Hierarchical decomposition and simulation of manufacturing cells using Ada

A useful tool in the development of flexible automation is a system description language which can generate a complete func tional description of a manufacturing cell of arbitrary complexity. We propose a description system based on the concept of hierar chical decomposition utilizing the Ada programming language in conjunction with established diagrammatical decomposition methods. The distinguishing aspect of our work is that it takes advantage of certain features of Ada (such as type checking) to create a description that can be automatically verified for con sistency Simulation is often an indispensable tool in the develop ment of manufacturing systems. We show how a simulation of the operation of the manufacturing cell can be embedded in its description. Finally, we apply the methodology to a specific instance of a manufacturing cell.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68498/2/10.1177_003754978604600402.pd

Détermination systématique des étapes de contrôle et des cotes de fabrication pour les procédés d'usinage

National audienceThe "academic" method of manufacturing dimensions determination through the decomposition of the manufacturing plan into several steps, each one corresponding to a part holder, is not usable when the part is produced by only one machine, like in the case of screw machining. The transfer of the condition dimensions in manufacturing dimensions is therefore not always direct because the setup operator might also want to control the position of the unfinished surfaces during the adjustment of the machine. This results in introducing intermediate control steps into the manufacturing plan. In this case and for some condition dimensions, several chains of dimensions are possible, thus several manufacturing dimension systems are possible

Modeling and Analysis of Re-entrant Production Systems

This paper presents a model and analysis of a re-entrant production line with finite buffers and unreliable machines. Semiconductor device and liquid crystal display (LCD) fabrication processes are characterized as a re-entrant process, in which a similar sequence of processing step is repeated several times. This re-entrant behavior of material flow with the stochastic nature of the system caused by machine failures or demand changes makes the system difficult predict and analyze. The decomposition method analyzes the behavior of the manufacturing systems by decomposing a long transfer line into small analytically tractable components, called two-machine line building blocks. Existing decomposition methods are limited to an in-linear production system without re-entrant flow. Since many manufacturing systems, particularly semiconductor and LCD production lines, consist of re-entrant flow paths, it is essential that models be developed to reflect this. The purpose of this paper is to present mathematical formulations and algorithms to analyze the material behavior of the re-entrant production system using the decomposition method. In developing equations for the two-machine building blocks for the re-entrant production line, we modify the existing decomposition model that has been created for the multiple-part type line. Two main performance measures are evaluated with the developed mathematical model: production rate and average inventory levels for each buffer space in the system. The qualitative behavior of the re-entrant production line under different machine parameters and demand scenarios is also described.Singapore-MIT Alliance (SMA

Octree-based production of near net shape components

Near net shape (NNS) manufacturing refers to the production of products that require a finishing operation of some kind. NNS manufacturing is important because it enables a significant reduction in: machining work, raw material usage, production time, and energy consumption. This paper presents an integrated system for the production of near net shape components based on the Octree decomposition of 3-D models. The Octree representation is used to automatically decompose and approximate the 3-D models, and to generate the robot instructions required to create assemblies of blocks secured by adhesive. Not only is the system capable of producing shapes of variable precision and complexity (including overhanging or reentrant shapes) from a variety of materials, but it also requires no production tooling (e.g., molds, dies, jigs, or fixtures). This paper details how a number of well-known Octree algorithms for subdivision, neighbor findings, and tree traversal have been modified to support this novel application. This paper ends by reporting the construction of two mechanical components in the prototype cell, and discussing the overall feasibility of the system

Control of Cross-Directional Systems using the Generalised Singular Value Decomposition

Diamond Light Source produces synchrotron radiation by accelerating electrons to relativistic speeds. In order to maximise the intensity of the radiation, vibrations of the electron beam are attenuated by a multi-input multi-output (MIMO) control system actuating hundreds of magnets at kilohertz rates. For future accelerator configurations, in which two separate arrays of magnets with different bandwidths are used in combination, standard accelerator control design methods based on the singular value decomposition (SVD) of the system gain matrix are not suitable. We therefore propose to use the generalised singular value decomposition (GSVD) to decouple a two-array cross-directional (CD) system into sets of two-input single-output (TISO) and single-input single-output (SISO) systems. We demonstrate that the two-array decomposition is linked to a single-array system, which is used to accommodate ill-conditioned systems and compensate for the non-orthogonality of the GSVD. The GSVD-based design is implemented and validated through real-world experiments at Diamond. Our approach provides a natural extension of single-array methods and has potential application in other CD systems, including paper making, steel rolling or battery manufacturing processes

Automatic generation of robot and manual assembly plans using octrees

This paper aims to investigate automatic assembly planning for robot and manual assembly. The octree decomposition technique is applied to approximate CAD models with an octree representation which are then used to generate robot and manual assembly plans. An assembly planning system able to generate assembly plans was developed to build these prototype models. Octree decomposition is an effective assembly planning tool. Assembly plans can automatically be generated for robot and manual assembly using octree models. Research limitations/implications - One disadvantage of the octree decomposition technique is that it approximates a part model with cubes instead of using the actual model. This limits its use and applications when complex assemblies must be planned, but in the context of prototyping can allow a rough component to be formed which can later be finished by hand. Assembly plans can be generated using octree decomposition, however, new algorithms must be developed to overcome its limitations

The Integration of Process Planning and Shop Floor Scheduling in Small Batch Part Manufacturing

In this paper we explore possibilities to cut manufacturing leadtimes and to improve delivery performance in a small batch part manufacturing shop by integrating process planning and shop floor scheduling. Using a set of initial process plans (one for each order in the shop), we exploit a resource decomposition procedure to determine schedules to determine schedules which minimize the maximum lateness, given these process plans. If the resulting schedule is still unsatisfactory, a critical path analysis is performed to select jobs as candidates for alternative process plans. In this way, an excellent due date performance can be achieved, with a minimum of process planning and scheduling effort