Vibration platforms: the most widely used kind of vibration equipment
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Electric vibration table is currently the most widely used of a vibrating device. Its wide frequency range, small shaking table frequency range 0 ~ 10kHz, large-scale shaking table frequency range of 0 ~ 2kHz; wide dynamic range, easy to implement automatic or manual control ; acceleration waveform well suited to generate random waves ; are greatly acceleration. Electric vibration table is based on the principle of electromagnetic induction designed in a constant magnetic field when energized conductor will experience a force , when the conductor in the pass to alternating current will produce vibrations. Vibration table at a high driving coil formal gap magnetic flux density , when the desired vibration signal from the signal generator or vibration control device generates and amplified by the power amplifier through the drive coil , when the vibration table will be generated to vibration waveform .
Electrodynamic shakers essentially drive coil and moving parts, moving parts, suspension and guide device , excitation and deactivation unit , platform and support means five parts. Drive coil and moving parts are the core components of the vibration table , it is a first-order resonance frequency determines the frequency range of the vibration table , the complex structure of the moving parts , a first-order resonance frequency calculation is very difficult to estimate rely on the experience , which often result in the design turnovers. 702 where the late 1980s for the first time the finite element method is used electrodynamic shakers moving parts resonant frequency calculation , not only improve the accuracy of the results , and easy to optimize the design of the structure , greatly increasing the vibration table design reliability.
Shaker drive coil current generation there is a direct and inductive . Direct output current of the amplifier is directly applied to the drive coil , in this way the vibration table of the mainstream. Induction is alternating flow into a fixed coil , and then through induction coil generates a current in the drive . Inductive drive coil vibration table not lead cable , the structure is simple, but relatively low efficiency of the vibration table . Some American companies UD shaker using this structure. 702 and other company's products are used in a direct style , as a good solution to the problem of the drive coil leads cable , and its products are more practical.
The magnetic field generated vibration table can be divided into permanent magnet type and field type . Permanent magnet-type magnetic field is constant generated by the permanent magnet , the magnet due to the large volume of production more difficult , the current structure is only suitable for small shaking table . If 702 produced 2202 shaker and the company's 4808 B & K type permanent magnet type vibration table belongs . For large-scale shaking table is required in the excitation coil through a DC current to generate a constant magnetic field , which is the excitation vibration units.
Excitation type vibration exciter units can be divided into single and double excitation . Only a single set of excitation excitation coil to form a magnetic circuit , this structure excitation efficiency is low , power consumption, a large magnetic flux leakage , needed to ensure that the work surface degaussing coil has a low magnetic field . Dual excitation magnetic field is generated by the two excitation windings , were placed in the upper and lower sides of the work of the magnetic gap , the magnetic gap in the working field superimposed on each other , and in magnetic fields cancel each other work surface , so that the magnetic field is small countertop . Same time as the double excitation magnetic shortened reluctance decreases, the excitation efficiency than the single field has improved significantly . 702 of the 2104 series of vibrating table, the United States and the United Kingdom LDS LING number of large shaker are all double magnetic excitation . The same structure is a double excitation , 702 under the stage two vibration magnetic field is asymmetric , while the other vibration table is symmetrical.
Shaker cooling method has natural cooling , forced air-cooled , water-cooled , oil-cooled in several ways . Cooling only in a small compact exciter power . Oil cooling mode due to structural complexity , in the newly developed vibration table have been rare , and now still using oil-cooled shakers pay attention to maintaining the quality and quantity of oil . Forced air cooling is commonly used for small shaker cooling, it is the use of high pressure air to Taiwan out of the body of the hot air continuously to achieve cooling . In this way the cooling , the drive coil and the field coil is relatively simple structure , easy installation , low cost, does not appear water-cooled units common leaks, clogged waterways and other faults . But high-pressure fan noise at work is very large, a great impact on the operating personnel . Air cooling efficiency is relatively low, is not suitable for large-scale shaking table cooling . Water is the medium-sized shakers common cooling, water cooling units usually are made of hollow enamelled winding wire wound , while the cooling water directly into the hollow interior of enamelled wire cooling , cooling efficiency, but not much noise. But the vibration table structure is more complex, higher cooling water quality , often distilled or deionized water. In water-cooled Taichung , U.S. and British equipment several companies there is a serious defect that leads to the drive coil cables and pipes excitation coil structure is irrational and unreasonable waterways , this structure is often leaking , but demanding on water quality to change the water often . 702 of the vibration table using waterway parallel circuit in series , water connectors are used to connect the new structure of the winding thread a good solution to these problems, its water quality requirements are not too high , water pressure, rarely leaking.
The power amplifier is electrodynamic shakers important part of the system , its own performance and the matching conditions with shaking table is directly related to system performance. PA development up to now has gone through three generations , from a tube amplifier transistor linear amplifier and then to a digital switching amplifier . Tube amplifier in new production equipment has been the basic need , switch mode amplifiers are developed abroad in recent years , and it takes advantage of the switching characteristics of transistors , tubes consumption is small , the efficiency can be as high as 90 percent , while the average efficiency of a linear amplifier only about 50% . It is because of switching amplifier itself less heat, cooling it very simple , dozens kVA output power amplifier with only a small axial fan can cool down , so that the device structure is simple and reliable. The same linear amplifier must be cooled with water , complex structure . Switching amplifier distortion at low power output is relatively large, and the need for better electromagnetic shielding enclosure , otherwise this will cause electromagnetic interference with surrounding equipment .
Electrodynamic Shaker Technical indicators are: rated sinusoidal thrust , thrust RMS random , operating frequency range , maximum acceleration , maximum speed, maximum displacement , the effective mass of moving parts , work surfaces allow direct bearing quality , work surfaces allow partial load torque , miscellaneous scattered magnetic field , acceleration waveform distortion , the work surface uniformity and lateral vibration acceleration ratio . Shaker thrust moving part is its quality and can achieve the quality of the product of the acceleration , and not to the weight of the specimen . Rated sinusoidal thrust is the effective mass of the moving parts of the product with the largest peak acceleration , thrust RMS random vibration table is according to the standard ( eg ISO5344) provides the power spectral density curve experiment , the effective mass of moving parts that can be achieved with the maximum acceleration RMS product .
Electrodynamic shaker vibration test will be the future of major equipment , the manufacturing technology will be developed in two ways . First, the application of new materials , magnetic materials with a large cost reduction , a large permanent vibration table will be possible, this vibration table structure is simple , energy saving, and high reliability. PA will use more digital and modular circuit , smaller and smaller , increasingly efficient . Second, the application of the new method , with the promotion of the finite element method , the dynamic characteristics of complex structures can be accurately and quickly calculated. Because vibration table with cars and other products is very small compared to the user , only small batches , which facilitate the different users , different specimens were designed to achieve the integration of moving parts and fixture design, so that each an experimental system to achieve the best performance.
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