CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of the copending
application having Serial No. 09/970,451, which was filed on October 2, 2001.
BACKGROUND OF THE INVENTION
This invention generally relates to load bearing assemblies
for elevator systems. More particularly, this invention relates to an arrangement
for readily detecting localized strain in an elevator load bearing assembly.
Elevator systems typically include a cab and counterweight
that are coupled together using an elongated load bearing member. Typical load bearing
members include steel ropes and, more recently, synthetic ropes and multi-element
ropes such as polymer coated, steel or synthetic cord reinforced belts. Synthetic
ropes and polymer coated, synthetic cord reinforced belts are particularly attractive
for elevator applications due to their greater strength-to-weight ratio compared
with steel ropes or belts.
Inspecting a load bearing member in an elevator system
has been accomplished in several ways. With conventional steel roping, a manual,
visual inspection of the rope allows the technician to determine when particular
strands of the steel rope are frayed, broken or otherwise worn. This inspection
method is limited, however, to the exterior portions of the rope and does not provide
any indication of the condition of interior strands of the rope. Additionally, a
visual inspection method is somewhat difficult and time consuming and does not always
permit complete inspection of the entire length of the load bearing arrangement.
There are similar limitations on using visual inspection
techniques on newer ropes. For example, the polymer coated, polymer cord reinforced
belts do not permit visual inspection because of the coating that is typically applied
over the cords, which are made up of strands of polymer material. Several advances
have been proposed for facilitating inspection of such load bearing arrangements.
One example is shown in United States Patent No. 5,834,942 where at least one carbon
fiber is included in the load bearing member. An electric current is passed through
the fiber. By measuring an electrical voltage across that fiber, a determination
is made regarding the condition of the load bearing member. This proposal is limited,
however, in that it does not provide any information regarding locations of maximum
strain along the length of the load bearing member. Moreover, there is no way of
guaranteeing that a loss of conductivity through the carbon fiber is directly correlated
to strain or damage to the load bearing member. Another shortcoming of such an arrangement
is that there is no qualitative information regarding degradation of the load bearing
member over time.
There is a need for improved arrangements and methods for
determining the condition of load bearing members in elevator assemblies. This invention
provides a unique solution to that problem.
SUMMARY OF THE INVENTION
In general terms, this invention is a load bearing assembly
for use in an elevator system. The inventive arrangement includes a plurality of
non-ferromagnetic fibers arranged into at least one cord. At least one ferromagnetic
element is associated with the cord. The ferromagnetic element is situated such
that a physical characteristic of the ferromagnetic element changes responsive to
strain on the non-ferromagnetic fibers. Such a change or changes in the ferromagnetic
element can be detected. The ferromagnetic element, therefore, provides an indication
of a condition of the assembly.
In one example, the ferromagnetic element breaks responsive
to excessive strain on the non-ferromagnetic fibers. The breaks in the ferromagnetic
element correspond to locations of the non-ferromagnetic elements that are strained.
The ferromagnetic element preferably is chosen so that it breaks responsive to localized
bending fatigue in the load bearing assembly.
A method of determining the condition of a load bearing
assembly according to this invention includes arranging a ferromagnetic element
in a selected relationship with a cord, which comprises a plurality of non-ferromagnetic
fibers. The ferromagnetic element preferably is positioned in a selected relationship
with the cord such that a physical characteristic of the ferromagnetic element changes
responsive to localized strain on the non-ferromagnetic fibers. By determining a
number of changes in the physical condition of the ferromagnetic element along the
length of the assembly, a condition of the assembly is determined.
In one example, the method includes determining a number
of breaks in the ferromagnetic element. By locating the breaks and comparing the
number of breaks to predetermined selection criteria, the condition of the assembly
can be determined to make a decision regarding the condition of the assembly to
determine whether repair or replacement is needed.
The various features and advantages of this invention will
become apparent to those skilled in the art from the following detailed description
of the currently preferred embodiments. The drawings that accompany the detailed
description can be briefly described as follows.
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPITION OF THE PREFERRED EMBODIMENTS
- Figure 1 schematically illustrates an elevator system.
- Figure 2 schematically illustrates an exemplary load bearing assembly designed
according to an embodiment of this invention.
- Figure 3 schematically illustrates selected portions of the load bearing assembly
of Figure 2.
- Figure 4 schematically illustrates a monitoring device and technique useful
with an embodiment of this invention.
- Figure 5 schematically illustrates, in partial cross section, another example
load bearing assembly designed according to an embodiment of this invention.
- Figure 6 schematically illustrates an alternative arrangement designed according
to an embodiment of this invention.
Figure 1 schematically shows an exemplary elevator system
20 that includes a cab 22 and a counterweight 24. A load bearing assembly 26 couples
the cab 22 and counterweight 24 together so that the cab 22 can be moved between
landings in a building, for example, in a conventional fashion.
The load bearing assembly 26 may take a variety of forms.
One example is a flat belt containing polymer reinforced strands. Other examples
include synthetic ropes and multi-element ropes. This invention is not limited to
"belts" in the strictest sense. A flat belt is used as one example of a load bearing
assembly designed according to this invention. Therefore, any reference to a "belt"
within this description is not intended to be limiting in any sense.
The example load bearing assembly 26 shown in Figure 2
includes a plurality of strands 30 that are wound together in a known manner to
form at least one cord 32. A number of cords preferably are aligned parallel to
each other and a longitudinal axis of the belt. A single cord is shown in Figure
2 for discussion purposes. A non-ferromagnetic, polymer material preferably is used
to form the strands 30. The illustrated strands are coated with a jacket 34, which
protects the strands from wear and provides friction characteristics for driving
the elevator system components as needed. This invention is not limited to coated
At least one ferromagnetic element 38 preferably is associated
with the cord 32. In the example of Figure 2, the ferromagnetic element 38 is integrally
placed within one of the strands 30 of the cord 32. There are a variety of ways
of associating a ferromagnetic element 38 with a cord comprised of non-ferromagnetic
fibers within the scope of this invention.
Referring to Figure 3, a ferromagnetic element 38 is illustrated
along with a plurality of non-ferromagnetic fibers 36 that are wound together in
a conventional fashion to form a cord. A helical winding arrangement, as known in
the art, provides the desired structural characteristics of the strands and the
The ferromagnetic element 38 preferably is chosen to have
physical characteristics that will not alter the performance of the load bearing
assembly or interfere with the integrity of the assembly provided by the non-ferromagnetic
fibers. In one example, a steel wire having an outside dimension that is similar
to an outside dimension of the non-ferromagnetic fibers is used as the ferromagnetic
element 38. The wire may be coated, depending on the needs of a particular situation.
The ferromagnetic element 38 is associated with the cord
32 such that strain on the non-ferromagnetic fibers of the assembly causes a corresponding
change in a physical characteristic of the ferromagnetic element. In one example,
the ferromagnetic element breaks responsive to bending fatigue experienced by the
non-ferromagnetic fibers. In another example, the cross sectional dimension of the
ferromagnetic element is reduced in locations where the non-ferromagnetic fibers
are strained. By providing a ferromagnetic element that is altered in locations
corresponding to strained fibers of the assembly, the ferromagnetic element 38 provides
the ability to utilize monitoring equipment otherwise known in the art to make a
determination regarding the condition of the assembly 26.
In one example, a magnetic flux leakage technique is used
to determine the number of breaks or other changes in the ferromagnetic element
38 along the length of the assembly 26. An example arrangement utilizing this technique
is schematically illustrated in Figure 4.
A monitoring device 40 includes a permanent magnet 42 and
a pair of Hall effect sensors 46. A permanent magnet 42 creates a magnetic field
as is schematically shown by the magnetic flux lines 50 in Figure 4. As the assembly
26 moves relative to the monitoring device 40, physical changes in the ferromagnetic
element 38 cause interruptions in the magnetic flux as schematically shown by the
flux lines 52. A break in the ferromagnetic element 38 is schematically illustrated
at 54. When the break 54 passes the Hall effect sensors 46 (as the belt moves relative
to the monitoring device 40), an output is generated indicating the presence of
the break 54. The controller 48 preferably is programmed to communicate with the
sensors 46 and to record data indicating the number of detected breaks and information
regarding the location of the breaks in the assembly 26.
More details regarding magnetic flux leakage techniques
for detecting breaks or other physical changes in the ferromagnetic element 38 can
be appreciated from the published PCT application WO 00/58706, published on October
5, 2000, which is commonly owned with this application.
The non-ferromagnetic material used to form the structural,
load bearing cords of the load bearing member assembly can be any one or more of
a variety of commercially available materials. The structural material of the load
bearing member may be, for example, PBO, which is sold under the trade name Zylon;
liquid crystal polymers such as a polyester-polyarylate, which is sold under the
trade name Vectran; p-type aramids such as those sold under the trade names Kevlar,
Technora and Twaron; or an ultra-high molecular weight polyethylene, an example
of which is sold under the trade name Spectra; and nylon. Given this description
and the known properties of such available materials, those skilled in the art will
be able to select appropriate materials to meet the needs of their particular situation.
Another example is shown in Figure 5. In this example,
a plurality of cords 32 are aligned along the length of the load bearing assembly
26. Each of the cords 32 comprise a plurality of non-ferromagnetic fibers 36 that
are wound together in a desired manner, such as in a known helical arrangement.
The cords 32 are coated with an elastomeric jacket 34. In one example, the jacket
34 comprises polyurethane. Such coatings or jackets are known in the art.
There are a variety of ways to incorporate the second material
element into the load bearing member assembly. The example of Figure 5 includes
a plurality of cords 32 supported within a single jacket 34 having a desired spacing
between the cords across the width of the assembly 26. A ferromagnetic element 38
preferably is associated with each of the cords 32. The ferromagnetic elements 38
are supported within the jacket 34 in a selected position relative to each cord.
In this example, the ferromagnetic elements 38 are supported immediately adjacent
to the cords extending parallel to an axis of a respective cord 32. In this example,
the ferromagnetic elements 38 are not integrated as part of the cords 32.
The example of Figure 5 schematically shows selected portions
of a monitoring device 40 having a plurality of Hall effect sensors 46 that are
positioned to detect physical changes in the ferromagnetic elements 38 as the assembly
26 moves relative to the monitoring device 40. A permanent magnet is not illustrated
in Figure 5 for simplicity.
The example of Figure 6 includes integrating the ferromagnetic
element 38 into the cords 32 of the load bearing assembly 26. In this example, the
ferromagnetic elements 38 are at the center of each cord.
As the non-ferromagnetic fibers 36 are subjected to strain
caused by such factors as bending fatigue, a physical characteristic of the ferromagnetic
element 38 changes in the regions where the assembly is strained. Example physical
characteristics that change include the continuity of the ferromagnetic element
38. In other words, the ferromagnetic element 38 in some examples will break responsive
to bending fatigue or other strain on the non-ferromagnetic fibers 36. In another
example, the physical, cross-sectional dimension of the ferromagnetic element 38
will change as the ferromagnetic element 38 is stretched (but not quite broken)
in a region that undergoes strain.
Other physical characteristics may be monitored to determine
where the assembly 26 has been strained. Breaks in the ferromagnetic element 38
(or portions with a reduced cross-section) provide a detectable change that can
be monitored using known magnetic flux leakage techniques, for example. Other physical
characteristic changes in the ferromagnetic element may be used, depending on the
monitoring technique chosen for a particular situation. Those skilled in the art
who have the benefit of this description will be able to make appropriate selections
for their particular situation.
A method of this invention preferably includes predetermining
correlating factors between a detected number of physical changes (i.e., breaks
or areas of reduced cross section) in the ferromagnetic element and the condition
of the assembly 26. For example, known testing devices and techniques can be used
to subject the assembly 26 to desired amounts of strain to simulate known amounts
of bending fatigue. The number of breaks or other physical changes in the ferromagnetic
element 38 for a particular embodiment preferably are monitored at different stages
of the testing. By correlating the number of changes with the known belt conditions
at various stages during testing, comparative data is assembled and utilized to
provide correlating factors so that field measurements of belts and service are
useable to make a determination regarding actual belt condition.
For example, a belt section having a loss of belt breaking
strength as derived from known bending fatigue tests can be utilized to provide
a sample of a load bearing assembly that may not be fit for continued operation.
The corresponding number of observed changes in the physical characteristic (i.e.,
cross-sectional dimension or continuity) of the ferromagnetic element within that
section provides an indication of such a belt condition. That measurement can be
used for comparisons to actual measurements on belts in service to discern a condition
of the belt.
The correlating data provides information to compute a
figure of merit or a belt condition index. Once a threshold figure is determined
for a given belt configuration, that information can be used in the field by elevator
technicians to determine what a belt's current condition is and to make a decision
whether replacement may be necessary.
In one example the belt condition index is based on a density
of breaks in the element 38 (i.e., a number of breaks within a certain length of
Devices that utilize the advances of this invention preferably
are programmed to provide a technician or mechanic with an output indicating a condition
of the belt assembly so that determinations can be made in the field regarding belt
condition to facilitate decisions regarding maintenance or replacement.
Because, such magnetic detection techniques are already
used for steel cord belt inspection, this provides an advantage for this invention
to be accommodated by current inspection machinery or devices.
The preceding description is exemplary rather than limiting
in nature. Variations and modifications to the disclosed embodiments may become
apparent to those skilled in the art that do not necessarily depart from the essence
of this invention. The scope of legal protection given to this invention can only
be determined by studying the following claims.