Strength Calculation Of Harmonic Gear Reducer In Assembly And Dynamic Operation Process

Since harmonic gear reducer designed by C.W.Musser had been applied into rocket,it has got continuous attention for its advantages in big transmission ratio,light weight,strong reliability,small volume,high drive accuracy and so on.Since the advent of two Bombs and one Satellite of our country,with the development of aerospace industry,harmonic gear reducer is widely applied into the transmission mechanism of rockets and satellites.However,in our country it is still needed to further study the failure mechanism,structure optimization and diversification design of harmonic gear reducers,especially about how to perform more accurate calculations about the strength of dynamic operation process and the fatigue life.Therefore,in this thesis,the strength and the failure mechanism of harmonic gear reducer is studied,a fatigue life assessment procedure based on stress-life method is presented,and finally the structure of harmonic gear reducer is improved.The main research contents are as follows:(1)The structure of harmonic gear reducer is designed and 3D model is built in SolidWorks.Tooth profile of the flexspline is involute,conjugate tooth profile of the circular spline is solved based on the envelopment method and is substituted by involute profile.The cam is standard ellipse.Appropriate simplification is made for the rolling ball bearing.(2)Based on the finite element analysis software ABAQUS,the assembly and dynamic operation processes are simulated for harmonic gear reducer.The calculations are emphasized on deformation response and stress distribution of the flexspline.The corresponding results are compared with the theoretical value.It is found that in the assembly process the maximal stress appears in the middle of dedendum of the flexspline,and in the dynamic operation the maximal stress occurs in the middle of addendum and at the same time the stress of the dedendum is also relative large.Hence,during the dynamic operation process the addendum of the flexspline usually encounters a contact fatigue wear failure and the dedendum often faces a fatigue fracture.(3)The stress variation of a single flexspline tooth is analyzed in detail from engaging to disengaging processes.Considering the character of wave motion and the symmetry of the flexspline,the periodic stress state of the flexspline tooth is got by superimposition of the stress state of 1/4 model,the stress loads of key position of the flexspline are counted and the fatigue life of the flexspline is assessed based on the stress-life method.(4)Because of the stress concentration problem caused by the rolling ball bearing,this thesis designs a harmonic gear reducer by employing flexible needle roller bearing for the first time and also conducts assembly and dynamic operation processes to obtain the deformation response and the stress distribution.These results are compared with those of the harmonic gear reducer with a flexible ball bearing.Through these comparisons,the feasibility and superiority of employing the flexible needle roller bearing are verified preliminarily and embody in:operating smoothly,no meshing interference in the addendum,structural strength and fatigue life increasing greatly.As a result,this thesis provides a reference to the diversity of harmonic gear reducer design.