The research and production of the vibration test bench began. Beijing Yashilin's vibration test equipment not only played a role in the aerospace field but also in other industries, and became an important civilian product of the institute. The vibration table system used for vibration test can be divided into three categories from its excitation mode: mechanical vibration table, electro-hydraulic vibration table and electric vibration table. According to the vibration direction of the vibration table, that is, the movement trajectory of the worktable, it can be divided into unidirectional (single-degree-of-freedom) and multi-directional (multi-degree-of-freedom) shaker systems. According to the functions of the vibration table, it can be divided into a single sinusoidal vibration test table and a vibration table system that can complete the vibration test and impact test of sine, random, sine plus random. The following is a brief discussion of various vibration tables, mainly the current status and development of the structure, performance and cost of electric vibration tables and their auxiliary equipment.
1. Mechanical Shaker
Mechanical vibration table can be divided into two types: unbalanced weight type and cam type. The unbalanced weight type uses the centrifugal force generated when the unbalanced weight rotates to excite the vibration table, and the excitation force is proportional to the square of the unbalanced torque and the speed. This kind of vibrating table can generate sinusoidal vibration, its structure is simple, and its cost is low, but it can only work in the frequency range of about 5Hz to 100Hz, the maximum displacement is 6mm peak-peak, the maximum acceleration is about 10g, and random vibration cannot be performed.
The displacement of the moving part of the cam type vibration table depends on the eccentricity of the cam and the arm length of the crankshaft, and the exciting force changes with the mass of the moving part. This kind of vibration table can realize large displacement, such as 100mm, when the excitation force is large in the low frequency domain. But the working frequency of this kind of vibration table is limited to low frequency, and the upper limit frequency is about 20Hz. The maximum acceleration is about 3g, and the acceleration waveform is greatly distorted. The characteristic of the vibration table is that the data is accurate, but the price is expensive, generally more than 200,000, and the site requirements are very strict.
2. Electro-hydraulic shaker
The working mode of the electro-hydraulic vibration table is to drive a controllable servo valve with a small electric vibration table, and the transmission device is vibrated by oil pressure. This kind of vibration table can produce a large excitation force and displacement, for example, the excitation force can be as high as 104kN, the displacement can be up to 2.5m, and a large excitation force can be obtained at a very low frequency. The hydraulic table with large excitation force is cheaper than the electric vibration table with the same thrust. The limitation of the electrohydraulic station is that its high frequency performance is poor, the upper limit operating frequency is low, and the waveform distortion is large. Although random vibration can be done, the rms rating of the random vibration excitation force can only be less than 1/3 of the sinusoidal rating. Because of its large thrust and large displacement, this type of vibration table can make up for the shortcomings of the electric vibration table, and it will still play a role in future vibration tests, especially in the shipping and automotive industries.
3. Electric Shaker
Electric vibrating table is currently the most widely used vibration equipment. It has a wide frequency range, and the frequency range of the small vibration table is 0 to 5000 Hz, which is easy to realize automatic or manual control; the acceleration waveform is good, suitable for generating random waves; and a large acceleration can be obtained. There are direct and inductive methods for generating the coil coil current. The direct type is to directly add the current output by the amplifier to the driving coil, which is the mainstream of the vibrating table. Inductive is to pass alternating current into a fixed coil, and then generate current in the driving coil through induction. The drive coil of the inductive vibration table does not need to lead out the cable, and the structure is simple, but the efficiency of this type of vibration table is relatively low. Some shakers of foreign companies have adopted this structure. Beijing Yashilin's vibration series products are direct type. Since the problem of the cable leading out of the driving coil is well solved, its products are more practical.
Vibration table magnetic field generation methods can be divided into permanent magnet type and excitation type. The constant magnetic field of the permanent magnet type is generated by permanent magnet steel. Due to the difficulty in manufacturing large-volume magnet steel, this structure is currently only suitable for small vibration tables. Excitation type vibration table can be divided into single excitation and double excitation. Single excitation only has a set of excitation coils to form a magnetic field loop. This structure has low excitation efficiency, large power consumption, and large magnetic leakage. Degaussing coils are needed to ensure that the work surface has a low magnetic field. The double excitation is generated by two sets of excitation windings, which are placed on the upper and lower sides of the working magnetic gap. At the same time, because the double excitation magnetic circuit is shortened, the magnetic resistance is reduced, and the excitation efficiency is significantly improved compared to the single excitation.
Source: Beijing Yashilin Test Equipment Co., Ltd.
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