Backgauge Controller

What kind of controller (?PLC) is it? I'm wondering if you could use some crafty tricks to do a kind of 'longhand' arithmetic to give you a reasonable result. Also, can you get a 128ppr encoder otherwise the same as the one you're using? It may help with the sums.

I am using a unitronics m-90 plc this unit can only process numbers up to 32767 before a math overflow occurs and the maximum travel of the backgague is about 700mm

A bit late for me to do sums tonight, but the sort of thing I'm suggesting is that you can, for example, use one of the integers in the file (the low-order count) to count up to (say) 1000, and reset to 0 & add 1 to another integer (the high-order count) location if >= 1000. On counting down, subtract one from the high-order count and reset the low-order to 999 when the low-order tries to go below 0.

This can be extended (to make things easier to follow) by using a series of locations, one for each decade. Just because one location can't count past 32767 isn't a problem - early computers were restricted to 127 (8 bits) before overflow - but could still do arithmetic to 20 or 30 significant (decimal) digits.

Even with the restrictions of ladder logic you can do amazing things if you think outside the box a bit.

Hi JohnDG

I like your idea, i have used this process in the past, for water metering. I will look into this further, i think you are on to something here. Why didnt i think of this!

Keep on thinking outside of the box, JohnDG

Hello Joe Sparky,

You have assumed 100 µ is precise enough. Iit may not be if you cut print. You need to be able to get 'infinite' adjustability between points. You do if you are talking of a paper Guillotine.

No problem if you are cutting plain paper or card. If, however you are cutting large printed sheets with say, Birthday cards, and gift tags, there is to many 'up' per sheet to allow the accurate folding of cards which can be as small as say 25 mm x 25 mm flat size and these have to be folded allowing a maximum fold-edge bleed of .5 mm.

How about splitting the length the program is dealing with in half, and using two programs, one for the back and one for the front of the screw, looking at it from the front?............That is one train of thought. Is that possible?

The other is to have a smaller screw pitch, say 5 mm, but still have as many stops possible.

I can understand why you chose 10 mm, because it made it easier.

You may have something entirely different in mind. Can you let me know please?

Hi Babybear

The gillitione that we want to use this system on is a sheet metal gillitione, we want accuraccy to 0.1mm.

Changing the screws is not a cost effective option.

Fitting a linear encoder is another option, but still not very cost effective.

Replacing the PLC with a 32 bit processor is another option, but it adds about $650.00 NZ Dollars to the cost.

What we are trying to do is supply a cost effective one stop solution, for all backgague,s.

The next step is to look at Press Brakes and look at using a the same software with some modifications to calculate the folding position for defined angles.

The idea is to replace some older controllers on machines and define settings using simple english language instead of abbreviated codes, to make setup and operation more simple and cost effective, so that every engineering workshop will want one.

There is no money in software development, if you only sell it once, my idea is to have a software package that can be adapted to all backgague controllers, and the installer sets the parrameters for that machine.

Using two programmes, i dont think it would be that easy or reliable, i have tried in the past to do this but it never worked that effectively (we can loose counts from the high speed encoder)

Hello JS,

Sounds like a really good idea! Working ± 100 µ is ambitious for a metal Gilly.

I will wish you luck and will keep an eye on your thread, and for the moment will back out. I know about paper gillies, but not much of metal ones!

=

Do you think something simple like an infrared or similar no-contact measure, as is used to measure buildings, rooms and the like, be accurate enough and work? I have in mind the unit screwed to the back gauge and aimed at the pressure-plate.

Take care.

Not sure how much help it would be but we use 1k pp/rpm encoders on our older printheads which I am upgrading to even higher resolutions via mitsubishi PLC. The encoder were used on a special built analogue controller and I believe I have about 10 of them. If I can persuade the boss to sell them. I will only need to keep 3 of the ten I have and most of them are used, so I imagine instead of the 1400 I paid for them we could let them go at a decent price for you.

At any rate I have 3 Heidelberg sutters here an with the exception of the newest one thay are all using 1k linear encoders that run the full length of the cut table. What you might find of interest is that they use a middle mark for a reference point and restarts the calculations at the halfway point each time it crosses it. Not sure if you can do this with a rotary encoder but its just a suggestion. I believe the math on it is calculated then added to the previous half to give the total as it is moving back and the reverse as it is moving forward.

Hope this is of some help to you.

Jeff