Nonlinear Synchronous Control Of Flexible Joint Robots

With the continuous expansion of the robotic application, the effective control is the key to ensure the robot complete tasks well. For the robot system to obtain high performance, it is necessary to consider the flexibility of the joints when modeling the dynamic and designing the controller. Compared with the conventional rigid robot, the flexible joint robots introduce additional degrees of freedom, such that the design of flexible joint robot controller becomes more complex.For multi degree of freedom flexible joint robot, whose end effector position is decided by all actuators. Therefore, it is necessary to use synchronous control method to make the motion coordinationally, in order to get the high control performance. This thesis introduces cross-coupling control strategy into the control of flexible joint robot, to realize the synchronous control of multi degrees of freedom flexible joint robot.Because of the influence of nonlinear factors such as modeling errors, external disturbances, and nonlinear friction, traditional linear controllers can’t ensure the flexible joint robot motion well. This thesis introduces a kind of nonlinear saturation function to improve linear controller and obtains a better control performance. The major contributions of this thesis are as follows:1. State feedback synchronous position control of flexible joint robot has been studied. Aiming at the problem that traditional PD controller plus real-time gravity compensation without considering synchronous control of actuator, this thesis proposes a kind of cross-coupling synchronous control law based position error.2. Output feedback synchronous position control of flexible joint robot has been addressed. Considering the speed information is not easy to obtain in practical engineering, this thesis proposes a kind of output feedback synchronous control law based on position measurements only. Further considering that the control torque which the actuator can provide is limited, and the parts that overtop the maximum level will be output limitly. A saturated output feedback synchronous control law has been further constructed for this problem.3. Model-free synchronous position control of flexible joint robot has been investigated. As the actual robot system is a complex nonlinear system that have multi variables, it’s difficult to obtain the accurate system model. But the above mentioned methods are required to know the gravity term exactly. In this thesis, the singular perturbation theory is used to simplify the model, and thus propose a kind of nonlinear PID synchronous controller with flexible compensation for the position control.4. Sliding-mode synchronous trajectory tracking control of flexible joint robot has been studied. For the trajectory tracking problem, a kind of nonlinear PID sliding-mode synchronous controller is formulated with flexible compensation to overcome the disadvantage of the traditional PID controller without global asymptotic stability.In this thesis, the proofs of the global asymptotic stability of all the close-loop systems resulting from the robot system and the proposed control algorithms are present. The effectivenesses and improved perforamces of the proposed controls are demonstrated by numerical simulations.