Pseudo-admittance Bilateral Telemanipulation with Guidance Virtual Fixtures
International Journal of Robotics Research
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This dissertation addresses three related topics in the application of virtual fixtures to bilateral telemanipulation systems. Bilateral telemanipulation is the direct human control of a remote robot, with force and/or tactile feedback, and virtual fixtures are guidance modes, implemented in software, that assist the user in accomplishing a telemanipulated task. The first topic addressed in this dissertation is the design of functional and stable forbidden-region virtual fixtures, which prevent robot motion into forbidden-regions of the workspace. Metrics are defined to evaluate the effectiveness of forbidden-region virtual fixtures, and a human-factors experiment uses these metrics to quantify how users interact with various combinations of forbidden-region virtual fixtures and telemanipulation control system. A method to predict system stability that incorporates an explicit model of the telemanipulator and bounding models of human users is created and experimentally verified. Next, a new condition is presented for the passivity of a virtual wall with sampling, sensor quantization, and friction effects, for an impedance-type robot. This condition is experimentally verified to correspond to recognizable physical behaviors. It is then shown that virtual fixtures and bilateral telemanipulators can be designed independently under passivity considerations, and then coupled to create a stable systems. The method presented generalizes to all types of virtual fixture and to robots with any mechanical characteristics. Finally, a novel bilateral telemanipulation control method called Pseudo-admittance is presented, and its stability properties are analyzed. This controller mimics admittance control on an impedance-type robot, and has many desirable properties, such as tremor attenuation, quasi-static transparency, and the ability to include guidance virtual fixtures that help the robot move along desired paths or surfaces in the workspace. The properties of Pseudo-admittance Bilateral Telemanipulation, with and without guidance virtual fixtures, are verified through experiment and simulation. The research in this dissertation is particularly relevant to robot-assisted surgical tasks---which require safety as well as precision---but it is also applicable to a broad range of telemanipulated tasks. The dissertation concludes with interesting topics for future work that build upon the results presented.