Measuring and testing – Rotor unbalance – Dynamic
Reexamination Certificate
1999-03-15
2002-07-09
Kwok, Helen (Department: 2856)
Measuring and testing
Rotor unbalance
Dynamic
C073S660000
Reexamination Certificate
active
06415661
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 198 11 101.0, filed on Mar. 13, 1998, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to balancing of flexible rotors, more specifically, to ascertaining unbalance compensating values that represent an unbalance of an elastic rotor and are required for an unbalance compensation of the elastic rotor. The invention further relates to ascertaining coefficients which have an influence on the balancing of unbalanced elastic rotors, which normally have a rigid behavior in a low r.p.m. range.
BACKGROUND INFORMATION
In order to balance rigid rotors having a simple cylindrical shape and rotating at a low r.p.m., it is customary to measure the resulting unbalance of all individual unbalances generally in the left bearing or support plane and in the right bearing or support plane. If a balancing is necessary, the measured resultant of the unbalances are compensated in two balancing planes. The balancing planes define locations around the rotor where balancing weights are to be applied. As a result of the compensation by the attachment of balancing weights, a rigid rotor rotates free of vibrations otherwise caused by an unbalance and free of bearing forces. Generally, non-symmetric masses are distributed over the entire length of a rotor. As a result, internal bending moments remain in the rotor due to centrifugal forces produced by individual unbalances. In connection with elastic rotors, such internal bending moments can cause forces that rise with the square of the r.p.m., thereby leading to unpermissibly large deformations which in turn cause unbalance effects. This fact can cause a dangerous situation, especially when the operational r.p.m. approaches a bending critical r.p.m. which could without damping cause an infinitely large bending or a permanent deformation of the rotor.
Theoretically, a rotor or a shaft has infinitely many critical r.p.m.s. In order to evaluate or judge the vibration characteristic at a definite r.p.m. only those critical r.p.m.s are taken into account which cause corresponding bending configurations or “modal shapes” that become troublesome. With regard to practical considerations, frequently it is sufficient for many rotor types to take but one critical r.p.m. into account which excites a rotor to assume a wave elasticity. However, under certain circumstances it may be necessary to take several critical r.p.m.s into account. A simple roller shaped or cylindrical rotor will bend in the shape of a U when approaching the first critical r.p.m. Such a simply rotor will bend into an S-configuration when approaching the second critical r.p.m. Such a simple rotor will bend into a W-configuration when approaching the third critical r.p.m. These bending configurations at critical r.p.m.s are referred to as “modal shapes” of the rotor.
One must count on the occurrence of elastical deformations the more so the higher the operational r.p.m. is. Thus, it is the aim of a balancing operation to reduce unbalance forces to a tolerable level over the entire permissible operational r.p.m. range. Such unbalance forces involve rigid body forces and forces caused by the wave elastic deformation or deflection of the rotor. These forces must be reduced to a tolerable level by the balancing operation or unbalance compensation. In practice, there are known several balancing methods which take into account such wave elastic characteristics of rotors.
One such method has become known from an article by K. Federn entitled “Overview Over Current Approaches, Guidelines, Standards, and Customary Methods for Balancing Wave Elastic Rotors”, VDI-Reports No. 161, 1971, pages 5 to 12. The just mentioned article describes a balancing in a plurality of measuring or sensing planes with a compensation in n+2 balancing or compensation planes. The balancing itself may be performed manually by applying the required balancing weights. In this connection it is necessary to perform a balancing operation in at least n+2 compensating or balancing planes if n-critical r.p.m.s are taken into account. According to Federn, first a conventional rigid body balancing operation is performed. Only then modal unbalances are eliminated with the aid of generally several test load sequences or test load runs. Such methods rely heavily on the experience and dexterity of the operator which effect the number of balancing sequences or runs required in order to achieve an optimal running characteristic at the operational r.p.m. of the rotor after the unbalance compensation is completed. As a rule, however, there are always a larger number of measuring sequence or runs required in order to achieve a good balancing result.
A textbook by W. Kellenberger, “Elastic Balancing”, Berlin, 1987, pages 317 to 325, describes a computer aided balancing method with test loads or test weights applied to the rotor sample for ascertaining influence coefficients. The Kellenberger method eliminates or at least reduces the rigid body compensation and the wave elastic bending by compensation masses calculated in common for both types of deformations. For performing the method, an initial unbalance measuring sequence or test run is performed, whereupon at least as many further unbalance measuring sequences or test runs with test weights are required as balancing planes are provided. Thus, at least four unbalance measuring sequences are required when considering the first critical r.p.m. of the rotor to be balanced. According to the Kellenberger method the influence coefficients that are measured in the several measuring sequences with testing weights, are stored in the memory of the computer. Hence, these influence coefficients can be used for subsequent testing of the same type of rotors under favorable circumstances so that only one unbalance measuring sequence needs to be performed. In any event, for all first time balancing operations of rotors, these rotors must be loaded with testing weights and the number of measuring runs with testing weights must correspond to the number of compensation or balancing planes that are to be taken into account.
A report by R. Gasch and J. Drechsler, entitled “Modal Balancing of Elastic Rotors Without Applying Testing Weights”, VDI-Reports No. 320, 1978, pages 45 to 53, describes a method that ascertains the required compensating or balancing masses without the above described testing weight measuring sequences in order to compensate for wave elastic deflections of the rotor. Gasch et al. suggest to first perform a rigid body balancing followed by an unbalance measuring sequence all the way into the critical r.p.m. ranges that must be taken into account and to thereby measure the rotor deflections with the aid of displacement pick-ups positioned at predetermined rotor locations. With the aid of the stored or registered elastic deflections of the rotor shaft and with the knowledge of the modal shape and the corresponding generalized masses, it is possible to identify, computer aided, modal unbalance components and to calculate respective compensating weights. Such a method has the disadvantage that first a conventional rigid body compensation must be performed and only thereafter it is possible to eliminate modal unbalances by additional measuring and compensating processes.
German Patent Publication DE 4,133,787 A1 discloses another balancing method for elastic rotors, wherein the compensation masses required for balancing are ascertained without the use of measuring sequences with testing weights, for compensating rigid body unbalances and wave elastic deflections of the rotor. The rotor to be balanced is first run for one unbalance measurement at an r.p.m. at which the rotor exhibits rigid body characteristics, whereby first at least one unbalance measured value is obtained. Then, at least one further unbalance measured value is obtained for each support or bearing plane and for each modal shape to be compensated. T
Fasse W. F.
Fasse W. G.
Kwok Helen
Schenck RoTec GmbH
LandOfFree
Ascertaining information for compensating an unbalance of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ascertaining information for compensating an unbalance of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ascertaining information for compensating an unbalance of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2878353