Design And Performance Analysis Of Rigid Flexible Coupling Elbow Assist Mechanism

As a new subject in mechanism research,rigid flexible coupled parallel mechanism makes up for the disadvantages of traditional rigid and bulky and poor support of flexible mechanism by virtue of the integration of the advantages of rigid mechanism and flexible mechanism.Based on the research status of elbow joint power assist mechanism and rigid flexible coupling parallel mechanism at home and abroad,this paper aims at the urgent demand for power assist device that can be attached to human body because people can not provide enough force in lifting heavy objects.Based on the analysis of the structure and motion characteristics of the elbow joint,a rigid flexible coupling wearable elbow joint assist mechanism is proposed.Through the fixation of the binding belt,the elbow and shoulder cooperate with each other to lift the object,so as to reduce most of the load generated by the human body.Firstly,the configuration design of rigid flexible coupling elbow assist mechanism is carried out.According to the structure and motion characteristics of human elbow joint,the degree of freedom of elbow joint is analyzed.On the basis of meeting the five design requirements,the configuration scheme of the rigid flexible coupling power assisted mechanism is determined,and a power assisted mechanism with three flexible cables and a rigid telescopic sleeve as the main body is proposed.On this basis,a rotating pair is connected in series through the boom sleeve to avoid the interference between the mechanism and the human body.The mechanism can realize three rotational movements,including bending /extension of elbow joint,rotation around its own axis and pronation / supination of forearm;It can realize the telescopic and translational movement of one sleeve,which is a 4-DOF power assisted mechanism.Then,the kinematics of the rigid flexible coupling power assisted mechanism is analyzed.According to the characteristics that the flexible cable in the rigid flexible coupling power assisted mechanism is not under pressure,the main part of the mechanism is finally simplified into a 3-UPS / up parallel mechanism model.Based on the screw theory,the screw matrix of3-UPS / up parallel mechanism is established,and the degree of freedom of the mechanism is obtained,which is verified by the improved G-K formula.The position of 3-UPS / up parallel mechanism is analyzed,and its inverse position solution is obtained;The positive position solution of the mechanism is analyzed by numerical iteration method,and the positive position solution is verified by particle swarm optimization algorithm.Within the range of constraint parameters,the workspace of the power assisted mechanism is obtained by MATLAB programming and three-dimensional coordinate search method.The results show that the workspace is continuous,indicating that the power assisted mechanism has no singular configuration and good motion characteristics.Then,the motion influence matrix is solved,and the dynamics of the mechanism is analyzed.The first-order influence coefficient matrix of the rigid flexible coupling elbow assist mechanism,that is,the velocity Jacobian matrix,is obtained by deriving the time on both sides of the equal sign of the position inverse solution expression.The dynamic model of the mechanism is constructed by using the influence coefficient method,and its dynamic analysis is carried out.The forces on the moving platform,three driving ropes and the middle branch chain are analyzed.The forces and moments are simplified at their respective center points,and the corresponding equivalent forces and equivalent moments are obtained.According to the principle of virtual work,the balance equation is listed,and the driving force and driving torque are obtained.Through MATLAB simulation,the smooth change diagram of flexible cable tension is obtained,and the results are basically consistent with the theoretical value.It verifies the correctness of the theoretical analysis of mechanism mechanics,and shows that the mechanism has stability and can realize stable assistance.Then,ADAMS software and Solid Works software are used for joint simulation to test the kinematic theoretical analysis.The flexible cable in the mechanism is equivalent and simplified,and the virtual prototype of the mechanism in Adams environment is reconstructed.The forward and inverse solutions of the mechanism are simulated to obtain the curves of buckling / extension and pronation / backspin.From the curves,the expansion and contraction changes of the branch chains I,II and III of the rigid flexible coupling booster mechanism in the X,y and Z directions are obtained,and the curves are smooth and continuous without protruding points.Through comparison,the inverse solution simulation and forward solution simulation curves of the kinematics of the mechanism in flexion / extension and pronation /supination assisted motion are obtained,which verifies the correctness of the theoretical analysis of forward and inverse solutions in kinematics.Finally,the mechanism is evaluated in anybody.It was found that the prime mover of flexion / extension movement was the most active at 30 ° ～ 130 °;When pronation /supination is performed at-20 ° ～ 50 °,the pronator and supinator muscles are the most active.Next,the anybody’s assistance performance is tested and analyzed.Within the angle range of the best muscle activity,the loads of four masses are increased respectively.The results show that the assistance performance provided by the assistance mechanism also changes for loads of different masses.The greater the load,the greater the power it can provide;The weight of the human body is slightly reduced,but there is a slight difference in the allowable response time.