Analysis of a precise instrument for measuring reference level involute

Reference level involute is used for evaluating other involutes, but it is very difficult to measure reference level involute exactly. Nowadays the available methods for measuring precise involute include single base disc mode, electronic generation mode, and CNC three-coordinate mode. But measurement accuracy of the modes above is not suitable for reference level involute. A precise instrument for measuring reference level involute, double base discs instrument, is introduced. It is consistent with generation principle of the involute entirely. Besides having the advantages of single basic disc instrument, the instrument can remove Abbe error caused by the stylus, and has no pressure deforming. The instrument's structure is described. The main sources of measurement errors are analyzed and methods for compensation are presented. Finally, uncertainty of the instrument is given, which meets reference level involute test specification.