Method and system for continuous condition monitoring of a hoist chain

Abstract

To provide an improved method and system for continuous condition monitoring of a hoist chain (3), - detecting the presence / absence of the chain links (3a, 3a', 3a'', 3a''', 3a'''', 3a'''', 3a''''') and / or the teeth (7a, 7a', 7a''') of the chain sprocket (7) using at least one sensor (9a, 9b); - determining, by means of an evaluation unit (11), time intervals (Ton1, Toff2, Ton3, Toff4) reflecting presence / absence using the signals obtained from the sensors (9a, 9b), and - determining the sums (SUM1, SUM2) of the time intervals using an evaluation unit (11); - determining the chain speed using an evaluation unit (11); - comparing, by means of an evaluation unit (11), the first sum (SUM1) with a second sum (SUM2) to determine the extension of the hoist chain (3), each time interval being determined at the same chain speed.

Description

[Technical Field]

[0001] The invention relates to a method for continuous condition monitoring of a hoist chain according to claims 1 and 2, to a monitoring system for continuous condition monitoring of a hoist chain according to claim 11, and to a chain hoist equipped with such a monitoring system according to claim 16. [Background technology]

[0002] To prevent chain hoist failures and accidents caused by defective hoist chains, periodic inspections of hoist chains are performed to evaluate the wear state of the hoist chain. Common methods for monitoring hoist chain wear are visual inspection and measurement using a chain gauge. The chain gauge is used to detect an increase in chain link length, which may be the result of chain wear. However, such monitoring methods require interruption of chain hoist operation during the time for visual inspection or measurement.

[0003] In connection with tub chains, for example drive chains, it is known to monitor chain wear using continuous condition monitoring, i.e. monitoring the chain while it is in operation.

[0004] EP 1464919 (B1) discloses a chain wear monitoring method and apparatus for detecting chain wear in a tub chain used as a drive chain. A first sensor is stationary, and a second sensor is movable along the chain's length. Two markers, spaced a predetermined distance apart, are applied to the chain to trigger the sensors. Initially, i.e., when the chain is unworn or unworn, the position of the first sensor coincides with the position of the first marker, and the second sensor coincides with the position of the second marker. Chain elongation is detected by determining a predetermined time delay between the triggering of the first and second sensors, moving the movable sensor to a position where substantially simultaneous triggering of the sensors resumes, and measuring the distance traveled by the sensor. Such a method and apparatus has the disadvantage that at least one of the sensors must be movable, and a movable support structure is more prone to failure than a non-movable support structure. Furthermore, such a method and apparatus has the disadvantage that markers must be applied to the chain, i.e., it can only monitor a predetermined chain segment.

[0005] WO 2008 / 024685 A2 discloses a chain wear monitoring device and method for detecting chain wear in a tub chain used as a drive chain. A first sensing device is used to detect the presence of a first chain portion when the first chain portion is in a predetermined position relative to the first sensing device. A second sensing device is used to detect a second chain portion, the second sensing device operating in response to an output signal from the first sensing device. The degree of wear in the chain section extending between the first and second chain portions is determined by comparing the distance between the first and second chain portions to an initial (unworn) distance.

[0006] U.S. Patent No. 5,563,392(A) discloses a method and apparatus for monitoring tab chain wear. The apparatus has a pair of sensors positioned at intervals along the chain, which detect the presence and absence of chain tabs. A first time interval (t1-t2) is determined by calculating the time difference between activation of the first and second sensors. A second time interval (t1) is determined by determining the time it takes for one chain pitch to pass one of the first and second sensors, where the chain pitch is the linear distance between common locations on successive tabs. The time ratio of the first time interval to the second time interval (TR) is calculated. n ) is calculated. This time ratio is compared to a predetermined value (TR0) to determine chain wear.

[0007] US Patent Application Publication No. 2011 / 093218 A1 and EP Patent Application Publication No. 1850087 A1 disclose methods for monitoring the condition of tab chains, using sensors to detect distance information and determining the elongation of each tab chain based on the detected distance information.

[0008] The document US 2019 / 0352140 A1 relates to defect monitoring of tub chains in passenger conveyors, and the document DE 102016109968 A1 relates to a method for determining the speed of a ferromagnetically active drive tub chain. Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the above, it is an object of the present invention to provide a method and monitoring system, as well as a chain hoist, that allows for simple and cost-effective continuous condition monitoring of a hoist chain. [Means for solving the problem]

[0010] This object is achieved by a method with the features of claim 1 or claim 2, a monitoring system with the features of claim 11, and a chain hoist with the features of claim 16. The dependent claims and the following description describe advantageous embodiments of the invention.

[0011] The present invention provides a method for continuous condition monitoring of a hoist chain, comprising: a) detecting the presence and absence of a chain link using a first sensor; b) using the evaluation unit to determine, using the signals obtained from the first sensor, a first time interval reflecting the presence of the first chain link, a second time interval reflecting the absence of a chain link between the first chain link and the third chain link, a third time interval reflecting the presence of the third chain link, and a fourth time interval reflecting the absence of a chain link between the third chain link and the fifth chain link; c) determining, using the evaluation unit, a first sum of the first time interval and the second time interval and a second sum of the third time interval and the fourth time interval; d) determining the chain speed using an evaluation unit; e) using the evaluation unit, comparing the first sum with the second sum to determine the extension of the hoist chain, wherein each time interval is determined at the same chain speed.

[0012] In other words, the first sum is subtracted from the second sum, or vice versa, to determine the difference between the two sums and therefore the extension of the hoist chain. Thus, the second sum constitutes a measure of the first sum, and vice versa.

[0013] If the difference between the two sums is equal to zero, the hoist chain is not stretched and is therefore unworn or "healthy". Since stretching occurs unevenly along the hoist chain, if the difference is not equal to zero, the hoist chain or at least one chain link is stretched (local stretching) and, as a result, the hoist chain can be considered worn. However, as explained below, the actual declaration of wear in the course of application of the method may depend on further circumstances.

[0014] Each total includes two time intervals, one reflecting the presence of a chain link and the other reflecting its absence. The length of each time interval depends on the shape and length of the chain link. However, if the hoist chain is unworn, each time interval reflecting the presence of a chain link should be the same. The same is true for each time interval reflecting the absence of a chain link.

[0015] Because this first embodiment of the method is performed using only one sensor, first and second successive time intervals are determined using signals obtained from the first sensor at a first "point in time," and third and fourth successive time intervals are determined using signals obtained from the first sensor at a second "point in time" different from the first "point in time." Thus, the reference comprises signal data received from the first sensor (used alone) at another "point in time."

[0016] There are no limitations regarding the type of data used by the evaluation unit to determine the chain speed according to method step (d). For example, the chain speed can be determined by the evaluation unit based on a sensor signal, or, as another example, by calculation using the rotational speed of the chain hoist motor. To avoid misinterpretations caused by changes in chain speed, the chain speed must be the same for each time interval involved in the comparison. If differences between time intervals could also be caused by different chain speeds at the time of detection, the time intervals cannot be compared to properly determine wear.

[0017] Thus, when the chain speed changes, the collection of signal data for a particular chain speed is interrupted. Collection can then continue when the particular chain speed is resumed, i.e., when the chain hoist is again operated at the particular chain speed. The same is true when the chain speed remains constant.

[0018] Alternatively, a known delta in chain speed may be utilized so that its effect on the signal obtained from the sensor can be taken into account or compensated for when collecting the signal data.

[0019] Hoist chains are link chains, distinct from tab chains. Link chains comprise a plurality of chain links oriented alternately in first and second planes, the first plane being oriented substantially perpendicular to the second plane. In other words, even-numbered chain links are oriented in a first plane, and odd-numbered chain links are oriented in a second plane, the second plane being oriented substantially perpendicular to the first plane.

[0020] Tab chains, on the other hand, have outer and inner tabs and chain pins connecting the tabs. Each inner tab of the chain is oriented in a first plane, and each outer tab is oriented in a second plane, the first and second planes being substantially parallel to each other. Tab chains are typically used as drive chains, with the tabs connected to each other in a continuous loop.

[0021] The first sensor is preferably an inductive sensor, such as a Hall sensor. Inductive sensors have the advantage that they work even when the hoist chain is contaminated with dirt or grease. Alternatively, the first sensor may be a mechanical switch or an ultrasonic sensor.

[0022] The first sensor changes its state when the hoist chain is moving in front of it. Detecting the presence of a chain link means that the respective sensor is activated when a chain link or part of it is present.

[0023] The first sensor preferably begins sensing at the leading edge of a chain link and ends sensing at the trailing edge of the same chain link. In other words, the rising edge of the sensor pulse corresponds to the leading edge of the chain link. The rising edges constitute the start of the first and third time intervals and the end of the second and fourth time intervals, respectively. The first and third time intervals, which reflect the presence of a single chain link, can also be referred to as "overpass times."

[0024] The first sensor, on the other hand, preferably switches off at the trailing edge of the chain link and remains off between the trailing edge of the chain link and the leading edge of the next chain link in the same plane. In other words, the trailing edge of the sensor pulse corresponds to the trailing edge of the chain link. The trailing edges constitute the end of the first and third time intervals and the start of the second and fourth time intervals, respectively.

[0025] Thus, if the rising and falling edges of the sensor pulses or time intervals coincide or are as close to each other as possible, the hoist chain is interpreted as not worn or unworn. Conversely, if the rising and falling edges of the sensor pulses become disjointed and therefore do not coincide, the hoist chain may be interpreted as worn.

[0026] Because the hoist chain can move in two directions to raise and lower a load, the leading edge of a chain link with the hoist chain moving in one direction is the trailing edge while the chain moves in the other direction. Therefore, signal data collection can be separated for the two directions. When the chain is moving in the other direction, the signal obtained from the sensor can be mirrored instead.

[0027] The first sensor can detect the presence of even-numbered or odd-numbered chain links. This is why it can detect the presence of the first chain link and the absence of a chain link between the first and third chain links, but cannot detect the presence of a second chain link located between the first and third chain links. The first chain link can be any of the chain links of the hoist chain. However, the numbering of the first, second, third, etc. chain links should be understood as consecutive chain links.

[0028] The main advantage of the method according to the invention is that the condition monitoring is carried out continuously while the chain hoist is in operation, so that there is no need to interrupt operation just for the purpose of monitoring. Another advantage of the method according to the invention is that the load on the chain hoist does not affect the condition monitoring.

[0029] The present invention further provides a method for continuous condition monitoring of a hoist chain, comprising: a) detecting the presence and absence of a chain link using a first sensor; a') detecting the presence and absence of teeth of a chain sprocket or the presence and absence of chain links using a second sensor; b') using the evaluation unit to determine, using the signal obtained from the first sensor, a first time interval reflecting the presence of the first chain link and a second time interval reflecting the absence of a chain link between the first chain link and the third chain link; b'') using the evaluation unit to determine, using the signals obtained from the second sensor, a third time interval reflecting the presence of the first tooth or the presence of the first chain link or the second chain link or the third chain link, and a fourth time interval reflecting the absence of a tooth between the first tooth and the second tooth or the absence of a chain link between the first chain link and the third chain link or between the second chain link and the fourth chain link or between the third chain link and the fifth chain link; c) determining, using the evaluation unit, a first sum of the first time interval and the second time interval and a second sum of the third time interval and the fourth time interval; d) determining the chain speed using an evaluation unit; e) using the evaluation unit, comparing the first sum with the second sum to determine the extension of the hoist chain, wherein each time interval is determined at the same chain speed.

[0030] This second embodiment of the method differs from the first embodiment primarily in that a second sensor is included. Like the first sensor, the second sensor is preferably an inductive sensor, but may alternatively be a mechanical switch or an ultrasonic sensor. The second sum is determined using a time interval, which, unlike the first embodiment, is determined using a signal obtained from the second sensor instead of the first sensor.

[0031] In a method including two sensors, the determination of the first and second time intervals can be performed at the same "point in time" as the determination of the third and fourth time intervals. In other words, when first and second sensors are used, the reference is constituted by signal data received from the first or second sensor simultaneously, or alternatively at a different "point in time." Thus, the signal of the second sensor may be used as a reference for the signal of the first sensor, and vice versa.

[0032] Additionally, two sensors can be used to determine which direction the hoist chain is traveling.

[0033] Another difference between the two embodiments of the method is that the second sensor can be used to detect a part of the chain hoist other than the hoist chain, in particular the sprocket, i.e. the second sensor can be installed to detect the hoist chain or it can be installed to detect the sprocket.

[0034] Thus, in contrast to the first embodiment, the two time intervals included in the second summation can reflect either the presence of a sprocket tooth (third time interval) and the absence of a sprocket tooth (fourth time interval), or the presence of a chain link (third time interval) and the absence of a chain link (fourth time interval).

[0035] If a second sensor is installed to sense the hoist chain and therefore used to detect the presence and absence of chain links like the first sensor, the second sensor will function in the same way as the first sensor, and therefore see what has been outlined above in this regard.

[0036] The second sensor can be positioned such that a predetermined distance between the two sensors along the hoist chain is equal to the distance between the leading edge of the first chain link and the leading edge of the third chain link, so that when the hoist chain is unworn, the first sensor detects the leading edge of the first chain link at the same time that the second sensor detects the leading edge of the third chain link.

[0037] Alternatively, the predetermined distance may be adjusted or zeroed so that, when the hoist chain is unworn, the first sensor detects the leading edge of the first chain link at the same time that the second sensor detects the leading edge of either the first or second chain link. In this regard, the second sensor may also detect the leading edge of the first chain link, for example, when the first and second sensors are positioned at an angle of approximately 180° from each other. Meanwhile, the second sensor may detect the leading edge of the second chain link, for example, when the first and second sensors are positioned at an angle of approximately 90° from each other.

[0038] If a second sensor is positioned to sense the sprocket and is therefore used to detect the presence and absence of sprocket teeth, the second sensor will change state when the sprocket is moving, i.e., rotating, in front of it.

[0039] The sprocket is used to move the hoist chain to raise and lower a load connected to the hoist chain, and is preferably pivoted in the chain guide housing and rotates to move the hoist chain. The sprocket includes a plurality of sprocket teeth adapted to engage with the chain links of the hoist chain.

[0040] Detecting the presence of a sprocket tooth means that the respective sensor is activated when a sprocket tooth or a portion thereof is present. The time intervals depend on the shape and length of the sprocket tooth. However, the time intervals reflecting the presence of a sprocket tooth should be the same when the hoist chain is unworn. The same applies to the time intervals reflecting the absence of a sprocket tooth.

[0041] If the second sensor senses the sprocket, the third time interval may be different from the first time interval determined using signal data from the first sensor, and the second time interval may be different from the fourth time interval, but while the hoist chain is in an unworn condition, the first sum and the second sum should be equal to each other.

[0042] The second sensor preferably begins sensing at the leading edge of a sprocket tooth and ends sensing at the trailing edge of the same sprocket tooth. In other words, the rising edge of the sensor pulse corresponds to the leading edge of the sprocket tooth. The rising edges constitute the beginning of the first and third time intervals and the end of the second and fourth time intervals, respectively. The first and third time intervals, which reflect the presence of a single sprocket tooth, can also be referred to as "overpass times."

[0043] The second sensor, on the other hand, preferably remains switched off between two sprocket teeth. In other words, the trailing edge of the sensor pulse corresponds to the falling edge of the sprocket tooth. The falling edges constitute the end of the first and third time intervals and the start of the second and fourth time intervals, respectively.

[0044] The second sensor may be preferably positioned to sense a portion of the sprocket teeth that does not contact the hoist chain and therefore does not wear at least as much as the hoist chain.

[0045] Preferably, it is envisaged that the method includes repeating steps a) to e) if the chain speed changes.

[0046] Chain speed, or hoisting speed, can vary during chain hoist operation. To ensure that different hoist speeds do not impair the accuracy of condition monitoring, signal data collection begins again when the chain speed changes.

[0047] The signal data set for a particular chain speed may then be stored separately from the signal data sets for other chain speeds, and signal data collection for each signal data set can continue when the particular chain speed is resumed.

[0048] The method is also not limited with regard to the type of data used by the evaluation unit to determine the chain speed according to method step (d).According to the invention, as a preferred alternative, it is proposed that the chain speed is determined by comparing the signal obtained from the first sensor with the signal obtained from the second sensor.

[0049] A predicted comparison of the two sensor signals allows for a more accurate determination of chain speed than can be determined from signal data from only one sensor.

[0050] Since determining the chain speed requires knowledge of the current length of the chain links, preferably in a first step, the change in chain speed is determined by detecting a change in the acquired signal of one of the sensors. Based on the known initial or previous chain speed, in a second step, the current chain speed is derived by taking into account the change in chain speed. In a third step, a comparison is made to verify the results using signal data obtained from the other of the sensors.

[0051] Alternatively, the chain speed may be determined by calculation using the rotational speed of the chain hoist's motor that drives the sprocket, or an input signal to the operating panel or hoist control system used to operate the chain hoist may be used to determine the chain speed.

[0052] Advantageously, the method may be provided comprising using the first sensor and / or the second sensor to detect an air gap between the respective sensor and the hoist chain.

[0053] Preferably, each sensor used to detect the gap is an analog sensor, and the size of the gap can be determined using the sensor signal.

[0054] The gap may exist due to the mechanical structure of the chain hoist, for example, its chain guide. The gap may increase due to wear of the hoist chain and / or chain guide.

[0055] The method may also advantageously comprise determining the size of the gap using an evaluation unit, and may advantageously be provided to take into account possible gap generation deviations during detection using the respective sensors when determining the extension of the hoist chain.

[0056] In other words, information about the size of the air gap can be used to at least reduce the air gap induced deviations in the signal obtained from the sensor, preferably to extract such deviations completely.

[0057] Preferably, it can be foreseen that the first and second sensors have different actuation sensitivities.

[0058] Due to the different sensitivities, the first sensor activates before or during the activation of the second sensor. The sensitivity is primarily related to the amount of material required to activate or trigger the sensor. Thus, when sensing the same size chain link or sprocket tooth at the same sensor location relative to the chain link or sprocket tooth, a sensor with lower sensitivity will trigger later and for a shorter time than a sensor with higher sensitivity.

[0059] Therefore, the time interval reflecting the presence of a chain link or sprocket tooth will be different for two sensors with different sensitivities, and the time interval reflecting the absence of a chain link or sprocket tooth will also be different. However, if the hoist chain is unworn, the sum of the above-mentioned time intervals will be the same for two sensors with different sensitivities.

[0060] The sensitivity may be adjusted so that the first and / or third time intervals correspond to the actual length of a chain link or the actual width of a sprocket tooth, in which case the current length of a single chain link or the current width of a single sprocket tooth can be determined by the respective time intervals.

[0061] Performing the method using sensors with different sensitivities has the advantage that the results of the comparison are more meaningful due to the more contrasting reference formed by one of the sensor signals.

[0062] In a preferred embodiment, the first sensor and the second sensor function independently of each other.

[0063] This means that, according to this embodiment, none of the sensors participating in the continuous condition monitoring are expected to sense in response to one or more of the other participating sensors, in other words, the sensors are not influenced by any of the other sensors or their sensor signals, either directly or indirectly, for example via the evaluation unit.

[0064] It may be advantageously provided that the method comprises comparing, with the evaluation unit, the difference between the first sum and the second sum with a predetermined threshold value.

[0065] The predetermined threshold should be understood as, for example, the limit of acceptable wear of the hoist chain to maintain safe operation of the chain hoist. The threshold depends on the geometry of the chain links, in particular their length and shape.

[0066] Furthermore, predetermined should be understood as preset, and the threshold value may be stored in the evaluation unit. The threshold value may be entered into the evaluation unit, for example, by an operator or maintenance personnel of the chain hoist. When predetermining or presetting the threshold value, manufacturing tolerances of the hoist chain and sprockets can be taken into account, so that the wear determination is less prone to errors.

[0067] It may also be advantageously provided that the method comprises generating, in particular by means of the evaluation unit, an output signal if the difference exceeds a predetermined threshold value.

[0068] The output signal should indicate, for example, to a chain hoist operator or maintenance personnel, that the hoist chain is worn. The output signal may be an optical and / or acoustic output signal.

[0069] The present invention further provides a monitoring system for continuous condition monitoring of a hoist chain, comprising: a first sensor, the first sensor being arranged and configured to detect the presence and absence of a chain link; a memory device configured to collect and store signals or signal data obtained from the first sensor; an evaluation unit configured to carry out the method according to the invention with the first sensor involved.

[0070] The first sensor is mounted near the hoist chain to be monitored and is fixedly positioned so that its sensor field extends essentially perpendicular to the direction of hoist chain movement. The first sensor is preferably an inductive sensor, such as a Hall sensor. Inductive sensors have the advantage of functioning even when the hoist chain is contaminated with dirt or grease. Alternatively, the first sensor may be a mechanical switch or an ultrasonic sensor.

[0071] The first sensor can generate either a digital or analog output signal. If the first sensor generates an analog output signal, it can be used to detect an air gap between the sensor and the chain as well as the size of the air gap. As described above, information about the air gap can be used to reduce air gap-induced deviations in the signal acquired by the sensor.

[0072] The memory device may for example be connected to the evaluation unit by suitable data or signal connections or may be part of the evaluation unit.

[0073] It may be advantageously provided that the monitoring system further comprises a second sensor arranged at a fixed distance from the first sensor, the second sensor being arranged and configured to detect the presence and absence of teeth of the chain sprocket or the presence and absence of chain links, the memory device being configured to collect and store signals or signal data obtained from the second sensor, and the evaluation unit being configured to perform the method according to the invention in a state in which the first sensor and the second sensor are involved.

[0074] When the second embodiment of the method is performed, which includes a first and a second sensor, a second sensor is required. However, even if the monitoring system has a second sensor, the first embodiment of the method can also be performed, which includes only the first sensor.

[0075] The second sensor is mounted near the monitored hoist chain or the monitored chain sprocket, respectively, and is fixedly positioned so that its sensor field extends essentially perpendicular to the direction of hoist chain movement or the direction of sprocket movement, or in the latter case, substantially parallel to the axis of rotation of the sprocket.

[0076] Like the first sensor, the second sensor is preferably an inductive sensor, but may alternatively be a mechanical switch or an ultrasonic sensor.

[0077] The second sensor can generate either a digital or an analog output signal. Preferably, one of the sensors generates a digital output signal and the other generates an analog output signal. It is also possible for both sensors to generate digital or analog output signals.

[0078] In a preferred embodiment of the monitoring system, both the first sensor and the second sensor are positioned upstream or downstream of the chain sprocket, or alternatively, the first sensor and the second sensor are positioned on different stream sides of the chain sprocket.

[0079] In other words, when viewed in the direction of chain travel, the two sensors can be positioned on the same side, in front of or behind the chain sprocket, so that both sensors are positioned on the load strand side, or both sensors are positioned on the slack side of the hoist chain.

[0080] Alternatively, the sensors can be positioned on different sides of the sprocket, so that one sensor is positioned on the load strand side and the other sensor is positioned on the slack side of the hoist chain.

[0081] Independently of the foregoing placement criteria, each sensor may be positioned under a sprocket between the load strand and slack sides of the hoist chain, or outside the "V" or "U" formed by the hoist chain.

[0082] In a preferred embodiment of the monitoring system, the first sensor and the second sensor are positioned at an angle of approximately 90° to each other.

[0083] In other words, the sensor field of the first sensor not only extends essentially perpendicular to the hoist chain movement direction, but also essentially perpendicular to the sensor field of the second sensor. Both sensors may be positioned at the same level so that the predetermined distance between them along the hoist chain is zero. The same applies to sensors positioned, for example, at an angle of approximately 180° to each other. However, if the angle between the two sensors is small or even zero, the sensors must be positioned at a predetermined distance from each other that is not equal to zero.

[0084] Preferably, it is envisaged that the first sensor has a first sensitivity and the second sensor has a second sensitivity different from the first sensitivity.

[0085] As outlined above, due to the different sensitivities, the sensors will react differently to the hoist chain or sprocket moving in front of them and therefore generate different sensor signals. However, when the hoist chain is unworn, the first and second sums will be the same despite the different sensitivities, so the different sensitivities will not lead to erroneous interpretations regarding hoist chain elongation.

[0086] Alternatively, two sensors with the same sensitivity may be used, but if such sensors are mounted at different distances from the hoist chain, i.e., with different gaps between each sensor and the hoist chain, the same effect as with different sensitivities will be achieved.

[0087] The invention also relates to a chain hoist equipped with a monitoring system according to the invention, the monitoring system being arranged in particular on or in the chain guide of the chain hoist.

[0088] The chain guide has a housing in which the sprocket is located and pivoted. Due to its "narrow" design, the hoist chain is guided within the chain guide. The monitoring system can be positioned inside and / or outside the chain guide. At least one sensor of the monitoring system is preferably attached to the outer contour of the housing, for example, by using an adapter to optimally position the at least one sensor.

[0089] Apart from the chain guide, the chain hoist further comprises an electric motor, a gearbox and a chain box for temporarily storing the unused portion of the hoist chain.

[0090] Furthermore, the following two methods for continuously monitoring a chain hoist can also be implemented using the above-described monitoring system, which can have only one sensor or two sensors.

[0091] First, a method for continuous condition monitoring of a hoist chain can be implemented, the method comprising: a) detecting the presence and absence of chain links during a first cycle and a second cycle using a sensor; b) determining, by means of an evaluation unit, a first sinusoidal signal curve reflecting the presence and absence of chain links during a first cycle using the signals obtained from the sensor; c) determining, by means of an evaluation unit, a second sinusoidal signal curve reflecting the presence and absence of chain links during a second cycle using the signals obtained from the sensor; d) determining the chain speed using an evaluation unit; e) comparing, by means of an evaluation unit, the amplitude values ​​of the first sinusoidal signal curve with the amplitude values ​​of the second sinusoidal signal curve at the same point in time, both sinusoidal signal curves being determined at the same chain speed.

[0092] In other words, the method uses a comparison of the sinusoidal signal curves of two cycles to determine whether the hoist chain is worn. In the course of this method or embodiment, each cycle should be understood as a load cycle. The two cycles are preferably consecutive cycles.

[0093] When the hoist chain is unworn, the difference in amplitude values ​​is zero, or at least close to zero. The sinusoidal signal curves of both cycles substantially overlap each other. When the hoist chain or at least one chain link is stretched, the difference in amplitude values ​​is not zero. The sinusoidal signal curves of both cycles may be offset and / or have different wavelengths. The difference in amplitude values ​​at a particular time point is related to such offset or wavelength difference.

[0094] This method or embodiment is preferably carried out using a single sensor. If two sensors are used, their sensitivities are preferably matched.

[0095] Secondly, a method for continuous condition monitoring of the hoist chain is also feasible, which method includes: a) detecting the presence and absence of chain links using a sensor; b) determining, by means of an evaluation unit, a signal curve reflecting the presence and absence of chain links using the signals obtained from the sensors; c) determining, using the evaluation unit, a first time interval reflecting the time distance from a first median value of the signal curve to a second median value of the signal curve and a second time interval reflecting the time distance from the second median value of the signal curve to a third median value of the signal curve; d) determining the chain speed using an evaluation unit; e) comparing the first time interval with the second time interval by means of the evaluation unit when the signal curve is determined at a constant chain speed.

[0096] In other words, in this method or embodiment, the time interval between the medians of the signal curve is taken for the determination of wear in the hoist chain. The median is derived from the specific shape of the signal curve, which may differ from a sinusoidal signal curve, and marks the peak of the signal curve. This method or embodiment is amplitude independent.

[0097] This method or embodiment is preferably carried out using a single sensor. If two sensors are used, their sensitivities are preferably matched.

[0098] Further details of the invention will become apparent from the following description of embodiments based on the following drawings. [Brief explanation of the drawings]

[0099] [Figure 1]1 shows a schematic combined (side and cross-sectional) view of a first embodiment of a monitoring system; [Figure 2] 1 shows a schematic diagram of a second embodiment of a monitoring system. [Figure 3] 1 shows a schematic diagram of a third embodiment of a monitoring system. [Figure 4] 10 shows a schematic diagram of a fourth embodiment of a monitoring system. [Figure 5] 10 shows a schematic diagram of a fifth embodiment of a monitoring system. [Figure 6a] 1 shows a schematic diagram of the signals obtained when performing the monitoring method according to the first embodiment using a second inductive sensor detecting the hoist chain and having the same sensitivity as the first inductive sensor, the hoist chain being in an unworn state; [Figure 6b] 6b shows a schematic diagram of the signals obtained when carrying out the monitoring method according to FIG. 6a, where the hoist chain is in a worn state; [Figure 7a] 1 shows a schematic diagram of the signals obtained when performing the monitoring method according to the second embodiment using a second inductive sensor sensing the hoist chain and having a different sensitivity than the first inductive sensor, the hoist chain being in an unworn state; [Figure 7b] 7b shows a schematic diagram of the signals obtained when carrying out the monitoring method according to FIG. 7a, with the hoist chain in a worn state; [Figure 8a] 10 shows a schematic diagram of the signals acquired when performing the monitoring method according to the third embodiment with a second inductive sensor sensing the chain sprocket, the hoist chain being in an unworn state. [Figure 8b] 8b shows a schematic diagram of the signals obtained when carrying out the monitoring method according to FIG. 8a, where the hoist chain is in a worn state; [Figure 9a] 1 shows a schematic three-dimensional exploded view of a chain guide equipped with a monitoring system comprising a digital inductive sensor. [Figure 9b] 9b shows a schematic three-dimensional view of the chain guide of FIG. 9a. [Figure 9c] 9b shows a further schematic three-dimensional exploded view of the chain guide according to FIG. 9a. [Figure 10] 9a shows a schematic three-dimensional view of a chain hoist with a chain guide according to FIG. 9a. [Figure 11] 1 shows a schematic three-dimensional exploded view of a chain guide with a monitoring system comprising an analog inductive sensor. DETAILED DESCRIPTION OF THE INVENTION

[0100] FIG. 1 shows a schematic combined (side and cross-sectional) view of a first embodiment of a monitoring system.

[0101] The monitoring system comprises a first inductive sensor 9 a and a second inductive sensor 9 b. The two inductive sensors 9 a, 9 b are connected to an evaluation unit 11 via a signal connection 16 for transferring signals from the respective inductive sensors 9 a, 9 b to the evaluation unit 11. The transferred signals or signal data can be stored in a memory device 12 connected to the evaluation unit 11.

[0102] The two inductive sensors 9a, 9b are positioned to continuously monitor the hoist chain 3 moving in front of them. The hoist chain 3 can move in both directions for lifting and lowering operations, but for simplicity, in the illustrated diagram, the hoist chain 3 moves in the indicated chain movement direction M. The hoist chain 3 comprises a number of chain links 3a connected to each other.

[0103] The links 3a are alternately oriented in a first and a second plane, the first plane being oriented substantially perpendicular to the second plane. In particular, the second chain link 3a'' and the fourth chain link 3a'''' are disposed in the first plane, and the first chain link 3a', the third chain link 3a''', and the fifth chain link 3a''''' are disposed in the second plane.

[0104] Two inductive sensors 9a, 9b are mounted near the hoist chain 3 to be monitored and are arranged fixedly so that their sensor fields SF extend essentially perpendicular to the chain movement direction M. The first inductive sensor 9a and the second inductive sensor 9b are able to detect the presence and absence of chain links 3a of the hoist chain 3.

[0105] In the illustrated arrangement of the inductive sensors 9a, 9b, both inductive sensors 9a, 9b can detect the presence of odd-numbered chain links 3a, i.e., the first chain link 3a', the third chain link 3a''', and the fifth chain link 3a'''''. On the other hand, the presence of even-numbered chain links 3a, i.e., the second chain link 3a'' and the fourth chain link 3a'''', which are located in a different plane, cannot be detected by the two inductive sensors 9a, 9b.

[0106] The first inductive sensor 9a and the second inductive sensor 9b are fixedly positioned at a predetermined distance L from each other. In the illustrated unworn state of the hoist chain 3, the distance L is equal to the distance between the leading edge LE of the first chain link 3a' and the leading edge LE of the third chain link 3a'''. The distance L therefore corresponds to the length of the first chain link 3a' and the gap between the first chain link 3a' and the third chain link 3a''', which gap corresponds to the distance between the trailing edge TE of the first chain link 3a' and the leading edge LE of the third chain link 3a'''.

[0107] FIG. 2 shows a schematic diagram of a second embodiment of a monitoring system.

[0108] Like the first embodiment, the monitoring system according to the second embodiment comprises a first inductive sensor 9a and a second inductive sensor 9b. The two inductive sensors 9a, 9b are connected to an evaluation unit 11 via a signal connection 16. A memory device 12 is connected to the evaluation unit 11.

[0109] In addition to the hoist chain 3 moving in the chain movement direction M, a chain sprocket 7 is shown. The chain sprocket 7 is used to move the hoist chain 3 to raise or lower a load connected to the hoist chain 3. The sprocket 7 has five teeth 7a that can engage with the chain links 3a of the hoist chain 3.

[0110] Both inductive sensors 9a, 9b are positioned and configured to detect the presence and absence of chain link 3a. Both inductive sensors 9a, 9b are located downstream of chain sprocket 7. This means that when the illustrated chain travel direction M is an uphill direction, both inductive sensors 9a, 9b are positioned on the slack side of chain sprocket 7.

[0111] FIG. 3 shows a schematic diagram of a third embodiment of a monitoring system.

[0112] The monitoring system according to the third embodiment also comprises two inductive sensors 9 a , 9 b which are connected via a signal connection 16 to an evaluation unit 11 , which in turn is connected to a memory device 12 .

[0113] The first inductive sensor 9a is positioned and configured to detect the presence and absence of a chain link 3a, as in the other two embodiments. However, the second inductive sensor 9b is positioned and configured to detect the presence and absence of a tooth 7a of the sprocket 7. Thus, the second inductive sensor 9b can detect the absence of a tooth, such as the first tooth 7a' and the second tooth 7a'', as well as between the first tooth 7a' and the second tooth 7a'', between the second tooth 7a'' and the third tooth 7a''', etc.

[0114] In the schematic diagram, the second inductive sensor 9b is shown sensing the tip of the sprocket tooth 7a for simplicity, however, the second inductive sensor 9b is actually positioned and configured to sense a portion of the sprocket tooth 7a that is not as exposed to the hoist chain 3 as other portions of the sprocket tooth 7a, and as a result experiences less wear than the hoist chain 3. This makes it possible to have a reference sensor signal obtained from the second inductive sensor 9b that contrasts more with the sensor signal obtained from the first inductive sensor 9a.

[0115] FIG. 4 is a schematic diagram of a fourth embodiment of a monitoring system.

[0116] In the fourth embodiment, both inductive sensors 9 a, 9 b are arranged and configured to detect the presence and absence of a chain link 3 a. As in the other three embodiments, the inductive sensors 9 a, 9 b are connected via a signal connection 16 to an evaluation unit 11, which is in turn connected to a memory device 12.

[0117] The first inductive sensor 9a is located on a different stream side of the sprocket 7 than the second inductive sensor 9b. In other words, taking into account the chain travel direction M, the first inductive sensor 9a is positioned downstream of the chain sprocket 7 and the second inductive sensor 9b is positioned upstream of the chain sprocket 7. This means that when the illustrated chain travel direction M is an uphill direction, the first inductive sensor 9a is located on the slack side and the second inductive sensor 9b is located on the load strand side.

[0118] FIG. 5 shows a schematic diagram of a fifth embodiment of a monitoring system.

[0119] The monitoring system according to the fifth embodiment also comprises two inductive sensors 9a, 9b and an evaluation unit 11 to which the two inductive sensors 9a, 9b are connected via a signal connection 16. The evaluation unit 11 is connected to a memory device 12.

[0120] In this figure, a cross-section of the hoist chain 3 is shown, where the first chain link 3a' and the second chain link 3a'' are visible. The cross-section clearly shows that the even-numbered chain links 3a, such as the second chain link 3a'', lie in a first plane, while the odd-numbered chain links 3a, such as the first chain link 3a', lie in a second plane oriented perpendicular to the first plane.

[0121] The first and second inductive sensors 9a and 9b are positioned at approximately a 90° angle to each other. The two inductive sensors 9a and 9b may be positioned at the same height, i.e., the predetermined distance between the two sensors is zero. The first inductive sensor 9a detects odd-numbered chain links 3a traveling in the second plane, and the second inductive sensor 9b detects even-numbered chain links 3a traveling in the first plane.

[0122] Figure 6a shows a schematic diagram of the signals obtained when carrying out the monitoring method according to the first embodiment using a second inductive sensor 9b that senses the hoist chain 3 and has the same sensitivity as the first inductive sensor 9a, the hoist chain 3 being in an unworn state.

[0123] The method in this case therefore comprises two inductive sensors 9a, 9b with the same sensitivity, both of which are arranged and configured to detect the presence and absence of a chain link 3a.

[0124] In the figure, two signals are shown, the upper signal reflecting the signal acquired from the first inductive sensor 9a and the lower signal reflecting the signal acquired from the second inductive sensor 9b. The signals were collected at the same chain speed. Each signal contains different portions that represent either the activated or deactivated state of the respective inductive sensor 9a, 9b.

[0125] The length of time of an activated or deactivated state, reached from a rising edge of the signal to the subsequent falling edge, or vice versa, is referred to as a time interval. For the signal of the first inductive sensor 9a, the first time interval Ton1 reflects the presence of the first chain link 3a', and the second time interval Toff2 reflects the absence of a chain link between the first chain link 3a' and the third chain link 3a'''. For the second inductive sensor 9b, the third time interval Ton3 reflects the presence of the third chain link 3a''', and the fourth time interval Toff4 reflects the absence of a chain link between the third chain link 3a''' and the fifth chain link 3a'''''.

[0126] A first sum SUM1 is formed by adding the first time interval Ton1 to the second time interval Toff2, and a second sum SUM2 is formed by adding the third time interval Ton3 to the fourth time interval Toff4.

[0127] Since the hoist chain 3 is not (yet) worn, the first sum SUM1 and the second sum SUM2 are equal to each other. In other words, the formula (Ton1+Toff2)-(Ton3+Toff4) used to compare the two sums SUM1, SUM2 is zero.

[0128] FIG. 6b shows a schematic diagram of the signals obtained when carrying out the monitoring method according to FIG. 6a, the hoist chain being in a worn state.

[0129] This schematic diagram shows that the first sum SUM1 and the second sum SUM2 are now different from the first and second sums SUM1, SUM2 shown in Fig. 6a, but also from each other, because the time intervals Ton1, Toff2, Ton3 and Toff4 are longer, which means that the length of some chain links 3a has changed compared to the unworn state shown in Fig. 6a.

[0130] Based on this difference between the first sum SUM1 and the second sum SUM2, the extension of the hoist chain 3 is determined. The hoist chain 3 may be interpreted as worn. However, this may depend on the actual use case. For example, if the difference between the sums SUM1 and SUM2 exceeds a predetermined threshold, it may be expected that the hoist chain 3 is interpreted as worn.

[0131] Figure 7a shows a schematic diagram of the signal obtained when performing the monitoring method according to the second embodiment using a second inductive sensor 9b that senses the hoist chain 3 and has a different sensitivity than the first inductive sensor 9a, the hoist chain 3 being in an unworn state.

[0132] Compared to the schematic diagram shown in Figure 6a, due to the different sensitivities of the two inductive sensors 9a, 9b, the first time interval Ton1 is different from the third time interval Ton3 and the second time interval Toff2 is different from the fourth time interval Toff4.

[0133] However, the first sum SUM1 is equal to the second sum SUM2 because the activation of the first inductive sensor 9a occurs before and ends after the activation of the second inductive sensor 9b, resulting in the second inductive sensor 9b being triggered for a shorter period of time. Meanwhile, the second inductive sensor 9b remains inactive for a longer period of time, and the difference between the first time interval Ton1 and the third time interval Ton3 is the same as the difference between the second time interval Toff2 and the fourth time interval Toff4.

[0134] FIG. 7b shows a schematic diagram of the signals obtained when carrying out the monitoring method according to FIG. 7a, with the hoist chain 3 in a worn state.

[0135] From this figure it can be extracted that the first sum SUM1 of the first and second time intervals Ton1, Toff2 based on the signals acquired from the first inductive sensor 9a and the second sum SUM2 of the third and fourth time intervals Ton3, Toff4 based on the signals acquired from the second inductive sensor 9b are not only different from the sums SUM1, SUM2 shown in Figure 7a but also different from each other.

[0136] Based on this difference between the first sum SUM1 and the second sum SUM2, the elongation of the hoist chain 3 is determined. Regarding the interpretation of the wear, the same applies as explained in the course of Figure 6b.

[0137] FIG. 8a shows a schematic diagram of the signals acquired when carrying out the monitoring method according to the third embodiment with the second inductive sensor 9b sensing the chain sprocket 7, the hoist chain 3 being in an unworn state.

[0138] In contrast to the embodiments shown in Figures 6a, 6b, 7a, and 7b, the second inductive sensor 9b is positioned and configured to detect the presence and absence of teeth 7a of the sprocket 7. The second inductive sensor 9b is positioned and configured to sense each sprocket tooth 7a in an area where no or little wear is expected.

[0139] At the sensing position of the second inductive sensor 9b, the spacing between the teeth 7a is greater than the width of the teeth 7a, so the fourth time interval Toff4 is longer than the third time interval ton3. However, the second inductive sensor 9b and / or its signal may be positioned and / or configured such that a second sum SUM2 including the third and fourth time intervals Ton3, Toff4 is equal to the fist sum SUM1.

[0140] FIG. 8b shows a schematic diagram of the signals obtained when carrying out the monitoring method according to FIG. 8a, with the hoist chain in a worn state.

[0141] Again, the first sum SUM1 in the illustrated state is different from the first sum SUM1 and the second sum SUM2 in the unworn state according to Figure 8a because the hoist chain 3 is stretched. The second sum SUM2 is the same for both conditions, i.e., the conditions shown in Figures 8a and 8b, because the second inductive sensor 9b senses each sprocket tooth 7a in an area where no or little wear is expected.

[0142] Figure 9a shows a schematic three-dimensional exploded view of a chain guide 2 with a monitoring system comprising digital inductive sensors 9a, 9b. Figure 9b shows a schematic three-dimensional view of the chain guide 2 according to Figure 9a.

[0143] The chain guide 2 has a housing in which a chain sprocket 7 (not shown) is located. The housing has a rear housing section 2a and a front housing section 2b. A hoist chain 3 having chain links 3a is moved or driven by the chain sprocket 7.

[0144] The monitoring system comprises two inductive sensors 9a, 9b connected to an evaluation unit 11 of the monitoring system. An adapter 8 is used to optimally position the two inductive sensors 9a, 9b for detecting the hoist chain 3. Each inductive sensor 9a, 9b is fixed to the adapter 8 by a pin 14. The adapter 8 is attached to this part of the housing by bolts 13 using boreholes 2d. The side wall 2c of the front housing part 2b is used to align the adapter 8.

[0145] Figure 9c shows a further schematic three-dimensional exploded view of the chain guide 2 according to figure 9a.

[0146] In this view, only the front housing part 2b is shown, and the bolts 13 for attaching the adapter 8 to the front housing part 2b are clearly visible.

[0147] FIG. 10 shows a schematic three-dimensional view of a chain hoist 1 with a chain guide 2 according to FIG. 9a.

[0148] Apart from the chain guide 2, the chain hoist 1 further comprises an electric motor 4, a gearbox (not shown) and a chain box 5 for temporarily storing unused parts of the hoist chain 3. Attached to the free end of the hoist chain 3 is a hook 6 which can be used to attach the hoist chain 3 to a load for lifting and / or lowering the load.

[0149] FIG. 11 shows a schematic three-dimensional exploded view of a chain guide 2 with a monitoring system comprising analog inductive sensors 9a, 9b.

[0150] 9a-9c, an adapter 8 is used to position and secure two inductive sensors 9a, 9b to the housing, particularly the front housing part 2b, of the chain guide 2. A magnet 15 is used when the inductive sensors 9a, 9b are analog inductive sensors 9a, 9b.

[0151] Although the description of the figures refers to inductive sensors, the same applies to other types of sensors, for example mechanical switches or ultrasonic sensors.

[0152] Those skilled in the art will clearly understand that the basic idea of ​​the invention can be implemented in many different ways, and therefore the method and monitoring system are not limited to the examples described above but can vary within the scope of the claims. [Explanation of symbols]

[0153] 1 chain hoist 2 chain guides 2a Rear housing part 2b Front housing part 2c side wall 2d borehole 3 Hoist Chain 3a chain link 3a' First chain link 3a'' second chain link 3a''' Third chain link 3a'''' 4th chain link 3a''''' 5th chain link 4 motors 5 Chain Box 6 Hooks 7 Chain sprocket 7a Tooth 7a' First tooth 7a'' second tooth 8 Sensor Adapter 9a First inductive sensor 9b Second inductive sensor 10 Fixed Elements 11 Evaluation Unit 12 Memory Devices 13 volts 14-pin 15 Magnet 16 Signal Connections FE Falling Edge L is the predetermined distance (between the inductive sensors) LE leading edge M Chain movement direction RE Raised edge SF Sensor Field SUM1 First sum SUM2 Second sum TE trailing edge Ton1 First time interval Toff2 Second time interval Ton3 Third time interval Toff4 Fourth time interval

Claims

1. A method for continuous condition monitoring of a hoist chain (3), comprising: a) detecting the presence and absence of a chain link (3a) using a first sensor (9a); b) using the evaluation unit (11) to determine, using the signals obtained from the first sensor (9a), a first time interval (Ton1) reflecting the presence of a first chain link (3a'), a second time interval (Toff2) reflecting the absence of said chain link between said first chain link (3a') and a third chain link (3a'''), a third time interval (Ton3) reflecting the presence of said third chain link (3a'''), and a fourth time interval (Toff4) reflecting the absence of said chain link between said third chain link (3a''') and a fifth chain link (3a'''''); c) determining, using the evaluation unit, a first sum (SUM1) of the first time interval (Ton1) and the second time interval (Toff2) and a second sum (SUM2) of the third time interval (Ton3) and the fourth time interval (Toff4); d) determining the chain speed using said evaluation unit (11); e) comparing, using the evaluation unit (11), the first sum (SUM1) with the second sum (SUM2) to determine the extension of the hoist chain (3), each time interval being determined at the same chain speed.

2. A method for continuous condition monitoring of a hoist chain (3), comprising: a) detecting the presence and absence of a chain link (3a) using a first sensor (9a); a') detecting the presence and absence of teeth (7a) of the chain sprocket (7) or the presence and absence of said chain links (3a) using a second sensor (9b); b') using the evaluation unit (11) to determine, using the signals obtained from the first sensor (9a), a first time interval (Ton1) reflecting the presence of a first chain link (3a') and a second time interval (Toff2) reflecting the absence of said chain link between the first chain link (3a') and a third chain link (3a'''); b'') determining, using the evaluation unit (11) and using the signals obtained from the second sensor (9b), a third time interval (Ton3) reflecting the presence of a first tooth (7a') or the presence of the first chain link (3a') or the second chain link (3a'') or the third chain link (3a'''), and a fourth time interval (Toff4) reflecting the absence of the tooth (7a) between the first tooth (7a') and the second tooth (7a'') or the absence of the chain link (3a) between the first chain link (3a') and the third chain link (3a'''), or between the second chain link (3a'') and the fourth chain link (3a''''), or between the third chain link (3a''') and the fifth chain link (3a'''''); c) determining, using the evaluation unit, a first sum (SUM1) of the first time interval (Ton1) and the second time interval (Toff2) and a second sum (SUM2) of the third time interval (Ton3) and the fourth time interval (Toff4); d) determining the chain speed using said evaluation unit (11); e) comparing, using the evaluation unit (11), the first sum (SUM1) with the second sum (SUM2) to determine the extension of the hoist chain (3), each time interval being determined at the same chain speed.

3. 3. The method of claim 1 or 2, wherein the method includes repeating steps a) to e) when the chain speed changes.

4. 4. The method according to claim 2 or 3, characterized in that the chain speed is determined by comparing the signal obtained from the first sensor (9a) with the signal obtained from the second sensor (9b).

5. The method according to any one of claims 1 to 4, characterized in that the method comprises detecting, using the first sensor (9a) and / or the second sensor (9b), an air gap between the respective sensor (9a, 9b) and the hoist chain (3).

6. 6. The method according to claim 5, characterized in that the method comprises determining the size of the gap by means of the evaluation unit (11) in order to take into account possible gap-creation deviations during detection by the respective sensors (9a, 9b) when determining the extension of the hoist chain (3).

7. Method according to any one of claims 2 to 6, characterized in that the first sensor (9a) and the second sensor (9b) have different actuation sensitivities.

8. Method according to any one of claims 2 to 7, characterized in that the first sensor (9a) and the second sensor (9b) function independently of each other.

9. 9. The method according to any one of claims 1 to 8, characterized in that the method comprises comparing, with the evaluation unit (11), the difference between the first sum (SUM1) and the second sum (SUM2) with a predetermined threshold value.

10. 10. The method according to claim 9, characterized in that the method comprises generating, in particular by means of the evaluation unit (11), an output signal if the difference exceeds the predetermined threshold value.

11. A monitoring system for continuous condition monitoring of a hoist chain (3), comprising: a first sensor (9a) arranged and configured to detect the presence and absence of a chain link (3a); a memory device (12) configured to collect and store signals or signal data obtained from said first sensor (9a); - an evaluation unit (11) configured to carry out the method according to any one of claims 1, 3, 5, 6, 9 and 10.

12. 12. The monitoring system according to claim 11, characterized in that the monitoring system further comprises a second sensor (9b) fixedly arranged at a predetermined distance (L) from the first sensor (9a), the second sensor (9b) being arranged and configured to detect the presence and absence of teeth (7a) of a chain sprocket (7) or the presence and absence of the chain links (3a), the memory device (12) being configured to collect and store signals or signal data obtained from the second sensor (9b), and the evaluation unit (11) being configured to perform the method according to any one of claims 2 to 10.

13. 13. The monitoring system according to claim 12, characterized in that both the first sensor (9a) and the second sensor (9b) are located upstream or downstream of the chain sprocket (7), or the first sensor (9a) and the second sensor (9b) are located on different stream sides of the chain sprocket (7).

14. 14. A monitoring system according to claim 12 or 13, characterized in that the first sensor (9a) and the second sensor (9b) are arranged at an angle of approximately 90° between each other.

15. 15. The monitoring system according to any one of claims 12 to 14, characterized in that the first sensor (9a) has a first sensitivity and the second sensor (9b) has a second sensitivity different from the first sensitivity.

16. A chain hoist (1) comprising a monitoring system according to any one of claims 11 to 15, the monitoring system being arranged in particular on or in a chain guide (2) of the chain hoist (1).

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