Communication protocols, often called Fieldbus, describe the set of rules to be used in communication between devices. The list of protocols used in today’s industrial robotics is quite large; here is a list of the main protocols and their characteristics.
The Common Industrial Protocol (CIP) family:
Managed by ODVA, CIP is a protocol that integrates control services, communication services, and routing capabilities based on Ethernet networks and the Internet. Each protocol differs from the physical link, data link, and network layer being used (see our previous post on the Communication protocols structure).
- EtherNet/IP: Ethernet Industrial Protocol is built on standard TCP/IP (IEEE 802.3) and communications use existing network infrastructure. Ethernet physical layer technology is used along TCP and UDP ports (44818 and 2222). Its main advantage comes from the inerrant progress of physical Ethernet, from 10 Mbits/s to 10/100 Mbits/s to 1 Gbits/s and more. EtherNet/IP also ensures Internet and enterprise connectivity for remote control.
- ControlNet: Built on its own physical and data link layer, ControlNet uses a single media link with (inexpensive) RG-6 coaxial cables and bus. It features a 5Mbits/s speed, upload/download of data, P2P communication, and up to 99 nodes.
- DeviceNet: Uses Controller Area Network (CAN-bus) as a backbone for physical and data link layer. CAN-bus consists of a host processor, a controller, and a transceiver linked by 2 twisted pair cables. Bit rates go from 1 Mbit/s at 40 m to 20 Kbit/s at 1200 m. DeviceNet uses the master/slave mode; it can have up to 64 nodes and the physical network can provide power to the devices (with limited consumption).
Other important protocols used in the industry:
- Modbus: Based on the master/slave mode and having up to 247 nodes, Modbus has many protocol versions depending on the physical layer being used. Every version uses the same base communication going from start, address, function, date, error check, and end. Some versions of Modbus:
- RTU (remote terminal units) using binary representation.
- ASCII using characters.
- Profibus: Using master-slave, slave-slave, and master-master communication on a bit serial field. The physical layer can be a twisted pair cable delivering power to the device and providing 9.6 kbit/s to 12 Mbit/s (maximum 1200 m) or an optical fiber cable.
- EtherCAT: Ethernet for Control Automation Technology is based on the Ethernet technology and uses twisted pair cables or coaxial cables with BNC adapters on a short distance (1000 m max.) and an optical fiber cable over long distances. Transfer rates are based on the Ethernet technology being used and EtherCAT can control up to 65535 nodes.
- CC-Link: An open protocol for industrial networks that include protocols for the information network, the controller network, and the device field network. The version of CC-link depends on the physical layer being used. The protocol can normally have up to 64 nodes and have speed going from 10 Mbps at 100 meters to 156 Kbps at 1200 meters.
We can see that many of the protocols used are based on either Ethernet with TCP/IP networking or serial cables with trademarked networking protocols. The communication protocols used in industrial robotics vary mostly from the features of the application layer (upper layer), although the performance is often determined by the physical layer (lowest layer).
Communication protocols supported by the different devices can cause high integration cost (and technical nightmares). When will we see a real standard supported by all robots and peripherals by default, just like in the computer industry? Until then, download our cheat sheet to figure out which robot speaks what protocol.
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