On any surface that has specified for excellent flatness less than 100 microns, there are available in the market optical Z axis inspection system utilizing an XY table. These systems come with a hefty list price (pushing $30K) especially when the targeted part size is greater that 12” (300mm).
Generally in manufacturing after grinding the surface is repeatably well defined and 100% inspection may not required. Applying a multi-point flatness inspection plate with 32 points spatially arrayed to accentuate known maximum deviation from a perfect plane allows for a much lower, cost effective, solution but yielding a 90% spatial flatness result. By implementing a non-contact sensor multiplexing solution to a well placed sensor array and using the Capacitec Bargrafx™ 16 to 32-point software application you can attain your flatness profiles at half the price.