Field

[0001] The present disclosure relates to electric toothbrushes, and more particularly to electric toothbrushes operating at sonic frequencies.

Background

[0002] Electric toothbrushes are convenient and known to be more effective for teeth cleaning and plague removal compared to manual toothbrushes. Electric toothbrushes are motor-driven and motor-driven tooth-brushing operations typically generate audible sounds which are somewhat monotonous.

Disclosure

[0003] An electric toothbrush which is configured to generate a musical tune as a by-product of toothbrushing motion and a method to operate an electric toothbrush are disclosed. The electric toothbrush comprises a drive assembly for driving a toothbrush head into tooth-brushing motion. The drive assembly comprises a motor having a drive shaft for driving the toothbrush head, a motor-driving circuit and a controller containing a set of instructions. The controller is configured to deliver a train of motor-driving signals on executing the set of instructions and the motor-driving circuit is configured to drive the motor and/or the toothbrush head to perform a tune while performing toothbrushing motion upon receipt of the train of motor-driving signals. The tune comprises a plurality of notes which forms a sequence of notes and each note has a note frequency and a note duration. The note frequency is a characterizing frequency of a music note. The train of motor-driving signals may compris a plurality of motor-driving signals and the motor driving signals are for generating toothbrushing vibrations and the tune.

[0004] The method comprises the controller executing stored instructions to send a train of motor driving signals to the drive circuit. The train of motor-driving signals comprises a plurality of motor driving signals. Each motor-driving signal may be a voltage pulse comprising a plurality of switching pulses for driving the motor into toothbrushing vibrations and the motor-driving signals are modulated by melodic data of the tune.

[0005] The method may comprise varying the duty ratio according to the melodic data.

[0006] The motor-driving signal may have a signal duration equal to the note duration and may comprise a plurality of switching pulses having a switching frequency equal to the note frequency.

[0007] A sonic toothbrush is a motor-driven toothbrush which is to operate at sonic frequencies. Sonic frequency is a band of frequency which is audible to the average human. A commonly accepted sonic frequency band is between 20Hz and 20kHz, although the actual upper limit of the sonic frequency band can be higher than 20kHz, for example, up to or above 25kHz. A sonic toothbrush typically operates at a frequency of between 100Hz and 450Hz, corresponding to between 6,000 rpm (revolutions per minute) and 27,000 rpm. Where the sonic toothbrush is to perform sweeping vibrations about a vibration axis, the sweeping frequency is double the brushing strokes rate.

[0008] Typical sonic toothbrushes available on the market currently operate at one or two brushstroke rates of between 30k bpm (brushstrokes per minute) and 40k bpm. Where the brush- head is to vibrate back-and-forth or clockwise-and-anti-clockwise about a vibration axis to perform a complete brushing cycle, the brushstroke rate is twice the vibration frequency of the toothbrush head or the vibration frequency of the drive shaft. Therefore, the brushstroke rates of 30k bpm and 40k bpm correspond to the brushing frequencies of 15k cpm (cycles-per-minute) and 20k cpm respectively, which in terms of cycles-per-second are 250 Hz and 333.3 Hz respectively.

[0009] Example sonic toothbrushes currently available on the market operate at 31 k bpm, 40k bpm, or alternately at 31 k bpm for a first duration and at 40k bpm for a second duration.

[0010] The controller is to execute stored instructions to drive the motor such that the motor shaft is to generate a sequence of vibrations corresponding to a sequence of music notes when driving the toothbrush head into brushing vibrations.

[0011] A pause may have a duration of at least 5ms, including 6ms, 7ms, 8ms, 9ms, 10ms, 11 ms, 12ms, 13ms, 14ms, 15ms, 16ms, 17ms, 18ms, 19ms. 20ms, 21 ms, 22ms, 23ms, 24ms, 25ms, or a range or any ranges formed by the aforesaid values.

[0012] The tune may have a melodic tempo of between 20 and 200 beats per minute, including 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200 beats per minute, or a range or any ranges formed by the aforesaid values.

[0013] A tune herein may comprise a plurality of more than 2 discrete musical notes, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13 or more discrete notes.

[0014] The toothbrush head may be configured to vibrate at between 150Hz and 400Hz to perform tune-generating toothbrushing motions.

[0015] The duty ratio of the motor driving signals may vary between 30% and 95%, including 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or a range or any ranges formed by the aforesaid values Figures

[0016] The present disclosure is described by way of example and with reference to the accompanying figures, in which:

Figure 1 A shows a side view of an example electric toothbrush according to the disclosure,

Figure 1 B shows the example electric toothbrush of Figure 1 A with toothbrush head detached,

Figures 1 C1 and 1 C2 are schematic views of a drive assembly of an example electric toothbrush according to the disclosure,

Figures 1 D1 , 1 D2, 1 D3 are mechanical drawings showing example dimensions of an example drive assembly of an example electric toothbrush according to the disclosure,

Figure 2 is a block diagram of an example electric toothbrush according to the disclosure,

Figure 2A is a block diagram of an example drive assembly of an example electric toothbrush according to the disclosure,

Figure 2B is a block diagram of another example drive assembly of an example electric toothbrush according to the disclosure,

Figure 3 is an example piece of melody,

Figure 4A is a schematic diagram of an example drive bridge for driving the motor,

Figure 4B shows an example train of voltage waveforms at the output of the drive bridge,

Figures 4C1 and 4C2 respectively show flow of current in a first direction and a second direction (opposite to the first direction) through a motor of an example sonic toothbrush,

Figures 4C3 and 4C4 show example current flow conditions in the drive bridge when no drive current flows through the motor in a stop condition,

Figures 5A and 5B respectively show relationships between average motor current (Y-axis) and selected motor vibration frequencies (X-axis) at different duty ratios at no-load and loaded motor conditions of an example motor under a motor operation mode,

Figure 5C shows relationships between average motor current and selected motor vibration frequencies at different duty ratios at loaded motor conditions of an example motor under another motor operation mode, with y-axis in an inverted scale,

Figure 6 shows example resonant curves of an example toothbrush at different duty ratios,

Figure 7 A shows relationship between vibration amplitude (Y-axis) and vibration frequencies (X- axis) of an example toothbrush, and

Figure 7B is a table showing relationship of music note symbols, characteristic vibration frequencies of the music notes, time periods and PWM duty ratios.

Description

[0017] An example electric toothbrush of the present disclosure comprises a hand-piece 100 and a toothbrush head 120, as depicted in Figures 1A and 1 B. The hand-piece 100 comprises a handle housing 102 and a drive assembly 110 which is mounted inside the handle housing. The toothbrush head 120 comprises a neck portion which is proximal to the handle housing and an end portion which is distal from the handle housing. A bristle carrier is disposed on the end portion. The toothbrush head 120 comprises a link mechanism which is to connect the bristle carrier to the drive assembly to obtain operational drive power from the hand-piece 100.

[0018] The handle housing comprises a main housing which is a hollow elongate housing extending along a longitudinal axis. The main housing comprises a hollow compartment inside which the drive assembly or a substantial portion thereof is housed. The handle housing comprises a handle portion which is ergonomically shaped for hand-held operations and a neck portion from which a drive shaft of the drive assembly protrudes. The handle housing is typically assembled from molded hard-plastic parts. The handle housing may have an adult version for adult use and a children version for children use.

[0019] The drive assembly is configured to drive the toothbrush head to perform reciprocating brushing motions relative to the handle housing during toothbrushing operations. An example drive assembly comprises a motor 112, a drive shaft driven by the motor for driving the toothbrush head, an electronic circuit assembly 114 and a battery 116. An example electronic circuit assembly comprises a motor-drive circuit (or drive circuit in short) for controlling operations of the motor, an electronic data storage device for storing data and/or instructions, and optional peripheral circuits such as sensor circuits, indicator circuits and battery charging circuits, as shown in Figure 2. The sensor circuits may comprise a pressure sensing circuit for detecting brushing pressure and the indicator circuits may comprise a tooth pressure indicator which is configured to send an alert signal to a user to indicate over-pressure or under-pressure brushing conditions. The data storage device is for storing musical and other data and may comprise RAM, ROM, EPROM, flash memories, or other solid-state memory devices. The drive circuit may comprise a controller, which may be a logic circuit controller such as a gate-array controller, a microprocessor-based controller, an ASIC (application specific integrated circuit)-based controller and other forms of solid-state controller. Circuit block diagrams of example drive assemblies are shown in Figures 2A and 2B. The drive assembly may be formed as a drive module for fitted reception as a single module unit inside the handle housing. The drive assembly may comprise a main printed circuit board (“PCB”) 118 on which all components of the electronic circuit assembly, as shown in Figures 1 C1 and 1 C2. Other peripheral components such as the battery etc. may also be held or mounted on the main PCB. In example embodiments, a plurality of operation switches for user-machine interaction is disposed on a surface of the main housing.

[0020] During toothbrushing operations, the drive assembly is to operate to drive the drive shaft and therefore the toothbrush head to execute toothbrushing motion. In example embodiments, the drive assembly is configured to drive the drive shaft and the toothbrush head to vibrate at sonic frequencies to perform toothbrushing motion and to generate a melodic tune as a byproduct of the toothbrushing motion. Example toothbrushing motion comprises toothbrushing vibrations, and more specifically reciprocating sweeping vibrations performed by the toothbrush head. When performing reciprocating sweeping vibrations, the toothbrush head is to vibrate repeatedly from left-to-right and from right-to-left about a vibration axis to perform repeated clockwise and anticlockwise toothbrushing motion. The drive shaft axis is an example vibration axis which is coaxial with the longitudinal axis of the handle housing and/or coaxial with a longitudinal center axis of the toothbrush head. The sweeping vibrations, when performed by bristles or bristle tufts mounted on the bristle carrier of the toothbrush head, are intended to brush away food residues, dirt, bacteria and plaque that sit on the teeth or hide in inter-teeth slits and gumline.

[0021] In order that a melodic tune is generated as a byproduct or consequence of toothbrushing motion, data of the melodic tune is prestored on the drive module and the controller is to execute stored instructions to retrieve stored data of the melodic tune to perform toothbrushing operations having pitch and beat characteristics of the tune.

[0022] A melodic tune may be represented by a sequence of notes which forms a set of notes. The set of notes comprises a plurality of notes and each note has a note symbol, a characteristic frequency referred to as note frequency, and a note duration, and notes having the same note frequency are represented by the same note symbol.

[0023] Notes are commonly represented by note symbols. The note symbols may be in the form of An, Bn, Cn, Dn, En, Fn or Gn, where n is a natural number. The characteristic note frequencies of example notes having the note symbols G3, A3, B3, C4, D4, E4, F4 and G4 are set out in Table 1 below.

[0024] Table 1

[0025] The characteristic note frequency of the note having the note symbol G4 is twice that of G3 so that the note frequency of G4 is at an octave above that of G3 and the note frequency of G3 is at an octave below that of G3. The note frequencies of Table 1 are only approximate note frequencies which are adapted for convenient audible signal reproduction by the drive shaft of an example motor or the example toothbrush head. For example, note C4 has a standard note frequency of 261.60Hz but a note frequency of 262 Hz is adopted herein. In addition to the example notes of Table 1 , notes such as A2-G2, C3-F3, A5-G5, and other notes including sharps and flats can be used to construct a piece of tune for toothbrush performance without loss of generality. A note herein means a musical note and includes a quasi-musical note. A quasi-musical note is one having a characteristic frequency close to but not equal to the frequency of a musical note. Some example standard music note frequencies are set out in Table 2 below.

[0026] Table 2

[0027] An example piece of musical tune which the example toothbrush is configured to play is “Happy Birthday to You”, as depicted in Figure 3. The example tune comprises a sequence of notes, a note duration associated with each note, and pause times between adjacent notes where the adjacent notes are notes having the same note frequency. The tune is arranged into an example plurality of eight bars and each bar has an example plurality of three discrete beats. A beat is a base time unit of a tune in music notation. A note may have a note duration longer than a beat or shorter than a beat. A note having a note duration of a beat is referred to as a quarter note, a note having a note duration of half a beat is referred to as an eighth note, and a note having a note duration of two beats is referred to as a half note. The beat time is uniform for the entire length of the music in this example. Each beat may be divided into a plurality of sub-beats, for example, a beat may be divided into an example plurality of two sub-beats or more than two sub-beats.

[0028] The example piece of tune comprises the notes a first note G3, a second note G3, a third note A3, a fourth G3 in the first bar; a fifth note C4, a sixth note B3 in the second bar; a seventh note G3, an eighth note G3, a ninth note A3, a tenth note G3 in the third bar; an eleventh note D4, a twelfth C4 in the fourth bar; a thirteenth note G3, a fourteenth note G3, a fifteenth note G4, a sixteenth note E4 in the fifth bar; C4, B3, A3 in the sixth bar; F4, F4, E4, C4 in the seventh bar; and D4, C4 in the eighth bar.

[0029] Each one of the first, the seventh, the thirteenth and the twentieth example notes has an example first sub-beat note duration of 350ms; and each one of the second, the eighth, the fourteenth and the twenty-first example notes has an example second sub-beat note duration of 375ms. There is a pause having an example pause time of 25ms between the first and second notes, between the seventh and the eighth notes, between the thirteenth and the fourteenth notes, and so forth. Each one of the third, fourth, ninth, tenth, fifteenth, sixteenth, eighteenth, nineteenth, etc. notes has an example single beat note duration of 750ms. The sixth, twelfth and the last note has an example double-beat duration of 1.5s.

[0030] The toothbrush is configured such that during example toothbrushing operations when the toothbrush is to execute vibrations to play the tune of Figure 3, the drive circuit is to deliver a train of motor-driving signals to operate the drive shaft so that the drive shaft is to vibrate at the respective note frequencies for the respective note durations according to the sequence of the notes.

[0031] For example, on executing instructions to perform the tune, the controller is to generate and transit a train of motor-driving signals to the drive circuit and drive the motor. The train of motor-driving signals for performing the first bar comprises a first driving signal having a switching frequency at the first note frequency (G3) for the first note duration (350ms), a stop signal for the pause time(25ms) afterthe end of the first driving signal, a second driving signal having a switching frequency at the second note frequency (G3) for the second note duration (375ms) to begin at the end of the pause time, a third driving signal having a switching frequency at the third note frequency (A3) for the third note duration (750ms) and to begin immediately at the end of the third driving signal, and a fourth driving signal having a switching frequency at the fourth note frequency (G3) and for the fourth note duration (750ms) to begin immediately at the end of the third driving signal.

[0032] The train of motor-driving signals for the second bar comprises a fifth driving signal having a switching frequency at the fifth note frequency (C4) and for the fifth note duration (750ms) and a sixth driving signal having a switching frequency at the sixth note frequency (B3) for the sixth note duration (750ms) to begin immediately at the end of the fifth driving signal.

[0033] The train of motor-driving signals for performing the third bar comprises a seventh driving signal having a switching frequency at the seventh note frequency (G3) for the seventh note duration (350ms), a stop signal for the pause time(25ms) after the end of the seventh driving signal, an eighth driving signal having a switching frequency at the eighth note frequency (G3) for the eighth note duration (375ms) to begin at the end of the pause time, a ninth driving signal having a switching frequency at the ninth note frequency (A3) for the ninth note duration (750ms) and to begin immediately at the end of the eighth driving signal, and a tenth driving signal having a switching frequency at the tenth note frequency (G3) and for the tenth note duration (750ms) to begin immediately at the end of the third driving signal.

[0034] The train of motor-driving signals for the fourth and the eighth bar has a time structure and timing allocation identical to that of the second bar.

[0035] The train of motor-driving signals for the fifth and the seventh bar has a timing structure and timing allocation identical to that of the second bar.

[0036] The train of motor-driving signals for performing the sixth bar comprises driving signals having different switching frequencies but same note durations. [0037] In this example, the first beat comprises the example note sequence“G3(350ms)-short- pause(25ms)-G3(375ms)” and the first bar consists of the note sequence“G3(350ms)-short- pause(25ms)-G3(375ms)-A3)750ms)-G3(750ms)”. The short pause of 25ms provide a clear audio break between the first note and the second note, which are notes of same note frequency. No pause or break is required between abutting adjacent notes of different note frequencies, since the difference in note frequencies between the abutting adjacent notes is significant enough to be audible. The first and second sub-beat may have the same sub-beat duration, for example, a sub beat duration of 360ms-365ms and an inter-note pause time of say between 30ms and 20ms separating immediately adjacent notes. The small difference in the duration of a note or of the inter-note pause would not be audibly noticeable. In some embodiments, the first sub-beat may be slightly longer than the second sub-beat or vice versa without loss of generality. The principle may apply mutatis mutandis where two or more notes of the same note frequency are in immediate adjacency.

[0038] The toothbrush may perform a melodic tune (“tune”) for the entire toothbrushing operation duration or part thereof. The example tune has an example rhythm of 80 beats-per-minute (bpm) and a total of 24 beats. To form a tune of 2-minute duration, which is a recommended toothbrushing duration, an example total of 160 beats would be required and this can be done by repeating the tune, concatenating different tunes, or playing variations of the tune, for example, at an octave above and/or below without loss of generality. In general, tunes having a tempo of between 20 and 200bpm may be configured for execution by the toothbrush, for example, the tempo may be selected from a range formed by a combination of any values selected from: 20, 40, 60, 80, 100, 120, 140, 160, 180, 200 bpm. Results of empirical trials show that tunes having a beat time selected from a range formed by a combination of any values selected from of 0.5s, 0.75s, 1 s, 1.25s, 1.5 s, 1.75, 2s, 2.25s, 2.5s, 2.75s, 3s would provide a pleasant toothbrushing and audio experience.

[0039] Well-known tunes such as“happy birthday to you”,“twinkle-twinkle litter star”,“it’s a small word” etc., may be adapted for the toothbrush. Alternatively, tunes may be custom created for the toothbrush. An appropriate tune which is suitable as a by-product of toothbrushing motion may comprises a sequence of notes wherein the notes comprises notes of same note frequency but having different note duration, notes of different note frequencies but having same note duration, notes having different note frequencies and different note durations, and a combination selected from any of the aforesaid. The notes which form a sequence of tune suitable for playing by the toothbrush may comprise notes having increasing note frequencies followed by notes having decreasing note frequencies, notes having decreasing note frequencies followed by notes having increasing note frequencies, or a combination of the aforesaid. The tune may comprise cycles of note frequency increment at different rates of frequency increments, cycles or note frequency decrement at different rates of frequency decrements, or a combination of the aforesaid.

[0040] So that the toothbrush can retrieve melodic data of a tune and to perform toothbrushing operations according to the melodic characteristics of the tune, the melodic data of the tune would need to be stored on the toothbrush, for example, on the data storage device, for retrieval by the controller during toothbrushing operations. The melodic data of a tune may comprise a sequence of notes comprising a plurality of notes, the note frequency of each specific note, the note duration of each specific note, the sequence position of each specific note, and whether there is a pause between adjacent notes. The specific note, the note duration of each specific note and the sequence position of each specific note collectively define a linked data which defines the audio characteristics of a specific note in the sequence of notes. In some embodiments, the linked data may include an amplitude parameter of the specific note.

[0041] To adapt a tune for toothbrush operation, the melodic data of a tune are pre-stored in the data storage device. On executing stored instructions to perform a stored melody, the controller is to convert the melodic data into a train of motor-driving signals and to operate the motor to perform toothbrushing vibrations according to the stored melodic data. Each motor-driving signal contains a melodic data and may have an optional parameter for controlling the amplitude of vibration. A PWM pulse having a pulse duration T and a plurality of switching pulses at a specific note frequency / is an example of motor-driving signal suitable for driving the motor to facilitate the example toothbrushing operations. Each PWM pulse has / x T number of switching pulses of switching frequency /. The PWM signal may be mono-polar or bipolar. In the example of PWM signals, the duty ratio is a suitable parameter for controlling the amplitude of vibration. The switching pulses when supplied to the motor will drive the motor drive shaft into clockwise and anti-clockwise rotation alternately to form toothbrushing vibrations.

[0042] A plurality of melodic tunes may be pre-stored on the data storage device of the toothbrush. In some embodiments, the drive circuit may comprise a data input interface to obtain new or updated melodic data from time to time, for example, by way of USB, by way of power line communication (PLC) or other data communication means without loss of generality. The melodic tunes may comprise melodies of, resembling or synthesized vocal or audible instrumental signals.

[0043] In example embodiments, the drive circuit, or more specifically the controller, is to operate to retrieve the melodic data of a tune at power-on or upon user selection through operation of a selection switch and to operate the motor according to the retrieved melodic data. The melodic data are rhythmic or musical data comprising a plurality of notes and a beat data associated with each note. The beat data determines the note duration during which a note is to be played.

[0044] An example drive circuit suitable to cooperate with the controller to facilitate the toothbrushing motion of the present disclosure comprises a drive bridge as shown in Figure 4A. The example driving circuit comprises a first switching branch S1, S4 and a second switching branch S3, S2 which are connected in parallel. The first switching branch comprises a first switch S1 , a second switch S4 which are connected in series with the first switch S1 , and an output note A (or OUT+) which is a node in common with the current path of the first and second switches. The second switching branch comprises a first switch S3, a second switch S2 which are connected in series with the first switch S3, and an output note B (or OUT-) which is a node in common with the current path of the first and second switches. The switches are in series connection herein when the current paths are connected in series. The first switch S1, S3 of each switching branch is connected to a first power supply rail such that its first terminal is tied to the voltage of the first supply rail. The second switch S4, S2 of each switching branch is connected to a second supply rail such that its second terminal is tied to the voltage of the second supply rail. In this example, the first supply rail is at a positive and higher supply voltage and the second supply rail is a ground, reference or zero voltage.

[0045] The switches S1 , S2, S3, S4 forming the drive bridge are electronic switches. Each electronic switch comprises a first terminal, a second terminal and a third terminal. The first terminal and the second terminal are current terminals which cooperate to define a current path when the switch is turned on to an on-state and through which a motor-driving current is to flow. The third terminal is a control terminal or a switching terminal which is to switch the electronic switch between an on-state during which a motor-driving current is to flow through the switch and an off-state during which the switch becomes a high impedance device allowing no flow of motor driving current through the current path. Field effect transistors (FET) such as MOSFETS or IGBT (insulated gate bipolar transistor) are example of electronic switches suitable for forming a drive bridge.

[0046] During example motor drive operations, a controller of the drive circuit is to transmit a train of switching signals to the switching terminals of the switches S1 , S2, S3, S4 to drive a switch alternately into the on-state and the off-state. The transmission of switching signals to the switching terminals will operate the drive circuit to provide an alternating current to drive the motor to vibrate in opposite directions. [0047] In example operations such as the present, the motor drive circuit is to alternate between two motor-driving modes. In the first motor-driving mode, the controller turns on the switches S1 and S2, and turns off the switches S3 and S4. As a result, a motor current will flow from the first supply rail into the motor winding after passing through the current path of the first switch S1 of the first switching branch S1, S4, and the first output terminal A and then flow out of the motor winding and flow into the second supply rail after passing through the second output terminal B and the current path of the second switch S2 of the second switching branch S3, S2, as depicted in Figure 4C1.

[0048] In the second motor-driving mode, the controller turns on the switches S3 and S4, and turns off the switches S1 and S2. As a result, a motor current will flow from the first supply rail into the motor winding after passing through the current path of the first switch S3 of the second switching branch S3, S2 and the second output terminal B and then flow out of the motor winding and flow into the second supply rail after passing through the first output terminal A and the current path of the second switch S4 of the first switching branch S1, S4, as depicted in Figure 4C2.

[0049] In example operations such as the present, the motor drive circuit is in a stop mode to stop the motor before the motor vibrates in opposite directions. In a first example stop mode, the controller turns off the switches S1 , S2, S3 and S4. As a result, no current will flow through the first output terminal A and the second output terminal B, as depicted in Figure 4C3.

[0050] In a second example stop mode, the controller turns on the switches S4, and S2, and turns off the switches S1 and S3. As a result, both first output terminal A and the second output terminal B will be connected to the second supply rail, no current will flow through the first output terminal A and the second output terminal B, as depicted in Figure 4C4.

[0051] When in the first motor-driving mode, the motor is to turn in a first rotation direction. When in the second motor-driving mode, the motor is to turn in a second rotation direction which is opposite to the first rotation direction. When the first rotation direction is clockwise, the second direction is counterclockwise, and vice versa.

[0052] By alternating between the first and second motor-driving mode, the motor shaft will be driven alternately in the clockwise direction and in the counterclockwise direction to generate a vibration about the axis of the drive shaft in the clockwise direction and in the counterclockwise direction respectively. The frequency of vibrations is dependent on the frequency of the switching signals. In example embodiments, the switching signals are in the form of a train of driving voltage pulses, and the output at the output terminals A and B has a waveform closely following the waveform of the switching pulses, as depicted in Figure 4B. [0053] In example operations such as the present, a train of switching signals comprising a first train of square voltage pulses is applied at the switching terminal of the first switch S1 and a second train of switching signals comprising a train of square voltage pulses in synchronization with the first train but having an opposite polarity is applied at the switching terminal of the second switch S4 such that when the first switch is turned on, the second switch is turned off and vice versa.

[0054] When in the first motor-driving mode, the first switching branch S1, S4 is in a first switching mode and the second switching branch S3, S2 is in a second switching mode. When in the second motor-driving mode, the first switching branch S1, S4 is in the second switching mode and the second switching branch S3, S2 is in the first switching mode.

[0055] When a switching branch S1, S4; S3, S2 is in the first switching mode, the first switch S1 , S3 is turned on and stays in the on-state during an on-duration, the second switch S4, S2 is turned off and stays in the off-state during an off-duration, and the output voltage at the output terminal A, B is at a“high” voltage close to the voltage of the first supply rail.

[0056] When a switching branch S1, S4; S3, S2 is in the second switching mode, the first switch S1 , S3 is turned off and stays in the off-state during an off-duration, the second switch S4, S2 is turned on and stays in the on-state during an on-duration, and the output voltage at the output terminal A, B is at a“low” voltage close to the voltage of the second supply rail.

[0057] During the example motor-drive operations, the voltage output at the output terminal A has the waveform of a train of square pulses as depicted in the uppermost row of Figure 4B, the voltage output at the output terminal B has the waveform of a train of square pulses as depicted in middle row of Figure 4B, and the output voltage across the output terminals A, B, which is the motor driving voltage, is depicted in the lowest row of Figure 4B. It will be noted that the driving pulses, characterized by positive voltage levels at the output terminals A, B, are non-overlapping.

[0058] An example motor supply voltage (V _A -V _B or V _0Ut+ -V _0Ut ) appearing at the output terminals A, B, which is also a motor-driving voltage across the motor terminals, comprises a positive pulse, a negative pulse and an off-duration between a pair of adjacent positive and negative pulses.

[0059] Referring to Figure 4B, the motor driving voltage comprises alternately disposed positive and negative voltage pulses, with an off-period spacing between a positive voltage pulse (positive pulse in short) and its immediately adjacent negative voltage pulse (negative pulse in short) and another off-period spacing between a negative pulse and its immediately adjacent positive pulse.

[0060] The alternately disposed positive and negative voltage pulses and the off-periods separating adjacent positive and negative voltage pulses cooperate to form a complete switching signal cycle. A switching signal cycle corresponds to a complete brush-driving cycle of the motor which is a vibration cycle in the present example.

[0061] The time between a beginning of a positive voltage pulse and the next beginning of a positive voltage pulse is the cycle time of a vibration cycle of the motor. The cycle time is also the time between a beginning of a negative voltage pulse and the next beginning of a negative voltage pulse, the time between an end of a negative voltage pulse and the next end of a negative voltage pulse, or the time between an end of a positive voltage pulse and the next end of a positive voltage pulse.

[0062] The ratio between the total on-off-durations and the cycle time is the duty ratio of a drive cycle, which is a vibration cycle in this example.

[0063] To generate audible signal of a selected pitch and a selected beat, the drive circuit is to operate the motor to vibrate at the frequency of the selected music note for the duration of the selected beat.

[0064] To generate a piece of melody, a controller of the drive circuit is to generate audible signals of selected pitches having corresponding beat times according to melody data stored in the data storage device when executing instructions to play the piece of melody.

[0065] By selecting the duty ratio, the amplitude of vibration and hence the amplitude of audible signal of a selected note pitch can be selected. The duty ratio can be selected by adjusting the on-duration and off-duration of the switching signals during a motor-driving cycle.

[0066] When the toothbrush operates as a vibratory musical instrument to perform a melodic tune while performing tooth brushing operations, the audible sound generated by the toothbrush head will be amplified when the bristles of the toothbrush head are in contact with teeth surface being brushed. The actual frequencies of the audible sound generated by the toothbrush may deviate from the designed note frequencies, since the pressure of contact may affect the load condition of the motor and change the motor shaft speed.

[0067] In example operations at different example duty ratios varied between 0.9 and 0.3, at duty ratio intervals of 0.1 , it is noted that the average current of the example motor, when drive by PWM signals at a voltage of 4.2V, varies according to the vibration frequencies, as shown in Figures 5A and 5B.

[0068] Referring to Figure 5A, the no load motor current (with the toothbrush detached) at the note frequency of 110Hz is highest at 0.9 duty ratio and lowest at 0.3 duty ratio. The motor current follows a decreasing trend on increasing note frequencies and falls gradually to reach a minimum at a trough frequency of about 300Hz. The motor current rises more sharply or abruptly after the trough frequency.

[0069] The loaded motor currents (with the toothbrush head attached) follow a similar trend, as shown in Figure 5B indicates similar trend.

[0070] The minimum motor current suggests that the motor is at minimum impedance at the trough frequency. The rapid rise in current at note frequencies immediately higher than the trough frequency suggests that motor impedance increases rapidly when the note frequencies is higher than the trough frequency. It is believed that the trough frequency is the resonant frequency of the motor. The rapid increase in impedance and motor current suggests that it would not be energy efficient to operate the toothbrush at vibration frequencies above the resonant frequency for this example motor.

[0071] Since the load current increases as the motor vibration frequency decreases from the resonant frequency, operating the motor at the lower end of the frequency spectrum is also not energy efficient. In example embodiments, the note frequencies to be performed by the toothbrush are selected to be below the trough frequency, for example, between the trough frequency and half the trough frequency so that a full octave can be covered. Of course, the frequency selection depends on the impedance properties of the motor. For example, where the motor has a higher resonant frequency, the range of note frequencies to be performed by the toothbrush will be larger than one octave and vice versa, assuming the rates of impedance change are the same.

[0072] As the motor load current is not uniform at different vibration frequencies, the motor current may need to be adjusted in order to compensate for drop in vibration amplitude due to increased motor impedance compared to the minimum impedance. The amplitude adjustment may be achieved by adjusting the duty ratios of different note frequencies. For example, the duty ratio of a note having a note frequency which is further from the resonant frequency may have a higher duty ratio compared to a note frequency which is closer to the resonant frequency as a rule of thumb, or the duty ratio of a note having a note frequency which is closer to the resonant frequency may have a lower duty ratio compared to a note frequency which is further to the resonant frequency as a rule of thumb. The duty ratio adjustment may be made with reference to relationships between motor current and vibration frequency at different duty ratios, since it is expected that the vibration amplitude at a vibration frequency will increase with an increase in duty ratio and vice versa. For example, amplitude adjustment may be made with reference to an adjustment factor. The adjustment factor may be based on the relationship of 1/[relative duty ratio]. This inverted relationship is shown in Figure 5C, where the Y-axis showing the relative duty ratio is in an inverted scale. The adjustment may be further adjusted empirically to fine tune vibration amplitudes of the different notes. In some embodiments, different notes on one side of the resonant frequency have different duty ratios. In other words, each note frequency on one side of the resonant frequency has a characteristic duty ratio which is unique to that note frequency. Frequencies which are on one side of the resonant frequency means that the note frequencies are all lower than the resonant frequency or are all higher than the resonant frequency. The duty ratio of a note frequency at or closest to the resonant frequency may have the minimum or lowest duty ratio among the note frequencies. In some embodiments, the duty ratios of a note in different tunes or even in the same tune may be different.

[0073] In the example motor of Figure 5C, the motor the motor current drawn at 175 Hz is 0.523A when the duty ratio is 70%. When the duty ratio is 40%, the motor current is only 0.263A.

[0074] In example embodiments, a uniform duty ratio may be selected for the melody. With a uniform duty ratio, the magnitude of audio signals having a frequency different from a characteristic resonant frequency of the toothbrush will be lower than that of the resonant frequency. The magnitude of drop in audio amplitude will increase when the difference in frequency with respect to the resonant frequency increases.

[0075] In example embodiments, the duty ratio may be selected with reference to the vibration frequency of the motor which determines the music note frequency generated by the toothbrush head. For example, the duty ratio for playing a particular music note may be selected according to the difference in frequency between a resonant frequency and the frequency of the music note. For example, where the example toothbrush has a resonant frequency, the duty ratio may be increased to increase the vibration amplitude, and the extent of increase in duty-ratio may depend on the extent of frequency deviation of the selected music note away from the resonant frequency or a reference frequency. The reference frequency may be the resonant frequency or a frequency of the selected notes forming a piece of melody and closest to the resonant frequency. This would operate to equalize or amplify the amplitude of the audio signal of the selected note with respect to the music note at or near the resonant frequency to compensate for the drop due to the resonant characteristics of the toothbrush. Example relationships between vibration amplitude, duty ratio and vibration frequencies of an example toothbrush at example vibration frequencies of between 125Hz and 375 Hz are depicted in Figure 6. In the example relationships of Figure 6, the tallest and largest curve has a duty ratio of 95 percent while the lowest and smallest curve has a duty ratio of 40%, with example duty ratios of 80%, 70%, 60% and 50% set out between the two extremes.

[0076] In example embodiments, the duty ratio of the driving signals for playing a music note is selected to be dependent on the frequency of the music note. For example, the duty ratio for playing a music note may be selected according to the difference in frequency between a resonant frequency and the frequency of the music note. For example, where the example toothbrush has a resonant frequency, the vibration amplitude of the toothbrush head, and more particularly the bristle carrier, is dependent not only on the duty ratio, but also the vibration frequency, and more specifically on the difference between the vibration frequency and the resonant frequency. For example, where the resonant frequency is at 250Hz, the vibration amplitude of the bristle carrier at the resonant frequency is about two-times that at 300Hz and more than 10 times that at 375Hz for the same duty ratio of 95%. The fall in amplitude as the vibration frequency deviates from the resonant frequency is rapid, and almost at an exponential rate at higher duty ratios, for example, above 60%, as shown in Figure 6. For example, the bristle carrier amplitude at 250Hz and 70% duty cycle is about the same as that at 300Hz and 95% duty ratio. The fall is very rapid in the frequency region near the resonant frequency and the fall slows down substantially when the frequency deviation from the resonant frequency increases. In the example embodiment, the fall in the initial region of 50-70Hz from the resonant frequency is the most rapid fall region. When it is desirable to compensate for the fall in vibration amplitude of the toothbrush head due to deviation of vibration frequency of the motor from the resonant frequency, an amplitude compensation scheme may be adapted. For example, the duty ratio is increased with an increase in deviation in motor vibration frequency from the resonant frequency, where the motor vibration frequency corresponds to the frequency of a selected music note to be played by the toothbrush head. This would operate to equalize or amplify the amplitude of the audio signal of the selected note with respect to the music note at or near the resonant frequency to compensate for the drop due to the resonant characteristics of the toothbrush.

[0077] To implement amplitude compensation schemes, relationship data between motor vibration frequency, bristle carrier vibration amplitude and duty ratio similar to those of Figure 6 are obtained with respect to an example toothbrush as a calibration sample as reference data. The reference data may be used to obtain relationship data on amplitude differences between a reference frequency and other frequencies different from the reference frequency. The reference frequency may be the resonant frequency or a music note frequency closest to the resonant frequency as a convenient example. The relative amplitude differences, in angular terms or percentage amplitude terms, between the reference frequency and the selected music note frequency may be obtained, by the controller or by pre-calculation, and the controller may be configured by stored instructions to utilize the difference date to implement compensation. The compensation need not be 100% and the extent of compensation may be selected according to designer preferences, type or nature of music, or other design factors without loss of generality. For example, a table correlating music note symbols, their characteristic frequencies as set out in Figure 6A may be added with data such as relative vibration amplitudes and duty ratios.

[0078] Where the duty ratio for playing a music note is selected to be dependent on the frequency of the music note, the duty ratios of the different note frequencies or relative duty ratios between the different note frequency and a reference frequency such as a resonant frequency are stored in the data storage device for the controller to utilized when amplitude compensation is required or activated.

[0079] In some embodiments, the duty ratio of the motor-driving signals for playing a music note is selected such that the amplitude remains substantially the same, forming a piece of melody with similar volume. Figure 7A shows relationship between vibration amplitudes, duty ratios and vibration frequencies of different musical notes of an example toothbrush. Referring to Figure 7B, various characteristic frequencies for various music note are further used to calculate the characteristic period time (1/frequency), period of OUT+/OUT- (half the characteristic period time), and time corresponding to 95%, 80%, 70% and 60% of PWM duty ratio. For example, where the target amplitude is 70%, the nearest duty ratio for F3 is 95%, the nearest duty ratio for G3 is 80%, the nearest duty ratio for A3 is 70%, the nearest duty ratio for B3 is 60%, the nearest duty ratio for C4 is 70%, the nearest duty ratio for D4 is 80% and the nearest duty ratio for E4 is 95%, as depicted in Figure 7A. The corresponding time for different duty ratio, depicted in Figure 7B, is stored in the storage device. For example, where the target amplitude is 70%, the nearest duty ratio for G3 and D4 is 80%, which corresponding to 2.04ms and 1.36 respectively.

[0080] An example published tune (“toothbrushing song”) comprises the following note sequence: [G3, E3, G3, G3, E3, G3, A3, G3, F3, E3, D3, E3, F3, G3, C3, C3, C3, C3, E3, G3] The notes forming the sequence has a minimum note frequency of 130Hz and a maximum note frequency of 220Hz. However, an example toothbrush has an example operational note frequency range of 170Hz to 330Hz. To adapt the tune for this toothbrush, the notes forming the sequence are translated into notes having note frequencies falling within the operational note frequency range. The translated note sequence becomes [D4, B3, D4, D4, B4, D4, E4, D4, C4, B3, A3, B3, C4, D4, G3, G3, G3, G4, B3, D4] and all notes in the translated note sequence have note frequencies in the operational note frequency range. The translation is by shifting each note of the sequence by the same number of note positions in the note ladder of Table 2, which in this example is 4.

[0081] An example drive assembly herein comprises a control logic as a controller, a motor drive circuit comprises a PWM signal generator for switching signal generation, and an H-bridge, a ROM for storing melodies and music notes, and a timer.

[0082] The example circuit arrangement of Figure 2B is substantially identical to that of Figure 2A, except that a microprocessor-based controller is used as a controller instead of a logic circuit controller.

[0083] In example embodiments, the motor, the drive circuit and the peripheral circuits including a charging circuit, and the battery are all mounted on a printed circuit board to form a drive assembly in the form of a drive module. Tufts of bristles are distributed and mounted on an example carrier base to form an oval pattern to form a brush head.

[0084] The example toothbrush comprises an example motor sub-assembly. The motor drive sub- assembly comprises a motor and a drive shaft which is a rotor shaft integral with the motor shaft. The example motor is a brushless DC motor having a permanent magnet rotor and a stator having stator windings to operate as an electromagnet having varying magnetic poles when a drive current of alternating directions flows through the stator winding. Example dimensions of the motor sub-assembly in millimeter (mm) are shown on the Figure as a convenient reference.

[0085] When the motor is driven in a vibration mode, the motor may be driven in different ways. In an example way of driving, a braking mode is introduced between clockwise rotation and counterclockwise rotation and/or between counterclockwise rotation and clockwise rotation. In another example way of driving, an off mode is introduced between clockwise rotation and counterclockwise rotation and/or between counterclockwise rotation and clockwise rotation.

[0086] In the braking mode, the second switches of the first and second switching branches are turned on while the first switches of the drive bridge are turned off. This provides a current path for current flow in the motor to flow and provides a sharp or more crisp braking.

[0087] In the off mode, all the first and second switches of the first and second switching branches are turned off. The turning off of all the switches which form a current path means it will take a longer time for the current which was flowing in the motor to drop and provides a smooth stop.

[0088] The braking mode may be used when notes of the same or closely similar pitch are in time abutment or in immediate adjacency to form a clear pause, such as the example of the fist beat of the first bar in the example melody, so that the presence of two discrete tones will be noticeable by the human ears. [0089] The off mode may be used when notes of the different pitches are in time abutment or in immediate adjacency as delineation between the different adjacent notes is readily detectable by the human ears.

[0090] The example motor comprises a rotor having a permanent rotor shaft, a stator having a stator core and a core winding, and a motor housing. The rotor is a permanent magnet rotor carrying a plurality of longitudinally extending magnet slabs and the magnet slabs are to surround the rotor shaft. The stator comprises a magnetic stator core formed of a ferromagnetic material and a core winding comprising a plurality of coils which is wound about the magnetic core to form an electromagnet. When a train of current pulses of opposite directions flow through the core winding, a train of pulsating magnetic fluxes comprising magnetic pulses of opposite magnetic polarities appears on the magnetic pole surfaces of the stator core to cause the rotor to vibrate about its rotor axis. The motor housing may completely or partially enclose the stator-and-rotor sub-assembly.

[0091] The example drive mechanism is a sonic drive assembly of a sonic toothbrush. The sonic toothbrush comprises a sonic drive assembly and an elongate handle housing, inside which the drive assembly, a drive circuit for generating and controlling brushing motions of the drive assembly and a battery are accommodated.

[0092] The drive assembly comprises a motor, a drive-assembly housing and a return spring. The motor comprises a motor body and a motor shaft having a shaft axis. The motor shaft has a protruding portion which protrudes axially from the handle housing to function as a drive shaft. The protruding portion of the motor shaft has a driving end which is adapted for engaging with a coupling end of a toothbrush attachment, which is also known as a toothbrush head, so that vibratory motion generated on the rotor shaft is delivered to the toothbrush head as a toothbrush attachment. The driving end is a free end of the motor shaft portion which protrudes from the top end of the handle housing and which is a distal end from the handle housing.

[0093] During operations, the motor is driven by the drive circuit into side-to-side vibrations about the rotor axis at a sonic frequency. More particularly, the rotor shaft is driven to vibrate, oscillate, or reciprocate at a sonic frequency alternately in clockwise direction about the rotor axis for a first angular amplitude smaller than 45 degrees and in anticlockwise direction for a second angular amplitude smaller than 45 degrees about the shaft axis. The rotor axis is also the motor axis which defines an axial direction of the motor as well as the toothbrush, and is parallel to the longitudinal center axis of the toothbrush.

[0094] The motor body comprises a stator which is mounted on the handle housing and a rotor which is supported on the handle housing and rotatable relative to the stator.

[0095] The rotor is a permanent magnet rotor having a rotor shaft and a permanent magnet assembly mounted on the rotor shaft. The permanent magnet assembly comprises a first magnet slab and a second magnet slab which are mounted on opposite diametrical sides of the shaft axis. Each of the first magnet slab and the second magnet slab is a generally rectangular slab having rectangular pole surfaces and having a longitudinal axis which is aligned with but parallelly offset from the rotor axis. The pole surfaces of the first and second magnets have approximately the same shape, the same dimensions, are edges and ends aligned, but have outward-facing pole surfaces of opposite magnetic polarities facing outwardly away from the rotor and parallel to the rotor axis. The magnet slabs are mounted on a plastic bracket and the plastic bracket is over molded on a length portion of the rotor shaft.

[0096] The effective portion of the permanent magnet assembly has a generally rectangular shape and having a generally uniform rectangular cross section along its length, is disposed intermediate the ends of the rotor shaft, and is more proximal to the end of the rotor shaft that is not the driving end.

[0097] The stator is elongate and comprises a U-shaped core which is formed of a ferromagnetic material and a stator casing. The U-shaped core has a generally uniform U-shape which extends in a longitudinal direction to define its magnetic length. The U-shaped stator core comprises a rectangular base portion which extends in the axial direction between a first longitudinal end and a second longitudinal end and which extends in a transversal direction between a first lateral end and a second lateral end, the transversal direction being orthogonal to the longitudinal direction. The U-shaped stator core comprises a first core arm extending orthogonally upwards from the first lateral end of the base portion and a second core arm extending orthogonally upwards from the second lateral end of the base portion. The first core arm and the second core arm are opposite facing, with approximately the same shape, the same dimensions, and are edges and ends aligned. The first core arm and the second core arm are symmetrically disposed on diametrically opposite sides of the rotor axis so that the air gap between the rotor and the first core arm and the air gap between the rotor and the second core arm are equal, including approximately equal.

[0098] The oppositely facing first core arm and second core arm cooperate to define an internal lateral clearance having a width which is slightly larger than the width of the permanent magnetic assembly. The first core arm, the second core arm and the base portion cooperate to define a U- shaped stator compartment having a lateral clearance such that the permanent magnetic assembly is to vibrate reciprocally about the rotor axis unobstructed on interaction with magnetic fluxes generated by the stator winding.

[0099] The length of the U-shaped stator compartment defines an effective magnetic length of the stator and the length of the U-shaped stator compartment is comparable to or slightly larger than the length of the permanent magnetic assembly for maximal utilization.

[0100] The U-shaped stator has a stator winding to form an electromagnet (EM). The stator winding comprises a plurality of coils and the coils are formed by winding a thinly insulated conductive wire about the base portion. The wire is wound in loops extending between the first and second longitudinal ends of the base portion and the loops have loop planes which are parallel to longitudinal axis of the stator core and the core arms. The coils are wound such that when a current of a first direction flows through the coil, a magnetic pole of a first polarity will appear on the first core arm, and a magnetic pole of a second polarity opposite to the first polarity will appear on the second core arm; when a current of a second direction opposite to the first direction flows through the coil, a magnetic pole of the second polarity will appear on the first core arm, and a magnetic pole of the first polarity will appear on the second core arm; and when no current flows through the winding, the first and second core arms are magnetic neutral and have no magnetic polarity.

[0101] The stator comprises a core casing which is integrally formed on the stator core. The core casing is a hard-plastic casing which is over-moulded on the stator core, and comprises a first end portion which extends axially forward of and away from the first longitudinal end of the stator core and a second end portion which extends axially rearwards and away from the second longitudinal end of the stator core. The first end portion comprises a plurality of forwardly extending studs and the second end portion comprises a plurality of rearwardly extending studs.

[0102] While the disclosure has been made with reference to example embodiments, the embodiments are non-restrictive examples which should not be used to restrict scope of the disclosure.

[0103] For example, while waveforms corresponding to a vibration frequency of 175.4Hz are shown in Figure 4B, the waveforms of Figure 4B will apply mutatis mutandis to other frequencies within the operation frequency range of the toothbrush without loss of generality.

[0104] For example, while the example embodiments have been described with reference to a selected melody example, other musical melodies can be played be the toothbrush upon the drive circuit executing stored instructions containing data of the music melodies without loss of generality.