SHPN models based simulation and control of mobile robotic systems integrated into A/DML

Purpose of this paper is to model, simulate and control wheeled mobile robotic systems integrated into an assembly mechatronics line for making it reversible, i.e. have the capacity to deal disassembly using mobile platforms equipped with a manipulator. For this purpose, synchronised hybrid Petri nets (SHPN) models will be used to simulate and control an assembly/disassembly (A/D) mechatronics line (A/DML), with a fixed number of workstations. Two cases are presented: to the first one, A/DML is served by a wheeled mobile robots (WMR) equipped with robotic manipulator (RM). To the second case, A/DML is served by two WMRs, collaborative or parallel working. The SHPN models are hybrid type, where A/DML is the discrete part, and WMRs are the continuous part. Moreover, the model operates in synchronised mode with signals from sensors. Disassembly starts after the assembly process and if the assembled piece fails the quality test, to recover disassembled parts. The WMRs are used only during disassembly, to transport parts from the disassembling locations to the storage locations.

I. Introduction

The approach proposed in this paper responds to the concepts of planning and control of the manufacturing of assembly/disassembly, (A/D), on a laboratory system, a mechatronics line served by mobile platforms equipped with manipulators, with emphasis on the planning of operations. The most eloquent correspondents in the real world are assembly processes in the automotive industry, car body, gearbox and engine block assembly. In most cases, robotic manipulators that have a fixed location serve these assembly and/or processing lines. Through this study, we extended the degree of automation and efficiency of this production line using mobile robotic systems equipped with manipulators. The assembly lines become reverse, being able to recover and reuse of components and subassemblies, in the event that the final product does not meet quality requirements. Synchronised Hybrid Petri Nets (SHPN) models are used for modelling an assembly/disassembly mechatronics line (A/DML) served by one or two wheeled mobile robots (WMRs). When the A/DML is serviced by a single WMR, a RM is used to manipulate disassembled part. When they are working in parallel, the first WMR, equipped with RM, is used for handling, whilst the second one is used for transporting disassembled part, from disassembling to the warehouse locations. As a main contribution of this paper, is a new approach for modelling, simulation and controlling of the A/D production flows, by aggregation of continuous and discrete events systems, in a hybrid system. The disassembly operations are performed on the same assembly line, consisting of a number of linear configured workstations. The first workstation takes the product to be disassembled, and the parts are disconnected on different workstations. A cycle terminates, i.e. the product leaves the line, whenever all its required parts are disassembled. SHPN models respect both approaches: the discrete approach for the elementary A/D cycles and the continuous approach for displacement of WMRs. The reversible A/DML served by mobile platforms has dynamics determined by events (events supplied by the control sequences of the automatic system) and by the interaction with the WMRs,. The A/D process can by decomposed into a sequence of elementary assembl y/ disassembl y tasks coupled in parallel with positioning tasks of work piece along conveyor, as in [1], [2] and [3]. The hybrid disassembly strategy is based on the hierarchical model proposed in [3], [5]–[7] and [8].