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Displacement Measurement Using Optical Measurement Techniques

Displacement measurement is a normal and very important part of today’s manufacturing world. Whether it is for Automotive, Aerospace, Civil or Sport, the need to understand how components move and displace during use and over time is critical.

Scenario 1; A car sits in a wind tunnel. The manufacturer is trying to track the displacement of the door during standard road condition. The setup for this test has taken many days/weeks of figuring out where to add clearance holes in order to attach sensors from the inside of the door skin. Also, holes have been added to the window frame, so dial gauges can be attached to track the displacement of the window line. Obviously, these sensors cannot be attached to the outside, as they would directly affect the result and most likely not survive the wind tunnel. During the test, an operator sits in the vehicle, to monitor the gauges at each wind and yaw condition to make sure the vehicle has “normalized” from the previous wind condition. Taking all of these factors in to consideration, all of this setup is so that the manufacturer can get only a single linear displacement. This must be redone, by a skilled professional, in order to achieve other coordinate displacements.

Scenario 2; A car sits in a wind tunnel. The manufacturer is trying to track the displacement of the door during standard road condition. The setup for this test has taken 15 minutes in order to place high precision sticker targets at all points of interest. A pair of cameras sits just outside the slip stream and calibrated to measure the entire door. Calibration takes another 15 minutes and the vehicle is put through the entire sequence. Dynamic images are taken at every wind condition and recorded. The data is processed and results show displacements in every vector and 6 Degrees of Freedom for all of the sticker targets placed on the door. Any displacement measurement point can be selected and reported onto a graph. They can be shown over time or load automatically. The test does not need to be repeated, as you have attained all needed data.
Displacement Measurement using Optical Measurement

(Fig. 1) – Picture of all data points attained from Optical Measuring

Displacement Measurement  With Optical Measurement 1
(Fig. 2) – Report of all displacements created from Optical Measuring

Standard practice shows us that Scenario 1 is how most current displacement measurement testing is conducted. Scenario 2 is a nice example of how the use of Optical measurement techniques can greatly increase displacement data and product knowledge. The time saved can now be used to make more effective decisions on how to move projects forward.

Now imagine performing a thermal test on a component for another vehicle. The interest here is to find out how this particular component displaces during hot or cold environmental changes. This is very important to the consumer and the manufacturer, as neither want it to fail prematurely. To put it simply, this test should be a before and after static test. Using Static Optical Measuring techniques, temperature stable sticker targets can be placed in all points of interest. Then imaged completely around the entire piece, the component can be placed into the thermal chamber and taken to the desired temperature. Once completed, the component can then be re-imaged and compared to the original or reference project. The results will show that all displacements, in every vector have been attained. They can be graphed and reported on automatically. The need to attach hard wiring and specialized gauging is no longer needed.

Dynamic Optical Displacement Measurement Techniques have shown to be a great benefit for many different applications. A random pattern of dots applied to any object can be tracked. The pattern can be made up of regular black and white paint, ink stamp, etc. The software computes the images and the random pattern becomes thousands of gauges that track displacements and strains.

On a tire dynamometer, manufacturers attain many important measurements. The preparation of the tire can be long a tedious. The wiring and the application of these sensors causes long down times and delays in data acquisition. By using dynamic optical measurement techniques, a random pattern is placed onto the entire tire and wheel. Cameras are placed in front of the test cell and images recorded. The software produces a polygonized mesh of thousands of measurement points. These points show complete displacements of the entire tire and wheel during the loading sequence. The results are quickly recorded and give any manufacturer a complete knowledge of the tire and wheel under a specified loading sequence. The knowledge is crucial for manufacturers to further understand their products before they get into the market.

Displacement Measurement With Optical Measurements
(Fig. 3) – Report of Tire and Wheel on a Dynamometer


Displacement Measurement With Optical Measurements 4
(Fig. 4) – Baseball Bat Test

The examples above have been from the automotive side of testing. Optical displacement measurement techniques can be used in all forms of industry. In Aerospace, this technology can be used for wing bending/loading, pressurizing airplane bodies, wind tunnel testing etc. Civil engineering applications are also benefiting from these methods. Optical displacement measurement techniques allow the ability to monitor bridges and buildings over long periods of time. Sporting Good Companies are able to use Optical measuring to better understand the behavior of their products in the field. Baseball bats are being monitored to see how they displace during game conditions. Shoes are also being tested to see how the rubber is displacing while running and walking. Regardless of the application or industry, using optical measuring techniques for displacement measurements will prove to be a more efficient method.

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Trilion Quality Systems

500 Davis Drive, Suite 200
Plymouth Meeting, PA 19462
Phone: 215-710-3000
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