Mechanical & Fluid Systems

Instrumented Bolt Measures Bending Moments Within Itself

The direction as well as the magnitude of bending can be determined. The Ultrabend bolt is a specially designed bolt instrumented with strain gauges (see figure) that are connected into twin Wheatstone-bridge circuits. The geometric arrangement of the strain gauges is such that by suitable electrical switching of the Wheatstone-bridge circuits, these circuits can be made to either (1) suppress responses to bending and torsional stresses while putting out signals indicative of axial preload or (2) suppress responses to axial and torsional stresses while putting out signals indicative of the magnitude and direction of the bending moment in the bolt. Switching between these two measurement modes is accomplished by use of field-effect transistors controlled by a logic circuit.

Posted in: Briefs, Mechanical Components

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Improved Piezoelectrically Actuated Microvalve

The improvements are intended to ensure less leakage and true normally-closed operation. Figure 1. The Previous Version of the Valve, like the present version, was opened by applying a voltage that caused the piezoelectric actuator to contract slightly.Efforts are underway to implement an improved design of the device described in “Normally Closed, Piezoelectrically Actuated Microvalve” (NPO-20782), NASA Tech Briefs, Vol. 25, No. 1 (January 2001), page 39. To recapitulate: This valve is being developed as a prototype of valves in microfluidic systems and other microelectromechanical systems (MEMS). The version of the valve reported in the cited previous article (see Figure 1) included a base (which contained a seat, an inlet, and an outlet), a diaphragm, and an actuator. With the exception of the actuator, the parts were micromachined from silicon. The actuator consisted of a stack of piezoelectric disks in a rigid housing. To make the diaphragm apply a large sealing force on the inlet and outlet, the piezoelectric stack was compressed into a slightly contracted condition during assembly of the valve. Application of a voltage across the stack caused the stack to contract into an even more compressed condition, lifting the diaphragm away from the seat, thereby creating a narrow channel between the inlet and outlet.

Posted in: Briefs, TSP, Mechanical Components

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Program Computes Pointing Corrections for a Radiotelescope

TLC is a computer program that determines corrections for radiotelescopepointing errors associated with tilts and elastic deformations. These errors occur because for rotation in azimuth, a radiotelescope is mounted on wheels that move on a circular track that deviates from perfect flatness. TLC processes radiotelescope field data through smoothing, filtering, segment-fitting, trend-removal, Fourier-transform, and high-passfiltering algorithms to generate a lookup table that contains the pointing corrections. The field data in question are readouts from four inclinometers, the relative positions of the inclinometers, and readouts from an azimuth-angle encoder. Written in the Matlab software system, TLC is a user-friendly program that provides a graphical user interface that enables even an unfamiliar user to proceed, step by step, to the final result.

Posted in: Briefs, TSP, Mechanical Components

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Lightweight, Low-Backlash Robot Wrist With Epicyclic Drive

Several design features contribute synergistically to versatility and efficiency. A unique lightweight wrist with three degrees of rotational freedom has been developed as a prototype of wrists for future anthropomorphic robots that would perform a variety of tasks on Earth and in outer space. The three degrees of freedom (two rolling, one bending) intersect at the center of the wrist. Included in the wrist is a power transmission with an epicyclic ring-gear configuration that enables efficient packaging and provides a wide internal passage through the center of rotation for routing of wires and drive cables. The power transmission combines lowbacklash planetary gearing and a tripleinput differential with a triple-loadpath, cable-driven output stage that generates minimal radial bearing loads and no thrust (that is, axial) bearing loads.

Posted in: Briefs, Mechanical Components

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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: Briefs, TSP, Mechanical Components

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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: Briefs, TSP, Mechanical Components

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"Smart" Actuators for Alleviating Buffet of Aircraft

Peak stresses could be reduced without sacrificing control authority. An active-control surface modal (ACSM) device has been developed as an improved means of alleviating buffet of an aircraft. The ACSM device is a "smart" actuator system that includes an array of antagonistic piezoelectric actuators installed within a rudder or other aircraft control surface (see Figure 1). These actuators are used to deform the control surface in what amounts to controlled vibration modes (see Figure 2), the frequencies and mode shapes being chosen to affect unsteady aerodynamic damping to suppress the dynamic effects of buffet.

Posted in: Briefs, TSP, Mechanical Components

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