Method and apparatus for correcting the unbalance present in a rotor

A method and an apparatus for correcting the unbalance present in a rotor in one or several correction steps by adding or removing material only to or from given points on the rotating body on which only a limited quantity of material is available for correction, with the unbalance being resolved into components as given by the design of the rotor, with correction being carried out in one of several given components, and with the unbalance determined being eliminated in the given components as to the possibility permitting the least quantity of material to be added or removed in a minimum number of correction runs, so that finally an uninterrupted sequence of correction points is available on the rotor.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for correcting the 
unbalance present in a rotor. 
DESCRIPTION OF THE PRIOR ART 
German published patent application DE-OS 2 830 070 describes a method of 
correcting the unbalance in rotating bodies, in which the correction 
points are selected among all possibilities between a maximum of one half 
thereof and a minimum of two points, each in reference to the unbalance 
vector, and in which a variable number of non-zero units can be provided 
at each correction point so as to eliminate the unbalance. 
As a result of this method, equal amounts of unbalance can be corrected at 
several points, but it is not possible to eliminate the unbalance by 
removing or adding the least quantity of material within the shortest 
possible time since the selected correction points are not arranged in an 
uninterrupted sequence, this in turn being due to the fact that maximum 
permissible units are provided for the individual correction points stored 
in one matrix memory. 
Furthermore, German published patent application DE-OS 2 651 883 describes 
an apparatus for detecting and processing the amount and location of the 
measured unbalance, which is indicated by a moving light spot on a display 
screen of a balancing machine, on which screen is arranged, around a 
central tolerance circle, at least one range of a plurality of correction 
fields referred to the given quantity which can be removed for unbalance 
elimination due to the specific design of the rotor, and arranged in an 
uninterrupted sequence. 
With this apparatus, a resolution of the unbalance into more than two 
correction points is not possible so that particularly in the event of an 
initial unbalance greater than the quantity of material that can be 
removed from these two correction points, the rotor will have to be 
considered a reject. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide a method and 
an apparatus for correcting the unbalance present in a rotor, i.e., for 
permitting unbalance correction at one or several correction points in 
consideration of the required tolerance, if necessary, and with the least 
quantity of material removed or added. 
In accordance with the inventive method and apparatus, the unbalance is 
resolved into one or several correction points in uninterrupted sequence 
depending on its amount and angular location, and the permissible 
tolerance, if any. Such resolution is performed, for example, by a logical 
decision circuit, which also decides if the correction steps are carried 
out simultaneously or one after the other. 
In addition, the correction points of the first correction step are stored 
and taken into account when the correction points of the second step are 
determined. 
The apparatus realizing the above-mentioned method is distinguished by a 
device making available the measured unbalance as to amount and phase 
position or components, and the device is followed by a logical decision 
circuit, a logical component selecting circuit, and a computer resolving 
the unbalance into components. These circuits control the correction unit 
altogether.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates part of an electric motor armature 10, which is 
representative of a rotor in which unbalance correction is possible only 
at given correction points, and having a limited quantity of material that 
can be removed for mass correction. With the electric motor armature 10, 
the unbalance can only be corrected on the laminations, preferably by 
milling. Other subtractive methods, such as drilling, or additive methods, 
such as insertion of correction weights into the armature slots between 
the segments, are also acceptable. 
The armature 10 in this preferred embodiment has eighteen segments, eight 
of which numbered 1 to 8, are illustrated in FIG. 1. Correction of 
unbalance will be performed on one or several of the segments 1 to 8, 
depending on the amount and phase position of the measured unbalance. The 
inventive method, of course, can be applied analogously to rotors having 
any other number of segments. Correction is carried out with single 
cutters 11 and/or 12, or respective double cutters, which are arranged 
preferably on a so-called sliding spindle of a conventional correction 
unit. 
FIG. 2 illustrates the maximum quantities m.sub.1 to m.sub.8 which can be 
corrected in the individual components, and the relative correction 
vectors, as well as all possible corrections of the preferred embodiment. 
Correction is performed in one component (e.g., m.sub.1 with "m" being the 
maximum quantity to be corrected) with one single tool, if the position of 
the unbalance coincides precisely with a segment (e.g., segment 1) and if 
the unbalance can be eliminated in this segment completely, or, on the 
other hand, if a minor unbalance is situated near a segment so that the 
residual unbalance to be expected after correction is within tolerance. 
Correction is carried out by means of two single tools separately 
controlled, if the unbalance is situated between two components (e.g., 
segments 1 and 2) and can be completely eliminated by correction in the 
two segments (possibility of correcting m.sub.1 +m.sub.2 =1.88 m). 
Correction is performed by means of a double tool if the unbalance is 
situated precisely between two segments, or if a minor unbalance is 
situated near the center line of the armature slot so that the residual 
unbalance expected after correction is within the preset tolerance limits. 
Correction is carried out by means of two double cutters separately 
controlled, if the unbalance is situated between two segments, or if it is 
situated on one segment and the unbalance is so large that it cannot be 
eliminated by mass removal from one segment only. 
If the unbalance is so large that its elimination is not possible in one 
correction step, rebalancing is carried out, preferably in the segments 4 
and 7 and 6 and 8, or in the segments 4 and 6 only, with the correction 
points (segments 1, 3, 2, and 5) and the correction possibilities m.sub.1 
+m.sub.2 +m.sub.3 +m.sub.5 =3.65 m of the first correction step being 
stored temporarily and taken into account when the unbalance is resolved 
into the components of the second correction step. 
Due to the sequence of correction points located next to each other without 
interruption, unbalance correction is possible with the least quantity of 
material removed. An uninterrupted sequence of adjacent correction points 
results in reduced removal of material. When the correction points are 
interrupted and the angle between the corrections points on the various 
components of the rotor is large, the amount of material that is required 
to be removed is greater. 
The correction possibilities of the different given correction planes are 
selected independent of each other by means of one or several analyzers. 
FIGS. 3 and 4 are block diagrams of the circuits controlling the correction 
unit, with processing of the measured data being performed either by 
analogue or digital means. 
In a balancing machine, the unbalance data of one or several planes are 
received by known transducers and passed to an electronic system 20 that 
determines the unbalance as to amount and location, or the unbalance data 
are received in respective components by digital means and entered into 
the electronic system 20 for further processing. The electronic system 20 
makes a determination of the unbalance according to the magnitude and 
direction of unbalance signals and can, for example, be executed in 
accordance with the teachings of Great Britain Pat. No. 860,847, 
incorporated herein by reference. As illustrated in FIG. 3, the amount of 
unbalance "M" is available on the output 21 of the device 20, and its 
phase position "f" is available on the output 22. 
These unbalance data are entered into the logical decision circuit 23 
(which is illustrated in more detail in FIG. 4), the logical component 
selecting circuit 24, and the computer 25. The components selected among 
those available are preset manually or automatically on the component 
selecting device 29, depending on the rotor, and entered into the logical 
decision circuit 23, the logical component selecting circuit 24, and the 
computer 25. The signals from the electronic system 20 are initially sent 
to the component computer 25 which then calculates the component's 
magnitudes in accordance with the number of components of a particular 
rotor. The component computer 25 can for example correspond to a computer 
in accordance with U.S. Pat. No. 3,890,845, incorporated herein by 
reference. For instance with the rotor illustrated in FIG. 1, the 
component selecting device would be set to indicate eighteen correction 
points because the armature 10 has eighteen segments. 
The unbalance is read out on meters and an indexing device is controlled as 
to the output signals of the logical decision circuit 23, which output 
signals are further used for selecting the correction tools, and are then 
entered into the logical component selecting circuit 24 and computer 25. 
The selecting circuit 24, depending on the number of correction points 
available, as set by device 29, the position, and the magnitude of the 
unbalance, selects the particular component or components of the rotor to 
be balanced. An indexing device indexes the rotor 10 such that the 
individual components to be corrected are situated below the correction 
unit, i.e., in the illustrated embodiment of FIG. 1, under one or both of 
the cutters 11 and 12 of the milling unit. 
The indexing device (not shown) is a conventional element which is 
implemented by digital or analogue logic. In the indexing device, a sensor 
senses the present position of the rotor and feeds a signal representative 
of the sensed position to a comparator. The comparator also receives a 
signal representative of the desired position of the rotor and generates a 
control signal representative of the deviation of the sensed position from 
the desired position. Depending on the size of the control signal, a motor 
is energized to rotate the rotor until the desired position is reached, 
thus achieving indexing in a conventional servo-like manner. 
The correction cuts in each of the components KI and KII of the correction 
planes I and II (indicated as outputs of computer 25 in FIG. 3) are 
preferably provided one after the other. If the correction tools are 
controlled accordingly, it is also possible to correct simultaneously each 
of the components KI and/or KII of the correction planes I and/or II, or 
even the resultant unbalance of the planes I and II. 
The output data of the computer 25 are preferably passed to control device 
26 which takes into account non-linearity of the correction tools in 
unbalance elimination. Since the compensating mass is not directly 
proportional to the feed action of the compensating tools, such correction 
is necessary. Thus, the output of the control device 26 takes into account 
the special shape of the milling machines or cutters 11 and 12 and serves 
to control the milling depth of the cutters 11 and 12. 
The correction points selected for the first correction step are stored in 
the memory 27. If a second step is required due to the high initial or 
residual unbalance, the stored correction points are called from the 
memory 27 by means of switch 28 and passed to the logical decision circuit 
23, the logical component selecting circuit 24 and computer 25, which will 
take them into account when selecting the correction points of the second 
step. 
The function of resolution into components is carried out by means of the 
computer 25, which maintains the selected components or changes them in 
accordance with the acknowledgement given by the logical decision circuit 
23. 
The logical component selecting circuit 24 is provided with the information 
already mentioned, and with the phase reference signal of the rotor 10, 
which is required for control of the indexing device. In the circuit 24, 
the components are selected for use in unbalance compensation, depending 
on the number of components handled by the component selecting device 29, 
as well as the magnitude and position of unbalance. 
The logical decision circuit 23 generally shown in FIG. 3 is illustrated in 
more detail in FIG. 4. 
The unbalance data, as to amount and phase position or components, which 
are available on the output of the device 20, are passed to the logical 
decision circuit 23 for resolution into components in component separation 
circuit 30, which is controlled by the component selecting device 29 (also 
shown, for convenience, in FIG. 4). In device 29, the number of equalizing 
points is preselected (with respect to the rotor 10, it is the number of 
poles), so that the circumference of the rotor 10 is divided into equal 
parts corresponding to the components. 
In the circuit 30, the determined unbalance is broken into components, both 
as to size and phase position. The number of components will be a function 
of the available number of correction points, and the amount and location 
of unbalance. In the circuit 30, recalculation of the determined unbalance 
which is present according to size and phase position (for example, in 
90.degree. components) takes place in accordance with known geometric 
rules. 
The data stored in the separate memories 31 to 35 depend on the number of 
components, which is preferably identical with the number of correction 
points, and the stored magnitudes conform, for example, to the values 
given in FIG. 2 and discussed in more detail below. 
The memories 31 to 35 are furthermore influenced by the adjuster 36, by 
means of which the maximum milling depth of the cutters 11 and 12 is 
preset. This adjuster 36 is followed by an equalizer taking into account 
non-linearity of the correction tools. 
The memory 37 stores the permissible tolerances which are preset, depending 
on the number of components. 
Memory 31 stores the maximum quantity of material to be removed ("m" in 
FIG. 2) for one component, memory 32 the maximum quantity for two 
components ("1.88 m" in FIG. 2), and memory 33 the maximum quantity for 
four components ("3.65 m" in FIG. 2), with all these components being 
arranged in an uninterrupted sequence. Memory 34 stores the maximum 
quantity of material which can be removed (maximum reduction magnitude for 
compensation) in two compensation steps ("5.27 m" in FIG. 2), and memory 
35 stores the maximum quantity which can be removed in the second 
compensation step above. According to FIG. 2, these are the compensation 
masses m.sub.7, m.sub.4, m.sub.6, and m.sub.8 (vector sum 5.27 m-3.65 
m=1.62 m). The output value of memory 35 is passed on by means of switch 
38 if a second correction run is necessary, and accordingly memory 34 is 
blocked. 
The adding circuit 39 carries out a vectorial addition of the component 
magnitudes K1 and K2, made available by the circuit 30 and depending on 
the unbalance determined, and the subtractor circuit 40 calculates the 
difference between the component magnitudes K1 and K2. The output data of 
the adding circuit 39 are passed to the comparator circuits 41 to 45, the 
outputs of which are connected to the inputs of the logical priority 
circuit 47. 
The comparator circuits 41 to 45 compare the output value of the adding 
circuit 39 with individual data from the memories as follows: comparator 
41: x equals circuit 39 and y equals memory 34 or 35; comparator 42: x 
equals circuit 39 and memory 33; comparator 43: x equals circuit 39 and y 
equals memory 32; comparator 44: x equals circuit 39 and y equals memory 
31; and comparator 45: x equals circuit 39 and y equals memory 37. The 
logical priority circuit 47 selects that one of the enabled outputs of the 
comparator circuits 41 to 45 having the highest priority. In FIG. 4, the 
order of priority of input to circuit 47 is from top to bottom. 
Thus, circuit 47 can determine that the initial unbalance is too great 
(K1+K2 greater than 5.27 m or the contents of memory 25 detected by 
comparator 41); it can select use of two double tools (K1+K2 equal to or 
less than 3.65 m detected by comparator 42); it can select use of one 
double tool or two single tools (K1+K2 equal to or less than 1.88 m 
detected by comparator 43); it can select use of one single tool (K1+K2 
equal to or less than m detected by comparator 44); it can determine that 
no correction is necessary because unbalance is within the preset 
tolerance (K1+K2 equal to or less than permissible tolerance preset in 
memory 37 detected by comparator 45); and it can determine a value 
subsequently used to determine whether single or double tools should be 
used for mass correction (K1-K2 equal to or less than permissible 
tolerance preset in memory 37 detected by comparator 46). 
With unbalance correction by means of two single tools, it is possible to 
compare, in circuit 48 (which is actually part of circuit 47), the preset 
tolerance with the difference calculated in comparator 40 between the two 
components K1 and K2 so that correction could be carried out with one 
double tool or two single tools, as the case may be. 
If the unbalance position occurs between two laminae and the unbalance can 
be completely compensated by the compensation in two laminae (m.sub.1 
+m.sub.2 =1.88 m), the compensation is made with two individual tools 
whose feed action is controlled separately. If now the unbalance is 
located relatively close to the middle line between two laminae, i.e., the 
two compensation components K.sub.1 and K.sub.2 are nearly equal, a double 
tool can be employed instead of two separately controlled individual 
tools. 
Thus, in the subtractor 40, the difference between K.sub.1 and K.sub.2 is 
determined and inserted in the comparator 46. The comparator 46 compares 
the difference between K.sub.1 and K.sub.2 with the pre-selectable 
tolerance magnitude 37 and inserts the result into the circuit 48. If the 
remaining rest unbalance is smaller than the tolerance, the compensation 
is made with a double tool; if, however, the remaining rest unbalance is 
greater than the tolerance, the compensation must take place with two 
separately controlled individual tools. 
The invention makes it possible to eliminate the unbalance by removing a 
minimum of mass in the shortest possible time. 
While the invention has been described herein in terms of preferred 
embodiments, numerous variations may be made in the arrangement 
illustrated in the drawings and herein described without departing from 
the invention, as set forth in the appended claims.