Mulit-postioning with pnuematics this year?

[ngreen]

Originally Posted by Leo M

OK, I took another shot at it.

Other than being a little excessive for the set out task. This could be a neat little way of making a super accurate 3rd position. Tweak the two incoming psig to determine exactly where the the third position would be. But as for multiple position (more than three) this wouldn't work because the forces would equalize each time to find that tweaked out third position.

[Leo M]

Hmmmm - I should think it would stop anywhere in the stroke, depending on the volume of air trapped on each side of the piston when both sides are pressurized, and the pressure settings on the regulators. Now, how precise the control would be - that would take an experiment. I sure wish I had the time and equipment to play with this some more!

[ngreen]

With two incoming constant pressures the volume has little factor. The two pressure will create forces that will either equalize somewhere or the force of one will overcome the other.

The previous system I used Close and opened on the exhaust of the double solenoid such that when it was open the cyclinder would extend or retract but when it closed why extending or retracting the cyclinder would continue to compress until the forces equalized out. It didn't depend on volumes although reducing the volume will create the system to react quicker.

[Mr. Ivey]

Just a thought, if you were to use two double solenoids to control the throw of the cylinder. Use port A on one for the throw out, and on the other solenoid use port B for in. You block the other ports, both exaust and output, then route the exaust of both solenoids to the third double solenoid, and that lock when you want to stop in mid throw. I think that should allow you to position anywhere you wish, and not have the pressure equalize, but stay in the desired position. I would test it, but I'm at home and I don't have a pnuematics system to test it with here.
mark

[Chris Fultz]

We are using one double solenoid and one single and can stop the cylinder at almost any location. It does not stop instantly but there is very little creep after the switch is released.

We have a three position rocker switch wired to both solenoids.

When pushed to the right, the switch opens the double solenoid in the extend direction and opens the vent on the single solenoid to allow the cylinder to move. When released, the rocker goes to the center position which closed the single solenoid and the cylinder stops.

When the switch is pushed to the left, the same things happen only the other side of the double solenoid opens to retract the cylinder.

By simply tapping the rocker, the cylinder can be stepped up or down to an infinite number of positions.

We originally thought we needed two separate switches, one to select the direction on the double solenoid, and one to release the exhaust air through the single - but the electronics team found a way to do it with one switch.

[Biff]

Earler in a thread (I can't find it now) someone mentioned doubles with "center off"
After asking where did they get such a thing, the reply was from their local SMC dealer. This got me going in the right direction. The double valves SMC gives First, (and then us) Have a part number SY3240-5LOU on them according to SMC ordering info; this is a 3000 series 2 positon double 24 volt (but they are labled 12 volt, I suspect this is why we get them) 300 mm lead wire and I am having touble figureing out what the O is, the U is with indicator light and surge suppressor (non-polar) What our local supplier has is a SY3340-6LOU The second three in the number is what tells you it's a 3 position closed center valve, the 6 indicates 12volts. We got two and they bolt right on the body with the fittings on them, they are not pulsing and they only will "pull in" with the correct polarity, red to positive. This solved our problem, we were having trouble with our piston action not being to go from down to up, once started down you had to go all the way down. I think this is do to the nature of pilot valves. Any way, on our pretend-a-bot programming table this valve works great and we got them at about $60.00 dollars as we didn't get the wires or the fitting body. We are also putting the flow control fittings on the ea and eb holes on the fitting body and can have different speeds for up and down. Hope this helps

[Mr. Ivey]

Unfortunately the multi-positioning solenoids are illegal accoring to the flow chart. But to ngreen's posts on the pressures equalizing, or one pressure overcomming the other and the piston continuing to move, depending on how you do it, I guess, this doesn't happen. The way you described is that you are connecting the exhaust of one double solenoid to the ouputs of another, and locking the exaust depending on what point you want it. The issue causing the creep in the piston is that you are not giving a "total cutoff", nor are you regulating pressure at all positions. The creep comming from not being able to cut everything off is because you are not switching the exaust to something that is pysically cut off, the pressure in port on a solenoid can sometimes allow exaust, that's why you may have the creep. The way to stop DEAD is by completly blocking all air through the exaust of one side of a solenoid. But even then you will have some drag, like a car slamming on breaks. The key is to eliminate as much of this drag as possible. That's what Leo and I did last night. We decided we would take the task on one more time. We used all legal parts, and we have reduced the drag to less than a half inch. But there is a down to every good thing, while reducing the drag, we have to slow the throw rate of the piston, so it moves somewhat slow. It's a way of running this that we had not expected, and in doing so we found two new ways from using 3 solenoids. Thus we have cut weight in the overall function. The first method requirments 2 double action solenoids, or 1 double action and 1 single and a piloted check valve, while the second requires 2 double solenoids and 2 check valves. I won't give a long drawn out explination, but I will include diagrams, showing the two ways.

[Biff]

[quote=Mr. Ivey]Unfortunately the multi-positioning solenoids are illegal accoring to the flow chart.
Rule 54 clearly states "There is no limit to the number of solenoid valves, air cylinders, and connecting fittings you may use on your robot. They must, however, be “off the shelf” pneumatic devices rated by their manufacturers for pressure of at least 125psi." The flow chart also says.
Is it an air cylinder ordered
from the Custom Cylinder
Order Form or any previous
year’s pneumatic component
except storage tanks,
pressure switches or
pressure regulators

The except and the logic structure is very confusing, So hopefully the inspectors will go with the clear wording of <R54> and not the confusing flow, of the flow chart.
Chears
[Edit] Checking the updates (10) there is an updated flow chart rev A 2/12/2004 that is easer to understand and indicates; That off the shelf and 125 psi are a YES.
Thanks.

[Pat Roche]

I've been going throught this thread and at all the skimatics i've looked at, the soliniod that feeds the piston seems to always be a double solinoid. How is it possible to have a double solinoid in that position when a double solinoid has 4 ports (two to the piston, two for exuast/pressure)? Wouldnt it have to be a single solinoid?

-Pat

[ngreen]

Originally Posted by T134guy

I've been going throught this thread and at all the skimatics i've looked at, the soliniod that feeds the piston seems to always be a double solinoid. How is it possible to have a double solinoid in that position when a double solinoid has 4 ports (two to the piston, two for exuast/pressure)? Wouldnt it have to be a single solinoid?

-Pat

Actually it is a five port manifold. You forgot the input.

You can use the double because the exhaust ports converge at a T and continue to the input of the next solenoid.

This year the solenoid combination makes no difference. You can use two single solenoids, two doubles, or one of each and this will work if you program it right. It is a control system. Last year we were limited in the number and type of solenoids we could use and this combination worked perfectly for what I wanted it to do.

BTW- Last year's and some of this year's single solenoids have five ports too. The difference between the singles and doubles is how it switches states and doesn't depend on the number of ports. (I think you were thinking of this years festo's with only one exhaust. And yes, they can be used too)

[Pat Roche]

When I am refering to single solinoids i mean the ones we have recieved in the past. The only ones i have seen have been 5 port, 1 input 2 exhuast and two feeds (like the festos from 2002 & 2003). The only double solinoid I've seen though was only four ports. So i guess my confussion stems from where your inputing with the double solinoid.

Thanks

-Pat

[Mr. Ivey]

The double solenoids I have are all SMC, the are SY3000 Serries and an NVJ5243Y. That's about all i know right on hand.
ivey

[ngreen]

Originally Posted by T134guy

When I am refering to single solinoids i mean the ones we have recieved in the past. The only ones i have seen have been 5 port, 1 input 2 exhuast and two feeds (like the festos from 2002 & 2003). The only double solinoid I've seen though was only four ports. So i guess my confussion stems from where your inputing with the double solinoid.

Thanks

-Pat

All the double solenoids I have seen from FIRST are like the drawing Mr. Ivey posted in #82. They have 5 ports (P, A, B, EA, EB).

[Pat Roche]

I figured out what you where talking about. I couldn't remember without looking on a valve that the the two exhausts were together. I was also able to make the system work too.

Thanks,
-Pat

[Liz*599]

the way our team achieved three positions from each joint, as opposed to two, was by coupling two cylinders together and then only fireing them independently, which worked very well for us.