Hybrid position/force output feedback second-order sliding mode control for a prototype of an active orthosis used in back-assisted mobilization

The problem of the design of an output feedback second-order sliding mode control for a class of nonlinear systems affine in the control law with non-matched uncertainties is considered in this paper. An observer-based backstepping design procedure is followed to construct a suitable sliding manifold that guarantees the attainment of a tracking control objective. The construction of the sliding manifold is performed so that the problem of steering the sliding quantity to zero in finite time turns out to be solvable locally through a second-order sliding mode control approach, as in the conventional matched uncertainty case, and the associated zero dynamics is minimum phase. On the other hand, the observer operates in first-order sliding mode, also fed by the control signal generated by the backstepping-second-order sliding mode algorithm. This signal presents the advantage of being continuous by virtue of the second-order sliding mode nature of the controller, enabling the fast convergence to zero of the observation error.

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On Application of Second Order Sliding Mode Control to Electro-Hydraulic Systems

Volume 3: Engineering Systems; Heat Transfer and Thermal Engineering; Materials and Tribology; Mechatronics; Robotics ◽

10.1115/esda2014-20470 ◽

2014 ◽

Cited By ~ 2

Author(s):

Lasse Schmidt ◽

Torben O. Andersen ◽

Henrik C. Pedersen

Keyword(s):

Sliding Mode Control ◽

Output Feedback ◽

Nonlinear Dynamic ◽

Sliding Mode ◽

Output Feedback Control ◽

Second Order ◽

Dynamic Effects ◽

Mode Control ◽

Hydraulic Valve ◽

Second Order Sliding Mode

This paper discusses the application of second order mode controls to hydraulic valve-cylinder drives with a special focus on the limitations resulting from nonlinear dynamic effects in flow control valves. Second order sliding mode algorithms appear highly attractive in the successive implementation of sliding mode control, achieving continuous control inputs, while maintaining the main properties of sliding modes. Under certain model assumptions, some of these controllers may even be applied as output feedback controllers. However, intrinsic nonlinear dynamic effects of hydraulic valves such as slew rates and time delays arising in the amplification stages, limits the applicability of such methods, and may lead to partial losses of robustness and limit cycles. These properties are analyzed and experimentally verified, and compensation methods are proposed. The application of the second order sliding algorithm known as the super twisting controller is considered for output feedback control and compared with conventional first order sliding mode control. The controllers under consideration are applied for position tracking control of a hydraulic valve-cylinder drive exhibiting strong variations in inertia- and gravitational loads. Results demonstrate that the super twisting algorithm may be successfully applied for output feedback control of hydraulic valve-cylinder drives, with modifications guaranteeing robust control performance in a small vicinity of the control target.

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