Sequential starting (and stopping !) with timers !

[markymark31]

Hi guys,

I have five belt conveyors in a straight line, lets call them 2,3,4,5 & 6. I have an operator working at conveyor 2 who can start and stop this conveyor by means of a local control station.

When he starts conveyor 2 I want to wait one second then start conveyor 3, then wait one second, then start conveyor 4 etc.

When he stops conveyor 2 I want to wait five seconds then stop conveyor 3, then wait five seconds, then stop conveyor 4 etc.

Each conveyor is controlled by a contactor and each contactor has the following line in my program, you can see an on delay and an off delay timer.

And this is the line in my program that runs the conveyor.

So what I am trying to do here is ......

Conveyor 6 will not run unless conveyor 5 has been running for one second. And conveyor 6 will keep running for five seconds after conveyor 5 has stopped.

Now ...... everything works fine if you let the sequence complete, eg start conveyor 2, then 3,4,5 & 6 start with a one second delay between them. Stop conveyor 2, then 3,4,5 & 6 stop with a five second delay between them.

The problem is what happens when you stop conveyor 2, and then restart conveyor 2 before the stop sequence is complete. What happens then is that each conveyor (even the running ones) stops then restarts again after one second. It works its way through the full sequence from start to finish.

What I want to happen is that if conveyors 2 & 3 are stopped and you restart conveyor 2 again, 2 & 3 restart, I don't want 4,5 & 6 stopping and starting for no reason.

Can anyone suggest a better way of doing this which would eliminate this problem ??

Many thanks for your help .....

Mark

 

[bernie_carlton]

Use the operator's control to set or clear a latched bit. Set equals turn on.

The XIC of the 'Turn On' bit starts a sequence of timers, each requiring the DN bit of the previous.

The XIO 'Turn On' bit starts its own sequence of timers again each requiring the DN bit of the previous.

A latched bit to turn on a given conveyor is turned ON by a one-shot of the appropriate 'Turn On' time DN bit. It is unlatched by a one-shot of the appropriate 'Turn Off' time DN bit (or an E-Stop as appropriate).

If a Turn On sequence is started then interrupted by a Turn Off the 'turning on' of conveyors stops but they don't turn off until the appropriate 'Turn Off' timer finishes. The same with a sudden re-turn on during a turn off sequence.

 

[markymark31]

Thanks for your help Bernie, the new program is written, tested, and is now live !

Mark.