How to use an up/down counter

hi,
I am working on mitsubishi PLC Fx1N. I have a table of rollers driven by a motor. Table length is 3 mtr and width is 2 mtr. this table is a part of a processing line. We are passing a sheet of plyboard through the table to unload by other device. I used a limit switch at entry to start the roller and one limit switch at end of the roller to stop the roller.
Now I want to put different size of sheet at the center of the table always.
In my case sheet is stop at the end of roller table.
I want to use a device which started counting when sheet start enter over roller table and stop count when sheet reached at the end of the roller table. When end limit switch was operated the roller must be run reverse a bit to back the sheet in the center of the table and then next cycle started.
Can I use a pulse counter using pulse of a proximity or use an incremental rotary encoder and how I can program a logic for this.

Hi mraj2001,

I noticed nobody responded to your post. Several years ago I had a similar application. Using a different PLC (GE 90-30).

mraj2001 said:

hi,
table is a part of a processing line. We are passing a sheet of plyboard through the table to unload by other device. I used a limit switch at entry to start the roller and one limit switch at end of the roller to stop the roller.

Click to expand...

My application was for a package of lumber. The lumber might be 20 feet long or it might be 6 feet long, or somewhere in between. Photo eyes were used instead of limit switches. An inductive prox was used to count teeth on a chain sprocket that powered the rolls. I needed to center the package in the rollcase just like you are attempting to do.

The photo eye was positioned before the table that the product needed to be centered on (the table was longer than all of the packages). As soon as the product triggered the photo eye a pair of counters started counting the prox pulses. One counter was for counting how long the package was. The other counter was for determining how far the leading edge of the package had moved. Once the package length had been determined I divided this length in half, This way I knew where the centerline of the package was in length. The number of prox pulses from the photo eye to the center of the table was already known. By adding the length of pulses from the photo eye to the the table centerline to the number of half the package length, I was able to determine the stopping point. When the number of the stopping point equaled (or greater) than the total travel, the rollcase was stopped. No reversing was required. Obviously some adjustment was needed to account for motor coast.

My reply will bring this thread to the top of the list, so someone with mitsubishi experience can help further, or improve on my suggestion.

hi,
Here I am looking for two systems.
1) I am looking for spare part of a touch screen NS10-TV00V2 of omron.Its touch key pad is not working due to scraches and I want to replace it. Can some body suggest me that Is Omron supplies this key pad as spare and how i can get it from seller.
2) I have a PLC system CPU586 (RBXM) of Robox, installed in a machine. I want to look its program. Which tools I should have and how I can get it as free/paid.
Can I get training in plcs.net for Robox PLC programmin.