| Reliability is an important indicator of aerospace products quality.The space remote-sensing camera usually can't be repaired or costs a lot to repair on orbit,in order to make sure the space remote sensing camera works normally,the reliability problem is important.As an important part of the space remote-sensing camera,the mechanism reliability is very important.At present,there is no comprehensive theoretical analysis data about the mechanism reliability of space remote-sensing camera,so it's necessary to research on mechanim reliability.In order to meet the requirements of reliability design of the focusing mechanism and rigid bracket in a large space remote-sensing camera,this paper studied on space mechanism reliability,and then designed,analyzed,tested the focusing mechanism and rigid bracket.The main contents are as follows:?1?Through literature investigation,the failure causes of previous space mechanism were analyzed and summarized,and the space environment factors are the main causes,another cause is design factor.In addition to the space environment factors,the wear between kinematical pair will make the accuracy lower,or lead to breakage of solid lubricating film and cold welding failure.The excessive force will also lead to large deformation of mechanism and reigidity failure.The types,funcions,structure features of mechanism using in space camera were analyzed.Method about calculating space mechanism reliability was proposed,through calculating the reliability of each kinematical pair,and then gets mechanism reliability by means of system reliability theory.?2?The characteristics of the space environment factors and their influence to the mechanism were analyzed,and the protective measures were summed up.The mean point method and checking point method based on the first-order second-moment method,direct sampling method,importance sampling method,checking point method based on MonteCarlo numerical simulation method were analyzed and compared.Finally,the calculation results of each method were compared by analyzing a stuctural performance function.The mean point method is simple,and the calculation accuracy is lower than the checking point method.The MonteCarlo method is suitable for a large range,but it needs a large number of samples and a large amount of calculation,the calculation accuracy is lower than the checking point method based on MonteCarlo method.?3?The performance function of wear reliability and rigid reliability of common kinematic pairs were deduced.The wear reliability and rigid reliability of revolute pair,cam pair,gear pair,ball screw pair,bearing pair,guide pair were analyzed by means of Archard wear model and Hertz contact theory.The stress distribution function and velocity distribution function in the contact region were deduced,and then got the specific performance function.The structural performance function about gear pair and worm pair were deduced by means of strength checking method.?4?A planar reflector style focusing mechanism based on the lead nut of a large space remote-sensing camera was designed.The reliability analysis and precision analysis were carried out,the precision of transmission is better than the design precision,and the precision reliability is about 1.MonteCarlo method was used to calculate the preload reliability of ball screw,when the accuracy was1×10-6,the reliability was 1.The wear reliability of bearing pair,worm gearing,guide pair were analyzed,and meet the design request.The reliability test which can simulate the environment of focusing mechanism on orbit was designed to test the reliability of the focusing mechanism.Before and after the test,the accuracy of focusing mechanism was tested,the test results were basically the same,the azimuth error of focusing mechanism is 1",the pitch error is 2",and the position accuracy is 4.3?m.The performance of the focusing mechanism designed meets the design requirements.?5?The auxiliary camera bracket was designed and analyzed.The bracket used two explosive bolts to produce a certain lateral swelling force to link up the upper and lower brackets.When the two explosive bolts unlock,the swelling force will disappear,and the constraints between the upper and lower brackets will be automatically discharged.Mechanical analysis shows that the camera bracket has mechanical amplification effect,the amplification factor is 3.19,and the unlocking reliability is better than 0.9999.Finally,through mechanical test,unlocking and impact response test,the rigid bracket is firmly connected,the unlocking is reliable and the impact is small.The rigid bracket can be used for the auxiliary connection between large space remote-sensing camera and satellite. |
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