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Vision System Heats Up Needle-Electrode Inspection Process

Wed, 05/03/2006 - 6:04am
The Project: Create an alternative to the inspection protocols that rely on a human operator to verify the quality of electrosurgery electrodes.

The Solution: Develop a 100% automated inspection system, that maintains rapid throughput, to ensure consistent results.

By Curtis Weibel, FNP
To achieve zero defect rates and reduce the risk of liability and product recalls, a growing number of today’s medical device manufacturers are moving towards 100% automated inspection. With recent advances in both machine vision and motion control technologies, device manufacturers can now perform the most critical quality inspections with a high degree of speed, accuracy, and repeatability.

An operator using the PointScan system and monitor.
Point Technologies Inc., a full-service medical device contract manufacturer, is a case in point. The company has recently integrated Cognex machine vision with motion control into a customized and fully automated needle-electrode inspection system that it calls PointScan.

The system dramatically reduces inspection time and improves yield by replacing a labor-intensive, manual inspection process in which operators examined individual electrodes using video comparators. It also helps improve customer satisfaction. This, according to the company’s Chief Science Officer Curtis Weibel, was a key driver for shifting to automation.

“Whether it’s a plastic surgeon or a neurosurgeon,” Weibel explains, “our customers have one thing in common: they all want 100% inspection. And, they want supplier data that documents the fact that their electrodes were manufactured within specification. None of this was possible with manual inspection, so we knew that in order to take our business to the next level, we had to automate.”
Electrodes That Measure Up
Electrosurgery electrodes are used to cut tissue and cauterize bleeding vessels in a wide range of procedures, ranging from facial plastic surgery to laparoscopy. The electrodes, which are typically inserted into hand pieces (called pencils), cut into skin tissue with a spark that is produced by the electrosurgery electrode tip.


Illustration of tip profile definition (0.015, 0.03, and 0.05 in. from tip)
One of the main challenges in manufacturing electrosurgery electrodes is making the tips small and fine enough so there is minimal impact on the skin and good electrical focus at the tip. This gives surgeons better tactical control of the needle and allows them to use lower wattages to produce a spark. This, in turn, decreases thermal damage and improves blood flow for faster healing, decreased pain, and less scarring.

To produce electrodes that minimize the amount of heat spread down into tissue, Point Technologies uses tungsten, a material that is up to 2 1/2 times stronger than stainless steel. The use of tungsten also enables the formation of the sharpest needle tips, which contributes to optimal current density during procedures.

“Needle tip diameters typically range from sub-micro to 100 microns, depending on type of electrode and the requirements of the surgical procedure,” explains Weibel. “Improper tip sizes require the surgeon to increase power levels, which decreases the feel and tactical control. This can lead to skin drag, smoke production, and slower cutting speeds.”

Point Technologies manufactures most of the tungsten electrosurgery electrodes used in the world today and produces more than 20 different types of electrodes, including both bent and straight-tip models. To ensure that each electrode measures up to the stringent requirements of its customers, a number of critical dimensional measurements need to be performed. This includes gauging the diameter of the tips to ensure they are isolinear or parabolic (depending on the specification), measuring taper angle and length, overall length, bend radius, and many other variables.
Automating the Process
In 2003, Point Technologies began its quest for an automated needle inspection system. The design team approached the project with a number of key requirements in mind. The system would have to be fast enough to keep pace with higher throughput and higher yield requirements, improve measurement accuracy and repeatability, and make measurement data accessible to various plant personnel via a shared server. The new automated system would also need to be easy to learn and operate, and provide data graphing and statistical analysis capabilities for process control.

The PointScan
system
including
the Cognex
camera
 
To achieve the required throughput and measurement repeatability, engineers decided to incorporate machine vision technology after running some feasibility tests with an In-Sight vision sensor from Cognex. The vision sensor, which offered repeatability within 0.00002 in., offered a fast learning curve and was equipped with a complete set of dimensional gauging tools.In less than a week, engineers were able to easily set up inspection routines with In-Sight using its unique vision spreadsheet development environment.

While the In-Sight made vision feasibility testing fast and efficient, the design team ultimately chose to design a Cognex VisionPro vision system into the new needle inspection system. VisionPro incorporates a Cognex MVS-8100D Series digital frame grabber, a high-resolution (1280 x 1024) Cognex CDC-200 digital camera with high-magnification telecentric lens to eliminate optical noise, and a 2 x 2 in. diffuse LED backlight for proper image formation.

As a PC-based system, VisionPro offered greater accuracy, speed, and repeatability, and would integrate more seamlessly with motion control equipment. The system did, however, require some programming, which in turn necessitated two weeks of in-house training from a Cognex Certified Vision Integrator. Additionally, a few challenges arose during the vision integration process.

First, any machine vibration could cause inspection failures due to the small size of the electrodes and high magnification of the vision system’s optics. To solve this problem, the inspection system was outfitted with vibration dampers.

Another issue dealt with the lengths of the electrodes. Based on the required camera-to-subject distance, the electrodes were too long to be fully inspected in a single frame. This, in turn, meant that additional vision programming was necessary in order to provide a single inspection result from multiple images.
100% Inspection
Electrodes are inspected immediately after a proprietary tapering process called electro-chemical pointing. Fixtures of tapered electrodes are cleaned, dried, and then loaded into the PointScan system. To activate the system, an operator simply selects their name from a pull-down menu on a touch screen and presses “Go.”

The fixture of electrodes is automatically indexed into the inspection zone, where the vision camera is positioned overhead. An automatic focus routine, designed for optimized measurement accuracy, is performed which puts a subject electrode in clear view. The vision system then captures an image of the needle and performs the sequence of dimensional measurements.

Once an electrode is inspected, the camera shifts to the next electrode and performs the same routine. Dimensional measurements of each electrode are plotted on the screen, allowing operators to compare results with specifications. This data is also stored on a database that allows the Quality Assurance Department to collate and provide complete and accurate data to the customer, saving them time and money from additional inspection routines at their facility with less accurate equipment.

“With PointScan, we can perform 100% inspection on a fixture of electrosurgery electrodes in three to five minutes,” said Weibel.Once an entire fixture of electrodes has been inspected, PointScan unloads the fixture and the operator retrieves the parts. Rejected electrodes are identified on the screen and can be disposed of appropriately.

Accepted electrodes are removed, and a corresponding label for each is printed, documenting the inspections for archival purposes. An inspection report is also generated at the QA operation that compares measurement data for each inspected part to customer specifications.

“This report is of great value to customers,” Weibel states. “It can help them better model their own processes, and gives them great assurance about product quality without having to perform their own internal inspections. At the same time, the documentation helps pinpoint inefficiencies in our production process and reduces the amount of time we need to spend on quality assurance.”
Conclusion
By automating the electrosurgery electrode inspection process with machine vision, Point Technologies’ designers have been able to reduce inspection time ten-fold. Fixtures of electrodes can now be inspected in minutes instead of hours and, since the inspection and analysis is done entirely within a PC, operators no longer have to manually record measurements, but can easily interpret data, pinpoint errors, and print out control charts and data graphs.

Perhaps most importantly, PointScan helps ensure that every electrode sent to a customer is correct “We’ve increased our competitiveness by eliminating electrode rejections from our customers; returns can cost up to ten times the original product costs,” said Weibel.

He adds, “By making sure things are correct the first time, we’ve been able to increase customer confidence in our products which leads to a significant amount of repeat business.”
Online
For additional information on the products and technologies discussed in this article, see Medical Design Technology online at www.mdtmag.com and the following websites:Curtis Weibel, FNP is director of medical applications for Point Technologies Inc., the medical device contract manufacturing division of Angiotech Pharmaceuticals Inc, 6859 N. Foothills Hwy., Boulder, CO 80302. He is responsible for working in support of the sales force to answer customer and sales force questions regarding medical uses and applications of Point Technologies’ products and services. Weibel is a nurse practitioner, formerly in private family practice for 10 years. He has worked with Point Technologies, first as its chief science officer, since 2000. He can be reached at 303-415-9865 or curtis@pointtech.com.
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