Commanding variable stiffness in three degrees of freedom through wiggling of a haptic master device

Abstract

Teleoperated semi-autonomous care robots aim to alleviate work pressure from care workers. Unlike many traditional stiff position-controlled robots, the care robot is operating in a shared environment with humans that is often unpredictable and unknown. Especially when dealing with tasks that involve contact with the environment, modulation of compliance is a key component to successfully execute autonomous manipulation tasks. Using Learning from Demonstrating (LfD) techniques, the teleoperator must have a system that allows intuitive demonstration of compliance to the robot. Current state-of-the-art systems are either not teleoperated, only allow limited modulation of the stiffness matrix or, are too complex and cumbersome for practical applications. This research tries to overcome these limitations and proposes a teleoperated stiffness commanding method that allows complete modulation of stiffness matrix in 3 Degrees of Freedom (DoF). The system uses the same haptic device (Geomagic Touch) as used for controlling robot manipulator, hence does not require specialized equipment. Through wiggling the stylus of the haptic device, stiffness is commanded to the robot and directly fed back to the operator through haptic and visual feedback. The system is illustrated in a simulated task where a task appropriate stiffness profile is demonstrated along a kinematic trajectory. Additionally, the performance and acceptance of the system is evaluated through a simulated user study. It shows how varying the commanded DoF, orientation, and size of the stiffness commands significantly influences the performance through the eigenvectors and eigenvalues of the stiffness matrix.