Abstract
In this paper, a novel nonlinear model and high-precision lifting motion control method of a hydraulic manipulator driven by a proportional valve are presented, with consideration of severe system nonlinearities, various uncertainties as well as valve backlash/deadzone input nonlinearities. To accomplish this mission, based on the independent valve orifice throttling process, a new comprehensive pressure-flow model is proposed to uniformly indicate both the backlash and deadzone effects on the flow characteristics. Furthermore, in the manipulator lifting dynamics, considering mechanism nonlinearity and utilizing a smooth LuGre friction model to describe the friction dynamics, a nonlinear state-space mathematical model of hydraulic manipulation system is then established. To suppress the adverse effects of severe nonlinearities and uncertainties in the system, a high precision adaptive robust control method is proposed via backstepping, in which a projection-type adaptive law in combination with a robust feedback term is conducted to attenuate various uncertainties and disturbances. Lyapunov stability analysis demonstrates that the proposed control scheme can acquire transient and steady-state close-loop stability, and the excellent tracking performance of the designed control law is verified by comparative simulation results.
Highlights
Hydraulic systems have been extensively applied in heavy manipulators [1,2,3,4] due to their good capabilities, such as high power/weight ratio, large output force, etc., especially in the operation of load-lifting with heavy load gravity
The control of electro-hydraulic systems is very challenging because the hydraulic system involves severe nonlinearities, such as mechanism nonlinearity, flow nonlinearity and friction nonlinearity, and various modeling uncertainties
The traditional linear control methods have become more and more difficult to satisfy the demand of modern hydraulic systems
Summary
Hydraulic systems have been extensively applied in heavy manipulators [1,2,3,4] due to their good capabilities, such as high power/weight ratio, large output force, etc., especially in the operation of load-lifting with heavy load gravity. The traditional linear control methods have become more and more difficult to satisfy the demand of modern hydraulic systems. They are much cheaper and have higher reliability because less accuracy is required in the manufacturing of spool and valve sleeve, and vulnerable nozzle-flapper structure is replaced by proportional elements. The electric feedback form is employed in proportional valves to construct their internal closed-loop control, so they are less sensitive to oil contamination and simultaneously retain satisfactory servo control performance. Thereby, they are more suitable for industrial environments
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