hydraulic actuator

hydraulic actuator

[hī′drȯ·lik ′ak·chə‚wād·ər]
(mechanical engineering)
A cylinder or fluid motor that converts hydraulic power into useful mechanical work; mechanical motion produced may be linear, rotary, or oscillatory.

Hydraulic Actuator


a device for shifting the control members of a hydraulic actuating mechanism, with simultaneous power amplification of the controlling action. Commonly used types of hydraulic actuators are those employing a throttling control or a jet control. The first type of design (throttling) is used more frequently and includes designs with and without feedback and designs featuring combinations of control types. Such designs are simple and are reliable in operation, and they do not change the basic characteristics of the hydraulic mechanisms with which they are used. A hydraulic actuator consists of two basic mechanisms: a control device (variable throttles, such as nozzles with slide gates or paired slide valves having an initial axial gap) and an actuating device (for instance, the piston of an actuating mechanism or a controlling slide valve).

In a hydraulic actuator the working fluid from a pressure line enters the control system through the stationary (constant) throttles and is carried to the variable throttles and to the actuator chambers. The electrical input signal is passed through an electromechanical converter and controls the position of the gate slide. The displacement of this slide changes the cross-sectional ratio of the actuating openings through which the pressure fluid passes (that is, the ratio of the clearances between the nozzles and the gate slide). Simultaneously, the pressures in the actuator chambers are changed, thus causing a displacement of the slide valves.

The power amplification coefficient of a hydraulic actuator often exceeds 100,000. Hydraulic actuators with a load feedback or with a speed feedback not only cause a power amplification of the controlling action but also substantially improve the static and dynamic characteristics and the efficiency of hydraulic control systems and allow less stringent requirements for precision and quality of manufacture of the main subassemblies of the hydraulic actuators. When compared with other types of power amplifiers or boosters (such as electromechanical amplifiers), modern hydraulic actuators offer the advantage of a low metal weight per unit of power, often not exceeding 50 g per kilowatt of output power.


Hydraulic actuator

A cylinder or fluid motor that converts hydraulic power into useful mechanical work. The mechanical motion produced may be linear, rotary, or oscillatory. Operation exhibits high force capability, high power per unit weight and volume, good mechanical stiffness, and high dynamic response. These features lead to wide use in precision control systems and in heavy-duty machine tool, mobile, marine, and aerospace applications. See Control systems

Cylinder actuators provide a fixed length of straight-line motion. They usually consist of a tight-fitting piston moving in a closed cylinder. The piston is attached to a rod that extends from one end of the cylinder to provide the mechanical output. The double-acting cylinder (Fig. 1) has a port at each end of the cylinder to admit or return hydraulic fluid. A four-way directional valve functions to connect one cylinder port to the hydraulic supply and the other to the return, depending on the desired direction of the power stroke.

Limited-rotation actuators are used for lifting, lowering, opening, closing, indexing, and transferring movements by producing limited reciprocating rotary force and motion. Rotary actuators are compact and efficient, and produce high instantaneous torque in either direction. Figure 2 shows a piston-rack type of rotary actuator. Hydraulic fluid is applied to either the two end chambers or the central chamber to cause the two pistons to retract or extend simultaneously so that the racks rotate the pinion gear.

Rotary motor actuators are coupled directly to a rotating load and provide excellent control for acceleration, operating speed, deceleration, smooth reversals, and positioning. They allow flexibility in design and eliminate much of the bulk and weight of mechanical and electrical power transmissions.

Motor actuators are generally reversible and are of the gear or vane type.

hydraulic actuator

hydraulic actuatorclick for a larger image
An actuator operated hydraulically, which uses hydraulic pressure as a mechanical force to move objects like controls.
References in periodicals archive ?
A Stable Neural Adaptive Force Controller for Hydraulic Actuator, Proc.
A piston rod of the hydraulic actuator imparts movement to a generally vertically oriented articulated linkage member.
As the maintenance team began to further investigate the malfunction, they discovered that the aircraft's left rudder hydraulic actuator had failed.
The open base and wide seat are designed to allow for independent transfers, and the manual hydraulic actuator can be used to go to the standing position independently.
A linear hydraulic actuator is connected to an electro-hydraulic control unit (EHCU) via hydraulic lines, and the EHCU varies the pressure--and, therefore, the force--dynamically.
First, each locking nut on the tiebars now has its own hydraulic actuator right at the split nut.
M-mac Actuators Inc, North Vancouver, BC, applied these developments to the creation of a self-contained hydraulic actuator that would fill the gap between the limits of force at which a mechanical actuator is practical, to applications where the magnitude of force dictates a conventional hydraulic system.
The system utilizes a proven scissors mechanism that incorporates a hydraulic actuator working in parallel with an air spring.
The axis itself could use anything from a hydraulic actuator to a ballscrew as a feed system.
The unit's rotation is powered with a rotary hydraulic actuator and eliminates the maintenance associated with rotary chain drives.
The needle is controlled either by an electrical power source or a hydraulic actuator.
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