Therefore, the structural flexibility characteristics of the robotic manipulator must be considered, and the system dynamics must also be considered to achieve high-precision and effective control of the flexible manipulator.
The flexible manipulator is a very complex dynamic system, and its dynamic equation has the characteristics of nonlinearity, strong coupling and real change. For the study of flexible arm dynamics, the establishment of its model is extremely important. The flexible manipulator is not only a rigid-flexible coupled nonlinear system, but also a nonlinear system in which the dynamic characteristics and control characteristics of the system are coupled with each other, that is, electromechanical coupling.
The control of the flexible manipulator generally has the following methods:
1. Rigid processing. The effect of the elastic deformation of the structure on the rigid body motion of the structure is completely ignored. For example, in order to avoid excessive elastic deformation from damaging the stability and end positioning accuracy of the flexible manipulator, the maximum angular velocity of NASA’s remote-controlled astronauts is 0.5deg/s.
2. Feedforward compensation method. The mechanical vibration formed by the flexible deformation of the manipulator is regarded as the deterministic disturbance to the rigid motion, and the method of feedforward compensation is used to counteract this disturbance. Bernd Gebler of Germany studies feedforward control of Industrial Robots with elastic rods and elastic joints. Zhang Tiemin studied the method of eliminating the dominant pole and system instability based on adding zero point, and designed a feedforward controller with time delay. Compared with the PID controller, it can eliminate the residual vibration of the system more obviously.
3. Acceleration feedback control. KhorramiFarShad and JainSandeep studied the end-trajectory control problem of flexible manipulators controlled by end-acceleration feedback.
4. Passive damping control. In order to reduce the influence of the relative elastic deformation of the flexible body, various energy-consuming or energy-storing materials are used to design the arm structure to control the vibration. Or using damping shock absorbers, damping materials, composite damping metal plates, damping alloys or using viscoelastic large damping materials to form additional damping structures on the flexible beams belong to passive damping control. In recent years, the use of viscoelastic large damping materials for vibration control of flexible manipulators has attracted great attention.
5. Force feedback control method. The force feedback control of the vibration of the flexible manipulator is actually a control method based on inverse dynamics analysis, that is, according to the inverse dynamics analysis, the torque applied to the driving end is obtained through the given motion of the end of the arm, and the driving end is detected by motion or force detection. The torque is compensated by feedback.
6. Adaptive control. Using combined adaptive control, the system is divided into joint subsystems and flexible subsystems. The parameter linearization method is used to design an adaptive control rule to identify the uncertain parameters of the flexible manipulator. A tracking controller is designed for a flexible manipulator with nonlinearity and parameter uncertainty. The controller design is based on the Lyapunov method for robust and adaptive control design. The system is divided into two subsystems by state transitions. The two subsystems are controlled by adaptive control and robust control, respectively.
7. PID control. As the most popular and widely used controller, PID controller is widely used in rigid manipulator control due to its simplicity, effectiveness and practicality. It is often used to adjust the gain of the controller to form a self-tuning PID controller or combine it with other control methods. Combined to form a composite control system to improve the performance of the PID controller.
8. Variable structure control. Variable structure control system is a discontinuous feedback control system, among which sliding mode control is the most common variable structure control. Its characteristics: on the switching surface, there is a so-called sliding mode. In the sliding mode, the system remains insensitive to parameter changes and disturbances. At the same time, its trajectory is located on the switching surface, and the sliding phenomenon does not depend on the system parameters. nature. The design of the variable structure controller does not require an accurate dynamic model of the manipulator, and the boundary of the model parameters is sufficient to construct a controller.
9. Fuzzy and neural network control. It is a kind of language controller, which can reflect the thinking characteristics of people when they carry out control activities. One of its main characteristics is that the control system design does not require the mathematical model of the controlled object in the usual sense, but requires the experience knowledge and operation data of the operator or expert.