Overhead garage door opening devices employing motor driven chains, worms and cables are old in the art. They are characterized by their use of long rigid track members which must be secured to the garage structure. Many are heavy and of complicated construction.
Many prior art devices have been activated by the use of radio waves, light beams, or sound frequencies. Radio waves have not been entirely satisfactory because passing airplanes have been known to open garage doors when overhead due to their high powered signaling waves. Also, the light beams offer little protection from outsiders who wish to gain entrance to the garage enclosure.
Ultrasonic and sound waves, when used as signaling means, are subject to some of the same objections as radio waves. Prior art difficulties of this type have been eliminated in the present invention by the use of a time delay receiving circuit which provides motor power only after the signal has been received and decoded for a predetermined length of time. This feature eliminates unlawful entry by the use of a siren type of generator which produces continuously variable frequency values.
A feature of the present invention is the simplified manner in which the motor operates the door by the use of a heavy cord and a capstan.
Another feature of the present invention is its light, compact, easy to install construction.
A further feature is its safe operation resulting from its cord and capstan drive.
A further feature is its low voltage power supply which operates from an internal power source.
Still another feature of the invention is a time limit switch which removes power from the motor after a predetermined time interval and then operates a motor reversing switch to place the circuit in condition for a return operation.
Another feature is an efficient drive system which permits low input mechanical power of approximately 1/20 H.P.
Yet another feature is its capability of installation in substandard head room conditions as defined by the Architectural Standards Association.