| With the development of the technology of industrial robots,higher requirements are put forward for the performance of robot's joint transmission mechanism,which makes the key technology design of the joint transmission face more severe challenges.As a key transmission gear of industrial robot joints,the contact characteristics,torsional stiffness and transmission accuracy of the precision cycloid reducer directly affect the working performance and life of the entire industrial robot.How to accurately evaluate and predict the mechanical characteristics and transmission characteristics of precision cycloid reducers is accordingly the prerequisite for developing a high-quality precision reducer.Due to the special structure of the precision cycloidal transmission mechanism,the nonlinearity of multi-tooth meshing,the randomness of various errors and other characteristics,the mechanism of the precision cycloidal transmission faces some difficulties including complicated mechanical problems,system stiffness problems and reasonable distribution of errors.It is thus necessary to study the performance index of the precision cycloid reducer structure in depth,and then to carry out the optimization design of the transmission performance,which could lay a foundation for establishing a key design theory system for a precision cycloid reducer.Under the support of the National Natural Science Foundation of China(51375064),this research carries out the optimization the design of the transmission characteristics of the precision cycloidal actuator such as contact characteristics,torsional stiffness and transmission accuracy,as well as the experimental investigations.The main contents are as follows:(1)A method of force calculation based on multi-body dynamics is proposed,and this method is furthermore used to study the law of load distribution of the cycloidal pin teeth and the law of force of the rotating arm bearing;this method is compared with the classical mechanical model,and the two have good consistency,thereby verifying the effectiveness and accuracy of the method.Furthermore,based on these results,considering the factors of gap,cycloidal modification and elastic deformation of components and their torque,the finite element method is used to study the contact characteristics of cycloidal pin and crank-rotor bearing.According to the above research,the following results are obtained: the law of stress distribution of the cycloidal pin wheel,such as the position of contact,the size and degree of coincidence of the cycloidal pin wheel is closely related to the structure and deformation of the cycloidal wheel;the contact stress of the swivel bearing is approximately linear with the load applied;the bearing needles have different stresses,and there is a phenomenon of single-sided contact stress.(2)A mathematical model of the stiffness of the whole cycloidal reducer system coupling the stiffness meshing central wheel and involute gear,the cycloidal pinwheel's meshing stiffness,the crankshaft's elastic deformation stiffness,the crankshaft's bearing stiffness and the carrier's stiffness is constructed,and an calculation is carried out with examples;using the finite element method and considering the nonlinearity and time-varying characteristics of multiple elements such as center wheel,planetary gear,crankshaft,cycloid,pin gear,left and right planet carrier,the finite element model of the stiffness of the full flexible system of the precision cycloid reducer is established;the influence of the stiffness of each component on the stiffness of the whole system is analyzed,which indicates that the stiffness of the cycloidal wheel has the greatest influence on the stiffness of the system,followed by the crank-rotor bearing and then by the crankshaft,whereas the planet carrier,center wheel,and planetary wheel have less impact.(3)Taking the manufacturing error,assembly error and initial phase of the center wheel and the planetary wheel into account,a mathematical model of the equivalent meshing error of the first-stage involute planetary gear transmission is established;considering the error of indexing circle of needle wheel,the error of slot radius of the needle tooth,the radius error of the cycloidal wheel,the pitch cumulative error of the cumulative tooth,the profile error of needle tooth,the clearance error of needle wheel and cog,the eccentricity error of crank shaft hole,the eccentricity error of crank shaft,the eccentricity error of bearing hole on planet carrier and planet carrier installation error,the mathematical model of the equivalent meshing error of the second-stage cycloidal pinion planetary gear is built;the mathematical model of the transmission error of the whole cycloid reducer system is furthermore derived.The method of Monte Carlo is used to simulate the random characteristics of component manufacturing and assembly error,and the influence of random coupling of components on the transmission error of the whole system is studied;based on this,a fast prediction algorithm for system transmission error is proposed;taking the various errors of the RV-80 E precision cycloidal reducer as an example,and based on this method,50,000 samples were simulated and mathematical statistics were performed.Results indicate that the transmission error of the whole system of the precision cycloid reducer is [1.6737",24.7712"],the confidence interval is [11.533",11.5797"],and the expectation is 11.5564".(4)The function of multi-objective optimization with minimum transmission error,minimum system output torsion angle and minimum stress on the arm bearing is constructed;the optimized mathematical model which satisfy the constraints such as those of short-amplitude coefficient,the width of cycloidal wheel,the notch of the cycloidal tooth profile,the pinion coefficient,the contact strength of the cycloidal wheel and the pinion,the modification of the cycloidal wheel,the pitch of the cycloidal wheel,etc.,is also established.The adaptive genetic algorithm is used to optimize the optimal parameters of the precision performance of the precision cycloid reducer.The results indicate that the system transmission error of the optimized cycloidal reducer is reduced by 36.5%,the output end torsion angle is reduced by 12.23%,and the maximum force of the rotary arm bearing is reduced by 6.04%.These results suggest that the transmission performance of the whole machine is improved and that the effectiveness of the algorithm of transmission performance optimization is proved.(5)For precision cycloid reducer prototype before and after optimization,a bench for testing transmission performance is built,and a test of the transmission performance is carried out on the prototype.The analysis indicate that after optimization,the precision of the precision cycloidal reducer improves by 26.21%,and the torsional rigidity of the whole system increases by 12.49%,which suggest that the transmission performance of the precision cycloid reducer has been greatly improved,and the expected objective has been achieved. |
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