4) Suspension and support of the moving coil
The table and the moving coil assembly are suspended in the narrow air gap in the magnetic circuit by the suspension and support devices. The suspension and support devices need to have sufficient rigidity to bear the total mass of the table and the moving coil assembly, the fixture and the test piece. Generally, for medium and small thrust electric vibration tables, mechanical components such as combined leaf springs and rocker roller devices can be installed. For large-thrust electric vibration tables, the load may weigh hundreds of kilograms or even thousands of kilograms, so an auxiliary load support system must be provided. By adjusting the supply pressure of high-pressure air to balance the weight of the load, the center line of the moving coil is always kept in the center of the air gap of the magnetic circuit to ensure that the maximum stroke of the vibration table is fully utilized during low-frequency vibration.
5) Guide device
The vibration test specification requires that the ratio of the lateral vibration perpendicular to the main vibration direction to the amplitude of the main vibration direction shall not exceed 25%~50%. Moreover, the air gap of the suspended dynamic coil is very narrow. The instability of the dynamic coil’s linear motion can easily cause the dynamic coil to touch and rub against the short-circuit ring or the excitation coil, wear the insulation of the dynamic coil winding, cause the dynamic coil to short-circuit, or even burn out. Therefore, it is necessary to have a guide device that limits the left and right shaking of the dynamic coil and prevents the dynamic coil from rotating around the central axis.
6) Degaussing coil
The huge thrust of the electric vibration table comes from the interaction of electromagnetics. There is a disconnected annular gap in the closed-loop magnetic circuit of the vibration table body. Where there is a gap, there is leakage magnetic flux. Many products that implement vibration tests are electrical and electronic products. During the test, it is not allowed to have obvious leakage magnetic flux on the installation table. Therefore, a “degaussing coil” is installed under the electric vibration table to generate a magnetic field in the opposite direction of the leakage magnetic field. By selecting a suitable installation position and carefully designing the current and number of the degaussing coil, the influence of the leakage magnetic field of the main magnetic field can be offset, and the leakage magnetic field of the table can be limited to an acceptable level for the test piece.
7) Rotation mechanism
Vertical electric vibration tables are usually equipped with a horizontal slide table. Sometimes it is necessary to rotate the vibration table 90° and connect it to the horizontal slide table to achieve horizontal vibration. Therefore, the bracket of the vibration table is equipped with ear shafts, bearings, rotary handles and other components (Figure 4.8), which can manually or automatically adjust the inclination angle of the table body to meet the requirements of implementing vertical vibration and horizontal vibration conversion.
8) Cooling device
Due to the winding resistance loss and eddy current loss in the alternating magnetic field, the current flowing through the dynamic coil and the excitation winding will generate a lot of “heat” inside the vibration table body during the operation of the electric vibration table. If this heat is not dissipated in time, the consequences of “heat accumulation” will cause the dynamic coil or excitation winding to short-circuit or even burn out.
Electric vibration tables with thrusts below 30~50kN usually use forced “air cooling”. It is only necessary to pay attention to adding ventilation channels in the structural design of the dynamic coil or excitation winding, and provide external fan ventilation cooling. In principle, electric vibration tables with thrusts above 50kN must use “water cooling”, “oil cooling” or “water cooling” + “oil cooling” mixed cooling methods.