Research On Position Control And Trajectory Tracking Method Of PAA Under-actuated Manipulator

Under-actuated manipulator is a kind of mechanical system with independent input less than degrees of freedom.It has lighter weight,consumes less energy and its structure is compact.The system is a kind of non-holonomic constraint system,which can't directly control the passive joint.The general smooth feedback control method is not applicable and its motion control problem is more difficult than the general manipulator.In the operation task,whether the end actuator of under-actuated manipulator can reach the target position accurately and stably depends on the accuracy and stability of the manipulator position control method.In addition,it can be treated as an under-actuated manipulator when the broken actuator of a normal manipulator may be difficult to be repaired.The under-actuated control method can be used to continue to complete the task as an emergency plan.Therefore,it has important theoretical value and broad application prospect to research on the position control and trajectory tracking methods of under-actuated manipulator to ensure that the manipulator can meet the requirements of specific operation tasks.The planar three-link passive-active-active(PAA)under-actuated manipulator is taken as the research object in this paper to carry out the following research:the two-stage switch position control method,bidirectional trajectory planning method and trajectory tracking control method of PAA under-actuated manipulator.The main research work is as follows:Firstly,the position control method of PAA under-actuated manipulator is studied.An improved particle swarm optimization algorithm based on simulated annealing method and artificial fish swarm method is proposed to solve the problem that inverse kinematics is easy to fall into local optimum.In the process of searching,the simulated annealing algorithm Metropolis criterion and the concept of artificial fish swarm algorithm crowding degree are introduced to increase the diversity of particles,improve the random search ability and reduce the probability of the algorithm falling into local optimum.A two-stage hybrid switching control method based on sliding mode control and Lyapunov function is proposed for the position control of PAA manipulator.At each control stage,we design the Lyapunov function to maintain the angle of an active joint unchanged while we build the sliding surface and select the power function as reaching law to make the other active joint converge to the target angle.The control law switches to next stage when the rotated joint converges to the target angle.Simulation results demonstrate that the proposed method has shorter steady-state adjustment time than that of existing typical control methods,and its overshoot is almost zero.Secondly,the trajectory planning method of PAA under-actuated manipulator is studied.Aiming at the trajectory smoothness of the under-actuated manipulator,the concept of dynamic operability was proposed,and the influence of dynamic operability on the coupling between joints and joint torque are analyzed.Then,according to the coupling relationship between the passive and active joints,bidirectional trajectory planning method is used to design the trajectory from the initial position and the end position to the intermediate position.The dynamic operability is taken as the index to optimize the middle position.The planned two trajectories are spliced without free swing at the intermediate position to ensure smooth changes in joint angle,angular velocity and torque during the operation of the robotic arm,and improve the operational reliability.Finally,aiming at the repeated operation tasks,the influence of the base position on the performance of the manipulator is analyzed,and the dynamic operability is taken as the index to optimize the base position and improve the reliability of the manipulator.Finally,the trajectory tracking method of PAA under-actuated manipulator is studied.Aiming at the problem that PAA under-actuated manipulator trajectory tracking control method does not consider the passive joint term,the hierarchical sliding mode control method is used to divide the system into nonlinear coupling subsystems,which share the driving and hierarchical design control laws.The first and second joints are regarded as the first subsystem,and the control law is designed to make the first subsystem stable.Considering the third joint as the second subsystem,the third joint torque is designed to keep the second subsystem and the overall system stable,realize the trajectory tracking control of the PAA-type manipulator.The trajectory tracking control of PAA manipulator is realized.