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Interactive tabletops are large horizontal displays that allow multiple users to simultaneously and directly interact with digital content by touching the surface, manipulating physical objects, or conducting gestures above the surface. In the last decade, these devices have aroused much interest in the research community, and first commercial products have been released. Interactive tabletops combine a dynamic graphical user interface, a natural way of input, and a platform that is suitable for collocated collaboration. However, they provide only limited haptic feedback. In contrast to physical controls that guide the users' motion, visual on-screen controls cannot be felt and require visual focus when being operated. Also, due to the large contact area of fingers, input by touch is less precise than by conventional controls, such as mice or keyboards. This thesis addresses the issue of limited haptic feedback on interactive tabletops, while focussing on precise input for productivity tasks. We introduce physical general-purpose controls that combine the benefits of haptic feedback with the dynamic nature of interactive tabletops. Our controls are passive, untethered, low-cost, and easy to prototype. Made of transparent materials and using the table's back projection, they can change their visual appearance on the fly and become versatile controls for various applications. Furthermore, we describe how to turn these controls into malleable user interfaces by employing an electromagnetic actuation mechanism. This allows to move a control or parts of it, to maintain the consistency between its physical and virtual state, and to change physical properties via software at run time. Finally, we present an output method that creates haptic feedback near the surface and only requires a minimal equipment worn by the user. The thesis provides an introduction to the field of interactive tabletops and embeds our contributions into the context of related work. We explain our design and interaction concepts, the underlying hardware engineering, and software technologies. We evaluate our contributions in user studies and measurements and provide evidence for the usefulness of our techniques. We also describe potential applications with focus on productivity tasks. Finally, we illuminate implementation challenges, discuss limitations, and provide a perspective on recent developments as well as future trends in the field of haptic feedback on interactive tabletops. |
