This research addresses real-time task scheduling in industrial process control. It includes a constraint-based scheduler which is based on MSP.RTL, a tool for real-time multiprocessor scheduling problems with a wide variety of timing constraints. This dissertation extends previous work in two broad directions: improving the tool itself and broadening the application domain of the tool to include wired and wireless industrial process control. For the tool itself, we propose enhancements to MSP.RTL in three steps. In the first step, we modify the data structure for representing the temporal constraint graph and cutting the memory usage in half. In the second step, we model the search problem as a constraint satisfaction problem (CSP) and utilize backmarking and conflict-directed backjumping to speed up the search process. In the third step, we perform the search from the perspective of constraint satisfaction programming. As a result, we are able to use existing CSP techniques efficiently, such as look ahead, backjumping and consistency checking. Compared to the various ad hoc heuristics used in the original version, the new approach is more systematic and powerful. To exercise the new MSP.RTL tool, we acquired an updated version of the Boeing 777 Integrated Airplane Information Management System(AIMS). This new benchmark problem is more complicated than the old one used in the original tool in that data communications are described in messages and a message can have multiple senders and receivers. The new MSP.RTL tool successfully solved the new benchmark problem, whereas the old tool would not be able to do so. In order to apply real-time scheduling in industrial process control, we carry out our research in two directions. First, we apply the improved tool to traditional wired process control. The tool has been successfully applied to solve the block assignment problem in Fieldbus networks, where each block comprising the control system is assigned to a specific device such that certain metrics of the system can be optimized. Wireless industrial control has received a lot of attention recently. We experimented with the tool to schedule communications on a simulated wireless industrial network. In order to integrate the scheduler in real wireless process control systems, we are building an experimental platform based on the WirelessHART standard. WirelessHART, as the first open wireless standard for process control, defines a time synchronized MAC layer, which is ideal for real time process control. We have successfully implemented a prototype WirelessHART stack on Freescale JM128 toolkits and built some demo applications on top of it. Even with the scheduler tool to regulate communications in a wireless process control, it may still be possible that communications cannot be established on an inferior wireless link within an expected period. In order to handle this type of failures, we propose to make the control modules aware of the unreliability of wireless links, that is, to make the control modules adapt to the varying link qualities. PID(Proportional, Integral, Derivative) modules are the most used control modules. We developed PIDPlus, an enhanced PID algorithm to cope with possible lost inputs and outputs. It has been shown that PIDPlus can drastically improve the stability of the control loop in cases of unreliable wireless communications. / text

Submitted by Marcos Rogerio Caldieri null (mrcaldieri@gmail.com) on 2016-12-14T23:11:29Z No. of bitstreams: 1 Marcos-Mestrado.pdf: 2168690 bytes, checksum: 11f237fc5587a57486d006c939b576af (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-12-19T17:40:14Z (GMT) No. of bitstreams: 1 caldieri_mr_me_bauru.pdf: 2168690 bytes, checksum: 11f237fc5587a57486d006c939b576af (MD5) / Made available in DSpace on 2016-12-19T17:40:14Z (GMT). No. of bitstreams: 1 caldieri_mr_me_bauru.pdf: 2168690 bytes, checksum: 11f237fc5587a57486d006c939b576af (MD5) Previous issue date: 2016-10-21 / A recente introdução de transmissores sem fio na indústria provocou um novo interesse em técnicas de medição e controle, porém a maioria das aplicações está restrita a medições de variáveis de processo em malha aberta ou aplicações de monitoramento. O motivo é a falta de confiabilidade devido aos problemas inerentes ao meio de transmissão, que pode ser a perda de pacotes de informação, atrasos de comunicação variantes no tempo, atualização muito lenta e não periódica da medição e vários tipos de interferências. A maior parte dos controladores industriais em controle de processos assumem que o ciclo de controle é executado de forma periódica e que uma nova medição está disponível para ser usada em intervalos de tempo conhecidos. No entanto esta situação não pode ser garantida quando sensores ou transmissores sem fio são usados em aplicações de controle em malha fechada, denominadas de Sistemas de Controle via Redes sem fio (WNCS – Wireless Networked Control Systems). Nesses tipos de aplicações, os transmissores sem fio devem transmitir novas medições de forma não periódica e somente se a medição da variável do processo tiver alterado significativamente. Para tornar esta tecnologia de WNCS mais confiável, muitas técnicas de controle têm sido pesquisadas, entre elas o PIDPlus que representa uma modificação do algoritmo PID para controle via rede sem fio. Este trabalho apresenta a implementação do protocolo Modbus para aplicações de WNCS. O protocolo Modbus TCP foi embarcado em hardware dedicado viabilizando a transmissão de dados via Ethernet TCP/IP e Wi-Fi. Uma comparação e avaliação de controladores PID para aplicação em WNCS sob condições de amostragem e atrasos de comunicações variáveis e de perdas de transmissão de mensagens foi realizada. Os resultados são analisados do ponto de vista de desempenho de controle e robustez. Resultados experimentais numa planta piloto comprovam a eficiência da implementação de uma malha de controle sem fio usando uma rede Wi-Fi com o protocolo Modbus embarcado e um controlador PIDPlus. / The recent introduction of wireless transmitters in the industry has driven a new interest in measuring and control techniques, but most applications are restricted to measurements of process variables in open loop or monitoring applications. The reason is the lack of reliability due to problems inherent to the transmission medium, which may be the packet loss, time varying delay, slow and aperiodic measurement updates and interference. Most industrial process controllers assume that the control cycle is performed periodically and that a new measurement is available to be used at known time intervals. However it cannot be guaranteed when wireless sensors or transmitters are used in closed loop control applications, called Wireless Networked Control Systems (WNCS). In these type of applications, wireless transmitters shall transmit new measurements not periodically and only if the process variable measurement has changed significantly. In order to enable and make this WNCS technology reliable, many control techniques have been researched including the PIDPlus that is a modified PID algorithm for wireless control. This paper presents the implementation of the Modbus protocol for WNCS applications. The Modbus TCP was embedded in dedicated hardware enabling the transmission of data via Ethernet TCP/IP and Wi-Fi. A comparison and evaluation of PID controllers for WNCS were done considering situations of variable sampling and communication delays and packet losses. The results are analyzed from the point of view of control performance and robustness. Experimental results in a pilot plant prove the efficiency of the implementation of a wireless control loop using a Wi-Fi network with embedded Modbus protocol and PIDPlus controller.