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TRANSPORTER'S MOTORS CONSERVE SPACE, THANKS TO DUPONT RYNITE
Innovative electric servomotors made with DuPont Rynite PET thermoplastic polyester resin deliver smooth, reliable power for the Segway Human Transporter, the first self-balancing, electric powered transportation machine designed for short-distance travel. Pacific Scientific, a Danaher Motion Company, helped develop space-saving motors that allow the Segway HT to move at speeds up to 12.5 miles per hour (20 km/h), about three times faster than the average walker. Two brushless servomotors in a space-saving design power the Segway HT. Each is about 40 percent smaller than a conventional motor with equivalent performance. The space saving is made possible by a novel encapsulated stator made with DuPont Rynite PET. In developing it, Pacific Scientific built on its proprietary stator encapsulation technology originally developed with DuPont technical assistance in the mid-1990s. Rynite PET provides the mechanical and electrical properties required, and it performs well in the encapsulation process, says Greg Rittmeyer, a project engineer on the Pacific Scientific development team. Rynite is preapproved for Class F (155C) service under UL 1446 and IEC 62114 standards. The encapsulation process allowed us to reduce motor size, simplify manufacturing and deliver added benefits of higher quality and improved motor performance, says Rittmeyer. The reduction in size results from the elimination of a separate metal end housing and other design enhancements. Both the front and rear ends of the motor are formed from Rynite within the envelope of the motor's steel laminate stack, and they are formed in the same production step that encapsulates the stator windings. Cost savings are another benefit achieved by injection molding the stator with Rynite, according to Rittmeyer. The production process requires fewer steps and has a lower inherent risk of manufacturing defects than a conventional stator, according to Pacific Scientific. Manufacture of the stator starts with two ring-shaped ground-insulating components from Rynite. These parts nest together and are wound with copper wire over a stack of steel laminate plates. Each of its six field coils is terminated on an integral post in one of the molded insulator components. The stator's structural body and inner-phase insulation are produced in a single injection molding step. The coil/stack assembly is placed in the lower half of a mold in an injection molding machine. Then the mold is closed and Rynite is injected, simultaneously providing inner-phase insulation and structures for both the front and rear ends of the motor as it fills the mold. The part that comes out of the tool requires only the removal of a small sprue and runner disk. Key features for subsequent assembly are integrated in the rear end bell formed during encapsulation. These include molded-in supports for a circuit board, which is soldered to the six paired coil terminals, and an integral well to catch excess solder and prevent it from falling into the stator's interior. In addition to its innovative encapsulated stator, the motor has several other features unique to brushless servomotor technology, and some are not seen on motors of any type, according to Rittmeyer. A new sensor design developed by Pacific Scientific allows precision feedback of the motor's drive electronics without the need for a traditional encoder or resolver. In addition, the stator, a patented construction, is hemispherically wound with redundant windings, creating essentially two completely functioning motors in a single housing. If one set of windings were to fail completely, the motor can continue to operate at reduced power. Pacific Scientific is a 45-year-old manufacturer of electric motors and drives providing innovative motion solutions to a wide range of technology markets worldwide. They are part of Danaher Motion, a business unit of Danaher Corporation, a leading manufacturer of process/environmental controls, tools and components. For additional information, call 815-216-3100 or visit www.pacsci.com on the World Wide Web.
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