Sway minimization system for elevator cables

A system for limiting oscillation of a stationary or moving elevator cable attached to suspended elevator equipment in an elevator shaft. The system includes a cable oscillation limiting member located at a predetermined vertical position in the elevator shaft. The limiting member is movable between an extended position vertically in line with the suspended elevator equipment and horizontally proximate the cable in its free-hanging state and a retracted position vertically out of line with the equipment and horizontally distal the cable. The extended position tends to limit oscillations of the cable and the retracted position permits the elevator equipment to pass the member without interference from the member or members and without substantial contact between the elevator equipment and the member under normal operating conditions. The system includes sensors to determine the need for moving the limiting member between its extended and retracted positions, depending upon the position of the elevator. The system may also use the magnitude of forces tending to induce oscillations in the cable for determining when to move the limiting member to and from the extended and retracted positions.

FIELD OF THE INVENTION 
The present invention relates to elevators and cable systems therefor, and 
in particular to a system and method for limiting oscillations in elevator 
cable systems. 
BACKGROUND OF THE INVENTION 
The oscillation of elevator cables, that is, cables having one end attached 
to an elevator car or to an elevator counterweight and being movable 
therewith, has been an ongoing problem for many years. Cable oscillations 
may be induced by the swaying motion of the structure, such as caused by 
wind, earthquake or other natural forces. Energy inputs particularly apt 
to induce cable oscillation are those where the energy input produces a 
lateral effect on the cable at or near one or more of the natural 
frequencies of oscillation of the cable. Cable oscillation may also be 
induced by air flow within the elevator shaft, such as that caused by 
stack action or elevator car movement. The motion of the elevator car 
itself may also contribute to elevator cable oscillation as the cable 
travels along with the car. Wind and earthquake-induced building 
oscillation can also be severely detrimental, leading to impacting of 
elevator cables against shaft walls, tangling of cables and the like. 
All elevator cable systems, including the hoisting, compensating and 
electrical cables, can have oscillations induced with building motion and 
can develop resonance. The most severe difficulties are commonly 
encountered under the following conditions: 
1) When building motion is induced by the wind or earthquake; 
2) When the elevator is stopped at a floor wherein the natural frequency of 
lateral oscillation of the cable coincides nearly coincides with the 
natural frequency of lateral oscillation of the building, often where the 
cable length is at or near a maximum; 
3) While the car is stopped and oscillatory motion is coupled from the 
building into the cables for some period of time; and 
4) When the elevator moves toward the other end of the cable, thus tending 
to shorten the cable, while oscillations are present in the cable. 
For the compensating cables and suspended utility cables such as control, 
power and communication cables, the most severe case generally occurs 
after the car has been parked at an upper floor, where the cable is at its 
maximum unsupported length, for some period of time. During subsequent 
descent of the elevator, oscillation coupled from the building into the 
cables is increased in frequency of vibration and sometimes amplified in 
amplitude by the continuous shortening of the cable, much as the 
oscillation of a violin string is amplified as the finger moves down the 
bridge. 
It can be shown that the swaying motions of tall buildings and the swaying 
modes of elevator cables within these buildings fall at or near one or 
more of the natural frequencies of oscillation of both building and cable. 
The period of oscillation of a tall building (fundamental approximately 
equal to N/10, where N is the number mode) is very of stories in the 
building. For more or less constant tension and weight, the period of 
oscillation of a free cable is proportional to some function of its 
length. For hoist cables and the like (i.e., cables suspended from above 
and supporting a load such as an elevator car or counterweight) the 
natural frequency of oscillation takes the form: 
##EQU1## 
For compensating cables, electrical cables and the like (i.e., cables 
suspended at each end), the frequencies are more complex but are of the 
form: 
##EQU2## 
From these expression it can be seen that by providing temporary lateral 
support to elevator cables (i.e., moving member 40 and/or member 70 to its 
extended position), at intermediate points of the shaft, the free 
vibration length of the cable can be effectively significantly reduced. 
For cables laterally supported at both ends, a support near the midpoint 
will double the natural frequency of the cable, supports near the third 
points triple the natural frequency of the cable and so forth. 
The problems of cable oscillation tend to worsen as building height 
increases. This is because of: 
a) the increased wind-induced dynamic oscillation of taller buildings; 
b) the increased elevator speeds in taller buildings and 
c) the tendency toward resonance of elevator cables with the natural period 
of taller buildings. 
Various approaches to ease the problem of cable oscillation in elevator 
cables have been proposed. In one system, described in U.S. Pat. No. 
1,145,914, excessive oscillation of a suspended electrical cable for an 
elevator is prevented by means of a stationary wire stretched vertically 
to one side of the path of the elevator between the bottom of the elevator 
and the top of the side wall of the shaft. This system cannot, however, be 
used to limit oscillation of the compensation and/or hoisting cables for 
the elevator. This system is also limited in oscillation can only be 
prevented in a side to side direction and only at the bight of the cable. 
Accordingly, this system is not readily adaptable to modern high rise 
structures. 
In another proposal, described in U.S. Pat. No. 3,666,051, a horizontal 
guide member through which cables of the elevator pass is supported at an 
intermediate vertical location by stops on tracks on either side of the 
path of the elevator. When the elevator reaches the guide as it is raised, 
the elevator picks up the guide and causes it to be raised therewith. This 
system is disadvantageous in that noise and thumping can occur when the 
elevator reaches the guide, which can be disconcerting to passengers. 
In another system, a dynamic damper consisting of an offset weighted bar is 
attached to the hoisting cables of the elevator near the elevator. This is 
said to cause lateral oscillations o the cable to be converted to twisting 
motions. This system, however, does not primarily limit the oscillations, 
but rather causes the oscillations to be damped once the have occurred. 
This system also apparently damps the motion of the cables at least in 
part by internal friction within the cables themselves, which can increase 
cable wear. Furthermore, the system is not readily adaptable to the 
suspended cables. 
In another system, described in U.S. Pat. No. 4,117,908, oscillation of 
hoisting cables is limited by fixed guides positioned near the top of the 
shaft. However, because these guides are located near the top of the 
elevator path, to accommodate the guides, the elevator shaft must be built 
somewhat higher than would otherwise be necessary. Furthermore, because 
the guides can only practically extend a small portion of the length of 
the shaft, the effectiveness of this system in limiting oscillations of 
the cable at the midpoint of the cable is limited. 
Various other approaches have been tried, including various damping 
systems, the use of traveling cars, the slowing of elevator cars, and 
programs for controlling the parking or continuous motion of elevator cars 
at levels within the elevator shaft so as to minimize the buildup of 
resonance-induced oscillator energy within the elevator cables. None, 
however, has proven entirely successful in limiting oscillations of 
elevator cables in modern high rise structures, except at very high cost. 
OBJECTS OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a system 
and method for limiting oscillations of elevator cables which overcomes 
the foregoing limitations and disadvantages. 
In particular, it is an object of the present invention to provide a system 
and method for limiting oscillations of elevator cables which can limit 
oscillations before they occur. 
It is another object of the present invention to provide a system and 
method for limiting oscillations of elevator cables which can be used to 
limit oscillations of hoisting, counterweight, compensating and electrical 
cables. 
It is a further object of the present invention to provide a system and 
method for limiting oscillations of elevator cables which can be used on 
any size building without limitation. 
It is a yet further object of the present invention to provide a system and 
method for limiting oscillations of elevator cables which does not require 
additional height to be added to the building. 
It is still another object of the present invention to provide a system and 
method for limiting oscillations of elevator cables which operates without 
noise objectionable to passengers. 
It is another object of the present invention to provide a system and 
method for limiting oscillations of elevator cables which does not 
significantly increase cable wear. 
It is another object of the present invention to provide a system and 
method for limiting oscillations of elevator cables which is simple, 
reliable and failsafe. 
It is still another object of the present invention to provide a system and 
method for limiting oscillations of elevator cables which can readily be 
retrofitted into existing buildings. 
SUMMARY OF THE INVENTION 
In accordance with a preferred embodiment of the present invention, a 
method for limiting oscillation of a stationary or moving elevator cable 
attached to suspended elevator equipment in an elevator shaft is provided 
having the steps of determining whether or not a predetermined condition 
exists and when the predetermined condition exists, positioning a cable 
oscillation limiting member or members located at a predetermined vertical 
position or positions in the elevator shaft in an extended position 
vertically in line with the suspended elevator equipment and horizontally 
proximate the cable in its free-hanging state whereby the member or 
members will limit oscillations of the cable. When the predetermined 
condition does not exist, the method includes the step of positioning the 
member or members in a retracted position vertically out of line with the 
equipment and horizontally distal the cable to permit the elevator 
equipment to pass the member or members without interference from the 
member or members and without substantial contact between the elevator 
equipment and the member or members under normal operating conditions. 
In a refinement of this embodiment of the invention, the method further 
includes the step of determining whether or not sufficient clearance 
exists between the elevator equipment to prevent substantial contact 
between the elevator equipment and the member under normal operating 
conditions and the predetermined condition requires at least the existence 
of such clearance. 
In another embodiment of the invention, a system for limiting oscillation 
of a stationary or moving elevator cable attached to suspended elevator 
equipment in an elevator shaft is provided having a cable oscillation 
limiting member located at a predetermined vertical position in the 
elevator shaft. The member is movable between an extended position 
vertically in line with the elevator equipment and horizontally proximate 
the position of the cable in its free-hanging state whereby oscillation 
greater than a predetermined amount will be limited by contact between the 
member and the cable. The member further has a retracted position 
vertically out of line with the elevator equipment and horizontally distal 
the cable so that the elevator equipment will be able to pass the member 
without interference from or substantial contact with the member. The 
system further includes means for determining whether a predetermined 
condition exists and means responsive to the existence of the 
predetermined condition to move the member from the retracted position to 
the extended position when the predetermined condition exists and from the 
extended position and the retracted position when the predetermined 
condition does not exist, this movement being accomplished without 
substantial contact between the elevator equipment and the member under 
normal operating conditions. 
In a refinement of this embodiment, the system further includes means for 
determining whether sufficient clearance exists between the elevator 
equipment and the cable oscillation limiting member to prevent contact 
between them under normal operating conditions. 
The present invention minimizes cable oscillations by providing lateral 
support to the cables. This effectively "shortens" the cables, thus 
separating the natural frequencies of oscillation of the building from the 
natural frequencies of oscillation of the cables by increasing the 
frequency of the cables out of the range of building oscillation. 
Additionally, the devices of the present invention limit cable motion at 
the point of the device. Both features tend to reduce the buildup of 
oscillatory energy within the cable thereby limiting excessive 
oscillation. Furthermore, devices in accordance with the present invention 
can also be constructed with the use of damping devices so as to consume a 
part of such energy of oscillation as may build up in the cable or cables.

DETAILED DESCRIPTION 
Turning now to the drawings in detail, and initially to FIGS. 1, and IA 
thereof, a cable oscillation limiting system 30 in accordance with a 
preferred embodiment of the present invention is depicted. The system 30 
includes a "semaphore" oscillation limiting member 40 swingably mounted by 
means of bracket 41 to a wall 31 of the elevator shaft 33 at a 
predetermined vertical location in the shaft. To maximize the 
effectiveness of the device, this vertical location is preferably away 
from either end of the shaft, generally near the midpoint of the shaft. 
Member 40 is conveniently constructed as a "T" bar with a beam 43 and cross 
bar 44, as depicted in FIGS. 2 and 3. However, a variety of other 
configurations may be employed depending upon the circumstances of the 
installation and characteristics of the cable system. Examples of limiting 
members 40', 40"and 40"' having different configurations are depicted in 
FIGS. 4-6. 
Returning now to FIG. 1, member 40 is movable between an extended position 
which is vertically in line with elevator car 32 and horizontally 
proximate the centrally mounted hoist cable 34 in its free hanging state, 
and a retracted position which is away from the cable 34 and vertically 
out of line with elevator car 32. In FIG. 1, member 40 is depicted in the 
extended position in solid lines, and in the retracted position in dotted 
lines. The limiting member in its extended position need not actually 
contact the cable in its free hanging state, although some contact in this 
condition would not generally be detrimental. Contact will occur, however, 
when the cable attempts to oscillate. 
Although the retracted position is depicted as above bracket 41, the member 
40 can be alternatively be made movable to a corresponding position below 
bracket 41. The member 40 can also be made to swing in a horizontal, 
rather than a vertical plane. It should be noted that, although the 
present invention is depicted and described as operating on the elevator 
car cables, it also may be employed to like effect on the cables attached 
to the counterweight, the compensating cables and on the utility cables. 
It should be further noted that with the elevator cable configuration 
depicted, compensation cable 36 is also centrally mounted on the elevator 
car. Accordingly, the extended position of the member 40 would also be 
horizontally proximate the compensation cable 36 and its retracted 
position would be horizontally distal to it. 
As can be seen, the limiting member 40 in its extended position extends 
into the elevator shaft and would, accordingly, interfere with the passage 
of the elevator car. Modern high rise elevators may move at speeds in 
excess of 30 miles per hour and contact between moving elevator equipment 
and limiting member 40 under normal operating conditions is undesirable. 
Accordingly, the movable limiting member 40 is preferably moved to the 
retracted, noninterfering, position before the elevator car contacts it, 
preferably when a sufficient safe clearance exists between the limiting 
member and the elevator car. This will prevent possible damage to the 
elevator car and limiting member, as well as prevent noise objectionable 
to passengers which would otherwise likely be caused by contact between 
the elevator car and the limiting member 40. 
An actuator 52 is employed to move limiting member 40 between its extended 
and retracted positions. Actuator 52 may be of any convenient design, 
including a pneumatic cylinder, hydraulic cylinder, electric motor. An 
electric motor is preferred, however, because of its greater convenience 
for most installations. 
A controller 38, which may conveniently be a suitably programmed 
microprocessor, is used to command actuator 52 to move cable limiting 
member 40 between its retracted position and its extended position, 
depending upon whether or not a predetermined condition is met. Such 
predetermined condition preferably include at least the existence of 
sufficient clearance between the elevator car and the limiting member 40, 
that is, that the elevator car would not contact cable limiting member 40 
if it were moved to its extended position. 
The existence of such clearance can be determined in a variety of 
acceptable manners. The simplest manner would be to input the vertical 
location information already present in the elevator controller 44 (which 
is conventionally present and used for operating the elevator) to the 
limiter controller 38. In FIG. 1, this information is schematically shown 
being input to controller 38 by means of input line 39. In addition to 
this, or alternatively, dedicated sensors 39A and 39B, which may be 
conveniently optical, electrical or magnetic sensors, can be placed in the 
elevator shaft above and below the position of the limiting member 40 to 
sense the presence or passage of the elevator car directly. Output from 
these sensors would then be feed to controller 38 and hence to controller 
44 via lines 49A and 49B to thus inform the controllers of the proximity 
of the elevator car to the limiting member 40. 
Preferably, the controller 38 is programmed to ensure that the limiting 
member 40 is moved to its retracted position before contact between the 
elevator car and the member can occur can be used to determine whether the 
limiting member 40 is to be moved to its extended or retracted position. 
For example, in general, it is preferable that the member 40 be retracted 
unless the elevator car is stationary. This will prevent friction between 
the otherwise moving cables and the member 40. To prevent excessive 
movement of the member between its extended and retracted position, 
information from elevator controller 44 as to whether there is a pending 
floor request, and to which floor, can be input to the controller 38. 
Thus, for example, if there is a pending floor request to a floor in the 
direction of or past the position of the member 40, the controller 38 can 
be programmed to prevent movement of member 40 to the extended position or 
to retract it, since movement to the retracted position would be required 
soon in any event. 
Oscillations, in general, require a period of time to build up, and do not 
tend to build up to as great an extent when the elevator is moving up and 
down, thus frequently changing the effective length of the cables. 
Accordingly, it some installations it may be desirable to retract the 
member 40 unless the elevator is "parked" for a period of time. Thus, for 
example an additional condition could be the absence of any pending floor 
request for the elevator car in any direction and/or nonmotion of the 
elevator for a predetermined period of time. 
As another example, it may be desirable in certain installations that the 
devices be kept in the retracted position when little oscillation limiting 
is required, such as during times where building motion, or other 
oscillation inducing energy, is small. Thus, in this example, the 
measurement of conditions associated with unacceptably higher amplitudes 
would, in addition to the presence of sufficient clearance between the 
limiting member 40 and the elevator car, become an additional requirement 
of the predetermined condition necessary before the limiting member 40 
would be caused to move into its extended position. To determine this 
condition, the cable motion can be sensed directly, such as by magnetic 
sensor 47. An accelerometer 43 to monitor buildings motion can also be 
used to measure building motion. Alternatively, or in addition to this, an 
anemometer 45 can be used to provide wind speed information to the 
controller, since wind will tend to induce building motion after a period 
of time. An accelerometer 46 could also be used to monitor ground 
acceleration caused by seismic forces. Any or all of this information can 
be input to controller 38 to enable it to determine whether this 
additional condition required for extension of the member 40 has been met. 
Under some circumstances, it may be desirable to permit the member 40 to be 
extended at certain times even when the car is in motion. This might be 
desirable in exceptionally tall buildings where oscillations tend to be 
large more frequently. In this case, the controller 38 would preferably be 
programmed to permit extension of the member 40 (providing other 
conditions were met) except when the elevator was moving toward, or about 
to move toward, member 40. 
Elevator controller 44, as is conventional, has a feedback system designed 
to preclude elevator car motion at times when certain safety systems (such 
as doors, for example) are not in their proper positions. Information from 
a variety of such safety systems is commonly input to controller 44, 
schematically represented as input 51. It is preferred to include the 
proposed oscillation limiting system in the feedback network so as to be 
able to inform controller 44 of the position of member 40. The position of 
the limiting member 40 can be determined in a variety of manners, 
including by means of limit switches, sensors, or other such means. In the 
embodiment of the system depicted in FIG. 1, a limit switch 55 is used. 
As noted above, preferably, controller 44 is programmed to preclude any car 
motion unless the limiting member 40 is in its fully retracted position. 
However, in cases where it is desired to permit the member 40 to be 
extended during motion of the car, controller 44 can be programmed instead 
to permit car motion under some circumstances, such as when such motion is 
in a direction away from the member 40. 
These control schemes are exemplary only, however, since the appropriate 
control scheme for a particular installation will depend upon factors 
unique to that installation, such as the height and natural frequency of 
the building, average wind speeds, acceptable amplitude of oscillations, 
frequency of use of the elevator, etc. 
The number of cable oscillation limiting members that may be necessary or 
desirable for a given building will depend upon the height and oscillation 
characteristics of the building and cable system. Although only one cable 
oscillation limiting member 40 is depicted, two or more may also be 
employed, if necessary. Often, such as in relatively short buildings, only 
one device may be needed. However, the installation of two or more devices 
may be desirable in taller structures and allows cables to be "tuned" to 
nearly any desired natural frequency higher than the natural frequency of 
the uncorrected system. 
It should be noted that for cable motion in a given plane, a limiting 
member need only be provided in one direction, i.e., on one side of the 
cables, to reduce oscillations in both opposing directions. However, 
limiting members can be provided on both sides, if desired. 
The semaphore cable limiting member may be configured to have an end which 
anchors in a guide on an opposing wall. This is depicted in FIGS. 6-9 and 
24. The limiting member 40"' is configured in the same way as the limiting 
member depicted in FIG. 6, with the exception that the limiting member is 
long enough to reach the opposing wall and that it has an enlarged end 70. 
At the opposing wall, there is a anchor guide 65 which cooperates with 
enlarged end 70 to retain it in position. During motion from the retracted 
position to the extended position, the elongated end 70 will fit into the 
anchor guide 65, thereby more securely holding the limiting member in 
place. 
On lateral impact from the elevator cables, the limiting member would be 
deflected in the direction of cable movement. Once a limit of deflection 
is achieved, the anchor guide will prevent further motion, and the 
limiting member goes into tension. As depicted in FIGS. 7-9 and 24, this 
configuration is readily adaptable to installations where it is desired to 
interdigitate the limiting member between cables. Of course, it is not 
required that the limiting member pass between cables. 
The anchor guides can be tapered or flared as depicted in FIGS. 11 or 12 as 
65' and 65" to allow for easy entry of the limiting member. This will also 
provide strength and stiffness. Preferably, the limiting member is made 
electrically conductive and electrical contacts are provided on the anchor 
guide to facilitate informing controller 38 of when the limiting member is 
fully in the extended position and properly positioned in the guide. 
In some installations it may be desirable to rotate the limiting member 
once it is in position to more securely prevent the cables from moving. 
With reference to FIGS. 16 and 17, the limiting member 40""' has a cross 
configuration with a cross member 44""' Initially, member 40""' is swung 
into its extended position with the cross beam 44""' in the vertical 
orientation. Once it is in this extended position, with the cross bar in 
between the cables, the control mechanism rotates the limiting member 
40""' until the cross beam 44""' is in the position depicted in FIG. 17. 
The foregoing examples of semaphore cable limiting member constructions are 
exemplary only, since a variety of configurations will be appropriate for 
various installations depending upon cable configurations and shaft 
design. 
In the event of failure of both of the retraction mechanism and of the 
electrical feedback network that prevents the elevator from moving, it is 
desirable that the device be swept aside by the passing elevator car 
without it affecting the life safety features of the elevator system. That 
is, the device (which projects into the elevator shaft) should be designed 
to be "fail-safe" so that, in the event of failure of control systems, the 
elevator car can pass the device without danger to passengers or serious 
damage to the car. Fittings to the top and the bottom of the car, which 
are conveniently rollers 60A and 60B are preferably installed for this 
purpose. 
The limiting member 40 can be made to be frangible such that it will be 
partially or wholly destroyed by unintended impact by the elevator car 
without serious damage to the elevator car or other elevator equipment. To 
accomplish this, cable limiting member 40 can be constructed of 
post-tensioned beams which are designed to self-destruct into relatively 
small pieces or by other methods. 
An example of a limiting member having such a frangible construction is 
depicted in FIG. 15. The beams of limiting member 40 are constructed of an 
outer layer having relatively short pieces 66 of high strength material 
with an inner wire 67 such as is used in post-tensioning systems. These 
pieces 66 have ends finished to allow full bearing on abutting pieces. 
Tensile load in the wire is transferred onto pieces 66 so as to create 
beam strength in the guide pole B, and further to provide electrical 
conductivity, if desired. 
In the event of accidental impact by the elevator car (or for other 
reasons) the wire 67 is designed to break (or its anchorages designed to 
fail) so as to allow the beam to safely break up into small pieces. 
It is not required that the limiting member be a relatively stiff beam as 
depicted in FIGS. 1 through 17. A configuration wherein a flexible wire 
alone is used as the limiting member is depicted in FIGS. 18 through 23. 
Turning first to FIG. 18, the limiting member is a wire stretching across 
the elevator shaft along a wall when it is in its retracted position. When 
it is desired to limit oscillations of the elevator cables, the ends of 
wire 70 is moved into position by transporters 79 sliding in tracks 78 on 
each side of the elevator shaft. 
Another configuration of a wire type cable limiter is depicted in FIG. 19. 
In this configuration, a recovery cable 83 is used to move the wire 70' 
from its retracted position indicated by the dotted line and its extended 
position indicated by the solid line. The wire is wound on and off of 
reels 94 and the recovery cable is wound back and forth on reels 80 and 81 
powered by preferably an electric motor (not shown). In other respects, 
the control system for wire-type systems is substantially the same as 
described previously with respect to FIG. 1. 
Elevator shafts commonly have guide rails 90 along their periphery for 
guiding the elevator up and down in a smooth straight line. In certain 
installations, the guide rail 90 may interfere with the retraction of 
wire. In unusual situations, it may not be possible to pass the wire 
through the line of the rail. In this event, a beam type configuration 
such as depicted in FIGS. 1 through 17 would be preferable. However, in 
most installations, it may be acceptable to a small slot in the guide rail 
90 to permit passage of the wire. Such a configuration is depicted in 
FIGS. 20 and 21. 
In a wire type system, the motor used to power the winding and unwinding of 
the wire can be conveniently used to damp the motion of the elevator 
cable. To do so, the control system for the motor may be designed so that 
as the cable strikes the wire, the motor will provide a level of torque 
which just allows the wire to unreel at an amount and at a rate which 
maximizes the energy expended by the motor. As the cable motion is stopped 
by the wire, the motor is designed to provide only enough torque to reel 
in the wire. This prevents the consumed energy from being reintroduced 
into the cables. A variety of other friction and viscous dampers can also 
be employed. 
Although the various embodiment of the present invention have been shown 
and described, there is no intention of limiting the present invention to 
only those embodiments, since many variations and equivalents of the 
present invention will be apparent to those skilled in the art. Rather, 
the scope of the present invention is defined by the appended claims.