Elevator

Abstract

An elevator includes a car, a counterweight, a rotatable drive member, and one or more suspension ropes interconnecting the car and the counterweight and passing over the rotatable drive member. Each of the suspension rope(s) has a first rope section on the first side of the drive member and a second rope section on the second side of the drive member, the first section(s) of the rope(s) being connected to the car to suspend the car. The second section(s) of the rope(s) are connected to the counterweight to suspend the counterweight. Drive machinery controls rotation of the drive member. The elevator includes a rope tension sensor mounted on the counterweight and arranged to sense tension of the second section(s) of the rope(s). The rope(s) include(s) electrically conducting member(s) extending continuously along the length of the rope(s) forming an electrically conducting connection between the car and counterweight. The rope tension sensor is functionally connected with the drive machinery via said electrically conducting connection between the car and counterweight such that reduced rope tension of the second rope section(s) sensed by the rope tension sensor triggers the drive machinery to brake rotation of the drive member and/or to stop rotating the drive member.

Claims

1. An elevator comprising: a car; a counterweight; a rotatable drive member; one or more suspension ropes interconnecting the car and the counterweight and passing over the rotatable drive member; a drive machinery for controlling rotation of the drive member; a sensor mounted on the counterweight and arranged to sense a state of an elevator component, a hitch plate connected to the one or more suspension ropes; and at least one spring mounted to said hitch plate and a counterweight frame, such that the at least spring is located between the hitch plate and the counterweight frame, wherein each of said one or more suspension ropes comprise at least one electrically conducting member extending continuously along the length of the rope forming an electrically conducting connection between the car and counterweight, wherein the sensor is functionally connected with the drive machinery via said electrically conducting connection between the car and counterweight such that a predetermined state change sensed by the sensor triggers the drive machinery to brake rotation of the drive member and/or to stop rotating the drive member, and wherein the sensor is provided adjacent to the hitch plate.

2. The elevator according to claim 1, wherein: each suspension rope has a first rope section on a first side of the drive member and a second rope section on a second side of the drive member, the first section being connected to the car to suspend the car, and the second section being connected to the counterweight to suspend the counterweight; the sensor is a rope tension sensor mounted on the counterweight and arranged to sense tension of the second section; and the rope tension sensor is functionally connected with the drive machinery via said electrically conducting connection between the car and counterweight such that a reduced rope tension of the second rope section sensed by the rope tension sensor triggers the drive machinery to brake rotation of the drive member and/or to stop rotating the drive member.

3. The elevator according to claim 2, wherein each electrically conducting member is embedded in a polymer isolating the electrically conducting member from other electrically conducting members of the rope.

4. The elevator according to claim 2, wherein each electrically conducting member is a load bearing member, which load bearing member is made of composite material comprising reinforcing fibers embedded in a polymer matrix, which reinforcing fibers are carbon fibers.

5. The elevator according to claim 2, wherein the elevator comprises a car unit mounted on the car, which car unit is electrically connected to the sensor by said at least one electrically conducting member.

6. The elevator according to claim 1, wherein each electrically conducting member is embedded in a polymer isolating the electrically conducting member from other electrically conducting members of the rope.

7. The elevator according to claim 6, wherein each electrically conducting member is a load bearing member of the rope in question, which load bearing member is made of composite material comprising reinforcing fibers embedded in a polymer matrix, which reinforcing fibers are carbon fibers.

8. The elevator according to claim 1, wherein each electrically conducting member is a load bearing member, which load bearing member is made of composite material comprising reinforcing fibers embedded in a polymer matrix, which reinforcing fibers are carbon fibers.

9. The elevator according to claim 1, wherein the elevator comprises a car unit mounted on the car, which car unit is electrically connected to the sensor by said at least one electrically conducting member.

10. The elevator according to claim 1, wherein: the elevator comprises a safety circuit, breaking of which is arranged to cause the drive machinery to brake rotation of the drive member and/or to stop rotating the drive member; and a predetermined state change sensed by the sensor is arranged to trigger via the electrically conducting connection between the car and the counterweight to break the safety circuit, and thereby to trigger the drive machinery to brake rotation of the drive member and/or to stop rotating the drive member.

11. The elevator according to claim 1, wherein each of said one or more suspension ropes comprise two electrically conducting members connected to each other by said sensor, said two electrically conducting members forming consecutive parts of an electrical circuit between the car and counterweight.

12. The elevator according to claim 1, wherein each electrically conducting member forms part of an electrical circuit breaking of which causes breaking of a safety circuit of the elevator, and the sensor is configured to break the electrical circuit between the car and counterweight if a predetermined state change is sensed by the sensor.

13. The elevator according to claim 1, wherein each electrically conducting member forms part of an electrical circuit between the car and counterweight, and the sensor is configured to break the electrical circuit between the car and counterweight if a predetermined state change is sensed by the sensor, and the car is arranged to break the safety circuit if said electrical circuit between the car and counterweight is broken.

14. The elevator according to claim 1, wherein said sensor comprises one or more rope tension sensors.

15. The elevator according to claim 1, wherein each electrically conducting member forms part of an electrical circuit between the car and counterweight, and the sensor is configured to change an electrical property of the electrical circuit between the car and counterweight if predetermined state change is sensed by the sensor, and a predefined change in said electrical properties is configured to cause breaking of a safety circuit of the elevator.

16. The elevator according to claim 1, wherein each said electrically conducting member forms part of an electrical circuit between the car and counterweight, and the sensor is configured to change an electrical property of the electrical circuit between the car and counterweight if a predetermined state change is sensed by the sensor, and the car unit is arranged to break the safety circuit if it detects a predefined change in the electrical properties of the circuit between the car and counterweight.

17. The elevator according to claim 1, wherein said sensor comprises one or more force sensors via which the one or more suspension ropes suspend the counterweight.

18. The elevator according to claim 1, wherein the elevator comprises a traveling cable connected to the elevator car inside which traveling cable a safety circuit passes.

19. The elevator according to claim 1, wherein said one or more suspension ropes are belt-shaped.

20. The elevator according to claim 1, wherein said sensor comprises one or more force sensors via which the one or more suspension ropes suspend the counterweight, via which the second section of each rope is fixed to the counterweight.

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. 1 illustrates schematically an elevator according to a preferred embodiment of the invention.

(3) FIG. 2 illustrates schematically a rope of the elevator.

(4) FIG. 3 illustrates an enlarged partial view of the cross section of a load bearing member of the rope.

(5) FIGS. 4a to 4c illustrate further preferred details for the elevator of FIG. 1 according to a first alternative.

(6) FIGS. 5a to 5c illustrate further preferred details for the elevator of FIG. 1 according to a second alternative.

DETAILED DESCRIPTION

(7) FIG. 1 illustrates an elevator according to a preferred embodiment. The elevator comprises a hoistway S, and a car 1 and a counterweight 2 vertically movable in the hoistway S. The elevator further comprises a rotatable drive member 3 and one or more suspension ropes 4 interconnecting the car 1 and counterweight 2 and passing over said rotatable drive member 3, which engages the rope(s) in a force transmitting manner. Each of the suspension rope(s) 4 has a first rope section 4a on the first side of the drive member 3 and a second rope section 4b on the second side of the drive member 3, the first section(s) 4a of the rope(s) 4 being connected to the car 1 to suspend the car 1, and the second section(s) 4b of the rope(s) 4 being connected to the counterweight 2 to suspend the counterweight 2. In this embodiment, the end of the second rope section 4b is fixed on the counterweight 2 and the end of the first rope section is fixed on the car 1.

(8) The elevator further comprises a drive machinery b,m,6,21,22 controlling rotation of the drive member 3. The drive machinery b,m,6,21,22 comprises one or more brakes b for braking the drive member 3 and a motor m for rotating the drive member 3. The drive machinery further comprises a control unit 6 connected with electrical connections 21,23 to the brake(s) b and the motor m via which connections it can control the brake(s) b and the motor m. Said electrical connection 23 is preferably electrical power supply for the motor m and said electrical connection 21 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 3 during the braking by frictional engagement either directly or via a component connected to rotate with the drive member 3. The brake(s) is/are preferably so called machine brake(s). The drive machinery b,m,6,21,22 comprises an elevator control 6, which comprises a frequency converter 6a and a monitoring unit 6b.

(9) The elevator further comprises a sensing means 7,7 mounted on the counterweight 2 and arranged to sense state of an elevator component 4b. The sensing means 7,7 are in this embodiment rope tension sensing means 7,7 mounted on the counterweight 2 arranged to sense tension of the second section(s) 4b of the rope(s) 4. Thereby, the system can notice a slack ropesituation on the counterweight side. Slackening of ropes 4 on the counterweight side indicates that the force balance at the rotatable drive member 3 is unsafe. For enabling prevention of the situation getting more dangerous and even to stalling, such situation is reacted to by the drive machinery b,m,6,21,22. For enabling reacting to an unsafe situation, the sensing means 7,7 (in this case the rope tension sensing means 7,7) mounted on the counterweight 2 are connected with the drive machinery b,m,6,21,22 functionally such that a predetermined state change (in this case reduced rope tension, i.e. a rope tension which is below a certain limit, of the second rope section(s) 4b sensed by the rope tension sensing means 7,7), triggers the drive machinery b,m,6,21,22 to brake rotation of the drive member 3 and/or to stop the rotating of the drive member 3. Said rope(s) 4 comprise electrically conducting members 5, each extending continuously along the length of the rope 4, the electrically conducting members 5 forming an electrically conducting connection between the car 1 and counterweight 2, via which electrically conducting connection said functional connection is established. In particular, the electrically conducting connection between the car 1 and counterweight 2 makes it possible that said functional connection is routed from counterweight 2 to the car 1 and further to the drive machinery b,m,6,21,22.

(10) In the preferred embodiment, the rope tension sensing means 7,7 are electrically connected to said electrically conducting members 5. The elevator furthermore comprises a car unit 8,8 mounted on the car 1, which car unit 8,8 is electrically connected to the rope tension sensing means 7,7 by said electrically conducting members 5. FIGS. 4 (4a to 4c) and 5 (5a to 5c) illustrate alternative configurations for the elevator of FIG. 1. In both of these more detailed embodiments, the elevator furthermore comprises a safety circuit 9 (also referred to as a safety chain) breaking of which causes the drive machinery b,5,6,21,22 to brake rotation of the drive member 3 and/or to stop rotating the drive member 3. In particular, the breaking of the safety circuit 9 causes that power supply 20 to the frequency converter 6a is broken (the power supply 20 being thereby also a power supply of the motor m) and/or that the power supply 21 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 22, which may be in the form of a relay, controlling switches of the power supply lines 20 and 21, as illustrated in the FIG. 1. Preferably, the safety circuit 9 is under voltage and the breaking thereof is arranged to cause the contactor 22 to release said switches to opened state and thereby to break the power supply of these power lines 20,21. Reduced rope tension of the second rope section(s) 4b sensed by the rope tension sensing means 7,7 is arranged to trigger via the electrically conducting connection between the car 1 and counterweight 2 the car unit 8,8 to break the safety circuit 9. In particular, the car unit 8,8 is arranged to break the safety circuit 9 if reduced rope tension of the second rope section(s) 4b is sensed by the rope tension sensing means 7,7. For this purpose, it preferably comprises a relay 8a,8a operating a safety switch s of the safety circuit. The relay 8a,8a is preferably a normally closedtype relay (NC), for instance relay in the form of a SPSTNCtype relay. As illustrated in FIGS. 1 and 4c and 5c, in both of the embodiments, the safety circuit 9 connects the car unit 8,8 and the drive machinery. Thereby, said functional connection is established via said electrically conducting connection between the car (1) and counterweight (2), and further via the car unit 8,8, and the safety chain 9. As illustrated in FIGS. 1 and 4c and 5c, in both of the embodiments, on both sides of the safety switch s the safety chain has a conductor 9a,9b passing away from the car inside a traveling cable 10 connected to the elevator car 1.

(11) FIGS. 2 and 3 illustrate a preferred structure for an individual rope 4. Each of the aforementioned electrically conducting members 5 is in this case a load bearing member 5 of a rope 4, which load bearing member 5 is made of composite material comprising reinforcing fibers f embedded in a polymer matrix m, which reinforcing fibers f are carbon fibers. With this material selection, the member 5 can provide good properties in terms of load bearing and electrical conductivity. Thereby, there is no need for embedding a conducting element in the rope 4, which does not contribute in the essential load bearing function of the rope 4. The aforementioned one or more ropes may comprise several of the ropes 4 as illustrated in FIGS. 2 and 3. It is not necessary that each of the ropes 4 has exactly two of the load bearing members 5 as disclosed in FIG. 2, but each rope 4 may have one or several of such load bearing members 5. Then, any two of the load bearing members 5 of the ropes 4, irrespective of whether they are comprised in the same rope 4 or in different ropes 4, can form a part of an electrical circuit which is formed between the counterweight 2 and the car 1. It is however preferable that there are at least two of such load bearing members 5 comprised in one rope which both form part of the aforementioned electrical circuit which is formed between the counterweight 2 and the car 1. In this way, the electrical connections are simple to provide, and the functional connection can be provided even with only one rope. For this purpose, it is advantageous that the ropes 4 are belt-like, as thereby it is easy to embed several of said electrically conducting/load bearing members 5 in one rope 4 to be spaced apart from each other in width direction of the rope 4. Several other alternatives for the structure of the rope 4 are illustrated and described in document WO2009090299A1.

(12) As illustrated in FIGS. 2 and 3, the electrically conducting members 5 forming the electrically conducting connection between the car 1 and counterweight 2, each of which is in this case a load bearing member 5 of a rope 4, are embedded in polymer coating p immediately against and surrounding the electrically conducting member 5, which polymer coating p isolates each electrically conducting member 5 from any other electrically conducting member of the rope 4 as well as from components external to the rope 4 with which component the conducting member 4 could otherwise get into contact. The coating p is preferably of polymer, most preferably of elastic polymer, such as of polyurethane, as it provides good wear resistance, protection and good friction properties, for instance for frictional traction contact with the rotatable drive member 3. The coating p forms in these embodiments the surface of the rope.

(13) As mentioned, rope 4 is preferably in the form of a belt, and thereby has a width w substantially larger than the thickness t thereof as presented in FIG. 2. This makes it well suitable for elevator use as bending of the rope is necessary in most elevators. So as to give a turning radius well suitable for elevator use, it is preferable that the width/thickness ratio of the rope is at least 2 or more, preferably at least 4, even more preferably at least 5 or more. Furthermore, so as to give a turning radius well suitable for elevator use, it is preferable that the width/thickness ratio(s) of said load bearing member(s) 5 is/are at least 2, preferably at least 3 or more. If the rope 4 is made to contain only one load bearing member 5, then it is preferable that this ratio is 5 or more. It is preferable, that all the load bearing member(s) 5 of the rope (irrespective whether there is only one or more of them in the rope) cover together majority, preferably 70% or over, more preferably 75% or over, most preferably 80% or over, of the width of the rope. Thus, the width of the rope is effectively utilized for the function of load bearing.

(14) The preferred composite structure of the load bearing member 5 is preferably more specifically as follows. The load bearing member 5, as well as its fibers f are parallel with the longitudinal direction the rope, and untwisted as far as possible. Individual reinforcing fibers f are bound into a uniform load bearing member with the polymer matrix m. Thus, each load bearing member 5 is one solid elongated rodlike piece. The reinforcing fibers f are preferably long continuous fibers in the longitudinal direction of the rope 4, the fibers f preferably continuing for the whole length of the load bearing member 5 as well as the rope 4. Preferably as many fibers f as possible, most preferably substantially all the fibers f of the load bearing member 5 are oriented parallel with the rope, as far as possible in untwisted manner in relation to each other. Thus the structure of the load bearing member 5 can be made to continue the same as far as possible in terms of its cross-section for the whole length of the rope. The reinforcing fibers f are preferably distributed in the aforementioned load bearing member 5 as evenly as possible, so that the load bearing member 5 would be as homogeneous as possible in the transverse direction of the rope. An advantage of the structure presented is that the matrix m surrounding the reinforcing fibers f keeps the interpositioning of the reinforcing fibers f substantially unchanged. It equalizes with its slight elasticity the distribution of a force exerted on the fibers, reduces fiber-fiber contacts and internal wear of the rope, thus improving the service life of the rope. The composite matrix m, into which the individual fibers f are distributed as evenly as possible, is most preferably of epoxy resin, which has good adhesiveness to the reinforcement fibers f and which is known to behave advantageously with carbon fiber. Alternatively, e.g. polyester or vinyl ester can be used, but alternatively any other suitable alternative materials can be used. FIG. 3 presents a partial cross-section of the load bearing member 5 close to the surface thereof as viewed in the longitudinal direction of the rope presented inside the circle in the figure, according to which cross-section the reinforcing fibers f of each load bearing member 5 are preferably organized in the polymer matrix m. The rest (not showed parts) of the load bearing member 5 has a similar structure. FIG. 3 presents also how the individual reinforcing fibers f are substantially evenly distributed in the polymer matrix m, which surrounds the fibers and which is fixed to the fibers f. The polymer matrix m fills the areas between individual reinforcing fibers f and binds substantially all the reinforcing fibers f that are inside the matrix m to each other as a uniform solid substance. A chemical bond exists between, preferably all, the individual reinforcing fibers f and the matrix m, one advantage of which is uniformity of the structure. To strengthen the chemical bond, there can be, but not necessarily, a coating (not presented) of the actual fibers between the reinforcing fibers and the polymer matrix m. The polymer matrix m is preferably of a hard non-elastomer. It can comprise additives for fine-tuning the properties of the matrix as an addition to the base polymer. The reinforcing fibers f being in the polymer matrix means here that the individual reinforcing fibers are bound to each other with the polymer matrix m, e.g. in the manufacturing phase by immersing them together in the fluid material of the polymer matrix. In this case the gaps of individual reinforcing fibers bound to each other with the polymer matrix comprise the polymer of the matrix. In this way a great number of reinforcing fibers bound to each other in the longitudinal direction of the rope are distributed in the polymer matrix. The reinforcing fibers are preferably distributed substantially evenly in the polymer matrix such that the load bearing member is as homogeneous as possible when viewed in the direction of the cross-section of the rope. In other words, the fiber density in the cross-section of the load bearing member does not therefore vary substantially. The reinforcing fibers f together with the matrix m form a uniform load bearing member, inside which abrasive relative movement does not occur when the rope is bent. The individual reinforcing fibers of the load bearing member 5 are mainly surrounded with polymer matrix m, but random fiber-fiber contacts can occur because controlling the position of the fibers in relation to each other in their simultaneous impregnation with polymer is difficult, and on the other hand, perfect elimination of random fiber-fiber contacts is not necessary from the viewpoint of the functioning of the invention. If, however, it is desired to reduce their random occurrence, the individual reinforcing fibers f can be pre-coated such that a polymer coating is around them already before the binding of individual reinforcing fibers to each other. In the invention the individual reinforcing fibers of the load bearing member can comprise material of the polymer matrix around them such that the polymer matrix is immediately against the reinforcing fiber but alternatively a thin coating, e.g. a primer arranged on the surface of the reinforcing fiber in the manufacturing phase to improve chemical adhesion to the matrix material, can be in between. Individual reinforcing fibers are distributed evenly in the load bearing member 5 such that the gaps of individual reinforcing fibers f are filled with the polymer of the matrix m. Most preferably the majority, preferably substantially all of the gaps of the individual reinforcing fibers f in the load bearing member 5 are filled with the polymer of the matrix m. As above mentioned, the matrix m of the load bearing member 5 is most preferably hard in its material properties. A hard matrix m helps to support the reinforcing fibers f, especially when the rope bends, preventing buckling of the reinforcing fibers f of the bent rope, because the hard material supports the fibers f. To reduce the buckling and to facilitate a small bending radius of the rope, among other things, it is therefore preferred that the polymer matrix is hard, and in particular non-elastomeric. The most preferred materials are epoxy resin, polyester, phenolic plastic or vinyl ester. The polymer matrix is preferably so hard that its module of elasticity (E) is over 2 GPa, most preferably over 2.5 GPa. In this case the module of elasticity (E) is preferably in the range 2.5-10 GPa, most preferably in the range 2.5-3.5 GPa. There are commercially available various material alternatives for the matrix m which can provide these material properties. Preferably over 50% of the surface area of the cross-section of the load bearing member 5 is of the aforementioned reinforcing fiber, preferably such that 50%-80% is of the aforementioned reinforcing fiber, more preferably such that 55%-70% is of the aforementioned reinforcing fiber, and substantially all the remaining surface area is of polymer matrix. Most preferably, this is carried out such that approx. 60% of the surface area is of reinforcing fiber and approx. 40% is of matrix material (preferably epoxy material). In this way a good longitudinal stiffness for the load bearing member 5 as well as good electrical conductivity are achieved.

(15) FIGS. 4 (4a to 4c) and 5 (5a to 5c) illustrate alternative configurations for the elevator of FIG. 1. FIGS. 4a to 4c illustrate a configuration where each of said electrically conducting members 5 forms part of an electrical circuit breaking of which causes breaking of a safety circuit 9 of the elevator, and the rope tension sensing means 7 are configured to break the electrical circuit between the car 1 and counterweight 2 if reduced rope tension of the second rope section(s) 4b is sensed by the rope tension sensing means 7. For this purpose, the sensing means 7 comprise a switch component 7a configured to normally close the electrical circuit between the car 1 and counterweight 2 formed at least partially by two electrically conducting members 5 of the ropes (in this case by two conducting members 5 of one and the same rope 4 and to open said electrical circuit in case of reduced rope tension of the second rope section(s) 4b. It is preferable that the electrical circuit is under voltage when it is closed. If said electrical circuit between the car 1 and counterweight 2 is broken the car unit 8 is arranged to break the safety circuit 9. Thus, educed rope tension of the second rope section(s) 4b sensed by the rope tension sensing means 7 is arranged to break said conducting connection between the car 1 and counterweight 2 and thereby trigger via the electrically conducting connection between the car 1 and counterweight 2 the car unit 8,8 to break the safety circuit 9 and thereby to trigger said braking of the drive machinery (b,5,6,21,22) and/or to stopping the rotating of the drive member (3). The switch component 7a is preferably spring-actuated, the rope tension working against the force of the spring(s) 7c, and configured such that in case of reduced rope tension the spring force overcomes the rope tension and actuates the switch to move into open state. As illustrated in FIG. 4b the ropes are mounted via said springs 7b. In particular, said springs 7b are mounted between the hitch plate 7c and the counterweight frame 2a to urge the hitch plate towards the tension sensor 7a. In case the tension of the second rope sections 4b drops, the spring force overcomes the rope tension force and moves the hitch plate 7c against the tension sensor 7a, which then is brakes the electrical circuit between the car (1) and counterweight (2) formed at least partially by two electrically conducting members (5). The car unit 8, in particular a relay 8a thereof opens a safety switch s of the safety chain 9 in response to breaking of the electrical circuit between the car (1) and counterweight (2) formed at least partially by two electrically conducting members (5, which has the consequence that the power supply 20 to the frequency converter 6a to break and/or the power supply 21 of the actuator(s) of the brake(s) b to break.

(16) FIGS. 5a to 5c illustrate a configuration where each said electrically conducting member(s) 5 forming said electrically conducting connection between the car (1) and counterweight 2 forms part of an electrical circuit between the car 1 and counterweight 2, and the rope tension sensing means 7 are configured to change an electrical property of the circuit between the car 1 and counterweight 2 if reduced rope tension of the second rope section(s) 4b is sensed by the rope tension sensing means 7, and a predefined change in the electrical properties is configured to cause breaking of a safety circuit 9 of the elevator. In particular, the car unit 8 is arranged to break the safety circuit (9) if it detects a predefined change in the electrical properties of the electrical circuit between the car 1 and counterweight 2. Said sensing means 7 comprise one or more rope tension sensors 7a configured to change the electrical properties of the circuit when the sensor(s) sense reduced rope tension. In this embodiment, the sensor(s) 7a is/are force sensor(s) 7a via which the rope(s) (4) suspend(s) the counterweight, in particular via which the second section(s) of the rope(s) is/are fixed to the counterweight. Thereby, the rope tension is transmitted to the force sensor(s) 7a. Said change in the electrical properties may be for instance a change in resistance caused by change in force directed to the force sensor(s) 7a. There may be one or more of the force sensor(s) 7a, for example sensing different ropes 4. In the example as illustrated in FIGS. 5a to 5c there is only on sensor 7a and one of said electrical circuits between the car 1 and counterweight 2. Said sensor 7a is preferably in the form a strain gauge. It is preferable that the electrical circuit is under voltage. For the purpose of detecting the change in the electrical property of the circuit at the car end, the car unit 8 comprises a monitoring unit 8b controlling a safety relay 8a. The car unit 8, in particular the monitoring unit 8b is configured to control said relay 8a to open a safety switch s of the safety chain 9 in response to the detected change in the electrical property of the electrical circuit at the car end, which has the consequence that the power supply 20 to the frequency converter 6a to break and/or the power supply 21 of the actuator(s) of the brake(s) b to break.

(17) In this application, the term load bearing member of a rope refers to the part that is elongated in the longitudinal direction of the rope, and which part is able to bear without breaking a significant part of the load exerted on the rope in question in the longitudinal direction of the rope. The aforementioned load exerted on the rope causes tension on the load bearing member in the longitudinal direction of the load bearing member, which tension can be transmitted inside the load bearing member in question all the length of the load bearing member, e.g. from one end of the load bearing member to the other end of it.

(18) In the application said reduced rope tension is considered to mean a rope tension, which is below a certain limit. Said limit is preferably predetermined substantially below a rope tension which is considered to be within normal variation of the rope tension of the second rope section(s) being sensed.

(19) In the examples presented in the application, the elevator comprises two of said electrically conducting members forming an electrically conducting connection between the car and counterweight, which are connected to each other by said tension sensing means, and forming consecutive parts of an electrical circuit between the car and counterweight. This is a preferred configuration, but some aspects of the configuration can be changed if desired. In particular, the number of said electrically conducting members could be greater or smaller. It is even possible to realize an electrically conducting connection functioning as described with only one of said electrically conducting members. In this case, the tension sensing means is preferable to equip with a battery for providing voltage, which is then utilized for sending an electrical signal to the drive machinery via the connection between the car and the counterweight so as to trigger the functions defined elsewhere in the application.

(20) As more specifically described and illustrated earlier with examples, a predetermined state change sensed by the sensing means is arranged to trigger via said electrically conducting connection the drive machinery to brake rotation of the drive member and/or to stop rotating the drive member. In the preferred embodiment of this idea, reduced rope tension of the second rope section(s) 4b sensed by the rope tension sensing means 7,7 is arranged to trigger via said electrically conducting connection the drive machinery b,5,6,21,22 to brake rotation of the drive member 3 and/or to stop rotating the drive member 3. In the preferred embodiment, said sensing means 7,7 mounted on the counterweight 2 and arranged to sense state of an elevator component 4b are in the form of a rope tension sensing means 7,7 mounted on the counterweight 2 and arranged to sense tension of the second section(s) 4b of the rope(s) 4, said predetermined state change being a reduced rope tension, i.e. the predetermined state change equals to reduction of rope tension below a certain limit. However, said sensing means 7,7 may be alternatively arranged to sense state of a different component than the second section(s) 4b of the rope(s), for example state of a brake acting on guide rails of the counterweight, the brake being in particular a safety gear, mounted on the counterweight 2. Thus, actuation of the brake is quickly noticed and reacted to. In another example of such different component the state of which is sensed; the component may be the guide rail of the counterweight 2 or a component which is dependent of counterweights 2 position relative to its guide rails, whereby (direct or indirect) sensing of counterweight derailment can be provided. Thus, derailment is quickly noticed and reacted to.

(21) 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.