Mechanical & Fluid Systems

Hollow Shaft Actuators with Harmonic Drive Gearing

They can be used in demanding applications such as industrial robots and servo systems. Harmonic drive gearing is recognized by designers for its zero backlash, high gear ratios, and compact design features. A recent development by HD Systems incorporates a large hollow shaft through the actuator, offering many benefits to the machine designer. The FHA hollow shaft actuator series allows cables, shafts, or tubing to be passed concentrically through the center of the actuator. Through this innovation, the series provides precision motion control and high torque capacity in very compact packages.

Posted in: Briefs

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Actuated Ball-and-Socket Joints

These joints would be relatively compact, lightweight, simple, and inexpensive. The term "actuated ball-and-socket" (ABS) characterizes a proposed class of ball-and-socket joints that would incorporate ultrasonic motors and other piezoelectric actuators to generate multidimensional actuation. In some applications, ABS joints could supplant traditional joint-and-actuator assemblies that include passive rotary joints actuated by electromagnetic motors via gears. In comparison with such assemblies, ABS joints offer potential advantages of compactness, relative mechanical simplicity, higher torque-to-weight ratios, no backlash, self-braking with power turned off, and lower cost. ABS joints are expected to be particularly attractive for use as robot joints and as general low-power orienting actuators for diverse applications that could include robot hands, tools, and mechanisms for aiming scientific instruments.

Posted in: Briefs, TSP

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Laser Anemometer Measures Flow in a Centrifugal Compressor

High-resolution data are representative of flows in practical centrifugal compressors. Detailed measurements of complex flow fields within the NASA Low Speed Centrifugal Compressor (LSCC) have been acquired. The measurement data provide insight into the fundamental physics of flow in centrifugal compressors, and can be used to assess computational fluid dynamics codes and to develop flow-physics models. The resultant benefit is better predictive computational tools and shorter design cycle times.

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High-Altitude Flight Test of the Perseus B Airplane

Flawless aerodynamic, propulsion, and control performance was observed. The Perseus B remotely piloted vehicle (RPV) has achieved a record altitude for a single-engine, propeller-driven airplane of 60,260 ft (18,367 m) on June 27, 1998. The Perseus B is one of the test-bed aircraft developed under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program for use in conducting high-altitude, long-duration missions carrying atmospheric sampling and sensing payloads for the scientific community within NASA and other agencies.

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Pneumatic Accelerator for Launching a Spacecraft

A report proposes the development of a ground-based launch-assist apparatus that would accelerate a spacecraft to a speed of about 270 m/s. The apparatus would include a track along which the spacecraft would ride on a sled coupled to a large piston driven by compressed air along a tube (more precisely, a concrete tunnel lined with stainless-steel sheet) below the track. The connection between the sled and the piston would be made via a coupling plate that would slide along a slot on top of the tube. The slot would seal after passage of the coupling plate. As described thus far, the apparatus could be characterized as a modern, high-acceleration, high-speed version of pneumatic drives with slot connections to rail cars that were used in Europe during the 1840s.

Posted in: Mechanics, Briefs, TSP

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High-Temperature Switched-Reluctance Electric Motor

Motors like this one would be incorporated into gas turbines as starter/generators. An eight-pole radial magnetic bearing has been modified into a switched-reluctance electric motor capable of operating at a speed as high as 8,000 rpm at a temperature as high as 1,000 °F (Å540 °C). The motor (see figure) is an experimental prototype of starter-motor/ generator units that have been proposed to be incorporated into advanced gas turbine engines and that could operate without need for lubrication or active cooling.

Posted in: Mechanics, Briefs

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Ice-Melting Probe Using Steam and Jets of Hot Water

This probe would overcome some of the deficiencies of prior ice-melting probes. An improved probe has been proposed for burrowing vertically into ice for scientific exploration of polar icecaps, glaciers, and the like. The predecessor of the improved probe is a Philbert probe, which contains an electric heater to melt the ice in contact with it and thereby make it descend through the ice under its own weight. A Philbert probe also contains a mechanism from which the wires for the electric heater and any sensors in the probe are paid out behind the probe; these wires become sealed into the overlying ice as the probe descends. The two major drawbacks of a Philbert probe are that (1) it tends not to go straight down and (2) a plug of dust, sand, rock, and/or other debris tends to build up in the meltwater ahead of the probe, eventually becoming large enough to halt the descent by interrupting the heat-transfer interface between the vehicle nose and the ice. The improved probe is designed to eliminate these drawbacks.

Posted in: Mechanics, Briefs, TSP

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