Many shape-changing interfaces use an array of actuated rods to create a display surface; each rod working as a pixel. However, this approach only supports pixel height manipulation and cannot produce more radical shape changes of each pixel (and thus of the display). Examples of such changes include non-horizontal pixels, pixels that overhang other pixels, or variable gaps between pixels. We present a concept for composing shape-changing interfaces by vertically stacking tilt-enabled modules. Together, stacking and tilting allow us to create a more diverse range of display surfaces than using arrays. We demonstrate this concept through TiltStacks, a shape-changing prototype built using stacked linear actuators and displays. Each tiltable module provides three degrees of freedom (z-movement, roll, and pitch); two more degrees of freedom are added through stacking modules (i.e., planar x- and y-movement).

The design of shape-changing interfaces to show emotions relies on craft skill with few clear guidelines. Through two experiments, we explore how to design such interfaces using theories of the relation between biological motion and affect. In the first experiment, 19 participants viewed six shape-changing behaviors that varied the velocity, fluidity, direction, and orientation of the movement of an extrusion from a small box in accordance with existing theories of affective motion. Participants were able to recognize four of the six intended basic Ekman emotions (sadness, fear, happiness, surprise) with above-chance probability. The second experiment used 36 shape-changing behaviors that systematically varied speed, regularity of motion, and direction. For each behavior, 23 participants rated valence, arousal, and dominance. Speed, direction, and orientation impacted emotion ratings significantly and in the predicted directions. These results offer an initial basis for the systematic design of emotions in shape-changing interfaces.

Research on shape-changing interfaces has explored various technologies, parameters for shape changes, and transformations between shapes. While much is known about how to implement these variations, it is unclear what affordance they provide, how users understand their relation to the underlying system state, and how feedback via shape change is perceived. We investigated this by studying how 15 participants perceived and used 13 shape-changing buttons. The buttons covered several aspects of affordance, system state, and feedback, including invite-to-touch movements, two styles of transition animation, and two actuation technologies. Participants explored and interacted with the buttons while thinking aloud. The results show that affordances are hard to communicate clearly with shape change; while some movements invited actions, others were seen as a malfunction. The best clue as to button state was provided by the position of the button in combination with vibration. Linear transition animation for changes in button state was the best received form of shape-change feedback. We discuss also how these findings can inform the design of shape-changing interfaces more generally.

We propose cutting as a novel paradigm for ad-hoc customization of printed electronic components. As a first instantiation, we contribute a printed capacitive multi-touch sensor, which can be cut by the end-user to modify its size and shape. This very direct manipulation allows the end-user to easily make real-world objects and surfaces touch-interactive, to augment physical prototypes and to enhance paper craft. We contribute a set of technical principles for the design of printable circuitry that makes the sensor more robust against cuts, damages and removed areas. This includes novel physical topologies and printed forward error correction. A technical evaluation compares different topologies and shows that the sensor remains functional when cut to a different shape.