Trajectory tracking control of a hydraulic-tendon actuator with an application to the exoskeleton

This paper presents a hydraulic actuator and tendon drive system that was specifically designed for a lower-limb exoskeleton to provide high power and low inertia. The dynamics of the actuator-tendon system were analyzed based on the exoskeleton system and an adaptive sliding-mode trajectory tracking controller was designed for the drive system. The stability proof indicates that the controller is globally stable. The experimental results demonstrated that the controller provides high tracking accuracy and is robust to external disturbances and unmodeled nonlinearities. Moreover, the controller has less errors than the conventional PID controller. Further tests that included the joints of the exoskeleton were conducted to verify the performance of the controller

Full- and Reduced-order Model of Hydraulic Cylinder for Motion Control

This paper describes the full- and reduced-order models of an actuated hydraulic cylinder suitable for system dynamics analysis and motion control design. The full-order model incorporates the valve spool dynamics with combined dead-zone and saturation nonlinearities - inherent for the orifice flow. It includes the continuity equations of hydraulic circuits coupled with the dynamics of mechanical part of cylinder drive. The resulted model is the fifth-order and nonlinear in states. The reduced model neglects the fast valve spool dynamics, simplifies both the orifice and continuity equations through an aggregation, and considers the cylinder rod velocity as output of interest. The reduced model is second-order that facilitates studying the system behavior and allows for direct phase plane analysis. Dynamics properties are addressed in details, for both models, with focus on the frequency response, system damping, and state trajectories related to the load pressure and relative velocity.Comment: 6 pages, 6 figures, IEEE conferenc

Adaptive super-twisting observer for fault reconstruction in electro-hydraulic systems

An adaptive-gain super-twisting sliding mode observer is proposed for fault reconstruction in electro-hydraulic servo systems (EHSS) receiving bounded perturbations with unknown bounds. The objective is to address challenging problems in classic sliding mode observers: chattering effect, conservatism of observer gains, strong condition on the distribution of faults and uncertainties. In this paper, the proposed super-twisting sliding mode observer relaxes the condition on the distribution of uncertainties and faults, and the gain adaptation law leads to eliminate observer gain overestimation and attenuate chattering effects. After using the equivalent output-error-injection feature of sliding mode techniques, a fault reconstruction strategy is proposed. The experimental results are presented, confirming the effectiveness of the proposed adaptive super-twisting observer for precise fault reconstruction in electro-hydraulic servo systems.Comment: Final versio

Fuzzy robust nonlinear control approach for electro-hydraulic flight motion simulator

AbstractA fuzzy robust nonlinear controller for hydraulic rotary actuators in flight motion simulators is proposed. Compared with other three-order models of hydraulic rotary actuators, the proposed controller based on first-order nonlinear model is more easily applied in practice, whose control law is relatively simple. It not only does not need high-order derivative of desired command, but also does not require the feedback signals of velocity, acceleration and jerk of hydraulic rotary actuators. Another advantage is that it does not rely on any information of friction, inertia force and external disturbing force/torque, which are always difficult to resolve in flight motion simulators. Due to the special composite vane seals of rectangular cross-section and goalpost shape used in hydraulic rotary actuators, the leakage model is more complicated than that of traditional linear hydraulic cylinders. Adaptive multi-input single-output (MISO) fuzzy compensators are introduced to estimate nonlinear uncertain functions about leakage and bulk modulus. Meanwhile, the decomposition of the uncertainties is used to reduce the total number of fuzzy rules. Different from other adaptive fuzzy compensators, a discontinuous projection mapping is employed to guarantee the estimation process to be bounded. Furthermore, with a sufficient number of fuzzy rules, the controller theoretically can guarantee asymptotic tracking performance in the presence of the above uncertainties, which is very important for high-accuracy tracking control of flight motion simulators. Comparative experimental results demonstrate the effectiveness of the proposed algorithm, which can guarantee transient performance and better final accurate tracking in the presence of uncertain nonlinearities and parametric uncertainties

Model based control strategies for a class of nonlinear mechanical sub-systems

This paper presents a comparison between various control strategies for a class of mechanical actuators common in heavy-duty industry. Typical actuator components are hydraulic or pneumatic elements with static non-linearities, which are commonly referred to as Hammerstein systems. Such static non-linearities may vary in time as a function of the load and hence classical inverse-model based control strategies may deliver sub-optimal performance. This paper investigates the ability of advanced model based control strategies to satisfy a tolerance interval for position error values, overshoot and settling time specifications. Due to the presence of static non-linearity requiring changing direction of movement, control effort is also evaluated in terms of zero crossing frequency (up-down or left-right movement). Simulation and experimental data from a lab setup suggest that sliding mode control is able to improve global performance parameters

Trajectory tracking control of a hydraulic-tendon actuator with an application to the exoskeleton

This paper presents a hydraulic actuator and tendon drive system that was specifically designed for a lower-limb exoskeleton to provide high power and low inertia. The dynamics of the actuator-tendon system were analyzed based on the exoskeleton system and an adaptive sliding-mode trajectory tracking controller was designed for the drive system. The stability proof indicates that the controller is globally stable. The experimental results demonstrated that the controller provides high tracking accuracy and is robust to external disturbances and unmodeled nonlinearities. Moreover, the controller has less errors than the conventional PID controller. Further tests that included the joints of the exoskeleton were conducted to verify the performance of the controller

Trajectory tracking control of a hydraulic-tendon actuator with an application to the exoskeleton

This paper presents a hydraulic actuator and tendon drive system that was specifically designed for a lower-limb exoskeleton to provide high power and low inertia. The dynamics of the actuator-tendon system were analyzed based on the exoskeleton system and an adaptive sliding-mode trajectory tracking controller was designed for the drive system. The stability proof indicates that the controller is globally stable. The experimental results demonstrated that the controller provides high tracking accuracy and is robust to external disturbances and unmodeled nonlinearities. Moreover, the controller has less errors than the conventional PID controller. Further tests that included the joints of the exoskeleton were conducted to verify the performance of the controller

Trajectory tracking control of a hydraulic-tendon actuator with an application to the exoskeleton

This paper presents a hydraulic actuator and tendon drive system that was specifically designed for a lower-limb exoskeleton to provide high power and low inertia. The dynamics of the actuator-tendon system were analyzed based on the exoskeleton system and an adaptive sliding-mode trajectory tracking controller was designed for the drive system. The stability proof indicates that the controller is globally stable. The experimental results demonstrated that the controller provides high tracking accuracy and is robust to external disturbances and unmodeled nonlinearities. Moreover, the controller has less errors than the conventional PID controller. Further tests that included the joints of the exoskeleton were conducted to verify the performance of the controller