Patent attributes
A ball rotation amount measurement system which includes a magnetic sensor fixed to a ball to measure geomagnetism in at least one axis direction, and a computation unit configured to compute the rotation amount of the ball using data of a large number of the geomagnetism time-sequentially acquired by the magnetic sensor. The computation unit includes a difference data calculation unit configured to calculate a difference between two of the time-sequential geomagnetic data to thereby time-sequentially obtain a large number of difference data, a difference waveform calculation unit configured to determine a difference waveform that represents a time variation waveform of a large number of the difference data, and a rotation amount calculation unit configured to calculate the rotation amount of the ball, based on information of zero cross points at which the difference waveform crosses a straight line indicating zero-difference within a predetermined period.
