Machine Vision

 

Modern, high-performance seed is expected to be highly effective, with as few seeds as possible failing to germinate and with a very high level of purity. After the seed drying process is complete and the drying box is emptied, a few seeds may remain stuck to the inside of the box. If the box is used for a different species during the next drying cycle, these remaining seeds will decrease the level of purity. Inspection with a vision system ensures that even the smallest amount of remaining seed is detected.

Since filling plants are very loud and dusty, the whole process is observed from within control centers located as far away from the actual machinery as possible. In the past, these conditions lead to the use of analog cameras connected to frame grabbers with long coaxial cables. The use of long coaxial cables in industrial environments frequently resulted in image interference, and for standard camera systems, resolution was limited to PAL size (720 x 576 pixels).

The use of Gigabit Ethernet (GigE) cameras has eliminated these problems and has even opened new application possibilities. GigE cameras use shielded, twisted-pair (STP) cable and allow cable lengths of up to 100 meters. The use of STP cable, along with the packet based data transmission protocol of an Ethernet network, results in much higher noise resistance.

With a 1628 x 1236 pixel resolution and excellent image quality, Basler’s scA1600-14gc scout camera delivers large, high-contrast images that provide clear differentiation between the small seed grains and the metallic background of a seed box. This makes it possible to automate the entire inspection process by using smart machine vision algorithms.

Based on the new DirectShow source filter in Basler’s pylon driver package, a GigE camera can easily be used within DirectShow applications. Microsoft’s DirectShow technique provides some major advantages compared to other programming technologies. Since they are based on a modular architecture, DirectShow applications are highly flexible and easily expandable. Many modules for capturing, filtering, and rendering video streams are currently available in the marketplace. Easy integration of modules is provided by a graphically orientated programming method, where the data flow structure is designed by simply connecting different modules. This high level of abstraction eliminates the need to work with bits and bytes and guarantees a high degree of hardware independence. Because Direct Show is part of Microsoft’s Windows operating system, the CPU load required for handling video streams is low.

This DirectShow example graph visualizes a simple video data flow. The system includes three modules: pylon’s DirectShow source filter, the MontiVision YUV to RGB converter, and the Windows Video Renderer. The Basler source acquires images from the scout camera device, the MontiVision module in the middle converts the video format from YUV to RGB, and the Windows Video Renderer outputs the video stream to the graphics card for display.

A disadvantage of DirectShow is its complex API, which requires a steep learning curve. The MontiVision Development Kit (http://www.montivision.com/products) was designed to eliminate this difficulty by inserting a layer between the DirectShow API and a custom application. The kit provides a comprehensive collection of image and video processing modules, a visual development environment for the creation of custom configurations, and a selection of ActiveX Controls for easy integration into applications based on programming languages such as Visual Basic, C#, or C++.

The software for the seed box inspection system was written in C# using the MontiVision Development Kit. The software accesses the camera via the DirectShow Source Filter in Basler’s pylon driver package, provides a simple user interface, and displays a live video window. On the hardware side, a Basler scout camera is connected to a Windows XP computer through a Gigabit Ethernet adapter and a 20 meter CAT6 Ethernet cable. Using these components and techniques, a high degree of seed purity is achieved.

A finalized version of Basler’s pylon driver package, including the pylon DirectShow source filter, will be available in March 2007.