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To address these challenges, this study proposes an enhanced lock-in method that utilizes pulse counting techniques to roughly estimate the frequency of the measurement signal and generates orthogonal signals for mixing with the measurement signal. Implementation and experiments on the FPGA platform demonstrate that the improved orthogonal lock-in method can achieve a resolution error of tens of picometers, with a maximum measurement speed exceeding 1 m/s. This research outcome effectively enhances the robustness of the lock-in method, aligning more closely with engineering requirements for high-precision phase measurement.
Non-contact cylindricity measuring of the small-size cylinder is investigated by the chromatic confocal sensor in both relatively fixed and unfixed manners. The uncertainties of the both cylindricity measurement systems need to be analyzed and compared. When applying both measurement systems, the measuring accuracy is negatively affected by angular misalignments of the small cylinder and the measuring light source when the linear scan method is used. When the unfixed scheme is applied, the motion error of the precise translation stage has negative impact on the scanning process. The mounting and distribution error of the light spots effect the scanning coordinate precise when using the fixed scheme. The different sources are discussed respectively. According to the uncertainty result of the coordinates, a measurement uncertainty analysis is carried out through numerical calculations based on a Monte Carlo method. Proven by the experiments, the final result shows the fixed line spot manner has advantages in accuracy due to the better stability of the measurement system.
We have developed an effective algorithm to filter noise from the 3D point cloud data and align the line scan data, reconstructing accurate geometric profile information of the blind vias with sub-micron inspection accuracy. Tested on copper-clad board blind via arrays, this method quickly and accurately detects the geometric parameters of blind vias, providing a powerful tool for real-time monitoring of blind via processing quality and a novel solution for quality control in electronic packaging, including BGA packaging. The method offers advantages such as fast measurement speed, wide measurement range, and non-destructive, non-contact operation, with broad application prospects in the electronics manufacturing industry. Compared to existing technologies, our proposed measurement method is faster, offers higher resolution, and covers a wider measurement range, meeting the increasing requirements for blind via detection in future chip packaging processes. Furthermore, this technology can be extended to size and morphology inspection in other micro-nano processing fields, offering significant theoretical and practical value.
To address sub-mirror alignment accuracy in large-aperture telescopes, we propose an absolute six-degree-of-freedom grating encoder based on spot position monitoring. This encoder achieves four degrees of freedom (θX, θY, θZ, Z) absolute position and orientation detection using gratings. Additionally, we employ right-angle prisms for absolute position and orientation detection in the X and Y directions, enabling six-degree-of-freedom absolute position and orientation monitoring for sub-mirrors. The monitoring results serve as feedback for sub-mirror pose correction. To mitigate the impact of grating motion on X and Y displacement calculations, we introduce a displacement calculation algorithm based on ray tracing for error compensation, enhancing the accuracy of X and Y displacement calculations and achieving high-precision six-degree-of-freedom measurement and computation.
In the dual-beam interference lithography setup with large-aperture optics, a reference grating is used to monitor the exposure field. The reference fringes are recorded by a CCD camera, and the drift values are calculated using a cross-correlation method. These values are used to generate the control signals, which actuate the motion mechanisms to dynamically adjust the phase and period of interference field. However, relying on a single reference grating is insufficient to capture the conditions across the entire exposure field.
Therefore, we conducted an analysis of the errors across the entire exposure field and identified period error as the primary cause of this phenomenon. To address this, fringe patterns from two reference gratings are used to monitor periodic variations in the interference field. The feedback calculated by these variations is used to adjust the motion mechanism. altering the angle between the two beams to achieve periodic compensation. Experimental results show that after implementing periodic compensation, the fluctuation RMS of the interference fringes decreased from 0.24λ to 0.06λ, demonstrating significant improvement.
In the traditional signal subdivision system, it is usually necessary to compensate each kind of error separately, which will consume many hardware and computing resources and cause a significant output latency, especially in the filtering section and normalization section. In this paper, a non-linear Kalman filter-based sin-cos wave subdivision method is proposed. Compared with the traditional filtering methods, non-linear Kalman filter has higher dynamic response and can provide instantaneous phasor estimation. In addition, it can simultaneously achieve filtering, amplitude normalization, decoupling DC bias, harmonic suppression, and phase compensation functions, which significantly reduces the computational burden and facilitates the implementation on low-cost processors.
In this study, a non-linear Kalman filter-based signal segmentation system is implemented on an FPGA platform and verified on a six-degree-of-freedom grating ruler platform. The results show that the single-channel output delay is only 1.8us at a 50MHz clock, which has a very high real-time ability. When the frequency and amplitude of the input signal varies, the non-linear Kalman filter can track instantaneously and has high dynamic characteristics. Experimental results show the effectiveness of this method.
An improved phase measuring deflectometry method for defect detection of specular reflection surface
An improved signal filtering strategy based on EMD algorithm for ultrahigh precision grating encoder
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