Development of a rapid profilometer with an application to roundness gauging

This paper presents the development of a real-time, contact-based, high frequency, response profilometer employed as a roundness gauge for measuring circular form error for 100% part inspection on the shop floor with an accuracy of better than 0.5 μm with measurement times of less than 1 s. The gauge head is a closed-loop controlled mechanism comprising a contact force probe that is rigidly attached to a high bandwidth linear translator. The gauge head assembly is, in turn, attached to a precision spindle. The objective of the complete tool is to contact the sidewall of the circular feature, translate the probe tip to produce a defined contact force with the workpiece and rotate the gauge head assembly. During rotation of the spindle, this contact force is maintained at a nominally constant value by dynamically translating the force probe along a radial direction to follow surface deviations. The gauge head assembly (including force probe and servo drive) has a fundamental mode natural frequency of 330 Hz while scanning the workpiece with a constant contact force typically less than 100 mN. Form error (deviation from a nominal circle) is measured using a capacitance-based displacement sensor measuring the relative radial displacement of the probe with the spindle rotating at a constant rotation speed. This paper discusses the design and characterization of this metrology tool.