Research On Shock Isolation Technology Of Ship Inertial Navigation Equipment

The navy is an important cornerstone for safeguarding the core interests of the country.Warships and submarines are the main weapon carrying platforms of the navy.During naval battles,warships will not only have to be disturbed by the marine environment and attacked by enemy weapons,but also bear the reaction force of their own weapons when they are launched.Under the condition of no major damage to the hull,the anti-impact ability of the weak part of the warships is the important factor that restricts the combat capability of the warships.Inertial navigation equipment is the key equipment to provide location information,and it is also a weak link for warships.Therefore,it is very important to ensure that the inertial navigation equipment can work effectively in a complex environment.Due to the unique requirements of isolation and protection of the inertial navigation equipment,it can not be effectively protected by commonly used isolators.The special requirements of the inertial navigation equipment isolation mainly have the following points.The isolation device should have the ability to unload high-frequency and large-amplitude impact loads in any direction.The isolation device should have the ability to completely transmit low-frequency and small-amplitude vibrations,so as to ensure the attitude sensitive accuracy requirements of the inertial navigation equipment.The isolation device should also have quick and accurate reset capability and durable reliability.In this paper,an opposed disc spring isolation device with a pre-tightening structure is proposed and developed to meet these requirements.And the main themes and contributions of the dissertation are stated as follows:(1)The shock response spectrum and its related concepts are introduced in this paper,which characterize the shock environment suffered by the warships.A theoretical analysis and mathematical derivation are made on the error mechanism of the shock response spectrum in the low frequency range during measurement.A new measuring instrument and correction method were proposed in this paper,on the basis of optimizing the existing measuring equipment.And this new correction method has been proved to be accurate,reliable and convenient by experiments.An accurate shock response spectrum is a necessary prerequisite for the evaluation of shock isolation effect of isolation mechanism developed later.(2)The opposed disc spring isolation device with a pre-tightening structure is proposed to protect the inertial navigation equipment,because the disc spring has the advantages of variable stiffness and self-damping characteristics.The nonlinear stiffness model of the opposed disc spring isolation unit is established.And the free vibration model and the forced vibration model under foundation excitation of the opposed disc spring isolation unit are established on the basis of its nonlinear stiffness model.The nonlinear vibration characteristics and vibration stability of the opposed disc spring isolation unit under different parameters are theoretically calculated and researched,so as to ensure the requirements of attitude sensitivity accuracy and vibration isolation performance of the inertial navigation equipment.Then,the theoretical calculation results are proved to be correct by the fixed frequency experiment results of the opposed disc spring isolation unit prototype.(3)An isokinetic shock distinguishing method,which can quantitatively distinguish between shock and forced vibration state,is presented.Then,the stiffness parameters and damping parameters of the disc spring isolation unit under the condition of the isokinetic shock loads are experimental investigated.Relying on the test datas,a shock dynamic model of the opposed disc spring shock isolation unit with pre-tightening under boundary friction condition is established.The shock acceleration ratio(SAR),shock displacement ratio(SDR),and relative displacement ratio(RDR)of the model are used as indicators to compare the isolation performance of the the opposed disc spring shock isolator with the common isolation unit under different parameters.The results are as follows: It has more excellent acceleration isolation ability for the disc spring isolation unit.Reducing the pre-tightening force and the number of the disc springs in the opposed disc spring isolation unit is beneficial to improve the acceleration isolation efficiency,but not conducive to the displacement isolation efficiency under the shock condition.The isolation performance of the disc spring isolation unit on acceleration is enhanced,but on displacement is weakened with the increase of external load frequency ratio under the condition of the isokinetic shock.Finally,an evaluation method of shock isolation effect based on shock response spectrum and pseudo-velocity isolation rate is proposed and applied.The results show that the components with natural frequency higher than 100 Hz are protected excellently by this disc spring isolation unit,but there is no protective effect for the components with natural frequency lower than 10 Hz.(4)The reliability model of the opposed disc spring isolation unit proposed in this paper is established to define the maintenance period of this equipment.Relying on the Wiener process degradation model,the reliability model of the opposed disc spring isolation unit is further described by considering the random effect of disc spring degradation rate,random impact and competitive failure factors.And the soft failure model considering the combined effect of random shock and degradation,the competitive failure model considering the sudden failure of random shock of the opposed disc spring isolation unit are established.Then,the estimation methods of the main parameters that affect the reliability of the isolation unit in these model are investigated.These methods provide theoretical basis for the measured model parameters in subsequent experiments.(5)An eight-legged Stewart platform isolation mechanism with a symmetrical layout is proposed due to the superiority of the traditional Stewart platform with multiple degrees of freedom,which is integrated by the designed opposed disc spring isolation units,so that this eight-legged Stewart platform isolation mechanism has the ability to isolate the shock in any direction and the ability to accurately reset.The virtual prototype of the eight-legged Stewart platform isolation mechanism is established in the simulation software rely on the theory of multi-body dynamics.The influence of the main geometric parameters of the structure in this virtual prototype on the vibration and shock isolation performance is researched by simulation calculation.Then,the vibration and shock test of the eight-legged Stewart platform isolation mechanism are carried out to verify the correctness of the simulation results.And The shock response spectrum and the pseudo-velocity isolation ratio are applied to evaluate the shock isolation effect of the eight-legged Stewart platform isolation mechanism during the full frequency domain rely on these shock experimental data.The results show that the inertial navigation equipment can be protected well by this isolation mechanism in any direction.Finally,the reset accuracy model of this eight-legged Stewart platform isolation mechanism after being disturbed by impact load is derived by the vector method.The influence rules of the machining reset accuracy of the components in the mechanism on the reset accuracy of the eight-legged Stewart platform isolation mechanism are demonstrated by an example.These can provide some technical references for isolation and protection design of multi-degree-of-freedom marine inertial navigation equipment.