Mechanical & Fluid Systems

Magnetically Moved Trim Masses for Fine Position Control

Control would be achieved without spurious effects generated by propulsion systems. Systems of caged trim masses manipulated by magnetic fields have been proposed for effecting fine control of the positions and/or orientations of spacecraft. The systems were conceived for use during observations by spaceborne interferometers, the component instruments of which (1) are located on multiple spacecraft flying in formation and (2) are required to be kept aligned with each other within narrow position and orientation tolerances. The proposed systems would make it possible to avoid the spurious effects generated by the spacecraft propulsion systems that would otherwise have to be used for fine position control; the spurious effects would include vibrations, exhaust, and flashes of light, which would be detrimental to the interferometric observations. Terrestrial versions of the proposed systems might be useful for fine horizontal positioning of delicate scientific instruments.

Posted in: Mechanics, Briefs, TSP

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Motor Drive for Multiple Horizontally Rotating Bioreactors

Bioreactors can be installed and removed easily. The figure depicts a mechanism that is capable of simultaneously rotating as many as six disposable bioreactor chambers about horizontal axes. The particular bioreactor chambers for which this mechanism is designed are high-aspect-ratio vessels (HARVs), which are round cylindrical vessels developed by NASA.

Posted in: Briefs

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Tip Fences for Reduction of Lift- Generated Airframe Noise

These simple, easily retrofitted devices reduce drag as well as noise. Tip fences have been invented to reduce the noise generated in the airflows about the high-lift systems (the flaps and slats) of airplane wings. Tip fences also afford an important secondary benefit by increasing lift-todrag ratios.

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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: Mechanics, Briefs

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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.

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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.

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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.

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