The electrodynamic shaker is an extremely widely used vibration test equipment in vibration testing, and its force ranges from hundreds of Newtons to thousands of Newtons. In practical applications, due to improper use, it often brings unexpected damage to the vibration table:
1 Travel limit
The maximum stroke of the standard electrodynamic shaker is usually ±25mm, which is sufficient for general sinusoidal sweep vibration and broadband random vibration with a frequency bandwidth of 10Hz-2KHz. The road transport spectrum simulation test for 3-500Hz is limited by the large displacement at low frequency. Some electrodynamic shakers used for shock simulation tests will increase the maximum stroke to ±30-50mm, but for the classic waveform shock and impulse response spectrum of long pulses, the required maximum stroke must be pre-estimated before it can be implemented.
2 Low Frequency Limits
Generally, electrodynamic shakers are indicated to operate in the frequency range of 5Hz-2kHz, and from the working principle of electrodynamic shakers, they are completely capable of operating at the low frequency below 5Hz. One of the reasons for the low frequency limit is the limitation of large displacement at low frequencies, and a more important reason is the limitation of the mechanical structure resonance of the electrodynamic shaker body, which requires the construction of a large inertia mass foundation when used at frequencies below 3Hz.
3 Excitation influence
Electrodynamic shaker is a kind of equipment using electromagnetic conversion principle to achieve large thrust excitation, there is a strong magnetic field effect around the table body, in order to reduce the amount of leakage above the table, in the table body are invariably installed above the degaussing coil. But this degaussing effect is limited, for some magnetic sensitivity is very strong engineering products can not be forced to minimize the residual magnetism of the shaking table and pay unnecessary manufacturing costs and costs. You can consider the use of excessive table or the use of products hanging above the table, the shaking table as a “source of excitation” use.
4 Eccentric load capacity
In general, small force electrodynamic shakers rely on mechanical structures such as combination leaf springs or rocker rollers to keep the moving coil suspended in the center of the excitation coil gap. Since these mechanical support devices have Anti-eccentric load capacity, it is important to emphasize that the combined center of gravity of the test piece and fixture should fall on the center axis of the shaker when installing the test piece on an electrodynamic shaker used vertically to avoid excessive deflection moments due to additional bending moment during vibration, which can lead to contact wear of the moving coil and excitation coil. In some large force electrodynamic shakers, in order to resist the damage of the eccentric load moment, additional auxiliary support devices, such as hydrostatic support auxiliary guides, are added to the shaker body to compensate the defect of the low eccentric load capacity of the electrodynamic shaker. When using, please pay attention to the shaker’s given eccentric load capacity limit.
5 Load Capacity
Small force electrodynamic shakers with combined leaf springs, rocker rollers, etc. are also mechanical components of the shaker to support the test load. For medium force electrodynamic shakers, an auxiliary bearing air bag is often added at the lower end of the moving coil, the use of compressed air to balance the load on the vibration table surface, reduce the consumption of the excitation force support load. Test must pay attention to the quality of the specimen can not exceed the rated load value.
6 Background noise
The background noise of the shaker is an important basic parameter to determine its dynamic range. The size of the background noise depends first of all on the effectiveness of the shaker, the design of the moving coil and manufacturing process and other factors, but in the field use of the shaker grounding conditions, whether the laboratory has independent use, a very small grounding resistance of the bottom line. When the shaking table surface suspension voltage is too high, or between the sensor and the table surface is not well insulated, will produce a high background noise, thereby reducing the shaking table “pressure control” ability, can not be well eliminated in the dynamic response characteristics of the peak valley differences, so that the vibration control accuracy significantly reduced.
7 Lead isolation
In the use of electrodynamic shakers, there are large excitation currents and amplifier drive currents from the power amplifier output to the shaker, and there are also weak electrical signals from the acceleration sensor feedback from the shaker back to the vibration control system, due to the electromagnetic conversion effect, when wiring, please separate these two leads to prevent the magneto-electric effect of large currents from interfering with the measurement of acceleration micro-charges.
8 Safety matters
The following points are involved in the safe use of the electrodynamic shaker.
A, Lower limitation usage: Use the maximum force of the shaker with caution. The maximum force of the electrodynamic shaker requires the maximum current output of the amplifier, and leads to the highest heating of the moving coil, long-term vibration under the maximum force is easy to make the moving coil overheat, 80% of the thrust of the derating for the best use of thrust.
B, Cooling effect: As the electric shaker moving coil and excitation coil are electric heating body, ventilation and cooling is very important. For air-cooled medium and small force electrodynamic shakers require the normal operation of cooling and ventilation, the inlet air temperature must be less than 30 degrees Celsius. High-powered water-cooled electrodynamic shakers should often pay attention to the shaker’s internal cooling circulating water system for leakage to ensure that the shaker is adequately cooled.
C, Use environment: the use of the laboratory environment should meet the requirements of the test specifications, especially so that the dust, space magnetic field, ambient temperature, ground, etc. to meet the requirements of the use of electrodynamic shaker.