A linear actuator is a device that generates linear motion from some source of energy. It can push, pull or move back and forth. The actuator generally accomplishes this task through some mechanical or hydraulic means. An electric linear actuator is a type of mechanical actuator that uses an electric motor to create motion, which is frequently non-linear in nature. A linear actuator converts this motion into linear motion.
An electric linear actuator makes this conversion with three basic types of mechanisms. The first is a screw actuator, the second is a wheel-and-axle actuator, and the third is a cam actuator. The electric motor in a screw actuator rotates a nut, which causes the shaft of the screw to move in a straight line. The rotation of a wheel-and-axle actuator causes a cable, belt or rack to move in a linear manner. The cam in a cam actuator has an eccentric shape that provides linear motion when it rotates against the base of a shaft.
The types of electric motors can include a direct current (DC) brush motor, DC brushless motor, induction motor or stepper motor. These motors typically create rotary motion, although the specific method varies according to the application requirements of the electric linear actuator. Some applications might require the motor to exert a large amount of force, whereas other applications might require a greater emphasis on accuracy.
An oil refinery might require an electric motor to drive a linear actuator with great force and speed. This application typically requires a high-power induction motor that uses alternating current. A linear actuator in laboratory instrumentation is more likely to need a low-power stepper motor that turns a fine-pitch screw to provide linear movement that is accurate to a thousandth of an inch (.0254 mm).
The standard construction technique for an electric linear actuator treats the electric motor as a separate component from the actuator. The motor in this type of construction typically is inside its own casing and attaches to the exterior of the actuator. The drive shaft of the motor then connects to the actuator’s drive screw.
Some applications require an electric linear actuator to use a compact construction technique. This generally involves treating the motor and actuator as part of the same unit to occupy the smallest possible volume. A common design approach to this problem is to hollow out the motor’s drive shaft so that the actuator’s drive screw and nut can fit inside the shaft. This design eliminates the need for a gear between the drive screw and the motor.