New Laser Technology in Turbine Blade Measurements

Abstract

Mechanical touch probes on CMMs (Coordinate Measuring Machines) are the most common sensors used for blade inspection. Most Blade Measurements today are based on a mechanical probe. The amount of useful data that can be collected using the mechanical touch probe is limited. Since blades are characterized by complicated free form 3D geometry shapes, the traditional solution of touch trigger probes on a CMM is very limited both in hardware as well as in measurement software. One of the major challenges of blade measurement is the “blade alignment” — finding the blade position relative to the CMM and moving the coordinate system from the CMM to the blade. It is a tricky trail and error approach, unless one is using very high precision (and very expensive) mechanical jigs. The recent trend from the touch trigger probe to a mechanical (Analog) scanning probe is a step in the right direction, in terms of data collection rate; however it is still limited by some major fundamental characteristics of the mechanical analog sensor: a. A mechanical probe needs to maintain continuous contact with the surface and thus is limited in its scanning speed. b. By nature, the dynamic range of a mechanical probe is only a few hundred microns, which makes the scanning pattern, the alignment routine and the programming of the scan path more complicated. c. Programming a mechanical probe for a cross-section scanning operation requires operator skill and experience. d. The resolution and size of the features that can be scanned are limited by the diameter of the stylus, so features such as leading and trailing edges are not good candidates for any mechanical or analog probe measurements.