Pawel Majdzik

Towards Robust Predictive Fault-Tolerant Control For A Battery Assembly System

Abstract The paper deals with the modeling and fault-tolerant control of a real battery assembly system which is under implementation at the RAFI GmbH company (one of the leading electronic manufacturing service providers in Germany). To model and control the battery assembly system, a unified max-plus algebra and model predictive control framework is introduced. Subsequently, the control strategy is enhanced with fault-tolerance features that increase the overall performance of the production system being considered. In particular, it enables tolerating (up to some degree) mobile robot, processing and transportation faults. The paper discusses also robustness issues, which are inevitable in real production systems. As a result, a novel robust predictive fault-tolerant strategy is developed that is applied to the battery assembly system. The last part of the paper shows illustrative examples, which clearly exhibit the performance of the proposed approach.

Distributed flow control design for repetitive manufacturing processes

Abstract This paper addresses resource allocation issues that are at the heart of a methodology proposed for the design of distributed control of a class of repetitive manufacturing systems. In particular, conditions sufficient for deadlock-free and starvation-free execution of a system of closed, sequential, repetitive manufacturing processes are considered. The relationship between system resource capacities and a set of admissible realizations of the component processes is discussed. Finally, a rapid prototyping procedure for designing systems with given performance parameters is presented.

Prototyping of distributed control procedures in concurrent cyclic processes systems

This paper addresses an issue of periodic job shop controlling where concurrent process flows have to compete safely (i.e. being starvation and deadlock-free) for access to shared system resources. A distributed flow control policy that restricts processes to access resources in a system is proposed. The main problem is reduced to determining a pair (a set of priority dispatching rules, an initial processes allocation belonging to the persistent period of a system flow), which can be treated as distributed control procedure. The processes are controlled by a set of dispatching rules that guarantee steady cyclic flow of the processes. Because various process flows lead to diverse values of the resource utilization rate, a proposal of an automated prototyping procedure of a system is considered. The prototyping procedure allows determining desired system flows for assumed factors such as system capacity or the value of rate of resource utilization. Thanks to determining the pair (a set of priority dispatching rules, an initial processes allocation belonging to the persistent period of a system flow) the result of this paper can be used along with the max-plus algebra formalism for an automated system flow prototyping.

A max-plus algebra predictive approach to a battery assembly system control

The paper deals with modeling and control of the real battery assembly system, which is under implementation in the RAFI GmbH Company (one of the leading Electronic Manufacturing Service Provider in Germany). To model the controlled battery assembly system a unified max-plus algebra and model predictive control framework is employed. The considered system belongs to some class of discrete event system, which contains a finite number of industrial tasks and a finite number of resources, which are utilised according to a mutual-exclusion protocol. The assembly task is organised in a completely automatic way, which involves a number of robots. Thus, the proposed computational framework is used to minimize robot energy consumption while satisfying the constraints imposed on the system.

A fault-tolerant approach to the control of a battery assembly system

The paper concerns fault-tolerant control of a real battery assembly system. The proposed framework is based on an interval analysis approach, which along with max-plus algebra, allows describing uncertain discrete event system such as the production one being considered in this paper. Having a mathematical system description, a model predictive control-based fault tolerant strategy is developed which can cope with both processing, transportation and mobile robot faults. As a result, a novel robust predictive fault-tolerant strategy is developed that is applied to the advanced battery assembly system. The final part of the paper shows the implementation and experimental validation of the proposed strategy. The proposed approach is tested against single as well as simultaneous faults concerning processing, transportation and mobile robots.

A cyclic scheduling approach to maintaining production flow robustness

The organization of flow production, which is typical found in assembly processes, involves a repetitive, fixed-takt time flow of same-size production batches. The cyclic nature of the production flow, which ensures a steady production rhythm, enables just-in-time planning and organization of the associated supply chains. Disruptions in the operation of machinery and equipment, which occur in practice, lead to deviations from nominal operation times. These types of local disturbances lead to changes in production takt time, making it necessary to adjust previously created schedules for delivery/reception of materials and products. Assuming that a control action can be taken to adjust transport operation times within a specified time range, the problem of cyclic scheduling of production flows boils down to seeking conditions the satisfaction of which will guarantee robustness to this kind of disruptions. Satisfaction of robustness conditions allows a return to the nominal production takt time and appropriate adjustment of the production flow trajectory (which makes it possible for the system to return to the previously scheduled delivery times). Numerous examples are included to illustrate the principles of the proposed research methodology aimed at finding solutions for robust scheduling of fixed-takt time production flow.

A receding-horizon approach to state estimation of the battery assembly system

The paper addresses the issue of the state estimation problem of a class of discrete-event systems. The receding-horizon approach is employed to solve above problem. The system and its variables are described within the (max,+) algebra. Thus making possible to incorporate robustness within the overall framework. The paper also shows the transformation of the interval cost function into the scalar one, and hence, making the computational procedure trackable within the quadratic programming framework. Resulting in interval estimates of the system state, which can be used for both fault diagnosis and control purposes.

Design of a Predictive Fault-Tolerant Control for the Battery Assembly Station

The paper deals with modeling and fault-tolerant control of a real battery assembly system, which is under implementation at RAFI GmbH Company. For that purpose a unified max-plus algebra and model predictive control framework is introduced. Subsequently, the control strategy is enhanced with the fault-tolerance features that enhance the overall performance of the production system. As a result, a novel predictive fault-tolerant strategy is developed that is applied to the battery assembly system. Finally, the last part of the paper shows an illustrative example, which clearly exhibits the performance of the proposed approach.

Modeling Discrete-Event Systems with Hard Synchronization Constraints

An issue of prototyping Systems of Concurrent Cyclic Processes (SCCP), in which a number of concurrently running processes compete to access to a set of resources is considered. The main outcome of this paper is an automated procedure of performance evaluation for such systems with desired values of a wide range of system functional characteristics, such as a schedule of processes flows and the system period. This stage is realised by a procedure of automatic building of an analytical model of SCCP, which is based on the (max, +) algebra formalism. In most cases the (max, +) algebra is used to model of discrete-event systems, while the synchronization is based on rendezvous protocol. However, in this paper - modeling of the systems is based on mutual exclusion protocol, moreover buffers are included. As an illustrative example example RAFI Battery Assembly System was given in this paper.

Modeling discrete-event systems with constraints

Prototyping Systems of Concurrent Cyclic Processes (SCCP), in which a number of simultaneously running processes compete to access to a set of resources, in an automated way is the main thread of this paper. Procedure of performance evaluation for such systems with desired values of a wide range of system functional characteristics, such as a schedule of processes flows and the system period, especially with multiple executions of single process cycles within single system cycle will be presented. This stage is realised by a procedure of automatic building of an analytical model of SCCP, which is based on the (max, +) algebra formalism. In most cases the (max, +) algebra is used to model of discrete-event systems, while the synchronization is based on randez-vous protocol. However, in this paper - modeling of the systems is based on mutual exclusion protocol, moreover buffers are included. Moreover the algorithm of determining of the system period and schedule of workflow - when there is no direct relation between eigenvalue of system matrix and system period - will be presented.