Analysis of the advantage of measuring straightness when characterising volumetric performance of machine tools by body diagonal kinematic tests

Testing the volumetric performance of machine tools is an increasingly demanding need in industry due to the growing complexity of workpiece geometries with tighter tolerances, and the development of more sophisticated machine tools with additional attachments and axes. Various techniques and methods have been devised to quantify the volumetric performance of machine tools when they are commanded to move with simultaneous motion of their axes. Some of these methods have been standardised and addressed in the ISO 230 series.

ISO 230-6:2002 standard addresses only positioning error of body and face diagonal trajectories. This paper explores whether it is valuable to measure the straightness errors of the diagonal trajectories from different perspectives including conceptual, numerical and practical aspects. It conceptually discusses why it is necessary to quantify diagonal straightness deviations alongside the diagonal positioning deviation for a nominal target position. Additionally, for the numerical analysis, this study investigates the sensitivity of these three diagonal errors through half a million simulations over more than 1.9 million possible combinations under various error profiles for each error motion of the linear axes of a 3-axis vertical machining centre (VMC). Moreover, nearly 600 practical body diagonal tests have been made on a 3-axis VMC with the same kinematic chain using a Renishaw XM-60 laser system to assess the feasibility and ease of setup for this kinematic test. The findings support measurement of diagonal straightness errors to supplement the tests specifies in ISO 230-6:2002.