By Robert Hirschinger, Principal Engineer, Rockwell Automation
The EtherNet/IP network camp claims this protocol can handle integrated motion control, especially when you integrate it with CIP Motion.
Machine builders have historically separated networks based on the application. For motion, they have typically chosen Sercos and used EtherNet/IP for plant floor and enterprise communication. EtherNet/IP, however, can be used for integrated motion control, effectively dissolving this separation.
A linear topology helps reduce wiring and gives you the largest network options.
Integrated motion control on EtherNet/IP helps manufacturers precisely coordinate multiple axes within a single network architecture – managing high-performance motion capabilities on the same network used to manage information flow throughout the manufacturing and IT enterprise.
Not all Ethernet networks suit plant-wide control, as they have proprietary elements that exacerbate routing, translation, and programming tasks. But the use of standard Ethernet and IP network technology, such as EtherNet/IP, allows you to use one network architecture.
With the introduction of CIP Motion, EtherNet/IP supports machine control, eliminating the need for dedicated purpose motion networks. This support comes through application profiles where you set position, speed, and torque loops within a drive. The protocol was developed for a broad range of drives (Vhz, vector, and servo) and operating modes to simplify integration, programming, and support.
Add CIP Sync technology — the IEEE-1588 compliant Precision Clock Synchronization protocol, which is also mapped into the CIP object model — and multiple axes can be coordinated for precise, synchronized motion control. CIP Sync supports 100 ns distributed time synchronization on EtherNet/IP. It is used for any time-related services, including drive synchronization, critical data time stamping, time scheduled outputs, and time-stamped inputs, events, and alarms.
While EtherNet/IP offers all the features and capabilities of a Sercos interface, there is one short-term disadvantage — its controller axes/ms capability carries an estimated 20-25% higher overhead than the Sercos counterpart. The additional overhead will be a non-issue when ICE 2-based platforms are deployed, but to address this issue in the meantime, EtherNet/IP performance has been increased from 10,000 packets per second (PPS) to 20,000 PPS in order to support motion. For the vast majority of applications, these performance levels are more than adequate.
The benefits of choosing EtherNet/IP for integrated motion applications include:
• Reduced cost
• No need to purchase additional Ethernet modules, you can use the same modules used on other devices on the machine
• No need to run a separate fiber ring for drives; you can connect drives to the same EtherNet/IP trunk that supports other EtherNet/IP devices
• EtherNet/IP handles a range of devices, including drives, EOI and I/O. This feature reduces network integration, commissioning, and maintenance
• Each EtherNet/IP module manages up to 250 drives versus Sercos, which supports 16 drives
• Each EtherNet/IP module handles multiple controllers versus one for Sercos
• EtherNet/IP uses low cost media and device terminations (cat5 versus fiber), and offers embedded switches, which eliminates the need for external switches
• Ethernet throughput is 100 Mbit; Sercos is 8 Mbits
• Cyclic channel support for drive read/write attributes with single cycle update throughput
• 100 ns time synchronization down to the drive for synchronous drive operation and
1 ms event time stamping
• Updated servo loops with compensation filters for higher bandwidth drive operation
• Single network technology for all devices, with support for any mix of EtherNet/IP devices on a common subnet
• Integrated servo, vector, and Vhz drives with common configuration, programming, commissioning diagnostics, and drive maintenance
• Application-type servo loop configuration settings assures proper drive configuration based on the application
• Out of the box defaults simplifies drive commissioning, eliminating the need for auto or manual tuning in most cases
• Time-stamped motion alarms and faults
• Embedded switch for line and Device Level Ring (DLR) topology simplifies device connection. It also gives you point of failure drive and media information.
• Per drive network diagnostics simplifies network trouble-shooting and configuration
• A choice of topology options including star, line, and ring (high availability with Device Level Ring (DLR)). Sercos uses only the ring topology. With these topology options, drives can continue operation when a drive is removed or fails.
The EtherNet/IP module can support 8 drives/ms, with 35% bandwidth remaining for support of other class 1 and class 3 traffic. In addition to drive attribute, read and write support is available through the cyclic channel for single coarse update rate throughput, and registration arming and relative homing is supported through the event channel for single cycle throughput.
Migrating from Sercos to EtherNet/IP
In the late 1980s, the Sercos interface became the first open, digital drive network. Successful in the marketplace, it boasts more than one million installed nodes. Today, however, many machine builders want the advantages of using one network infrastructure. The good news is that Sercos and EtherNet/IP are similar from a programming, configuration and commissioning standpoint, thus simplifying the migration process. Plus, Sercos interface drives and EtherNet/IP connected drives can be mixed in the same chassis and fully coordinated, which protects your investment.
How to implement an EtherNet/IP-based Motion Application
Implementing an EtherNet/IP-based motion application requires the following steps:
1) Choose the appropriate drive, motor, and actuator devices
2) Select an EtherNet/IP topology for the machine
3) Configure, program, and commission the application
When selecting the appropriate hardware for an EtherNet/IP-based motion application, first consider whether the application requires a servo drive or vector/variable frequency drive (VFD). Consider motor type, desired performance/accuracy, power range, and other factors. With EtherNet/IP, the configuration, programming, commissioning and maintenance of both types of drives is the same.
CIP Motion in Ethernet/IP supports machine control. The programming is simple.
After selecting the drive technology, consider which EtherNet/IP network topology to deploy. Because EtherNet/IP-based motion uses standard, unmodified Ethernet, you have a broad range of topology options. The standard Ethernet implementation helps ensure compatibility with existing plant Ethernet infrastructure. Example topologies include linear (daisy chain) which minimizes wiring; Device Level Ring (DLR), which delivers single fault resiliency; and Star for connection of a broad range of devices. Drives can be integrated with other Ethernet devices including human-machine interfaces, distributed I/O, robotics, valves, vision systems, and smart actuators.
CIP Sync technology, the IEEE-1588 compliant Precision Clock Synchronization protocol, is used for any time-related services, including drive synchronization, critical data time stamping, time scheduled outputs, and time-stamped inputs, events, and alarms. Screen 2.eps
Next, configure, program, and commission the control system. To configure the control system, simply specify the catalog number of the drive, motor and actuator for automatic setting of the required parameters. The configuration information is saved in the machine project and automatically downloaded to the devices over EtherNet/IP on system powerup or when a device is replaced. The application program defines the motion sequencing using any of 41 motion instructions in ladder, ST, and SFC application program languages. These instructions provide basic motion control function – such as Jog, Move, and Fault Reset – as well as more advanced motion control, such as Position and Time Cam, Gear, Multidimensional Coordinated Motion, and Kinematics. Commissioning the systems involves powering up each drive and insuring proper tuning. In most cases, the default parameters assigned based on the catalog number specification are optimal and further tuning is not required. If additional tuning is required, integrated auto and manual tuning tools are available.
The last and arguably most important step is to maintain the entire system throughout its lifetime. Extensive diagnostics give you detailed information on the operation of the machine and help diagnosis issues. Fault and alarm information is time stamped to help identify the source of machine faults. When drives are replaced, the system automatically flashes the replacement drive to the proper firmware revision and downloads the configuration information over the EtherNet/IP connection.
Filed Under: Factory automation, Motion control • motor controls, Networks • connectivity • fieldbuses