31,327 research outputs found
The design and implementation of a flexible manufacturing system for a surface mounting production line
A project report submitted to the Faculty of Engineering,
University of the Witwatersrand, Johannesburg, in partial
fulfillment of the requirements for the degree of Master of
Science in Engineering.The viability of introducing a Surface Mount
production line is chiefly determined by the
reliability characteristics of the components being
used. Surface Mount Technology (SMT) is entirely new
and although related to traditional through-hole
processes, requires different components, assembly
techniques and design methods. The purpose of the
literature survey is primarily to determine whether
surface mount components meet today's industrial
requirements with respect to their manufacturing
reliability and availability. A brief review of the
evolution of SMT is also presented. This study finds
that the implementation of SMT should be given highest
priority by manufacturing companies in order to
maintain their share of the marketplace.
Surface Mount Technology embodies a totally new
automated circuit assembly process, using a new
generation of electronic comporents: surface mounted
devices (SMDs). Smaller than conventional components,
SMDs are placed onto the surface of the substrate.
From this, the fundamental difference between SMD
assembly and convencional through-hole component
assembly arises; SMD component positioning is
relative, not absolute.
When a through-hole component is inserted into a pcb,
either the leads go through the hales or they don't.
An SMD, however, is placed onto the substrate surface,
it's position only relative to the solder lands, and
placement accuracy is therefore influenced by
variations in the substrate track pattern, component
size, and placement machine accuracy.
Other factors influence the layout of SMD substrates.
For example, will the board be a mixed-print ( a
combination of through-hole components and SMDs) or an
all-SMD design? Will SMDs be placed on one side of the
substrate or both? And there are process
considerations like what type of machine will place
the components and how will they be soldered?
This project describes in detail the processes
involved in setting up an SMT facility. A simulation
program was developed to verify the viability of these
processes. The simulation program was also applied to
an existing SMT facility and together with developed
optimization software, attempted to identify and
resolve some of the major problems. All this was
achieved, and the extent to which simulation could be
used as an efficient production tool, was highlighted.AC201
RAID-2: Design and implementation of a large scale disk array controller
We describe the implementation of a large scale disk array controller and subsystem incorporating over 100 high performance 3.5 inch disk drives. It is designed to provide 40 MB/s sustained performance and 40 GB capacity in three 19 inch racks. The array controller forms an integral part of a file server that attaches to a Gb/s local area network. The controller implements a high bandwidth interconnect between an interleaved memory, an XOR calculation engine, the network interface (HIPPI), and the disk interfaces (SCSI). The system is now functionally operational, and we are tuning its performance. We review the design decisions, history, and lessons learned from this three year university implementation effort to construct a truly large scale system assembly
James Webb Space Telescope Optical Simulation Testbed I: Overview and First Results
The James Webb Space Telescope (JWST) Optical Simulation Testbed (JOST) is a
tabletop workbench to study aspects of wavefront sensing and control for a
segmented space telescope, including both commissioning and maintenance
activities. JOST is complementary to existing optomechanical testbeds for JWST
(e.g. the Ball Aerospace Testbed Telescope, TBT) given its compact scale and
flexibility, ease of use, and colocation at the JWST Science & Operations
Center. We have developed an optical design that reproduces the physics of
JWST's three-mirror anastigmat using three aspheric lenses; it provides similar
image quality as JWST (80% Strehl ratio) over a field equivalent to a NIRCam
module, but at HeNe wavelength. A segmented deformable mirror stands in for the
segmented primary mirror and allows control of the 18 segments in piston, tip,
and tilt, while the secondary can be controlled in tip, tilt and x, y, z
position. This will be sufficient to model many commissioning activities, to
investigate field dependence and multiple field point sensing & control, to
evaluate alternate sensing algorithms, and develop contingency plans. Testbed
data will also be usable for cross-checking of the WFS&C Software Subsystem,
and for staff training and development during JWST's five- to ten-year mission.Comment: Proceedings of the SPIE, 9143-150. 13 pages, 8 figure
Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4
Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences
Printed Circuit Board (PCB) design process and fabrication
This module describes main characteristics of Printed Circuit Boards (PCBs). A brief history of PCBs is introduced in the first chapter. Then, the design processes and the fabrication of PCBs are addressed and finally a study case is presented in the last chapter of the module.Peer ReviewedPostprint (published version
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