Comparision of Contact and Contactless Measuring Methods for Form Evaluation

Coordinate measuring machines (CMM) are mostly used with contact sensors. High accuracy and very good results in repeatability are advantages of contact systems. Sometimes it is necessary to measure parts, which are not suitable for contact measurement. Usually they are compliant, stylus tip may scratch measured surface or the measured part have areas, which can not be reached by tactile probe. For this purposes there are also contactless methods of points collecting. Two contactless methods are selected for this study. One of them uses optical sensor based on CCD camera and another one uses computing tomography for contactless scanning of the part. Both systems have advantages and limitations. Not every part can be measured with all three systems. For example huge steel parts are not suitable for industrial tomographs, flatness cannot be satisfactorily measured by optical camera systems or measurement of line width on PCB is not achievable for stylus tip. This paper de-scribes differences among these three systems and refers possibilities of form deviations evaluation on example part.