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An electromagnetic actuator is any device that provides working motion courtesy of an internal electromagnetic field. These devices fall into two broad categories — solenoids and linear electromagnetic motors — both of which function according to the same principle, but differ significantly in design. Both types, however, provide the movement used for actuation by exposing a free moving plunger or armature to the magnetic field created by energizing a static wire coil. The field attracts the plunger or armature that, in turn, moves, thus providing the required actuation. Varying degrees of actuation functionality can be achieved with an electromagnetic actuator, ranging from simple single-cycle, single-speed actions to fairly sophisticated control of both actuation time and positioning.
Electromagnetic switching is one of the most widely utilized remote actuation methods available and may be found in heavy industrial manufacturing and domestic applications of all descriptions. The basic principle that underpins electromagnetic switching or actuation may be clearly seen when a simple bar magnet is used to pick up spilled sewing pins off of the floor. The basic requirement in remote switching and actuation is movement and, in the case of the electromagnetic actuator, a static coil is used to attract a ferrous metal plunger or armature that, in turn, provides the movement required. This movement can, depending on the actuator design, be a fairly simple single-directional, single-speed movement, or fully controllable in terms of speed and extent.
The term electromagnetic actuator can be applied to two basic categories of devices. The first are solenoids, which are the more simple and common of the two types. These devices consist of a static, hollow-centered wire coil and a movable ferrous metal plunger. In the neutral state, the solenoid plunger is positioned in such a way in relation to the opening of the core that, when the coil is energized by an electric current, the magnetic field created in the coil attracts the plunger. This pulls it smartly into the center of the coil and provides the movement necessary to actuate a secondary mechanism.
The linear electromagnetic motor is the second and more sophisticated of the electromagnetic actuator types. They consist of a hollow tube with a wire coil wound around the inside surface. A permanent magnet armature is positioned inside the core with the actuator arm attached to it. When the core is energized, the armature reacts to the magnetic field my moving up or down the tube, the movement being transferred by the actuator arm to a secondary device. By manipulating the way that the electric current is applied to the static coil, a far more complex range of movement in terms of extent and duration can be achieved with this type of actuator.