Ercihan Kiraci, Glen A Turley, Alex Attridge, Alan Olifent, Mark A Williams
A COMPARISON STUDY OF ON-CMM LASER SCANER AND TOUCH TRIGGER PROBE FOR AUTOMOTIVE MEASUREMENT APLICATIONS
Coordinate Measuring Machines (CMMs) are considered as the most accurate metrology equipment and are used widely in the manufacturing sector. Traditionally, touch trigger probes have been employed but more recently non-contact laser scanning sensors have been developed, offering potential advantages in terms of speed and number of points captured. Laser scanning is attracting significant interest from industry due to its ability to characterise complex, free-form surface geometries which are becoming common in the styling of automotive body panels. However, laser scanning sensors do not currently offer the accuracy and repeatability that can be achieved with touch trigger probes. Furthermore, there are no recognised standards for qualifying non-contact probes, making reliable verification of measurements difficult to achieve. Past research has attempted to qualify the capability of different non-contact probing technologies using small artefacts designed for technology validation; however, little work has been done on the verification of on-CMM laser scanning technologies for large volume, industry-relevant measurement applications. This study used a full-scale machined physical representation of a sheet metal vehicle body to evaluate the measurement agreement and repeatability of a laser scanning sensor, relative to touch trigger probe measurements, mounted on a horizontal arm CMM using individual surface points, edge points and circular holes, located across the entire structure. Through the use of a static repeatability analysis it was found that there was good correlation between touch trigger probe and laser scanner measurements. Repeatability of the laser scanner was found to be better than 28 µm for surface, edge and circular holes measurement. Accuracy of the laser scanner relative to the touch trigger probe measurements fell within a range of 50 µm which is a factor of 10 lower than typical automotive body-shell manufacturing tolerances. The results collected demonstrate that laser scanning sensor and CMM used in this study would provide a level of accuracy and repeatability better than which is typically required by automotive manufacturers for body-in-white quality inspection applications.