METHOD AND SYSTEM FOR DETERMINING PROPAGATION TIME OF ULTRASONIC WAVE FROM MOVABLE OBJECT

摘要

[PROBLEMS] To detect only the direct wave first arriving at the receiver without being influenced by the reflected wave of an ultrasonic signal and measure the propagation time of an electronic pen so as to precisely determining the position of the electronic pen using an ultrasonic wave. [MEANS FOR SOLVING PROBLEMS] A trigger signal representing a transmission timing, an infrared signal including data representing an M-sequence initial condition and an M-sequence of an ultrasonic signal are simultaneously transmitted from an electronic pen in a constant cycle. A receiver installed in a predetermined position receives the infrared signal from the electronic pen and creates an M-sequence model waveform from M-sequence initial condition data included in the infrared signal. The receiver receives the ultrasonic signal from the electronic pen and computes the correlation value between the ultrasonic signal and the M-sequence model waveform, detects the first peak value of the computed correlation value, and computes the propagation time of the ultrasonic wave from the electronic pen from the point of time when the trigger signal is previously received and the point of time when the correlation peak value is detected.