Pneumatic actuators are components that convert forms of energy (e.g., air pressure) into mechanical energy used to position control valves. Usually, a pneumatic actuator consists of a piston or stem, a spring, and valves or ports. Pneumatic actuators transmit energy through a stem with the help of both spring force and air pressure.
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Applications of Pneumatic Actuators
Pneumatic actuators can be used for a wide variety of applications, such as the lifting, pushing, rotating, or moving of equipment or products during manufacturing procedures.
Industries that utilize pneumatic actuators include:
- Material Handling
- Food Processing
Pneumatic Actuator Design and Function
Within the housing, two separate air chambers are created by a rubber diaphragm. The upper chamber receives air from an opening located at the top of the housing. A spring is located in the bottom chamber, and it applies force to the diaphragm so that it halts mechanical stops in the upper chamber. Roughly halfway through the bottom chamber, a local position indicator can be found connected to the stem, which indicates the valves position. The indicator is controlled by the fluctuating air pressure located in the upper chamber. The positioning device is very complex.
The parts featured on the outside includes an input connection for the control valve, a supply air connection, a supply air input connection, a supply air vent connection, and a feedback linkage. The inside of the chamber features an elaborate series of air lines, linkages, valves, necessary adjustments, and electrical transducers. A lack of air will lead the spring to continuously hold the valve open. As the air supply increases, more force is applied to the diaphragm, which will overpower the force of the spring, subsequently making the valve close. The valve’s positioning depends on how much air is supplied to the machine’s top chamber. The valve is held in place once the desired position is achieved and the air pressure stops changing.
One of the most important features of a pneumatic actuator is the controller. A controller can be added to a pneumatic actuator for the purpose of positioning the valve per the requirements of the machine’s operator. The controller functions by sending a signal to the positioner that indicates where the valve should be positioned. Since the controller is pre-programmed to maintain a certain valve position, it adjusts quickly upon any change in the controlled variable relative to the valve’s setpoint.
Notable Types of Pneumatic Actuators
Pneumatic actuators come in a variety of types. Some of these types include:
- Pneumatic Valve Actuators
- These actuators are defined by the use of valves in their overall function. In addition to pneumatic, other varieties of valves actuators that are available include those powered hydraulically and electrically.
- Tie Rod Cylinders
- These types of actuators get their name from their structure. A set of bolts hold them in place through a pair of castings, each located on either end of the barrel. Tie rod cylinders are very simple in design, and they generally come with fixed stroke lengths and bore sizes, which may put manufacturers at a disadvantage when developing new equipment.
- A pneumatic gripper is a device that functions as a set of fingers or jaws, enabling manufacturers to hold an object so it can be manipulated. The fingers are not part of the gripper itself, but rather a specialized custom set of tools. Two main actions can be performed by a gripper. The first, external, involves the gripper jaws closing, and the force of the jaws holds the object. This method requires the shortest stroke length and is the most simplistic; it is the most frequently used method of holding items. The internal method involves the gripper’s opening force holding the object. The internal method requires the gripper to hold the object from the center, which is useful for cases where the exterior of the object may have to be accessed.
- Pneumatic Artificial Muscles
- These devices consist of a contractile or extensional pneumatic bladder that is designed to hold pressurized air. The bladder is a thin membrane, making the device itself lightweight and enabling the actuator to be directly connected to the structure that they power. This flexible membrane also enables the actuator to mimic biological systems, such as human muscle.
Factors to Consider When Purchasing Pneumatic Actuators
Pneumatic actuators are generally affordable, user-friendly, and have a simplistic structure. However, they are noisy and their position is hard to control. Therefore, it is important to weigh the pros and cons of a pneumatic linear actuator within the context of the desired application before making an investment.