Method and device for determining a deterioration state in a suspension member for an elevator

Abstract

A method for determining a deterioration state in a suspension member arrangement having a suspension member including a plurality of electrically conductive cords includes the steps of: counting a number of bending cycles applied to the suspension member; measuring an electrical characteristic of the suspension member upon applying an electrical voltage to at least one of the cords; performing at least one of (a) determining a critical deterioration state upon monitoring both the bending cycles number and the electrical characteristic, and (b) determining an unexpected deterioration state based on deriving a current actual deterioration state of the suspension member based on the electrical characteristic and assuming a currently expected deterioration state based on the bending cycles number and comparing the current actual deterioration state with the currently expected deterioration state; initiating a defined procedure upon determining at least one of the critical deterioration state and the unexpected deterioration state.

Claims

1. A method for determining a deterioration state in a suspension member arrangement for an elevator, the suspension member arrangement having a suspension member including a plurality of electrically conductive cords, the method comprising the steps of: counting a number of bending cycles applied to the suspension member; determining an electrical characteristic of the suspension member; performing at least one of (a) determining a critical deterioration state upon monitoring both the counted number of bending cycles applied to the suspension member and the determined electrical characteristic of the suspension member; and (b) determining an unexpected deterioration state based on deriving a current actual deterioration state of the suspension member based on the determined electrical characteristic and assuming a currently expected deterioration state based on the counted number of bending cycles and comparing the current actual deterioration state with the currently expected deterioration state; initiating a defined procedure for the elevator upon the determining at least one of the critical deterioration state and the unexpected deterioration state; and wherein the suspension member is subdivided into several sections and wherein a number of section bending cycles applied to each section of the suspension member is counted for each of the sections and wherein the number of bending cycles applied to the suspension member is set to correspond to a maximum of all the numbers of section bending cycles counted for each of the sections of the suspension member.

2. The method according to claim 1 wherein the critical deterioration state is determined upon occurrence of at least one of: the counted number of bending cycles applied to the suspension member exceeding an allowable maximum number; and the determined electrical characteristic of the suspension member deviating from a reference characteristic by more than an allowable maximum deviation.

3. The method according to claim 2 wherein the allowable maximum deviation is at least one of determined taking into account the counted number of bending cycles applied to the suspension member and fixedly predetermined.

4. The method according to claim 2 wherein the allowable maximum number is at least one of determined taking into account the determined electrical characteristic of the suspension member and fixedly predetermined.

5. The method according to claim 2 wherein the reference characteristic is determined based upon measuring the electrical characteristic of the suspension member in a non-deteriorated condition.

6. The method according to claim 1 wherein the determining of the electrical characteristic of the suspension member comprises at least one of: determining an electrical resistivity through the suspension member; determining an electrical conductivity through the suspension member; determining an inductivity through the suspension member; determining the electrical characteristic using magnetic measurements applied to the suspension member; and determining the electrical characteristic using phase measurements applied to the suspension member.

7. A method for determining a deterioration state in a suspension member arrangement for an elevator, the suspension member arrangement having a suspension member including a plurality of electrically conductive cords, the method comprising the steps of: counting a number of bending cycles applied to the suspension member; determining an electrical characteristic of the suspension member; performing at least one of (a) determining a critical deterioration state upon monitoring both the counted number of bending cycles applied to the suspension member and the determined electrical characteristic of the suspension member; and (b) determining an unexpected deterioration state based on deriving a current actual deterioration state of the suspension member based on the determined electrical characteristic and assuming a currently expected deterioration state based on the counted number of bending cycles and comparing the current actual deterioration state with the currently expected deterioration state; initiating a defined procedure for the elevator upon the determining at least one of the critical deterioration state and the unexpected deterioration state; and wherein the determining of the electrical characteristic of the suspension member comprises at least one of: electrical measurements indicating that at least one of the cords in the suspension member is broken; electrical measurements indicating that an electrical connection between a voltage supply for applying the electrical voltage to the at least one cord and the at least one of the cord is interrupted; electrical measurements indicating that the at least one cord is electrically connected to ground potential; electrical measurements indicating that at least two of the cords in the suspension member are shorted together; and electrical measurements indicating that an electrical conductivity through the at least one cord changed over time.

8. A method for determining a deterioration state in a suspension member arrangement for an elevator, the suspension member arrangement having a suspension member including a plurality of electrically conductive cords, the method comprising the steps of: counting a number of bending cycles applied to the suspension member; determining an electrical characteristic of the suspension member; performing at least one of (a) determining a critical deterioration state upon monitoring both the counted number of bending cycles applied to the suspension member and the determined electrical characteristic of the suspension member; and (b) determining an unexpected deterioration state based on deriving a current actual deterioration state of the suspension member based on the determined electrical characteristic and assuming a currently expected deterioration state based on the counted number of bending cycles and comparing the current actual deterioration state with the currently expected deterioration state; and initiating a defined procedure for the elevator upon the determining at least one of the critical deterioration state and the unexpected deterioration state; and wherein, upon determining the electrical characteristic, an electric indicator current correlating to a net sum of all phases of a multi-phase alternating current is measured, wherein at least one of the phases of the multi-phase alternating current is applied to one of the cords of the suspension member.

9. The method according to claim 8 wherein the indicator current is measured using a measuring arrangement comprising a measuring device for contactless measuring of an electrical current in a conductor arrangement, the measuring device being one of a current transformer and a Hall effect current sensor.

10. A method for determining a deterioration state in a suspension member arrangement for an elevator, the suspension member arrangement having a suspension member including a plurality of electrically conductive cords, the method comprising the steps of: counting a number of bending cycles applied to the suspension member; determining an electrical characteristic of the suspension member; performing at least one of (a) determining a critical deterioration state upon monitoring both the counted number of bending cycles applied to the suspension member and the determined electrical characteristic of the suspension member; and (b) determining an unexpected deterioration state based on deriving a current actual deterioration state of the suspension member based on the determined electrical characteristic and assuming a currently expected deterioration state based on the counted number of bending cycles and comparing the current actual deterioration state with the currently expected deterioration state; and initiating a defined procedure for the elevator upon the determining at least one of the critical deterioration state and the unexpected deterioration state; and wherein the measuring of the electrical characteristic of the suspension member comprises the steps of: providing a multi-phase alternating current circuitry including multiple electrically conductive legs; applying at least one phase of a multi-phase alternating current to at least one of the cords of the suspension member by the at least one cord being electrically connected to one of the legs of the multi-phase alternating current circuitry; applying at least one other phase of the multi-phase alternating current to at least another cord of the suspension member and at least one separate resistor being electrically connected to at least one other leg of the multi-phase alternating current circuitry, wherein a peak current in each phase is shifted by a phase angle with respect to a peak current in another phase; measuring an electric indicator current being at least one of a net sum of all phases of the multi-phase alternating current, and an electric bypass current through a neutral wire being connected in parallel to the multi-phase alternating current circuitry; and determining the measured electrical characteristic of the suspension member based on the measured indicator electric current.

11. The method according to claim 10 wherein the indicator current is measured using a measuring arrangement comprising a measuring device for contactless measuring of an electrical current in a conductor arrangement, the measuring device being one of a current transformer and a Hall effect current sensor.

12. A method for determining a deterioration state in a suspension member arrangement for an elevator, the suspension member arrangement having a suspension member including a plurality of electrically conductive cords, the method comprising the steps of: counting a number of bending cycles applied to the suspension member; determining an electrical characteristic of the suspension member; performing at least one of (a) determining a critical deterioration state upon monitoring both the counted number of bending cycles applied to the suspension member and the determined electrical characteristic of the suspension member; and (b) determining an unexpected deterioration state based on deriving a current actual deterioration state of the suspension member based on the determined electrical characteristic and assuming a currently expected deterioration state based on the counted number of bending cycles and comparing the current actual deterioration state with the currently expected deterioration state; and initiating a defined procedure for the elevator upon the determining at least one of the critical deterioration state and the unexpected deterioration state; and wherein the suspension member has a first group and a second group of electrically conductive cords, and wherein the measuring of the electrical characteristic comprises the steps of: applying a first alternating voltage to a first end of the first group of cords; applying a second alternating voltage to a first end of the second group of cords, wherein the first and second alternating voltages have same waveforms and a phase difference of 180°, and wherein a second end of the first group of cords and a second end of the second group of cords are electrically connected via a connecting electrical resistance; determining at least one of (i) a summed voltage correlating to a sum of a third voltage between the second end of the first group of cords and a common electrical potential and a fourth voltage between the second end of the second group of cords and the common electrical potential; (ii) a differential voltage correlating to a difference between the third voltage and the fourth voltage; and determining the electrical characteristic of the suspension member based on at least one of the summed voltage and the differential voltage, wherein any deviation from a state in which the summed voltage comprises no alternating voltage component and the differential voltage comprises an alternating voltage component is interpreted as indicating an electrical characteristic relating to the critical deterioration state in the suspension member.

13. A monitoring arrangement configured to perform the method according to claim 1 for determining the deterioration state in the suspension member arrangement.

14. The monitoring arrangement according to claim 13 comprising: a counter device for counting a number of bending cycles applied to the suspension member based on information obtained from an elevator control device for controlling operation of the elevator; an electrical measuring device electrically connected to at least one of the cords in the suspension member for measuring the electrical characteristic of the suspension member upon applying an electrical voltage to the at least one cord; a determination device for determining at least one of (a) a critical deterioration state of the suspension member upon monitoring both: the counted number of bending cycles applied to the suspension member, and the determined electrical characteristic of the suspension member, and (b) an unexpected deterioration state of the suspension member based on deriving a current actual deterioration state of the suspension member based on the determined electrical characteristic and assuming a currently expected deterioration state based on the counted number of bending cycles and comparing the current actual deterioration state with the currently expected deterioration state.

15. An elevator comprising the suspension member, a car connected to the suspension member and a monitoring arrangement according to claim 14.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an elevator in which a method according to an embodiment of the invention may be applied.

(2) FIG. 2 shows an exemplary suspension member.

(3) FIG. 3 shows an exemplary embodiment of a monitoring arrangement according to an embodiment of the present invention.

(4) FIG. 4 shows an alternative exemplary embodiment of a monitoring arrangement according to an embodiment of the present invention.

(5) FIG. 5 shows an example of an electrical measuring device for measuring electrical characteristics in a suspension member for a monitoring arrangement according to an embodiment of the present invention.

(6) FIG. 6 shows another example of an electrical measuring device for measuring electrical characteristics in a suspension member for a monitoring arrangement according to an embodiment of the present invention.

(7) FIG. 7 visualizes electrical parameters to be induced or measured during measuring electrical characteristics of a suspension member with an electrical measuring device as shown in FIG. 6.

(8) The figures are only schematic representations and are not to scale. Same reference signs refer to same or similar features throughout the figures.

DETAILED DESCRIPTION

(9) FIG. 1 shows an elevator 1 in which a method according to embodiments of the present invention may be implemented.

(10) The elevator 1 comprises a car 3 and a counterweight 5 which may be displaced vertically within an elevator shaft 7. The car 3 and the counterweight 5 are suspended by a suspension member arrangement 9. This suspension member arrangement 9 comprises one or more suspension members 11, sometimes also referred to a suspension traction media (STM). Such suspension members 11 may be for example ropes, belts, etc. In the arrangement shown in FIG. 1, end portions of the suspension members 11 are fixed to a supporting structure of the elevator 1 at a top of the elevator shaft 7. The suspension members 11 may be displaced using an elevator traction machine 13 driving a traction sheave 15. The car 3 and the counterweight 5 may be held by the suspension members 11 by winding the suspension members 11 around pulleys 16. An operation of the elevator traction machine 13 may be controlled by a control device 18. For example at opposite end portions of the suspension member arrangement 9 components of a monitoring device 17 for determining a deterioration state in the suspension member arrangement 9 may be provided.

(11) It may be noted that the elevator 1 and particularly its suspension member(s) 11 and its monitoring device 17 for determining the deterioration may be configured and arranged in various other ways than those shown in FIG. 1.

(12) The suspension members 11 to be driven for example by the traction machine 13 may utilize metal cords or ropes to support a suspended load such as the car 3 and/or the counterweight 5 that is moved by the traction machine 13.

(13) FIG. 2 shows an example of a suspension member 11 which is embodied with a belt 19. The belt 19 comprises a plurality of cords 23 which are arranged parallel to and spaced from each other. The cords 23 are enclosed in a matrix material 21 forming, inter alia, a coating or jacket. Such coating may mechanically couple neighbouring cords 23. The coating may have a textured or profiled surface including longitudinal guiding grooves. The cords 23 may typically consist of or comprise wires made from a metal such as steel. The matrix material 21 may consist of or comprises a plastic or elastomeric material. Accordingly, the cords 23 are typically electrically conductive such that an electric voltage may be applied to and/or an electric current may be fed through the cords without significant losses. Furthermore, the cords 23 are preferably electrically isolated from each other via the interposed electrically insulating matrix material 21 such that, as long as an integrity of the coating is not deteriorated, an electrical current or voltage between neighbouring cords cannot be transmitted, i.e. no significant shunt current can flow from one cord 23 to another.

(14) FIGS. 3 and 4 show an exemplary embodiment of a monitoring arrangement including a control device 18 and a monitoring device 17 for determining the deterioration state in the suspension member 11 of the elevator 1. The monitoring arrangement (17+18) comprises a counter device 25, an electrical measuring device 27 and a determination device 29. These devices 25, 27, 29 may be implemented as separate units. Alternatively, these devices 25, 27, 29 may be integrated into one single unit. Also, the control device 18 and the monitoring device 17 may be embodied as separate devices, or may me embodied as a single device, e.g. all incorporated in an elevator control unit for controlling the overall functionality or operation of the elevator. In one embodiment, the control device 18 may be substantially identical to the elevator control unit, while in others, the control device 18 may be a part or subsystem of the elevator control unit. In further embodiments, the control device 18 may be separate from the elevator control unit. The individual parts may be distributed between the control device 18 and the monitoring device 17. Devices 25-29 may be embodied as distinct devices or units in hardware, while an embodiment as a computer program, thus as software within a computing unit, e.g. of an elevator control unit or within the control device 18 or the monitoring device 17 may be conceivable as well.

(15) E.g. in FIG. 3, substantially all of the above indicated devices 25-29 are, at least logically, associated with the monitoring device 17. In FIG. 4, e.g. the counter device 25 may be, at least logically associated with the control device 18. Further, also the determination device 29.

(16) In the exemplary embodiment of FIG. 3, the counter device 25 is connected to the elevator control device 18 such as to receive data or information from the control device 18 as visualised with the arrow 24. Such data or information may indicate for example whether or not the elevator is currently operated, i.e. whether or not the elevator traction machine 13 currently displaces the suspension member 11. Furthermore, the control device 18 may provide data or information correlating to a current position of the car 3 and/or the counterweight 5. Upon receiving such information, the counter device 25 may derive information allowing counting a number of bending cycles applied to the suspension member 11. For example, each time the suspension member 11 is displaced during a trip of the elevator 1 or each time a motion direction of the elevator is reversed, the number of bending cycles applied to the suspension member 11 is incremented. In other words, one alternative to increment the number of bending cycles may be embodied as a trip counter, even if successive trips are in the same direction of elevator/car motion, while another alternative is to only count, thus increment a bending cycle counter, if the direction of motion changes. This may be applied when counting bending cycles for the whole suspension member 11 or also during the sectional approach.

(17) Preferably, the counter device 25 does not simply act like a trip counter. To the contrary, by for example taking into account the provided information about the current position of the car 3 and the counterweight 5, additional information may be derived indicating locations at which the suspension member 11 is currently being bent. Accordingly, the counter device 25 may be enabled to not simply count bending cycles for the suspension member 11 in its entirety but, instead, may count section bending cycles applied to each section of a multiplicity of sections forming the entire suspension member 11. For example, one section of the suspension member may correspond to a portion of the suspension member extending between two neighbouring floors of a building. Principles, further details and possible advantages of such preferred counter device 25 and the method for counting bending cycles performed thereby are disclosed in the applicant's earlier patent applications WO 2010/007112 A1 and EP 2 303 749 B1 which shall be incorporated herein in their entirety by reference.

(18) The counted number of bending cycles applied to the suspension member 11 is provided from the counter device 25 to the determination device 29, as indicated with the arrow 26.

(19) The electrical measuring device 27 is electrically connected to the suspension member 11. For example, the electrical measuring device 27 comprises a voltage source for generating an electric voltage V and applying such electric voltage V to one or several cords 23 of the suspension member 11. Preferably, the voltage source is adapted for generating two or more phases of an alternating voltage, these phases being shifted relative to each other and each phase being applied to one or a group of cords 23 or, alternatively, to a separate resistor. As further detailed below, the electrical measuring device 27 may measure electrical characteristics of the suspension member by applying the electrical voltage to at least one of the cords 23 and by then monitoring electrical parameters in the cords 23.

(20) The electrical measuring device 27 may then provide the information about the electrical characteristics of the suspension member 11 to the determination device 29 as indicated with the arrow 28.

(21) The determination device 29 may use the information/data from the counter device 25 and the electrical measuring device 27 for determining whether a critical deterioration state is present in the suspension member 11.

(22) The presence of such critical deterioration state is assumed in case the counted number of bending cycles provided by the counter device 25 exceeds an allowable maximum number. For example, such allowable maximum number of bending cycles may be predetermined as a result of experiments performed with an exemplary non-deteriorated suspension member under normal operation conditions. In such experiments, it is repeatedly tested after having bent the suspension member multiple times whether or not the suspension member still has a sufficient load bearing capacity of more than 60% or more than 80% of its initial value. Typically, an allowable maximum number of bending cycles is determined from such experiments to be in a range of 15 million to 20 million bending cycles but may also be higher or lower, dependent e.g. from specific operating conditions and/or characteristics of a specific type of suspension member 11. Accordingly, at the latest after such allowable maximum number of bending cycles has been counted for the present suspension member 11, the determination device 29 will assume that the repeated bendings will have deteriorated the suspension member 11 to a degree such that a critical deterioration state has been reached and, typically, the suspension member 11 should be replaced.

(23) As a second decisive parameter, the determination device 29 takes into account the electrical characteristics measured and provided by the electrical measuring device 27. As long as these electrical characteristics do not deviate excessively from reference characteristics, it is assumed that the suspension member 11 is operated under normal operation conditions, i.e. not for example damaged or corroded beyond a normal state. As long as this is true, the determination device 29 will base its decision whether or not the suspension member 11 can be further operated only on the determination of whether or not the suspension member 11 has been bent more than the allowable number of bending cycles. However, as soon as this is not true, i.e. electrical characteristics are measured in the suspension member 11 which deviate from the reference characteristics by more than the allowable maximum deviation, it may be assumed that significant deterioration or damage occurred to the suspension member 11 which cannot only be attributed to repeated bendings thereof. Based on the specific type of deviation from the reference characteristics, the determination device 29 may then decide whether this deviation indicates a critical deterioration state upon which operation of the elevator 1 should be directly stopped or whether other countermeasures should be initiated.

(24) FIG. 4 shows an alternative embodiment of a monitoring arrangement 17 for determining the deterioration state in the suspension member 11 of the elevator 1. Therein, while still forming part of the monitoring arrangement 17, the counter 25 is no more included in a same housing as the determination device 29 and the electrical measuring device 27 but forms part of the elevator control device 18. Typically, in such control device 18, a number of elevator trips or a number of motion reversals upon such trips is counted and such information may be provided to the determination device 29 as indicated with the arrow 26.

(25) Further e.g., the control device 18 may equal the elevator control unit. Such elevator control unit may (already) comprise a counter device 25 for counting trips, bending cycles and/or sectional bending cycles. Here, monitoring device 17 may only provide a signal/information as indicated with the arrow 30 to the elevator control being indicative of the determined electrical characteristic as such or being indicative of a current actual deterioration state of the suspension member. Said information may be provided to the control device 18/the elevator control unit, which in turn evaluates the signal/information, respectively, and conducts the method of the invention within the control device 18/the elevator control unit. As such, it is also feasible that the determination unit 29 is, at least logically, associated with/arranged within the control device 18/the elevator control unit. The determination unit 29 may even be a computing part within the control device 18/the elevator control unit, e.g. being embodied in the control program of the control device 18/the elevator control unit. In such an embodiment, the signal/information as indicated with the arrow 26 may not be present at all or may be a simple indication to the monitoring device 17 that a determination of an electrical characteristic shall be performed.

(26) In FIGS. 5 and 6, possible principles and features to be implemented in examples of an electrical measuring device 27 are briefly explained. However, it shall be mentioned that such principles and features are explained in significantly more details in the applicant's prior patent applications U.S. 62/199,375 and U.S. Ser. No. 14/814,558 (for the implementation shown in FIG. 4) and EP 16 155 357 A1 and EP 16 155 358 A1 (for the implementation shown in FIG. 5). Accordingly, reference is made to these prior patent applications, the disclosure of which shall be incorporated in its entirety into the disclosure of the present invention.

(27) FIG. 5 shows an example of a multi-phase alternating current circuitry 131 comprising three electrically conductive legs 127 wherein both, a source side 133 and a load side 135 are configured in a Wye-configuration. Alternating voltage sources Va, Vb, Vc are provided in a Wye-configuration at the source side 133. Resistors Zya, Zyb, Zyc are provided in a Wye-configuration at the load side 135. Both Wye-configurations have a neutral point 129 at which the voltage sources Va, Vb, Vc or the resistors Zya, Zyb, Zyc, respectively, are all interconnected. The alternating voltage sources Va, Vb, Vc are connected via the lines a, b, c forming the legs 127 to associated ones of the resistors Zya, Zyb, Zyc. Accordingly, current phases Ia, Ib, Ic of a multi-phase alternating current may be applied to each line a, b, c of the legs 127.

(28) Furthermore, in the exemplary multi-phase alternating current circuitry 131 of FIG. 5, a neutral wire 137 is connected to each of the neutral points 129 at the Wye-configuration at the source side 133 and the Wye-configuration at the load side 135. In other words, the neutral wire 137 is connected between the common points 129 of the supply side and the load side of the multi-phase alternating current circuitry, respectively. The neutral wire 137 comprises a resistance Zn. In the neutral wire, a bypass current I.sub.n may flow.

(29) A multi-phase alternating current comprises at least two phases wherein in each phase the current alternates over time. There is a phase-shift between the phases such that for example a peak current strength in one phase is shifted by 2 π/n (n=2, 3 4, . . . ) with respect to a peak current strength of another phase. The currents may alternate for example in a sinusoidal manner. However, also other alternation patterns, such as digital, stepwise, or others, may be applied.

(30) In other words and in the example of three phases, in electrical circuit design, three-phase electric circuits generally have three conductors for example formed by lines a, b, c carrying voltage waveforms that are 2 π/3 radians (i.e. 120° or ⅓ of a cycle) offset in time.

(31) Where the three conductors carrying the voltage waveforms are “balanced”, a net sum of phase currents throughout all legs 127 of the multi-phase alternating current circuitry 131, i.e. a vector sum of Ia, Ib, Ic is 0 (i.e. Ia+Ib+Ic=0, wherein Ia, Ib, Ic shall be vector currents and thus include information about their phases). In a balanced three-phase circuit, all three sources Va, Vb, Vc are generally represented by a set of balanced three-phase variables and all loads Zya, Zyb, Zyc as well as lines a, b, c within the legs 127 of the circuitry have equal impedances. Furthermore, in such balanced circuit, not only the net sum of the phase currents is 0, but also an electric bypass current In through the neutral wire 137 being connected in parallel to the legs 127 is 0 (i.e. In=0).

(32) Following Kirchhoff's voltage law, when there is an imbalance in the conductor loads of the three-phase circuit, any resulting imbalance of phase currents in the legs 127 of the circuitry 131 will be resolved as a current In in the neutral wire 137 and/or as a net sum phase current throughout all phases a, b, c of the multi-phase alternating current being no more equal to 0.

(33) Such deviation of the bypass current I.sub.n through the neutral wire 137 or of the net sum of all other phase currents I.sub.a, I.sub.b, I.sub.c may be interpreted and named herein as “electric indicator current”. As soon as this indicator current deviates from a reference current value by more than a predetermined difference value, this may be taken as signal indicating that critical deterioration has occurred within at least one of the suspension members and checking and, if necessary, replacing the suspension member may be initiated for example. The reference current value may be, for example a current value of the bypass current I.sub.n or a net sum of the phase currents Ia, Ib, Ic measured with a non-deteriorated suspension member arrangement such as for example directly after fabrication or installation of a suspension member arrangement.

(34) The indicator current may be measured in various ways. For example, a vector net sum of all currents I.sub.a, I.sub.b, I.sub.c throughout all of the legs 127 of the multi-phase alternating current circuitry 131 may be measured together, i.e. with a common measuring circuitry. Alternatively, each of the phase currents I.sub.a, I.sub.b, I.sub.c in the lines a, b, c forming the legs 127 may be measured separately and a net sum of these separately measured phase currents may then be determined subsequently, for example in a summing device. Alternatively, the indicator current may be derived from the bypass current I.sub.n flowing through the neutral wire 137 upon any imbalance within the multi-phase alternating current circuitry 131.

(35) For example, with reference to the circuitry 131 shown in FIG. 5, voltages Va, Vb, Vc are applied to lines a, b, c forming the legs 127 and are held constant, i.e. equal to each other, and 2 π/3 radians shifted apart. At least one of the lines a, b, c may comprise at least one of the cords comprised in a suspension member of the suspension member arrangement of the elevator. For a net sum (I.sub.a+I.sub.b+I.sub.c) and/or a bypass current I.sub.n in the neutral wire 137 to be equal to 0 under initial conditions, such as when the suspension member is newly installed, voltage drops across each of the lines a, b, c plus voltage drops across each of the loads Zya, Zyb, Zyc in each of the legs 127 must be equal.

(36) In practical terms, the voltage drops across for example steel cords in a suspension member will not necessarily be initially equal due to for example various small differences and tolerances created by for example manufacturing tolerances of the steel cords in the suspension member. In this case, the loads Zya, Zyb and Zyc may be adjusted to compensate for such differences until a desired initial current condition for I.sub.n=0, i.e. no current flow in the neutral wire, is obtained. Alternatively the multi phase source voltages Va, Vb, Vc 33 may be independently adjusted to likewise establish a desired initial current condition for In. Intuitively for those skilled in the art, an alternative to adjusting the loads Zya, Zyb, Zyc and/or the multi phase source voltages Va, Vb, Vc for an initial zero In current would be to capture a non-zero value of I.sub.n as the initial reference current value.

(37) Suspension members that contain multiple metal cords are generally capable of having the cords acting as electrical conductors or lines. The suspension member may also be construed with metal cords that are isolated electrically from each other by a physical separation, such as with electrically non-conductive materials like an elastomeric coating. Where the metal cords in suspension members are electrically isolated from each other, they may be connected for example in a Wye-configuration or a Delta-configuration and be part of various legs of a multi-phase alternating current circuitry. Each of the cords may then become an electrical conductor in the circuitry.

(38) For example, in a Wye-configuration of FIG. 5, three isolated cords in a suspension member are represented by ZIa, ZIb, ZIc. In an initially balanced state, the sums of resistances ZIx+Zyx (x=a, b, c) in each of the lines a, b, c formed by the cords are substantially equal. However, upon deterioration of one of the cords, the resistance ZIx created thereby in one of the lines changes and the entire multi-phase alternating current circuitry 131 comes into imbalance. Such imbalance may then be determined by measuring the indicator current I.sub.n or (I.sub.a+Il.sub.b+I.sub.c). If this indicator current exceeds a certain predetermined value, this may be taken as indication that at least one of the cords comprised in a suspension member is significantly deteriorated and the suspension member may have to be checked and/or replaced.

(39) Instead of forming all lines a, b, c or, more generally, all legs 127 of a multi-phase alternating current circuitry 131 by including one of the cords of a suspension member, for example only one or a few of those lines may include cords of the suspension member. For example, as described further below with respect to various examples, all cords of a suspension member or of plural suspension members may be connected in series or in parallel and may be included into only one of the legs 127 whereas the other legs 127 do not comprise any cords but are formed only with the loads Zyx. These loads Zyx may be fixed or dynamic. For example, dynamic loads may be implemented for setting up initial conditions for In and/or compensating any temperature effects modifying electrical characteristics in the loads Zyx, the lines a, b, c, the cords comprised in the multi-phase circuitry and/or other components of the multi-phase circuitry.

(40) It may be noted that setting up initial conditions for In and/or compensating for the effects of temperature or other phenomena may also be accomplished by dynamically adjusting the loads Zya, Zyb, Zyc and/or the multi phase source voltages Va, Vb, Vc.

(41) As indicated above, further details of the approach for measuring electrical characteristics in suspension members 11 as briefly explained herein with respect to FIG. 5 are explained in the applicant's prior patent applications U.S. 62/199,375 and U.S. Ser. No. 14/814,558.

(42) FIG. 6 shows an exemplary embodiment of a device 217 for detecting a deterioration state in a suspension member arrangement 9 for an elevator 1. Therein, the suspension member arrangement 9 may comprise one or more suspension members 11 such as for example belts as shown in FIG. 2 including a plurality of electrically conducting cords 223. In FIG. 6, the cords 223 are only indicated schematically as twelve elongate cords 223 being arranged parallel to each other.

(43) The multiplicity of cords 223 may be divided into two groups 224a, 224b of cords. For example, a first group 224a of cords may comprise all odd numbered cords 223 whereas a second group 224b of cords may comprise all even numbered cords 223.

(44) The device 217 comprises an alternating voltage generator arrangement G which is adapted for applying a first alternating voltage U.sub.1 to a first end 225a of the first group 224a of cords 223 and for applying a second alternating voltage U.sub.2 to a first end 225b of the second group 224b of cords 223.

(45) In the embodiment shown in FIG. 6, the alternating voltage generator arrangement G comprises a first alternating voltage generator G.sub.1 and a second alternating voltage generator G.sub.2. The two alternating voltage generators G.sub.1, G.sub.2 may be separate devices and may operate in principle independently from each other. However, the two alternating voltage generators G.sub.1, G.sub.2 should be synchronized such as to operate with a stationary phase relationship with respect to each other.

(46) The alternating voltage generators G.sub.1, G.sub.2 are electrically connected, on their one side, to an electrical ground potential, whereas, on their other side, they are electrically connected to the first ends 225a, 225b of the first and second groups 224a, 224b of cords 223, respectively. The alternating voltage generators G.sub.1, G.sub.2 generate first and second generated voltages U.sub.G1, U.sub.G2, respectively.

(47) An internal electrical resistance of each of the alternating voltage generators G.sub.1, G.sub.2 is represented in FIG. 6 by R.sub.3, R.sub.4. Due to such internal resistances R.sub.3, R.sub.4, the actual first and second voltages U.sub.1, U.sub.2 applied to the cords 223 may generally be lower than the generated voltages U.sub.G1, U.sub.G2 generated by the alternating voltage generators G.sub.1, G.sub.2 themselves.

(48) The alternating voltage generator arrangement G with its alternating voltage generators G.sub.1, G.sub.2 is configured to generating the first and second alternating voltages U.sub.1, U.sub.2 with same waveforms and with a fixed phase difference of essentially 180°. Therein, the waveforms should differ from each other at most by an acceptable tolerance of for example less than 5% and the phase difference should differ from 180° at most by an acceptable tolerance of for example less than 10°, preferably less than 5° or less than 2°.

(49) In examples and embodiments described herein below, it will be assumed that the alternating voltage generator arrangement G has a specific exemplary implementation in which it generates first and second generated voltages U.sub.G1, U.sub.G2 having an amplitude of 6 V and oscillating around a DC voltage of 6 V. In other words, the first and second generated voltages U.sub.G1, U.sub.G2 oscillate between U.sub.min=0 V and U.sub.max=12 V. Therein, the waveform is sinusoidal. An oscillation frequency is selected to be 280 Hz. The internal resistances R.sub.3, R.sub.4 are selected to be 450 Ohm.

(50) However, it shall be noted that the alternating voltage generator arrangement G may be implemented in various other manners. For example, the first and second generated voltages U.sub.G1, U.sub.G2 may be generated with other waveforms such as rectangular waveforms or triangular waveforms. Furthermore, the amplitude and/or frequency of the first and second alternating generated voltages U.sub.G1, U.sub.G2 may be selected in various other manners. For example, the generated voltages U.sub.G1, U.sub.G2 may oscillate between other minimum and maximum voltages U.sub.min, U.sub.max. Specifically, the alternating voltages do not necessarily have to oscillate around a fixed non-zero DC voltage but may also oscillate around 0 V, i.e. oscillate between a negative voltage—U.sub.max and a positive voltage +U.sub.max. Such implementation may be advantageous with respect to electro-corrosion characteristics.

(51) Furthermore, the internal resistances R.sub.3, R.sub.4 may be selected in various manners and may be specifically adapted to a specific application, for example depending on electrical resistances generated by the cords 223 to which the first and second alternating voltages U.sub.1, U.sub.2 shall be applied.

(52) Furthermore, instead of providing the alternating voltage generator arrangement G with two separate alternating voltage generators G.sub.1, G.sub.2, a single alternating voltage generator may be provided and this single alternating voltage generator may provide for a direct output and an inverse output such that alternating generated voltages U.sub.G1, U.sub.G2 may be output with a phase-shift of 180°. For example, such single alternating voltage generator may be coupled to a transformer including for example a primary and a secondary coil wherein an inverse output voltage may be generated at a contact in a middle of the secondary coil, such inverse voltage output being shifted by 180° to a direct voltage output generated at outer contacts of the secondary coil. In such embodiment, the first and second alternating voltages U.sub.1, U.sub.2 are automatically synchronized with a stationary phase-shift of 180° such that, for example, no specific synchronization of two separate alternating voltage generators G.sub.1, G.sub.2 is required.

(53) The first alternating voltage U.sub.1 is applied to the first end 225a of the first group 224a of cords 223 of a suspension member 11 whereas the second alternating voltage U.sub.2 is applied to a first end 225b of the second group 224b of cords 223 of the same suspension member 11. Within one group of cords 224a, 224b, all cords 223 comprised in this group 224a, 224b may be electrically connected to each other.

(54) Preferably, the cords 223 of one group 224a, 224b are connected in series. In such series connection, for example all odd numbered cords 1, 3, 5, etc. are electrically connected in series to each other such as to form a kind of long single electrical conductor. Similarly, all even numbered cords 2, 4, 6, etc. may be connected in series. In such implementation, the first alternating voltage U.sub.1 may be applied for example to a first end 225a of the first group 224a of cords 223 being formed by a free end of a cord 223 number 1, an opposite end of this cord number 1 being electrically connected in series to an end of a cord number 3, an opposite end of this cord number 3 again being electrically connected to a free end of a cord number 5 and so on. Accordingly, a second end 227a of this first group 224a of cords 223 is formed by a free end of a last odd numbered cord 223. Similarly, all even numbered cords 223 may be connected in series such as to electrically connect a first end 225b of this second group 224b of cords 223 to an opposite second end 227b via a single long conductor formed by the series of even numbered cords 223. In such series connection arrangement, both alternating voltages U.sub.1, U.sub.2 applied to first ends 225a, 225b of both groups 224a, 224b of cords 223 are transferred throughout the entire series connections formed in both groups 224a, 224b by the respective cords 223 comprised therein. Accordingly, when no electric current flows, the first and second alternating voltages U.sub.1, U.sub.2 also apply to the second ends 227a, 227b of both groups of cords 224a, 224b. However, in case any electric current is flowing through the cords 223 as a result of the applied alternating first and second voltages U.sub.1, U.sub.2, such current has to be transferred through the respective group 224a, 224b of cords 223 and thus experiences electrical resistances created by the respective cords 223. As a result, voltage drops occur throughout the respective cords 223. Accordingly, by measuring third and fourth voltages U.sub.3, U.sub.4 at opposite second ends 227a, 227b of each group 224a, 224b of cords 223, information about a condition within the groups 224a, 224b of cords 223 may be derived as it may be for example determined whether any electric current flows through the cords 223 in each of the groups 224a, 224b and, if this is the case, how such current “behaves”.

(55) In order to connect the alternating voltage generator arrangement G to the suspension member and suitably interconnecting all cords 223 in advantageous series connections, a connector arrangement (not shown in FIG. 6 for clarity of visualization) for establishing a series connection of all even numbered cords in the suspension member and a series connection of all odd numbered cords in the suspension member and for establishing an electrical connection for applying the first and second alternating voltages (U.sub.1, U.sub.2) to first ends of the series connection of even numbered cords and the series connection of odd numbered cords, respectively, may be provided.

(56) As a side note only, it shall be noticed that the first and second groups 224a, 224b of cords 223 may be arranged and electrically connected in various other ways. For example, while it may be advantageous to include all even numbered cords and all odd numbered cords in one of the groups 224a, 224b of cords 223, respectively, it may also be possible to include each of the cords 223 of one or more suspension members 9 in other configurations to the two groups 224a, 224b of cords 223. For example, all cords 1 to n may be comprised in the first group 224a, whereas all cords n+1 to x may be comprised in the second group of cords 224b. Preferably, both groups 224a, 224b of cords 223 comprise a same number of cords 223. Furthermore, while it may be beneficial to connect all cords 223 of one group 224a, 224b in series to each other, also parallel electrical connections of all or some of the cords 223 comprised in one of the groups 224a, 224b may be possible.

(57) At the second ends 227a, 227b of both groups 224a, 224b of cords 223, a first voltage measurement arrangement 231 and/or a second voltage measurement arrangement 233 may be provided as forming part of a determination unit 229. These components 229, 231, 233 are shown in FIG. 5 only in a schematic manner.

(58) The first voltage measurement arrangement 231 may be adapted for determining a summed voltage U.sub.+ which correlates to a sum of a third volume U.sub.3 and a fourth voltage U.sub.4. Therein, the third voltage U.sub.3 applies between the second end 227a of the first group 224a of cords 223 and a common electrical potential such as a ground potential. The fourth voltage U.sub.4 applies between a second end 227b of the second group 224b of cords 223 and the common electrical potential.

(59) The second voltage measurement arrangement 233 is adapted for determining a differential voltage U.sub.− correlating to a difference between the third voltage U.sub.3 and the fourth voltage U.sub.4.

(60) Therein, both the summed voltage U.sub.+ and the differential voltage U.sub.− shall “correlate” to the sum and difference, respectively, of U.sub.3 and U.sub.4 in an unambiguous manner. For example, the summed voltage U.sub.+ may be equal to the sum U.sub.3+U.sub.4 and the differential voltage U.sub.− may be equal to the difference U.sub.3−U.sub.4. Alternatively, the summed voltage U.sub.+ and/or the differential voltage U.sub.− may correlate to such sum U.sub.3+U.sub.4, U.sub.3−U.sub.4, respectively, in other manners such as being for example a multiple thereof. For example, U.sub.+ may be equal to x*(U.sub.3+U.sub.4) and/or U.sub.− may be equal to y*(U.sub.3−U.sub.4), x and y being possibly any rationale number, for example x=y=½ or x=y=2, etc.

(61) In principle, it may be sufficient to provide the device 217 with only one of the first and second voltage measurement arrangements 231, 233 as already from such single voltage measurement arrangement determining only the summed voltage U.sub.+ or the differential voltage U.sub.−, some useful information about a current deterioration state of the suspension member 11 may be derived. However, in order to obtain more useful information about the deterioration state, it may be beneficial to provide the device 217 with both the first voltage measurement arrangement 231 and the second voltage measurement arrangement 233 in order to enable for example distinguishing between various types or degrees of deterioration within the suspension member 11.

(62) In the embodiment shown in FIG. 6, the device 217 is provided with both the first and second voltage measurement arrangements 231, 233. Therein, the two voltage measurement arrangements 231, 233 are implemented by including a first and a second voltage determining unit 235a, 235b. These voltage determining units 235a, 235b and/or other voltage determining units comprised in voltage measurement arrangements of the device 217 may be e.g. electronic devices which are adapted for electronically and preferably automatically measure electric voltages within a circuitry. Therein, the first voltage determining unit 235a is connected on its one side to the second end 227a of the first group 224a of cords 223 whereas the second voltage determining unit 235b is connected with one side to the second end 227b of the second group 224b of cords 223. An opposite side of both voltage determining units 235a, 235b is connected to an electric ground potential. Accordingly, the first and second voltage determining units 235a, 235b are adapted for measuring the third voltage U.sub.3 and the fourth voltage U.sub.4, respectively. Both voltage determining units 235a, 235b are then connected to the determination unit 229 in which the first voltage measurement arrangement 231 is adapted for determining the summed voltage U.sub.+ and the second voltage measurement arrangement 233 is adapted for determining the differential voltage U.sub.−.

(63) Additionally to the components of the circuitry explained herein before to be used during actually measuring the summed voltage and the differential voltage, the device 217 shown in FIG. 6 comprises a pull-up voltage source 236. This pull-up voltage source 236 may apply a constant DC voltage to both first ends 225a, 225b of both groups 224a, 224b of cords 223 during an idle mode in which the alternating voltage generator arrangement G is deactivated or couple-off. Such idle mode will be described further below. The constant DC voltage may be substantially equal to the maximum voltage U.sub.max of the alternating generated voltages U.sub.G1, U.sub.G2 generated by the alternating voltage generator arrangement G. The pull-up voltage source 136 comprises internal electrical resistances R.sub.1, R.sub.2.

(64) Furthermore, the device 217 may comprise a third and a fourth voltage determining unit 235c, 235d for measuring the first and second voltages U.sub.1, U.sub.2, respectively. Depending on the current flowing through the entire circuitry of the device 217, voltage drops at the internal resistances R.sub.3, R.sub.4 of the alternating voltage generator arrangement G may differ such that the first and second voltages U.sub.1, U.sub.2 may differ accordingly. Thus, by measuring the first and second voltages U.sub.1, U.sub.2 with third and a fourth voltage determining unit 235c, 235d, information about the electrical current flowing through the circuitry may be derived. This information then includes information about the deterioration state of the suspension member 11 as the electrical current flowing through the circuitry strongly depends on electrical resistances occurring within the cords 223 of the suspension member 11.

(65) Next, a function principle of the device 217 and a method for detecting a deterioration state in a suspension member arrangement 9 performed thereby shall be described in an exemplary manner for a state where the suspension member 11 is non-deteriorated, i.e. neither the cords 223 nor the cover 21 is deteriorated or even damaged in any manner and therefore all cords 223 have same physical and electrical characteristics. Voltages, which are generated or which are measured during such method will be described with reference to FIG. 7.

(66) In the method for monitoring the deterioration state, the alternating voltage generator arrangement G generates two alternating voltages U.sub.G1, U.sub.G2 which alternate in a sinusoidal manner with a frequency of 280 Hz and an amplitude of 6 V around a base direct voltage of 6 V. Such generated voltages U.sub.G1, U.sub.G2 result in first and second alternating voltages U.sub.1, U.sub.2 (not shown in FIG. 7 for clarity reasons) which are applied to first ends 225a, 225b of the first group 224a and the second group 224b of cords 223 of the suspension member 11, respectively. Of course, depending on whether or not an electric current is flowing through the circuitry, the first and second alternating voltages U.sub.1, U.sub.2 may be slightly lower than the generated voltages U.sub.G1, U.sub.G2 due to a voltage drop in the electrical resistances R.sub.3, R.sub.4.

(67) The first and second voltages U.sub.1, U.sub.2 are then transmitted through the series connection of odd numbered cords 223 of the first group 224a and the series connection of even numbered cords 223 of the second group 224b, respectively, such that a third and a fourth alternating voltage U.sub.3, U.sub.4 occur at the opposite second ends 227a, 227b of both groups of cords 224a, 224b.

(68) When there are no shunts and no electrical connection between these two second ends 227a, 227b, no electrical current will flow such that the third and fourth alternating voltages U.sub.3, U.sub.4 will be the same as the applied first and second alternating voltages U.sub.1, U.sub.2. In other words, as long as no deterioration occurs in the suspension member 11, the third and fourth alternating voltages U.sub.3, U.sub.4 will exactly follow the applied first and second alternating voltages U.sub.1, U.sub.2. Accordingly, upon determining such alternating voltage behaviours for the third and fourth alternating voltages U.sub.3, U.sub.4, it may be determined that the suspension member 11 is in a normal condition in which no further action is required.

(69) In such non-deteriorated state, due to the 180° phase-shift between the third and fourth alternating voltages U.sub.3, U.sub.4, a summed voltage U.sub.+ corresponding to the sum of the third and fourth alternating voltages U.sub.3, U.sub.4 is a constant voltage, i.e. a DC voltage being the sum of the base DC voltages of the generated alternating voltages U.sub.G1, U.sub.G2 (i.e. in the given example: U.sub.3+U.sub.4=6 V+6 V=12 V). Accordingly, in such state, the summed voltage U.sub.+ has no alternating voltage component (i.e. U.sub.+,AC=0). A differential voltage U.sub.− corresponding to a difference of the third and fourth alternating voltages U.sub.3, U.sub.4 alternates with a same frequency as the generated voltages U.sub.G1, U.sub.G2 and with double the amplitude of these generated voltages U.sub.G1, U.sub.G2 around a DC voltage of 0 V (i.e. in the given example, U.sub.− alternates between −12 and +12 V).

(70) As will be described in further detail below, in cases where the suspension member 11 is deteriorated or even damaged, such initial conditions for the third and fourth voltage U.sub.3, U.sub.4 do no longer apply. Particularly, when at least one of the cords 223 in the suspension member 11 is broken or if there is a short-circuit 245, 247 between cords 223 or if there is an electrical connection to ground 241, 243 for at least one of the cords 223, either an electrical connection between the first ends 225a, 225b and the second ends 227a, 227b is partly interrupted (i.e. in the case of a broken cord) or electrical currents will flow (i.e. in the case of short-circuits or connections to ground). Accordingly, in such deteriorated conditions, the third and fourth voltages U.sub.3, U.sub.4 will no longer follow the generated voltages U.sub.G1, U.sub.G2 in the same manner as in the non-deteriorated state and, as a result, the summed voltage U.sub.+ and/or the differential voltage U.sub.− will change their behaviour.

(71) Accordingly, any deviation from a state in which the summed voltage U.sub.+ comprises no alternating voltage component U.sub.+,AC and the differential voltage U.sub.− comprises an alternating voltage being non-zero may be interpreted as indicating a deterioration or even a damage in the monitored suspension member 11.

(72) While, in principle, a simple circuitry of the device 217 in which the second ends 227a, 227b of the first and second groups 224a, 224b of cords 223 are not electrically connected might be sufficient for monitoring the suspension member 11 as it may at least detect whether or not the suspension member 11 is deteriorated or not, it may be advantageous to modify such open circuitry by connecting the second ends 227a, 227b of the two groups 224a, 224b of cords 223 via a connecting electrical resistance R.sub.5. Such connecting electrical resistance R.sub.5 may have a resistance in a range of several tens or hundreds of Ohms, i.e. a resistance which is significantly higher than resistances typically occurring throughout the series connections of cords 223 in the suspension member 11 (such resistances being typically in a range of some Ohms to a few tenth of Ohms, depending on the length of the suspension member). In the example given in FIG. 6, R.sub.5 is assumed to be 100 Ohm.

(73) Due to such electrical connection of the second ends 227a, 227b and the third and fourth voltages U.sub.3, U.sub.4 occurring at these second ends 227a, 227b, an electrical current may flow through the entire circuitry of the device 217. As a result of such electrical current, voltage drops will occur at all resistances included in such circuitry, thereby directly influencing all voltages U.sub.x (x=1, 2, 3, 4) at the various positions within the circuitry. For example, the first and second voltages U.sub.1, U.sub.2 will be lower than the generated voltages U.sub.G1, U.sub.G2 due to the internal resistances R.sub.3, R.sub.4. The third and fourth voltages U.sub.3, U.sub.4 at the second ends 227a, 227b will be lower than the first and second voltages U.sub.1, U.sub.2 due to electrical resistances within the series connections of cords 223 of the suspension member 11.

(74) Using the principles of measurement indicated before, various types of damages or deterioration to suspension members may be determined. The following table briefly indicates some possibilities of detectable electrical characteristics relating to specific damages or deteriorations and of voltages occurring during respective measurements.

(75) TABLE-US-00001 Phase U.sub.+ U.sub.− angles AC DC AC DC U.sub.3 U.sub.4 Comment OK No signal ~½ Sinusoidal 0 V G.sub.1 G.sub.2 U.sub.max signal Broken cord Sinusoidal U.sub.max No signal 0 V G.sub.xx No load signal side still on U.sub.1 and 2U.sub.max connected U.sub.2 peak to peak STM not No signal 0 V No signal 0 V — — No load attached or on U.sub.1 and both cord U.sub.2 pairs broken Multiple No signal 0 V No signal 0 V — — Load on connections to U.sub.1 and U.sub.2 ground Elevator (measurement must mode) move to detect all faults Single Sinusoidal <=½ Sinusoidal <=½ G.sub.xx Elevator connection to signal U.sub.max signal <= U.sub.max side not must ground U.sub.3 + U.sub.4 having move to (measurement ground detect mode) fault all faults Adjacent No signal U.sub.max No signal 0 V — — Elevator connection of must cords move (symmetrical) to detect all faults Adjacent Sinusoidal U.sub.max No signal 0 V G.sub.xx Load on connection of signal side of U.sub.1 and U.sub.2 cords the Elevator (asymmetrical) generator must being move closer to to detect the fault all faults Damaged Deviation from initial values cords

(76) As indicated above, further details of the approach for measuring electrical characteristics in suspension members 11 as briefly explained herein with respect to FIGS. 6 and 7 are explained in the applicant's prior patent applications EP 16 155 357 A1 and EP 16 155 358 A1.

(77) Finally, it should be noted that terms such as “comprising” do not exclude other elements or steps and that terms such as “a” or “an” do not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

(78) In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.