Patent ID: 8170831

Claim:
A method for measuring a dimension of a circular object using an apparatus comprising a track and first to third sensors above the track, a distance between the first and second sensors being u 1 and a distance between the second and third sensors being u 2 , the method comprising: while the circular object is moving on the track, using the apparatus to record a time instant t 0 when the circular object reaches the first sensor, a time instant t 1 when the circular object reaches the second sensor, a time instant t 2 when the circular object reaches the third sensor, and a time instant t 3 when the circular object leaves the first sensor; and calculating a chord length of the circular object according to D e =u 1 (t 3 /t 1 )(t 3 2 −t 3 t 1 )[u 2 −u 1 (t 2 −t 1 )/t 1 ]/t 2 (t 2 −t 1 ); thereby determining the dimension of the circular object.