Structure Design And Motion Control Of A Parallel Metamorphic Mechanism

The metamorphic mechanism is capable of varying DOFs and topological structures,which is called the metamorphic characteristic.By integrating the metamorphic mechanism into the design of the parallel mechanism,the parallel mechanism with metamorphic characteristics can be obtained,which is called the parallel metamorphic mechanism.In practical engineering,more and more actuators need to have the characteristics of multi-function,faced with different work tasks,only simple operation can realize the switch of functions.The existence of the parallel metamorphic mechanism provides the possibility for this demand.Firstly,a new type of metamorphic joint is proposed in this research,it can be equivalent to three hinges under different conditions,subsequently,six kinds of branch chains constituted of the joint are analyzed.Then,based on the screw theory,a new mechanism is analyzed,its degrees of freedom from 3 to 6.It has been verified the validity of the theoretical analysis through practical experiments.To make its motion controllable,the actuating constraint schemes of this new mechanism under different configurations are analyzed.On this basis,the inverse kinematics model is established.Secondly,a new dynamic modeling method is proposed,and the universal steps of this method are explained systematically.Two constraints,structural constraints and kinematic constraints are proposed.The U-K method was used to obtain the dynamic model of the 3-(aLV)PS parallel metamorphic mechanism,and the biggest advantage of this method is that the dynamic model in analytical form can be obtained.On the one hand,it has been used Matlab for numerical simulation of its dynamics model,and on the other hand,it can be used Adams for virtual simulation.By contrast,the validity of this new method can be verified.Finally,based on the U-K theory,a control method for the new mechanism is raised.The controller is designed by this method:(1)Realize trajectory tracking control of the platform;(2)The analytical force required by the actuator when the expected trajectory is satisfied;(3)When the expected trajectory is satisfied,the analytic solution of each generalized coordinate is obtained.Matlab is used to compare the actual motion trajectory with the expected.In this paper,the theoretical research of parallel metamorphic mechanisms has been enriched,meanwhile,a new method was provided for dynamic modeling and motion control of parallel metamorphic mechanisms.