From Manual to Auto?

I am currently writing a program for a simple machine. It has 7 pneumatic cylinders for the different movements. So far it is simple! But when the operator changes from Auto to Man, or worse, from Man to Auto my problem appears!

The machine stops in the middle of the sequence (the sequence is always a one shot) because some movement has jammed. The operator change to Manual mode and recitfies the problem (probably with a hammer) and runs the machine manually to the next sequence step. Everything seems OK and he swithes back to Auto.
And this is the problem: The Auto-sequence is still where it left off. But the operator has run the machine to next step.
Back in Auto the machine will stop immidiately! The sequence does not correspond with the positions of the different movements.

Which is the best solution?
A: A fault should always reset the machine and force the operator to restart the sequence. Simple solution!
or
B: Force the sequence (in dummy mode) to follow the manual steps done by the operator. So back to Auto should be seamless! The best, but complicated solution!

Gentlemen, your opinions please!

If there are sensor feedbacks as a result of your movements then B shouldnt be that hard and complicated so I would say if your sequence transitions depens on sensors then with a litlle work you can figure out B option which would be better than A.

By the way if your code has English comments and if it is OK for you, just post your code so we can have a look.

Thanks.

If your automated sequential process can be repeated freely with no harm neither to machine or product, I would choose solution with automatical initialization of machine based onto following principle:
- if it runs in AUT mode and any mistake happen, machine immediately stops all movements (safety for operator!) and cancels AUT mode.
- operator then "repairs" or removes root cause of problem.
- after problem is removed, operator puts machine to AUT READY mode and starts "big green button"
- machine then goes to AUT initialization (moves cylinders etc. to start positions, initialization has results: done_ok or done_with_error)
- after this initialization procedure is done (result: done_ok = true), machine continues with AUT mode

Reasons for this option? You always know, what the machine will do and in what status it is (light signals, displays etc.). If any problem in AUT mode occures => operator is always forced to do AUT initialization. If operator in MAN mode somehow puts machine into status, in which machine cannot operate in AUT mode - no problem, machine "recovers" by itself by AUT initialization again.

This principle is also not so difficult to program (and very important note is that the more complicated program you write, the more difficult is to find mistakes). On the other hand, software which would check what operator has done in MAN mode to try to continue sequence in AUT mode could be much more difficult to write. But this depends on complexity of automatic sequence.

How many pieces of product are in the machine at once?

How long is a machine cycle?

How long does it take to initialize and start producing product?


Answer these questions first. Basically, ask yourself "If I stop the Auto cycle and force a compete restart, how much time, how much product, i.e. how much money... do I lose?"

Also, if you write a state-based program it is pretty simple for the logic to simply "sit" until the OPR clears the fault, then continue from that point. I hasten to add this only applies if letting the machine sit in the failed state is safe, everywhere on the machine.

For example... I have a rotary table machine with 12 positions on the table, and a couple dozen cylinders. It assembles and tests little plastic parts. When a cylinder fails to move, the machine simply sits and waits until the OPR or Tech clears the fault, then it continues. None of the 12 stations does anything with heat, compressed gasses, spinning heads, etc.

I have another machine... a silk screener we bought from a vendor... that uses IR heat lamps to cure the ink placed on the parts, which are plastic boxes with graphics on the face. It carries the boxes on pallets through three print stations and their associated heat lamps. When the pallets jam between stations... the heat lamps, which may be working over a pallet behind the jammed one, don't turn off because they programmed the lamps to stay on as long as a photoeye next to the lamp detects a part present. This sets the machine on fire.

So, ask yourself how complicated is it to clear and restart the machine every time there's a fault. Also, search on "state programming" and see if it would help on your machine.

electrical_geek said:

And this is the problem: The Auto-sequence is still where it left off. But the operator has run the machine to next step.
Which is the best solution?
A: A fault should always reset the machine and force the operator to restart the sequence. Simple solution!
or
B: Force the sequence (in dummy mode) to follow the manual steps done by the operator. So back to Auto should be seamless! The best, but complicated solution!

Click to expand...

C: Give the operator a step forward/backward button and let him choose the step before returning to auto.

If you can detect that the system is in the correct position to allow auto to start, then allow it to start. Otherwise inform the operator that he needs to return it to start conditions manually. This way you don't need to monitor manual operations but you know that you are starting auto at the home position.

Bryan

Thank you for valuable input! There are no right or wrong answers here, I just needed some other points of vue to this.
I will most likely take the "chicken way" out. Reset and force the operator to restart.
As always there are two ways of writing a program. For me or for the operator. In this case and a very simple machine I don´t think it matters. It is better to put the effort to a programming task vere it really is important.
Have a nice weekend!

is it the same sequence everytime?
if so we have something similar on a machine at my plant.
if you use a man/auto switch you simply break auto condition and switch over to manual condition and by simply pushing a button you step forward one step at a time and then by putting it in auto again it will resume the current step with its conditions.