[BBray_T1296]

The sensors we used to automate our cube are:

Beam-break sensors, which is an all-in-one IR sender/reciever that trips anytime something reasonably reflective is in the way. The totes were plenty reflective for several inches, and using the retro-reflective vision tape will trip them from several feet away. Putting something dark and matte behind the sensor (or just lots of open air) keeps them from tripping falsely.

We also use hall-effect sensors (can find at WCP) which detect when a magnet passes in front of it. Our tote lifter was on a chain run, and we mounted a magnet to one link of chain, and placed beam-breaks at the top and bottom in the necessary positions. The stacker simply lifted until the sensor tripped and lowered until the other one tripped.

Both these options are great because they work without contact. We found using mechanical limit switches can be tricky as they can bend over time and the positioning changes. Without contact the sensors aren't going to move, heck all of our sensors were simply Velcro-d on, so we could manually adjust them if necessary.