Touch screens are widely used to present a user with an intuitive pointing interface. For example, touch screens are used in automatic teller machines, scientific and industrial control devices, public kiosks, and hand held computing devices, to name but a few common touch applications. Touch screens can use resistive, capacitive, acoustic, or infrared sensors. In most touch screen applications, the touch sensitive surface is permanently mounted on a display device such as a cathode ray tube (CRT), or a liquid crystal display (LCD).
During operation of most prior art touch screens, a formatted image is rear projected through the touch screen while a transmitter drives signals across the x- and y-axis of the touch screen. As the user touches the screen with a finger or stylus, pointing out specific parts of the image, receivers detect the location of specific x- and y-coordinates of where the screen is touched. The receivers are coupled to processes that can then take appropriate actions in response to the touching and the currently displayed image.
Recently, there has been interest in extending touch technologies to electronic whiteboard applications. There, the main difference is one of scale. As stated above, traditional touch screen are designed for use with small displays and a single user, whereas whiteboards are large displays, generally used in group situations.
While it is possible to scale up touch screen, specifically with acoustic signals, prior art touch screens do not differentiate among the touches by multiple users. Also, most prior art touch screen cannot distinguish multiple, none identify simultaneous touches by one or multiple users.
While electronic whiteboards are useful for group discussions, turning the interactive surface into a table that a number of users can be seated around would facilitate longer work sessions. A problem with this arrangement is that users tend to put items on tables, such as books, paper, and cups. For pressure sensitive surfaces, static objects generate spurious touch points. In a single touch system, any such object causes the surface to malfunction. Therefore, an improved interactive touch surface should have the following characteristics: detects multiple, simultaneous touches, detects which user is touching each location, objects left on the touch surface should not interfere with normal operation, withstand normal use without frequent repair or recalibration, not require additional devices, e.g. no special stylus, body transmitters, and the like, and be inexpensive.