Optimal layout and reconfiguration of a fixturing system constructed from passive Stewart platforms

The distinguishing property of Reconfigurable Manufacturing Systems (RMS) is that they can rapidly and efficiently adapt to new production requirements, both in terms of their capacity and functionalities. For this type of systems to achieve the desired efficiency, it should be possible to easily and quickly setup and reconfigure all of their components. This includes fixturing jigs that are used to hold workpieces firmly in place to enable a robot to carry out the desired production processes.In this paper, we formulate a constrained nonlinear optimization problem that must be solved to determine an optimal layout of reconfigurable fixtures for a given set of workpieces. The optimization problem takes into account the kinematic limitations of the fixtures, which are built in shape of Sterwart platforms, and the characteristics of the workpieces that need to be fastened into the fixturing system. Experimental results are presented that demonstrate that the automatically computed fixturing system layouts satisfy different constraints typically imposed in production environments.     

Design and implementation of robot-operated adaptable and modular fixtures

This paper presents the design issues and hardware implementation for robot-operated automatic modular and adaptable fixtures. Modular fixtures are workholding devices made from stackable self-contained modular elements. Adaptable fixtures provide surface contact with the workpiece and therefore can adapt to the workpiece geometry. These fixtures are shown to have several advantages over conventional fixtures. Issues in modularity and adaptability for workpiece fixturing are discussed for the purpose of evaluating automatic modular fixtures in flexible manufacturing systems. The basic design requirements for robot-operated modular and adaptable fixturing systems are developed and classified into mechanical and operational. Automatic assembly issues such as the use of special mating surfaces, compact actuators for active modules, as well as the importance of communications between the robot manipulator and the modular fixture are discussed.

Hardware design and implementation of a shape memory alloy actuated locking module and a discrete conformable surface module are presented. Performance characteristics such as free-play, stiffness and time response were evaluated experimentally for the locking module. Several workpiece geometries are tested on the comformable surface module.     

A CAD-Based hierarchical approach to interference detection among fixture modules in a reconfigurable fixturing system

A reconfigurable fixturing system has been developed for a computer-integrated assembly environment. The fixturing system employs a number of fixture modules which are set-up, adjusted and changed automatically by the assembly robot. A dedicated software program has been developed for the design, analysis, and verification of the fixture layout. The software program has been integrated with a commercially available computer-aided design (CAD) package to provide a user-friendly platform for modeling and display purposes. The robot program for setting up, adjusting, and dismantling the designed fixture is generated automatically. Interference between fixture modules during the fixture construction may arise due to incorrect selection of the fixture contact points at the design stage. The objective of the work described here is to develop a hierarchical approach for calculation of interference between fixture modules in a reconfigurable fixturing system. The formulation for the interference detection employs geometrical constraints as the basis. The approach does not require detailed simulation of the fixture construction for interference detection.     

Automated setup and reconfiguration for modular fixturing

Current trends in manufacturing have identified the need for automation and flexibility in fixture design. The majority of flexible fixturing systems, however, are not well suited for automation. Modular fixtures can be designed to meet the requirements for traditional fixtures in addition to those for modern automation. This paper discusses the issues involved in the automation of modular fixtures with emphasis on automated planning. These issues include proper design, determination of layout requirements, feasibility and automatic reconfiguration. Requirements and guidelines for each issue will first be presented in a general format, and then applied specifically to sheet-metal fixturing.     

Strategies for planning and implementation of flexible fixturing systems in a computer integrated manufacturing environment

In general, for any manufacturing operation to be successful, parts must be located and held to remain in position and orientation when subjected to external forces during the manufacturing operations. The traditional approach to fixturing involves designing and manufacturing special-purpose fixtures. These fixtures are generally dedicated devices designed and manufactured for specific parts and manufacturing operations. Flexible fixturing technology involves employing a single fixturing system to hold workpieces of various shapes and sizes. Such systems have reached the embryonic stage of implementation into manufacturing environment. Therefore the integration of current and future flexible fixturing systems into the manufacturing processes becomes an important issue for future work in computer-integrated manufacturing (CIM) environment.

The approach to CIM is dependent on the functional model of the company. Therefore, the implementation of any sub-systems within it must be studied on an individual basis. However, in order to plan and implement new technologies, such as flexible fixturing systems, within CIM environment, certain requirements must be met and guidelines must be followed. The strategies for planning and implementation of flexible fixturing systems within the larger frame work of CIM environment are presented. Some guidelines for designing and developing the interconnection of the data bases are also discussed.     

Multiobjective layout optimization of robotic cellular manufacturing systems

This paper proposes a multiobjective layout optimization method for the conceptual design of robot cellular manufacturing systems. Robot cellular manufacturing systems utilize one or more flexible robots which can carry out a large number of operations, and can conduct flexible assemble processes. The layout design stage of such manufacturing systems is especially important since fundamental performances of the manufacturing system under consideration are determined at this stage. In this paper, the design criteria for robot cellular manufacturing system layout designs are clarified, and objective functions are formulated. Next, layout design candidates are represented using a sequence-pair scheme to avoid interference between assembly system components, and the use of dummy components is proposed to represent layout areas where components are sparse. A multiobjective genetic algorithm is then used to obtain Pareto optimal solutions for the layout optimization problems. Finally, several numerical examples are provided to illustrate the effectiveness and usefulness of the proposed method.     

Phase change fixturing for flexible manufacturing systems

Fixturing is fundamental to many manufacturing operations, hence, if computer integrated flexible manufacturing systems are to be truly flexible, then the fixturing must also be flexible. That is, it must be capable of accomodating parts of different geometries and sizes. This paper reports on an innovative class of flexible fixtures which utilizes materials that undergo a phase change between solid and liquid states. When in the liquid state, the fixturing medium can accommodate a wide variety of different part geometries, while in the solid state the part is held fixed. A mathematical model is developed which governs the holding ability of a particular class of these fixtures and some results of parametric computer studies are then presented.     

Planning for Modular and Hybrid Fixtures

Fixturing encompasses the design and assembly of fixtures to locate and hold a workpiece during a manufacturing operation such as machining or assembly. We have implemented an automated design algorithm for a fixturing toolkit called the fixture vise; the fixture vise involves two fixture plates mounted on jaws of a vise and modular fixturing elements (pegs or flatted pegs). Generally, a fixture vise can handle appropriately sized prismatic workpieces in many different ways. The design algorithm runs in O(A) time, where A is the number of configurations achieving simultaneous contact between the modeled object and four fixture elements; since simultaneous contact is a necessary but not sufficient precondition for force closure, A provides an upper bound on the number of force closure fixture configurations. Received June 6, 1994; revised November 17, 1994, February 1, 1995, February 28, 1995, and July 11, 1995.     

Towards the design and development of a knowledge-based universal modular jigs and fixtures system

Jigs and fixtures are one of the important aspects of manufacturing. Parts may have different sets of fixturing requirements and call for different design strategies. Although there are numerous possibilities for fixture designs, a few basic configurations are clearly identifiable. Computer aided design (CAD) has done a little in assisting designers to design jigs and fixtures, making decisions of the best design selection, and providing designers with suggestions. The goal of this paper is to develop and document the design parameters and specifications utilized in jigs and fixtures design using universal modular jigs and fixtures design system (UMJFS). This is the first step to develop a knowledge-based Jigs and Fixture design and selection system. This application has the advantages of making the fixture design information completely modular and transparent, providing better match to the working conditions, reducing lead-time, and generally providing a significant enhancement of fixture productivity and economy. UMJFS has different standard and modular elements. This makes jigs and fixtures elements interchangeable and reusable. Designing a UMJFS then becomes a task of selecting and assembling the proper elements together.     

Hierarchical Capacity Planning With Reconfigurable Kits in Global Semiconductor Assembly and Test Manufacturing

Kits (such as accessories, fixtures, jigs, etc.) are widely used in production for many industries. They are normally product- and machine-specific, so a large kit inventory must be maintained when the product-mix variation is high. Fortunately, many kits are reconfigurable. That means they can be dissembled into components and then these components themselves (or together with some other components) can be reassembled into new types of kits. Therefore, we can save money and improve supply chain responsiveness by purchasing components instead of entire kits. However, research on capacity planning with reconfigurable kits has not been reported. We proposed a two-level hierarchical planning methodology to generate a complete capacity planning solution using mixed-integer linear programming. MaxIt covers mid-range monthly planning and automated capacity allocation system covers short-range weekly planning. These systems are integrated to generate optimal capacity plans considering kit components. This methodology has been successfully implemented in Intel's global semiconductor assembly and test manufacturing since 2004. In this paper, we present the hierarchical modeling framework and focus on MaxIt modeling with kit reconfiguration. We also verify the methodology by numerical experiments in a real production environment.     

Analysis of a linear walking worker line using a combination of computer simulation and mathematical modeling approaches

It has become increasingly important in the last few years to develop rapid, dynamic, responsive and reconfigurable manufacturing processes and systems. This is because manufacturing enterprises are now being forced to develop and constantly improve their production systems so that they can quickly and economically react to unpredictable conditions such as varying production volumes and product variants with small lot size, high quality and low costs. One effective method to achieve this is to create a more flexible, highly skilled and agile workforce capable to perform multiple or all the required tasks in a production area where the system can be reconfigured easily as needed to accommodate changes of production requirement on a daily or weekly basis.This paper presents a study of a so-called linear walking worker assembly line based on a combination of computer simulation and mathematical analysis. The linear walking worker assembly line is a flexible assembly system where each worker travels down the line carrying out each assembly task at each station; and each worker accomplishes the assembly of a unit from start to finish. This design attempts to combine the flexibility of the U-shaped moving worker assembly cell with the efficiency of the conventional fixed worker assembly line. The paper aims to evaluate one critical factor of in-progress waiting time that affects the overall system performance providing a dynamic simulation outlook as well as an insight into the mechanism of such a flexible and reconfigurable manufacturing system.     

An integrated fixture planning and analysis system for machining processes

Fixture planning is an important part of computer-aided process planning (CAPP), which is the link between design and manufacturing in a CIM environment. This paper presents a rational approach to computer-assisted fixture planning (CAFP), emphasizing integration of fixture planning with process planning, an issue that has not been adequately addressed until very recently. A systematic approach to fixture selection is outlined for planning of modular fixtures. A prototype CAPP-CAFP system has been developed at UCLA and linked to a commercial CAD system, namely, CADAM. Part design information can be extracted from the CAD model and multiple-view engineering drawings of a part stored in the CADAM system. Modular fixture elements can be selected automatically by the CAPP-CAFP system and the generated fixture layout can be displayed on the screen. Included also in the system is a fixture analysis module for verification and rationalization of a fixturing scheme. The force analysis module has a built-in local optimization routine that can determine the clamping forces of more reasonable magnitudes. The friction forces between the fixture and the workpiece can also be considered for simple cases.     

Smart hardware integration with advanced robot programming technologies for efficient reconfiguration of robot workcells

The manufacturing industry is seeing an increase in demand for more custom-made, low-volume production. This type of production is rarely automated and is to a large extent still performed manually. To keep up with the competition and market demands, manufacturers will have to undertake the effort to automate such manufacturing processes. However, automating low-volume production is no small feat as the solution should be adaptable and future proof to unexpected changes in customers’ demands. In this paper, we propose a reconfigurable robot workcell aimed at automating low-volume production. The developed workcell can adapt to the changes in manufacturing processes by employing a number of passive, reconfigurable hardware elements, supported by the ROS-based, modular control software. To further facilitate and expedite the setup process, we integrated intuitive, user-friendly robot programming methods with the available hardware. The system was evaluated by implementing five production processes from different manufacturing industries.     

Evaluation of virtual fixtures for a robot programming by demonstration interface

We investigate the effectiveness of several types of virtual fixtures in a robot programming by demonstration interface. We show that while all types of virtual fixtures examined yield a significant reduction in the number of errors in tight tolerance peg-in-hole tasks, color and sound fixtures generally outperform a tactile fixture in terms of both execution time of successful trials and error rate. We have found also that when users perceive that the task is very difficult but the system is providing some help by means of a virtual fixture, they tend to spend more time trying to achieve a successful task execution. Thus, for difficult tasks the benefits of virtual fixturing are better reflected in a reduction of the error rate than in a decreased execution time. We conjecture that these trends are related to the limitations of currently available interfaces for human-robot interaction through virtual environments and to the different strategies adopted by the users to cope with such limitations in high-accuracy tasks.     

Toward an object-oriented and automated approach for achieving robotic assembly

This paper elaborates an object-oriented and automated approach for generating assembly sequences and achieving robotic assembly. This system, built with database and artificial intelligence (AI) techniques, provides the robot with the assembly sequence layout for the automatic handling rule. The critical set of problems is derived from various schemes such as model-based object recognition, features information, geometric and physical constraints between components, knowledge interpretation and robot task sequencing. Pattern recognition regarding shapes and features, along with a knowledge-based assembly, are the key issues of the authors' work. The methodology is shown through two illustrative examples involving different designs of parts in an assembly environment.     

A new reconfigurable parallel mechanism using novel lockable joints for large scale manufacturing

A new lockable spherical joint is proposed in this paper, and it can be used as a revolute joint, a universal joint or a spherical joint. Three locking methods are introduced to construct the lockable spherical joint. Based on the proposed lockable spherical joint, a new reconfigurable parallel mechanism (RPM) with large positioning workspace is presented. The RPM has a tripod architecture with a lockable joint in each limb, which enables it three types of parallel mechanisms in six motion cases. Mobility analysis of the six motion cases is conducted. The new RPM can realize both translation and rotation by changing operative modes, which can be employed as machine tools, fixtures or manipulators. Based on the new RPM, two modular reconfigurable manufacturing systems are designed for aircraft assembly production, and a reconfiguration strategy is presented.     

Case based reasoning method for computer aided welding fixture design

This paper presents a case-based reasoning (CBR) method for welding fixture design, a critical issue in the manufacturing of large and complicated equipment. However, previous fixture design research has mainly focused on machining fixtures rather than welding fixtures. In this paper, an approach of data abstraction for fixture design information representation is proposed, first to systemize and manage myriads of fixture related resources, e.g., past fixture design solutions, fixture units depository. Based on this approach, a multi-level CBR method for welding fixture design is then presented. This method could help designers, by referencing previous design cases, to make a conceptual fixturing solution quickly and, finally, finish the detailed solution of fixture design.     

Reconfigurable handling systems as an enabler for large components in mass customized production

Manufacturing companies today are exposed to increasingly dynamic market requirements. Particularly in high-wage countries, there is also a clear trend toward standing out from global competitors by means of product differentiation. At the same time, however, prices have to remain competitive. As a consequence, many companies choose a mass customization strategy to reconcile individualized products with advantages of the economies of scale. So far, this aim is mainly reached in the consumer goods sector by flexible production systems with a high degree of automation. The approach presented here is capable of transferring the benefits of mass customization to large products with lower production quantities such as aircraft by means of a highly reconfigurable automated handling system. Instead of manual operations or specific jigs and fixtures for each component, the new system is characterized by supporting large work pieces at several distributed points by multiple robotic arms. The individual robots are simple in design and very lightweight so that they can be easily switched in order to reconfigure the assembly system for different tasks. The development does not only comprise hardware construction, but also new methods for programming, commissioning and control of cooperating handling devices in a modular and reconfigurable system layout.     

Automated fixture configuration for rapid manufacturing planning

The wide adoption of agile manufacturing systems has necessitated the design and use of fixtures or work holding devices that have in-built flexibility to rapidly respond to part design changes. Despite the availability of reconfigurable fixtures, practical fixture configuration largely remains an experience driven manual activity to enable customization for varying workpiece geometry, and most automated solutions do not scale well to accommodate such variation. In this paper, we address the problem of rapidly synthesizing a realistic fixture that will guarantee stability and immobility of a specified polyhedral work-part. We propose that the problem of automated fixture layout may be approached in two distinct stages. First, we determine the spatial locations of clamping points on the work piece boundary using the principles of force and form closure, to ensure immobility of the fixtured part under external perturbation. In particular, we show that the candidate restraints mapped to the six dimensional vector space of wrenches (force–moment pairs) may be hashed in a straightforward manner to efficiently generate force closure configurations that restrain part movement against large external wrenches. When clamps are allowed to exert arbitrarily high reaction forces on the part, the spatial arrangement of the clamping locations ensures the part is in form closure. On generating force/form closure configurations, the chosen locations are matched against a user-specified library of reconfigurable clamps to synthesize a valid fixture layout comprising clamps that are accessible and collision free with each other and the part. Additionally, in the case of determining machining setups the clamps are chosen to avoid collisions with the moving cutting tool. We demonstrate fast algorithms to perform both location selection and fixture matching, and show several results that underscore the practical application of our solution in automated manufacturing process planning.     

利用决策支持系统分析可重构制造系统中的问题

可重构制造系统是面向新世纪的先进制造模式 .本文提出利用决策支持系统解决可重构制造系统所面临的重构决策问题 ,在系统决策、加工单元布局、以及可重构产品的生产计划问题上采用智能化算法 ,可以得到满意的结果