Development of An Air-Magnetic Hybrid Suspension Unit for Microgravity Testing

The high frictional interference in traditional passive follow suspension methods has affected the accuracy of micro gravity tests. A prototype of air magnetic hybrid suspension unit was designed by utilizing the extremely low friction characteristics of air bearings to improve the accuracy of micro gravity tests with passive follow suspension methods in this article, which combined the advantages of suspension methods and air flotation methods. The operating principle of the air-magnetic hybrid suspension unit was introduced firstly, and the layout scheme of the air bearing and magnetic module was preliminarily selected. The structural form of the combination of annular air thrust bearing and central magnetic force unit was selected finally. The unique permanent magnet-electromagnetic module was designed to maintain the magnetic force at about 2 kN when the air gap thickness was about 0.65 mm. The electromagnetic force characteristics was analyzed for getting the change curve of the load capacity and stiffness under the range of 0.3~1.0 mm. The large porous graphite restrictor was used in air thrust bearings to achieve maximum load capacity in a smaller space dimension. The load capacity of air thrust

bearing was analyzed by finite element method and the grid independence analysis was also executed for determining the scale of the computational model. The influence laws of main parameters, such as supply pressure and permeability were analyzed, and the load capacity of 2 kN could be achieved under the selected working parameters when the air film thickness was at 20 μm. The structural design of the air-magnetic hybrid suspension unit was completed and three prototypes were developed. The permeability of porous materials was tested for air bearing part. The load capacity of the air magnetic hybrid suspension unit was tested by reverse tension test method in order to avoid security risks, and the test device was also designed. The maximum bearing capacity and load-displacement characteristics of the air-magnetic hybrid unit were tested. Based on the assumption of constant magnetic force and nonlinear magnetic force, the load-displacement characteristics of the air-magnetic hybrid unit were transformed into the load-displacement characteristics of the air bearing, and was compared with the theoretical analysis results of the air bearing load capacity. The experimental results showed that the maximum bearing capacity of the prototypes was above 2.4 kN, under the safety factor of 3, it could carry the heavy suspension load of 80 kg, the magnetic force should be calculated and calibrated by using non-linear assumptions in design process, and the experimental results of air bearing load capacity could be in well agreement with the theoretical analysis.