Linear actuator
Since liquids are nearly incompressible, a hydraulic cylinder can provide controlled precise linear displacement of the piston.
Air actuators are not necessarily used for heavy duty machinery and instances where large amounts of weight are present.
One of the reasons pneumatic linear actuators are preferred to other types is the fact that the power source is simply an air compressor.
As a result, piezoelectric actuators can achieve extremely fine positioning resolution, but also have a very short range of motion.
In addition, piezoelectric materials exhibit hysteresis which makes it difficult to control their expansion in a repeatable manner.
Electromechanical actuators may also be used to power a motor that converts electrical energy into mechanical torque.
When considering an actuator for a particular application, the most important specifications are typically travel, speed, force, accuracy, and lifetime.
For example, a linear actuator using an integral horsepower AC induction motor driving a lead screw can be used to operate a large valve in a refinery.
For electromechanical linear actuators used in laboratory instrumentation robotics, optical and laser equipment, or X-Y tables, fine resolution in the micron range and high accuracy may require the use of a fractional horsepower stepper motor linear actuator with a fine pitch lead screw.
In the majority of linear actuator designs, the basic principle of operation is that of an inclined plane.
Most focus on providing general improvements such as a higher mechanical efficiency, speed, or load capacity.
In either case the screw may be connected to a motor or manual control knob either directly or through a series of gears.
Generally it is not possible to vary the static load capacity of screw actuators without additional technology.
The screw thread pitch and drive nut design defines a specific load capacity that cannot be dynamically adjusted.
In some cases, high viscosity grease can be added to linear screw actuators to increase the static load.
Static load capacity can be added to a linear screw actuator using an electromagnetic brake system, which applies friction to the spinning drive nut.
For example, a spring may be used to apply brake pads to the drive nut, holding it in position when power is turned off.
When the actuator needs to be moved, an electromagnet counteracts the spring and releases the braking force on the drive nut.
Dynamic load capacity is typically referred to as the amount of force the linear actuator is capable of providing during operation.
Dynamic load is the figure which most actuators are classified by, and is a good indication of what applications it would suit best.
The duty cycle of a motor refers to the amount of time the actuator can be run before it needs to cool down.
If the duty cycle rating is exceeded, then overheating, loss of power, and eventual burning of the motor is risked.
While high capacity is possible, the material and/or motor limitations on most designs are surpassed relatively quickly due to a reliance solely on magnetic attraction and repulsion forces.
Linear motors have an advantage in outdoor or dirty environments in that the two halves do not need to contact each other, and so the electromagnetic drive coils can be waterproofed and sealed against moisture and corrosion, allowing for a very long service life.
A common form is made of concentric tubes of approximately equal length that extend and retract like sleeves, one inside the other, such as the telescopic cylinder.
