| Light, high-speed, high-acceleration, high-precision flexible parallel robots are widelyused in industry, such as in the electronic assembly industry, precision machining andmeasurement field, aerospace industry and so on. The elastic deformation of its flexiblecomponents is very likely to be caused under the external force and inertia force. Thoseelastic deformations do not only affect kinematic accuracy and positioning precision, but alsocause fatigue and damage of the flexible components because of the heavy internal stress. Inorder to clearly understand the dynamic characteristics of the flexible parallel robots and thecoupling mechanism between the flexible component and the other flexible components, theflexible component and the rigid component, its dynamic model must be deeply researched.And, in order to suppress the elastic vibration of the flexible components and improve theperformance of the flexible parallel robots, the vibration control of the flexible componentsmust be systematically investigated. However, both elastodynamic modeling and vibrationcontrolling of complex flexible parallel robots have ever been a challenging task. In this paper,elastodynamic modelling and active vibration control of planer3-RRR flexible parallel robotsare systematically analyzed and studied. The main contributions in this thesis are listed asfollows:(1) Based on the finite element method (FEM) and Lagrange equation, elastodynamicmathematics model was established, in which the coupling influence of the elasticdeformation motion and the rigid-body motion, the axial deformation displacement and thetransverse deformation displacement of flexible beam were considered while its sheardeformation was ignored. The different constraint relationships of the system including rigidmotion constraint, elastic deformation motion constraint and dynamic constraint of themoving platform are derived. The dynamic characteristics of the system including sensitivityanalysis, frequency characteristics, model analysis and dynamic stress analysis are studied.The dynamic characteristics of planar3-RRR and3-PRR flexible parallel robots are presented.A comparative analysis of one-step method (KED method) and two-step method for solvingrigid-flexible coupling nonlinear dynamic equations is given. In consideration of the second-order coupling quantity of the axial displacement caused by the transversedisplacement of flexible beam, the first-order approximation coupling (FOAC) model ofplanar3-RRR flexible parallel robots is presented, and compared with the conventionalzero-order approximation coupling (ZOAC) model.(2) In general, the strain and stress are caused not only by the external exciting force, butalso temperature change. The effect of temperature change on dynamic performances ofplanar3-RRR flexible parallel robots is studied in this paper. Based on the Hamilton principleand the finite element method, the general thermal-elastic coupling dynamic equations of the3-RRR systems are determined. The flexible link maximum stress and elastic displacement ofthe moving platform and the flexible links with respect to temperature changes are studiedusing qualitative and quantitative method. The commercial software ANSYS13.0is used toconfirm the validity of the theory model.(3) The theoretical and experimental research for active vibration control of planar3-RRR flexible parallel robots. In theoretical study, both strain rate feedback controller andoptimal state feedback controller are designed based on general dynamic equations of thesystem. The simulation results reveal that two kinds of controllers can effectively suppressresidual vibration of the system. Moreover, comparing the strain rate feedback (SRF) control,the optimal state feedback control can obtain better control results in a lower control voltage.At the same time, the control result of pasting a pairs PZT film actuators is better than pastingjust one PZT film actuator. In experimental study, we only consider that passive links areflexible and each passive flexible link pastes two pairs of PZT actuator and one PZT filmsensor. Four control schemes that include three passive flexible links simultaneously control,only exert control to passive flexible link1, only exert control to passive flexible link2andonly exert control to passive flexible link3are designed based on the strain rate feedbackcontrol strategy. A comparative study is presented on four control schemes. The experimentalresults show that controlling one passive flexible link can only suppress elastic vibration itself.And when three passive flexible links simultaneously exert control, elastic vibration of allflexible links can be suppressed. |
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