Research On The Large Range Flexure Hinges And Related Planar Compliant Parallel Manipulators

High-precision transmission technology is an important supporting technology for modern precision equipment.With the development of precision engineering,mechanical transmission devices that provide motion accuracy of micron under centimeters' motion range are highly demanded.However,the traditional compliant parallel mechanism can only provide a micron-scale workspace due to the limited hinge angle range.To solve this problem,this thesis investigated the design and control of long stroke planar compliant parallel manipulators(CPM)with the support of National Natural Science Foundation of China.The main contents include structural design,mechanical modeling,and performance analysis of the large range flexure hinges,and optimization design,inverse kinematics modeling and trajectory tracking control of compliant parallel mechanisms.A variable thickness flexure pivot(VTFP)is designed to improve the performance of the traditional flexure pivot,which can be considered as a combination of the conventional notched flexure hinge and the spring leaf flexure pivot.The VTFP has better motion accuracy and better ability to resist axial force compared with the conventional flexure pivot since the deformation of the VTFP is more concentrated on the designed rotational center.Two static deformation models of the VTFP are established based on the nonlinear beam bending theory and the corotational beam element.The effectiveness of deformation models are verified by finite element analysis software ANSYS and experiments.Based on the static deformation model,four indexes are defined to evaluate the rotation performance of the VTFP,and the influence of the geometric parameters on performance indexes are investigated.A superelastic flexure hinge is proposed to enlarge the motion range of the notched flexure hinge,due to the excellent deformability of shape memory alloy(SMA).The superelastic behavior of the SMA is described by the Brinson's constitutive model,and the material constitutive parameters are obtained by uniaxial tensile test.A load-displacement relationship of the superelastic flexure hinge is established by combining the constitutive model and the nonlinear beam bending theory.To improve the computational efficiency of the static deformation model,a linearized constitutive model is proposed and substituted into the corotational beam element.The effectiveness of the model is verified by finite element analysis and experiments.Based on the deformation model,the potential of the superelastic flexure hinge to construct long stroke compliant mechanisms is illustrated,and the parametric analysis is also performed.Multi-objective optimization of the VTFP and the superelastic flexure hinge are conducted by applying the NSGA II algorithms to obtain the optimal parameters of the flexure hinges to minimize the performance deviation between the flexure hinge and the ideal rotational joint.The dimension parameters of the 3-PRR manipulator are also be optimized to maximize the global condition index under the regular workspace of the manipulator.By integrating the optimized flexure hinges and the 3-PRR manipulator,two 3-PRR CPMs,i.e.,VTFP-3PRR and SEFH-3PRR,are designed and fabricated.In order to consider the parasitic rotational center shift of the VTFPs,an accurate compliant inverse kinematic model(CIKM)is established for the VTFP-3PRR CPM,numerical results show the accuracy of the proposed method compared with the rigid inverse kinematic model.A finite time disturbance observer based integral sliding mode control(FTDOISMC)is designed to compensate the friction,the dead zones and the nonlinear perturbations in a linear ultrasonic motor(LUSM)based linear stage.Experiments show that the trajectory tracking accuracy of LUSM based stage can reach 300 nm under the FTDO-ISMC.Resolution and repeatability tests of the manipulators are performed by precisely controlling the LUSM based stage.To suppress model mismatches and external disturbances of the 3-PRR CPMs,a disturbance observer based inverse kinematics control(DOB-IKM)method is proposed,where the unmodeled factors of the system is approximated through an online learning radical basis function neural network(RBFNN),and the external disturbances of the CPM is observed and compensated by the DOB.Experiment results show that the proposed 3-PRR manipulators can achieve micron scale translational tracking accuracy and micro-degree rotational tracking accuracy under the proposed DOB-IKM control scheme.