Sensor systems for interactive surfaces

Abstract

This paper describes four different systems that we have developed for capturing various manners of gesture near interactive surfaces. The first is a low-cost scanning laser rangefinder adapted to accurately track the position of bare hands in a plane just above a large projection display. The second is an acoustic system that detects the position of taps on a large, continuous surface (such as a table, wall, or window) by measuring the differential time-ofarrival of the acoustic shock impulse at several discrete locations. The third is a sensate carpet that uses a grid of piezoelectric wire to measure the dynamic location and pressure of footfalls. The fourth is a swept radio frequency (RF) tag reader that measures the height, approximate location, and other properties (orientation or a control variable like pressure) of objects containing passive, magnetically coupled resonant tags, and updates the continuous parameters of all tagged objects at 30 Hz. In addition to discussing the technologies and surveying different approaches, sample applications are given for each system.

Tracking and characterizing knocks atop large interactive displays

“…In general, most approaches used in conventional touch screens [3] don't scale gracefully to large displays. Pressure-sensitive resistive sandwiches, the most common technique, aren't made large 2 enough to cover very large windows, and because their operational principle requires compression of the sensing surfaces, they would need to be mounted on the window's outside (active) surface, where they would be subject to potential damage over time, especially for outdoor installations. Active acoustic touch screens detect the absorption of ultrasound launched into the outer surface of the glass when a finger is in contact.…”

“…Time-of-flight laser rangefinding has also been used to scan the surface of large displays [2] and find hands, but the potentially expensive laser scanner must be mounted outside the window, leading to reliability difficulties for outdoor operation. 3 …”

“…In our earlier work [2,11], we derived the (x,y) impact coordinates by running the timing results through a third-order polynomial that was determined via a linear least-squares fit to data collected on a regular grid. To avoid this lengthy calibration process (which was prone to overfitting), we have subsequently developed a deterministic algorithm [12].…”

Pushpin Computing System Overview: A Platform for Distributed, Embedded, Ubiquitous Sensor Networks

“…Certainly, some success in harvesting and responding to multiple data streams originating from a quantity of sensors has been demonstrated (e.g. [2]), but such examples do not scale; using traditional sensing methods, even adding one more sensor to an array of a couple dozen sensors presents a formidable challenge on both the hardware and software fronts. As the number of sensors increases to the thousands, hundreds of thousands and beyond, any tractable solution will have to rely on principles of self-organization at the level of the sensors themselves in order to guarantee the proper scaling properties.…”

Passive acoustic knock tracking for interactive windows

“…Although they are steadily improving, such vision-based approaches can be slow and are often sensitive to image clutter, target reflectance, and changes in background lighting. Laser rangefinding has also been used to scan the surface of large displays [3] and track hands, but the potentially expensive laser scanner must be mounted outside the window, leading to reliability difficulties for outdoor operation. Figure 1 shows a block diagram of our system.…”