Machine Vision Improves Jet Engine Blade Measurement

To comply with internal safety regulations, a leading manufacturer of aircraft engines needed to measure the length of jet engine blades after every 7,000 hours of use. Constant exposure to centrifugal force and extreme heat causes blades to stretch, and if blade length exceeds tolerance, it could cause engine damage.

12/15/1999


To comply with internal safety regulations, a leading manufacturer of aircraft engines needed to measure the length of jet engine blades after every 7,000 hours of use. Constant exposure to centrifugal force and extreme heat causes blades to stretch, and if blade length exceeds tolerance, it could cause engine damage.

Determining blade "growth" is a traditionally manual process. Human inspectors center a blade under a microscope, measure distance from the root end of a blade to the center of a reference mark, and read the micrometer display. The results are then compared to a record of the blade's original size. Blade surfaces can become so severely degraded, however, that inspectors can't precisely identify the exact center of the reference mark and make an accurate measurement.

The company evaluated several noncontact photoelectric sensors and laser scanners for the job. However, these approaches weren't powerful enough. "Inconsistent metallic reflections and the round shape of the blade itself were problematic," says Mark Granahan, president of Avtex LLC (Avon, Conn.), a system integrator called in to help provide a solution. "We felt an advanced vision system would be better able to handle these degradations and make precise, repeatable measurements."

Mr. Granahan and his team put together a turnkey solution based on a Cognex (Natick, Mass.) Checkpoint machine vision system. The entire system, which Avtex calls the Gage-300B, is housed in an industrial enclosure and includes a Checkpoint 900 vision system, a Sony XC-75 CCD camera, a rugged industrial mounting fixture for the vision camera, a high-magnification lens and LED focused ring light, and an IBM Pentium PC with a 17-in. Sony monitor.

"Once a blade is placed under the vision camera," says Mr. Granahan, "the vision system acquires an image of the blade and uses robust pattern location software algorithms to precisely locate the center of its reference mark. Upon finding the true center, which happens in milliseconds, the system automatically gages the distance between the reference mark and root end of the blade. It then triggers a ball-peen marker via serial communications to inscribe the measurement on the blade's root end. If it has stretched within acceptable limits, it can be ground down and reused. Blades that have stretched beyond tolerance are discarded."

The system, according to Mr. Granahan, produces measurements that are 40 times more reliable than those made manually. "The Gage-300B measures blade length to an accuracy of

The display also features image graphics, giving operators instant visual feedback as to whether the blade was successfully measured. Operators know instantly when a blade has not been properly measured.

By producing measurements that are 40 times more reliable than those made manually, the Gage-300B has helped the manufacturer consistently comply with internal safety regulations. "It's more precise, easier to use, and more objective than older manual methods. It also eliminates the chance of error associated with performing the measurements manually," says Mr. Granahan.

Comments? Send e-mail to: mdrakulich@cahners.com

For more information about Cognex, visit www.controleng.com/freeinfo





No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Additive manufacturing advancements; Machine vision enhances robotics; Fieldbus evolution; Process safety; Advice from System Integrators of the Year; Road to IANA
Salary and career survey: Benchmarks and advice; Designing controls; Remote data collection, historians; Control valve advances; Hannover Messe; Control Engineering International
System integration: Best practices and technologies to help; Virtualization virtues; Cyber security advice; Motor system efficiency, savings; Product exclusives; Road to Hannover
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
PLCs, robots, and the quest for a single controller; how OEE is key to automation solutions.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Getting to the bottom of subsea repairs: Older pipelines need more attention, and operators need a repair strategy; OTC preview; Offshore production difficult - and crucial
Digital oilfields: Integrated HMI/SCADA systems enable smarter data acquisition; Real-world impact of simulation; Electric actuator technology prospers in production fields
click me