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Unread 15-12-2004, 17:41
Rickertsen2 Rickertsen2 is offline
Umm Errr...
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Re: Mulit-postioning with pnuematics this year?

Not ALL valves are air piloted. There are quite a few companies that make valves with entirely magnetically actuated spools.

BTW i would highly caution against the above setup for anything with a dynamically varying load. I will also note that changing direction wastes alot of air and is generally somewhat unstable. If the cylinder will only be required to resist in one direction, there is a much more stable and air efficient version of this.
Use a spring return cylinder. If the assembly will return by itself (IE by the weight of gravity etc, the spring is counterproductive and not necessary).
Use a 5/3 double actuated vavle with a closed center as mentioned above. Plug port 2/A/output1 (different manufacturers call it different things. Plumb port 1/input/whatever to supply. Plumb port 4/B/output2/whatever to the port on the cylinder that corresponds to the direction that you want it to apply force in. To regulate extension speed put a flow regulator in series with the supply to the valve. To regulate retraction speed, screw a flow regulator into port 5/BE/exhaust2. you could also use unidirectional flow regualtors in series with the line from the valve to the cylinder. This setup will still drift when the load changes, but it uses MUCH less air and is MUCH more stable when changing directions.

Food for thought: The REAL way to accomplish multipositioning is with a proportional valve, a position sensor, and a feedback controller of some sort.
The position sensor, porportional valve and feedback controller are normally
electronic. This wouldn't be a problem except that FIRST tells us that we can only drive solenoids from spikes. Most porportional valves take either an analog input or have some sort of digital interface. I will give people a hint and tell you that there are a number of ways that are FIRST legal an to create a entirely analog entirely pneumatic feedback position control loop. WOOT for pneumatic amplifiers differential regulators etc! In fact, the first PID controllers were entirely pneumatic. First person to come up with a workable scheme wins a prize.. well not really but i would like to see what people come up with.
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Last edited by Rickertsen2 : 15-12-2004 at 17:53.