The mechanical vibration shaker can be divided into two types: unbalanced mass type and cam type. The unbalanced mass type uses the centrifugal force generated by the rotating unbalanced mass to excite the vibration shaker, and the excitation force is proportional to the unbalanced moment and the square of the rotational speed. This vibration shaker with simple structure and low cost can produce sine vibration, but it can only work in the frequency range of about 5Hz~100Hz, with a maximum displacement of 6mm and maximum acceleration of about 10g, and it cannot perform random vibration. The displacement of the cam type vibration shaker depends on the eccentricity of the cam and the length of the crankshaft, and the excitation force varies with the mass of the moving part.
In the low-frequency region, the vibration shaker can achieve a very large displacement such as 100mm when the excitation force of this vibration shaker is large,. However, this vibration shaker is only suitable for low-frequency, with an upper frequency limit of about 20Hz. The maximum acceleration is about 3g, and the acceleration waveform distortion is significant. Due to the limitations of its performance, the use of mechanical vibration shakers will be smaller in the future.
The electro-hydraulic vibration shaker is driven by a small electric vibration shaker that controls a controllable servo valve to generate vibration through oil pressure. This vibration shaker can produce a large excitation force and displacement, and can obtain a large excitation force at very low frequencies. Hydraulic shakers with large excitation force are cheaper than electric vibration shakers with the same force. The limitations of the electro-hydraulic table are poor high-frequency performance, low upper working frequency, and significant waveform distortion. Although random vibration can be performed, the rms rated value of the random vibration excitation force can only be below 1/3 of the sine rated value. This vibration shaker can still play a role in vibration tests due to its large force and displacement which can make up for the shortcomings of electric vibration shakers in the future, especially in the ship and automobile industries.
CME mainly produces electro-hydraulic vibration shakers (KRD70 series). The electro-hydraulic vibration shaker of CME is a dynamic test machine that converts the energy of high-pressure liquid into reciprocating motion of the actuator through electro-hydraulic servo valves. Due to its good low-frequency performance, strong bearing capacity and large force, it can be widely used in materials, components, parts, and instruments, as well as small equipment, vibration environment, and comprehensive stress environment screening tests in the fields of aviation, aerospace, automobiles, shipbuilding, military, information, and electronics, in order to evaluate the adaptability and structural integrity of the test products to the vibration environment.
The electric vibration shaker is the most widely used type of vibration equipment. Its frequency range is wide, with a frequency range of 0~10kHz for small vibration shakers and 0~2kHz for large vibratio shakers. It has a wide dynamic range and is easy to achieve automatic or manual control. The acceleration waveform is good and suitable for generating random waves, and high acceleration can be obtained.
The electric vibrating table is set according to the principle of electromagnetic induction. When the constant magnetic field at the energized conductor will be subjected to force, and the semiconductor will vibrate when the alternating current passes through it. The driving coil of the vibration shaker is in a gap with high magnetic induction intensity. When the required vibration signal is generated from the signal generator or vibration controller and passed to the driving coil after being amplified by the power amplifier, the vibrating table will generate the required vibration waveform.
The electric vibration shaker is basically composed of five parts: driving coil and moving parts, moving parts suspension and guiding device, the field current and demagnetization unit, table body, and supporting device. The structure of the driving coil and moving parts is complex, and the calculation of the first-order resonance frequency is very difficult, it must be estimated by experience, which often leads to design errors. Applying the finite element method to the calculation of the resonant frequency of the moving parts of the electric vibration shake not only improves the accuracy of the calculation results, but also facilitates the optimal design of the structure, greatly increasing the design reliability of the vibration shaker.