Calibration With Respect to the Beam Direction of a Non Contact Point Sensor

Abstract

Accurate calibration is required for high-precision mechanical stages used for inspection of mechanical parts. Because of the high cost involved in purchasing and maintaining Coordinate Measuring Machines (CMM), it is common that a dedicated or reconfigurable inspection machine is designed and built to give a solution for a specific inspection task. High precision stages and high precision sensors that are needed for this task can be purchased as off the shelf products. However, when precision is needed, the assembly of the sensor to a linear stage becomes a complex task. This task becomes even more complex when using a non-contact probe since them are more unknowns added to the problem. In this paper we give a method for calculating the angle between the probe beam and the motion stage. The calculation is done directly from the measurements obtained by the non calibrated system. Using the calculated angle, the inverse of the affine transform resulting from the lack of perpendicularity between the probe beam and the motion stage can be determined and can be fixed in software. The method utilizes a high precision cylinder for the task. By using the proposed method, the assembly of a non contact probe to a linear motion stage becomes as simple as bolting down the bolts on the sensor connection panel. The method has been verified by computer simulation, with and without random noise added to the measurements. The results are presented via graphs and tables at the end of this paper.