GB2515062A - Method and apparatus for balancing a rotor - Google Patents

Abstract

The method includes the steps of: mounting the rotor 12 in a machine 10 with chucks 14,16 capable of rotating the rotor about its axis and performing calibration for each of first, second and third axial planes. This calibration includes: attaching a calibration weight of known mass to a surface of the rotor in that plane; causing the rotor to rotate about its axis; determining the effect of the balancing weight attached in that plane on the unbalance of the rotor; storing a calibration value indicative of said effect; and causing the rotor to rotate about its axis; determining the unbalance of the rotor; accessing data representative of a set of discrete balancing masses; determining, using the stored calibration values, a selection of one or more balancing weights each to be attached to the rotor in a respective one of the axial planes, the balancing weights being selected from a set of balancing weights having respective masses corresponding to the set of discrete balancing masses, the selection of weights and respective one of the first, second or third axial plane in which each weight is to be placed providing an optimal correction of any unbalance of the rotor from all possible permutations of available balance weights and axial planes, attaching each of the selected balance weights to a surface of the rotor in its selected axial plane.

Description

Title: Method and apparatus for balancing a rotor Descrirtion of Invention The present invention relates to a method and apparatus for balancing a rotor such as a propshaft.

Propshafts, and more generally rotors, can be formed of a single rotor portion or multiple rotor portions linked together in end-to-end alignment. Rotors formed of multiple rotor portions may comprise two or three such portions, and less commonly may comprise four portions.

Balancing is typically carried out on rotors to overcome or lessen the problem of unbalance' -the uneven distribution of mass around the axis of rotation of the rotor. Unbalance is when the inertia axis of the rotor is offset from its central axis of rotation, which results from the mass of the rotor not being distributed uniformly about its central axis. Rotors suffering unbalance may generate a moment when rotating which leads to vibration.

It is known to balance a single piece rotor using two balance planes. Each balance plane is a plane disposed substantially perpendicular to the axis of the rotor. When balancing a multiple piece rotor, balancing is carried out in additional balance planes: a two piece rotor may be balanced in three planes, a three piece rotor may be balanced in four planes, and a four piece rotor may be balanced in five planes.

Correction for unbalance is typically carried out by welding balance weights to the rotor. Rotors are designed with zones where balance weights can be added corresponding to the number of balancing planes, which are usually near the end of each rotor portion.

Using known balancing methods and apparatuses, a rotor is loaded in to a balancing machine. Each end of the rotor is located in a respective chuck, to hold that end of the rotor. The chucks are then fitted to spindles, which in turn are mounted to bearings. If the rotor comprises multiple rotor portions, the connection of the two rotor portions are mounted and clamped on centre bearer supports. If a two piece rotor was to be balanced in two separate halves, then one chuck and the centre support would tend to be used rather than mounting that rotor portion in two chucks.

The mechanism for correcting unbalance is automated, by which balance weights are welded to the rotor at a set position along the axis of the rotor for each plane, within specified balance zones. Once weights for all planes (where required) are applied to the rotor, the rotor unbalance is measured again using the same method. If the unbalance measured in any plane remains outside of a predefined tolerance threshold, a second step of correction is carried out within the corresponding balance zone.

The balance weights are typically selected from a known and predefined set of masses. For example, the masses may increase in 1 gram increments, from 1 gram up to the maximum initial unbalance limit. The weight having the mass that is closest to the desired mass is selected from the set of masses. Where the exact mass is not present in the set of masses, a degree of inaccuracy will result after its connection to the rotor. This may necessitate a second step of correction, or it may be the case that the rotor is balanced to an acceptable tolerance.

Another method that avoids or reduces the inaccuracy associated with selecting balancing weights from a predefined set of masses, is to cut the correct mass from a strip roll during the balancing process. The benefit of this method is the exact mass is used in the balancing plane, but this process requires additional expensive equipment to be added to the balancing machine, and this equipment needs to be maintained to a high level to produce reliable results. On the other hand, predefined sets of masses are bulk produced and inexpensive, and require no further equipment to be provided. However, the inaccuracies incurred using predefined sets of masses results in an error in the amount of unbalance corrected to a plane when the weights are applied to the rotor. Further steps of measurement and correction may be performed to eliminate or reduce the error sequentially, but the addition of extra weights and further steps increases the length of time it takes to balance a rotor, and increases the number of times the machine must rotate the rotor to take measurements of unbalance.

To take accurate measurements and carry out accurate balancing, flexible rotors must be balanced at or near normal operational speed. The unbalance in flexible rotors is not linear due to the change of shape in the rotor when rotating at speed, and when weights are applied to the rotor. Flexible rotors requiring high accuracy and high volume production are calibrated according to rotor type and in each balancing plane, to compensate for any unbalance crossover effects which occur when the amount and angle of unbalance in one plane affects that in another plane. To resolve the crossover effect between planes when balancing a rotor, "specific calibration" or "matrix calibration" is performed.

When balancing a new rotor type, a measurement of the unbalance present in the rotor is taken. A temporary calibration weight is then added to a first plane, and the effect of the calibration weight in that plane is tested by measuring unbalance in the rotor, and comparing it to the unbalance in the rotor with no weights attached. Then the weight is moved to a second plane and measurements of unbalance in the rotor are taken again. This process is repeated for each balancing plane. A single matrix is then calculated determining the effect of applying weights in each combination of planes. If measurements are taken in relation to four planes (which would be the case for a three piece rotor), this results in the generation of a four by four matrix of calibration results.

To overcome or reduce the inaccuracies incurred by selecting weights from a limited predefined set of masses when balancing a rotor, a second balancing step (known as a trim step) may be carried out, but only once the first correction step has been made and the rotor spun again to determine any residual unbalance. Additional weights may be added to the rotor to improve the balancing. The additional weights are attached in a position slightly offset from the original balancing plane (i.e. offset axially along the length of the rotor -known as the trim plane'), since weights are already in place on the original planes, so as to further refine the balance of the rotor. To test the impact of a weight being added in such an offset position, during the calibration stage the temporary calibration weight is applied adjacent to each of the balancing planes at the respective trim planes. A step of adding further weights to address inaccuracies in the balancing is required in approximately 30% of industrial balancing operations. In half of these cases (i.e. 15% of all) this second step of adding weights to the trim planes would not be required if the exact weight required to be applied to the rotor in the first stage of balancing is was available.

Even so, by adding balancing weights to the trim planes, and retesting the effect of those weights on the unbalance measurements taken in the balancing planes, the time taken to carry out balancing is increased. The more often a system requires the use of the trim step, the slower the process is on average, Furthermore, the machinery must be operated to rotate the rotor, and to spin the rotor to a speed sufficient for testing to be carried out. This method is inefficient in terms of cost, time and use of resources.

According to a first aspect of the invention we provide a method of balancing a rotor having only a single rotor portion, the method including the steps of: mounting the rotor in a machine capable of rotating the rotor about its axis; performing calibration for each of first, second and third axial planes, including: attaching a calibration weight of known mass to a surface of the rotor in that plane; causing the rotor to rotate about its axis; determining the effect of said balancing weight attached in that plane on the unbalance of the rotor; storing a calibration value indicative of said effect; and causing the rotor to rotate about its axis; determining the unbalance of the rotor; accessing data representative of a set of discrete balancing masses; determining, using the stored calibration values, a selection of one or more balancing weights each to be attached to the rotor in a respective one of the axial planes, the balancing weights being selected from a set of balancing weights having respective masses corresponding to the set of discrete balancing masses, the selection of weights and respective one of the first, second or third axial plane in which each weight is to be placed providing an optimal correction of any unbalance of the rotor from all possible permutations of available balance weights and axial planes, attaching each of the selected balance weights to a surface of the rotor in its selected axial plane.

According to a second aspect of the invention we provide a method of balancing a rotor including a plurality (N) of rotor portions which are connected to each other, the method including the steps of: mounting the rotor in a machine capable of rotating the rotor about its axis; performing calibration for each of (N+2) axial planes (F1, P2... PN+2) including: attaching a calibration weight of known mass to a surface of the rotor in that plane; causing the rotor to rotate about its axis; determining the effect of said balancing weight attached in that plane on the unbalance of the rotor; storing a calibration value indicative of said effect; causing the rotor to rotate about its axis; determining the unbalance of the rotor; accessing data representative of a set of discrete balancing masses; determining, using the stored calibration values, a selection of one or more balancing weights each to be attached to the rotor in a respective one of the axial planes, the balancing weights being selected from a set of balancing weights having respective masses corresponding to the set of discrete balancing masses, the selection of weights and respective one of the axial planes (P1, F2...PN+2) in which each weight is to be placed providing an optimal correction of any unbalance of the rotor from all possible permutations of available balance weights and axial planes, attaching each of the selected balance weights to a surface of the rotor in its selected axial plane.

According to a third aspect of the invention we provide an apparatus for balancing a rotor, the apparatus including: a machine for mounting a rotor and capable of rotating the rotor about its axis; one or more measuring devices operable to measure unbalance in the rotor; a calibration system operable to perform calibration on each of a first, second and third axial plane, in turn, including: attaching a calibration weight of known mass to a surface of the rotor in that plane; determining the effect of said balancing weight in that plane on the unbalance of the rotor using one or more of the measuring devices; storing a calibration value indicative of said effect; and determine the unbalance of the rotor; accessing data representative of a set of discrete balancing masses; determine, using the stored calibration values, a selection of one or more balancing weights each to be attached to the rotor in a respective one of the axial planes, the balancing weights being selected from a set of balancing weights having respective masses corresponding to the set of discrete balancing masses, the selection of weights and respective one of the first, second or third axial plane in which each weight is to be placed providing an optimal correction of any unbalance of the rotor from all possible permutations of available balance weights and axial planes, a balancing system operable to attach each selected balance weight to a surface of the rotor in its selected axial plane.

Further features of the various aspects of the invention are described in the appended claims.

Embodiments of the invention will now be described, by way of example only, with reference to the following figures, of which: Figure la is a diagrammatic view of rotor having only a single rotor portion mounted in a rotor balancing apparatus of embodiments of the invention; Figure lb is a diagrammatic view of rotor having two rotor portions connected to each other which is mounted in a rotor balancing apparatus of embodiments of the invention; Figure ic is a diagrammatic view of rotor having two rotor portions connected to each other which is mounted in a rotor balancing apparatus of embodiments of the invention; Figure 2 is a diagrammatic view of a rotor mounted in a rotor balancing

apparatus of the prior art;

Figures 3 and 4 are diagrammatic views of a rotor mounted in a rotor balancing apparatus of embodiments of the invention; and Figures 5 to 7 are diagrammatic views of rotors comprising two, three and four rotor portions, respectively, mounted in rotor balancing apparatuses of embodiments of the invention.

With reference to the drawings, Figure 1 shows some, but not all, component parts of a rotor balancing apparatus 10 onto which a rotor 12, having only a single rotor portion, is mounted. The rotor 12 may be of any suitable type, as is commonly known in the field, such as propshafts including driveshafts and Cardan shafts, for example. The rotor balancing apparatus 10 comprises a machine having first and second chucks 14, 16 for mounting the rotor 12 by supporting either end of the rotor 12. Each chuck 14, 16 is fitted to a spindle.

The balancing machine is operable to rotate the rotor 12 about its axis to a specified speed of rotation.

If the rotor comprises multiple rotor portions, the connection of the two adjacent rotor portions are mounted and clamped on centre bearer supports 218, 318 (illustrated in Figures lb and lc).

The apparatus 10 includes (one or more) measuring devices operable to measure unbalance in the rotor 12. The measuring devices are of a standard type generally known in the art, for measuring unbalance in a rotor. Typically, the rotor 12 is spun to a predefined speed and the unbalance is measured by a computer based electronic measuring system. The measuring system receives a signal from a pickup transducer mounted to each bearer support -the number of pickup transducers corresponding to the number of balancing planes. Once per revolution of the rotor, a signal from an encoder is used to determine the angle of unbalance. The unbalance amount and angle may be displayed on a display screen.

The apparatus 10 provides a calibration system that is operable to attach a calibration weight of known mass to a surface of the rotor 12. In embodiments the attachment and/or removal of calibration weights to the rotor 12 is automated, and in other embodiments the calibration weights may be attached to and/or removed from the rotor 12 manually (e.g. by hand placement). The calibration system is also operable to determine the effect of placing the balancing weight on the rotor by measuring the unbalance of the rotor using the measuring devices.

During testing, once calibration has been carried out using the calibration system, a controller is operable to calculate required masses of balancing weights, if any, that should be connected to the rotor 12 in order to balance the rotor, based on the determined effects of attaching the calibration weights to the surface of the rotor as determined by the calibration system. The balancing weights are selected from a known set of available balancing weights, and the planes in which to place those respective weights are selected accordingly given knowledge of the available selection of weights. In this way, by using knowledge of the available weights, and the impact on unbalance of applying a weight in each plane, the system may optimise the choice of weights and planes in which to place those weights so as to minimise unbalance in the rotor 12 in an optimal manner.

Known balancing systems select a combination of weights for placement on the rotor, where each weight is chosen on the basis that the weight is the closest weight available to the desired value calculated using the calibration test results. For example, where weights of mass 1.78g and 2.09g are required to achieve the optimum level of unbalance, prior art systems would choose two weights of 2g each, since the values would be rounded to 2g (to the nearest 0.Sg, for example). However, through calculating the selection of weights and respective axial planes providing an optimal unbalance of the rotor from the set of all possible selections, the system of the present invention may, for example, calculate that in fact from the set of weights available, it is preferable to apply 1.5g and 2.5g, respectively, to the balancing planes since this has been calculated give a better overall optimisation of unblanace. In other words, rounding values to the nearest available weight, as is currently performed by prior art systems, often leads to an unsatisfactory adjustment to the unbalance. This results in a second set of balancing weights having to the added to the rotor in a second balancing operation. Whereas, the invention ensures that, more often that not, the unbalance is corrected to within an acceptable tolerance in a single application of balancing weights.

The apparatus also includes a balancing system that is operable to attach balance weights to a surface of the rotor 12, in accordance with the mass values calculated by the controller. In embodiments, the attachment of balance weights to the surface of the rotor 12 is automated. In other embodiments, the attachment of weights is carried out manually (e.g. by hand placement). The balancing system employs standard known equipment for attaching balancing weights to a rotor, e.g. by welding or adhering.

With reference to Figure 2, a rotor balancing apparatus 110 of the prior art is shown, having a pair of chucks 114, 116 for mounting the rotor 12, as previously described. First and second axial planes A, B are located towards either end of the rotor 12. By axial plane, we mean a plane lying transverse to the axis of the rotor.

The method of balancing using the apparatus of the prior art involves rotating the rotor about its axis, and then measuring any unbalance in the rotor. A calibration weight of known mass is attached to a surface of the rotor 12 in a first axial plane A which is positioned towards one end of the rotor 12, and the effect of that balancing weight on the unbalance of the rotor is measured. The calibration weight is then removed from the first plane A, and applied to the rotor in a second axial plane B which is positioned towards an opposite end of the rotor 12. The unbalance of the rotor is then measured again. The effects of placing calibration weights in trim planes, close to each of the planes A and B may also be determined, in a similar manner.

Using the determined effects of attaching the calibration weights to the surface of the rotor 12, first and second unbalance values are calculated, corresponding to the mass of the balancing weight that should be applied to the rotor in the first and second planes A, B, respectively, to balance the rotor 12.

Balancing weights having approximately those masses calculated in the previous step (the exact masses required are unlikely to be available) are then attached to the rotor in those respective planes. The rotor 12 is then tested again to determine if the rotor 12 is balanced. If the rotor 12 is found to be unbalanced, and the unbalance is outside a threshold tolerance value, a second step of attaching balancing weights and subsequent testing must be performed (i.e. a trim step), using the separate data collected by placing the calibration weights in the trim planes, if such a step was performed. One or more weights are placed in a position slightly offset from each balancing plane, in the respective trim planes.

The method of operation of the apparatus of the present invention is now described with reference to figures 3 to 7. Figure 3 shows a similar arrangement to the apparatus of the prior art, wherein a single piece rotor 12 is mounted on the chucks 14, 16 of the machine. The machine causes the rotor 12 to rotate about its axis. The speed of rotation may be predetermined, and is typically substantially the same as the intended operating speed of rotation of the rotor 12 when in end use.

A calibration system is operated that involves performing calibration for each of first Al, second Bl, third A2 and fourth B2 axial planes. The first axial plane Al is positioned towards one end of the rotor 12, and the second axial plane Bl is positioned towards an opposite end of the rotor 12. In embodiments, third and fourth axial planes A2, B2 are positioned close to, and axially spaced from, the first axial plane Al and second axial plane B1, respectively. In other words, the third and fourth planes A2, B2 are the respective trim planes of the first and second planes Al, B1. By close to', we mean that the first plane Al and third plane A2 are positioned relatively axially near to each other so as to enable, at a particular angular position, balancing weights to be placed in the main and trim planes which either abut or lie close to each other. In other embodiments, the third and fourth axial planes A2, B2 are not trim planes of the first and second axial planes Al, Bl, and are positioned at other locations along the length of the rotor 12.

For each of these planes in turn, a calibration weight of known mass is attached to a surface of the rotor 12 in that plane. The rotor 12 is then caused to rotate about its axis, and when the rotor 12 is rotating at sufficient speed, the measuring devices measure the effect of the calibration weight in that plane on the unbalance in the rotor 12 and all other planes in this operation. A calibration value indicating the determined effect of the calibration weight in that plane and the effect in each of the other planes is then store by the system. Once this has been completed, the calibration weight is removed from the rotor 12. Rotation of the rotor 12 must be stopped while placing each weight on the periphery of the rotor 12 and then spun back up to speed in order to carry out each measurement. This is carried out in turn to observe the effect of placing the calibration weight in each of the planes. It should be appreciated, though, that removal of each calibration weight from its respective plane is not necessary in order to determine the effect of the calibration weights on the unbalance of the rotor in each of the planes. For example, a calibration weight may be attached in plane Al first, and left there, whilst a second calibration weight is placed in plane Bl. A third calibration weight may then be placed in plane A2, and left there, whilst a fourth calibration weight is placed in plane B2. A combination of the weights may be left in situ, or each removed after each calibration step. Furthermore, a calibration weight may be placed in each plane before calibration is undertaken, and for each plane, all or part of the calibration weight may be removed in order to undertaken calibration in that plane. The calibration "weight" may, in some circumstances be the removal of weight from the plane.

In embodiments, measuring the unbalance of the rotor 12 at each plane includes measuring the angular position of said unbalance around the axis of the rotor 12, knowledge of which can be used to place the balancing weights at the appropriate angular positions on the rotor 12.

Once calibration is complete, and the system has stored calibration values relating to each of the axial planes, the balancing system causes the rotor 12 to rotate about its axis once more, and the measuring devices are used to determine the unbalance of the rotor 12 without any weights attached to it.

The balancing system accesses data representative of a set of discrete balancing masses, equivalent to the masses of the balancing weights that are available for use in balancing the rotor 12. By a set of discrete masses, we mean that only a limited selection of weights is available. The masses of those weights may be spread across a range of discrete values. For example, the weights may have masses of 0.5g. 1g. 2g. 3g. 4g. and 5g.

Using the stored calibration values, the controller determines a selection of one or more balancing weights each to be attached to the rotor 12 in a respective one of the axial planes. The balancing weights are selected from the set of balancing weights available to the system (having respective masses corresponding to the set of discrete balancing masses). Using all of the stored calibration values, and knowledge of the limited set of balancing weights available, the controller determines an optimal allocation of those weights to be positioned at respective planes on the rotor 12. It may be the case that weights are not required in each of the planes. The selection of weights and respective axial plane in which each weight is to be placed is made by the system such that an optimal correction of any unbalance of the rotor from the set of all possible selections of said weights I planes is achieved. This selection will often differ from that of prior art systems in which required masses are calculated for each plane, and then rounded to the nearest mass from the selection of available weights, without any calculation being made in advance as to the likely balancing effect of those weights on the rotor.

The controller may also calculate an angular position on the surface of the rotor 12 at which to place the respective balancing weight(s) at that plane Al, A2, Bi, B2.

Using known techniques, the balancing system attaches the selected balancing weights Wl, W2 to the surface of the rotor 12 in the respective planes Al, A2, Bl, B2, as determined by the controller. The position of balancing weights Wi, W2 on the first and second planes Al, Bl respectively, is shown in Figure 4 by way of example.

Using this method, and enabling the system to consider all possible combinations of available weights being positioned in the primary (i.e. first and second Al, B1) or the trim planes (A2, B2), or combinations of primary and trim planes, the rotor 12 may be balanced more efficiently in the first unbalance correction step operation. This reduces the likelihood that a further balancing step is required when measuring the unbalance in the rotor 12 subsequent to attaching the weighs. The process is therefore likely to involve fewer spin-ups of the rotor 12, which take time and significant additional power to achieve, particularly when carrying out industrial-scale operations.

By contrast, systems of the prior art consider only the primary planes (and not trim planes) for placement of weights in the first unbalance correction step operation. Furthermore, those systems determine an unbalance value to be applied in those planes, and then select a weight that most closely approximates that value. By using such a method, inaccuracies occur with the placement of each and every weight, since it is very rare that the exact required mass is available. Therefore if several weights are attached to the rotor, the total inaccuracy in respect of the unbalance correction is increased considerably.

A reduction in the quantity of predefined balancing weights used to balance a rotor 12 in an automated balancing machine is achievable, since fewer remedial weights are required to correct inaccuracies occurring after balancing weights have been applied. This results in an improvement in Takt time on high volume production lines. Furthermore, by attaching fewer balancing weights to a rotor 12, potential fatigue on the rotor 12 is reduced, and the balance accuracy is typically improved.

In embodiments, the system determines the selection of a balancing weight (if required) to be applied to the rotor 12 by selecting a weight to be placed in one of the first or third axial planes Al, A2, but not both. The system also determines a balancing weight (if required) to be applied to the rotor 12 by selecting a weight to be placed in one of the second or further axial planes 31, 32, but not both. It is preferable to place a weight in either the main or trim plane at a location on the rotor 12, so that a second balancing may be placed at that location (in the other of the main and trim plane) if a second stage of balancing is required.

With reference to Figures lb and 5, the rotor may include first and second rotor portions 212 which are connected to each other end-to-end. The apparatus 210 has respective chucks 214 and 216 for holding the rotor ends, and a bearer support 218 for mounting and clamping a centre bearer housing between the two rotor portions 212.

Calibration weights are placed at a fifth axial plane Cl which is positioned in between the first and second planes Al, 31, and at a sixth axial plane C2 which is positioned close to, and axially spaced from, the fifth axial plane Cl, and corresponding calibration values are determined and stored.

Similarly, where the rotor is formed of three rotor portions 312, or four rotor portions 412, the respective apparatuses 310, 410 are configured to determine calibration values for further balancing planes. In the case of balancing a rotor comprising three rotor portions 312 (as shown in Figures lc and 6), calibration values are determined for a seventh axial plane Dl which is positioned in between the first and second planes Al, Bi, and at an eighth axial plane D2 which is positioned close to, and axially spaced from, the seventh axial plane Dl. Where the rotor comprises four rotor portions 412 (see Figure 7), calibration values are determined for placing weights at a ninth axial plane El which is positioned in between the first and second planes Al, 31, and at a tenth axial plane E2 which is positioned close to, and axially spaced from, the ninth axial plane El.

This enables the controller to consider the effects of placing weights in the fifth and sixth planes Cl, C2 when determining which weights to select and where to attach them to the rotor 12 (and seventh/eighth, ninth/tenth planes in the case of rotors comprising three and four rotor portions, respectively).

The balancing system is then operable to attach balance weights, if required, to the surface of the rotor in one or more of the planes in accordance with the calculated fifth and sixth (and seventh, eighth, ninth and tenth, as appropriate) determined weights, from the set of weights available.

The information collected during the calibration procedures is used to calculate a row calibration matrix, where N is the number of planes that would typically be considered for placement of weights using a system of the prior art. So, for example, using a previous system to balance a three piece rotor, only four planes would have been considered when determining where to attach weights to attach to the rotor. Using the method of the present invention, 2 rows are required to represent the unique combinations of main and trim plane positions where weights may be applied. The following table sets out these possible combinations.

Where a cell contains M', this indicates positioning a weight in the main balancing plane (i.e. Al for the first plane). A T' indicates positioning a weight in a position offset from the balancing plane, in the trim plane, (i.e. A2, or the third plane, in relation to original balancing plane Al). As illustrated in the table, the method of the present invention provides far greater choice for selecting the positioning of balancing weights to achieve the best balancing results first time, particularly when provided with a predetermined set of masses from which to select balancing weights.

Row Planel (A) Plane2 (B) Plane3 (C) PIane4 (D) 1 M M M M 2 M M M T 3 M M I M 4 M M I I

M T M M

6 M I M I 7 M T T M 8 M T T T 9 T M M M

T M M T

11 T M T M 12 T M T T 13 T T M M 14 I I M I

T T T M

16 T T T T M=Main position I=Trim position When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (21)

1. CLAIMS1. A method of balancing a rotor having only a single rotor portion, the method including the steps of: mounting the rotor in a machine capable of rotating the rotor about its axis; performing calibration for each of first, second and third axial planes, including: attaching a calibration weight of known mass to a surface of the rotor in that plane; causing the rotor to rotate about its axis; determining the effect of said balancing weight attached in that plane on the unbalance of the rotor; storing a calibration value indicative of said effect; and causing the rotor to rotate about its axis; determining the unbalance of the rotor; accessing data representative of a set of discrete balancing masses; determining, using the stored calibration values, a selection of one or more balancing weights each to be attached to the rotor in a respective one of the axial planes, the balancing weights being selected from a set of balancing weights having respective masses corresponding to the set of discrete balancing masses, the selection of weights and respective one of the first, second or third axial plane in which each weight is to be placed providing an optimal correction of any unbalance of the rotor from all possible permutations of available balance weights and axial planes, attaching each of the selected balance weights to a surface of the rotor in its selected axial plane.
2. 2. A method according to claim 1 wherein balancing weights are only selected for and attached to two of the first, second and third axial planes.
3. 3. A method according to claim 1 or 2, wherein calibration is performed for a fourth axial plane, wherein the method includes: determining, using the stored calibration values, a selection of one or more balancing weights each to be attached to the rotor in a respective one of the axial planes, the balancing weights being selected from a set of balancing weights having respective masses corresponding to the set of discrete balancing masses, the selection of weights and respective one of the first, second, third or fourth axial plane in which each weight is to be placed providing an optimal correction of any unbalance of the rotor from all possible permutations of available balance weights and axial planes, attaching each of the selected balance weights to a surface of the rotor in its selected axial plane.
4. 4. A method according to claim 3 wherein balancing weights are only selected for and attached to two of the first, second, third and fourth axial planes.
5. 5. A method according to any preceding claim wherein determining a selection of balancing weights comprises determining a selection of one or more balancing weights to be applied to one of the first or third axial planes and/or one or more balancing weights to be applied to one of the second or fourth axial planes.
6. 6. A method according to claim 5, wherein the third axial plane is positioned close to and axially spaced from the first axial plane, and the fourth axial plane is positioned close to and axially spaced from the second axial plane.
7. 7. A method of balancing a rotor including a plurality (N) of rotor portions which are connected to each other, the method including the steps of: mounting the rotor in a machine capable of rotating the rotor about its axis; performing calibration for each of (N+2) axial planes (F1, P2... PN+2) including: attaching a calibration weight of known mass to a surface of the rotor in that plane; causing the rotor to rotate about its axis; determining the effect of said balancing weight attached in that plane on the unbalance of the rotor; storing a calibration value indicative of said effect; causing the rotor to rotate about its axis; determining the unbalance of the rotor; accessing data representative of a set of discrete balancing masses; determining, using the stored calibration values, a selection of one or more balancing weights each to be attached to the rotor in a respective one of the axial planes, the balancing weights being selected from a set of balancing weights having respective masses corresponding to the set of discrete balancing masses, the selection of weights and respective one of the axial planes (Ri, P2... PN+2) in which each weight is to be placed providing an optimal correction of any unbalance of the rotor from all possible permutations of available balance weights and axial planes, attaching each of the selected balance weights to a surface of the rotor in its selected axial plane.
8. 8. A method according to claim 7, wherein calibration is performed for further planes (FN+3...F2N+2), wherein the method includes: determining, using the stored calibration values, a selection of one or more balancing weights each to be attached to the rotor in a respective one of the axial planes, the balancing weights being selected from a set of balancing weights having respective masses corresponding to the set of discrete balancing masses, the selection of weights and respective one of the planes (Pl...P2N+2), in which each weight isto be placed providing an optimal correction of any unbalance of the rotor from all possible permutations of available balance weights and axial planes, attaching each of the selected balance weights to a surface of the rotor in its selected axial plane.
9. 9. A method according to any preceding claim, wherein the step of measuring unbalance includes measuring the angular position of said unbalance around the axis of the rotor.
10. 10. A method according to any preceding claim, wherein the step of a selection of one or more balancing weights to be connected to the rotor further includes calculating an angular position on the surface of the rotor at which to place the or each respective balancing weight.
11. 11. A method according to any one of claims 7 to 10 wherein balancing weights are only selected for and attached to PNI or fewer axial planes.
12. 12. A method according to any preceding claim, further including the steps of: after the step of attaching the balance weights: causing the rotor to rotate about its axis; determining the unbalance of the rotor; determining, using the calibration values, a selection of one or more balancing weights each to be attached to the rotor in one or more of the axial planes that did not previously receive a balancing weight, the balancing weights being selected from the remaining set of balancing weights having respective masses corresponding to the set of discrete balancing masses, the selection of weights and respective axial plane in which each weight is to be placed providing an optimal correction of any unbalance of the rotor from all possible permutations of available balance weights and axial planes, and attaching each of the selected balance weights to a surface of the rotor in its selected axial plane.
13. 13. A method according to any preceding claim wherein the method includes the step of removing the calibration weight from the surface of the rotor, subsequent to or in advance of the step of storing a calibration value indicative of said effect.
14. 14. An apparatus for balancing a rotor, the apparatus including: a machine for mounting a rotor and capable of rotating the rotor about its axis; one or more measuring devices operable to measure unbalance in the rotor; a calibration system operable to perform calibration on each of a first, second and third axial plane, in turn, including: attaching a calibration weight of known mass to a surface of the rotor in that plane; determining the effect of said balancing weight in that plane on the unbalance of the rotor using one or more of the measuring devices; storing a calibration value indicative of said effect; and determine the unbalance of the rotor; accessing data representative of a set of discrete balancing masses; determine, using the stored calibration values, a selection of one or more balancing weights each to be attached to the rotor in a respective one of the axial planes, the balancing weights being selected from a set of balancing weights having respective masses corresponding to the set of discrete balancing masses, the selection of weights and respective one of the first, second or third axial plane in which each weight is to be placed providing an optimal correction of any unbalance of the rotor from all possible permutations of available balance weights and axial planes, a balancing system operable to attach each selected balance weight to a surface of the rotor in its selected axial plane.
15. 15. An apparatus according to claim 14, wherein the or each measuring device is configured to measure the angular position of said unbalance around the axis of the rotor.
16. 16 An apparatus according to claim 14 or claim 15, wherein the controller is operable to calculate an angular position on the surface of the rotor at which to place the balancing weight(s) in each respective plane.
17. 17. An apparatus according to any one of claims 14, 15 or 16 wherein the rotor includes a plurality (N) of rotor portions and wherein the calibration system is operable to perform calibration on each of (N+2) axial planes (Fi, F2... PN+2) and wherein the selection of weights and respective one of the planes (Pl...FN+2) in which each weight is to be placed providing an optimal correction of any unbalance of the rotor from all possible permutations of available balance weights and axial planes,
18. 18. An apparatus according to any one of claims 14, 15, 16 or 17 wherein the rotor includes a plurality (N) of rotor portions and wherein the calibration system is operable to perform calibration on each of (2N+2) axial planes (F1, P2... P2N+2) and wherein the selection of weights and respective one of the planes (P1...P2N+2) in which each weight is to be placed providing an optimal correction of any unbalance of the rotor from all possible permutations of available balance weights and axial planes,
19. 19. A method as hereinbefore described with reference to and/or as shown in the accompanying drawings.
20. 20. An apparatus as hereinbefore described with reference to and/or as shown in the accompanying drawings.
21. 21. Any novel feature or novel combination of features described herein and/or as shown in the accompanying drawings.