Bounded Positioning Control of Manipulators Subject to Base Oscillation and Payload Uncertainty

Abstract

Mounting base oscillation poses a significant challenge to the control of these mechanical systems called oscillatory base manipulators (OBMs). The positioning accuracy of the system is severely affected by base oscillations. Many control strategies have been investigated, but most of them require measurement or prediction of base oscillations. This paper focuses on a unique type of OBMs—the vehicle-mounted manipulator that operates completely within the non-inertial task space (base-fixed space). It is a great challenge to obtain its base oscillation in practical applications. In addition, the inherent payload uncertainty and actuator saturation make its control design more challenging. To solve above problems, this study developed a novel control strategy. A nonlinear dynamics model is constructed firstly, where the base-oscillation term is considered as the external disturbance of the system. Then, a positioning control, which can be regarded as a proportional derivative (PD) control with continuous time-varying gains, is proposed based on the implicit Lyapunov method. Finally, the simulations and hardware experiments are carried out to certify the effectiveness of the proposed control. Results demonstrate that, even though without prediction or measurement of the base oscillations, the proposed control offers superior positioning performance in terms of robustness against the base oscillation and payload uncertainty as well as assurance of boundedness of the control input.

Keywords

• base oscillatory manipulators
• robust control
• bounded control
• Lyapunov method
• nonlinear control