Patent ID: 8094138

Claim:
A position detecting device, comprising: a light-guide plate for placement upon a displaying surface of a displaying device, and made of a translucent material; an emitting unit for emitting, from sides of said light-guide plate, arranged in line along an X-axis and a Y-axis, a plurality of light beams each of a predetermined width, so as to be totally reflected thickness-wise within said light-guide plate and to travel heading in predetermined directions parallel to the light-guide-plate plane; an emission-control unit for controlling said emitting unit so as to perform a scanning by making the light beams each scan said light-guide plate in progression along the sides thereof, in an X-axis direction and in a Y-axis direction; at least one indicating device having a light-guiding part for guiding, by contacting said light-guide plate, thereinto light traveling within said light-guide plate, and a detection unit for outputting, by detecting the light guided via the light-guiding part, a detection signal; and a coordinate calculating unit for calculating, based on a scanned position derived from the detection signal and said emission-control unit, a coordinate position where said at least one indicating device contacts said light-guide plate, wherein the emitting unit has a first plurality of light sources along one side arranged in line along the X-axis, and a second plurality of light sources along another side arranged in line along the Y-axis, wherein the emission-control unit performs a first control causing the first and second pluralities of light sources to simultaneously emit according to a first pattern a predetermined time before the initial light beam emission is performed in the scanning, thus notifying the coordinate calculating unit of a start time of the scanning; a second control causing the first and second pluralities of light sources to simultaneously emit according to a second pattern a predetermined time after the final light beam emission is performed in the scanning, thus notifying the coordinate calculating unit of a stop time of the scanning; and a scanning type control in between the first and second controls that causes each of the first and second pluralities of light sources to emit a light beam scanning in progression along the X-axis and the Y-axis, respectively, and wherein the first pattern causes the first and second pluralities of light sources to simultaneously emit twice in predetermined time intervals, and the second pattern causes the first and second pluralities of light sources to simultaneously emit once for a predetermined time.