Method and device for monitoring chain tension

Abstract

Chain tension monitoring device (40) is configured for monitoring a chain tension force (F.sub.C) of a drive chain (27) extending in a longitudinal direction forming closed loop between two sprockets (26, 28). The chain tension monitoring device (40) comprises a sensor device (41) configured for mechanically contacting the drive chain (27), detecting movement of the drive chain (27) transversely, in particular orthogonally, to the longitudinal direction of the drive chain (27), and providing a detection signal indicating the detected movement of the drive chain (27); and an evaluator (50) configured for receiving the detection signal provided by the sensor device (41) and determining a chain tension force (F.sub.C) of the drive chain (27) from said detection signal.

Claims

1. Chain tension monitoring device configured for monitoring a chain tension force (F.sub.C) of a drive chain extending in a longitudinal direction forming a closed loop between two sprockets, the chain tension monitoring device comprising: a sensor device configured for mechanically contacting the drive chain, detecting a movement of the drive chain transversely to the longitudinal direction of the drive chain, and providing a detection signal indicating the detected movement of the drive chain; and an evaluator configured for receiving the detection signal provided by the sensor device, determining at least one frequency (f) of the detected movement from said detection signal and determining a chain tension force (F.sub.C) of the drive chain from the at least one frequency (f).

2. Chain tension monitoring device according to claim 1, wherein the evaluator is configured for determining the at least one frequency (f) of the detected movement, by employing a Fast-Fourier-Transformation.

3. Chain tension monitoring device according to claim 2, wherein the evaluator is configured for determining the current chain tension force (F.sub.C) of the drive chain employing the formula: $F_c={\left(\frac{2L}{C_r}\times \frac{f}{k}\right)}^2\times m-r^2\times {\omega }^2\times m$ wherein: C.sub.r is a resonance factor of the drive chain, L is the distance between the two sprockets, k is the mode number of chordal vibration, f is the chordal frequency of the respective mode, ω is the rotational speed of one of the sprockets, r is the pitch diameter of the respective sprocket, and m is the mass per unit chain length.

4. Chain tension monitoring device according to claim 1, wherein the sensor device comprises a movable element which is configured for contacting the drive chain, and which is movable perpendicularly to the longitudinal direction of the drive chain.

5. Chain tension monitoring device according to claim 4, comprising an elastic element configured for urging the movable element against the drive chain.

6. Chain tension monitoring device according to claim 4, comprising a motion sensor configured for detecting a movement of the movable element transversely to the longitudinal direction of the drive chain, and providing a corresponding detection signal.

7. Chain tension monitoring device according to claim 1, further comprising a controller configured for comparing the chain tension force (F.sub.C) determined by the evaluator with a predefined lower limit (F.sub.low) and/or with a predefined upper limit (F.sub.high) and issuing an alarm signal in case the chain tension force (F.sub.C) determined by the evaluator is smaller than the predefined lower limit (F.sub.low) or in case the chain tension force (F.sub.C) determined by the evaluator is larger than the predefined lower limit (F.sub.high).

8. Chain tension monitoring device according to claim 7 further comprising a tensioning mechanism coupled with the controller and configured for adjusting the chain tension force (F.sub.C) of the drive chain when an alarm signal is issued.

9. People conveyor comprising a drive chain and a chain tension monitoring device according to claim 1.

10. Chain tension monitoring device according to claim 4, wherein the movable element comprises a sliding shoe.

11. Chain tension monitoring device according to claim 5, wherein the elastic element comprises a spring.

12. Chain tension monitoring device according to claim 6, wherein the motion sensor is configured for detecting the movement of the movable element orthogonally to the longitudinal direction of the drive chain.

13. Chain tension monitoring device according to claim 1, wherein the chain tension force (F.sub.C) is determined as a function of (i) the at least one frequency (f), (ii) a distance (L) between the two sprockets and (iii) a rotational speed (ω) of at least one of the two sprockets.

Description

DRAWING DESCRIPTION

(1) In the following exemplary embodiments of the invention are described with reference to the enclosed figures.

(2) FIG. 1 depicts a schematic side view of an escalator.

(3) FIG. 2 depicts a schematic side view of a moving walkway.

(4) FIG. 3 depicts an enlarged side view of a transmission element and a chain tension monitoring device according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION

(5) FIG. 1 shows a schematic side view of a people conveyor 1, in particular an escalator 1a, comprising a band 12 of conveyance elements 13 (steps 13a) extending in a longitudinal conveyance direction between two landing portions 20, 21. The conveyance elements 13 comprise rollers 23 guided and supported by guide rails (not shown). For clarity, only some of the conveyance elements 13 are depicted in FIG. 1, and not all conveyance elements 13/rollers 23 are provided with reference signs.

(6) In turnaround portions 17 next to the landing portions 20, 21, the band 12 of conveyance elements 13 passes from a conveyance portion 16 into a return portion 18, and vice versa. A conveyance chain 15 extending along a closed loop is connected to the band 12 of conveyance elements 13. Balustrades 4 supporting moving handrails 6 extend parallel to the conveyance portion 16.

(7) The conveyance chain 15 is configured for driving the band 12 of conveyance elements 13. The conveyance chain 15 is driven by a conveyance chain sprocket 32 mounted to a rotating shaft 30.

(8) FIG. 2 depicts a schematic side view of a people conveyor 1, which is provided as a moving walkway 1b.

(9) The moving walkway 1b comprises an endless band 12 of conveyance elements 13 (pallets 13b) moving in a longitudinal conveyance direction in an upper conveyance portion 16 and opposite to the conveyance direction in a lower return portion 18. Landing portions 20, 21 are provided at both ends of the moving walkway 1b. In turnaround portions 17 next to the landing portions 20, 21 the band 12 of conveyance elements 13 passes from the conveyance portion 16 into the return portion 18, and vice versa. Balustrades 4 supporting moving handrails 6 extend parallel to the conveyance portion 16.

(10) Similar to the embodiment shown in FIG. 1, the band 12 of conveyance elements 13 is connected with an endless conveyance chain 15. In at least one of the turnaround portions 17, the endless conveyance chain 15 is in engagement with a conveyance chain sprocket 32.

(11) In both configurations depicted in FIGS. 1 and 2, the people conveyor 1 further comprises a people conveyor drive 25 including a motor 29, which is configured for driving a drive sprocket 26 (not shown in FIG. 2).

(12) A drive chain 27 acting as a transmission element engages with said drive sprocket 26 and a driven sprocket 28 mounted to the rotating shaft 30 for rotating integrally with the conveyance chain sprocket 32. Optionally, the driven sprocket 28 and the conveyance chain sprocket 32 may be formed integrally as a single sprocket comprising two different rims, a first rim corresponding to the conveyance chain sprocket 32 and a second rim corresponding to the driven sprocket 28, respectively.

(13) As a result, the conveyance chain sprocket 32 may be driven by the motor 29 of the people conveyor drive 25 via a mechanical connection provided by the drive sprocket 26, the drive chain 27, and the driven sprocket 28.

(14) Two or all three sprockets 26, 28, 32 may have the same diameter/number of teeth, or the diameters/numbers of teeth of the sprockets 26, 28, 32 may be different.

(15) In both configurations depicted in FIGS. 1 and 2, a chain tension monitoring device 40 according to an exemplary embodiment of the invention is arranged next to the drive chain 27.

(16) FIG. 3 depicts an enlarged side view of the drive sprocket 26, the driven sprocket 28, the drive chain 27 extending between and engaging with the two sprockets 26, 28. FIG. 3 further depicts a chain tension monitoring device 40 according to an exemplary embodiment of the invention.

(17) The chain tension monitoring device 40 comprises a sensor device 41 with a movable element 42, such as a sliding shoe. The movable element 42 is supported by a guide 44 in a configuration allowing the movable element 42 to move, in particular to shift or slide, transversely, in particular orthogonally, to the longitudinal moving direction of the drive chain 27.

(18) The sensor device 41 further comprises an elastic element 46, such as a spring, configured for urging the movable element 42 against the drive chain 27. As a result, the position of the movable element 42 with respect to the guide 44 is determined by the interaction between the urging force applied by the elastic element 46 and the chain tension force F.sub.C of the drive chain 27.

(19) The portion of the movable element 42 contacting the drive chain 27 may be covered with a coating 43, such as a coating 43 including Teflon® or a similar material, configured for reducing the wear and the friction between the movable element 42 and the drive chain 27 passing along the outer surface of the movable element 42.

(20) The movable element 42 is mechanically coupled with a motion sensor 48, in particular with an accelerometer. The motion sensor 48 is configured for detecting any movement of the movable element 42 transversely, in particular orthogonally, to the longitudinal moving direction of the drive chain 27 and for generating a corresponding detection signal.

(21) The detection signal generated by the motion sensor (accelerometer) 48 is supplied to an evaluator 50.

(22) The evaluator 50 is configured for calculating at least one frequency f of the movement of the movable element 42. The evaluator 50 in particular may perform a Fourier-Transformation of the detection signal provided by the motion sensor (accelerometer) 48. Such a Fourier-Transformation in particular may be implemented as a Fast-Fourier-Transformation (FFT).

(23) The chain tension force F.sub.C of the drive chain 27 may be calculated from said at least one frequency f using the formula:

(24) $F_c={\left(\frac{2L}{C_r}\times \frac{f}{k}\right)}^2\times m-r^2\times {\omega }^2\times m$

(25) In said formula, L is the distance between the two sprockets 26, 28, k is the mode number of chordal vibration, f is the chordal frequency of the respective mode, m is the mass per unit chain length, ω is the rotational speed of one of the sprockets 26, 28, r is the pitch diameter of the respective sprocket 26, 28, and C.sub.r is a resonance factor of the drive chain 27, which may be determined experimentally.

(26) It is noted that the product ω×r employed in the formula is identical for both sprockets 26, 28. Thus, the rotational speed ω and the pitch diameter r of any of the two sprockets 26, 28 may be used for the calculation, even if the pitch diameters r of the two sprockets 26, 28 are different, as long as the rotational speed ω and the pitch diameter r of the same sprocket 26, 28 are used.

(27) Usually, the first chordal frequency f (k=1) is used, which in the case of a people conveyor usually is less than 1 Hz. However chordal frequencies f of higher order (k>1) may be used as well.

(28) The chain tension monitoring device 40 further comprises a controller 52, which is configured for comparing the calculated chain tension force F.sub.C with a predefined lower limit F.sub.low. In case the calculated chain tension force F.sub.C is smaller than said predefined lower limit F.sub.low (F.sub.C<F.sub.low), the chain tension force F.sub.C is considered as being too low and the controller 52 is configured to issue an alarm signal.

(29) Alternatively or additionally, the controller 52 additionally may be configured for detecting and indicating a too large chain tension force F.sub.C, i. e. a chain tension force F.sub.C exceeding a predefined upper limit F.sub.high (F.sub.C>F.sub.high).

(30) The alarm signal issued by the controller 52 may cause the motor 29 of people conveyor drive 25 to stop in order to avoid a malfunction of the people conveyor 1 and/or damage of the transmission element 27 and/or of the sprockets 26, 28, as it may be caused by a wrong chain tension force F.sub.C.

(31) Optionally, the people conveyor 1 may comprise a tensioning mechanism 54 configured for adjusting the chain tension force F.sub.C, e.g. by moving at least one of the sprockets 26, 28 in the longitudinal direction. In such a configuration, the alarm signal issued by the controller 52 may trigger the tensioning mechanism 54 to adjust the chain tension force F.sub.C.

(32) The tensioning mechanism 54 in particular may be configured for adjusting the chain tension force F.sub.C as long as an alarm signal is issued, i.e. as long as the detected chain tension force F.sub.C is smaller than the predefined lower limit F.sub.low, or larger than the predefined upper limit F.sub.high, respectively.

(33) Such a configuration allows automatically adjusting the chain tension force F.sub.C, thereby preventing undesirable down-times of the people conveyor 1 after a wrong chain tension force F.sub.C has been detected.

(34) In case the tensioning mechanism 54 does not succeed in increasing the chain tension force F.sub.C at least to the predefined lower limit F.sub.low, or decreasing the chain tension force F.sub.C at least to the predefined upper limit F.sub.high, within a predetermined amount of time, further operation of the people conveyor drive 25 may be stopped and a mechanic may be requested to visit the people conveyor 1 in order to fix the problem.

(35) While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adopt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention shall not be limited to the particular embodiment disclosed, but that the invention includes all embodiments falling within the scope of the dependent claims.

REFERENCES

(36) 1 people conveyor 1a escalator 1b moving walkway 4 balustrade 6 moving handrail 12 band of conveyance elements 13 conveyance elements 13a steps 13b pallets 15 conveyance chain/first drive chain 16 conveyance portion 17 turnaround portion 18 return portion 20, 21 landing portions 23 rollers 25 people conveyor drive 26 drive sprocket 27 transmission element/second drive chain 28 driven sprocket 29 motor 30 rotating shaft 32 conveyance chain sprocket 40 chain tension monitoring device 41 sensor device 42 movable element/sliding shoe 43 coating 44 guide 46 elastic element/spring 48 motion sensor/accelerometer 50 evaluator 52 controller 54 tensioning mechanism C.sub.r resonance factor of the drive chain F.sub.C chain tension force F.sub.high upper limit of the chain tension force F.sub.low lower limit of the chain tension force f chordal frequency k mode number of chordal vibration L distance between the sprockets m mass per unit chain length, r pitch diameter ω rotational speed