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At least 1,117 records · Page 62

Lightweight Exoskeletons with Controllable Actuators

A proposed class of lightweight exoskeletal electromechanical systems would include electrically controllable actuators that would generate torques and forces that, depending on specific applications, would resist and/or assist wearers movements. The proposed systems would be successors to relatively heavy, bulky, and less capable human-strength-amplifying exoskeletal electromechanical systems that have been subjects of research during the past four decades. The proposed systems could be useful in diverse applications in which there are needs for systems that could be donned or doffed easily, that would exert little effect when idle, and that could be activated on demand: examples of such applications include (1) providing controlled movement and/or resistance to movement for physical exercise and (2) augmenting wearers strengths in the performance of military, law-enforcement, and industrial tasks. An exoskeleton according to the proposal would include adjustable lightweight graphite/epoxy struts and would be attached to the wearer's body by belts made of hook-and-pile material. At selected rotary and linear joints, the exoskeleton would be fitted, variously, with lightweight, low-power-consumption rotary and linear brakes, clutches, and motors. The exoskeleton would also be equipped with electronic circuitry for monitoring, control, and possibly communication with external electronic circuits that would perform additional monitoring and control functions.

Bar-Cohen, Yoseph↗

Failure Mode Analysis of V-Shaped Pyrotechnically Actuated Valves

Current V-shaped stainless steel pyrovalve initiators have rectified many of the deficiencies of the heritage Y-shaped aluminum design. However, a credible failure mode still exists for dual simultaneous initiator (NSI) firings in which low temperatures were detected at the booster cap and less consistent ignition was observed than when a single initiator was fired. In order to asses this issue, a numerical framework has been developed for predicting the flow through pyrotechnically actuated valves. This framework includes a fully coupled solution of the gas-phase equation with a non-equilibrium dispersed phase for solid particles as well as the capability to model conjugate gradient heat transfer to the booster cap. Through a hierarchy of increasingly complex simulations, a hypothesis for the failure mode of the nearly simultaneous dual NSI firings has been proven. The simulations indicate that the failure mode for simultaneous dual NSI firings may be caused by flow interactions between the flame channels. The shock waves from each initiator interact in the booster cavity resulting in a high pressure that prevents the gas and particulate velocity from rising in the booster cap region. This impedes the bulk of the particulate phase from impacting the booster cap and reduces the heat transfer to the booster cap since the particles do not impact it. Heat transfer calculations to the solid metal indicate that gas-phase convective heat transfer may not be adequate by itself and that energy transfer from the particulate phase may be crucial for the booster cap burn through.

Sachdev, Jai S.↗

Deep Drilling and Sampling via the Wireline Auto-Gopher Driven by Piezoelectric Percussive Actuator and EM Rotary Motor

The ability to penetrate subsurfaces and perform sample acquisition at depths of meters is critical for future NASA in-situ exploration missions to bodies in the solar system, including Mars and Europa. A corer/sampler was developed with the goal of acquiring pristine samples by reaching depths on Mars beyond the oxidized and sterilized zone. To developed rotary-hammering coring drill, called Auto-Gopher, employs a piezoelectric actuated percussive mechanism for breaking formations and an electric motor rotates the bit to remove the powdered cuttings. This sampler is a wireline mechanism that is incorporated with an inchworm mechanism allowing thru cyclic coring and core removal to reach great depths. The penetration rate is being optimized by simultaneously activating the percussive and rotary motions of the Auto-Gopher. The percussive mechanism is based on the Ultrasonic/Sonic Drill/Corer (USDC) mechanism that is driven by piezoelectric stack and that was demonstrated to require low axial preload. The Auto-Gopher has been produced taking into account the a lessons learned from the development of the Ultrasonic/Sonic Gopher that was designed as a percussive ice drill and was demonstrated in Antarctica in 2005 to reach about 2 meters deep. A field demonstration of the Auto-Gopher is currently being planned with objective of reaching as deep as 3 to 5 meters in tufa subsurface.

Auto-Gopher↗

Magnetically Actuated Seal

This invention is a magnetically actuated seal in which either a single electromagnet, or multiple electromagnets, are used to control the seal's position. This system can either be an open/ close type of system or an actively controlled system.

Pinera, Alex↗

Sweeping Jet Actuators - A New Design Tool for High Lift Generation

Active Flow Control (AFC) experiments performed at the Caltech Lucas Wind Tunnel on a generic airplane vertical tail model proved the effectiveness of sweeping jets in improving the control authority of a rudder. The results indicated that a momentum coefficient (C(sub u)) of approximately 2% increased the side force in excess of 50% at the maximum conventional rudder deflection angle in the absence of yaw. However, sparsely distributed actuators providing a collective C(sub u) approx. = 0.1% were able to increase the side force in excess of 20%. This result is achieved by reducing the spanwise flow along the swept back rudder and its success is attributed to the large sweep back angle of the vertical tail. This current effort was sponsored by the NASA Environmentally Responsible Aviation (ERA) project.

Graff, Emilio↗

Aeroelastic Wing Shaping Control Subject to Actuation Constraints.

This paper considers the control of coupled aeroelastic aircraft model which is configured with Variable Camber Continuous Trailing Edge Flap (VCCTEF) system. The relative deflection between two adjacent flaps is constrained and this actuation constraint is accounted for when designing an effective control law for suppressing the wing vibration. A simple tuned-mass damper mechanism with two attached masses is used as an example to demonstrate the effectiveness of vibration suppression with confined motion of tuned masses. In this paper, a dynamic inversion based pseudo-control hedging (PCH) and bounded control approach is investigated, and for illustration, it is applied to the NASA Generic Transport Model (GTM) configured with VCCTEF system.

aeroelasticity↗

Propellant Flow Actuated Piezoelectric Igniter for Combustion Engines

A propellant flow actuated piezoelectric igniter device using one or more hammer balls retained by one or more magnets, or other retaining method, until sufficient fluid pressure is achieved to release and accelerate the hammer ball, such that it impacts a piezoelectric crystal to produce an ignition spark. Certain preferred embodiments provide a means for repetitively capturing and releasing the hammer ball after it impacts one or more piezoelectric crystals, thereby oscillating and producing multiple, repetitive ignition sparks. Furthermore, an embodiment is presented for which oscillation of the hammer ball and repetitive impact to the piezoelectric crystal is maintained without the need for a magnet or other retaining mechanism to achieve this oscillating impact process.

Wollen, Mark A.↗

Magnetic Gearing Versus Conventional Gearing in Actuators for Aerospace Applications

Magnetic geared actuators (MGA) are designed to perform highly reliable, robust and precise motion on satellite platforms or aerospace vehicles. The design allows MGA to be used for various tasks in space applications. In contrast to conventional geared drives, the contact and lubrication free force transmitting elements lead to a considerable lifetime and range extension of drive systems. This paper describes the fundamentals of magnetic wobbling gears (MWG) and the deduced inherent characteristics, and compares conventional and magnetic gearing.

Puchhammer, Gregor↗

Auto-Gopher: A Wireline Deep Sampler Driven by Piezoelectric Percussive Actuator and EM Rotary Motor

The ability to penetrate subsurfaces and perform sample acquisition at depth of meters may be critical for future NASA in-situ exploration missions to bodies in the solar system, including Mars and Europa. A corer/sampler was developed with the goal of enabling acquisition of samples from depths of several meters where if used on Mars would be beyond the oxidized and sterilized zone. For this purpose, we developed a rotary-hammering coring drill, called Auto-Gopher, which employs a piezoelectric actuated percussive mechanism for breaking formations and an electric motor that rotates the bit to remove the powdered cuttings. This sampler is a wireline mechanism that can be fed into and retrieved from the drilled hole using a winch and a cable. It includes an inchworm anchoring mechanism allowing the drill advancement and weight on bit control without twisting the reeling and power cables. The penetration rate is being optimized by simultaneously activating the percussive and rotary motions of the Auto-Gopher. The percussive mechanism is based on the Ultrasonic/Sonic Drill/Corer (USDC) mechanism that is driven by piezoelectric stack and that was demonstrated to require low axial preload. The design and fabrication of this device were presented in previous publications. This paper presents the results of laboratory and field tests and lessons learned from this development.

piezoactuation↗

Robust Landing Using Time-to-Collision Measurement with Actuator Saturation

This paper considers a landing problem for an MAV that uses only a monocular camera for guidance. Although this sensor cannot measure the absolute distance to the target, by using optical flow algorithms, time-to-collision to the target is obtained. Existing work has applied a simple proportional feedback control to simple dynamics and demonstrated its potential. However, due to the singularity in the time-to-collision measurement around the target, this feedback could require an infinite control action. This paper extends the approach into nonlinear dynamics. In particular, we explicitly consider the saturation of the actuator and include the effect of the aerial drag. It is shown that the convergence to the target is guaranteed from a set of initial conditions, and the boundaries of such initial conditions in the state space are numerically obtained. The paper then introduces parametric uncertainties in the vehicle model and in the time-to-collision measurements. Using an argument similar to the nominal case, the robust convergence to the target is proven, but the region of attraction is shown to shrink due to the existence of uncertainties. The numerical simulation validates these theoretical results.

parametric uncertainty↗

Studies of the Effects of Actuator Errors on the HCIT/PIAA Contrast Performance

The High Contrast Imaging Testbed Phase Induced Amplitude Apodization (HCIT/PIAA) coronagraph system at JPL relies on an Electric-Field Conjugation (EFC) wavefront correction algorithm to obtain the required high contrast. This algorithm works with one deformable mirror (DM) to estimate the electric-field to be controlled, and with one or multiple DM's to create a "dark-hole" in the image plane. We have investigated the effects of DM actuator errors on the efficiency of the EFC algorithm. The structural design of the optical system as well as the parameters of various optical elements used in the analysis are drawn from those of the HCIT/PIAA system that have been and will be implemented with one or two DM's. The simulation takes into account the surface errors of various optical elements. In this paper, we report our findings in the case of narrowband wavelength light.

PIAA↗

Active Control of Low-Speed Fan Tonal Noise Using Actuators Mounted in Stator Vanes: Part III Results

A test program to demonstrate simplification of Active Noise Control (ANC) systems relative to standard techniques was performed on the NASA Glenn Active Noise Control Fan from May through September 2001. The target mode was the m = 2 circumferential mode generated by the rotor-stator interaction at 2BPF. Seven radials (combined inlet and exhaust) were present at this condition. Several different error-sensing strategies were implemented. Integration of the error-sensors with passive treatment was investigated. These were: (i) an in-duct linear axial array, (ii) an induct steering array, (iii) a pylon-mounted array, and (iv) a near-field boom array. The effect of incorporating passive treatment was investigated as well as reducing the actuator count. These simplified systems were compared to a fully ANC specified system. Modal data acquired using the Rotating Rake are presented for a range of corrected fan rpm. Simplified control has been demonstrated to be possible but requires a well-known and dominant mode signature. The documented results here in are part III of a three-part series of reports with the same base title. Part I and II document the control system and error-sensing design and implementation.

Sutliff, Daniel L.↗

Ball Screw Actuator Including a Compliant Ball Screw Stop

An actuator includes a ball nut, a ball screw, and a ball screw stop. The ball nut is adapted to receive an input torque and in response rotates and supplies a drive force. The ball screw extends through the ball nut and has a first end and a second end. The ball screw receives the drive force from the ball nut and in response selectively translates between a retract position and a extend position. The ball screw stop is mounted on the ball screw proximate the first end to translate therewith. The ball screw stop engages the ball nut when the ball screw is in the extend position, translates, with compliance, a predetermined distance toward the first end upon engaging the ball nut, and prevents further rotation of the ball screw upon translating the predetermined distance.

Wingett, Paul T.↗

Ball Screw Actuator Including a Stop with an Integral Guide

An actuator includes a housing assembly, a ball nut, a ball screw, and a ball screw stop. The ball nut is rotationally mounted in the housing assembly, is adapted to receive an input torque, and is configured, upon receipt thereof, to rotate and supply a drive force. The ball screw is mounted within the housing assembly and extends through the ball nut. The ball screw has a first end and a second end, and is coupled to receive the drive force from the ball nut. The ball screw is configured, upon receipt of the drive force, to selectively translate between a stow position and a deploy position. The ball screw stop is mounted on the ball screw to translate therewith and is configured to at selectively engage the housing assembly while the ball screw is translating, and engage the ball nut when the ball screw is in the deploy position.

Wingett, Paul T.↗

Control System Design Implementation and Preliminary Demonstration for a Tendon-Actuated Lightweight In-Space MANipulator (TALISMAN)

Satellite servicing is a high priority task for NASA and the space industry, addressing the needs of a variety of missions, and potentially lowering the overall cost of missions through refurbishment and reuse. However, the ability to service satellites is severely limited by the lack of long reach manipulation capability and inability to launch new devices due the end of the Space Transport System, or Space Shuttle Program. This paper describes the design and implementation of a control system for a Tendon-Actuated Lightweight In-Space MANipulator (TALISMAN), including; defining the forward and inverse kinematics, endpoint velocity to motor velocity, required cable tensions, and a proportional-integral-derivative (PID) controller. The tensions and velocities necessary to maneuver and capture small and large payloads are also discussed. To demonstrate the utility of the TALISMAN for satellite servicing, this paper also describes a satellite servicing demonstration using two TALISMAN prototypes to grasp and inspect a satellite mockup. Potential avenues for improving the control system are discussed.

Komendera, Erik E.↗

Structural Sizing Methodology for the Tendon-Actuated Lightweight In-Space MANipulator (TALISMAN) System

The Tendon-Actuated Lightweight In-Space MANipulator (TALISMAN) is a versatile long-reach robotic manipulator that is currently being tested at NASA Langley Research Center. TALISMAN is designed to be highly mass-efficient and multi-mission capable, with applications including asteroid retrieval and manipulation, in-space servicing, and astronaut and payload positioning. The manipulator uses a modular, periodic, tension-compression design that lends itself well to analytical modeling. Given the versatility of application for TALISMAN, a structural sizing methodology was developed that could rapidly assess mass and configuration sensitivities for any specified operating work space, applied loads and mission requirements. This methodology allows the systematic sizing of the key structural members of TALISMAN, which include the truss arm links, the spreaders and the tension elements. This paper summarizes the detailed analytical derivations and methodology that support the structural sizing approach and provides results from some recent TALISMAN designs developed for current and proposed mission architectures.

Jones, Thomas C.↗

Computations of Combustion-Powered Actuation for Dynamic Stall Suppression

A computational framework for the simulation of dynamic stall suppression with combustion-powered actuation (COMPACT) is validated against wind tunnel experimental results on a VR-12 airfoil. COMPACT slots are located at 10% chord from the leading edge of the airfoil and directed tangentially along the suction-side surface. Helicopter rotor-relevant flow conditions are used in the study. A computationally efficient two-dimensional approach, based on unsteady Reynolds-averaged Navier-Stokes (RANS), is compared in detail against the baseline and the modified airfoil with COMPACT, using aerodynamic forces, pressure profiles, and flow-field data. The two-dimensional RANS approach predicts baseline static and dynamic stall very well. Most of the differences between the computational and experimental results are within two standard deviations of the experimental data. The current framework demonstrates an ability to predict COMPACT efficacy across the experimental dataset. Enhanced aerodynamic lift on the downstroke of the pitching cycle due to COMPACT is well predicted, and the cycleaveraged lift enhancement computed is within 3% of the test data. Differences with experimental data are discussed with a focus on three-dimensional features not included in the simulations and the limited computational model for COMPACT.

Jee, Solkeun↗