Mechanical & Fluid Systems

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

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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

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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

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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

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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

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Automated System for Fluid and Electrical Connections

The Smart Umbilical Mating System (SUMS) is an automated, three-degreeof- freedom, scalable system for quickly mating, demating, and/or remating ganged umbilicals. SUMS connects electrical and fluid paths between spacecraft and ground support equipment whether liftoff or side mount for NON T-0 umbilicals. SUMS prevents electrical arcing and leakage of fluids by providing for automated alignment of mating connectors and verification of mating. SUMS could readily be adapted to such other applications as servicing of aircraft, orbiting spacecraft, or ground vehicles. Major elements of SUMS include mating cones equipped with force sensors with integral latches; computer control; robotic vision with tracking aided by laser beams; actuation by a compliant pneumatic motor; and a secondary mate plate, which holds the ground-side fluid electrical connectors in proper alignment, is pneumatically actuated to complete mating once the cones have been latched, and is the only part of the system that one must change to adapt SUMS to different applications. A commercial version plumbed with electrical power, communications, fuel, lubricants, and coolant fluids could be installed at a central location for servicing land vehicles. SUMS could be utilized between moving vehicles. Automated functions could include electronic identification of vehicles to prevent errors; recording of data about the vehicle; its consumption of fluids; sampling for wear analysis; maintenance scheduling; distance traveled; and topping off or changing of all fluids in the correct amounts.

Posted in: Briefs, TSP, Mechanical Components

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Sonic-Boom Tests of Model of a Supersonic Business Jet Plane

A report discusses wind-tunnel tests of a scale model of a con- ceptual two-engine jet airplane designed to carry 10 passengers, have a range of 4,000 miles (≈6,400 km), cruise at a mach number of 2.0, and generate a low sonic boom [char- acterized by a shock overpressure of ≤ 0.5 lb/ft2 (≤24 Pa)]. The model could optionally include either of two differently sized nacelle submodels representing alternative engine designs. In each test, the pressure was measured at intervals along a horizontal line at a specified height below the model. One conclusion drawn from predicted and measured pressure values is that it is more difficult to tailor the geometry of this airplane for low sonic boom than it is to do so for a larger supersonic airplane capable of carrying 300 passengers and for which the allowable shock overpressure is 1.0 lb/ft2 (48 Pa). It was found that decreasing the allowable overpressure intensifies the conflicts between the design choices for reducing sonic boom and those for increasing aerodynamic efficiency. It was also found that due to the nacelles’ aft location, their contribution to the shock overpressures could be expected to be small enough to be unnoticeable by an observer on the ground.

Posted in: Briefs, TSP, Mechanical Components

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