Design and Mechanical Evaluation of a Capacitive Sensor-Based Indexed Platform for Verification of Portable Coordinate Measuring Instruments

Abstract

During the last years, the use of Portable Coordinate Measuring Machines (PCMMs) in industry has increased considerably, mostly due to their flexibility for accomplishing in-line measuring tasks as well as their reduced costs and operational advantages as compared to traditional coordinate measuring machines (CMMs). However, their operation has a significant drawback derived from the techniques applied in the verification and optimization procedures of their kinematic parameters. These techniques are based on the capture of data with the measuring instrument from a calibrated gauge object, fixed successively in various positions so that most of the instrument measuring volume is covered, which results in time-consuming, tedious and expensive verification procedures. In this work the mechanical design of an indexed metrology platform (IMP) is presented. The aim of the IMP is to increase the final accuracy and to radically simplify the calibration, identification and verification of geometrical parameter procedures of PCMMs. The IMP allows us to fix the calibrated gauge object and move the measuring instrument in such a way that it is possible to cover most of the instrument working volume, reducing the time and operator fatigue to carry out these types of procedures.

Verification of an articulated arm coordinate measuring machine using a laser tracker as reference equipment and an indexed metrology platform

“…Three reference spheres located on each platform, allows the determination of the reference systems of both platforms and the possibility to express the coordinates of a captured point by the AACMM in the fixed lower platform global coordinate system during verification procedures. The IMP has also a high mechanical position repeatability, 4 lm, fact that allows to measure with high precision the orientation and position of the upper platform with respect to the lower platform, Brau et al [41]. This feature is accomplished with the use of six capacitive sensors with nanometer resolution and measuring range of 100 lm for an output voltage from 10 to À10 V and an operational range from 100 to 200 lm with their sensors and targets assembled in the upper and lower platforms respectively.…”

“…Brau et al [41], proposed the use of this platform whose main advantage resides in the reduction of the time and physical effort required to carry out these type of procedures, by fixing the calibrated gauge object and placing the AACMM on the IMP upper platform throughout the verification procedure.…”

“…global coordinate system located in the lower platform of the IMP. By means of a mathematical model explained in Brau et al[41] a homogenous transformation matrix (HTM) is found allowing the change of coordinate systems required.…”

Virtual Distances Methodology as Verification Technique for AACMMs with a Capacitive Sensor Based Indexed Metrology Platform

“…An indexed metrology platform is proposed by Brau et al [26] as an auxiliary instrument for use in calibration and verification procedures for portable coordinate measuring instruments. The methodology developed in this work using the indexed metrology platform tries to improve the verification procedures for AACMMs in terms of the testing time and working space required compared to the procedures described in the standards [4,5,6].…”

“…Using the capacitive sensor readings, we are able to generate a homogenous transformation matrix (HTM) that links the coordinate reference systems through the mathematical model of the platform [26]. Thus, a point captured with the AACMM and expressed in the arm’s coordinate reference system may be expressed on the lower platform or global coordinate reference system.…”