CCW Confusion

Not sure it buys anything at all, just throwing it out there. I'm having a hard time reading the text on the drawing, so I just kind of winged it. If he already has a mechanism in the code that tracks the queue, then the hard part is probably done. If not I have a few further thoughts on this.

You would have to keep track of how many boxes are on the belt (a "boxes on belt" counter) so you could add the next one in the right place. Basically, if "1" is a small box and "2" is a large box, your array might look like this:
0,0,0,0,0,0,1,1,2,1,2,2,1,2,1
The brake would look at the "right" end of the array to see that it has to release, in this case, a small box. It would then trigger a "word shift right" (just making up terms here) and decrement the "boxes on belt" counter. The preceding machine would look at the "boxes on belt" counter to figure out where in the array to stick its 1 or 2 for the box it's adding to the queue.

As far as overfilling the conveyor, a simple photo-eye near the entrance end would fix that. Don't add a box to the queue unless the photo-eye is clear.

Actually, one advantage I can see is that you can use a single array instead of multiples. To use bit arrays, you would need an array for each size box that will be run. Also, the numbers here could be directly used as timer presets. Instead of "1" and "2", you could use "500" to represent 0.5s for the small box and "1200" for 1.2s for the larger box. If you change the size of the box, or add a third size, it's easy enough to update the code.

Why do we care what size box is on the accumulation line? If the labeller needs to know, we can add a PE to the brake or scale and count the ticks.
Accumulation to me means that I want product nonstop. This is going to be the worst area to regulate or predict. A 100% full PE near the gates will indicate when to quit releasing into the accum zone. For the brake release, if it's feeding the scale, why wouldn't you base it on a scale exit PE? If a box hasn't cleared the scale don't send one.
The number and size of boxes in the accumulation zone is important because? If we need to know the quantity and length why not get them at a controlled area like the brake or on the scale?
If we need to regulate which line is releasing we should add some upstream photos to indicate when either line is in flowstop and needs a higher priority.
If your going to base it on package length, you might as well pass off the accumulator contents for each package. It will identify runaways easier as well. Shift through the array with a MOVE. The total array length is a fixed number but the total members of the array can vary based on how many fit into the total. When the box arrives, it already has a count of ticks attached to it. All you need to do is run for the number of ticks it has. The question here is what if there is a jam and packages get rearranged? How do you flag the queue as dirty and how do you recover from it? How do we handle runaways from the gates?
What kind of conveyor is the 2:1? What is the accum zone conveyor, roller or indexed belt? What kind of brake, belt or something that blocks carton?

My understanding of the problem is that he needs to know whether the next box released from the conveyor is large or small so he knows how long to release the brake. If the large boxes are taller than the smaller ones, it's probably much easier to use a photo-eye to detect the taller box and forget about the array altogether.

Why do we care what size box is on the accumulation line?

Click to expand...

Line one is running small boxes (they have a shorter brake release time) and line two is running big boxes (they have a longer brake release time).

Click to expand...

The number and size of boxes in the accumulation zone is important because?

Click to expand...

Because, to refresh your memory, the question was:

Is there a way to do this using one of the many function blocks in CCW?

Click to expand...

If your going to base it on package length, you might as well pass off the accumulator contents for each package.

Click to expand...

No, the question is how to do it using a function block in CCW. The OP's instructions are contained on the sketch he posted. I suspect this is a training project from DCAM's boss.

...attached is crude drawing of the conveyor system in question

Click to expand...

I simply raised a few questions. I fully realize what he wants. Perhaps there is a better, more efficient way to accomplish what he wants but he can't visualize it.

What happens if the boxes get out of sequence? If a large box goes across the scale but the counts are only for a small box, what happens?

If a large box goes across the scale but the counts are only for a small box, what happens?

Click to expand...

If the shift register contains a bit for a small box (maybe a 0 = Small), but the box is really Big (should = 1), then the brake will not release long enough for the box to move onto the scale section. Then there will be a box half-on, half-off of the scale, resulting in the first incorrect weight being recorded. Then the next box will be in the wrong position, resulting in another incorrect weight. This error would "domino" all up the line of waiting boxes, until manually corrected.

As another different way to skin the cat.....

What about installing a photoeye just past the brake (by an inch or so), when the next box is ready to be released, then release the brake by only the amount of time for a small box. If the photoeye is then not clear, release the brake for the incremental amount of time to equal a large box.

So in summary, assume every box is small and release the brake for that amount of time. If the box hasn't cleared the brake, then release the brake a second time. No tracking or bit shifting is necessary.

Bruce, now that has to be called "thinking about boxes outside the box"!
I don't see why it won't work. Good job.

Lancie1 said:

Bruce, now that has to be called "thinking about boxes outside the box"!
I don't see why it won't work. Good job.

Click to expand...

Thanks Lancie1, it isn't often I hear good job, just when will the line be back running!

Here is a project update on the box conveyor from Dcam on another thread, Post #3:

http://www.plctalk.net/qanda/showthread.php?p=491178#post491178

After starting the design process, We determined that mixing small and big boxes would not work for production. The case labeler is only capable of 16 small boxes a minute and large boxes would lessen small box number by more than half. I really apriciate everyones input. If anyone is learning CCW and 800 series, let me know what u think and maybe give me some pointers.

Click to expand...