Method and device for detecting non-uniform and uniform deteriorations in a suspension member arrangement for an elevator based on AC voltage measurements
11479444 · 2022-10-25
Assignee
Inventors
Cpc classification
B66B5/0018
PERFORMING OPERATIONS; TRANSPORTING
B66B7/1223
PERFORMING OPERATIONS; TRANSPORTING
G01R31/008
PHYSICS
D07B1/145
TEXTILES; PAPER
B66B7/1215
PERFORMING OPERATIONS; TRANSPORTING
G01R31/08
PHYSICS
G01R31/31723
PHYSICS
B66B19/007
PERFORMING OPERATIONS; TRANSPORTING
International classification
B66B7/12
PERFORMING OPERATIONS; TRANSPORTING
D07B1/14
TEXTILES; PAPER
G01R31/00
PHYSICS
B66B5/00
PERFORMING OPERATIONS; TRANSPORTING
G01R31/08
PHYSICS
B66B7/06
PERFORMING OPERATIONS; TRANSPORTING
G01M5/00
PHYSICS
Abstract
A method and device detect non-uniform and uniform deterioration states in an elevator suspension member having first and second groups of electrically conductive cords. First ends of the groups are electrically connected to an alternating voltage generator arrangement and second ends are electrically connected to each other through first and second resistors via a neutral point at which electrical resistances of the groups are the same in a non-deteriorated state of the suspension member. The method includes: applying first and second alternating voltages to the first end of the first and second groups, respectively; determining a neutral point voltage between the neutral point and an electrical reference potential; determining difference voltages between first and second difference measurement points located between the second ends of the groups and the respective resistors; and determining the deterioration state based on both the determined neutral point voltage and the determined difference voltage.
Claims
1. A method for detecting non-uniform and uniform deterioration states in a suspension member arrangement for an elevator, the suspension member arrangement including a suspension member having first and second groups of electrically conductive cords, wherein first ends of the first and second groups are electrically connected to an alternating voltage generator arrangement including a first voltage generator for applying a first alternating voltage to the first end of the first group and a second voltage generator for applying a second alternating voltage to the first end of the second group, wherein second ends of the first and second groups are electrically connected to each other via a neutral point at which electrical resistances to the first voltage generator and to the second voltage generator, respectively, are of a same value in a non-deteriorated state of the suspension member, and wherein first and second electrical resistors are arranged between the neutral point and the second ends of the first and second groups respectively, the method comprising the steps of: applying the first alternating voltage to the first end of the first group and applying the second alternating voltage to the first end of the second group; determining a neutral point voltage between the neutral point and an electrical reference potential; determining a difference voltage between a first difference measurement point, located between the second end of the first group and the first electrical resistor, and a second difference measurement point, located between the second end of the second group and the second electrical resistor; and determining a deterioration state of the suspension member based on both the determined neutral point voltage and the determined difference voltage.
2. The method according to claim 1 wherein the determining of a deterioration state is based on a comparison of the difference voltage as currently determined with a reference difference voltage value.
3. The method according to claim 2 wherein the reference difference voltage value correlates to the difference voltage as measured in the non-deteriorated state of the suspension member.
4. The method according to claim 1 including indicating an excessive deterioration in the suspension member in response to a deviation from a state in which: as a first criterion, the neutral point voltage does not include an alternating voltage component larger than a predetermined first tolerance; and as a second criterion, the difference voltage differs from the reference difference voltage value by less than a predetermined second tolerance.
5. The method according to claim 4 wherein, in the second criterion, an amplitude of an alternating voltage component of the difference voltage shall differ from an amplitude of the reference difference voltage value by less than the predetermined second tolerance.
6. The method according to claim 1 wherein the first and second alternating voltages have same waveforms and a phase difference of substantially 180°.
7. The method according to claim 1 wherein an electrical resistance of a sum of the first and second electrical resistors is larger than an electrical resistance through each one of the first and second groups in the non-deteriorated state of the suspension member.
8. A device for detecting non-uniform and uniform deterioration states in a suspension member arrangement for an elevator, the suspension member arrangement including a suspension member having first and second groups of electrically conductive cords, the device comprising: an alternating voltage generator arrangement including a first voltage generator adapted to apply a first alternating voltage to a first end of the first group and a second voltage generator adapted to apply a second alternating voltage to a first end of the second group; and a voltage measurement arrangement including, a circuitry adapted to electrically connect second ends of the first and second groups to each other via a neutral point at which electrical resistances to the first voltage generator and to the second voltage generator are a same value in a non-deteriorated state of the suspension member arrangement, and including first and second electrical resistors arranged between the neutral point and the second ends of the first and second groups respectively, a neutral point voltage determining unit for determining neutral point voltages between the neutral point and an electrical reference potential, a difference voltage determining unit for determining a difference voltage between a first difference measurement point, located between the second end of the first group and the first electrical resistor, and a second difference measurement point, located between the second end of the second group and the second electrical resistor, and wherein an electrical resistance of a sum of the first and second electrical resistors is larger than an electrical resistance through each one of the first and second groups in the non-deteriorated state of the suspension member.
9. The device according to claim 8 including a determination unit for determining a deterioration state of the suspension member based on both the neutral point voltages and the difference voltage.
10. The device according to claim 8 wherein the device is adapted for performing the following method steps: applying the first alternating voltage to the first end of the first group and applying the second alternating voltage to the first end of the second group; determining the neutral point voltage between the neutral point and the electrical reference potential; determining the difference voltage between the first difference measurement point and the second difference measurement point; and determining the deterioration state of the suspension member based on both the determined neutral point voltage and the determined difference voltage.
11. A device for detecting non-uniform and uniform deterioration states in a suspension member arrangement for an elevator, the suspension member arrangement including a suspension member having first and second groups of electrically conductive cords, the device comprising: an alternating voltage generator arrangement including a first voltage generator adapted to apply a first alternating voltage to a first end of the first group and a second voltage generator adapted to apply a second alternating voltage to a first end of the second group; a voltage measurement arrangement including, a circuitry adapted to electrically connect second ends of the first and second groups to each other via a neutral point at which electrical resistances to the first voltage generator and to the second voltage generator are a same value in a non-deteriorated state of the suspension member arrangement, and including first and second electrical resistors arranged between the neutral point and the second ends of the first and second groups respectively, a neutral point voltage determining unit for determining neutral point voltages between the neutral point and an electrical reference potential, and a difference voltage determining unit for determining a difference voltage between a first difference measurement point, located between the second end of the first group and the first electrical resistor, and a second difference measurement point, located between the second end of the second group and the second electrical resistor; and wherein the device is adapted for performing the following method steps: applying the first alternating voltage to the first end of the first group and applying the second alternating voltage to the first end of the second group; determining the neutral point voltage between the neutral point and the electrical reference potential; determining the difference voltage between the first difference measurement point and the second difference measurement point; and determining the deterioration state of the suspension member based on both the determined neutral point voltage and the determined difference voltage.
Description
DESCRIPTION OF THE DRAWINGS
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(16) 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
(17) Background
(18)
(19) 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
(20) It may be noted that the elevator 1 and particularly its suspension member(s) 11 and its device 17 for detecting the deterioration may be configured and arranged in various other ways than those shown in
(21) 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.
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(23) Alternatively, suspension members 11 may have other shapes or configurations. For example, a belt may have several cords included into a body formed of matrix material, the body being non-profiled (i.e. flat) or having other shapes as those shown in
(24) Typically, wires or cords of the suspension member 11 have a specified minimum strength to ensure an integrity of the suspension member arrangement 9 during its use in an application within an elevator 1. In certain suspension applications, such as for lifts or elevators, a factor-of-safety requirement for strength combined with other measures, such as protective coating of the cords 23 for example within the matrix material 21, may sustain an initial strength of a suspension member beyond an effective life of the protective measures employed to retain strength.
(25) Particularly in such cases, where the initial strength of the suspension member 11 is not expected to change during its useful life in an application, a simple electronic method may be employed and may be sufficient to detect an indication that for example initial physical properties of the suspension members have unexpectedly changed and trigger for example a replacement of the suspension member 11 or other counter-measures.
(26) Prior Art Approaches
(27) In prior art, methods have been employed to ensure that suspension members do not fall below a specified minimum strength, such methods involving for example visually counting of broken wires of cords or wire rope strands over a length of the suspension members. Alternatively, complex electronic methods that measure small changes in an electrical resistance of for example metal cords and compare such measurements with reference values or a rate of change in resistance have been proposed.
(28) Although such methods may be effective, they may have certain disadvantages. For example, counting broken wires may be a tedious task to be periodically performed by persons maintaining the suspension members of an elevator and may be flawed by human error. In cases where suspension members have an opaque coating on the metal cords or the metal cords are incorporated into a matrix material, it is generally not possible to visually count broken wires. Where methods employ monitoring a change in electrical resistance or impedance of metal cords, the measurements are generally made across electrical connections to the steel cords and may introduce, by nature of such electrical connections, a significant source of possible errors due to for example very low values of electrical resistances being monitored. Furthermore, over time, such electrical connections may deteriorate due to effects of e.g. oxidation and/or contamination and may increase a potential for errors by the monitoring method. Additionally, such methods typically involve complex circuits necessary for measuring the very small changes in resistance or impedance and comparing them for example to target reference resistance values that may drift over time or due to effects of temperature. Furthermore, some prior art approaches may require extensive correlation to map a change in resistance or impedance of the steel cords with changes in a strength and/or physical deterioration of the steel cord.
(29) New Approach
(30) Accordingly, there may be a need for a less complex and/or more effective monitoring method for detecting a deterioration in suspension members in an elevator, particularly, in case these suspension members are expected to retain their initial strength over the life of their application.
(31) As described herein, a simple and reliable method may be achieved using a two-phase current monitoring of e.g. steel cords in a suspension member, particularly where only a significant change in initial physical conditions of the cords need to be monitored.
(32) Details of embodiments of the invention described in the priority documents will now be described with reference to
(33)
(34) The multiplicity of cords 23 may be divided into two groups 24a, 24b of cords. For example, a first group 24a of cords may comprise all odd numbered cords 23 whereas a second group 24b of cords may comprise all even numbered cords 23.
(35) The device 17 comprises an alternating voltage generator arrangement G which is adapted for applying a first alternating voltage U.sub.1 to a first end 25a of the first group 24a of cords 23 and for applying a second alternating voltage U.sub.2 to a first end 25b of the second group 24b of cords 23.
(36) In the embodiment shown in
(37) 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 25a, 25b of the first and second groups 24a, 24b of cords 23, respectively. The alternating voltage generators G.sub.1, G.sub.2 generate first and second generated voltages U.sub.G1, U.sub.G2, respectively.
(38) An internal electrical resistance of each of the alternating voltage generators G.sub.1, G.sub.2 is represented in
(39) 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°.
(40) 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.
(41) 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 −Umax and a positive voltage +Umax. Such implementation may be advantageous with respect to electro-corrosion characteristics.
(42) 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 23 to which the first and second alternating voltages U.sub.1, U.sub.2 shall be applied.
(43) 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.
(44) The first alternating voltage U.sub.1 is applied to the first end 25a of the first group 24a of cords 23 of a suspension member 11 whereas the second alternating voltage U.sub.2 is applied to a first end 25b of the second group 24b of cords 23 of the same suspension member 11. Within one group of cords 24a, 24b, all cords 23 comprised in this group 24a, 24b may be electrically connected to each other.
(45) Preferably, the cords 23 of one group 24a, 24b 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 25a of the first group 24a of cords 23 being formed by a free end of a cord 23 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 27a of this first group 24a of cords 23 is formed by a free end of a last odd numbered cord 23. Similarly, all even numbered cords 23 may be connected in series such as to electrically connect a first end 25b of this second group 24b of cords 23 to an opposite second end 27b via a single long conductor formed by the series of even numbered cords 23. In such series connection arrangement, both alternating voltages U.sub.1, U.sub.2 applied to first ends 25a, 25b of both groups 24a, 24b of cords 23 are transferred throughout the entire series connections formed in both groups 24a, 24b by the respective cords 23 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 27a, 27b of both groups of cords 24a, 24b. However, in case any electric current is flowing through the cords 23 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 24a, 24b of cords 23 and thus experiences electrical resistances created by the respective cords 23. As a result, voltage drops occur throughout the respective cords 23. Accordingly, by measuring third and fourth voltages U.sub.3, U.sub.4 at opposite second ends 27a, 27b of each group 24a, 24b of cords 23, information about a condition within the groups 24a, 24b of cords 23 may be derived as it may be for example determined whether any electric current flows through the cords 23 in each of the groups 24a, 24b and, if this is the case, how such current “behaves”.
(46) In order to connect the alternating voltage generator arrangement G to the suspension member and suitably interconnecting all cords 23 in advantageous series connections, a connector arrangement (not shown in
(47) As a side note only, it shall be noticed that the first and second groups 24a, 24b of cords 23 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 24a, 24b of cords 23, respectively, it may also be possible to include each of the cords 23 of one or more suspension members 11 in other configurations to the two groups 24a, 24b of cords 23. For example, all cords 1 to n may be comprised in the first group 24a, whereas all cords n+1 to x may be comprised in the second group of cords 24b. Preferably, both groups 24a, 24b of cords 23 comprise a same number of cords 23. Furthermore, while it may be beneficial to connect all cords 23 of one group 24a, 24b in series to each other, also parallel electrical connections of all or some of the cords 23 comprised in one of the groups 24a, 24b may be possible.
(48) At the second ends 27a, 27b of both groups 24a, 24b of cords 23, a first voltage measurement arrangement 31 and/or a second voltage measurement arrangement 33 may be provided as forming part of a determination unit 29. These components 29, 31, 33 are shown in
(49) The first voltage measurement arrangement 31 may be adapted for determining a summed voltage U.sub.+ which correlates to a sum of a third voltage U.sub.3 and a fourth voltage U.sub.4. Therein, the third voltage U.sub.3 applies between the second end 27a of the first group 24a of cords 23 and a common electrical potential such as a ground potential. The fourth voltage U.sub.4 applies between a second end 27b of the second group 24b of cords 23 and the common electrical potential.
(50) The second voltage measurement arrangement 33 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.
(51) 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=1/2 or x=y=2, etc.
(52) In principle, it may be sufficient to provide the device 17 with only one of the first and second voltage measurement arrangements 31, 33 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 17 with both the first voltage measurement arrangement 31 and the second voltage measurement arrangement 33 in order to enable for example distinguishing between various types or degrees of deterioration within the suspension member 11.
(53) In the embodiment shown in
(54) 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 17 shown in
(55) Furthermore, the device 17 may comprise a third and a fourth voltage determining unit 35c, 35d 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 17, 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 35c, 35d, 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 23 of the suspension member 11.
(56) Next, a function principle of the device 17 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 23 nor the cover 21 is deteriorated or even damaged in any manner and therefore all cords 23 have same physical and electrical characteristics. Voltages, which are generated or which are measured during such method will be described with reference to
(57) 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
(58) The first and second voltages U.sub.1, U.sub.2 are then transmitted through the series connection of odd numbered cords 23 of the first group 24a and the series connection of even numbered cords 23 of the second group 24b, respectively, such that a third and a fourth alternating voltage U.sub.3, U.sub.4 occur at the opposite second ends 27a, 27b of both groups of cords 24a, 24b.
(59) When there are no shunts and no electrical connection between these two second ends 27a, 27b, 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 behaviors 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.
(60) 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.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).
(61) 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 23 in the suspension member 11 is broken or if there is a short-circuit between cords 23 or if there is an electrical connection to ground for at least one of the cords 23, either an electrical connection between the first ends 25a, 25b and the second ends 27a, 27b 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 behavior.
(62) 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.
(63) While, in principle, a simple circuitry of the device 17 in which the second ends 27a, 27b of the first and second groups 24a, 24b of cords 23 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 27a, 27b of the two groups 24a, 24b of cords 23 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 23 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
(64) Due to such electrical connection of the second ends 27a, 27b and the third and fourth voltages U.sub.3, U.sub.4 occurring at these second ends 27a, 27b, an electrical current may flow through the entire circuitry of the device 17. 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 27a, 27b 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 23 of the suspension member 11.
(65) Such condition is shown in the diagram of
(66) Accordingly, also with such closed circuitry with the second ends 27a, 27b of both groups of cords 24a, 24b being connected via the connecting electrical resistance R.sub.5, a state in which the summed voltage U.sub.+ comprises no alternating voltage component and the differential voltage U.sub.− comprises an alternating voltage component being non-zero may be interpreted as indicating that the suspension member 11 is in a good condition whereas any deviation from such state may be interpreted as indicating a deterioration or even damage in the suspension member 11.
(67) Next, two alternative embodiments or implementations of devices 17 for detecting the deterioration state in a suspension member arrangement 9 will be described with reference to
(68) In the embodiment shown in
(69) Specifically, the second ends 27a, 27b are electrically connected to each other via two separate connecting electrical resistances R.sub.6, R.sub.7. A first voltage measurement arrangement 31 comprises a first AC voltage determining unit 37a and a first DC voltage determining unit 37b. Both first voltage determining units 37a, 37b are connected to a center point 38 between the separate connecting electrical resistances R.sub.6, R.sub.7, on the one side, and a ground potential, on the other side. Accordingly, these first voltage determining units 37a, 37b may measure an alternating voltage component U.sub.+,AC and a direct voltage component U.sub.+,DC of a summed voltage U.sub.+ being proportional to the sum of the third and fourth voltages U.sub.3, U.sub.4. Specifically, assuming that R.sub.6=R.sub.7, the summed voltage U.sub.+ is in this case U.sub.+=(U.sub.3+U.sub.4)/2. A second voltage measurement arrangement 33 comprises a second voltage determining unit 37c which is directly connected to each of the second ends 27a, 27b. Accordingly, this second voltage determining unit 37c measures a voltage difference between the second ends 27a, 27b. In other words, the second voltage determining unit 37c measures a differential voltage U.sub.− corresponding to U.sub.3−U.sub.4. Specifically, it may be sufficient that this second voltage determining unit 37c only measures an alternating voltage component U.sub.−,AC of such differential voltage U.sub.−.
(70)
(71) Next, some deterioration states or even damage states in a suspension member 11 and ways for detecting such deterioration states with the device and method proposed herein will be described. For some of these cases, typically occurring voltages will be explained with reference to
(72) i) Broken Cord
(73) A critical state to be determined in a suspension member 11 is a case where at least one of the cords 23 comprised in the suspension member 11 is broken. Such broken cord may reduce the load bearing capacity of the suspension member 11 such that the suspension member 11 might have to be replaced.
(74) In case a single cord 23 is broken or multiple cords comprised in either one of the first and second groups 24a, 24b of cords 23 are broken, an electrical connection between a respective first end 25a, 25b and an associated second end 27a, 27b of one of the groups 24a, 24b of cords is interrupted. Accordingly, the entire circuitry of the device 17 is open, i.e. there is no closed electrical circuit anymore, and no electrical current flows any more through the connecting electrical resistance R.sub.5. As a result, both the third and the fourth voltages U.sub.3, U.sub.4 are same and follow the respective one of the generated voltages U.sub.G1, U.sub.G2 connected to the group of cords 24a, 24b that is not broken. Thus, the third voltage U.sub.3 and the fourth voltage U.sub.4 are in phase (i.e. no phase-shift any more) and have the same phase angle as the connected one of the alternating voltage generators G.sub.1, G.sub.2.
(75) The occurring voltages are shown in the diagram of
(76) ii) Suspension Member not attached or both Cord Groups Interrupted
(77) In a next case, it will be assumed that an electrical connection between components of the device 17 and the suspension member 11 is faulty or interrupted such that no voltages may be applied to the cords 23 comprised in the suspension member 11. A same or corresponding situation occurs when cords in not only one but in both groups 24a, 24b of cords are interrupted. In such cases, no electrical current flows through the connecting electrical resistance R.sub.5. Instead, this connecting electrical resistance R.sub.5 will be floating and both the third and fourth voltages U.sub.3, U.sub.4 will be measured as being constantly substantially 0 V. The first and second voltages U.sub.1, U.sub.2 will see no electrical load and may follow the generated voltages U.sub.G1, U.sub.G2 with their maximum voltage amplitude U.sub.max. In such case, as indicated in
(78) iii) Single Cord Connected to Ground
(79) When a single cord 23 or only cords of one of the groups 24a, 24b of cords 23 are electrically connected to a ground potential (as indicated by a faulty first connection to ground 41), an electrical current will flow to ground. Accordingly, in such case of a single cord fault, an asymmetrical load to the alternating voltage generator arrangement G occurs. Since still electrical current flows through the connecting electrical resistance R.sub.5, the third and fourth voltages U.sub.3, U.sub.4 generally both have the same phase and follow the alternating voltage generator G.sub.1 or G.sub.2 attached to the group 24a, 24b of cords 23 not having the ground fault.
(80)
(81) iv) Cords in both Groups Connected to Ground
(82) In case, cords 23 in each of the groups 24a, 24b of cords are simultaneously connected to ground (as indicated by a faulty first connection to ground 41 and a faulty second connection to ground 43 in
(83) Furthermore, in such case, electrical current may be flowing to ground such that electrical load will be put on the two alternating voltage generators G.sub.1, G.sub.2, thereby resulting in smaller first and second voltages U.sub.1, U.sub.2.
(84) It may be noted that such a double or multiple ground connection generally only appears when the suspension member 11 runs for example over a grounded pulley.
(85) Furthermore, it shall be noted that electrical connections to ground can either be permanent or may just occur when the elevator car is at certain locations, i.e. when the suspension member arrangement is moved along pulleys of the elevator and when for example a specific damaged location of the suspension member where the cords 23 are no more isolated by the cover 21 electrically comes into contact with the grounded pulley. It may therefore be necessary for specific embodiments of the detection method presented herein to move the suspension member arrangement along pulleys of the elevator during determining the summed voltage U.sub.+ and the differential voltage U.sub.−. In such cases, a position where at least one electrical connection to ground of one of the cords 23 is present may be determined based on a point in time where a respective deterioration state is determined.
(86) In other words, when the summed voltage U.sub.+ and the differential voltage U.sub.− are permanently monitored during displacing the elevator car and, suddenly, a significant change in the summed voltage U.sub.+ and/or the differential voltage U.sub.− is detected, such change indicating that a single cord is connected to ground or several cords comprised in both groups of cords are connected to ground, a location where such ground connection occurs may be identified based on a point in time at which such change is detected. Therein, it may be used that, typically, an elevator control always knows precisely where the elevator car is currently situated and therefore it is known where the suspension members 11 of the suspension member arrangement 9 contact for example pulleys within the elevator arrangement. Accordingly, knowing the point in time when a ground connection is detected, the location of such ground connection within the suspension member 11 may be identified. In such identification, several influencing parameters such as a pulley diameter, an angle of wrap, a speed of the elevator and a roping factor may be taken into account.
(87) Furthermore, for obtaining more detailed information about a single or multiple ground connections, various voltages may be measured and all first to fourth voltages U.sub.1, U.sub.2, U.sub.3, U.sub.4 may be permanently monitored and compared against their initial values. Both, in case of single ground failures as well as in case of multiple ground failures, these voltage values will be different when compared to the initial values. From the occurring voltage differences between actual values and initial values, additional information about the type, number and/or degree of electrical ground connections may be derived.
(88) v) Shorts between Adjacent Cords
(89) Another deterioration state to be detected may be a case in which neighboring cords 23 come into electrical contact with each other. This may occur for example when an isolating cover 21 is locally damaged and portions of one or more cords 23 are locally exposed. Then, either adjacent cords 23 may be getting into contact by mechanically touching each other directly or by both coming for example into contact with a conducting object such as a conductive pulley (which may be isolated from ground) such that the adjacent cords 23 come into indirect electrical contact. For the indirect adjacent connection of cords 23 via a pulley, it is obvious that the detection of the deterioration state should take place when the elevator moves, i.e. when the suspension member arrangement 9 is moved along the pulleys of the elevator.
(90) As a result of such shorts between adjacent cords 23, an electrical current usually flowing through the connecting electrical resistance R.sub.5 is bypassed by the fault. As a result, the third and fourth voltage U.sub.3, U.sub.4 will generally be the same since they measure a connection point voltage to ground and therefore the differential voltage U.sub.− will generally be zero.
(91) Generally, two types of shorts between adjacent cords 23 may be distinguished. In a first situation named herein “symmetrical short” 45 (as visualized as a broken line in
(92) In an asymmetrical situation called herein “asymmetrical shunt” 47 (as indicated in
(93) vi) Damaged but Non-Interrupted Cords (Corrosion/Rust)
(94) A load bearing capacity of a suspension member 11 may, inter alia, be deteriorated when cords 23 within the suspension member 11 are for example corroded. Rusty locations at the cords 23 may reduce their cross-section thereby reducing their load bearing capacity. It is generally assumed that such corrosion not only decreases mechanical properties of the suspension member 11 but also changes its electrical properties. Particularly, it may be assumed that a diameter of a cord reduced by corrosion generally results in a reduced electrical conductivity through such cord.
(95) When the suspension member 11 is included into the device 17 proposed herein, such reduced electrical conductivity in at least one of the cords 23 may significantly change at least some of the first to fourth voltages U.sub.1, U.sub.2, U.sub.3, U.sub.4. Accordingly, these voltages may be measured for example in an initial state of the suspension member arrangement 9 and measured initial reference values may be stored e.g. once a new suspension member arrangement got installed and put into operation. During subsequent operation of the elevator, some or all of these first to fourth voltages U.sub.1, U.sub.2, U.sub.3, U.sub.4 may be measured and compared to the initial reference values.
(96) Detected differences may show different patterns. For example, when all values actually measured changed in a same manner when compared to the initial reference values, it may be assumed that a homogeneous damage or deterioration, i.e. for example a homogeneous corrosion, occurred to all of the cords 23. Alternatively, if it is observed that some of the actually measured values have changed with respect to the initial reference values but other measured values have not changed, it may be assumed that just certain cords or connection points are faulty.
(97) For completeness, it shall be indicated that, additionally to a measurement mode in which the device 17 may perform a method for detecting various deterioration states as described herein before, the device 17 may also be set into a so-called “idle mode”.
(98) Such idle mode is visualized in
(99) However, in case of deteriorations occurring in the suspension members 11, such voltages U.sub.1, U.sub.2, U.sub.3, U.sub.4 may change. For example, when electrical connections to ground occur at one or more of the cords 23, currents may flow to ground and depending on where the connection to ground occurs, one or more of the first to fourth voltages U.sub.1, U.sub.2, U.sub.3, U.sub.4 may change and, particularly, may be less than U.sub.max.
(100) Summarizing, various deterioration states to be detected with the device 17 and the method described herein may be identified as follows:
(101) a state in which the summed voltage U.sub.+ comprises an alternating voltage component (i.e. U.sub.+AC≈0) and the differential voltage U.sub.− comprises no alternating voltage component (i.e. U.sub.−,AC=0) may be interpreted as indicating that at least one of the cords 23 comprised in one of the group of cords 24a, 24b is interrupted and none of the cords 23 comprised in the other group of cords 24b, 24a is interrupted;
(102) a state in which the summed voltage U.sub.+ comprises no alternating voltage component (i.e. U.sub.+,AC=0) and the differential voltage U.sub.− comprises no alternating voltage component (i.e. U.sub.−,AC=0) may be interpreted as indicating at least one of the following deterioration states:
(103) either: at least one of the cords comprised in one of the groups of cords is interrupted and at least one of the cords comprised in the other group of cords is also interrupted, or: the voltage supplies applying the first alternating voltage U.sub.1 and the second alternating voltage U.sub.2 are both interrupted;
(104) a state in which the summed voltage U.sub.+ comprises an alternating voltage component (i.e. U.sub.+,AC≠0) and the differential voltage U.sub.− comprises an alternating voltage component (i.e. U.sub.−,AC≠0) is interpreted as indicating an electrical connection to ground of at least one of the cords 23 in the suspension member 11; a state in which the summed voltage U.sub.+ comprises no alternating voltage component (i.e. U.sub.+,AC=0) but a direct voltage component (i.e. U.sub.+,DC≠0) and the differential voltage U.sub.− comprises no alternating voltage component (i.e. U.sub.−,AC=0) is interpreted as indicating that one of the cords 23 comprised in one of the groups 24a, 24b of cords is short-circuited with a cord 23 comprised in the other group 24b, 24a of cords in a symmetrical manner;
(105) a state in which the summed voltage U.sub.+ comprises an alternating voltage component (i.e. U.sub.+,AC≠0) and a direct voltage component (i.e. U.sub.+,DC≠0) and the differential voltage U.sub.− comprises no alternating voltage component (i.e. U.sub.−,AC=0) is interpreted as indicating that one of the cords 23 comprised in one of the groups 24a, 24b of cords is short-circuited with a cord 23 comprised in the other group 24b, 24a of cords in an asymmetrical manner.
(106) Particularly, it has been found that information about the deterioration state may advantageously be derived based on an analysis of a phase in an alternating voltage component U.sub.+,AC, U.sub.−,AC of at least one of the summed voltage U.sub.+ and the differential voltage U.sub.−. In other words, when analyzing the summed voltage and/or the differential voltage, also phase angles of the third voltage and the fourth voltage U.sub.3, U.sub.4 and/or of the first voltage and the second voltage U.sub.1, U.sub.2 (or a mathematical combination thereof) may be considered for simplifying a diagnostics.
(107) Furthermore, for obtaining further detailed information about a current deterioration state, initial values of the summed voltage U.sub.+ and/or the differential voltage U.sub.− may be determined and stored in an initial state of the elevator and subsequent values of the summed voltage U.sub.+ and the differential voltage U.sub.− may be determined in a subsequent state of the elevator (i.e. during normal operation thereof). The deterioration state of the suspension member may then be determined during the subsequent state based on a comparison of the initial values of the summed voltage U.sub.+ and the differential voltage U.sub.− with the subsequent values of these summed and differential voltages U.sub.+, U.sub.−, respectively.
(108) Furthermore, for obtaining additional information about the deterioration state, initial values of the applied first and second alternating voltages U.sub.1, U.sub.2 may be determined and stored in an initial state of the elevator and subsequent values (e.g. during normal operation) of the applied first and second alternating voltages U.sub.1, U.sub.2 may be determined in a subsequent state of the elevator. Therein, the deterioration state of the suspension member may be determined during the subsequent state taking into account a comparison of the initial values of the applied first and second alternating voltages U.sub.1, U.sub.2 with the subsequent values of the applied first and second alternating voltages U.sub.1, U.sub.2, respectively.
(109) A brief overview of various possibilities of error detection or deterioration detection in a measurement mode of the device 17 may be obtained from the following chart:
(110) TABLE-US-00001 U.sub.+ U.sub.− Phase angles AC DC AC DC U.sub.3 U.sub.4 Comment OK No signal ~½ U.sub.max Sinusoidal 0 V G.sub.1 G.sub.2 signal Broken cord Sinusoidal U.sub.max No signal 0 V G.sub.x No load on signal .sub.x side still U.sub.1 and U.sub.2 2U.sub.max peak connected to peak STM not No signal 0 V No signal 0 V — — No load on attached or both U.sub.1 and U.sub.2 cord pairs broken Multiple No signal 0 V No signal 0 V — — Load on connections to U.sub.1and U.sub.2 ground Elevator (measurement must move mode) to detect all faults Single Sinusoidal <=½ U.sub.max Sinusoidal <=½ U.sub.max G.sub.x Elevator connection to signal signal <= .sub.x side not must move ground U.sub.3 + U.sub.4 having ground to detect (measurement fault all faults mode) Adjacent No signal U.sub.max No signal 0 V — — Elevator connection of must move cords to detect (symmetrical) all faults Adjacent Sinusoidal U.sub.max No signal 0 V G.sub.x Load on connection of signal .sub.x side of the U.sub.1 and U.sub.2 cords generator Elevator (asymmetrical) being closer to must move the fault to detect all faults Damaged cords Deviation from initial values
(111)
(112) Next, some structural and/or functional details of possible embodiments of the device 17 for detecting the deterioration state will be described.
(113) As indicated with reference to the embodiment shown in
(114) Each or at least one of the first voltage measurement arrangement 31 and the second voltage measurement arrangement 33 may be adapted for measuring at least an alternating voltage component U.sub.+,AC of the summed voltage U.sub.+ or an alternating voltage component U.sub.−,AC of the differential voltage U.sub.−. However, additional information may be acquired if additionally to such ability for measuring the alternating voltage component, the first voltage measurement arrangement 31 and/or the second voltage measurement arrangement 33 are also adapted for measuring a direct voltage component U.sub.+,DC of the summed voltage and/or U.sub.−,DC of the differential voltage U.sub.−.
(115) Furthermore, it may be beneficial to provide the first voltage measurement arrangement 31 and/or the second voltage measurement arrangement 33 with a transformation unit which is adapted for transforming a voltage measurement from a time domain into a frequency domain. For example, such transformation unit may be adapted for performing a Fast Fourier Transformation (FFT). Alternatively, the transformation unit may be adapted for performing other transformations which enable transforming a time-dependency of a voltage periodically varying over time into a frequency domain. Accordingly, any change in a frequency of an alternating voltage component may be easily identified in the representation of the alternating voltage component in the frequency domain. Furthermore, it may also be possible to detect any phase-shift in such alternating voltage component. Detected changes in a frequency or a phase-shift of alternating voltage components U.sub.+,AC, U.sub.−,AC of the summed voltage U.sub.+ and/or the differential voltage U.sub.− may therefore easily be identified and taken as indicating specific types or degrees of deterioration in a suspension member.
(116) Furthermore, the first voltage measurement arrangement 31 and/or the second voltage measurement arrangement 33 may comprise a frequency filter for transmitting only alternating voltage components with a specific frequency spectrum. For example, only alternating voltage components with a frequency corresponding to a frequency of the first alternating voltage U.sub.1 may be transmitted.
(117) For example, such frequency filter may be a band-pass filter. Such band-pass filter may filter-out specific high and/or low frequencies and/or frequency-bands. Accordingly, when analyzing any changes in the alternating voltage components of e.g. the summed voltage U.sub.+ or the differential voltage U.sub.−, signals representing such alternating voltage components may first be filtered such that only those frequencies are actually analyzed which provide important information about the deterioration state of the suspension member, such frequencies typically corresponding to the frequencies of the generated voltages U.sub.G1, U.sub.G2. Other frequency components such as for example high frequency components being unintendedly coupled into the voltage measurement signals may be filtered out. Thus, using such frequency filter, alternating voltage components of a measured voltage may be analyzed in a simplified manner.
(118) The alternating voltage generator arrangement G, possibly with its alternating voltage generators G.sub.1, G.sub.2, may comprise at least one microcontroller generating an alternating voltage using pulse width modulation (PWM). Such PWM microcontroller may generate digital or, preferably, binary signals which may be used for example for controlling transistors. Possibly, a first PWM microcontroller may generate the signals for generating the first generated alternating voltage U.sub.G1 whereas a second microcontroller (or alternatively an inverted output port of the same microcontroller) may generate the signals for generating the second alternating generated voltage U.sub.G2. By suitably turning on and off for example two transistors with a first PWM signal and a second inverted PWM signal, suitable digital PWM signals may then be transmitted through a low-pass filter in order to, finally, generate an analog generated alternating voltage U.sub.G1 or U.sub.G2. The low-pass filters might be implemented as RC filters containing e.g. the two capacitors 39a and 39b and the two resistors R.sub.3 and R.sub.4 as depicted in
(119) Preferably, the alternating voltage generator arrangement G, possibly with its alternating voltage generators G.sub.1, G.sub.2, may be adapted for generating an alternating voltage with a frequency that is neither an integer multiple nor an inverse integer multiple of one of 50 Hz and 60 Hz. In other words, it may be preferable that the voltage generator arrangement generates the alternating voltage with a frequency which is substantially different to the frequency of a typical alternating power supply voltage. Expressed differently, the alternating voltage generators should use a frequency that is different from 50 Hz and 60 Hz and their harmonics. Thereby, measurements of the alternating voltage components may be made robust and immune against any EMC effects which otherwise could disturb the proposed method for detecting the deterioration state in the elevator. Furthermore, particularly when the frequency of the voltage generators significantly differs from any frequency of the power supply voltage, for example a Fast Fourier Transformation or similar algorithm may be used to transform the measured alternating voltage from its time domain into a frequency domain. In such frequency domain, only the frequency matching the alternating voltage generator's frequency may be considered. Furthermore, phase angles of the voltage measurement signal may be detected in order to determine the source generator G.sub.1 or G.sub.2.
(120) Next, an implementation of the device 17 for an elevator having a suspension member arrangement 9 comprising a multiplicity of suspension members 11 will be described.
(121) Typically, a suspension member arrangement 9 for an elevator comprises at least two, preferably three, four or more suspension members 11 such as multiple separate belts in order to securely suspend the elevator car and/or the counterweight. The device 17 may be adapted for detecting deterioration states in each of such multiple suspension members 11. Therein, in order to save device resources and costs, some components of the device 17 may not be provided for each of the suspension members 11 but, instead, are provided only once and are therefore to be shared for detecting the deterioration state in each of the multiple suspension members 11. For example, the device 17 may comprise a power supply, a microcontroller and its software, alternating voltage generators, analog/digital converters and/or serial communication interfaces to an elevator controller. Therein, such components may be provided only once and may be shared for all of the suspension members 11.
(122) As shown in principle in
(123)
(124) Therein, as shown in
(125) As shown in
(126)
(127) However, in comparison to the devices shown in
(128) Particularly, the present device 17 may, despite its reduced complexity and therefore possible reduced costs, determine major non-uniform deteriorations such as interrupted cords 23, shorted cords 23 or cords 23 with faulty connections to ground 41. Furthermore, the present device 17 may determine uniform deteriorations such as corrosion to the cords 23 which result in a general increase of electrical resistances homogeneously for all of the cords 23 in the suspension member 11.
(129) In more detail, in the present device 17, there are no first and second voltage determining units 35a, 35b at the first ends 25a, 25b of the first and second groups of cords 24a, 24b. The present device 17 comprises only the neutral voltage determining unit 35 and the difference voltage determining unit 40.
(130) The neutral voltage determining unit 35 is electrically connected between a neutral point 30 and an electrical reference potential 34 such as an electrical ground. Therein, the neutral point 30 is electrically connected to both, the second end 27a of the first group 24a of cords as well as to the second end 27b of the second group 24b of cords via intermediate first and second resistors R.sub.a, R.sub.b, respectively. Specifically, the neutral point 30 is arranged such that overall electrical resistances between the neutral point 30 and each of the voltage generators G.sub.1 and G.sub.2 are equal. In other words, a first overall electrical resistance including the electrical resistance of all of the cords 23 comprised in the first group 24a of cords 23 connected in series as well as the optional internal electrical resistance devices R.sub.3 and the first resistor R.sub.a is substantially equal to a second overall electrical resistance including the electrical resistance of all of the cords 23 comprised in the second group 24b of cords 23 connected in series as well as the optional internal electrical resistance devices R.sub.4 and the second resistor R.sub.b.
(131) The neutral voltage determining unit 35 is adapted for measuring neutral point voltages U.sub.n between the neutral point 30 and the reference potential 34. Such measured neutral point voltages U.sub.n may then be provided to and analyzed in a determination unit 29.
(132) The difference voltage determining unit 40 is connected between a first difference measurement point 57 and a second difference measurement point 59. The first difference measurement point 57 is located upstream of the first resistor R.sub.a, i.e. between the second end 27a of the first group 24a of electrically conductive cords 23 and the first electrical resistor R.sub.a, whereas the second difference measurement point 59 is located upstream of the second resistor R.sub.b, i.e. between the second end 27b of the second group 24b of electrically conductive cords 23 and the second electrical resistor R.sub.b. Accordingly, the first and second difference measurement points 57, 59 are electrically separated from each other by the intermediate first and second resistors R.sub.a, R.sub.b. On the other hand, the first and second difference measurement points 57, 59 are electrically connected to the first and second voltage generators G.sub.1, G.sub.2, respectively, via the cords 23 of the first and second group, respectively. Accordingly, the first and second voltages U.sub.1, U.sub.2 applied to these groups of cords at their first ends 25a, 25b will be forwarded to their second ends 27a, 27b and to the first and second difference measurement points 57, 59 after having been diminished by voltage drops due to resistance losses throughout the cords 23 in the first and second group 24a, 24b of cords, respectively. Thus, the difference voltage U.sub.d sensed by the difference voltage determining unit 40 is sensitive to any resistance changes throughout the groups 24a, 24b of cords resulting from uniform deteriorations. Such measured difference voltages U.sub.d may then also be provided to and analyzed in a determination unit 29.
(133) Upon performing a method for detecting a deterioration state in the suspension member arrangement 9 in accordance with an embodiment of the present invention, both alternating voltage generators G.sub.1, G.sub.2 may be controlled such that a first alternating voltage U.sub.1 is applied to the first end 25a of the first group 24a of cords of the suspension member 11 and a second alternating voltage U.sub.2 is applied to the second end 25b of the second group 24b of cords of the suspension member 11 with both alternating voltages U.sub.1, U.sub.2 having same waveforms but being shifted against each other with a phase difference of 180°.
(134) Upon having applied such symmetric first and second alternating voltages U.sub.1, U.sub.2, the voltage determining unit 35 measures the neutral point voltage U.sub.n. As long as no significant deteriorations or failures occur within the cords 23 of the suspension member 11, such neutral point voltage U.sub.n should comprise no alternating voltage component due to the fact that, at the neutral point 30, both the alternating voltage applied by the first voltage generator G.sub.1 and the second voltage applied by the second voltage generator G.sub.2 compensate each other due to their same amplitudes and 180° phase shift.
(135) However, as soon as the neutral point voltage U.sub.n comprises a non-zero AC component, this may be taken as indication for a substantive non-uniform deterioration or failure within the cords 23 of the suspension member 11. In case of detecting such substantive deterioration or failure, the determination unit 29 may issue a signal for example to the elevator's 1 control device 18 in order to stop operation of the elevator 1.
(136) Measuring the neutral point voltage U.sub.n and thereby monitoring the suspension member 11 for an occurrence of specific types of non-uniform deteriorations or failures may be performed continuously or repeatedly in short time intervals of e.g. some seconds, minutes or hours.
(137) In same or substantially longer time intervals, the device 17 may measure the difference voltage U.sub.d. Compared to the above mentioned non-uniform deteriorations, the uniform deteriorations to be detected by analyzing the difference voltage U.sub.d typically develop in longer time ranges of some days, weeks, months or even years such that it may be sufficient to measure the difference voltage U.sub.d in such longer time intervals.
(138) While the difference voltage U.sub.d will generally have a certain non-zero alternating voltage component due to the phase shift of the applied first and second alternating voltages U.sub.1, U.sub.2, a specific degree or amplitude of such alternating voltage component may generally depend on an electrical resistance through the cords 23 comprised in the first and second groups 24a, 24b of cords.
(139) Accordingly, while, in the method presented herein, no electrical resistances are measured directly but only voltages are measured, the degree or amplitude of the alternating voltage component comprised in the measured difference voltage U.sub.d may provide information about actual electrical resistances through the groups 24a, 24b of cords 23 in the suspension member 11. From such information, indications about the uniform deterioration state of the suspension member 11 may be derived. Particularly, information about a deterioration state resulting from homogeneous corrosion of all cords 23 in the suspension member 11 may be derived from the measured difference voltage U.sub.d.
(140) For example, the measured difference voltage U.sub.d may be compared to a reference difference voltage value U.sub.dr which correlates for example to a difference voltage U.sub.d which has been measured for example in a non-deteriorated state directly after installing the suspension member arrangement 9 and has then been stored in a memory e.g. of the determination unit 29.
(141) In case the currently measured difference voltage U.sub.d differs from the reference difference voltage value U.sub.dr by more than a predetermined tolerance, for example by more than 2%, 5%, 10%, 20%, 30% or 40%, it may be assumed that excessive deterioration resulting in increased electrical resistance occurred in the cords 23 of the groups 24a, 24b of cords and the device 17 may go into an error mode in which e.g. the determination unit 29 sends a signal to the elevator's control device 18 for stopping or modifying the operation of the elevator 1.
(142) It shall be noted that all measured or determined values, particularly all voltage values, indicated herein are understood by one skilled in the art as “substantial” values. I.e. when a measured or determined value is said to be a specific numeral value, insignificant deviations of e.g. up to 2% relative or even up to 5% relative may still be included. For example, if it is stated that no DC voltage and/or no AC voltage are measured this may mean that within acceptable tolerances no such voltages are measured but that for example due to noises some minor electric voltages may still occur.
(143) 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.
(144) 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.
LIST OF REFERENCE SIGNS
(145) 1 elevator 3 car 5 counterweight 7 elevator shaft 9 suspension member arrangement 11 suspension member 13 traction machine 15 traction sheave 17 device for detecting deterioration states 18 control device 19 belt 21 matrix material 23 cords 24a first group of cords 24b second group of cords 25a first end of first group of cords 25b first end second group of cords 27a second end of first group of cords 27b second end second group of cords 29 determination unit 30 neutral point 31 first voltage measurement arrangement 32 voltage measurement arrangement 33 second voltage measurement arrangement 34 reference potential 35 neutral point voltage determining unit 35a first voltage determining unit 35b second voltage determining unit 35c third voltage determining unit 35d fourth voltage determining unit 36 pull-up voltage source 37a first AC voltage determining unit 37b first DC voltage determining unit 37c second voltage determining unit 38 center point 39a,b capacitors 40 differential voltage determining unit 41 faulty first connection to ground 41a,b switches 43 faulty second connection to ground 45 symmetrical short 47 asymmetrical short 49 PWM microcontroller 51 multiplexer arrangement 53a-d drivers 55a-d low pass filters 57 first difference measurement point 59 second difference measurement point A-D voltage measurement arrangements U.sub.1 first alternating voltage U.sub.2 second alternating voltage U.sub.3 third alternating voltage U.sub.4 fourth alternating voltage G alternating voltage generator arrangement G.sub.1 first alternating voltage generator G.sub.2 second alternating voltage generator U.sub.G1 first generated voltage U.sub.G2 second generated voltage U.sub.+ summed voltage U.sub.− differential voltage U.sub.+,AC alternating voltage component of the summed voltage U+ U.sub.−,AC alternating voltage component of the differential voltage U− U.sub.+,DC direct voltage component of the summed voltage U+ U.sub.−,DC direct voltage component of the differential voltage U− U.sub.n neutral point voltage U.sub.d differential voltage U.sub.dr reference difference voltage R.sub.a, R.sub.b first and second electrical resistors R.sub.1-R.sub.4 electrical resistances R.sub.5 connecting electrical resistance R.sub.6, R.sub.7 separate connecting electrical resistances t.sub.1-t.sub.6 periods of time during multiplexing t.sub.s sleep period