Patent ID: 7982141

Claim:
A coordinate detecting device used in combination with a writing instrument including a body, a first transmitting unit provided in the body, a second transmitting unit provided in the body, and a tip that is provided at the body spaced from the first transmitting unit and the second transmitting unit, wherein the first transmitting unit generates a first signal, and the second transmitting unit generates a second signal delayed with respect to the first signal, the coordinate detecting device comprising: a first receiving unit that receives the first signal from the first transmitting unit and the second signal from the second transmitting unit; a second receiving unit that is spaced from the first receiving unit, and that receives the first signal and the second signal; a position calculating unit that calculates a position of the first transmitting unit based on a time at which the first receiving unit receives the first signal and a time at which the second receiving unit receives the first signal on a predetermined coordinate plane, and calculates a position of the second transmitting unit based on a time at which the first receiving unit receives the second signal and a time at which the second receiving unit receives the second signal on the predetermined coordinate plane; an interpolating unit that includes an interpolation-time calculating unit that calculates an interpolation time based on times of generation of the first signal and the second signal, and an interpolation-position calculating unit that calculates the interpolated position of the first transmitting unit and the interpolated position of the second transmitting unit, each of the positions being at the interpolation time; and an estimating unit that estimates a position of the tip on the predetermined coordinate plane based on the interpolated position of the first transmitting unit and the interpolated position of the second transmitting unit, wherein the interpolating unit calculates a time point between a generation timing of the first transmitting unit and a generation timing of the second transmitting unit as the interpolated time point wherein the interpolated time point is different from both of the generation timing of the first transmitting unit and the generation timing of the second transmitting unit.