Design And Experiment Research Of An Underactuated Cable-truss Gripper

With the increase of space activities and the continuous development of spacerobot, underactuated mechanisms become one of the important research directionsof space agencies. Underactuated mechanis ms are mechanisms in which the numberof its actuators is smaller than that of its degrees of freedom(DOF). Compared withthe other mechanis ms, they take the advantages of light weight, small number ofdriving motors, simple structure, high reliability and wide adaptability.Two design schemes of the underactuated cable-truss mechanisms are putforward according to the characteristics of the existing undertactuated mechanisms.By comparing the advantages and disadvantages of the two schemes, the design baseon the parallelogram cable-truss is chosen and the3D model is established. Thefeasibility of the structural design is proven with the introduction of the workingprinciple and the mechanical analysis of the mechanism.Coordinate transformation method is used to build the coordinate system of thecontact rods and the relationship equation between the driving ropes and parametersof the institutions. Through analyzing the characteristics of the different capturestrategies, one of them, which is most suitable for the actual work and easy torealize, is collected and the problems of the inverse kinematics and forwardkinematics are solved. The correctness of the theoretical analys is is verified with thehelp of the kinematics simulation by using ADAMS software.By means of combining with the vector method and the principle of virtualwork, the equations representing the relationship between the grasping forces anddriving forces, includ ing the tensions of the ropes and the friction torques of thefriction joints, are obtained. The influence of the proportion relationship betweenthe length and width of the essential units to the stiffness of the mechanism isdiscussed. The mechanis m dynamics equations are established based on Lagrangeequation and the dynamics equations corresponding to the capture strategy that hasbeen chosen are separately listed. The statics simulation and dynamics simulationused ADAMS software are presented to prove the correctness of the analysis.The institutions prototype is made and the experiment to verify the agencyfunctions is conducted. The tests to choose the material of the friction joint and todemarcate the friction torque are done. The adaptability of the mechanism is verifiedthrough a series of experiments to the targets with different size and shape.