467 research outputs found
The application of robotics to the assembly of flexible parts by sewing.
This thesis concerns the development of a robotic cell to
perform assembly and handling operations on cloth.- A
flexible automation approach was adopted, in which the
robot was required to control the cloth panel during both
handling and sewing operations, without the aid of hard
automation attachments which might limit the flexibility of
the system. The cell consisted of an adaptively controlled
robot, a hierarchy of controllers, a conventional sewing
machine, a two-fingered fabric steering end-effector, and
several sensor systems.
A technique was developed for producing a seam parallel to
an edge of arbitrary contour, in which two cameras, a
cloth tension sensor and the sewing machine's shaft encoder
provided the sensory input. Two sensory servo control
systems were required, one control system generated the
robot's trajectory to maintain a small constant cloth
tension, and the other directed the robot to manipulate the
cloth panel to maintain a constant seam width.
The design of the cloth tension control was based on the
measured frequency response of the open loop system. The
seam width control was designed using simulation studies,
which accounted for the control transfer function, and nonlinearities
such as camera pixel resolution, time delays
and robot motion limitations.
Several robotic handling techniques were developed, so that
a cloth panel placed arbitrarily on the sewing table could
be set up for an edge seaming operation, and the cloth
could be rotated about the needle. The system's flexibility
was demonstrated in the assembly of an irregularly shaped
cloth panel, in which three adjacent sides were sewn up
Development and Improvement of Airborne Remote Sensing Radar Platforms
With the recent record ice melt in the Arctic as well as the dramatic changes occurring in the Antarctic, the need and urgency to characterize ice sheets in these regions has become a research thrust of both the NSF and NASA. Airborne remote sensing is the most effective way to collect the necessary data on a large scale with fine resolution. Current models for determining the relationship between the world's great ice sheets and global sea-level are limited by the availability of data on bed topography, glacier volume, internal layers, and basal conditions. This need could be satisfied by equipping long range aircraft with an appropriately sensitive suite of sensors. The goal of this work is to enable two new airborne radar installations for use in cryospheric surveying, and improve these systems as well as future systems by addressing aircraft integration effects on antenna-array performance. An aerodynamic fairing is developed to enable a NASA DC-8 to support a 5-element array for CReSIS's MCoRDS radar, and several structures are also developed to enable a NASA P-3 to support a 15-element MCoRDS array, as well as three other radar antenna-arrays used for cryospheric surveying. Together, these aircraft have flown almost 200 missions and collected 550 TB of unique science data. In addition, a compensation method is developed to improve beamforming and clutter suppression on wing-mounted arrays by mitigating phase center errors due to wing-flexure. This compensation method is applied to the MVDR beamforming algorithm to improve clutter suppression by using element displacement information to apply appropriate phase shifts. The compensation demonstrated an average SINR increase of 5-10 dB. The hardware contributions of this work have substantially contributed to the state-of-the-art for polar remotes sensing, as evidenced by new data sets made available to the science community and widespread use and citation of the data. The investigations of aircraft integration effects on antenna-arrays will improve future data sets by characterizing the performance degradation. The wing-flexure compensation will greatly improve beam formation and clutter suppression. Increased clutter suppression in airborne radars is crucial to improving next generation ice sheet models and sea-level rise predictions
Simulation-Oriented Methodology for Distortion Minimisation during Laser Beam Welding
Distortion is one of the drawbacks of any welding process, most of the time needed to be suppressed. One doubtful factor that could affect welding deformation is the shape of the liquid melt pool, which can be modified via variation of process parameters. The aim of this work was to numerically study the dynamics of the weld pool and its geometrical influence on welding distortion during laser beam welding. To achieve such a goal, a promising novel process simulation model, employed in investigating the keyhole and weld pool dynamics, has successfully been invented. The model incorporated all distinctive behaviours of the laser beam welding process. Moreover, identification of the correlation between the weld pool geometry and welding distortion as well as, eventually, weld pool shapes that favour distortion minimisation has also been simulatively demonstrated
Simulation-Oriented Methodology for Distortion Minimisation during Laser Beam Welding
Distortion is one of the drawbacks of any welding process, most of the time needed to be suppressed. One doubtful factor that could affect welding deformation is the shape of the liquid melt pool, which can be modified via variation of process parameters. The aim of this work was to numerically study the dynamics of the weld pool and its geometrical influence on welding distortion during laser beam welding. To achieve such a goal, a promising novel process simulation model, employed in investigating the keyhole and weld pool dynamics, has successfully been invented. The model incorporated all distinctive behaviours of the laser beam welding process. Moreover, identification of the correlation between the weld pool geometry and welding distortion as well as, eventually, weld pool shapes that favour distortion minimisation has also been simulatively demonstrated
Deployable antenna phase A study
Applications for large deployable antennas were re-examined, flight demonstration objectives were defined, the flight article (antenna) was preliminarily designed, and the flight program and ground development program, including the support equipment, were defined for a proposed space transportation system flight experiment to demonstrate a large (50 to 200 meter) deployable antenna system. Tasks described include: (1) performance requirements analysis; (2) system design and definition; (3) orbital operations analysis; and (4) programmatic analysis
Ninth DOD/NASA/FAA Conference on Fibrous Composites in Structural Design, volume 1
This publication contains the proceedings of the Ninth DOD/NASA/FAA conference on Fibrous Composites in structural Design. Presentations were made in the following areas of composite structural design: perspectives in composites; design methodology; design applications; design criteria; supporting technology; damage tolerance; and manufacturing
Textile hybrid kinetic adaptive structures: a case study
Dissertação de mestrado integrado em Engenharia CivilThis thesis has the main objective to study three distinct typologies of structures. These structures are,
form-active structures, in particular membrane structures, bending-active structures and the integration
of both concepts with a kinetic principle, therefore adaptive hybrid structures. Both membrane and
bending-active are structures that require form finding, since the form of these structures is dependent
on the loading and boundary conditions, thus only known a posteriori. These structures are subject to
large deformations and thus, geometric nonlinearities must be considered during the calculation.
Additionally, the flexibility of membrane structures conjugated with the elastic behaviour of bending-active
structures creates the perfect conditions for the development of hybrid kinetic structures that adapt
according to the external loading conditions present. This study intends to elaborate an exploratory
approach on these concepts, thus bringing forward the main problems that originate when analysing a
structure of this type. Therefore, firstly a study on membrane, bending-active, hybrid and kinetic structures
is presented, containing the most relevant knowledge that currently exists regarding these topics. Then,
the structural aspects that are inherent to these structures are exposed. Three routines are developed in
Sofistik® in order form find and calculate the above-mentioned structures. Validations are made on these
routines and software analysis. The structural feasibility of an architectural concept proposed by Costa
(2017) of a hybrid adaptive concept is studied by applying these routines, and the kinetic hybrid concept
is simulated in Sofistik®. The adaptive principle is also extended to function structurally, by taking
advantage of the bending prestress implied by the bending-active elements. Finally, external wind loads
are applied to this structure, in order to test the effectiveness of the structural adaptive concept. It was
concluded that there is significant importance of the bending adaptive movement in the loadbearing
capacity of the overall system. Additionally, the choice of the initial shape of the structure defines a crucial
step on the definition of the structure, since it affects the process of form finding, that latter affects the
structural performance.A presente dissertação tem como objetivo principal estudar três tipologias distintas de estruturas. Estas
estruturas são as estruturas de forma ativa, particularmente as estruturas em membrana, as estruturas
de flexão ativa e a integração de ambos os conceitos com um princípio cinético, ou seja, estruturas
hibridas adaptativas. Tanto as estruturas de membranas como as estruturas de flexão ativa são estruturas
que requerem determinação da forma pois, como a forma destas estruturas é dependente das condições
de tensão e de fronteira, apenas é conhecida a posteriori. Estas estruturas estão sujeitas a grandes
deformações e, portanto, as não linearidades geométricas devem ser consideradas durante o cálculo.
Para além disto, a flexibilidade das estruturas de membrana conjugada com o comportamento elástico
das estruturas de flexão ativa geram condições perfeitas para o desenvolvimento de estruturas cinéticas
hibridas que se adaptam de acordo com as condições de carregamento presentes. Este estudo pretende
elaborar uma aproximação exploratória a estes conceitos, trazendo para primeiro plano os principais
problemas originários da análise deste tipo de estruturas. Desta forma, primeiramente é apresentado um
estudo sobre estruturas de membrana, flexão ativa, hibridas e cinéticas, contendo a informação mais
relevante que existe atualmente sobre estes assuntos. De seguida, os aspetos estruturais inerentes a
estas estruturas são expostos. Três rotinas são desenvolvidas no Sofistik® de forma a determinar a forma
e calcular as estruturas anteriormente mencionadas. São realizadas validações destas rotinas e da
análise preconizada pelo software. A viabilidade estrutural de um conceito de arquitetura proposto por
Costa (2017) sobre uma estrutura hibrida adaptativa é estudada através da aplicação destas rotinas, e
o princípio cinético hibrido é simulado através do Sofistik®. O princípio adaptativo é alargado de modo a
funcionar estruturalmente, tirando partido da pretensão implícita pelos elementos de flexão ativa.
Finalmente, são aplicadas cargas externas de vento à estrutura, de forma a testar a eficácia do principio
adaptativo estrutural. Foi concluído que o movimento adaptativo de flexão tem uma importante
significância ao nível da carga admissível na estrutura. Adicionalmente, a escolha da geometria inicial da
estrutura define uma etapa fundamental na definição da estrutura, pois afeta o processo de form finding,
que mais tarde afeta o desempenho estrutural
NASA Tech Briefs, April 1992
Topics covered include: New Product Ideas; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences
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