May 2019

n TECHNOLOGY May 2019 www.drivesncontrols.com 18 RESEARCHERS AT MIT (the Massachusetts Institute of Technology) in the US have developed a system that uses RFID (radio- frequency identification) tags to help robots home in on moving objects with “unprecedented” speed and accuracy. Using the system, called TurboTrack, robots can locate tagged objects within 7.5ms on average, and with an error of less than 1cm. The system could enable robot arms to be more precise and versatile when, for example, picking up, assembling, and packaging items on assembly lines. The researchers believe that it could replace computer vision in some tasks. An RFID tag is attached to the object being tracked. A reader sends a wireless signal that reflects off the tag and other nearby objects. An algorithm sifts through the reflected signals to find the RFID tag’s response. The tag’s movement is used to improve the localisation accuracy. To validate the system, the researchers attached one RFID tag to a bottle and another to a bottlecap. A robot arm was able to locate the cap and place it onto the bottle, held by a second robot. The researchers believe that the RFID system could overcome some of the drawbacks of machine vision, such as limitations when viewing objects in cluttered environments. RF signals have no such restrictions; they can identify targets even in cluttered environments and through walls. “If you use RF signals for tasks typically done using computer vision, not only do you enable robots to do human things, but you can also enable them to do superhuman things,” says Fadel Adib, an assistant professor and principal investigator in the MIT Media Lab, and founding director of the Signal Kinetics Research Group. “And you can do it in a scalable way, because these RFID tags are only 3 cents each.” Although there have been other attempts to use RFID tags for localisation tasks, they have usually involved trade-offs in either accuracy or speed. To be accurate, it can take them several seconds to find a moving object; if they increase speed, they lose accuracy. The challenge for the MIT researchers was to achieve both speed and accuracy simultaneously. Their system combines a standard RFID reader with a “helper” component that’s used to localise the RF signals. It shoots out a wideband signal containing multiple frequencies, building on a modulation scheme used in wireless communication, called orthogonal frequency-division multiplexing. The system captures the signals rebounding off any objects in the environment, including the RFID tag. The signal that’s specific to the tag reflects and absorbs an incoming signal in a pattern that the system can recognise. Because the signals travel at the speed of light, the system can compute a “time of flight” – measuring a distance by calculating the time it takes for a signal to travel between a transmitter and receiver – to gauge the location of the tag, as well as the other objects. MIT’s work was sponsored, in part, by the US National Science Foundation. RFID helps robots to track objects and could replace machine vision systems NORD HAS ANNOUNCED a range of cabinet-mounting inverters whose functions can be extended using plug-in control, safety and option modules. The bookshelf-format Nordac Pro SK 500p inverters span ratings from 0.25– 5.5kW and can be mounted side-by-side. The inverters have built-in PLCs and can operate in open- or closed-loop configurations, as well as controlling both synchronous and asynchronous motors. Precise current vector control can optimise torque in various load and speed situations and offers reliable operation with high overload reserves. Brake choppers for four- quadrant operation are built in, as are a motor brake management capability, and STO and SS1 safety functions. An industrial Ethernet multi-chip allows most real-time Ethernet standards – including ProfiNet, EtherNet IP, PowerLink and EtherCat – to be used via a single interface. The inverters can also be parameterised via a USB port without needing an external power supply. Also available are: five or six digital and two analogue inputs; two digital and one analogue outputs; two potential-free relays; an HTL /TTL incremental encoder interface; and an encoder interface. As well as fully equipped“application inverter”versions, there are also“machine inverter”versions with fewer interfaces, but still offering a built-in PLC, closed-loop control and positioning. www.nord.com Bookshelf inverters can be extended using plug-in modules In a test of their RFID-based location system, the MIT researchers used it to place a cap on a bottle held by a second robot