Kako podijeliti ukupno dopušteni ostatni neubalansirani dio između dva nivoa
For a two-support rotor, the total permissible residual unbalance (U_{mathrm{per}}) is distributed between two correction planes based on rotor geometry and the rotor center of mass (CM) position. Below are the core rules from ISO 21940-11, including the 70:30 limitation set out in Clause 7.2.2 of the standard.
Definitions
- (U_{mathrm{per}}): total permissible residual unbalance for the rotor.
- (U_{mathrm{per}A}), (U_{mathrm{per}B}): permissible residual unbalance allocated to planes A and B.
- (L): rastojanje između nivoa A i B.
- (L_A): rastojanje od centra mase do nivoa A.
- (L_B): rastojanje od centra mase do nivoa B.
- Geometrijska veza: (L = L_A + L_B).
1) Simetričan rotor
Ako je rotor simetričan i centar mase se nalazi približno na sredini između nivoa, podijelite dozvolu ravnomjerno:
(U_{mathrm{per}A} = U_{mathrm{per}B} = dfrac{U_{mathrm{per}}}{2})
Ova metoda se primjenjuje na većini standardnih slučajeva gdje je rotor blizu simetričan.
2) Asimetričan rotor (pravilo poluge)
Ako se centar mase pomjeri prema jednoj oslonskoj točki, distribuirajte dozvolu koristeći pravilo poluge, proporcionalno rastojanju od centra mase do suprotnog nivoa:
(U_{mathrm{per}A} = U_{mathrm{per}} cdot dfrac{L_B}{L})
(U_{mathrm{per}B} = U_{mathrm{per}} cdot dfrac{L_A}{L})
Ovdje je (L) rastojanje između nivoa, a (L_A) i (L_B) su rastojanja od centra mase do nivoa A i B redom.
Važno ograničenje: pravilo 70:30
To avoid extreme accuracy requirements in one plane, ISO 21940-11:2016 (Clause 7.2.2) stipulates for inboard rotors — i.e. with the centre of mass located between the bearing planes — that the split shall be limited to a 70:30 ratio. Even if the CM is very close to one plane/support:
- The smaller share should not be less than (0.3 cdot U_{mathrm{per}}).
- The larger share should not exceed (0.7 cdot U_{mathrm{per}}).
(0.3 cdot U_{mathrm{per}} le U_{mathrm{per}A},, U_{mathrm{per}B} le 0.7 cdot U_{mathrm{per}})
Note: these limits apply to inboard rotors. For outboard (overhung) rotors, Clause 7.2.3 of the standard allows the larger share to reach (1.3 cdot U_{mathrm{per}}), while the smaller share must still be at least (0.3 cdot U_{mathrm{per}}).
Calculator
Enter (U_{mathrm{per}}) and distances. The calculator supports symmetric split and lever-rule split. It also applies the 70:30 limitation when enabled.
