Research On Force Limited And Control Technology Of Space Two-dimensional Turntable Vibration Tset

Space Two-dimensional turntable is a core equipment used for precise measurement of spatial and temporal parameters in space.It is used to stabilize system optical axis and track targets in complex sapce environments,which is widely used in space observation and laser communication.During satellite launch,the turntable will inevitably withstand harsh mechanical environments such as vibration and shock brought by the launch vehicle.In order to prevent unnecessary failures of the turntable during launch,vibration tests need to be conducted on the ground to verify the rationality of the structural design.But vibration tests on the ground is difficult to simulate the mechanical environment during launch accurately.Due to differences in mechanical impedance at the installation interface and the effect of dynamic absorption,the turntable that originally met the actual launch requirements may be damaged during vibration tests,which lengthen the development cycle of the turntable and increase costs.Based on the traditional acceleration tests,force limited and control technology introduces interface force characteristics to perform dual control tests,which can effectively reduce the degree of overtesting,ensure the safety of the product.Due to the characteristics of high load-bearing ratio,cantilever installation,and non-linear connection of bearings and locking devices,the stiffness of the turntable is poor,and the lower natural frequency of the turntable cannot avoid the mechanical environment during the launch phase,resulting in serious resonance.At this time,the response of the turntable shows amplification of external excitation.In vibration tests,this response amplification is more serious and may cause damage to the structure.This article focuses on the significant response amplification effect,and conducts research on the application of force limited and control technology in vibration tests,mainly including the following works:(1)The concept of mechanical impedance is introduced to explain the mechanism of overtesting from three aspects: envelope acceleration testing spectrum,mechanical impedance differences in turntable mounting structures,and dynamic absorber effects under different mounting boundary conditions.The principle of force-limited control technology in reducing overtesting is discussed.Introduced the acquisition methods of several commonly used force limited tests spectrum,compared several methods and points out the advantages of the complex two-degree-of-freedom method over other methods.(2)This article focuses on the equipment-level force limited tests of the space twodimensional turntable,which divides the turntable/satellite coupling system into the load system(turntable)and the source system(satellite).The substructure modal synthesis method is used to simplify the coupling system into an equivalent model composed of effective modal mass,and the modal parameters of the turntable and satellite subsystems are analyzed and the transfer function of the free boundary system and the fixed boundary system are drived.Based on the transfer function,the equivalent model is further simplified to obtain a complex two-degree-of-freedom model,and the calculation method of the force limited tests spectrums is derived(3)The system parameters required to calculate force limited spectrums can be obtained through FEM,but it’s requires high accuracy of the FEM.Aim at the problem of distortion in FEM of bearings and locking devices in space two-dimensional turntables,this article proposes an equivalent modeling method using generalized spring elements.The system stiffness characteristics are analyzed through theoretical calculation and parameter identification based on modal test data,while the system damping characteristics are analyzed through parameter identification based on lowlevel frequency sweep test data.An accurate FEM of the two-dimensional turntable is established,the maximum relative error between simulation results and experimental results on nature frequency and response is 4.1% and 3.2%.When calculating the system parameters through FEM,the parameters of the free boundary system can be directly obtained through modal analysis,while the parameters of the fixed boundary system need to be modified.This article introduces a method to obtain mass parameters by setting the critical damping of the system.(4)An FEM of the turntable/satellite coupling system was established,and a sine load with range of 5～100 Hz was applied to the satellite to extract the acceleration and force responses at the interface between the turntable and the satellite.The interface acceleration was enveloped with a certain margin to obtain the acceleration spectrums for turntable simulation.The interface force was used to verify the accuracy of the force limited test spectrums calculation.Due to the lack of equipment for conducting force limited tests,this article uses the force limited tests spectrums as the input of the turntable to conduct frequency response analysis of interface force control,and uses acceleration control frequency response analysis as a control for comparison,extracting the response and stress of critical points on the turntable.Compared with acceleration control,under the interface force control spectrums,the stress of the X-direction critical point is reduced by 62%,and the stress of the Y-direction is reduced by 63%.The X-direction acceleration response is reduced by 68%,and the Y-direction acceleration response is reduced by73%.The results show that interface force control can effectively reduce the tests overtesting and protect the test piece.Based on the analysis results,the feasibility of using force limited control technology to achieve lightweight design of the turntable is discussed.