Grzegorz Bocewicz

Design of Admissible Schedules for AGV Systems with Constraints: A Logic-Algebraic Approach

The subject matter of the study are the automated guided vehicle (AGV) operation synchronisation mechanisms in flexible manufacturing systems. Since each AGV can be treated as an autonomous object capable to undertake decisions regarding its routing, entering path sectors, etc., hence a class of transportation systems considered can be seen as a class of multi-agent ones. In many practical cases transport operations are repetitive. The processes examination has to guarantee the collision-free and deadlock free AGVs flow. In this paper the problem of determination of the rules coordinating access of the vehicles to the shared travel route intervals, ensuring the collision-free and deadlock-free execution of the repetitive processes was reduced to determination of the sufficient conditions of the form of a pair (initial state, a set of priority rules). In particular the problem of searching for a pair is defined in the form of the constraint satisfaction problem (CSP) and is solved with use of the logic programming techniques.

Automated guided vehicles fleet match-up scheduling with production flow constraints

The paper describes a Multimodal Transportation Network (MTN) in which several unimodal networks (Automated Guided Vehicles (AGVs), hoists, lifts, etc.) interact with each other via common shared workstations as to provide a variety of demand-responsive material handling operations. The material handling transport modes provide movement of work pieces between workstations along their manufacturing routes in the MTN. The main contribution of this work is the solution to a constraint satisfaction problem aimed at AGVs fleet match-up scheduling while taking into consideration assumed itineraries of concurrently manufactured product types. In other words, assuming a given topology of the MTN and schedules of operation sequences modeling concurrently manufactured product types, the main objective is to provide a declarative framework aimed at determining conditions allowing one to adjust the AGVs fleet schedule due to the timetable of operations executed in an assumed multi-product manufacturing environment.

Iterative Multimodal Processes Scheduling

Abstract The paper considers the problem of Automated Guided Vehicles (AGVs) fleet scheduling subject to the right match-up of local cyclic acting AGV schedules to given workpiece machining schedules. The main contribution of this work is the solution to a constraint satisfaction problem aimed at AGVs fleet match-up scheduling while taking into consideration assumed itineraries of concurrently manufactured product types. In other words, assuming a given layout of FMS’s material handling and production routes of simultaneously manufactured work orders as well as cyclic schedules of concurrently manufactured product types, the goal is to provide a declarative model enabling multimodal processes, i.e. employing AGVs, hoists, lifts, etc. demand-responsible scheduling of transportation/handling services. An algebra-like driven approach to cyclic scheduling based on step-by-step composition of multimodal transportation network sub-structures is proposed. Results of computational experiments assessing scalability of the method provided are presented as well.

Constraint Programming Approach to Time-Window and Multiresource-Constrained Projects Portfolio Prototyping

Constraint Programming (CP) is an emergent software technology for declarative description and effective solving of large combinatorial problems especially in the area of integrated production planning. In that context, CPcan be considered as an appropriate framework for development of decision making software supporting small and medium sized enterprises (SMEs) in the course of projects portfolio prototyping. The paper deals with problem considered multiresource problem in which more than one resource type may be required by every activity in the project and the availability of each type is time-windows limited. The problem belongs to a class of NP-complete ones. The aim of the paper is to present a CPbased projects portfolio prototyping framework providing a prompt service to a set of routine queries stated both in straight and reverse way, e.g., concerning the projects portfolio makespan implied by a given resources allocation, and the feasible resources allocation guaranteeing an assumed projects portfolio makespan. The way the responses to the routine queries can be guaranteed while may be available in an on-line mode is illustrated in the example enclosed.

Agvs distributed control subject to imprecise operation times

The subject matter of the study are the automated guided vehicle (AGV) operation synchronization mechanisms in flexible manufacturing systems, where transport processes can be modeled as a system of cyclic concurrent processes sharing common resources, i.e., some preset travelling route intervals. In this paper the problem of determination of the local rules coordinating access of the vehicles to the shared travel route intervals, ensuring the deadlock-free execution of the repetitive processes was reduced to determination of the sufficient conditions. In that context the problem considered can be seen as a problem of multi-agent coordination, and defined as the constraint satisfaction problem (CSP) subject to precise and imprecise operation times, and then solved with use of the logic programming techniques.

A methodology for implementation of mobile robot in adaptive manufacturing environments

With the rapid development of technologies, many production systems and modes has been advanced with respect to manufacturing, management and information fields. The paper deals with the problem of the implementation of an autonomous industrial mobile robot in real-world industrial applications in which all these fields are considered, namely mobile robot technology, planning and scheduling and communication. A methodology for implementation consisting of: a mobile robot system design (Little Helper prototype), an appropriate industrial application (multiple-part feeding), an implementation concept for the industrial application (the Bartender Concept), a mathematical model and a genetic algorithm-based heuristic is proposed. Furthermore, in order for the mobile robot to work properly in a flexible (cloud-based) manufacturing environment, the communications and exchange of data between the mobile robot with other manufacturing systems and shop-floor operators are addressed in the methodology. The proposed methodology provides insight into how mobile robot technology and abilities contribute to cloud manufacturing systems. A real-world demonstration at an impeller production line in a factory and computational experiments are conducted to demonstrate the effectiveness of the proposed methodology.

Declarative Approach to Cyclic Scheduling of Multimodal Processes

In this chapter, we deal with the cyclic scheduling problem usually observed in the FMS producing multi-type parts where the AGVS plays a role of a material handling system. Finding the conditions guaranteeing the AGVs deadlock-free and collision-free movement policy is the aim of this work. The AGVs co-sharing the common parts of the transportation route while executing repetitive processes, can be modeled in terms of Cyclic Concurrent Process Systems (CCPSs). The chapter suggests a novel approach for schedulability analysis employing the declarative modeling. In turn, the schedulability analysis for a given CCPS answers the question whether a cyclic schedule exists or not. A reference model of constraint satisfaction cyclic scheduling problem shows that unschedulability can be caused by a relation among an initial state and dispatching rules selected. The sufficient conditions guaranteeing CCPS schedulability are discussed and the recursive approach to their designing is proposed. Possible implementations are illustrated on example of the flexible manufacturing system operation.

Cyclic Steady State Refinement: Multimodal Processes Perspective

The cyclic scheduling problem modeled in terms of Cyclic Concurrent Process Systems is considered. The problem can be seen as a kind of Diophantine problem, hence its solvability, i.e. schedulability, plays a pivotal role in many supply-chain problems. In contradiction to the traditionally offered solutions the approach proposed allows one to take into account such behavioral features as transient periods and deadlocks occurrence. So, the contribution’s aim is the modeling framework enabling an evaluation of cyclic scheduling problems solvability, i.e., the declarative approach to reachability problems regarding cyclic steady states determination as well as conditions guaranteeing assumed performance of multimodal processes executed within a concurrent cyclic processes environment.

Production flows scheduling subject to fuzzy processing time constraints

Effective sequencing and scheduling of material handling systems (MHSs) have a major impact on the productivity of a manufacturing system. Since the main function of a MHS is to supply the right materials at the right locations at the right time, the design of automated guided vehicles (AGVs) fleet-oriented, distributed and scalability-robust control policies ensuring deadlock-free operations is of crucial importance. In this context, a given design of a flexible manufacturing system (FMS) where vehicles serve workstations located along different modes of cyclic guided paths in a 3D environment composed of rails/lifts/hoists is considered. Furthermore, fuzzy processing time constraints on transportation operations, a production flows scheduling problem subject to an assumed set of constraints imposed by admissible production routes and schedules of AGV fleet in a given MHS are considered. Since this type of problem can be treated as a fuzzy constraint satisfaction problem, the main objective is to provide analytical formulas enabling the avoidance of time-consuming computer-simulation-based calculations of AGV fleet schedules, as well as vehicles deadlock and collisions, while keeping the throughput at the maximum achievable level. Results of computational experiments assessing the scalability of the proposed method are presented as well.

Multimodal Processes Rescheduling: Cyclic Steady States Space Approach

The paper concerns cyclic scheduling problems arising in a Multimodal Transportation Network (MTN) in which several unimodal networks (AGVs, hoists, lifts, etc.) interact with each other via common shared workstations as to provide a variety of demand-responsive material handling operations. The material handling transport modes provide movement of work-pieces between workstations along their manufacturing routes in the MTN. The goal is to provide a declarative framework enabling to state a constraint satisfaction problem aimed at AGVs fleet match-up scheduling taking into consideration assumed itineraries of concurrently manufactured product types. In that context, treating the different product types as a set of cyclic multimodal processes is the main objective to discuss the conditions sufficient for FMS rescheduling imposed by production orders changes. To conclude, the conditions sufficient for an FMS rescheduling imposed by changes of production orders treated as cyclic multimodal processes are stated as the paper’s main contribution.