Patent ID: 7471054

Claim:
A method for detecting unbalanced conditions of a rotating load driven by a synchronous electric motor in washing machines and similar household appliances including a rotatable drum and wherein at least a transient step is provided with angular speed (w) variation of the rotatable drum, the method comprising the following steps: constantly monitoring and detecting the instantaneous current (Iq) absorbed by the motor; calculating in real time the value of an unbalanced mass (m) on the basis of the variation (Δ) of said current (Iq) and starting from a predetermined reference obtained by experimental results and by applying a calculation formula representative of the kind of load imbalance; checking that said value of unbalanced mass is lower than a predetermined acceptable reference value (Δ(Iq 1 ) AMM ) and slowing down the angular speed (w) of said drum in case of negative result; said current (Iq) driving as a feedback signal said motor according to said value of unbalanced mass (m) adjusting the angular revolution speed of the motor in real or continuous time, wherein an imbalance signal is computed as a difference between the last sampled value of the current signal (Iq), in the time instant wherein the absolute value of the first derivate of said current signal (Iq) is less than a predetermined threshold and the second derivate of the same signal Iq is positive, and the last sampled value of said current signal (Iq) in the time instant wherein the absolute value of the first derivate of said current signal (Iq) is less than a predetermined threshold and the second derivate of the same signal Iq is negative.