Design, control and implementation of CoCoA: a human-friendly autonomous service robot
Çoruhlu, Gökay (2014) Design, control and implementation of CoCoA: a human-friendly autonomous service robot. [Thesis]
The growing demand to automate everyday tasks combined with the rapid development of software technologies that can furnish service robots with a large repertoire of skills, are driving the need for design and implementation of human-friendly service robots, i.e., safe and dependable machines operating in the close vicinity of humans or directly interacting with them in social domains. The technological shift from classical industrial robots utilized in structured factory oors to service robots that are used in close collaboration with humans introduces many demanding challenges to ensure safety and autonomy of operation of such robots. In this thesis, we present mechanical design, modeling and software integration for motion/navigation planning, and human-collaborative control of a human-friendly service robot CoCoA: Cognitive Collaborative Assistant. CoCoA is designed to be bimanual with dual 7 degrees-of-freedom (DoF) anthropomorphic arms, featuring spherical wrists. Each arm weighs less than 1.6 kg and possesses a payload capacity of 1 kg. Bowden-cable based transmissions are used for the arms to enable grounding of motors and this arrangement results in lightweight arms with passive back-driveability. Thanks to passive back-driveability and low inertia of its arms, the operation of CoCoA is guaranteed to be safe not only during physical interactions, but also under collisions with the robot arms. The holonomic base of Co- CoA possesses four driven and steered wheel modules and is compatible with wheelchair accessible environments. CoCoA also features a single DoF torso, and dual one DoF grippers, resulting in a service robot with a total of 25 active DoF. The dynamic/kinematic/geometric models of CoCoA are derived in open source software. Inverse kinematics, stable grasp, kinematic reachability and inverse reachability databases are generated for the robot to enable computation of kinematically-feasible collision-free motion/grasp plans for its arms/grippers and navigation plans for its holonomic base, at interactive rates. For the real-time control of the robot, motion/navigation plans characterizing feasible joint trajectories are passed to feedback controllers dedicated to each joint. The joint space control of each joint is implemented in hardware, while communication/synchronization among di erent DoF is ensured through EtherCAT/RS-485 eldbuses running at high sampling rates. To comply with human movements under physical interactions and to enable human collaborative contour tracking tasks, CoCoA also implements passive velocity eld control that guarantees user safety by ensuring passivity of interaction with respect to externally applied forces. The feasibility of the design and the applicability of the overall planning and control framework are demonstrated through dynamic simulations and physical implementations of several service robotics scenarios.
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