A multilevel input system with force-sensitive elements

Force-sensitive multilevel input elements are introduced as the basic building blocks for compact-size input devices in mobile environments. Compared with switch-type keys, multilevel elements can decrease the number of keys on a keyboard while maintaining the input capacity. A multilevel input mechanism using force-sensitive sensor pads is demonstrated in a three-level three-element tactile chording system with multimodal feedback. Two schemes are introduced to segment the output range of the sensor into levels. For relatively unpracticed users, the scheme based on maximum finger forces gives an average error rate of 20.2% and an input time of 2.24 s for a chord of three inputs. Reclassification of the experimental data using Gaussian segmentation shows that significant improvement of the performance can be expected.