Research On Space Capturing Mechanism Actuated By Shape Memory Alloy

In recent years,with the rapid development of the on-orbit services,the onorbit capture for space uncooperative targets are drawing more attentions around the world.A series of background research on space uncooperative targets capturing technologies are investigated and compared.Current traditional robotic grippers for on-orbit capture missions have several disadvantages: large volume and weight,huge energy consumption and high cost.To overcome these problems,a novel design of parallel gripper actuated by a large-stroke shape memory alloy(SMA)actuator is proposed.According to the technical specifications and design requirements of the SMA gripper,the mechanical design and operationg principles of the gripper is presented,including the SMA actuator,the coupler mechanism and the gripping claws.In order to evaluate the working performance of the proposed SMA gripper,three theoretical models are developed for bias element selection,gripping force calculation and capture range analysis.A sensory feedback system is developed for the SMA gripper to obtain the crucial information of the SMA gripper during the capturing mission and to determine if the capture mission is successful.There are two characteristics of SMA materials,including shape memory effect(SME)and pseudoelasticity(PE).Based on Brinson's macroscopic phenomenological one-dimensional constitutive models,the stress-strain relationship of the SMA wire is established,and the design theories and methods of SMA actuator is developed.The driving properties of three typical types of SMA actuators,such as one-directional SMA actuator,bias force SMA actuator and differential SMA actuator are investigated respectively.The thermomechanical behavior of SMA wire is presented and different parameters and their relationships are investigated to make use of SMA wire as an actuator.A novel theory model for analyzing potential driving energy and mechanical efficiency of SMA actuator is proposed.A structural statics simulation analysis is given on the four types of sliding shafts and transient dynamic simulation analysis on the cross-shear hinge mechanism through CAE.Characteristics of the SMA wire used in this research are tested and a multifunctional experimental system was designed to investigate the output performance of SMA actuator.A prototype of the SMA gripper is fabricated and a series of experiments are conducted.Four cylindrical acrylic shells of different sizes are firstly selected to validate the graspi ng function of the SMA gripper.The results indicate that the proposed SMA gripper can grasp targets reliably and adaptively.The gripping force and capturing range under different bias forces and different currents are tested.The experimental observation s are in good agreement with the theoretical results which demonstrates the correctness of the proposed theoretical models.Finally,the capture accuracy of the SMA gripper is investigated and the research results indicate that the SMA gripper can grasp the target precisely and adaptively.