A Novel Method for the Calibration of the Displacement Encoder of the Rockwell Hardness Tester

The depth measurement scale of the hardness test must be verified with an accuracy of 0.0001 mm. A novel optical setup is designed and developed using a flat mirror interferometer and indigenously fabricated fixtures to calibrate a Rockwell tester. One needs to repeatedly move and position the indenter of the machine to the pre-decided scale markings for calibrating the displacement to achieve the recommended accuracy. Usually, the spindle of the Rockwell tester cannot be precisely moved to a desirable position. To avert this hurdle, the measurements are taken in the time-based mode of a commercial displacement measuring laser interferometer. A new algorithm is devised to remove the unwanted readings from these time-based measurements. The deviations of the depth measuring system of the Rockwell tester are determined by applying the proposed algorithm. Further, the uncertainty of measurement associated with the displacement of the Rockwell tester is estimated.