There are many forms of mechanical forces that electronic devices are subjected to. Among them, vibration and shock are the most harmful, and they cause about 80% of the failures. There are two main forms of damage caused by them, one of which is strength damage. The device generates a large amplitude resonance at a certain excitation frequency, and the stress caused by the final vibration acceleration exceeds the ultimate strength that the device can withstand damage. Or the impact stress caused by the impact exceeds the ultimate strength of the equipment and is destroyed. The second is fatigue damage. Although the stress caused by vibration or impact is much lower than the strength of the material, the stress generated by long-term vibration or multiple impacts exceeds the fatigue limit, causing fatigue damage to the material. The vibration characteristics of the system are affected by three parameters, namely mass, stiffness and damping. For vibration and shock isolation of electronic equipment, the quality of the vibration isolation system generally refers to the quality of the electronic equipment, while the stiffness and damping are provided by the support device of wire rope isolators damping
. Under the influence of mechanical environment, especially in ships, tanks, off-road vehicles, aircraft and other vehicles, the equipment and its internal electronic components, mechanical structures, etc. are difficult to withstand the interference of vibration and shock.
In order to reduce or prevent the effects of vibration and shock on electronic equipment, two measures are usually taken:
a) Enhance the vibration and impact resistance of equipment and components through material selection and reasonable structural design;
b) Install a shock isolator on the equipment or components to effectively reduce the effects of vibration and shock on the electronic equipment by isolating vibration and shock.
Vibration isolation is to isolate or reduce the transmission of mechanical vibrations between the device and the device by installing shock isolators
. An elastic support, that is, a damper, is installed between the electronic device and the foundation to reduce the influence of the basic vibration on the electronic device, so that the electronic device can work normally or not. This measure of isolation of electronic equipment is called passive vibration isolation. Under normal circumstances, the vibration isolation of instruments and precision equipment is passive vibration isolation. There are three basic factors in controlling vibration and its transmission in the vibration isolation system: the stiffness of the isolator, the mass of the isolated object, and the damping ratio of the system support, ie, the isolator. The effects are as follows: the greater the stiffness of the isolator, the worse the vibration isolation effect, and the better the vibration isolation effect. For a properly designed vibration isolation system, the stiffness calculation of the support must consider both the vibration isolation effect and the bearing capacity. The mass of the object to be isolated keeps the support system relatively stationary, the greater the mass of the object, the smaller the vibration of the object under the determination of the vibration force. The resonance peak is reduced in the resonance region, and the resonance amplitude is suppressed. However, in the vibration isolation zone, as the damping ratio increases, the vibration isolation coefficient also increases, and the vibration isolation effect deteriorates.
Shock is a sharp momentary effect. For example, the take-off and landing of an airplane, the start and stop of a train, a car, the lifting and falling of an object can have a large impact. When the impact occurred, although the time was quite short, the effect was very strong. Under impact, when the impact stress of the parts of the electronic equipment exceeds its maximum allowable value, the equipment will be damaged, and sometimes fatigue accumulation will occur due to multiple impacts, causing fatigue damage to the equipment. Therefore, the effect on the impact must also be isolated. The energy theorem tells us that when the external impact energy is constant, if the impact force is applied for a longer period of time, the impact force of the device is smaller and the impact acceleration is smaller. Therefore, if the contact time of the impact force can be prolonged, the impact of the impact of the electronic device can be alleviated. Most of the electronic devices belong to the passive isolation, and a wire rope isolator is installed between the support base and the electronic device for impact isolation. When an external impact force acts on the support base, the elastic element and the damping element in the damper are deformed, absorbing energy and prolonging the contact time of the impact force. This reduces the impact force transmitted to the device a lot and achieves the purpose of buffering. The stiffness of the damper and the greater the damping is smaller, and the impact time of the impact force is longer and the deformation of the damper is greater. The impact of the device is less, and the buffering effect is better.