Conventional Hydraulic Actuators Research Articles

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Nowadays, electro hydrostatic actuator (EHA) has shown great advantages over the conventional hydraulic actuators with valve control system. This paper presents a position control for an EHA using a modified back stepping controller. The controller is designed by combining a backstepping technique and adaptation laws via special Lyapunov functions. The control signal consists of an adaptive control signal to compensate for the nonlinearities and a simple robust structure to deal with a bounded disturbance. Experiments are carried out to investigate the effectiveness of the proposed controller.

Extending the operation range of electrorheological actuators for vibration control through novel designs

Electrohydraulic actuators with electrorheological fluids were lately introduced for active vibration decoupling. They are suited especially for active isolation of heavy machines and apparatuses. Compared to conventional electrodynamic or hydraulic actuators, these electrorheological systems have considerable advantages because of very high force density and broad frequency range. However, the potential of the electrorheological technology does not remain used up to now completely. In this study, new designs are introduced, which extend the operation borders of the electrorheological actuators for vibration decoupling by utilization of hydrostatic as well as to hydrodynamic forces. The theoretically determined dynamic behaviors of the new actuator principles form the basis for the choice and adaptation of the electrohydraulic systems to special vibration isolation problems and show the advantages to conventional hydraulic actuators.

A Switched Control Strategy for Antilock Braking System With On/Off Valves

In this paper, a switched control strategy for an antilock braking system (ABS), which has conventional hydraulic actuators equipped with on/off valves, is presented. The investigated system contains the continuous dynamics of the vehicle and the inherent discontinuous characteristics of the on/off valves. Accordingly, a novel approach based on nonlinear state feedback and a switching strategy renders a controller that assures that the wheel slip converges into the target equilibrium set. Then, the convergence condition of the closed-loop system is analyzed using Lyapunov theory in the Filippov framework, and the influence of controller parameters on the system is also discussed. It is shown that the proposed controller has few tuning parameters, and each parameter has an explicit physical meaning. Both the illustrative hardware-in-the-loop simulation and experimental results show that the switched control approach is robust enough to guarantee a good performance, even if the uncertainties of the actuator characteristics, road-adhesion coefficient, and vehicle speed are considered.

Special Issue on Precise Positioning

Precise positioning is a basic, essential technology in a wide variety of automation considerations. It has recently been extended to micron and nanometer positioning including basic components such as mechanical elements, mechanisms, actuators, and controllers. Improving positioning accuracy requires advances in individual components, behind which there has been conducted much research and development. This special issue focuses on actuator, control technology, and mechanical elements and mechanisms. Constructing precise positioning involves conventional electrical, hydraulic, and pneumatic actuators. A piezoelectric actuator is useful for micron and nanometer positioning. An appropriate mechanism is required to transmit power from the actuator to the object being positioned. An effective control scheme must also be introduced into system with available sensors. In this regard, this issue includes advanced papers representative of individual fields that should prove interesting, stimulating, and of great practical use to both general readers and specialists. We thank the authors for their many interesting papers contributed to this issue.

Model Predictive Control of a Two Stage Actuation System using Piezoelectric Actuators for Controllable Industrial and Automotive Brakes and Clutches

High bandwidth actuation systems that are capable of simultaneously producing relatively large forces and displacements are required for use in automobiles and other industrial applications. Conventional hydraulic actuation mechanisms used in automotive brakes and clutches are complex, inefficient and have poor control robustness. These lead to reduced fuel economy, controllability issues and other disadvantages. Recently, a two-stage hybrid actuation mechanism was proposed by combining classical electromechanical actuators like DC motors and advanced smart material devices like piezoelectric actuators. This article discusses the development and implementation of a model predictive control methodology for controlling this two-stage actuation system in tracking various reference inputs. Additionally, this methodology also employs a unit-step delayed disturbance estimate to account for actuator hysteresis, other nonlinearities and unmodeled dynamics in the system. Finally, the article highlights the effectiveness of this control methodology experimentally by tracking various reference inputs.

Performance of a Magnetorheological Hydraulic Power Actuation System

The performance of a magnetorheological (MR) hydraulic power system is analytically and experimentally assessed. Four MR valves are implemented as a Wheatstone bridge hydraulic power circuit to drive a hydraulic actuator using a gear pump. The compact hydraulic power actuation system is a Wheatstone bridge network driving a conventional hydraulic actuator. A key advantage of using MR valves in hydraulic actuation systems is that the valves have no moving parts. This reduces complexity and enhances durability compared to conventional mechanical valves. In such a system, an MR fluid is used as the hydraulic fluid. A constant volume pump is used to pressurize the MR fluid. If a change in direction is required, the flow through each of the valves in the Wheatstone bridge can be controlled smoothly via changing the applied magnetic field. A magnetic field analysis is conducted to design a high-efficiency compact MR valve. The behavior and performance of the MR valve is expressed in terms of nondimensional parameters. The performance of the hydraulic actuator system with a Wheatstone bridge network of MR valves is derived using three different constitutive models of the MR fluid: an idealized model (infinite yield stress), a Bingham plastic model, and a biviscous model. The analytical system efficiency in each case is compared to experiment, and departures from ideal behavior, that is, a valve with infinite blocking pressure, are recognized.

Development of Smart Missile Fins with Active Spoiler

For conventional missiles, electric or hydraulic actuators are mounted inside the missile fuselage to activate the aerodynamic control surfaces. These internally mounted actuators occupy considerable volume which otherwise can be used for payload or additional fuel. Reducing the size of the internal actuators and hence lowering the total actuator weight may improve the overall performance of missile significantly. The goal of this research is to develop a light-weight, low cost smart missile fin capable of surviving the supersonic operating environment while providing necessary performance comparable to existing missile fins. In this study, in an alternative to facilitate realistic design concepts and to generate enough actuation forces required for missile controls, smart fins with trailing-edge-mounted retractable wedge are considered. The retractable wedge stretches in or out appropriately to decrease the applied pitching moment of the missile fin. For the theoretical calculation, a commercial CFD software package is used to obtain the forces and the moments generated by the fin with retractable wedge. The piezoelectric actuation mechanism that is applicable to the wedge type actuator is also investigated.

Dynamics and control of limit cycling motions in boosting rockets

An investigation concerning the prediction and control of observed limit cycling behavior in a boosting rocket is considered. The suspected source of the nonlinear behavior is the presence of Coulomb friction in the nozzle pivot mechanism. A classical sinusoidal describing function analysis is used to accurately recreate and predict the observed oscillatory characteristic. From this analysis, insight is offered into the limit cycling mechanism and confidence is gained in the closed-loop system design. Nonlinear simulation is used to support and verify the results obtained from describing function theory. Insight into the limit cycling behavior is, in turn, used to adjust control system parameters to indirectly control the oscillatory tendencies. Tradeoffs with the guidance and control system stability/performance are also noted. Finally, active control of the limit cycling behavior, using a novel feedback algorithm to adjust the inherent nozzle sticking-unsticking characteristics, is considered. HE ballistic tactical target vehicle (BTT V) is a suborbital rocket whose re-entry vehicle serves as a target for advanced air defense and theater defense systems under development.1'2 Flight telemetry results from the first two missions indicate the presence of low-amplitude, low-frequency steady oscillations in both the vehicle attitude and actuator piston displacement.3'4 Figure 1 illustrates this characteristic in the vehicle pitch attitude response during second stage boost of the first mission. Note the flight data has been post processed. The impact of the oscillatory motions on the guidance and control objectives appear to have been minor; however, their presence was unexpected and is of concern, especially with regards concerning the origins of the oscillatory behavior and the physical mechanism by which they occur. The hardware in question is the decommissioned Minuteman I Stage 3 system which is used as the second stage for the BTTV vehicle. After discussions with individuals intimately familiar with the Minuteman I Stage 3 characteristics, it became known that this system has a long history of exhibiting small, slow periodic motions during the boost phase. These characteristics are, in fact, so common that routine preflight analysis is used in estimating the oscillatory motion for the specific flight vehicle/control system in question. The results are then compared with an existing database to deter- mine whether the oscillatory motions will impact the guidance and control mission objectives. This database suggests the oscillatory motions are limit cycling behavior due to nonlinearities present in the actuator-nozzle system, a conventional hydraulic actuator driv- ing vectorable nozzles. Coulomb or dry friction present in the nozzle pivot is the primary culprit. Additional nonlinearities are present but are not considered here. The first goal of this research is to provide an accurate prediction, if possible, of the oscillatory behavior experienced by the BTTV flight vehicle.5 This analysis should provide insight as to the ori- gin of and the mechanism by which the characteristics occur. Si- nusoidal describing function theory and nonlinear simulation are to be employed in achieving this goal. A second goal of this re- search is to explore means by which the oscillatory motions may be controlled to lessen the impact upon the guidance and control performance.5 The implemented control systems should also have minimal impact on the performance of the guidance and control feedback loops, while simultaneously providing sufficient robust- ness against reasonably expected modeling uncertainties and errors.