modular design are realized when the modules can be re-used. Examples include multiple module instances in the same machine and modules replicated across multiple machines.

Special consideration should be given to the physical layout, EtherCATClosed ***EtherCAT is an open, high-performance Ethernet-based fieldbus system. The development goal of EtherCAT was to apply Ethernet to automation applications which require short data update times (also called cycle times) with low communication jitter (for synchronization purposes) and low hardware costs network topology, and the application code architecture to design a modular machine. Modular machines are well suited to distributed EtherCAT device topologies, such as the AKD-C/N drives, but can also be applied to other EtherCAT device(s).

Examples of Modular Machine Design Uses

  • Machine with Multiple Variants:
    1. Machine Variant = Base module + one, two, (or more) additional module(s)
    2. Base Module - Each machine variant has the same base set of EtherCAT devices.
    3. Additional Module(s) - Each module contains one (or more) EtherCAT devices.
  • Module Maintenance:
    1. One (or more) modules are removed during machine operation.
    2. The machine continues to operate with the remaining base + module(s).
  • Share Modules across Machines in a Factory Line:
    1. Remove a module from machine A.
    2. Continue to operate machine A with the remaining base + module(s).
    3. Move the module to machine B.

Modular Design Guidelines

The following sections provide some helpful guidelines for modular design:

Start with the full topology of EtherCAT devices planned for the maximum machine configuration. Perform an EtherCAT scan to discover the full set of EtherCAT devices and save the project file. Then, the PLCClosed "Programmable Logic Controller" A Programmable Logic Controller, PLC, or Programmable Controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. Used to synchronize the flow of inputs from (physical) sensors and events with the flow of outputs to actuators and events code in the KAS project can be adapted to handle the cases where modules containing EtherCAT devices are disconnected and removed for different machine configurations, maintenance, etc.

The first EtherCAT device with Distributed Clocks (DC) must be included in the base module. A Kollmorgen drive (AKD, AKD2G, etc.) would be a good choice for the first EtherCAT device. The first EtherCAT device with Distributed Clocks and all devices upstream from the DC device cannot be disconnected/removed.

Map the axes to the drives for the maximum EtherCAT topology. The axis to drive map will remain consistent if drives are disconnected/removed. Whether drives are disconnected and removed from the end or from the middle of an EtherCAT network, the axis to drive map relationship will remain the same.

The PLC application code will need to adapt to the disconnected/removed devices. Because disconnected drives will behave as simulated axes/drives, the application code can perform many normal axis operations without code adaptations. This capability provides flexibility for how the application code is designed to handle disconnected/removed drives.

FSoE Masters may not support modular EtherCAT designs. If a safety device is disconnected and removed, the FSoE master will not allow normal machine operation.

Also see ECATDeviceAction for information on how to add the ability to connect/disconnect an EtherCAT device to your program..

Backing up Modular EtherCAT devices

The following steps should be taken to backup EtherCAT devices when the modular EtherCAT feature (see Modular EtherCAT Concept for more information) is used to remove devices to create a machine variant.

  1. Run the KAS application which sets up the correct EtherCAT topology for the machine variant.
  2. Stop the KAS application.

    • Do not power cycle or reboot the controller between steps 2 and 3.
  3. Backup the EtherCAT devices (see Backup Steps).

Limitations

  • The first EtherCAT device with Distributed Clocks cannot be disconnected/removed and must remain the same. Only devices downstream from the first DC device can be removed.
  • The device topology order cannot be rearranged.
  • The Modular EtherCAT features are not supported with imported ENI files.

The feedback position will become zero if the device providing the Feedback Position for the Digitizing axis is removed using the ECATDeviceAction function block. The feedback position data coming from the device will automatically be connected to the digitizing axis when the device is reconnected to the EtherCAT network.

Currently the Restore function only supports conditions where the network topology exactly matches the topology of the EtherCAT devices backup.

There are a number of permutations and combinations which are possible when the Modular EtherCAT feature is used to create a machine with multiple variants. If a machine has a base EtherCAT module and a varying number of optional EtherCAT modules then it is recommended that multiple backups are created: a base EtherCAT module backup, and an optional EtherCAT module backup.

Example

The system shown below has a base EtherCAT module and a varying number of optional type "A" modules and type "B" modules.

We recommend that EtherCAT Devices backups be made with the following configurations in order to meet different scenarios.

  • Backup #1: Base EtherCAT Module + one of Optional Module Type A
  • Backup #2: Base EtherCAT Module + one of Optional Module Type B

With the two EtherCAT Devices backups, you may be able to easily restore various combinations by removing the other Optional Modules, keeping only the module you need to restore.