Type Synthesis And Control Of 3T1R Displacement Output For Parallel Mechanisms

Three translational and one rotational(3T1R)mechanism is a kind of lower-mobility PM,which is applied to high-speed transmission,pick-and-place and assembly operations of materials in industries of electronics,foods,packaging and other fields.The complexity of the mechanism is difficult to synthesize,and often has overconstraints,which is difficult to establish a unified kinematics and dynamics model.However,there is a lack of the non-independent parameter mechanism with the advantage of less actuators and a simple structure,and the mechanism with large rotational capability,these mechanisms have great potentials in practical application.The main reason is the lack of an effective type synthesis theory for the mechanism with non-independent parameters and large rotational capability.The three translational(3T)displacement output mechanism,3T1R displacement output mechanism and the semi-circular rotational mechanism are synthesized,respectively.The generalized theoretical model of the 3T1R mechanism is established,the dynamics of the synthesized mechanisms are built.To meet fast picking requirements,the control system of the mechanism is designed.The main contents of the paper are as follows:(1)For 3T mechanism with non-independent parameters,a generalized link group synthesis method is proposed,which further extends the theory of link groups applied in the space.The concept of infinitesimal displacement parameters is proposed to describe the displacement parameters.The dependence on the change in the degree of freedom(DOF)and displacement parameters of the output link are analyzed.The link groups with3T displacement parameters are synthesized,and the intersection operation rules are given.Based on the single-loop mechanism,the 1-,2-and 3-DOF dual-loop mechanisms are obtained by adding corresponding 0-DOF generalized link groups.The multi-loop mechanisms are obtained by adding 0-DOF generalized link groups.(2)For 3T1R mechanism with non-independent parameters,a generalized link group synthesis method for 3T1R displacement output mechanism is proposed.The internal relation on the change in the DOF and displacement parameters of the output link after adding 0-DOF generalized link group is analyzed.The link groups with 3T1R displacement parameters are synthesized.The single-loop mechanisms are are synthesized,the 2-,3-,and 4-DOF multi-loop mechanisms are obtained by adding 0-DOF generalized link groups.(3)For the 3T1R mechanism,synthesis method of a family of semi-circular rotational mechanism is proposed.Three kinds of moving platform structures are designed to ensure that the parallel mechanism has a wide range of rotating ability,and three parallelogram structures are analyzed,and the corresponding limb structure is synthesized,a family of semi-circular rotational PM are obtained.The 6×6 Jacobian matrix and 6×6×6Hessian matrix of the proposed 4-P(2-SS)R PM are derived.The singularity configurations of the PM and the range of rotation of the moving platform are analyzed.(4)For two type constrained couple limbs of the 3T1R mechanism,the unified modeling method of 2×6 constrained Jacobian matrix and 2×6×6 constrained Hessian matrix are established,the kinematics model of the 4-RRRRR mechanism is established by the method.The singular configuration of the 3T1R mechanism affected by the constrained Jacobian matrix is analyzed.The unified dynamic model of the 3T1R mechanism is established,the kinematics and dynamics of the 2-(UPU)~2R mechanism are established,and the singularity affected by the Jacobian matrix is analyzed.(5)For the improved 2-(PUU)~2R mechanism,the kinematics and dynamics of the mechanism is established,a adaptive fuzzy terminal sliding mode control algorithm with disturbance observer is proposed.Disturbance observer is introduced to feed into the terminal sliding mode control(TSMC)which have improved the ability to resist the external disturbance.In addition,the chattering caused by the TSMC is eliminated by approximating the switching gain with the usage of adaptive fuzzy logic,the stability of the control system can be proved by Lyapunov stable theory.Compared with control effects of three control methods under high frequency and low frequency tracking trajectories,the proposed method has the better robustness and higher precision.