Comprehensive effects coming from measurement noises, matched and mismatched uncertainties make it difficult for electro-hydraulic servo systems to further attain high-accuracy tracking level. The existing control strategies often consider these control issues one-sidedly. Accordingly, we develop two different control strategies combining integral robust control and direct adaptive control for high-precision position control of double-rod electro-hydraulic systems to account for these control issues concurrently. Specially, by skillfully introducing a filtered error function, a novel desired compensation adaptive control framework will be integrated into the controller design to reduce environmental noises. Moreover, an improved noise-alleviation method is proposed to achieve high-accuracy calculation of the standard sign function in nonlinear integral robust terms. Furthermore, each of the control algorithms can guarantee asymptotic position tracking performance in general. Comparative experiments and simulation results show the evident superiorities of the developed control strategies.

High-precision motion servo control of double-rod electro-hydraulic actuators with exact tracking performance

Hydraulic servo system plays a significant role in industries, and usually acts as a core point in control and power transmission. Although linear theory-based control methods have been well established, advanced controller design methods for hydraulic servo system to achieve high performance is still an unending pursuit along with the development of modern industry. Essential nonlinearity is a unique feature and makes model-based nonlinear control more attractive, due to benefit from prior knowledge of the servo valve controlled hydraulic system. In this paper, a discussion for challenges in model-based nonlinear control, latest developments and brief perspectives of hydraulic servo systems are presented: Modelling uncertainty in hydraulic system is a major challenge, which includes parametric uncertainty and time-varying disturbance; some specific requirements also arise ad hoc difficulties such as nonlinear friction during low velocity tracking, severe disturbance, periodic disturbance, etc.; to handle various challenges, nonlinear solutions including parameter adaptation, nonlinear robust control, state and disturbance observation, backstepping design and so on, are proposed and integrated, theoretical analysis and lots of applications reveal their powerful capability to solve pertinent problems; and at the end, some perspectives and associated research topics (measurement noise, constraints, inner valve dynamics, input nonlinearity, etc.) in nonlinear hydraulic servo control are briefly explored and discussed.

Model-based nonlinear control of hydraulic servo systems: Challenges, developments and perspectives

For valve-controlled hydraulic servo system, the suppression of mechanical dynamics uncertainties and the analysis of internal pressure dynamics stability (i.e. the pressure into the two chambers of the actuator) are still the widespread concern issues. This study presents an easy-to-implement observer-based output feedback control scheme for hydraulic valve-controlled single-rod actuator system with addressing mismatched mechanical dynamic uncertainties and proving internal pressure dynamics stability analysis. The singular value perturbation approach is used to simplify the system model, and then a practical output feedback controller augmented with extended-state observer is developed through back-stepping design approach. The main contribution of this study is two-fold. First, a practical reduced-order model-based back-stepping controller is developed. Second, the stability issue of internal pressure dynamics is analysed. Besides giving theoretical analysis, extensive comparative co-simulations and experiments are carried out to illustrate the effectiveness of the proposed method. The present method can guarantee prescribed tracking transient performance in the presence of uncertain disturbances. Also, the stability of internal dynamics is proved.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-cta.2019.0346

Disturbance observer-based output feedback control of hydraulic servo system considering mismatched uncertainties and internal pressure dynamics stability

This paper proposes a novel nonlinear energy-based coupling control for an underactuated offshore ship-mounted crane, which guarantees both precise trolley positioning and payload swing suppressing performances under external sea wave disturbance. In addition to having such typical nonlinear underactuated property, as it is well known, an offshore ship-mounted crane also suffers from much unexpected persistent disturbances induced by sea waves or currents, which, essentially different from an overhead crane fixed on land, cause much difficulty in modeling and controller design. Inspired by the desire to achieve appropriate control performance against those challenging factors, in this paper, through carefully analyzing the inherent mechanism of the nonlinear dynamics, we first construct a new composite signal to enhance the coupling behavior of the trolley motion as well as the payload swing in the presence of ship′s roll motion disturbance. Based on which, an energy-based coupling control law is presented to achieve asymptotic stability of the crane control system′s equilibrium point. Without any linearization of the complex nonlinear dynamics, unlike traditional feedback controllers, the proposed control law takes a much simpler structure independent of the system parameters. To support the theoretical derivations and to further verify the actual control performance, Lyapunov-based mathematical analysis as well as numerical simulation/experimental results are carried out, which clarify the feasibility and superior performance of the proposed method over complicated disturbances.

An Energy-based Nonlinear Coupling Control for Offshore Ship-mounted Cranes

Nonlinear and high-order characteristics could directly hinder the application of many advanced control algorithms for electro-hydraulic system which is a coupling system with double-dynamics of mechanical and hydraulic components. In this paper, a practical torque tracking control using singular perturbation theory is proposed for electro-hydraulic load simulator. The system model is transformed into a singularly perturbed form including a slow mechanical system and a fast hydraulic system. To achieve high accuracy and strong robustness, an active disturbance rejection control based on desired model compensation is developed for the slow mechanical system. It is proved that the mechanical system with developed slow controller is exponentially stable. A proportional control law is employed for the fast hydraulic system. This hydraulic system with developed fast controller is demonstrated to be exponentially stable. Stability of the whole closed-loop system is theoretically analyzed using the extended Tikhonov's theorem. Experimental results validate the presented control scheme.

Practical torque tracking control of electro-hydraulic load simulator using singular perturbation theory.

The utility model discloses a movable mechanical arm for recycling and placing road cones. The movable mechanical arm comprises a mechanical arm body, a vertical moving slide block, a vertical guide rail, a transverse moving slide block, a transverse guide rail and a fixed base, wherein the fixed base is fixed to a vehicle body, the transverse guide rail is connected with the fixed base in a rotating mode and parallel to the vehicle body, the transverse moving slide block is arranged on the transverse guide rail and forms a slide pair together with the transverse guide rail, the vertical guide rail is connected with the transverse moving slide block in a rotating mode and perpendicular to the transverse guide rail, the vertical moving slide block is arranged on the vertical guide rail and forms a slide pair together with the vertical guide rail, and the mechanical arm body is arranged on the vertical moving slide block and forms a rotating pair together with the vertical moving slide block. The road cones can be rapidly, efficiently and stably placed and recycled under the joint action of the mechanical arm body, a transverse slide block and guide rail pair and a longitudinal slide block and guide rail pair; the movable mechanical arm is flexible in action and high in adaptability, has low requirements for a vehicle driver, and is less influenced by the environment.

Movable mechanical arm for recycling and placing road cones

The invention discloses a friction compensation adaptive control method for a controlled emission platform, belonging to the electro mechanical servo control field. The friction compensation adaptive control method disclosed by the invention comprises steps of establishing a mathematic model of the controlled emission platform having a friction dynamic condition, designing an adaptive controller having friction compensation, and performing a stability test on the adaptive controller having friction compensation. The friction compensation adaptive control method for the controlled emission platform fuses the sliding die observation and friction compensation concept, compensate the friction through the adaptive control strategy, the adaptive friction parameter and the system parameter, increases the system tracking performance, effectively compensates the non-linear friction of the system and the inter-framework coupling interference torque, guarantees the good control performance of a servo-system and guarantees the global progressive stability.

Friction compensation adaptive control method for controlled emission platform

The invention discloses a finite-time continuous sliding mode control method for the disturbance compensation of a direct drive motor system. The method comprises the steps of establishing a mathematical model for the direct drive motor system; designing a disturbance observer for the direct drive motor system and proving the observation accuracy of the disturbance observer; and designing a disturbance observer-based finite-time convergence type continuous sliding mode controller. According to the technical scheme of the invention, the buffeting phenomenon of the sliding mode control is avoided. Meanwhile, the steady-state performance of the system with no finite-time tracking error even under the effect of the interference is still enabled. Moreover, the capability of the sliding mode control method in standing up to the interference of the direct drive motor system and eliminating the buffeting phenomenon of the sliding mode control is enhanced. In addition, the good tracking performance is realized.

Finite-time continuous sliding mode control method for disturbance compensation of direct drive motor system

The invention provides a method for calculating double reinforced regular hexagon honeycomb axial compressive stress. The method comprises the following steps of: step1, based on a geometrical configuration of a double reinforced regular hexagon honeycomb, calculating total bending deformation energy absorbed by four additional plane units; step 2, calculating total thin film deformation energy absorbed by four additional plane units; step 3, based on energy conservation, according to the total bending deformation energy and total thin film deformation energy obtained in the above steps, calculating axial compressive stress of the double reinforced regular hexagon honeycomb under the axial compression. The method disclosed by the invention is not limited to predict the static mechanical properties and explain the deformation mechanism, and can calculate the axial compressive stress by using super-folded element theory based on the principle of conservation of energy. The calculation method has the advantages of simple analytical expression, high precision and high reliability and can rapidly judge energy absorption ability of the honeycomb energy-absorbing devices of different cell-element sizes.

Method for calculating double reinforced regular hexagon honeycomb axial compressive stress

The invention discloses an adaptive error symbol integration robust repetitive control method for an electromechanical servo system, which comprises the steps of establishing a mathematical model of the electromechanical servo system; constructing a system design model; and designing an adaptive error symbol integration robust repetitive controller and a performance theorem and stability certification of the adaptive error symbol integration robust repetitive controller. The control method disclosed by the invention can enable the electromechanical servo system to acquire semi-global progressive tracking performance. In addition, compared with a traditional internal mold principle based linear respective control method, the adaptive error symbol integration robust repetitive control method can also effectively reduce the sensibility of the repetitive controller for noises and avoid a high memory requirement of the controller.

Adaptive error symbol integration robust repetitive control method for electromechanical servo system

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