Mechanics of Encoder Rollover ??

[milmat1]

Could someone outline the process involved in handling a rollover count.
I use a HSC to keep track of pieces entering a machine, Then I have several stations along the line that need to fire at certain
intervals. And there can be more than one piece in the machine at a time. I can handle the logic to make this happen, However i am not familiar with dealing with a rollover when there will still be pieces traveling along the feed belt that I still need to keep track of.
Is this a matter of capturing the counts at rollover then adding them back to the total as the HSC rolls over etc. ??
I generally am talking about a GE IC693APU300 HSC. But use others as well.
I just need an outline of what needs to happen during a Rollover...

Any Info will be helpfull..


THANKS

 

[Steve Bailey]

The mechanics of rollover are pretty straightforward. When the accumulated count increases to the maximum value, the next count in the up direction will be the minimum value.

There are any number of strategies to deal with this in ladder logic. If the direction remains constant, you can keep track of the accumulated value in the previous scan and if the accumulated value in this scan is less than the previous scan you know a rollover has occurred. You can then subtract the maximum value from all of the stored values for the parts you're tracking.

As you capture a value for a specific part, you can test to see if a rollover will occur before that part reaches the point where you have to make a decision about it and if so, subtract the maximum value before you store the value.

Without knowing more about what you have to do, it's hard to get more specific than that.

 

[milmat1]

That is a great explaination !! Thank You !!

I have a feed through machine, Parts are traveling along at 50 FPM or so. And they are usually 12" or more apart, I trigger from a single limit switch at the front, And an Encoder on the drive motor shaft. I then keep track of the counts as the part moves through the machine. I then have to fire a "Jump" sol. Valve at the leading edge of each piece, And keep it on for a certain number of counts.(distance).
Where it becomes tricky is that there may be several parts in the machine at any givin time. And the accumulator may reach it's max count several times a day.(unpredictably)
If it rolls over while no parts are present in the machine, Then there is no problem.
However if it happens while there are parts in the machine, Those parts will not be machined correctly and are waisted.
This is a feed through Woodworking edge machine we are talking about.And the "Jump" Stations may be to feed a band out, or move a profile cutter in/out etc. As the part passes.Usually they want to cut only the first few inches of the piece as it goes by.

Thanks For the explaination, I was just not understanding the process of the rollover correction.....THANKS!!

MATT