Traveling-wave surface haptics to guide bare finger movement over touch surfaces

Abstract

Touch is fundamental to our perception of the world and to interaction with our physical surroundings. With touch we can intuitively and effortlessly move and shape objects and control complex machines. In most modern machines, the part that interfaces with user often integrate touchscreens or touchpads, owing to their ease of use. However, these interfaces often deliver very poor tactile feedback, which limits the usability in contexts such as driving, low-light environments, and for users with visual impairments. Existing solutions like vibrotactile feedback, are poor substitute to the richness of natural touch and offer only transient sensations. Surface haptic devices offer more complexity, but since they rely on friction modulation, they require continuous movement and cannot nudge the user to arbitrary directions. These limitations highlight the need for active lateral force devices that can guide users in an arbitrary direction. This thesis introduces the Ultra loop, an active surface haptic device that generates net lateral forces using resonant traveling waves. Built around an oblong ring-shaped structure, the Ultra loop provides a large and flat interaction area with uniform force generation. Unlike existing active haptic devices, it operates at resonance, achieving a high vibration amplitude-to-input ratio, resulting in a more salient force feedback. Additionally, this thesis introduces a planar adaptation of the Ultra loop, the flat Loop, which is more compact with a height of just 5 mm, facilitating integration into consumer electronics. These devices can guide users via their sense of touch and render complex forces fields by modulating the wave amplitude and phase control as a function of the position and velocity of the user. To evaluate their effectiveness, this thesis investigates two types of rendered haptic environments: position-based elastic potential fields and velocity based viscous damping. Experimental user studies show that participants could perceive virtual 3D shapes (e.g., bumps and holes) and stepwise force fields that enhance their target-search performance. Moreover, directional cues provided by the force feedback enabled users to navigate toward a target without visual feedback, while viscous damping environments, where lateral force is a function of finger speed, reduced oscillations during selection, and improved overall targeting performance. This doctoral work systematically explores the benefits of active force feedback in touch interactions by introducing resonant traveling wave-based haptic displays and performing user studies. By advancing surface-haptic technology, this research paves the way for next-generation touch interfaces that support eye-free interaction and effortless control of complex machines.