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Some robots like it hot
Unique cam is key to design of a robotic welder that repairs steam pipes-from the inside
Joseph Ogando, Senior Editor -- Design News, September 2, 2001
New York — New York—Hot, tight spaces are no problem for WISOR. This robotic repairman carries out machining and welding operations inside the city's steam pipes, where temperatures can reach 300F. And though it measures eight feet long and weighs upwards of 700 lbs, WISOR plies its trade in pipes that narrow to just 16 inches across. It's an operating environment that would give most industrial robots a bad case of claustrophobia, not to mention the sweats.
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WISOR, a robotic welder, has three sections. The first performs a machining operation to clean the flange joints prior to welding; the middle handles the robot's incheworm-style propulsion; and the third contains the arc-welding head. |
Honeybee Robotics Ltd., which created WISOR for Consolidated Edison, already has plenty of experience designing for temperature extremes. The company built its reputation with small-but-powerful robots that collect geologic samples during space missions. And WISOR' s space design draws on the company's work for NASA, according to Honeybee Senior Engineer Roopnarine. "Every single component on WISOR has to withstand high temperatures—every bearing, every O-ring, every motor," he says, explaining that the thermal requirements not only made parts sourcing more difficult but also complicated the overall design. WISOR, for example, sports thermally evacuated walls and air guns to cool its electronics. And the sweltering working environment also affected the Honeybee's ability to squeeze WISOR's components into a package as narrow as 10 inches around. "High-temperature components aren't usually the same thing as miniature components," Roopnarine notes.
Yet despite the importance of thermal requirements, WISOR's biggest innovations have little to do with its ability to take the heat. The robot also features mechanical solutions to a big problem: How does one large robot move and work inside pipes that vary in size from just 16 to 24 inches?
The solution comes from the robot's worm-like layout and motion. WISOR consists of three connected sections. Steel-encased front and rear modules respectively house WISOR's milling and welding heads, as well as identical sets of three retractable legs. Between these two modules, the robot consists of a telescoping section whose high-temperature-rubber cover conceals air-motor and a lead screw. With the legs from either module braced against the pipe wall, this middle section muscles the rest of the robot in the other direction—for a top speed of 135-inches every half hour. "It essentially moves like an inchworm," says Roopnarine.
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A unique cam drives WISOR's three legs into the surrounding pipe walls at a constant force, keeping the robot centered during machining and welding operations. |
A related design challenge involved the three equally spaced legs that extend from within the milling and welding modules to brace the robot against the pipe walls. Regardless of variations in the pipe size, the leg system has to keep WISOR precisely centered as the milling and machining heads rotate along the interior walls. And for the inchworm motion to work, the legs have to prevent WISOR from slipping along the walls. "You need a high force against the walls during locomotion," says Roopnarine, pointing out that the heavyweight robot drags a steel-jacketed umbilical cord that carries air, power, and video signals.
Honeybee engineers tackled the bracing requirements in two ways. First, they added interchangeable extensions—or "feet"—that let the legs reach well beyond their two-inch stroke. The engineers also came up with a limited-rotation cam that drives all three legs into the pipe wall at a constant force. "No matter how far the legs are extended, they each exert 400 psi on the pipe," Roopnarine says.
This air-actuated cam consists of a half-inch-thick steel disc incised with three grooves that curve from the center of the cam disc toward its outer edge. A roller rides in each groove and connects to the bottom of a leg, whose outward translation corresponds to the position of the roller in the grooves. According to Roopnarine, the key to the cam's ability to keep the legs at a constant force is the groove's patented profile. "We use a nautilus profile," he reveals.
Currently in final testing, WISOR is slated to hit the pipes this month.
| Additional Details | ||
| Contact Roopnarine, Honeybee Robotics Ltd., 204 Elizabeth St., New York, NY 10012; Tel: (212) 966-0661; E-mail: roop@hbrobotics.com ; or Enter 502 | ||
