Personal hygiene device

1. A personal hygiene device, extending in a 3-dimensional space that is spanned by an x-y-z coordinate system, the device comprising:

a drive unit having a support and a stator fixedly mounted at the support;

an armature that is spring-mounted at the support for driven linear oscillating motion along a first longitudinal direction that is parallel to or coincides with the x-axis of the x-y-z coordinate system, the armature having a center of gravity located in rest at a coordinate [x a , y a , z a ] and a drive shaft fixedly coupled with the armature, the drive shaft having a center of gravity located in rest at a coordinate [x d , y d , z d ];

a first treatment head assembly detachably connected to the drive shaft, the first treatment assembly having a center of gravity located in rest at a coordinate [x t1 , y t1 , z t1 ] and a secondary mass element spring-mounted at the support for essentially linear oscillating motion along the first longitudinal direction, the secondary mass element having a center of gravity located in rest at a coordinate [x m , y m , z m ];

wherein at least the coordinate [x a , y a , z a ] of the center of gravity of the armature has an offset in at least one of the y-direction and z-direction with respect to the coordinate [x d , y d , z d ] of the center of gravity of the drive-shaft or with respect to the coordinate [x t1 , y t1 , z t1 ] of the center of gravity of the first treatment head assembly, wherein y a ≠y d and/or y a ≠y t1 and/or z a ≠z d and/or z a ≠z t1 , and the secondary mass element is configured such that the coordinate [x m , y m , z m ] of the center of gravity of the secondary mass element is aligned with coordinate [x j , y j , z j ] of a joint center of gravity of a combination of the drive shaft, the first treatment head assembly, and the armature in the at least one offset direction, wherein y m =y j and z m =z j , so that a line connecting the coordinate [x m , y m , z m ] of the center of gravity of the secondary mass element and the coordinate [x j , y j , z j ] of the joint center of gravity is parallel to or coincides with the x-axis,

wherein an alignment of the coordinates in the offset direction has a residual offset of from 5 μm to 100 μm.

2. The device of claim 1 , having a handle housing that can be grasped by a hand of a user and a first treatment head housing that is detachably attached to an attachment portion of the support.

3. The device of claim 2 , wherein the support of the drive unit is mounted for a pivoting motion around a pivot axis with respect to the handle housing such that the pivot axis is generally parallel to the y-axis of the x-y-z coordinate system and a resilient element is arranged between the handle housing and the support to provide a restoring force against the pivoting motion and wherein a pressure or force applied at the first treatment head housing having a pressure or force component along a direction parallel to the z-axis of the x-y-z coordinate system leads to a pivoting motion of the support around the pivot axis against the restoring force of the resilient element.

4. The device of claim 3 , wherein the support is coupled with a pressure sensor or force sensor for measuring the pressure or force applied at the first treatment head housing based on the deflection of the support with respect to the handle housing.

5. The device of claim 2 , wherein the first treatment head assembly is movably mounted at the first treatment head housing and the first treatment head assembly and the first treatment head housing together form a first replacement head.

6. The device of claim 5 , wherein the first treatment head assembly comprises a first motion transmitter that is detachably coupled with the drive shaft and with a first treatment head that is movably mounted at the first treatment head housing for driven oscillatory rotation around a rotation axis that is parallel to the z-direction.

7. The device in accordance with claim 6 , wherein the motion transmitter and the drive shaft are coupled by a magnetic coupling.

8. The device of claim 5 , wherein the drive unit is arranged to drive the first treatment head assembly with a frequency selected from the group consisting of a frequency between 100 Hz and 200 Hz, a frequency between 120 Hz and 170 Hz, and a frequency between 140 Hz and 150 Hz.

9. A personal hygiene device kit comprising the device of claim 5 , the kit comprising at least a second replacement head comprising a second treatment head housing and a second treatment head assembly, wherein in the attached state the center of gravity of the second treatment head assembly has a coordinate [x t2 , y t2 , z t2 ] that has an offset with respect to the coordinate [x t1 , y t1 , z t1 ] of the center of gravity of the first treatment head assembly in at least one of the y-direction or z-direction or where the first treatment head assembly has a weight that is different to the weight of the first treatment head assembly.

10. The device of claim 1 , wherein a ratio of the weight of the support and parts mounted at the support to the weight of the handle and parts mounted at the handle other than the support is 0.2 or below.

11. The device of claim 1 , wherein the secondary mass element is made from stacked metal sheets.

12. The device of claim 1 , wherein the armature and the secondary mass element are mounted at the support by leaf springs that each extend at rest in a plane parallel to the y-z plane of the x-y-z coordinate system.