Contact Image Sensors

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Stemmer Imaging has added Contact Image Sensors (CIS) to its product portfolio, which offer an alternative approach to conventional line scan cameras for industrial web applications, such as the inspection of paper, textiles, glass or plastics. The technology offers significant advantages in terms of space requirements, ease of alignment, and resolution. With line rates up to 100kHz, scanning widths up to 4 metres, very high resolutions and integral light sources, the CIS can be a very cost-effective choice in certain applications.

The CIS head consists of a lens array using graded rod lenses, with each individual lens capturing an image of a very small section of the target object. There are a wide range of resolution options available, from 25dpi up to 3,600dpi with pixels sizes of 1mm down to 7µm. A clear, sharp image is produced along the narrow line of the sensor head, which is made up of silicon photodiodes using either CCD or CMOS technology. 

Contact image sensors benefit from a flat construction, so that they fit into narrow spaces. They come as a system complete with optics, illumination and encoder logic and can be joined together to suit the resolution and width of the web with no reduction of line rate as the width increases. This provides a consistent viewing angle, sharpness and brightness across the width.

Integral LED line lights are pulsed to offer long operating lifetimes and maximise image quality. Built-in timer control includes encoder inputs for triggering and light control and is configured via RS232 or Ethernet. Signal processing allows for high data rates independent of the scanning width. Interface to the image processing system is via industry standard Camera Link or Gigabit Ethernet.

Contact image sensors operate with a fixed working distance (typically around 10mm) and a depth of field of around 2-3mm so are best suited for inspecting very flat objects where there is no vertical movement of the object at the point of inspection. Conventional line scan cameras, however, remain the preferred option for many applications, so it is important to get independent advice to make the best choice. In addition to a range of CIS, Stemmer Imaging also offers cameras from leaders in line scan technology and so can provide clear, independent advice as to what is the best solution for any particular web inspection application.

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