Abstract: Improved force generator (FG) devices and methods are provided herein. A FG device (10) includes a housing (16, 18), a shaft (S) centrally disposed within the housing, and multiple imbalance rotors (30, 32, 34, 36, 38) disposed within the housing and provided along the shaft. At least two pairs (PA, PB) of imbalance rotors are provided in a nested configuration with respect to each other along the shaft. The at least two pairs (PA, PB) of imbalance rotors are supported in the nested configuration by large and small bearings (BA, BB). Any two imbalance rotors are paired to rotate together in a same direction according to a desired vibration canceling force. A method of controlling vibration within a structure is provided. The method includes detecting vibration, receiving a force command at a FG device, and pairing any two imbalance masses together and rotating a pair of imbalance masses via the rotors together in a same direction to cancel the detected vibration.