 |
| I. Introduction The performance or the accuracy of a CNC machine tool is determined by the volumetric positioning accuracy, which includes the linear displacement error, the straightness error, the angular error and the elastic error. A complete measurement of those errors is very complex and time consuming, for those reasons the measurement of the body diagonal displacement errors is recommended by many international standards such as ISO 230-6 and ASME B5.54 [1] for a fast check of the volumetric performance. This is because the body diagonal displacement measurement is sensitive to all of the error components. However, if the errors exceed the specification, there is not enough information for the identification of the error sources and for their compensation. Recently, a new laser vector technique [2,3] is developed by Optodyne for the measurement of the volumetric errors, including 3 displacement errors, 6 straightness errors, and 3 squareness errors by using a laser Doppler Displacement Meter (LDDM). Using this laser vector measurement technique the volumetric positioning errors of an AWEA vertical machining center model FV-1000 with Fanuc 18M controller has been measured. II. Body Diagonal Displacement Measurement The body diagonal displacement measurement method is recommended for a fast check of the positioning and geometrical accuracy of a machine. Briefly, similar to a laser linear displacement measurement, instead of pointing the laser beam in the axis direction, pointing the laser beam in the body diagonal direction as shown in Fig.1a. Mount a retroreflector on the spindle and move the spindle in the body diagonal direction, for example from the lower left corner (X=0 Y=0 Z=0) to the upper right corner (Xmax, Ymax, Zmax). Starting from the zero position and at each increment of the three axes, which are moved together to reach the new position along the diagonal, the displacement error is measured. The accuracy of each position along the diagonal depends on the positioning accuracy of the three axes, including the straightness errors, angular errors and squareness errors. Hence the body diagonal displacement measurement is a good method for the machine verification, but there is not enough information for the identification of the error sources. III. Vector or Sequential Diagonal Measurement The new vector measurement method or Sequential Diagonal Measurement Method differs from the traditional method because each axis is moved separately and the positioning error is collected after each single movement of the X axis, of the Y axis and than of the Z axis. For this reason, 3 times more data is collected and also the positioning error due to each single axis movement can be separated. The collected data can be processed as the projection of the displacement of each single axis along the diagonal. |
 |
 |
 |
 |
 |
 | |
 |
 | |||||