Mechanical Components

Integral Flexure Mounts for Metal Mirrors for Cryogenic Use

These mounts are compact and relatively inexpensive. Semi-kinematic, six-degree-of-freedom flexure mounts have been incorporated as integral parts of metal mirrors designed to be used under cryogenic conditions as parts of an astronomical instrument. The design of the mirrors and their integral flexure mounts can also be adapted to other instruments and other operating temperatures. In comparison with prior kinematic cryogenic mirror mounts, the present mounts are more compact and can be fabricated easily using Ram-EDM (electrical discharge machining) process.

Posted in: Mechanical Components, Briefs

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Fastener Options for Clinching Into Stainless

Differing stainless hardness levels and degrees of corrosion resistance can complicate fastener selection. Designers often turn to self-clinching fasteners when they need a practical method to provide threads in thin metal sheets. The fasteners install permanently, reduce hardware, and promote thinner and lighter designs. In stainless applications, though, designers may run into some particularly hard choices. A prevalent misconception is that all stainless self-clinching fasteners will perform as intended in all stainless sheets. But, the relative hardness of the fastener and sheet looms as an overriding influence, because self-clinching requires that the fastener always be harder than its host sheet. In general, installation of self-clinching fasteners is accomplished by pressing the fastener into place in a properly sized drilled or punched hole. This process causes displaced sheet material (softer than the fastener) to cold-flow into a specially designed annular recess in the shank or pilot of the fastener, permanently locking the fastener in place.

Posted in: Mechanical Components, Briefs

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Controlling Attitude of a Solar-Sail Spacecraft Using Vanes

A paper discusses a concept for controlling the attitude and thrust vector of a three-axis stabilized Solar Sail spacecraft using only four single degree of freedom articulated spar-tip vanes. The vanes, at the corners of the sail, would be turned to commanded angles about the diagonals of the square sail. Commands would be generated by an adaptive controller that would track a given trajectory while rejecting effects of such disturbance torques as those attributable to offsets between the center of pressure on the sail and the center of mass. The controller would include a standard proportional + derivative part, a feed forward part, and a dynamic component that would act like a generalized integrator. The controller would globally track reference signals, and in the presence of such control actuator constraints as saturation and delay, the controller would utilize strategies to cancel or reduce their effects. The control scheme would be embodied in a robust, nonlinear algorithm that would allocate torques among the vanes, always finding a stable solution arbitrarily close to the global optimum solution of the control effort allocation problem. The solution would include an acceptably small angle, slow limit-cycle oscillation of the vanes, while providing overall thrust vector pointing stability and performance.

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Tool for Coupling a Torque Wrench to a Round Cable Connector

Torque is applied without offset. A tool makes it possible to couple a torque wrench to an externally knurled, internally threaded, round cable connector. The purpose served by the tool is to facilitate the tightening of multiple such connectors (or the repeated tightening of the same connector) to repeatable torques.

Posted in: Mechanics, Mechanical Components, Briefs

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Excitations for Rapidly Estimating Flight-Control

Parameters Parameters are estimated, in nearly real time, from responses to these excitations. A flight test on an F-15 airplane was performed to evaluate the utility of prescribed simultaneous independent surface excitations (PreSISE) for real-time estimation of flight-control parameters, including stability and control derivatives. The ability to extract these derivatives in nearly real time is needed to support flight demonstration of intelligent flight-control system (IFCS) concepts under development at NASA, in academia, and in industry. Traditionally, flight maneuvers have been designed and executed to obtain estimates of stability and control derivatives by use of a post-flight analysis technique. For an IFCS, it is required to be able to modify control laws in real time for an aircraft that has been damaged in flight (because of combat, weather, or a system failure).

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Estimation of Stability and Control Derivatives of an F-15

Parameters can be estimated in nearly real time for use in adaptive flight control. A technique for real-time estimation of stability and control derivatives (derivatives of moment coefficients with respect to control-surface deflection angles) was used to support a flight demonstration of a concept of an indirect-adaptive intelligent flight control system (IFCS). Traditionally, parameter identification, including estimation of stability and control derivatives, is done post-flight. However, for the indirect-adaptive IFCS concept, parameter identification is required during flight so that the system can modify control laws for a damaged aircraft.

Posted in: Mechanical Components, Briefs

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Active Struts With Variable Spring Stiffness and Damping

These struts would act as linear actuators and controllable shock absorbers.Controllable active struts that would function as linear actuators with variable spring stiffness and damping have been proposed as components of advanced suspension systems of future wheeled ground vehicles. The contemplated advanced suspension systems would include computer-based control subsystems that would continually adjust the actuator responses to obtain optimal combinations of safety and comfort under operating conditions ranging from low speeds over smooth roads to high speeds over rough, unpaved ground. The proposed struts and suspension systems were originally intended for use in military vehicles, but there could also be a broad commercial market for them in trucks and sport utility vehicles.

Posted in: Mechanical Components, Briefs

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