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.