Percorrer por data de Publicação, começado por "1999-07-24"
A mostrar 1 - 10 de 10
Resultados por página
Opções de ordenação
- Process and execution planning for manufacturing systemsPublication . Moura, António Machado e; Rocha, João; Ramos, Carlos; Vale, ZitaThis paper deals with a system called TPMS (task planning for manufacturing systems). The main aim of this system is to automatically generate programs or sets of commands for robots, AGV's, numerical control machines, etc., without spending much time programming the flexible manufacturing system components. A description of how to automatically generate a high level plan for the task is presented as well as a methodology to automatically calculate the duration of each operation from the machine program. The main contributions include: to link symbolic and execution planning; the referred aims at working for complete manufacturing systems (not for controlling only one robot); different industrial operations (assembly, welding, drilling, etc.) can be considered at the same time.
- Meta-heuristics for the single-machine scheduling total weighted tardiness problemPublication . Madureira, Ana MariaSome general features of single-machine scheduling problems are described, and some of their structural properties are used to design local search procedures based on alternative definitions of neighbourhoods. In particular, the traditional idea of "exchanging the position of two jobs" is replaced by the idea of "exchanging jobs not apart more than a given number of positions (considered as a parameter of the algorithm)". For generating initial solutions, some traditional priority rules were tested with some degree of randomisation, introducing in general, a positive effect in the performance of the algorithms. Through a set of computational tests, the importance of the different parameters was evaluated, and their values for different meta-heuristic procedures (tabu search, and randomised local search) were tuned. Though these tests have been exhaustive only for a given problem (weighted tardiness), the results already available show these approaches are robust and flexible, and that, in general, satisfactory solutions can be obtained in an efficient way.
- CEPP: Conversion and execution of process plansPublication . Ramos, Carlos; Figueiredo, LinoThis paper deals with a method to produce a program in numerical control (NC) language from a part drawing in a CAD system. This method is applied to any piece with revolution axis that can be machined in a CNC lathe. The method was developed with the goal of being integrated in the control software of the flexible manufacturing system existent in the CIM center of ISEP. The proposed method involves three phases, which are presented and explained.
- Constraint programming approach to solve facility layout design problemsPublication . Tavares, José António; Neves, José; Ramos, CarlosWe propose a methodology to solve the facility layout design problem by using constraint logic programming (CLP), which has proved to be a technology that gives good results when applied to a combinatorial problem optimisation. Methods to solve facility layout problems have to deal with a large set of factors, namely sales and production estimations, manufacturing process compatibilities, delivery dates, quality, spatial requirements, economics, management, human resources and environment. These factors make the facility layout design an extremely complex problem to solve. This complexity motivated the development of a methodology to solve the facility layout design problem using CLP.
- Process planning using a genetic algorithm approachPublication . Rocha, João; Ramos, Carlos; Vale, ZitaThis paper presents a system for computer aided process planning (CAPP), using a precedence graph representation of the operations and their restrictions. Description of machine and tool selection is described, as well as the operation sequencing. A genetic algorithm is used to generate the sequence of operations and to select the machine and tools that minimize some criteria (machining time).
- Infrastructures and scheduling method for holonic manufacturing systemsPublication . Silva, Nuno; Ramos, CarlosManufacturing systems are changing structure and organisation. Supply chains are evolving to more coupled organisations like virtual enterprises, though maintaining the single entities autonomy, adaptability and dynamism properties. Such organisations imply organisational and technological shift through agility, distribution, decentralisation, reactivity and flexibility. New organisational and technological paradigms are needed in order to reply to the modern manufacturing systems challenges. The paper proposes and justifies the holonic manufacturing system concept as the main organisational paradigm presents the infrastructures needed to assure system operation, security, coherence and coordination. Additionally, the scheduling sub-system is presented along with a scheduling method developed as a case study.
- Multi-agent simulation for balancing of assembly linesPublication . Ramos, Carlos; Praça, IsabelOne of the main applications of simulation is in manufacturing systems. The complexity of this kind of systems is related to the number of decisions that must be taken in shorter time. The main difficulty is to predict the effects of decisions on the overall system performance. In this context simulation becomes an important tool by means of which it is possible to predict the future performance of the system, and so compare and analyse different decisions. The actual discrete-event simulation scenario reveals a systematic demand for more sophisticated and powerful computational tools in order to fulfil the increasing problem of complexity. Computer network technology provides the computational power needed. The combination of distributed simulation with that of multi-agent systems presents a very interesting perspective to design and develop such kinds of environments. We propose an architecture based on multi-agent simulation to help solving problems in balancing and distributing the human resources in manual assembly lines, and in the future we hope to extend the model to other kinds of manufacturing systems.
- Dynamic scheduling of manufacturing orders: A decision support system approachPublication . Almeida, Ana; Ramos, Carlos; Silva, S. D. C.This paper presents a decision support system (DSS) based architecture and a new method for the dynamic scheduling of manufacturing systems. The proposed architecture is based on the DSS paradigm. The typical scheduling problems, namely the order allocation and order sequencing problems, are to be solved for a given production plan which defines a set of manufacturing orders to be processed. These specify product types to be manufactured, their quantities and due dates. The allocation problem deals with the assignment of n orders to m manufacturing processors, under the given production plan, and the solution to the sequencing problem identifies the input sequence and the instants of processing of the assigned orders on each manufacturing processor.
- Distributed task schedulingPublication . Sousa, Paulo; Ramos, CarlosProposes an architecture for manufacturing enterprises based on the holonic concept. The main advantage of this approach is the decentralised, distributed nature of the system as well as its heterarchic organisation as opposed to the rigid hierarchic and centralised nature of computer integrated manufacturing (CIM). The system models products, resources and tasks and the planning, scheduling and order management functions of the enterprise. A negotiation protocol is defined for task assignment that is an extension of the contract net protocol. The protocol is based on the task-resource abstraction and is suited for negotiation in several situations not only for the dynamic scheduling of manufacturing orders. The negotiation protocol is able to handle exceptions such as machine breakdowns and rush orders.
- Decision support system for dynamic production schedulingPublication . Marinho, José; Ramos, Carlos; Bragança, AlexandreThis paper presents a system to support decision-making of the production manager when scheduling the manufacturing orders. This system is mainly appropriate for small and medium size enterprises with productive systems like batch or job-shop. The manufacturing orders are dynamically scheduled considering namely deadlines and resource allocation. The system combines three modules: pre-scheduling, dynamic scheduling and re-scheduling. Each module applies heuristics to select the best solutions depending on the scheduling policies defined by the production manager.