Design And Research Of Foldable Capture Mechanism Based On Spatial Linkages

Non-cooperative objects in space have the characteristics of unknown motion parameters and often present uncontrolled free tumbling motion in space.However,the traditional spatial capture mechanism generally adopts the form of series manipulator,which requires the target to have a fixed capture point,so the capture of space free tumbling target has certain limitations.Spatial folded mechanism is widely used in space technology because of its large folding ratio.However,the application of spatial capture technology has not been studied in detail.Based on the background of spatial non-cooperative target capture,this paper gives full play to the advantages of large folding ratio of spatial folded mechanism,and proposes a new spatial 8R folded mechanism.The specific research contents are as follows:(1)Firstly,it is classified according to the different service objects of the spatial free tumbling target,so as to obtain the motion characteristics of the spatial capture target.The commonly used coordinate system in space is defined and the mathematical model of free tumbling motion of spatial object is established by using quaternion method.According to the relationship between the rolling axis and the butt axis of the target,the motion characteristics of the target are classified,the initial motion conditions of the target under different initial conditions are given,and the motion range of the target is obtained according to the established mathematical model.After analyzing the motion characteristics of the space target,two design requirements of the capture mechanism are put forward.Firstly,it has the feature of large folding ratio to meet the conditions that it is convenient to transport and store under full folding.Secondly,the workspace of the spatial capture mechanism can achieve the envelopment of the movement of the target.(2)According to the motion characteristics of the target and the design requirements of the spatial capture mechanism,the method of embracing outer envelope capture is proposed to capture the target.According to the geometric parameters,a spatial 8R folded mechanism with complete folded characteristics is designed.By using the helical theory to analyze the degree of freedom(DOF)and the geometric method to analyze the kinematics and bifurcation characteristics of the mechanism,the instantaneous 3 DOF of the mechanism is obtained,and the loop equation of the mechanism at the general position and bifurcation position is established.The results of kinematics analysis verify that the workspace of the spatial capture mechanism can achieve the envelop of the motion of the target.(3)The 3D model established in Solidworks was imported into Adams for simulation analysis,and the optimal expansion time of the mechanism was obtained by analyzing the curve of the relation between the input driving torque value of the spatial capture mechanism and the time through simulation.By setting the parameters of the target,the target presents a free tumbling motion according to the predetermined parameters,and by carrying out tolerance and overload analysis,the contact force at its end can be stabilized near a constant value.Thus,it is verified that the mechanism can achieve the stable capture of the target,and the input driving force torque value required by the mechanism to achieve the stable acquisition is obtained.(4)According to the results of theoretical analysis,the design of typical joint segment of 1:1 prototype and scale prototype of the capture mechanism were carried out.By carrying out ground demonstration experiments,the folding function of the spatial capture mechanism and the capture function tests for targets of different sizes and shapes are realized.Moreover,the angle value of input driving joint is measured and compared with the theoretical value to verify the correctness of the theoretical analysis.(5)Finally,in order to increase the folding ratio of the mechanism and improve the mechanical performance of the member,two networked assembly forms of the spatial 8R mechanism were proposed,that is,by expanding the spatial 8R mechanism as the unit module and assembling the shear fork spatial 8R mechanism as the unit module.This kind of mechanism can expand to a sphere while having the folding function so as to achieve the motion envelope of the target.