Study On Position Control Method Of Planar Flexible Link Manipulator

For the manipulator with slender structure,such as space manipulator,when it moves with heavy load and high acceleration,it is difficult to ignore the flexible feature of the manipulator links.This feature will lead to elastic vibration of the links.Therefore,for the position control of this kind of manipulator,it is necessary not only to make the links of the manipulator stabilize to their target angles,but also to suppress the vibration of the links.However,the position control of the flexible link manipulator is much more difficult than that of the traditional rigid link manipulator,because this system has underactuated characteristic.In addition,the residual vibration in the position control will lead to the delay of the subsequent operation of the manipulator.The research on the position control strategy of flexible link manipulator,especially the fast position control strategy of the system with the condition of vibration amplitude,model uncertainties and joint motor damage,has important theoretical value and application prospect for the fields of aerospace and deep sea exploration.In this thesis,the planar flexible link manipulator is taken as the research object,and based on the modeling and characteristic analysis of this kind of system,the position control problem of this system is studied.Furthermore,we discuss how to deal with the vibration amplitude constraint,model uncertainties and joint motor damage of the system in this thesis.The main research results and innovations of this thesis are as follows:1)To solve the problem that the vibration state of the planar flexible link manipulator cannot be controlled directly by the joint motor,a control strategy based on system energy and online intelligent optimization is proposed to achieve the fast position control of the system.The control inputs of a planar flexible link manipulator are provided by the joint motors.However,the joint motors can only control the rotation angles of the links,and cannot control the vibration of the links directly.Hence,this type of system has underactuated characteristic.Based on the motion characteristics of the planar flexible link manipulator,a position control strategy based on system energy is proposed.This strategy uses the control torques provided by the joint motors to stabilize the links of the manipulator to their target angles,and makes the total energy of the system converge to zero to realize the angle control and vibration suppression of the flexible link.In order to further improve the control performance of the system,an on-line parameter optimization method based on Fuzzy-Genetic Algorithm(FGA)is proposed.By optimizing the design parameters of the controller on-line,the controller can adjust different control intentions according to the different motion stages of the manipulator.In this way,when the link of the manipulator is far away from its target angle,it can move quickly to the target angle,and when it is close to the target angle,the total energy of the system can converge to zero quickly,which enables the position control objective of the system can be quickly achieved.Two sets of simulation experiments are carried out to verify the effectiveness and rapidity of the proposed control strategy.2)To solve the problem of residual vibration in the position control of planar flexible link manipulator,a position control strategy is proposed based on trajectory planning and tracking control,which can make the vibration of the flexible link converge to zero simultaneously when the system links reach their target angles.In order to further improve the speed of position control for the planar flexible link manipulator on the basis of control strategy 1),a position control strategy with zero residual vibration is proposed.By transforming the position control problem of the system into the problem of trajectory planning and tracking control,the vibration of the flexible link converges to zero simultaneously when the links of the manipulator reach their target angles.Thus,the zero residual vibration is realized in the position control of the system.In this way,the manipulator can carry out the subsequent operation immediately after the links reach the target angles,and the time of waiting for the residual vibration suppression is saved.First,based on the dynamic model and motion characteristics of the system,the bidirectional trajectory planning method is used to plan a forward trajectory and a reverse trajectory for the links of the manipulator.Then,the planned two trajectories are combined by using the time reversal method and the trajectory optimization method based on Genetic Algorithm.In this way,a desired trajectory,which makes the system move from the initial state to the target state,is obtained.A sliding mode trajectory tracking controller is designed,so that the links of the manipulator can track the planned desired trajectory with high precision,and the control objective of the system is achieved.The effectiveness and rapidity of the proposed control strategy are verified by three sets of simulation results.3)An adaptive position control strategy based on trajectory planning and neural network is proposed to overcome the influence of model uncertainties and realize highprecision position control of uncertain planar flexible link manipulator under the vibration amplitude constraint.An adaptive position control strategy based on trajectory planning and neural network is proposed to deal with the situation that the system has vibration amplitude constraints and model uncertainties in the position control of the planar flexible link manipulator.In trajectory planning,a virtual damping technique and an on-line trajectory correction technique are used to make the planned trajectory not only ensure that the links of the system can be stable at their target angles along the planned trajectory,but also ensure that when the system has model uncertainties,the vibration of the flexible link can converge to zero by tracking the planned trajectory.In addition,the relationship between the maximum tip vibration amplitude of the flexible link and the parameters of the planned trajectory is analyzed.According to this relationship,the maximum tip vibration amplitude of the flexible link can be limited to meet the vibration amplitude constraint by adjusting the parameters of the planning trajectory.In order to make the links of the system track the planned trajectory under model uncertainties,an adaptive tracking controller based on the Radial Basis Function(RBF)Neural Network and sliding mode control is designed.Thus,the position control objective of the system is achieved.The effectiveness of the proposed control strategy and the superiority of the planned trajectory and the proposed tracking controller are verified by simulation experiments.4)To solve the position control problem of a planar flexible link manipulator with one damaged joint motor,by using the dynamic coupling relationship among the system links,a control strategy based on the system energy and intelligent optimization is proposed for the remaining joint motors to achieve the position control objective of the manipulator.When a joint motor of the manipulator is damaged and cannot provide control torque,this joint can be called a passive joint and its corresponding link is the passive link.The joint where the joint motor works normally is called an active joint,and its corresponding link is the active link.For a planar flexible link manipulator with a passive joint,its position control requires that all the links of the system are stabilized to their target angles,and the vibration of the flexible links is effectively suppressed.However,because there is no control torque at the passive joint,the corresponding link of the manipulator can not be controlled directly.So,it is a very challenging task to use the remaining joint motors to achieve the position control objective of the whole system.By studying the integrable characteristics of the state constraint equation in the system model caused by the passive joint,the dynamic coupling relationship between the passive link and the active links is obtained.An energy-based controller is designed for the active links,which can not only realize the angle control of the active links,but also make the energy of the system converge to zero,so as to suppress the vibration of the flexible links.Then,based on the dynamic coupling relationship among the links,the genetic algorithm is used to optimize the design parameters of the controller to achieve that while the control objective of the active links is realized,the passive link is also stabilized at its target angle.Thus,the position control objective of the whole system is realized.The effectiveness of the proposed control strategy is verified by two sets of simulation examples.Finally,the work of this thesis is summarized,and the contents that can be improved or further studied in the future work are prospected.