Advantages of reconfigurable and variable-impedance haptic user interfaces

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BACKGROUND: Haptic interaction is the human's most basic way to understand an environment and effect change in it. Haptic feedback provides humans who operate machines (e.g., planes, excavators, or robots such as the Canadarm or Mars rovers) with a sense of touching objects they are not actually touching but are manipulating by the machines. Haptic feedback allows the human operators of machines to handle objects more gently, safely, reliably, and precisely. Haptic interfaces (HIs) produce the illusion of touch by applying forces to the users' hands. An HI should have a big workspace. It should also satisfy the requirements of back-drivability, low apparent inertia and low friction for the best perception of small reflected forces, and large intrinsic stiffness and force feedback capability for the best perception of large reflected forces. Then, the HI can recreate soft and stiff contact experiences for the user with high fidelity. OBJECTIVES: The currently available HIs are either parallel mechanisms with higher force feedback capability, a higher intrinsic stiffness and a smaller workspace or serial mechanisms with lower force feedback capability, a lower intrinsic stiffness and a larger workspace. Since a high force feedback capability, a high intrinsic stiffness and a large workspace are desirable, this research will secure the best of both worlds by appropriate design and control (including variable-impedance control) of redundant haptic interfaces (RHIs), which have more degrees of freedom than minimally required to perform a task. SPECIFIC AIMS: * SA 1: Achieve as many of the desirable HI characteristics as possible using appropriately designed RHIs for more intuitive and effective user/RHI interaction. We will investigate the intrinsic advantages of RHIs, which can be obtained through mechanical design, e.g., a lower inertia and a larger workspace (compared to non-redundant HIs). * SA 2: Leverage the kinematic redundancy of RHIs toward a secondary objective to optimize its kinematic and dynamic characteristics further. Secondary objectives will target further manipulability enhancement, apparent inertia minimization and force feedback capability maximization. Such advantages obtained via joint-level closed-loop control are over and above the intrinsic advantages obtained in SA 1. * SA 3: Supplement the design in SA 1 and the control in SA 2 with RHI redundancy resolution and impedance modulation based on the requirements of a given task/user. Task- and user-dependent Cartesian-level variable-impedance control and joint-level redundancy resolution of RHIs will further improve the haptic interaction fidelity and the user's task performance. NOVELTY: While there is ample research on redundant manipulators that interact with task environments, little attention has been paid to the design and control of RHIs. This research helps create haptic interaction and teleoperation systems with enhanced safety and performance.