BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a door operator, more particularly to a door operator for a fireproof door. 
     2. Brief Description of Prior Art 
     Generally, the door operator used in a fireproof door is classified into two types depending on its operational mode: one is a failsafe mode and the other is a non-failsafe mode. In the case of the failsafe mode, a brake is immediately released by a brake device so as to shut the fireproof door in the absence of electrical power regardless of the reason of power failure. If fire breaks out in the presence of electrical power, the power is cut off by, for example, smoke detectors, temperature sensors or other fire detecting devices, or is cut off mechanically by a fusible link device which is molten at a high temperature in the fire in such a manner that the brake is released, and the door curtain shuts the fireproof door by its own weight. In this mode, the flame or escape of dense smoke can be blocked instantly when the fire occurs, if the cause of power failure is a fire indeed. Therefore, the main feature of the failsafe mode is more active for fire prevention. However, if the cause of the power failure is not a fire, a manually operating means has to be used for driving the door operator to open the door so as to maintain regular access for personnel. 
     On the other hand, in non-failsafe mode, the brake device is still maintained in a brake-actuated state without closing the fireproof door immediately in the absence of electrical power, regardless of the reason of power failure. Only if the occurrence of a fire is definitely confirmed by, for example, smoke detectors, temperature sensors or other fire detecting devices, a current transiently supplied from a reserved power source such as a capacitor, a battery or the like is supplied to the brake device for releasing the brake for a short period of time, or a fusible link is molten at a high temperature for mechanically actuating the brake device so as to release the brake, in such a manner that the door curtain falls down and shuts the fireproof door by its own weight. In this mode, the main advantage is that no inconvenience is encountered for personnel regular access is the main advantage, if the fire is not the cause of power failure. However, if the power failure is caused by a fire, and if the fire point is remote from the fire detecting devices or the fusible link, it is impossible to close the fireproof door immediately. Therefore, this mode is less safe for fire prevention. 
     Some documents associated with a failsafe mode door operator of a fireproof door have been proposed, such as U.S. Pat. Nos. 5,673,514 and 5,893,234 in which two electromagnets are used to maintain the brake-actuating state in the presence of electrical power, or to release the brake immediately so as to close the fireproof door in a power failure condition. The structure thereof is very complicated and has a large volume. On the other hand, a lot of documents concerning non-failsafe mode door operator of fireproof door such as U.S. Pat. Nos. 5,203,392 and 5,386,891 are disclosed, in which manual operation has to be conducted by switching operation mode, or a chain disk is rotated by pulling an endless chain and meanwhile the brake is released so as to rotate the rotary shaft. Thus, there is still room for further improvements on the implementation and the structure of a door operator. 
     SUMMARY OF THE INVENTION 
     The main object of the present invention is to provide a novel door operator of a fireproof door capable of obviating the disadvantages such as complexity in structure, large volume and inconvenience in operation present in prior art. 
     In order to achieve the aforementioned and the other objects, the door operator of the fireproof door according to the present invention comprises: a force applying end, which is activated to drive a rotary shaft; and a loading end for supporting the weight of the door curtain, the rotary shaft comprising an internal shaft and an external shaft. The force applying end and the loading end are applied on the internal shaft and the external shaft respectively, and the internal shaft and the external shaft are normally coupled by a clutch mechanism. A torsion spring brake mechanism is used to normally brake or release the rotary shaft by reducing or enlarging the inner diameter of the torsion spring. When an external force is exerted on the force applying end in a manner that the torsion spring is de-twisted or its inner diameter is enlarged, the rotary shaft is released and rotated. In the case that no external force is exerted thereto, the loading from the weight of the door curtain is normally transferred to the torsion spring so that the torsion spring is twisted or its inner diameter is reduced, whereby braking the rotary shaft. In this way, the clutch mechanism is controlled to interrupt the coupling of the internal shaft and the external shaft such that the door curtain falls and shuts the fireproof door in the event of a fire alarm. Thus, flame or smoke can be blocked immediately. 
     According to the present invention, each end of the torsion spring is provided with a protrusion loop having a twisting side and a de-twisting side. The external force exerted from the force applying end is applied on the de-twisting side so that the torsion spring is de-twisted or its inner diameter is enlarged and the rotary shaft is released and rotated by the external force. Alternatively, the loading on the loading end from the weight of the door curtain is applied on the twisting side so that the torsion spring is twisted or its inner diameter is reduced to brake the rotation of the rotary shaft caused by the weight of the door curtain. With aid of the torsion spring brake mechanism, not only is the external force allowed to roll up or down the door curtain, but also the rotation of the rotary shaft caused by the weight of the door curtain is braked. 
     According to the present invention, the rotary shaft of the door operator is simplified and compact in structure by arranging the internal shaft in the external shaft. 
     According to the present invention, the door operator of the fireproof door can be adapted to a failsafe door operator by introducing an electromagnetic clutch or into a non-failsafe door operator by introducing a mechanical clutch. Most of the components used in both cases are the same. Not only lower manufacturing cost, fewer components and simplicity in production can be achieved, but also smaller inventory and simplicity in assembly can be realized. 
     According to the present invention, the door operator of the fireproof door further has a circuit by which the electromagnetic clutch can be excited in the presence of a normal power supply. The circuit may further include a delay circuit formed by a plurality of capacitors, which are charged in the presence of the normal power supply. In the event of a power interruption caused by a fire, the electromagnetic clutch can be excited for a short time excitation so as to delay shutting of the fireproof door for the personnel evacuation. 
    
    
     
       BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS 
         FIG. 1  is a sectional view showing the door operator of a failsafe type fireproof door according to the present invention. 
         FIG. 1   a  is a partially enlarged view of the encircled portion in  FIG. 1  in which the clutch mechanism is shown to be in a separated state. 
         FIG. 1   b  is a partially enlarged view of the encircled portion in  FIG. 1  in which the clutch mechanism is shown to be in an engaged state. 
         FIG. 1   c  is a sectional schematic view taken along the line  1   c - 1   c  of  FIG. 1 . 
         FIG. 1   d  is a perspective sectional view showing the door operator of  FIG. 1 . 
         FIG. 1   e  is an exploded perspective view showing the torsion spring brake mechanism of the present invention. 
         FIG. 1   f  is an exploded perspective enlarged view in another direction showing the torsion spring brake mechanism in  FIG. 1   e  of the present invention. 
         FIG. 1   g  is a schematic view showing a circuit used in the door operator of a failsafe type fireproof door according to the present invention. 
         FIG. 1   h  is a schematic drawing showing the state of use of the present invention. 
         FIG. 1   i  is a sectional view taken along the line  1   i - 1   i  in  FIG. 1   d.    
         FIG. 2  is a sectional view showing an embodiment of a non-failsafe type door operator of fireproof door of the present invention. 
         FIG. 2   a  is a schematic sectional view taken along the line  2   a - 2   a  in  FIG. 2 . 
         FIG. 2   b  is a dynamic schematic view of the clutch mechanism in  FIG. 2  in which the clutch mechanism is shown to be in separated state. 
         FIG. 2   c  is a sectional perspective view showing the door operator in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The technical contents of the present invention will become more apparent from the detailed description of the preferred embodiments in conjunction with the accompanying drawings. It is noted that the preferred embodiments which are purely illustrative do not intend to restrict the implementation range of the present invention. 
     Firstly referring to  FIGS. 1 ,  1   a  to  1   i , an embodiment of a failsafe type door operator of a fireproof door of the present invention is described. The door operator  1  of the present invention is used to release a reel A of a door curtain D so as to close the fireproof door in the event of power failure. The door curtain is composed of a plurality of slats. The door operator  1  essentially comprises a housing  10  defining an accommodation space. A central shaft  12  is rotatably arranged in the housing  10 . A torsion spring brake mechanism  20  is arranged to encircle around the circumference at the left end of the central shaft  12  for braking or releasing the central axis  12  by twisting or de-twisting one or more torsion springs  201  of the torsion spring brake mechanism  20 . The details of the torsion spring brake mechanism  20  will be described later. A drive mechanism  30  is disposed on the central shaft  12  in such a manner that the torsion springs  201  is de-twisted to the effect that the inner diameter thereof is enlarged when an external force is exerted on the drive mechanism  30  whereby releasing and rotating the central shaft  12 . A first external shaft  14  is rotatably mounted on the central shaft  12 . A clutch mechanism  50  is disposed on the central shaft  12  at the right end of the first external shaft  14  for connecting and disconnecting the central shaft  12  and the first external shaft  14  in a control manner. A second external shaft  16  adjacent to the left end of the first external shaft  14  is rotatably mounted on the central shaft  12  and firmly provided with an output pulley  161  which is coupled with the reel A of the door curtain D (as shown in  FIG. 1   h ). A reduction mechanism  40  includes gear trains  401 ,  401 ′. As shown in  FIG. 1   i , a first external shaft  14  is coupled to a second external shaft  16  through gear  401 , gear  401   a , gear  401   b  and gear  401 ′ in sequence so as to reduce the speed of the first external shaft  14 , and transfer the reduced speed to the second external shaft  16 . When no external force is exerted on the drive mechanism  30 , the loading from the weight of the door curtain is normally transmitted to the torsion spring  201  through the output pulley  161 , the second external shaft  16 , the reduction mechanism  40 , the first external shaft  14 , the clutch mechanism  50  and the central shaft  12  so that the torsion springs  201  are twisted to the effect that the inner diameter thereof is reduced, whereby braking and holding the central shaft  12 . In the event of the fire alarm and power failure, the clutch disconnects the first external shaft  14  from the central shaft  12  such that the door curtain falls down by its own weight and shuts the fireproof door. 
     According to the present invention, a centrifugal brake mechanism  60 , which is well known, is arranged to encircle the outer circumference of the first external shaft  14  for limiting the rotation speed of the first external shaft  14  by a friction on the brake drum caused by a centrifugal force. The centrifugal force is generated when the first external shaft  14  rotates. The housing  10  is partitioned into a plurality of spaces by a plurality of partitioning plates  101 ,  101 ′. The brake drum  601  is fixed on one of the partitioning plates  101 . One end of the first external shaft  14  is rotatably and is centrally aligned with the brake drum  601 , while the other end is provided with a driven disc  141 . 
     The clutch mechanism  50  is located on the opposite side of the driven disc  141  which comprises an electromagnet  501  fixed on the other one of the partitioning plates  101 ′ of the housing  10 . A drive member  503  has an end face adjacent to the electromagnet  501  and is fixed on the central shaft  12 . A follower  505  which is provided with a brake shoe  533  and interposed between the drive member  503  and the driven disc  141  is biased by an elastic plate  507  and is coupled with the driven disc  141 . When the electromagnet  501  is not excited, the follower  505  is biased toward the driven disc  141 , as shown in  FIG. 1   a . At the same time, the coupling of the central shaft  12  and the first external shaft  14  is disconnected. On the other hand, when the electromagnet  501  is excited, the follower  505  is pushed toward the drive member  503  by the electromagnet  501  against the elastic plate  507 , as shown in  FIG. 1   b . In the same time, the central shaft  12  and the first external shaft  14  are coupled. Moreover, a circuit is provided to excite the electromagnet  501  in the presence of the normal power supply, so that the central shaft  12  and the first external shaft  14  are normally coupled. 
     Furthermore, the housing  10  is provided with a second housing  10 ′ for supporting one end of the second external shaft  16 , and the torsion spring brake mechanism  20  is received in the second housing  10 ′. The torsion spring brake mechanism  20  is provided with a hub  18  which rotatably supports one end of the central shaft  12 . One end of the hub  18  is fixed on the second housing  10 ′. As shown in  FIGS. 1   e  and  1   f , the torsion spring brake mechanism  20  has one or more torsion springs  201 . Two ends of each torsion spring  201  are free ends. Each torsion spring  201  constricts the circumference of the other end of the hub  18 . Each free end of each torsion spring  201  is formed with a protrusion loop  201   a . An inner ring portion  203  and an outer ring portion  205  are concentric and rotatable with respect to each other. The inner ring portion  203  is fitted and fixed on the central shaft  12 . A pair of blocking plates  2031  are erected on one top face of the inner ring portion  203  in the longitudinal direction and arranged opposite to each other in the radial direction. A pair of push-plates  2051  are erected on one top face of the outer ring portion  205  at the same side with the blocking plates  2031  and arranged opposite to each other in the radial direction in such a matter that the blocking plates  2031  and the push-plates  2051  are disposed alternately around the torsion springs  201 . The blocking plates  2031  and the push-plates  2051  are concentric and arranged at the same radius. The protrusion loop  201   a  is received in a gap between one blocking plate  2031  and one push-plate  2051  which are adjacent to each other. Each protrusion loop  201   a  has a twisting side a and a de-twisting side b. The “twisting side” refers to as the side on which a force is exerted, causing the torsion to be twisted. The “de-twisting side” refers to as the side on which a force is exerted, causing the torsion to be de-twisted. The blocking plates  2031  are respectively arranged between two twisting sides a and would be blocked by the twisting sides a. Rotation of the outer ring portion  205  causes the push-plates  2051  to be abutted on the de-twisting sides b and hence causes the torsion springs  201  to be de-twisted as shown in  FIG. 1   c  so that the rotation of the outer ring portion  205  is kept going. In addition, the drive mechanism  30  includes a chain wheel  301  and a chain wound on the outer circumference of the chain wheel  301 . The chain wheel  301  is fixed on the outer ring portion  205 . 
     The central shaft  12  can be indirectly rotated by pulling the chain. 
     Referring to  FIGS. 1 and 1   g , the coil R 1  of the electromagnet  501  of the clutch mechanism  50  is excited in the presence of the normal power supply such that the central shaft  12  and the first external shaft  14  are coupled with each other normally. At this moment, if the chain is pulled, then the push-plates  2051  are rotated and abutted on the de-twisting sides b of the protrusion loops  201   a  of the torsion springs  201  so that the torsion springs  201  are subject to a de-twisting torque and hence de-twisted. The inner diameter of the torsion springs  201  is enlarged and the hub  18  is released from the torsion springs  201 . Then, the torsion springs  201  are rotated along the circumference of the hub  18 , so the blocking plates  2031  on the other side of the protrusion loops  201   a  are also rotated together. The drive force applied on the central shaft  12  is transferred through the first external shaft  14  and the second external shaft  16  to the reel of the door curtain so as to roll up or down the door curtain. On the other hand, if the drive mechanism  30  is not operated, the loading of the weight of the door curtain on the output pulley  161  is transferred to the central shaft  12  through the first external shaft  14  and the second external shaft  16 . In such a case, the blocking plates  2031  of the inner outer portion  203  are abutted on the twisting sides a of the protrusion loops  201   a  of the torsion springs  201  so that a twisting torque is applied to the torsion springs  201  and the torsion springs  201  are further twisted. As the torsion springs  201  are further twisted, the torsion springs  201  constrict on the hub  18  more firmly and hence become unmovable and unrotatable about the hub  18 . As a result, the blocking plates  2031  are blocked by the unmovable and unrotatable torsion springs  201 , and hence the central shaft  12  is braked and held. 
     In the event of power failure, the clutch mechanism  50  immediately interrupts the coupling of the central shaft  12  and the first external shaft  14  such that the door curtain falls down by its own weight. Even when fire breaks out in the presence of the power supply, the power supply can be interrupted by conventional fire detecting devices, for example, smoke detectors, temperature sensors or other fire detecting devices. Furthermore, a delay circuit C 1  formed by a plurality of capacitors may be included in the circuit. The capacitors which are charged in the presence of the power supply supply a current to the coil R 1  of the electromagnet  501  for a short time in the event of the power failure the electromagnet  501  is excited transiently, for example for about 10 seconds, so as to delay the shutting of the fireproof door for immediate personnel evacuation. 
     Furthermore,  FIGS. 2 to 2   c  illustrate an embodiment of a non-failsafe door operator of a fireproof door of the present invention. This embodiment different from the preceding one in that a mechanical type of clutch mechanism  50 ′ is included to couple the central shaft  12  and the first external shaft  14  or disconnect them from each other. According to this invention, the other end of the central shaft  12  is rotatably support on the other partitioning plate  101 ′ at the outer side of the partitioning plate  101 ′. The clutch mechanism  50 ′ has a bushing  52  disposed on the right side of the driven disc  141 . The bushing  52  is arranged in such a manner that the bushing  52  can slide axially therein and rotate together with the central shaft  12 , but cannot rotate with respect to the central shaft  12 . A circumferential sliding groove  521  is formed along the outer circumference of the bushing  52 . A disk spring  54  is interposed between the bushing  52  and the partitioning plate  101 ′. One end of the bushing  52  is biased by the disk spring  54  such that the other end thereof is normally abutted against the driven disk  141 . A first teeth portion  141   a  is formed on the end face of the driven disk  141  which is to be engaged with a second teeth portion  523  formed on the end face of the other end of the bushing  52 , as shown in  FIGS. 2 and 2   a.    
     According to the present invention, a rocking lever  56  is provided. The middle portion of the rock lever  56  is pivoted on the housing  10 . The inner end of the rocking lever  56  is provided with a protruding pin  561  extending into the sliding groove  521 . The outside end of the rocking lever  56  extends outside of the housing  10 . A guide member  57  is fixed on the housing  10  corresponding to the outer end of the rocking lever  56 . A slider  58  inserted in the guide member  57  is slidably guided in the guide member  57 . The slider  58  is biased by an elastic element  59  and connected with a conventional fire detecting device  70 . The slider  58  is arranged in place so that the outer end of the rocking lever  56  can be operated by one end of the slider  58 . The slider  58  is held by the fire detecting device  70  so that the slider  58  is not abutted to the rocking lever  504 . The fire detecting device  70  may be a smoke detector, temperature sensor or other fire detecting device, preferably a fusible link which is molten and broken at a temperature exceeding its melting point so that the slider  58  is released and hits the outer end of the rocking lever  56  and swings the inner end of the rocking lever  56 . Due to the projecting pin  561  extending into the sliding groove  521 , the bushing  52  is axially moved by the projecting pin  561  against so as to resist the disk spring  54  such that the bushing  52  is separated from the driven disc  141 . As a result, the coupling of the central shaft  12  and the first external shaft  14  is disconnected. 
     According to the present invention, the door operator can be modified into a failsafe door operator or a non-failsafe door operator easily. The most of components for the door operator can be applied to either the failsafe one or the non-failsafe one. Therefore, not only low manufacturing cost, fewer components and simplicity in production can be achieved, but also smaller inventory and easy replacement can be realized. 
     While the preferred embodiments have been described as above, it is noted that the preferred embodiments are not intended to restrict the scope of implementation of the present invention. Modifications and variations can be made without departing from the spirit and scope of the claims of the present invention.
A door operator of the fireproof door comprises a force applying end for releasing the reel of a door curtain, and a loading end for sustaining the weight of the door curtain. The rotary shaft comprises an internal (central) shaft and a plurality of external shaft coupled to each other via a clutch mechanism. The force applying end and the loading end act on the internal shaft and the external shaft respectively. A torsion spring brake mechanism is provided to resist the potential energy of the loading end by varying the inner diameter of the torsion spring so as to constantly restrain the rotary shaft from rotating, or to release the rotary shaft when the brake mechanism is subjected to an external force from the force applying end.