Design of a novel modal space sliding mode controller for electro-hydraulic driven multi-dimensional force loading parallel mechanism

The electro-hydraulic driven multi-dimensional force loading parallel mechanism can meet the requirements of complex force loading. However, the force loading performance is affected by the strong dynamic coupling due to flexible load and structure characteristics of parallel mechanism, which is analyzed from the mathematical model built by the Newton-Euler method. In order to solve the coupling problem, a novel control strategy, modal space sliding mode control, is proposed. It can realize multi-dimensional force loading decoupling by a coordinating modal space controller. The modal space control framework is established based on the vibration theory, and the decoupling characteristics of modal space are analyzed. Furthermore, it is discussed that the consistency of modal space channels is required for the decoupling condition in degree of freedom space. In order to improve the tracking performance of modal space channels, a sliding mode controller is designed in the modal space by using the decoupling property of modal space. The modal space sliding mode controller not only reduces the chattering caused by coupling force, but also greatly improves the dynamic performance of modal space channels, as well as the consistency of modal space channels. The stability condition of the modal space sliding mode controller is given and proved by Lyapunov theorem. The experimental results show the effectiveness of the proposed modal space sliding mode control, which can significantly reduce coupling force and improve the dynamic tracking performance.

An Improved Force-Angle Stability Margin for Radial Symmetrical Hexapod Robot Subject to Dynamic Effects

This paper presents a study on stability monitoring for a radial symmetrical hexapod robot under dynamic conditions. The force-angle stability margin (FASM) measure method has been chosen as the stability criterion. This is because it is suitable for the stability analysis, in terms of external forces or manipulator loads acting on the body. Considering that a radial symmetrical hexapod robot can tumble along the contact point besides tip-over axis, this paper proposes an improved FASM measure method. Furthermore, it provides the method for calculating the stability angle of contact point and simplifies the algorithm of FASM. To verify the improved FASM measure method, three potential dynamic situations have been simulated. The simulation results confirm that, under dynamic conditions, the improved FASM is efficient, simple in terms of calculation cost and sensitive to manipulator loads and external disturbances. This means it has practical value in on-line controllers.