Flatness-based control in successive loops for industrial and mobile robots

A flatness-based control approach which is implemented in successive loops is used to solve the control problem for the multivariable and nonlinear dynamics of industrial robotic manipulators and autonomous vehicles. The state-space model of these robotic systems is separated into two subsystems, which are connected between them in cascading loops. Each one of these subsystems can be viewed independently as a differentially flat system and control about it can be performed with inversion of its dynamics as in the case of input-output linearized flat systems. The state variables of the second subsystem become virtual control inputs for the first subsystem. In turn exogenous control inputs are applied to the first subsystem. The whole control method is implemented in two successive loops and its global stability properties are also proven through Lyapunov stability analysis. The validity of the control method is confirmed in two case studies: (a) control of a 3-DOF industrial rigidlink robotic manipulator, (ii) control of a 3-DOF autonomous underwater vessel.