Research On The 5-dof Compliant Parallel Posture Adjustment Mechanism For Large-aperture Grating Tiling

The world energy crisis is a major problem for human beings.The controllable laser inertial confinement fusion is considered as an important way to solve this problem.Diffraction grating,the core functional element in laser fusion system,is the key to deciding whether laser fusion can be realized or not.The gratings are highly susceptible to physical damage in the process of shooting.Increasing the apertures of the gratings becomes one of the main methods to enhance the output energy of laser fusion system.Because of the limitation of processing technology,the grating tiling mechanism is usually used to prepare large-aperture gratings by multiple small-aperture gratings.To ensure the success of laser shooting,the translation and rotation error between the tiling gratings must reach nanometer and micro-radian level.The grating tiling mechanism must also remain stable for a long time during the laser shooting process.Therefore,the motion accuracy and pose maintenance accuracy of the grating tiling mechanism are the bottleneck problems that limit the output energy of laser fusion system.In this dissertation,the mechanical modeling of flexure spherical hinges,the kinetostatic modeling of compliant parallel mechanisms,the optimization of the grating tiling mechanism and its control method for pose maintenance are studied with the focus on the high motion accuracy and pose maintenance of the grating tiling mechanism,aiming to provide the theoretical and technical basis for designing tiling mechanisms of heavy load,high accuracy and high pose maintenance.Since the mechanical modeling of flexure spherical hinges is the basis for the design and analysis of compliant parallel mechanisms,the mechanical model of flexure spherical hinges is firstly established based on Castigliano's second theorem in this dissertation.Introducing the elliptical eccentricity angle as the integration variable,the closed-form equations for compliances of elliptical-arc flexure spherical hinges are derived.The performance indices of elliptical-arc flexure spherical hinges are defined for mechanical property evaluation.The performance indices of various elliptical-arc flexure spherical hinges are analyzed using the established mechanical model to reveal the influence of the geometric parameters on the performance indices.Then,the elliptical-arc flexure spherical hinge with the optimal performance indices is selected.Finally,considering the effect of stress concentration,an accurate mechanical model of circular-arc flexure spherical hinges with different geometric parameters is established.It lays the foundation for the kinetostatic modeling of compliant parallel mechanisms.It also provides a theoretical foundation for the structural design and dimensional optimization of grating tiling mechanisms.Considering the characteristics of compliant parallel mechanisms such as coupling of kinematic,elasto-mechanic behaviors and complex configurations,an energy-based for kinetostatic modeling of generalized compliant parallel mechanisms is proposed,which can avoid the complex internal force analysis and kinematic solution.Since the number of elements in the proposed kinetostatic model is large and it cannot describe the force-displacement relationship between the input/output of the compliant parallel mechanisms in the form of an explicit expression.Combining the compliance matrix method and the transfer matrix method,a kinetostatic modeling method based on the substructure condensation is proposed to describe all the kinematic and static performances of compliant parallel mechanisms from the perspective of the input/output with a minimum number of elements,which provides a concise and efficient modeling method for the design and analysis of grating tiling mechanisms.To solve the contradiction between "heavy load" and "high accuracy" in the compliant parallel mechanism.A new 5-DOF compliant parallel mechanism for grating tiling is proposed based on constraint design method by decoupling driving and loading units.Based on the sub-structure condensation,the kinetostatic model of the grating tiling mechanism is established.Then,the input compliance and output compliance,the kinematic modeling and the coupling of the chains of the grating tiling mechanism are studied.To obtain the optimal performance of the grating tiling mechanism,taking the working space,the kinematic resolution and the stiffness of the mechanism as objectives,the non-dominated sorting genetic algorithms is adopted for mechanism design,and the performance indices of the optimized grating tiling mechanism is analyzed and evaluated.To achieve the high pose maintenance accuracy of the grating tiling mechanism in the laser shootiung process,the closed-loop control technology of the tiling mechanism is studied.Firstly,the motion control model of the grating tiling mechanism is derived.Then,the pose detection method is studied to realize the real-time pose detection of the grating tiling mechanism.Finally,the motion control algorithm,the pose detection algorithm and the closed-loop control algorithm are applied to achieve high pose maintenance accuracy of the grating tiling mechanism.The mechanical system,control system and measurement system of the grating tiling mechanism are established and integrated,and the experimental tests on the pose detection capability,open-loop motion performance and closed-loop pose maintenance are carried out based on the integrated system.By testing the performance indices,it is verified that the grating tiling mechanism designed in this dissertation can meet the design requirements.