Abstract
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.
Highlights
On-machine measurements are required for fast and accurate defect inspection in manufacturing systems without reducing production rates [1,2,3,4]
Vibration isolation can be realised by optimising the mechanical structure of the instrument, such as employing lattice-structures produced by additive manufacturing (AM) [11,12]
DTi represents the variation of the reference frame transformation on feature i due to part geometric errors allowed by the allocated tolerances
Summary
On-machine measurements are required for fast and accurate defect inspection in manufacturing systems without reducing production rates [1,2,3,4]. Vibration isolation can be realised by optimising the mechanical structure of the instrument, such as employing lattice-structures produced by additive manufacturing (AM) [11,12] Another strategy is to compensate the vibrational effect, for example, a piezo-electric transducer has been used for an on-machine wavelength scanning interferometer to compensate the fluctuations in the optical path length caused by vibration from the surrounding environment [13]. Reducing thermo-mechanical errors can be carried out by using materials of low coefficient of thermal expansion for the critical structures, applying thermally-induced motion error compensation and placing the machine or instrument in a temperature-controlled environment [14,41]. 2. Requirements on the compact FVM sensor FVM is an optical surface topography measurement method where the sharpness of a surface image at optimal focus positions in axial direction is used to determine the surface height. The use of off-the-shelf components reduces the total manufacturing cost of the sensor
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