Hi folks,

First off I am fairly new to hydraulics and I hope the below is clear enough.

My question is on a system design using a double acting cylinder. I am planning on using a 3-position, 4-way/spring return to neutral manual valve to control the movement of it. Is it possible to use a electric valve to do the same, however keeping a manual override valve?

As well, I am thinking of using limit switches to control the electric valve, e.g. setting the switches on a slider, so they can be moved to the return or stop position.

My actual goal is to have the ram semi automated. Example would be: set limit switch to 10", ram reaches this and then retracts to 8" automatically - then does the whole thing again until it's manually stopped. This would be a similar principle as a milling machine power feed table.

Thanks in advance for the feedback.

Tom

quote:

Originally posted by hcksharp:
Hi folks,

First off I am fairly new to hydraulics and I hope the below is clear enough.

My question is on a system design using a double acting cylinder. I am planning on using a 3-position, 4-way/spring return to neutral manual valve to control the movement of it. Is it possible to use a electric valve to do the same, however keeping a manual override valve?

As well, I am thinking of using limit switches to control the electric valve, e.g. setting the switches on a slider, so they can be moved to the return or stop position.

My actual goal is to have the ram semi automated. Example would be: set limit switch to 10", ram reaches this and then retracts to 8" automatically - then does the whole thing again until it's manually stopped. This would be a similar principle as a milling machine power feed table.

Thanks in advance for the feedback.

Tom

I am not a designer, but I like your simple design request. I am curius about following....

1. What type of application is this?
2. What type and size of force is involved? Gravity and/or frictional?
3. What speed is the cylinder expected to generate? will design require speed ramps before changing direction??....extend speed and retract speed might not be the same with a double acting cyl....there is a few options to solve that.....
4. You mention 8" and 10" limit switches....does that mean that 0" is the limit of fully retracted cylinder?
5. What is the purpose with the manual override? I think there is control valves available with both electric and manual control.....
6. What type of hydralic power unit are you planning to use?? Fixed/variable pump, open/closed center system??

I am sure the semi automated part of your design will be easy to solve, either, with PLC and a built in transducer in cylinder, or build a simple logic, with 12v switching auto-relays for a few $$. Limit switches can also either be contact-mechanical or non-contact-inductive. Hydraulic pressure switches is also an option....

You could either plum in two seperate control valves parrallel to each other, or use one control valve that has solonoids as well as a manual lever. Without knowing more information I can't suggest a valve, but look into a valve like a Sauer Danfoss PVG32. This valve also has travel limits you could use to set your extend/retract speeds (they will still change somewhat based on change in load)

Thanks for the quick answers.

To the above questions:

1. forging steel - pretty much a press
2. friction
3. speed is not that crucial
4. yes - 0" is the fully retracted cylinder. The numbers I gave where just random, but I want to have the ram stop and retract a preset distance from the bottom dies. Those distances do vary.
5. Manual override for safety I am thinking and do other task with the same press
6. I have a piston pump with an variable output up to 13.2 GPM open system with a 5.5" ram

Folks use simple stops of metals to obtain a certain thickness, but I am thinking this is hard on the frame and components. So I am searching for a better solution. I like the idea of the simple logic any link to a plan or more info?

Will also have to look more into the PVG32.

Thanks so much for the quick answers.

Tom

quote:

Originally posted by hcksharp:
Thanks for the quick answers.

To the above questions:

1. forging steel - pretty much a press
2. friction
3. speed is not that crucial
4. yes - 0" is the fully retracted cylinder. The numbers I gave where just random, but I want to have the ram stop and retract a preset distance from the bottom dies. Those distances do vary.
5. Manual override for safety I am thinking and do other task with the same press
6. I have a piston pump with an variable output up to 13.2 GPM open system with a 5.5" ram

Folks use simple stops of metals to obtain a certain thickness, but I am thinking this is hard on the frame and components. So I am searching for a better solution. I like the idea of the simple logic any link to a plan or more info?

Will also have to look more into the PVG32.

Thanks so much for the quick answers.

Tom

Do you have any data about that variable displacement piston pump? ID plate? if not, please post a couple of pic of the pump, ports and the compensator valve(s). It is possible your pump will allow a closed center, constant pressure, (unloaded), system.....

Being hard on the frame and components is all about what force (pressure) you allow the piston to apply on the your forging object on the die.....an extend controlled bye a limit switch combined with adjustable pressure switch with a gauge (whatever comes first will call the retract, might be the way to go...
That 5.5" bore cylinder, will give you about 11.9 tons of force, from every 1000psi of pressure...

The relay logic can be a fun challenge for the rest of the forum....they are so spoiled with PLC's in these days...
OMRON 2-pole 12v DC model# MY2IN1-D2, have a built in lcd indicator and a test button...a few of these with a socket and some diodes should make it, not to forget switches and limit switches.....

quote:

Originally posted by AKKAMAAN:The relay logic can be a fun challenge for the rest of the forum....they are so spoiled with PLC's in these days...

These days? I saw my last drum relay machines back in the early 80s.
There is a good plc forum at www.plcs.net and another at www.mrplc.com.

The PLC program will be easy to write if it is only going from limit switch to limit to pressure switch and back.

quote:

Originally posted by Peter Nachtwey:

quote:

Originally posted by AKKAMAAN:The relay logic can be a fun challenge for the rest of the forum....they are so spoiled with PLC's in these days...

These days? I saw my last drum relay machines back in the early 80s.
There is a good plc forum at www.plcs.net and another at www.mrplc.com.

The PLC program will be easy to write if it is only going from limit switch to limit to pressure switch and back.

Yes i know Peter!
I just grow up with boxes of relays in the 70's and 80's.....all logging processors and harvesters had them....
I would go for PLC any time, but with limited budget...relays might be less bucks$$....

Btw....why dont you post him an estimate on the cost for a simple PLC....

I would love to learn program a PLC for this simple application....

quote:

Originally posted by AKKAMAAN:
I would go for PLC any time, but with limited budget...relays might be less bucks$$....

Btw....why dont you post him an estimate on the cost for a simple PLC....

A small one cost about $100. You may be able to find cheaper if you know the I/O count. Just ask on the PLC forums but search first as this topic has been covered a few times. There are many options. I simply list one with a reputation for have a good bang-for-the-buck for simple applications.
http://www.automationdirect.co...ck_-a-_Modular)#dl05
http://www.automationdirect.co...specs/chooseaplc.pdf
I like the sections that say Why this is important.

Beware when buying a PLC. Sometimes proprietary cables are required and the cable cost $75!!!
I would never use a PLC that can't be programmed over a standard communication device like a USB, Ethernet or serial cable.

quote:

I would love to learn program a PLC for this simple application....

Excellent attitude! It is better to learn a little about PLCs rather than to refer to PLCs as "electronic thingies". I am kind of a hands on guy. If I want to learn about something I buy one.

It would take only a few minutes with our motion controller but it costs much more that a simple PLC.

Right now there is a thread(s) on the www.plcs.net forum about a PLC programmer that has the opposite problem. He doesn't understand the PLC hardware or the hydraulics and his project isn't working. This is why I like Bud's term mechafluidtronics. One needs to know at least a little about hydraulics, electronics and control programming so that the project will succeed. Otherwise one ends up with three people pointing their finger of blame at each other.

Loads of new stuff for me. Did some reading on the PLC's and if I understand correctly they work on a similar principle to PID controllers?

I have some knowledge on working with PID's in controlling temperatures, so I am sure I am figuring things out once I do a bit more reading. Usually best for me to have it in front of me and try and go from there.

So, the programmed PLC get's its info from sensors, then it switches a "electric loop" on/off/reverse so to speak. In hydraulics the PLC would be wired to switch a solenoid to reverse flow?

Again going from a PID controller standpoint, I can program them to ramp (up or down) to set point, hold, ect. and I am able to have a number of different programs I can run of the unit.

Would I be able to do the same with a PLC? E.g. have program 1 go 2" ram extension, program 2, go 4" ram extension ect. after all has been programmed? Would I now need additional sensors, or would 2 suffice?

Would it be possible to just use two limit switches with an solenoid to cycle the ram without a PLC?

I hope the above made enough sense.

Thanks, Tom

quote:

Originally posted by hcksharp:
Would it be possible to just use two limit switches with an solenoid to cycle the ram without a PLC?

I hope the above made enough sense.

Thanks, Tom

I have made a simple design w relays, electric over ride included, but I need to double check it before I post it....
back later with that....

I hope this will work....anybodys input appreciated.....

Full size drawing on this link

This message has been edited. Last edited by: AKKAMAAN,

A PLC may have PIDs but basically a small PID is a relay replacer. A PLC has lots of virtural relays that are wired up electronically.

A PID is for closed loop control like the temperature control. In your example it would control position but you need to ramp the positions smoothly from point to point. PLC PIDs are fast enough for temperature control but not fast enough for good motion control.

There is a thread on the www.plcs.net forum where a PLC programmer named Erdemsvri is trying to control at test system with a cycle time of 5 Hz. If you search for his threads you will see the difficulty he is having.

The limit switch and pressure switch idea would be simple to implement.

The servo system with MDT feedback would be simple too but much more expensive. A lot depends on the budget and how much you value your time.

quote:

Originally posted by hcksharp:
Would it be possible to just use two limit switches with an solenoid to cycle the ram without a PLC?

I hope the above made enough sense.

Thanks, Tom

I have made a simple design w relays, electric over ride included, but I need to double check it before I post it....
back later with that....


Here it is.....
I hope this will work....anybodys input appreciated.....

Full size drawing on this link

quote:

Originally posted by AKKAMAAN:
I hope this will work....anybodys input appreciated..

This is as amazing has Maglub asking about PIDs.
This is an excellent start.
Dwell time timers may be needed, especially on the retract side to allow parts to be removed and new blanks inserted. I would use a pressure switch instead or maybe in parallel to the extend limit switch so the system will wait until a pressure is reached or a position is reached. The LS should be used to avoid a die on die contact if the press is closed without a blank part in the system. Usually mechanical stops are used instead because the relays and valve may not respond fast enough.

There is free software for the smallest Rockwell PLCs at
http://www.ab.com/programmable...c/pico/picosoft.html
I don't know how much the small PLCs cost though. AKKAMAAN, ladder logic is similar relay logic.

This message has been edited. Last edited by: Peter Nachtwey,

quote:

Originally posted by AKKAMAAN:

I have made a simple design w relays, electric over ride included,
Here it is.....
I hope this will work....anybodys input appreciated.....

The elegant simplicity of your solution is pleasing/satisfying to the engineer in me.
An arrangement of components that's easy to trouble shoot ( if required ) and to repair.

Cheers Woody

This message has been edited. Last edited by: Woodygb,

Thank you Peter and Woodygb, I do appreciate the credits.....Well this is what I have have dealt with most of my career on logging equipment, it is not that hard....just need to understand some different simple ways to use the relay's...
Thank's again, and I'm looking forward to some help with RC delay circuits etc...

edit:
Btw....there are two X's on the drawing....I forgot to put in the double pole pressure switch....one pole parallell to L1 on the left, and one pole in serie with L1 up at the right....