Problem with auto - man - auto

Dear all

It is Sunday afternoon, I am tired (in fact exhausted) been programming solid for two days and the old brain is entering automatic shutdown.
My workload at the moment is just impossible. I have three plc projects on the go at once, and another seven awaiting urgent attention.
These are all design and build from scratch projects. It’s at the ‘I’m scared as to how I am going to cope’ level.

Now the problem I have at the moment is – how to get back from Manual operation to Automatic operation and continue the automatic operation from a set point.

Here is the problem in a nutshell;
I am using a Mitsubishi PLC and a HMI. The machine has two modes, Automatic and Manual.
I am using a sequencing method of programming the automatic part. (STL).
Mitsubishi sequencing works like this;
The whole ladder logic is scanned normally plus just the active step(s). The inactive steps are not scanned.
This allows double coiling (within limits) and nice easy programming of sequential blocks.

This machine is basically a ‘pick n place’ it cubes bricks for transporting away.
The bricks come down a conveyor; the grab picks up a row of bricks and places them on another conveyor, it then goes back and places another row of bricks on top of the last layer.
This goes on until a cube is made then the outgoing conveyor moves the cube down the line.
When a problem arises, i.e. the grab drops the bricks, something breaks etc. The machine is put into manual mode and the next layer is often done by hand, but not always, sometimes they need to start from exactly the same point in the sequence, sometimes further in the sequence.
They then want to put the machine back in automatic.
When the machine is put into manual, the STL part is reset and none of it is scanned. This is to avoid double coiling in manual mode (the same output may be needed in manual as well as the active step and this would cause conflicts within the program)
So, I need the correct step in the sequence to be activated when going back to auto.
The way I have done it is to have the HMI give the operator a choice on the screen of which part of the sequence to start in. i.e. PICK UP LAYER 7 or PLACE LAYER 5 etc. But, because of the size of the program (massive) and the many differing types of bricks. I have nearly 100 sequence steps. I cannot fit them all on one screen.
Other ideas I am toying with is, just give the operator 2 choices – pick or place. (simple is better)
I have an encoder on the grab up/down for accurate positioning and so could take a reading from the ‘place mode’ as to which layer it is on. (there is also a ‘back-off switch’ to tell the grab it has landed when placing)
But even so, if I use this last method, how do I then set the appropriate STL step. As you can tell from this ramble, the cognitive reasoning is overloaded; I am resting for a while to await inspiration,,,,,,,any suggestions would be appreciated.

There are a couple ways you could do it.
One is to have only certain points where you could go to Auto from.
i.e. after a cube has been finished
This would require the operator to finish the one he has started on manual.
You need to now exactly where in the sequence you are before switching from manual to auto.

Another would be to allow the operator to select the step of the sequence he is one. How about allowing him to advance the steps using a pushbutton. This way you would not need all the steps on the screen at the same time.

Good Luck

Further to what Kim has suggested.
Have Two manual operations.

One would be semi auto.
With one or two Push buttons, allowing you to 'step forward' and/or 'step backward'. then continue with the automatic cycle.

The second is Manual.
This will require all nescessary manual steps to be undertaken.
Prior to enabling the return to Automatic operation.

If the HMI is good enough, i suggest a number of position display screens for fault tracing.

I have a couple of further Querys about the HMI.
Can you move screens from the PLC program? If so, use multiple screens for the station control.
If you can not change screens from the PLC. Can you overlap them or insert "next" and "previous" buttons?

Goody:

Some clarification - are you looking for a redesign, or a patch?

Possible patch:
Is it possible for the PLC to help limit the available choices on the screen, based on it's known inputs (and ouputs)?

If it's just a standard 8-step pick & place, (down, close, up, over, down, open, up, home), then the PLC should be able to tell, from just the outputs, what step it should be on (i.e, "if it's up and over the receiving line and the jaws are closed, it must resume on step 5).

From your description, you're sequence is more complex than that, but the PLC might be able to limit the choices that the operator has.

FWIW

Thanks folks, some super ideas for the ailing brain; yes it is possible for the outputs to select an appropriate page and limit the choices. I am presuming too that it will only be one layer maximum out of sync too. The cogs are turning again. I have food for thought again. Still considering my options....but thankyou all very much. Now, how much do I owe you?

Goody,

I ran into the same situation on a process that had a dozen sequences running concurrently.

The original program allowed the operators to go to manual any time they wanted - actually, semi-automatic. It also allowed them to jump right back into auto.

The program did not know what transpired while in manual and the operators did not know exactly where they were when they got back into auto. Input conditions changed, don't ya know.

The larger the process the more unmanageable this becomes.

I ended up declaring that...

"AUTO is AUTO and MANUAL is MANUAL and Never the Twain shall meet!"

If the process had to go to manual, then as has been suggested, the process had to be finished in manual up to a good stop/start point at which it was OK to go back to auto.

Make every step of the auto equal to an integer value, then have any manual action also change the integer value. Since integers are retentive you can always drop back into the sequence anytime.
Doesnt matter how manner steps, I have just finished one with 17 unique steps in the cycle.
Regards Alan Case

Canadian overhead cranes do a similar operation with anodes in a smelter I once worked in
1 conveyor drop off point 2,anode pick up points 35, storage locations 7 layers deep by 8 anodes high.
From memory operators had to check actuall storage amounts against PLC stored values.
Could also be manual or auto but as stated by others manual had set start/stop points.

Could possible chase up code. If this description sounds like what u r after.

Since you're using a Mitubishi, I won't explain specifics of the following. You should understand.

I had a similar situation where I needed to hold a bit coded into an STL Step. Rather than just 'OUT' the output, I 'SET' the output and 'RST'd' it in sequence. If an alarm (or whatever) situation came up where I generally 'ZRST'd' the sequence steps but the 'SET' outputs remained until I did whatever I needed to in the way of problem correction. I imagine a similar solution could be used here.

Wouldn't it be possible to increment each step by a value of 1 and store it to a word... have it increment the value even in manual mode. Also if possible to reverse the sequence you could subtract 1 from the value as well.
Then when you want to re-initiate auto mode the program would know exactly where it is in the sequence (due to comparators at the beginning of each rung)...
then you could theoretically switch from manual to auto as often as you'd like and really play with the sequence (well if you were bored on a Saturday night I s'pose)...
Then again I could be completely wrong.. I've never worked with that processor, but it should work...



Regards,
Russ

TW wrote - If the process had to go to manual, then as has been suggested, the process had to be finished in manual up to a good stop/start point at which it was OK to go back to auto.
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Is was waiting to see if anybody objected to this... No?

Are we not programmers?

What do you want Sir?
I want'a da machine to do this...
OK Sir this is the price.

No just do it.

This is where Grafcet becomes handy... you have two sets of code in parallel, with a third section where the actual outputs reside.

They are commanded by the code on operation. When you switch to manual, you do not reset the Auto mode. So the Steps will be on a sleeping type of mode...

When you go back to Auto, you code a small sequence only for positionning the devices... then you go on with what it was doing earlyer.

Not a thing to add to an existing program. It has to be coded from the beginning.

It still is not such a complicated task. IF YOU CODE IT FROM THE BEGINNING

Pierre,

The way I see it, it depends to a great extent upon the size of the system AND what the operators might do while the system is in Manual.

One of my systems is rather large - physically and program-wise. This system can be brought to manual and operated entirely in manual control if the operators so desire. The problem with this system is that there are physical places where the program does not "see" the product. In Auto-Mode the process knows that a product is leaving Point-A and moving to Point-B. The process watches to see that the product arrives at the expected time - if not, Jam-Alarm.

If the operators feel the need to go to Manual-Mode, there must be a reason... probably a jam of some kind. (Oh Yeah! They can happen! Even on one of my machines! $hit Happens, don't cha know?)

While in Manual-Mode the operators could have removed product or relocated it. If they do so in one of those "Can't-See" areas then the system might be confused.

When the machine goes to Manual-Mode my system automatically disregards any product that was "in-transit" through a "Can't-See" area (there are only two of those areas). This is because the controller has absolutely no way of knowing what has happened to those parts! Did the operator remove them? Relocate them?

So, having gone to Manual-Mode - obviously to clear-up a problem - I tell the operators, bring the machine to a state that the system recognizes - a state of positive indications. Then, and only then, go back to Auto-Mode.

As I said before, the handling of this issue "depends" on the system. If there are long spaces between stations, it's probably not reasonable to have a sensor every 6 inches.

If it is a conveyor line where the down-line station simply handles what comes its way, fine, no big deal. If, however, the space is supposed to contain a specific number of items and one or more of those items is removed... well, you see the potential problems.

The method I suggested will ALWAYS work. The method you are talking about might work - it depends on the system.

I agree with Terry. While I always try to make the system transition to auto as easliy as possible, there are somethings you just can't do.
You don't want to start a milling cutter in the cut for example, you must back it out first.