Modeling of rotary variable motion and shedding driving mechanism based on motion synthesis
Objective In order to achieve and optimize the stop-rise-stop motion characteristics of heald frames to meet the shedding requirements,a variable speed motion model was established and different driving mechanisms adopted to achieve variable speed motion was analyzed.A systematic design method was proposed for the rotating variable speed mechanism with different configurations.Method Based on the principle of motion synthesis,a method of constructing the rules of movement of the heald frames was proposed.The model of rotating motion was accordingly established to analyze the characteristics of the shedding mechanism under different parameters.From the perspective of mechanism of combination,the rotating-variable-speed motion driving mechanism and its improvement were put forward.The relative motion transfer function models of different heald frame driving mechanisms were established,and the scale optimization was carried out using objective optimization.Results By comparing and analyzing the motion characteristics of the cycloidal function under different offset coefficients,changing the offset coefficients of the cycloidal function can meet the technological requirements of the loom at different rest times.The cycloidal rest time,relative displacement and velocity extremes decrease with the increase of the offset coefficient,and the acceleration is the least when the offset coefficient(b)is 0.199 1.When the offset coefficient is 0.414 7 and radius of roller(rc)is 31 mm,the kinematic characteristics of the fixed cam-gear rotating transmission mechanism with different gear ratios are analyzed.With the reduction of the transmission ratio,the rotor arm displacement,cam pressure angle and cam curvature also decrease.The dimensional design of the evolved mechanism is carried out by means of objective optimization method,and its motion characteristics are analyzed.When the offset coefficient is 0.414 7 and the transmission ratio is lower than 0.9,the size of the hinged four-bar mechanism satisfying the constraint conditions can be obtained.The transmission ratio of the hinged four-bar mechanism and the guide slider mechanism both fluctuate uniformly above and below the transmission ratio.The transmission ratio range of the guide bar slider mechanism increases with the increase of the transmission ratio,while the transmission ratio range of the hinged four-bar mechanism is small.With the increase of transmission ratio,the error fluctuation of guide bar slider mechanism increases,and the error fluctuation of hinged four-bar mechanism is the smallest when the transmission ratio is 0.90.Under the same transmission ratio,the transmission performance of the guide bar slider mechanism is better than that of the hinged four-bar mechanism.By reducing the center distance of the hinged four-bar mechanism,the transmission performance of the mechanism is improved,the CAM pressure angle is reduced by 2.95％,and the transmission angle of the connecting rod is increased by 2.93％.The maximum diameter of the CAM rod is reduced by 2.90％.Conclusion In the motion period,the relative angular displacement,angular velocity and angular acceleration curves of the corrected cycloid motion law are continuous without sudden change,and the offset coefficient is the only control parameter,which can meet the different process requirements of loom.When a four-bar mechanism is used instead of a gear mechanism to realize the transmission of relative motion,the transmission of relative motion can only be approximately realized,and the transmission ratio fluctuates within a certain range.By reducing the distance from the center,the size of the rotary gear can be reduced,the transmission performance of the return gear can be improved,and the speed of the loom can be increased.
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