Autofocus Microscope Research Articles

Image-Based Auto-Focus Microscope System with Visual Servo Control for Micro-Stereolithography.

Micro-stereolithography (μSL) is an advanced additive manufacturing technique that enables the fabrication of highly precise microstructures with fine feature resolution. One of the primary challenges in μSL is achieving and maintaining precise focus throughout the fabrication process. For the successful application of μSL, it is essential to maintain the sample surface within a focal depth of several microns. Despite the growing interest in auto-focus devices, limited attention has been directed towards auto-focus systems in image-based auto-focus microscope systems for precision μSL. To address this challenge, we propose an image-based auto-focus microscope system incorporating visual servo control. In the optical design, a transflective beam splitter is employed, allowing the laser beam to pass through for fabrication while reflecting the focused beam on the sample surface to the microscope and camera. Utilizing captured spot images and the Foucault knife-edge test, a deep learning-based laser spot image processing algorithm is developed to determine the focus position based on spot size and the number of spot pixels on both sides. Experimental results demonstrate that the proposed auto-focus system effectively determines the relative position of the focal point using the laser spot image and achieves auto-focusing through visual servo control.

Maximum Acceptable Tilt Angle for Point Autofocus Microscopy.

The complete and accurate acquisition of geometric information forms the bedrock of maintaining high-end instrument performance and monitoring product quality. It is also a prerequisite for achieving the 'precision' and 'intelligence' that the manufacturing industry aspires to achieve. Industrial microscopes, known for their high accuracy and resolution, have become invaluable tools in the precision measurement of small components. However, these industrial microscopes often struggle to demonstrate their advantages when dealing with complex shapes or large tilt angles. This paper introduces a ray-tracing model for point autofocus microscopy, and it provides the quantified relationship formula between the maximum acceptable tilt angle and the beam offset accepted in point autofocus microscopy, then analyzing the maximum acceptable tilt angle of the objects being measured. This novel approach uses the geometric features of a high-precision reference sphere to simulate the tilt angle and displacement of the surface under investigation. The research findings show that the maximum acceptable tilt angles of a point autofocus microscope vary across different measured directions. Additionally, the extent to which the maximum acceptable tilt angles are affected by the distances of the beam offset also varies. Finally, the difference between the experiment results and the theoretical results is less than 0.5°.

Autofocus microscope system based on blur measurement approach

Blurred (out-of-focus) images hinder the process of accurate cell counting in medical images. Cell counting is considered an important method to quantify cells for disease diagnosis and medical research. The hemocytometer is used to count cells as it is a cheaper and simple method. The specimen which contains cells is loaded into the hemocytometer and placed on a microscope. In this paper, a new autofocus technique is proposed to automatically adjust the microscope knobs by controlling the movement of adjusting knobs. This method is based on measuring and evaluation of the amount of blur annoyance in cell images. Whereas, adjusting knobs of microscope is a time consuming especially for beginners. Also, the automatic adjustment avoids losing the knob gear if it is used for several times or used in a wrong way. A CCD camera is attached to the microscope to capture images of specimen under test. An efficient blur metric is used to evaluate the amount of blur in captured images. The microscope knob is attached to a stepper motor to control its movement. The movement is stopped when the well-focused image is obtained. The proposed method has proved that it is an efficient method to automatically adjust the microscope knobs and get a well-focused image. The proposed method is compared with another recent approach that is based on an evaluation of a contrast measurement in images to automatically control the microscope knobs. The results proved that the output in-focus images by using the proposed approach for auto-focusing the microscope system have low blur values and much closer to the quality of the original reference images. Moreover, the proposed method which is based on blur measurement gives a higher image quality than one of the most recent approaches that depends on contrast measurement.

A Proposal for a High-Speed Autofocus Microscope Based on Synchronous Control of a Resonant Variable-Focus Lens and a Short-Time Exposure Camera

A Proposal for a High-Speed Autofocus Microscope Based on Synchronous Control of a Resonant Variable-Focus Lens and a Short-Time Exposure Camera

Design Of Autofocus Microscope With Histogram Method For Tuberculosis Bacteria Observation

This research was conducted to design an autofocus microscope with a histogram method that can observe Tuberculosis (TB) bacteria. The bacteria observed were preparations or phlegm preparations which had been stained with Ziehl Neelsen. The microscope is designed to be equipped with a program to control the focus motor that moves the microscope tube and the program to digitally display the image and histogram of TB bacteria. Histograms are analyzed based on intensity values spread between 0-255 and the entropy value is sought. The measurement results that have been carried out as many as 20 times the field of view of the TB bacteria show that the most focused areas have the highest entropy value with an accuracy level ranging from 81.90476% to 100% at 1000 times the magnification.

Design of a laser-based autofocusing microscope for a sample with a transparent boundary layer

This study proposes a new type of autofocusing microscope. The microscope was combined with a polarized beam-splitting system and an image-processing program to overcome the complex signals generated when focusing on a transparent boundary layer. The polarized beam-splitting system divides a source laser beam into four parallel beams using a birefringent crystal. It also uses an axicon lens to focus individually on different positions of the sample surface when light is incident on the objective lens to observe multiple-spot defocusing information simultaneously. The transparent boundary layer exhibits intricate signals when a sensor detects laser spots. Therefore, an image-processing program is proposed to filter unnecessary signals for calculating the evaluation function and driving the motor, which enables a focused view of the test sample to be attained conveniently. To prove the feasibility of the proposed autofocusing microscope, a frame was developed using a simulation software for observing the initial characteristics of the microscope and for conducting a qualitative analysis. Moreover, the image-processing effect on the sample was tested to determine whether the aim of the study was achieved. The experimental results matched suitably with the simulation results, which indicates that the proposed autofocusing microscope can solve the problem caused by the transparent boundary layer and can achieve a high focusing accuracy within a short focusing time.

A New Search Model for Liquid-based Cervical Cells Based on Auto-focus Microscope System

Liquid-based cervical cytology test which one of the most important method of detecting cervical lesions has a good effect on diagnosis and prognosis of cervical carcinomas. Speed of manual scanning is slow, furthermore large quantities of works repeated due to the presence of visual fatigue that lead to misdiagnosis. Automatic screening method for pathological cells is proposed based on auto-focus microscope system combined advanced machine vision technology and image processing technology, convenient for doctors find suspicious cells. This way can improve the efficiency of medical workers and avoid misdiagnosis. The key technology of auto-focus microscope system is that scanning automatically of liquid-based cervical cell. An efficient and accurate focus method can find a clear image quickly, which is of great significance to the detection of abnormal cells. In this paper, we proposed a new research mode for auto-focus microscope system, based on the micrograph characteristics of liquid-based cervical cytology. Results show that the approach outperforms with high accuracy and comparable performance.

Proportion quantitative analysis and etching of {110} planes on tungsten single crystal coating surface

Tungsten single crystal and poly crystal were treated by electrolytic etching in a 3% by weight solution of NaOH in distilled water. The method for determining the proportion of {110} planes and characteristic morphology on the coating surface after electrolytic etching were investigated using EBSD and auto-focusing microscope. Then the optimization of process parameters for electrolytic etching is achieved. In order to compare the effect of process parameters, three process parameters were selected for the tungsten single crystal electrolytic etching. Through analyzing the change of {110} planes' proportion, we found that when the coatings are etched with 1.4 amp/cm2 and 3 min, {110} planes can be exposed in the greatest degree that can reach 61.4% on tubular surfaces. The proposed approach greatly improves the proportion of {110} planes relative to the original surface.

Design and characterization of high-performance autofocusing microscope with zoom in/out functions

Autofocusing is a critical function in on-line or off-line automated vision inspection in the manufacturing fields. Accordingly, design of high-performance autofocusing microscopes is an important issue. The present group recently developed a novel laser-based autofocusing microscope comprising two optical paths, which provided a large linear autofocusing range and a rapid response with no reduction in the focusing accuracy (Liu et al. in Appl Phys B 109:259–268, 2012). In the present study, the focusing response of the developed autofocusing microscope is further improved by replacing the two optical paths with one tunable optical zoom system. The proposed autofocusing microscope is characterized numerically by means of commercial software ZEMAX simulations and is then verified experimentally using a laboratory-built prototype. The simulation and experimental results show that compared to the developed autofocusing microscope with two optical paths, the proposed autofocusing microscope achieves a rapid focusing response (less than 3.5 s) under the same autofocusing range (±1500 μm) and focusing accuracy (focusing accuracy of ≤1 μm, repeatability of ±1 μm). Consequently, it confirms the proposed autofocusing microscope has potential for automated vision inspection and optical applications.

Precise autofocusing microscope with rapid response

The rapid on-line or off-line automated vision inspection is a critical operation in the manufacturing fields. Accordingly, this present study designs and characterizes a novel precise optics-based autofocusing microscope with a rapid response and no reduction in the focusing accuracy. In contrast to conventional optics-based autofocusing microscopes with centroid method, the proposed microscope comprises a high-speed rotating optical diffuser in which the variation of the image centroid position is reduced and consequently the focusing response is improved. The proposed microscope is characterized and verified experimentally using a laboratory-built prototype. The experimental results show that compared to conventional optics-based autofocusing microscopes, the proposed microscope achieves a more rapid response with no reduction in the focusing accuracy. Consequently, the proposed microscope represents another solution for both existing and emerging industrial applications of automated vision inspection.

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

Due to consumer preference for products with ever higher performance, a requirement exists for precise autofocusing microscope systems to perform the inspection process in automated mass production lines. Accordingly, the present study proposes a laser-based microscope system in which a precise autofocusing capability is achieved using a position feedback signal based on the distance L between the geometrical center (X c , Y c ) of the image captured by the CCD sensor and the centroid (x centroid , y centroid ) of the image. The experimental results show that the proposed system has a positioning accuracy of 2.2 μm and a response time of 1 s given a working range of ±200 μm. The autofocusing performance of the proposed system is thus better than that of a conventional centroid-based system, which typically achieves a positioning accuracy of around 5.2 μm.

Design and Characterization of Precise Laser-Based Autofocusing Microscope with Reduced Geometrical Fluctuations

The present study proposes a laser-based microscope system in which a precise autofocusing capability is achieved using a position feedback signal based on the distance L between the geometrical center (Xc, Yc) of the image captured by the CCD sensor and the centroid (xcentroid, ycentroid) of the image. The experimental results show that the proposed system has a positioning accuracy of 2.2 μm given a working range of ±200 μm. The autofocusing performance of the proposed system is thus better than that of a conventional centroid-based system, which typically achieves a positioning accuracy of around 5.2 μm.

Design and experimental validation of novel optics-based autofocusing microscope

This study designs and characterizes a novel precise optics-based autofocusing microscope with both the large linear autofocusing range and the rapid response. In contrast to conventional optics-based autofocusing microscopes with centroid method, the proposed microscope comprises two optical paths, namely one optical path which provides a short linear autofocusing range but an extremely high focusing accuracy and a second optical path which achieves a long linear autofocusing range but a reduced focusing accuracy. The two optical paths are combined using a self-written autofocus-processing algorithm to realize an autofocusing microscope with a large linear autofocusing range, a rapid response, and a high focusing accuracy. The microscope is characterized numerically using commercial software ZEMAX and is then verified experimentally using a laboratory-built prototype. The experimental results show that compared to conventional optics-based autofocusing microscopes with centroid method and a single optical path, the proposed microscope achieves both a longer autofocusing range and a more rapid response with no reduction in the focusing accuracy. Overall, the results presented in this study show that the proposed microscope provides an ideal solution for automatic optical inspection and industrial applications.

The impact of germanium doping on the dislocation distribution in directional solidified mc-silicon

In this paper experimental results on the effect of the Ge doping on the distribution of dislocations in directional solidified multi-crystalline (mc) Si are presented. The dislocation density distribution is analyzed on the basis of the average dislocation density and the cumulative probability by means of etch pits counting via optical auto-focus (AF) microscope and the Photovoltaic (PV) scan method. The Ge doped ingots show a significantly lower average dislocation density and dislocations are more homogeneously distributed in the Si matrix, whereas the undoped ingot contains large areas of accumulated dislocations. Apparently, the overall dislocation density is reduced by the induced strain field and the lower mobility of dislocations due to the pinning effect.

Fast and Adaptive Auto-focusing Microscope

Fast and Adaptive Auto-focusing Microscope

Development of the fast astigmatic auto-focus microscope system

In this paper, a fast auto-focus microscope system was developed based on the astigmatic method. A collimated infrared laser beam was employed in the infinite-corrected microscope optical axis by the beam splitter and reflected by the sample surface. By embedding an astigmatic lens in the system, the reflected laser beam has different focal lengths in the sagittal and tangential planes. As the microscope's relative distance varies, the reflected laser beam shape also varies and can be detected by an embedded four-quadrant photodiode, i.e., the focus error signal (FES) can be found. Then, a fast auto-focus system can be realized by converting the FES to the microscope's defocus distance. We designed an astigmatic auto-focus system for a 20× objective lens with a ±50 µm working range, and this system could also be used for 10× and 5× objectives with ±200 µm and ±800 µm working ranges, respectively.

A microscope system based on bevel-axial method auto-focus

A microscope system based on bevel-axial method auto-focus (BAM-AFS) is proposed. The purpose is to establish an auto-focus microscope system that calculates the focus position one or many times. In this paper, we propose a bevel-axial method that had an included angle between CCD sensor and image plane with multi-parameters fusing from image to obtain the in-focus position directly in the first phase and combined Kalman estimate to obtain the in-focus position for different objects in the second phase. We discuss the relation between focus positions and image focus at the end.

Performance Evaluation of Teleoperation for Manipulating Micro Objects Using Two-Fingered Micro Hand

We developed a dexterous micromanipulation system consisting of a two-fingered micro hand, an autofocusing optical microscope, an image processor, and user interfaces. The micro hand has 6 degrees of freedom (DOF), 3 DOF each for two fingers that work similar to a thumb and forefinger or chopsticks. This hand grasps, moves, rotates and releases micron-scale objects. In teleoperation mode, the user controls hand motion with a joystick or keyboard while observing the microscope image on a TV monitor. We evaluate teleoperation performance for manipulating micron-scale objects. Several types of motion command methods proposed include a keyboard or joystick as operation device, and position or rate command modes. The tasks experimentally evaluated are picking, grasping, moving, and releasing micron-size objects, i.e., a glass grain in air and a yeast cell in liquid. These are compared in positioning accuracy and task execution time.

Application of Imaging Techniques to Geometry Analysis of Aggregate Particles

This paper presents image analysis techniques by which to characterize the texture, angularity, and form of aggregate particles used in highway construction and geotechnical applications. For texture analysis, wavelet decomposition in gray scale images of particles is performed. The results demonstrate that multiscale wavelet representation is a powerful tool by which to capture the texture and to differentiate true texture from false texture caused by variations of natural color on a particle surface. Angularity and form analyses of particles are done using binary images. A gradient-based method is employed to describe angularity. This method is shown to differentiate between particles with different angularity characteristics. Form analysis of the particles includes computing the shape factor and sphericity index, which are based on measurements of the shortest, intermediate, and longest axis of the particle. Particle thickness is measured using the feature of an autofocus microscope. The width and length are calculated by an eigenvalue decomposition method of two-dimensional particle projections. Details of an interactive software developed to compute the different aggregate shape factors are discussed. The results indicate that these calculated values of the particle dimensions match very closely the values measured manually using a digital caliper.

Frameless optical computer-aided tracking of a microscope for otorhinology and skull base surgery.

To integrate a digitally controlled operating microscope without a laser autofocus system into a frameless optical computer-aided surgery system and to test the accuracy and usability of this system in otorhinological surgery. Experimental study and case series. Department of Oto-Rhino-Laryngology, Head and Neck Surgery, Inselspital, and the Maurice E. Müller Institute for Biomechanics, University of Bern, Bern, Switzerland. Eight computer-aided microscopic surgical procedures were performed between January and October 2000 on patients with various diseases of the anterior and lateral skull base. The practical accuracy of the navigated microscope on the lateral side of a cadaver skull was 2.27 +/- 0.25 mm and on the anterior side of the same skull was 2.07 +/- 0.35 mm. In all 8 cases of computer-aided microscopic surgery, no complications occurred. Clinical inaccuracy was 2 to 3 mm. Integration of a low-cost, non-laser autofocus microscope into our computer-aided surgery system was successfully performed and offers surgeons the ability to combine the precise optics of the operating microscope with the localization power of a computer-aided system.