Surface haptics is the creation of programmable haptic effects on physical surfaces such as touch screens and touch pads. Unlike traditional force feedback devices 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, including vibrotactile, shape morphing, and variable friction. The PI and his team have pioneered an approach in which the surface generates controlled shear forces on each fingertip. Force Feedback for Fingertips (F3), gives fingertips the opportunity to interact with physics-based virtual environments, much like force feedback devices enable the whole hand to do. With F3, fingers can interact with virtual objects that have mass, stiffness and damping as well as more complicated dynamics (e.g., collisions, mechanisms, and force fields). By coordinating haptic effects at multiple fingertips, even more compelling illusions can be generated.
The technology, underlying science, and application of F3 are, however, still in their infancy. F3 works by coupling lateral vibrations to some form of rectification. For example, one approach involves high-frequency lateral vibrations of the surface synchronized with a friction reduction effect, resulting in a slip-push transition at each oscillation. The friction is modulated by means of electrostatic forces or acoustical stimulation. Current approaches work at ultrasonic frequencies, but little is known about the mechanical or electrical behavior of fingertips at these frequencies, or how energy transfer from a surface to the finger can be optimized.
This research will produce new knowledge in three main areas: the physical underpinnings of F3, device design and interaction design. First, both tribological and acoustic measurements will be made to elucidate the mechanisms by which shear forces are generated. A high-bandwidth tribometer and optical imaging system will allow friction to be studied, and a custom-built exciter will allow the propagation of acoustic energy in the fingertip to be studied. Laser Doppler vibrometry will be used to measure surface wave propagation while magnetic resonance elastography will be used to study shear wave propagation within the subcutaneous tissues. Fractional calculus and finite element techniques will then be used to build biologically plausible models of fingertip tribology and mechanics that match the data. Second, a new generation of high-performance F3 devices will be developed. Armed with good models, it will be possible to design impedance-matched devices so that force production is maximized and energy wastage is minimized. Additionally, these new devices will provide control over the force vector at each of multiple fingertip locations. Thirdly, novel multi-finger interactions will be designed. The key idea is that sophisticated percepts, such as "objects" that can be grasped and that feel as though they are moving relative to the surface, can emerge from properly coordinated fingertip forces due to Gestalt-like grouping principles.
Broader Impacts: Historically, the PI and his team have had greatest impact when providing technology to and collaborating with colleagues in human-computer interaction. Inspired by this, an open source F3 kit will be developed and shared. In addition, undergraduate and high school students will participate in the research, developing software routines and sample applications for the open source kit. Finally, the kit will be integrated with two pedagogical innovations already implemented by the investigators: flipped classrooms and portable laboratories.
