Research On 3-PPSR Parallel Manipulator System With High Aspect Ratio Flexibel Hinges

With the gradual improvement in the robot technology,the kinds of robots for the special operation are continuously increased.These robots expand their application fields to micro-electric manufacturing,MEMS(Micro Electric Mechanical System)packing and assembly,high-precision machining and assembly,bio-chips manufacturing,large-scale and high-speed scanning and other industries.Subsequently,the robots' performances in those industries are demanded higher and higher,which need high positioning accuracy,high repeatability,high resolution,and simultaneously large motion range,light mass,and low energy consumption etc.In recent years,in order to meet the needs of human beings to explore the small world,as an important branch of the development of robot technologies,the micro robot manipulator has become a very active research field.According to a wide literature review on current compliant precision positioning systems,parallel precision positioning systems,and aiming at the current actual requirements for the simultaneous large motion range and high precision positioning,a high aspect ratio flexure hinge's conceptual design is proposed in this paper,based on which a three-link high aspect ratio flexure hinge parallel positioning robot system is established.In order to meet the needs of the ultra high-precision positioning,the PZT actuators are integrated in the parallel links to constitute a parallel system,in which the design thinking of the integration of actuation,structure and sensor-feedback is fully exhibited.On the aspect of the structure element design,aiming at the problem of the currently used flexure hinges' small motion range,a high aspect ratio flexure hinge's conceptual design is proposed based on the general spherical and rotating flexure hinges.On the aspect of the parallel structure design,a novel thinking of establishing high aspect ratio flexure hinge-based parallel system is given,in which the high aspect ratio flexure hinges substitute the conventional motion joints used in the general parallel manipulator systems.In the high aspect ratio flexure hinge-based parallel system's kinematics modeling,the mathematics model of the high aspect ratio flexure hinge is firstly deduced,utilizing the mechanics basic theory and the small deformation suppose.Based on the mathematics model's explicit formulation in the global coordinates system,the deformation expression of the whole individual kinematics link is established via the stiffness assembly method.And then utilizing the motion displacement constrained formulations and the force constrained formulations,the displacement model of the whole parallel positioning system is established.The elements in the parallel structure system,especially the wide-range flexure hinges,undergo large scale rigid motion when offer motion outputs via self deformation for the whole parallel structure,which leads displacement model of the high aspect ratio flexure hinge-based parallel system is a typical geometric nonlinearity problem.So,the stiffness matrix's recursive model is deduced,based on which the displacement of this model can be solved out utilizing the NewtonLeverson method.Since the iterative type of the geometric nonlinear solution,the model behaves in a bad real-time characteristic,which is very difficult to be replanted to solve in the real-time control system.Based on a plenty of attempts,the BP neutral networks method is adopted,in which a 3 layers and 6-inputs/6-outputs neutral networks structure is established,so it promotes the displacement model solution's velocity at the same time of convenient to real-time programming control.Since the displacement model of the high aspect ratio flexure hinge-based parallel system includes not only the displacement information also the relevant force and stiffness information,the stiffness model of this kind of compliant parallel systems is given based on the former displacement model,which provides powerful and visual tools for this compliant para llel structures' synthesis and optimization in the future.Finally,a 3-PPSR parallel positioning prototype system utilizing the high aspect ratio flexure hinges as the passive joints is proposed,in which the piezoelectric motors are adopted as the actuators and the precise linear encoders are adopted as the displacement sensors respectively.And this prototype system can realize micrometer level precision in the cubic centimeters level's workspace.Combined the steady state error of the combined force tracking model,it is to control external environmental force by adjusting the initial reference position.The analyses have been accomplished that the force tracking control based on the position by using the accurate environmental variables and the adaptive control by using a adaptive controller to control the deviation force while in uncertain external environment variable conditions.This dual actuation parallel system can meet the requirements of the large motion range and high precision simultaneously.