Development of a compact focus variation microscopy sensor for on-machine surface topography measurement

On-machine areal surface topography measuring instruments are required for fast and accurate measurement of parts inside production machines without reducing production rates. This paper presents the design and development of a compact focus variation microscopy sensor that can be integrated into various types of machine tools. The paper focuses on the development of the linear stage of the sensor, which was the major engineering challenge. The overall developed sensor has dimensions of 78 mm diameter and 200 mm length, with a 20 mm travel range. Simulations of tolerance stack-ups for the sensor assembly were performed before the manufacturing of the sensor’s linear motion components to assure they can be appropriately assembled. The linear motion accuracy of the sensor is 2 μm, calibrated using laser interferometry. From measurement in a controlled laboratory, the measurement noise of the sensor is 0.4 μm. Finally, demonstrations of calibrated artefact measurements with the sensor are presented. A single image field measurement with the sensor requires less than 20 s.