Importance

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Abstract

A power antenna for automatically stopping an electric motor when a telescoping trouble occurs with the antenna to thereby cause a load of more than a predetermined magnitude to be applied to the electric motor and preventing the electric motor from being burned out and a telescoping operating mechanism from getting damaged, whereby the occurrence of an erroneous operation of the antenna such as repeated contracting and expanding operations thereof can be controlled. A worm wheel (2) inside an antenna mechanism is pivotally supported in such a manner as to slide in an axial direction and an engagement groove (21) is formed in an annular fashion, and an operating portion (32) of a movable body (17) of a limit switch (30) provided in a driving circuit for the motor is brought into engagement with the engagement groove (21) of the worm wheel. A columnar engagement body (34) adapted to be activated by an elastic member (7) is brought into engagement in a square groove type engagement recessed portion (33) of the movable body (17) within a height range which is not more than a radius of the columnar engagement body, and a cam portion (35) of a joint portion is disposed on the side of the square groove type engagement recessed portion of the movable body for keeping the engagement body (34) unlocked from the engagement recessed portion (33) when an abnormal operating force is generated relative to the antenna elements.

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First Claim