Knitting Ready-Made, Tactile, and Highly Responsive Spacer-Fabric Force Sensors for Continuous Input


As part of the TextileUX project, we explored haptic user interface elements made from 100% textile material. With spaceR, we demonstrate how to create multi-component knits that can be utilized as pressure-sensitive UI elements, most notably for continuous (i.e., non-binary) input by finger-press. Our implementation can be manufactured on a v-bed weft-knitting machine and is based on so-called spacer fabric knits, which provide a soft and elastic appeal, comparable to foams. spaceRs can be created with different contours, profiles, thickness, sizes, and firmness, by varying manufacturing parameters and material composition, which provides several opportunities in designing their visual and haptic appearance.

Incorporating yarn with high electrical resistance along the Nylon filler, the spaceR elements work similarly to a common Force Sensitive Resistor (FSR) and can therefore be easily operated with straightforward readout electronics, such as a voltage divider sampled by an ADC (e.g., using an Arduino board). In contrast to a printed foil FSR however, our sensors show excellent sensitivity, reacting also to slight touch. Furthermore, the elements are highly responsive with only little hysteresis and provide good consistency.

Our spaceR and can be easily embedded into a variety of basic surrounding knit structures, such as plain knit, interlock, cardigan, but also many complex 3D-knit structures. Due to their haptic properties, the sensors can be discovered and operated eyes-free, intuitively. The surface profile and elasticity offer the affordance of being “pressable” and therefore instantly communicate functionality and usage.

In our research paper, we push the boundaries of the design by demonstrating several variations. We combine spaceRs of different sizes (e.g., for up/down control), and also incorporate multiple sensitive regions into one single element, for example to create a rocker-button or even a 4-way controller that provides an input modality similar to a thumbstick on a gamepad, i.e., 2D directional control. The knitting programs can be easily generated using our Knitting Utils scripting library. Based on the Knitout format and tools by CMU Textiles Lab, we created a pipeline for generating knitting machine programs from bitmap images, that encode structure and material use via pixel color and can therefore be easily modified using standard drawing tools. For more details please see the paper (Open Access). JS code and Knitout programs can be found in the supplementary material.