| A precision reducer,as the core component of industrial robot,has an important effect on the performance of the whole machine.Lost motion is the key index to characterize the performance of precision reducers,and its measurement and evaluation is an important foundation to improve the performance of precision reducers.However,at present,some key problems in static measurement and dynamic measurement of the lost motion of precision reducers are still unsolved,and a functional application oriented evaluation system has not been established,which seriously restrict the development of precision reducers industry in China.In this paper,through the innovation of theory and method,the lost motion evaluation system of the whole life cycle of precision reducers is established.The key problems such as the accurate evaluation of the geometric lost motion in the static measurement of the lost motion of precision reducers,the characterization and acquisition of the static lost motion curve and the determination of the optimal measurement speed in the dynamic measurement of the lost motion,are solved.Aiming at the above four innovations,experiments are carried out respectively,and the experimental results verify the correctness and validity of the proposed methods and theory.The methods proposed in this paper are applicable to the measurement and evaluation of the lost motion performance of various precision reducers.The main contents of this paper are as follows.(1)The lost motion evaluation system of the whole life cycle of precision reducers is proposed.Considering the influence of measurement position,load torque and service time,this paper discusses and analyzes the type of lost motion function of precision reducers,and unifies static measurement and dynamic measurement into the same function.The evaluation index of the lost motion is constructed,including the precision index and the precision holding index.Static evaluation model and dynamic evaluation model are established.The statistical method,that is maximum value,minimum value,mean value and standard deviation,is used to evaluate each evaluation index.The above contents constitute the evaluation system of the whole life cycle of precision reducers.It can realize the scientific and reasonable evaluation of the lost motion of precision reducers in the whole life cycle.(2)A new method for geometric lost motion evaluation is proposed.The traditional measurement scheme is optimized.A closed hysteresis curve can be obtained by single cyclic loading and unloading,which overcomes the influence of the error introduced by curve fitting because the hysteresis curve is not closed.By analyzing the hysteresis characteristics of precision reducers and considering the coupling effect of nonlinear elastic deformation and friction,the hysteresis curve model of precision reducers is established,and the functional relationship between torsion angle and torque is clarified.A new method of evaluating geometric lost motion in static measurement of the lost motion of precision reducers,namely,the method of median curve,is proposed,and the model of median curve is established.The experimental results show that the method can solve the problem of accurate evaluation of geometric lost motion in static measurement,which is more clear and convenient,and improves the accuracy of measurement.(3)The representation and acquisition method of static lost motion curve of precision reducers are proposed.Based on the analysis of the peak point variation law of the major and minor hysteresis curves of the precision reducer,the anhysteretic curve and the static lost motion curve of the precision reducer are proposed and defined.The mathematical models of the anhysteretic curve and the static lost motion curve are established.According to the characteristics of the overlap between the peak point and the loading curve under major hysteresis curve,the static lost motion curve of the single measurement position of the precision reducer is obtained.The experimental results show that the static lost motion curve can be obtained by fitting the data points of the loading curve on the major hysteresis curve under the premise of improving the measurement accuracy.The theoretical system of static measurement of the lost motion of precision reducers is perfected.(4)The nonlinear friction characteristics of precision reducers are studied.The friction model of precision reducers is established based on the Tustin empirical model by analyzing the variation of friction torque at different speeds of precision reducers.Based on the analysis of the variation law of friction torque of precision reducers under stable rotational speed,the data processing method of friction torque is put forward,and the one-to-one correspondence between friction torque and measurement speed is obtained.The experimental results show that the precision reducer has typical Stribeck friction effect,which verifies the correctness of the friction model and data processing method.The Stribeck curve of precision reducers and the parameters of Stribeck friction model are obtained by least square fitting,which lays a theoretical foundation for determining the optimal measurement speed of precision reducers.(5)A method for determining the optimal measurement speed of dynamic measurement of the lost motion is proposed.Based on the analysis of Stribeck friction effect of precision reducers,a method for determining the optimal measurement speed of transmission error and lost motion is put forward,and the calculation model of optimal measurement speed is established.A geometric transmission error separation method based on optimal measurement speed is proposed and the transmission error measurement experiments are carried out under different speeds.A method based on the optimal measurement speed is proposed to separate the geometric lost motion.The dynamic measurement experiment of the lost motion under different speeds and load torques are carried out.The experimental results show that the precision reducer has the smallest friction torque,the minimum peak to peak value of transmission error and the minimum mean value of lost motion under the optimal measurement speed.The determination of optimal measurement speed is helpful to improve the dynamic measurement accuracy of geometric lost motion and to realize the objective evaluation of the lost motion of precision reducers.(6)Taking the RV reducer as an example,the measurement and evaluation experiment of the lost motion is carried out.The type A and B precision reducer used in the experiment,and the RV reducer comprehensive performance tester developed by our research group are introduced.The static and dynamic measurement evaluation experiments of type A and B precision reducer are carried out,and the results are compared and analyzed.Through the actual measurement experiment,the evaluation system and the application effect of the measurement method established in this paper are verified. |
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