Concepts for detecting a deterioration state of a load bearing capacity in a suspension member arrangement for an elevator
Methods and devices detect a deterioration state of a load bearing capacity in an elevator suspension member arrangement having several suspension members, such as belts, including electrically conductive cords incorporated into an elastomer material. Deterioration is determined by applying alternating electric voltages to the cords included in legs of a circuitry. Phase shifts between the alternating voltages, for example by determining sum voltages and/or differential voltages, provide valuable information about a condition of the belt. A fixation arrangement of the suspension member arrangement is adapted to enable or simplify the proposed measurements. Furthermore, counting a number of performed bending cycles provides further information to be taken into account for determining the current deterioration state of the belts. Overall, deteriorations in a suspension member such as broken cords, shunts between cords, connections between cords and ground potential and/or deterioration due to corrosion of cords may be easily detected.
1. A method for detecting a deterioration state of a load bearing capacity in a suspension member arrangement for an elevator, the suspension member arrangement comprising at least one suspension member having a first group and a second group of electrically conductive cords, the method comprising 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°;
determining at least one of (i) a summed voltage correlating to a sum of a third voltage between a second end of the first group of cords and a common electrical potential and a fourth voltage between a second end of the second group of cords and the common electrical potential, and (ii) a differential voltage correlating to a difference between the third voltage and the fourth voltage; and
determining the deterioration state of a load bearing capacity in a suspension member based on at least one of the summed voltage and the differential voltage.
2. The method according to claim 1 wherein the second end of the first group of cords and the second end of the second group of cords are electrically connected via a connecting electrical resistance.
3. The method according to claim 1 wherein any deviation from a state in which the summed voltage has no alternating voltage component and the differential voltage has an alternating voltage component is interpreted as indicating a deterioration in the suspension member arrangement.
4. The method according to claim 1 wherein a state in which the summed voltage has an alternating voltage component and the differential voltage has no alternating voltage component is interpreted as indicating that at least one of the cords in one of the groups of cords is interrupted and none of the cords in another of the groups of cords is interrupted.
5. The method according to claim 1 wherein a state in which the summed voltage has no alternating voltage component and the differential voltage has no alternating voltage component is interpreted as indicating at least one of deterioration states of:
at least one of the cords in one of the groups of cords is interrupted and at least one of the cords in another of the groups of cords is interrupted; and
the voltages of the first alternating voltage and of the second alternating voltage are both interrupted.
6. The method according to claim 1 wherein a state in which the summed voltage has an alternating voltage component and the differential voltage has an alternating voltage component is interpreted as indicating an electrical connection to ground of at least one of the cords in the suspension member.
7. The method according to claim 1 wherein a state in which the summed voltage has no alternating voltage component and includes a direct voltage component and the differential voltage has no alternating voltage component is interpreted as indicating that one of the cords in one of the groups of cords is short circuited with a cord in another of the groups of cords in a symmetrical manner.
8. The method according to claim 1 wherein a state in which the summed voltage has an alternating voltage component and a direct voltage component and the differential voltage has no alternating voltage component is interpreted as indicating that one of the cords in one of the groups of cords is short circuited with a cord in another of the groups of cords in an asymmetrical manner.
9. The method according to claim 1 including determining a position where a state of at least one of a connection to ground of one of the cords and a state of a short circuit between cords of the groups of cords is present based on a point in time when the respective state is determined.
10. The method according to claim 1 wherein initial values of the summed voltage and the differential voltage are determined and stored in an initial state of the elevator and wherein subsequent values of the summed voltage and the differential voltage are determined in a subsequent state of the elevator and wherein the deterioration state of the suspension member is determined during the subsequent state based on a comparison of the initial values of the summed voltage and the differential voltage with the subsequent values of the summed voltage and the differential voltage, respectively.
11. A device for detecting a deterioration state of a load bearing capacity in a suspension member arrangement for an elevator, the suspension member arrangement having at least one suspension member having a first group and a second group of electrically conductive cords, the device comprising:
an alternating voltage generator arrangement for applying a first alternating voltage to a first end of the first group of cords for applying a second alternating voltage to a first end of the second group of cords, wherein the alternating voltage generator arrangement is configured to generating the first and second alternating voltages with same waveforms and a phase difference of 180°;
at least one of (i) a first voltage measurement arrangement for determining a summed voltage correlating to a sum of a third voltage between a second end of the first group of cords and a common electrical potential and a fourth voltage between a second end of the second group of cords and the common electrical potential, and (ii) a second voltage measurement arrangement for determining a differential voltage correlating to a difference between the third voltage and the fourth voltage; and
a determination unit for determining the deterioration state of a load bearing capacity in a suspension member based on at least one of the summed voltage and the differential voltage.
12. The device according to claim 11 wherein the determination unit is adapted to determine a deterioration in the suspension member arrangement based on any deviation from a state in which the summed voltage has no alternating voltage component and the differential voltage has a non-zero alternating voltage component.
13. The device according to claim 11 wherein at least one of the first voltage measurement arrangement and the second voltage measurement arrangement includes a transformation unit for transforming a voltage measurement from a time domain to a frequency domain.
14. The device according to claim 11 including a third voltage measurement arrangement for measuring the first alternating voltage and a fourth voltage measurement arrangement for measuring the second alternating voltage.