Customer SolutionsScalable Integrated Vision Inspection System Using TestStand, IMAQ Vision, and LabVIEW
Author(s):David McAndrew, Mink Hollow Systems
Industry:Imaging Equipment
Product:LabVIEW, NI TestStand, PXI/CompactPCI, Vision
The Challenge:Increasing production throughput and quality by integrating a scalable optical inspection system with enterprise connectivity capable of database communication and statistical process control (SPC).
The Solution:Using TestStand test executive for out-of-the-box database connectivity and report generation for rapid test development, as well as LabVIEW and IMAQ Vision to yield advanced pattern-matching algorithms for efficient and robust inspection tests.Background Mink Hollow Systems, Inc., a National Instruments Alliance Program member and systems integrator, has more than 50 years of test automation experience. We have successfully deployed numerous automated test stations including complex enterprisebased, multithreaded, multi-units under test (UUT) parallel production testing, and bench top, low-volume testing. Focusing on vision, we have experience developing both inspection and measurement systems for quality control and process monitoring. Focused Approach to Test System Development We designed the vision inspection system to be a robust and scalable solution capable of adding new tests and new test stations with minimal programming. At the core, we used NI TestStand test management environment, which provides a focused approach to test system development by separating the individual test from common overhead functions. With TestStand, we used a process model to run all shared tasks, such as report generation, database connectivity, results recording, and UUT tracking, while a graphical user interface (GUI) serves as the interface to the operation. By separating the GUI and the process model, TestStand releases test developers from incorporating these common features in every test, freeing them to concentrate on developing the test itself. Because the process model functions independently and works with all tests, it can provide enormous savings in terms of development time and scalability. By modifying the process model, the process model can distribute a single test to multiple test stations or run in parallel on one station. Additionally, because TestStand reuses common functions, we can implement tests more consistently, improving efficiency. The GUI provides a common interface to use across all production stations reducing training costs and software maintenance. With a single GUI, operators do not need extensive retraining on multiple test stations. After you know how to run one test, you can run them all. Furthermore, using a single GUI removes the burden of maintaining multiple copies of station-specific interface software. Executing a Vision Inspection System To execute the vision inspection system, the GUI interacts with the TestStand engine to run test sequences with a particular process model and provides the operator feedback on the test station. The process model calls individual test sequences and dynamically tests specific parts based on part number. The process model we developed is a modification of the Sequential Model shipped with TestStand and takes care of database and SPC connectivity, as well as report generation for the test sequence. Although we can develop the tests in any language that handles ActiveX, we chose National Instruments LabVIEW, so that we could take advantage of the sophisticated image processing capabilities available in NI IMAQ Vision. A more detailed description of the inspection system from within the process model must begin with the optical character recognition (OCR) routine we used to start individual tests. When we introduce a new part into the camera field of view, the software immediately searches for a serial number. When found, the OCR translates the serial number into ASCII text used by the process model to query the database. If the serial number is found in the database, it displays information, such as part number and part description, and runs the corresponding unique test. Although the vision test system can handle any number of unique tests, it is currently configured to run two types of tests for four different parts. One test inspects a printed circuit board for integrated circuit (IC) and jumper placement. If the system does not find the IC or any of the three jumpers, the test fails. The second test examines a board for existence of a proper connection and a resistor. When the part test is complete, the test station generates a report, and it begins the OCR routine again, waiting until it recognizes a new serial number. One obvious advantage of the current implementation is that we could easily transition the current bench-top system to a fully automated production line system. We can also easily scale the system to handle any number of parts and tests. Because we store all the test and part number relationships, including test limits, in the database, we can associate any test with any part number simply by modifying the database. Moreover, we can assign unique sets of test limits to the same test sequence and load based on part number, which enhances re-usability of existing code. The system requires no software modifications to change the individual test or limits associated with a part, decreasing the logistical burden associated with testing in today’s competitive market. Easy to Integrate Hardware The vision system is PXI-based with a National Instruments IMAQ-1408 image acquisition board and an imbedded PXI-8156 controller with a 300 MHz processor running Microsoft Windows 98. We chose PXI because of its compact size, ease of integration, and hardware compatibility. A miniature 8-bit monochrome RS170 CCD camera with a 12 mm pinhole lens provides the image input. With the small size of the camera, we can generate an image, even in tight spaces. A substantial benefit to the PXI-based solution is that it can handle any industry-standard camera. A minor hardware change can quickly transform the system into a high-resolution black and white imager by simply upgrading the camera. Additionally, we can modify the monochrome RS170 camera and image acquisition board to handle color imaging with minimal software modification. Results – Rapid Test Development and Scalability We used our expertise in test automation and vision systems to produce a scalable optical inspection system for improved quality and increased production throughput. Implementing a TestStand solution helped us create a test station that uses a single GUI to run multiple, varying vision inspection tests on different parts, while communicating with company-wide databases and generating standardized reports.
For more information, contact: Todd Wilson Mink Hollow Systems, Inc. Tel: (301) 854-1579 Fax: (301) 854-9746 E-mail: twilson@minkhollowsystems.com, Web: minkhollowsystems.com
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