Iwona Paprocka

The Graph Representation of Multivariant and Complex Processes for Production Scheduling

The paper presents a solution useful for production scheduling in the context of the constraints arising from the complexity of the structures of realized processes and possibilities of use variants of their implementation. The proposed method uses both activity on arc and activity on node types of graph for describing multivariant processes. Representation of complex (composed) structures the AND-OR graphs are used that combines both conjunction and disjunction relations between nodes.

Pareto Optimality of Production Schedules in the Stage of Populations Selection of the MOIA Immune Algorithm

In the paper, the problem of achieving Pareto optimal solutions set with application of the elaborated Multi Objectives Immune Algorithm is presented. The Pareto frontier provides a variety of compromise solutions for contradictive criteria to a decision maker. We propose the application of the selection based on the Pareto optimality to maintain solutions with great diversity in an immune memory. Stimulation and suppression mechanisms are used to control the diversity of generated solutions. Computer simulations are done for a job shop scheduling problem.

Estimation of Reliability Characteristics in a Production Scheduling Model with Failures and Time-Changing Parameters Described by Gamma and Exponential Distributions

In the paper a classical model of failures is considered in that successive failure-free times are supposed to have Gamma distributions and are followed by exponentially distributed times of repairs. It is assumed that parameters of these distributions, in general, change with time. Basing on information about the number of failures and failure-free times in a number of periods of the same duration in the past, three different methods of estimation unknown parameters of the model are proposed. Next, predictions of the most important reliability characteristics are found.

A Survey on Capp Systems Development Methods

Process planning is one of the most important links in planning of the manufacturing system functioning, it coordinates and integrates processes planners, designers and economists intentions. The main goal to reach during the process planning phase is to determine the process plan structure it is manufacturing operations and cuts which have to be applied in order to transform given semifinished product into a product with the strict determined design and properties. Simultaneously process planers strive for working out such a process plan which satisfies criteria of the lowest manufacturing cost and labour consumption taking into account current accessibility of manufacturing resources. Process planning is still one of the most difficult, complex and time consuming process planner activities. Traditionally the process plan is designed with so-called manual method. During process planning with this method a process planner is forced to analyse the sequence of manufacturing cuts and operations in the process plan structure and also to analyse alternative processes taking into consideration achieving as low as possible unit manufacturing cost. In this case the process plan quality in principle depends exclusively on process planner knowledge and skills. Taking into account above the methods of process planning functions automation are searched. This goal can be reached by application of computer tools. Computer methods of process planning went through the long evolution process and their development is characterized by the following features: decreasing of process planner participation in the planning of the base structure of process plan, broad application of technological databases, broad application of technological knowledge bases, and possibilities of cooperation with commercial CAD/CAM/CAE systems [1,. In this paper the detailed information on methods of computer aided process planning are given. The variant, semi generative and generative methods are discussed. The main merits and drawbacks for each method are shown.

Study on Transient Queueing Delay in a Single-Channel Queueing Model with Setup and Closedown Times

A single-channel queueing model with finite buffer capacity, Poisson arrival stream and generally distributed processing times is considered. After each busy period the service station is being switched off but this operation requires a randomly distributed closedown time. Similarly, after the idle time, the first service in a new busy period is preceded by a random setup time, during which the processing is still suspended and the server achieves full readiness for the service process. A system of integral equations for transient conditional queueing delay distribution is derived, by using the idea of embedded Markov chain and the formula of total probability. The solution of the corresponding system written for Laplace transforms is obtained via the linear algebraic technique. Numerical examples are attached as well.

Estimation of overall equipment effectiveness using simulation programme

A queuing system of the M/M/1/N type with cyclic failure-free and repair times and cyclic defective production is used as a model of a single machine production system. Production tasks arrive according to an exponential process and are served with normally disturbed processing time. Successive working (failure-free) times, repair times and defect-free production have exponential distributions. Defective products can be recirculated and back to the production line according to a Bernoulli distributions. The objective is to evaluate effectiveness of the production system using Overall Equipment Effectiveness before and after introducing improvement initiatives.

Robust Scheduling, a Production Scheduling Model of Failures

In the paper a production model with failures is presented where successive failure-free times are supposed to have normal distributions and are followed by normally distributed times of repairs. Unknown parameters of the distribution are estimated using e.g. empirical moments approach. Predictions of unknown parameters are done using classical regression method. Having Mean Time To First Failure, and Mean Time of Repair a disturbance robust predictive schedule is generated using an immune algorithm and rule Minimal Impact of Disturbed Operation on the Schedule.

UML Models of Design and Knowledge Representation for Technical Production Preparation Needs

Having in mind the need of the computer adding of the technical production preparation functions the elaboration of models of the design and knowledge representation is essential. In order to prepare these models the object paradigm in the meaning of object oriented techniques and the UML language would be applied. Thanks to this solution the coherent representation of the design and manufacturing knowledge in the framework of a new created CAPP is possible to achieve. The main purpose of the presented work is to show and discuss original models of a design and manufacturing knowledge representations. In the proposed solution the product design is represented by means of the hierarchical class structure in which a particular class is responsible for representing a characteristic type of the model feature. The manufacturing knowledge similarly to knowledge representation is also represented by means of the hierarchical class structure. Each class in the manufacturing knowledge model stores a certain amount of manufacturing knowledge. This model allow representing both procedural and declarative knowledge. The declarative character of the model results from storing of manufacturing process planning rules whilst procedural one from recording of manufacturing instrumentation, cutting parameters etc. selection procedures. Having these models done it is possible to undertake a research on connections between a design and manufacturing knowledge representations.

Time to Buffer Overflow in a Finite-Capacity Queueing Model with Setup and Closedown Times

A single-channel queueing model with finite buffer capacity, Poisson arrivals and generally distributed processing times is investigated. According to frequent energy saving requirements, after each busy period the service station is being switched off during a randomly distributed closedown time. Similarly, the first processing in each busy period is preceded by a random setup time, during which the service process is suspended and the machine is being switched on and achieves full readiness for the processing. A system of Volterra-type integral equations for the distribution of the time to the first buffer overflow, conditioned by the initial level of buffer saturation, is built, by applying the idea of embedded Markov chain and continuous version of total probability law. Using the linear algebraic approach, the solution of the corresponding system written for Laplace transforms is obtained explicitly.

Time-dependent solution for the manufacturing line with unreliable machine and batched arrivals

Time-dependent queue-size distribution in a finite-buffer manufacturing line with unreliable machine is investigated. Successive jobs arrive in batches (groups) with sizes being generally distributed random variables, and are being processed individually with exponential service times. Applying the approach based on the memory less property of exponential distribution and the total probability law, a system of integral equations for the transient queue- size distribution conditioned by the initial level of buffer saturation is derived. The solution of the corresponding system written for Laplace transforms is found via linear-algebraic approach.