Performance Analysis And Key Manufacturing Technologies Of Planar Double Enveloping Hourglass Worm Gears

The planar double enveloping hourglass worm gears has the advantages of strong bearing capacity,high transmission efficiency and long service life,and it is a highperformance worm transmission form.After more than 40 years of development,the application range of the transmission has expanded from metallurgy,mining and other fields to strategic emerging industries such as industrial robots,rail transit,equipment,etc.,however,its market scale has not been significantly expanded,its promotion and application are mainly limited in China.This is mainly caused by some factors such as: complex manufacturing process,difficult precision control,and tedious assembly position adjustment.With the rapid expansion of the application range,the manufacturing level and testing method of planar double enveloping hourglass worm gear reducer have been unable to meet the actual demand and can't keep up with the development pace of the manufacturing industry.Therefore,it is necessary to strengthen the research on basic theory,key technologies and key process and improve the competitiveness through scientific and technological innovation.The main contents of this thesis are as follows:(1)Meshing analysis of planar double enveloping hourglass worm gears.According to the meshing principle and the homogeneous coordinate change matrix,the theoretical tooth surface model of the planar double enveloping hourglass worm and the planar double enveloping worm wheel are established.The feature line model is established by meshing the worm and the worm wheel respectively.The variation of the macro-tooth structure and micro-meshing performance of the worm gears caused by different center distance modification is analyzed.By analyzing the relationship between the trajectory of the cutting edge of the hob and the theoretical tooth surface,the equation of the transition zone of the modified drive worm wheel is constructed.It is found that the curvature interference limit curve of the tooth surface of the Type II drive worm wheel always be cut off,regardless of the size of the shape modification,and the problem of the cutting of the curvature interference limit curve is clarified.Taking the reference helix as the research object,the lubrication angle,the relative entrainment speed,the induction normal curvature radius coefficient,the minimum oil film thickness coefficient and the total length of the instantaneous contact line from the inlet to the outlet process are systematically analyzed,and further analyzes changes in various parameters caused by different amounts of modification.The study found that the minimum oil film thickness coefficient of the Type I drive greater than that of the Type II drive,and the running test also shows that the transmission efficiency is higher than that of the Type II drive.However,the two type drives are still in mixed lubrication.Compared with the modification design,reducing the roughness of the tooth surface can significantly increase the film thickness ratio,thus achieving complete elastohydrodynamic lubrication.(2)Error reverse correction of the planar enveloping hourglass worm surface is inversely adjusted.Based on the virtual rotary center technology,a four-axis linkaged grinding positioning method for hourglass worm is proposed to solve the problem of tool setting before grinding.Secondly,the adjustment requirements of the tooth surface grinding machine and the changes of the processed worm parameters caused by the adjustment error of the process system are clarified.Furthermore,the topological error and feature line error of worm surface are analyzed qualitatively according to the hypothetical parameters.It is found that the indexing error of the reference helix and the axisymmetric section of the throat can characterize the error of the entire tooth surface.By defining the error influence coefficient,the feature line errors of different specifications of worms and different parameter variations are quantitatively analyzed,and the relationship between feature line error and worm design parameter variables is proved,and a kind of adjustment card of machine tool is developed for calculating the inverse adjustment amount.Finally,a reverse correction method for the tooth surface error is proposed.After reverse the correction amount according to the feature line error,the tooth surface error can be reduced by inversely adjusting the grinding program parameters.(3)Accurate control of tooth thickness of planar enveloping hourglass worm.For the problem that the planar enveloping hourglass worm is a variable tooth worm,it's difficult to accurately control the tooth thickness during the grinding process.The variation curve of worm tooth thickness obtained by processing both sides of tooth surface according to the theoretical envelope relation is studied and maximum tooth thickness is solved.The variation rate of tooth thickness near maximum tooth thickness and the relationship between the circumferential feed angle of worm and maximum tooth thickness are analyzed.A method to accurately control the tooth thickness of the hourglass worm is proposed by controlling the positional relationship of the corners of the generating plane on both sides is proposed.(4)A contact zone adjustment method of hourglass worm gear pair is presented.Breaking the bottleneck of solving contact zone is complicated to calculate with traditional tooth contact analysis method.By establishing the assembly coordinate system,the meshing equation is replaced by the shortest arc length of the tooth surface is zero as the criterion for judging the meshing point.By studying the variation of the contact zone and the transmission error curve caused by the assembly error of the worm gear pairs in the center distance,the worm wheel throat plane,the throat of worm and the shaft angle error,a method for adjusting the assembly position of the hourglass worm gear pair is proposed,and used to guide the adjustment of the assembly position.Through innovation in theory,method and technology,this thesis has solved the key problems in the performance analysis and manufacturing process,such as the influence of modification on meshing performance of hourglass worm gear pair,improvement of precision of hourglass worm tooth surface,precise control of worm tooth thickness and adjustment of contact zone of hourglass worm gear pair.The software,such as parameter analysis,hob design,manufacturing error simulation and correction,worm gear pair assembly error analysis,is developed and put into production application.The meshing performance of more than 30 kinds of the hourglass worm drive performance has been analyzed.Combined with the NC machining program and the error measurement software,the precision of worm surface processed by the hourglass worm grinding machine is improved from 8 to 6 and the error consistency is guaranteed,and the mass production of more than a thousand worms has been achieved.Taking the test planar double enveloping hourglass worm gear reducer as an example,the transmission efficiency is improved by nearly 7 percentage points compared with the national standard by modification,controlling the precision of the tooth surface and adjusting the assembly poisition.It provides a powerful support for the production of high performance planar double enveloping hourglass worm gear reducer by economical and efficient technical means.