Model based assertions : a system design tool for cyber-physical systems

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Idler, Garrett Warne

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Cyber-physical systems (CPS) are a class of systems with electronic and mechanical components that use computer control, information networking, and physical behavior to accomplish designated tasks. CPS have become ubiquitous in society and are taking roles with important safety and reliability concerns. To address these concerns, many types of tools and design methodologies are being developed specifically for cyber-physical systems. This thesis introduces the concept of model based assertions, a programming construct for capturing the physical behavior of the system in the cyber side of the system by using numerical models to represent the physical system characteristics of interest. The model based assertions are proposed to be used for the verification and validation of CPS software. In order to set up discussion of model based assertions, several definitions of cyber-physical systems from researchers in the area are presented and discussed along with a brief overview of tools for cyber-physical system design, modeling, and evaluation. A robotic ground vehicle is adopted as a cyber-physical system test platform, as it displays the critical characteristics of a CPS. In order to formulate example model based assertions, three different types of numerical models of the robotic vehicle are introduced and discussed with bond graphs used as an approach for deriving state equations which describe the physical system dynamics. After introducing the numerical models, three examples of using model based assertions for tests with the robotic vehicle platform are presented. In the examples, model based assertions are used to verify expected motion of the vehicle and predict when the vehicle is going to slip during advanced maneuvers, both using preprocessed model simulations and real-time slip prediction during program execution. The thesis concludes with discussing possible use cases of model based assertions and situations where the assertions could present useful information to a cyber-physical system designer. Finally, future work related to developing model based assertions for additional applications is discussed.



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