Fixture Assembly Research Articles

Fixture assembly planning in a web-based collaborative environment

Collaboration is essential for enterprises' survival in today's competitive global market. Web-based environments enable designers to communicate and perform functionalities with their geographically distributed partners. Although much research has been conducted in fixture design theory and verification, little attention was paid to fixture assembly planning in a distributed collaborative environment. Fixture assembly planning is subject to geometrical and functional constraints related to the fixture in a working environment. This paper presents a fastener based geometrical approach to fixture assembly planning in a distributed environment. The topological disassemblability of fixture elements and fasteners, the assembly tool feasibility, and fixture functionality are analysed based on geometrical constraints. The developed system is implemented in a three-tier client/server architecture. The example demonstrates the developed system.

Stiffness Analysis for a Novel Parallel-Robot Based High-Precision Flexible Assembly Fixture

In this paper, a novel parallel mechanism (3-RRRS/UPR) used in flexible fixture with configuration composed of two parallel robots (2-RR and 3-RRRS/ UPR) is presented. First, system modeling including the mobility study is conducted. Then a novel methodology is proposed that makes use of screw theory to analyze the deformation and stiffness of the mechanism: firstly we identified the existence of the deformation of the subchain, in terms of the relationship between the effective screw and deformation screw; then we took the deformation as an infinitesimal motion of the mechanism, and the stiffness matrix corresponding to the deformation can be deduced. Finally the global stiffness matrix of the whole mechanism is modeled by assembling different stiffness characters based on the presented methodology.

Simultaneous optimization of fixture and joint positions for non-rigid sheet metal assembly

This paper presents an optimization methodology for non-rigid sheet metal assembly variation by considering part variation, fixture variation, fixture layout, and joint positions, as well as the assembly spring back. The proposed algorithm integrates the finite element analysis (FEA) with a powerful global optimization algorithm, called the mode-pursuing sampling (MPS) method to simultaneously search for the optimal fixture and joint positions in order to minimize the assembly variation. An example application study is presented to demonstrate the optimization procedure and its effectiveness.

Gated x-ray detector for the National Ignition Facility

Two new gated x-ray imaging cameras have recently been designed, constructed, and delivered to the National Ignition Facility in Livermore, CA. These gated x-Ray detectors are each designed to fit within an aluminum airbox with a large capacity cooling plane and are fitted with an array of environmental housekeeping sensors. These instruments are significantly different from earlier generations of gated x-ray images due, in part, to an innovative impedance matching scheme, advanced phosphor screens, pulsed phosphor circuits, precision assembly fixturing, unique system monitoring, and complete remote computer control. Preliminary characterization has shown repeatable uniformity between imaging strips, improved spatial resolution, and no detectable impedance reflections.

Flexible fixture design with applications to assembly of sheet metal automotive body parts

PurposeTo design a reconfigureable flexible fixture for the assembly of a set of sheet metal automotive body parts. Reconfigureable fixturing permits different parts to be grasped for assembly by a fixture without the need to conduct costly redesign and fabrication of hardware fixtures, which is an industry standard in widespread use in industry. While somewhat more complex than fixtures in current use, reconfigureable fixtures provide one solution to the problem of costly redesign of fixtures due to changes in dimensions, or geometry of parts to be assembled.Design/methodology/approachWe propose a novel reconfigureable fixture for robotic assembly of a number of different parts. Motivated by the marine organism, O. vulgaris, commonly referred to as an octopus, which grasps different objects or prey using suction cups, the proposed fixture has three fingers, each equipped with a suction cup, to facilitate the grasping process and increase grasp flexibility. Using this design approach, the fixture is sufficiently general in design to grasp several different parts. To position the suction cups located on the flexible fixture, two linkage‐based mechanisms are employed. Pneumatic cylinders and electric motors are used as actuators. A prototype flexible fixture has been built and experimental results with this prototype confirm the effectiveness of the proposed flexible fixture. Software has been developed to calculate the relative positions and angles in the mechanism as required for reconfiguration.FindingsThe proposed reconfigureable fixture, used as an end‐of‐arm tool, permits each of a set of four sheet metal parts to be successfully grasped permitting assembly of these four components, in a robotic assembly work cell.Research limitations/implicationsThe proposed flexible fixture is a simple proof‐of‐concept device that is suitable for a laboratory setting. We do not consider part localization of parts when grasped by the reconfigureable fixture.Practical implicationsAssembly operations, in industrial manufacturing operations, are typically heavily reliant on hardware fixtures devices to orient and clamp parts together during assembly operations. While of great importance in such operations, hardware fixtures are very costly to design and build. Further, fixtures are designed for use with parts of specific dimensions and geometry, hence cannot be used to grasp or orient parts with even very small differences in dimensions or geometry. Typically, if parts with different dimensions or geometry are to be assembled, new hardware fixtures must be designed and manufactured to grasp and orient these parts. This lack of flexibility leads to substantial manufacturing costs associated with fixturing. Reconfigureable fixtures permit parts with different geometries to be grasped and oriented for assembly.Originality/valueReconfigureable fixtures for use in the automotive manufacturing sector is an important development due to the highly competitive nature of this industry. Rapid introduction of new models of vehicles is greatly facilitated through the use of reconfigureable fixtures which can be reprogrammed to grasp parts of different geometries required for new vehicle models.

Assembly Fixture Fault Diagnosis Using Designated Component Analysis

A new approach to fixture fault diagnosis, designated component analysis (DCA), is proposed for automotive body assembly systems using multivariate statistical analysis. Instead of estimating the fault patterns solely from the process data as in principal component analysis (PCA), DCA defines a set of mutually orthogonal vectors identified from known product/process knowledge to represent fault patterns, estimates their significance from data, and analyzes the correlation among the designated components. Hence, the sheet metal dimensional variation is mathematically decomposed into a series of mutually orthogonal rigid body motions with known patterns. Remaining deflections can be estimated by PCA after rigid body motions have been removed from the data. As a result, the designated components, along with their correlations, facilitate the diagnosis of multiple fixture faults that exist simultaneously and isolate deflections from other variation components. An application example is used to illustrate DCA’s effectiveness and potentials.

組立用アクティブ・フレキシブル治具の開発 (第1報)

組立用アクティブ・フレキシブル治具の開発 (第1報)

Visibility Analysis for Assembly Fixture Calibration Using Screen Space Transformation

In a number of manufacturing processes—tooling installation, calibration, and maintenance—guarantee the precision of fixtures and play important roles toward the overall quality of products. Recently, a new type of measurement equipment called a “laser tracker” was developed and utilized for assembly fixture calibration to shorten calibration time and improve the accuracy of the currently used theodolite systems. Though calibration of the assembly fixture is critical for product quality, as such, calibration time creates a significant burden for productivity of multistation assembly processes. In order to shorten calibration lead time, the number of necessary setups, determined by visibility analysis, needs to be minimized. This paper presents a screen space transformation-based visibility analysis that allows minimizing the number of setups. The screen space transformation is applied to transform the visibility problem from three- to two-dimensional space, thus, efficiently solving the visibility problem. A case study illustrates the procedure and verifies the validity of the proposed methodology. This methodology can be applied not only for manufacturing processes, such as in-line fixture calibration, but also toward analysis and optimization of AGVs, robot navigation systems, and building security.

Flexible assembly fixturing layout modeling and optimization based on genetic algorithm

Flexible assembly fixturing layout modeling and optimization based on genetic algorithm

Correction of milling tool paths by tool positioning defect compensation

In considering errors due to elastic deformations in milling, the workpiece-work-holding fixture assembly is generally considered to be infinitely rigid, at least when the geometrical features so permit. The tool-tool-holder-spindle assembly and the machine axes are then deformed under the action of the cutting forces. This deformation leads to a positioning defect of the tool in relation to the theoretical position. With the aim of taking this positioning defect into account in manufacturing, a ‘Virtual Worker’ was implemented that was capable of predicting this defect, in relation to the type of machining, and of compensating for it. It was built on a set of data blocks drawn up for each tool. In order to fill in these tool data blocks quickly, a master workpiece was elaborated that brought together the milling operation characteristics for the tool's behaviour at work. By milling and then measuring this master workpiece, the behaviour of the tool-tool-holder-spindle assembly was able to be fully characterized at work.

A genetic algorithm-based fixture locating positions and clamping schemes optimization

Optimizing the locator positions and clamping schemes of a fixture was proven to improve the dimensional and form accuracy of a workpiece significantly. A number of approaches have been developed to optimize the designs of sheet-metal assembly fixtures and machining fixtures. However, in these previous works, the optimal selection of the positions of locators and clamps were based on a stationary set of locator and clamp conditions; i.e. the numbers of the locators and clamps were fixed during optimization. This paper proposes a genetic algorithm (GA)-based optimization method to select automatically the optimal numbers of locators and clamps as well as their optimal positions in sheet-metal assembly fixtures, such that the workpiece deformation due to the gravity effect and resulting variation due to part dimensional variation are simultaneously minimized. The application result of a real industrial part demonstrated that the proposed algorithm effectively achieves the objective.

Computer-aided tolerance chain and stability analysis

The present paper describes a methodology and a software tool that allow assemblies to be evaluated and analysed with respect to degree of geometrical coupling and robustness on any hierarchical level of the assembly structure. Based on the assembly sequence and the mating conditions of a number of components fulfilling a number of functional requirements, a function means hierarchy with a pertinent set of relations between sub-assemblies, components and features is automatically generated and used for tolerance chain and stability analysis. Based on mating conditions and specified geometrical constraints, tolerance chains are automatically detected and presented in the structure. Geometrical couplings between sub-systems, components and individual features are detected and presented in stability matrices. The analysis tools assist in the iterative work of concept improvement and the decomposition of top-level geometrical constraints (tolerances on critical product dimensions) into bottom level feature constraints (tolerances on individual surfaces). The two analysis toots utilize the basic ideas in robust design and axiomatic design (the independence axiom), and can be used to compare and evaluate assembly concept solutions including different assembly fixturing solutions. The similarities between uncoupled robust assembly design and uncoupled robust tolerancing of individual parts are discussed and illustrated. Two examples are used to describe the methodology and the software tool.

Predicting Assembly Dimensions with Functional Build: A Case Study Using DOE

When using the functional build approach to manufacturing validation during new product development, manufacturers use preproduction assemblies to evaluate whether components within an assembly may build dimensionally correct products. This approach allows some individual component characteristics to not meet their original design specifications, provided the resultant assembly meets its requirements. In applying this functional build methodology, manufacturers assume that the preproduction assemblies provide data representative of what the manufacturer will encounter in the regular production process. This paper evaluates the predictive validity of the functional build approach by utilizing a design of experiment to examine the effect of two factors—build fixture and method of attachment—in constructing functional build preproduction assemblies of stamped sheet metal components. The results confirm the importance of using assembly fixtures that closely resemble regular production processing.

Rapid Deployment of Reconfigurable Assembly Fixtures using Workspace Synthesis and Visibility Analysis

Due to rapid changes In recent market demands, shortened production ramp-up/launch and model changeover of new products with simultaneous manufacturing of family of products on a single production line Is becoming Inevitable. This requires systematic methods for rapid design and analysis of reconfigurable fixture workspace synthesis and visibility. This paper presents an integrated approach for rapid reconfigurable fixture deployment which is based on (1) the procrustes analysis Integrated with a pairwise optimization for fixture workspace configurations synthesis; and (2) screen space transformation-based visibility analysis for rapid fixture calibration. A case study and simulations illustrate the proposed approach.

Fixture Configuration Design for Sheet Metal Assembly with Laser Welding: A Case Study

The role of assembly fixtures is gaining importance in order to meet the special requirement of metal fit-up for sheet metal assembly with laser welding. Fixture configuration methodologies based on a new proposed locating scheme have been developed. In order to demonstrate the feasibility of the proposed fixture design principles in industrial applications, an industrial case study with cross-members assembly is presented. In order to obtain a physical model with the actual tolerances, reverse engineering technologies are employed for geometric modelling of the assembled parts. For achieving modelling accuracy a CMM-based finite-element model is produced and performance characteristics of the 3D features obtained. In the case study, the assembly weld patterns are designed first, to determine the weld locations. Then the general design, the deterministic optimisation and the robust design of the fixture configuration are carried out sequentially. The results of the case study show that the proposed fixturing principles are applicable and effective.

Quality and reliability information integration for design evaluation of fixture system reliability

AbstractQuality and reliability are two important factors in manufacturing‐system design. However, the analysis and optimization of manufacturing‐system reliability and product quality are normally conducted separately in practice. There is no general framework to integrate these two important factors, quantitatively analyze the interactions between them, and further study their integrated effects on the manufacturing‐system performance. In this paper, the QR‐Co‐Effect of product/part quality and manufacturing‐system component reliability is investigated in an assembly fixture system. The concept, model and analysis of QR‐Co‐Effect are addressed in this paper. Copyright © 2001 John Wiley & Sons, Ltd.

Fixture Failure Diagnosis for Sheet Metal Assembly with Consideration of Measurement Noise

This paper expands previously developed assembly fixture fault diagnosis methodology (Ceglarek and Shi, 1996) by considering the impact of measurement noise on the diagnostic results. The proposed solution provides a new analytical tool to address the diagnosability issue during the assembly process design stage. An evaluation of fault diagnosis index as a function of noise, fixture geometry, and sensor location is presented. The index is derived from the general class of covariance matrices describing tooling faults. Simulation based on the real fixture is presented to illustrate the proposed method.

Visibility Analysis and Synthesis for Assembly Fixture Certification Using Theodolite Systems

In automotive sheet metal assembly, part positioning and clamping is accomplished by fixtures consisting of fixture elements, such as pins and blocks. The locations of these elements are determined during process design and need to be certified during the construction and installation of an assembly line. Usually, theodolite systems are used to certify the locations of these elements by measuring the trihedron points on the fixture elements. However, no systematic method exists for the selection and placement of measuring systems. As a result, the current certification procedure is very time-consuming and is prone to error. This paper presents an algorithm for the optimal setup and placement of theodolite systems based on visibility analysis and synthesis. For a given tooling fixture, the visibility map is introduced to represent the set of potential measurement locations when a number of fixture elements are to be measured. From the set of potential measurement locations, an optimal setup will be selected based on minimizing the number of theodolite heads by optimally locating these theodolites. This approach will minimize measurement setups and improve measurement accuracy.

Computer Aided Assembly Robustness Evaluation

This paper presents a methodology and a software that allows assemblies to be evaluated with respect to robustness and geometrical stability. The assembly robustness evaluation aims at detecting design and assembly solutions that are sensitive to variation and may cause problems later during production. It is based on Suh's independence axiom, stating that in a good, uncoupled design, each functional requirement is satisfied by one and only one design parameter. The methodology enables the designer to evaluate the geometrical sensitivity of the assembly, what the sources of variation are, their importance for the overall robustness and in what order to improve the design. A possible result from the analysis may be that the concept must be changed in some way, either by changing the way parts are located with respect to each other or by using assembly fixtures for positioning. The software is implemented in a Microsoft Windows environment and has an IGES interface that enables the designer to import computer aided design (CAD) geometry from an arbitrary CAD system, and perform assembly robustness analysis.

Assembly Process and Assembly Control Development – A Holistic and Consistent Approach

Simultaneous engineering usually covers the integration of design and planning during product development. Yet there is still a gap between the planning and the subsequent implementation of assembly systems. This article describes an approach to the consistent integration of assembly systems planning into the control system of a real assembly facility within the same environment. The control mechanism developed can be used to simulate manufacturing cells for validation purposes as well as to communicate with real assembly fixtures and equipment.