SHAPE MEASURING INSTRUMENT FOR TUBE BODY

PURPOSE:To measure many indispensable measurement items as to a shape and size required for quality control over a steel pipe, etc., by rotating a noncontact optical displacement gauge around one point in the tube body opposite the internal and external surfaces of the tube body. CONSTITUTION:The angle of rotation detected by a rotation angle detecting means (swivel arm 4, etc.) and a measuring means (displacement gauges 5a and 5b) are used by a position calculating means (calculator) to calculate plane coordinates of respective measurement points based upon the center of rotation as the origin. Then the equation of a circle which approximates all measurement points best is determined by, for example, a minimum squaring method. The center of the approximate circle which is thus found is considered to be the center of the body to be measured, so the respective coordinates of the measurement points are so corrected that the center of the approximate circle is the center, thereby obtaining the coordinates based upon the center of the tube body to be measured as the origin. The necessary shape and size values are calculated from the coordinates after the correction. The thickness of the tube body is calculated from distances to both internal and external surfaces at respective angles of rotation by rotating the couple of displacement gauges 5a and 5b opposite the internal and external surfaces of the tube body.