| With the development of science and technology,aerospace,aviation,and nuclear power have gradually become important areas to highlight the power of a country.Regular inspection and maintenance are necessary for ensuring the operation of equipments such as spacecraft,large aircraft,and nuclear facility.While such equipments often have complex structures so that the workspace available for inspection and maintenance is very confined.The cable-driven hyper redundant manipulator with strong flexibility can cross the confined space and adapt to the extreme environment,so it has great potential applications.However,its kinematics modeling,trajectory planning and control are much more complex than traditional joint-driven manipulator.Based on these reasons,this paper carried out the research on the above theories,and established experiment system for demonstration.A segmented geometry method is proposed to resolve the end-effector pose(position and attitude)and plans the configuration for a spatial hyper-redundant manipulator.The key of this method lies in segmenting the the manipulator into multiple sections,and analytically resolving the joint angles of each section.Similar to the human arm,the manipulator is segmented into three sections,i.e.the shoulder,elbow and wrist.The shoulder has four degrees of freedom,which is redundant for positioning the elbow.It makes the start point of the elbow move in a reasonable space.The wrist is actually one universal joint.Its joints are determined according to the direction vector from the elbow and the end-effector.The rest joints constitute the elbow.The joint angles of the elbow are solved according to the space arc parameters.The interior singularity problem is then avoided.Based on the segmented geometry method,the configuration for a practical task can be planned using the given armangle,the space arc parameters and the desired direction vector.The proposed method solves the 3D pose determining and configuration planning problems.In order to control the redundancy of hyper-redundant manipulator,a modified modal method is proposed to solve the inverse kinematics.The spatial backbone of the manipulator is defined using mode function.Two adjacent universal joints comprise a group.The whole manipulator is then segmented into M/2 submanipulators.Each sub-manipulator has 4 degrees of freedom(4-DOFs)and is redundant for position.The last sub-manipulator is used to match the desired direction vector and the position of the end-effector.The remaining sub-manipulators are used to control the relative position between each other with one redundant degree of freedom.The equivalent link of each sub-manipulator is fitted to the backbone.The Cartesian coordinates of each node of the backbone is then determined by combining the total length of the manipulator and the mode function.Then,the joint angles are solved through the position of each node.For each 4-DOFs group,a parameter called arm-angle is used to denote the redundancy and optimize its local configuration.With both efficiency and accuracy considered,a hybrid obstacle-avoidance method of spatial hyper-redundant manipulators is also proposed.The space around an obstacle is classified into safe,warning,and dangerous zones.A two-level protection strategy is then addressed to handle the obstacle-avoidance problem from qualitative and quantitative perspectives,respectively.The boundary between the safe and warning zones is represented by the super-quadric function.The minimum pseudo-distance of the whole manipulator relative to the warning boundary is then calculated in real time.Once the manipulator enters the warning zone,the minimum Euclidean distance between the manipulator and dangerous boundary represented by the practical geometry function is calculated.Correspondingly,the modified modal method is used to plan the collision-free trajectory of the manipulator by maximizing the minimum pseudo-distance or Euclidean distance in different zones.Some parameters,including the arm-angle parameters and the equivalent link length parameters,are defined to represent the manipulator configuration.They are adjusted to maximize the minimum distance to avoid the obstacles.When the problems of inverse kinematics and trajectory planning are solved,it is necessary to consider the dynamic control of the hyper-redundant manipulator.The cable-driven hyper-redundant manipulator is composed of a number of universal joints.The motors and transmission mechanism are placed on the base of the manipulator.The rotation of the universal joint is controlled by the force of cable.And each universal joint(2-DOFs)is drived by three cables.So the whole manipulator owns several special characteristics,such as large number of degrees of freedom,non-linearity,strong coupling and cable-driven mechanisms.Base on these characteristics,the multi-level kinematics and dynamics mathematics models are established.Then,the dynamic simulation model is built based on the toolbox of Matlab/Sim Mechanics.Further,the closed-loop control simulation of computed torque control method is realized based on the above dynamic model.Finally,the simulation system based on Open Scene Graph(OSG)and the physics experiment system are developed.The simulation and experiments of the trajectory planning and control method are carried out.The results show that the method is very efficient for controlling cable-driven hyper-redundant manipulators. |
