Formal design and analysis of a hybrid supervisory control structure for Virtual Production Systems

Abstract

Virtual Production Systems (VPSs) is a dynamic paradigm for production resources structure, which was proposed to cope with changing and uncertain manufacturing environment. However, the high performance of VPSs relies on a high-quality control in practice. Motivated by both local quick responses and global optimization, a supervisory control structure based on autonomous and coordination mechanisms is proposed for VPSs in this paper. This hybrid supervisory control structure is formally designed and analysed with timed automata on the platform of an integrated tool named UPPAAL. First, the Discrete Events Dynamic Systems (DEDS) model of VPSs is established. Then autonomous and coordinated supervisory controllers are further designed under the guidance of heuristic scheduling rules, such that the desired characteristics of both performance (production flow and time) and activity (overflow-, conflict-and deadlock-free) can be ensured. Finally, system analysis, including deadlock-free analysis, calculation and simulation of time-optimal scheduling, is made through verification. A case study is made to illustrate that control and scheduling can be well integrated into this hybrid supervisory control structure in practice.

A generic deadlock-free reactive scheduling approach

“…Using the commercial statistical software MINITAB v13 4 In addition, Figure 4.4 shows that RMFT significantly decreases when RFLX is high.…”

“…Although this has reduced the gap between the two hierarchical levels, the literature on deadlock-free scheduling still lacks a formal approach that can transform a schedule into an implementable supervisor, and the literature on supervisory control still considers the supervisor as the sole decision maker in the control system. A few attempts, however, have been made to integrate both levels, but these either lacked a global view of the system when performing the scheduling task [4], or realized a poorer performance via the supervisor when compared to schedules resulting from pure deadlock-free scheduling approaches [5].…”

Hierarchical Performance-Oriented Control of Flexible Manufacturing Cells

“…However, a wide gap exists between the contributions found in the scheduling literature and those pertaining to actual implementation (supervision) on the shop floor (Sun et al, 2006). A few attempts, however, have been made to integrate deadlock-free scheduling and supervision, but these either lacked a global view of the system (Li & Jiang, 2006), or realized a poorer performance when compared to pure deadlock-free scheduling approaches.…”