Method and apparatus for detecting the location of an object on a surface

Abstract

A device and method for detecting the location of an object in a surface employs a first plurality of light sources disposed along a first row adjacent the surface. A first plurality of light detectors is disposed along a second row adjacent the surface and spaced apart from the first row. Each detector outputs an analog signal representative of the intensity of light being detected. A control means causes each of the light sources to be illuminated at a different time. A calculating means determines the location of the object based on the analog signals from the detectors. The calculating means determines the location of the object by determining coordinates of a first line and a second line, the first line extending from a first light source to a centerpoint of a first shadow cast upon a first neighboring group of the detectors and the second line extending from a second light source to a centerpoint of a second shadow cast upon a second neighboring group of the detectors. The calculating means determines the location of each shadow end as being a point a distance from an end of a detector equal to the width of the detector times the value of the signal from the detector divided by the value of the signal corresponding to the detector being fully illuminated by a beam. In an alternative embodiment, the calculating means further determines the width of the object.