Circulative respiratory mask
BACKGROUND OF THE INVENTION 
     U.S. patent application of Ser. No. 516,687 filed on July 25, 1983 now U.S. Pat. No. 4,549,542 by the same applicant discloses a multiple-effect respirator comprising a driving motor, a supplying air fan, an exhausting air fan, two ventilating air fans and a mask wherein all the fans are mounted on a helmet and commonly driven by the single motor so that the driving force of the motor is only partially distributed to supplying air fan and exhausting air fan for circulating the air for wearer&#39;s breathing as partial driving force of the motor is shared by the two ventilating fans directing air into wearer&#39;s helmet to thereby greatly reduce the forced circulation effect within the mask. 
     The present inventor has found this defect and invented the present respiratory mask. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a respiratory mask including a mask portion adapted for wearer&#39;s mouth and nose, a central casing, a driving motor, a pair of supplying air fans, a pair of exhausting air fans and a pair of canisters disposed on both sides on the casing wherein the air may be filtered through both canisters and circulated by the fans to perform a forced circulation of air for comfortable breathing of the mask wearer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The FIGURE is a sectional illustration of the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention as shown in the FIGURE comprises: a mask portion 1 adapted for wearer&#39;s mouth and nose, a casing 2b connected with the mask portion 1, a driving motor 3b mounted on a partition plate 21b formed in the casing 2b and having holes 21c formed on the plate 21b to fluidically communicate with a discharge chamber 60 and the mask portion 1, a supplying air fan 4b formed on an outer side of a rotating disk 31c for operatively sucking the incoming air through a canister 8 formed on the outer end of the casing 2b in front of a suction chamber 40, and an exhausting air fan 6b formed on an inner side of the rotating disk 31c opposite to said fan 4b for operatively sucking exhaled air from the mask portion 1. 
     The rotating disk 31c has its central portion axially fixed on a motor shaft 31b protruding outwardly from the discharge chamber 60 of the motor 3b. A suction chamber 40 is defined among the canister 8, the rotating disk 31c having the supplying air fan 4b formed thereon, and the casing 2b. The discharge chamber 60 is defined among the rotating disk 31c having the exhausting air fan 6b formed thereon, the partition plate 21b and the casing 2b. 
     A delivery tube 43 is fluidically communicated with the suction chamber 40 and the mask portion 1. An exhausting vent 61c formed on the lower portion of casing 2b is fluidically communicated with the discharge chamber 60 to discharge the exhaled air as sucked by the exhausting air fan 6b through the holes 21c. The partition plate 21b is positioned between the discharge chamber 60 and the mask portion 1. 
     Upon the driving of the motor 2b, an air stream will be sucked by said supplying fan 4b through the canister 8, the suction chamber 40, the delivery tube 43 to the mask portion 1 for wearer&#39;s inhaling and the exhaled air in mask portion 1 will be sucked by the exhausting fan 6b through the holes 21c on partition plate 21b and finally discharged through the vent 61c. 
     In order to dampen the possible back pressure developed in discharge chamber, a back-pressure damper having a central hole is fixed on the lower edge of said mask portion 1.