Haptic Interfaces

Touchscreens are used to provide a highly interactive interface with virtual ideas and visualizations. However, the physical interaction is one-way: the user inputs touch, but feels only a smooth surface in response. A prototype device has been developed at the UMass Amherst site in collaboration with the Center for eDesign industry member FTL Labs to add physical feedback to touchscreens. The “haptic mouse” is a handheld robot which rests on a large touchscreen surface (Playsurface, FTL Labs). It allows the user to feel the boundaries of virtual objects push back on their hand as it slides against them.

The device works by steering a single wheel in free-rolling contact with the touchscreen surface, which it controls by communicating with haptic touchscreen applications developed in the open source game engine Unity. The haptic mouse can simulate varying mechanical properties of the virtual objects it collides with, providing harder or softer boundaries as the developer desires. This technology allows for design tools where collisions and interference can be felt when they may not be seen, path restrictions in touchscreen operation panels to encourage a specific workflow, force-feedback enriched upper limb physical therapy, and other potential applications in simulation, virtual reality, gaming, and touchscreen accessibility for disabled people.

One out of every 200 people in the United States has had an amputation, and from 1988-1996 38.5% of those were upper-limb amputations. While prosthetics have been in existence since ancient Egyptian times, the human-prosthetic interface remained largely unchanged until the 1960s with the advent of myoelectric prosthetics. While myoelectric prosthetics have improved amputees’ lives, the high visual demand necessary to operate them has led to amputees indicating in several surveys the need for sensory feedback. Without sensory feedback, amputees must rely on visual attention alone for precise control of the prosthesis, which can be time consuming. As a result of this, haptic feedback devices have been explored as a means of providing sensory feedback for upper limb amputees. A modular device was created during a Research Experience for Undergraduates in the MRRL to serve as a haptic feedback device for upper limb amputees. The device uses normal stimulations and is light in weight (10 g). In an experiment with five participants, 20 trials of individual stimulations and 20 trials of pattern stimulations were performed on each participant. Participants reported 86% accuracy in correctly locating a single stimulus and 97% accuracy in distinguishing between four basic stimulation patterns. Future work will compare the effectiveness of using normal stimulation against shear stimulation through experimentation and redesigns of the modules to increase performance and decrease size.