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Shock and Vibration Testing
Herbert Pötzl
May 11, 2016
Abstract
Simple mechanisms and procedures for shock and vibration testing
suitable for the AXIOM camera.
Contents
1 Mechanisms
1.1 Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 Shock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
2
2
2
2 Instrumentation
2.1 Measuring acceleration . . . . . . . . . . . . . . . . . . . . . .
2.2 Measuring the Effect on the DUT . . . . . . . . . . . . . . . .
2.3 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
3
3
3
3 Procedures
3.1 Short Burst Tests . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Long Term Testing . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Typical and Expected Stress . . . . . . . . . . . . . . . . . . .
4
4
4
4
1
1.1
Mechanisms
Vibration
A simple but efficient way to create various low frequency vibration scenarios
is by mounting the camera on a platform which itself rests on a number of
springs and is agitated by one or more eccentric rotating mass vibration
motors (ERMs).
Both, springs and ERMs are readily available and can be easily adjusted to
various scenarios providing a cost efficient solution for realistic testing.
High frequency low amplitude testing can be accomplished by utilising a
large speaker to agitate the platform.
1.2
Acceleration
A mechanism to apply acceleration forces to a device under test (DUT) can
be efficiently built by locking a platform mounted on a number of springs in
compressed state and then suddenly releasing the lock.
The lock can be a simple mechanical or a solenoid which is electrically released.
Note that continuous acceleration beyond the expected gravitational forces
is not to be expected in real world scenarios and thus does not need to be
tested in the lab.
1.3
Shock
In contrast to the typical acceleration scenarios, shock usually is caused when
the DUT in motion hits another object or a moving object hits the DUT
causing a shock wave propagating through the device..
An efficient mechanism to simulate this event is to extend the mechanism for
acceleration testing by limiting the movement at a specific point, for example
by blocking the way with a stopper.
2
2
2.1
Instrumentation
Measuring acceleration
Thanks to the advances in micro-electro-mechanical systems (MEMS) and
the fact that inertial measurement unit (IMUs) have become commodity over
the past decade, rather cheap and small devices are available to record 3D acceleration of the DUT in all of the described test mechanism scenarios.
2.2
Measuring the Effect on the DUT
Besides the obvious case where the DUT suddenly stops working a continuous
but easily verifiable test loop needs to be designed and implemented and the
resulting data recorded and evaluated.
Care needs to be taken to design the test loop in a way which resembles
normal operation to avoid testing unrealistic scenarios.
2.3
Calibration
Obviously all involved measurement devices need to be tested and calibrated
before they are attached to the DUT, otherwise the results would be inconclusive.
IMUs can be calibrated with the help of gravitation while the test loop typically will produce some kind of error rate which only needs to be specified.
3
3
3.1
Procedures
Short Burst Tests
Acceleration and shock testing typically makes a lot of sense when applied in
short bursts with detailed analysis about the effect on the DUT, varying the
strength or type of test as well as the DUT configuration to identify potential
problems within reasonable limits.
3.2
Long Term Testing
Exposure to long term vibrations of periodic or random nature can help
finding mechanical design flaws and characterise the durability of the camera
design, both mechanical and electrical.
3.3
Typical and Expected Stress
Recording data from existing cameras equipped with IMUs is an excellent
way to identify typical vibration, acceleration and shock scenarios which need
to be expected in the field and thus tested for.
As this information is only of statistical value, a reasonable safety margin
should be added to all testing, so that the typical stress will be well within
the tested scenarios.
Note that there are test conditions where the DUT is expected to survive, but
is allowed to stop working correctly and there are less extreme test conditions
where the DUT is expected to continue working without any problems.
4
References
[1] Kenneth G. McConnell and Paulo S. Varoto Vibration Testing: Theory
and Practice 2nd Edition
[2] Allan Piersol and Thomas Paez Harris’ Shock and Vibration Handbook
6th Edition
[3] Wayne Tustin Random Vibration & Shock Testing, Measurement, Analysis & Calibration
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