CN116917643A - Drive unit and personal care device having a drive unit - Google Patents

Abstract

The application relates to a drive unit arranged for converting rotational movement into linear reciprocating movement in operation, the drive unit having: a motor having a motor shaft, the motor being arranged in operation to provide rotational movement of the motor shaft about a longitudinal axis of the motor shaft; a motor shaft extension comprising at least a first eccentric shaft element arranged eccentrically with respect to the longitudinal axis of the motor shaft such that, in operation, the first eccentric shaft element moves on a circle around the longitudinal axis of the motor shaft, the circle extending in a plane perpendicular to the longitudinal axis; at least one elastically deformable unit having a coupling element arranged for coupling with a driven element, wherein the first eccentric shaft element is coupled with the deformable unit to periodically deform the deformable unit such that a longitudinal position of the coupling element of the deformable unit in the direction of the longitudinal axis of the motor shaft is periodically changed, and wherein the deformable unit has: a first arm section having a first end and a second end; and a second arm section having a first end and a second end, wherein the second end of the first arm section and the first end of the second arm section are connected to each other, wherein the first end of the first arm section is connected to a mounting structure that is fixed relative to the motor, and the second end of the second arm section is arranged at a distance from the first end of the first arm section in the direction of the longitudinal axis of the motor shaft.

Description

Drive unit and personal care device having a drive unit

Technical Field

The present disclosure relates to a drive unit comprising a motor having a motor shaft which is driven in rotation and which comprises a motion converter for converting a rotational motion into a reciprocating motion. The present disclosure also relates to a personal care device comprising such a drive unit to drive a driven element of the personal care device in a reciprocating or oscillating motion.

Background

It is generally known to convert rotational movements, which can be provided by the shaft of a DC motor, into oscillating movements by means of a suitable gear mechanism, for example by means of a four-bar linkage as described in DE 3937854 A1.

It is also known to provide a conversion mechanism with the above-described functions by an arrangement comprising fewer gears. DE 3430562C1 describes a device for converting the rotary motion of an eccentric driven by a motor shaft into a reciprocating motion of a working tool of an electrically driven small electrical appliance. The switching mechanism comprises a connecting rod which is connected to the eccentric and to the first lever arm of the double-arm rocker. The connecting rod includes a film hinge having a central axis intersecting a longitudinal axis of the first lever arm. The first lever arm is designed to be elastically torsionally movable about its longitudinal axis. The double arm rocker is pivotally mounted at the housing of the appliance and further includes a shaft pin coupled with the work tool. In operation, the shaft pin moves in an oscillating wiping motion relative to the pivotal mounting of the double armed rocker.

Document US4367658A1 describes a bell crank lever having substantially rigid lever arms substantially at right angles to each other, which are connected to a fixed part by means of film hinges fixed near the junction of the lever arms and defining a bending axis at right angles to the plane of the bell crank lever. An oscillating arm is fixed to a free end of one of the lever arms and extends substantially parallel to the other of the lever arms and is bendable in and at right angles to the plane of the bell crank lever about a film hinge defining bending axes at right angles to each other. The oscillating beam is connected to the other of said lever arms by a film hinge defining a bending axis at right angles to the plane of the bell crank lever. The oscillating arm has a bearing hole at its free end portion for connection to a drive crank pin. The oscillating beam is substantially aligned with the axis of rotation of the crankpin.

It is an object to provide a drive unit arranged to convert a rotational movement provided by a motor into a linear reciprocating movement for driving a driven element of a personal care head, such as a personal care apparatus, preferably wherein the conversion is achieved in an efficient and/or low noise manner.

Disclosure of Invention

According to one aspect, there is provided a drive unit arranged for converting rotary motion into linear reciprocating motion in operation, the drive unit comprising: a motor having a motor shaft, the motor being arranged in operation to provide rotational movement of the motor shaft about a longitudinal axis of the motor shaft; a motor shaft extension comprising at least a first eccentric shaft element arranged eccentrically with respect to the longitudinal axis of the motor shaft such that, in operation, the first eccentric shaft element moves on a circle around the longitudinal axis of the motor shaft, the circle extending in a plane perpendicular to the longitudinal axis; at least one elastically deformable unit having a coupling element arranged for coupling with a driven element, preferably wherein the coupling element is coupled or is capable of being coupled with a drive shaft, wherein the first eccentric shaft element is coupled with the deformable unit to periodically deform the deformable unit such that the longitudinal position of the coupling element of the deformable unit in the direction of the longitudinal axis of the motor shaft is periodically changed, preferably wherein the deformable unit is an integral single unit, and wherein the deformable unit comprises a first arm section having a first end and a second arm section having a first end and a second end, wherein the second end of the first arm section and the first end of the second arm section are connected to each other, wherein the first end of the first arm section is connected with a mounting structure fixed with respect to the motor, and the second end of the second arm section is arranged at a distance from the first end of the first arm section in the direction of the longitudinal axis of the motor shaft, preferably wherein the second end of the second arm section is connected with the coupling element.

According to one aspect, a personal care device comprising the proposed drive unit is provided.

Drawings

The disclosure will be further elucidated by a detailed description of exemplary embodiments and with reference to the drawings. In the drawings of which there are shown,

FIG. 1 is a depiction of a personal care device implemented as an electric toothbrush including a handle section and a head section, wherein the head section includes a driven element implemented as a personal care head;

FIG. 2 is a cross-section through the top of a handle section of a personal care device including an exemplary drive unit according to the present disclosure;

FIG. 3 is a depiction of an exemplary drive unit in accordance with the present disclosure, wherein a deformable unit may be at least partially made of bent sheet metal;

FIG. 4 is a depiction of another exemplary deformable unit that may be used in the drive units disclosed herein;

FIG. 5 is a depiction of another exemplary drive unit in accordance with the present disclosure, wherein the deformable unit may be at least partially made of a plastic material;

FIG. 6 is a depiction of another exemplary drive unit according to the present disclosure, wherein the drive unit includes a frame structure;

FIG. 7 is a depiction of another exemplary drive unit in accordance with the present disclosure, wherein the deformable unit includes only two arm sections;

FIG. 8A is a graph showing power consumption of several drive units under various load conditions at a rotation frequency of 85 Hz; and is also provided with

Fig. 8B is a graph showing power consumption of several drive units under various load conditions at a rotation frequency of 100 Hz.

Detailed Description

The present disclosure relates to drive units and personal care devices including such drive units that are constructed and arranged to convert in operation rotational motion provided by a shaft of a motor, such as a DC motor, into linear reciprocating motion, preferably wherein the direction of the linear reciprocating motion coincides with or is parallel to a longitudinal axis of the motor shaft. It is generally known to provide linear reciprocation by resonating a linear drive, but such drives typically have high manufacturing costs and require complex control concepts that may utilize high performance microprocessors. The drive unit of the present disclosure may utilize a standard DC motor that is available as an off-the-shelf component and thus has a typical low cost configuration. In order to achieve the described conversion, the motor shaft comprises a motor shaft extension comprising at least a first eccentric shaft element, which is arranged eccentrically with respect to the longitudinal axis of the motor shaft, such that in operation the first eccentric shaft element moves on a circle around the longitudinal axis of the motor shaft, which circle extends in a plane perpendicular to the longitudinal axis. The motor shaft extension may be integral with the motor shaft or may be a separate component that is removably or non-removably connected to the motor shaft.

According to the proposed drive unit, the first eccentric shaft element is coupled with a deformable unit constructed and arranged to be periodically deformed when the motor shaft rotates, wherein typically the rotational frequency of the motor shaft is the frequency of the periodic deformation of the deformable unit. In particular, the deformation is achieved by a mechanical interaction of at least the first eccentric shaft element with the deformable unit, e.g. the first cross beam may connect the first eccentric shaft element and the deformable unit to transfer motion from the first eccentric shaft element to the deformable unit. The deformable unit comprises a coupling element which itself may be connected or connectable with a drive shaft intended to ultimately move the driven element. The deformable unit is arranged to be periodically deformed such that the longitudinal position of the coupling element is periodically changed. The coupling element or a part of the deformable unit may be coupled with the linear guide such that the periodic movement of the coupling element is substantially constrained to a linear reciprocating movement in the longitudinal direction. The longitudinal direction may in particular be defined by a longitudinal axis of the motor shaft (i.e. the rotational axis of the motor shaft).

In some aspects, the deformable unit has a length extension in the direction of the longitudinal axis of the motor shaft that changes periodically in operation due to deformation of the deformable unit. The coupling element may then be arranged at the top of the deformable unit, i.e. at the most distal point of the deformable unit in the longitudinal direction relative to the motor shaft, but this is only one example, and the coupling element may also be arranged at another position of the deformable unit.

The first eccentric shaft element may be coupled to the deformable unit by a connecting rod or a cross beam. The deformable unit may be realized essentially as an integral single unit which may be elastically, preferably resiliently deformed to realize a periodically varying length extension. Implementing the deformable unit as a single unit that is capable of elastically and/or resiliently deforming results in a relatively efficient (i.e., low power consumption) conversion mechanism and/or a relatively quiet (i.e., low noise generation) conversion mechanism. As a result of being implemented as an integral unit, there is no frictional connection via which electrical energy may be converted into lost thermal energy, and thus the energy efficiency of such conversion mechanisms will be reduced. In particular, the resiliently deformable unit stores energy during deformation, the stored energy being released when the resiliently deformable unit is deformed back to its natural or rest state, wherein the latter occurs when the load causing the deformation is released. A gear mechanism comprising interacting elements such as meshing gears has a tendency to generate noise due to mechanical tolerances of the meshing counterparts, which noise may reach a level that is uncomfortable for the user of the device utilizing such a drive unit, and may require additional measures to be taken to suppress the noise. According to at least one aspect, the deformable unit and preferably the entire drive unit are free of any meshing gears and/or friction wheels. Preferably, the deformable unit is at least partially resilient/spring-like, such that at least a portion of the energy for deforming the deformable unit from the rest state to the deformed state is stored in the spring-like portion of the deformable unit and released upon returning the deformable unit to its rest state.

According to the present disclosure, the first eccentric shaft element (and potentially any other eccentric shaft element) is coupled with the deformable unit such that an eccentric movement of the first eccentric shaft element about the longitudinal axis of the motor shaft is transformed into a deformation of the deformable unit in the following manner: the coupling element performs a linear reciprocating movement along a virtual line coinciding with or parallel to the longitudinal axis of the motor shaft. As already mentioned, a linear guide structure/linear guide may be used to substantially constrain the freedom of movement of the coupling element to linear reciprocating movement. According to some aspects, the deformable unit is configured to provide a linear guiding function alone, as will be explained by reference to further examples below.

In the context of the present specification, "personal care" shall mean the cultivation (or care) of skin and its appendages (i.e., hair and nails) and teeth and oral cavity (including tongue, gums, etc.), wherein the aim is to prevent diseases and to maintain and strengthen health on the one hand, and to cosmetically treat and improve the appearance of skin and its appendages on the other hand. It should include maintaining and enhancing well-being. This includes skin care, hair care and oral care, and nail care. This also includes grooming activities such as beard care, shaving and dehairing. Thus, "personal care device" refers to any device for performing such nutritional or grooming activities, for example a (cosmetic) skin treatment device such as a skin massaging device or a skin brush; a wet shaver; an electric razor or trimmer; an electric dehairing device; and oral care devices such as manual or electric toothbrushes, (electric) flossing, (electric) irrigators, (electric) tongue cleaners, or (electric) gum massagers. This should not exclude that the proposed personal care device may have more pronounced benefits in one or several of these nutritional or device areas than in one or several other of these areas. In this specification, the electric toothbrush is selected to present the details of the proposed personal care device, which should be understood as non-limiting. To a certain extent, these details are not specific to an electric toothbrush, and the proposed technology may be used in any other personal care device.

The drive unit presented herein may be used in a personal care device, preferably to drive a driven element, such as a treatment head of a personal care device, e.g. a brush head of an electric toothbrush. The drive unit described herein is designed to convert the rotational movement provided by the motor via the motor shaft into a linear reciprocating movement of the drive shaft along an axis that coincides with or is parallel to the longitudinal axis about which the motor shaft rotates.

The deformable unit may comprise a plurality of arm segments or arm segments. While the present application also provides the basis for a broader construction (see third last and second last paragraphs of this specification), the present disclosure relates to a deformable unit comprising two arm sections or three arm sections or four arm sections, etc. According to the present disclosure, the deformable unit comprises at least two arm sections, namely a first arm section and a second arm section, each of the arm sections having a length along a length axis, a width along a width axis and a thickness along a thickness axis, wherein the length is greater than the width and the width is greater than the thickness, preferably wherein the length may be at least twice as great as the width and at least five times as great as the thickness. Each of the arm sections has two ends, a first end and a second end, which are opposite to each other in the length direction. The first end of the first arm section is fixedly mounted on the mounting structure relative to the motor and the second end of the first arm section is connected with the first end of the second arm section, preferably such that the first arm section and the second arm section meet at an obtuse angle (i.e. at an angle greater than 90 degrees) in the rest or neutral state of the deformable unit, even though this would not preclude the arm sections from meeting at an angle of 90 degrees or at an acute angle or at 180 degrees. Although reference is made herein to a stationary or neutral state of the deformable unit, it is understood that the deformable unit may be incorporated into the drive unit such that it never reaches such a stationary or neutral state, but rather it only has a state of minimal deformation possible during the cyclic deformation process.

A coupling element, which may comprise a drive shaft or may be connectable with the drive shaft, may be connected to or may be part of the second end of the second arm section. Further preferably, the second end of the second arm section may be coupled with a linear guide that substantially limits the freedom of movement of the second end of the second arm section to linear movement, e.g. linear reciprocation, in a direction coincident with or parallel to the longitudinal axis of the motor shaft. As will be discussed in more detail below, such linear guides may be provided by other arm sections of the deformable unit. The second end of the second arm section may alternatively or additionally be guided by a linear guide rail. The second end of the first arm section is arranged at a distance from the first end of the first arm section with respect to a longitudinal axis defined by the motor shaft, and the second end of the second arm section is arranged at a distance from the second end of the first arm section and also at a distance from the first end of the second arm section, the first end of the second arm section being connected with the second end of the first arm section.

According to some aspects, the deformable unit comprises two other arm sections, namely a third arm section and a fourth arm section each having a first end and a second end, and each of the arm sections has a length along a length axis, a width along a width axis, and a thickness along a thickness axis, wherein the length is greater than the width and the width is greater than the thickness, preferably wherein the length may be at least twice as great as the width and at least five times as great as the thickness. The first end of the third arm section may be fixedly mounted relative to the motor, e.g., the first end of the third arm section may be mounted at the same mounting structure as the first end of the first arm section. The second end of the third arm section may be connected with the first end of the fourth arm section, and the second end of the fourth arm section may be connected with the second end of the second arm section.

The deformable element may be designed as a convex quadrilateral type structure, such as a diamond shape. The deformable element may thus be described as having four sides and four vertices, even though it should be understood that the vertices may not be punctiform (this is understood as an abstract term for a real structure and should indicate that the vertices have a larger or smaller minimum size extension), but may in fact be implemented as "extended vertices". For example, two arms of a convex quadrilateral type structure may be mounted at the mounting structure, but the mounting ends of the arms may not meet (the "meeting" arm ends would result in a fairly small dimensional extension), but may be mounted at a distance. Despite the vertices thus extending, it is understood that a basic convex quadrilateral type structure is maintained. This is illustrated in connection with fig. 3.

The deformable unit comprises arm sections mechanically connected to each other. In one implementation, the two arm sections are connected by a hinge-like structure such that the two arm sections can move relative to each other by moving about a hinge point. The hinge-like structure may be realized by a pivot. As an alternative to the pivot, the arm sections may be connected by living hinges or film hinges. Instead of rigid arm sections being connected by hinges, the arm sections themselves may be at least partially resiliently deformable when the deformable unit is deformed, and the connection points of the arm sections may be rigid, i.e. the connection points may not be realized as hinges or pivots. In embodiments with a hinge or pivot, the arm section may include a stiffening structure that substantially avoids deformation of the arm section itself, but rather substantially deforms in the hinge. In this regard, it should be understood that the deformable unit may be made of deformable (e.g., bendable) and in particular resilient (i.e., spring-like) material, and that certain construction details are used to concentrate the deformation onto certain areas of the deformable unit, for example, film hinges and stiffening structures are examples of such construction details. In some examples, two or more materials may be combined to create a deformable unit, e.g., a metal sheet may be partially overmolded with a plastic material to form a deformable unit.

The deformable unit may in particular be realized as a single, in particular one-piece unit made of a single piece of material (e.g. from a bent sheet metal or from injection molded plastic). This should not exclude that the deformable unit is realized by connecting two or more elements in a preferably non-detachable manner, for example by welding two or more metal elements together. The deformable unit may also be made of two or more of the materials mentioned in the preceding paragraph, for example the arm sections may be made mainly of sheet metal and the hinge may be realized of injection molded plastic.

For transmitting the movement from at least the first eccentric shaft element to the deformable unit, a first connecting rod or a first cross beam may be used. In some examples, the first cross beam or the first connecting rod is integral with the deformable unit, e.g. it may be made with the deformable unit in a plastic injection moulding process. But the first cross beam or the first connecting rod may alternatively be a separate element which may be detachably or non-detachably connected with the deformable unit. The first cross member or the first connecting rod may extend along a first cross member axis that is substantially perpendicular to the longitudinal axis of the motor shaft. When the first eccentric motor shaft element rotates about the longitudinal axis of the motor shaft, the first cross beam or the first connecting rod may be coupled with the first eccentric shaft element such that only a movement of the first eccentric shaft element along one axis is transmitted by the first connecting rod or the first cross beam to the deformable unit. For example, the first cross beam or the first connecting rod comprises an elongated hole through which the first eccentric shaft element extends, which may extend in a direction substantially perpendicular to the longitudinal axis of the motor shaft and substantially perpendicular to the first cross beam axis (which is the extension axis of the first cross beam or the first connecting rod). The elongated hole may have a width substantially corresponding to the diameter of the first eccentric shaft element such that the first eccentric shaft element moves without play in the elongated hole and will therefore not substantially cause noise due to play during operation. The inner surface of the elongated bore and/or the outer surface of the first eccentric shaft element may be coated with a friction reducing material or both surfaces may be made of a material having a low friction coefficient.

In some examples, at least a second eccentric shaft element is provided, which may be arranged at a 180 degree offset with respect to the first eccentric shaft element, such that during rotation of the motor shaft the second eccentric shaft element follows the first eccentric shaft element at a 180 degree offset. The second eccentric shaft element may be arranged eccentrically with respect to the longitudinal axis of the motor shaft such that, in operation, the second eccentric shaft element moves on a circle around the longitudinal axis of the motor shaft, which circle extends in a plane perpendicular to the longitudinal axis, wherein the second eccentric shaft element has a circumferential position around the longitudinal axis which is offset by 180 degrees with respect to the circumferential position of the first eccentric shaft element. As described for the first eccentric shaft element, a second cross beam or a second connecting rod may be used to transfer the movement of the second eccentric shaft element to the deformable unit. The description of the connection through the elongated hole also applies to the second eccentric shaft element and the second cross beam or the second connecting rod. In the case of a 180 degree offset, the first beam may then be arranged to move in one direction (e.g. left) and the second beam arranged to then move in the opposite direction (e.g. right) and vice versa. The first cross member may be connected with the deformable unit, in particular in the region where the first arm section and the second arm section are connected, and the second cross member may then be connected with the deformable unit in the region where the third arm section and the fourth arm section are connected. Such a design with a first and a second cross beam may thus be used in particular in connection with a deformable unit comprising four arm sections, for example, wherein the deformable unit is realized as a convex quadrilateral type structure.

The deformable unit may be mounted at a frame structure as a mounting structure, which frame structure may at least partly enclose the deformable unit and which frame structure may realize a linear guide for the deformable unit, e.g. the frame structure may comprise a guide for the coupling element or for a drive shaft fixed at the coupling element such that the movement of the coupling element is substantially constrained to a linear reciprocating movement in a direction coinciding with or parallel to the longitudinal axis of the motor shaft. The frame structure may be substantially rigid such that the deformable unit may be deformed substantially independently of the frame structure, which then provides one or several spatially fixed mounting positions, wherein spatially fixed shall mean spatially fixed with respect to the motor.

As mentioned, the drive unit discussed herein may be used in a personal care device such as an electric toothbrush or an electric hair removal device, wherein the drive unit is utilized to drive a driven element in motion, such as a personal care head such as a brush head or a lower wire cutter for a razor.

Fig. 1 is a depiction of an exemplary personal care device 1 implemented as an electric toothbrush, the personal care device 1 comprising a handle section 10 and a head section 20, wherein the head section 20 may comprise a driven element 21, here implemented as a brush head. The handle section 20 may comprise a drive unit for driving the movement of the driven element 21 as discussed herein.

Fig. 2 is a cross-section through a handle section 20A of a personal care device, for example, the handle section 20A may be used as a handle section of a personal care device as depicted in fig. 1. The lower bottom of the shank segment 20A is not shown. The handle section 20A includes a handle housing 21A in which a motor carrier 22A is mounted and an attachment shaft 23A for detachable attachment of the head section, as generally shown in fig. 1. The handle section 20A further comprises a drive unit 25A described below, and wherein a similar drive unit 25B will be described in more detail with reference to fig. 3.

A motor 30A is fixed at the motor carrier 22A, the motor 30A having a motor shaft 31A for providing a rotational movement R about a longitudinal axis a of the motor shaft 31A. The motor shaft 31A extends through a motor shaft extension 40A, which in the embodiment shown comprises a first eccentric shaft element 41A, a second eccentric shaft element 42A and a third eccentric shaft element 43A. The first 41A and the third 43A eccentric shaft elements have the same circumferential position about the longitudinal axis a, and the second 42A eccentric shaft element has a circumferential position offset by 180 degrees with respect to the first 41A and the third 43A eccentric shaft elements. In operation, the three eccentric shaft elements 41A, 42A and 43A move on a circle about the longitudinal axis a, which extends in a plane perpendicular to the longitudinal axis a. The first eccentric shaft element 41A and the third eccentric shaft element 43A are coupled with the first cross beam 80A. The first cross beam 80A has a fork-like structure with two tines, wherein each of the tines is coupled with one of the first and third eccentric shaft elements 41A, 43A. Thus, the first eccentric shaft element 41A and the third eccentric shaft element 43A work together like a single eccentric shaft element to provide a periodic linear reciprocating movement of the first cross beam along a first cross beam axis perpendicular to the longitudinal axis a. The second eccentric shaft element 42A is also coupled with the second cross beam 81A, and when the second eccentric shaft element 42A rotates about the longitudinal axis a, the second eccentric shaft element 42A causes the second cross beam 81A to perform a periodic linear reciprocating motion along a second cross beam axis that coincides with or is at least parallel to and offset 180 degrees from the first cross beam axis, i.e. when the first cross beam moves to the right, the second cross beam moves to the left, and vice versa (wherein left and right are defined herein with respect to the paper plane).

The first beam 80A and the second beam 81A are each connected to the deformable unit 50A. The deformable element 50A is implemented here as a diamond-shaped structure having four sides and four vertices, but this should not be considered limiting. Diamond-shaped structures are special cases of convex quadrilateral-type structures from a more general class, which represent one class of possible implementations of deformable elements. Four sides of the diamond-shaped structure are realized here by four arm sections 51A, 52A, 53A and 54A. The first arm section 51A has a first end secured at a mounting structure 60A, the mounting structure 60A being fixedly mounted at the motor 30A. Opposite the first arm section 51A in the diamond-shaped structure is a third arm section 53A having a first end also secured at the mounting structure 60A such that the first end of the first arm section 51A and the first end of the third arm section 53A form a first vertex 55A of the diamond-shaped structure of the deformable unit 50A. The second end of the first arm section 51A is connected with the first end of the second arm section 52A at a substantially obtuse angle, and the connection point is considered to be the second vertex 56A of the diamond-shaped structure formed by the deformable unit 50A (or "knee section" due to the obtuse angle at which the first and second arm sections meet). The second end of the second arm section 52A is connected with a coupling element 59A. A first end of the fourth arm section 54A opposite the second arm section 52A connects with a second end of the third arm section 53A at an obtuse angle, forming a third vertex 57A (or another "knee section"). The second end of the second arm section 52A and the second end of the fourth arm section 54A are fixed to each other at the coupling element 59A, thereby forming a fourth vertex 58A.

The first beam 80A is connected to the second vertex 56A, and the second beam 81A is firmly connected to the third vertex 57A. Once both the first and second beams move outwardly or both move inwardly, the deformable unit 50A deforms and the coupling element 59A is set for linear reciprocation along axis A1. When the two beams 80A, 81A are moved outwards, the coupling element 59A is pulled down to the motor 30A, and when the two beams 80A, 81A are moved inwards, the coupling element 59A is displaced upwards away from the motor 30A, a periodic linear reciprocating movement M is generated as indicated by the double arrow, which linear reciprocating movement M takes place along an axis A1, which axis A1 is here parallel to the longitudinal axis a of the motor shaft, i.e. the rotational axis of the motor shaft as indicated by the arrow R. The four vertices 55A, 56A, 57A, and 58A may be implemented as a substantially rigid structure without hinge functionality. Then, the arm sections 51A, 52A, 53A and 54A each need to be capable of deforming from their substantially linear extension (which represents their natural or resting state as shown in fig. 2) to a deformed state, e.g., the arm sections 51A, 52, 53A and 54A extend more over an S-shaped curve between the respective vertices. The arm sections 51A, 52A, 53A and 54A may be made substantially of a resilient material, such as spring steel or a resilient plastic material, such that the energy required to deform the arm sections 51A, 52A, 53A and 54A is stored in the resilient material and released again when the arm sections 51A, 52A, 53A and 54A return to their natural state. The deformable unit 50A does not have any meshing gear elements and also does not include any frictionally engaged elements, and thus has a design that is inherently quite quiet in operation and quite energy efficient, i.e. it requires only a low power level compared to other conversion mechanisms including meshing gear elements or the like, which is also illustrated in fig. 8A and 8B.

This aspect will be discussed in more detail with respect to fig. 3, but the first and second cross beams 80A and 81A may be coupled to the eccentric shaft elements 41A, 42A, and 43A through elongated apertures.

The motor 30A forms a drive unit 25A according to the present disclosure together with the shaft extension 40A, the first and second cross beams 80A, 81A and the deformable unit 50.

Fig. 3 is a depiction of another exemplary drive unit 25B having various structural similarities with the drive unit 25A shown in fig. 2 and discussed with reference to fig. 2. The drive unit 25B includes a motor 30B (only partially shown) having a motor shaft 31B and a shaft extension 40B attached to the motor shaft 31B. In general, the shaft extension 40B may be integral with the motor shaft 31B or may be a separate element fixedly secured to the motor shaft 31A. In the latter case, the shaft extension 40B may be snap-fit onto the motor shaft 31B, may be friction locked, welded, glued, or securely attached in any other manner known to the skilled artisan. In the illustrated embodiment, the drive unit 25B is connected to a drive shaft 70B, which may be coupled to a driven element. When the motor shaft 31B is to provide rotational movement about its longitudinal axis, this movement is converted by the drive unit 25B, and the drive shaft 70B is to provide periodic linear reciprocation along an axis coincident with or parallel to the longitudinal axis of the motor shaft 31B (for an indication of the respective axis or direction, see fig. 2). The shaft extension 40B includes a first eccentric shaft element 41B, a second eccentric shaft element 42B, and a third eccentric shaft element 43B. Eccentric shaft elements 41B, 42B and 43B are offset relative to the longitudinal axis and thus rotate about the longitudinal axis in operation along a circular path, as also described with respect to fig. 2. Similarly, as described for fig. 2, the first eccentric shaft element 41B and the third eccentric shaft element 43B have the same circumferential position and thus move in a position-aligned manner, while the second eccentric shaft element 42B is positioned circumferentially with a 180 degree offset. The first 41B and third 43B eccentric shaft elements are coupled to the deformable unit 50B by a first cross beam 80B, which is also fork-shaped, having two tines 801B and 802B. Tines 801B and 802B are here parallel to each other, but this should not be construed as limiting and any other configuration may be chosen, see for example fig. 4. The second eccentric shaft element 42B is coupled to the deformable unit 50B by a second cross beam 81B. The first beam 80B and the second beam 81B can be said to extend parallel to each other. The first beam 80B is arranged to move along a first beam axis perpendicular to the longitudinal axis of the motor shaft 31B, and the second beam 81B is arranged to move along a second beam axis parallel to the first beam axis, which then is of course also perpendicular to the longitudinal axis of the motor shaft 31B.

The deformable element 50B is also designed to have a generally diamond-shaped structure with four sides and four vertices. The first side is realized by the first arm section 51B, the second side is realized by the second arm section 52B, the third side is realized by the third arm section 53B, and the fourth side is realized by the fourth arm section 54B. The first arm section 51B and the third arm section 53B are each mounted with a first end on a mounting structure 60B, which is here firmly connected at the motor 30B or firmly connected relative to the motor 30B. The mounting points together form a first vertex 55B of a diamond-shaped structure, wherein the vertex is a so-called "extended vertex" in that the mounting sides of the first end of the first arm section 51B and the first end of the second arm section 53B are at a distance. The first arm section 51B and the third arm section 53B are curved outwardly with respect to the central axis of the diamond-shaped structure. The first arm section 51B has a second end connected to a first end of the second arm section 52B to form a second vertex 56B of the diamond-shaped structure. As seen in fig. 3, the first arm section 51B and the second arm section 52B meet at an obtuse angle, which should not be considered limiting depending on the design of the deformable unit, and these arm sections may meet at an obtuse or acute angle, or the angle between the two arm sections may be about 180 degrees in the resting state of the deformable unit, including the design of the arm sections substantially as discussed in the present context. Further, the second end of the third arm section 52B is connected with the first end of the fourth arm section 54B and forms a third vertex 57B. The second end of the second arm section 52B and the second end of the fourth arm section 54B are connected to form a fourth vertex 58B, wherein the coupling element 59B is also integrated into this slightly extending fourth vertex 58B. The drive shaft 70B is connected here to the coupling element 59B.

As can be seen in the perspective view shown in fig. 3, the arm sections 51B, 52B, 53B and 54B are realized as "double arm sections", i.e. each of the arm sections comprises two parallel arm elements arranged at a distance, which on the one hand makes the deformable unit 50B as a whole quite light, but on the other hand still stable, in particular resistant to torsional deformations. In the design shown, the first arm section 51B includes two parallel arm elements 511B and 512B, the second arm section 52B includes two parallel arm elements 521B and 522B, the third arm section 53B includes two parallel arm elements 531B and 532B, and the fourth arm section 54B includes two parallel arm elements 541B and 542B. At the second vertex, the third vertex and the fourth vertex, the parallel arm members are connected by a vertical bar member. The second and third vertices 56B and 57B each include mounting elements 561B and 571B, respectively, that provide a fixation point for the first and second beams 80B and 81B.

The first cross beam 80B comprises a first cross beam arm 801B and a second cross beam arm 802B, which here are parallel to each other over an extension length so as not to collide with the second cross beam 81B moving between the two cross beam arms 801B and 802B, wherein the first cross beam arm 801B is coupled to the first eccentric shaft element 41B by an elongated hole 804B and the second cross beam arm 802B is coupled to the third eccentric shaft element 43B by an elongated hole 805B. The elongated holes 804B and 805B are oriented perpendicular to the longitudinal axis of the motor shaft and perpendicular to the first beam axis. The first eccentric shaft element 41B extends through the elongated aperture 804B and the third eccentric shaft element 43B extends through the elongated aperture 805B. The first cross member 80B includes a connecting portion 803B at which the first cross member arm 801B and the second cross member arm 802B meet, and the connecting portion 803B is firmly connected with the mounting element 561B of the second apex 56B of the deformable unit 50B. The first cross member 80B and the mounting element 561B may be connected by over-molding, caulking, screwing, gluing, welding, or by any other connection means known to the skilled person. The elongated holes 804B and 805B are sized such that the first and third eccentric shaft elements 41B and 43B, respectively, fit substantially tightly through the elongated holes 804B and 805B with respect to the direction defined by the first beam axis, and are free to move in the longitudinal direction of the elongated holes 804B and 805B when the motor shaft 31B rotates the shaft extension 40B. Due to this design, the elongated holes 804B and 805B transfer only the movement of the first 41B and third 43B eccentric shaft elements in the direction of the first beam axis to the second apex 56B. Note again that the first eccentric shaft member 41B and the second eccentric shaft member 41C move in alignment. Similarly, the second cross member 81B includes a connecting portion 813B firmly connected to the mounting member 571B of the third vertex 57B. The elongated aperture 814B is sized such that the second eccentric shaft element 42B fits substantially tightly through the elongated aperture 814B relative to the direction defined by the second beam axis and is free to move in the longitudinal direction of the elongated aperture 814B when the motor shaft 31B rotates the shaft extension 40B. With this design, the elongated hole 814B transfers only the movement of the second eccentric shaft element 42B in the direction of the second beam axis to the third vertex 57B. When the second eccentric shaft element 42B is circumferentially offset by a distance of 180 degrees with respect to the first 41B and third 43B eccentric shaft elements, the first and second beams 80B, 81B move in a counter-oscillating manner, i.e. when the first beam moves to the right (to the "right" defined with respect to the plane of the paper), the second beam moves to the left, and vice versa, which means that the directions of movement of the two beams are periodically reversed at the same moment. Due to this design, when the first beam 80B moves to the right and the second beam 81B moves to the left, the deformable unit 50B is first "widened", which causes the coupling element 59B to be pulled toward the motor 30B, and when the first beam 80B moves to the left and the second beam 81B moves to the right, the deformable unit 50B is then "squeezed together", which causes the coupling element 59B to move upward and past its resting position to a maximum deflection away from the motor 30B. This linear reciprocation of the coupling element 59B occurs periodically and in a direction coincident with or parallel to the longitudinal axis of the motor shaft 31B.

In the example shown in fig. 2 and 3, the first cross beam has a fork-like structure and cooperates with two axially displaced eccentric shaft elements, which allows the coupling portion of the first cross beam to have the same axial position as the coupling portion of the second cross beam. This allows the first and third arm elements and the second and fourth arm elements to have the same length design. With reference to fig. 5, an embodiment that is asymmetric in this respect will be discussed.

In the example of fig. 2 and 3, the deformable units 50A and 50B are each made of a spring metal sheet material. The knee sections (vertices 56B and 57 in fig. 3) may be relatively rigid, i.e., non-pivotable and/or non-articulating, and the arm sections 51B, 52, 53B, 54B may then resiliently deform upon deformation of the deformable unit 50B. The arm sections then store energy during deformation and release substantially the same amount of energy when the load causing the deformation is released.

It is believed that the vibration profile of a drive unit having two beams is limited if the mass of the first beam and the second beam are approximately the same.

Fig. 4 is a depiction of an exemplary deformable unit 50C shown in substantial isolation, wherein a first beam 80C and a second beam 81C are integral with the deformable unit 50C. The deformable unit 50C may be made in a single plastic injection molding step with the cross beams 80C, 81C, or alternatively, the deformable unit 50C may be made of metal and the cross beams 80C, 81C also made of metal and welded to the deformable unit 50C. The deformable unit 50C as shown also includes four arm sections 51C, 52C, 53C and 54C, and includes four vertices 55C, 56C, 57C and 58C, with the bottom vertex 55C and the top vertex 58C being only slightly extended vertices. The fourth or top apex 58C is connected to or integral with a coupling unit 59C arranged hollow to receive the drive shaft. The first or bottom apex 55C is fixedly secured at the mounting structure 60C.

Fig. 5 is a depiction of another exemplary drive unit 25D that includes a deformable unit 50D that may be made by a plastic injection molding process. The drive unit 25D comprises a motor 30D (only partially shown) having a drive shaft 31D connected with a shaft extension 40D comprising a first eccentric shaft element 41D and a second eccentric shaft element 42D. The deformable unit 50D includes four arm sections 51D, 52D, 53D, and 54D, and four vertices 55D, 56D, 57D, and 58D. The deformable unit 50D is integral with a first cross beam 80D and a second cross beam 81D, wherein the first cross beam is coupled with the first eccentric shaft element 41D and the second cross beam 81D is coupled with the second eccentric shaft element 42D. The first beam 80D is integrally formed and thus firmly connected with the second vertex 56D, and the second beam is integrally formed and thus firmly connected with the third vertex 57D. In the design shown, the second cross member 81D is implemented in a single-prong design, and when the first and second cross members 80D, 81D extend parallel to each other, the third vertex 57D is positioned above the second vertex 56D along a longitudinal direction through the motor shaft 31D, where "above" here refers to a position further away from the motor shaft 31D. Due to this particular design, the deformable unit 50D is not symmetrical as in the examples shown in fig. 2, 3 and 4, but is asymmetrical. Arm segments 51D, 52D, 53D, and 54D include stiffening structures, such as structure 521D, that cause arm segments 51D, 52D, 53D, and 54D to become relatively rigid and stiff between the vertices. The arm sections 51D, 52D, 53D and 54D are specifically shaped around the second vertex 56D and the third vertex 57D to form a living hinge that allows the otherwise relatively rigid arm sections 51D, 52D, 53D and 54D to pivot around the vertices 56D and 57D. The top vertex 55D and the bottom vertex 58D are implemented as extended vertices, with the mounting structure 60C extending between the first end of the first arm section 51D and the first end of the third arm section 53D. The second end of the second arm section 52D and the second end of the fourth arm section 54D are connected or integral with the coupling section 59D that houses the drive shaft 70D. The second end of the second arm section 52D and the second end of the fourth arm section 54D are also shaped to form a living hinge.

Fig. 6 is an exemplary drive unit 25E that differs from the previous examples in several configurations and is outside the scope of the claimed application. First, the driving unit 25E includes a frame structure 90E surrounding a deformable unit 100E fastened at the frame structure 90E. In the illustrated example, the frame structure 90E and the deformable unit 100E may be one single integral element that may be manufactured by plastic injection molding. The frame structure 90E is relatively rigid, it may be made of metal or other material that provides high rigidity and stiffness, or it may be only reasonably thicker than the deformable portion of the deformable unit 50E. The frame structure 90E as shown is substantially rectangular, i.e., the frame structure 90E appears substantially like a photo frame. The frame structure 90E is firmly mounted at or at least with respect to the motor 30E (only partially shown), the motor 30E having a motor shaft 31E extending into the first 41E and second 42E eccentric shaft elements (the central portions of the eccentric shaft elements 41E and 42E are shown, in which the eccentricity is not visible). The first eccentric shaft element 41E is connected to the first substantially L-shaped arm section 101E, and the second eccentric shaft element 42E is likewise connected to the second substantially L-shaped arm section 102E. The first arm section 101E and the second arm section 102E of the L-shape are connected to the frame structure 90E at the upper end of the L. The first arm section 101E has a living hinge section 1012E via which it is connected to the frame structure 90E, and the second arm section 102E has a living hinge section 1022E via which it is connected to the frame structure 90E. Furthermore, the first arm section 101E has a further living hinge section 1011E arranged in the corner region of the L-shaped first arm section 101E. As the first eccentric shaft element 41E rotates, the lateral portions of the L-shaped first arm section 101E are repeatedly pushed inward and outward (the frame structure 90E may include cutouts to allow the corner portions of the first arm section 101E to move outward). Similarly, the second arm section 102E has another living hinge section 1021E arranged in a corner region of the L-shaped second arm section 101E. Centrally disposed coupling element 109E is connected to first arm section 101E at about one third of the length of the vertical arm of L by living hinge section 1023E and to second arm section 102E at about one third of the length of the vertical arm of L by living hinge section 1013E. During the periodical movement of the eccentric shaft elements 41E and 42E, the coupling element 109E periodically moves up and down, i.e. the coupling element 109E will reciprocate linearly in a longitudinal direction coinciding with or parallel to the longitudinal axis of the motor shaft 31E. The coupling element 109E accommodates the drive shaft 70E, which drive shaft 70E is also guided by a guiding element 91E provided by the frame structure 90E, which guiding element 91E enables a linear guide for the movement of the drive shaft 70E and thus for the coupling element 109E.

Fig. 7 is a depiction of an exemplary deformable unit 50F comprising a first arm section 51F and a second arm section 52F, wherein a first end of the first arm section 51F is mounted on a mounting support 60F that itself is securely mounted relative to a motor (not shown). The deformable unit 50F may be at least partially made of plastic, for example at least partially made by a plastic injection molding process. The second end of the first arm section 51F is connected with the first end of the second arm section 52F, the connection region forming a "knee" section where the first and second arm sections meet at an obtuse angle in the rest state, and the second end of the second arm section 52F is connected with a coupling element 59F configured to receive a drive shaft (not shown) in the cylindrical receptacle, wherein the coupling element and thus the drive shaft is intended to move in a linear reciprocating motion along the axis A1, as indicated by the double arrow A2. Although the motor itself is not shown, a motor shaft extension 40F is shown on which a first eccentric shaft element 41F is arranged, which first eccentric shaft element 41F is designed like the example cylindrical element discussed above. Once the motor shaft extension 40F is attached to the motor shaft, the first eccentric shaft element will rotate about the longitudinal axis of the motor shaft as indicated by arrow R2. The mounting support 60F includes a substantially circular cutout such that at least one motor shaft may extend through the cutout for attachment with the motor shaft extension 40F. The first eccentric shaft element 41F extends through an elongated hole of a first cross beam 80F, which transfers movement in the direction M1 as indicated by the double arrow to the deformable unit 50F. The first cross member 80F is connected to the mentioned knee segment where the first arm segment and the second arm segment meet. This movement of the first beam 80F will cause the deformable unit 50F to deform such that the coupling element 59F begins to move. It is assumed here that the coupling element 59F is limited to movement in a direction M2, the direction of movement M2 being substantially perpendicular to the direction of movement M1. It is assumed that this motion constraint is implemented by a linear guide. Such a linear guide may, for example, guide the coupling element 59F itself, or it may guide the drive shaft to be attached to the coupling element 59A. In contrast to the example shown in fig. 4, the deformable unit 50F of fig. 7 does not guide itself linearly (in fig. 4 the movement of the coupling element 59C is guided linearly by the further arm sections 53C and 54C), since the coupling element represents the free end of the deformable unit 50F, and thus a further linear guide may be required. The drive shaft will generally be guided anyway by a guide provided in the housing of the device in which the drive unit comprising the deformable unit is utilized, and thus the linear guide may be realized by such elements that are not part of the deformable unit or the drive unit.

Fig. 8A and 8B illustrate measured power consumption P in watts according to the applied load of various exemplary electric toothbrushes including different driving units, wherein the load applied at the brush holder of the brush head is 0 newton (N), 1 newton, 2 newton or 3 newton, wherein fig. 8A indicates power consumption at a rotation frequency of 85Hz and fig. 8B indicates power consumption at a rotation frequency of 100 Hz.

Lines 1001 and 1011 indicate the power consumption of the driving unit substantially according to the structure shown in fig. 3. Lines 1002 and 1012 indicate the power consumption of a toothbrush with a drive unit, wherein the tilting wobble plate is connected to the motor shaft of the DC motor, and wherein the plate is in frictional contact with two friction wheels that transfer the up and down motion of the tilting wobble plate to a drive shaft that is guided by a spring to move along a linear axis. Lines 1003 and 1013 indicate power consumption of a toothbrush having a drive unit, wherein a gear is attached to a motor shaft and the gear meshes with a crown gear having an eccentric rod coupled with a drive shaft, wherein the drive shaft is guided by a spring arrangement to move along a linear axis. Line 1004 and line 1014 indicate the power consumption of a toothbrush with a drive unit, wherein the motor shaft extends through two eccentric shaft elements, each connected with a U-shaped element, which is pivotally mounted and each connected with a drive shaft to move the drive shaft up and down. Lines 1005 and 1015 indicate the power consumption of an existing toothbrush (Oral-B PRO 1200) comprising a four bar linkage gear unit to convert the rotation of the shaft of the DC motor into an oscillating rotation of the drive shaft about its longitudinal axis. Now, without going into detail, it can be seen that the line 1001 and the line 1011 representing the drive unit according to the present description show the lowest power consumption for two different rotation frequencies and for four different load conditions. It is believed that low power consumption is associated with the deformable unit not having any meshing gears or friction coupling elements.

According to one aspect, there is provided a drive unit arranged in operation to convert rotary motion into linear reciprocating motion, the drive unit comprising

● A motor having a motor shaft, the motor being arranged in operation to provide rotational movement of the motor shaft about a longitudinal axis of the motor shaft;

● A motor shaft extension comprising at least a first eccentric shaft element arranged eccentrically with respect to the longitudinal axis of the motor shaft such that, in operation, the first eccentric shaft element moves on a circle around the longitudinal axis of the motor shaft, the circle extending in a plane perpendicular to the longitudinal axis;

● At least one elastically deformable unit having a coupling element arranged for coupling with a driven element, preferably wherein the coupling element is coupled or coupleable with the drive shaft; and is also provided with

● Wherein the first eccentric shaft element is coupled with the deformable unit to periodically deform the deformable unit such that the longitudinal position of the coupling element of the deformable unit in the direction of the longitudinal axis of the motor shaft is periodically changed, preferably wherein the deformable unit is an integrated single unit.

All other features mentioned herein are considered to be preferred features in this respect.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Rather, unless otherwise indicated, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "40mm" is intended to mean "about 40mm".

Claims (15)

1. A drive unit arranged for converting rotational movement into linear reciprocating movement in operation, comprising:

a motor having a motor shaft, the motor being arranged to provide rotational movement of the motor shaft about a longitudinal axis of the motor shaft in operation;

a motor shaft extension comprising at least a first eccentric shaft element arranged eccentrically with respect to the longitudinal axis of the motor shaft such that, in operation, the first eccentric shaft element moves on a circle around the longitudinal axis of the motor shaft, the circle extending in a plane perpendicular to the longitudinal axis;

at least one elastically deformable unit having a coupling element arranged for coupling with a driven element, preferably wherein the coupling element is coupled or coupleable with a drive shaft;

Wherein the first eccentric shaft element is coupled with the deformable unit to periodically deform the deformable unit such that a longitudinal position of the coupling element of the deformable unit in the direction of the longitudinal axis of the motor shaft is periodically changed, preferably wherein the deformable unit is an integral single unit; and is also provided with

Wherein the deformable unit comprises a first arm section having a first end and a second arm section having a first end and a second end, wherein the second end of the first arm section and the first end of the second arm section are connected to each other, wherein the first end of the first arm section is connected to a mounting structure fixed relative to the motor, and the second end of the second arm section is arranged at a distance from the first end of the first arm section in the direction of the longitudinal axis of the motor shaft, preferably wherein the second end of the second arm section is connected to the coupling element.

2. The drive unit of claim 1, further comprising a linear guide, and wherein the second end of the second arm section is coupled with the linear guide such that when the deformable unit is periodically deformed, the second end of the second arm section is substantially constrained to reciprocal linear movement in the direction of the longitudinal axis of the motor shaft.

3. The drive unit according to claim 1 or claim 2, wherein the deformable unit further comprises a third arm section having a first end and a second end, and a fourth arm section having a first end and a second end, wherein the second end of the third arm section and the first end of the fourth arm section are connected to each other, wherein the first end of the third arm section is coupled to the mounting structure, and preferably wherein the second end of the fourth arm section and the second end of the second arm section are coupled to each other, further preferably wherein the third arm section and the fourth arm section implement a linear guide for the second end of the second arm section.

4. A drive unit according to claim 2 or claim 3, wherein the deformable unit has a convex quadrilateral-type structure, preferably a diamond-type structure, having four sides and four vertices, preferably wherein at least one of the bottom vertex and the opposing top vertex formed at the mounting structure is an extended vertex.

5. A drive unit according to any of claims 1-4, wherein the second end of the first arm section and the first end of the second arm section are connected by a hinge, such as a living hinge, preferably wherein the hinge is at least partially resiliently deformable such that the first arm section and the second arm section store energy during deformation and release the energy again when the load causing the deformation is released.

6. The drive unit according to any one of claims 1 to 4, wherein the second end of the first arm section is firmly or rigidly connected with the first end of the second arm section, and the first and second arm sections are each at least partially resiliently deformable such that the first and second arm sections store energy during deformation and release the energy again when the load causing the deformation is released.

7. A drive unit according to any one of claims 1 to 6, wherein the coupling element is arranged at a distal end of the deformable unit, and the deformable unit is deformed in operation such that a length extension of the deformable unit changes periodically in a direction coinciding with or parallel to the longitudinal axis of the motor shaft.

8. The drive unit according to any one of claims 1 to 7, comprising a first cross beam extending along a first cross beam axis perpendicular to the longitudinal axis, the first cross beam having a first end coupled with the first eccentric shaft element such that only movement of the first eccentric shaft element along the first cross beam axis is transmitted from a first eccentric element to the first cross beam, and the first cross beam having a second end attached to the deformable unit such that movement of the first cross beam along the first cross beam axis results in deformation of the deformable unit, preferably wherein the first end of the first cross beam is coupled to the first eccentric shaft element through an elongated hole provided in the first end of the first cross beam and extending in a direction perpendicular to the first cross beam axis and perpendicular to the longitudinal axis, the first eccentric shaft element extending through the elongated hole.

9. The drive unit of claim 8, the motor shaft extension further comprising at least a second eccentric shaft element arranged eccentrically with respect to the longitudinal axis of the motor shaft such that, in operation, the second eccentric shaft element moves on a circle about the longitudinal axis of the motor shaft, the circle extending in a plane perpendicular to the longitudinal axis, wherein the second eccentric shaft element has a circumferential position about the longitudinal axis that is offset 180 degrees from a circumferential position of the first eccentric shaft element; and is also provided with

The drive unit further comprises a second cross beam extending along a second cross beam axis perpendicular to the longitudinal axis, the second cross beam having a first end coupled with the second eccentric shaft element such that only movement of the second eccentric shaft element along the first cross beam axis is transferred from the second eccentric element to the second cross beam, and the second cross beam having a second end attached to the deformable unit such that movement of the second cross beam along the first cross beam axis causes deformation of the deformable unit to be aligned with the deformation caused by the first cross beam, preferably wherein the first end of the second cross beam is coupled to the second eccentric shaft element through an elongated aperture provided in the first end of the second cross beam and extending in a direction perpendicular to the second cross beam axis and perpendicular to the longitudinal axis, the second eccentric shaft element extending through the elongated aperture, further preferably wherein the first and second cross beams have substantially the same mass.

10. Drive unit according to any one of claims 1 to 9, wherein the deformable unit is at least partly made of metal, preferably of sheet metal such as spring steel, in particular wherein the deformable unit is realized by bending sheet metal.

11. A drive unit according to any one of claims 1 to 10, wherein the deformable unit is at least partly made of plastic, preferably injection molded plastic.

12. A drive unit according to any one of claims 1 to 11, wherein the deformable unit is fixed to or integral with a frame structure at least partly surrounding the deformable unit, preferably wherein the frame structure provides a linear guide for a drive shaft connected with the coupling element.

13. A drive unit according to any one of claims 1 to 11, wherein the deformable unit is at least partially resiliently deformable such that energy is stored in the deformable unit during deformation and the energy is released to the extent that the load causing the deformation is released.

14. A personal care device comprising a drive unit according to any one of claims 1 to 13, preferably wherein the personal care device is an electric toothbrush.

15. The personal care device of claim 14, wherein the personal care device comprises a personal care head implementing the driven element coupled with the deformable unit such that deformation of the deformable unit causes movement of the driven element.