Automotive – Accelerometers Vs ASDEC RoboVib

At ASDEC we are frequently asked “How accurate is it?”  This sounds a simple question, but it quickly becomes a complicated subject when you start looking into it.  Our first response is to ask a question of our own. “How do you define accuracy?” This is a subject we have touched upon in a previous blog post and newsletter.  Another way to begin to look at the subject of accuracy is to answer a slightly different question.  That is “How does it compare to more traditional techniques?” Engineers are very comfortable with structural dynamics and modal analysis results by taking measurements using accelerometers.  Therefore, we set our technical team the challenge of comparing results acquired by the ASDEC RoboVib system with results acquired traditionally by accelerometers.

The plan was to undertake an industry standard modal analysis on a vehicle body-in-white multiple times.  Five measurements made traditionally with roving accelerometers and five measurements made using the full capability of the ASDEC RoboVib system.  We would then compare the results.

BIW (Body In White)

It is critical to the industry that there is transparency of results regardless of the measurement technique and location.  Peaks and troughs in workload mean that sometimes it is necessary to contract work out to third party organisations.  This is only beneficial to development cycles if the results returned from the third party are comparable to those taken in house.

Part of the process designed into this test was to ensure that we removed the vehicle body-in-white from the test laboratory between each individual test.  Each test therefore involved positioning the body-in-white into the laboratory area. Attaching all appropriate instrumentation.  Taking the measurements and then removing the body-in-white from the laboratory.  We repeated these steps eight times, five for each measurement technique.

Part of the process designed into this test was to ensure that we removed the vehicle body-in-white from the test laboratory between each individual test.  Each test therefore involved positioning the body-in-white into the laboratory area. Attaching all appropriate instrumentation.  Taking the measurements and then removing the body-in-white from the laboratory.  We repeated these steps ten times, five for each measurement technique.

What did we find in our results?

Well, simply put the two techniques proved extremely comparable. We analysed the measurements in all cases using Siemen’s LMS Test.Lab Polymax modal solving tool to obtain first and second torsion and first and second bend.  We solved for the first modes in each case and these are shown in the following chart. With the accelerometer data in blue and the Robovib data in red.  These graphs show the calculated Sum Modes for each run.

The following table shows the Standard Deviation for each of the first and second modes for each measurement technique.

It is clear that both techniques are highly comparable in terms of both the values of the results and the standard deviation amongst them. 

ASDEC’s customers can therefore have a high level of confidence that tests undertaken with the RoboVib facility will prove compatible with equivalent tests undertaken by other parties.

However, it is important to understand that whilst the RoboVib results compare exceptionally well with accelerometer data the time taken to obtain the results was considerably less with the RoboVib.  Once we have created the robot program, the testing process becomes a simple exercise of pressing “go” on the system. It does not matter how many times you wish to repeat the test. Our process removes the need for hands on engineer and technician effort to cable up and stick accelerometers repeatedly on the body-in-white.  The robot does the hard work, 24/7, whilst your engineers spend their time adding value developing the best in class next generation of vehicle.