Business Process Simulation is a useful and widely adopted technique that provides process designers and data analysts with the necessary information to estimate the performance impact of business decisions before they are actually deployed. Manufacturers can bene t from such simulations especially when a strong changeability of the assembly work ows and systems is required. In order to integrate the simulation into existing manufacturing plants, simulations need to consider not only full simulations but also mixed simulations which include virtual and real operating resources. In this work, we present a new simulation framework which allows the process designer to model mixed simulations by de ning virtual operating resources. These can be coupled with real hardware allowing the simulation to interact with manufacturing components to test the integrated system for robustness at runtime.
Business process simulation (BPS) is a technique to quantitatively analyze the
process in terms of performance measures, such as time, cost, quality and
exibility [
Developments aiming at smarter factories require solutions for the concept of changeability. Changing the manufacturing system, e.g. by adding new devices or exchanging existing ones, cost time if the device start-up fails leading to downtimes and further debugging. Thus, a exible and extensible simulation framework is necessary to allow a virtual start-up in the existing manufacturing system and to test its compatibility with the running system ex-ante.
We propose a framework allowing mixed simulations running virtual and real resources together. The framework consists of a Web-based dashboard and the Basis Simulation System (BaSS) which mediates between the BPM engine and the virtual as well as the real resources. The framework allows an easy integration of new resources and the adding and exchange of resources at runtime. Di erent states of resources are coupled through event-based communication with a BPMN process which can be adapted easily by process designers to control the assembly ow simulated entirely or partly.
In the following, we present the framework's architecture and the simulation interface in Section 2. The usage of the system, its graphical user interface and an exemplary assembly process which are part of this demo, are illustrated in Section 3. In Section 4, we draw a brief conclusion. 2
The Framework and the Basis Simulation System The framework's architecture can be seen in Figure 1. The core of the framework is the BaSS. It contains the BPM Engine Handler, a distributed Data Store and an unde ned number of virtual operating resources. Simple events emitted by the BPM engine are processed by the BPM Engine Handler and enriched with assembly-speci c data from the data store to form complex events. These complex events are propagated to the respective virtual resources via a common communication interface. The receiving virtual resources can be coupled with real resources. In this case, they act as adapters which transmit the events to the real resources. If there is no real resource, the virtual resource simulates the real one based on the implemented simulation for this resource. This mechanism allows mixed simulations of factory resources. In addition, the Data Store o ers a REST-Application Programming Interface (API) for monitoring and con guration purposes and thus, provides valuable data input for visualizing and logging simulated processes aiming at evaluating simulations. A Web-based Dashboard has been implemented to visualize live and historic process data.
All components within the BaSS are implemented as OSGi services in Java. OSGi is a modular system and a service platform allowing the modular design of the framework in so-called bundles. It enables an easy exchange of bundles, among others representing resources, during runtime which avoids a redeployment of the framework and thus interruptions of the assembly process.
Communication between the individual components is realized by using the Message Queue Telemetry Transport Protocol (MQTT) protocol. It is a lightweight and well adopted communication protocol in the Internet of Things. As such, it provides an e ective way of communicating thanks to the broker-based publish / subscribe architecture and the Quality of Service (QoS) levels o ered. The loose coupling of the event-based architecture supports the modular architecture of our framework. High scalability is provided by using MQTT clustering.
A virtual resource is an abstraction of a real operating resource whose API
it implements. In addition, each real as well as virtual resource has a uniform
life-cycle based on Packaging Machine Language (PackML), cf. [
The BaSS and a BPM-Engine Handler, which is based on the Camunda BPM Engine, together with the visualization dashboard shown in Figure 2 is available from our cloud server 1. After starting the application, the following two Web interfaces are available to the user: Con guration Admin Apache Felix Console for OSGi bundle con guration.
It is used to set-up the BaSS services. It comes with pre-con gured bundles for the MQTT communication and the necessary operating resources. Live Dashboard Used for process management and real time visualization of the process ow. It is connected to the underlying BPM-Engine and can initialize and destroy processes. Important information like the current process execution or task execution times can be watched easily. In addition, audit logs are available showing the process history of the selected process.
For the demo to work, the pre-con gured operating resources and the communication must be started. This is done in the con guration admin interface which forms the control center for starting and stopping resources represented by 1 https://cloud.dfki.de/owncloud/index.php/s/sZpJZC9HKiqemBS the respective bundle implementations. To enable publish / subscribe communication, a suitable MQTT broker must be installed on the system, e.g. ActiveMQ.
Afterwards, the implemented processes can be started. There are three processes included in this demo (see Figure 3): Initialization Initializes all operating resources according to their PackML state. So, each resource must be reset and started for being able to execute concrete commands.
Main Assembly A press process is simulated in the demo. First, a button needs to be pushed before the press is able to perform the press action. Finalization After the main assembly process, the operating resources can be completed and stopped according their PackML state model. 4
By providing an easy-to-use framework for the mixed simulation of operating resources in factory plants, operating resources can be tested individually in a real manufacturing context. This may be crucial to avoid wrong expectations on the process which is only simulated entirely. Due to the PackML life-cycle, virtual resources can easily be de ned and coupled with real resources. Manufacturers may also provide virtual resources which act as simulated operating resources implementing the state machine of the concrete operating resource. Thereby, simulated and real components share the same API and can be easily integrated in processes models.
Starte Prozess Activate press with push-button
Do press
Raise press pressed Press Error
press raised Acknowledgments. This research was funded in part by the German Federal Ministry of Education and Research (BMBF) under grant number 01IS16022E (project BaSys4.0). The responsibility for this publication lies with the authors.