Pneumatic cylinder

From Team 449 Wiki

Double-action cylinder operation.

Pneumatic cylinders, or pistons, have a rod in them that moves in and out when air is put in. Single-action cylinders have only one air input, which drives the cylinder one direction. They also have a spring on on the inside to return them to their original position. They can be either spring-extended (rod is naturally out) or spring-returned (rod is naturally in). Double-action cylinders are more commonly used, and are generally preferable to single-action cylinders. They have two air inputs, generally one at each end. When air is put into the bottom, the rod extends; into the top, the rod retracts.

Dimensions

A cylinder is primarily characterized by its bore diameter and stroke length. The bore diameter is the inner diameter of the cylinder. The stroke length is the difference in length between the extended and retracted positions.

Design

Stroke Length

The a cylinder's stroke length is how far it will extend from its retracted position. The stroke length is used to determine various geometries based on what lengths are needed. It is to note that unlike with motors, it is not harmful to the cylinder to be "stalled" - if the cylinder is not allowed to extend fully but is still pressurized, no harm is done to it.

Bore Diameter

A cylinder's bore diameter determines the amount of force it can apply. This is calculated by the equation F=PA, where F is the force applied, P is the system's pressure, and A is the area of the bore. This force is the maximum force that can be applied by the piston, but it is to note that when the piston is first actuated, its pressure will not immediately go up to the pressure of the system, and thus its force is not constant at the maximum force throughout its whole extension.

Load Ratio

A mechanism's load ratio on a piston can be calculated as the force applied by the mechanism (due to gravity, springs, or other resistant forces) divided by the maximum force available to the piston, expressed as a percentage. If there is no load, the load ratio is 0%, and if there is load equal to the max force of the piston, the load ratio is 100%.

Max Speed

A cylinder's shaft's maximum speed is determined by the flow rate going into, the bore diameter, and the load ratio applied on the cylinder. The maximum speed increases as flow rate increases, and decreases as the bore diameter and load ratio increase.