METHOD FOR DETERMINING THE DISCARD LIFE OF A PLASTIC ROPE

Description

[0001] The invention relates to a method for determining the degree of damage to a plastic rope of a hoist connected to a load-carrying device in order to determine the discarding age, wherein the rope is partially wound on a rope drum of the hoist connected to a drive and having a braking device, according to patent claim 1.

[0002] Ropes play a major role in materials handling and lifting technology. Especially where ropes perform safety-relevant functions, such as in hoists or cable cars, it is necessary to determine the wear that occurs over the rope's service life. To do this, strand breaks or other phenomena that indicate potential rope failure must be detected early.

[0003] Various methods have been developed for the examination of wire ropes that enable the metrological investigation and assessment of rope wear. For example, the magnetic induction wire testing method utilizes the property that inhomogeneities in a wire rope generate magnetic stray fields. By measuring the rope circumference with a measuring coil, wire breaks, corrosion, and damage to the rope can be located using diagrams. Another method, radiographic testing, creates a surface image of the volume density of the rope in a plane. Gamma rays from a radioactive isotope penetrate the rope and, with varying degrees of attenuation, strike an X-ray film on the back of the rope.

[0004] Recently, synthetic ropes have also been increasingly used. These ropes have proven to be extremely robust and durable, as well as significantly lighter. However, the problem with synthetic ropes is that the testing methods established for steel wire ropes to determine the wear point cannot be used for synthetic ropes. At this point, a method is required that enables the testing and assessment of rope wear on synthetic ropes. DE 10 2011 018535 A1 discloses a rope test rig in which a synthetic rope is tested, as well as a method according to the preamble of claim 1.

[0005] This is where the present invention comes in. The invention is based on the object of providing a method for determining the discard date of a plastic rope of a lifting device. According to the invention, this object is achieved by a method having the features of patent claim 1.

[0006] It has been found that a plastic rope exhibits a changed vibration behavior with increasing wear. By comparing the vibration behavior of a rope with the vibration behavior of a reference rope, in particular the same rope in new condition, the state of wear and thus the discard date of the plastic rope can be determined. For this purpose, a defined load is attached to the plastic rope wound on the rope drum of the hoist and this load is raised or lowered over a defined distance until a defined rope length is unwound from the rope drum. At this position, the rope is braked, causing the load connected to the rope to vibrate. The mass vibration initiated by this is recorded as a rope force measurement over time using a arranged force sensor.The vibration curve thus obtained is then compared with a reference vibration curve previously determined, preferably using the same method, for the same rope in new condition. Based on empirically determined vibration curves of ropes with different wear curves, the discard point can then be determined from the difference between the measured vibration curve and the reference vibration curve.

[0007] In a further development of the invention, the reference oscillation curve and the respective obtained oscillation curve are transformed into the frequency domain for comparison. This enables an analysis of oscillation components. The transformation is preferably carried out using a Fourier transformation. This allows the decomposition of an existing oscillation superposition into its individual oscillations. The frequency and amplitude of each occurring oscillation can thus be determined. This is advantageously achieved computationally using a Fast Fourier Transformation (FFT). Alternatively, the transformation can also be performed using a Laplace transformation.

[0008] In an embodiment of the invention, the characteristic natural frequencies of the obtained vibration curve are compared with the characteristic natural frequencies of the reference vibration curve. Advantageously, the previously empirically determined natural frequency of the hoist or crane system is used to determine the natural frequency of the rope from the transformed vibration curve.

[0009] In a further embodiment of the invention, the load-handling device is a bottom block, with the force sensor being a load cell, which is preferably arranged on the load hook, the rope anchor point, the bottom block, or the rope drum bearing. This makes the method easy to implement at the hoist's installation site.

[0010] In a further development of the invention, the recorded vibration curve is stored in a vibration curve history and compared with previously stored rope vibration curves. This allows the wear process of a plastic rope to be mapped over time.

[0011] In an embodiment of the invention, several lowering and lifting processes are performed, followed by deceleration. The resulting rope vibrations are recorded over time by the force sensor. Averaged parameters based on the vibration curves obtained are then compared with corresponding parameters of the stored reference vibration curves. This increases the accuracy of the investigation. Preferably, the natural frequencies of the vibration curves are used as parameters.

[0012] In a further embodiment of the invention, the degree of rope damage or the degree of change in the deformation behavior of the rope is evaluated on the basis of the change in the characteristic natural frequency.

[0013] In a further embodiment of the invention, the local maxima of the amplitude spectrum of the transformed oscillation curve are recorded and compared with stored local maxima of a transformed reference oscillation curve. This creates distinctive, easily comparable reference parameters.

[0014] The invention is further based on the object of providing a lifting device that enables the determination of the discard status of its plastic rope. According to the invention, this object is achieved by a lifting device having the features of patent claim 11. By arranging a force sensor that is connected to a control and evaluation unit, which is connected to a database in which at least one reference vibration curve for a plastic rope is stored, wherein the control and evaluation unit is configured to carry out a method according to one of the aforementioned claims, the discard status can be determined on-site at any time.

[0015] In a further development of the invention, a sequence control is stored in the control and evaluation unit, allowing the method to be carried out at least partially automatically. This enables a largely automatic determination of the discard point of the hoist's plastic rope with a defined load. For example, the sequence control can be implemented in the form of a programmable logic controller (PLC). This can, of course, also be part of the software installed in the control and evaluation unit.

[0016] In one embodiment of the invention, a weighing device for detecting a picked-up load is arranged, which is connected to the control and evaluation unit. This enables direct determination of the picked-up load.

[0017] In a further embodiment of the invention, the cable drum is connected to a rotation sensor, which can detect the unwound cable length and is connected to the control and evaluation unit. This enables the detection of the cable length present before the braking process.

[0018] In a further development of the invention, the control and evaluation unit is connected to an optical and / or acoustic signal generator and configured such that, upon reaching a defined discard range, a signal is emitted via the signal generator. This prevents further operation of the hoist with a discarded plastic rope. Preferably, the control and evaluation unit is configured such that continuous signaling occurs until an authorized reset occurs after the plastic rope has been replaced.

[0019] Further developments and refinements of the invention are specified in the remaining subclaims. An exemplary embodiment is illustrated in the drawings and described in detail below. They show: Figure 1: the schematic representation of a lifting device with a load taken up by a load-carrying device of a plastic rope; Figure 2: the representation of the lifting device from Figure 1 without housing and crane bridge; Figure 3: the representation of a force sensor of the hoist from Figure 1 rope force oscillation curve measured over time (filtered using a high-pass filter and offset correction); Figure 4: the representation of the oscillation curve from Figure 3 after Fast Fourier Transformation (FFT); Figure 5 the representation of the oscillation curve from Figure 3 over a reference vibration curve; Figure 6 shows the representation of the vibration curves from Figure 5according to Fast Fourier Transformation (FFT) and Figure 7 the classification of the peaks of the natural vibration of a rope in relation to a reference peak (rope in new condition) and a specified discard peak.

[0020] The hoist 1 chosen as an exemplary embodiment comprises a trolley 12 arranged on a crane bridge 11. The trolley 12 comprises a cable drum 14 connected to a drive 13, onto which a plastic cable 2 is wound and which has a braking device for braking the plastic cable 2. The free end of the plastic cable 2 is fixed to a cable anchor point 15. The plastic cable 2 can be wound onto the cable drum 14 or unwound from the cable drum 14 via the drive 13. The plastic cable 2 receives a load-handling device 3 in the form of a bottom block which has a load hook 31. The load hook 31 receives a load 4. A force sensor 32 in the form of a load cell is arranged between the load hook 31 and the load 4. The trolley 12 also has a control and evaluation device 5 which is connected to the force sensor 32.The control and evaluation device 5 is designed to carry out a method for determining the discard state of a plastic rope and for this purpose comprises a database in which reference vibration curves for plastic ropes in new condition are stored.

[0021] In the method chosen as an exemplary embodiment for determining the discard date of a plastic rope 2 of the hoist 1 connected to a load-handling device 3, a defined load 4 is first connected to the load-handling device 3. The load is lifted by controlling the drive from a lower lifting position to a predetermined rope length (upper lifting position) and decelerated at this defined position, causing the mass of the load 4 to vibrate. At the same time, the hoist 1 (or the crane system with trolley 12 and crane bridge 11) is also vibrated.

[0022] The force transmitted via the plastic rope 2 is recorded over time by the control and evaluation device 5 via the force sensor 32. This results in a vibration curve (rope force-time function) that decays over time, which is first shifted to the ordinate via an offset and then filtered via a high-pass filter to eliminate any transient low-frequency rope force components (see Fig. Fig. 3 ). On closer inspection, the recorded vibration curve is a vibration superposition curve, which - in addition to other natural vibrations of secondary systems such as the hall floor or similar, which are neglected here - includes the natural vibration of the plastic rope 2 and the natural vibration of the hoist 1 (or the crane system).

[0023] To differentiate the individual vibration components, the vibration curve is transformed from the time domain to the frequency domain by the control and evaluation device 5 using a Fast Fourier Transformation. The superimposed overall vibration is thereby decomposed into its individual vibrations. Figure 4 A schematic representation of such a fast Fourier transformation of the recorded vibration curve is shown. By evaluating the peaks of this transformed curve, the peak of the natural vibration f EK of hoist 1 (or the crane system) and the peak of the natural vibration f ES of plastic rope 2 are identified. The evaluation is carried out using empirically determined natural vibration data of hoist 1 (or the crane system), which are stored in the database for this purpose.

[0024] Subsequently, the fast Fourier transformation of the recorded vibration curve is compared with a fast Fourier transformation of a reference vibration curve stored in the database. In the exemplary embodiment, the reference vibration curve is a vibration curve obtained by the previously described method using the same plastic rope in its new state (reference plastic rope). It can be seen that the peak f ES of the natural frequency of the plastic rope 2 moves to the left with increasing wear. The discard condition is then assessed based on the distance between the peak f ES,Ist of the natural frequency of the plastic rope 2 and the peak f ES,New of the natural frequency of the reference plastic rope.

[0025] As an evaluation criterion, a critical discard area can be defined based on empirical measurements with synthetic ropes with varying degrees of wear. Against this background, a position of the peak f ES,AR is determined (see Figure 6). From the distance of a determined peak f ES,Ist to this discard peak f ES,AR, the remaining service life of the plastic rope can be determined (cf. Figure 7 ).

[0026] By creating a synthetic rope vibration database in which the vibration curves obtained using the method and their Fast Fourier Transformation are stored, the critical discard range can be optimized. The synthetic rope vibration database can also include vibration curves and their Fast Fourier Transformation for different rope lengths and / or absorbed loads. The assessment of discard readiness can be performed either by an operator or by the control and evaluation device by comparing it with a peak-to-peak distance or peak-to-peak distance range stored in the database.

Claims

1. Method for determining the degree of damage of a plastic rope (2) of a hoist (1) connected to a load-carrying means in order to determine the discard state, wherein the plastic rope (2) is partially wound onto a rope drum (14) of the hoist (1) connected to a drive (13), which has a braking device comprising the following method steps: - picking up a defined load (4) by the load-carrying means; - raising or lowering the load (4) by activating the drive (13) until a defined rope length unwound from the rope drum (14) is reached; characterised in the following method steps: - performing a defined braking action by the braking device at the defined rope length; - detecting the mass oscillation initiated thereby via an arranged force sensor (32) as a rope force measurement over time; - comparison of the oscillation curve obtained in this manner with a stored reference oscillation curve.

2. Method according to claim 1, characterised in that the reference oscillation curve and the oscillation curve respectively obtained is transformed into the frequency range for the comparison.

3. Method according to claim 1 or 2, characterised in that the characteristic natural frequencies of the oscillation curve obtained are compared with the characteristic natural frequencies of the reference oscillation curve.

4. Method according to claim 3, characterised in that the previously empirically determined natural frequency of the hoist (1) or the crane system is used to determine the natural frequency of the rope from the transformed oscillation curve.

5. Method according to one of the previous claims, characterised in that the load-carrying means (3) is a hook block, wherein the force sensor (31) is a load cell, which is preferably arranged on the load hook (31), on the rope anchor point (15), on the hook block or on the rope drum bearing.

6. Method according to one of the previous claims, characterised in that the recorded oscillation curve is stored in an oscillation curve history and is compared with oscillation curves already stored.

7. Method according to one of the previous claims, characterised in that several lowering and lifting processes are carried out with a subsequent braking action, wherein the respectively initiated rope oscillations are recorded over time via the force sensor (32) and subsequently, on the basis of the oscillation curves obtained in this manner, averaged parameters are compared with corresponding parameters of the stored reference oscillation curves.

8. Method according to claim 7, characterised in that the natural frequencies of the oscillation curves are used as parameters.

9. Method according to one of the previous claims, characterised in that the degree of damage to the rope or the degree of change in the deformation behaviour of the rope is evaluated on the basis of the change in the characteristic natural frequency of the rope.

10. Method according to claim 9, characterised in that the local maxima of the amplitude spectrum of the transformed oscillation curve are recorded and compared with stored local maxima of a transformed reference oscillation curve.

11. Hoist comprising a rope drum connected to a drive (13), on which a plastic rope (2) is wound and which has a braking device, characterised in that a force sensor (32) is arranged, which is connected to a control and evaluation unit (5), which is connected to a database, in which at least one reference oscillation curve for a plastic rope is stored, wherein the control and evaluation unit (5) is set up to perform a method according to one of the previous claims.

12. Hoist according to claim 11, characterised in that the control and evaluation unit (5) contains a sequence control, by means of which the method can be carried out automatically.

13. Hoist according to claim 11 or 12, characterised in that a weighing device for detecting a picked up load (4) is arranged, which is connected to the control and evaluation unit (5).

14. Hoist according to one of claims 11 to 13, characterised in that the rope drum (14) is connected to a rotation sensor, via which an unwound rope length can be detected and which is connected to the control and evaluation unit (5).

15. Hoist according to one of claims 11 to 14, characterised in that the control and evaluation unit (5) is connected to an optical and / or acoustic signal transmitter and is set up in such a manner that when a defined range for the discard state is reached, a signal is emitted via the signal transmitter.