High speed vision system inspects medical devices

2019/05/14

A high-speed vision system uses five cameras and a variety of lighting techniques to inspect medical device wells for defects

In the past, the process of checking trays of plastic wells used in microwell plates was carried out manually by operators who removed trays from a conveyor belt on a production line to visually inspect them. However, the subjective nature of the operation meant that the process was prone to human error.

Micro Well
Micro Well

So when a UK medical manufacturer decided to automate the inspection of its plastic medical device products, it turned to engineers at Industrial Vision Systems to build an automated special purpose vision machine specifically for the purpose, including full validation to GAMP5 (Good Automated Manufacturing Practice) pharmaceutical regulations.

Machine vision
Machine vision

Microwell plates typically have ninety-six white plastic wells arranged in rows that are used as small test tubes in laboratories to analyze cell cultures. During a multi-stage production process, the wells are coated with active chemical compounds. In use, these compounds bind to specific targets when serum or plasma is deposited in the wells. When they do, they cause color changes that can be detected by medical instruments to test for the presence of disease.

Ensuring the consistency of the color of the coated white plastic wells is important to ensure that when they are used in the field, the color change detected by the medical instrumentation provides a reliable indication of the chemical changes taking place in the sample.

The issue is compounded by the fact that chemicals used in the coating process are themselves colored. Although the chemicals should be washed from the wells in the production process, if any remain, when serum or blood is tested for disease, the instrumentation could produce erroneous results. Aside from ensuring the consistency of the color of the wells, detecting any particulate matter that might remain in the well as a result of the production process is also vital to ensure the accuracy of such tests.

Interior and exterior

In the design of the IVS system, four vision-based inspection stations are used to check the interior and exterior color of the wells, and ascertain whether any particulates are present. Once any wells that fail to meet the manufacturer’s specification are removed from the tray by the system, a final vision check is performed to ensure the reject process was successful

In operation, each individual tray of ninety-six wells is picked off an existing conveyor line by a custom pick and place unit that uses a combination of pneumatics and an Allen Bradley linear axes drive. At a rate of one every three seconds, the unit places them onto a servo-controlled walking beam system that employs multiple grippers which engage the trays from either side and indexes them sequentially through the vision inspection, well removal and tray removal stations.

Prior to the first inspection, a data matrix scanner reads a data matrix code on the outside of the plastic tray containing the wells and transfers the data over an Ethernet interface to the PLC. In this way, each tray can be tracked through the process, so that if any faulty wells, or faulty trays of wells, are identified by the vision system, they can be removed from the line at a later stage. In addition, all data and results are transferred to the customer’s master database.

Gray levels

At the first vision inspection station, the coated, plastic wells are inspected to verify that their whiteness falls within a given specification. To do so, the station employs a monochrome line scan camera. This camera is mounted inside a stainless steel shroud to shield it from ambient light.

As the shroud containing the camera transverses the top of the tray of wells under servo control, the bottom of the tray is illuminated by a high intensity light which moves in synchronization with the camera.

The gray scale check is one of the key functions performed by the vision system. The monochrome line scan camera chosen for the task enables high resolution images to be captured and processed in an acceptable one second time frame, while the single wavelength red line light provides consistent lighting across all of the wells.

An image captured by the line scan camera from above a tray of wells is transferred over a Camera Link interface to one of three Industrial PCs in the system where the image is processed using IVS software.

The software then consecutively computes the gray scale intensity of the areas in the image bounded by the circular edge of the wells. More specifically, it calculates the maximum and minimum gray scale intensity, the average and the standard deviation from the average.

Having done so, the gray scale intensities are compared to a template of acceptable gray scale values. This template is created during system set up by teaching the system what range of gray scale values are unacceptable by capturing images of failed parts. Should one or more of the wells fail the inspection, the location of the well within the tray is transferred over an Industrial Ethernet/IP network to the PLC which logs the details.

Vision system camera
Vision system camera

You can watch the video below for more information:

Source : industrialvision.co.uk

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