This paper proposes a saturated nonlinear PID regulator for industrial robot manipulators. Our controller considers the natural saturation problem given by the output of the control computer, the saturation phenomena of the internal PI velocity controller in the servo driver, and the actuator torque constraints of the robot manipulator. An approach based on the singular perturbations method is used to analyze the exponential stability of the closed-loop system. Experimental essays show the feasibility of the proposed controller. Furthermore, the theoretical results justify why the classical PID used in industrial robots preserves its exponential stability despite the saturation effects of the electronic control devices and the actuator torque constraints.
Unit quaternions have become a useful tool for describing rotations in space. This paper shows the application of unit quaternions (also called Euler parameters) to solve the problem of modeling and control of robot manipulators. First, a quaternion-based algorithm that allows to obtain the direct kinematic model of serial manipulators from the Denavit-Hartenberg parameters is introduced. This method is an alternative to the traditional one using homogeneous matrices. Then, a novel kinematic controller that uses Euler parameters as a set of nonminimal state variables is studied, including its Lyapunov stability analysis. Finally, to show the feasibility of the proposed scheme, the kinematic model of a typical spherical wrist is obtained and some simulations are carried out, showing the fulfillment of the control aim.
SUMMARYOperational space control of industrial robots is addressed in this document. We analyze a two-loop hierarchical control with the resolved motion rate controller (RMRC) as outer loop and the joint velocity PI controller as inner loop; the latter is the typical velocity controller used in industrial robots. We prove, by the first time, that these simple controllers make the solutions of the closed-loop system uniformly ultimately bounded. Additionally, we give some simple guidelines for the selection of the control gains so as to ensure an explicit bound of the tracking error.
The paper addresses a robust navigation strategy of a rotorcraft class having a simple robotic arm to perform rapid in-flight retrieving operations in presence of wind gusts and aerodynamic effects. The target-acquiring trajectory planner is based on a cosinusoidal dynamic pattern. The mathematical model is extended to account not only the dynamics of the robotic arm but also the aerodynamics. The navigation control scheme is based on a soft integral slidingmode control (ISC) to stabilize both inner-and outer-loop dynamics regarding the rejection of not only the dynamic couplings but also aerodynamic disturbances. Detailed simulations including realistic aerodynamic effects results show the validity of the proposed navigation strategy while tracking the objectto-retrieve trajectory.
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