Abstract
The measurement and compensation of volumetric error in milling machines of medium and large size is a key aspect to meeting the precision requirements of the most demanding applications. There are several solutions for volumetric error measurement—usually based on laser or in calibrated artifacts—that offer different specifications and lead to a variety of levels of precision, complexity of implementation and automation, cost of equipment, and measurement time, amongst others. Therefore, it is essential to have tools that allow, in each case, analysis as to which is the optimal calibration strategy, providing the criteria for evaluating different measurement equipment and strategies. To respond to this need, several tools have been developed which are able to simulate the entire calibration and compensation process (machine, measurement, model adjustment, etc.) and apply optimization methods to find the best measurement strategy for each application. For a given machine architecture and expected error ranges, the compensation error for each strategy is obtained by propagating measurement uncertainties and expected machine errors through the measurement and compensation model fitting process by Monte Carlo simulations. The use of this tool will be demonstrated through the analysis of the influence of the main design parameters of a measurement strategy for the calibration of a 3-axis machine tool, based on the measurement of tool position with a laser tracker.
Highlights
Geometric errors are one of the most important aspects when evaluating the precision of a machine tool
The positioning points of the laser trackers (LTs) studied in this paper show minor influence in the quality of the calibration process
This article has presented a new strategy for optimizing volumetric error calibration processes based on laser tracker by means of simulation of the whole calibration process
Summary
Geometric errors are one of the most important aspects when evaluating the precision of a machine tool. The form and assembly errors of the components of the machine (guideways, spindles, linear encoders, etc.) affect the position of the tool center point (TCP), causing a volumetric error that varies according to the position of the axes of the machine [1,2] These errors have been measured by means of the so-called direct methods, measuring the error components of each axis (positioning, straightness, orientation) and their relative orientation (perpendicularity, parallelism) individually, to compensate mechanically or by numerical control. Due to the high cost in time and the difficulties of measuring some errors individually, the so-called indirect methods have been developed in recent years These procedures, usually based on calibrated artifacts [3] or laser interferometry with tracking (laser trackers) [4], directly measure the deviations of the TCP in different positions of the working volume and analytically infer the geometric errors that cause such deviations. A model is obtained that can be extrapolated to other points in the workspace, performing a complete volumetric calibration by means of a single procedure
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