Machine tool accuracy characterization, error modeling and compensation using telescopic ballbar and laser interferometer
"This dissertation presents the results of the research investigation on the machine tool accuracy characterization, error modeling and error compensation using telescopic ballbar and laser interferometer. Increasing demand for both higher machine tool accuracy and machining tolerances has resulted in a great need to measure and characterize the accuracy of NC machine tools and minimize machine tool induced errors on machined components before manufacturing parts, instead of inferring it from parts already machined. Using a telescopic magnetic ballbar, the results of the accuracy assessment of an old Bridgeport Series I CNC 2 1/2 axes vertical machining center are presented in the form of dynamic and static circularity and repeatability errors, reversal spike, backlash, cyclic and squareness errors. The effects of speeds and feeds are also investigated. Furthermore, accuracy of a Vertical Machining Center (VMC) is characterized in the form of linear/ angular errors and temperature variation using a low powered He-Ne laser (Renishaw®) calibration system along with environmental controller unit. The machine investigated is Cincinnati Milacron Sabre 750 3-axes CNC Vertical Machining Center with Acramatic 2100 CNC open architecture controller. Results shows that drive motors of the X, Y and Z-axes are major heat sources. Linear positional accuracy is best when the machine is in cold condition and deteriorates with increasing machine operation time for all three axes. Although the form of linear displacement errors of X, Y and Z-axes slides varied with temperature (machine operation hour), it is found out that their basic profiles along the axis travel did not change drastically. Using Rigid Body Kinematics and small angle approximation of the errors, each slide of the three axes vertical machining center is modeled using Homogeneous Transformation Matrix (HTM). By synthesizing the machine's parametric errors such as linear positioning errors, roll, pitch and yaw etc., an expression for the volumetric errors in the multi-axis machine is developed. The developed mathematical model is used to calculate and predict the resultant error vector at the tool workpiece interface for error compensation"--Abstract, p. iv
Missouri University of Science and Technology
Networked Digital Library of Theses and Dissertations