Back again with project 2

[PeterW]

should it not be if either hand switch is depressed then the other must be depressed within a very short (extremely short) time.

Same for footswitches.

Any hand or foot release should imediately stop the machine.

But hey, as already said, anyone programing a safety circuit like this should be shot anyway, unless its a validated safety system i.e. PILZ PLC's where you'd only see a block call anyway.

Never seen hand and foot switches used this way, always two hands only.

The way shown could be tricked with a couple of matches.

 

[Ken Moore]

I don't agree with using the PLC for anti-tiedown either.

But here is one possible solution, I don't usually do homework assignments, but I did this time, who knows why. It may not match your assignment exactly, but will give you a few ideas anyway.

 

[PeterW]

I don't agree with using the PLC for anti-tiedown either.

But here is one possible solution, I don't usually do homework assignments, but I did this time, who knows why. It may not match your assignment exactly, but will give you a few ideas anyway.

That looks quite good, I'd just add all the switcheds in series on the last network, to stop if anything is released.

 

[bryan372002]

Thanks guys, I have made another attempt, Thanks rick I think i changed the right and's to or's which makes it work more as lancie described, which makes more sense. also put a cycle complete switch in to hold machine relay in, seeing how I dont really know what type machine we are dealing with or what constitutes a cycle, i just threw this cycle complete switch in there.

 

[bryan372002]

Guys I realize Plc shouldnt be used as a safety device/circuit, this is just a project given in class and will not be used in any machinery.

 

[TimWilborne]

First calm down Terry. Just a small small small thought here. No need for alarm

What is suppose to happen when you let off of the switches before the cycle is complete?

 

[Clay B.]

Anybody mees with any real old stamping machines

I must be the only one that still works on the really OLD stuff. This is an actual control circuit. It predates light curtains and yes it did reside in the PLC. But you did have a redundant relay circuit. Basically the relays made sure the switches had been pushed and the PLC checked for tie downs. The reason for both footpedals and hand switches was to confirm the operator was on the correct side of the operator station.
I also noticed that it was an index start in that once started it went thru its entire cycle then stopped and waited to be reloaded, then started again.

If your curious the machine was so old it had british standard thread on it and a fly wheel that weighed more than my car.

 

[Lancie1]

Clay, good point. No you are not the only one that knows the old stuff. I also think that latching the machine IN THIS CASE is not required. The problem does not mention that a latch is required, unless the "relay" was supposed to be the latch. If that is true, then where is the Index Output?

A quick review of the project requiremnts is called for here. Buddies, on these student problems, you cannot read things in that you think should be there, even if it would be good to have them.

Material need for this project is

2- start buttons
2- timers
2- foot switches
1- relay

Bryan, I see TWO items in your ladder that are not mentioned in the above list.

Normally, that part of an old machine would have been "stand-alone". That is, once the machine receives the Index signal from the PLC (or more likely from a relay control panel before PLCs were even invented), the machine starts, and only stops if a hand or foot is removed before the machine reaches the "point of no return". Once that point is reached, the machine internally latches, and there is no stopping the machine, even if a hand is removed. Let's face it, once one of those giant stamping presses, with a die head the size of a car, gets about halfway down, nothing short of Superman will be able to stop it.

Who knows how the Teacher will interpret this language? Perhaps he will ASSUME that the latch has to be in the PLC and not the machine. So far, his record is not very inspiring...

if the 2 foot switches, OR the 2 palm switches are made for more than 3 seconds timer 1 will time out...

Hypothetical Question: What is the second Timer 2 to be used for?
Hint: See Steve Bailey.

 

[MikeW]

Lets see, typing MGD into google and hitting the I'm Feeling Lucky button I get this.
http://www.informatics.jax.org/
Are you using mice to test with?????????

Of course the second hit on google would be my favorite.

While Google is good for many searches, I typically use an acronym finder such as http://www.acronymfinder.com/af-query.asp?Acronym=MGD&Find=find&string=exact to check out other possibilities. For example, can you image a #5 quantity of the #3 in the above search? BURP!

 

[Lancie1]

What is suppose to happen when you let off of the switches before the cycle is complete?

Exactly. The whole point of having switches that must be manually held in is when they are NO LONGER held by hands and feet (maybe operator had a heart attack), then the machine should stop if possible. Otherwise, if it did not matter, a simple Start-Stop Selector switch would have been used to keep the machine in Run mode.

 

[Clay B.]

Bryan, I see TWO items in your ladder that are not mentioned in the above list.

.

Like Lancie said, your on the right track now simplify. Basically your code is a bit fat. Look at how you can COMBINE your lines to reduce your code.

 

[bryan372002]

Well Guys went to class today and this is what The Instructor showed me that he wanted. Once again there was a lot that was Unclear as to what was expected. anyway this is the wanted solution

Thanks everyone, Look Out the next project is Traffic Lights. Stay home You Guys.......lol

 

[Clay B.]

Question on Coments:
Did you label your timers backwards. Cause to me T4:0 is you index timer and T4:1 is your anti tie down timer.

FYI...Teach wanted a latch....

 

[Steve Bailey]

Where is the OTE or OTL instruction for the "Machine Index Relay", B3:3/0?

 

[TimWilborne]

Wanted to wait until you went to class so you wouldn't just copy it.

Here is Chakorule's sample of an anti-tie down
http://forums.mrplc.com/index.php?showtopic=935