A thin stretchable interface for tangential force measurement

We have developed a simple skin-like user interface that can be easily attached to curved as well as flat surfaces and used to measure tangential force generated by pinching and dragging interactions. The interface consists of several photoreflectors that consist of an IR LED and a phototransistor and elastic fabric such as stocking and rubber membrane. The sensing method used is based on our observation that photoreflectors can be used to measure the ratio of expansion and contraction of a stocking using the changes in transmissivity of IR light passing through the stocking. Since a stocking is thin, stretchable, and nearly transparent, it can be easily attached to various types of objects such as mobile devices, robots, and different parts of the body as well as to various types of conventional pressure sensors without altering the original shape of the object. It can also present natural haptic feedback in accordance with the amount of force exerted. A system using several such sensors can determine the direction of a two-dimensional force. A variety of example applications illustrated the utility of this sensing system.