To better understand the mechanism of ejecting spray droplet and raindrop, a high-speed image analysis for droplet characterization technique was proposed in this study. In our design, three basic units containing a high-speed CCD camera, a light source, and automatic image acquisition and data processing unit, are integrated to assess the droplet motion. Next, a set of multistage image processing algorithms, the droplet detection and droplet tracking, were developed and conducted to analyze the droplet trajectories of the grabbed frames. By controlling a very short exposure time, the droplet size and velocity can be obtained to generate the droplet size distribution (DSD). To examine our proposed approaches, a commercially available spray nozzle and raindrop are used to evaluate the effectiveness. Meanwhile, the pair-matching rate is also involved to validate the recognition rate of the droplet tracking algorithm. Using this proposed framework, it can be used to provide valuable data to assess the spray droplet or the precipitation status by their droplet size to droplet velocity.
The white-light scanning interferometer (WLSI) and confocal microscope (CM) are the two major optical inspection
systems for measuring three-dimensional (3D) surface profile (SP) of micro specimens. Nevertheless, in practical
applications, WLSI is more suitable for measuring smooth and low-slope surfaces. On the other hand, CM is more suitable
for measuring uneven-reflective and low-reflective surfaces. As for aspect of surface profiles to be measured, the
characteristics of WLSI and CM are also different. WLSI is generally used in semiconductor industry while CM is more
popular in printed circuit board industry. In this paper, a self-assembled multi-function optical system was integrated to
perform Linnik white-light scanning interferometer (Linnik WLSI) and CM. A connecting part composed of tubes, lenses
and interferometer was used to conjunct finite and infinite optical systems for Linnik WLSI and CM in the self-assembled
optical system. By adopting the flexibility of tubes and lenses, switching to perform two different optical measurements
can be easily achieved. Furthermore, based on the shape from focus method with energy of Laplacian filter, the CM was
developed to enhance the on focal information of each pixel so that the CM can provide all-in-focus image for performing
the 3D SP measurement and analysis simultaneously. As for Linnik WLSI, eleven-step phase shifting algorithm was used
to analyze vertical scanning signals and determine the 3D SP.
In general, the manufacture of contact lenses is conventionally labor intensive, requiring manual handling and inspection of the cast lens during production. This paper is to build an AOI (automatic optical inspection) system, which include suitable light source, camera and image processing algorithms, for contact lenses defect inspection. The mainly defect type are missing lens and surface defect on the contact lenses. An illumination system with fixed focal lens and charge coupled device (CCD) is used to capture the images of contact lenses. After images are captured, an algorithm is employed to check if there are flaws showed on the images. Five kinds of defect can be detected by the designed algorithm. A prototype of the AOI system for contact lenses inspection is implemented. The experimental result shows that the proposed system is robust for in-line inspection.
A novel concept of confocal sensor based on focal lens is proposed to measure the displacement. The light source is a stabilized fiber coupled LED. A 1x2 graded-index multimode fiber optic coupler is used in this sensor. One port is a LED input port via SMA connector, another port is a LED output port connected to a reflective collimator and the other port is a reflective sensor port connected to a photo detector. The focusing sensor head is the cascade of a focal lens and a 20X objective lens. In this confocal displacement sensor, LED passes through a focal lens and an objective lens so that the LED beam focuses at a fixed focal point. A test target is placed after the objective lens. The displacement between the sensor head and a target can be measured quickly by detecting the reflective power according to the confocal principle. The long-term stability of LED is under 0.5%. The effective back focal length is varied from 5.67mm to 6.57mm by 0-290mA current driving so that the measuring range is about 0.9mm. The FWHM resolution of displacement is about 50μm. This sensor has the features of low cost, high stability, high precision and compact.
This paper presents a high resolution optical surveillance system which integrated an omni-directional imager as an event finder/ system trigger. The omni-directional optics, a fish-eye camera in this study, provides a wider field of view (FOV) which can monitor widely range continuously without scanning mechanism but offers sufficient information which includes sign of field event and direction and then drive high resolution surveillance camera for detail imaging. To archive an optical triggering surveillance system, the scale-invariant feature transform (SIFT) is implemented to detect features both from images taken by omni-directional imager and the high resolution surveillance camera. Considering the FOV of high resolution surveillance system is narrow, to ensure the pointing of high resolution surveillance system, feature matching is also implemented in this system to identify the images obtained by high resolution surveillance system are identical to the existing omni-directional image obtained from fish-eye camera. This provides a robust and accurate solution to the problem of optical radar surveillance system localization in unknown environments. An experiment is performed on outdoor image sequences with demonstrating the efficiency of our algorithm.
The digital image correlation (DIC) method has been well recognized as a simple, accurate and efficient method for
mechanical behavior evaluation. However, very few researches have concentrated on the relationship between the
characteristics of the camera lens and the measurement error of the DIC method. The modulation transfer function (MTF)
has commonly used for evaluation of the resolution capability of camera lens. In practice, when the DIC method is
used, it is possible that the captured images become too blur to analyze when the object is out of the focus of the camera
lens or the object deviates from the line-of-view of the camera. In this paper, the traditional MTF calibration specimen
was replaced by a pre-arranged speckle pattern on the specimen. For DIC images grabbed from several selected locations
both approaching and departing from the focus of the camera lens, corresponding MTF curves were obtained from the
pre-arranged speckle pattern. The displacement measurement errors of the DIC method were then estimated by those
obtained MTF curves.
In this paper, a multi-camera DIC system with semi-circular configuration which can capture images from three different view angles at the same time is introduced. The multi-camera DIC system associated calibration method is proposed, the internal- and external- parameters of all system’s cameras by utilizing a planar plate with circular marks on it. A cracked cylindrical were reconstructed with images obtained by the proposed three-camera systems, with the help of digital image correlation method is also demonstrated and discussed.
In this paper, the digital caustic technique was used to determine the transient thermal stress intensity factors (SIFs) of edge-cracked semi-infinite plates subjected to a sudden temperature change on the plate edge. Effects of different crack lengths and orientations on SIFs were studied. By using the self-developed image processing software on a locally supported digital caustic system, caustic patterns were analyzed and SIFs were then obtained. The correlation expressions between the variations of transient thermal SIFs with the time, temperature difference and geometrical parameters of the cracks were obtained by a regression procedure.