Types Of Actuators | Function of Actuators used in Machines

ACTUATORS

One of the important components of mechatronic control system is the actuator. Actuators are the devices that accept a control command and produce a change in the physical system by generating force, motion, heat, flow, etc. It is a device that makes something to move. Normally, the actuators are used in conjunction with the power supply and a coupling mechanism. The power unit provides either AC or DC power at the rated voltage and current. The coupling mechanism acts as the interface between actuator and physical system. Typical mechanisms include rack and pinion, gear drive, belt drive, lead screw and nut, piston and linkages.

Primary functions of mechanical actuation systems

1. Transformation of a rotary motion into a translating motion as in the case of cam and follower mechanism where the rotational motion of the cam is changed into translational movement of the follower.
2. Transformation of rotary motion for a long distance which is not possible by using gears, as in the case of belt drives.
3. Transformation of rotary motion for a medium distance without slipping which is not possible by using belt drives, as in the case of belt drives.
4. Transformation of linear motion into rotational motion as in the case of rack and pinion mechanism.
5. Locking of rotating elements as in the case of ratchet and pawl mechanism.

types of actuator
types of actuator

Types of Actuators :

Actuators are basically classified into the following two types based on their movement.

  • Translational
  • Rotational

It is possible to convert one form of actuation to another. For example, translational motion is converted into rotational and vice versa by suitably designing the interfacing components around the actuator. Rack and pinion, gears, pulleys, lead screw and nut, and cams can be used as interfacing components.

Actuators can be classified into the following types based on the type of energy.

  1. Electrical
  2. Electromechanical
  3. Electromagnetic
  4. Hydraulic
  5. Pneumatic

Eletrical actuators are the choice of actuators for most of the on-off type control action. Switching devices such as diodes, transistors, TRIACs, MOSFET and relays are used as electrical actuators. These actuators accept a low energy level command signal from the controller and switch on or off electrical devices such as motors, valves and heating elements.

Electromechanical actuators are electrical motors that convert the electrical energy into mechanical motion. Motors are the principal means of converting electrical energy into mechanical energy in industry. Broadly, they are classified into DC motors, AC motors and stepper motors.

An electromagnetic actuator is a device that provides working motion due to an internal electromagnetic field. The solenoid is the most common electromagnetic actuator. A solenoid consists of a static, hollow-centered wire coil and a movable ferrous metal plunger. When the wire coil is energized, a magnetic field establishes that provides the force to push or pull the metal plunger.

Hydraulic and pneumatic actuators are normally either rotary motors or linear pistons/cylinders. They are ideally suited for generating very large force coupled with large motion. Pneumatic actuators use the compressed air that is more suitable for low to medium force, short stroke and high speed applications. Hydraulic actuators use oil under pressure which is incompressible. They can produce very large force coupled with large motion in a cost-effective manner. The rotary motors are usually used in applications where low speed and high torque are required. The cylinder/piston actuators are suited for the application of linear motion. A proper selection of actuators and their drive systems for a particular application is of utmost importance in the design of mechatronic systems.

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