Abstract:
A method and apparatus for facilitating closure of an elevator hoistway door generally comprises the steps of affixing a door closer device to the hoistway door and securing a cable, extended from the door closer device, to a terminal off the hoistway door. The door closer device comprises a sheave repeatedly circumscribed by an elongate channel for receiving the cable therein and a spring adapted to oppose extension of the cable from said door closer device. The channel, which generally prevents overlap of the cable during retraction into the door closer device, preferably forms a conical helix during the final retraction of the cable, thereby increasing the force exerted upon the door by the cable as the door approaches the door closed position.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to elevator safety devices.  
           [0002]    More particularly, the invention relates to a mechanical door closer for increasing the closing force on the door as it approaches the door closed position.  
         BACKGROUND OF THE INVENTION  
         [0003]    Modern elevator installations typically comprise one or more hoistway door panels  41  on each landing to block access to the hoistway door  10  when the elevator cab is not present. As shown in FIG. 1, the hoistway door panels  41  are typically suspended from the hoistway header  16  by a plurality of hangers  11 . The panels  41  are usually affixed to the hangers  11  with conventional mounting bolts  14 . The hangers  11 , which usually comprise one or more pulleys  12 , allow lateral translation of the door panels  41  along a track  15  affixed to the hoistway header  16 . A relating cable  17  is generally provided in multiple panel installations in order to coordinate the opening and closing of the panels  41 . As is generally known to those of ordinary skill in the art, a relating cable door clamp  18  affixed to one hoistway door panel  41  and a relating cable dead end clamp  19  affixed to the other hoistway door panel  41  establishes the desired operating relationship between the panels  41 .  
           [0004]    As is also known to those of ordinary skill in the art, the hoistway door  10  is opened and closed in normal operation through interaction with the cab door (not shown) as the cab comes to rest at a particular landing. In particular, a power door operator, which is normally located atop the cab, opens or closes the cab door through a drive arm, cable, belt, screw drive or the like. A clutch mechanism engages a roller assembly  20  to couple the cab door to the hoistway door  10  for opening and closing. A vertically disposed clutch on the cab door then engages an upper clutch roller  22  and lower clutch roller  23  as the cab settles upon a landing. Because the lower clutch roller  23  is generally offset from the upper clutch roller  22 , engagement of the clutch with the rollers  22 ,  23  serves to release a mechanical latching device  25  through an interposed clutch linkage  24 . Release of the mechanical latching device  25  allows the hoistway door  10  to be opened as a lateral force is applied from the cab door to the rollers  22 ,  23  through the clutch.  
           [0005]    As the cab prepares to leave a particular landing, the power door operator reverses the position of the drive arm (or other device) to force the cab doors closed. The clutch engages the rollers  22 ,  23  from their side opposite that engaged during the opening operation, thereby forcing the hoistway door  10  closed and re-engaging the mechanical latching device  25 . Additionally, electrical contacts  26 , typically collocated with the mechanical latching device  25  in an interlock assembly, will then signal the elevator controller to confirm that the hoistway door  10  has in fact been closed, enabling the elevator cab to depart the landing.  
           [0006]    Because the device  25  may fail, however, additional safety devices are generally required in order to ensure that the hoistway door  10  closes and remains closed if, for any reason, the elevator cab leaves the landing prior to door closing. Typically, a door closer device  27  is provided to facilitate and ensure closing of the hoistway doors  10 . In the past, the door closer device  27  has generally comprised a closer reel attached to one of the hoistway door panels  41  by a bearing or bushing assembly  30  located in a passage  42  around the central axis  31  of the door closer device  27 . A spring  32  within a spring cavity  28  engages a ratchet  29  within the door closer device  27  to produce tension on a closer reel cable  33 , which may be extended from the door closer device  27 . A distal end of the closer reel cable  33 , generally terminated with a cable eyelet  34 , is fixedly secured to the hoistway header  16  through a cap screw  35 . As is known to those of ordinary skill in the art, however, the cable eyelet  34  may, in multiple door installations, be affixed to a second hoistway door panel  41 . Likewise, as is known to those of ordinary skill in the art, the door closer device  27  could be affixed off of the hoistway door  10 —for example, on the hoistway header  16 , while the cable  33  is affixed to one of the door panels  41 .  
           [0007]    In operation, as the hoistway door  10  opens, the closer reel cable  33  is extended from the door closer device  27 . As the closer reel cable  33  is pulled from the doors closer device  27 , increasing opposing force is applied on the reel cable  33  from the spring  32 . In the event of an electrical or mechanical failure preventing the otherwise normal closing of the hoistway door  10 , tension on the closer reel cable  33  serves to ensure that the hoistway door  10  closes and remains closed. Unfortunately, the door closers as presently known the art are often ineffective in extreme conditions.  
           [0008]    In windy areas, such as coastal or lakeshore regions, or in air conditioned buildings with windows that may be opened, an in rush of air is often created during heavy traffic hours as a result of the negative pressure in the building. This in rush of air causes an air current in the hoistway, which acts as an air duct. As the elevator cab reaches a landing, air pressure within the hoistway escapes rapidly through the hoistway door  10 . As the door  10  attempts to close, a jet nozzle effect is created whereby the resultant high wind velocity puts such a stress on the hoistway door  10  that it often fails to close, causing the elevator to initiate a recycle mode. In this condition, the known door closer devices  27  are generally unable to force the hoistway door  10  to close. To date, the solution to this problem has resided in a call-back for maintenance for the elevator. In response to the call-back, the service technician generally adds a loop of the closer  20  reel cable  23  about the closer reel, thereby increasing tension on the spring  32 . Unfortunately, as wind conditions change, or traffic flows through the building lessen, the excess tension on the closer reel cable  33  can cause the hoistway door  10  to close too rapidly in the absence of the jet nozzle effect. The door panels  41  come together with excess force and the result is again that the elevator enters a recycle mode and fails to operate. To date, as before, the typical response has been yet another maintenance call-back whereafter the service technician will remove the previously added cable loop from about the closer reel.  
           [0009]    It is therefore an overriding object of the present invention to improve upon the prior art by providing a door closer device and method that is able to effectively operate a hoistway door in a variety of weather and/or usage conditions.  
           [0010]    It is a further object of the present invention to provide such a door closer device that is reverse compatible with existing installations and of comparable expense to those presently available.  
           [0011]    Finally, it is yet another object of the present invention to provide such a door closer device that has an extended life cycle, thereby reducing cost to the elevator owner and maintaining elevator contractor.  
         SUMMARY OF THE INVENTION  
         [0012]    In accordance with the foregoing objects, the present invention—a method and apparatus for facilitating closure of an elevator hoistway door—generally comprises the steps of affixing a door closer device to the hoistway door and securing an end of a cable to a terminal off the hoistway door. The door closer device comprises a sheave repeatedly circumscribed by an elongate channel, for receiving the cable, and a spring adapted to oppose extension of the cable from the door closer device. In the preferred embodiment, the channel forms a conical helix during the final retraction of the cable as it moves the door to the door closed position, thereby countering any weakening of the spring as the cable is finally retracted into the door closer device and producing an increased force on the cable near the door closed position.  
           [0013]    Finally, many other features, objects and advantages of the present invention will be apparent to those of ordinary skill in the relevant arts, especially in light of the foregoing discussions and the following drawings, exemplary detailed description and appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    Although the scope of the present invention is much broader than any particular embodiment, a detailed description of the preferred embodiment follows together with illustrative figures, wherein like reference numerals refer to like components, and wherein:  
         [0015]    [0015]FIG. 1 shows, in a partial side elevational view, a typical center opening hoistway door installation as may incorporate the teachings of the present invention;  
         [0016]    [0016]FIG. 2 shows, in an exploded perspective view, the door closer device as manufactured according to the preferred embodiment of the present invention;  
         [0017]    [0017]FIG. 3 shows, in a bottom cross-sectional view taken along the line  3 - 3  of FIG. 5, the door closer device of FIG. 2;  
         [0018]    [0018]FIG. 4 shows, in a top cross-sectional view taken along the line  4 - 4  in FIG. 5, the door closer device of FIG. 2;  
         [0019]    [0019]FIG. 5 shows, in a side elevational view, the door closer device of FIG. 2;  
         [0020]    [0020]FIG. 6 shows, in a side cross-sectional view taken along the lines  6 - 6  in FIG. 4, the door closer device of FIG. 2;  
         [0021]    [0021]FIG. 7 is a graph showing the relationship, in a conventional commercially available door closer, between the force produced by the spring and the force produced at the end of the cable;  
         [0022]    [0022]FIG. 8 is a graph showing the relationship, in a prior art door closer of one design, between the force produced by the spring and the force produced at the end of the cable;  
         [0023]    [0023]FIG. 9 is a graph showing the relationship, in a prior art door closer of another design, between the force produced by the spring and the force produced at the end of the cable; and  
         [0024]    [0024]FIG. 10 is a graph showing the relationship, in a door closer of this invention, between the force produced by the spring and the force produced at the end of the cable. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    Although those of ordinary skill in the art will readily recognize many alternative embodiments, especially in light of the illustrations provided herein, this detailed description is exemplary of the preferred embodiment of the present invention, the scope of which is limited only by the claims appended hereto.  
         [0026]    Referring now, in particular, to FIGS. 2 through 6, the door closer device  27  of the present invention is shown to generally comprise a sheave or reel  36  formed by providing an elongate channel  37  repeatedly about the circumference of the closer reel. In a preferred embodiment, the channel  37  forms a section of more-or-less constant diameter on one side of the reel and a conical helix  38  in approximately the last twelve inches of draw of the closer reel cable  33 . In particular, conical helix  38  is calculated so the cable  33  delivers a door closing force that increases during the last movement of the cable  33  despite the fact that the spring  32  is delivering less force near the door closed position as will be more fully explained hereinafter in conjunction with the description of FIGS.  7 - 10 . Although the exact dimensions for the conical helix  38  will vary depending upon the particular installation, the calculations necessary to arrive at the desired result are readily within the grasp of those of ordinary skill in the art. As also shown in the Figures, a top plate  39  and a bottom plate  40  are provided as known in previously employed embodiments. The top plate  39  in the present invention serves also to ensure that should the closer reel cable  33  become disengaged from the channel  37  that the cable  33  will remain about the sheave  36 , whereafter one cycle of the door closer device  27  the cable  33  will automatically reengage the channel  37 .  
         [0027]    In operation, the tension provided to the closer reel cable  33  from the spring  32 , which ordinarily falls off during the final retraction of the cable  33  due to operation of spring  32  at the extent of its effective region, is compensated by two factors. First, maintenance of cable the closer reel  33  within the channel  37  prevents overlapping of the cable  33 , thereby maintaining the radius of the moment arm about central axis  31  through the door closer device  27 . Second, during the final retraction of the cable  33 , direction of the closer reel cable  33  into the conical helix  38  reduces the radius of the moment arm about central axis  31 . In this manner, the reduction in force resultant operation in the weaker region of the spring  32  is counteracted by the design of the sheave  36 .  
         [0028]    FIGS.  7 - 10  are analogous. Each shows the force produced by a spring of a door closer and the force produced by the cable. The door closed position is shown on the right and the door open position is shown on the left. The slopes of the lines are exaggerated for purposes of illustration. The values in FIG. 10 for the force produced by the cable were obtained by attaching the cable to the hook of a weighing device of the type incorporating a spring. The force produced by the cable was measured at various distances from the door closer.  
         [0029]    [0029]FIG. 7 shows a line  43  representing the force produced by the spring of a conventional commercially available door closer and a line  44  representing the force produced on the end of the cable of a conventional commercially available door closer. A conventional commercially available door closer includes a spiral spring driving a reel of constant diameter on which the cable is wound. A typical commercially available door closure is Model ML-4402 available from the Hunter Spring Division of Ametek, Hatfield, Pa. A comparison of the lines  43 ,  44  shows that the reel provides no mechanical advantage to the cable, which is predictable because the reel is of constant diameter. It will be seen that the line  43 , being above the line  44 , shows that the spring delivers slightly more force than is delivered by the cable, the difference being lost in conventional mechanical ways, as through friction and the production of heat. It will also be seen that the spring and cable produce the minimum force when the door is at, or approaches, the door closed position and the maximum force when the door is at, or approaches, the door open position. In a way, this is logical because at the door open position, the door closer has to produce a maximum force to overcome inertia of the door and door closing mechanisms.  
         [0030]    [0030]FIG. 8 shows a line  45  representing the force produced by the spring of the device shown in Australian Patent 113,360 and a line  46  representing the force produced on the end of the cable of a conventional commercially available door closer. This door closer has a reel which is conical from back to front in a more-or-less constant manner. A comparison of the lines  45 ,  46  shows that the reel provides an increasing mechanical advantage to the cable as the cable approaches the door closed position, which is predictable because the reel is of minimum diameter at the door closed position and maximum diameter at the door open position. Thus, the lines  45 ,  46  diverge toward the door open position where the mechanical advantage is least. It will be seen that the line  45 , being above the line  46 , shows that the spring delivers slightly more force than is delivered by the cable, the difference being lost in conventional mechanical ways, as through friction and the production of heat.  
         [0031]    [0031]FIG. 9 shows a line  47  representing the force produced by the spring of the device shown in U.S. Pat. No. 5,054,162 and a line  48  representing the force produced on the end of the cable of this device. This door closer has a reel which is conical from back to front and is steeply sloped toward the back of the reel. A comparison of the lines  47 ,  48  shows that the reel provides a substantially increasing mechanical advantage to the cable as the cable approaches the door closed position, which produces a constant force on the cable from the door open position to the door closed position. Thus, the line  47 , representing the force delivered by the spring, slopes to a minimum force at the door closed position while the line  48 , representing the force delivered by the cable, is substantially constant throughout. It will be seen that the line  47 , being above the line  48 , shows that the spring delivers slightly more force than is delivered by the cable, the difference being lost in conventional mechanical ways, as through friction and the production of heat.  
         [0032]    [0032]FIG. 10 shows a line  49  representing the force produced by the spring of this invention. Spiral springs of the type used in door closing devices produce force diagrams of substantially different shape and slope, depending on the design of the spring and the line  49  is merely representative of a typical spiral spring. Thus, the line  49  is illustrated as generally linear which is a typical force diagram of a spiral spring of modern design. So far as is known, all commercially available spiral springs produce greater force when they are wound up, i.e. at the door open position, than when they are paid out, i.e. at the door closed position.  
         [0033]    The curve  50  represents the force produced on the end of the cable of this device. It will be seen that the curve  50  is of complex shape having a section  51  which is more-or-less parallel to the line  49  and represents the situation where the cable is being wound or unwound off the large more-or-less constant diameter section of the reel or sheave  36 . The shape of the curve  50  changes at a location  52  which is where the cable begins to wind or unwind on the conical helix  38 . The section  53  of the curve  50  shows that the force applied by the cable increases as the door approaches the door closed position. Thus, the location  52  is about twelve inches from the end of cable movement although this distance is subject to considerable selection.  
         [0034]    Thus, the door closer of this invention provides an optimum force for the operation of hoistway doors. The maximum force of the spring is available at the door open position which is advantageous to start movement of the door and overcome its inertia and the inertia of the door moving mechanisms shown in FIG. 1. Instead of the force of the cable falling off to a minimum, or even remaining constant, at the door closed position, the force delivered by the cable  33  increases to overcome any extraneous forces on the door, such as induced by wind, tending to prevent the door from closing.  
         [0035]    The delivery of optimum forces by the door closer of this invention is accomplished with a door closer of minimum thickness which allows the door closer to be used to retrofit existing conventional door closers and occupy the limited space available.  
         [0036]    Applicant has found, through testing, that the force obtained as a result of this novel implementation is generally sufficient to overcome the jet nozzle effects of wind without the necessity for the repeated maintenance call-backs inherent in the prior art. Additionally, in the preferred embodiment of the present invention, Applicant has found that the cable lifetime may be extended through operation within the channel  37  due to the prevention of kinking and bending as the cable  33  would otherwise overlap itself. Finally, because the sheave  36  of the present invention is preferably manufactured of a lubricant impregnated plastics material, minimum friction with the cable  33  is generated and the components coming into contact with the sheave  36  are protected from corrosion.  
         [0037]    While the foregoing description is exemplary of the preferred embodiment of the present invention, those of ordinary skill in the relevant arts will recognize the many variations, alterations, modifications, substitutions and the like as are readily possible, especially in light of this description, the accompanying drawings and claims drawn thereto. In any case, because the scope of the present invention is much broader than any particular embodiment, the foregoing detailed description should not be construed as a limitation of the scope of the present invention, which is limited only by the claims appended hereto.