The Theoretical And Eexperimental Study Of Novel Large-stroke Compliant Parallel Mechanism

With the constantly developing technology in the military engineering, opticalcommunication engineering, biological engineering, precision mechanical engineering andprecision optical engineering, there is an urgent need for the new-type robots, which possessmuch better performances in all aspects, that can adapt to the increasingly higherrequirements of operation. A well-designed compliant parallel mechanism has relatively goodperformances with respect to the operation accuracy, response speed, load-bearing capacity,controllability and flexibility. However, its rotational angle is so strictly limited by the type ofthe compliant hinge, material stiffness and the material elastic limit that the workspacegenerally tends to be small.In this paper, we study the design of the large-deformation compliant hooke hinge andthe large-stroke compliant parallel mechanism. The study mainly consists of the followingthree parts:(1) A new-type multi-reed hooke joints with large deformability is designed. Based onthe pseudo-rigid-body model and the nonlinear finite-element simulation results, we verify theeffectiveness of the hinge structure and the validity of the hinge model. This design accordwith the rotation characteristics of the hooke hinge. On the basis of the preliminary design ofthe hooke hinge, the multi-objective optimization designwith respect to all the hinge’sperformance indexes is implemented. The optimization is aimed at increasing the strokedistanceand the stiffness of the hinge at the non-functional direction, improving theload-bearing capacity, and reducing the manufacturing difficulty etc.. The optimizationproduces an ultimate structure called the assembled Compliant Hooke Joint that can achievehigh-precision, wide-angle, two-dimension rotational motion. The symmetric layout of thecomposite straight-curving flexible reeds improves both the axial and radial stiffness of thehinge. When only the torque is applied, there is no substantial axial drift. Therefore, theCompliant Hooke Joint is an excellent compliant hooke joint with large deformability.(2) Based on the large-deformation compliant hooke joint, a PUU kinematic chain isdesigned. Arranging four PUU kinematic chain symmetrically, we build a large-stroke3-DOFs spatial compliant parallel mechanism. The freedom of motion of the PUU kinematicchains and the parallel mechanism are analyzed by using the spiral theory. And the equivalentpseudo-rigid-body model of the3-DOFs compliant parallel mechanism is established. Therobot’s inverse solution of the position and the Jacobi matrix of the speed are derived. Results from the non-linear finite-element simulation show that the equivalent pseudo-rigid bodymodel of the robot is effective. According to angle range of the compliant hooke hinge, the3-DOFs compliant parallel mechanism can reach a workspace of cubic centimeters.(3) Based on the large-deformation compliant hooke joint, a PURU and a UC kinematicchain are designed. Arranging four PUU kinematic chains and one UC kinematic chain, webuild a large-stroke4-DOFs spatial compliant parallel mechanism. The DOFs of the PUUkinematic chains, the UC kinematic chain and the parallel mechanism are analyzed by usingthe spiral theory. And the equivalent pseudo-rigid-body model of4-DOFs compliant parallelmechanism is established. The robot’s inverse solution of the position and the Jacobi matrix ofthe speed are derived. With respect to angle range of the compliant hooke hinge, theworkspace of the4-DOFs compliant parallel mechanism is analyzed. According to thecomparison results of the nonlinear finite-element, this compliant robot can produce ahigh-precision large output of three-dimension rotation and one-dimension translation.(4) Based on the above-mentioned studies, we conducted the experiments of3-DOFs and4-DOFs large-stroke compliant parallel mechanisms. Afterwards, the experiment errors werediscussed. And we then corrected the equivalent pseudo-rigid body model of the compliantparallel mechanisms according to the source of the errors. The experiment results of themodified formula shows that the modified formula is valid and can significantly reduce theexperiment errors.