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Now showing 1 - 4 of 4

Citation - WoS: 8
Citation - Scopus: 8
Reconfigurability of Behavioural Specifications for Manufacturing Systems
(Taylor & Francis Ltd, 2017) Schmidt, Klaus Werner
Reconfigurable manufacturing systems (RMS) support flexibility in the product variety and the configuration of the manufacturing system itself in order to enable quick adjustments to new products and production requirements. As a consequence, an essential feature of RMS is their ability to rapidly modify the control strategy during run-time. In this paper, the particular problem of changing the specified operation of a RMS, whose logical behaviour is modelled as a finite state automaton, is addressed. The notion of reconfigurability of specifications (RoS) is introduced and it is shown that the stated reconfiguration problem can be formulated as a controlled language convergence problem. In addition, algorithms for the verification of RoS and the construction of a reconfiguration supervisor are proposed. The supervisor is realised in a modular way which facilitates the extension by new configurations. Finally, it is shown that a supremal nonblocking and controllable strict subautomaton of the plant automaton that fulfils RoS exists in case RoS is violated for the plant automaton itself and an algorithm for the computation of this strict subautomaton is presented. The developed concepts and results are illustrated by a manufacturing cell example.
Citation - WoS: 10
Citation - Scopus: 10
An Integrated Scheduling and Control Model for Multi-Mode Projects
(Springer, 2013) Hazir, Oncu; Schmidt, Klaus Werner
In today's highly competitive uncertain project environments, it is of crucial importance to develop analytical models and algorithms to schedule and control project activities so that the deviations from the project objectives are minimized. This paper addresses the integrated scheduling and control in multi-mode project environments. We propose an optimization model that models the dynamic behavior of projects and integrates optimal control into a practically relevant project scheduling problem. From the scheduling perspective, we address the discrete time/cost trade-off problem, whereas an optimal control formulation is used to capture the effect of project control. Moreover, we develop a solution algorithm for two particular instances of the optimal project control. This algorithm combines a tabu search strategy and nonlinear programming. It is applied to a large scale test bed and its efficiency is tested by means of computational experiments. To the best of our knowledge, this research is the first application of optimal control theory to multi-mode project networks. The models and algorithms developed in this research are targeted as a support tool for project managers in both scheduling and deciding on the timing and quantity of control activities.
Citation - WoS: 9
Citation - Scopus: 10
Computation of Supervisors for Reconfigurable Machine Tools
(Springer, 2015) Schmidt, Klaus Werner
The rapid reconfiguration of manufacturing systems is an important issue in today's manufacturing technology in order to adjust the production to varying product demands and types. In this paper, we study the control of reconfigurable machine tools (RMTs) with the aim of fast reconfiguration and an easy controller implementation. We first formulate a particular reconfiguration problem for RMTs in a discrete event system setting, and then provide a necessary and sufficient condition for its solution. Moreover, we propose a polynomial-time algorithm for the construction of a reconfiguration supervisor as the composition of one modular supervisor for each separate RMT configuration. Each modular supervisor operates in three modes. In the first mode, it tracks the plant state if its corresponding configuration is inactive. In the second mode, it performs a configuration change if its corresponding configuration becomes active and in the third mode, it follows the specified behavior of its corresponding configuration if the configuration is active. An important property of the proposed reconfiguration supervisor is that it performs reconfigurations in a bounded number of event occurrences. In addition, the modular realization of our reconfiguration supervisor enables controller modifications such as adding or removing configurations during run-time. All results presented in the paper are illustrated by an RMT example.
Citation - WoS: 6
Citation - Scopus: 7
Modeling Distributed Real-Time Systems in Tioa and Uppaal
(Assoc Computing Machinery, 2016) Kartal, Yusuf Bora; Schmidt, Ece Guran; Schmidt, Klaus Werner
The mission- and life-critical properties of distributed real-time systems require concurrent modeling, analysis, and formal verification in the design stage. The timed input/output automata (TIOA) framework and the UPPAAL software package are two widely used modeling and verification tools for this purpose. To this end, we develop the algorithm TUConvert for converting distributed TIOA models to UPPAAL behavioral models and formally prove its correctness. We demonstrate the applicability of our algorithm by the formal verification of a distributed real-time industrial communication protocol that is modeled by TIOA.

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