Rope of a lifting device for an elevator and a condition monitoring method for the rope

Abstract

In a rope of a lifting device, particularly of a passenger transport elevator and/or freight transport elevator, the width of which rope is greater than the thickness in the transverse direction of the rope, which rope includes a load-bearing part in the longitudinal direction of the rope, which load-bearing part includes carbon-fiber reinforced, aramid-fiber reinforced and/or glass-fiber reinforced composite material in a polymer matrix, and which rope includes one or more optical fibers and/or fiber bundles in connection with the load-bearing part and the optical fiber and/or fiber bundle is laminated inside the load-bearing part and/or the optical fiber and/or fiber bundle is glued onto the surface of the load-bearing part and/or and that the optical fiber and/or fiber bundle is embedded or glued into the polymer envelope surrounding the load-bearing part, as well as to a condition monitoring method for the rope of a lifting device.

Claims

1. A rope of a lifting device for an elevator, wherein: a width of the rope is greater than a thickness of the rope in a transverse direction of the rope, the rope comprises: a load-bearing part in a longitudinal direction of the rope, the load-bearing part comprises a composite material in a polymer matrix, a cross-section of the load-bearing part in the transverse direction of the rope has two parallel edges extending in the transverse direction of the rope, said parallel edges having a length greater than a thickness of the load-bearing part that is perpendicular to the parallel edges, one or more optical fibers and/or fiber bundles in connection with the load-bearing part, and at least one of the one or more optical fibers and/or fiber bundles is located outside of the load-bearing part, wherein the composite material comprises carbon-fibers, aramid fibers and/or glass-fibers in the polymer matrix, wherein the load-bearing part is completely surrounded by an envelope comprising a polymer and is continuous in the longitudinal direction of the rope, and wherein the at least one of the one or more optical fibers and/or fiber bundles located outside of the load-bearing part is embedded in the envelope.

2. The rope according to claim 1, wherein the structure of the rope continues essentially the same for the whole length of the rope, and the load-bearing part comprises prepeg reinforcement layers laminated together and at least one other optical fiber and/or fiber bundle of the one or more optical fibers and/or fiber bundles is laminated between and/or on the surface of the reinforcement layers.

3. The rope according to claim 1, wherein fibers of the load-bearing part are arranged in a longitudinal direction and are laminated into the polymer matrix, and at least one other optical fiber and/or fiber bundle of the one or more optical fibers and/or fiber bundles is arranged to be mixed into the reinforcement.

4. The rope according to claim 1, wherein the load-bearing part comprises at least one other optical fiber and/or fiber bundle of the one or more optical fibers and/or fiber bundles, which extends essentially a length of the load-bearing part, and the at least one other of the optical fiber and/or fiber bundle extends continuously in the direction of the load-bearing part essentially from a first end of the load-bearing part to a second end of the load-bearing part at least once.

5. The rope according to claim 1, wherein an input and a reception of a light pulse of the one or more optical fibers and/or fiber bundles is at a same end of the rope or the input and the reception of the light pulse of the one or more optical fibers and/or fiber bundles are at opposite ends of the rope.

6. The rope according to claim 1, wherein a single-mode or multimode fiber is used as a sensor fiber of the one or more optical fibers or fiber bundles and an input of the light pulse occurs with a laser transmitter or with a LED light source.

7. The rope according to claim 1, wherein the one or more optical fibers and/or fiber bundles comprises a Fabry-Perot-type sensor fiber.

8. The rope according to claim 1, wherein the one or more optical fibers and/or fiber bundles comprises a sensor fiber, comprising a Bragg grating structure.

9. The rope according to claim 1, wherein the one or more optical fibers and/or fiber bundles comprises a sensor fiber, which functions as a Brilloun distributed fiber sensor.

10. The rope according to claim 1, wherein the one or more optical fibers and/or fiber bundles comprises a sensor fiber, in which fiber the time-of-flight of a light pulse is measured.

11. A rope arrangement of a lifting device of an elevator, which rope arrangement comprises a plurality of ropes, which are arranged to move the elevator car, wherein at least one of the ropes is the rope according to claim 1.

12. The rope according to claim 1, wherein the at least one of the one or more optical fibers and/or fiber bundles is glued onto the surface of the load-bearing part and is embedded into the polymer envelope surrounding the load-bearing part and at least another of the one or more optical fibers and/or fiber bundles are located inside the load-bearing part.

13. An elevator comprising: an elevator car, a traction sheave, a power source for rotating the traction sheave, and the rope according to claim 1, wherein the elevator car is arranged to be moved by aid of the rope.

14. The elevator according to claim 13, wherein the rope is arranged to move the elevator car and a counterweight.

15. The elevator according to claim 13, wherein the rope is an overspeed governor rope and/or a compensating rope.

16. The elevator according to claim 13, wherein the elevator comprises a device configured to monitor a condition of the optical fiber and/or a fiber bundle, which comprises a number of optical fibers, the device configured to monitor a condition of the optical fiber by monitoring a strain and/or displacement and/or condition of the optical fiber and/or fiber bundle of the load-bearing part of the rope.

17. A condition monitoring method for a rope of a lifting device for an elevator, the condition monitoring method comprising the steps of: monitoring a condition of the rope by monitoring a condition of an optical fiber and/or fiber bundle, the rope including: a load-bearing part, wherein the optical fiber and/or fiber bundle being located outside of the load-bearing part, a cross-section of the load-bearing part in the transverse direction of the rope having two parallel edges extending in the transverse direction of the rope, said parallel edges having a length greater than a thickness of the load-bearing part that is perpendicular to the parallel edges; and when a detected strain and/or displacement of the optical fiber and/or fiber bundle has increases, and/or the condition of the optical fiber and/or fiber bundle has decreases, beyond a pre-defined limit value, diagnosing a need to replace or overhaul the rope and starting rope replacement work or rope maintenance work, wherein the rope comprises the load-bearing part in a longitudinal direction of the rope, the load-bearing part comprises a composite material in a polymer matrix, wherein the rope comprises one or more additional optical fibers and/or fiber bundles in connection with the load-bearing part, wherein the composite material comprises carbon-fibers, aramid fibers and/or glass-fibers in the polymer matrix, wherein the load-bearing part is completely surrounded by an envelope comprising a polymer and is continuous in the longitudinal direction of the rope, and wherein the optical fiber and/or fiber bundle located outside of the load-bearing part is embedded in the envelope.

18. The method according to claim 17, wherein a width of the rope is greater than a thickness in the transverse direction of the rope.

19. The method according to claim 18, wherein at least one of the one or more additional optical fibers and/or fiber bundles is embedded in the load-bearing part and wherein at least another one of the one or more additional optical fibers and/or fiber bundles is glued onto the surface of the load-bearing part.

20. The method according to claim 17, wherein a single-mode or multimode fiber is used as the sensor fiber of the optical fiber or fiber bundle and the input of the light pulse occurs with a laser transmitter.

21. The method according to claim 17, wherein the optical fiber and/or fiber bundle comprises a sensor fiber and a reference fiber, with which common mode errors, caused by changes in temperature, are eliminated.

22. The method according to claim 17, wherein the optical fiber and/or fiber bundle comprises a Fabry-Perot-type sensor fiber, with which the strain and/or displacement of the rope is measured.

23. The method according to claim 17, wherein the optical fiber and/or fiber bundle comprises a sensor fiber, comprising a Bragg grating structure, with which the strain and/or displacement of the rope is measured.

24. The method according to claim 17, wherein the optical fiber and/or fiber bundle comprises a sensor fiber, which functions as a Brilloun distributed fiber sensor, with which the strain and/or displacement of the rope is measured.

25. The method according to claim 17, wherein the optical fiber and/or fiber bundle comprises a sensor fiber, the time-of-flight of a light pulse in which fiber is measured, and with which the strain and/or displacement of the rope is measured.

26. The method according to claim 17, wherein the time-of-flight of a light pulse and/or strain are measured in a number of ropes, and when the measured values of which ropes differ a predetermined amount from each other, a need to replace or overhaul the rope or ropes is diagnosed and rope replacement work or rope maintenance work is started.

27. The method according to claim 17, wherein at least one of the one or more additional optical fibers and/or fiber bundles is disposed in the polymer envelope.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention will now be described mainly in connection with its preferred embodiments, with reference to the attached drawings, wherein:

(2) FIGS. 1a-1j present schematically one embodiment of each rope according to the invention.

(3) FIG. 2 presents schematically a magnified detail of a cross-section of a rope according to the invention.

(4) FIG. 3 presents one embodiment of an elevator according to the invention.

(5) FIG. 4 presents schematically a measuring system according to one embodiment of the condition monitoring method for a rope according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIGS. 1a-1j present schematically preferred cross-sections of hoisting ropes according to the different embodiments of the invention, as viewed from their longitudinal direction. The rope 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 presented by FIGS. 1a-1j is belt-like, i.e. the rope possesses in the first direction, which is at a right angle to the longitudinal direction of the rope, a measured thickness t, and in a second direction, which is the longitudinal direction of the rope and at a right angle to the aforementioned first direction, a measured width w, which width w is essentially greater than the thickness t. The width of the rope is thus essentially greater than the thickness. In addition the rope preferably, but not necessarily, possesses at least one, preferably two, wide and essentially flat surfaces, in which case a wide surface can be efficiently used as a force-transmitting surface utilizing friction or positive contact, because in this way an extensive contact surface is achieved. The wide surface does not need to be completely flat, but instead there can be grooves in it or protrusions on it, or it can have a curved shape. The structure of the rope continues preferably essentially the same for the whole distance of the rope. The cross-section can also, if so desired, be arranged to change intermittently, e.g. as toothing.

(7) The rope 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 comprises a load-bearing part 11, 21, 31, 41, 51, 61, 71, 81, 91, 101, which is carbon-fiber reinforced, aramid-fiber reinforced and/or glass-fiber reinforced composite, which comprises carbon fibers, aramid fibers and/or glass fibers, most preferably carbon fibers, and also one or more optical fibers, more preferably one or more fiber bundles, in a polymer matrix. The reinforcing fibers and optical fibers are longitudinal to the rope, for which reason the rope retains its structure when bending. Individual fibers are thus aligned in essentially the longitudinal direction of the rope, in which case the fibers are aligned with the force when the rope is pulled. An optical fiber and/or fiber bundle can be one continuous fiber or bundle laminated inside, or in the proximity of the surface of, the composite structure such that the fiber goes inside the structure at a first end of the rope, turns back at the other end of the rope and comes out of the structure again at the first end of the rope. A fiber and/or a fiber bundle can be coiled, i.e. the fiber can have one or more turns inside, or on the surface of, the structure such that however only one fiber and/or fiber bundle is used for the measurement, and the aforementioned fiber and/or fiber bundle can go into and come out of the same end or different ends of the rope. Also a number of parallel fibers or bundles can be used for measuring, laminated in a corresponding manner inside the composite structure or in the proximity of its surface.

(8) The rope 10 presented in FIG. 1a comprises a load-bearing composite part 11 that is essentially rectangular in its cross-sectional shape, which is surrounded by a polymer envelope 1. In the cross-section of the composite part 11 of the figure, an optical fiber and/or fiber bundle 2, which can be the same fiber coiled or different parallel fibers, is seen in three points. In this way good measurement accuracy, e.g. for strain, is achieved with the system. Alternatively the rope can be formed without a polymer envelope 1.

(9) The rope 20 presented in FIG. 1b comprises a load-bearing composite part 21 that is essentially rectangular in its cross-sectional shape, which is surrounded by a polymer envelope 1. A wedge surface is formed on the surface of the rope 20 with a plurality of wedge-shaped protrusions 22, which are preferably an integral part of the polymer envelope 1. In the figure, at the point of the three wedge-shaped protrusions, an optical fiber and/or fiber bundle 2 is glued essentially onto the surface of the composite part, which optical fiber and/or fiber bundle preferably comprises at least a sensor fiber, preferably also a reference fiber. The reference fiber can also be installed inside the envelope such that strain caused by the structure to be measured is not exerted on it.

(10) The rope 30 presented in FIG. 1c comprises two load-bearing composite parts 31 side by side that are rectangular in their cross-sectional shape, which are surrounded by a polymer envelope 1. The polymer envelope 1 comprises at the midpoint of the wide side of the rope 30, in the center of the area between the parts 31, a protrusion 32 for guiding the rope. There can be more than two composite parts 51 side-by-side in this manner in the rope 50, as presented in FIG. 1e. In FIGS. 1c and 1e, an optical fiber and/or fiber bundle 2, which preferably comprises a sensor fiber and a reference fiber, is disposed both in the composite part and embedded in the polymer envelope between the composite parts. The reference fiber can also be installed inside the envelope such that strain caused by the structure to be measured is not exerted on it. The polymer envelope can also be without protrusions or a protrusion can be situated at a different point of the polymer envelope.

(11) The rope 40 presented in FIG. 1d comprises a load-bearing composite part 41 that is rectangular in its cross-sectional shape, which is surrounded by a polymer envelope 1. The edges of the rope comprise bulges 42, which are preferably a part of the polymer envelope 1. An advantage of the bulges 42 is that they protect the edges of the composite part e.g. from fraying. An optical fiber and/or fiber bundle 2 is embedded in the bulge 42 in the proximity of the surface of the composite part for monitoring the condition of the composite part and/or for data transfer. A fiber and/or fiber bundle can also be glued to the surface of the polymer envelope.

(12) The rope 60 presented in FIG. 1f comprises a plurality of load-bearing composite parts 61, which can also be braidings, of round cross-sectional shape, and which are surrounded by a polymer envelope 1, and in a part of which composite parts 61 is disposed an optical fiber and/or fiber bundle 2, which preferably comprises at least an actual sensor fiber.

(13) The rope 70 of rectangular cross-sectional shape presented in FIG. 1g comprises a plurality of load-bearing composite parts 71 that are rectangular in their cross-sectional shape and that are placed side-by-side in the width direction of the belt, which are surrounded by a polymer envelope 1. In the proximity of the surface of the composite parts 71, and/or between them, is an optical fiber and/or fiber bundle 2 laminated into the polymer envelope, which preferably comprise at least a sensor fiber and preferably also a reference fiber.

(14) The rope 80 presented in FIG. 1h comprises two load-bearing composite parts 81 side-by-side that are rectangular in their cross-sectional shape and which are surrounded by a polymer envelope 1. The polymer envelope 1 comprises in the wide side of the rope 80 at a point of the area between the parts 81 a groove 82 for making the rope flexible, in which case the rope shapes itself well against, inter alia, curved surfaces. The rope can alternatively be guided by the aid of the grooves. In this way there can be more than two composite parts 101 side-by-side in this manner in the rope 100, in the manner presented in FIG. 1j. In the composite parts 81, 101 and in the proximity of the surface of the composite parts 81, 101 or between the composite parts is an optical fiber and/or fiber bundle 2 embedded into the polymer envelope 1, which preferably comprise at least a sensor fiber and a reference fiber. The reference fiber can also travel e.g. inside groove such that strain caused by the structure to be measured is not exerted on it. The polymer envelope can also be without a groove, the groove can be situated asymmetrically in relation to the symmetry axis of the rope, or it can be disposed in a different point than what is presented in the figure.

(15) The rope 90 presented in FIG. 1i comprises a load-bearing composite part 91 that is rectangular in its cross-sectional shape, on both sides of which is a wire 92, both of which composite part 91 and which wire 92 are surrounded by a polymer envelope 1. The wire 92 can be a rope or a strand or a braiding and it is preferably from a shear-resistant material such as metal or aramid fiber. The wire can also comprise in connection with the rope or strand or braiding an optical fiber or fiber bundle 2, which preferably comprises at least a sensor fiber and a reference fiber. Instead of a wire, just an optical fiber and/or fiber bundle 2 can be at the side of the rope. Preferably the wire is at the same distance from the surface of the rope as the composite part 91. The metal protection can also be of another type, e.g. a metal batten or metal mesh following the composite part.

(16) FIG. 2 presents a preferred structure for a load-bearing composite part 11, 21, 31, 41, 51, 61, 71, 81, 91, 101. A partial cross-section of the surface structure of the load-bearing composite part (as viewed in the longitudinal direction of the rope) is presented inside the circle in the figure, according to which cross-section the reinforcing fibers of the load-bearing parts presented elsewhere in this application are preferably in a polymer matrix. The figure presents how the reinforcing fibers F are essentially evenly distributed in the polymer matrix M, which surrounds the fibers and is fixed to the fibers. An optical fiber and/or fiber bundle O, which function as actual sensor fibers, are disposed in the plurality of reinforcing fibers F. The reinforcing fibers can also be composed of unidirectional reinforcement layers laminated on above the other, preferably of prepeg layers. The polymer matrix M fills the areas between the reinforcing fibers F and the optical fibers O and binds essentially all the fibers F, O that are inside the matrix to each other as an unbroken solid substance. In this case relative abrasive movement between the fibers F, O and abrasive movement between the fibers F, O and the matrix M is essentially prevented. A chemical bond exists between, preferably all, the fibers F, O and the matrix M, one advantage of which is the homogeneity of the structure. To strengthen the chemical bond, there can be, but not necessarily is, a sizing (not presented) between the fibers F, O and the polymer matrix M. The polymer matrix M is of the kind described elsewhere in this application and can thus comprise additives for adjusting the properties of the matrix as a supplement to the base polymer. The polymer matrix M is preferably a hard thermosetting plastic, e.g. epoxy resin or polyester resin. The fact that the fibers F, O are in the polymer matrix in the load-bearing part means that in the invention the individual fibers F, O are bound to each other with a polymer matrix M, e.g. in the manufacturing phase by embedding them into the material of the polymer matrix. An optical fiber and/or fiber bundle can also be disposed in the manufacturing phase between the prepeg unidirectional layers or glued to the surface in the direction of the layers. In this case the intervals of individual fibers F, O bound to each other with the polymer matrix comprise the polymer of the matrix. Thus in the invention preferably a large amount of reinforcing fibers F and optical fibers O bound to each other in the longitudinal direction of the rope are distributed in the polymer matrix.

(17) The reinforcing fibers are preferably distributed essentially evenly, i.e. homogeneously, in the polymer matrix such that the load-bearing part is as homogeneous as possible when viewed in the direction of the cross-section of the rope. In other words, the fiber content in the cross-section of the composite part does not therefore vary greatly. The reinforcing fibers and optical fibers together with the matrix form an unbroken load-bearing part, inside which relative abrasive movement does not occur when the rope bends. The individual fibers of the load-bearing part are mainly surrounded with the polymer matrix, but contacts between fibers can occur in places because controlling the position of the fibers in relation to each other in the simultaneous impregnation with the polymer matrix is difficult, and on the other hand totally perfect elimination of random contacts between fibers is not wholly necessary from the viewpoint of the functioning of the invention. If, however, it is desired to reduce their random occurrence, the individual fibers can be pre-coated such that a polymer sizing is around them already before the binding of individual fibers to each other. In the invention the individual fibers of the load-bearing part can comprise material of the polymer matrix around them such that the polymer matrix is immediately against the fiber, but alternatively a thin sizing of the fiber, e.g. a primer arranged on the surface of the fiber in the manufacturing phase to improve chemical adhesion to the matrix material, can be in between. An optical fiber can be protected with polyimide.

(18) Individual reinforcing fibers are distributed evenly in the load-bearing part such that the intervals of individual reinforcing fibers comprise the polymer of the matrix. Preferably the majority of the intervals of the individual reinforcing fibers in the load-bearing part are filled with the polymer of the matrix. Most preferably essentially all of the intervals of the individual reinforcing fibers in the load-bearing part are filled with the polymer of the matrix. The matrix of the load-bearing part is most preferably hard in its material properties. A hard matrix helps to support the reinforcing fibers, especially when the rope bends. When bending, tension is exerted on the fibers of the outer surface of the rope and compression on the fibers of the inner surface in their longitudinal direction. Under the influence of compression the fibers try to buckle. When a hard material is selected as the polymer matrix, the crumpling of fibers can be prevented because the hard material is able to support the fibers and thus to prevent their crumpling and to equalize the stresses inside the rope. To reduce the bending radius of the rope, among other things, it is thus advantageous that the matrix material is a polymer that is hard, preferably something other than an elastomer (e.g. rubber) or something else that behaves elastically or gives way. The most preferred materials are epoxy, polyester, phenolic plastic and vinyl ester.

(19) In the method according to the invention for monitoring the condition of a rope and/or roping, which rope 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 and/or roping R comprises a plurality of load-bearing parts, inside which and/or in the proximity of the surface of which, and/or in the polymer matrix surrounding which one or more optical fibers and/or fiber bundles are integrated as sensor fibers and/or as reference fibers, and in the method the condition of the sensor fibers is monitored, e.g. by measuring the time-of-flight of a light pulse in a sensor fiber. The rope and/or roping is according to what is presented elsewhere in this patent application, e.g. in FIGS. 1a-1j. In the method the condition of all or part of a rope and/or roping is monitored by monitoring the condition of the sensor fibers, and if it is detected that a part of a sensor fiber has broken or the condition of it has fallen to below a certain predefined level, a need to replace or overhaul the rope or ropes is diagnosed and rope replacement work or rope maintenance work is started. In the method the time-of-flight of a light pulse can also be measured in different ropes, the times-of-flight of the light pulses can be compared with each other, and when the difference between the times-of-flight of the light pulses increases to above a predefined level, a need to replace or overhaul the rope or ropes is diagnosed and rope replacement work or rope maintenance work is started.

(20) FIG. 3 presents one embodiment of an elevator according to the invention, in which the hoisting roping of the elevator is according to what is presented elsewhere in this patent application, e.g. according to what is defined in the description of any of FIGS. 1a-1j. The roping 10, 20, 30, 40, 50, 60, 70, 80, 90 100, R is fixed at its first end to the elevator car 4 and at its second end to the counterweight 5. The roping is moved with a traction sheave 3 supported on the building, to which traction sheave a power source, such as e.g. an electric motor (not shown), that rotates the traction sheave is connected. The rope is preferably any of the type presented in FIGS. 1a-1j in its structure. The elevator is preferably a passenger transport elevator and/or freight transport elevator, which is installed to travel in an elevator hoistway S in a building.

(21) FIG. 4 presents one embodiment of a condition monitoring method for a rope or roping of an elevator according to the invention, wherein the elevator preferably comprises a separate condition monitoring arrangement functioning on the Time-Of-Flight TOF principle, which condition monitoring arrangement comprises a condition monitoring device 7 connected to the sensor fibers 2a and to the reference fibers 2b of the rope, which device comprises means, such as a computer comprising a laser transmitter, receiver, timing discriminator, a circuit measuring a time interval, a programmable logic circuit and a processor 6. The condition monitoring arrangement comprises one or more sensors S1, S.sub.N/3, each of which sensors comprises e.g. reflectors R1, R2, R3, R.sub.N−2, R.sub.N−1, R.sub.N, where N is the number of reflectors, and a processor 6, which when they detect a change, e.g. in the time-of-flight of the light pulse in the sensor fiber 2a, raise an alarm about excessive wear of the rope. With the reference fibers 2b common mode errors, caused e.g. by changes in temperature, can be eliminated. A number of sensor fibers 2a and the reference fibers 2b can be connected to each other in series and reflectors R1, R2, R3, R.sub.N−2, R.sub.N−1, R.sub.N are situated in the fiber connectors. On the basis of the time-of-flight of a light pulse, preferably by comparing with the aid of the processor to predetermined limit values, the condition monitoring device is arranged to deduce the condition of the load-bearing part in the area between the reflectors. The condition monitoring device can be arranged to initiate an alarm if the time-of-flight of the light pulse does not fall within the desired value range or differs sufficiently from the measured values of the time-of-flight of the light pulse for other ropes being measured. The time-of-flight of the light pulse changes when a property that depends on the condition of a load-bearing part of the rope, such as strain or displacement, changes. For example, owing to breaks the time-of-flight of the light pulse changes, from which change it can be deduced that the load-bearing part is in poor condition.

(22) The property to be observed can also be e.g. a change in the amount of light traveling through the rope. In this case light is fed into an optical fiber with a laser transmitter or with a LED transmitter from one end and the passage of the light through the rope is assessed visually or by the aid of a photodiode at the other end of the fiber. The condition of the rope is assessed as having deteriorated when the amount of light traveling through the rope clearly decreases.

(23) In one embodiment of the condition monitoring method for a rope an optical fiber functions as an optical Fabry-Pérot-type sensor. A Fabry-Pérot interferometer FPI comprises two reflective surfaces, or two parallel highly reflective dichroic mirrors, at the end of the fiber. When it hits the mirrors a part of the light passes through and a part is reflected back. After the mirror the light passing through travels e.g. through air, after which it is reflected back from the second mirror. Some of the light has traveled a longer distance in a different material, which has caused changes in the properties of the light. Strain causes changes in e.g. the phase of the light. The light with changed properties interferes with the original light, after which the change is analyzed. After the lights have combined they end up in a receiver and in a signal-processing device. With the method the strain of the fiber, and thus the condition of the rope, is assessed.

(24) In one embodiment of the condition monitoring method for a rope an optical fiber is used, which fiber comprises Bragg gratings, i.e. the so-called Fiber Bragg Grating FBG method is applied in the condition monitoring of the rope. Periodic grating structures are made in a single-mode fiber for the FBG sensor, which grating structures reflect a certain wavelength of the light corresponding to the grating back. When light is conducted into the fiber, the wavelength of the light corresponding to the grating is reflected back. When strain is exerted on the grating structure, the refractive index of the fiber changes. Changing of the refractive index affects the wavelength of the light being reflected back. By monitoring changes in wavelength, a change in the strain exerted on the grating can be ascertained, and thus also the condition of the rope. There can be tens or hundreds of gratings by the side of the same fiber.

(25) In one embodiment of the condition monitoring method for a rope a distributed sensor fiber based on Brillouin spectrum measurement is used. Ordinary single-mode fiber or multimode fiber can be used as a sensor. The optical fiber functions as a distributed sensor, which can function as a sensor that is hundreds of meters long, which measures throughout its length and corresponds if necessary to thousands of point-form sensors. Backscattering of light occurs continuously as the light propagates in the fiber. This can be utilized by monitoring the strength of certain backscattering wavelengths. Brillouin scattering arises in the manufacturing phase in non-homogeneous points created in the fiber. By observing the wavelengths of the original and the scattered light signal the strain of the fiber, and thus the condition of the rope, is determined.

(26) The effect of temperature on strain measurements can be eliminated by, inter alia, using a reference fiber as an aid, which reference fiber is installed such that strain caused by the structure to be measured is not exerted on it.

(27) It is obvious to the person skilled in the art that in developing the technology the basic concept of the invention can be implemented in many different ways. The invention and the embodiments of it are not therefore limited to the examples described above, but instead they may be varied within the scope of the claims.