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BACKGROUND OF THE INVENTION 
     The invention relates to freight elevator landing doors and, in particular, to a device for stopping a vertically operating door in the event its suspension fails. 
     PRIOR ART 
     Freight elevator doors are typically arranged to slide vertically to open and close the opening to a hoistway and an elevator car. A common arrangement for such a door comprises a pair of bi-parting panels, an upper panel and a lower panel, that move vertically towards one another to close and vertically away from one another to open. Other vertically sliding door panel arrangements include slide up to open single or double panels, for example, and slide down to open panels. Ordinarily, each door panel is suspended by a chain, cable or other flexible strand-like element adjacent its vertical edges. The suspension chains and related components can fail through undetected wear and/or accidental damage, for example. Where a chain breaks, the door panel has the potential to fall and cause personal injury and/or property damage to objects below the panel as well as to the panel itself. In such a circumstance, it is desirable to provide a safety stop or brake that will automatically deploy upon failure of a chain and prevent the door panel from falling. U.S. Pat. No. 4,696,375 proposes an elevator door check that is activated when a suspension chain breaks. The device shown in this patent involves a wedge block that must be mounted in such a way as to permit movement relative to the door panel. The inertia of the block can slow its reaction time and any resistance on the surfaces constraining its movement can lead to a malfunction. This patent does not disclose an arrangement that can be used with a lower panel of a bi-parting door unit. From the foregoing, it is apparent that there exists a need for a door panel brake responsive to failure of the suspension chain that is reliable, simple to install and adjust and that can be readily utilized on both the upper and lower panels of a bi-parting door. 
     SUMMARY OF THE INVENTION 
     The invention provides a safety brake for vertically sliding freight elevator doors that is responsive to the failure of a suspension chain. The brake is readily adapted to conventional door panels and combinations of panels such as found in bi-parting door types, raise to open types, and lower to open types. The brake of the invention comprises a caliper housing or block fixed to the door panel and a roller cam in the caliper that work in conjunction with a door guide rail. The roller cam is released from an inactive position when a chain breaks, thereby enabling it to wedge lock the caliper to the guide rail. The caliper block and roller cam are preferably configured to enable to the roller cam to be retained in the inactive position, against a bias spring by a cable. The cable restraint feature enables the same basic brake caliper and roller cam components to be used on both upper and lower door panels with only limited variation in hardware to accommodate differences in the locations of a suspension chain relative to the associated door panel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational view of a freight elevator landing door having the safety brake device of the invention installed thereon; 
         FIG. 2  is a side elevational view of a safety brake device associated with an upper door panel taken along the line  2 — 2  in  FIG. 1  in a normal condition; 
         FIG. 3  is a sectional view of the safety brake device of  FIG. 2  taken in the staggered plane  3 — 3  in  FIG. 2 ; 
         FIG. 4  is a side elevational view similar to  FIG. 2 , but with an associated section of chain missing to represent breakage thereof and with the device in a door panel braking position; 
         FIG. 5  is a view of the braking device taken in the staggered plane  5 — 5  in  FIG. 4 ; 
         FIG. 6  is a side elevational view of a safety brake device associated with a lower door panel taken in the plane  6 — 6  in  FIG. 1  in a normal condition; 
         FIG. 7  is a sectional view of the safety brake device of  FIG. 6  taken in the staggered plane  7 — 7  in  FIG. 6 ; 
         FIG. 8  is a side elevational view similar to  FIG. 6 , but with an associated section of chain broken and with the device in a door panel braking position; and 
         FIG. 9  is a view of the braking device taken in the staggered plane  9 — 9  in  FIG. 8 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and, in particular to  FIG. 1 , there is shown a freight elevator landing door  10  from the hoistway or shaft side of the door. The illustrated door  10  is a bi-parting type having upper and lower vertically sliding panels  11  and  12 . In a conventional manner, the door panels  11 ,  12 , move in opposite directions-toward one another to close and away from one another to open. Typically, the panels  11 ,  12  are fabricated of sheet steel and structural steel elements such as angles and channels. The panels  11 ,  12  are guided for vertical movement on parallel vertical guide rails  16 , one adjacent each vertical edge  17 ,  18  of the panels  11 ,  12 , respectively. The guide rails  16  are fixed to the building or other static structure by bolting, welding, or other appropriate technique. The guide rails have a U-shape or J-shaped shape cross-section; one of the flanges of each rail is fixed to the static structure as described and the opposite flange, designated  21  in the figures, serves to guide the respective edges  17 ,  18  of the panels  11  and  12  for vertical movement. Replaceable guide shoes  22 , two pair per panel  11 ,  12 , are bolted to angles  23  at the vertical panel edges  17 ,  18 . The guide shoes  22  are slotted to permit them to receive the guide rail flange  21  of the adjacent guide rail  16 . This arrangement, which is generally conventional, assures that the panels  11 ,  12  to which the guide shoes  22  are fixed, move vertically in alignment along the guide rails  16 . 
     In a conventional manner, the weight of each door panel  11 ,  12  is used to counterbalance the weight of the other door panel. This is accomplished with roller chains  26  trained over rotatable pulleys  27  fixed in the hoistway at points generally overlying the vertical edges  17 ,  18  of the door panels  11 ,  12 . Weights can be added to one of the door panels to balance the other, as necessary. 
     Safety brake devices  31 ,  32 , constructed in accordance with the invention, are mounted on the door panels  11 ,  12 , respectively and, in response to breakage of the chain  26  are effective to stop or check downward free-fall movement of the respective panel. The safety brake devices  31 ,  32  are symmetrical with one another from one vertical edge  17  to the other  18 .  FIGS. 2–5  depict a safety device  31  employed on the upper panel  11 . The device  31  includes a caliper housing or block  33 , a roller cam  34 , and an actuating spring  36  of the compression type. The caliper block  33  is preferably made of steel or other suitable high-strength material and can be cast, forged, machined, or otherwise formed into the illustrated configuration. The caliper block  33  can be made of an integral body or can be assembled from two or more parts. The block  31  is bolted to the panel vertical edge angle  23  by bolts assembled through a set of three holes  37  extending through the block. In its installed orientation, the block  33  has a vertical slot  38  that is adapted to receive the flange  21  of the adjacent guide rail  16 . The slot  38  is bounded on opposite sides by a vertical surface  39  and a wedging surface  41  tilting from the vertical and converging towards the opposed surface  39  such that it is closer to the vertical surface with increasing elevation or distance upwards along the slot  38 . In the illustrated construction, the surfaces  39 ,  41  are planar and are aligned such that an imaginary horizontal plane passing through these surfaces will intercept each surface at a line which is parallel to the line at the other surface. 
     A lower end of the wedging surface  41  merges with a more or less semi-cylindrical surface  42  having a radius preferably at least slightly larger than the outer surface  43  of the roller cam  34 , which is preferably cylindrical. As shown in  FIG. 2 , the roller cam  34  is adapted to be received in a cavity bounded by the cylindrical surface  42  and wedging surface  41 . When in this cavity, the roller cam  34  does not contact the guide rail flange  21 . The roller cam  34  is held or restrained in this cavity in normal conditions by a cable  46  wrapped around it and received in a peripheral groove formed in the outer surface  43  at its mid-section. The groove is of sufficient depth and width to fully receive the diameter of the cable  46  such that the cable is radially inward of the outer cylindrical surface  43 . The adjacent end of the cable  46  is crimped onto the cable in a known manner to form a loop into which the roller cam is assembled and which is loose enough to enable the roller cam to rotate in the loop. The compression spring  36  is received in a cylindrical hole  49  drilled or otherwise formed in the caliper block and communicating with the cavity. A bracket  51  fixed on a lower end of the block  33  with bolts  50  retains the compression spring  36  in the hole  49 . The bracket  51  has a depending clevis portion  52  that carries a pin  53  on which a bell crank lever  54  pivots. The cable  46  is assembled through the center of the spring  36 , a hole in the bracket  51  and has its end remote from the roller cam  34  secured at a hole in an upper arm  57  of the lever  54  by a crimped collar  58 . 
     An extension  59  on a lower arm  61  of the bell crank lever  54  bears against the chain  26  normally carrying the weight of the upper panel  11  as well as the lower panel  12 . Tension in the chain  26  allows each panel  11 ,  12  to balance the weight of the other panel. The chain  26  is attached to the upper panel  11  with a chain rod  71  assembled through and anchored to a bracket  72  bolted to the upper panel  11 . Tension in the chain  26 , due to the weight of the door panels  11 ,  12 , ordinarily prevents counterclockwise rotation of the bell crank lever  54  (as viewed in  FIG. 3 ). The length of the cable  46  is arranged to control and keep the roller cam  34  in the cylindrical portion of the cavity when the chain  26  maintains the bell crank  54  in the position illustrated in  FIGS. 2 and 3 . Inspection of  FIG. 2  reveals that the caliper housing or block  33 , rigidly fixed to the door panel  11 , is ordinarily arranged to slide freely along the door guide rail flange  21 . 
     In the event that the chain  26  supporting the door panel  11  breaks or otherwise suffers a loss of tension, the bell crank lever  54  is released. The bell crank  54  is thereby enabled to pivot counter-clockwise under a bias force developed by the compression spring  36  and transmitted by tension in the cable  46 . Tension in the cable  46  is released when the bell crank  54  is freed by loss of tension in the chain  26  to pivot counter-clockwise and, in turn, the cable releases the compression spring  36  from the compressed condition of  FIGS. 2 and 3 . The spring  36  forces the roller cam  34  upwardly out of the cavity or seat area into contact with the guide rail flange  21  and the wedging surface  41 . The outer cylindrical surface  43  of the roller cam  34  can be knurled to increase its friction with the guide rail flange  21  and caliper block surface  41 . While the roller cam  34  is being raised relative to the caliper block  33  by the spring  36 , the associated upper door panel  11  and the caliper block fixed to it have a tendency to begin to free fall. The roller cam  34 , as a result of its upward movement in the caliper block  33  and any initial downward movement of the caliper block relative to the guide rail flange  21 , is very quickly wedged tightly between the guide rail flange and the wedging surface  41 . This action causes the caliper block  33  to be frictionally locked to the guide rail flange  21  and the door panel  11  is thereby immediately braked against further downward movement. More specifically, because of the wedging action by the wedging surface  41  against the roller cam, the vertical surface  39  forming one side of the slot  38  is tightly frictionally locked against the guide rail flange  21 . From the foregoing discussion, it will be evident that the caliper block  33  is frictionally locked to the guide rail  16  and the door panel  11  is thereby braked against further downward movement. 
     The lower door panel  12  at each vertical edge  18  is suspended by a length of the chain  26  secured to a chain rod  71 . The chain rod  71  is assembled with a slip fit through bores in a bracket  72  fixed to the lower door panel. Jam nuts  73  threaded on a lower end of the chain rod  71  adjustably locate the chain rod relative to the door panel  12 . Assembled on the rod  71  above the nuts  73  is a tension plate  74 . From this description, it will be understood that the chain rod  71  and, of course, the chain  26 , bears the weight of the lower door panel  12  at the respective end or vertical edge  18  of the panel. The safety brake device or assembly  32 , like the device or assembly  31  described above in connection with the upper panel  11  is fixed to each vertical edge or end  18  of the panel  12 . Like the safety brake devices  31  associated with the upper panel, the lower panel safety brake devices  32  are symmetrical from one vertical edge  18  to the other. The safety brake device  32  mounted on the right vertical edge  18  of the lower panel  12  in  FIG. 1  is shown in greater detail in  FIGS. 6–9 . The brake device or assembly  32  includes a caliper block  33 , roller cam  34 , and compression spring  36  that can, as shown, be identical to that described in  FIGS. 2–5  for the upper panel  11 . As with the upper door panel, the caliper block  33  is rigidly fixed to the vertical structural angle  23  with three bolts assembled through holes  37  in the block and the slot  38  is arranged to receive and normally slide along the vertical guide rail flange  21 . 
     A J-shaped bracket  76  is secured to the bottom of the caliper block  33  with bolts  50 . The bracket  76  has a pair of holes in vertical alignment with the axis of the spring receiving bore or hole  49 . A cable  77  having one end looped around and locked into the peripheral groove in the roller cam  34  is threaded through the bracket holes  78 ,  79 . The cable  77  is routed over a lower face  81  of a flange  82  of the bracket  76  and vertically over an outer face of a web  83  of the bracket. An end of the cable  77  remote from the roller cam  34  is anchored in a threaded bolt  84 . The bolt  84  is received in a hole or slot in the tension plate  74  associated with the chain rod  71 . A threaded nut  86  on the bolt  84  permits the bolt to be axially adjusted in the vertical direction in the plate  74  so that when the various parts are assembled, the cable  77  can be properly tensioned to control and hold the roller cam  34  in the recess or cavity and out of contact with the guide rail flange  21 . 
     In the event that the suspension chain  26  breaks or some other mishap occurs where the chain supporting the weight of the respective end of the lower panel  12  loses tension, the chain rod  71  is enabled to drop in the bracket  72  and move downwards relative to the door panel  12 . Relative motion between the chain rod  71  and tension plate  74  releases tension on the cable  77  so as to allow the compression spring  36  to extend and force the roller cam into a wedging action between the wedging surface  41  and guide rail flange  21 . In a manner like that described in connection with the upper panel  11  and the associated safety brake device  31 , the lower safety brake device  32  very quickly stops any tendency of the lower panel to free fall by frictionally locking the device relative to the guide rail  16 . 
     It will be seen that the devices  31 ,  32  share common parts so as to minimize cost and inventory. The control of the roller cam  34  through simple cables  46  and  77  enables the devices  31 ,  32  to be constructed without close dimensional tolerances and with minimal inertia so as to assure a quick response in release of the roller cam  34 . It will be understood that the safety brake devices  31 ,  32  at each end or vertical edge of a panel are symmetrical with the devices on the opposite panel end. 
     While the invention has been shown and described with respect to particular embodiments thereof, this is for the purpose of illustration rather than limitation, and other variations and modifications of the specific embodiments herein shown and described will be apparent to those skilled in the art all within the intended spirit and scope of the invention. Accordingly, the patent is not to be limited in scope and effect to the specific embodiments herein shown and described nor in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention.

Summary:
A vertically sliding freight elevator landing door with a safety brake that deploys when a chain suspending the door breaks. The safety brake is adapted for use on both panels that slide up to open or that slide down to open. The brake, which is simple in construction and installation, comprises, principally, a caliber block fixed to the door and a roller cam assembled in the block. A spring biases the roller cam towards a wedge lock position while a cable normally holds the roller cam in an inactive position. The cable and, therefore, the roller cam are released when the associated door suspension chain breaks. The roller cam, operating between a tilted internal surface in the caliper block and a door guide rail quickly frictionally brakes the door on the guard rail.