SensoPart vision sensor recognizes bevel breaks on solar wafers

The SensoPart FA 46 vision solar sensor measures each wafer or each cell individually to recognize minimal bevel breaks with sub-pixel accuracy.

Content Dam Etc Medialib New Lib Vision Systems Design Online Articles 2010 08 59212


SensoPart Industriesensorik GmbH (Wieden, Germany) has expanded its program of vision sensors by adding an industry-specific solution for photovoltaics: The new vision solar sensor FA 46 is the only sensor in its price category available on the market that measures each individual cell and is consequently able to identify the smallest bevel inconsistencies. Thereby, it offers ideal conditions for its use in handling areas of wafer and cell manufacturing.

The vision solar sensor FA 46 examines cracks and defects of crystalline solar cells - it is simple, reliable and cost-effective. On account of its high precision, it closes the gap between PC-based image processing systems and simple contour-comparing vision sensors.

Silicon wafers are brittle and break easily - making it all the more important to prematurely recognize bevel breaks and blemishes during the manufacturing process, in order to avoid unnecessary costs due to machine stoppage during the subsequent processes. Currently break controls take place by use of classic, PC-based image processing systems. However, on the one hand the acquisition and installation of these are costly, and on the other they are simple contour-comparing vision sensors that do not always measure up to the demands of precision. The vision solar sensor FA 46 by SensoPart closes this gap: As a standardized industry solution based on the compact vision camera, it offers precise measurement technology at a low sensor price. Consequently, considerable cost advantages for quality assurance of solar cells become possible.

The acquisition of the vision solar sensor FA 46 is not only cost-effective, but in comparison with a PC-based image processing solution its installation is also substantially easier. All relevant functions for the wafer and cell inspection, ranging from the recognition of wafer geometry over the localization of defects and to the adjustment of processing speed and measurement accuracy, have already been previously configured. No knowledge of image processing is required for configuration. The user essentially only has to input the relevant inspection criteria, such as the tolerance for wafer size, position and rotation as well as the size and number of allowed damages to the contour of wafers. Then its application is ready for operation.

Automatic Recognition of the Wafer and Cell Form
The vision solar sensor FA 46 independently recognizes different wafer or cell forms (e.g. mono crystalline / with bevel and poly crystalline / without bevel). This makes a learning of contours or patterns unnecessary - only during its initial commissioning is the sensor used once for the dimensional stability inspection using a reference pattern. During operation the FA 46 measures each wafer or each solar cell individually, independently of rotation, and, thereby, achieves a high precision and dependability - e.g. it also recognizes bevel defects in case of parameter deviations of a wafer or a cell. Consequently, it fundamentally differs from all other solar sensors within the same price category as these only perform one contour comparison.

Before the evaluation each captured image undergoes a directory correction. The contour algorithm has been optimized for different handling variants so that incidental light and shining-through light inspections can be guaranteed to have the same level of precision. Solar cell contours, which are shadowed by the handling system, can be faded out in order to avoid false diagnoses. Furthermore, the FA 46 is equipped with an automatic position tracking, which allows the cell form to be recognized independently of the cell position in the handling system. The same is true for faded-out areas, which are also tracked depending on their position.

The vision solar sensor FA 46 measures each wafer or each cell individually and, therefore, recognizes even minimal bevel breaks. By analyzing sub-pixels the accuracy is increased even more.

The maximum resolution for recognizing bevel breaks is 2 x 2 pixels; the measurement as well as the determination of position and location of the cells can even take place with the precision of sub-pixels. Even severely damaged cells are correctly localized; in this case a customizing function examines whether the damaged wafer can possibly be further processed as a customization.

Autarchic, User-friendly Image Processing System
The vision solar sensor FA 46 is a complete image processing system, consisting of a camera in the compact sensor format (45 x 45 x 64) with an efficient digital signal processor, integrated infrared, red light or white light LEDs. Ethernet and serial RS422 interface as well as input and output sockets. All measurement and inspection data can be chosen to be delivered either by Ethernet or RS422. A PC is only necessary for the installation of the sensor; during operation the system is autarchic.

The installation of the sensor takes place with the assistance of the lucid configuration software "SensoConfig" and requires four navigation steps (job, position tracking, detectors, output). During these steps the respective relevant functions can be selected and adjusted. A context-sensitive online help service provides customer support should the user get lost or require background information for specific adjustments. In order to save critical functions from user errors, graded usage rights (administrator, maintenance) can be assigned.

The operation of SensoConfig is reserved for the administrator. Next to the adjustment capabilities, the configuration program offers extensive simulation functions "with the live sensor": With one mouse-click the user can switch between sensor operation and simulation, and the configuration of the sensor can also be performed offline by use of sample pictures, which have previously been recorded with the integrated record function. For users without administrator rights a monitoring module with limited operating capabilities ("SensoView") is available. It allows the display, monitoring and documentation of inspection results and inspection pictures as well as - after entering a maintenance password - the switching and uploading of parameters via the serial interfaces or digital inputs of the sensor. Opening saved parameters, when switching products e.g., can, therefore, be quickly and easily performed.

The software operation concept is identical for all vision sensors of the FA 46 series. Thereby, the deployment of further vision products by SensoPart, e.g. a code reader, is especially simple.

-- Posted by Vision Systems Design

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