Motor/brake assembly takes aircraft-seat comfort to new heights 9-21-98

September 21, 1998 Design News

DESIGN APPLICATIONS From the regional editors

Motor/brake assembly takes aircraft-seat comfort to new heights

Spur-gear drive is faster, stronger, and less expensive than worm-gear-driven designs

John Lewis, Northeast Technical Editor

Woodland Hills, CA--Airlines fighting fierce competition for frequent fliers know that comfort wins favor. Since passengers spend the duration of flights in their seats, comfortable chairs are a clear foremost priority. Fortunately, P.L. Porter Controls Inc. has developed a new generation of first- and business-class aircraft-seat controllers--sold internationally to global players such as B/E Aerospace Inc., Italy-based Avio interiors, and Britax Rumbold (with aircraft interior divisions in Germany and Sweden)--that permit precise seat adjustments. By incorporating a customized brush-commutated dc motor from Harleysville, PA-based Pittman, P.L. Porter designed a compact linear actuator for the control system that is not only faster and stronger but also less expensive than previous designs.

The new Electronic Comfort Control System (ECCS) GEN IV World System is a microprocessor-based controller that operates the seat back recline, leg rest, footrest extension, lumbar, and headrest actuators. It is compact, lightweight, and easy to operate. And its redundant safety features are integrated into the controller and actuators through both hardware and software.

To keep the price of the ECCS GEN IV system as low as possible, an economical motor and brake assembly for P.L. Porter's compact linear actuator was vital. Company engineers chose Pittman's Series 8000 LO-COGr brush-commutated dc motor.

"The Pittman motors take a totally different approach than the motors we used in past designs," explains Eric Lau, R&D team leader at P.L. Porter Controls, Inc. "Previously, we were using worm-gear-driven actuators mounted perpendicular to the lead screw. Now we mount the LO-COG motor, a spur-gear-driven actuator, parallel to the lead screw. Because of this, the Pittman motor provides faster speeds and higher torque, and overall is more efficient for the actuator."

Series 8000 servomotors are permanent-magnet field motors that experience minimal cogging at low speeds, resulting in smoother, more efficient motion. The armatures, configured in a seven-slot design, are skewed for optimal reduction of reluctance torque. Laminations are silicon steel that has been impregnated with polyester resin, baked, and wound with film-insulated magnet wire. To ensure concentricity, long brush life, and low maintenance, Pittman turns the commutators after the armature is assembled. This motor series provides peak torque of 5.05 to 16.8 oz-inch, and no load speeds in the 7,700- to 10,650-rpm range for standard motors at rated voltages.

Ready for takeoff. With the LO-COG motor, the compact linear actuator offers a minimum compressed mounting length of 5.55 inches, maximum extended mounting length of 8.05 inches, and a static load capacity of 500 lbs. For this application, Pittman customized the Series 8000 motor with a spur gearhead, which provides a 31:1 reduction ratio to increase output torque. P.L. Porter also chose wide-face gears to support 175 oz-inch of torque in a small motor. The sintered nickel-steel gears provide economy, moderate torque handling, and low audible noise. The porosity of these gears helps maintain lubrication while reducing noise levels.

Pittman added a power-off brake on the rear of the motor to prevent backdriving. When power is cut off, the 24V brake holds the motor in position and supplies 16 oz-inch of holding torque. A custom ball-bearing output shaft increases assembly life and handles higher loads--even when the system is at rest--to support the passenger's feet and head. A carbon-impregnated rubber RFI ring encircles the motor's commutator bars, dissipating electromagnetic interference.

Pittman tests the critical operating parameters of Series 8000 motors under both load and no-load conditions in a computerized testing station, and permanently stores the resulting data for future reference. Independent P.L. Porter tests confirm the LO-COG motor provides faster speeds, higher torque, and long life to help ensure long-term operation of the actuator.

During the design phase, P.L. Porter needed quick product delivery to get to market fast. "We required a delivery time of three weeks or less," says Bob Clough, ECCS product manager. "Pittman was able to meet that requirement even with extensive motor customization. They also supplied us with several prototypes customized with various EMI/RFI suppression components to support our electrical noise tests.

"With Pittman's help, we decreased an 8-month development-to-production cycle for the entire system to approximately 10 weeks, and maintained stringent cost objectives," continues Clough. "While matching the durability and performance of previous generations, the ECCS GEN IV system costs only half as much."

Additional details?Contact Richard Green, Pittman, 343 Godshall Dr., Harleysville, PA 19348-0003; (215) 256-6601

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