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 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 satisfy the requirements of back-drivability, low apparent inertia, large workspace, 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.

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 of redundant haptic interfaces, which have more degrees of freedom than minimally required to perform a task.

This research helps create haptic interaction and teleoperation systems with enhanced fidelity and performance. To achieve this, first, we introduce the intrinsic benefits of redundant haptic interfaces in terms of better kinematic and dynamic characteristics. Then, a quantifiable measure of the combined HI-slave system manipulability is formulated that can be used in the kinematic design of HIs as well as their controller design. Next, a null-space controller is developed for the redundant haptic interface that employs the proposed manipulability index to enhance the performance of teleoperation tasks by matching the kinematics of the redundant HI to the kinematics of the slave robot. We also propose two task-dependent null-space controllers in which the internal motion of the redundant haptic interface is appropriately controlled to achieve a desired performance, i.e., low back-drive friction in case of free-space motion and soft contact or large force feedback capability in case of stiff contact. The advantages and effectiveness of the proposed approaches are demonstrated through experiments.