Stiffnes Characteristics Analysis Of Multi-Arc Beam And Applications In Compliant Mechanism

Compliant mechanisms have been increasingly used in fields such as bionic robotics,lowloss picking,precision polishing,and flexible operations,showing great scientific,economic,and social value.The demand for large-stroke high-precision force or displacement transmission for such applications is getting stronger and stronger.How to improve the deformation capacity of flexible mechanisms and realize flexible configuration of stiffness characteristics,so as to achieve high-precision force and displacement transfer in the large stroke range gradually becomes one of the key common technologies in the above-mentioned fields.In view of the contradiction between the deformation capacity of the flexible unit and the manufacturing difficulty,the lack of accurate modeling and rapid analysis methods for multisegment circular arc beams,and the lack of flexibility in the configurable stiffness of the flexible unit,this paper proposes a multi-segment circular arc beam structure with circular arc as the basic unit.A general theoretical analysis model based on the chain beam constraint model is then derived.And automated modeling and analysis is realized based on a nonlinear finite element method.Based on this,the stiffness configuration design method of multi-segment circular arc beam is proposed.Three basic multi-segment circular arc beam configurations with positive/negative/equal stiffness are designed and their stiffness characteristics are analyzed.The stiffness prediction model is then established and verified.Further,a quasi-constant force mechanism based on multi-segment circular arc beam is obtained through the stiffness synthesis.A curved-beam based steady state module is further introduced to design a large-stroke constant force gripper for force sensitive manipulation.The details of the study are as follows:Firstly,based on Euler-Bernoulli beam theory,methods to improve the deformation capacity of flexible beam unit is discussed.A new flexible beam unit based on multi-segment circular arc is proposed,and the formation principle of its large deformation is analyzed.Then,the geometric equations and displacement-deformation equations under general parameter conditions are derived.A general static model applicable to multi-segment circular arc beam is further established.Meanwhile,consdering the limitations of numerical solution methods on theoretical analysis models in parametric research applications,an automated modeling and analysis method based on nonlinear finite elements for multi-segment circular arc beams is proposed.And automatic analysis scripts based on Python and Abaqus and Abaqus modeling plug-ins are developed to realize parametric modeling,batch calculation and post-processing of multi-segment circular arc beams.In addition,for the problem of deviation of manufacturing prototype performance due to the process dependence of fused deposition manufacturing accuracy and the complexity of circular arc beam configuration parameters,the manufacturing prototype dimensions(central angle and radius)are measured and analyzed for manufacturing errors using vision technology.Thus,an effective set of tools is provided for the prediction of mechanical properties,performance evaluation,and parametric analysis of multi-segment circular arc beams.Secondly,based on the above method,the stiffness characteristics of multi-segment circular arc beam under concentrated load are numerically simulated,and the influence of the number of arcs,structure and material parameters on the stiffness of multi-segment circular arc beam is analyzed and summarized with the help of force-displacement curve and stressdisplacement curve.The method of simplifying the structural parameters of circular arc beam based on constraints is elaborated.Then,the stiffness characteristics of multi-segment circular arc beam are studied,and the stiffness design method of multi-segment circular arc beam is then proposed.The asymmetric output force/stiffness characteristics and stiffness matching method of four-segment circular arc beam structure are studied;the influence law of fivesegment circular arc beam structural parameters on the response quantities of ultimate load,critical displacement,minimum force,steady-state stroke,and the influence factors of the difference of stiffness in each direction of two-segment circular arc beam are analyzed.Positive/negative/equal stiffness circular arc beam configuration are designed.The prediction equations for the performance parameters of the corresponding configurations are then established and verified,which expand the existing library of flexible units and lay the foundation for the subsequent application of multi-segment circular arc beams in quasi-constant force mechanisms and force-sensitive gripper.Again,based on the analysis of the stiffness characteristics of multi-segment circular arc beams,the application of circular arc beams in quasi-constant force flexible mechanisms is explored from the perspective of single-arm beam design and optimization.Firstly,for the demand of precise force control of flexible mechanism in large range of force sensitive manipulaiton,a quasi-constant force mechanism of circular arc beam type compatible with fused deposition manufacturing technology is designed,which takes four segments of circular arc beam as the basic functional unit.A static model describing the mechanical characteristics of quasi-constant force mechanism is established,and the mechanism is verified by finite element analysis and experiment.A performance index accurately describing the stiffness characteristics of constant force mechanism is proposed.Design solution conducting quasiconstant force output in a wide range is obtained through parameter optimization.The design is compared with existing studies in terms of stress distribution,relative travel,and ease of fabrication.The results show that the theoretical analysis,finite element simulations and experimental results agree well and all show significant performance improvements over the existing results.Further,the application of multi-segment circular arc beams combined with conventional functional module units to meet complex functional requirements is explored based on module synthesis.A constant force gripper for grasping actively deforming objects is proposed for grasping large-stroke,variable-stiffness objects.The design utilizes a flexible constant force mechanism based on a four-segment circular beam to obtain quasi-constant force output over a wide range,and a bistable mechanism based on curved beam to eliminate the non-constant force range of motion,and also to enable switching between two grasping modes.Within the framework of the chain beam constraint model,a theoretical analytical model of the gripper is developed to predict its mechanical behavior,and then a multi-objective optimization method is used to optimize the parameters of stiffness and stroke.A gripper prototype is obtained by assembling constant force and steady-state functional units fabricated by fused deposition.The performance of proposed gripper is verified by comprehensive experimental studies.The results showed that the maximum fluctuation of the gripping force is 0.35 N when the size of the heart model is varied periodically between 53 mm and 65 mm at a frequency of 1 Hz,confirming the performance of the gripper.