5 trends in wireless motion control
Wireless control of robotics can be achieved by implementing control of an automated guided vehicle (AGV) upon which a robot can ride. Alternatively, with an appropriate safety protocol present, one could implement robot control via mobile device, according to a June 17 Control Engineering interview with Rob Snyder, Rockwell Automation product manager, at RSTechED in Orlando.
Ensuring a reliable connection with low latency and jitter can best be achieved with an industrial access point (AP) and wireless client. The wireless client for machine and skid applications is a very important piece of the connection, Snyder said, as important as having capable APs and often overlooked when planning a wireless implementation.
Wireless robotic connections
Wireless automation can be applied in a wide range of implementations, Snyder said. Some applications could:
1. Communicate wirelessly even for fixed nodes, additional human machine interface (HMI) terminals or connecting an existing “island of automation” for data harvesting, for instance.
2. Wirelessly track or position a robot, relaying positional information from the moving unit to the wayside (fixed) network.
3. Send wireless alerts about robot status to mobile tablets, smartphones, or smart watch-like interfaces, which can function like a smarter pager.
4. Make robots mobile on AGVs to serve multiple workstations or move where needed, part of an interesting efficiency trend in some applications where the machine is more mobile and parts more fixed. (Less refixuring in parts production can save significant time, increasing manufacturing efficiency.)
5. Communicate signals to robot end effector.
While wireless could be used for transmitting signals to robotic tools (end effectors), Allen-Bradley EtherNet/IP modules with QuickConnect reduced wired connection speed to less than 360 ms, decreasing robotic downtime between tool changes and reducing maintenance costs, Snyder said.
Wired and wireless
Even with industrial wireless communications, though, wired communications are needed at some point in the system and should be taken into consideration, Snyder noted. Rockwell Automation offers the Stratix 5100 Wireless Access Point/Work Group Bridge uses IEEE 802.11 a/b/g/n wireless, which supports Ethernet. EtherNet/IP Ethernet protocol can be used for the wired and wireless communications. EtherNet/IP extensions, CIP Motion and CIP Sync from ODVA CIP (common industrial protocol) family, are "only very cautiously (limited) recommended" for use over a wireless connection; see "Wireless Design Considerations for Industrial Applications" below for more detailed recommendations, Snyder said.
While CIP Motion is not recommended for use over wireless, wireless control of "motion" is certainly possible. "Depending on application performance requirements," Snyder said, "one could employ the use of Produce/Consume Virtual Axis techniques over wireless."
Check the skillset
For those seeking to only save on wire installation costs, wireless may not be the best choice, Snyder noted, because wireless requires a different skill set and different level of commitment than wired networking. However, wireless normally can offer much more value than just replacing the wire by enabling greater efficiencies, related to a more mobile and informed workforce (uptime and troubleshooting), cloud usages, and big data analysis. (See related article: Mobility apps should provide self-direction, portability, freedom.)
With wireless installation, Snyder recommended following best practices, such as performing a site survey to determine environmental conditions (microwaves, metal infrastructure, and moving assets), the best AP locations, and optimal frequency and channel selection. Working with, rather than against, the IT department will result in a better installation.
"In most cases, IT will have established wireless media within the factory zone. A collaborative relationship between IT and operations / automation is key to success. Personalities may precede the performance of protocol packets," Snyder added; "wireless is truly a shared media."
– Mark T. Hoske, content manager, CFE Media, Control Engineering, firstname.lastname@example.org.
Rockwell Automation offers PDFs on related wireless resources: