Troubleshooting Pneumatic Interlock Switch for Machine Safety

[WilliamHerron]

I have a machine that when operator presses button, it will move upwards.

When it gets to the end position, a switch is made and that causes a double acting pneumatic cylinder to engage... pushing a pin into a sort of "Dead bolt" safety position.. to lock machine in place.

Operator then does their task.

When operator finishes doing their task, I want to have a momentary button ("Unlock") that operator will press.. which will retract the cylinder(unlocking the "safety" position).

They will then press a button to cause the machine to lower back into home position
I am using a 4 way MAC valve (Model #1 80304-512-0304)

I have the limit switch in series with the "lock" pilot.. and, I have a momentary pushbutton switch in series for the "unlock" pilot.

Problem is... once the upper limit is reached, the "lock" pilot stays pressurized.. keeping the operator from being able to operate the "unlock" pilot... and then being able to lower the machine back to Home position.

Anyone have ideas as how to rectify this?

Thanks!

 

[WilliamHerron]

Also... anyone know of decent free Pneumatic Circuit simulator software?

Nothing elaborate. I just to want to be able to practice connecting diff types of valves.. and trigger outputs.

 

[Dullard]

You could put a normally closed (NC) contact from the momentary switch in the lock pilot. You'll have to hold the momentary switch until the limit switch clears.

 

[WilliamHerron]

I'm hoping to do this with just pneumatic device
(No electrical devices)

 

[Baluncore]

The safety pin must be inserted only once the load reaches operating height. I expect you will need to lift the load off the safety pin before the pin can be withdrawn. That will require a pin interlock and a status flip-flop.

When the load is falling, a press button should be held continuously.

A state diagram for the system would really help.
All possible state changes should be shown.

 

[WilliamHerron]

When the platform reaches upper limit, a limit switch is made.

That switch fires the small double acting cylinder that pushes the steel pin into the deadbolt for safety... to hold platform in place in case of loss of air pressure.

There is a button ("Unlock") that when pressed will unlock the safety deadbolt cylinder.

Limit switch causes cylinder to extend.. and "unlock" button causes it to retract.

Problem is, when operator presses "unlock", the "lock" condition is still being forced by the upper limit still being made.So.. the cylinder is trying to push and pull at same time.Is there an easy way to interlock the upper limit switch and the "unlock" switch .. so that the "unlock" will actually engage even when upper limit is made?

Thanks

 

[WilliamHerron]