Actuator is a mechanical device for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion. Linear actuator is an actuator that creates linear motion, whereas rotary actuator creates rotary motion. Mechanical and hydraulic actuation are the most common methods of achieving the linear motion. Many linear actuators are driven by a non-linear motion.

Types of Linear Actuators

  • Mechanical Linear Actuators – Mechanical linear actuators typically operate by conversion of rotary motion into linear motion. Conversion is commonly made via a few simple types of mechanisms:
    • Screw Actuators: Screw jack, ball screw and roller screw actuators all operate on the principle of the simple machine known as the screw. By rotating the actuator’s nut, the screw shaft moves in a line.
    • Wheel and Axle Actuators: Hoist, winch, rack and pinion, chain drive, belt drive, rigid chain and rigid belt actuators operate on the principle of the wheel and axle. By rotating a wheel/axle (e.g. drum, gear, pulley or shaft) a linear member (e.g. cable, rack, chain or belt) moves.
    • Cam Actuators: Cam actuators function on a principle similar to that of the wedge, but provide relatively limited travel. As a wheel-like cam rotates, its eccentric shape provides thrust at the base of a shaft.
  • Hydraulic Actuators – Hydraulic actuators or hydraulic cylinders typically involve a hollow cylinder having a 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.
  • Pneumatic Actuators – Pneumatic actuators, or pneumatic cylinders, are similar to hydraulic actuators except they use compressed gas to provide pressure instead of a liquid.
  • Piezoelectric Actuators – The piezoelectric effect is a property of certain materials in which application of a voltage to the material causes it to expand. Very high voltages correspond to only tiny expansions. As a result, piezoelectric actuators can achieve extremely fine positioning resolution, but also have a very short range of motion.
  • Electromechanical Actuators – Electromechanical actuators are similar to mechanical actuators except that the control knob or handle is replaced with an electric motor. Rotary motion of the motor is converted to linear displacement of the actuator.

Selection of Proper Linear Actuator for your Application

In order to select the proper motors or linear actuators, several factors must be considered. Is linear or rotary motion required? Following is a list of some of the basic requirements to consider when choosing a motor or linear actuator for the required industrial application.

  • How much force is required from the linear actuator?
  • What is the duty cycle of the linear move?
  • What is desired step increment from the linear actuator?
  • What is the step rate or speed of travel?
  • Bipolar or unipolar coils in the stepper motor prime mover?
  • Stepper motor coil voltage?
  • Must the lead screw hold position with power off or must it be “backdrivable” with power off?
  • Are there size restrictions (max footprint of the linear actuator)?
  • What is anticipated life requirement?
  • Temperature of operating environment?
  • Captive, external, or non-captive linear actuators?