On the right track?

Hello all!

I've started writing my program for my machine, and I thought I'd post the first section of it for some constructive critism. This is just the "logic" (in quotation marks because I did it, and I am seldom logical) for the enable push button and initial start button sequence.

SOP:

PLC looks for safety input. If no safety input, illuminated PB "Enable" flashes.
When safety input is present, "Enable" light goes off.
Operator presses "Enable" which energizes "Enable" PB light and energizes clamp soloniods A and B to open for a period of 5 seconds.
Operator presses "Start" PB.
Clamp solonoids A and B close, and "Start" PBL becomes energized.

There is more to be done, but this is as far as I've got and I just wanted some feedback from the professionals.

Thanks in advance for your input!

Operator presses "Enable" which energizes "Enable" PB light and energizes clamp solenoids A and B to open for a period of 5 seconds.
Operator presses "Start" PB.

Click to expand...

Enable PBL will only stay on for the period of its contacts being closed.
What will happen if: Safety circuit is closed, operator pressed the Enable PB followed by the Start Cycle PB?

Irish said:

SOP:

PLC looks for safety input. If no safety input, illuminated PB "Enable" flashes.

Click to expand...

When the Enable PB is pressed, the light goes solid whether or not the Safety monitoring input is true.

Irish said:

When safety input is present, "Enable" light goes off.

Click to expand...

Unless the Enable PB is being pressed.

Irish said:

Operator presses "Enable" which energizes "Enable" PB light and energizes clamp soloniods A and B to open for a period of 5 seconds.

Click to expand...

Actually, when the operator presses the Enable PB, the Unclamps solenoids are turned on and will stay turned on for fifteen seconds after the Enable PB is released, at which time they will turn off.

Irish said:

Operator presses "Start" PB.
Clamp solonoids A and B close, and "Start" PBL becomes energized.

Click to expand...

That part works as advertised.

Suggestion:
List all the steps broken down into every little action that needs to take place. In many cases what seems like one step to the operator might be better handled in the PLC as three or four smaller "sub-steps". This may not be the case for your machine.

List all the what ifs, like what if the operator holds the start button, and then presses enable, should anything happen?

What if the safety drops out while any of these steps is going on...what should happen to the outputs? Should the machine "remember" what part of the sequence is being performed and resume from there when the safety is reset? Should the machine always start from the beginning of the sequence? Or, does it depend on which step is being performed whether or not the machine should "start over" or otherwise change steps.

How does (should) the hardwiring of the machine affect its cycle?

Just some thoughts to get you to thinking...

Paul

Thanks very much for the input and suggestion, guys. If I get a chance today at work, I will fix some of my problems and continue with programming and re-post for some feedback.