Allen Bradley Minotaur Safety Relay

Hello, I am having to go old school on a project at work and I am having a major hair pulling event...help please!!! What we have is a 150 ton hydraulic press that I had to build the controls for from scratch, easy enough, make it go up and down...simple. Problem is that I have to use a 2 handed safety relay for the close function, namely an Allen Bradley Minotaur safety relay, but what has to happen when the press is about an inch from closing is that it makes a proximity switch which in turn starts a timer(got that one figured out) and it needs to keep the hydraulic solenoid energized in order to keep pressure on the part. Now, I cannot figure out how to keep the solenoid energized, because it seems that you have to trick the safety relay into thinking that the 2 close buttons are still being engaged...I tried multiple scenarios and I have not been able to get this one nailed down...is it possible with this type of safety relay to do this? I realize that this is not a plc question and I apologize, I just know that there is a vast amount of knowledge here on this message board...believe me, any help would be greatly appreciated.

Hello,

First off let me say that I know nothing about safety relays, the correct or legal code standards for using safety relays nor do I know anything about the operation or situation of your press.

That being said, it sounds like you need to have the press start in downward motion by an operator using 2 handed switch to activate the safety relay contacts, which will energize the Down Solenoid Relay Coil.

Once the press reaches 1 inch from bottoming out you have a prox that energizes, and you need to have this press maintain pressure (Down solenoid coil stay energized) until a timer times out.

But you want the operator to be able to let go of the 2 handles that he used to start this process.

I dont know if this is legal but what you are asking for would look something like this.
(or I should say something like this will make the press do what you are asking for.)

Safety Relay closes -- Down Solenoid Energizes---when prox is reached and Safety relay still engaged it will energize Timer Coil through a second safety relay contact---- Timer Relay contact pulls in, seals in timer coil and energizes Seal-IN Relay Coil--- Seal-IN Realy Contacts Close and Seal-In Down Solenoid Coil until timer times out---Down Solenoid coil will then de-energize.

You will need to use 2 handed seal in to repeat process.

You may also want to include a Pilot Light off the the Seal-In Relay contact so the operator will know when he can release the 2 handed start.

You did not mention anything about an up solenoid so I did not include an up feature in this drawing.

Hopefully this does not break too many codes and something like this will work for you.

Good Luck
BCS

....it seems that you have to trick the safety relay into thinking that the 2 close buttons are still being engaged....

Click to expand...

When do the 2 close buttons dis-engage? Should not they be required to stay engaged until the press is down that last 1 inch?

After looking at this again I have revised my drawing to give an added safety feature.

I now pick up the power for the Timer & Seal-In Relay Contacts from the Load Side of the Prox Switch.

This way the the Press needs to be in the Down position already before power is avalible at the line side of these contacts.

You will need to varify that the prox is rated to handle the current of the 3 relay coils. If not you will need to add another relay.

BCS

Since I don't know your operation, here are some critical questions.

1. if the operator releases the pushbuttons during the cycle, can he reach into the press?
2. is there a safety guard protecting all the openings of the press except the load / unload opening?
3. if you remove ANY safety guard, will the press stop?
4. is there a light curtain protecting the load / unload side?

in short, if any one can get inside the press during the cycle, you must add more safety.

common sense I know, and I am not trying to slam you in any way, just asking questions that you may not have thought of.

IF the operator can release the pushbuttons during the cycle, then I would look for a cam switch which will turn on (2) relays with contacts wired in series to simulate the pb's being held. a second cam switch will break the signal.

regards,
james

I'm a little fuzzy on your question?

We have a bunch of unguarded presses with 2 handed switches and you have to hold them in the whole the whole time the press is going down or it will stop. Going up, you just hit a return button (the unsafe part is obviously going down). It all depends on how things are hardwired and tied into a PLC.

Our other guarded presses have 2 handed switches that you hold in for 2 press cycles and then the program takes over automatically.