3240 Construction of an error map of rotary axes by static R-test

Abstract

This paper presents an efficient and automated scheme to calibrate error motions of rotary axes on a five-axis machining center by using the R-test. During a five-axis measurement cycle, the R-test sensors nest measures the three-dimensional displacement of a sphere attached to the spindle relative to the machine table. This paper demonstrates intuitive, graphical presentation of R-test measurements to understand how error motions of rotary table changes in three-dimensional space depending on the swiveling angle. The separation of the influence of linear axis error motions, particularly squareness errors of linear axes, from the R-test measurement is also discussed.

Comparing approaches for multi-axis kinematic positioning in machine tools

“…Note that, due to the mechanical structure illustrated in Figure 1, the error motion parameters associated with the B-axis depend only on B-axis motion, whereas parameters associated with the C-axis are dependent upon the angular position of both axes. 7 Five more parameters define the position and orientation errors of the axis average line, defined in ISO230-7 as 'a straight line segment located with respect to the reference coordinate axes representing the mean location of the axis of rotation'. These parameters -also known as the axis shift, or location errors-comprise two positional errors, two orientation errors and one zero position error.…”

“…Static variants of the R-Test, wherein the procedure and equipment setup is replicated but data is collected at discrete intervals, has been applied for complete error map construction of all location errors and the larger class of position-dependent geometric errors. 7 The R-Test is a fast and reliable method for kinematic error identification in machine tool rotary-axes, but it has the drawback of requiring specialist equipment to conduct. A common alternative is to use a touch trigger probe to inspect an artefact of precisely known dimension, in a procedurally similar manner to the static R-Test.…”

Indirect Measurement of Volumetric Accuracy for Three-Axis and Five-Axis Machine Tools: A Review

“…Fig. 11 shows a prototype R-test device by Ibaraki et al [130]. A nest of three displacement sensors is fixed on a rotary table to measure the three-dimensional displacement of a precision sphere attached to the machine spindle relative to the work table.…”

“…Many past works [15,28,136] presented the application of the R-test to the identification of location errors of rotary axes by best-fitting measured data to the five-axis kinematic model. Ibaraki et al presented its extension to numerical mapping of component errors of rotary axes [27] as well as their graphical presentation for more intuitive understanding of rotary axes error motions [130].…”

“…A uncertainty study is essential for assessing the calibration reliability under the influence of linear axis error motions [134,140,141]. Ibaraki et al [130] showed that error motions of rotary axes can be calibrated with the minimum influence of linear axes error motions, when the sphere is placed nominally on the axis average line of a rotary table. It is in principle equivalent to the test described in ISO 230-7:2006 [14].…”