Hapstick: A Soft Flexible Joystick for Stiffness Rendering via Fiber Jamming

Continuum robots are well-suited for applications in delicate and constrained environments, such as minimally invasive surgery, due to their inherent compliance and ability to conform to highly curved paths. Yet the kinematic dissimilarity between continuum robots and conventional, off-the-shelf input devices, along with the general lack of haptic feedback available with such devices, can lead to non-intuitive control. In this work, we present Hapstick - a soft, flexible haptic joystick that uses fiber jamming to modulate its stiffness and provide feedback to users during teleoperation tasks. We characterize the performance of Hapstick, showing that the bending stiffness increases linearly with the increase in applied vacuum load. A psychophysical study is also conducted to obtain the just noticeable difference in stiffness that users can perceive using Hapstick. Lastly, we perform a study in which participants use Hapstick to teleoperate a physical tendon-driven continuum robot in a simulated colorectal cancer screening task. Users correctly identify the position and development stages of cancerous tissues in 25 out of 27 trials, illustrating the potential of jamming-based mechanisms as bidirectional interfaces capable of providing effective haptic feedback.