Scanner card smooths Smart Pump pumping arm
Fill 'er up, Robby. Robot arms, similar to those that build autos, will soon be gassing them up too. Realizing this refueling vision wasn't easy, but it was recently achieved with the help of a device-level network and scanner card.In 1993, Shell Oil Co. (Houston, Tex.) asked the robotics division of International Submarine Engineering Ltd.
Fill 'er up, Robby. Robot arms, similar to those that build autos, will soon be gassing them up too. Realizing this refueling vision wasn't easy, but it was recently achieved with the help of a device-level network and scanner card.
In 1993, Shell Oil Co. (Houston, Tex.) asked the robotics division of International Submarine Engineering Ltd. (ISE, Port Coquitlam, B.C., Canada) to design and build a completely autonomous refueling system. Conceptual development and prototyping took several years and yielded early prototypes that were entirely hard-wired. This voluminous wiring was expensive, hard to test and rewire, and also caused significant electrical noise problems.
"Just the cost of all the conduits necessary to carry the sensor leads back to a central processor would have been exorbitant," says Mike Macdonald, ISE's executive vp. "So we wanted to go with a distributed sensor network of some kind because our I/O points were spread across the robot arm, and almost all the wiring had to go through flexible couplings and links."
Less wiring, more flexibility
ISE eventually chose DeviceNet's device-level network and a PC/104 DeviceNet scanner card from SST (Waterloo, Ontario, Canada), which is part of Woodhead Connectivity. Besides main power and a few serial links that had to be maintained, SST's DeviceNet card was able to handle all data and control, including the arm's approximately 20 servo-valves and on-off valves.
PC/104's ability to minimize costly wiring made room for Smart Pump's fuel hoses, motor wiring, and pneumatic hoses, which also run through the arm's flexible couplings. Smart Pump's five flexible couplings include three gantry cable tracks and two rotational links at the refueling tool.
During the arm's development, ISE engineers found using a sensor network like DeviceNet meant evolving I/O device requirements no longer needed major redrawing, rewiring, or testing. Changes could be localized to the immediate area around one node. They also discovered that PC/104 handled all DeviceNet-related protocol, which meant engineers only had to identify what nodes they wanted to scan and indicate parameters associated with that node. This allowed ISE to devote more software development time to the arm's system and control capabilities.
In beta testing since April 1997, Smart Pump's prototype has a gantry with bridges going fore and aft, up and down, and left and right across the car. This requires three separate motors, each with a node controlled by the PC/104 card. Another node is housed in the control compartment's purge container. These allow Smart Pump to sense, grab, and open fuel doors on either side of a car; insert its nozzle through a special transponder-enabled gas cap and pump fuel; and finally reverse these steps once the gas is safely loaded.
"For us, DeviceNet eliminated wiring, reduced costs, and improved noise immunity," says Mr. Macdonald. "It's performance was essential in getting us to the final prototype. This project wouldn't have been feasible without a distributed sensor network." ISE may also use DeviceNet and SST's PC/104 card to run diagnostic utilities to find electrical and mechanical problems in future SmartPump systems.
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