Machining, Measurement, and Control Laboratory

A New Formulation of Laser Step Diagonal Measurement to Identify Three-dimensional Volumetric Errors
Soichi Ibaraki, Takafumi Hata, Atsushi Matsubara

The laser step diagonal measurement modifies the diagonal displacement measurement by executing a diagonal as a sequence of single-axis motions. It has been claimed that the step-diagonal test enables the identification of all the volumetric error components in the three-dimensional workspace, including linear errors, straightness and squareness errors, by only using a linear laser interferometer. This paper first discusses that an inherent issue with the conventional formulation of the step diagonal measurement is that setup errors of mirror and laser directions potentially impose a significant estimation error. Furthermore, when the machine's volumetric errors are unknown, it is generally not possible to completely eliminate setup errors. To address this issue, this paper proposes a new formulation of the laser step diagonal measurement, in order to accurately identify three-dimensional volumetric errors even under the existence of setup errors. The effectiveness of the proposed modified identification scheme is experimentally investigated by an application example of three-dimensional laser step diagonal measurements to a high-precision vertical machining center.
Key Words: Step diagonal measurement, volumetric errors, machine tool, laser interferometer.