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Feature Articles

Machine Vision Fights for a Node on the Network

by Winn Hardin, Contributing Editor - AIA

Tuyen Duong, a process engineer at a wireless component manufacturer, just installed an automated optical inspection (AOI) system on a new production line. While the main reason for the system is tweaking new ceramic manufacturing process, Duong said that one of the most valued features that he uses each day is the ability to review a day's worth of data from his office desktop; in other words, remote access across the plant network.
"A main reason for networking machine vision systems is process enhancements," explained Mark Sippel, vision product marketing manager for Omron (Schaumburg, IL). "But it's also that human inclination toward wanting to visually see what went wrong. Think about it. A temperature controller doesn't need a lot of LED read outs to operate, but we want to see it, to know what caused it. It plays to our instinct to see the actual bad part."

Beyond the host  
Groups like the Automated Imaging Association (AIA) along with corporate partners have helped to develop standards like CameraLink and adopted other consumer networks like Firewire (IEEE 1394) to transmit high-bandwith images between the camera and the host processor, but getting that information out across the larger network remains an elusive goal. Many machine vision systems have the ability to store still images, which can be accessed from the desktop's hard drive, but when it comes to the major industrial network protocols, real time high-resolution video transmission remains an area for development.
"Communication to other devices is always important," said Mike Scheiber, technical support specialist at DVT Corp. (Norcross, GA), particularly when it comes to robot guidance. "We spend a lot of time to make data available to anything out on the factory floor. We work on EtherNet/IP, Allen Bradley, Motoman, Fanuc, ABB, etc., just to make life easier to our end users. You have to be able to get the data out."

Plant managers have several main networking protocols to choose from today: Allen-Bradley's DeviceNet, Siemens Profibus, the Actuator Sensor Interface (AS-Interface), and Ethernet. In addition to these protocols, champions for each protocol are developing "safety" version that allows the network to include deterministic priority communications to control safety mechanisms on the network and insure that packets of information reach their end node within a certain maximum time limit.

Safety and speed
According to several US vendors, Profibus and AS-Interface typically are deployed in Europe with less emphasis in the US. Allen-Bradley's DeviceNet has a large installed base in the US, and Ethernet is a growing player in the industrial arena because of the growing industrial base and low-cost networking components.
Working with Allen-Bradley and others, Omron and SICK (Bloomington, MN) helped to create the DeviceNet Safe protocol, "...but we haven't had much demand ...beyond the confines of networks already using DeviceNet," said Omron's Sippel. "What's interesting is the push to use Ethernet/IP as the implemented protocol, and that's where the interest has been."
Although Omron continues to support DeviceNet protocols, Sippel adds that Ethernet/IP offers several advantages over competing communications methodologies including distance and bandwidth. "Ethernet offers 100 Mbaud compared to DeviceNet's 500 Kbaud. Ethernet has huge advantage in regards to distance because of repeaters and hubs compared to serial [RS232] communications. This allows you to distribute a single vision system along the entire process, spreading the cost of the vision system along the production line and network products together to a single controller, which makes the whole process more simplistic."
When safety and deterministic communication or priority communication are not mission critical, Ethernet TCP/IP can significantly ease the set up of distributed AOI networks. "The Impact product line is TCP/IP compatible and allows multiple [network] clients to access and control the system," said Bob Kuhl, director of product development for PPT Vision (Eden Prairie, MN).
The industrial protocol version, Ethernet/IP, offers two additional advantages compared to standard TCP/IP communications: static addressing and information reliability. While static addressing requires specific addressing of each node by an IT administrator in many cases, it helps to insure reliability in the transmission time and allows for built in redundancy in the network, which might be compromised by continually shifting network addresses.
Redundancy is a crucial element to safety that is its way into safe PLCs, according to SICK's product manager for safety systems Jim O'Laughlin, if not yet into vision systems. "Traditional PLCs are not control-reliable devices, which led to the Safe PLC. "Safe PLCs typically utilize multiple processors to provide this redundancy as well as evaluate the software and hardware to detect any fault conditions," O'Laughlin said. "Now that I have this safety-rated controller, the question becomes how do I talk to it. Without a safety-certified protocol, I have an element that's not control reliable and safe networks are only as good as the weakest link."
Fixed networks that are safety-certified are critical to creating safe networks that alleviate the need to hardwire safety mechanisms as dictated by national consensus standards such as B11.19.  Similarly, its easy to envision how AOI systems could benefit from control-reliable, high-bandwidth transmissions, especially in terms of closed loop control of processes in manufacturing when real time data is critical to maintaining efficient production.

Flexible networks are key 
AIA's sister organization, the Robotics Industry Association (RIA) director of safety Jeff Fryman said that his organization is carefully monitoring the development of safety networks, but that more work is needed. "RIA's working on a technical report on communications for FTP and Ethernet, but not safe Ethernet just yet. We know it's under development, but it's not quite there yet," Fryman said.
In the meantime, AOI vendors must choose which network protocols to accommodate and how much. Speaking on Cognex's Insight line of smart sensors, product manager Carl Gerst said, "There are capabilities built into the product to support low level networking elements like FTP, or telnet connections and others. So the capability is there, but the user interfaces need to be developed to hide those low level networking elements behind intuitive buttons that do it all. That's where we're going," Gerst said.

For plant mangers considering the importance of control reliable networks, SICK's O'Laughlin shares that some plants have considered running two separate networks until they prove to themselves that safety protocols will not lack performance. Once satisfied, the networks can be joined relatively easily. In the meantime, the vision industry will have to continue to work with champions of networking protocols to include greater bandwidth for image and video data, bringing new levels of functionality and remote access to safer, more secure networks.









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