Study Of The Multi-Functional Confocal Measurement System

With the development of technology, more and more high-precision equipments appear in many fields such as aerospace, material, photoelectron, biomedicine and IT, and miscellaneous minute and delicate components have been widely used. For surface quality of the element is exactly the key factor influencing on the precision of instrument, high requirement is proposed to satisfy the 3-D measurement of the unit surface profile. Surface measurement, analysis and evaluation come to be a multi-disciplinary subject, which has shown great theoretical significance and application value.The current high-accuracy optical surface instruments are mainly used for one-parameter measuring, and often can't solve the contradiction between the procession and measuring range well. The stylus profile instrument can get high resolution in a rather large range, but simultaneously bringing about mechanical pressure and damage of stylus, which effected on the measuring accuracy. And it can't be used for the soft and high precision surface measuring, with the limited application. Therefore, it's necessary to develop a non-contact, high-accuracy, multifunctional instrumentation system for the surface measurement, which contains more rich information and scratches prohibition.According to this, a multi-functional confocal surface measurement system was presented, covering high-precision and large measurement range. The system was made up of confocal, microscope and optical visual displacement measurement. With microscope coarsely aligning, confocal system precise aiming, little-range and high-resolution measuring, and accompanying with the movement of the focused eye lens, the large-range measurement could be accomplished by accurate visual displacement system. Furthermore, the depth information and image reconstitution technology could be used to get the subject surface topography. Thus, the system could solve the problem of high-precision, rich information and soft material profile measurement, and at the same time, it could offer the ability of micro-examination, which was helpful to analyze the surface characteristics in detail. As a novel device with plenty of technology contents, the system could be used widely and had showed broad application prospect and utility value in the fields of microelectronic, micromechanics, optical fabrication, aerospace, biomedicine and materials science et al.Firstly, the cause of the confocal system having the ability of providing high lateral and axial direction resolution was clarified and the correlative factors affecting the resolution were analyzed, which had given the theoretical basis for further optimum design.A multi-functional confocal surface measurement system was developed and the main components of the system were represented, which were confocal detection head, micro optical observation and precise visual displacement measurement of lens. The investigation and analysis of the key factors of confocal optical detection were also given in detail, such as light source, object lens, pin holes and electro-photonic detectors.To increase the accuracy of surface measurement, exactly separate and extract the required characteristic signal, the determination of the criteria for evaluation was focused on, which was the core technology of the surface assessment. Based on double density wavelet transform (DDWT), a novel roughness separation method for engineering surface analysis was proposed. With individual analysis by simulating data and actual measurement of surface roughness comparator, the accuracy of roughness parameter Ra could be improved about 4% by DDWT line than that of Gaussian line or DB wavelet line. Furthermore, the roughness, waviness and shape inaccuracy could be easily separated from the surface topography error signal.To make further observation and analysis of the surface characteristics, the high-accuracy focusing reconstruction was accomplished based on microscopy serial images. A de-noising method of double-density wavelet with soft threshold was proposed to eliminate interference by focusing evaluation function. While eliminating the interference, the data location was kept and the signal-to-noise ratio was improved.Finally, performance test and experimental research were executed on this new system, and the comparison of axial response curves was obtained by characteristic-different surfaces.With this new system, surface roughness comparator and step measurement were accomplished and the analysis of the error sources was performed. Results showed that this new system had the superior properties of high precision, multi function, little size and convenience in application.