Method and device for accurately measuring a longitudinal contour of a measuring object, such as a screw thread and similar geometries

A method for accurately measuring longitudinal internal or external contours of an object, the method comprising:

• providing a measuring device comprising:
• clamping members for retaining the object;
• a scanning arm which is pivotable about an axis transverse to a longitudinal center line of the object and having a free end;
• at least one scanning needle on the free end of the scanning arm, extending transverse to the scanning arm, for scanning a surface of the object;
• a driving device supporting the scanning arm which, in operation, can move the scanning arm in at least a first phase in one linear direction of movement parallel to the longitudinal center line of the object;
• means for detecting angular displacement of the scanning arm and position of the scanning arm in the linear direction of movement;
• and
• a processor for processing information regarding the angular displacement and the position of the scanning arm;
• clamping the object with the clamping members, the object having a contour with a plurality of descending contour flanks, a plurality of profile grooves and at least one ascending contour flank;
• and
• measuring the contour in such a manner that during movement of the scanning arm in the linear direction of the first phase, the scanning needle contacts only the descending contour flanks and the profile grooves, but does not contact the at least one ascending contour flank during the first phase, each of the descending contour flanks being measured in a downward direction of the scanning needle when the scanning arm is moved in the linear direction of the first phase.