Automatic door opener

In a combination of a roller curtain door having a door curtain which is wound on and off a roller door drum to open and close the door respectively, an automatic opener for the door, and a locking facility for mechanically locking the door in a closed position in which the automatic opener includes a reversible electric drive motor having a pinion gear drivably connected therewith and arranged to mesh with a ring gear connected to said door drum to drive said door drum to wind the door curtain on and off said door drum, and an electric control circuit connected to operate the electric motor from a source of electric power, and in which said circuit controls the operation of said electric drive motor, the improvement comprising:

• sensing means connected in series with said electric circuit to sense a change in the electrical current drawn by said circuit above that which is normal for operation of said circuit and motor and to disconnect said circuit in such circumstances,
• said sensing means further comprising a switching means connected to switch off power from said source to said circuit once the current flowing through said switching means to said circuit is sensed above that which is normal and to automtically restablish the power after a time interval, and further operable in the event said circuit re-experiences electrical current above that which is normal to again switch off the power and to continue to cycle in such on/off mode until the electrical current demand condition returns to normal,
• said reversible electric motor mounted on an arm which is mounted for swinging movement about an axle, the central longitudinal axis of said axle being substantially parallel with a central longitudinal axis of said drum and spaced from a central axis of the pinion gear,
• said swinging movement being such that the reversible electric motor can be drive engaged or disengaged with said ring gear by swinging of said arm about said axle to allow said door curtain to be opened manually in the event of power failure by disengaging said drive.