Linear actuator
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A linear actuator is a type of electric motor that develops force and motion linearly.
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[edit] Basic operation
A linear actuator is a device to generate controlled physical linear displacement. There are various means of achieving this linear displacement. A few common examples are listed below;
a) Hydraulic actuators: These typically involve, hollow cylinder having piston inserted in it. The two sides of the piston are alternately pressurized/de-pressurized to achieve controlled precise linear displacement of the piston and in turn the entity connected to the piston. The physical linear displacement is only along the axis of the piston/cylinder.
b) Electro-mechanical actuators: These involve conversion of rotary motion into equivalent linear displacement. Typically, a rotary driver (e.g. electric motor or hydraulic motor) is mechanically connected to long shaft termed as screw. The rotary motion of electric motor here will make the screw shaft to rotate also. The screw shaft has a continuous helical thread machined on its circumference running along the length, these are termed as ball grooves because there are spherical balls that roll in this groove. The screw is inserted in to another mechanical body termed as ball-nut. The ball-nut also has similar helical thread machined on its inside diameter (envision the ball-nut as hollow cylinder) and has built in system to re-circulate the spherical balls. The spherical balls are trapped in the mating ball grooves on screw shaft and ball-nut and convert the rotary motion of the screw shaft into linear displacement of the ball-nut. The screw shaft and ball-nut together are also termed as ball screws.
c) Linear motor: This is in simplicity essentially rotary electric motor laid down on flat surface.
[edit] Advantages
They are self-contained, requiring only electrical power and a control interface. They can be operated in parallel, using multiple actuators to perform a single task. They can be very precise
[edit] Disadvantages
Hydraulic actuators can start leaking and are difficult to control. Electro-mechanical actuators are prone to mechanical wear and tear. Linear motors cannot achieve high load capacity normally required.
[edit] See also
- Linear motor, an actuator converts an electrical signal (V/I) to mechanical displacement. Mostly used in robotics, actuators are also used in applications such as televisions, and for opening and closing windows in cars.
- Power screw
