Pneumatic Actuator Basics

There are thousands of industrial applications that require linear motion during the sequence of operation. One of the simplest and most cost-effective ways to accomplish this is a pneumatic actuator. The pneumatic actuator works very cleanly because the working fluid is a gas, preventing leaks from dripping and contaminating the environment.

This section describes the basic configuration and functions of a pneumatic actuator, its relationship to a fluid power system, and instructions for selecting a pneumatic actuator or air cylinder.

Basic style

Pneumatic actuators convert compressed air into linear motion. There are several types of pneumatic actuators, such as the diaphragm cylinder, the rodless cylinder, the telescopic cylinder, and the thru-cylinder.

The most widely used pneumatic actuator consists of a piston and a rod that move inside a closed cylinder. However, a variety of construction techniques and materials exist to suit a wide range of applications and user preferences. Body materials can be aluminum, steel, stainless steel, and certain polymers. The structure is not repairable or repairable. This style of actuator can be subdivided into two types, single acting and double acting according to the working principle.

The single-acting cylinder has a single port through which compressed air can enter the cylinder and move the piston to the desired position. An internal spring, or sometimes gravity, is used to return the piston to the "home" position when the air pressure is removed. Single-acting cylinders are suitable for one-way work, such as lifting an object or pressing an object with another object.

The double-acting cylinder has ports at both ends, moving ports alternately that receive high-pressure air to move the piston back and forth. It uses roughly twice as much energy as a single-acting cylinder, but is necessary when the load needs to move in both directions, such as opening and closing a door.

In typical applications, the actuator body is connected to the support frame and the rod end is connected to the mechanical element to be moved. A control valve is used to send compressed air to the extension port while opening the shrink valve into the atmosphere. The pressure difference on both sides of the piston produces a force equal to the pressure difference multiplied by the piston area. If the load connected to the rod is less than the resulting force, the piston and rod expand, moving the mechanical element. If the valve is changed to send compressed air to the reverse port with the expansion port open to the atmosphere, the cylinder assembly will retract to the "start" position.

The pneumatic actuator is at the working end of the fluid power system. Before these devices, which create visible load movement work, are compressors, filters, pressure regulators, lubricators, control valves, and flow control devices. The connection of all these elements is a suitable plumbing or plumbing network (rigid or flexible).

 

When choosing these upstream system components to ensure desired performance, the pressure and flow requirements of the actuators in the system must be considered. Small upstream components can degrade the performance of the pneumatic actuator or prevent the load from moving.

Speed

If the cylinder force (F) is known, the above formula can find the diameter of the hole (d). F is the required force (lb) and P is the supply pressure (psi). The stroke length is determined by the required movement of the mechanical element driven by the actuator. The speed at which the cylinder can move the load is directly related to the speed at which the compressed air flows through the pneumatic system to the piston.

It can be a little difficult to calculate since the resistance of the system (basically the friction of the air that moves through pipes and parts) increases non-linearly as the flow increases. As a result, the pressure drop from the supply (air compressor) to the cylinder increases. If the pressure drop is so great that the available pressure in the cylinder cannot move the load, the cylinder will stop. If speed is critical to machine operation, you may need to test 2 to 3 valve, tube, and cylinder combinations to achieve the desired performance.

Mounting:-

The last bit of the basic selection criterion is the cylinder mounting device. Different configurations are available from various manufacturers. The most common include rigid nose or tail mounts, trunnion mounts, rear pivot mounts and foot mounts. Studies of the required mechanical movement generally show which mounting configuration is the best option.

Knowing the basic size and configuration of the actuator, the final selection should take into account other options, such as stroke end cushions, magnetic pistons (for position sensing switches), or special seals.

Cushion:-

The cushion does an excellent job of preventing the piston from hitting the end cap at the end of the stroke. The flow control valve can also prevent tilting, but will slow down movement. The cushion slows down movement for only about half an inch. The cushions are very useful when the design requires a higher speed or cycle speed, and a smooth start and stop.

Magnetic piston:-

With a magnetic piston, a simple magnetic proximity sensor can be mounted on the cylinder, allowing the control system to obtain feedback on the position of the cylinder. Most cylinders expand or contract, so two proximity switches can monitor cylinder operation. This can be very useful for machines that require a series of tasks. Due to the nature of the compressed air system, the exact cylinder speed may differ slightly due to various factors beyond the control of the mechanical control system, such as a change in supply pressure, moisture content in the air, or temperature. ambient. Therefore, if step 1 is determined to be complete, the control sequence beginning with step 2 is a much more robust design.

Extreme temperature:-

When sealing pneumatic systems, special sealing materials such as Viton may be required for environmental conditions such as extreme temperatures or corrosive substances. Most manufacturers offer these special stamps as options.

Since pneumatic actuators are at the working stage of a fluid power system, when choosing upstream parts, you should consider working to visually verify the actuator load, pressure, and flow requirements. Small upstream components can degrade the performance of the pneumatic actuator or prevent the load from moving.