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A new robust sliding mode controller for a hydraulic actuator
Abstract
We present the design of a robust sliding mode controller for the
force control of a hydraulic actuator in presence of significant system
nonlinearities and uncertainties. Our control strategy is based on
sliding mode control. The design of a switching surface is based on
Lyapunov techniques, and a variable structure control law is designed
using the theory of sliding mode control. For the control we use a
nonlinear mathematical model of a hydraulic system interacting with the
environment. We try and consider most of the nonlinear and uncertain
dynamics of this system in order to achieve robust performance over a
range of operating conditions. The simulation results show that the
proposed sliding mode controller is not sensitive to a large variation
of parameters such as flow gain, supply pressure or environmental
stiffness, and has an excellent tracking performance for various set
point forces under uncertainties
... which reduces the system (21) to the form ...
... Combining equations (21) to (29), the complete model of the generator is presented in the state-space form ⎡ ⎢ ⎣ẋ ...
... This work is motivated by coffee harvest automation, where in order to shake the tree branches, electro-hydraulic actuators are very useful. Several control algorithms have been used to force tracking for electro-hydraulic actuators [2], including sliding mode control [21], [4]. These controllers were designed based on the plant physical model and, therefore, the plant parameters knowledge is required. ...
The dynamics of the most of the industrial plants (for example electric power system, electromechanical system, electro-hydraulic
system and so on) are highly nonlinear and, moreover, include actuator dynamics which increase the relative degree of the
complete system. To stabilize the plant dynamics it is naturally to applied some feedback linearization (FL) technique: block
control [18], backstepping [14] or input-output linearization [11], since the model of these plants can be presented in the
nonlinear block controllable form or (the same) strict-feedback one. All these control techniques require to calculate the
time derivatives of the plant dynamics vector fields (Lie derivatives), results in a computationally expensive control algorithm,
and moreover, the closed-loop system is susceptible to plant parameter variations and disturbances. To simplify the control
algorithm the actuator fast dynamics are usually skipped, and to overcome the robust problem the sliding mode (SM) control
[25] in combination with FL technique [18], [17] can be can be applied. However, the presence of the actuator unmodeled fast
dynamics can destroy the desired behavior of the SM control systems causing lost of robustness and accuracy and provoking
the chattering effect [25], [8]. Therefore, the problem of control design for the systems with unmodeled actuator dynamics
becomes to be a big challenge.
... Owing to their simplicity, linear controllers of PID type [3,4], input/output linearization controllers [5][6][7][8][9], and also sliding mode controllers (SMC) [10][11][12][13] have been used to control the hydraulic servo systems. However, such controllers were designed based on the plant physical model and, therefore, the plant parameters knowledge is required. ...
... However, we have seen in the second section that the first-order sliding mode controller with a linear sliding surface is not robust with respect to perturbation and mismatched uncertainty. In fact, by using the fact that on the sliding surface the system behaves in a similar way to a linear second-order system, it can be easily shown that as far as the sliding motion is preserved, the system is asymptotically stable if the closed loop eigenvalues are chosen as in (11) and thus the steady state error due to the uncertainty is expressed by (12). Also, the steady state error due to the constant perturbation is given by (13). ...
This paper deals with the position control of a hydraulic servo system rod. Our approach considers the surface design as a case of virtual controller design using the backstepping method. We first prove that a linear surface does not yield to a robust controller with respect to the unmatched uncertainty and perturbation. Next, to remedy this deficiency, a sliding controller based on the second-order sliding mode is proposed which outperforms the first controller in terms of chattering attenuation and robustness with respect to parameter uncertainty only. Next, based on backstepping a nested variable structure design method is proposed which ensures the robustness with respect to both unmatched uncertainty and perturbation. Finally, a robust sliding mode observer is appended to the closed loop control system to achieve output feedback control. The stability and convergence to reference position with zero steady state error are proven when the controller is constructed using the estimated states. To illustrate the efficiency of the proposed methods, numerical simulation results are shown.
... A linear controller using local linearization of nonlinearities has been applied to EHAs [1]. Variable structure control (VSC) methods were studied to obtain robust control of EHAs in [2][3][4][5]. A control method using input-output (IO) linearization has been developed for the control of EHAs without considering servo valve dynamics [6][7][8][9]. ...
We propose a nonlinear position control using a differential flatness concept with a load torque observer to compensate for the sinusoidal load torque in electro-hydraulic actuators (EHAs) EHAs. In an EHA with a rotational joint, the load torque is a sinusoidal disturbance, whose magnitude can be estimated via a load torque observer. In the proposed load torque observer, the load torque can be estimated without requiring its maximum frequency to be known. The position controller tracks position and comprises an inner-loop load pressure controller and an outer-loop position controller. The former tracks the desired pressure via near input–output linearization. The desired pressure is developed using the differential flatness of the mechanical system in the EHA. The feedback plus feedforward outer-loop position controller is designed to track the desired position and to compensate for the load torque. The stability of the closed-loop system is mathematically proven using the input-to-state stability property.
... (2) and Eq. (3), the following fluid dynamic equation of the actuator is derived: and Lamnabhi-Lagarrigue, 2001;Alleyne and Liu, 2000;Kaddissi et al., 2007). In Fig. 1, the dynamic equation of the hydraulic actuator can be defined as follows (Yao et al., 2000): ...
A new robust sliding mode control with disturbance and state observers has been proposed to control the nozzle angle of a water-jet system for a Unmanned Surface Vehicle (USV). As the water-jet system of a ship is subjected to direct disturbances owing to the exposure to the marine environment in water, it requires a robust control. A state observer and a disturbance observer are added to the water jet nozzle control system to achieve a robust control against disturbances. To verify the performance of the proposed algorithm, a test bed is constructed by a propulsion system used in the popular USV. This proposed algorithm has been evaluated by comparing to the existing algorithm through experiments. The results show that the performance of the proposed algorithm is better than that of the conventional PID or sliding mode controller when controlling the steering of the USV with disturbances.
... However, recent research developments in the field of nonlinear control finally allowed to overcome some of the aforementioned limitations and to guarantee reasonably good performance. Among these non-linear control strategies, Sliding Mode Control (SMC) is probably the most widespread solution when dealing with hydraulic actuators [7,8]. More recently, in [9] a 1 st -order SMC scheme was applied to control a 1-DoF hydraulic crane, while in [10] a 2 nd -order SMC scheme for the same system was proposed. ...
Nowadays the vast majority of high performance servomechanisms is composed by electrical servomechanisms. Nevertheless, hydraulic actuation systems are still very popular in several application domains (construction and earthworks machinery, mining industry, agriculture and forestry) since they offer multiple convenient features, like for instance: high power density, reliability, and relatively low maintenance cost. Typically, these actuators are controlled either manually by human operators opening and closing valves, or by using heavily approximated linear controllers. As a consequence, the resulting motion is often characterized by very low accuracy and very limited repeatability, thus leading to limited working efficiency, poor safety during operations and need for skilled operators. As a matter of fact, developing an accurate position control for such kind of servomechanisms is a quite complex task, mainly due to the highly non-linear dynamics describing the behavior of valves, and to the parametric uncertainty affecting the mathematical models of the different components. Recent research developments in the field non-linear control allowed to overcome these limitations and to guarantee reasonably good performance. Among these nonlinear control strategies, Sliding Mode Control (SMC) is probably the most widespread solution when dealing with hydraulic actuators. The contribution of this work consists in two main elements. First, the paper details the development and the validation of several control strategies aiming at achieving accurate position control of a standalone hydraulic servomechanisms. Starting from a previously validated dynamic model of a generic hydraulic servomechanisms, a linear cascade control with static compensation of the dead-zone and SMC has been synthesized. The tracking performance of time-varying reference signals of the SMC scheme has been improved by introducing a feed-forward model-based action. Finally, the performance of the different closed-loop control systems have been tested on an experimental test-bench and a comparative evaluation of the performance of the proposed control strategies is presented.
... In the previous studies, the most common varied parameter by the researchers is the supply pressure [7][8][9][10][11][12][13][14][15][16][17][18][19]. It is well known that, supply pressure plays vital role in the dynamic of an EHA system. ...
It is well known that the electro-hydraulic actuator (EHA) system is exposed to the disturbances, uncertainties, and parameter variations which are caused by the changes in operating conditions for instance, total moving mass, supply pressure, servo-valve gain, bulk modulus, leakage coefficient, and friction. These problems pose to a great challenge in modelling and controller development for an EHA system. Degradation of the desired performance can be imposed if an improper control strategy is utilized. This paper discusses the fundamental study on the significant effect that leads to degradation of EHA system performance due to variation in the system parameters. A nonlinear EHA system model is developed and implemented in the simulation studies in open-loop and closed-loop control configuration. The finding shows that the servo-valve gain resulted the most influential parameters to the EHA system performance as compared to the total moving mass and supply pressure parameters. In order to overcome these issues, the utilized controller should be robust enough to overcome the entire operating range that against such disturbances, uncertainties, and parameter variations. Therefore, a nonlinear and the intelligent control approach may be necessary to be designed in order to overcome these difficulties.
... Examples of the latter case include e.g. [1][2][3][4][5] in relation to hydraulic drive analysis and control design, just to name a few. Also, the inclusion of the HPU dynamics complicates drive analysis and control design, and may often only have little impact on the drive performance. ...
Hydraulic power units operated as constant supply pressure systems remain to be widely used in the industry, to supply valve controlled hydraulic drives etc., where the hydraulic power units are constituted by variable pumps with mechanical outlet pressure control, driven by induction motors. In the analysis of supplied drives, both linear and rotary, emphasis is commonly placed on the drives themselves and the related loads, and the supply system dynamics is often given only little attention, and usually neglected or taken into account in a simplified fashion. The simplified supply system dynamics used in such analyzes is often justified by short supply lines and/or the utilization of accumulators near valve inlets, accounting for the majority of possible supply pressure variations. Such considerations are reasonable in many test benches, where the supply pressure variations are small enough such that limited impact on the drive dynamics is observed. Such ideal properties however, are not necessarily present in industrial hydraulic applications for various reasons, with the most common being large volumes of supply lines. Long supply lines, hence large supply line volumes, between the supply system and drives will reduce the flow-to-pressure gain of the supply system, and hence increase the time constant of the supply pressure dynamics. A consequence of this may be large variations in the supply pressure, hence large variations in the pump shaft torque, and thereby the induction motor load torque, with possible excitation of the induction motor dynamics as a result. In such cases, the coupled dynamics of the pressure controlled pump and induction motor may influence the supply pressure significantly, possibly affecting the dynamics of the supplied drives, especially in cases where pilot operated valves with internal pilot supply are used. This paper is concerned with the analysis and characterization of the coupled pump-induction motor dynamics, confined to hydraulic power units constituted by an axial piston pump with mechanical outlet pressure control, driven by an induction motor operated at grid conditions. Furthermore, a simplified general model representation of the coupled dynamics is established, accounting for the entire dominating dynamics of the supply unit. Results demonstrate the accuracy of the simplified model representation.
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... Various methods exist today that focus on force control of EH systems. Some of them are: feedback linearization control, sliding mode control, and fuzzy control [11,[15][16][17][18][19][20][21]. Similarly, another challenge related to the use of electrohydraulic actuators is their positioning and force control [12]. ...
... Here a literature review is presented. A nonlinear sliding made controller was used by M. Jerouane et al [1], for a nonlinear mathematical model of a hydraulic system interacting with the environment. The proposed controller shows its insensitivity to a large variation of parameters such as flow gain, supply pressure or environmental stiffness, and has an excellent tracking performance for various set point forces under uncertainties. ...
This paper deals with the problem of designing a robust controller for the
electro-hydraulic position servo system (EHPSS). The sliding mode control design
methodology is utilized here to design a robust controller with respect to system
parameters uncertainty. Because the relative degree of the mechanical sub-system with
respect to hydraulic force is two, the switching function is constructed in two stages
in order to reduce the relative degree to one. As a result of the proposed controller, the
switching function reaches the zero level in a finite time, after that the state tracks the
reference value asymptotically. The simulations result using MATLAB/ Simulink tools
reveal the effectiveness and the robustness of the proposed control in forcing the
position to track the reference value in spite of the uncertainty in system parameters.
The uncertainty in hydraulic system model depends mainly on the variation on load
mass (20 kg to 250 kg). Namely, the robustness is tested for two load masses 75 kg
and 200 kg.
... However, the modelling and robust control of electro-hydraulic systems is a difficult task due to their nonlinear dynamics. Several control algorithms have been used to force tracking for electro-hydraulic actuators [2][3][4], including sliding-mode control [5, 6]. These controllers were designed based on the plant physical model and, therefore, the plant parameters knowledge is required. ...
This paper presents a novel scheme for identification and control of an electro-hydraulic system using recurrent neural networks. The proposed neural network has the nonlinear block control form structure. A sliding-mode control technique is applied then to design a discontinuous controller, which is able to track a force reference trajectory. Due to the presence of an unmodelled dynamics, the standard sliding-mode controller produces oscillations (or 'chattering') in the closed-loop system. The second-order sliding mode is used to eliminate the undesired chattering effect. Simulations are presented to illustrate the results.
... 유압 시스템에 사용되는 기름의 압축성과 서보 밸브의 복잡 한 유동 특성으로 인하여 EHS의 동역학 특성은 비선형성을 가지 게 되며, 이러한 EHS의 위치 혹은 힘 제어 성능을 향상시키기 위하여 90년대부터 최근까지 다양한 제어 방법이 연구 되어 왔 다. EHS의 비선형성을 보상하기 위해 가변구조방식을 이용한 제 어방법들이 제시 되었지만 chattering을 유발 할 가능성이 있다 는 단점이 있다 [2]- [3]. EHS의 동역학은 strict feedback 형태 의 구조를 가지고 있기 때문에 backstepping과 passivity 기반의 제어기 설계 방법들이 연구되었다 [4]- [7]. ...
We propose a disturbance observer(DOB) based feedback linearization control to improve position tracking performance in the presence of disturbance. The proposed method consists of a disturbance observer and a feedback linearization controller. The disturbance observer is designed to estimate the load force disturbance in electro-hydraulic systems. An auxiliary state variable is proposed in order to avoid amplification of the measurement noises in the disturbance observer. Using the estimated disturbance enables the Electro-hydraulic servo systems(EHS) dynamics to be changed into feedback linearization from. In order to compensate for the disturbance and to track the desired position, the feedback linearization based controller is proposed. The proposed method has a simple structure which can easily be implemented in practice. As a result, the proposed method improves the position tracking performance in the presence of disturbance. Its performance is validated via simulations.
... On the other hand, a fruitful and relatively simple approach, especially when dealing with nonlinear plants subjected to perturbations, is based on the use of Variable Structure Control technique with sliding mode (Utkin et al., 1999). A sliding mode controller was proposed in (Jerouane and Lamnabhi, 2001) to control the hydraulic actuator force. In this case the relative degree turns out to be two. ...
Various robust control techniques such as Integral Block Control, Sliding Mode Control and H-infinity Control are combined to design a controller, forcing an electro-hydraulic actuator driven by a servovalve to track a chaotic reference trajectory. This approach enables to compensate the inherent nonlinearities of the actuator and reject external disturbances. The capabilities of the approach are illustrated in a simulation study.
... Dies trifft bei realen Systemen nur bedingt zu. Mit adaptiven robusten Reglern[203] und robusten Sliding-Mode Reglern[81] versucht man deshalb Robustheit gegenüber Parameterunsicherheiten wie Leckflüsse, Reibung und der Temperaturabhängigkeit des ArbeitsmediumsÖl im Entwurf zu berücksichtigen 8 . Dies ist besonders relevant bei mobilen Maschinen, da sie stark wechselnden Temperaturen ausgesetzt sind. ...
Diese Arbeit behandelt die Problemstellung der approximativen Modellierung und Systemidentifikation
basierend auf der Systemklasse der gewichteten Kombinationen lokaler Zustandsraummodelle mit dem Ziel der modellbasierten Reglersynthese. Am Beispiel geregelter fluidischer Antriebe werden die Möglichkeiten, aber auch die Grenzen dieser Methode untersucht und experimentell erprobt.
Fluidische Antriebe zeichnen sich allgemein durch ein stark nichtlineares Verhalten aus. Hierbei verursacht die nichtlineare Kopplung zwischen ventilgesteuerten Massenflüssen und dem Druckaufbau in den Zylinderkammern der Antriebe, sowie dem Druckaufbau und der mechanischen Last eine Änderung der Antriebsdynamik, insbesondere die der positions- und lastabhängigen Dynamik. In der industriellen Praxis werden fluidische Antriebe in Servosystemen meist mit linearen Reglern betrieben. Da die lineare Regelung
eines nichtlinearen Systems nur in der Nähe eines Arbeitspunktes optimal ist, sind aufgrund des nichtlinearen Verhaltens der Antriebe die damit erzielten Regelgüten begrenzt. Viele Anforderungen, die an zukünftige Servosysteme gestellt werden, können damit nicht mehr erfüllt werden. Es ist daher erforderlich, das nichtlineare Verhalten der Antriebe im modellbasierten Reglerentwurf zu berücksichtigen, um die Regelgüte, wie z.B. die Positioniergenauigkeit, in weiten Stellbereichen zu verbessern. Hierzu wird ein approximativer Modellansatz zur Beschreibung nichtlinearer Systeme verwendet, der auf einer gewichteten Kombination lokal linearer und affiner Zustandsraummodelle basiert. (auch bekannt als Takagi-Sugeno Fuzzy System). Dieser wird im Hinblick auf die Approximationsgenauigkeit zunächst allgemein und dann anhand von Fallbeispielen analysiert. Im anwendungsorientierten Teil dieser Arbeit werden problemangepasste Modellstrukturen von fluidischen Linearantrieben als Streckenbeschreibung für den Entwurf von Gain-Scheduling PI-Zustandsreglern hergeleitet. Die unbekannten Modellparameter werden mit Systemidentifikationsverfahren aus Messdaten in verschiedenen Arbeitspunkten geschätzt und danach im globalen Modell experimentell validiert. Dann wird theoretisch nachgewiesen und durch Experimente an einem servopneumatischen Antrieb gezeigt, dass die approximative Modellbeschreibung ausreicht, um einen Gain-Scheduling-Regler zu entwerfen, der spezielle harte Anforderungen erfüllt, die an die Regelung im Globalen, d.h. im gesamten Arbeitsbereich gestellt wird. Darüber hinaus wird gezeigt, dass sich dieser neue Ansatz zur Beschreibung des Stribeck-Effekts zur Reibkraftkompensation in fluidischen Antrieben effektiv einsetzen lässt.
... Variable Structure Control (VSC) has been studied as an alternative control law for a hydraulic servo system (?), (Huang et al., 1994), (Lee and Lee, 1990). It appears that most VSC laws require the differentiability of the arbitrary load or resistive torques (Huang et al., 1994), or the use of the derivatives of piston velocity (?), (Jerouane and Lamnabhi-Lagarrigue, 2001), which is difficult to obtain. In addition, little attention has been given to the dynamic characteristics of the reaching laws. ...
This paper describes the design and experimental analysis of a variable structure control (VSC) law using three reaching law strategies for a hydraulic servo control system. For this purpose we use a non-linear mathematical model to develop a stable variable structure force control. The controller is designed using a sliding mode equivalence control and is augmented by a reaching law approach to further improve the performance. Three reaching laws are developed to bring the system states to the sliding mode surface. The feasibility of each reaching law structure on the closed loop performance (i.e. reaching time, chattering and quality of tracking) are experimentally evaluated and analysed.
... On the other hand, a fruitful and relatively simple approach, particularly when dealing with nonlinear plants subjected to perturbations, is based on the use of a variable structure control technique with sliding mode (SM) [5]- [10]. A sliding mode controller was proposed in [11] to control the hydraulic actuator force. In this case, the relative degree turns out to be two. ...
Various robust control techniques, such as integral-block, sliding-mode, and H -infinity controls, are combined to design a controller, forcing an electrohydraulic actuator which is driven by a servovalve to track a chaotic reference trajectory. This approach enables one to compensate the inherent nonlinearities of the actuator and reject matched external disturbances and attenuate mismatched external disturbances. The capabilities of the approach are illustrated in a simulation study.
... Nonlinear control of hydraulic systems has attracted considerable attention in the past decade and various nonlinear force and position control laws were developed ([1], [5]-[6]). To name a few, Chen et al. [7] designed a variable structure controller for an electro-hydraulic force control system. ...
In this article we design and experimentally evaluate a variable structure force control law for a hydraulic system interacting with the environment. For this purpose we use a nonlinear mathematical model where the nonlinear dynamics are explicitly addressed in order to achieve robust performance over a wide range of operating conditions. The sliding mode procedure is carried out to design a robust controller that satisfies performance specifications for force regulation. The controller is derived using the equivalent control method complemented by a reaching law approach to further improve the performance. After deriving the dynamics of the equilibrium manifold, rigorous stability verification for the system is provided. The controller was implemented on a fully instrumented hydraulic actuator. A set of experiments were performed to study the effect of variation in force set-point, supply pressure, hydraulic parameters, and environmental stiffness. The experimental results show that the proposed controller is robust to the variation of hydraulic parameters as well as environmental stiffness.
... On the other hand, a fruitful and relatively simple approach, especially when dealing with nonlinear plants subjected to perturbations, is based on the use of Variable Structure Control (VSC) technique with sliding mode [7]. Note that a sliding mode controller was proposed in [6] to control the electro-hydraulic actuator force; considering a relative degree equal to two. ...
This paper combines block control, sliding mode control and integral control techniques to design a controller, which is able to force an electrohydraulic actuator driven by a servovalve to track a given chaotic reference trajectory. This approach enables to compensate the inherent nonlinearities of the actuator and to reject external constant disturbances. A friction model incorporating Karnopp's stick-slip model and the Stribeck effect is used for the plant model. Simulations illustrate the approach applicability.
The hydraulic flight motion simulator (HFMS) is the key equipment for the hardware-in-the-loop simulation in the field of aerospace and has been widely used on occasions requiring high maneuverability and large power. However, three mismatched uncertainties, including nonlinear friction torque, unbalanced gravity torque, and unknown inertia, bring some certain difficulties for receiving the high-precision outer frame position control of the HFMS. In this article, first, by means of an ingenious experimental design, the coupled friction torque and gravity torque were identified separately. Subsequently, through combining the established mathematical model and identification results, an adaptive robust controller with model compensation was investigated in which adaptive controller is not only used to estimate unknown system parameters but also able to online correct identified parameters, and the robust controller is able to guarantee the stability of the whole system. Additionally, the zero bias of the servo valve was also introduced to assist controller implementation. Finally, experimental results show that by using the method of torque identification to improve the model accuracy, the burden of parameter adaptation and robust items can be effectively alleviated, and the high-precision outer frame position control of HFMS can be realized.
This paper presents control of a typical Electro-Hydraulic Servo System (EHSS) using measurable outputs. Detailed modeling of EHSS is described which takes into account the nonlinearities of solenoid coil, hydraulic pressures and spool motion. Two different controllers are proposed using two different surfaces. The two surfaces considered are finite time converging and asymptotically converging respectively. Second order sliding mode approach is used to device the control laws. The method is validated in simulation. Comprehensive comparison of the two controllers is presented.
This paper investigates the force control problem of a single-rod electrohydraulic actuator system based on sliding mode strategy. On the basis of the force tracking error dynamics, in order to facilitate the controller design, the whole system is divided into a linear subsystem and a nonlinear subsystem. By forcing the output of nonlinear subsystem to track the expected fictitious input of linear subsystem, and specifying suitable sliding mode functions for nonlinear subsystem and linear subsystem respectively, the cascaded sliding mode controller is created according to the reaching law approach. The stability of the closed-loop system is proved. Simulation results verify the effectiveness of the proposed cascaded sliding mode force control method for the single-rod electrohydraulic actuator system.
A position tracking and flatness controller with disturbance observer (DOB) is proposed in hydraulic servo systems (HSSs). In this paper, we assume that the disturbance is a biased sinusoidal signal with unknown frequency. DOB is designed in the form of 2nd high pass filter to estimate the disturbance. The nonlinear controller is designed to compensate the estimation error of the disturbance and to track the desired position and load pressure as a near IO linearizing inner-loop load pressure controller and a feedback plus feedforward outer-loop position controller. The desired load pressure is designed using differential flatness property of the HSS mechanical subsystem. The performance of the proposed method is validated via simulations.
Force control of a single-rod electrohydraulic actuator is investigated. The model considers the friction effect of the actuator. First, a non-linear force controller using a feedback domination approach, which can globally finite-time stabilise the force tracking error system without the friction parameter uncertainties, is proposed. Then, another feedback domination controller is proposed to cope with the friction parameter uncertainties. To estimate the unmeasurable states, an observer with finite-time convergence is developed. Rigorous stability analysis is given. Compared with the conventional output feedback backstepping control method, the proposed output feedback domination control scheme provides a faster convergence rate and a higher tracking accuracy for force tracking. Numerical simulation results demonstrate the effectiveness of the proposed control design.
A nonlinear position tracking controller with a disturbance observer (DOB) is proposed to track the desired position in the presence of the disturbance for electrohydraulic actuators (EHAs). The DOB is designed in the form of a second-order high-pass filter in order to estimate the disturbance. The nonlinear controller is designed for position tracking as a near input-output linearizing inner-loop load pressure controller and a backstepping outer-loop position controller. Variable structure control is implemented in order to compensate for the error in disturbance estimation. The desired load pressure is designed to generate the pressure using the differential flatness property of the EHA's mechanical subsystem. The disturbance within the bandwidth of the DOB can be cancelled by the proposed method. The performance of the proposed method is validated via simulations and experiments.
In this paper we present an output feedback nonlinear control for position tracking of electro-hydraulic systems (EHSs). Although previous nonlinear control methods improved the position tracking performance of EHS, all of the methods require full state feedback. However, due to cost and space limitations, it is not always possible to measure the full state of the EHS. The proposed method consists of a high gain observer and a passivity-based controller. The high gain observer is designed to estimate the full state, and the passivity-based control is implemented for position tracking. In order to design the passivity-based controller with the high gain observer, a defined Lyapunov condition guarantee that the origin of the tacking error dynamics is exponentially stable by selecting the controller gain. The stability of the closed-loop is studied using the singular perturbation theorem. The performance of the proposed method is validated through simulations and experiments.
In this paper, a flatness based control with adaptive load torque compensation is proposed for position tracking of electro hydraulic actuators (EHAs). The proposed method is implemented on a rotational joint driven by a linear type EHA. The proposed method consists of a position tracking controller and a load torque estimator. The position tracking controller is designed to track the desired position and load pressure as a near Input-output linearizing inner-loop load pressure controller and a feedback plus feedforward outer-loop position controller. The desired load pressure is designed using differential flatness property of the EHA mechanical subsystem. The load torque estimator is designed to estimate the unknown amplitude of the sinusoidal load torque. Then the load torque is compensated by a feedforward-loop. The performance of the proposed method is validated via simulations. Index Terms—Electro hydraulic actuator, Adaptive control, Position tracking
A quadruped robot driven by hydraulic cylinders has advantages for heavy loads, but the nonlinear and uncertain dynamics of the hydraulic actuators have to be considered. In this paper, a multi-strategy combination fuzzy sliding mode controller is adopted for the dynamic force control of a hydraulic servo system. First, a nonlinear mathematic modeling of a hydraulic actuator is given. Based on the modeling, a sliding mode controller is designed using the Lyapunov techniques. Second, a fuzzy scheduling mechanism is designed for boundary layer width tuning to reduce the chattering. Finally, a set of experiments were performed to analyze the effect of variation in given force, hydraulic parameters, supply pressure and environmental stiffness. The results show that the proposed fuzzy sliding mode controller is effective for a nonlinear hydraulic system, and makes the system response robust in presence of uncertainties.
We present a high gain observer-based nonlinear position control for electro-hydraulic servo systems. We design passivity based control for improve tracking performance. The passivity based control needs the full states information. Since the electro-hydraulic servo system has nonlinearities, we designed a modified high gain observer to estimate its states without the transformation for normal form. To reduce the effect of nonlinear terms, we use a high gain technique. We analyze the stability of the closed-loop system using the singular perturbation method. Simulations show that the proposed controller has better position tracking performance than a standard PI controller.
This paper presents a new scheme for identification and control of an electro-hydraulic system using recurrent neural networks. The proposed neural network has the nonlinear block control form (NBC form) structure. A sliding mode control technique is applied then to design a discontinuous controller, which is able to track a force reference trajectory. Due to the presence of an unmodelled dynamics, the standard sliding mode (SSM) controller produces oscillations (or "chattering") in the closed-loop system. The relative new approach high order sliding mode (HOSM) is used to eliminate the undesired chattering effect. Simulations are presented to illustrate the results
The dynamical behavior of a variable structure system (VSS) in sliding mode is determined by the sliding surface. On the surface, the system trajectory is immune from all uncertainties and external disturbances which are in the range of the control space, i.e., disturbances and uncertainties satisfy the so called matching condition. This property of invariance towards matched uncertainty makes sliding mode an attractive methodology for designing robust controllers for uncertain systems. However, the attribute of disturbances rejection for the variable structure system is lost if the sliding surface function contains uncertainties due to the presence of disturbances. In this paper, we present a simple way to construct discontinuous sliding surface to control an electro-mechanical systems. We show that disturbance rejection still can be attained even when matching condition in the original system is not satisfied.
There are many distinct advantages of a hydraulic control system, such as a higher speed of response with fast motions and possible speed reversals, a higher torque stiffness and a continuous operation. The hydraulic control system is becoming the most common form of precise manipulation system. However, some nonlinear phenomena, such as the relationship between input current and output flow, the fluid compressibility and the deadband due to internal leakage and hysteresis, make the control of the hydraulic system difficult. A novel variable structure control (VSC) with a time-varying switching gain, a second-order relation between sliding surface and uncertainties, and a boundary layer for the sliding surface, is employed to deal with the position control of the electrohydraulic servomechanism which is subjected to parameter uncertainties and external disturbances. Furthermore, the robust stability of the system is verified by a Lyapunov stability criterion. Finally, the simulations show that the proposed appraoch can achieve an accurate and robust tracking performance.
The research results described present the performance of the Generalized Predictive Control (GPC) algorithm with a changing estimator and predictor model order for a specific application. The application is a hydraulically actuated heavy duty manipulator. Hydraulically actuated robotic manipulators, used in the large resource based industries, have a complex dynamic response in which, primarily due to the hydraulic actuator subsystems, the order of the dynamic model is not initially known and can change as the manipulator is operated. A nonlinear simulation model of the manipulator system is utilized in the work and the GPC controller is implemented with a CARIMA estimator together with an on-line, gradient based estimator model order determination technique. The results given show that with proper use of the order determination technique cost function and tuning of the GPC parameters, good performance and stability can be achieved.
For the velocity control of an asymmetric hydraulic actuator the servovalve is not operated in the vicinity of zero. Thus the linearized model is not easily defined and the classical controller cannot be readily found. Also, because of its asymmetry, a fixed reference model of adaptive control cannot result in optimal performances for both directions.
In this paper, to minimize the performance index associated with the estimated model and control penalty, the self-optimization α-adaptive control shows an ability to adapt to variations in directions and operating conditions. Thus it will provide similarly optimal performances for both extending and retracting processes. Then, comparing with the variable gain control, the experimental results clearly show its superior performance and disturbance rejection.
A force control design problem is investigated for a hydraulic
actuator in the presence of several uncertainties. A method based on
nonlinear quantitative feedback theory (QFT) is proposed to design a
robust time-invariant controller. The plant model is identified by a
family of transfer functions, based on experimental input-output
measurements, performed on a hydraulic actuator equipped with a low-cost
proportional valve. The designed QFT controller is of low-order which is
desirable from practical point of view. Experimental results show that
the compensated system is not sensitive to variation of parameters such
as environmental stiffness or pump pressure and can equally work well
for various set-point forces
An integral variable structure controller (IVSC) for robust
servotracking is proposed. It comprises an integral controller, which is
designed for achieving zero steady-state error under step input, and a
variable structure controlled (VSC) which is designed for enhancing
robustness. A procedure is developed for determining the coefficients of
the switching plane and the integral control gain such that the overall
closed-loop system has the desired eigenvalues. Furthermore, a modified
proper continuous function is introduced to overcome the chattering
problem. An electrohydraulic velocity servocontrol system using the
proposed IVSC approach is illustrated. Simulation results show that the
proposed IVSC approach can achieve accurate servotracking and is fairly
robust to plant parameter variations and external load
disturbances
The design of variable-structure control (VSC) systems for a class
of multivariable, nonlinear, time-varying systems is presented. Using
the Utkin-Drazenovic method of equivalent control and generalized
Lyapunov stability concepts, the VSC design is described in a unified
manner. Complications that arise due to multiple inputs are examined,
and several approaches useful in overcoming them are developed. Recent
developments are investigated, as is the kinship of VSC and the
deterministic approach to the control of uncertain systems. All points
are illustrated by numerical examples. The recent literature on VSC
applications is surveyed
Perfor-mance of generalized predictive control woth on line model order determination for a hydraulic robotic manipulator M'sirdi Nacer, Laurent L a d , and Canudas Jean-Charles, Hm force control of (I hydraulic servo -actuator with environmental uncertainties
- D B Kotzev
- P D Cherchas
- Lawrench
Kotzev, D. B. Cherchas, and P. D. Lawrench, Perfor-mance of generalized predictive control woth on line model order determination for a hydraulic robotic manipulator, Robotics, Vol. 13,pp. 55-64, Jan.-Feb. 1994. 191 M'sirdi Nacer, Laurent L a d, and Canudas Jean-Charles, Hm force control of (I hydraulic servo -actuator with environmental uncertainties, in Proc.1996 IEEE Conf. Robot. Automat., Minneapolis, MN, Apr.1996, pp. 1566-1571.
Utkin, and 0. Bzgiiner, A Control Enginnering Guide to Sliding Mode Control
- K D Young
K. D. Young, V. I. Utkin, and 0. Bzgiiner, A Control Enginnering Guide to Sliding Mode Control, IEEE Trans-actions on Control Systems Technology, Vol. 7, No. 3, May 1999.
Design and ezperimen-tal evaluation of 0 mbust force controller for on electro-hydraulic actuator via quantitative feedback theory Control Enginnering Practice Ezperiments and Simuln-tions on the Nonlineor Control of a Hydraulic Seruosystern
- N Ill
- N Niksefat
- G Sepehri
- J E Sahl
- Bohrow
Ill] N. Niksefat, N. Sepehri, " Design and ezperimen-tal evaluation of 0 mbust force controller for on electro-hydraulic actuator via quantitative feedback theory. " Control Enginnering Practice, pp. 1335-1345, 8 ~ 2000. I121 G. A Sahl and J. E. Bohrow, Ezperiments and Simuln-tions on the Nonlineor Control of a Hydraulic Seruosystern, IEEE, Tkans. Coutr. Sys. Tech., Vol 7, No 2, pp. 238-247, March 1999.