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Original Authors: Paul Attwell, Circuit Check Inc
Edited by Cyth Systems
The Challenge
Developing a clean room-compatible automated test system for industrial inkjet printing that adds more measurement detail and increases reliability, whilst achieving higher throughput.
The Solution
Using the PXI platform, LabVIEW software, and TestStand software as a test executive to create a parallel test system that is modular, flexible, and capable of simultaneously testing six print heads.
A client asked NI Gold Alliance Partner Circuit Check Inc to design a solution to parallel test industrial inkjet print heads in dramatically less time. As an added challenge, the tester needed to be compliant with a class 10,000 clean room on the production floor. The test system also needed a high level of flexibility to deliver testing capabilities for future products.
Left: PXI Within the Test System Contacts the PXI-2594 and PXI-2593 switch cards and the NI PXIe-5160 oscilloscope, Right: Report View, Bond Data Across a Print Head.
The Platform and Instrumentation
We designed a unit and built it into a 19 in. cabinet. We also built a custom fixture to fit six print heads simultaneously and provide the connection interface to the PXI modules. We built the core of the system on the PXI platform with an NI PXIe-5160 2-channel, 2.5 GS/s oscilloscope in an NI PXIe-1062Q chassis. We connected a PC running LabVIEW software and TestStand software to the chassis through MXI link. The PXI system also contains a number of high-speed switching cards to deliver the required channel count to the print head test fixture.
The modular approach of PXI means we can adapt the system if the test requirements change. This helped satisfy the customer’s desire for a flexible test system capable of meeting future requirements.
The print heads were driven with a special digital pattern. We developed a custom state machine to control the print head driven by an Ethernet interface. This was a crucial component in making a fast solution. We could deliver test patterns in milliseconds instead of seconds, leading to spectacular reductions in test time.
LabVIEW was the perfect choice for the heavy lifting of the analysis this because of its easy to understand graphical design method and build in multi-threaded support.
Using TestStand and LabVIEW
We chose TestStand as the test executive because it delivered a comprehensive framework beyond that of a simple test sequencer. Key features within TestStand include:
A test sequencer provides control of the test execution order (with loop s and branches)
Parallel execution makes it possible to execute a single sequence concurrently for each print head using the batch process model
A custom user interface shows the test execution in real time and reports the status of the test (for example, pass or fail)
An administrative structure delivers operator traceability with server login and access
Database connectivity manages test limits and results storage
We implemented individual tests with LabVIEW VIs that used the PXI digitiser and a programmable power supply to take voltage and current readings. TestStand brought these individual tests together into a sequence to meet the test specification. This structure inherently encouraged code reuse and a disciplined approach to test specification implementation.
Due to the complexity of the test system, we used a simple LabVIEW user interface for TestStand, which eased system use for the operator. We expended considerable effort to ensure that hardware errors caused by the device under test were recovered gracefully and fully logged to file. TestStand delivered the ideal framework for a solid foundation whilst maintaining the flexibility to customise the environment when necessary. For this application, we customised the recovery, user interfaces, and custom steps, as well as elements of the data handling to meet the specific user requirements.
Conclusion—The Deployed System
The tester could test parts from two stages of the process, automatically detecting the state of the device under test and changing the sequence, thanks to the flexibility of the PXI cards used in the system. The tests generate better quality measurements than before, due to the use of the more accurate digitiser and better signal management. This means we can refine the tests in the future to give even more diagnostic information on faults. The fixturing is more accessible for support staff, leading to faster turnaround for preventative maintenance. The system is free-standing and easily moved, which suits a dynamic customer that relocates often.
The primary objective of this test system was to reduce test times. The new tester reduced a 6–7 minute test to just over 1 minute, and more speed improvements are possible with the 64-bit upgrade now available in TestStand. This is a revolution to the manufacturing process, setting the standard for future testers.
Original Authors:
Paul Attwell, Circuit Check Inc
Edited by Cyth Systems