A Novel, Wave-based Control Architecture for Collaborative Haptic Virtual Environments
Abstract: Haptic feedback, the introduction of sense-of-touch into virtual environments, has been shown to have many benefits in practical applications. One such area of interest, is the increased performance of tasks that require collaboration. In the literature however, a tradeoff has been identified between transparency and consistency among remotely connected users. The purpose of this thesis is to explore the realisation of a hybrid network architecture to try to gain the transparency benefits of a peer-to-peer (P2P) architecture, and the consistency and scalability benefits of a client-server (CS) architecture. Unlike the conventional CS case where the client only has a static local copy of the object, the hybrid architecture introduces a dynamics engine on the client side. There is still a central node in the topology, designated the Observer, which contains the central model and all information about the virtual environment. To maintain consistency, the Observer is connected to each client model by a consensus controller, which act as a virtual coupling. Different distributed control strategies and choice of parameter distributions are investigated and evaluated in simulation. To ensure passivity, and thus stability, wave variable transforms are proposed as an alternative to power variables, which also removes the controller design from the analysis. A passivity-preserving, prediction-based reflection compensation algorithm is also proposed to improve the user experience during collaboration. The proposed solution is generalised for an arbitrary amount of users, for any degree of freedom, while the evaluation is limited to two users in a 1-DOF use-case. Finally, a comparison is performed in simulation between the proposed hybrid architecture and the state-of-the-art P2P and CS architectures. The findings are evaluated in regards to stability, consistency, and transparency.
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