HCC: Medium: Collaborative Research: Force Feedback for Fingertips

Surface haptics is the creation of programmable haptic effects on physical surfaces such as touch screens and touch pads. Unlike traditional force feedback manipulanda that require the operator to grasp an end effector, surface haptic devices must provide feedback directly to the fingertips. With the dramatic rise of touch screen interfaces in recent years, many approaches to surface haptics have been explored in both academic and commercial settings. Among these are vibrotactile , shape morphing , and variable friction . Our group has pioneered the active forcing approach in which the surface applies controlled shear forces to each fingertip. We think of this approach as “force feedback for the fingertips,” and we speculate that it will give individual fingertips the opportunity to interact with physics-based virtual environments, much like force feedback manipulanda enable the whole hand to do. With active forcing, fingers can interact with virtual objects that have mass, stiffness and damping as well as more complicated dynamics. Because these objects can be graphically displayed directly under the fingers and accompanied by sound, strong multi-sensory integration can be achieved. By coordinating haptic effects at multiple fingertips, compelling haptic illusions can also be generated. The technology – and more importantly – the underlying science of active forcing are, however, still in their infancy. Active forcing depends critically on strong, steady, controllable forces and should not be accompanied by unintended effects such as audible sound. Moreover, to be practical, the surface cannot move appreciably . As such, all known approaches to active forcing depend on vibration of the surface coupled with some form of rectification. The proposed research will be organized in three parts: fingertip mechanics; fingertip-surface interaction; and device design. The first step is to characterize the propagation of mechanical and electrical energy into the fingertip structure at near ultrasonic frequencies. A custom exciter will be developed and used to study propagation of surface waves and subsurface waves . Electrical impedance measurements will also be made, and fractional calculus methods will be used to develop both mechanical and electrical models. The second step is to study the transfer of energy from a vibrating and/or charged surface to the fingertip. A custom tribometer will be developed and used in conjunction with laser Doppler vibrometry and FTIR (frustrated total internal reflection) imaging of contact regions. Ultimately, however, it is essential to develop engineering approaches to the design and manufacture of such surfaces. The third step is to develop those approaches and demonstrate their efficacy by prototyping high-performance active forcing surfaces.