Product category:
Vision and Colour Sensors
News Release from: Cognex UK | Subject: Arrow International
Edited by the Engineeringtalk Editorial
Team on 13 May 2002
Automated inspection ensures defect-free
products
A manufacturer of disposable catheters for critical and cardiac care has increased productivity and quality, and reduced labour costs, all using machine vision technology.
Anyone who winces at the thought of a catheter kinking during insertion or pulling apart on removal understands the necessity of test and inspection for catheter manufacturers Arrow International is a manufacturer of disposable catheters for critical and cardiac care that recently increased productivity and quality, and reduced labour costs, all using machine vision technology
This article was originally published on Engineeringtalk on 12 Mar 2001 at 8.00am (UK)
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A short time ago, the company automated assembly of its catheter sheaths and began using an In-Sight 2000 machine vision sensor from Cognex to ensure proper assembly.
The sensor consists of a compact industrial hardened processing unit, a 640 x 480 x 8bit progressive scan CCD camera, and a Nintendo-like handheld controller, as well as a library of vision software tools.
In-Sight automatically measures the distance between the end of a sheath body and a flex-straw-like piece of corrugated plastic extrusion that is insert-moulded to the body to ensure the gap is within tolerance.
"The inspection was necessary", explains Kevin Grover, a control systems project engineer for Arrow, "because if the gap were too big, the corrugated extrusion may kink, instead of bending at the corrugation as it is being inserted into the patient".
Grover integrated the vision sensor onto a custom-built machine that is designed for the ultrasonic welding of caps onto the bodies.
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To prevent a second mode of failure, the automated assembly machine has a pull-test station.
"The pull test checks the strength of the insert-moulded joint between the extruded catheter material and the moulded sheath body", Grover explains.
"If the joint is too weak, the assembly might pull apart when withdrawn from the patient".
During production, an operator puts a valve into a sheath body, caps it, then loads one sheath, valve and cap-assembly at a time into six separate transports on a rotary dial.
The rotary dial indexes the assembly to the ultrasonic welding station, which welds the cap to the body.
Next, the transport indexes to the pull-test station that checks the insert-moulded joint.
Once the caps have been welded to the devices and the assemblies pass the pull test, the parts are indexed on their respective transports in an upright position, one at a time, in front of the side-mounted In-Sight vision camera.
Red backlighting behind the device helps optimise contrast between the device and background to give the vision sensor the clearest possible view of the measurement area, according to Grover.
As a device enters the camera's field of view, an Allen-Bradley MicroLogix 1000 PLC that is linked to the sensor through I/0 triggers the camera to capture an image of the device.
"The image capture trigger is based on input from the indexer", says Grover.
Then the image is instantly transferred to the vision-processing unit for analysis with a variety of vision software tools.
After inspection, the transport drops the catheter device into a tube that shifts between good and bad bins based on pass or fail outputs from the vision-processing unit to the PLC.
"If we get three failures in a row", explains Grover, "a signal is sent from In-Sight to the PLC to stop the machine.
This way, an operator can go in and investigate the problem on the spot".
To set up the inspection, Grover used the In-Sight sensor's vision spreadsheet interface.
The process involved selecting vision tools, such as In-Sight's PatFind, and parameters from drop-down menus using the handheld control pad.
The vision spreadsheet then automatically generates tool results into worksheet cells, which are linked together to set up the measurement operation.
"To first find the pattern in the field of we used the PatFind tool, which determines the overall position of the device", says Grover.
"It remembers what that part looks like in any orientation".
To measure the gap, Grover used one of the In-Sight edge detection tools, which finds two points and calculates the distance between them.
During operation, the edge-detection tool finds the two edges, measures the distance between them, and outputs a value.
"We had to set the high and low reject limits", explains Grover.
" Anything between those two values passes".
A Cognex-supplied flat-panel LCD monitor that is mounted above the machine displays live images of each device being inspected and corresponding pass/fail data for the operator.
According to Grover, since the sensor has been installed, it has been inspecting approximately 6000 devices per eight-hour shift with a high degree of reliability.
"By adding inspection capability to our automated assembly process, we are able to ensure that all products leaving our facility are defect free.
This helps eliminate the possibility of failure in the field". Request a free brochure from Cognex UK ...
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