Method for Operating a Chain Drive and Assembly having a Chain Drive

Abstract

A method of operating a chain drive that includes sprockets. Tensile chain moments on the sprockets are determined and a specification value for operating the chain drive is determined therefrom in an automated manner. A corresponding assembly has a chain drive with sprockets and with a control device at least partly associated with the chain drive. The control device is configured for carrying out the method and a specification value for load distribution among the two drives for operating the chain drive is determined therefrom in an automated manner.

Claims

1-11. (canceled)

12. A method of operating a chain drive having sprockets, the method comprising: determining tensile chain moments acting on the sprockets; and determining from the tensile chain moments a specification value for operating the chain drive in an automated process; and operating the chain drive with the specification value.

13. The method according to claim 12, wherein the step of determining the specification value comprises taking into account four forces, the four forces each corresponding to a tensile chain force at a contact point between a chain and a sprocket and a tensile chain force at a release point of each of the sprockets.

14. The method according to claim 12, which comprises analyzing a time-dependent or angle of rotation-dependent profile of the tensile chain moments.

15. The method according to claim 12, which comprises determining extreme sprocket moments for each of the tensile chain moments and determining therefrom a tensile chain force at a contact point and a tensile chain force at a release point of each of the sprockets in each case.

16. The method according to claim 12, wherein the step of determining the specification value comprises determining a chain tension or an adjustment value for adjusting an axle spacing between the sprockets as the specification value.

17. The method according to claim 12, wherein the step of determining the specification value comprises determining a specification value for a load distribution among drives for operating the chain drive as the specification value or from the specification value in an automated manner.

18. The method according to claim 12, which comprises determining a tensile chain moment with a sensor.

19. The method according to claim 18, wherein the sensor is at least one sensor selected from the group consisting of a revolution rate sensor, a force sensor, and a torque sensor.

20. The method according to claim 18, wherein the sensor is disposed either on the sprocket, on a drive of the sprocket or on a gearbox associated with the sprocket and the drive.

21. The method according to claim 12, which comprises determining a tensile chain moment indirectly.

22. The method according to claim 21, which comprises determining the tensile chain moment indirectly from a characteristic variable or a control variable of a drive of the sprocket.

23. An assembly, comprising: a chain drive with sprockets; a control device associated with said chain drive, wherein said control device is configured for carrying out the method according to claim 12.

24. The assembly according to claim 23, wherein said chain drive is a component of a chain scraper conveyor or a shearing machine.

25. The assembly according to claim 24, wherein said chain drive is a component of a mining shearing machine.

Description

[0041] The solution according to the invention is described below using figures. The same reference characters in different figures refer to the same or similarly acting components or functions, so that in this regard the description of the further figures can also be obtained. In the figures:

[0042] FIG. 1 shows in a simplified schematic representation the basic design of a chain drive;

[0043] FIG. 2 shows examples of profiles of components of a sprocket moment;

[0044] FIG. 3 shows examples of profiles of components of a dynamic sprocket radius;

[0045] FIG. 4 shows a sprocket in a further operating position; and

[0046] FIG. 5 shows examples of profiles of components of a dynamic sprocket radius of a flat chain.

[0047] FIG. 1 shows an example of a chain drive 1 configured as a chain conveyer with two sprockets 2, 3 and a conveyer belt 4 driven thereby with an upper run 5 and a lower run 6. A drive 7 is disposed as a primary drive on the sprocket 2 shown on the left in order to drive said sprocket. A further drive 8 is disposed as an auxiliary drive on the other sprocket 3 in order to drive said sprocket.

[0048] A control device 9 is used to actuate the drives 7, 8. By way of example, the control device 9 is connected via lines 10, 11 to the drives 7, 8, wherein other transmission systems can also be used, in particular for measurement and control signals. In particular, control signals s1, s2 can be transmitted from the control device 9 to the drives 7, 8 to actuate the drives 7, 8. The conveyer belt 4 that can be driven by means of the drives 7, 8 is used to transport a transported material 12, for example small pieces of coal.

[0049] Owing to the spatial extent of rigid chain links that engage with the sprockets 2, 3 or the toothing of the sprockets 2, 3, an effective sprocket radius or chain drum radius between an axle of the respective sprocket and the outer periphery thereof changes during the rotation of the sprockets 2, 3. This is represented by a polygon as a respective sprocket 2, 3 with an outer circle 13 and an inner circle 14 in each case that represent a range of adjustment of the sprocket radius. For a chain tension of the chain drive 1, maximum and minimum extreme values of a respective sprocket moment M.sub.max, M.sub.min acting on the sprocket 2, 3 result from a resulting maximum sprocket radius r_max and a resulting minimum sprocket radius r_min.

[0050] The extreme values of the sprocket moments M.sub.max, M.sub.min each result from a tensile chain force F.sub.on on the sprocket 2 or 3 at the contact point and a tensile chain force F.sub.off on the sprocket 2 or 3 at the release point.

[0051] A further control device or said control device 9 is designed to provide a chain tension depending on a sprocket or chain drum moment M1 or M2 detected on the sprockets 2, 3 in each case. For detecting said total sprocket moments M1, M2, the assembly comprises moment sensors 15 or 16 that detect a respective power on the associated drives 7, 8, for example.

[0052] To determine a specification value ΔL, in particular an adjustment value that indicates a required change of an axle spacing between axles of the sprockets 2, 3, the respective two chain forces T1, T2, T3, T4 acting on the sprockets 2, 3 are used, which result from the respective tensile chain forces F.sub.on, F.sub.off on the sprockets 2 or 3. These can in particular be determined from the sprocket moments M1 or M2.

[0053] The specification value ΔL is output to an operator by the control device 9, for example via a display device, so that said operator can adjust the axle spacing manually, in an automated manner or partly in an automated manner. Optionally, a tensioning device 17 is disposed on one or both sprockets 2, 3, which enables a change of the chain tension by means of the control device 9 in an automated manner.

[0054] To carry out the method, accordingly a polygon effect is taken into account, which relates to a deviation of a sprocket 2, 3 or drum from an ideal circle. Depending on the number of teeth, a periodic change of a dynamic chain drum radius results therefrom.

[0055] Most sprockets, in particular of chain conveyers or stage loaders, have an odd number of teeth. In the case of a sprocket with 7 teeth for example, an effective sprocket radius periodically changes by approx. −10%. If the chain is also under tension downstream of the sprocket, then the polygon effect acts both at the contact point and at the release point. In the case of sprockets with odd numbers of teeth, the effect at the release point is displaced by half a tooth angle compared to the contact point. For constant chain forces, the polygon effect thus causes a typical pattern in the sprocket moment.

[0056] FIG. 2 shows acting moments of a sprocket or chain drum over the range of rotation angles thereof. By way of example, constant tensile chain forces in the upper run and lower run of F.sub.on=1000 kN or F.sub.off=400 kN and a periodic change of the associated dynamic chain drum radius according to FIG. 3 are assumed. A total moment M.sub.total is composed of the superimposed tensile chain forces, i.e. the moment M.sub.on of the tensile chain force F.sub.on on the sprocket at the contact point and the moment M.sub.off of the tensile chain force F.sub.off on the sprocket at the release point. In particular, the total moment M.sub.total acts on the sprocket with a zig-zag type profile with slight profile curvature or dynamic radii between minima of the sprocket moment M.sub.min and maxima of the sprocket moment M.sub.max.

[0057] The total moment M.sub.total is measured with the moment sensor 15 or 16 for example. The total moment is given by

M.sub.total=F.sub.on.Math.r.sub.dyn,on−F.sub.off.Math.r.sub.dyn,off.

[0058] The dynamic or effective radii r.sub.dyn,on, r.sub.dyn,off are dependent on the sprocket diameter or chain drum diameter and the current rotation angle, and are thus geometrically fixed. FIG. 3 shows examples of profiles of an effective sprocket radius r.sub.dyn with a profile dependent on the rotation angle j of the sprocket. In this case, the effective radii r.sub.dyn,on, r.sub.dyn,off are again effective at the contact point and release point.

[0059] The tensile chain force F.sub.on at the contact point and the tensile chain force F.sub.off at the release point can be calculated as chain run forces by an analysis of the qualitative profiles of the total moment M.sub.total in the region of the peaks.

[0060] The determination of the run forces can be carried out for example by analyzing the extreme values of the sprocket moment M.sub.max and M.sub.min. The null point of the rotation angle j of the sprocket is selected so that hereby the maximum sprocket radius r_max exists for the contacting chain 5. The maximum sprocket radius r_max for the contacting chain 5 then always results if the remainder of j/tw is <w.Math.dt, wherein tw is a tooth pitch angle with tw=360°/zn, zn is the number of teeth of the sprocket, dt is a time increment between two measurement values and w is the angular speed of the sprocket. For illustration, it is assumed for simplicity that the contacting and releasing chains 5, 6 are parallel, i.e. an angle between the tensile chain forces F.sub.on and F.sub.off=180°, then there is a minimum sprocket diameter r_min for the releasing chain at this point in time and the resulting sprocket moment is at a maximum M.sub.max, as illustrated using the sprocket shown in FIG. 1 on the left.

[0061] FIG. 4 shows that the sprocket moment is at a minimum M.sub.min if the sprocket radius is at a minimum for the contacting chain 5 and is at a maximum for the releasing chain 6. This is exactly the case if the remainder of (j+tw/2)/tw is <w.Math.dt.

[0062] The following equations apply to the calculation of the extreme sprocket moments M.sub.max and M.sub.min:

M.sub.max=F.sub.on.Math.r_max−F.sub.off.Math.r_min,  (I)

M.sub.min=F.sub.on.Math.r_min−F.sub.off.Math.r_max.  (II)

[0063] By way of example, it is assumed for illustration purposes that the tensile chain forces F.sub.on and F.sub.off do not change significantly during a tooth engagement, i.e. a rotation of the sprocket by the tooth pitch angle tw. Then (I) and (II) are two equations with the two unknowns F.sub.on and F.sub.off that can be solved for F.sub.on and F.sub.off, for example by solving (I) for F.sub.on and inserting F.sub.on into (II). This gives:

F.sub.off=max(0.0,(M.sub.min−M.sub.max.Math.rk)/B),

F.sub.on=(M.sub.max/r_max)+rk.Math.F.sub.off

with rk=r_min/r_max and B=(r_min.sup.2/r_max)−r_max.

[0064] A measurement is thus carried out so that the local maximum and minimum of the sprocket moment M.sub.max and M.sub.min are determined for each tooth engagement interval and the respective two chain forces F.sub.on and F.sub.off are calculated therefrom according to the equations.

[0065] This enables an analysis of the chain forces regarding chain pretension and power distribution. If all chain forces on the two drives are known, i.e. on the primary drive 7 with the run forces or tensile chain forces T1:=F.sub.on and T2:=F.sub.off and on the auxiliary drive 8 with the tensile chain forces T3:=F.sub.on and T4:=F.sub.off, then the actual chain pretension T.sub.0,actual can be calculated:

T.sub.0,actual=(T1+T2+T3+T4)/4.

[0066] The tensile force requirement T.sub.erf,OT of the upper run is

T.sub.erf,OT=T1−T4

and the tensile force requirement T.sub.erf,UT of the lower run is

T.sub.erf,UT=T3−T2.

[0067] An ideal chain pretension T.sub.0,setpoint for the current situation, still without a reserve against dynamic load peaks, should be

T.sub.0,soll=(T.sub.erf,OT+T.sub.erf,UT)/4.

[0068] For a chain stiffness, the following applies

c.sub.Chain=E.Math.A/(2.Math.axle spacing)

with E as the modulus of elasticity of the chain of approx. 50 kN/mm.sup.2, for example, and A as the cross-section in mm.sup.2 of a section of the chain link. The specification value for the change of the axle spacing of the sprockets 2, 3 is derived from the chain stiffness c.sub.chain of c.sub.chain=361.6 kN/m, for example, according to:

ΔL=(T.sub.0,soll−T.sub.0,actual)/c.sub.Chain.

[0069] Optionally, further aspects can be taken into account, in particular for actuation of the drives 7, 8 and/or of the specification value ΔL.

[0070] For example, the combined adjustment of chain pretension, power distribution and overload protection is also enabled with the following process.

[0071] In a first step, the auxiliary drive draws the power requirement of the lower run plus a preload force, which covers a difference between the current peripheral force and the maximum peripheral force according to the overload protection. In the subsequent step, the primary drive draws the power requirement of the upper run minus the component applied by the auxiliary drive by means of the pretension. Consequently, the chain pretension is adjusted so that the force downstream of the auxiliary drive is exactly zero. The overload protection is then adapted to the position of the chain drive, for example a cutting machine and the current power requirement. Once the power requirement of the primary drive reaches the rated power, further increases are applied by the auxiliary drive. If both drives have reached the rated power thereof, a further increase is distributed equally to both drives. If the power requirement reduces again, said logic is followed in reverse, i.e. equal load reduction on the two drives until the rated power is reached, then load reduction of the auxiliary drive until the target value of the first step is reached.

[0072] A possible reduction of the chain force and thereby the protection of the system is advantageous, and the reduction of the power requirement is greater, the smaller the current power requirement in relation to the installed power.

[0073] As excessive chain forces owing to unavoidable alignment errors and constraining forces in the chain guide resulting therefrom produce a higher tensile force requirement, the tensile force requirement T.sub.erf,OT and T.sub.erf,UT comes out lower than calculated in practice. Optionally, they can therefore be suitably further readjusted and a targeted reduction of the power requirement—and thereby an accompanied reduction of the wear—can also be optionally established.

[0074] The tensile chain forces are in practice highly fluctuating. Accordingly, the signal for the sprocket moments M1, M2 is very noisy. As it is known where and for what reason the measurement value is to be sought in the signal and the analysis is not time-critical, the necessary information can be generated from the moment measurement. In particular, the signal can be filtered and/or smoothed.

[0075] For example, a tooth engagement frequency can be searched for or observed and analyzed and for this purpose a relevant frequency range may be filtered.

[0076] The measurement of the rotation angle of the sprocket is not absolutely necessary. It is sufficient to determine the local maxima and minima of the sprocket moment at the time intervals. However, if the rotation angle j is known, then for example disruptions of the system, in particular wear on the sprocket and chain, can be concluded from the displacement of the maxima/minima relative to the expected position. Thus, wear on the chain drum for example can be derived from the moment measurement, so that the amount by which the effective chain drum radius and the phase position of the polygon effect are shifted can be taken into account.

[0077] The determination or measurement of the moment, in particular the sprocket moment M1, M2, and of the rotation angle on the sprocket can in principle be carried out at different points in the drive train. The sprocket moment can also be measured at a different point than directly on the sprocket. The measurement can for example also be carried out in the case of using a hydrodynamic clutch on the output side of the clutch, in particular the on the turbine wheel of said clutch or on the gearbox input and can be converted for the sprocket. For this purpose, a moment measurement on the gearbox output/drum can be implemented, which provides a particularly good signal at this point. In particular, the required moment measurement can be integrated within a turbo coupling, which results in a significant gain in functionality. When using a hydrodynamic clutch between the engine and the gearbox input, the moment fluctuation at the gearbox input caused by the polygon effect on the sprocket is noticeable as a combination of moment fluctuations and revolution rate fluctuations. If the chain force determination is thus to be carried out in the hydrodynamic clutch or at the gearbox input, then this can be implemented by a suitably accurate measurement of the moment and revolution rate.

[0078] As an example of an indirect moment measurement, a moment determination by means of an electric motor/frequency converter can also be implemented with a current measurement for example, which advantageously does not require an additional sensor and is preferably implemented in combination with a very rigid engine/gearbox coupling. For this purpose, a rotationally elastic connection between the engine and the sprocket is preferable, and in particular no turbo coupling is used. The method can thus also be used for frequency converter drives. It can also be exploited that the chain force or chain tensile force can be indirectly influenced by means of a frequency converter. In particular, it can be used in combination with drives with a hydraulic clutch.

[0079] The corner tensile forces, i.e. the tensile chain force before and after the primary drive and the auxiliary drive, can be determined continuously and control variables can be generated therefrom. This is carried out in particular by a sufficiently accurate detection of the drive moments with suitable signal processing. In particular, control variables are the specification value ΔL as a specification of a change in tensioning travel of the chain tensioning device for optimum chain pretension, a target moment for the primary drive, a target moment for the auxiliary drive, a moment limit for the primary drive and/or a moment limit for the auxiliary drive.

[0080] Optionally, the magnitudes of the dynamic load peaks can also be taken into account, for which a safety pretension is maintained. For example, load peaks in shearing systems result from fluctuations of cutting forces, in face conveyors from suddenly increasing loading as a result of caving in or as a result of a material jam upstream of the portal of a cutting machine. A preferred design of a chain tensioning system thus also contains a suitable load limiter in the drive train.

[0081] If a chain guide is implemented in the region of the sprocket such that the angle between the contacting and releasing chain deviates from 180°, then the phase shift between the maxima and minima accordingly deviates from tw/2. The stated equations are then adapted accordingly.

[0082] If a chain is used for which the upright chain links have a different pitch from that of the lying links, such as is the case for example for a flat chain and that is shown in FIG. 5, then this is taken into account when calculating the maximum and minimum radii.

[0083] As the chain forces are not constant during an engagement, the calculated chain forces fluctuate, as can be seen in FIG. 5. This can be reduced by forming a sliding average for example. The accuracy can also be enhanced by detecting the next maximum of the sprocket moment M.sub.max2 in addition to the pair of values of the extreme sprocket moments M.sub.max and M.sub.min and determining the forces F.sub.on2 and F.sub.off2 from the pair of values M.sub.min and M.sub.max2 by solving equation (II) for F.sub.on2 and inserting it into equation (I):

F.sub.off2=max(0.0,(M.sub.max−M.sub.min*rg)/B2)

F.sub.on2=(M.sub.min/r_min)+rg*F.sub.off2
with rg=r_max/r_min and B2=(r_max.sup.2/r_min)−r_min. The average value of F.sub.off and F.sub.off2 and F.sub.on and F.sub.on2 is then formed.

[0084] Further modifications and extensions can be implemented. Instead of the example of a chain conveyor from coal mining, an implementation in other industries, technical fields and also with different embodiments with chain drives can be achieved. All numerical values and dimensional specifications are stated purely by way of example.

REFERENCE CHARACTER LIST

[0085] 1 chain drive, in particular chain conveyer [0086] 2, 3 sprockets [0087] 4 conveyer belt [0088] 5 upper run [0089] 6 lower run [0090] 7, 8 drives [0091] 9 control device [0092] 10, 11 lines [0093] 12 transported material [0094] 13 outer circle [0095] 14 inner circle [0096] 15, 16 moment sensors [0097] 17 tensioning device [0098] F.sub.on tensile chain force at the contact point [0099] F.sub.off tensile chain force at the release point [0100] j rotation angle of the sprocket [0101] M1, M2 sprocket moments [0102] M.sub.on moment of the tensile chain force F.sub.on at the contact point [0103] M.sub.off moment of the tensile chain force F.sub.off at the release point [0104] M.sub.max, M.sub.min extreme sprocket moments [0105] r.sub.dyn effective radius [0106] r.sub.dyn,on, r.sub.dyn,off effective radius at the contact and release points [0107] r_max maximum sprocket radius [0108] r_min minimum sprocket radius. [0109] s1, s2 control signals [0110] T1, T2, T3, T4 acting chain forces as run forces [0111] ΔL adjustment value or specification value for axle spacing