Design And Kinematotropic Characteristics Study Of Single-loop Overconstrained Mechanisms

Single-loop mechanism is an essential foundation for the study of multi-loop complex mechanism such as parallel,hybrid and redundantly actuated mechanism.The kinematotropic mechanism in variable-degree-of-freedom mechanism has wide application prospect in multi-function,multi-mode operation equipment and so on.In recent years,researchers have proposed some configurations for single-loop kinematotropic mechanisms,but there is still no systematic method.In this paper,a design method of single-loop overconstrained mechanism is proposed and applied to single-loop kinematotropic mechanisms.A limb design method of the single-loop overconstrained mechanism is proposed based on the screw theory and the influence of overconstraint on the degree of freedom of the single-loop mechanism.The limb parameter Lcn is defined.From the spatial relations of adjacency revolute joint axes,the alternative limb libraries of different spatial adjacency relations are established,and the wrench system that these branches can provide is analyzed.The limb wrench system is combined to study the common constraint types which can be obtained by limb combination.By means of the intersection relation of wrench systems,the composing solution of single-loop overconstrained mechanism with different constraint types,different link numbers and different configurations is obtained.Based on the degree of freedom of the single-loop mechanism and the limb design method of the single-loop overconstrained mechanism,the dual-limb scheme of the single-loop 6R overconstrained mechanism is proposed.The geometric conditions which can make the dual-limb provide the coincident force constraint are proposed.A new type of 6R overconstrained mechanism is designed based on one of the geometric conditions which guarantee the existence of the common force constraint.The twist system of 6R overconstrained mechanism is analyzed,and the closed loop equations of the mechanism are established.The principle and design principle of the kinematotropic mechanism are clarified.The concept of critical instantaneous configuration,pairing joint and pairing triggering motion of a kinematotropic mechanism is proposed.The 4R limb of L4PIP is selected according to the limb design method proposed in Chapter 2,and a common couple constraint geometric condition is proposed to construct an 8R single-loop kinematotropic mechanism with RR pairing joints.From the point of view of geometry closure,8R kinematotropic mechanism is obtained,which has four motion branches under two initial positions.From the point of view of the critical instantaneous configuration of the kinematotropic mechanism,according to the triggering movement of pairing joints,the mechanism has three mutually exclusive modes.Based on the new 8R kinematotropic mechanism,a biped/wheel dual-mode mobile robot is designed.The robot's walking function is realized by the 8R kinematotropic mechanism in the non-triggering motion branch.Respectively,different combinations of different active joints were applied;the kinematics simulation of the 8R mechanism was carried out.The kinematic characteristics such as the degree of freedom of the corresponding motion branch are verified,and the driving scheme is given.The basic gaits of the robot in biped walking mode are planned.The switch of 8R kinematotropic mechanism is realized by topology expansion.The wheeled robot is designed with the advantage of the critical instantaneous configuration of the mechanism.The mechanical structure of the robot is designed and the support of the robot is solved in double working modes.Finally,a prototype of the dual-mode robot is established.