Robotic actuators – Hydraulic and Pneumatic

The actuators are used in the robots for providing the power to the robot joints. It can be powered by anyone of the following sources:

  • Hydraulic – pressurized fluid
  • Pneumatic – compressed air
  • Electric – electricity

Hydraulic and Pneumatic actuators:

Both hydraulic and pneumatic actuators use moving fluids for powering a device. Here, the fluid represents pressurized oil for hydraulic and compressed air for pneumatic actuators.

When these actuators are compared with each other, two things can be observed such as:

  • Both actuators are similar in terms of their operational functions.
  • These actuators differ only in their capability to pressure the fluid.

The hydraulic actuator is capable of providing the pressure at 1000 – 3000 lb/in2, while the pneumatic actuator can only deliver around 100 lb/in2.

Let us consider a cylinder, which is one of the simplest devices for powering the fluids. In this device, a moving piston is available for actuating the linear joint.

This type of device is known as single – ended cylinder, because it has only one end in which the piston rod comes out. There are also some types of cylinders like:

  • Rodless cylinder
  • Double – ended cylinder

A set of relationships describe the particular interest of the actuators:

  • The actuator velocity relating to the input power.
  • The actuator force relating to the input power.

These relationships for a cylinder-type actuator can be given by:

V (t) = f (t) / A

F (t) = P (t) A


P (t) represents the fluid pressure.

V (t) represents the piston velocity.

F (t) represents the force.

A represents the piston area.

f (t) represents the flow rate of the fluid.

The relations illustrated to select a suitable robot can be according to the requirements of a robot that is necessary for carrying a load at a specified speed.

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