Kinematics – Actuation of Machines: Part III – Pneumatic Actuation How pneumatic actuators work Types of pneumatic actuators

Pneumatic Actuation

Pneumatic Actuation system transforms the energy stored in compressed gases to mechanical energy which is further used to move parts of mechanisms. The motion achieved can be either linear or rotary. The source of power in any pneumatic actuation system is the compressed gas. The energy is stored in the gases, generally air, by compression using compressors or pumps.
The advantage of pneumatic actuation system over hydraulic actuation system is the freely available working fluid for pneumatic actuators, that is air. Whereas the working fluid for hydraulic system, the hydraulic oil is very costly and requires major effort to check its leakage and need to replenished as and when required.

Types of Pneumatic Actuators

A typical Pneumatic Actuator has set up for supply of compressed gas, pipes for flow of compressed gas and valves to control the flow of gas. The requirement of any system and the convenience of use dictates which actuation system to be used. Based on application and design constraints pneumatic actuators are designed in different configurations.
Types of pneumatic actuators commonly used in industries are linear motion actuators, rotary motion actuators, grippers and special purpose pneumatic vacuum grippers for lifting smooth objects. A different type of pneumatic actuator whose functionality resembles the human muscle is also used for controlled motion of mechanisms or structures. It is called as Pneumatic Artificial Muscle (PAM).

Linear Actuator

Linear pneumatic actuators are very similar to linear hydraulic actuators in construction but there is a basic difference in their operation. Like the linear hydraulic actuator its counterpart pneumatic actuator is an assembly of piston, cylinder and valves to control the actuator.

In the hydraulically operated actuator the hydraulic fluid is pumped in the cylinder to move the piston out and fluid is sucked or released in the hydraulic circuit itself to retract the piston, so as to keep the fluid in the circuit without any wastage of the hydraulic fluid. Whereas in the pneumatic actuator the moving out process is same but for moving the piston inside the pressure is released by letting the compressed air out of the cylinder by operating a release valve.

Rotary Pneumatic Actuator

Rotary pneumatic actuators converts the energy of pressurized flowing gases into the rotatory motion, similarly as a gas turbine. In this instead of compressed fluid being pressed against the piston walls, the gases flow past the actuator and generates the motion. Rotary Pneumatic actuators are generally fitted with rack and pinion to have high torque output.

Rotary Pneumatic Actuator

Pneumatic Grippers

Pneumatic gripper is an assembly of pneumatic actuators producing simultaneous motion to give a gripping action. They are used to ensure secure gripping while lifting heavy objects and are fitted with proximity switches to monitor open and closed position of the gripping jaws.

Gripper

Pneumatic Vacuum Grippers

Vacuum grippers are used lift objects with smooth surfaces which cannot be handled otherwise due to absence of any ends to pick the objects. Vacuum grippers work by creating a low pressure at the actuator end by venturi action generated by pressurized gases moving at fast speed past the nozzle. The actuator end is brought close to the object to be picked, the objects sticks to the end which can be released where required by stopping the gas flow. Advance vacuum grippers can pick multiple objects even with rough surfaces.

Vacuum Gripper

Pneumatic Artificial Muscle (PAM)

PAMs work similar to the animal muscles, that is, they contract and expand when given the corresponding signal. Like other pneumatic actuators PAMs are operated by pressurized air. Between the two ends of the PAM there is a balloon type construction, when inflated makes the two ends move closer thus resulting in compression of the PAM. As PAMs can only apply force while contracting, they are used in antagonistic arrangement where the two muscles in the pair can apply force in opposite directions. Spring loaded PAMs can work in single also, they will extend when air pressure is released.

Pneumatic Artificial Muscle

This post is part of the series: Kinematics – Design of Mechanisms

Machines as simple as livers, machines such as James Watt’s steam engine and the industrial robots such as PUMA all are composed of mechanisms whether simple, complex or combination of many simple and complex mechanisms. These mechanisms are governed by Kinematics – the study of geometry and motion.
  1. Kinematics – Design of Mechanisms: Introduction
  2. Analysis and Synthesis in Machine Design
  3. Types of Kinematic Joints
  4. Degrees of Freedom
  5. Kinematics – Design of Mechanisms: Kinematic Inversion
  6. Kinematics – Actuation of Machines: Part I – Electrical Actuation
  7. Kinematics – Actuation of Machines: Part II – Hydraulic Actuation
  8. Kinematics – Actuation of Machines: Part III – Pneumatic Actuation
  9. Kinematics – Analysis of Mechanisms: Methods and Techniques
  10. Kinematics – Synthesis of Mechanisms: Methods and Techniques
  11. Four Bar Linkages in Machine Design
  12. Straight Line Mechanisms
  13. Kinematics – Special Mechanisms: Straight Line Mechanisms – II
  14. Exact Straight Line Mechanisms