Machinedesign 1530 Cassini Huygens Spacecraft904 0 0

Fasteners in space

Sept. 1, 2004
When the Cassini-Huygens spacecraft entered Saturn’s orbit this summer, it had to be able to handle the vibration, shock, and temperature extremes of a rocket launc

When the Cassini-Huygens spacecraft entered Saturn’s orbit this summer, it had to be able to handle the vibration, shock, and temperature extremes of a rocket launch. In addition, the Huygens probe has to dive into the atmosphere of Titan, Saturn’s largest moon, to measure atmospheric composition all the way down to the frigid surface. For the Cassini orbiter and Huygens probe to be successful, several hundred bolts must maintain vacuum-tight sealed cavities for the entire seven-year mission, with no thread loosening or stripping.

Madison Heights, Mich.-based Spiralock Corp. had the answer: A new thread form with a 30° “wedge” ramp cut at the root of the female thread. Under clamp load, the crests of the threads on any standard bolt are drawn tightly against the wedge ramp. Thread contact forces are therefore applied at approximately 60° from the bolt axis, rather than 30° as in a standard thread form. The angular relationship between the wedge ramp and the male thread restricts bolt or screw movement. The wedge ramp not only eliminates the transverse motion that causes loosening under vibration but also distributes the loads of the threaded joint throughout the engaged threads.

The wedge ramp lets the fastener spin freely until clamp load is applied. At that point, the crests of the standard male thread form are drawn tightly against the wedge ramp, eliminating radial clearances and creating a continuous spiral line of contact along the entire length of thread engagement. This spreads the clamp force more evenly over all engaged threads, reducing fatigue failure and increasing the integrity of the threaded joint.

For atmospheric measurement of Saturn and Titan on the Cassini-Huygens mission, NASA used the Spiralock internal thread form to resist vibration and temperature-induced thread loosening on mass spectrometer instrumentation.

“To survive the vibration and high temperatures of launch, we needed the most reliable locking engagement thread,” said Dan Harpold, a NASA scientist who worked on the project. “Screws had to remain tight because there is no opportunity for retightening. With conventional threading, however, screws loosened up and backed out under testing.”

Among the tests carried out were a series of about 12 high-temperature “bake outs,” in which screws and their matching internal thread forms were heated from room temperature to 300°C to simulate temperature-induced thread loosening.

“The Spiralock thread form retained a tight seal,” says Harpold. “Once torqued down properly, the screws stayed put in the threads.”

Lasers go industrial

Lasers, already used for everything from price scanning at supermarkets to eye surgery, could change largescale manufacturing, remote sensing, defense, and construction industries. A new report from the National Institute of Standards and Technology (NIST) predicts “tremendous” applications for laser scanning devices known as Ladars (Laser Detection and Ranging) and pushes for the creation of next-generation Ladar — a coffee-cup-size device with millimeter accuracy.

Industry has used Ladar, which creates 3D images of areas and objects, since the late 1970s. But advances in microchip lasers, optics, microelectromechanical systems, and computers have increased Ladar’s data-acquisition speed, range accuracy, and reliability, as well as reduced its size and costs. Ladars are now used to generate topographic images, survey the depths of large bodies of water, and as 3D documentation of construction when building plans aren’t available. Manufacturers are also beginning to use Ladar to recreate critical machine components from single examples.

NIST is testing Ladar for navigating unoccupied military vehicles, which could lead to collision-avoidance advances for civilian automobiles. To encourage industrial use, NIST is working to develop test objects for Ladar performance standards to instill confidence in laserscanning readings and system comparisons.

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DSP keeps electric scooters fast and eco-friendly

Thanks in part to a digital signal controller from Texas Instruments, Houston, lightweight electric motor scooters from Vectrix Corp. offer performance and acceleration levels that match 250-cc gasoline-powered motorcycles — without the polluting emissions usually found in two stroke gas engines.

The LF2401A DSP-based controller helps the scooters’ motor operate more efficiently than traditional MCUs or analog designs. “We began using traditional microcontrollers for motor control, but switched to the LF2401A when we realized we needed a highly integrated digital signal controller to reduce the size and complexity of the scooter’s electronic system,” says Peter Hughes, vice president of technology at Vectrix. “Thanks to these benefits, plus the flexibility inherent in programmable digital technology, our overall development was simplified, and we were able to pack all the scooter’s control functionality onto a single board.”

The LF2401A also delivers advanced motor control functions such as tuning the motor’s phase angle advance. These functions boost scooter performance by providing up to 75 miles of travel at 25 mph before the battery has to be recharged. In addition to motor control, the controller handles system startup, lights and safety, and battery recharge. External communications can also be supported for future vehicle requirements.

The DSP-based motor control is paired with a high-performance, customdesigned brushless servomotor from Parker SBC, part of the Parker Automation Div. The direct-drive dc motor peaks at 20 kW with current to 300 A and 65 N-m of torque to provide an acceleration of 0 to 30 mph in 3.6 sec. The motor also features a high pole-count design for maximum torque per Watt and an innovative single-tooth segment winding for higher reliability. Prototypes of the scooter are being test-driven on the streets of major European cities.

Learn more about motors

The Electrical Apparatus Service Association presents the following two seminars this fall, open to members and non-members. Principles of Large AC Motors — Oct.1-2, Charlotte

Discusses motor applications, safety considerations, vibration, starting methods, and reconditioning. Information covers induction motors from 300 to 5,000 hp, but most principles apply to ac motors of all sizes.

Root Cause Failure Analysis — Nov. 5-6, New Orleans

Explores causes of motor failures, from the most common to the unusual. Also presents a methodology for identifying the most probable cause of failure.

To learn more, or to enroll, contact EASA at (314) 993-2220 or visit

Conference focuses on motors and drives

The focus of SMMA The Motor & Motion Association’s Fall Technical Conference is enabling technologies for the motors and drives industry. The conference runs Nov. 3 to 5 at the Marriott St. Louis Airport Hotel. Topics and speakers are organized in the following segments: design and analysis of motors and drives; simulation and testing; and new materials. The conference will include tabletop exhibits for SMMA supplier member companies and speakers. Papers scheduled for presentation include:

• An Innovative Low-Cost Linear Brushless Servomotor

• A Cost-Function-Based Closed-Loop Torque Ripple Mitigation Strategy for Permanent Magnet Synchronous Machines

• Dynamic Simulation of Electric Motors

• Brushless Speed Controls Provide Superior Performance • Recent Progress on Losses in Lamination Seals

For more information about the conference, call (508) 979- 5935 or visit

Company news

Galil Motion Control Inc., Rocklin, Calif., has promoted Wayne Baron, chief technical officer and vice president of engineering, to president and chief executive officer. Baron assumes the position from Dr. Jacob Tal, who will now serve as chairman of the board and remain an active member of Galil’s technical team.

Omron Corp. announces that it will establish, as part of its Industrial Automation Business Co., a new facility in Shanghai to strengthen and integrate Chinese design, development, and manufacturing functions, as well as offer a customer support center. The facility is expected to be complete in the second half of 2006.

Turck Inc., Minneapolis, has acquired 100% of the shares of InterlinkBT, an independent industrial network company. The acquisition combines sensing, connectivity, networks, and interface technologies into one for all automation goals.

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