Belt pretensioning of an elevator car door synchronization and positioning system

Abstract: A pretensioning system for a relating cable (46) synchronizing movement of elevator car doors (12,14) includes a compression spring (76) and a spacer (78) disposed on one end of the relating cable. The compression spring is compressed to the length of the spacer disposed internally to the spring to calibrate tension in the relating cable so than a no slip condition is ensured.

Description: The present invention relates to elevator systems and, more particularly, to the movement and positioning of elevator car doors. In conventional elevator systems, elevator car doors are opened and closed by door operators which are electromechanical devices that use a rotary electric motor, mechanical drive linkages, and a controller box. In a two door center opening bi-parting configuration, the electric motor drives one of the elevator car doors through the mechanical linkage that is attached to that door. The other door is physically pulled by a relating cable extending over two pulleys with one end of the cable attached to one door and the other end attached to the other door. The relating cable is usually secured to the elevator car doors by means of tie rods so that tension in the cable can be adjusted periodically. Typically, an elevator maintenance person performs a visual inspection of the door operation and of tension in the cable. If the maintenance person observes that the relating cable is either too tight or too loose, he readjusts the cable in accordance with his visual observations. Although such process of adjustment of the relating cable is time consuming, labor intensive, and leaves some margin for error, it has been adequate, because the relating cable was primarily used for physically pulling the second door to either open or closed positions. However, if the relating cable is to be utilized for other purposes, an improved technique for setting proper tension in the relating cable is desired. Furthermore, for some applications it is critical to maintain a predetermined tension in the relating cable throughout the operation of the elevator car door system to minimize slippage between the pulleys and the relating cable. US 5,297,782 discloses a snubber for a tension member such as is used in garage door openers, and including a spring precompressed for use in a snubber when tightening a tension member and compensating gradual stretching thereof, and at the same time also keeping the tension actually applied within upper and lower limits relative to an initial tension setting. In this prior art solution the spring is mounted in a sub-assembly which releasably holds it in a precompressed state corresponding to an exact value of the return force; the spring is kept precompressed until the sub-assembly has been incorporated into a snubber and the tension member linked to the spring via a tie rod set up with its tension nut only finger-tight. If the spring is now released from the hold imposed. by the sub-assembly, its compression force will transfer to the tie-rod; however although the spring return force was exactly determined as long as it was held by the sub-assembly, some of this accuracy will inevitably be lost at this stage due to inherent residual slackness in the snubber's tension path. Viewed from one aspect the present invention provides a pretensioning system for a relating cable as claimed in claim 1. Viewed from a second aspect the invention provides a method of setting proper tension in a relating cable as claimed in claim 2. The invention allows the relating cable to be exactly tensioned and, therefore, minimizes slippage between the relating cable and its pulleys. An advantage of the invention is that it eliminates the need for a trial and error tensioning method and replaces visual tension setting with an exact method therefor. Another advantage of the invention is that it is cost efficient. First, the time spent by the maintenance person may be significantly reduced during initial installation and during periodic adjustments. Second, the pretensioning system itself need not be costly. An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- FIG. 1 is a schematic perspective view of a door system; FIG. 2 is a cut-away schematic perspective view of the door system of FIG. 1 including a pretensioning device, according to the present invention; and FIG. 3 is an enlarged schematic perspective view of the pretensioning device of FIG. 2. Referring to FIG. 1, a door system 10 for opening and closing a first door 12 and a second door 14 includes a first door hanger 16 and a second door hanger 18 suspending the first and second doors 12,14 therefrom, respectively. The door system 10 also includes a first linear motor primary 20 and a second linear motor primary 22, secured to the first and second door hangers 16,18 respectively, and a motor secondary 24 secured to a header bracket 28 which is attached to an elevator car (not shown). Referring to FIG. 2, a synchronization system 36 includes a first pulley 38 and a second pulley 40, attached to the header bracket 28 at opposite ends thereof. A relating cable 46 having a first end 48 and a second end 50 extends over the first and second - pulleys 38,40 to form a substantially continuous loop with an upper loop portion 52 and a lower loop portion 54. The pulleys 38,40 are lined with high friction polymer liners 59. A first door hitch 60 fixedly attaches the lower loop portion 54 of the relating cable 46 to the first door hanger 16. A second hitch 62 secures the first and second relating cable ends 48 and 50 to the second elevator car door hanger 18. Referring to FIG. 3, the first relating cable end 48 is fixedly secured within a first tie rod 66 that includes a threaded end 68 screwed into a first opening 69 in the second door hitch 62 and secured therein by means of bolts. The second relating cable end 50 is fixedly secured within a second tie rod 70 having a threaded end 72. The second tie rod 70 protrudes through a second opening 73 in the second door hitch 62. A pretensioning device 74 includes a compression spring 76 and a spacer 78 which are disposed between the tie rod end 72 and the second door hitch 62 and are secured thereon by means of a tension nut 80 and a lock nut 82. In operation, the linear motor drives the elevator car doors 12, 14 between open and closed positions. The motor primaries 16,18 respectively move the doors 12,14 in opposite directions. As the doors travel in opposite directions, the relating cable 46 interconnects the doors to synchronize their movements. The simultaneous response of both doors is achieved when the synchronization system 36 and the pretensioning device 74 ensure a no slip condition. The synchronization system 36 includes the high friction polymer liners 59 to minimize slippage between the pulleys 38,40 and the cable 46. The pretensioning device ensures that the optimum tension for a no-slip condition in the cable is set initially and can be easily adjusted during regular maintenance. To calibrate appropriate tension in the relating cable 46 during initial set up, the first end 48 of the relating cable 46 is secured in the first threaded opening 69 of the hitch 62 and adjusted to take up slack. Then the second end 50 of the cable is inserted through the second opening 73 of the hitch 62 to protrude therefrom, with the pretensioning device 74 placed on the protruding second end 50 of the relating cable. The tension nut 80 is placed on the second end of the cable to maintain the pretensioning device thereon and is adjusted until the coil compression spring 76 is compressed to meet the length of the spacer 78. When the compression spring is compressed to the length of the spacer, the optimal tension for a no-slip condition is established. To secure the load on the spring, which equals the tension load on the cable, lock nut 82 is tightened to meet the hitch 62. During regular maintenance, the maintenance person has to ensure that the tension nut 80 has not become loose, and that the spring remains compressed to the length of the spacer. The length of the spacer 78 is dictated by the spring constant of the coil compression spring 76 so that when the spring is compressed to the length of the spacer, the tension of the relating cable (which equals compression load of the spring) ensures a no slip condition. To ensure the no slip condition and to minimize stretching of the relating cable during operation of the elevator car doors, a prestretched aircraft cable of three millimeters (3 mm) diameter is used. An effective type of high friction polymer for fabricating the pulley liners is urethane. While the present invention has been illustrated and described with respect to a particular embodiment thereof, it will be appreciated that various modifications may be made. For example, although the illustrated embodiment depicts the pretensioning device operating on a door system driven by a linear motor, the present invention can be implemented on any type of a door operating system where slippage between cable and pulleys must be minimized. Also, although the illustrated embodiment depicts a two door center opening bi-parting configuration, the pretensioning system of the present invention is applicable to other door configurations such as a single slide door.

Claims: A pretensioning system for a relating cable (46) synchronizing movement of elevator car doors (12,14) in an elevator system, said relating cable extending over a first pulley (38) and second pulley (40) and being attached to said elevator car doors by means of first and second hitches (60,62), said relating cable having a first cable end (48) secured in a first threaded tie rod (66) and a second cable end (50) secured in a second threaded tie rod (70), said first tie rod being connected in use to the second hitch (62) such that the first cabte end (48) is disposed to one. side of the second hitch; said pretensioning system comprising: said second hitch (62) and said second tie rod (70), whereby said second tie rod (70) is connected to the second hitch (62) such that the second cable end (50) is disposed to the opposite side of the second hitch; a tension nut (80) threadedly engaged upon said second tie rod (70); a compression spring (76) disposed about said second tie rod so as to present a first end in cooperation with the tension nut (80) and to present a second end in cooperation with said one side of said second hitch (62); a spacer (78) disposed on said second tie rod (70) between said tension nut and said second hitch such that when said tension nut (80) is adjusted in use to compress said compression spring (76) to a length corresponding to that of said spacer (78) a predetermined tension is applied to said second tie rod relative to the second hitch (62); and a lock nut (82) threadedly engaged upon said second tie rod on said opposite side of said hitch (62) so as to be adjustable in use so as to lock said spring at the length determined by said spacer (78). A method of setting proper tension in a relating cable (46) synchronizing movement of elevator car doors (12,14) in an elevator system, said method comprising the following steps: securing a first tie rod (66) to a hitch (62) attached to a door hanger (18) a first end (48) of said relating cable being disposed to one side of said hitch and being joined to said first tie rod; securing a second tie rod (70) to said hitch whereby said second tie rod is joined to a second end (50) of said relating cable disposed to the opposite side of said hitch, and said securing is performed by disposing both a compression spring (76) and a spacer (78) about said second tie rod each, with a first end thereof in cooperation with a tension nut (80) threadedly engaged upon said second tie rod and with a second end thereof in cooperation with said one side of said second hitch; adjusting said first tie rod of said relating cable to take up slack; adjusting the tension nut (80) disposed on said second tie rod of said relating cable until the compression spring (76) is compressed to a length corresponding to that of the spacer (78) ; and adjusting a lock nut (82) threadedly engaged upon said second tie rod so as to cooperate with said second hitch on said opposite side thereof so as to lock said spring compressed to the length determined by said spacer (78). An elevator system comprising a pretensioning system as claimed in claim 1.

Inventors: BARRET DALE R, RIVERA JAMES A, SWAYBILL BRUCE P, BARRET, DALE R., RIVERA, JAMES A., SWAYBILL, BRUCE P.
Applicants: OTIS ELEVATOR CO, OTIS ELEVATOR COMPANY
Application year: 1997
Main classification: B66B13
IPC codes: F16H7, F16G11, B66B13