A personal care appliance 10 comprises an actuator 14, a current sensor 28 for monitoring a driving current, and a controller 24. The actuator 14, operable according to a non-linear response characteristic 58 of amplitude versus frequency, includes a movable shaft 18 configured for resonant movement 38 in response to a drive signal 25, further for being coupled with a workpiece 20. The controller 24 (i) detects at least one of a plurality of different characteristic load states (100,102,104,106,108,110) in response to a perturbation in the monitored driving current 29 and (ii) actively delivers the drive signal 25 to the actuator 14 selected from at least two different drive signals (66,70) as a function of a detected characteristic load state. In this manner, the controller 24 implements self-adaptive amplitude regulation of the movable shafts resonant movement 38 among the plurality of difference characteristic load states that include additional loads of force, spring, mass, and/or damping to a given load state of a resonant spring mass system of actuator 14 coupled with workpiece 20.
