Configuration Synthesis And Performance Analysis Of Overconstrained/Non-Overconstrained Parallel Legs

A walking robot with overconstrained/non-overconstrained parallel legs has the advantages of good stability,large bearing capacity,flexible movement and good adaptability to complex road environment.The overconstrained/non-overconstrained parallel leg mechanism is reconfigurable(switching between overconstrained mode and non-overconstrained mode),and its reconfiguration principle is as follows: through self-motion of the deformable moving platform,so that the axis direction of the rotating pairs directly connected with the deformable moving platform at the end of the branched-chain is changed,then the constraint screws and degree of freedom of the parallel leg mechanism are changed,so as to realize reconfiguration of parallel leg mechanism between the overconstrained mode and non-overconstrained mode.Firstly,deformable moving platform of parallel leg mechanism is designed,introduce passive motion pairs into an overconstrained Goldberg mechanism to obtain a non-overconstrained Goldberg mechanism,five kinds of 6-bar single closed-loop mechanisms are obtained by combining non-overconstrained Goldberg mechanisms,according to the conditions of good symmetry,easy control and simple assembly,the 6-bar single closed-loop mechanism is optimized,finally,5R1 S space single closed-loop mechanism is selected as the deformable moving platform of parallel leg mechanism(that is,the foot ball of robot with parallel legs).When the robot walks on the ground,the overconstrained parallel leg mechanism with three-movements and one-revolution degrees of freedom are synthesized based on the screw theory,at this point,the center of mass of all pairs of the deformable moving platform of the parallel leg mechanism is located in the same plane;When the robot walks on uneven ground,the deformable moving platform of parallel leg mechanism moves itself,according to the principle of reconfigurable,non-overconstrained parallel leg mechanisms with three-movements,two-movements and one-revolution,one-movement and two-revolutions three kinds of degrees of freedom are obtained.To optimize and improve the overconstrained/non-overconstrained parallel leg mechanisms,and finally,the 3-R(2-RPR)R mechanism with the overconstrained mode as three-movements and one-revolution degrees of freedom and the non-overconstrained mode as two-revolutions and one-movement degrees of freedom is determined as the parallel legs mechanism of the quadruped walking robot.The kinematic analysis of deformable moving platform is carried out,the degrees of freedom of deformable moving platform under general position and plane position are both 2,and the closed-loop equations(input-output motion parameters equations)is obtained according to the transformation matrix between coordinate systems.Then,the kinematic performance of 3-R(2-RPR)R parallel leg mechanism with overconstrained mode as three-movements and one-revolution degrees of freedom and non-overconstrained mode as two-revolutions and one-movement is analyzed.The degrees of freedom of two modes are verified based on the screw theory,thus proving the correctness of the configuration synthesis.The closed-loop vector method is used to solve the inverse solution of two modes,and the derivative of the inverse solution is used to obtain the jacobian matrix.When the determinant of the jacobian matrix is 0,the singular configurations of two modes are obtained.By analyzing the degree of freedom of singular configurations,the correctness of the inverse solution and the singular configurations of the mechanism are proved.The workspace of two modes are obtained by boundary search method.The kinematic simulation of the overconstrained mode and the non-overconstrained mode switch process of the parallel leg is carried out,and the displacement curves of each drive are obtained to prove the feasibility of the reconfiguration of the parallel leg.In this paper,a cycloid with no mutation in velocity and acceleration in the x and z directions is designed as the trajectory of the foot end of the quadruped robot,so that the movement and force transfer performance of parallel legs is good when the robot walks.By analyzing the stability of the quadruped robot,the condition that the stability margin is greater than 0 is obtained.The center of gravity adjustment scheme and gait planning of quadruped robot in parallel leg with overconstrained mode and non-overconstrained mode are designed respectively,and the walking simulation of robot is carried out by using Solid Works,thus,the rationality of the quadruped walking robot design and the feasibility of walking are proved.