Micro-Electrode Visual Inspection System Utilizing Image Processing Tools

This system eliminates the need for manual inspections using microscopes.

A system was devised to aid in the inspection of micro-electrode assemblies utilized in clinical lab instruments to conduct impedance measurements on living cells in a 384 bottomless well casing with the electrode layer bonded to the housing, creating the closed-cell, real-time data acquisition instrument for assay tests.

Previous inspection was conducted manually utilizing microscopes. The drawback to this process is that it is extremely strenuous to the quality technicians since they are constantly using their human visual sensory ability and cognitive reasoning in making the pass/fail decision. Furthermore, OSHA regulations limit the activity of cognitive ergonomics exposure, which is concerned with mental processes such as perception, memory, reasoning, and motor response as they affect interactions among humans and other elements of a system. Relevant topics include mental workload, decision-making, skilled performance, human-computer interaction, human reliability, work stress, and training as they relate to human-system design.

The purpose of this automated vision inspection system is to inspect microelectrodes for opens on an electrode assembly layer (card) mounted on PET film. A separate system was devised to inspect the electrode cards for shorts across the interdigital Electrode (CTI Short Tester). The real-world measurement width of the fingers of the interdigital electrodes is only 100 μm. During various post-processing techniques of the electrode assembly, there is a large probability of damaging the vacuum vapor-deposited gold layer on PET film. False accepts cannot be tolerated since this would make the final test plate defective in the field measurement instrument. This design requirement drove all the hardware selection decisions and engineering sizing for the system.

The user application was created in Visual Basic (VB) 6.0. Besides the image acquisition and processing, VB also supports the host user interface and logic for the entire system integration (I/O and CNC robot). The CNC robot utilized is a standard, commercially available, 3-axis robot that locates the card to be inspected under the camera. A Z-axis is utilized to set the camera focus.

The vision portion was developed inside the Halcon Vision Application Development Environment (Halcon 8.0). The vision algorithm was then exported with a built-in software tool for use of the code inside the Visual Basic Software Development Environment (SDK). The system is easily reconfigurable for different workpieces that fit the inspection table.

irst, a matching algorithm is applied to locate the electrode in the field of view (FOV) of the inspection camera. Once a successful match has occurred, the Region of Interest (ROI) is determined with the electrode at its center. A region count is applied in the ROI to determine how many electrode elements are present. There should only be two electrodes present. If only one, or more than two, regions are detected, the system will prompt the operator for disposition of the electrode assembly (reject or continue). A second check is applied to verify that the electrode area is within a certain tolerance range utilizing a threshholding algorithm and area calculation. Electrode areas out of size specification would result in skewed field measurements once the electrode layer is used in the clinical instrument.

The inspection system is comprised of a robot to locate the workpiece under the camera, a work table with backlighting to illuminate the workpiece, optics to focus and magnify the inspection features, a monochrome imaging camera for image acquisition, imaging software to analyze the captured images, custom software for user interaction, and an industrial PC with user display and rack to house all the hardware interfaces for all the discrete systems.

This work was done by Conductive Technologies. For more information, visit http://info.hotims.com/28053-163.