Thickness Measurement for Glass Slides Based on Chromatic Confocal Microscopy with Inclined Illumination

Design and Research of Chromatic Confocal System for Parallel Non-Coaxial Illumination Based on Optical Fiber Bundle

Conventional chromatic confocal systems are mostly single-point coaxial illumination systems with a low signal-to-noise ratio, light energy utility and measurement efficiency. To overcome the above shortcomings, we propose a parallel non-coaxial-illumination chromatic-confocal-measurement system based on an optical fiber bundle. Based on the existing single-point non-coaxial-illumination system, the optical fiber bundle is used as the optical beam splitter to achieve parallel measurements. Thus, the system can yield measurements through line scanning, which greatly improves measurement efficiency. To verify the measurement performance of the system, based on the calibration experiment, the system realizes the measurement of the height of the step, the thickness of the transparent specimen and the reconstruction of the three-dimensional topography of the surface of the step and coin. The experimental results show that the measuring range of the system is 200 μm. The measurement accurcy can reach micron level, and the system can realize a good three-dimensional topography reconstruction effect.

Turned Surface Monitoring Using a Confocal Sensor and the Tool Wear Process Optimization

Laser scanning technology has been used for several years. Nevertheless, no comprehensive study has been conducted to prove that the application of confocal chromatic sensor (CCHS) laser technology is effective and suitable to verify the integrity parameters of machined surfaces in terms of cutting tool damage. In this paper, the optimization and effects of five factors (cutting speed, feed, depth of cut, attachment length of the workpiece, and tip radius) on the roundness deviation measured by CCHS and, at the same time, on the amount of wear on the back side of the cutting part of the tool were studied according to ISO 3685, which was measured with a microscope. The results obtained were evaluated using the gray relational analysis method (GRA), in conjunction with the Taguchi method, and the significance of the factors was demonstrated using the analysis of variance (ANOVA) method.

Scanning-free digital holography for decoupling the refractive index and thickness via a constrained equation of higher degree

Digital holography is one of the most popular quantitative phase imaging techniques, but the refractive index and the thickness are always coupled in the phase. To solve the decoupling problem, multiple scanning methods such as tomography and total reflection are usually used, which is time-consuming. To increase the imaging speed and reduce the system cost, it is urgent to seek the decoupling method of scanning-free digital holography. In this paper, we find that the decoupling method of scanning-free digital holography can be transformed into a problem of solving constrained higher order equations. By introducing the Fresnel reflection formula, a six-degree equation about refractive index is constructed and the corresponding algorithm for solving the equation is given. By using the algorithm, the refractive index and thickness can be decoupled successfully. A series of results show that the proposed method is effective and has high anti-noise performance. This method provides a mathematical possibility for scanning-free digital holography to decouple the refractive index and complex pixel stepped thickness distributions. Therefore, it may provide a theoretical basis for the subsequent development of a real scanning-free digital holography system, which may have potential applications in the measurement of optical devices produced by the modern film deposition process and etching process.

Error Analysis and Correction of Thickness Measurement for Transparent Specimens Based on Chromatic Confocal Microscopy with Inclined Illumination

As a fast, high-accuracy and non-contact method, chromatic confocal microscopy is widely used in micro dimensional measurement. In this area, thickness measurement for transparent specimen is one of the typical applications. In conventional coaxial illumination mode, both the illumination and imaging axes are perpendicular to the test specimen. At the same time, there are also geometric measurement limitations in conventional mode. When measuring high-transparency specimen, the energy efficiency will be quite low, and the reflection will be very weak. This limitation will significantly affect the signal-to-noise ratio. The inclined illumination mode is a good solution to overcome this bottleneck, but the thickness results may vary at different axial positions of the sample. In this paper, an error correction method for thickness measurement of transparent samples is proposed. In the authors’ work, the error correction model was analyzed and simulated, and the influence caused by the different axial positions of sample could be theoretically eliminated. The experimental results showed that the thickness measurement of the samples was practically usable, and the measurement errors were significantly reduced by less than 2.12%, as compared to the uncorrected system. With this error correction model, the standard deviation had decreased significantly, and the axial measurement accuracy of the system can reach the micron level. Additionally, this model has the same correction effect on the samples with different refractive indexes. Therefore, the system can realize the requirement of measurement at different axial positions.