Parallel Assembly Research Articles

Development of surface micromachined magnetic actuators using electroplated permalloy

Results on design, fabrication and testing of silicon micromachined magnetic actuators are presented. Magnetic actuators are capable of providing large force (in the order of mN) and large displacement (micrometer to millimeter range) within micro electromechanical devices and systems. Electroplated permalloy (Ni 80Fe 20) material is the media for magnetic interaction and force generation. The permalloy piece is supported by a structural plate, which consists of polycrystalline silicon thin film. Applications of such magnetic actuators in massive parallel assembly and high-yield surface-structure release are discussed.

Statistical representation and computation of tolerance and clearance for assemblability evaluation

The design of tolerances should take the functionality, manufacturability, assemblability and cost effectiveness of a product into consideration. This paper presents a method of analyzing and evaluating the assemblability of a product under given tolerance specifications in order to provide a tool to aide for tolerance design. Introduced is the range of feasible displacement of a part of an assembly as a result of the accumulation of clearances between mating parts along the serial as well as parallel chain of assembly, which can play a role of compensating for the pose error of the corresponding part due to the accumulation of tolerances. Assemblability is determined by the probability that all the parallel as well as serial chains of the assembly can be f ormed successfully under given statistical properties of tolerances. This requires to numerically compute the probability that a pair of mating parts forming a parallel chain can align themselves within the error margin defined by their mating clearance, accounting for the possible compensation of the ranges of pose errors associated with the mating parts due to tolerance accumulations by the ranges of feasible displacements of the mating parts due to clearance accumulations. Simulation results are shown.

Lane selection in an AGV-based asynchronous parallel assembly line

Automated Guided Vehicles (AGVs) have the flexibility to meet the material handling requirements of asynchronous assembly lines. Furthermore, AGVs can select from among alternative paths in accordance with a prescribed lane selection rule, thereby facilitating the use of parallel server workstations. In this paper, motivated by our work in the automotive industry, several new lane selection rules are proposed. One of these, First Available Server/First Available Buffer/Balanced Work Content (FAS/FAB/BWC), is compared to two existing rules: Alternating Server, and First Available Server/First Available Buffer/Expected Completion Time (FAS/FAB/EC). Three performance measures — job throughput, workload balance among servers, and alteration of input job sequence — are employed. A SIMAN simulation model of a small, asynchronous parallel assembly line is used to study the impact on system performance of both the lane selection rule and the number of parallel servers. Interaction between these two factors is studied through ANOVA. A number of interesting findings are reported for results of the lane selection rules with respect to the three performance measures. Their interpretation is used to motivate further research.

Technology challenges for integration near and below 0.1 μm

Technology challenges for silicon integrated circuits with a design rule of 0.1 /spl mu/m and below are addressed. We begin by reviewing the state-of-the-art CMOS technology at 0.25 /spl mu/m currently in development, covering a logic-oriented processes and dynamic random access memory (DRAM) processes. CMOS transistor structures are compared by introducing a figure of merit. We then examine scaling guidelines for 0.1 /spl mu/m which has started to deviate for optimized performance from the classical theory of constant-field scaling. This highlights the problem of nontrivial subthreshold current associated with the scaled-down CMOS with low threshold voltages. Interconnect issues are then considered to assess the performance of microprocessors in 0.1 /spl mu/m technology. 0.1 /spl mu/m technology will enable a microprocessor which runs at 1000 MHz with 500 million transistors. Challenges below 0.1 /spl mu/m are then addressed. New transistor and circuit possibilities such as silicon on insulator (SOI), dynamic-threshold (DT) MOSFET, and back-gate input MOS (BMOS) are discussed. Two problems below 0.1 /spl mu/m are highlighted. They are threshold voltage control and pattern printing. It is pointed out that the threshold voltage variations due to doping fluctuations is a limiting factor for scaling CMOS transistors for high performance. The problem with lithography below 0.1 /spl mu/m is the low throughput for a single probe. The use of massively parallel scanning probe assemblies working over the entire wafer is suggested to overcome the problem of low throughput.

Stream-of-Variation Theory for Automotive Body Assembly

Manufacturing systems usually consist of processes and machines in a multi-leveled hierarchy. As a result, dimensional variation in the final product is accumulated as the product moves along the manufacturing system. This paper discusses the prediction and diagnosis of dimensional variation in a multi-leveled automotive body assembly system. By combining engineering structural models with statistical analysis, the evolution of the variability and stiffness characteristics of sheet metal parts is studied in terms of assembly configurations, i.e., serial or parallel. The diagnosability of serial and parallel assembly systems is evaluated. These results are integrated with correlation clustering to form a complete diagnostic strategy. Predicting and diagnosing variation in a multi-leveled manufacturing system constitute the two aspects of what we call the “Stream-of-Variation Theory.”

Chromatin Assembly Coupled to DNA Repair: A New Role for Chromatin Assembly Factor I

DNA repair in the eukaryotic cell disrupts local chromatin organization. To investigate whether the resetting of nucleosomal arrays can be linked to the repair process, we developed model systems, with both Xenopus egg extract and human cell extracts, to follow repair and chromatin assembly in parallel on circular DNA templates. Both systems were able to carry out nucleotide excision repair of DNA lesions. We observed that UV-dependent DNA synthesis occurs simultaneously with chromatin assembly, strongly indicating a mechanistic coupling between the two processes. A complementation assay established that chromatin assembly factor I (CAF1) is necessary for this repair-associated chromatin formation.

A parallel solver for the hp-version of finite element methods

A prototype software system has been implemented for the parallel solution of linear systems associated with the hp-version, using the master/slave model and the Parallel Virtual Machine (PVM) message passing library. In a series of performance tests, significant speed-up was achieved in those typical cases for the hp-version where there was sufficient computational granularity to justify use of the parallel method. These tests indicate that the algorithms devised for element ordering, load distribution and load balancing are sufficiently robust. These tests also indicate that, even though communication overhead in a network environment is relatively high, there is significant potential for scaling the method to larger processor ensembles. The solution method developed was implemented as a four step procedure. In step 1, a dynamic load distribution algorithm selects an element for each idle process based on the mesh topology. In step 2, element descriptions are communicated to each process where local matrix computations are performed in parallel. In step 3, regional assembly and elimination operations are carried out in parallel to produce multiple ‘frontal matrices’ which are eventually returned to a host process for final solution. In step 4, the solution to the global stiffness matrix is back-substituted into each previous frontal matrix to determine the values of all unknowns eliminated during the parallel assembly procedure.

Analysis of partial setup strategies for solving the operational planning problem in parallel machine electronic assembly systems

In this paper, we analyse the operational planning problem in an electronic assembly system with multiple placement machines operating in parallel. The partial setup strategy is proposed as an effective methodology for this problem. This strategy attempts to determine the balance between processing time and changeover time during system operation. The Tour primary issues are determining the assignment of products to machines, the sequence of products on each machine, the assignment of components to feeder locations for each product, and the component placement sequence for each product. Four solution procedures for unique and partial setup strategies are developed and tested. The computation results show that for low to medium volume high mix environments, the partial setup procedures offer significant improvement over the unique setup strategies. The results also show that no single fixed strategy dominates in all scenarios, and therefore, an adaptable procedure that will choose the best solution for eac...

Tolerance Analysis for Sheet Metal Assemblies

Traditional tolerance analyses such as the worst case methods and the statistical methods are applicable to rigid body assemblies. However, for flexible sheet metal assemblies, the traditional methods are not adequate: the components can deform, changing the dimensions during assembly. This paper evaluates the effects of deformation on component tolerances using linear mechanics. Two basic configurations, assembly in series and assembly in parallel, are investigated using analytical methods. Assembly sequences and multiple joints beyond the basic configurations are further examined using numerical methods (with finite element analysis). These findings constitute a new methodology for the tolerancing of deformable parts.

Nonlinear structural analysis on distributed-memory computers

A computational strategy is presented for the nonlinear static and postbuckling analyses of large complex structures on massively parallel computers. The strategy is designed for distributed-memory, message-passing parallel computer systems. The key elements of the proposed strategy are: (a) a multiple-parameter reduced basis technique; (b) a nested dissection (or multilevel substructuring) ordering scheme; (c) parallel assembly of global matrices; and (d) a parallel sparse equation solver. The effectiveness of the strategy is assessed by applying it to thermo-mechanical postbuckling analyses of stiffened composite panels with cutouts, and nonlinear large-deflection analyses of HSCT models on Intel Paragon XP/S computers. The numerical studies presented demonstrate the advantages of nested dissection-based solvers over traditional skyline-based solvers on distributed memory machines.

Algorithm for Multiple Disassembly and Parallel Assemblies

We consider the geometric problem of generating efficient sequences for disassembling components. First, a classification of assemblies is proposed based on logical, dimensional and geometric complexities, and a simple method is outlined for recognizing parallel and sequential assemblies. Next, an efficient algorithm is outlined for removing multiple components from an assembly. Finally, we consider parallel assemblies and outline two algorithms for their disassembly.

Impact of resequencing on parallel assembly systems

Introduction of flexible parallel assembly in vehicle manufacturing has mitigated some of the quality and throughput problems faced in conventional assembly lines; however, because of lack of coordination with materials downstream the sequence of jobs through parallel machines is not retained. Jobs are resequenced to the input sequence after processing at parallel workstations. This paper considers the effect of resequencing on system performance in terms of throughput and work in process. Results show the relationships between different system parameters that can be used to trade off capital and operating costs. Using a first-come first-serve policy (which is adopted in practice), an algorithm determines the effect on throughput of given system parameters, such as number of parallel stations, number of carriers, and size of the resequencing bay. Strategic implications for design of such systems are discussed based on performance results obtained from simulation.

Impact of resequencing on parallel assembly systems : Anant Kumar, Haresh Gurnani, Sunder Kekre, pp. 109–117

Impact of resequencing on parallel assembly systems : Anant Kumar, Haresh Gurnani, Sunder Kekre, pp. 109–117

Client Education Brochures Win Award of Excellence

Introduction of flexible parallel assembly in vehicle manufacturing has mitigated some of the quality and throughput problems faced in conventional assembly lines; however, because of lack of coordination with materials downstream the sequence of jobs through parallel machines is not retained. Jobs are resequenced to the input sequence after processing at parallel workstations. This paper considers the effect of resequencing on system performance in terms of throughput and work in process. Results show the relationships between different system parameters that can be used to trade off capital and operating costs. Using a first-come first-serve policy (which is adopted in practice), an algorithm determines the effect on throughput of given system parameters, such as number of parallel stations, number of carriers, and size of the resequencing bay. Strategic implications for design of such systems are discussed based on performance results obtained from simulation.

Postbuckling and large-deflection nonlinear analyses on distributed-memory computers

A computational strategy is presented for postbuckling and nonlinear static analyses of large complex structures on distributed-memory parallel computers. The strategy is designed for message-passing parallel computer systems. The key elements of the proposed strategy are: (a) a multiple-parameter reduced basis technique, (b) a nested dissection (or multilevel substructuring) ordering scheme, (c) parallel assembly of global matrices, and (d) a parallel sparse equation solver. The effectiveness of the strategy is assessed by performing thermomechanical postbuckling analyses of stiffened composite panels with cutouts, and nonlinear large-deflection analyses of High Speed Civil Transport models on three distributed-memory computers. The numerical studies presented demonstrate the advantages of nested dissection-based solvers over traditional skyline-based solvers on distributed-memory machines.

Protein folding and assembly in vitro parallel intracellular folding and assembly. Catalysis of folding and assembly of the human chorionic gonadotropin alpha beta dimer by protein disulfide isomerase

Although purified proteins will refold and assemble in vitro, it is not known if cellular factors change the mechanisms of these processes. Based on the gel migration of folding intermediates, the kinetic relationships between these intermediates, and on the order of formation of six disulfide bonds, we have found that the in vitro folding pathway of the human chorionic gonadotropin beta subunit (hCG-beta) is indistinguishable from the intracellular folding pathway. The same rate-limiting event was found in both folding environments; however, the t1/2 for this step in a cell is 4 min, whereas in vitro the t1/2 was > or = 80 min. Protein disulfide isomerase (PDI) increased the in vitro rate of this event (t1/2 = 25 min) without changing the order of disulfide bond formation. PDI also catalyzed the in vitro rate of assembly of hCG subunits. In intact cells, assembly of the alpha beta heterodimer occurs before all of the intramolecular disulfide bonds of beta are formed. In vitro, assembly was increased after reduction of two of the carboxyl-terminal disulfide bonds of hCG-beta by PDI. These results strongly suggest that both in intact cells and in vitro, partially unfolded hCG-beta is more assembly-competent than is fully folded hCG-beta. The comparison of in vitro and intracellular hCG-beta folding and hCG subunit assembly which is shown in this report indicates that the assisted folding and assembly pathway that occurs in cells, where proteins such as PDI play a role, differs only in rate but not in the order of disulfide bond formation or in the precursor-product relationships among the folding intermediates.

Overcoming the effects of polishing induced stress when fabricating fused polished couplers

The tendency of the polished fibres to separate due to the thermal relaxation of polishing induced stress during the fabrication of fused polished couplers is overcome by depositing a thin layer of silica in the form of either a silica sol-gel or an aqueous suspension of silica powder on the parallel fibre assembly prior to the application of heat.

Disassembling Parallel Assemblies

We consider the problem of automatic generation of assembly sequences for a difficult class of assemblies. Conceptualizing the assembly process as an inverse of the disassembly process, we concentrate on parallel assemblies - ones that cannot be disassembled one component at a time. Recognizing such assemblies and choosing the proper subassembly to initiate the disassembly process without addressing the combinatorics directly, is the focus of our research. In this paper, we present our work in progress that deals with disassembling isothetic parallel assemblies.

Parallel and vectorial solving of finite element problems on a shared-memory multiprocessor

Some alternatives for speeding up finite-element computations by use of a vector-parallel shared memory multiprocessor are presented. The whole solution process is dealt with, including the calculation of element contributions (integration), global matrix construction (assembly), and resolution of the large sparse linear systems thus arising. The vector-parallel algorithms are implemented and compared on an Alliant FX/80, providing an automatic compiler, thus making parallel programming easier. The best choice between the possible combinations of the algorithms presented is discussed, considering the global performances. The ICCG (incomplete Cholesky preconditioned conjugate gradient) method, associated with parallel assembly and vectorial integration on finite elements, is the best for smooth problems. With nearly singular matrices, or when a smaller residual on the solution is needed, the direct method gives less time-expensive solutions. >

Self‐assembly of plant cell walls

ABSTRACTThe object of this paper is to define criteria for distinguishing between self‐assembly and template‐based assembly in plant cell walls. The example of cellulose shows that cell wall polymers biosynthesized at a membrane may retain parallel chain packing arrangements that are thermodynamically unstable and cannot be reproduced in vitro, making the experimental testing of the self‐assembly hypothesis difficult. Also, natural cellulose is ordered on a number of scales of pattern, each of which may be constructed by either self‐ or template‐based assembly independently of the rest. These conceptual problems apply equally to the self‐assembly of complete cell walls and other cell wall polymers. It is suggested that the self‐assembly concept should be applied only to one stage or level in the synthesis of a cell wall, and that an additional concept of parallel assembly may be useful for understanding the synthesis of some polysaccharides.