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Hey Dan,
There are two ways that I can recommend to acheive an intermediate position for a pneumatic cylinder. Both require the use of a second cylinder, plus a second valve. 1. Telescoping method: You would start with a cylinder that has the stroke of the intermediate position (cylinder 1). To the end of cylinder 1, you would add a second cylinder (cylinder 2), to achieve the remainder of the stroke. Each of these cylinders would be controlled by there own valve. To start this system in the intermediate position, have cylinder 1 extended and cylinder 2 retracted. Then by extending cylinder 2, or retracting cylinder 1, you can get to your end positions. 2. Perpendicular method: You would start with a cylinder (cylinder 3) that has the total stroke. A second cylinder (cylinder 4, typically with a very sort stroke) would be mounted perpendicular, in such a way that when extended, it would block the cylinder 3 from fully extending. Again, each cylinder is controlled by it's own valve. This system would start with both cylinders extended, with cylinder 4 blocking the full extension of cylinder 3. Retracting cylinder 4 allows cylinder 3 to fully extend, and retracting cylinder 3 allows for the other end position. Comparison of the 2 methods The telescoping method allows easily for the intermediate position to be reached while either extending or retracting. The perpendicular method is best suited for acheiving an intermediate position when approached while extending, but in it's simple form cannot stop in the intermediate position when retracting (although it can be done). The telescoping method is longer than the perpendicular method (since you have 2 cylinders mounted end to end). The perpendicular method requires that the room exists such that 2 cylinders can be mounted perpendicular to each other. The perpendicular method typcially has a lower cylinder cost (but see next point regarding life), since the "stopper" cylinder typically has a shorter stroke, and can be a smaller bore size (since it is mearly blocking the extending cylinder). The life of the perpendiclar set-up is shorter since the "stopper" cylinder is seeing side loading (which the cylinders in the kits are not designed for). A linear bearing can be added, but makes the system more complicated to assemble, and adds cost. Hope this helps. Regards, Scott358 Festo Corp Sponser of Hauppauge HS |
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