[HayZee518]

ok, first I am thinking to use a chain and a couple of pulleys connected to the door with a counterweight with enough of weight to open the door. to close the door use an air cylinder. BIMBA makes a lot of thin cylinders. for detection maybe you could make use of an outdoor motion sensor - use the sensor to open the door [de-energize the cylinder] and a timer to close the door. an electric eye at floor level could detect a body or object to stop the motion. and upon removal of power the counterweight will open the door.