MultiChannel

MultiChannel makes it possible to record an object, e.g. sheet material, with several lighting setups in just one run with a monochrome line scan camera. The lighting is synchronised with the camera exposure through time multiplexing. A total of eight lighting signals are available, which can be distributed to up to eight image channels as required. Each image channel can be freely configured up to the maximum speed of the camera. This means that each channel can work with an individual exposure time. In contrast to many other applications where the slowest clock determines the line frequency, MultiChannel allows the recording speed to be significantly optimised. MultiChannel technology is scalable and can therefore be extended to any inspection width. One frame grabber serves as the master and controls both the illumination and the image acquisition of all other frame grabbers (slaves).

The mixed image data stream from the camera is sorted in the frame grabber without CPU load so that the individual channels are placed next to each other in the transmitted image. Example: 3 channels in an 8k camera generate an image 24k wide (3 x 8k). As each pixel corresponds to the exact same pixel in the other channels, merging the data is very simple. This is the great advantage over conventional systems, where a camera is used for each illumination. Here, merging the image data is almost impossible due to the lack of a clear reference. MultiChannel has been developed and established for the CameraLink and CoaXPress interface and is compatible with all triggerable lighting (TTL/HTL).

Applications

Due to the high degree of flexibility (eight image channels and lighting signals each), there are countless areas of application for MultiChannel. Some common technologies are listed below, which can also be combined as required. Please contact us with your specific application and together we will find the optimum lighting constellation for you.

MultiAngle

One lighting technique is often not sufficient to capture different types of defects with high contrast. In glass inspection, for example, a dark field arrangement is required for scattering defects (scratches, bubbles), a direct reflection is needed for coating defects and transmitted light is required for material inclusions. With MultiChannel, these illumination techniques can be easily combined without one illumination being influenced by the others. Areas of application: Glass, steel, film

MultiSpectral

To differentiate between different materials, their spectral properties can often be analysed. If the necessary differences are to be reduced to a few wavelength bands for which triggerable LED illumination is available, MultiChannel is the optimal recording technology. Up to eight different wavelength bands can be analysed, whether in the visual, UV or SWIR range. The only important thing is that the camera used is sensitive in the spectrum under consideration. Areas of application: Material sorting (agricultural, plastics, recycling, …), semiconductors, UV/IR inspection

PhotometricStereo

Photometric Stereo (also known as Radiometric Stereo or Shape From Shading) is used to separate the shape of an object (surface normal, curvature) from its texture (albedo). At least three images of the same object taken with different and known lighting directions are required. In most applications, four lighting directions are used. MultiChannel enables the acquisition of these four images, to which the Photometric Stereo algorithm can then be applied in subsequent image processing (e.g. in Halcon, Cognex, CVB, Matrox, …) and thus curvature, texture and X/Y inclination can be calculated. As the algorithm is very computationally intensive, the incoming data volumes can often not be processed sufficiently quickly by the CPU for fast applications and/or the inspection of continuous materials. In this case, MSTVision offers the option of using the optional PhotometricStereo extension to MultiChannel to calculate curvature, texture and X/Y inclination directly in the FPGA. This also enables continuous web inspection with many line scan cameras at high bandwidth and low CPU load. Areas of application: steel, batteries, packaging, structured decorative films

MultiDelay

The completely flexible time behaviour opens up new application possibilities for line scan camera applications. For example, heat flow thermography can be realised in which a pulse is first sent to an IR source and the object is then examined with several exposures.

Areas of application: Delamination defects, layer thicknesses, welded joints

MultiIntensity

Materials with very different textures or structures often need to be inspected in both light and dark areas. For this purpose, a single light can be used with different exposure times to create an HDR (high dynamic range) image.

Areas of application: Semiconductors, printed circuit board inspection

System architecture

A programmable frame grabber from Basler AG (formerly SiliconSoftware) is a prerequisite for the use of MultiChannel. The MultiChannel technology is provided in the form of a hardware applet (*.hap) and can be installed on the frame grabber. A licence is required for use, which is linked to the serial number of the frame grabber. In the simplest case, the microDisplay(X) tool, which Basler provides within the frame grabber runtime installation, can be used for image acquisition. In addition, all MultiChannel parameters can be addressed directly here. However, as the configuration of MultiChannel is very complex, it is recommended to use the MultiChannel GUI software provided by MSTVision, at least for the initial parameterisation. For further details on microDisplay(X), please refer to the Basler documentation. In the application, image acquisition can be integrated into your own software (C, C++, C#, Python) via Basler’s Software Development Kit (SDK), or third-party interfaces (Halcon, Cognex, CVB, Matrox, …) can be used.

Configuration

With the MultiChannelGUI, even complex configurations can be realised quickly and easily. The clear and visual representation of all parameters and signals enables uncomplicated configuration in order to utilise the full flexibility of MultiChannel. For example, adjustable reference points for each lighting signal make it easy to make changes, as the signals are automatically shifted relative to their reference point.

The MultiChannelGUI can be run on any Windows PC. Only the saved configuration file must then be available on the target computer.
For further details, please refer to the MultiChannel documentation.

Motion compensation

Due to the constant relative movement between the object and the line scan camera, there is also an offset in the transport direction between the individual channels within an image line. Although the offset between the first and last channel is less than one pixel, this can have a negative effect on subsequent image processing. The effect is particularly visible with PhotometricStereo. To minimise this effect, MultiChannel offers the motion compensation function. The time behaviour of the individual image channels is continuously analysed for each line and the offset is compensated individually for each image channel. As an example, an extract of the curvature image of pharmaceutical packaging with printed text and Braille is shown on the right. Without motion compensation (top image), the offset between the input images means that both the Braille and the print can still be clearly recognised. When motion compensation is activated (bottom image), however, the print has almost disappeared and only the relevant topographical effects are visible.

Monitoring of the timing behaviour

In any inspection system, it can happen that a single line is lost. As this occurs extremely rarely, it is generally not noticeable in standard applications and has no influence on further image acquisition. With MultiChannel, however, the loss of a single line leads to a permanent change in the sequence of the image channels. By monitoring the timing behaviour, lost lines are detected and this undesirable behaviour (‘channel jump’) is prevented.

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