Mechanical & Fluid Systems

Fail-Safe, Continue-to-Operate Concept for Jackscrews

Redundant nut increases reliability and facilitates inspections.

A fail-safe, continue-to-operate design concept for machine jackscrews calls for the incorporation of a redundant follower nut that would assume the axial jack load upon failure of the primary nut. Heretofore, the way to design for increased reliability of jackscrews has been to provide for multiple jackscrews operating in unison. The present fail-safe, continue-to-operate design concept offers an alternative for preventing catastrophic failures in jackscrews, which are used widely in aeronautical, aerospace, and industrial applications.

Posted in: Briefs, Mechanical Components, Mechanics, Failure analysis, Product development, Wear, Fasteners, Reliability

Pulse-Tube Refrigerator for Liquid Hydrogen

An unusually high operating frequency enables reductions of size and weight.

An improved closed-loop, two-stage pulse-tube refrigerator provides 4 W of cooling power at a temperature of 15 K. The original intended application of this refrigerator is in preventing boiloff of liquid hydrogen from a propellant tank aboard a spacecraft. The basic refrigerator design can also be adapted to terrestrial applications like cooling superconducting electronic devices.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Liquid propellants, Thermal management, Spacecraft

Ultrasonic/Sonic Vibrating/Rotating Tool Bits

Teeth are made asymmetric to induce rotation without need for rotary actuators.

An easy-to-implement design concept shows promise for improving the performances of impact tool bits used in abrading surfaces, drilling, and coring of rock and rocklike materials. The concept is especially applicable to tools actuated with a combination of ultrasonic and sonic vibrations, as in the cases described in “Ultrasonic/Sonic Drill/Corers With Integrated Sensors (NPO- 20856), NASA Tech Briefs, Vol. 25, No. 1 (January 2001), page 38. Such tools were originally intended to be used in scientific drilling and coring of rock; they might also be useful for drilling, coring, and surface grinding of rock for art and construction.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Tools and equipment, Product development, Drilling, Vibration

Water-Jet Accelerator for Launching a Spacecraft

A proposed ground- based apparatus would accelerate a spacecraft to speed of about mach 1, thus making it possible to increase the payload and/or reduce the cost of launching the space- craft into orbit. The apparatus would include a track along which the spacecraft would ride on a sled. Hundreds of small water jets energized by compressed-air packs would be located under, and at small intervals along, the track. Each jet would be activated in turn as the sled passed by, aiming a high-speed (possibly supersonic) stream of water at baffles on the underside of the sled. The force of water impinging on the baffles would provide levitation and accelerate the sled along the track. Unlike a previously proposed launch-assisting linear electric motor, the water-jet apparatus would function without need for expensive electric-power-conditioning equipment. Unlike another launch-assist concept involving a piston driven along a pneumatic tube, the present concept does not present problems of how to (1) couple the piston to the sled and (2) exert fine control over acceleration. Another advantage of the water-jet concept is redundancy: even if several water jets were to malfunction, the remaining many functional water jets should suffice.

Posted in: Briefs, Mechanical Components, Mechanics

Modular, Highly Maintainable, and Flexible Control Software

This software also lends itself to multitasking and distributed processing.

Model Rocket Engine Software System (MRECS) is a system of control software that was originally intended for use in controlling rocket engines but is also applicable to almost any real-time, closed- loop process-control system — for example, the feedback control system of a robot. MRECS affords the capabilities necessary for feedback control, actuation of valves and other devices by use of discrete and/or analog commands, processing of sensor readings, and generation of alarms by comparison of various quantities with limiting values. MRECS is capable of real-time multitasking and is amenable to distributed processing. It is designed, from the outset, to be highly maintainable and to be flexible in the sense that, in response to changing requirements, it can be quickly and reliably modified and tested.

Posted in: Briefs, Mechanical Components, Mechanics, Computer software and hardware, Electronic control systems, Sensors and actuators, Robotics, Rocket engines

Advances in Cooperative Transport by Two Mobile Robots

Two mobile robots move in formation while transporting a long payload.

Special gimbal mech- anisms and algorithms that implement decentralized compliant control have been developed for use in research on the sensors, the actuators, and the design and functional requirements for systems of multiple mobile robots cooperating in site-clearance and construction operations. The gimbal mechanisms and control algorithms were designed, in particular, to enable two robotic exploratory vehicles (i.e., rovers) to transport a long payload while moving along the ground in a commanded formation. Although these developments are parts of a continuing effort to develop robotic capabilities for exploration of Mars, the same robotic capabilities could be expected to find application on Earth.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

Magnetostrictive Motor and Circuits for Robotic Applications

Notable features include power-factor correction, speed control, and high position resolution.

A magnetostrictive motor and its drive circuit and control system have been designed to be especially suitable for robotic applications in which there are requir- ements for precise, high-force linear actuators. The motor includes a laminated armature made of the magnetostrictive alloy Tb0.27Dy0.73Fe0.2. The armature is sandwiched between two double-layered, three-phase stators, which are energized to make the armature move linearly in “inchworm” fashion. The total range of linear motion is 25 mm. Like other magnetostrictive motors, this motor offers the advantages (relative to geared-down conventional motors) of reduced weight, extreme ruggedness, fewer moving parts, greater reliability, and self braking when power is not applied.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Sensors and actuators, Robotics, Electric motors, Reliability

Electroactive-Polymer Actuators With Selectable Deformations

There are numerous options for selecting materials, config- urations, and modes of operation.

Efforts are underway to develop compact, lightweight electro- mechanical actuators based on electroactive polymers (EAPs). An actuator of this type is denoted an electroactive-polymer actuator with selectable deformation (EAPAS). The basic building blocks of these actuators are sandwichlike composite-material strips, containing EAP layers plus electrode layers, that bend when electric potentials are applied to the electrodes. Prior NASA Tech Briefs articles that have described such building blocks as parts of actuators for specific purposes include “Robot Hands With Electroactive-Polymer Fingers” (NPO-20103), Vol. 22, No. 10, (October 1998), page 78; “Robot Arm Actuated by Electroactive Polymers” (NPO-20393), Vol. 23, No. 6 (June 1999), page 12b; “Wipers Based on Electroactive Polymeric Actuators” (NPO-20371), Vol. 23, No. 2 (February 1999), page 7b; and “Miniature Electroactive-Polymer Rakes” (NPO-20613), Vol. 25, No. 10 (October 2001), page 6b.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Architecture, Sensors and actuators, Product development, Polymers

Mechanisms for Reliable One-Time Deployment of Panels

These mechanisms overcome the disadvantages of both pyrotechnic and thermal release mechanisms.

Mechanisms denoted restraint/ release/deployment-initiation (RRDI) devices have been invented to enable the rapid, reliable, one-time deployment of panels that have been hinged together and stowed compactly by folding them together at the hinges. Although the RRDI devices were originally intended for use in deploying the solar photovoltaic panels that generate electric power for a spacecraft, they are also suitable for deploying other, similarly hinged panel arrays (including solar photovoltaic panels) in terrestrial applications. The RRDI devices overcome the disadvantages (shock and the consequent potential for damage) of explosive release devices as well as the disadvantages (slowness and high power demand) of electrically actuated thermal release devices.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Sensors and actuators, Solar energy, Product development, Spacecraft

Apparatus for Friction Stir Welding of Pipes

FSW heads would move circum- ferentially and pipes would be supported against FSW loads.

A proposed apparatus would effect friction stir welding (FSW) along a circumferential path to join two pipes. The apparatus is denoted an “orbital FSW system” because the circum- ferential motion of the FSW head would be similar to the motions of welding heads in commercial orbital fusion welding systems.

Posted in: Briefs, Mechanical Components, Mechanics, Manufacturing equipment and machinery, Welding

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