When motion applications require high speed and linear movement, you may want to consider using pneumatic actuators. Pneumatic actuators use air pressure and flow to create high force and velocity. They are used in a variety of industries, such as packaging, food processing, and medical design.

Heavy loading and rapid movements are the norm in milling operations, requiring the use of large-bore pneumatic cylinders to hold the logs in position during sawing.

What pneumatic actuator attributes are most tightly linked to speed, and how do they affect it?

Frank/Festo: Airflow into the actuator and friction are critical parameters in achieving speed. How fast you can put air into the actuator relates directly to how fast you can accelerate the piston. Friction is the force that works against the motion of the piston. It can be found between the piston seal and cylinder and also on the bearing seal and rod itself.

Phil/Bosch: Bore size and air pressure affect speed, as does the volume of air to be exhausted (assuming a double-acting cylinder). As for pressure, the net force applied to the cylinder piston is a function of its crosssectional area and the differential pressure across it.

Walt/PHD: Air pressure and flow have the greatest effect when it comes to obtaining speed from pneumatic actuators. The valve, port size, fittings, and tubing must be properly sized to obtain the required speed. If you cannot obtain the flow and pressure required, you will not obtain the desired speed. Another factor is the distance from the valve to the actuator. This is most relevant when reaction time is combined with a requirement for actuator speed. Reaction time can be greatly reduced by applying a valve directly to the actuator, eliminating the pneumatic tubing and the volume of air within.

Gary/Beswick: To maximize speed, you'll want to minimize the internal volume of the actuator. You also want to make sure the actuator has large ports and well designed internal airways to minimize pressure drop as the fluid enters. Naturally, internal friction should be kept as low as possible; rolling diaphragm designs are best in this regard. It's also important that actuation shafts and rods have a small diameter as well as support from low-friction bushings or bearings. The mass of the moving components should be minimized as well.

What are some of the limiting factors associated with speed, and how do you overcome them?

Phil/Bosch: Rate of exhaust is the primary limiting factor. Quick release valves installed into the cylinder port can exhaust directly to atmosphere for minimum exhaust times. For higher speeds, two 3/2 valves with independent solenoid control may be used. In this case, pressurized cylinder chambers can be exhausted before the cylinder is required to move, creating maximum differential pressure across the piston. Tube inside diameter and length also limit speed. The longer the tube, the greater the pressure drop and more restrictive the air path.

Frank/Festo: How air is ported into the cylinder can make a big difference on speed. Porting the cylinder axially rather than perpendicular to piston motion greatly improves airflow into the cylinder. Cylinder barrel surface finish and lubrication also impact speed. The surface inside the barrel should let the grease spread without being swept to the end of the cylinder. Too smooth a surface is as bad as too rough a surface.

Walt/PHD: One of the biggest limiting factors with pneumatic actuators is decelerating the load or mass at the end of travel. It's one thing to accelerate a load using air, and another to decelerate that load in a short distance or time. This can be overcome with built-in deceleration; adjustable pneumatic cushions, hydraulic shock absorbers, and deceleration circuits that control backpressure at the end of travel.