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#61
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Re: Mulit-postioning with pnuematics this year?
"White paper" posted in the technical section.
It is two pages - one text and one picture. |
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#62
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Re: Mulit-postioning with pnuematics this year?
which page is it on
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#63
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Re: Mulit-postioning with pnuematics this year?
Quote:
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#64
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Re: Mulit-postioning with pnuematics this year?
Thanks
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#65
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Re: Mulit-postioning with pnuematics this year?
here's a corrected version of the schematic. Our skilled engineers (students) actually got working on our pnuematics board. includes relief valves to prevent overpressures on the exhaust side.
http://ndofwrldaswenoit.tripod.com/robotics/index.html |
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#66
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Re: Mulit-postioning with pnuematics this year?
wow that is genus. i am amazed. speechless. perfect thread.
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#67
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Re: Mulit-postioning with pnuematics this year?
Against my better judgment, I am going to try to ride this horse one more time.
I have been thinking about this problem, and in experiments with the solenoids and trying out the ideas in this thread we have determined that – exactly as the manufacturer states – the valves will not change state reliably unless there is 30 psig at the ‘P’ port on the valve. In trying to make this happen with the ‘P’ port connected to the exhausting side of the cylinder, the 30 psig is not always there, and the valve will not shift reliably. In addition, we want to avoid any rule-breaking involving going over the 60 psig limit for working air pressure, and not have to use a cumbersome solution involving regulators or relief valves in several different parts of the pneumatic circuit. It is possible to purchase three –position solenoid valves with the center position having all ports blocked, or having the outlet ports pressurized. However, there is some question in my mind about the legality of these valves – it appears to me, at least, that the pneumatics rules and the flow chart are not in precise agreement. We would prefer to avoid the discussion with the judges if at all possible. I have come up with a compromise solution shown in the accompanying file. Using two double solenoids, it is possible to supply air to the ‘P’ port of each valve, plug the ‘B’ outlets, direct the ‘A’ outlet of one valve to the ‘extend’ port, and the ‘A’ outlet of the other valve to the ‘retract’ port on the cylinder. To extend the piston, shift the valve on the extend port to supply air to the cylinder, and the valve on the retract port to exhaust. The 60 psig supply air at the ‘P’ ports will ensure that the valves shift when commanded. To retract, reverse the positions of both valves. And, to stop in mid-position, shift the valves so that air is supplied to both ports on the cylinder. In the event that a force is applied to the device moved by the piston, any increase in air pressure above 60 psig will be relieved by the main regulator. Otherwise, the cylinder will be more-or-less locked in place by the 60 psig on both sides of the piston. Push hard enough and it will move, of course, but it will be possible to stop in mid-position as desired, using unquestionably legal components. The 60 psig working air pressure limit will not be exceeded, and the use of extra regulators or relief valves is avoided. |
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#68
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Re: Mulit-postioning with pnuematics this year?
Leo,
If you applied the 60 psig to each side through both the solenoids wouldn't the cyclinder just continue to slowly extend since the forces won't equalize out? Also if you shorten the tubing from the double exhaust to the single you should not have trouble getting 30 psig for port "P". I believe reducing the regulator to ~55 psi will take care of the 60+ psi problem. You have to give up a little strength for control. These are just my thoughts. Have you tested that circuit yet? Just curious to how well it worked. |
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#69
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Re: Mulit-postioning with pnuematics this year?
Unfortunately, I haven't been able to experiment as much as I would like to. This is just a concept. I thought I'd throw it out to the forum and see if anyone else could make something of it. There are a lot of other considerations in designing a system like this - what exactly is attached to the piston; how do static forces such as weight, or dynamic forces of parts in motion, affect the relative motion of the mechanism; how much time and money do you have to complete the system? The complicated nature is illustrated by the length of this thread. It holds some kind of fascination for us - I just know there is a way to solve this elegantly without violating rules, spending too much money, or needlessly complicating the circuit.
Maybe if we put check valves in the air supply lines to the solenoids??? Naaah - cuts off the regulator from the cylinder. A good, hard problem - really fights back! |
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#70
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Re: Mulit-postioning with pnuematics this year?
I have actually worked with Leo on this one. It was going to be part of our bot this year, but the original use of the piston changed, so that now the idea of multi-positioning the piston is no longer needed. But back to the point, Leo and I have spent a good amount of time working on the concept. We have also found a way to make a piston stop in mid position where you want to just about every time you want it to, and it is pretty quickly at that. I'll give you guys a picture of it full out, full in and paused in mid throw. If there are any questions, PM me. I will say first off that you are best tho have the third solenoid to back pressure the system so that you get an quick responce from the solenoid that controls exaust from the main solenoid.
ivey |
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#71
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Re: Mulit-postioning with pnuematics this year?
We built and tested our pnumatics circuit and its reliable. It performs the same way every time, we used the circuit in my last post. It is one of the cooler functions of our robot. Also the 60+psi overpressure issue never arose for us, so we didn't even need to include the second regulator.
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#72
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Re: Mulit-postioning with pnuematics this year?
Quote:
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#73
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Re: Mulit-postioning with pnuematics this year?
What we used this year were off the shelf items called pilot operated check valves. You attach two single solenoids to the check valves and the cylinder will hold any position you'd like it to
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#74
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Re: Mulit-postioning with pnuematics this year?
what i am playing with now with spare parts (we were going to do multi postition and then they bailed out on me because it looked to "complacated") is multi postition using the 3 valve system, with limit switches and the edu-controler. so far it works with 3 (all open and all closed not included) and its pretty good. there is a needle valve on the exaust valve, and i realy have to fine tune it because if its too far in it SLOW and if its too far out it overshoots by a lot (bad edu code i guess, im not using intruputs).
by next season im gonna have a nice display board and a white paper (WITH CODE). or so i plan... |
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#75
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Re: Mulit-postioning with pnuematics this year?
OK, I took another shot at it. I may well be working under restrictions that are excessive or unnecessary, but Hey - that's part of the fun. My last sketch would not work for the reasons pointed out by Mr. Green, and also because my line-up had a shunt between the two ports on the cylinder, so it wouldn't be locked in place. Here's another attempt - it adds a 60 psig regulator ahead of each solenoid valve. Now, the shunt line is eliminated, but the system is still protected from overpressure. This design does add a component, but regulators are reliable and (usually) trouble-free. It does give you the option of setting the pressure to the extend and retract ports separately, so any force imbalance due to area can be corrected by changing the pressure. At this point in the build, it is academic, but brains need exercise as much as muscles, especially as we get older (you'll find out). Besides, this is a good thread, and I hate to see it end.....
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