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

Advanced Diagnostic Techniques Applied to Polymer Electrolyte Fuel Cells

Polymer electrolyte fuel cells (PEFCs) are among the most promising energy conversion technologies for a broad range of applications, offering zero-emission electricity generation by converting hydrogen directly into electrical energy at high efficiencies. Tremendous advancements have been made in terms of performance and durability but technological challenges still exist which hinder their widespread adoption; these challenges range from material durability to system design and operating strategies. Developing this technology requires a comprehensive understanding of its fundamental operation, coupled with effective diagnostic techniques. Performance, temperature and hydration in a PEFC is a complex relationship governed by cause-and-effect, where a change in one factor alters the other. These problems are exacerbated during scale-up, advancing from small lab-scale single cells to large commercial automotive stacks, where operational heterogeneities encourage large current and temperature variations, resulting in varied local degradation rates and inefficient PEFC performance. This study characterises these parameters in-operando by adopting diagnostic techniques such as current, temperature and pressure mapping, coupled with electrochemical techniques, to garner a broader understanding of the formation of these heterogeneities. The development of new diagnostic techniques for both research and industry is also crucial for the commercialisation of PEFCs, as stack-level diagnostic resources are limited. These are required to be straightforward in application and interpretation, cost-effective and with short testing times. Novel diagnostic techniques are presented in this study which aim to bridge this gap in the diagnostic sector. Lock-in thermography is used to image sub-surface water content during cell operation using a thermal imaging camera, producing water distribution images at various penetration depths. A complementary transfer function technique is also developed, termed heat-stimulus thermo-electric impedance spectroscopy (HS-TEIS), which considers the complex relationship between imposed temperature change and electrical response as a function of frequency

NASA Tech Briefs, August 2000

Topics include: Simulation/Virtual Reality; Test and Measurement; Computer-Aided Design and Engineering; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery/Automation; Manufacturing/Fabrication; Mathematics and Information Sciences; Medical Design

18th Annual International Conference on Contaminated Soils, Sediments and Water

Conference at a Glance Monday, October 21, 2002 Workshops Workshops # 1, 2 & 3 - 10:00 am - 5:00 pm Workshops # 4 & 5 - 1:00 - 5:00 pm 1: The Indoor Air Exposure Pathway from Chlorinated Solvent Contaminated Groundwater 2: Theory and Use of Field Portable X-ray Fluorescence for Soil Analysis 3: In-Situ Chemical Oxidation Workshop 4: Workshop on Current Spectrochemical Techniques for Determining Heavy Metals in Sediments and Soils 5: Practical Remediation of Volatile Organic Compounds in Soil and Groundwater Tuesday, October 22, 2002 Platform Presentations 8:30am-Noon Session 1: Advances in In-Situ Remediation Session 2: Phytoremediation Session 3: Heavy Metals 1:30pm-5:30pm Session 1: MTBE Session 2: Sediments I Session 3A: RBCA Session 3B: Regulatory Poster Session, 4:00 pm - 6:00 pm , Exhibit Area, First Floor, Campus Center Social: 4:30-6:00 pm Exhibit Area, First Floor Campus Center Workshops (Evening 7:00-10:00 pm) 6: State of the Science in Assessing MTBE Degradation II 7: Recent Improvements in the Practice of Risk Assessment as Illustrated through Case Studies Wednesday, October 23, 2002 Platform Presentations 8:30 am-Noon Session 1: Environmental Forensics I Session 2: MGP Site Closure Session 3: Bioremediation 1:30pm-5:30pm Session 1: Sediments II Session 2: Remediation - Soils Session 3A: Chemical Oxidation Session 3B: Training Range Residues Session 4: Biomarkers for Contamination: Hierarchical Approaches Poster Session, 1:00-3:00 pm, Exhibit Area, First Floor, Campus Center Social: 4:30-6:00 pm Exhibit Area, First Floor Campus Center Workshops (Evening 7:00-10:00pm) 8: Forensic Environmental Geochemistry: Petroleum Fuels 9: MGP Site Closures: Experiences from the Trenches - Point Counter Point Technology Review 10: Environmental Fate of Hydrocarbons in Soils and Groundwater Thursday, October 24, 2002 Platform Presentations 8:30 am-Noon Session 1: Environmental Forensics II Session 2: Remediation - Groundwater Session 3: Arsenic Session 4: Site Assessment/Environmental Fate 1:30pm-5:30pm Session 1: Sediments III Session 2: Risk Assessmen

Safety and Mission Assurance Acronyms, Abbreviations, and Definitions

This NASA Technical Handbook compiles into a single volume safety, reliability, maintainability, and quality assurance and risk management terms defined and used in NASA safety and mission assurance directives and standards. The purpose of this handbook is to support effective communication within NASA and with its contractors. The definitions in this handbook are updated when the definition of the acronym or term is updated in the originating document

Spring contact probes: wear characteristics testing for electrical and mechanical parameters

The study considers the development and evaluation of spring contact probes used for automated testing of printed circuit boards (PCBs) and assemblies. It considers the evolution of circuit technology which originated from the introduction of the thermionic valve at the beginning of the century. Since the introduction of the integrated circuit in the 1960's, the industry has seen considerable advances in integrated and printed circuit miniaturisation with its associated effect on the testability of the completed assembly. The close spacing between the tracks and pads within the printed circuit board, which is possibly loaded on both sides with integrated circuits and other components with fine pitch termination spacings, has initiated the rapid development of a specialised electronic test industry to ensure product quality. [Continues.

Adaptive deformable mirror : based on electromagnetic actuators

Refractive index variations in the earth's atmosphere cause wavefront aberrations and limit thereby the resolution in ground-based telescopes. With Adaptive Optics (AO) the temporally and spatially varying wavefront distortions can be corrected in real time. Most implementations in a ground based telescope include a WaveFront Sensor, a Deformable Mirror and a real time wavefront control system. The largest optical telescopes built today have a ~ 1 Om primary mirror. Telescopes with more collecting area and higher resolution are desired. ELTs are currently designed with apertures up to 42m. For these telescopes serious challenges for all parts of the AO system exist. This thesis addresses the challenges for the DM. An 8m class telescope on a representative astronomical site is the starting point. The atmosphere is characterized by the spatial and temporal spectra of Kolmogorov turbulence and the frozen flow assumption. The wavefront fitting error, caused by a limited number of actuators and the temporal error, caused by a limited control bandwidth, are the most important for the DM design. It is shown that ~5000 actuators and 200Hz closed loop bandwidth form a balanced choice between the errors and correct an 8m wavefront in the visible to nearly diffraction limited. An actuator stroke of ~5.6J.!m and ~0.36J.!m inter actuator stroke is thereby needed. Together with the nm's resolution, low power dissipation, no hysteresis and drift, these form the main DM requirements. The design, realization and tests of a new DM that meets these requirements and is extendable and scalable in mechanics, electronics and control to suit further Extremely Large Telescopes (ELTs) is presented. In the DM a few layers are distinguished: a continuous mirror facesheet, the actuator grid and the base frame. In the underlying layer - the actuator grid - low voltage electromagnetic push-pull actuators are located. Identical actuator modules, each with 61 actuators, hexagonally arranged on a 6mm pitch can be placed adjacent to form large grids. The base frame provides a stable and stiff reference. A thin facesheet is needed for low actuator forces and power dissipation, whereby its lower limit is set by the facesheets inter actuator deflection determined by gravity or wind pressure. For both scaling laws for force and dissipation are derived. Minimum power dissipation is achieved when beryllium is used for the mirror facesheet. Pyrex facesheets with 100J.!m thickness are chosen as a good practical, alternative in the prototype development. Struts (00.1 x 8mm) connect the facesheet to the actuators and ensure a smooth surface over the imposed heights and allow relative lateral movement of the facesheet and the actuator grid. Measurements show 3nm RMS surface unflattness from the glued attachment. The stiffness of the actuators form the out-of-plane constraints for the mirror facesheet and determine the mirrors first resonance frequency. and is chosen such that the resonance frequency is high enough to allow the high control bandwidth but not higher that needed to avoid excessive power dissipation and fix points in the surface in case of failure. The electromagnetic variable reluctance actuators designed, are efficient, have low moving mass and have suitable stiffness. Other advantages are the low costs, low driving voltages and negligible hysteresis and drift. The actuators consist of a closed magnetic circuit in which a PM provides static magnetic force on a ferromagnetic core that is suspended in a membrane. This attraction force is increased of decreased by a current through a coil. The actuators are free from mechanical hysteresis, friction and play and therefore have a high positioning resolution with high reproducibility. The actuator modules are build in layers to reduces the number of parts and the complexity of assembly and to improve the uniformity in properties. Dedicated communication and driver electronics are designed. FPGA implemented PWM based voltage drivers are chosen because of their high efficiency and capability to be implemented in large numbers with only a few electronic components. A multidrop LVDS based serial communication is chosen for its low power consumption, high bandwidth and consequently low latency, low communication overhead and extensive possibilities for customization. A flat-cable connects up to 32 electronics modules to a custom communications bridge, which translates the ethernet packages from the control PC into LVDS. Two DMs prototypes were successfully assembled: a 050mm DM with 61 actuators and a 0l50mm DM with 427 actuators. In the second prototype modularity is shown by the assembly of seven identical grids on a common base. The dynamic performance of each actuator is measured, including its dedicated driver and communication. All actuators were found to be functional, indicating that the manufacturing and assembly process is reliable. A nonlinear mathematical model of the actuator was derived describing both its static and dynamic behavior based on equations from the magnetic, mechanic and electric domains. The actuator model was linearized, leading to expressions for the actuator transfer function and properties such as motor constant, coil inductance, actuator stiffness and resonance frequency. From frequency response function measurements these properties showed slight deviations from the values derived from the model, but the statistical spread for the properties was small, stressing the reliability of the manufacturing and assembly process. The mean actuator stiffness and resonance frequency were 0.47kN/m and 1.8kHz respectively, which is close to their design values of 500N/m and 1.9kHz. The time domain response of an actuator to a 4Hz sine voltage was used to determine hysteresis and semi-static nonlinear response of the actuator. This showed the first to be negligible and the second to remain below 5% for ±10J.!m stroke. Measurements showed that in the expected operating range, the total power dissipation is dominated by indirect losses in FPGAs. The static DM performance is validated using interferometric measurements. The measured influence matrix is used to shape the mirror facesheet into the first 28 Zernike modes, which includes the piston term that represents the best flat mirror. The total RMS error is ~25nm for all modes. The dynamic behavior of the DM is validated by measurements. A laser vibrometer is used to measure the displacement of the mirror facesheet, while the actuators are driven by zero-mean, bandlimited, white noise voltage sequence. Using the MOESP system identification algorithm, high-order black-box models are identified with VAF values around 95%. The first resonance frequency identified is 725Hz, and lower than the 974Hz expected from the analytical model. This is attributed to the variations in actuator properties, such as actuator stiffness. The power dissipation in each actuator of the 050mm mirror to correct a typical Von Karmann turbulence spectrum is ~ 1.5m W