Estop routine help

Hi

I'm been using ladder to program my sequence logic all the while. However due to customer req, I have to use SFC this time.

Any experts in this forum can give advice on the following conversion from ladder to SFC:

In laddder, I always write my sequence control in between an MCR and MCREND. The condition to trigger the MCR is when Estop button is not pressed and I will always go back to the start of sequence control when Estop is released and reset button is pressed. Therefore during Estop condition, all the rungs in between the MCR and MCREND will not be true.

My question is in SFC programming, how can I do a Estop routine in an efficient way to immediately stop my sequence and reset to the start of the SFC? Right now, I'm putting the Estop bit in every SFC transition so that the sequence will not jump to the next step when Estop happens. Thks a zillions in advance

What equipment are you using?

AB ControlLogix 5555 platform to do a simple 2 axis pick and place application

is estop on your machine controlled only by PLC logic?

I suggest you use a combination of SFC and Ladder. Both have their strong and weak points.

SFC is great for controlling sequences of operations and inherently interlocks mutually exclusive operations. They are not so great for exception handling.

Put your outputs in a MCR zone in ladder and operate them with auxiliary bits that are controlled in the SFC.

Look up the SFR and SFP ladder instructions to learn how to reset the SFC.

Gerry is on the right track. Use the SFR.

If you are strictly limited to SFC, I would suggest adding a P routine to the reset state (runs once on state entry) and code into that routine to turn off the relevant outputs.

I hope the Estop is actually hardwired and you are just aligning the PLC to the realities of the machine, not really doing the Estop with the PLC.

Alaric said:

Gerry is on the right track. Use the SFR.

If you are strictly limited to SFC, I would suggest adding a P routine to the reset state (runs once on state entry) and code into that routine to turn off the relevant outputs.

I hope the Estop is actually hardwired and you are just aligning the PLC to the realities of the machine, not really doing the Estop with the PLC.

Click to expand...

Are you implying you would not trust your life to a PLC????

Actually, I trust PLCs quite a bit. But code is code.