Elevator

Abstract

The invention relates to an elevator comprising a hoistway; an elevator car vertically movable in the hoistway; a plurality of ropes connected to the car; a rotatable traction member comprising a circumferential traction surface area for each of the several ropes; each rope being arranged to pass around the rotatable traction member resting against a circumferential traction surface area of the traction member; drive machinery for controlling rotation of the rotatable traction member. The elevator comprises means for detecting displacement of each of the ropes over a first limit position of the rope in the first axial direction of the rotatable traction member, and over a second limit position of the rope in the second axial direction of the traction member; and in that displacement of one or more of said ropes in axial direction of the rotatable traction member over the first or second limit position is arranged to trigger the drive machinery to stop the rotation of the rotatable traction member.

Claims

1. An elevator comprising an elevator car vertically movable in a hoistway; a plurality of ropes connected to the elevator car; a rotatable traction member suspended from a top of the hoistway, the rotatable traction member including a plurality of circumferential traction surface areas, each of the plurality of ropes configured to pass around the rotatable traction member within a corresponding one of the circumferential traction surface areas while having a first end directly connected to the elevator car and a second end directly connected to a counterweight such that the rotatable traction member sustains a weight of the elevator car and the counterweight in the hoistway; a drive machinery configured to control rotation of the rotatable traction member; a detector configured to detect displacement of each of the ropes over a first limit position in a first axial direction of the rotatable traction member, and over a second limit position in a second axial direction of the traction member, the detector including sensing members at the first limit position and the second limit position that are pivotally displaceable around an axis parallel with an axis of the rotatable traction member; and a controller configured stop the drive machinery from rotating the rotatable traction member based on the detector detecting the displacement over one or more of the first limit position and the second limit position.

2. The elevator according to claim 1, wherein the first sensing member is at the first limit position, the first sensing member configured to trigger the controller to instruct the drive machinery to stop the rotation of the rotatable traction member in response a respective one of the plurality of ropes colliding into and displacing the first sensing member, and the second sensing member is at the second limit position, the second sensing member configured to trigger the controller to instruct the drive machinery to stop the rotation of the rotatable traction member in response a respective one of the plurality of ropes colliding into and displacing the second sensing member.

3. The elevator according to claim 2, wherein the sensing members are mounted displaceably via a common displaceable carrier body.

4. The elevator according to claim 3, wherein the detector comprises: at least one electrical sensor configured to sense a position of the displaceable carrier body, and wherein the controller is configured to trigger the controller to instruct the drive machinery to stop the rotation of the traction member, if the position of the displaceable carrier barrier varies pivotably.

5. The elevator according to claim 2, wherein the first sensing member and the second sensing member are displaceable at least in a longitudinal direction of respective ones of the plurality of ropes in response to the respective ones of the plurality of ropes colliding into and displacing a respective one of the first sensing member and the second sensing member in a respective one of the first axial direction and the second axial direction.

6. The elevator according to claim 1, wherein the plurality of ropes are belts.

7. The elevator according to claim 1, wherein the controller is configured to stop the rotation of the rotatable traction member by braking rotation of the rotatable drive member with mechanical brake(s) of the elevator and/or stopping the motor from rotating the rotatable traction member.

8. The elevator according to claim 1, wherein the elevator further comprises: a safety circuit configured to trip in response to the displacement of one of the plurality of ropes to perform a braking procedure, the braking procedure including one or more of braking rotation of the traction member with at least one mechanical brake of the elevator, and stopping the motor from rotating the rotatable traction member.

9. The elevator according to claim 1, wherein the ropes pass around the rotatable traction member adjacent each other in axial direction of the rotatable traction member as well as in the width-direction of the ropes, the wide sides of the ropes against the traction member.

10. The elevator according to claim 1, wherein the rotatable traction member is a traction wheel.

11. The elevator according to claim 1, wherein each circumferential traction surface area of the rotatable traction member has an individual crowning shape.

12. The elevator according to claim 1, wherein the drive machinery comprises: a motor configured to rotate the rotatable traction member.

13. An elevator comprising: an elevator car vertically movable in a hoistway; a plurality of ropes connected to the elevator car; a rotatable traction member including a plurality of circumferential traction surface areas, each of the plurality of ropes configured to pass around the rotatable traction member within a corresponding one of the circumferential traction surface areas; a drive machinery configured to control rotation of the rotatable traction member; a detector configured to detect displacement of each of the ropes over a first limit position in a first axial direction of the rotatable traction member, and over a second limit position in a second axial direction of the traction member, the detector including sensing members positioned at the first limit position and the second limit position and mounted pivotally displaceable around an axis parallel with the first axial direction and the second axial direction of the traction member; and a controller configured stop the drive machinery from rotating the rotatable traction member based on the detector detecting, via pivotal displacement of one or more of the sensing members, the displacement of one of the plurality of ropes over one or more of the first limit position and the second limit position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the present invention will be described in more detail by way of example and with reference to the attached drawings, in which

(2) FIG. 1a illustrates schematically an elevator according to an embodiment of the invention.

(3) FIGS. 1b and 1c illustrate details for the elevator of FIG. 1a.

(4) FIG. 2 illustrates a preferred arrangement for triggering the drive machinery of the elevator of FIG. 1a to stop the rotation of the rotatable traction member.

(5) FIG. 3 illustrates a first preferred embodiment for the means for detecting displacement of the ropes of the elevator in axial direction of the rotatable traction member.

(6) FIG. 4 illustrates a partial and enlarged view of FIG. 3.

(7) FIG. 5 illustrates a second preferred embodiment for the means for detecting displacement of the ropes of the elevator in axial direction of the rotatable traction member.

(8) FIG. 6 illustrates a partial and enlarged view of FIG. 5.

(9) FIG. 7 illustrates the means for detecting displacement of the ropes of FIG. 5 as viewed in said axial direction.

(10) FIG. 8 illustrates the three-dimensionally the means for detecting displacement of the ropes of FIG. 5.

(11) FIG. 9a illustrates a third preferred embodiment for the means for detecting displacement of the ropes of the elevator in axial direction of the rotatable traction member.

(12) FIG. 9b illustrates a preferred structure for a sensing device of FIG. 9a.

DETAILED DESCRIPTION

(13) FIG. 1a illustrates an elevator according to a preferred embodiment. The elevator comprises a hoistway H, an elevator car 1 and a counterweight 2 vertically movable in the hoistway H. The elevator further comprises a rotatable traction member 6, in particular a traction wheel located in or at least in proximity of the upper end of the hoistway H. The rotatable traction member 6 engages an elevator roping R, comprising several ropes, which are connected to the car 1 and pass adjacent each other around the rotatable traction member 6. The roping R suspends the elevator car 1, and in this case, also a counterweight 2. The elevator comprises a drive machinery M for controlling rotation of the rotatable traction member 6, which drive machinery M comprises a motor 7 for rotating the rotatable traction member 6, and a control unit 100 for controlling the motor 7 and a brake b for braking rotation of said rotatable traction member 6. Force for moving the car 1 and counterweight 2 is transmitted from the motor 7 to the car 1 via the rotatable traction member 6 and the roping R, whereby car movement can be controlled by controlling rotation of the rotatable traction member 6. The elevator comprises plurality of landings L.sub.0 to L.sub.n, at which the elevator car 1 is arranged to stop during use of the elevator.

(14) The rotatable traction member 6 has a circumferential traction surface area 11a,11b,11c for each of the several ropes 3a, 3b, 3c, i.e. a specific area individually for each rope against which the rope in question is intended to pass. As illustrated in FIG. 1c, each of said ropes 3a,3b,3c is arranged to pass around the rotatable traction member 6 resting against the circumferential traction surface area 11a,11b,11c of the traction member 6 provided for it.

(15) The elevator comprises means (10,12a-13c; 30; 50) for detecting displacement of each of the ropes 3a,3b,3c in axial direction of the rotatable traction member (6). Said means are provided for detecting displacement of each of the ropes 3a,3b,3c away from between a first limit L1a,L1b,L1c position and a second limit position L2a,L2b,L2c, which first and second limit positions L1a, L2a; L1b, L2b; L1c,L2c are apart from each other in axial direction of the traction member 6. More specifically, said means (10,12a-13c; 30; 50) are provided for detecting displacement of each of the ropes 3a,3b,3c over a first limit position L1a,L1b,L1c defined for the rope in question in the first axial direction X.sub.1 of the rotatable traction member 6, and over a second limit position L2a,L2b,L2c defined for the rope in question in the opposite direction, i.e. the second axial direction X.sub.2 of the traction member 6, which limit positions are on opposite sides of the rope 3a,3b,3c in question in axial direction of the rotatable traction member 6. Displacement of one or more of said ropes 3a,3b,3c away from between the first limit position L1a,L1b,L1c and the second limit position L2a,L2b,L2c in the axial direction of the traction member 6, i.e. in the first or second axial direction over the first or the second limit position L1a, L2a; L1b, L2b; L1c,L2c respectively is arranged to trigger said stopping, i.e. said drive machinery M to stop the rotation of the traction member 6, preferably to brake rotation of the rotatable traction member 6 by activating mechanical brakes b and/or to stop the motor from rotating the rotatable traction member 6. Thereby said limit positions define the allowed range of movement of the rope 3a,3b,3c in question in direction of said axis. Upon displacement of a rope 3a,3b,3c away from its range of movement, stopping of the rotation of the traction member is triggered. The limits positions L1a, L2a; L1b, L2b; L1c,L2c are preferably such that when the rope 3a,3b,3c in question is completely between the first and second limit position L1a, L2a; L1b, L2b; L1c,L2c thereof, its rope surface area placed against the traction member 6 and the circumferential traction surface area 11a,11b,11c meant for the rope in question at least substantially coincide. Drifting of the rope 3a,3b,3c away from its circumferential traction surface area 11a,11b,11c is thus reacted to by bringing the elevator into a swift stop.

(16) The ropes are in the illustrated embodiments in the form of belts as illustrated in FIG. 1c, for instance. Belt-shaped ropes are prone to wandering in axial direction of the rotatable traction member 6, because they are difficult to control without damaging the rope and without complicated arrangements. The solution presented is particularly preferable in case each circumferential traction surface area 11a,11b,11c of the rotatable traction member 6 has an individual crowning shape for preventing movement of the rope placed to pass against it from moving away from its circumferential traction surface area 11a,11b,11c in axial direction of the rotatable traction member 6.

(17) FIG. 2 shows a preferred arrangement for triggering of said stopping i.e. the triggering of the drive machinery M to stop the rotation of the rotatable traction member 6 in a swift and reliable manner. In this case, the elevator comprises a safety circuit 9 (also referred to as a safety chain) breaking of which is arranged to cause the drive machinery M to brake rotation of the traction member 6 (with brake(s) b of the elevator) and to stop the motor from rotating the rotatable traction member 6, and displacement of one or more of said rope 3a,3b,3c in axial direction of the traction member 6 over the first or second limit position is arranged to trigger said stopping i.e. the drive machinery M to brake rotation of the rotatable traction member 6 and to stop rotating the rotatable traction member 6 by triggering a series of one or more actions including at least breaking of said safety circuit 9.

(18) It is preferable, that the breaking of the safety circuit 9 causes that power supply 60 to the frequency converter 100a is broken (the power supply 60 being thereby also a power supply of the motor 7) and/or that the power supply 61 of the actuator(s) of the brake(s) b is broken, which actuator(s) keep(s) the brake(s) b normally in released state when powered. For this purpose the safety circuit 9 is connected to a contactor 62, which may be in the form of a relay, controlling switches of the power supply lines 60 and 61, as illustrated in the FIG. 2. Preferably, the safety circuit 9 is under voltage and the breaking thereof is arranged to cause the contactor 62 to release said switches to opened state and thereby to break the power supply of these power lines 60,61. For the purpose of breaking the safety circuit 9 in context of said triggering, said means (10,12a-13c; 30; 50) preferably comprise a relay r operating a safety switch s of the safety circuit 9. The relay r is preferably a normally closed-type relay (NC), for instance relay in the form of a SPSTNC-type relay. The safety circuit 9 may be seen to form part of the drive machinery M.

(19) As mentioned, the drive machinery comprises an elevator control unit 100, This elevator control unit 100 preferably comprises a frequency converter 100a and a monitoring unit 100b. The control unit 100 is preferably connected with electrical connections 61,63 to the brake(s) b and the motor 7 via which connections it can control the brake(s) b and the motor 7. Thus, in context of said triggering the actions can be realized via these connections. Said electrical connection 63 is preferably electrical power supply for the motor 7 and said electrical connection 61 is preferably electrical power supply for the brake(s) b. The brake(s) are preferably mechanical brake(s). The brake(s) is/are preferably arranged to act on the drive member 6 during the braking by frictional engagement either directly or via a component connected to rotate with the drive member 6. The brake(s) is/are preferably so called machine brake(s). The brake b and the motor 7 are preferably both operable by said control unit 100.

(20) FIG. 3 illustrates a preferred first embodiment for the means 10,12a-13c for detecting the above mentioned displacement of each of the ropes 3a,3b,3c in axial direction of the rotatable traction member 6. As mentioned, the rotatable traction member 6 comprises a circumferential traction surface area for each of the several ropes 3a, 3b, 3c and each rope 3a,3b,3c is arranged to pass around the rotatable traction member 6 resting against a circumferential traction surface area 11a,11b,11c of the traction member 6. In the preferred embodiment these circumferential traction surface areas 11a,11b,11c have each a surface roughness or a surface texture substantially different than the circumferential surface areas 12a,13a;12b,13b,12c,13c of the traction member 6 next to it in said axial direction of the traction member 6, whereby drifting of the rope 3a,3b,3c away from its circumferential traction surface area 11a,11b,11c to rest against the surface area 12a,13a;12b,13b,12c,13c next to it changes sound and/or vibration produced in the contact area during passage of the ropes against the rotatable traction member 6. Said means 10,12a-13c for detecting displacement of one or more of said ropes 3a,3b,3c comprise a sensing arrangement 14,15 comprising one or more sensors 14 for sensing sound and/or a vibration, which sensing arrangement 14,15 is arranged to trigger said stopping i.e. to trigger the drive machinery M to stop the rotation of the traction member 6, if the sound and/or vibration sensed by the sensing arrangement 14,15 meet(s) predetermined criteria, such as reaches a predetermined limit or changes in a predetermined way. For determining whether the sound and/or vibration sensed by the sensing arrangement 14,15 meet(s) predetermined criteria the sensing arrangement 14,15 preferably comprises a processing unit 15 arranged to carry out said determination and said triggering to stop the rotation of the rotatable traction member 6 if the predetermined criteria is/are met.

(21) In this embodiment the position of each of the limit position L1a, L2a; L1b, L2b; L1c,L2c is defined by said criteria, in particular such that each limit position is in the position that the rope has reached when the criteria are met. The criteria are preset such that the sound and/or vibration meet(s) the predetermined criteria, such as reaches a predetermined limit or changes in a predetermined way, when the rope has drifted axially to be positioned to a certain amount against the circumferential surface 12a,13a;12b,13b,12c,13c of the traction member 6 having different surface roughness than the circumferential traction surface area 11a,11b,11c of the rope in question. In practice, the criteria are preset such that for each rope the first limit position L1a, L1b, L1c is located within the axial length of the circumferential surface 12a;12b,12c of the traction member next to the circumferential traction surface area 11a,11b,11c on the first axial side thereof, and that for each rope 3a,3b,3c the second limit position L2a, L2b, L2c is located within the axial length of the circumferential surface 13a;13b,13c of the traction member 6 next to the circumferential traction surface area 11a,11b,11c on the second axial side thereof.

(22) In the preferred embodiment, the circumferential traction surface areas 11a,11b,11c are each smoother, such as have a surface roughness lower or more even surface texture, than the circumferential surface areas 12a,13a;12b,13b,12c,13c of the rotatable traction member 6 next to it in said axial direction of the traction member 6, whereby drifting of the rope 3a,3b,3c away from its circumferential traction surface area 11a,11b,11c to rest against the circumferential surface area 12a,13a;12b,13b,12c,13c of the traction member 6 next to it on either axial side thereof, increases sound and/or vibration produced in the contact area during passage of the rope against the rotatable traction member 6.

(23) As mentioned, the circumferential traction surface areas 11a,11b,11c can each be smoother than the circumferential surface areas 12a,13a;12b,13b,12c,13c of the rotatable traction member 6 next to it in said axial direction of the traction member 6 by having a more even surface texture than the latter. For this purpose, said circumferential surface areas of the traction member next to said circumferential traction surface areas preferably have each an uneven texture, such as a pattern machined into the surface of the traction member 6. Said uneven texture is preferably a serrated texture machined into the surface of the traction member 6. Said circumferential traction surface areas are then preferably unserrated.

(24) FIG. 5 illustrates a preferred second embodiment for the means for detecting the above mentioned displacement of each of the ropes 3a,3b,3c in axial direction of the rotatable traction member 6. Said means 30 comprise for each rope on opposite sides of the rope 3a,3b,3c in said axial direction of the traction member 6 a first and a second sensing member 31,32; 32, 33; 33,34. In the embodiment as illustrated, there are several ropes whereby there are sensing members which extend between the ropes next to each other. Each sensing member comprises a contact face which the rope next to it can contact when the rope in question is displaced in said axial direction. Each first sensing member 31,32,33 is positioned at the first limit position L1a,L1b,L1c of the rope in question, such that a contact face c thereof is positioned at the point of the limit position L1a,L1b,L1c. Each second sensing member 32,33,34 is positioned correspondingly at the second limit position L2a,L2b,L2c of the rope in question such that a contact face c thereof is positioned at the point of the limit position, and each sensing member 31,32; 32, 33; 33,34 is arranged to be displaceable pushed by the rope, which is displaced in said axial direction such that it collides into contact with the sensing member in question. Displacement of each sensing member 31,32,33,34 is arranged to trigger said stopping i.e. to trigger the drive machinery M to stop the rotation of the traction member 6. FIG. 6 illustrates a partial and enlarged view of FIG. 5. For the sake of clarity, only a small number of the sensing members are marked with reference numbers and illustrated in FIG. 6. The rest of the sensing members visible in FIG. 5 works similarly as the ones discussed here.

(25) Each of said sensing members 31,32,33,34 is displaceable at least in the longitudinal direction of the rope 3a,3b,3c, whereby the rope 3a,3b,3c, when it moves in its longitudinal direction during elevator use, in particular during car movement, and is displaced in said axial direction to collide into contact with the sensing member 31,32,33,34, is arranged to engage the sensing member 31,32,33,34 next to it and push it at least in the longitudinal direction of the rope 3a,3b,3c. Thus, when the rope 3a,3b,3c has engaged with a sensing member 31,32,33 or 34 next to it, the rope 3a,3b,3c can displace the sensing member 31,32,33,34 in question by its movement. The sensing member 31,32,33 or 34 in question moves then along with the rope 3a,3b,3c after said engagement, whereby chafing between the rope 3a,3b,3c and the sensing member 31,32,33 or 34 engaging it, is not extensive enough to cause damage to the rope 3a,3b,3c. Said engagement is preferably frictional. The contact surface c of each sensing member 31,32,33,34 is preferably elastically displaceable in said axial direction so as to ensure gentle contact. For this purpose the contact surface c is made of elastic material and/or the sensing member is elastically bendable in said axial direction. The elastic material is preferably elastomer, such as rubber, silicon or polyurethane, for instance. The elasticity of the contact surface c also facilitates firm frictional engagement between the rope 3a,3b,3c and the sensing member 31,32,33,34. In this embodiment, displacement of each sensing member 31,32,33,34 at least in the longitudinal direction of the rope 3a,3b,3c is arranged to trigger said stopping.

(26) So as to provide for the sensing members said displaceability at least in the longitudinal direction of the rope 3a,3b,3c, preferably each of said sensing members 31,32,33,34 is mounted pivotally displaceably around an axis a, which axis is parallel with the axial direction X.sub.1, X.sub.2 of the traction member 6. Pivoting displacement of each sensing member 31,32,33,34 is arranged to trigger said stopping i.e. to trigger the drive machinery M to stop the rotation of the traction member 6. In the preferred embodiment, the sensing members 31,32,33,34 are mounted displaceably in the above defined way via a common pivotally displaceable carrier body 35. Thus, the displaceability need not be provided for them individually. Thus, the structure has small amount of moving parts, whereby it is reliable, simple, and easy to manufacture. The carrier body 35 is preferably mounted pivotally on a frame 37 mounted stationary.

(27) In the preferred embodiment, each of said sensing members 31,32,33,34 is mounted pivotally displaceably towards either turning direction around said axis a. Thus, the sensing members 31,32,33,34 can be engaged by the rope 3a,3b,3c and be displaced pushed by the rope at least in the longitudinal direction of the rope 3a,3b,3c independently of the movement direction of the rope.

(28) In the preferred embodiment, said means 30 for detecting displacement comprise at least one electrical sensor 36, arranged to sense position of the displaceable carrier body 35. The sensor is preferably in the form of a switch having a sensing nose 40 sensing the position of the carrier body 35. In the preferred embodiment, the sensing nose 40 extends into an opening 42 formed in one of two flanges 41 of the carrier body 35, via which flanges 41 the carrier body 35 is pivotally mounted on a stationary mounted frame 37, in particular on flanges 38 thereof. The means 30 preferably also comprise means 39 for resisting said displacement of the carrier body 35. Said means 30 are in the embodiment illustrated in FIG. 8 in the form of one or more spring 39 arranged to resist pivoting of the carrier body 35. The spring(s) is preferably also used for keeping the sensing members positioned such that the sensing members can pivot towards either direction around axis a. The spring(s) is preferably a helical spring mounted coaxially along the axis a between the carrier body 35 and the frame 37. For achieving the triggering of the drive machinery M to stop the rotation of the rotatable traction member 6 said sensor 36 can either include or be connected to a relay r (as described referring to FIG. 2) operating a safety switch s of the safety circuit 9, for instance.

(29) FIG. 9a illustrates a preferred third embodiment for the means 50 for detecting the above mentioned displacement of each of the ropes 3a,3b,3c in axial direction of the rotatable traction member 6. Said means 50 comprise sensing devices 52-55 for receiving electromagnetic radiation or ultrasonic sound from said limit positions L1a,L2a;L1b,L2b;L1c,L2c and a monitoring unit 51, connected to the sensing devices and arranged to trigger said drive machinery M to stop the rotation of the traction member 6 if electromagnetic radiation or ultrasonic sound received from one or more of said limit positions L1a,L2a;L1b,L2b;L1c,L2c meet(s) predetermined criteria, such as reaches a predetermined limit or changes in a predetermined way. Each sensing device 52-55 may be in the form of a photocell, infrared, microwave or laser beam sensor, ultrasonic sound sensor for instance. Said sensing devices 52-55 each comprise a receiver for receiving electromagnetic radiation or ultrasonic sound from a limit position L1a,L2a;L1b,L2b;L1c,L2c it is associated with. FIG. 9b illustrates a preferred structure for a sensing device of 52,53,54,55. Preferably, in addition to a receiver 56 each sensing device 52-55 additionally comprises a sender 57 for sending electromagnetic radiation or ultrasonic sound (if the receiver is a receiver for receiving ultrasonic sound) towards the limit position L1a,L2a;L1b,L2b;L1c,L2c it is associated with, whereby the electromagnetic radiation or ultrasonic sound sent by the sender towards the limit position L1a,L2a;L1b,L2b;L1c,L2c is reflected from a rope displaced over the limit position in question. Electromagnetic radiation or ultrasonic sound received by the receiver associated with the limit position L1a,L2a;L1b,L2b;L1c,L2c in question is arranged to be monitored by the monitoring unit 51, and if the electromagnetic radiation or ultrasonic sound received from one or more of said limit positions L1a,L2a;L1b,L2b;L1c,L2c meet(s) predetermined criteria, the monitoring unit 51 is arranged to trigger said drive machinery M to stop the rotation of the traction member 6, e.g. in the elsewhere defined way. For achieving the triggering of the drive machinery M to stop the rotation of the rotatable traction member 6 said monitoring unit is connected to a relay r (as described referring to FIG. 2) operating a safety switch s of the safety circuit 9, for instance. In FIG. 9, the positions whereto the sensing devices 52-55 are arranged to send said electromagnetic radiation or ultrasonic sound, and wherefrom the sensing devices 52-55 are arranged to receive said electromagnetic radiation or ultrasonic sound from are illustrated as beams drawn in dashed line. In case the means 50 are provided without senders, the ambient light conditions and sound conditions provide electromagnetic radiation and ultrasonic sound to such a degree that displacement of the rope over the limit position changes the observation of the receiving device to a detectable amount whereby it is possible to implement the device without a sender.

(30) Alternative to the multiple sensing devices for receiving electromagnetic radiation or ultrasonic sound from said limit positions L1a,L2a;L1b,L2b;L1c,L2c described, said means 50 may comprise only one of said sensing devices for receiving ultrasonic sound or electromagnetic radiation from limit positions L1a,L2a;L1b,L2b;L1c,L2c, i.e. one sensing device for receiving ultrasonic sound or electromagnetic radiation from several limit positions, and a monitoring unit connected to the one sensing device and arranged to trigger said drive machinery M to stop the rotation of the traction member 6 if the ultrasonic sound or electromagnetic radiation received from one or more of said limit positions L1a,L2a;L1b,L2b;L1c,L2c meet(s) predetermined criteria, such as reaches a predetermined limit or changes in a predetermined way. In this case, the one or more sensing devices can be in the form of an ultrasonic sensing device, optical camera, scanner, a machine vision device or a pattern recognition device. In these cases, the sensing device can comprise one or more senders for sending ultrasonic sound or electromagnetic radiation towards said limit positions L1a,L2a;L1b,L2b;L1c,L2c.

(31) The elevator illustrated is an elevator provided with a counterweight; however the elevator may be alternatively configured to be without a counterweight. The means for detecting displacement of the ropes can be adapted to work independent of whether the elevator comprises a counterweight or not. In the above, said triggering is carried out via the safety circuit 9, which is preferable as the safety circuit is a part normally present in any elevator, but this kind of implementation is not necessary, because said triggering could be carried out in many alternative ways.

(32) The ropes 3a,3b,3c next to each other have both a limit position defined for it between them. For each of the ropes 3a,3b,3c two limit positions L1a, L2a; L1b, L2b; L1c,L2c are defined. However, it is possible that for each, rope limit positions in addition to said first and second are defined, and displacement of the rope over this additional limit can trigger an action different from the action described in the above, such as a warning signal in case the additional limit is within the first and second limit positions.

(33) It is to be understood that the above description and the accompanying Figures are only intended to illustrate the present invention. It will be apparent to a person skilled in the art that the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.