On 2/6/2016 10:51 AM, Jeff Wisnia wrote:
That photoelectric stuff wasn't around when I installed the original openers,
so I never really had any experience with it and didn't think of it at first as
being the cause of the door reversing near fully closed. I know better now.

IME, the photocells aren't worth their cost. They really only detect things
that are ON the garage floor IN the path of the beam.

E.g., a kids wagon or bicycle typically won't trip the detector (the light
shines under or through). The same is true of vehicles (unless their front
or rear axles are in the path.

Openers that sense closing force (reversing when the feel "resistance")
also have too heavy of a hand in sensing (i.e., they'd crease the hood
of a vehicle parked beneath it). The door mechanism would have to be
critically damped to make them practical (at very low forces).