Balancing machine bearing mounting for flexible rotors

In a bearing mounting for flexible rotors there are provided bearing heads for the journals of the flexible rotors and a foundation to support such bearing heads. For the purpose to influence the natural frequency of the combined system rotor - rotor support which is dependent also on the support stiffness it is desirable to change the support stiffness in the simplest possible manner in such a way that starting from the effects of the flexible rotor to be treated on the signal pick-ups, a control and/or closed loop control of counter-effects is possible to find the balancing quality of a flexible rotor independent of the present support stiffness.

BACKGROUND OF THE INVENTION 
The invention concerns a balancing machine bearing mounting for flexible 
rotors in which the mountings are provided with bearing heads for the 
journals of the flexible rotors and a foundation to support such bearing 
heads. 
Balancing machines for flexible rotors present a problem in that the 
natural frequencies of the unit consisting of the flexible rotor and 
bearing support are also dependent on the stiffness of the bearings in the 
balancing machine. Thus, it is desirable that the bearing stiffness be 
adjusted in the simplest possible manner within wide ranges. 
For this purpose, a substantially rigid bearing mounting for a rotating 
body is known (U.S. Pat. No. 3,754,801) with support for each bearing 
location by means of a spring bar system located in a plane perpendicular 
to the main bearing axis. The overall system consists of spring bars, 
inflexible to tension, compression and buckling but consisting, in one or 
several sections, of spring bars which are flexible to bending and which 
secure the bearing housing against rotational movement around the main 
axis of the bearing and provide equally hard support against the machine 
base in all radial directions. On the other hand, this arrangement permits 
tumbling motions of the rotational axis of the rotating body around two 
axes, perpendicular to one another through the center point of the support 
location. An additional device is provided for purposes of tuning the 
oscillatory system of the test body plus bearing support, namely in such a 
form that additional supports are solidly anchored on one side, spring 
actuated and positively locked to the machine base, and connected at the 
other end to the bearing housing for intermittent tuning, namely via a 
friction connection, which can be remotely controlled and which obstructs 
the tumbling motions of the bearing housing as little as possible. 
Although such a bearing mounting for a balancing machine permits 
adjustment of the spring stiffness of the bearings, it is not suitable for 
direct reaction to the stresses emanating from the rotor to be 
investigated, even though, as is disclosed in this patent, a remote 
control is arranged for the friction connection that is provided. Nor is 
it suitable in order to obtain continuous selection of values for spring 
stiffness and damping. 
SUMMARY OF THE INVENTION 
On the basis of the above prior art, the purpose of the present invention 
is to change the bearing stiffness of a balancing machine within wide 
ranges and, if required, the damping thereof as well, for purposes of 
testing flexible rotors, particularly with respect to their balancing 
qualities. According to the invention, this problem is solved whereby that 
in order to determine the movements of bearing head and/or bearing 
journal, at least one measuring device is provided per bearing journal 
resting in a bearing, that the measurement signal from the measurement 
device acts upon at least one signal transformer, and that at least one 
power source induces corresponding forces in predetermined proportions at 
the bearing heads and/or bearing journals. 
The problem upon which the invention is based can also be solved in such a 
manner that, in order to determine the movement of bearing head and/or 
bearing journal, at least one measurement device per bearing journal is 
provided to determine its support forces. The measurement signal from the 
measurement device acts upon at least one signal transformer, and at least 
one power source induces corresponding forces in predetermined proportions 
at the bearing heads and/or bearing journals. These inventive solutions of 
the problem describe an active balancing machine bearing mounting, 
whereby, on the basis of those effects of the flexible rotors to be 
investigated which act upon measurement transformers, it is possible to 
achieve an adjustment and a control of counter-effects in order to 
determine the balance qualities of a flexible rotor to be investigated, 
independently of a given bearing stiffness, and, on the whole, to achieve 
a selection of spring and damping characteristics of the support. This 
makes it possible, on one hand, to achieve a balancing condition which is 
largely independent of the bearing conditions, and, on the other hand, to 
avoid dangerous conditions in case of approaching resonance or 
instability, and furthermore, it will be possible to make investigations 
into the principles of the rotor behavior with variable bearing 
characteristics. 
Absolute and relative pickups can be equally well applied as measurement 
devices for the movement of bearing head and/or bearing journal, deriving 
the measurement values of the movement from the displacement, from the 
velocity, or from the acceleration of the bearing head and/or the bearing 
journal. To determine the effects of forces, strain gauges, or oil 
pressure, are used as relative recorders. For simultaneous determination 
of the measurement values from bearing head and bearing journal, it is 
preferable, according to the invention, that the measurement values for 
the bearing journals are obtained by non-contacting probes for the bearing 
journal against the bearing head, while the measurement values for the 
bearing head are determined as absolute values. 
The measurement values obtained in this manner are fed to a signal 
transformer, which now, accordingly, generates forces with predetermined 
proportionality. Hereby, the reactive forces may have an absolute effect, 
i.e., be attached to the bearing head, if it is a question of rotating or 
oscillating vibrators, or, they may occur as forces with relative effect, 
if hydraulic pistons, piezo-vibrators, or magnetostrictive vibrators are 
applied. If magnet vibrators are used, they can also be located on the 
bearing journal. Thus, the bearing mounting for a balancing machine 
according to the invention allows control of the bearing stiffness in 
dependence of the rotor to be investigated, as well of its damping, either 
combined or individually. This also makes it possible to immediately 
influence critical conditions triggered during the acceleration to the 
rate of speed of measurement or at the measurement speed proper, either 
due to resonance phenomena between the rotor under investigation and the 
bearing mounting, or to the critical speed of the rotor, namely to such an 
extent that destruction of the balancing machine bearing mounting is 
definitely avoided.

DETAILED DESCRIPTION OF THE INVENTION 
The invention is explained in greater detail with reference to a 
schematically illustrated balancing machine bearing mounting for one 
bearing location of a flexible rotor to be investigated. However, the 
invention is not limited to the individual bearing location represented in 
the execution example, since if the flexible rotor to be investigated 
should have multiple bearing locations, the other bearing locations are 
executed in the same manner. Furthermore, the process control according to 
the invention can be achieved with all mentioned measurement devices with 
absolute and relative effect as well as with all power sources with 
absolute and relative effect, for instance, if the recorder proper makes 
it possible, by itself or in conjunction with a bearing, to measure the 
movement of the flexible rotor. 
In addition, the execution example clarifies only the movement of a bearing 
head by means of a measuring device and further processing of the signals 
obtained there, but not the movement of a bearing journal by itself or in 
conjunction with the measurement of the movement of the bearing head. 
A first movement device 3 and a second measurement device 4 are located on 
a bearing head 1, by which is supported a bearing journal 2 for the 
flexible rotor, e.g., commercially available friction bearing. In the 
present case, it is assumed, that these are measurement devices with 
absolute effect, such as described, for example, in the brochure Schenck, 
Vibration Measuring Equipment, Publication No. A 1076. The bearing head 1 
itself is connected with a base 7 by means of springs 5, 6. The base may 
be the bearing bed of a balancing machine which is not represented. 
When the bearing journal 2 rotates, the first measurement device 3 and the 
second measurement device 4 generate measurement signals which are 
variable as to time due to the rotation of the rotational body. However, 
the measurement signals may also contain a constant component if 
displacement recorders are used, which react to static dislocations. 
Via measurement lines 8, 9, the signals generated by the first measurement 
device 3 and the second measurement device 4 are fed into a signal 
transformer and control unit 10. If required, the signals may be 
influenced here, by means of integration or differentiation over time, so 
that, for example, signals proportional to displacement and velocity will 
be available in parallel. However, each measurement device may also--as 
shown in the figure--contain two systems, which produce speed proportional 
and displacement proportional signals in parallel. Furthermore, if 
desired, signals from several measurement devices may be mixed in the 
signal transformer and control unit in order to obtain the desired 
effects. 
The signals obtained in this manner generally represent the actual values 
of the displacement and/or the velocity at the measurement points. The 
signals are then fed into a control unit and compared with reference 
values 11, 12 which are assumed, as an example, to represent 0 in FIG. 1 
for displacement and velocity. By way of explanation, the expression u is 
the abbreviation for a specified displacement in one measurement 
direction, v is the abbreviation for the other specified displacement in 
the other measurement direction, and u, v represent the time derivations, 
i.e. the velocity in the respective measurement directions. If desired, 
the difference between actual values and reference values multiplied with 
a proportionality factor, are then fed via control lines 13, 14, to 
hydraulic devices 15, 16 which are arranged at right angles to one 
another, namely according to the common rules of control technology. The 
control lines 13, 14 contain the information concerning desired damping 
and stiffness (e.g. the signal portion proportional to displacement or 
velocity) so that the hydraulic devices 15, 16 can be acted upon by 
proportional stiffness and/or proportional damping as selected. As 
relative power sources, the hydraulic devices 15, 16 rest against supports 
17 and 18, respectively. Also, the supports 17 and 18 may constitute the 
foundation for the balancing machine. The oil supply, which is not 
represented in the drawing, is correspondingly controlled by means of 
control valves 20, 21. 
Instead of the supports 17 and 18, absolute power sources may be located 
directly at the bearing head 1, namely as represented by rotating 
vibrators or oscillating vibrators 22, as shown in FIG. 2. For this 
purpose, it is then only required to connect the control lines 13 and 14 
to the vibrators as shown. Such vibrators are described in the brochure 
Schenck Vibration Exciters, Publication No. S 7057. 
If the hydraulic device 15, 16 is utilized, it is to be considered an 
inventive execution that thick-walled cylinders which extremely short 
stroke are utilized there, which cylinders are very rigidly supported. 
Thereby, one obtains extremely high degree of oil spring stiffness, so 
that both stiffness and damping of the bearing head 1 can be adjusted in a 
practically linear manner. 
A preferred embodiment of the invention is to install in a radial plane 
through each bearing the measurement devices of a right angle to one 
another and also to install the power sources at a right angle to one 
another.