Contact Image Sensor Research Articles

Effect of hard and soft re-coater blade on porosity and processability of thin walls and overhangs in laser powder bed fusion additive manufacturing

AbstractSpreading powder into thin layers is a fundamental step in the laser powder bed fusion (PBF-LB) additive manufacturing process. This step is called re-coating and it is typically performed using either a hard, soft or brush-type re-coater blade or a rotating roller, depending on the machine brand and model. With such variety in powder spreading approaches, the question arises whether the used re-coater type has a significant effect on the quality of parts produced? In this study, an industrial contact image sensor integrated to the re-coater of a PBF-LB system was used for powder bed quality monitoring. Powder bed images at 21 µm/pixel resolution, 184 mm scanning width and 95 mm/s re-coating speed were acquired. With this, the effect of using either soft (rubber) or hard (steel) re-coater blade on the processability of challenging features such as thin walls and steep overhangs was studied. In addition, porosity and dimensional accuracy of parts produced using either the soft or hard blade was analyzed with X-ray computed tomography. It is shown that when building bulk material without any complex features, both the hard and soft re-coating blade results in extremely low porosity ≤ 0.001% without any issues in the processability. However, when thin walls and overhangs are produced, differences in processability, porosity and dimensional accuracy are observed as a function of re-coater blade and part orientation. This is an important factor in understanding all the significant sources contributing to the variability on quality of parts produced using different PBF-LB machines.

Continuous Contactless Measurement of Blood Volume Inside Venous Reservoirs for Cardiopulmonary Bypass

During a cardiopulmonary bypass (CPB) procedure using a heart-lung machine, the volume of blood inside the venous reservoir is a crucial piece of information for the perfusionist to make clinical decisions. In existing CPBs, venous reservoir blood volume can only be visually estimated by the perfusionists from the marks on the reservoirs. Such manual reading has poor resolution and it is unpractical to continuously track the blood volume over a long period. In this work, we introduce a blood volume sensor that can automatically measure and monitor the blood volume inside the venous reservoir in real time, with high accuracy and high resolution. Our sensor implements an optical scheme, in which the liquid level of blood is optically scanned by a contact image sensor comprised of a linear array of CMOS sensor pixels. The liquid level is then converted into blood volume. For a changing blood volume, the net flow rate into the reservoir is also instantly calculated from the recorded volumes. The demonstrated sensor prototype has been calibrated for a specific commercial reservoir and tested in a simulated CPB experiment using bovine blood. The results showed that the blood volume inside the reservoir and the flow rate can both be reliably monitored using our sensor. The reading can cover the entire operable range of venous blood volume (250 mL – 4000 mL), and the resolution has reached better than 2 mL. Our blood volume sensor shows great promise for improving the monitoring and management of patient blood volume during CPB procedures.

Weaving with a new warp yarn break detection system using contact linear image sensors instead of drop wires

A thin metal plate called a drop wire is placed on warp yarns during a weaving process in order to stop the loom in case of a broken warp yarn and to fix it. Drop wires are placed on each warp yarn to ensure the flow of warp yarns at a certain tension level and to stop the loom when a warp yarn is broken. In some cases, the drop wire may not fall due to dirtiness or abrasion of the drop wire and the weaving process continues with a broken warp yarn which is an unwanted situation. In this study, an alternative method to detect broken warp yarn is proposed based on contact image sensor. Therefore the need for drop wires is eliminated. The contact image sensor is not at full scale of the weaving machine, it can only acquire a linear image only a small portion of the total warp yarns, therefore a carrier module is implemented on the machine to carry the sensor and cover all the warp yarns. A complete image is then formed at the end of each cycle, and the total number of warp yarns is evaluated. If this value is less than the expected number of warp yarns, a broken warp yarn is detected, and the system generates an alarm. The system is implemented on an industrial scale weaving machine and the warp yarns are detected with 99% performance.

Determining the optical properties of solar cells using low cost scanners

This paper investigates the use of consumer flatbed scanners for the use of monitoring solar cell precursors. Two types of scanners are investigated a contact image scanner and scanners with more conventional optical setups. The contact image sensor is found to be more suitable as it does not require additional flat field calibration. The scanners’ ability to monitor variation in sample texture was investigated by monitoring the reflection of multi-crystalline and mono-crystalline textured wafers. For a baseline, a comparison was made to a high-end tool used in industry. Both good qualitative agreement and statistical correlation were achieved between the scanner and industry tool for the isotropic multi-crystalline wafers.

A Procedure to Integrate a CIS Sensor in an Additive Manufacturing Machine for In-Situ Digitizing of Deposited Material Layers

A notable constraint to the industrial application of additive manufacturing processes is the lack of geometric accuracy of the parts produced. In-situ inspection systems, therefore, need to be developed to detect and compensate for any geometric deviations that appear during the process. This article proposes a noncontact system for the digitization of deposited material layers, based on a contact image sensor extracted from a low-cost flatbed paper scanner. The viability of using this sensor for such a purpose was analyzed by integrating it in a tailor-made test bench with the dual capability of fused filament fabrication and digitizing of deposited layers. The integration procedure includes analysis of the sensor's operating principle, development of the hardware and control routines required for PC operation, and image processing. To validate the integration, two specimen parts were built and digitized in the test bench. The measurements performed on the captured images showed low discrepancies with respect to those obtained on a coordinate measuring machine.

Scanner model classification with characteristic brightness variations.

Analog documents and scanned digitized files are now considered equivalent in legal contexts, and the widespread supply of multi-functional printers has led to a surge in the use of scanned documents. With image editing tools, there has been more cases of forgery involving scanned files. This has highlighted the importance of integrity and authenticity verification of scanned documents submitted as court evidence. Extensive studies have been conducted on source scanner identification and detection of alteration in scanned documents. Past research usually relied on machine learning with Support Vector Machine (SVM) and Convolutional Neural Network (CNN), and was focused more on images rather than text documents. Brightness variations are produced depending on the repetitive arrangement and relative intensity of light sources, and such patterns can be clearly observed in scanned images by the Charged Coupled Device (CCD) type flatbed scanner. The separate image module of the Contact Image Sensor (CIS) also leads to characteristic brightness variations. To extract and enhance these brightness variations, image processing techniques such as separating color channel and adjusting gradation and contrast are applied. The proposed method was tested on five scanner models, and the results confirmed that each scanner had unique brightness variations. This study is the first to extract brightness variations as a unique characteristic of each scanner model and recognize the potential of brightness variations in source identification and manipulation detection. A major advantage is that brightness variations are physical, robust, and visible. The research will be expanded with multicolor documents, counterfeit documents, and text-independent detection.

Conoscopic Holography feasibility for form error in-situ monitoring in Additive Manufacturing

The lack of standardization and the low quality of parts produced by Additive Manufacturing requires in certain cases the use of in-situ monitoring techniques based on the use of different types of sensors, each of which has advantages and disadvantages depending on the type and nature of the signatures to be analyzed. Therefore, in this work the feasibility of Conoscopic Holography (CH) technology is analyzed for in-situ monitoring of form errors that take place during the creation of each layer in an AM process. The results obtained using this sensor are compared to those of a Coordinate Measuring Machine used as ground truth. The CH sensor is also compared to a Contact Image Sensor in terms of metrological performance, proving the former to be more suitable and versatile for monitoring this type of errors.

Contact Image Sensor integration in Fused Filament Fabrication machines for layer inspection

One of the limiting factors for industrial application of additive manufacturing (AM) is the lack of geometrical accuracy of manufactured parts. To improve precision, non-contact sensors should be integrated into AM machines, capable of performing in-situ inspection of the part and being able to detect and compensate for the actual geometrical errors. A non-contact digitizing system is proposed in this work for the inspection of the deposited material layers, based on a Contact Image Sensor (CIS) extracted from a commercial flatbed paper scanner. In order to integrate this sensor in an AM machine, a methodology was developed that includes the sensor operation analysis, the design of the necessary hardware and software to be externally controlled and the subsequent processing of the captured images. Results prove that the CIS sensor can be integrated in any device external to the original scanner.

Research on signal processing technology optimization of contact image sensor based on BP neural network algorithm

Research on signal processing technology optimization of contact image sensor based on BP neural network algorithm

Develop a high energy proton beam position monitor using linear contact image sensor

A compact beam-position monitor was constructed using a linear contact image sensor attached to a plastic scintillator and tested using a 230 MeV proton beam. The results indicate that the beam position can be obtained in real-time, and the beam position with a precision of up to 0.03 mm. The compactness and high precision of the device hold considerable potential for it to be used as a beam-position monitor and offline, daily quality assurance monitor in hadron therapy.•The method can provide a high precision and high resolution beam position for flash irradiation in particle therapy in real-time.•The method using contact image sensor with scintillator does not require a long focal length for camera and it is free of image distortion.•The method can be integrated into medical particle accelerator for feedback control and daily quality assurance.

A high-resolution and large field-of-view scanner for in-line characterization of powder bed defects during additive manufacturing

Powder bed defects are irregularities in the powder layer, which alter the energy input during the powder bed fusion process. As a result, they are directly responsible for the formation of flaws in the consolidated material, which cause quality and property variability in additive manufactured parts. Because of their small size and ubiquity across the powder bed, powder bed defects are difficult to detect and correct. In this work, we propose a new method to assess powder bed defects across the entire powder bed at the remarkable spatial resolution of ~5 μm. Our method relies on the integration of a contact image sensor taken from a flatbed document scanner to the powder re-coater module. Owing to the narrow depth-of-field of the sensor, we detect powder bed defects by identifying out-of-focus regions in the acquired scans using numerical image analysis techniques. Moreover, we show that we can assess the defects height (or depth) by quantifying the degree of “blurriness” in such regions. Our “powder bed scanner” is a rapid and cost-effective tool for in-line characterization of the powder bed quality. This technology may be instrumental to develop novel close loop strategies aimed at improving the consistency of additive manufactured parts.

Image reconstruction for color contact image sensor (CIS)

The color contact image sensor is often used to capture the surface of some materials for the defect detection in industry. However, the special imaging mode leads a special image pattern of the color contact image sensor. This pattern of the sensor can be used to increase the resolution of the image, while none of the algorithms is able to properly process it, recently. This paper presents an approach for the reconstruction of the color contact image sensor. We combine the sparse prior that often used in super-resolution and the inter-channel correlation prior that the majority of image demosaicing algorithms used to solve this problem. Extensive experiments on simulated image and the real image captured by color contact image sensor show that our method achieves good results in terms of both objective and human visual evaluations.

A Cardholder Identification System Based on Face and Double-sided ID Information

In this paper, a cardholder identification system based on identity card (ID) and camera video was proposed. Firstly, we realize the double-sided image acquisition of ID card using Acorn RISC Machine(ARM) and Field-Programmable Gate Array (FPGA) with two Contact Image Sensor (CIS) and read the face image from the ID's built-in chip through radio frequency technology, and simultaneously capture the cardholder's face from USB camera video. Then a matching algorithm was used to compare the three faces: the segmented face image from ID double-sided image, the face image stored in built-in ID chip and the cardholder's face image captured from the camera video. Finally, based on the matching results, we can identify the authenticity of the ID and judge whether the cardholder is holding his own ID. Another advantage of our system is that we can print the collected double-sided ID images rapidly without manual flip and alignment. Many functions are combined into this system.

Detecting Local Scour Using Contact Image Sensors

AbstractThe paper presents a novel contact image sensor (CIS) to monitor the local scour process around a model pile in water flows. The CIS is an optical sensor that tracks the evolution of the in...

Hand-Held Reader for Colorimetric Sensor Arrays.

An inexpensive hand-held device for analysis of colorimetric sensor arrays (CSAs) has been developed. The device makes use of a contact image sensor (CIS), technology commonly used in business card scanners, to rapidly collect low-noise colorimetric data for chemical sensing. The lack of moving parts and insensitivity to vibration allow for lower noise and improved scan rates compared to other digital imaging techniques (e.g., digital cameras, flatbed scanners); signal-to-noise ratios are a factor of 3-10 higher than currently used methods, and scan rates are up to 250 times faster without compromising sensitivity. The device is capable of real-time chemical analysis at scan rates up to 48 Hz.

A wide field-of-view scanning endoscope for whole anal canal imaging.

We report a novel wide field-of-view (FOV) scanning endoscope, the AnCam, which is based on contact image sensor (CIS) technology used in commercialized business card scanners. The AnCam can capture the whole image of the anal canal within 10 seconds with a resolution of 89 μm, a maximum FOV of 100 mm × 120 mm, and a depth-of-field (DOF) of 0.65 mm at 5.9 line pairs per mm (lp/mm). We demonstrate the performance of the AnCam by imaging the entire anal canal of pigs and tracking the dynamics of acetowhite testing. We believe the AnCam can potentially be a simple and convenient solution for screening of the anal canal for dysplasia and for surveillance in patients following treatment for anal cancer.

宽幅扫描仪色差一致性校正与边缘融合拼接

针对CIS (Contact Image Sensor)宽幅扫描仪多根CIS传感器之间存在的物理差异导致采集到图像存在色彩差异的问题，提出了一种基于多传感器像素映射的图像色差一致性校正算法。针对特殊的工程图纸存在底色干扰问题，提出了一种底色消除像素映射算法，以最大可能的保留图像内容和细节。由于多根CIS传感器安装位置存在交叉，导致直接采集到的图像边缘有像素重叠现象，需要对采集图像进行融合与拼接。本文提出了一种行匹配的窗口算法实现图像的融合拼接。测试结果表明，色差一致性校正算法、底色消除算法和图像边缘融合拼接算法能有效解决CIS宽幅扫描仪技术问题，具备良好的算法性能与图像处理效果。 A correction algorithm of chromatic aberration is proposed by mapping functions for different sensors, which have physical differences leading to chromatic aberration, when scanned by CIS. A new algorithm of pixel mapping function is proposed, which can eliminate the background noise of drawings and retain some important contents and details. An algorithm of matching line window is also proposed, which can solve the problem of image fusion and combination. It is called pixel overlap from two images due to intersecting location of sensors. The final test shows that the algorithm of chromatic aberration and the algorithm of pixel mapping function can solve the key problems by CIS effectively with good performance and image processing effects.

Identification of scanner models by comparison of scanned hologram images

A method to identify scanner models that had been used to forge low-level counterfeit currencies was proposed in this study. The method identified a scanner model by characterizing differences between hologram images that exist in low-level counterfeit currencies. Twenty scanners of 18 different models were used to make samples of hologram images used in this study. The method was divided into two steps: identification of capturing conditions and identification of the scanner model. The first proposed protocol used correlations of spatial distribution of brightness to identify capturing conditions. A second proposed protocol used correlations of color distributions to identify a scanner model. The effectiveness of the protocols was demonstrated with numerical methods and sample images.The preliminary study revealed that it is necessary to consider the orientation of the holograms when the scanner models were identified, but 180° rotations can be ignored. Moreover, it is necessary to consider position in the main scanning direction of the bed for charged-coupled-device scanners. The demonstration showed that the first protocol could correctly identify the capturing conditions of almost all hologram images. However, one image could not be identified correctly; the protocol could distinguish images captured by charged-coupled-device scanners and those captured by contact image sensor scanners if the hologram was placed on the right or left edge of the scanner bed, but could not distinguish them if the hologram was placed on the inside. The demonstration also showed that the second protocol could correctly identify scanner models of all hologram images.

用二次触发法改进接触式传感器线阵相机的曝光性能

As the frequency changing of external trigger signal from an external trigger Contact Image Sensor(CIS)camera will cause the nonuniform of a scanned image gray value,a new exposure method——two-trigger method was proposed.First,the reason that the frequency changing of external trigger signal affects the image gray value was analyzed.Then,the two-trigger method was introduced.With the method,an external trigger signal was converted to two trigger signals,the first one was used to control the exposure and the second one was used to control the CIS to output data.Finally,it explained that the method can improve the image quality theoretically.A 1.6meter non-distortion long-term array CIS camera was fabricated based on this method.The experimental results show that the fluctuation range of scanned image gray value is reduced by 75%,and the horizontal stripes on the image is eliminated at different trigger frequencies.When it is applied to an intelligent visionstitch digital printing machine,the image of 1mm×1mm hole in the embroidered cloth is clear.It concludes that the proposed method reduces the effect of the frequency changing of external trigger signal on images effectively and improves the image quality successfully.

A CIS-Based for Check-Scanning System

In this paper, we describe a sophisticated scanning system, which is based on an advanced Contact Image Sensor (CIS), used to scan the image and to verify the authenticity of the checks. The entire structure works on the FPGA platform, and the CIS is responsible for sampling the image information served as analog signal that is sent to A/D converter subsequently, aiming to convert analog signal to digital signal. It is important that those digital signal is sent to PC through Cypress non-destructively because those data need to be analyzed by a software on PC to acquire the useful information. This implementation not only clearly scans the image of checks, but it is high precision, simple design, and easy to carry.