Storage door or any door for that matter can be automated, so that man does not have to be directly involved in their being opened or closed. By applying one three-phased motor where you can change direction of its movement, doors can be lifted up and lowered back down.
Ultrasonic sensor is used in recognizing presence of a vehicle by the doors, and photo-electric sensor is used to register a passing vehicle. When a vehicle approaches, the doors move up, and when a vehicle passes through the door (a ray of light is interrupted on photo-electric sensor) they lower down.
By setting a bit IR000.00 at the PLC controller input where ultrasonic sensor is connected, output IR010.00 (a switch is attached to this output) is activated, so that a motor lifts the doors up. Aside from this condition, the power source for lifting the doors must not be active (IR010.01) and the doors must not be in upper position already (IR000.02). Condition for upper limit switch is given as normally closed, so change of its status from OFF to ON (when doors are lifted) will end a condition for bit IR010.00 where power source for lifting the doors is (Segment 1).
Photo-electric switch registers a vehicle that passes by, and sets flag IR200.00. DIFD instruction is used. This instruction is activated when a condition that precedes it changes status from ON to OFF. When a vehicle passes through a door, it interrupts a ray and bit IR000.01 status changes from ON to OFF (Segment 2).
By changing status of an assisting flag from OFF to ON a condition for lowering a door is executed (Segment 3). Aside from this condition, it is necessary that a unit power source for lifting a door is turned off, and that door is not in lower position already. Bit which operates this power source for lowering, IR010.01 is automatic, so doors are lowered until they come to the bottom limit switch which is represented in a condition as normally closed. Its status change from OFF to ON interrupts a condition of the power source for lowering doors. With oncoming new vehicle, cycle is repeated. Ladder diagram: