Method and device for positioning workpieces to be balanced

A workpiece to be balanced, which during a measuring run is driven or rotating in the coupling-free mode and is provided with a mark for contact-free pick-off to generate a reference signal, is to be positioned subsequently, that the unbalance is at a predetermined location below a marking or correcting device. To this end pulse sequences synchronous with the supporting rollers carrying the workpiece are generated. The pulses are counted in a counter between the reference signal and an unbalance position signal derived from the unbalance signal. For the positioning the counter is counted down to zero by these pulses starting from the reference pulse. When the counter passes through zero the unbalance is in the plane of the pick-off device for detecting the mark.

The invention relates to a method for positioning workpieces to be balanced 
such that the unbalance measured on supporting rollers by means of an 
unbalance measuring machine assumes a predetermined position, wherein 
(a) a reference signal is generated with each revolution of the workpiece, 
when the workpiece assumes a particular, predetermined angular position. 
It is known to measure the unbalance of a workpiece on an unbalance 
measuring machine, wherein the workpiece is disengaged from a driving 
mechanism during measurement and runs down freely (U.S. Pat. No. 
3,076,342). Such a kind of measurement offers the advantage that 
influences of the driving mechanism on the unbalance measurement are 
eliminated. A mark is applied to the workpiece and is picked up by a 
photoelectric pick-off device. The photoelectric pick-off device provides 
a reference signal. The phase of an unbalance measuring signal provided by 
the unbalance measuring machine relative to this reference signal 
corresponds to the angular position of the measured unbalance relative to 
the mark applied to the workpiece. In the U.S. Pat. No. 3,076,342 the 
reading of an unbalance indicating instrument is locked when the running 
out workpiece passes through a nominal rotational speed. This results in 
storage of the measured value. 
It is also known to drive a workpiece to be balanced by means of a belt, by 
compressed air or by an electromagnetic field. In all these cases it is 
not possible to use a driving motor coupled with the workpiece as a 
reference for the unbalance position. Instead a reference signal is 
generated, as in U.S. Pat. No. 3,076,342, by scanning the periphery of the 
workpiece and detecting a mark applied thereto. 
Instead of storing the unbalance measuring signals "mechanically", as in 
the U.S. Pat. No. 3,076,342, the signals may also be stored electrically. 
The electrically stored unbalance measuring signals can be supplied to an 
unbalance correcting machine for automatic unbalance correction (for 
example U.S. Pat. Nos. 3,446,100 or 2,779,217 or 4,214,481). 
For unbalance correction it is necessary to rotate the unbalance into a 
particular position, for example to below a drilling machine, which 
removes material from the workpiece to correct for the unbalance. When the 
measuring run is carried out without positively driving the workpiece, 
this presents certain problems. A mark is applied to the workpiece and 
provides the reference signal and defines a reference longitudinal plane 
of the workpiece. The unbalance measuring machine provides a reading of an 
unbalance position angle, i.e. an angle by which the unbalance is 
angularly spaced from the reference longitudinal plane. It is by no means 
simple to find therefrom the exact spot of the workpiece in which the 
unbalance has to be corrected for. When the workpiece is connected with 
the driving motor in well-defined angular position through a coupling, a 
angle graduation can be provided on the rotor of the driving motor and the 
workpiece can be rotated together with the driving motor into a position 
corresponding to the stored unbalance position angle by means of this 
granduation. If, however, there is no such coupling, this mode of 
positioning is not possible. 
It is known to stick stickers provided with graduations or to attach 
graduated discs with magnetic holding devices to one of the shaft ends of 
the workpiece, centered and such that the origin of the graduation points 
into the direction of the reference signal generating mark. Then the 
workpiece is adjusted after this graduation. As these graduations are 
attached spaced from the correction plane, in which the mark is located, 
it is difficult, in practice, to attach the sticker or the graduated disc 
correctly. Inaccuracies in the transfer of the measured unbalance position 
angle result in errors of the unbalance correction. Thereby additional 
measuring runs and additional correction procedures become necessary. 
Furthermore it is known to attach graduated discs firmly to workpieces to 
be balanced and driven in the coupling-free mode. Also these methods have 
not proved satisfactory in practice. Graduated discs of film or paper can 
get loose during the measuring run and fly away. Sleeves of plastics are 
known which are provided with an angle graduation and are placed on the 
shaft end. Such sleeves can, however, easily be rotated unintentionally. 
Because of their mass and their tolerance of fit they impede the balancing 
accuracy that can be achieved. Thereby the advantage of increased 
balancing accuracy, which is to be achieved by a coupling-free driving 
mechanism, gets lost again. At any rate this method is not useful with 
single workpieces. 
A device is known (German Offenlegungsschrift No. 2,852,468) which is held 
in contact with the periphery of the workpiece at the location of the mark 
generating the reference, signal, or is attached there magnetically. This 
device contains a mass rotatably suspended as pendulum. A pointer is 
affixed to this mass and therefore is always vertical. This pointer is 
movable over an angle graduation provided on the device. When the 
workpiece is rotated and therewith also the device is rotated relative to 
the vertical, the pointer will rotate in front of the angle graduation and 
indicate the angle of rotation of the workpiece. Then the workpiece is 
rotated about its axis, until the pointer indicates, on the angle 
graduation, the measured unbalance angle. The handling of this device is 
impractical or impossible with many types of workpieces. 
Balancing machines are known, wherein during the measuring run on the 
unbalance measuring machine a pulse-like unbalance position signal is 
generated from the usually sinusoidal unbalance measuring signal with each 
revolution of the workpiece, said unbalance position signal having a 
fixed, predetermined phase relation with the unbalance measuring signal. 
Such an unbalance position signal serves to control a stroboscope, which 
illuminates the rotating workpiece. An angle graduation is provided on the 
periphery of the workpiece which permits reading of the position of the 
unbalance, if the workpiece is observed stroboscopically. 
U.S. Pat. No. 4,046,017 discloses a wheel balancing apparatus for balancing 
an out-of-balance wheel that is mounted on a rotatable shaft. This 
apparatus includes force transducers positioned in a horizontal plane 
against resiliently supported bearings for the shaft to thereby detect 
horizontal components of the unbalance forces created by the 
out-of-balance wheel. Photosensitive switches associated with the shaft 
produce phase-displaced analog signals, which signals are supplied to a 
pulse producing circuit for generating a train of count pulses on one of 
two output lines depending on the direction of rotation of the shaft. A 
counter, which has a capacity exactly equal to the number of pulses 
generated by the pulse producing circuit per revolution of the shaft, is 
set when the horizontal component of the unbalance force for a particular 
correction plane associated with the counter equals zero. When a command 
to stop spinning the shaft has been issued, the shaft will slow down until 
it comes to a stop, but the counter will continue to count through each 
cycle of shaft revolution so that it will stop at a position wherein the 
relative rotative position of the unbalanced weight can be determined. A 
digital-to-analog converter responsive to the counter output provides a 
ramp voltage to drive a null meter and thereby permit the operator to 
rotate the wheel after it stops until the position of weight unbalance for 
the particular correction plane is provided in the predetermined location 
for providing a corrective weight--as is ascertained by bringing the null 
meter to the null position. 
In this prior art apparatus, the body to be balanced is not mounted on 
supporting rollers and there is no coupling-free rotation during the 
measuring run. The body to be balanced is affixed to a shaft which forms 
part of the balancing apparatus. There is no reference mark on the body to 
be balanced. Thus the unbalance cannot be measured, while the body to be 
balanced is rotating freely from any drive mechanism. Once the body has 
been removed from the balancing apparatus, the measured unbalance position 
gets lost. 
Similar balancing machines are disclosed in German Auslegeschrift No. 27 24 
696 and German Offenlegungsschrift No. 25 18 459. 
Eventually it is known to mount the workpiece to be balanced on pairs of 
supporting rollers (German Pat. No. 632,893, U.S. Pat. No. 2,779,217). 
It is the object of the invention to provide a method and a device for 
positioning workpieces to be balanced which permits positioning of any 
type of workpieces without the need of attaching thereto any additional 
components, graduated discs or the like. 
The method of the invention is characterized in that 
(b) during the measuring run on the unbalance measuring machine, an 
unbalance position signal is generated with each revolution of the 
workpiece from an unbalance measuring signal, said unbalance position 
signal having a fixed, predetermined phase relation with the unbalance 
measuring signal, 
(c) with each revolution of the supporting rollers a sequence of angle 
increment signals synchronized therewith is generated, each one of which 
corresponds to a fixed angle increment of the supporting roller, 
(d) during the measuring run, these angle increment signals are counted 
from the reference signal to the unbalance position signal and the number 
thereof is stored, and 
(e) for the subsequent positioning, the workpiece is rotated in the 
direction of rotation of the measuring run starting from a predetermined 
angular position through an angle which is a function of the stored number 
of angle increment signals. 
Thus a measure of the rotation to be made is derived from the rotation of a 
supporting roller on which the workpiece to be balanced is mounted. The 
angle of rotation of the supporting roller is determined by counting the 
angle increment signals which have been counted from the reference signal 
to the unbalance position signal. The angle of rotation of the supporting 
roller associated with a particular angle of rotation of the workpiece and 
thus the number of the angle increment signals depends on the ratio of the 
diameters of the workpiece and of the supporting roller. If, however, the 
workpiece is positioned on the same or identical (i.e. equal diameter) 
supporting rollers, this ratio will cancel out. A device for carrying out 
the method with an unbalance measuring machine, in which the workpiece is 
mounted on supporting rollers, comprising 
(a) a contact-free pick-off device which is arranged to pick-off a mark on 
the workpiece to generate a reference signal, the mark being detected by 
the pick-off device in said predetermined angular position 
is characterized in that 
(b) a device for generating unbalance measuring signals is provided, which 
represent, both with respect to amount and position, the unbalance to be 
measured, and 
(c) a signal shaping circut is provided to which the unbalance measuring 
signal is applied to generate a pulse-like unbalance position signal which 
has a fixed, predetermined phase relation with the unbalance measuring 
signal, 
(d) an angle increment signal generator is provided at least one supporting 
roller of the unbalance measuring machine, and generates a sequence of 
angle increment signals, which are synchronized with the supporting roller 
and each one of which corresponds to a fixed angle increment, 
(e) the angle increment signals are applied to a counter, which is arranged 
to be switched on by the reference signal and to be switched off by the 
unbalance position signal, and 
(f) means are provided for rotating the workpiece, starting from a 
predetermined angular position, in which the mark generates the reference 
signal, through an angle, which is a function of the number of angle 
increment signals stored in the counter. 
Modifications of the method are subject matter of sub-claims 2 to 7. 
Modifications of the device are subject matter of sub-claims 9 to 15.

Referring to FIGS. 1 and 2, workpiece 10 to be balanced is mounted in 
bearings 12 and 14. as can be seen from FIG. 2, each bearing 12 and 14 
comprises two supporting rollers 16 and 18, which are mounted easily 
rotatably on a vibration bridge 20. 
The vibration bridge 20 is located in conventional manner between two 
parallel surfaces 22 and 24 of a pedestal. A force measuring pick-up 26 is 
arranged in front of surface 24. The vibration bridge 20 is pressed 
against the force measuring pick-up 26 by a spring 28. In similar manner 
the bearing 14 is constructed with a force measuring pick-up 30 and a 
spring 32. 
In FIG. 2 it has been assumed that the workpiece 10 has an unbalance 34. A 
mark 36 is provided on the periphery of the workpiece 10. This mark is 
picked-off by a photoelectric pick-off device. 
The workpiece 10 is driven in appropriate manner, the measurement being 
made in the coupling-free mode. This can be done in the manner described 
in U.S. Pat. No. 3,076,342 or by belt, compressed air or rotary field 
drive. The unbalance 34 creates a centrifugal force directed radially 
outwards, of which the respective horizontal component becomes effective 
on the force measuring pick-up 26. The horizontal component varies 
sinusoidally during rotation of the workpiece 10. The force measuring 
pick-up 26 generates a sinusoidal voltage therefrom. The centrifugal force 
is measured in the bearing planes, while the correction of the unbalance 
is effected usually in correction planes different therefrom. Therefore a 
signal processing circuit 40 is provided which computes the unbalances in 
the correction planes from the forces measured in the bearing planes. This 
signal processing circuit may, for example, be of one of the types 
disclosed in U.S. Pat. No. 2,815,666, U.S. Pat. No. 2,962,899 or U.S. Pat. 
No. 3,159,034. In the signal processing circuit also the angular position 
of the unbalance 34 relative to the mark 36 is determined from the phase 
of the a.c. voltage obtained relative to the signals received from the 
pick-off device. The informations thus obtained are stored in a signal 
memory 42. 
From the sinusoidal a.c. voltage the phase of which depends on the position 
of the unbalance in the correction plane a sequence of pulse-like signals, 
the phase of which is determined by the phase of the a.c. voltage is 
generated in a signal shaping circuit 44. This signal shaping circuit 44 
can be similar to the signal shaping circuits in the prior art unbalance 
measuring machines mentioned above, wherein the angular position of the 
unbalance is determined by having a stroboscope controlled by the a.c. 
voltage generated by the unbalance. 
An angle increment signal generator 46 is coupled with the supporting 
roller 18, as shown in FIG. 2. To this end a frictional wheel 48 with a 
friction coating 50 engages the supporting roller 18. The frictional wheel 
48 carries a code disc or drum 52 which is scanned optically or 
magnetically by a pick-off device 54, as schematically illustrated in FIG. 
2. 
The angle increment signal generator 46 provides with high resolution an 
angle increment signal in the form of a pulse with each angle increment, 
as is illustrated in simplified form by the pulse sequence 56 in FIG. 3. 
Actually the number of pulses generated with one complete revolution 
(2.pi.) of the workpiece 10 is substantially higher than in FIG. 3. 
The angle increment signals 56 from the angle increment signal generator 46 
are applied to a counter 60 through line 58. The counter 60 is arranged to 
be switched on by the reference signal 62 (FIG. 3) from the pick-off 
device 38 through line 64, and to be switched off by an unbalance position 
signal 66 (FIG. 3) from the signal shaping circuit 44 through line 68. 
Thus the counter 60 counts a pulse sequence 70 (FIG. 3) the number of 
which is proportional to the time between reference signal 62 and 
unbalance position signal 66 and thus proportional to the angle between 
mark 36 and unbalance 34. The ratio of the diameters of frictional wheel 
48 and supporting roller 18 and the usually unknown ratio of the diameters 
of the supporting roller 18 and the shaft of the workpiece 10 enter into 
the proportionality factor. These ratios, however, cancel out with the 
positioning, as will become apparent hereinbelow. 
By the unbalance position signal the count is moved to a memory 72 through 
a gate 70. The counter is reset for the next count. This is known 
technique and therefore is not described in detail. A mean taking device 
74 takes a mean value m.sub.n of the numbers m.sub.i of angle increment 
signals counted and stored during a plurality of consecutive revolutions 
of the workpiece 10. The mean value m.sub.n is stored in a memory 76. The 
value stored in the memory 76 is displayed by a display device 78. 
After the measuring run the workpiece 10 is stopped. Now the unbalance 34 
is to be rotated into a well-defined, for example horizontal, position. 
This procedure is called "positioning" of the workpiece. 
In order to position the workpiece, a switch 80 is actuated, while the 
counter 60 and the mean taking device 74 are switched off and no longer 
affect the state of the memory 76. 
When the workpiece 10 is rotated now, the angle increment signals 46 are 
applied to one input 82 of an AND-gate 84. The other input 86 of the 
AND-gate 84 is, at first, still in its state "L" (low), whereby the 
AND-gate 84 is non-conducting at first. When the mark 36 passes by the 
pick-off device 38, the latter provides a reference signal. This reference 
signal now sets flip-flop 88 through the closed switch 80. Flip-flop 88 
applies a signal "H" (high) to the input 86 of the AND-gate 84. Thereby 
the AND-gate passes the angle increment signals from the angle increment 
signal generator 46 to a "down" input 90 of the memory 76, which is 
constructed similar to a counter. When the memory has been counted down to 
zero, it provides a signal at an output 92. A positioning indicator may be 
controlled by this signal to indicate that the workpiece has now been 
positioned properly, and the unbalance 34 is in a predetermined position, 
namely in the plane of the pick-off device 38. The workpiece may, however, 
also be positioned by means of the display device 78 which permits 
reading, when the memory or counter 76 passes through zero. Instead or in 
addition thereto the signal at the output 92 may serve to actuate a 
marking device 96, by which a mark is applied to the workpiece 10 at the 
location of the unbalance 34 for later unbalance correction. 
As it is possible that the workpiece 10, when it is being positioned, is 
rotated beyond its end position and is then rotated back, the angle 
increment signal generator is preferably adapted to generate signals 
depending on the sense of rotation. The memory or counter 76 is a 
bidirectional counter the direction of counting of which is determined by 
the signals depending on the sense of rotation, as a function of the sense 
of rotation of the workpiece 10. When the workpiece 10 is rotated in the 
direction of the arrow in FIG. 2, in which direction it rotates also 
during the measuring run, the memory or counter 76 will be counted down. 
Then the counter reading becomes zero, when the unbalance 34 is in the 
plane of the pick-off device 38, thus is horizontal in FIG. 2. If the 
workpiece 10 is rotated in opposite direction, the memory or counter 76 is 
counted up again. The angle increment signal generator 46 can, for 
example, be of the type disclosed in U.S. Pat. No. 3,902,063. 
The mean taking device 74 can be constructed such that the numbers m.sub.1, 
m.sub.2 . . . m.sub.n, of which the mean is to be taken, are compared with 
each other and only such numbers are utilized for taking the mean, the 
deviations of which from the others or from the mean value of the others 
are below a predetermined threshold "a". An error signal is triggered, 
when a deviation is above the threshold "a". 
A possible embodiment of the mean taking device 74 is illustrated in FIG. 
4. 
A number m.sub.n+1 of counted angle increment signals is compared in a 
comparator 98 to a formerly taken mean value 
##EQU1## 
If .vertline.m.sub.n+1 -m.sub.n .vertline.&lt;a, "a" being a threshold, a gate 
100 will be opened and m.sub.n+1 is passed to the mean taking circuit 102 
for computing a new mean value. If .vertline.m.sub.n+1 -m.sub.n 
.vertline.&gt;a, an error signal will be generated, as indicated by block 
104. 
FIG. 5 shows another embodiment with an unbalance measuring machine 110 and 
an unbalance correcting machine 112 separate therefrom. The unbalance 
measuring machine 110 serves to determine the unbalance of a workpiece 114 
to be balanced. Subsequently the workpiece 114 is placed on the unbalance 
correcting machine 112 and is positioned, and then the unbalance is 
corrected by means of a drilling machine. 
As has been described with reference to FIGS. 1 and 2, the components of 
the centrifugal forces are measured in the bearing planes by pick-ups 
118,120. The signals from the pick-ups 118,120 are supplied to a signal 
processing circuit 122. The signal processing circuit provides a.c. 
voltages which are analog to the unbalances in the correction planes. A 
pick-off device 124 detects a mark 126 on the workpiece 114 and generates 
a reference signal. The signal processing circuit 122 provides measured 
values of the amount and, if desired, of the position of the unbalance, 
which are stored in a memory 128. A signal shaping circuit 130 generates, 
from said a.c. voltage, a pulse-like unbalance position signal. In this 
respect the unbalance measuring machine 110 of FIG. 5 is identical with 
the unbalance measuring machine of FIG. 1. 
Also the mounting of the workpiece 114 on the supporting rollers and the 
construction of an angle increment signal generator 132 coupled with the 
support rollers corresponds substantially to the embodiment of FIG. 2. 
With the embodiment of FIG. 5 the angle increment signals from the angle 
increment signal generator 132 are applied to a bidirectional counter 134. 
The counter 34 is switched on by the reference signal from the pick-off 
device 124 and is switched off by the pulselike unbalance position signal 
from the signal shaping circuit 130. Thus, a number of angle increment 
signals proportional to the angle between mark and unbalance is counted in 
the counter, as illustrated in FIG. 3. 
The workpiece 114 is then placed on the unbalance correcting machine 112. 
The unbalance correcting machine 112 has supporting rollers which are 
identical with (i.e. have the same diameter as) the supporting rollers of 
the unbalance measuring machine 110 and correspond substantially to the 
arrangement of FIG. 2. As in FIG. 2, an angle increment signal generator 
is coupled with one supporting roller. 
The mark 126 of the workpiece 114 is detected by a pick-off device 136, 
which is similar to the pick-off device 124 and provides a reference 
signal for the positioning. The reference signal from the pick-off device 
136 sets a flip-flop 138. Thereby a signal H is applied to one input 140 
of an AND-gate 142, the other input 144 of which is connected to the angle 
increment signal generator 132. The output of the AND-gate 142 is 
connected to a count down input 146 of the counter 134. The counter 
controls, through a switch 148, a driving mechanism 150 which is arranged 
to rotate the workpiece 114 slowly. 
When the switch 148 is closed, the drive mechanism rotates the workpiece 
114. The angle increment signal generator 132 generates angle increment 
signals which, however, at first do not reach the count-down input 146 of 
the counter 134, as the AND-gate 142 is closed by the signal L at the 
input 146. When the mark 126 passes by the pick-off device 136, the 
reference signal sets the flip-flop 138, and the AND-gate gets the signal 
H at its input 140. It allows the angle increment signals to pass to the 
count down input 146 of the counter 134. The counter 134 is counted down 
to zero and then stops the drive mechanism 150. Then the unbalance is in 
the plane of the pick-off device 136. This plane contains also the 
drilling machine 116, which in FIG. 5 has been illustrated offset by 
180.degree. for clarity. 
With different workpieces different numbers of angle increment signals are 
associated with a certain angle of rotation of the workpiece 10 or 114, 
depending on the diameter of the shaft of the workpiece. As, however, the 
workpiece is mounted, with the measuring run and with positioning, on 
identical or similar supporting rollers, this does not affect the 
measurement and positioning: Equal numbers of angle increment signals, at 
any rate, correspond to equal angles of rotation of the workpiece. 
The angle increment signal generator can form part of the supporting 
roller. 
The angle increment signal generator 46 in FIG. 1 may be a stepping motor. 
If such a stepping motor is rotated, it generates angle increment signals. 
This same stepping motor can then be used to position the workpiece 10. To 
this end pulses are applied to the stepping motor, whereby the stepping 
motor positions the workpiece 10 through the supporting roller 18. These 
pulses, at the same time, become effective as angle increment signals on 
line 58. The pulses applied to the stepping motor can be switched off, 
when the memory 76 has been counted down to zero. 
In the embodiment of FIG. 5 a stepping motor for positioning the workpiece 
114 can be coupled with one of the supporting rollers of the unbalance 
correcting machine 112. This stepping motor can, at the same time, 
represent the angle increment signal generator, the stepping signals 
supplied to the stepping motor serving as angle increment signals. The 
functions of the components 135 and 150 of FIG. 5 are then combined in 
component 150 which provides the angle increment signals too, as has been 
indicated by the dashed line 152. Component 135 and the line from it to 
the input 144 can then be omitted. 
Of course, also the angle increment signal generator 132 may be a stepping 
motor.