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Does your new Air Double-Acting Cylinder stutter when it extends? To fix a stuttering pneumatic cylinder, ensure the flow controls, such as "meter-in" vs. "meter-out," are correctly positioned.
At this point, you've probably figured out all the pneumatic actuators and air valves for your new project, but now you need to ensure you have a consistent speed from the pneumatic actuators. For some, the way to confirm this is done correctly is through flow control. But did you know that there is a performance difference depending on where it is in your system?
Even if you have a flow control on the line and know that it will regulate the speed, there is a chance for stuttering to happen still. To avoid this issue, you need to have your flow control metering the air supply going in, known as "meter-in," or find the flow control metering the exhaust air or "meter-out."
When to use “Meter-Out” Configuration
For your air cylinder to stop stuttering, you need to use a "meter-out" configuration because you want to control the exhaust air out of a double-acting air cylinder. These cylinders give a smoother airflow and act as a speed limit to the pressurized air chamber.
Think of it like pushing against an untied balloon while holding it partially open. The balloon resists by pushing back and shrinks as fast as you allow air to leave the opening. The larger the opening, the faster air will flow out, and the quicker your cylinder will move. Making the opening smaller or larger is the same as opening up or closing down the flow control in the pneumatic system.
When to use “Meter-In” Configuration
The "meter-in" configuration will slow down the compressed air entering the cylinder chamber, slowly building pressure. A minimum air pressure is needed to break the piston seals free from stiction with the cylinder body. This stickiness or stiction will always exist.
A way to visualize this is to consider the air cylinder an adjustable volume chamber. When the piston breaks the stiction and moves, a larger air chamber increases with more volume. Controlling the incoming flow of air will slowly refill the larger air chamber allowing the piston time to stop and slowly build pressure again until it can break the stiction. As this continuously happens, the cylinder rod starts and constantly stops, creating a stuttering motion.
Is there ever a time you want to use the "meter-in" flow control for speed control? The short answer is yes, sometimes. Using a single-acting spring return cylinder, you want to use the "meter-in" flow control to regulate the speed. The spring limits the speed of the pressurizing chamber, just like the flow control on the exhaust acted to push back on the piston. The "meter-in" flow control slowly supplies the air cylinder to be able to move. When pressure is built to the minimum needed to break the piston free to move, the spring pushes back on it instead of jumping so the air pressure can constantly be moving the piston. It will not jump because this resistance of compressing the spring will allow the cylinder to move smoothly.
If you still have stuttering issues or cannot get the configurations right on your pneumatic systems, contact us at Motion Automation Intelligence today. We have reps on standby that would be happy to help!
