Looking for a Sensor

I am working with stepper motors trying to get bags on rolls to stop a the same place every time not working out by setting steps. I have two much play in the gears that feed the bags so Now I am thinking of using a sensor to read a white strip on the bag to stop it in the same place every time. witch type of sensor would work the best for this app. Thank you

Bag is:







Hi it is a plastic bag with a with a logo in the center but it has a clear part around the edge of 1/2" witch has a white line 1/16" wide at the bottom of the corner 1/2" up from the bottom

If sensing the white strip is critical it's going to co$t. If just sensing the leading/trailing edge of the bag, aiming a photocell down through the rollers at a cornercube reflector target below is a good stepping off point.

Is there a drive belt traveling under the rollers? This would rule out a retro-reflective type. A small PE shooting across the conveyor might also work.

Just MHO but you'll get there faster with an industrial grade device as opposed to cobbling together a DIY solution.

Banner Engineering makes all sorts of photosensors - they probably have one that would work for you.

Hi thanks for the help the bags are on a roll with a serration between them no belt they go through rollers that are gear driven.