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Resistance of vibration and shock – Criteria of hardware components for mobile applications

In many application cases of automation and the robotization of mobile systems, various hardware components are exposed to unfavorable circumstances like high temperatures, water, dirt, permanent vibrations or shocks. In these extreme conditions the components also need to work flawlessly to ensure the functionality of the whole system. To guarantee the reliability at such conditions, the components are tested in different  domains.  Therefore, we want to take a closer look at the vibration- and shock tests in this article.

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American companies use the so-called “Highly Accelerated Life Test” to detect and improve the reliability of products. Therefore, the energy input of the created vibrations is accumulated in “Grms” (root mean square acceleration). In Europe the IEC-standards are used as a binding procedure to provide information about the lifetime and the toughness of a device. The manufacturer declares on the technical data sheet, if the devices fulfill these European standards.

The mechanical shock defines a short but also very strong impact. A car accident could be such a scenario. The vehicle is abruptly slowed down to 0 km/h with high accelerating forces taking effect. Another example is a water melon falling down from a roof. When hitting the asphalt the melon will abruptly be slowed down to 0 km/h, too. The tests that give evidence about shock tolerance are performed according to the IEC 60068-2-27 standard.

At the vibration tests the stresses are less strong, but permanent. Usually these stresses are typical for mobile machinery, compressors or less sensitive transport. These vibration tests are realized according to IEC 60068-2-64 standard.

In case of the manufacturer having proved his products against vibration and mechanical shock, he will list it on the data sheet. Here you can see the maximum stress (mostly expressed as a multiple of the gravity [g=9,81m/s²]) the product was tested for. Vibrations will normally be between 50 and 2000 Hz with an acceleration of up to 20 g (rocket launch). Rotating machinery for example are exposed to 2 g.
In shock tests, these values can exceed several hundred g (force per mass) for several milliseconds. Obviously theses tests are only passed if the device has no functional damages. Our Generic Control Box “Ruggedized” was exposed to these tests and fulfils the IEC-standards.

How exactly are these IEC-standards implemented?

For example in a vibration test, the object is tested with defined acceleration and defined frequencies. The test object starts to vibrate. This stress is now kept for a few minutes and a higher frequency will be brought in. Some frequencies are kept up for several hours. The proven resistance to vibration then gives information about the accelerations and according frequencies that did not lead to functional damages. An unlimited life-span can be expected when the tested device passed 10⁷ cycles without any functional damages.

At the mechanical shock test the input stresses are much higher. Test objects are typically exposed to three shocks within six directions. Here again, the test is only passed when no functional damages occur.

Conclusion

In order to give a binding statement about the resilience of the distributed devices the presented vibration and shock tests are ideal and very representative. The conducted tests simulate an artificial accelerated aging to detect weaknesses and design flaws. The guidelines of the European standards are continuously optimized and renewed, in order to make an accurate statement about the resilience of the proven devices for the consumers.

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