An actuator is an automated device used to control or produce motion in a mechanism or system. The energy required to control or produce such motion is obtained from five main sources: mechanical, hydraulic, pneumatic, thermal and magnetic.
Actuators are often considered a class of motors. However, there is a key difference between the two - motors produce rotary motion, while actuators typically produce linear, constrained motion. There are exceptions.
Actuators convert input energy to produce a desired type of motion.
A typical example of an actuator application is a butterfly valve.
Types of actuators
1. Mechanical actuators utilize mechanical devices such as screws, screw jacks, ball screws, roller screws, wheel spindles or cams to convert rotary motion into linear motion.
However, mechanical actuators cannot be used for automation and can only be operated manually.
2. Hydraulic actuators use a hollow cylinder filled with mechanical fluid and a piston inserted into it.
When an unbalanced pressure is applied to the piston, it creates a force that can move an external object. These actuators produce a precise displacement along the axis of the piston.
3. Pneumatic actuators are similar to hydraulic actuators except that they use a compressed gas rather than a liquid to generate force.
4. Piezoelectric actuators use special materials to generate a voltage when mechanical pressure is applied. These materials expand when a voltage is applied.
They are used to produce extremely precise movements and require very high voltages to operate. 5.
5. Electrohydrostatic actuators have pumps that rotate back and forth to draw fluid from a pressurized vessel through a set of valves. The precise motion of the rotating pump in these actuators is achieved by using a digital positioner for feedback and a servo controller to control the pump.
These are used for inlet guide vane drives, remote subsea drives, etc.
How to select an actuator
Actuator selection is based on a variety of mechanical parameters, including load, stroke length and time.
Suitability and advantages are also important considerations in selecting an actuator for your specific application.
1. Hydraulic actuators provide high force in a small size, but require a hydraulic source.
2. Pneumatic actuators use factory air.
3. Electric actuators offer better controllability and are less prone to leakage, giving them an advantage in cleanroom environments. Although they have a high initial cost, they are more economical in the long run.
4. pneumatic valve actuators - double-acting and spring-return - utilize pressure differentials as either powered or non-powered actuators.
5. Piezo actuators are designed for micro-positioning and use piezoelectric crystals to produce high-precision motion for applications such as optics and semiconductor manufacturing.
Other Factors to Consider
There are several other factors and parameters to consider when selecting the right actuator for an application. Some of these are listed below.
Installation Configuration
After selecting the ideal actuator, you will need to decide how it will be mounted on the equipment you want to start.
Output Torque
Output torque describes the rotational force that an actuator can apply to a valve to close it. It applies to both electric and fluid power rotary actuators.
Maximum Thrust
It is the maximum force that the actuator can apply to push or hold the working fluid.
Maximum Speed
It is the maximum linear or rotational speed that the device can provide. It is usually expressed in rpm for rotary actuators and in millimeters per second for linear devices.