Benedito Di Giacomo

CMM uncertainty analysis with factorial design

The purpose of this research is to present a method to estimate the Coordinate Measuring Machine (CMM) measurement uncertainty. The approach is based on a performance test using a ball bar gauge and a factorial design technique. A factorial design was applied to carry out a performance test and to investigate CMM errors associated to orientation and length in the work volume. The CMM measurement uncertainty was estimated with components of variance obtained after statistical analysis of variance applied to volumetric measurement errors. An application was performed with a Moving Bridge CMM and the results were compared to the volumetric performance test proposed by ANSI/ASME B89.4.1 standard. The results showed that the proposed method is suitable to investigate CMM hardware performance and determine the contribution of machine variables to measurement uncertainty.

Development of an automated and dedicated measuring system for straightness evaluation

This work presents an automated and dedicated system aiming at the measurement of straightness errors of mechanical components, using an industrial robot. A multi-probe error separation technique was used to make measurements independent from the coordinate system of the robot. A mathematical model that takes into account the readings from three sensors was specifically designed for the proposed measurements and produces inspection results by means of the solution of a system of linear equations, in only one operation. Also in this work, a new approach was developed to minimize the influence of the zero-adjustment errors of the sensors, which represent the major source of errors in the separation process. Experimental tests applied to the measurement of straightness errors of mechanical components were accomplished, which demonstrated the effectiveness of the employed methodology.

Mapping by Optimization of the Minimum Volumetric Error in Coordinate Measuring Machines

The CMM (coordinate measuring machines) are able to perform dimensional inspections in workpieces with complex geometries, in a short time compared to conventional methods, however, errors on volume of CMM harm the performance of measurement. Faced with this, the purpose this investigation is to identify regions in the machine with large and small values of volumetric errors. The mapping of volumetric error is performed by optimization of objective function with SQP method. The objective function is defined by modeling errors of the CMM using a method of the homogeneous transformation, and, by calibration curves of individual errors. The optimization allowed to obtain the smallest value of volumetric error, 1.1796 μm, located near the linear encoder of the y axis. The mapping the volumetric error by optimization allows to know regions with minor harm the performance of measurement, therefore, its possible to select regions of measurement to obtain reliable results.

Calibration of Positional Errors in Coordinate Measuring Machines and Machine Tools Using a Laser Interferometer System

Dimensional inspections in manufactured workpieces allow assess the quality of the manufacturing process, in this context the quality and development of measurement systems are issues addressed by many researchers. The coordinate measuring machines (CMMs) are versatile systems, can measure complex geometries quickly and accurately. Positional errors are parts of volumetric error and affect the correct positioning of probe in CMMs or of the tool in machine tools. Faced with this, the purpose this investigation is show a method to calibrate the positional errors in a bridge-type coordinate measuring machine, this method collects data in dynamic mode and reduces cyclic errors. The calibration of positional errors was performed using laser interferometry in the “on-the-fly” mode and a method to reduce cyclic errors was applied. The highest value of position error occurred in x axis with value positive of 10μm in the position of 220mm, while in the y and z axis the higher absolute values were 2μm and 6μm respectively. From calibration and compensating of positional errors it is possible to reduce the effects of the volumetric errors in machines with axis of linear displacements as the CMMs and machine tools.