Linear actuator | Types | THE INSTRUMENT GURU

Table of Contents

Introduction-

A Linear actuator is an actuator that basically delivers motion in a straight line in response of received control signal. They are used in a wide range of industrial applications where linear positioning is needed. such actuators can be either manual operated or powered by some energy source such as compressed air, fluid pressure, electrically powered. Pneumatic or hydraulic piston cylinders, diaphragm mechanism provides linear motion directly. Besides that, circular motion of a conventional motor can also be used to generate linear motion using some geared or threaded mechanism. These actuators are also referred as sliding stem actuator and used in machine tools, industrial machinery, process control valves and dampers, in computer peripherals such as disk drives and printers, and in so many other places. Linear type of actuators can be various types as mentioned below-

Mechanical actuator
Pneumatic actuator
Fluid powered or hydraulic actuator
Linear motors
Piezoelectric actuators
Electro-mechanical actuators
Solenoid operated actuator
Telescoping actuator

Mechanical linear actuator-

A mechanical linear actuator is such actuator that functions to execute movement by rotary motion into linear motion. Such actuators provide linear displacement through the translation of manually rotated screw, cam, or wheel and axle mechanisms. They typically convert rotary motion of a control knob or handle into linear displacement via screws or gears attached. A diagram for different mechanism used for mechanical actuators are shown below-

Pneumatic linear actuator-

When pneumatic actuators deliver linear motion in response of controlled air pressure applied to it, it is referred as pneumatic linear actuator. Mostly such actuators are used for glove valve application to precisely regulate fluid flow and gate valve too. A diagram of pneumatic actuator for linear motion delivery is shown below-

Hydraulic linear actuator-

When hydraulic actuators deliver linear motion in response of controlled signal pressure applied to it, it is referred as linear hydraulic actuator. Mostly such actuators are used for slide valve, gate valve, damper, louver applications to regulate fluid flow. In such actuator, piston actuator stem is directly connected to load. A diagram of hydraulic actuator with sliding stem configuration is shown below-

Linear motor actuator-

When electric actuator delivers linear motion in response of controlled signal received, it is referred as electric linear actuator. Since motor delivers rotary motion so it is required to convert rotary motion into linear. This is done by means of two main components a gearbox (rotary motion) and a lead screw (linear motion). There are 3 types of lead screws used in electric linear actuators- “Machine Screw, Ball Screw & Roller Screw”. Electric motors rotation drives the primary gear of the gearbox, and gearbox output shaft (final gear) the lead screw and translate rotary motion into linear. A diagram of electric linear actuator is shown below-

Piezoelectric actuator-

Piezoelectric actuator can also deliver linear motion by converting electrical energy into a mechanical displacement or stress. It works based on piezoelectric effect. The basic principle of piezoelectric effect defines as when a force is applied to the crystal, it produces electrical charge. This is reversible phenomenon i.e. when a voltage is applied across its surface, crystal start deforming or vibrating. They are used to control small linear displacement at very high speed as well as in so many applications where accurate or precise position control is desired such as in robotics. Diagram of some piezoelectric actuators is shown below-

Electro-mechanical Actuator-

Mechanical actuators when operated using electrical power, it is referred as electro-mechanical actuators. Electromechanical actuators are such mechanical actuators where the control knob or handle has been replaced by an electric motor and the rotary motion of the motor is converted into linear displacement. The simplified design uses various mechanisms to transfer motor motion into linear displacement. A diagram showing electro-mechanical actuator is shown below-

Solenoid actuator-

Linear solenoid actuator is electrically operated actuator that uses electric supply to deliver linear motion of plunger. It consists of an electric coil with a movable ferromagnetic core (plunger) in its centre. When electric voltage is applied to the coil, current passes through the coil which creates a magnetic field. The magnetic field forces the plunger to move upward and enables opening the orifice or closing of orifice depending on its valve configuration. They can be used with various valve configuration as per their requirement A linear solenoid valve is shown below-

Telescoping linear actuator-

Telescopic actuator is special type of actuator that is used to deliver linear stroke. Such actuators are used where space restriction exist i.e. where we have limited space to install actuator. Telescopic actuator can produce very good stroke length (many times greater than the actuators own fixed length). These actuators can be based on any principle such as electric, pneumatic or hydraulic type. A diagram of telescopic actuator is shown below-

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