The basic elements of an elevator system are five fold, namely: a sheave, a counterweight, an elevator car, a compensating cable or counterweight, a hoist rope and a traveling cable. All of these elements are assembled in an elevator well or shaft in a well known manner. As a general rule the elevator car (or cab) is connected to the counterweight by a hoist rope threaded over one or more sheaves or pulleys in the upper reaches of the shaft. One end of the compensating cable is connected to the counterweight and the other to the bottom of the car, and in some cases, a "U" shaped portion therebetween is threaded over a compensating or guidance sheave located in the bottom of the elevator well. In most instances, however, the compensating cable is left to hang free without its midsection being threaded over a compensating or guidance sheave. One end of the traveling cable is connected to the car bottom and the other to a junction box affixed to an elevator sidewall over which signals are sent to a means causing the car to obey the commands sent thereover. The counterweight is essentially the same weight as the car and the weight of the hoist ropes essentially equal the weight of the compensating cable, as more fully disclosed hereafter.
The prime function of the compensating cable is to provide a dynamic counter balancing weight to the weight of the hoist rope(s) as the car goes up and down in the elevator shaft, i.e., to provide a dynamically balanced system. For optimum performance the aggregate weight of the hoist rope and traveling cable should be essentially equal to the weight of the compensating cable at any given position of the car in the elevator shaft. In addition, the length of the hoist rope between the car and and the overhead sheave should be equal to the length of the compensating cable between the counter weight and the lowest portion of the compensating chain or cable. Stated alternatively, the length of the hoist rope from car to counter weight is essentially equal to the length of the compensating cable from car to counter weight.
Before the recent introduction of an elevator compensating cable under the trademark "WHISPER-FLEX," prior art compensating cable usually were basically a link chain. Constantly raising and lowering of the elevator cab or car caused the chain to be raised and lowered, rubbing one link against another, resulting in noise and abrasion. Link chains when hung free in an elevator shaft (no bottom sheave) have a tendency to form a "point" and not a loop, i.e., the side legs of the chain tend to converge on a single link and form a point at the terminal "loop" formed by the chain. Such a configuration results in the propensity of one leg of the chain to rub against the other during car movement. Noise and abrasion result. More often than not, chain type compensating cable bang into the sidewalls of elevator shaft and cause damage and additional noise. Such noise was so much of a problem that some prior art compensating chain type cables either use a sash cord (a rope woven in the links of the chain) or employed a plastic coating over the link chain. One such commercially available compensating chain, sold under the mark "QUIET LINK" and advertised to reduce noise and the need for a sash cord, was a link chain disposed in a plastic sheath, the plastic sheath being drawn down as close as possible to the individual link members. See, for example, U.S. Pat. No. 3,574,996.
Disclosed in U.S. patent application Ser. No. 405,147 filed Aug. 8, 1982 entitled "Elevator Compensating Cable," is a solution to the problems previously encountered by the prior art at cab speeds of 350 fpm and less. However, at speed in excess of 350 fpm, several problems of unwanted cable motion arose, not previously recognized by the prior art. One problem was vertical or longitudinal vibrations encountered once an elevator cab came to a halt after a prior travel speed of over 350 fpm. The car and cable tend to vibrate slightly along the vertical axle of the elevator well, i.e., along the longitudinal axis of the compensating cable. Another and more significant problem not previously recognized by the prior art was the failure of the compensating cable to travel a truly "U" shaped path as the elevator car or cab went up and down at speeds in excess of 350 fpm. Motionless the compensating cable would ultimately hang true (a truly vertical "U" shaped) representing the lowest form of free energy of the cable. It would travel true at speeds of 350 fpm or less, but once the speed was increased beyond the 350 fpm barrier, the true vertical axis of the "U" shaped compensating cable began to deviate and lean to one side or the other (left or right) depending on whether the car was descending or ascending. For example, the vertical axis of the "U" shaped compensating cable would lean towards the leg of the "U" attached to the counter weight on descent and towards the leg of the "U" attached to the car on ascent.
Because of a "lean" (deviation of the vertical axis of the "U" shaped portion of a compensating cable from true vertical) one way or the other arising out of a car speed in excess of 350 fpm, there is a danger that the cable would collide with the sidewalls of the elevator shaft. Furthermore, upon stopping the car, the compensating cable attempted to seek a true vertical position (one of lowest free energy), thus setting up a pendulum or swinging action, resulting in a harmonic action in the cab and other cables attached thereto. One solution to such a problem is to use a guidance/stabilizer means (a sheave in the bottom of the elevator well), but this is expensive and shortens the wear life of the cable. A desirable solution would be one that does not require a guidance/stabilizer means and it is towards such a solution that the present invention is directed.