Design and characterization of precise laser-based autofocusing microscope with reduced geometrical fluctuations

Precise and rapid focus detection is an essential operation in several manufacturing processes employing high-intensity lasers. However, the detection resolution of existing methods is notably low. This paper proposes a technique that provides a rapid-response, high-precision, and high-resolution focus inspection system on the basis of geometrical optics and advanced optical instruments. An ultrafast interface position detector and a single-slit mask are used in the system to precisely signal the focus position with high resolution. The reflected images on the image sensor are of a high quality, and this quality is maintained persistently when the target surface is shifted along the optical axis. The proposed system developed for focus inspection is simple and inexpensive, and is appropriate for practical use in the industrial production of sophisticated structures such as microcircuits and microchips.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

High-Speed Focus Inspection System Using a Position-Sensitive Detector

Cao

Hoang

Ahn

et al. 2017

“…Sensors 2020, 20, x FOR PEER REVIEW 3 of 13 1. The results of their simulations and experiments demonstrated that the values of positioning accuracy and repeatability are both less than ±1.5 μm within the measuring range of ±200 μm based on the respective response intensity of dual near-focusing position [41].…”

Section: Methodsmentioning

confidence: 99%

“…Due to its good reliability, high throughput, and relatively low cost, machine vision systems are an attractive solution for the inspection process in automated mass production lines. In practice, such systems always need a highly precise autofocusing capability to obtain sufficiently sharp images of the object of interest [1][2][3][4]. Autofocusing systems have been widely applied in recent decades in a variety of industrial manufacturing and measurement fields, such as in cellphone camera modules, automatically available optical inspection, and dynamic tracking systems [4].…”

Section: Introductionmentioning

confidence: 99%

Implementation and Optimization of a Dual-confocal Autofocusing System

Jan

Liu

Yang

2020

Self Cite

This paper describes the implementation and optimization of a dual-confocal autofocusing system that can easily describe a real-time position by measuring the response signal (i.e., intensity) of the front and the rear focal points of the system. This is a new and systematic design strategy that would make it possible to use this system for other applications while retrieving their characteristic curves experimentally; there is even a good chance of this technique becoming the gold standard for optimizing these dual-confocal configurations. We adopt two indexes to predict our system performance and discover that the rear focal position and its physical design are major factors. A laboratory-built prototype was constructed and demonstrated to ensure that its optimization was valid. The experimental results showed that a total optical difference from 150 to 400 mm significantly affected the effective volume of our designed autofocusing system. The results also showed that the sensitivity of the dual-confocal autofocusing system is affected more by the position of the rear focal point than the position of the front focal point. The final optimizing setup indicated that the rear focal length and the front focal length should be set at 200 and 100 mm, respectively. In addition, the characteristic curve between the focus error signal and its position could successfully define the exact position by a polynomial equation of the sixth order, meaning that the system can be straightforwardly applied to an accurate micro-optical auto-focusing system.

“…However, the timing fluctuations of the laser source introduce noise, thereby degrading the measurement accuracy [ 32 , 33 , 34 , 35 ]. As a result, this study proposes a method to measure and compensate for fluctuations in the laser beam geometry.…”

Section: Structure Layout and Measuring Principlementioning

confidence: 99%

Design of a Measurement System for Simultaneously Measuring Six-Degree-Of-Freedom Geometric Errors of a Long Linear Stage

Liu

Chen

et al. 2018

Self Cite

This study designs and characterizes a novel precise measurement system for simultaneously measuring six-degree-of-freedom geometric motion errors of a long linear stage of a machine tool. The proposed measurement system is based on a method combined with the geometrical optics method and laser interferometer method. In contrast to conventional laser interferometers using only the interferometer method, the proposed measurement system can simultaneously measure six-degree-of-freedom geometric motion errors of a long linear stage with lower cost and faster operational time. The proposed measurement system is characterized numerically using commercial software ZEMAX and mathematical modeling established by using a skew-ray tracing method, a homogeneous transformation matrix, and a first-order Taylor series expansion. The proposed measurement system is then verified experimentally using a laboratory-built prototype. The experimental results show that, compared to conventional laser interferometers, the proposed measurement system better achieves the ability to simultaneously measure six-degree-of-freedom geometric errors of a long linear stage (a traveling range of 250 mm).