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Hydraulics experts please help

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awemawson:
My hydraulic press has electrically operated valves, but operated by a remote button station on a long umbilical cord. It allows me to be out of the firing line  :zap:

shipto:
I have almost completed my press (full build on my blog) and now need to do the electrics and I think I have come up with quite a good circuit although its not totally idiot proof. I thought I would post in case anyone else needs it and in the hope that the drawbacks might get resolved.

s1 send the power either to the "up" footswitch for manual mode or to the relay for the 2 automatic modes.
s6 chooses which automatic mode you need A) press "down" footswitch and it returns as soon as you let go or B) a single press will send press down till it breaks the limit switch then go back up.

As well as this circuit there will be a failsafe pair of limit switches that will feed the stop coil on the pump itself just in case things go wrong.

Just to prove to myself it worked I used it with my variable power supply to bend some metal today and I am impressed by the results. second bit shows a bit of 3mm plate and a bit of 12mm square bar.

sparky961:

--- Quote from: shipto on June 11, 2016, 06:09:22 PM ---<snip> or B) a single press will send press down till it breaks the limit switch then go back up. <snip>

--- End quote ---

You may want to reconsider this one in terms of safety.  In working with CNC press brakes, I can tell you that they only close when your foot is on the switch.  You have to hold the switch until the cycle completes the down stroke and any dwell (delay), but it will continue to rise if you let off while it's on the up stroke.

They also have the safety feature where moderate pressure is used on the pedal to activate the cycle but hard pressure on the pedal will move it even more and trip the e-stop, with possibly a retract - can't recall for sure on that one.  Presumably if you get a body part stuck in the machine you're either going to let go of the foot switch or STOMP down on it.  Don't know about you, but either way my preference would be for the machine to stop.

I didn't have a good look at your circuit but you'll want to ensure that a disconnection or failure in your limit switches is fail safe too.  You don't want someone (including you) inadvertently yanking a wire out and causing the machine to start squashing whatever happens to be in the path of destruction.

shipto:
I get the safety concerns but the B) auto mode will only get used for repeat operations like punching holes and as such will only be used for very short strokes. In the case of punching the holes I need the only thing that fits in the jig I made is the 3mm plate so if i make the top of the stroke still inside the stripper bar then there is no chance of a finger getting in the way.

Also the limit switches are closed and open up to stop the stroke so a wire getting pulled free will stop it.

I dont intend anyone else to use this machine so I am just going to have to take care with it.

shipto:
I knew when I posted the circuit above there was a problem but I couldnt figure out what it was until testing today.
If S6 is in full auto position when S2 is pressed then the limit switch S5 is bypassed and the press can squish the limit switch, so I have updated it with a extra diode to stop this happening.

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