Patent ID: 7275631

Claim:
An engaging/disengaging fail-safe door closing device for a rolling fire door, provided between a power means ( 10 ) and a speed reducing means ( 50 ) of a door machine ( 1 ), used to close said rolling fire door immediately in a condition of power failure, comprising: an electromagnet means ( 30 ) fixed inside a housing ( 2 ) of said door machine ( 1 ) and disposed around the outside of a shaft ( 11 ) of said power means ( 10 ); a brake means ( 40 ) including a shaft sleeve ( 41 ), loosely embracing around the outside of said shaft ( 11 ) of said power means ( 10 ) and being capable of sliding between said shaft and said electromagnet means ( 30 ), on one end of said shaft sleeve ( 41 ) there is provided an attracted plate ( 43 ) facing said magnet means ( 30 ) and coming off said magnet means ( 30 ) by way of the biasing force of an elastic element ( 35 ), while on the other end of said shaft sleeve ( 41 ) there is radially formed a brake disk ( 44 ); a driving plate ( 12 ) fixed on said shaft ( 11 ) of said power means ( 10 ) and facing a position where said brake disk ( 44 ) is allowed to contact; and a circuit ( 53 ) used to control said power means ( 10 ) so as to actuate the brake when said power means ( 10 ) is switched on and said electromagnet means ( 30 ) is disconnected or release the brake when said power means ( 10 ) is disconnected and said electromagnetic means ( 30 ) is switched on.