Electric toothbrushes are known and widely used having a set of bristles mounted to a brush head that is driven by an elec- tric motor inside a toothbrush handle. The motor may be pow- ered by a battery, also inside the handle, or from a power supply socket adjacent a point-of-use. The brush heads are ro- tated and/or vibrated by the motor to enhance the operation of the toothbrushes for cleaning teeth. For vibrating a brush head, it is already known to provide various mechanical coup- lings, including gears, to convert rotational motion of the motor into oscillating motion at the brush head. Such mechani- cal couplings tend to be complex, possibly unreliable, or ex- pensive.

It is an object of the invention to overcome or at least re- duce such problems.

According to the invention there is provided an electric toothbrush having a handle and an elongate shank having a lon- gitudinal axis, an electric motor, an elongate drive shaft ro- tatable about the longitudinal axis with a laterally off-set pusher at its remote end, a brush head mounted to the shank to rotate about a laterally extending axis, a pair of vertically opposed lugs at opposed sides of the longitudinal axis mounted to a periphery of the brush head for intermittent mechanical engagement by the pusher, such that when the shaft is rotated by the motor the brush head is rotationally oscillated.

The lugs preferably have arcuate bearing surfaces against which the pusher intermittently bears in turn as the shaft ro- tates.

The arcuate surfaces are preferably shaped in such a manner that during each time the lugs are urged by the pusher the brush head is substantially uniformly rotationally accelerated from rest.

Two rotatable brush heads may be supported by the shank in which the second brush head is oscillated by a link member that extends between the said brush head to transfer oscilla- tions for the said brush head to the second brush head.

The second brush head may be mounted to rotate about a sub- stantially vertical axis that is angled to some extent with respect to the rotational axis of the said brush head.

Each of the brush heads may have a tuft block base and a re- movable tuft block that releasable fits into the tuft block base.

Toothbrushes according to the invention will now be described by way of example with reference to accompanying drawings in which: Figure 1 is a sectional top plan view of the toothbrush.

Figure 2 is an isometric side view of an end of a shank of the toothbrush.

Figure 3 is a schematic plan view of a rotational drive ar- rangement of the toothbrush.

Figure 4 is a side view of the rotational drive arrangement; and Figure 5 is an exploded view of a toothbrush head for the toothbrush.

Figure 5a is an illustration of a preferred embodiment of the lugs.

Referring to the drawings, in Figure 1 the toothbrush has a handle 10 and an elongate shank 11 having a central longitudi- nal axis A. A drive shaft 12 is supported to rotate about the longitudinal axis A and is coupled to a rotor of an electric motor 13 mounted inside the handle. The drive shaft has crank 14 at its remote end forming an off-set pusher. Batteries 15 are housed inside the handle 10 for supplying power to the mo- tor 13.

Two in-line brush heads 16 and 17 are shown in Figures 1 and 2 vertically rotatably mounted to adjacent an end of the shank 11. It will be noted that the axis of rotation of the brush heads are angled to some extent with one another to enable the brushing action to move conveniently fit to a normal tooth configuration of a user. The brush head 16 has two vertically opposed lugs 18 and 19 mounted to a peripheral surface of the brush head for engagement by the pusher 14 when the drive shaft rotates. This causes the brush head 16 to rotationally oscillate when the drive shaft 12 is rotated by the motor 13.

The brush head 16 is also provided with a rigidly connected link 20 extending towards and into an open slot 21 in a peri- pheral surface of the brush head 17.

The mechanical connections between the drive shaft 12 and the brush heads is clearly seen in Figures 3 and 4. When the drive shaft 12 rotates, the cranked end or pusher 14 intermittently and in turn moves the lugs 18 and 19 sideways, in opposite di- rections, to cause the brush head 16 to oscillate back and forth. As the brush head 16 oscillates, the link 20 moves back and forth about an arc and by engaging in the slot 21 causes the brush head 17 to oscillate. The brush heads are preferably integrally formed with stub axles 21 and 22 that have bearing surfaces and that snap fit into appropriate and respective apertures (not shown) formed in the shank 11.

In Figure 5, it will be noted that the lugs 18 and 19 are ver- tically opposed with facing surfaces that are arcuate. Prefe- rably the arcuate surfaces are curved such that when the pusher 14 engages each arcuate surface, in turn, the appropri- ate lug is moved laterally to one respective side with a gene- rally uniform acceleration starting from rest. This reduces noise and makes the transfer of movement between the pusher 14 and the lugs 18 and 19 more efficient.

In a preferred embodiment, shown in Figure 5a, the inner sur- face 30 of the arcuate lugs, against which the pusher is ar- ranged to push, has a pusher entry side 31 and a pusher exit side 32. The entry side of the inner surface is angled out- wards to some extent in respect to a plane extending through the longitudinal axis A of the elongate shank and a laterally extending axis B, when the lugs are in the position where the longitudinal axis extends in the middle of the space between the lugs. The exit side is parallel to the said plane. This reduces noise and improves the transfer of movement between the pusher 14 and the lugs 18 and 19 even further.

It will also be noted that the lug 18 is vertically lower than the lug 19 to ensure, for clockwise rotation of the pusher 14, that the pusher does not jam. For anticlockwise rotation, the lug 19 is fixed, or integrally formed, in a position appropri- ately lower that the lug 18. In any event, the complete verti- cal separation extending between the lugs 18 and 19 makes it unlikely that debris will collect or that the toothbrush can- not be easily cleaned in order to remove any debris that does collect around the pusher 14 and prevents the pusher being readily rotated to carry out its function.

Figure 5 shows that the brush head 16 (or 17) is formed in two separable parts, a tuft block base 23 and a tuft block 24. The base 23 has apertures 25 to receive integrally formed stubs 26. Raised lips 27 are formed on the inside of the base serve to overlap a peripheral skirt 28 on the tuft block to hold the tuft block down in the base 23. A recess 29 allows a blunt in- strument, screw driver tip say, to enter under the skirt 28 for prising the tuft block 24 upwards over the lips 27 to fa- cilitate removal of the tuft block when required.

It will be noted that in the described toothbrush two brush heads are used. It is possible to have only one brush head, or three or more. In the latter cases, the brush head (with lugs) is used to pass oscillatory drive to the other brush heads via suitable links 20.

The pusher 14 is provided above by a cranked end of the drive shaft 12. Other forms of pusher may be used including a short piece of shaft welded at one side to an end of a straight or uncranked drive shaft. A noncircular disc can also be used that is mounted on or integrally formed at end of the drive

shaft. A circular disc may be used where the disc is mounted off-centre adjacent the end of the drive shaft 12.

In an alternative embodiment the pusher is arranged to push against the outside surfaces of the lugs (18,19), instead of the inside, in order to cause the brush head (16) to oscil- late.

The described lugs have arcuate shaft-engaging surfaces. It will be appreciated that planar shaft-engaging surfaces may be used, although as mentioned above, such surfaces may cause more noise to be generated in operation. In this case and in- deed in the described embodiment, the separation between the lugs can be relatively significant (allowing easy removal of debris if required) because effective practical oscillations of the brush head overall can be achieved through an overall arc of around 20°.