Mechanical & Fluid Systems

Electromechanically Actuated Valve for Controlling Flow Rate

A ball screw would be both an actuator and a flow-control component. A proposed valve for controlling the rate of flow of a fluid would include an electric-motor-driven ball-screw mechanism for adjusting the seating element of the valve to any position between fully closed and fully open. The motor would be of a type that can be electronically controlled to rotate to a specified angular position and to rotate at a specified rate, and the ball screw would enable accurate linear positioning of the seating element as a function of angular position of the motor. Hence, the proposed valve would enable fine electronic control of the rate of flow and the rate of change of flow.

Posted in: Briefs, TSP

Read More >>

Magnet-Based System for Docking of Miniature Spacecraft

The capture envelope for this system is approximated by a 5-in. (12.7-cm) cube. A prototype system for docking a miniature spacecraft with a larger spacecraft has been developed by engineers at the Johnson Space Center. Engineers working on Mini AERCam, a free-flying robotic camera, needed to find a way to successfully dock and undock their miniature spacecraft to refuel the propulsion and recharge the batteries. The subsystems developed (see figure) include (1) a docking port, designed for the larger spacecraft, which contains an electromagnet, a ball lock mechanism, and a service probe; and (2) a docking cluster, designed for the smaller spacecraft, which contains either a permanent magnet or an electromagnet.

Posted in: Mechanics, Briefs

Read More >>

Low-Friction, High-Stiffness Joint for Uniaxial Load Cell

Friction and hysteresis are minimized. A universal-joint assembly has been devised for transferring axial tension or compression to a load cell. To maximize measurement accuracy, the assembly is required to minimize any moments and non-axial forces on the load cell and to exhibit little or no hysteresis. The requirement to minimize hysteresis translates to a requirement to maximize axial stiffness (including minimizing backlash) and a simultaneous requirement to minimize friction. In practice, these are competing requirements, encountered repeatedly in efforts to design universal joints. Often, universal-joint designs represent compromises between these requirements.

Posted in: Briefs

Read More >>

Prolonging Microgravity on Parabolic Airplane Flights

Techniques for improving the approximation of free fall are proposed. Three techniques have been proposed to prolong the intervals of time available for microgravity experiments aboard airplanes flown along parabolic trajectories. Typically, a pilot strives to keep an airplane on such a trajectory during a nominal time interval as long as 25 seconds, and an experimental apparatus is released to float freely in the airplane cabin to take advantage of the microgravitational environment of the trajectory for as long as possible. It is usually not possible to maintain effective microgravity during the entire nominal time interval because random aerodynamic forces and fluctuations in pilot control inputs cause the airplane to deviate slightly from a perfect parabolic trajectory (see figure), such that the freely floating apparatus bumps into the ceiling, floor, or a wall of the airplane before the completion of the parabola. Heretofore, free-float times have tended to be no longer than a few seconds.

Posted in: Briefs, TSP

Read More >>

Device for Locking a Control Knob

A simple, effective, easy-to-use device locks a control knob in a set position. In the initial application for which this device was conceived, the control knob to be locked is that of a needle valve. Previously, in that application, it was necessary for one technician to hold the knob to keep the valve at the desired flow setting while another technician secured the valve with safety wire — a time-consuming procedure. After attachment of the wire, it was still possible to turn the knob somewhat. In contrast, a single technician using the present device can secure the knob in the desired position in about 30 seconds, and the knob cannot thereafter be turned, even in the presence of harsh vibrations, which occur during space shuttle launch. The device includes a special-purpose clamp that fits around the control knob and its shaft and that can be tightened onto the knob, without turning the knob, by means of two thumbscrews. The end of the device opposite the clamp is a tang that contains a slot that, in turn, engages a bolt that protrudes from the panel on which the control knob and its shaft are mounted.

Posted in: Briefs, TSP

Read More >>

Cable-Dispensing Cart

A versatile cable- dispensing cart can support as many as a few dozen reels of cable, wire, and/or rope. The cart can be adjusted to accommodate reels of various diameters and widths, and can be expanded, contracted, or otherwise reconfigured by use of easily installable and removable parts that can be carried onboard. Among these parts are dispensing rods and a cable guide that enables dispensing of cables without affecting the direction of pull. Individual reels can be mounted on or removed from the cart without affecting the other reels: this feature facilitates the replacement or reuse of partially depleted reels, thereby helping to reduce waste. Multiple cables, wires, or ropes can be dispensed simultaneously. For maneuverability, the cart is mounted on three wheels. Once it has been positioned, the cart is supported by rubber mounts for stability and for prevention of sliding or rolling during dispensing operations. The stability and safety of the cart are enhanced by a low-center-of-gravity design. The cart can readily be disassembled into smaller units for storage or shipping, then reassembled in the desired configuration at a job site.

Posted in: Briefs

Read More >>

Quasi-Sun-Pointing of Spacecraft Using Radiation Pressure

A report proposes a method of utilizing solar-radiation pressure to keep the axis of rotation of a small spin-stabilized spacecraft pointed approximately (typically, within an angle of 10° to 20°) toward the Sun. Axisymmetry is not required. Simple tilted planar vanes would be attached to the outer surface of the body, so that the resulting spacecraft would vaguely resemble a rotary fan, windmill, or propeller. The vanes would be painted black for absorption of Solar radiation. A theoretical analysis based on principles of geometric optics and mechanics has shown that torques produced by Solar-radiation pressure would cause the axis of rotation to precess toward Sun-pointing. The required vane size would be a function of the angular momentum of the spacecraft and the maximum acceptable angular deviation from Sun-pointing. The analysis also shows that the torques produced by the vanes would slowly despin the spacecraft — an effect that could be counteracted by adding specularly reflecting "spin-up" vanes.

Posted in: Briefs, TSP

Read More >>

White Papers

Inclinometers for Motion Control
Sponsored by Fraba Posital
100% Non-Cytotoxic Rechargeable Batteries for Medical Devices
Sponsored by Cymbet
Introduction to Hypervisor Technology
Sponsored by Curtiss-Wright Controls Embedded Computing
Force and Torque Measurement Traceability
Sponsored by Morehouse
Tubing & Hose Buying Tips, Part 2
Sponsored by Newage Industries
Selection of Materials for Medical Applications
Sponsored by RTP

White Papers Sponsored By: