Mechanical & Fluid Systems

Phase-Oriented Gear Systems

Larger mechanical advantages can be realized in smaller packages. Phase-oriented gear systems are differential planetary transmissions in which each planet gear has two sets of unequal numbers of teeth indexed at prescribed relative angles (phases). The figure illustrates an application of the phase-oriented gearing concept to a relatively simple speed-reducing differential planetary transmission that includes a sun gear, an idler gear, three identical planet gears, a ground internal ring gear, and an output internal ring gear. Typically, the ground internal ring gear and output internal ring gear have different numbers of teeth, giving rise to a progressive and periodic phase shift between the corresponding pairs of teeth engaged by each successive planet gear. To accommodate this phase shift, it is necessary to introduce a compensating phase shift between the groundgear- engaging and output-gear-engaging sections of each planet gear. This is done by individually orienting each planet gear.

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Free-to-Roll Testing of Airplane Models in Wind Tunnels

Causes of, and cures for, wing-drop/rock behavior can be evaluated. A free-to-roll (FTR) test technique and test rig make it possible to evaluate both the transonic performance and the wing-drop/rock behavior of a high-strength airplane model in a single wind-tunnel entry. The free-to-roll test technique is a single degree-of-motion method in which the model is free to roll about the longitudinal axis. The rolling motion is observed, recorded, and analyzed to gain insight into wing-drop/rock behavior.

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Measuring Dynamic Transfer Functions of Cavitating Pumps

Flow and pressure perturbations are imposed; transfer functions are computed from responses. A water-flow test facility has been built to enable measurement of dynamic transfer functions (DTFs) of cavitating pumps and of inducers in such pumps. Originally, the facility was intended for use in an investigation of the effects of cavitation in a rocket-engine low-pressure oxygen turbopump. The facility can also be used to measure DTFs of cavitating pumps in general.

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Robot Would Climb Steep Terrain

This walking robot could even climb under overhangs. The figure depicts the steep terrain access robot (STAR) — a walking robot that has been proposed for exploring steep terrain on remote planets. Robots based on the STAR concept could also be used on steep terrain on Earth for diverse purposes that could include not only scientific exploration but also military reconnaissance and search-and-rescue operations.

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First-Order Theory of Control of Motion of a Crane and Load

Suitably modulated motion of the crane could prevent swinging of the load. A first-order mathematical model has been developed in a theoretical study of the dynamics of a load suspended by a cable from a crane that moves along a straight track. The model is the basis of a proposed method of computer control of the velocity as well as the position of the crane to minimize or prevent swinging of the load. (Traditionally, only the position of the crane is controlled; there is no engineering provision against swinging of the load.) Velocity and position control to prevent swinging would be highly desirable, especially in situations in which there are requirements for precise placement of large loads and/or the delays incurred in waiting for damping of pendulum oscillations of loads are unacceptable. Because most modern cranes are already controlled by computers and include position-indicating control subsystems, the implementation of this method of control would entail little or no additional equipment and thus should be relatively inexpensive.

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Hollow Shaft Actuators with Harmonic Drive Gearing

They can be used in demanding applications such as industrial robots and servo systems. Harmonic drive gearing is recognized by designers for its zero backlash, high gear ratios, and compact design features. A recent development by HD Systems incorporates a large hollow shaft through the actuator, offering many benefits to the machine designer. The FHA hollow shaft actuator series allows cables, shafts, or tubing to be passed concentrically through the center of the actuator. Through this innovation, the series provides precision motion control and high torque capacity in very compact packages.

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Actuated Ball-and-Socket Joints

These joints would be relatively compact, lightweight, simple, and inexpensive. The term "actuated ball-and-socket" (ABS) characterizes a proposed class of ball-and-socket joints that would incorporate ultrasonic motors and other piezoelectric actuators to generate multidimensional actuation. In some applications, ABS joints could supplant traditional joint-and-actuator assemblies that include passive rotary joints actuated by electromagnetic motors via gears. In comparison with such assemblies, ABS joints offer potential advantages of compactness, relative mechanical simplicity, higher torque-to-weight ratios, no backlash, self-braking with power turned off, and lower cost. ABS joints are expected to be particularly attractive for use as robot joints and as general low-power orienting actuators for diverse applications that could include robot hands, tools, and mechanisms for aiming scientific instruments.

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