Actuation in robotics means the systems that enable physical movement. The most common ways of actuation are by electric motors, pneumatic and hydraulic systems, which we will introduce below. But note that there are other actuation systems as well, achieved by shape memory alloys, piezoelectric action, electromagnetism, movement achieved through thermal properties of materials and more. Now let’s take a closer look at Electric motor, Pneumatic and Hydraulic actuation.
Electric Motor Actuation:
This is the most common way, where, movement is achieved by electric motors, which can run on AC or DC power.
Electric motors offer a high degree of precision and motion control and may be used for almost any type or size of robotic applications.
Pneumatic systems make use of the powerful action obtained from compressed air, that moves pneumatic cylinders (pistons). It is commonly used for robotic arms and industrial robots including especially assembly lines, where strong and swift movements are essential. Note that this comes at the expense of relatively lower precision, in comparison to electrical actuation by motors.
The air can either be generated by a compressor exactly when needed, or be stored in a compressed air tank. Air flow is controlled by valves.
The back and forth movement of a piston in two directions is achieved by different means, which depends on the particular application and operating environment:
-In a single acting cylinder, the pressure is supplied only from one side and the reverse movement may be achieved by a spring, gravity, or the pressure difference between the compressed / depressurized air and the air pressure from the external environment. So in a single acting cylinder there must be an external force to achieve the movement in reverse direction.
-The compressed air can also be introduced from both directions as necessary. This is called a double acting cylinder. Of course when introducing air from one side, it must be released from other side which must be coordinated. Double control of the cylinder from both sides means better control of the overall movements.
The control system manages this two way movement by controlling the valves and compressors in proper timing and sequencing.
These systems use pressured liquids, usually oil, which can provide the strongest movements. Remember that construction equipment use this type of actuation.
Due to the incompressible nature of liquids, strength can be achieved in a small volume (even by a small amount of movement), and also precise movements are easy to obtain.
Therefore hydraulic systems are used where we need both strength and precise control.
If we want to compare Pneumatic vs. Hydraulic systems:
Hydraulic systems are
affected less by temperature variations,
can be more difficult to maintain
than Pneumatic systems.