Henrik Mäkitaavola

Efficient XML Interchange in factory automation systems

The advent of Service-Oriented Architecture (SOA) in the automation domain has made possible the cross-layer vertical integration of devices, manufacturing systems and business processes. However, the use of standard web service technologies is not always possible in an industrial environment with high real-time requirements and limited hardware resources due to the overhead connected to XML processing. The work presented in this paper analyses the opportunities, advantages and challenges when applying the newly emerged Efficient XML Interchange (EXI) standard for XML encoding to the factory automation systems. The two major SOA-based automation middleware architectures, namely OPC Unified Architecture (OPC UA) and Devices Profile for Web Services (DPWS), were investigated. Furthermore, we present an EXI-based approach for extending the reach of the service technology covering deployments on resource constrained embedded devices.

Towards a lightweight CEP engine for embedded systems

Industrial process automation systems are adopting event based communication. Pushing control loops towards low-level devices implies a need for lightweight embedded devices that are able to recognize and to react to events. Atomic events however, such as a value read by an individual sensor exceeding certain value, do not separately suffice to capture scenarios where a reaction should occur to a sequence of low-level events matching certain pattern, rather than to a single atomic event. Therefore, it becomes desirable that resource-constrained low-level devices are equipped with some, possibly lightweight, form of event filtering and processing. In this paper we propose to implement a lightweight complex event processing using the concurrent reactive objects (CRO) model. A core feature of the CRO model is its s ability to react to atomic events. Between the reactions, which basically are function executions, the system remains idle, and thus does not occupy the CPU and is energy-efficient. Additionally, CRO models can be executed in an efficient and predictable manner onto resource constrained platforms and offers low-overhead real-time scheduling through exploiting underlying interrupt hardware according to given time constraints.

Independence and interdependence of systems in district heating

In this paper, a fully operational wireless sensor and actuator network is presented. The network has the ability to control a district heating substation to ensure indoors comfort while minimizing energy waste by maximizing heat extraction from the distribution network. Introduced here is the foundation for a systems of systems approach within a district heating application, where several substations cooperate with the heat production plant. Presented are also the first steps to a service oriented architecture (SOA) where sensor nodes in the district heating network can cooperate with other nodes and systems, for example a ventilation control network.

Application of Service Oriented Architecture for Sensors and Actuators in District Heating Substations

Hardwired sensor installations using proprietary protocols found in todays district heating substations limit the potential usability of the sensors in and around the substations. If sensor resources can be shared and re-used in a variety of applications, the cost of sensors and installation can be reduced, and their functionality and operability can be increased. In this paper, we present a new concept of district heating substation control and monitoring, where a service oriented architecture (SOA) is deployed in a wireless sensor network (WSN), which is integrated with the substation. IP-networking is exclusively used from sensor to server; hence, no middleware is needed for Internet integration. Further, by enabling thousands of sensors with SOA capabilities, a System of Systems approach can be applied. The results of this paper show that it is possible to utilize SOA solutions with heavily resource-constrained embedded devices in contexts where the real-time constrains are limited, such as in a district heating substation.

Real-time complex event processing using concurrent reactive objects

Service Oriented Architectures (SOAs) and Complex Event Processing (CEP) are established technologies in the area of business automation. In combination, SOA and CEP allow for event centric management and processing of information in complex distributed systems. Whereas systems for process monitoring and control traditionally have been deployed using dedicated buses and proprietary (often scan-based) protocols, a recent trend in process automation is towards adopting open Internet-based technologies. This trend is driven by the increasing number and capabilities of devices used for monitoring and control. In such setting, SOA enabled devices can operate both as producers and consumers of (complex) events. To this end a lightweight CEP engine has recently been proposed, defining the translation of a subset of CEDR clauses into Concurrent Reactive Objects (CROs). In this paper we extend the proposed mechanism to incorporate non-deterministic execution, reoccurring events, overlapping timing windows and real-time properties. The extension allows timing properties to be either explicit, given as the deadline for a CEP query, or being derived from subqueries. Additionally, the described extensions form a foundation for future studies of timing properties for query processing and communication, in distributed heterogeneous systems. As a proof of concept, we demonstrate how the proposed mechanism can be encoded in the CRO based Timber language.

TinyMulle: A Low-Power Platform for Demanding WSN Applications

The research area of Wireless Sensor Networks (WSN) is growing rapidly. WSN technology is making entrance into new application areas, for example industrial control and Critical Infrastructure (CI) environments. Energy efficiency is a highly prioritized goal of communication protocols and application design for WSN. However, the usage of WSN in both industrial and CI environments are starting to require more and more complex applications. In this paper, we present a new low-power wireless sensor platform nicknamed TinyMulle. The TinyMulle architecture consists of a 16-bit micro controller with a maximum speed of 20 MHz and 31kB of RAM, an IEEE 802.15.4 compatible radio transceiver and several on-board sensors. Even with its small physical size, it is a powerful node capable of meeting the ever more demanding requirements of todays applications. Power consumption experiments indicate that operational lifetimes for TinyMulle in the range of months to years is feasible. The support for TinyOS enables the new platform to reuse existing software components developed for other sensor platforms.

A Cluster-Based Localization Method Using RSSI for Heterogeneous Wireless Sensor Networks

In this paper, we investigate the performance of cluster-based localization using received signal strength indicator (RSSI). The proposed solution is designed to meet the requirements of monitoring of firefighters or similar applications. The empirical relationship between signal strength and distance is determined using experiment data. One of the most popular localization algorithms found today, Min-Max, is used for our testbeds. Our solution is implemented in TinyOS and experimentally evaluated on a Mulle v5.2 IEEE 802.15.4 platform. The aim of our research is to develop a heterogeneous wireless sensor network consisting of inter connected body area networks, or clusters. Using localization, the networks robustness and reliability, as well as the safety of its users, can be improved.

Leveraging tinyos for integration in process automation and control systems

The number and complexity of networked sensors and actuators in industrial monitoring and control systems is rapidly increasing. This calls for flexible yet efficient methods (w.r.t. time and money) for designing, deploying and maintaining such systems. To this end, Service Oriented Architectures (SOAs) and wireless technologies are foreseen to play important roles. In the area of Wireless Sensor Networks (WSNs), TinyOS (TOS) has gained wide spread use, mainly because it offers a simple programming model. Moreover TOS comes with a ready made code base (e.g., protocol stacks needed to implement SOA enabled devices) and is available for a large number of light-weight target platforms. However, TOS has yet to make its way into industrial applications where real-time operation is required (which is typical to monitoring and control systems). As being designed primarily with simplicity in mind, the TOS execution model for tasks is non-preemptive, limiting system responsiveness and schedulability. To overcome this problem preemptive TOSThreads has been introduced. However, this introduces the additional complexity of traditional multi-thread programming, thus the main benefit of TOS is lost. In this paper we present an alternative execution model for TOS, that allows preemptive execution while preserving the simplicity of vintage TOS. We exemplify the impact of scheduling to a typical sensor/actuator node scenario. Our results indicate that the proposed preemptive execution model is capable of reducing both delay and drop rate for the given scenario.

A SOA approach to delay and jitter tolerant distributed real-time Complex Event Processing

The combination of Service Oriented Architectures (SOAs) and Complex Event Processing (CEP) is gaining momentum for event centric management and processing of information in complex distributed systems (e.g., business automation). Whereas systems for factory automation have traditionally been deployed using dedicated buses and proprietary (often scan based) protocols, a recent trend in process automation is towards adopting open internet based technologies and event based communication. This trend is driven by the increasing number and capabilities of devices used for monitoring and control, and the increased flexibility, maintainability and price/performance gains expected from IP (potentially SOA/CEP) enabled systems. In this paper we discuss the challenges involved to apply SOA and CEP to the field of factory automation. In particular, realtime aspects are highlighted, both w.r.t. to accurate time-stamping of physical events in a distributed system, as well as end-to-end timing including communication and CEP processing. We approach the challenges by an architecture combining state-of-the-art synchronisation mechanisms for wired and wireless networks together with real-time communication and distributed query processing based on the notion of time constrained reactions. We discuss the impact of synchronisation inaccuracies and delays introduced by processing and communication, and present a method for implementation of safe potential- and certain matches.

A feasibility study of SOA-enabled networked rock bolts

The use of rock bolts in the mining industry is a widely used approach for increasing mine stability. However, when compared to the automation industry, where the use of sensors and real-time monitoring of processes have evolved rapidly, the use rock bolts have not changed a lot during the last 100 years. What is missing are technologies for keeping installed rock bolts under real-time and online monitoring. One problem is that rock bolts can become damaged by seismic activities or movements within the rock, and thus lose their load bearing capacity. If that happens, the outer shell of a tunnels walls or ceiling can collapse, with disaster as a result. Therefore, there is a clear need for online and real-time monitoring solutions for strain and thereby stress, as well as seismic activity. In this paper, the current state of art in research around intelligent rock bolts is presented. An intelligent rock bolt is the combination of a traditional rock bolt with an Internet of Things device, i.e. a rock bolt with embedded sensors, actuators, processing capabilities and wireless communication. In the proposed architecture, every rock bolt has its own IPv6 address and can establish a wireless mesh network in an ad-hoc manner. By measuring strain and seismic activity and exposing the sensors in the form of services, large gains in terms of safety and efficiently can be achieved. A number of mining related activities such as stress on the rock bolt can be detected, falling rocks and the presence of mobile machinery can be observed. Since the network is based on standard communication protocols such as IPv6, it is vital to add security mechanisms to prevent eavesdropping and tampering of data traffic. By utilizing the real-time monitoring capabilities of a network of Internet-connected intelligent rock bolt, it is possible to drastically improve monitoring of mining activities and thereby providing workers with a safer working environment.