| 摘要 |
<p>PURPOSE:To prevent the degradation in the measuring accuracy of an input coordinate caused by a temperature by detecting the temperature of a propagation body of an ultrasonic signal and correcting a found range between a coordinate input pen and an ultrasonic sensor. CONSTITUTION:The average temperature of a tablet detected plural times at time intervals is derived by a temperature sensor 37. Subsequently, a corrected phase speed is derived from phase speed at the time of initial correction of an input pen, and correction coefficient set in advance in accordance with the thermal expansion coefficient of a propagation body. Also, by using the time determined by detecting the zero crossing point of a specific phase, a distance (r) brought to temperature correction against respective sensors 2a - 2d is derived from the product to the corrected phase speed. Based on these distances (r), X and Y coordinates of the input pen 39 are calculated and brought to display/output. These processings are executed with a CPU 31 controlled by a control program stored in a ROM 311.</p> |
