Sun shines on servomotor

Nov. 1, 2003
North Dakota may not be the sunniest place on the map, but that didn’t stop the Sunsetters, a solar race team from North Dakota State University, from placing first in the Stock class of the American Solar Challenge in July

North Dakota may not be the sunniest place on the map, but that didn’t stop the Sunsetters, a solar race team from North Dakota State University, from placing first in the Stock class of the American Solar Challenge in July. The 10-day, 2,300- mile race — the world’s longest solar vehicle race — took the students from Chicago to Los Angeles along Route 66. Teams participated in either the Open or Stock class of the race, which is comparable to professional and amateur, respectively.

The NDSU vehicle, Prairie Fire GT, was the only solar racer with an electric motor built by a conventional motor manufacturer, Bodine Electric Co. of Chicago. All the other teams used electric motors specifically built for solar racing, which can cost as much as $17,000 each. The Bodine Electric e-TORQ motor is a high-torque industrial servomotor typically used in packaging and converting machinery and medical equipment. The 14-in.- diameter motor produces about 10 hp with more than 90% energy efficiency. (See It’s in the gap.)

“The e-TORQ motor helped us achieve our goal of building a cost-effective car. It performed flawlessly while other teams had numerous problems with their motors,” said Keith Richtman, the Sunsetters mechanical engineering team leader and co-driver.

It’s in the gap

• Zero cogging at low speeds
• High accuracy
• High torque (up to 100 lb-in. at 6,000 rpm)
• Quiet, smooth operation
• Alternative to planetary gearmotors
• High torque linearity

There’s more than one way to convert electrical current into mechanical torque. Most motors pass current through a coil, generating an electromagnetic force that acts across a radial air gap — the space between a cylindrically shaped rotor and its corresponding stator. This classic design is a reflection of Michael Faraday’s early work in electromagnetism and how he envisioned magnetic fields.

Another way to produce torque is to arrange the current-carrying coils into the form of a disc. The corresponding electromagnetic force propels a discshaped rotor, acting across the space between the facing flat surfaces of the rotor and stator. Such axial-gap motors employ principles developed by H.A. Lorentz.

Although radial-gap motors are the most common, they are not the most efficient. Their magnetic and mechanical forces are in a constant state of contention, always trying, in a sense, to “reshape” the motor. By contrast, the forces that drive axial-gap motors are more optimally aligned, resulting in almost no mechanical energy loss. Energy optimization, in turn, means that axialgap motors can produce high peak torque, eliminating the need for gearheads in certain applications.

In the case of Bodine Electric Co.’s e-TORQ motors, optimization goes one step further. Instead of an iron core, e-TORQ stators consist of wire and nonferrous materials. This eliminates iron saturation common in most other motors, and allows the motor to run smoothly at extremely low speeds, even when powered by a standard drive.

Packed in Las Vegas

There was a lot more than usual to see in Las Vegas Oct. 13 to 15, as more than 800 companies parading the latest in packaging technology — and 17,000 people wanting to see them — filled the Las Vegas Convention Center for Pack Expo 2003. The exposition showcased state-of-the-art advances in packaging machinery, converting machinery, materials, packages, and containers.

In addition to the show floor, the Pack Expo Las Vegas/Food Processing Machinery Expo 2003 sponsored a conference that covered RFID technology, FDA packaging regulation initiatives under the Bioterrorism Preparedness Act, and trends in food cans, closures, meat and poultry trays, and glass packaging.

Pack Expo, a biennial event held on odd-numbered years, is sponsored and produced by the Packaging Machinery Manufacturers Institute.

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Blowing down the cost of wind energy

In reaction to the worldwide growth of wind energy, researchers at the Department of Energy’s Sandia National Laboratories are developing ways to lower the cost of this alternative energy and enable turbines to produce more power.

Current wind turbines are cost effective in very windy sites. The goal of the DOE wind program is to make convenient sites that are not as windy just as gainful, which can be done by enlarging the rotor’s swept area and slowing the rotation rate.

“We are looking at methods of building larger, stronger blades for turbines using a hybrid of carbon graphite fibers and fiberglass that sweep a greater area without greater cost,” says Paul Veers, manager of Sandia’s Wind Energy Technology Department.

Today, the most widely used commercial wind turbines have 35-m blades on 65 to 80-m-high towers. They produce about 1.5 MW each, and the blades are made primarily of fiberglass. By next summer the researchers hope to have six to 12 different blades to test.

Smooth stop-n-go

Automated pouching systems need smooth intermittent motion to position, fill, and heat-seal pouches, well, smoothly. Such was the case with a stand-up pouching system from Robert’s Packaging, Battle Creek, Mich., which fills and seals 220 pouches/min. with food products such as potato chips, rice, candy, and nuts, as well as pet food.

Controlling the high-speed, intermittent motion of the polypropylene film was a major concern, especially at the sealing station where the system’s servomotor draws the preprinted film forward through a series of rubber-covered rollers, stops to heat seal a completed pouch, and instantly restarts to repeat the cycle. An indexing cycle occurs every 0.3333 sec, with approximately half that time for film advance and the remaining time used for sealing.

A Zero-Max Model 6A37C single- flex CD coupling with clampstyle hubs connected to a 2-kW, 3,000-rpm, vertically mounted Yaskawa servomotor delivers the efficient cycling. The combination provides rapid start/stop film advance while preventing misalignment problems. The motor draws the film smoothly in-register, while the CD coupling damps any backlash forces, thereby eliminating misfeeds.

The CD coupling features a composite disc pack design, so that while it transmits torque similar to other couplings, it damps backlash and shock without fatiguing, which can happen in fast-moving systems. The open-arm disc design is made of a highly durable composite disc material that absorbs and cushions any tendency for backlash from the servomotor’s intermittent motion.

The CD coupling also allows the use of a single-flex, single-disc model, which is less costly and does the work of most other metal double-disc designs. It does so in less space and with greater misalignment capability. And while misalignment wasn’t the major consideration in the Robert’s Packaging pouching system, it makes a difference in assembly time as no lasers or special alignment tools are needed; users simply tighten one screw on each hub of the coupling to install.

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