Apparatus and method for determining the wear condition of a chain

Abstract

In a method for determining the elongation of segments of a chain of a chain drive during operation, a plurality of measured values is determined at different positions of the chain. A plurality of length values is determined from the plurality of measured values and the length values are assigned to the segments of the chain, with the length of the segments of the chain being smaller than the length of the chain.

Claims

1. A method for determining an elongation of segments of a chain of a chain drive during operation, said method comprising: recording a plurality of measured values at different positions of the chain with a first sensor and a second sensor arranged at a defined distance from each other; determining a plurality of length values of the segments of the chain from the plurality of measured values based on the defined distance, a time interval between two successive signals of one of the first and second sensors, and a time interval between a signal of the first sensor and a next following signal of the second sensor; assigning the plurality of determined length values to the segments of the chain, respectively, wherein a length of the segments of the chain is smaller than a length of the chain; monitoring segments of the chain; identifying elongated segments of the chain by comparing the plurality of length values with stored values; and replacing only the identified elongated segments of the chain.

2. The method of claim 1, wherein at least 5 of the segments are distributed over the length of the chain.

3. The method of claim 1, wherein a number of the segments corresponds to a number of chain links of the chain which are guided past one or more sensors as the measured values are recorded during operation.

4. The method of claim 1, wherein a measurement for recording the measured values is continuously repeated during operation of the chain drive.

5. The method of claim 1, wherein a change in length values is determined from a comparison with a reference measurement or reference value.

6. The method of claim 1, further comprising detecting a position of the segments of the chain.

7. The method of claim 6, wherein a local significance of the chain is determined for detecting the position of the segments of the chain.

8. The method of claim 7, wherein the local significance includes a structural change in the chain.

9. The method of claim 8, wherein the structural change of the chain comprises a strap fixed to the chain and/or a permanent magnet fixed to the chain.

10. The method of claim 7, further comprising assigning the determined length values to individual segments of the chain on the basis of the position of the segments of the chain and/or the position of the determined local significance in the chain.

11. The method of claim 1, wherein a number of measured values determined is at least equal to a number of segments of the chain or greater than a number of segments of the chain.

12. The method of claim 1, wherein a number of segments of the chain is acquired from the measured values.

13. A system for determining an elongation of segments of a chain of a chain drive during operation, said system comprising: a chain, said chain comprising: a plurality of chain links; a plurality of segments formed by the chain links; a local significance detectable by a sensor device; and a sensor device for determining a length of a segment of the chain, said sensor device comprising: a first sensor configured to record measurement data to determine a position of the segment of the chain, and/or a second sensor arranged at a defined distance from the first sensor. said second sensor configured to record measurement data to determine a length value of the segment of the chain, said sensor device further comprising a control unit configured to control at least one of the first and second sensors and to record and process the measurement data captured by the first sensor to determine an elongation of the segment of the chain and/or the measurement data captured by the second sensor based on the defined distance, a time interval between two successive signals of one of the first and second sensors, and a time interval between a signal of the first sensor and a next following of the second sensor.

14. The chain of claim 13, wherein the local significance is a local structural characteristic.

15. The chain of claim 13, wherein the local significance is a local change in a physical property of the chain.

16. A computer program for executing a method for acquiring and processing measurement data of a sensor device, said computer program embodied in a non-transitory computer readable medium and comprising: program instruction for controlling a first sensor for acquiring measurement data to determine length values of segments of a chain; program instruction for controlling a second sensor for acquiring measurement data to determine a position of a segment of the chain; program instruction for determining the length values based on a defined distance between the first sensor and the second sensor, a time interval between two successive signals of one of the first and second sensors, and a time interval between a signal of the first sensor and a next following signal of the second sensor; program instruction for assigning the determined length values to the segments of the chain, respectively; program instruction for monitoring segments of the chain; and program instruction for identifying elongated segments of the chain that need to be replaced by comparing the determined length values with stored values.

17. The computer program of claim 16, wherein the first and second sensors are identical.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

(2) FIG. 1 is a schematic illustration of a sensor device with two sensor units for monitoring a closed chain drive in accordance with the present invention;

(3) FIG. 2a is a schematic illustration of a sensor device with two sensor units for monitoring a chain running past the sensor device;

(4) FIG. 2b is a graphical illustration of signals of the two sensor units of FIG. 2a;

(5) FIG. 3a is a schematic illustration of a sensor device with two sensor units for monitoring a chain running past the sensor device in anticlockwise and clockwise rotation;

(6) FIG. 3b is a graphical illustration of signals of the two sensor units of FIG. 3a for the chain passing in anticlockwise and clockwise rotation;

(7) FIG. 4a is a schematic illustration of a chain with chain segments with the length of one chain link;

(8) FIG. 4b is a schematic illustration of a chain with chain segments with the length of three chain link; and

(9) FIG. 4c is a schematic illustration of a chain with chain segments with the length of six chain link.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(10) Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments may be illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

(11) Turning now to the drawing, and in particular to FIG. 1, there is shown a schematic illustration of a sensor device, generally designated by reference numeral 1 and including two inductive proximity sensors 2, 3, which are arranged close to a closed chain 11. Chain 11 is guided around two sprockets 10 and has a large number of chain links 12. Three chain links 12 each form a chain segment 13. Sensor device 1 is located on the side of the load run 14 and opposite the side of the empty run 15. The distance d between the two inductive proximity sensors 2, 3 is selected such that n+⅓ chain links 12 are located between the two sensors 2, 3.
d=n*g+f  (1)

(12) Here n describes the number of chain links 12 between the first sensor 2 and the second sensor 3 and g the length of a chain link. In this design example, f=⅓ was selected. When sensor device 1 is mounted on the load run 14, not only the elongation due to wear is measured but also the elongation due to load. In contrast, when sensor device 1 is mounted on the empty run 15, only the elongation due to wear is measured.

(13) FIG. 2a shows a sensor device 1 with two sensor units 2, 3 for monitoring a chain 11 running past sensor device 1. The length of a chain link 12 is indicated here by g and f is the partial length of a chain link 12 by whose amount the second sensor 3 is displaced by an integer multiple of the chain link length g compared to the first sensor 2. In FIG. 2b the signals A, B of sensors 2, 3 are shown. The chain link length g is proportional to the time tp between two consecutive signals of one of sensors 2, 3 and f is proportional to the time between two consecutive signals of the first sensor 2 and the second sensor 3. When the chain is elongated, the clockwise direction of movement f.sub.r or t.sub.Br becomes smaller, and the anticlockwise direction of movement f.sub.l or t.sub.Bl becomes larger. The phase length of the frequencies of signals A and B of sensors 2, 3 is measured by measuring t.sub.B and t.sub.p. The ratio t.sub.B/(t.sub.p*(n+t.sub.B)) in accordance with
L/d=t.sub.B(t.sub.p*(n+t.sub.B))  (2)
is the speed-independent relation between chain segment length L and the sensor distance d. It is important that the sensor distance for a new chain 11 is selected so that f<0.5*g. It is assumed that the chain 11 does not undergo an elongation greater than the length g of a half chain link 12 within the selected sensor spacing d.

(14) FIG. 3a shows the conditions when the direction of chain travel changes from clockwise r to anticlockwise l. FIG. 3 b) shows the respective signals for clockwise and anticlockwise travel of chain 11. The ratio of the change in length ΔL of chain segment 13 to chain segment length in initial state L.sub.0 results from the following equation (3):
ΔL/L.sub.0=(L.sub.x−L.sub.0)/L.sub.0=L.sub.x/L.sub.0−1  (3).

(15) With Lx as the length of chain segment 13 at the time of measurement. For clockwise circulating chain 11, length Lxr of chain segment 13 results from
L.sub.xr/d=n+t.sub.pxr/(n+t.sub.pxr+t.sub.Bxr)  (4),
wherein t.sub.pxr is the time interval between two successive signals A, B of one of sensors 2, 3 of clockwise circulating chain 11 in loaded state and t.sub.Bxr is the time interval between the signal A of the first sensor 2 and the next following signal B of sensor 3 of the clockwise circulating chain 11 in loaded state. Length L.sub.0r of chain segment 13 in initial state L.sub.0r is obtained from
L.sub.0r/d=n+t.sub.p0r/(n+t.sub.p0r+t.sub.Bor)  (5),
wherein t.sub.pxr is the time interval between two successive signals A, B of one of sensors 2, 3 of clockwise circulating chain 11 in loaded state and t.sub.Bxr is the time interval between the signal A of the first sensor 2 and the next following signal B of sensor 3 of clockwise circulating chain 11 in initial state of chain 11.

(16) According to equation (3), the ratio of the change in length ΔL.sub.r to output length L.sub.0r of chain segment 13 for clockwise circulating chain 11 results from
ΔL.sub.r/L.sub.0r=(t.sub.B0r/t.sub.p0r−t.sub.Bxr/t.sub.pxr)/(n+t.sub.Bxr/t.sub.pxr)  (6).

(17) For clockwise circulating chain 11, length L.sub.xl of chain segment 13 results from
L.sub.xl/d=(n+1)+t.sub.pxl/((n+1)+t.sub.pxl+t.sub.Bxl)  (7),
wherein t.sub.pxl is the time interval between two successive signals A, B of one of sensors 2, 3 of the anticlockwise circulating chain 11 in loaded state and t.sub.Bxl is the time interval between the signal A of the first sensor 2 and the next following signal B of sensor 3 of the anticlockwise circulating chain 11 in loaded state. Length L.sub.0r of chain segment 13 in initial state L.sub.0l is obtained for anticlockwise circulating chain 11 from
L.sub.0l/d=(n+1)+t.sub.p0l/((n+1)+t.sub.p0l+t.sub.B0l)  (8).

(18) According to equation (3), the ratio of the change in length ΔL.sub.r to output length L.sub.0r of chain segment 13 is obtained for anticlockwise circulating chain 11 from
ΔL.sub.t/L.sub.0l=(t.sub.Bxl/t.sub.pxl−t.sub.B0l/t.sub.p0l)/((n+1)−t.sub.Bxl/t.sub.pxl)  (9).

(19) FIG. 3b shows the signals A and B of sensors 2 and 3 for a clockwise circulating chain 11 and for an anticlockwise circulating chain 11. In this design example, f=⅓ was selected. For clockwise circulating chain 11, t.sub.Br/t.sub.pr=0.33. If chain 11 runs in reverse, the value jumps to t.sub.Bl/t.sub.pl=1−0.33=0.67. The direction of the chain movement can thus be clearly determined and ambiguities for the ratio t.sub.B/t.sub.p are excluded. Consequently, the distance between sensors 2 and 3 must be selected so that f is ≠0 and f is ≠0.5. For a ratio t.sub.B/t.sub.p<0.5, equation (6) is used to calculate the elongation of chain 11. If the ratio t.sub.B/t.sub.p>0.5, the elongation of chain 11 is calculated from equation (9). The operating conditions for the sensor device are such that the sensor distance must not be so large that chain 11 in the section between the sensors is not elongated more than ΔL=f*g. At f=0.25*g, this corresponds to a maximum elongation ΔL.sub.max of ΔL.sub.max=0.25 for 10 chain links 12 and a maximum elongation ΔL.sub.max of ΔL.sub.max=2.5% for 100 chain links 12.

(20) In FIGS. 4a to 4c, chains 12 with chain segments of varying lengths are shown. For the chain in FIG. 4a, the length of a chain segment L.sub.s at L.sub.s=g. The chain in FIG. 4b shows a chain 11 with a chain segment length L.sub.s of L.sub.s=3*g, while in FIG. 4c a chain with a chain segment length L.sub.s with L.sub.s=6*g is shown.

(21) An endless conveyor chain 11 with 7020 chain links 12 (16B chain according to ISO 606) used in food production is divided into 390 chain sections (design example 1). A chain section comprises 18 chain links 12, whereby each of the 18 links has a conveying strap arranged on chain 11, i.e. a chain section comprises 18 chain links 12 and a conveying strap. Chain links 12 have a length of g=2.54 cm according to ISO 606. To detect the position of chain 11, a magnet is fixed on the outer strap as a local significance. Alternatively, the magnet could also be arranged on the plug-in strap. To detect the change in length of chain segments 13 during operation of chain 11, a chain condition monitoring controlled (CCM controlled) sensor device 1 based on reluctance sensors was arranged in the immediate vicinity of chain 11. The position of chain 11 is also monitored by means of a Hall sensor 2, 3. This is connected via the controller to a display on which the position of the defective chain segment 13 is displayed in case of a corresponding measurement result. During monitoring, measured values are recorded for all chain links 12 with regard to their change in length. At a chain speed of 0.1-0.2 m/s, this results in a time interval of 0.15-0.25 s between two consecutive measurements. For this purpose, the change in length of chain segments 13 in comparison to the initial length of chain links 12 is determined in %. To determine the position of chain 11, a performance map of the individual graduations is created and continuously updated. Subsequently, chain 11 must be counted manually or the machine moves to the affected chain link 12 with an appropriate control routine. A marking on the chain is used to assign the measured values to the individual chain links 12. During the measurement, each chain link passing sensors 2, 3 is measured. The values determined are compared with a reference value. The reference value is stored in the CCM memory. Alternatively, the reference value can also be transmitted wirelessly via the CCM monitor or via I/O link to the programmable logic controller (PLC).

(22) In a second design example, an endless chain applied in food production is used as in design example 1 described above. In contrast to design example 1 described above, only 390 measuring positions per chain circulation are provided here—one per chain section, whereby the chain section comprises 18 chain links and a conveying strap. Such a chain section corresponds to exactly one chain segment here. As a result, the change in length is not determined here for each chain link 12 as described above but only for the 390 chain segments 13. At a chain speed of 0.1-0.2 m/s, this results in a time interval of 2.3-4.5 s between two consecutive measurements. When detecting a critical length value for one of these chain segments 13, only chain segment 13 with 18 chain links 12 and one conveying strap must be replaced. It is advisable to select the length of chain segment 12 so that it comprises the same elements regardless of its position in chain 11. This ensures that there is a high degree of identical parts when selecting the required spare parts, which makes servicing much easier, as no knowledge of the type of defective component is required.

(23) In another application example (design example 3), an endless chain 11 with 3150 chain links 12 is used. This is a chain 11 of type 10B-1 according to ISO 606. In initial state, the chain links 12 have a length of 15.875 mm (nominal pitch). Each outer link is provided with a gripper element. A chain segment length of two chain links 12 is provided for wear monitoring. The number of chain segments 13 is therefore 1575. A magnet is arranged on an outer strap to determine the chain position. Alternatively, the magnet could also be arranged on the plug-in strap. To determine the length values of the chain segments 13, a CCM-controlled sensor device 1 on the basis of reluctance sensors 2, 3 is used, which detects the position of the outer strap of the chain equipped with the magnet to the CCM-controlled sensor device 1 via a Hall sensor 2, 3. During monitoring of chain 11, all measured values for each chain link 12 are recorded. At a chain speed of 0.6-0.8 m/s, this results in a time interval of 0.2-0.3 s between two consecutive measurements. For this purpose, the change in length of chain segments 13 in comparison to the initial length of chain links 12 is determined in %. The nominal pitch is specified according to ISO 606 and stored as a reference value. To determine the position of chain 11, a performance map of the individual pitches is created and continuously updated. Subsequently, chain 11 must be counted manually or the machine moves to the affected chain link 12 with an appropriate program. The assignment of the length values to the individual chain links 12 is made via the direction of movement of chain 11 and the number of determined length values after the magnet attached to the outer strap has passed through Hall sensor 2, 3.

(24) The fourth application example describes a chain 11 for a lifting application with change of rotational direction. Unlike the previous examples, this is not an endless chain 11. The 20B-2 chain 11 has chain links 12 with a nominal pitch (length of a chain link 12) of 31.75 mm in accordance with ISO 606 231. The length of chain segment 13 is also 31.75 mm, since a length value is assigned to each chain link 12. A magnet is arranged on an outer strap to determine the position of chain link 12 marked by the magnet in relation to sensor 2, 3 to detect the length values. The length values are detected by a CCM-controlled reluctance sensor device and the position of chain 11 to the CCM-controlled reluctance sensor device 1 via the detection of the magnet by a Hall sensor 2, 3. For each chain link 12 passing through the CCM-controlled reluctance sensor device 1, a measured value is recorded from which the current length or the percentage deviation of the length of the respective chain link 12 from the nominal pitch is determined. To determine the position of chain 11, a performance map of the individual pitches is created and continuously updated. At an average chain speed of 0.6 m/s, one measurement value is recorded every 0.05 s.

(25) While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.