Force sensor providing continuous feedback for a resonant drive toothbrush using a hall sensor

The power toothbrush includes a handle portion which includes a power drive assembly and a brushhead assembly (32) which includes a brushhead arm (36) and a brush element (38) at a distal end thereof. A V-spring assembly (14) converts the action of the power drive assembly to drive the brushhead assembly in a back-and-forth action. A mounting member (55) at the rear end of the V-spring assembly provides a base for a magnet (56). The V-spring assembly and the brushhead assembly comprises a unit which moves about a pivot point at the forward end of the V-spring assembly, so that the back end of the V-spring assembly is displaced in accordance with pressure applied to the brush member. A Hall effect sensor (58) is mounted within the changing magnetic field produced by the magnet as the rear end of the V-spring assembly is displaced due to pressure on the brushhead. A processor (65) is responsive to the output from the Hall sensor and stored information to produce a signal indicative of the pressure on the brushhead and to provide an indication of when the pressure exceeds a threshold value.