METHOD FOR MONITORING AND CONTROLLING MIXER OPERATION

Abstract

A mixer machine assembly having a drive unit with an electric motor, a drive shaft assembly connected to the electric motor, and a propeller. The propeller has a hub, a plurality of blades, and a propeller shaft from the drive shaft assembly. The control unit is operatively connected to the electric motor, and is configured for monitoring and controlling the operation of the mixer machine. The control unit monitors a drive shaft torque about a drive shaft of the drive shaft assembly. The control unit determines an average torque range based on at least one torque range, wherein each torque range is the difference between the highest and the lowest torque value detected during a predetermined angle of rotation of the propeller during operation of the mixer machine assembly. The control unit compares the determined average torque range with a predetermined torque range limit value.

Claims

1.-14. (canceled)

15. A method for monitoring drive shaft assembly load of a mixer machine of a mixer machine assembly during operation, the mixer machine assembly comprising: a drive unit comprising an electric motor, and a drive shaft assembly connected to and driven in rotation by the electric motor during operation of the mixer machine assembly; a propeller comprising a hub, a propeller shaft of the drive shaft assembly connected to the hub, and extending in an axial direction (Z), and a plurality of blades connected to the hub and extending in a radial direction; and a control unit operatively connected to the electric motor and configured for monitoring and controlling the operation of the mixer machine; the method comprising the steps of: monitoring, by the control unit, a drive shaft torque (Tz) about the drive shaft of the drive shaft assembly; determining, by the control unit, an average drive shaft torque range (ATzR) based on at least one drive shaft torque range (TzR), each drive shaft torque range (TzR) of the at least one drive shaft torque range (TzR) equaling a difference between a highest drive shaft torque value (Tzmax) about the drive shaft detected during a predetermined angle of rotation of the propeller during operation of the mixer machine assembly and a lowest drive shaft torque value (Tzmin) about the drive shaft detected during the predetermined angle of rotation of the propeller during operation of the mixer machine assembly, and comparing, by the control unit, the determined average drive shaft torque range (ATzR) with a predetermined torque range limit value (TzRlimit).

16. The method of claim 15, wherein the determination of the average drive shaft torque range (ATzR) is based on a plurality of drive shaft torque ranges (TzR).

17. The method of claim 16, wherein the plurality of drive shaft torque ranges (TzR) correspond to ranges measured during 15 or more propeller revolutions

18. The method of claim 16, wherein the plurality of drive shaft torque ranges (TzR) correspond to ranges measured during 30 or more propeller revolutions.

19. The method of claim 16, wherein plurality of drive shaft torque ranges (TzR) correspond to ranges measured during 90 or fewer propeller revolutions.

20. The method of claim 16, wherein plurality of drive shaft torque ranges (TzR) corresponds to ranges measured during 60 or fewer propeller revolutions.

21. The method of claim 15, wherein the predetermined angle of rotation of the propeller is equal to or more than one blade pass.

22. The method of claim 21, wherein one blade pass comprises a predetermined portion of one propeller revolution, the predetermined portion equaling 360 angular degrees divided by a total number of blades of the propeller.

23. The method of claim 15, wherein the predetermined angle of rotation of the propeller is equal to or less than three propeller revolutions.

24. The method of claim 23, wherein the predetermined angle of rotation of the propeller is equal to or less than one propeller revolution.

25. The method of claim 15, wherein the average drive shaft torque range (ATzR) is a weighted average drive shaft torque range (WATzR) based on the value of the highest drive shaft torque value (Tzmax) detected during each predetermined angle of rotation of the propeller.

26. The method of claim 15, wherein the propeller of the mixer machine has a rotational speed equal to or less than 400 rpm during normal operation of the mixer machine assembly.

27. The method of claim 15, wherein the propeller of the mixer machine has a rotational speed equal to or less than 200 rpm during normal operation of the mixer machine assembly.

28. A mixer machine assembly comprising: a mixer machine, the mixer machine comprising: a drive unit comprising an electric motor, and a drive shaft assembly connected to and driven in rotation by the electric motor during operation of the mixer machine assembly; a propeller comprising a hub, a propeller shaft of the drive shaft assembly connected to the hub and extending in an axial direction (Z), and a plurality of blades connected to the hub and extending in a radial direction; and a control unit operatively connected to the electric motor and configured for monitoring and controlling the operation of the mixer machine, the control unit including configured functions for: monitoring a drive shaft torque (Tz) about a drive shaft of the drive shaft assembly; determining an average drive shaft torque range (ATzR) based on one or more drive shaft torque ranges (TzR), each drive shaft torque range (TzR) equaling a difference between a highest drive shaft torque value (Tzmax) about the drive shaft and a lowest drive shaft torque value (Tzmin) about the drive shaft detected during a predetermined angle of rotation of the propeller during operation of the mixer machine assembly, and comparing the determined average drive shaft torque range (ATzR) with a predetermined torque range limit value (TzRlimit).

29. The mixer machine assembly of claim 28, wherein the control unit is integrated into the mixer machine.

30. The mixer machine assembly of claim 28, wherein the control unit comprises a variable frequency drive (VFD).

31. The mixer machine assembly of claim 28, wherein the mixer machine is a submersible mixer machine.

32. A computer program product comprising a non-transitory computer-readable medium storing a program including instructions that, when executed by a control unit of a mixer machine assembly of claim 28, causes the mixer machine assembly to: monitor the drive shaft torque (Tz) about the drive shaft of the drive shaft assembly, determine the average drive shaft torque range (ATzR) based on the one or more drive shaft torque ranges (TzR); and compare the determined average drive shaft torque range (ATzR) with the predetermined torque range limit value (TzRlimit).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] A more complete understanding of the abovementioned and other features and advantages of the present invention will be apparent from the following detailed description of preferred embodiments in conjunction with the appended drawings, wherein:

[0025] FIG. 1 is a schematic perspective view of an inventive mixer machine assembly,

[0026] FIG. 2 is a semi-transparent schematic side view of the mixer machine assembly, and

[0027] FIG. 3 is a schematic front view of the mixer machine assembly.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Reference is initially made to FIG. 1. The present invention relates especially to a mixer machine assembly, generally designated 1, suitable for treatment/transportation of liquid comprising solid/biological matter, such as wastewater/sewage, and relates especially to a method for monitoring and controlling such a mixer machine assembly 1.

[0029] The inventive mixer machine assembly 1 is configured to be at least partly located in a basin/tank housing the liquid to be treated/transported. The basin can be constituted by a treatment basin at a treatment plant, such as a race track/circulation channel, the basin can be constituted by a digester tank at a biogas plant, etc. The mixer machine assembly 1 comprises three major parts, a drive unit, generally designated 2, a propeller 3 and a control unit 4 (ECU). The control unit 4 controls the drive unit 2, the drive unit 2 drives the propeller 3 and the propeller 3 propels the liquid. The drive unit 2 and the propeller 3 are always parts of a mixer machine, and in the disclosed embodiment the control unit 4 is integrated into and constitutes a part of the mixer machine. In an alternative embodiment the control unit 4 is constituted by a separate member and is operatively connected to the mixer machine. The mixer machine is also called flow generating machine or mixer. In the disclosed embodiment the mixer machine is a submersible mixer machine, i.e. configured to be located entirely submerged. However, it shall be pointed out that a submersible mixer machine can be partly located above the liquid surface during operation.

[0030] An electric cable 5 extending from a power supply, for instance the power mains, provides power to the mixer machine assembly 1, the mixer machine assembly 1 comprising a liquid tight lead-through 6 receiving the electric cable 5. The electric cable 5 may also comprise signal wires for data communication between the mixer machine and an external control unit (not shown).

[0031] Reference is now also made to FIG. 2, wherein some internal parts of the mixer machine assembly 1 are schematically disclosed. The drive unit 4 comprises an electric motor, generally designated 7, and a drive shaft assembly 8 connected to and driven in rotation by said electric motor 7 during operation of the mixer machine assembly 1. The electric motor 7 comprises in a conventional way a stator 9 and a rotor 10. In the disclosed embodiment the drive shaft assembly 8 comprises a drive shaft 11, i.e. a rear end portion, and a propeller shaft 12, i.e. a forward end portion, wherein a mechanical transmission unit 13 is arranged between the drive shaft 11 and the propeller shaft 12. The rotor 10 is connected to and co-rotational with the drive shaft 11 of the drive shaft assembly 8. The propeller 3 is connected to and co-rotational with the propeller shaft 12 of the drive shaft assembly 8 in a conventional way. The transmission unit 13 has a fixed gear ratio wherein the propeller 3 has a lower rotational speed than the rotor 10 of the electric motor 7, i.e. reduced gearing. The gear ratio is preferably equal to or less than 100:1, more preferably equal to or less than 60:1, and preferably equal to or higher than 2:1, more preferably equal to or higher than 15:1. According to an alternative embodiment the gear ratio is 1:1, i.e. no gearing, the drive shaft 11 and the propeller shaft 12 being constituted by the same shaft member. The drive unit 2 also comprises necessary bearings and seals, which are particularly exposed to wear due to bending forces on the propeller shaft 12.

[0032] In the disclosed embodiment the drive shaft 11 and the propeller shaft 12 both extends in an axial direction, and are preferably collinear. According to an alternative embodiment the mechanical transmission unit 13 is angled, i.e. it is an angle between the drive shaft 11 and the propeller shaft 12, for instance 90 degrees. In the latter case, the propeller shaft 12 extends in the axial direction.

[0033] The rotational speed of the propeller 3 during normal operation of the mixer machine assembly 1 is equal to or less than 400 rpm, preferably equal to or less than 200 rpm, and equal to or higher than 10 rpm. This type of mixer machine assembly 1 is often called a slowly operated mixer machine assembly 1.

[0034] The electric motor 7 is located in a housing 14 and in the disclosed embodiment the propeller 3 is located in direct contact with the housing 14, the housing 14 being a liquid tight housing. However, in alternative embodiments the propeller 3 is located at a distance from the housing 14, i.e. the propeller shaft 12 of the drive shaft assembly 8 is visible between the housing 14 and propeller 3. According to the alternative embodiment the drive unit 4 is usually located in a dry environment. In most applications the mixer machine is a submersible mixer machine, i.e. both the drive unit 2 and the propeller 3 are located under the liquid surface during operation. In alternative embodiments the housing 14 and the electric motor 7 are not located in the liquid at the same time as the propeller 3 is located under the liquid surface, i.e. so-called top-entry or side-entry mixer machines.

[0035] The propeller 3 comprises a hub 15 connected to the propeller shaft 12 of the drive shaft assembly 8 and a plurality of blades 16 connected to said hub 15, wherein the propeller shaft 12 extends in an axial direction (Z) and each blade 16 extends in a radial direction seen from its base to its top, wherein the blade 16 is connected to the hub 15 at its base and wherein the top of the blade 16 is the outermost part of the propeller 3. In the disclosed embodiment both the leading edge 17 and the trailing edge 18 of the blade 16 are curved, the leading edge 17 is convex and the trailing edge 18 is concave. It shall be pointed out that the blades 16 naturally also have an extension in the axial direction, i.e. has a pitch, in order to generate thrust to the liquid. The control unit 4 is operatively connected to the electric motor 7, the control unit 4 being configured for monitoring and controlling the operation of the mixer machine. The electric motor 7 is configured to be driven in operation by the control unit 4. Thus, the control unit 4 is configured to control the rotational speed at which said electric motor 7 of the mixer machine is to be driven, for instance by controlling the frequency of the current operating the electric motor 7. According to the disclosed embodiment, the control unit 4 comprises a Variable Frequency Drive (VFD) 19.

[0036] It is essential for the present invention that the control unit 4 of the inventive mixer machine assembly 1 is configured to perform the inventive method, and that the method comprises the steps of: monitoring a drive shaft torque (Tz) about the drive shaft 11of the drive shaft assembly 8, determining an average drive shaft torque range (ATzR) based on at least one drive shaft torque range (TzR), wherein each drive shaft torque range (TzR) is equal to the difference between the highest drive shaft torque value (Tz.sub.max) about the drive shaft 11 and the lowest drive shaft torque value (Tz.sub.min) about the drive shaft 11 detected during a predetermined angle of rotation of the propeller 3 during operation of the mixer machine assembly 1, and comparing the determined average drive shaft torque range (ATzR) with a predetermined torque range limit value (TzR.sub.limit).

[0037] The torque range limit value (TzR.sub.limit) is calculated/predetermined for each given propeller 3 and/or mixer machine.

[0038] The drive unit 4 is configured to determine/calculate the drive shaft torque (Tz) about the drive shaft 11 according to known procedures, for instance based on measuring of different electric signals available for the drive unit 4, such as current, electric voltage, output frequency of the VFD 19, rotational speed of the drive shaft 11, etc. According to a preferred embodiment, the inventive method also comprises the step of performing precautionary measures when it is determined that the determined average drive shaft torque range (ATzR) exceeds the predetermined torque range limit value (TzR.sub.limit). The precautionary measures are for instance sending alarm information to operator, saving alarm information in the control unit 4, decreasing the rotational speed of the propeller 3, etc. One precautionary measure performed by the operator based on alarm information from the control unit 4 is to balance the propeller, i.e. removing or adding weight to the top of one or more blades 16.

[0039] According to a preferred embodiment the determination of the average drive shaft torque range (ATzR) is based on a plurality of drive shaft torque ranges (TzR), and preferably the drive shaft torque ranged (TzR) of the plurality of drive shaft torque ranges (TzR) are in succession. According to an alternative embodiment, the plurality of drive shaft torque ranges (TzR) is constituted by every second drive shaft torque range (TzR).

[0040] Reference is now also made to FIG. 3. The predetermined angle of rotation (α) of the propeller 3 is equal throughout the operation of the mixer machine and is preferably equal to or more than one blade pass. It is also plausible that the predetermined angle of rotation of the propeller is equal to a multiple of blade passes. One blade pass is constituted by a predetermined portion of one propeller revolution, wherein said predetermined portion is equal to 360 angular degrees divided by the number of blades 16 of the propeller 3. Thus, in the disclosed embodiment one blade pass equals 120 angular degrees. The location of the interface between two adjoining blade passes, or between two adjoining predetermined angle of rotation, is of less importance.

[0041] Preferably, the predetermined angle of rotation of the propeller 3 is equal to or less than three propeller revolutions, preferably equal to or less than one propeller revolution.

[0042] According to an alternative embodiment the average drive shaft torque range (ATzR) is a weighted average drive shaft torque range (WATzR), for instance based on the value of the highest drive shaft torque value (Tz.sub.max) detected during each predetermined angle of rotation of the propeller 3, or based on the value of the lowest drive shaft torque value (Tz.sub.min) detected during each predetermined angle of rotation of the propeller 3.

[0043] Preferably, the plurality of drive shaft torque ranges (TzR) serving as basis for the determination of the average drive shaft torque range (ATzR) are equal to or more than 15 propeller revolutions, preferably equal to or more than 30 propeller revolutions. Thereto, the plurality of drive shaft torque ranges (TzR) serving as a basis for the determination of the average drive shaft torque range (ATzR) are preferably equal to or less than 90 propeller revolutions, preferably equal to or less than 60 propeller revolutions.

[0044] The mixer machine assembly 1 comprises means adapted to execute the steps of the above method. Many of the steps of the above method are preferably performed/controlled by the control unit 4, and thus the term “the mixer machine assembly 1 comprises means . . . ” does not necessarily imply that said means has to be located within the housing 14. Thus the term also includes means accessible/available/operatively connected to the mixer machine.

[0045] A computer program product/package comprising instructions to cause the mixer machine assembly 1 to execute the steps of the above method, is accessible/available/operatively connected to the mixer machine. Said computer program product is preferably located/run in the control unit 4.

[0046] There is a relationship between the average propeller shaft torque range (ATzR) about the propeller shaft 12 based on the torsional torque about the propeller shaft 12 and an average bending torque range (ATxyR) based on the bending torque about an axis in a radial plane, i.e. a plane perpendicular to the axial extension of the propeller shaft 12. Thus, the drive shaft torque (Tz) about the propeller shaft is a torsional torque and the radial torque (Txy) is a bending torque. ATxyR=k*ATzR, wherein k=5±2. The average bending torque range ATxyR is more critical than the average propeller shaft torque range ATzR, and it shall be pointed out that it is equivalent to use the bending torque range TxyR instead of the drive shaft torque range TzR in view of the inventive method.

Feasible Modifications of the Invention

[0047] The invention is not limited only to the embodiments described above and shown in the drawings, which primarily have an illustrative and exemplifying purpose. This patent application is intended to cover all adjustments and variants of the preferred embodiments described herein, thus the present invention is defined by the wording of the appended claims and thus, the equipment may be modified in all kinds of ways within the scope of the appended claims.

[0048] It shall also be pointed out that even though it is not explicitly stated that features from a specific embodiment may be combined with features from another embodiment, the combination shall be considered obvious, if the combination is possible.