Patent ID: 8290740
Filing Date: 2012-10-16
Classification: G01B,G05B

Abstract:
1. A form measuring instrument operative to rotate a workpiece about a first axis, and measure a displacement of a surface of the workpiece at each angular position of rotation of the workpiece, the workpiece being a rotating object, the instrument comprising: a contact piece having a tip capable of contacting with the workpiece; first placing means operative to place the workpiece at a first position; first measuring means operative to move the contact piece from the first position in parallel with a second axis perpendicular to the first axis such that the contact piece traces the surface of the workpiece, thereby to measure an amount of displacement of the contact piece at each position along the second axis to obtain a first profile; second placing means operative to rotate the workpiece about the first axis by 90 degrees to place the workpiece at a second position from the first position; second measuring means operative to move the contact piece from the second position in parallel with the second axis such that the contact piece traces the surface of the workpiece, thereby to measure an amount of displacement of the contact piece at each position along the second axis to obtain a second profile; extremum position calculating means operative to fit circles to the first profile and second profile respectively, and calculate positions, in a direction parallel with the second axis, of a first extremum and a second extremum indicating extremums of the respective circles; and moving means operative to move the workpiece in the direction parallel with the second axis and in a direction parallel with a third axis perpendicular to the first axis and second axis, such that the positions, in the direction parallel with the second axis, of the first extremum and second extremum become 0.