handle an emergency stop and resume the action

[Piet]

Hello, I had a testset on loan from unitronics. It is really simple. I am not done yet, I still have to figure out how to handle an emergency stop and resume the action, so I do not have to junk a half finished produkt.

[Joe Tauser]

I'm guessing your product is such that the work can be restarted.

I would use a State Machine and define a "pause state" that will turn everything off but remember the state number of where you stopped.

Take a look at this thread-

 

Joe T.

[Gabriel Franco]

5 hours ago, Piet said:

Hello, I had a testset on loan from unitronics. It is really simple. I am not done yet, I still have to figure out how to handle an emergency stop and resume the action, so I do not have to junk a half finished produkt.

To do so, I would add an alarm pointing to e-stop with acknowledge  bit. Then use this bit to resume process.

[Flex727]

Even without a State Machine (which I use almost religiously thanks to learning about it from Joe), it's not that difficult to write a program that allows things to restart gracefully since all operands are retained automatically. The programmer must be cognizant of any timers and power-ups, but it's not that difficult.

[Piet]

First I need to tell what I use the system for.

I give old machines a second live by replacing an old and usually defective control system

Mostly bending machines. Due to the long tubes that are swinging around  and the forces involved the emergency stop is extremely important.

For hydraulic machines this is simply a matter of cutting the valve tension and switching off the hydraulic pump.

The status of the machine cylcle stays unalterred and can be resumed or aborted as needed.

For servo it is completely different. It needs to be brought to a controled stop. (I think) 

So I made a test program with 2 sequences

 - abs, abs, abs, rel,rel, rel

 - abs, rel, abs, rel, abs, rel, wich run perfectly, in both directions at will.

When I simulated an emergency I did the following:

I saved the complete input status of the servo axis

then I executed an axis stop and after the stop-done an axis reset

After reinstating the abs position or the rel distance, I put on target position or the remaining rel distance and the start bit again.

It would not resume where it left off. So maybe I should live with junking a halve finished product.

[Piet]

On 1/27/2023 at 8:28 PM, Flex727 said:

Even without a State Machine (which I use almost religiously thanks to learning about it from Joe), it's not that difficult to write a program that allows things to restart gracefully since all operands are retained automatically. The programmer must be cognizant of any timers and power-ups, but it's not that difficult.

You are right, in the days of relais, it was called cascade logic. For plcs it is difficult to do otherwise.