Am I doing this correctly? Please help!!

[dandelo]

So, then what I have drawn up is incorrect? I know that anti tie down means that all buttons involved have to be pressed nearly simultaneously, and in my head what I drew out is what I would do to start the machine. I didn't think about the jokers out there that would 'lockdown' a button so they could have a hand or foot free.

Without giving me a direct answer, what would I need to think about to correct the situation?

 

[SimonGoldsworthy]

Another assumption - you need a timer for the two footswitches and a timer for the two palm controls. Lets just deal with the footswitches and you can copy the logic for the palm controls.

1. When any footswitch is pressed, you need to start the timer
2. If both footswitches are pressed whilst the timer has not timed, allow the footswitches to enable the next part of the circuit.

 

[bryan372002]

This is hilarious, guess what Guys this project is my exact same next project, which means I guess hello Dandelo, seems we have the same instructor and or class that the project came from that caused so much confusion and distress here... http://www.plctalk.net/qanda/showthread.php?t=24967

Once again there is much left to guess with this project as well.

e-mail me at [email protected] if you want, we can be of help or harm to one another maybe....lol

 

[PeterW]

I hate to be the one to throw a monkey wrench into the works, but "anti tie down" generally means that the two palm buttons must be closed within a fraction of a second of each other and both must make the transition from opened to closed within that tome frame.

The idea behind it is to require that both of an operator's hands are on the buttons before the cycle can start. The anti tiedown feature prevents an operator from jamming one of the buttons closed. Note that in the real world you should be using two-hand anti tiedown devices specifically engineered for the purpose rather than doing it in PLC logic.

What dandelo has posted looks more like a "Start delay" which is typically used to ring a warning bell or flash a light before allowing the machine to start.

I'm with him. Only just got to the thread and was thinking I was seeing it wrong.

The way I see it, one timer is to ensure that both footswitches are depressed simulataneously (with very small delta time allowed) and the other timer is to do the same for the hand switches.

The output would be on until release of any switch. (Note: the output == the relay).


Never seen 2 footswitches and 2 pushbuttons, love to see how they would all be pressed, I imagine coco the clown as he'd need big feet

 

[STL???]

Two hand start.
timers are on delay.

button 1 and not button 2 starts timer 1
button 2 and not button 1 starts timer 2

button 1 and not timer 1 and button 2 and not timer 2 = ok
or ok and button 1 and button 2 = ok

Hope this helps

 

[Clay B.]

This is a real world app.

Steve Bailey - that's not a monkey wrench - I think you've put this thread on track. A quick search on Google gives the following for anti tie-down

Provides a maintained output signal when both
buttons are pressed within 0.3 seconds and held.

What you are looking for is a circuit that start you time if either the one of the foot pedals or start switches are pressed the "usual" reason for 2 timer is so you can make the hand buttons seperate from the foot switches. I have seen this on stampping machines. The reason for the foot pedals is to have the operator on the correct side of the start switch. It predates light curtains.

 

[STL???]

Two hand start.
timers are on delay.

button 1 and not button 2 starts timer 1
button 2 and not button 1 starts timer 2

button 1 and not timer 1 and button 2 and not timer 2 = ok
or ok and button 1 and button 2 = ok

Using exclusive or (1 timer)

Two hand start.
timer type = on delay (You define the delay time)

button 1 and not button 2 or button 2 and not button 1 = timer 1

button 1 and button 2 and not timer 1 or ok and button 1 and button 2 = ok


Same again for Footpedal

 

[Clay B.]

Using exclusive or (1 timer)

Two hand start.
timer type = on delay (You define the delay time)

button 1 and not button 2 or button 2 and not button 1 = timer 1

button 1 and button 2 and not timer 1 or ok and button 1 and button 2 = ok


Same again for Footpedal

I get everything but the ok. what does the ok do?

 

[STL???]

Hi,
Ok is your maintained contact/Internal coil or output, In this case you would have a anti tie down ok signal, a Footpedal ok condition on another rung in series before an external action/output is energised.

In a real scenario, You would have a specific safety relay to perform each operation not software based.

Regards

 

[darrenj]

Just to clarify..to index the machine means to run the machine..just a different way of saying it..

Steve Bailey hit the nail..the key is Anti tie down..Also the OP said in his fist post both buttons and both foot switches must be hit at the same time to make it work..In theory no delays are needed however we all know that it would impossible for the operator to hit all 4 switches at the same time..so some delays are built in..I think the OP is on the right track just has to look at how his timers are used..

For a newbie its a little tricky at first..but once you get it done you will see its not that hard..

Good luck and stick with it!!

 

[SimonGoldsworthy]

darrenj - are you saying the machine should latch into run i.e. when you let go of a footswitch it keeps going or it is hold to run as I've suggested and it stops when you let go ?

 

[PeterW]

darrenj - are you saying the machine should latch into run i.e. when you let go of a footswitch it keeps going or it is hold to run as I've suggested and it stops when you let go ?

I would say stop when let go.

 

[Clay B.]

Hi,
Ok is your maintained contact/Internal coil or output, In this case you would have a anti tie down ok signal, a Footpedal ok condition on another rung in series before an external action/output is energised.

In a real scenario, You would have a specific safety relay to perform each operation not software based.

Regards

Duh...was focused on the anti tie down.

 

[darrenj]

Well that depends on what we are talking about!! In the OP's description there is no mention of holding or releasing so do what you want..In real life it would depend on the application..

and before i get bashed please remember the term index.. I know i said it was basically the same as run..

Take a paper shear for example..The operator lines it up and has the blade millimeters above the slice point..He sets the paper the pushes both buttons..(Anti tie down..to make sure he doesn't loose any digits)..His hands are slightly faster than the machine..he pushes the machine "INDEXES 1 Time!!!!" you get one slice then the machine holds for the next 2 handed push.. This is different from a machine that starts and doesn't stop until something tells it to..an indexing machine usually runs for one cycle and thats it ..no matter if the operator is chatting to bubba and forgot to take his hands off the buttons..

Now as terry likes to point out..we look at the description that is given to us not what we think..so as per the description the machine "Indexes" if all conditions are met within a time period..there is no mention of stopping so we don't worry about that..Who knows..maybee stopping the machine is the next assignment and we are doing this guys homework even thinking about it??

 

[Staines]

huh?

I dont know about similtaneosly, but you are showing that you have to hold 2 hand for 5 sec, and 2 foot for 5 sec, then it will operate, but you have latched the output so it will never stop.