Model-driven Performance Analysis of Reconfigurable Conveyor Systems used in Material Handling Applications Kyoungho An, Adam Trewyn, Aniruddha Gokhale Shivakumar Sastry ∗Department of Electrical Engineering and Computer Science †Department of Electrical and Computer Engineering Vanderbilt University The University of Akron Nashville, TN 37235, USA Akron, OH 44325, USA Email: {kyoungho.an, adam.c.trewyn, a.gokhale}@vanderbilt.edu Email: {ssastry}@uakron.edu Abstract—Reconfigurable conveyors are increasingly being terminals, engineers and layout planners for the conveyor adopted in multiple industrial sectors for their immense flexibility systems must often grapple with numerous questions including in adapting to new products and product lines. Before modifying but not limited to: What is the maximum sustainable rate of the layout of the conveyor system for the new product line, however, engineers and layout planners must be able to answer flow of goods in the system? Can handling of certain types many questions about the system, such as maximum sustainable of goods be prioritized over others? Does a certain layout of rate of flow of goods, prioritization among goods, and tolerances the conveyor system lead to starvation of certain paths in the to failures. Any analysis capability that provides answers to system? What is the impact of failures of certain sections of these questions must account for both the physical and cyber the conveyor system on the overall throughput and hence the artifacts of the reconfigurable system all at once. Moreover, the same system should enable the stakeholders to seamlessly change monetary costs? How to plan the inter material spacing on the the layouts and be able to analyze the pros and cons of the conveyors such that the goods do not collide when they are layouts. This paper addresses these challenges by presenting a switched through transfer elements (called turnarounds)? model-driven analysis tool that provides three important capa- A naive solution based on trial-and-error does not scale bilities. First, a domain-specific modeling language provides the when dealing with large deployments. A straightforward ap- stakeholders with intuitive artifacts to model conveyor layouts. Second, an analysis engine embedded within the model-driven plication of techniques such as combinatorial optimization tool provides an accurate simulation of the modeled conveyor or queuing theory in isolation do not suffice either for the system accounting for both the physical and cyber issues. Third, following reason. The intertwined relationships between the generative capabilities within the tool help to automate the cyber elements, i.e., the micro-controllers that regulate each analysis process. The merits of our model-driven analysis tool unit and the wireless transceivers that provide communication are evaluated in the context of an example conveyor topology. Keywords: Reconfigurable conveyors, design-time analysis, model- links between micro-controllers in physically adjacent units, based, simulations. and the physical transfer of parts over the conveyor units present formidable challenges in readily finding answers to I. INTRODUCTION the above questions. Many industrial sectors, such as manufacturing, automo- Answering the questions faced by the engineers and layout tive, and material handling, are increasingly moving towards planners obviously requires a design-time solution in contrast adopting reconfigurable conveyor systems in their processes to the need for physically deploying a system and iterating over since they offer significant flexibility in readily adapting to multiple possibilities. A critical requirement for such a design- newer products and product lines, while making efficient use time “what-if” analysis capability is the need for it to account of available space, and all of these at a fraction of cost for in tandem both physical artifacts of a conveyor system that otherwise would be incurred if an entirely new conveyor (e.g., speed of belts, inter-material spacing, size and type of system is to be installed. To quote from a recent article [1]: the the material being handled, response time of commands to key factor in a truly reconfigurable modular conveyor system is control belt motor speeds, rate of flow of material into the the ability to connect and reconnect a wide variety of modules input source of the system, and sensors that scan moving and accessory modules that allow engineers the freedom to goods) and cyber artifacts (i.e., message formats and signaling tweak production lines when necessary without the cost of protocols between the individual units of the reconfigurable a brand new conveyor or the risk of losing the conveyor’s system, timing of the messages, and synchronization policies integrity. among the highly concurrent executing software artifacts). When faced with the task of using reconfigurable systems Model-driven performance analysis [2] of the reconfigurable in businesses, such as a material handling system used in conveyor cyber physical system (CPS) [3] provides a promis- facilities like FedEx, UPS, and baggage handling in airport ing solution [4] to address these requirements. In particular, our model-driven analysis tool comprises three primary arti- Another work closely related to ours appears in [11]. The facts: motivation of the work is to assess the reconfiguration in layout 1) A domain-specific modeling language [5] within our tool of a manufacturing systems as the product mix changes. The provides intuitive abstractions to engineers and layout metrics used to evaluate the layout include material handling planners to describe the proposed layouts of their system costs and operational performance factors. The authors of this without unduly tightly coupling their intentions to any work use open queuing networks to develop a mathematical specific analysis capability. model of the system. A related recent work that uses Petri 2) An analysis engine we designed that implements the Nets to develop analytical models of reconfigurable systems behavior of the conveyor units in the MATLAB appears in [12]. Despite the similarity in the goals of these Simulink/Stateflow simulation engine by tightly inte- related works, to the best of our understanding, these works grating the cyber and physical aspects of the conveyor do not explicitly account for the tight integration between the system along with the critical timing properties [6], [7]. cyber and physical issues. Instead, performance estimates are 3) A generative capability [8] that synthesizes artifacts for collected based on expected arrival patterns of parts. the analysis engine and helps to completely automate In [13], the authors present a framework to assess reconfig- the design-time analysis process. urability of manufacturing systems. Although this work applies to a more broader range of reconfigurability than our work, By augmenting the simulation with synthetic data that is it is more focused on assessing the manufacturing degrees of derived from our experience with real conveyor systems, freedom, i.e., identifying the different ways in which a product we validate the design of the conveyor system layout using can be manufactured. Thus, although both approaches pertain our model-driven analysis tool. This approach allows us to to design-time analysis and are model-based, the goals and evaluate several system-level performance parameters, such outcomes are quite diverse. as throughput and end-to-end latency at design-time thereby A tutorial on reconfigurable modular systems focusing pri- providing insights into the efficiency of the proposed layout marily on pallet-based conveyor systems is presented in [14]. to meet the business objectives. The relevance of this related work to ours stems from the fact The remainder of this paper is organized as follows. Sec- that the authors present a broad range of metrics to assess tion II compares our work to related research; Section III flexibility of the system. Among the list provided by the describes the system model of our reconfigurable conveyor authors, our work focuses on evaluating the performance of system alluding to the kinds of material that we consider layout modifications and assess scalability. flowing on the conveyors; Section IV presents the design of Verification of the logical controllers in reconfigurable the model-driven analysis framework for the reconfigurable systems is considered in [15]. The authors use the concept conveyor system; Section V presents results evaluating our of timed transition models to model the behavior of the tool on an example topology; and finally Section VI offers controllers to verify its properties. The authors also use their concluding remarks and next steps. technique to iteratively arrive at a desirable controller for the reconfigurable system. Our work is orthogonal to the goals II. RELATED WORK of this related work in that we are concerned with measuring Although a large literature in model-driven engineering of different performance factors of a given layout and controllers large-scale systems exists, in this section we present related while the related work focuses on the synthesis and verifying research in the field of reconfigurable systems focusing primar- the correctness of logical controllers for reconfigurable con- ily on those works that deal with assessing performance of the veyor systems. system along different metrics. Moreover, we present works Li et. al [16] describe an approach to model reconfigurable that are closely related to the different