Research On An Under-actuated Self-adaptive Space Capture Device Based On Differential Mechanism

With the progress of science and technology, the competition in space resource isbecoming increasingly fierce, so that more and more spacecrafts are sent into space fortasks. Running out of fuel and structural failure or aging will both make the spacecraftlose effectiveness. Orbiting control technology makes it possible to improve thesurvivability and control efficiency of the spacecraft in space track. It has significanteconomic and military significance. Satellite capture plays an important role in orbitingcontrol technology and has drawn the attention of the world. Recently many countrieshave made further research in it. China has also started the research on space control inrecent years but it is just a beginning and it’s in the lack of effective technical means insatellite capture.To meet the requirements of lighert weight, smaller volume and the adaptation totargets in space capture device design, this paper develops a kind of under-actuatedself-adaptive space capture device which can perform several actions, such as folding,unfolding and grasping. The conceptual and structure designs of the capture device areproposed in this paper. The capture device consists of three3-dof under-actuatedmechanical fingers.4motors are adopted to drive9joints. The under-actuatedself-adaptive space capture device has a series of advantages. There are less motors andsimple structure in the device, so that the system is easy to be controlled. It is light inweight and occupies less space and it is reliable in capture function and self-adaptive totargets in different shapes and sizes.According to the kinematic characteristics of the capture device, the coordinates ofthe capture device single finger are established. Furthermore, the kinematics and inversekinematics are deduced and analyzed. The dynamic model of capturing is simplified asquasi-statics model. With deducing the mechanical equation, the relationship among thegrasping forces, the driving torques and damping torques is obtained. The influences ofdriving and damping torques, the structure parameters and the target sizes on thegrasping forces are also discussed. The quasi-static model is verified by the ADAMSmodeling and simulation.Lagrange equation method is adopted in the theoretical kinetics analysis of the theprocess of capture device folding and unfolding. The Lagrange equation of the capturedevice rigid system is established and the relationships among the Lagrange equationscoefficients are also analyzed. The simulation model of the capture device folding isestablished. The theoretical kinetics model is verified by comparing the simulationresults and the theoretical analysis results.The simulation model of the capture device capturing is established in the ADAMS. Different states of the capture device grasping a target in the inner finger multiple pointgrasping strategy are simulated by varying the driving sequence and driving velocitiesof the joints. The analysis results show that the capture device is self-adaptive to thetarget in the way of inner finger multiple point grasping. According to the structuredesign, the finger prototype of the capture device is developed. Through the control ofthe drive system, the tests of folding, unfolding and grasping functions areaccomplished. The curves of parameters in the process of folding, unfolding andgrasping are obtained. The test results show that the capture device automatically adjustthe relative position of the joints when grasoping targets in different shapes and sizes. Itcan completely envelop the targets and its self-adaptiveto different targets.