  The paper presents an improved mass balancing procedure for fast rotating
machinery, while it is being rotated at speeds considerably slower than the
"critical speeds", where dangerously high vibration amplitudes may arise. By
utilizing tuned dual frequency parametric excitation along with optimized
nonlinear feedback terms, the slow imbalance forces are projected onto a chosen
mode of vibration. This allows to identify the imbalance projection on that
specific mode, and to cancel these forces by adding or reducing mass. The
scheme benefits from two kinds of parametric excitation yielding combination
and principal parametric resonances. The former is used to project the
imbalance forces onto a selected vibration mode, and the latter significantly
amplifies the response. By tuning the parametric excitation and the nonlinear
terms in an optimal manner, a pseudo-linear behavior is formed. This behavior
enables to increase both amplification and sensitivity to the imbalance forces
without having to compromise between the two.
