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Unread 01-05-2002, 09:37 PM
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Stopping a Piston...

Is it possible to set a center return point for a piston, so you have a central 'ready' position and motion available both fore and aft of the ready? If so, how?
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Unread 01-05-2002, 11:13 PM
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Thumbs up Stopping a piston

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
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Unread 02-01-2002, 01:45 PM
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easy way to stop a piston in mid stroke

as on robot last year we were able to stop a piston any where in the stroke length both Extending and retracting


the best way to do this is to use the double soleniods
EXHAUST ports to do this
and yes- it was legal

email me if you want be to email you the diagram

or if i get real energetic I will have my of the students diargam it today and have it posted here and in the white pages



dahl
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Unread 02-01-2002, 02:39 PM
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We'd love to see it...

This question comes up every year. If you have a good solution and are willing to share it, a lot of folks will be very pleased.

Joe J.
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Unread 02-01-2002, 03:20 PM
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I talked to the guys at SMC (who supply a lot of our pneumatic stuff) and they were highly against the second method, as you are side loading a piston with a LOT of force.
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Unread 02-01-2002, 05:04 PM
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I should have a nice pic/diagram up by the end of the weekend
(of course after my beloved PATRIOTS win a squeaker a the superbowl






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Unread 02-02-2002, 09:34 AM
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Additional note w/r/t "second" method

If you are going to block one cylinders motion with another perpendicular cylinder, and side loading is an issue, the perpendicular cylinder can be used to position a plate (or something else) to block the motion. The load should be taken by an external bearing. This was what I was reffering to in the original post, when I stated a linear bearing can be added.

One of the easiest ways of doing this is to have a simple plate, which will be placed in the path of the extending cylinder. This plate, which can be sliding in the channels of 2 parallel sections of Bosch extrusion (or be sliding on some other form of linear bearing), is moved in and out of the blocking position by the second cylinder.

Hope this helps with the side loading issue.

Scott358
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Unread 02-02-2002, 10:36 AM
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stoppinh pstion mid stroke with pilot valvbe

did we get a pilto lavel in this years kit- upon looking back thru our diagrams and white papers
we were able to do it with the pilot valve-

i think there is a work around using the double soloniods

i will check--

\
dahl
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