Inner Circumferential Length Measuring Device for Circular Member

An inner circumferential length measuring device for a circular member, comprising:

• a support on which the circular member is placed;
• a two-dimensional sensor disposed allowing for movement relative to the support;
• a rotation driving mechanism configured to rotate the two-dimensional sensor;
• and
• a calculation unit configured to receive measurement data from the two-dimensional sensor;
• the support being raisable from a horizontal state to an upright state;
• the support comprising a plurality of projection portions on a surface, the plurality of projection portions being spaced from one another and projecting from the surface;
• by an inner circumferential surface of the circular member being engaged with two of the plurality of projection portions of the support in an upright state, the circular member being able to be placed on the support;
• by the support on which the circular member is placed being put in a horizontal state, the circular member being able to be placed flat on the support in an unrestrained state;
• by the two-dimensional sensor disposed facing the inner circumferential surface of the circular member at a predetermined measurement position being rotated about a predetermined position inward of the circular member via the rotation driving mechanism, a separation distance from the two-dimensional sensor to the inner circumferential surface being measured by the two-dimensional sensor in a non-contact state with the circular member in a range of an entire circumference of the circular member;
• and
• the calculation unit calculating an inner circumferential length of the circular member based on the separation distance measured and a distance from the predetermined position to the two-dimensional sensor in a plan view.