Personal care device

Abstract

Disclosed concepts provide a personal care device for cleaning a surface of a user, that utilises the generation of a bubble to affect the cleaning of the surface of the user. Specifically, a cleaning element is provided having a space for retaining a fluid, and a heat source evaporates the fluid to generate a bubble. The generated bubble then either directly impacts the surface of the user during use, or the generation of the bubble causes movement of the cleaning element which may impact the surface of the user during use.

Description

[0001] PERSONAL CARE DEVICE

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a personal care device.

[0004] BACKGROUND OF THE INVENTION

[0005] Many personal care devices (e.g., toothbrushes, skin scrubbers) exist for cleaning a surface of a user. It is desirable for such devices to driven in such a way to provide a deep clean of the surface. However, deep cleaning action can result in damage to the user surface and surrounding area if controlled incorrectly.

[0006] By way of example, it may be desirable to provide a safe device that can remove tartar during daily tooth cleaning. Tartar are hard deposits on the teeth that may pose aesthetic and / or health problems. Typically, tartar is removed in a professional environment using mechanical methods, such as by using a metallic scraper or pick, or vibrating scaler. This process requires a skilled person to operate to avoid excessive damage to surrounding oral surfaces. Thus, the current methods for tartar removal cannot be safely implemented in a personal care device as this would result in probable injury to the user.

[0007] Accordingly, there exists a need for a personal care device capable of removing hard deposits on the surface of the user with a reduced chance of damage to the surface.

[0008] SUMMARY OF THE INVENTION

[0009] According to examples in accordance with an aspect of the invention, there is provided a personal care device.

[0010] The personal device comprises a cleaning element comprising a space for retaining a fluid; and a heat source configured to generate a bubble in the space by evaporating fluid retained by the space.

[0011] The generation of the bubble in the space affects movement of the cleaning element, or the generated bubble impacts a cleaning area of a user during use of the personal care device.

[0012] Disclosed concepts provide a personal care device for cleaning a surface of a user, that utilises the generation of a bubble to affect the cleaning of the surface of the user. Specifically, a cleaning element is provided having a space for retaining a fluid, and a heat source evaporates the fluid to generate a bubble. The generated bubble then either directly impacts the surface of the user during use, or the generation of the bubble causes movement of the cleaning element which may impact the surface of the user during use.

[0013] It has been realised that the generation of a bubble may be used to supply a force suitable for cleaning a surface of the subject. That is, the rapid expansion of fluid by evaporation provides a pressure pulse that may either be used for direct cleaning / impact on a surface of a user during use of the device, or for affecting movement of the cleaning element itself. Indeed, the resultant pressure pulse may provide a larger force in a small area, which may be ideal for cleaning surfaces covered in hard materials.

[0014] For example, the force provided by the expansion of fluid by evaporation may be particularly suitable for removing tartar from a tooth surface. To remove tartar, a large force is required in a relatively small area, as the tartar forms a hard covering. It has been discovered that sufficient force may be generated by generation of a bubble in a small area, thus providing the needed pressure for removal of tartar.

[0015] One means by which this generated force may be used is to affect movement of the cleaning element. To this end, example embodiments provide that a bubble is generated in a space defined by the cleaning element, thereby causing the cleaning element to move. In other words, the generation of the bubble from a fluid results in expansion of the fluid in a space, with the expansion force is then translated to movement of the cleaning element. The movement may be a deformation of the cleaning element in a predictable direction.

[0016] Another means for taking advantage of the generated force is a direct impact of a surface by the generated bubble. This may be simpler to implement that by configuring the cleaning element to be movable by the generated bubble / generation of the bubble, and may be used to provide greater force to a target cleaning surface. However, in some circumstances this may also be less controllable / predictable for cleaning than movement of the cleaning element.

[0017] In essence, disclosed embodiments of the invention provide a novel means for affecting cleaning of a surface of a user. Specifically, the personal care device utilises the force provided by the rapid expansion of a fluid in a space by either affecting movement of a cleaning element, or by directly impacting a surface of a user.

[0018] The space of / defined by the cleaning element may be any part of the cleaning element suitable for retaining the fluid. That is, the space may be enclosed so as to contain fluid, or the space may simply hold fluid during evaporation of the fluid.

[0019] The heat source may be any means suitable for evaporation of the fluid in the space, such as an electrical heater or a laser heater. The heat source may be provided in the space, or may be thermally coupled to the space so as to provide the heat necessary for evaporation of the fluid.

[0020] In some cases, the heat source may be configured to generate the bubble by evaporating 10-30pm3of fluid in the space in less than 100ns.

[0021] This evaporation and associated expansion of fluid in the space in a short amount of time may provide sufficient force for the removal of hard substances / materials on a target cleaning surface. Indeed, this fast formation of the bubble may produce a first shock wave, and the generated bubble may then collapse providing a second shockwave.

[0022] For example, this may be particularly useful for removal of tartar on a tooth surface. That is, the rapid expansion of the fluid generates high forces that may directly destroy tartar, or may be used to cause movement of the cleaning element which may result in the destruction of tartar.

[0023] The fluid may be provided to the space during use of the personal care device.

[0024] That is, fluid may be present in the space and therefore retained by the cleaning element when the personal care device is being used for cleaning of a surface of a user. The fluid may be actively provided to the space (e.g., by a fluid supply means, or held in a fluidcontaining chamber of the space), or may be passively provided (e.g., may incidentally be provided during use, such as saliva in a mouth being cleaned).

[0025] The personal care device may further comprise a controller configured to control the heat source to generate the bubble in the space at a target frequency.

[0026] The heat source is driven by a controller, which causes the heat source to evaporate the fluid in the space at a target frequency. Indeed, it may be beneficial to generate many bubbles to impact a target cleaning surface or affect movement of the cleaning element in order to achieve an adequate clean (rather than a single bubble).

[0027] The target frequency may be a range of frequencies, or a frequency scheme that may be dependent upon the application of the personal care device, or the current use / context of the personal care device. The target frequency of the controller may not simply be one frequency that the heat source may be driven at to generate the bubble, but merely a benchmark frequency.

[0028] Specifically, the target frequency may be between 200Hz and 20kHz.

[0029] Generating the bubble at lower frequencies will require less power, and therefore may be more appropriate for portable applications of the personal care device (e.g., due to lower battery size requirements, and associated weight requirements), but may reduce the efficacy of the cleaning of the surface. Generating the bubble at very higher frequencies (e.g., 17kHz - 20kHz) may mean that a sound associated with the generation is non-audible to most adults. Likewise, generating the bubble at specific lower frequencies (e.g., approximately 260Hz) may provide a more pleasant, and therefore less disruptive sound.

[0030] An option to maintain cleaning efficacy, whilst potentially providing a less disruptive sound (by driving the generation for the bubble at 260Hz, for example), may be to split the generation of the bubble between several cleaning elements. For example, providing four cleaning elements each having an associated bubble generation at 250Hz may have a similar cleaning efficacy of a single cleaning element being driven at 1kHz - albeit over a wider area.

[0031] In some cases, the target frequency may be between 1kHz and 5kHz.

[0032] This frequency range may provide an ideal trade-off between cleaning efficacy and power requirements.

[0033] In some embodiments, the heat source may be an RF pulsed power source.

[0034] The RF pulsed power source may be an electrical source having an RF pulsed power amplifier, which converts a low-power RF electrical input into a high power output, suitable for evaporation of the fluid.

[0035] The RF pulsed power source provides an inexpensive and lightweight option for the provision of sufficient heating to the fluid to generate the bubble. Thus, the RF power source may be ideal for cases where the cleaning device needs to be lightweight, portable, and of a reasonable cost.

[0036] The RF pulsed power source may comprise a first electrode and a second electrode physically separated within the space. In this case, the RF pulsed power source may be configured to generate the bubble by providing a current between the first electrode and second electrode through the fluid in the space.

[0037] The first electrode and the second electrode may be shaped, and positioned within the space so that an electrical discharge between them provides energy sufficient to evaporate the fluid. A spark discharge between the two electrodes may provide the energy to the fluid, or the current flowing through the fluid in the space between the two electrodes may heat the fluid directly (by resistive heating).

[0038] The RF pulsed power source may further comprise a first capacitor provided in series between the first electrode and the RF pulsed power amplifier, and a second capacitor provided in series between the second electrode and the RF pulsed power amplifier.

[0039] The high electrical tension between the first and second electrode may be a safety hazard under specific conditions if not handled correctly. Thus, the first and second capacitors connected in series with the electrodes may avoid high tension at low frequency of the RF pulsed power source. Indeed, the electrical tension only provides a safety hazard at low frequency.

[0040] Additionally or alternatively, the RF pulsed power source may further comprise a transformer electrically coupling the first electrode and the second electrode to the RF pulsed power amplifier.

[0041] The transformer may be used instead of, or in addition to the capacitors to limit the current. A size of the core of the transformer may limit the current that may flow between the first and second electrodes when soft magnetic core material is used in the transformer, and therefore the energy provided in each cycle. Accordingly, safety of the personal care device may be improved.

[0042] In addition, the transformer may be used as a switching matrix between the RF pulsed power amplifier and multiple cleaning elements as disclosed. In other words, multiple cleaning elements having a space for retaining fluid, and first and second electrodes in the space, may be driven by one RF pulsed power amplifier using a switching matrix of transformers. In an implementation, the RF pulsed power amplifier may be connected to each primary winding of the transformers, with a secondary winding corresponding to the primary winding connected to the first and second electrode. By sweeping a field (e.g., by moving a magnet between transformers) only one of the transformers may not be in saturation and so conducts power to the corresponding first and second electrodes of one of the cleaning elements.

[0043] The RF power source may comprise a metal structure provided within the space. In this case, the RF power source may be configured to generate the bubble by providing a current through the metal structure.

[0044] Another method to transfer power from the RF power source may be to provide a metal structure that may predictably heat, and therefore transfer energy, to fluid in the space. This may transfer energy at a slower rate than by directly running current through the fluid, but may generate bubbles in a more predictable manner. That is, the fluid resistance may not be known with complete certainty, and therefore the energy provided to the fluid may not be known with certainty, whereas the resistance of a metal structure may be known from which energy transfer can be derived.

[0045] The metal structure may comprise one or more Wollaston wires, which may be well suited for supplying the appropriate energy to the fluid. It is worth noting that different heating mechanisms may be combined to generate the bubble.

[0046] The personal care device may further comprise a sensor arrangement configured to measure a load impedance of the RF pulsed power source; and a controller configured to switch off the RF pulsed power source responsive to the measured load impedance meeting a predetermined safety criterion.

[0047] Accordingly, excessive tissue heating (corresponding to a surface being cleaned) may be avoided. That is, if the measured load impedance changes beyond establish / predetermined parameters, then the RF pulsed power source may be switched off (i.e., made to provide no power for a given period of time). Thus, tissue heating may be avoided in a straightforward, quick and efficient manner.

[0048] In some embodiments, the space may be enclosed by a shell defining a volume containing the fluid.

[0049] The shell (i.e. a cavity) may form part of the cleaning element. In other words, the cleaning element may be shaped so as to have a shall that defines a volume for containing / holding the fluid. Thus, rather than being exposed to the surrounding environment, the space in which the fluid is evaporated so as to generate the bubble is enclosed by the shell.

[0050] As a result, the generation of the bubble affects the movement of the cleaning element by providing a force onto an inside wall of the shell - either deforming the shell or moving the cleaning element in a direction.

[0051] The fluid contained in the shell may comprise a solution having high salinity.

[0052] As the shell contains the fluid, the fluid may have certain properties. For example, a solution having high salinity may form a part of the fluid. Therefore, resistance of the fluid may be decreased by the salinity, meaning that heating by providing a current through the fluid may be increased (and controlled) without increasing a provided power. That is, higher salinity of the fluid decreases resistivity of the fluid, so a lower voltage is needed to deliver the power. The lower voltage is safer and needs less space in the leads for insulation.

[0053] Furthermore, the fluid contained in the shell may comprise a hydroscopic substance.

[0054] A shell / cavity of the cleaning element may not be perfectly impervious to diffusion, and therefore fluid may slowly escape from the shell. By providing a hydroscopic substance as part of the fluid, the fluid may be more effectively contained within the shell.

[0055] The hydroscopic substance may be at least one of glycerol and calcium chloride. The shell may be formed of a flexible substance, and may further comprise a plurality of rigid protrusions on an outer surface of the shell.

[0056] As the shell is formed of a flexible substance, the generation of the bubble in the shell may cause the shell to deform and thus provide a cleaning action. In other words, as the shell is compliant, the expansion of the fluid into a bubble may cause the shell to flex and thus may be used to provide movement for cleaning of a target surface.

[0057] In order to provide enhanced cleaning, rigid protrusions of a suitable hardness for cleaning of the surface, while avoiding excessive damage to the surrounding surface, may be provided. The rigid protrusions may be in the form of ridges or spikes formed over at least part of an outer surface of the shell.

[0058] In some embodiments, the cleaning element may comprise a tip portion and a body portion. In this case, generation of the bubble in the space may affect movement of the tip portion relative to the body portion.

[0059] The body portion may be the main portion of the cleaning element that may connect to a body of the personal care device, whereas the tip portion may be the end of the cleaning element intended to be in contact with a target surface of the user for cleaning.

[0060] By this configuration, there may arise sideways (i.e. perpendicular to the direction of the length of the cleaning element) movement of the tip, which may be particularly suitable for removing hard materials on the surface of the user.

[0061] In some implementations, the tip portion and the body portion may be connected by an element acting as a joint so that the tip rotates relative to the body portion upon generation of the bubble. However, other implementations provide that the tip portion effectively acts as a device propelled by generation of the bubble, with no requirement for relative bending between the body portion and tip portion.

[0062] According to examples in accordance with an aspect of the invention, there is provided an oral care device having the features of any disclosed personal care device. In this case, the cleaning element is flexible.

[0063] The disclosed personal care device may be particularly suitable as an oral care device to remove tartar or hard calcified plaque. The generation of bubbles by evaporation of fluid has been shown to provide adequate forces for the removal of such hard substances from an oral surface, whilst also avoiding excessive damage to surrounding oral surfaces.

[0064] In this case, the cleaning element should be flexible / compliant, so that over pressuring of the cleaning element on the surface may be prevented, and therefore damage to gums avoided. That is, at least part of the cleaning element may be formed of a flexible material so as to bend when excessive pressure is exerted by the cleaning element on an oral surface.

[0065] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0066] BRIEF DESCRIPTION OF THE DRAWINGS

[0067] For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0068] Figure 1 presents a simplified schematic diagram of a cleaning element of a personal care device according to an embodiment of the invention;

[0069] Figure 2 presents a simplified schematic diagram of another cleaning element of a personal care device according to a further embodiment of the invention; and

[0070] Figure 3 presents a simplified schematic diagram of a cleaning element of a personal care device according to another embodiment of the invention.

[0071] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0072] The invention will be described with reference to the Figures.

[0073] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0074] It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0075] Disclosed concepts provide a personal care device for cleaning a surface of a user, which utilises the generation of a bubble to affect the cleaning of the surface of the user. Specifically, a cleaning element is provided having a space for retaining a fluid, and a heat source evaporates the fluid to generate a bubble. The generated bubble then either directly impacts the surface of the user during use, or the generation of the bubble causes movement of the cleaning element which may impact the surface of the user during use.

[0076] It has been shown that the rapid generation of a bubble from fluid may provide sufficient forces for the cleaning of a user surface. The generation of a bubble arises from the rapid expansion of the fluid, with the expansion force being utilised to either directly impact the surface, or to affect movement of a cleaning element that may in turn impact the surface.

[0077] The generation of a force using the generation of the bubble in such a way may be utilised for cleaning hard but brittle substances / materials on the surface of the user, whilst avoiding undue damage to the underlying and surrounding (mainly soft) surface. This may be particularly beneficial for personal care devices for use in the cleaning of oral tissue (e.g., for use in toothbrushes or mouth pieces). Nonetheless, this idea may also be implemented in other personal care devices that are used for cleaning of the user.

[0078] By way of explanation, removal of tartar during daily tooth cleaning is not currently possible for the average person. In the professional environment, tartar removal is mainly achieved using mechanical methods by a trained dental professional such as a dentist or dental hygienist. This removal relies on the fact that tartar is much softer and more brittle than the tooth itself. More particularly, the trained dental professional can remove calculus by scratching with a metallic pick or scraper over the teeth. Alternatively, or additionally, the trained dental professional may use a vibrating scaler. The vibrating scaler uses the same scratching approach as the metallic pick, only with higher frequency.

[0079] Put another way, high pressures for substance removal are reached by focusing a moderate force on a small spot by means of a metallic tip. This works well when the tip is placed at the correct position, but the necessary force is high enough to punch through surrounding tissue, or create scratches in underlying tissue if not properly operated. Ultrasound may be employed in the tipped device to reduce the risk of damage, with the tip moved sideways over the surface. Surface irregularities focus the force on the hard surface material, thus relying on fundamentally same mechanism as the plain scratching. The mechanism that makes the ultrasonic action safer is the relatively small amplitude and relatively high velocities of the scratching. The high velocities reduce the needed normal force therefore avoiding a deep punctuation of the gum tissue when the gum is accidentally touched. As the gum is relatively soft, it can be moved some distance without ripping apart. So, the ultrasound only moves the gum but, if parameters are set right, does not much harm.

[0080] It is impractical for a regular user to use such a tool on themselves due to a high risk of gum or tooth tissue injury. In essence, the main problem with the current technology is that it requires hard metal scrap ers / picks to work which are hazardous as it is easy to apply damaging pressures on tooth or gum structures.

[0081] To mimic this process in a personal care device, without exerting excessing stress on surrounding oral tissue (e.g., gum, exposed tooth), disclosed concepts use a pressure pulse generated at or near the tip of cleaning element. The pressure pulse generation mechanism is based on the rapid generation of a bubble at or near the tip of a cleaning element by a heat source, which may have low spatial and temporal dimensions to only impact a small area. For example, an electrical discharge with low spatial and temporal dimensions may be utilised to generate the bubble.

[0082] Therefore, short pulse action at the tip of a compliant structure is desired. Such compliant structure would prevent non-trained users to overpressure the tip leading to the potential damage, while the short pulsed mechanical action, if properly controlled, can deliver sufficient mechanical force to remove tartar without damaging the tooth structure below. Secondly, strong mechanical pulses should not be applied directly on the gum tissue, or they should be controlled in such a way that they are not damaging for soft tissues. In addition, the cost of the device needs to be reasonably low.

[0083] Put another way, disclosed concepts utilise a similar principle to that utilised by cast saws or other low vibration amplitude cutting tools. These tools are, in the most part, safe when in contact with tissue, but cut very well into harder materials. To implement this basic concept into a personal care device, it is proposed to use a fast heating and evaporation of fluid to generate a pressure pulse (in the form of a bubble) to remove hard substances on the surface (e.g., tartar on oral tissue).

[0084] Specific examples provide two electrodes as a heat source in a space of the cleaning element adapted to retain the fluid (i.e. a fluid compartment). As a result, this can be integrated into a tip of the cleaning element (i.e. a tip of a bristle). Other quick heating methods, such as lasers, could also be utilised as the heat source, but may be more costly that the electrode method and so the suitability of such a heat source would depend on the application of the personal care device.

[0085] The cleaning element may be flexible / compliant, so that over-pressurising by the cleaning element on a surface of the user may be avoided. The space for retaining the fluid may be exposed to the environment, such that the fluid may be a mixture of toothpaste and saliva when the personal care device is for oral use. Other examples, provide the fluid inside a shell of the cleaning element for containing the fluid. In the case that electrodes are provided in the space, an RF power source may be provided to apply a high frequency voltage (e.g., > 10 MHz) to the electrodes. Accordingly, a fluid volume of approximately 10pm3to 30pm3may be evaporated to generate the bubble within about 100ns or less. The rapid expansion generates high forces that can destroy hard substances such as tartar by moving the cleaning element against the hard substance, but additionally the force can be controlled by the RF power source to prevent damage of underlying user surface. In any case, the small high frequency movement may be relatively benign for the surrounding tissue of the user in comparison to the hard material deposits to be cleaned.

[0086] In some cases, a hard material structure may be provided at the tip of the cleaning element to effectively break up hard substances / materials on the surface of the user. For example, hard and / or abrasive particles in the material forming the cleaning element may provide this function.

[0087] The generation of a cavitation bubble at the surface may be an alternative to the affecting of a movement of the cleaning element thereby providing a cleaning action. That is, the bubble itself and its associated generation may provide the force to directly impact a target cleaning surface of the user, and therefore provide the cleaning action. It should be noted that this may be more difficult to control the force provided by the bubble itself, than the force by the bubble via the cleaning element movement, and therefore damage to surrounding and / or underlying surface may be more likely. However, the direct impact by the cavitation bubble may also provide highly effective cleaning with relatively low power.

[0088] Overall, embodiments of the invention enable the removal of hard substances on a user surface (such as hard plaque, tartar) compared to existing personal devices for cleaning. In addition, compared to professional devices (such as scrapers and vibrating scalers), implementations of the invention enable fine control of the forces and force dynamics that are used on target cleaning surface, enabling effective cleaning without potential damage. This enables the use of the personal care device by a user on themselves, for example integrated in a toothbrush or skin scrubber.

[0089] Moving on to Fig. 1, there is depicted a system that may be implemented in a personal care device. The system comprises a cleaning element 110 (e.g., a bristle) comprising a space 112 for retaining a fluid, and a heat source 120. The system may optionally further comprise a controller. The personal care device may comprise a plurality of cleaning elements 110, and one or more heat sources 120. In this case, each cleaning element 110 may have a different orientation, and thus a different surface action.

[0090] The heat source 120 is configured to generate a bubble in the space 112 by evaporating fluid retained by the space 112. Either the generation of the bubble in the space 112 affects movement of the cleaning element 110, or the generated bubble impacts a cleaning area of a user during use of the personal care device.

[0091] The main objective of the invention is to generate locally high pressures and tangential forces at a cleaning surface. Only a sufficiently high pressure or tangential force can destroy hard substances on the cleaning surface. This is achieved by the fast formation of a bubble by evaporation of fluid, which may produce a first shock wave. In addition, when the bubble collapses (i.e. cavitation collapse) a second shock wave may be generated, which may also provide force sufficient for cleaning. These forces can either be used to directly impact a target cleaning surface (during use of the personal care device), or to drive movement / motion of cleaning elements 110 that may, in turn, impact a target cleaning surface.

[0092] The heat source 120 may be configured to generate the bubble by evaporating 10- 30pm3of fluid in the space 112 in less than 100ns. By evaporating this volume of fluid in this amount of time, the first and second shock waves may be generated, thereby providing large amounts of force with relatively little power. Of course, larger / small amounts of fluid can be evaporated in longer amounts of time that will still provide a force via the expansion of the fluid into a bubble, but this range of values may provide a particularly large amount of force. Indeed, this range may provide a suitably large force while not overheating the heating element and / or causing excessive damage.

[0093] The fluid may be provided to the space 112 during use of the personal care device. That is, fluid is in the space 112 so that it can be evaporated into a bubble by the heat source 120, thereby affecting movement of the cleaning element 110 or impacting the target cleaning area. The fluid may always be present in the space 112 (i.e. the space 112 may hold the fluid), or the fluid may be cycled in the space 112 during use. For example, if the personal care device is for use on an oral surface, the fluid may be saliva that is passively provided by the user during use. Alternatively, if the personal care device is for use on a skin surface, the personal care device may be for use in the shower or bath in which water is continuously provided to the skin surface.

[0094] In some cases, the personal care device may comprise a controller 130 configured to control the heat source 120 to generate the bubble in the space 112 at a target frequency. That is, the controller may drive the heat source 120 to generate the bubble at a certain rate. The controller may be a separate component to the heat source 120, or may be an integrated part.

[0095] The target frequency may be between 200Hz and 20kHz. Preferably the target frequency is between 1kHz and 5kHz to ensure a balance between power consumption and cleaning efficacy. The target frequency may be a predetermined frequency, or may be set based on user preferences, or a use of the personal care device. The controller may control the heat source 120 at various frequencies around the target frequency.

[0096] The heat source 120 may be any means suitable for evaporating a fluid in a space 112. For example, the heat source 120 may be a laser, or a resistive heater. The heat source 120 may be thermally coupled to the space 112 for retaining the fluid, so that thermal energy can be transferred to the space 112 for evaporation of the fluid and hence generation of the bubble.

[0097] In some embodiments, the heat source 120 is a radio frequency (RF) pulsed power source (i.e. an electrical power source comprising an RF pulsed power amplifier). Specifically, the RF pulsed power source may comprise a first electrode and a second electrode physically separated within the space 112. Accordingly, the bubble is generated by providing a current between the first electrode and second electrode through the fluid in the space 112. Alternatively, or additionally, the RF power source may comprise a metal structure provided within the space 112. Accordingly, the bubble is generated by providing a current through the metal structure (e.g., one or more Wollaston wires). In fact, any means, or combination thereof, of converting electrical energy from the RF power source to thermal energy in the space 112 may be suitable for implementation of the heat source 120.

[0098] By way of explanation, electrical discharges can produce large amounts of power in a small volume. Indeed, spark discharges have been shown to provide enough power in a small enough space 112 to be suitable for kidney stone removal. To provide the spark discharge, a first and second electrode may be in direct contact with the fluid in the space 112. Accordingly, a spark discharge between the first and second electrode may evaporate, for example, 20pm3of fluid into a 200pm gas bubble.

[0099] The energy required for the example bubble formation is approximately 20pJ. The energy may be delivered in about the time sound travels through the bubble (~100ns). Therefore, the power to be supplied to the fluid to cause this is around 200W. It may be desirable to restrict the power consumed by the cleaning element 110 to approximately 0.1W, and therefore 5000 pulses (i.e. 5000 bubbles) may be generated per second. Of course, this may be split between several cleaning elements. Alternatively (or additionally), in small dimensions of the cleaning element 110, a real arc discharge is also not required to provide the energy to evaporate the fluid. That is, the fluid may be heated by running a current directly through the fluid. A typical resistivity of the fluid may be about 50kQ (for IQm typical isotonic fluid conductivity). Thus, for the 200W power input, the electric tension needs to be approximately 3kV. This is relatively high, but electrical arcing may not be inevitable. By careful electrode design (e.g. more length, annular shaped, etc.), the resistivity may be reduced to approximately IkQ, leading to a necessary tension of 450V. The current rating depends on the used voltage. For the above examples of 3kV and 450V, the current rating may be between 60mA and 450mA. As a lead resistance to the electrodes may be below IQ, almost all of the energy is delivered to the fluid.

[0100] Nevertheless, other methods to deliver high power into a small volume of fluid can produce the same magnitude of shock waves as electrical discharges and direct current flow. Lasers are an example of such alternative energy delivery methods. The main drawback is the bulkiness and high cost of these methods compared to the RF power source.

[0101] In order to improve safety of the device, a few methods may be employed.

[0102] Firstly, the RF pulsed power source may further comprise a first capacitor provided in series between the first electrode and the RF pulsed power amplifier, and a second capacitor provided in series between the second electrode and the RF pulsed power amplifier. This may avoid high electrical tension at low frequency (in which the high tension poses a hazard).

[0103] Secondly, the RF pulsed power source may further comprise a transformer electrically coupling the first electrode and the second to the RF pulsed power amplifier. This may be in addition to, or instead of, the capacitors.

[0104] The size of the cores of the transformer may limit the energy that can be transferred in each cycle of the RF pulsed power supply, therefore making the device safe. As an additional, the transformer may be used as a simple and inexpensive switching matrix between the heat source 120 and different cleaning elements 110. The RF pulsed power supply may be connected to all the primary windings of transformers connected to different electrodes in spaces of different cleaning elements 110. By moving a magnet, or by sweeping a field, only one of the transformers is not in saturation and then conducts the power to the electrode of the respective cleaning element 110.

[0105] Furthermore, the personal care device may further comprise a sensor arrangement configured to measure a load impedance of the RF pulsed power source. In this case, the controller may be configured to switch off / disconnect the RF pulsed power source responsive to the measured load impedance meeting a predetermined safety criterion. This may avoid excessive heating of a surface of the user by switching off the heat source 120 outside the established parameters, thereby preventing evaporation of fluid and formation of a bubble.

[0106] The cleaning element 110 depicted in Fig. 1 may be implemented in a personal oral care device (e.g., a toothbrush or mouthpiece). In this case, the cleaning element 110 must be flexible to avoid damage to oral surfaces. The cleaning element 110 must be flexible (e.g., soft and compliant as brushes use in typical toothbrushes) while provide high pressure for a very low displacement distance.

[0107] An alternative implementation of the cleaning element 110 in presented in Fig. 2. In figure 2, the space 112 of the cleaning element 110 is enclosed by a shell 114 defining a volume containing the fluid. That is, the cleaning element 110 comprises / defmes a cavity within which the fluid may be contained / held for evaporation.

[0108] The depicted cleaning element 110 may have enhanced safety characteristics over the cleaning element 110 with a space 112 open to the environment. Indeed, the heat source 120 may not be exposed to the environment and therefore risk of injury (by excessive heating or by electrical discharge) may be reduced. Here, the bubble is generated inside a cavity of the cleaning element 110. The cavity / space 112 in the bristle may have a flexible outer shell 114 to effectively transmit the pressure pulses produced by generation of the bubble.

[0109] The fluid contained in the shell 114 may comprise a solution having high salinity. This may be beneficial when the heat source 120 comprises first and second electrodes in the space 112, as the high salinity reduces a resistivity of the fluid. Indeed, taking the examples above into account, the required electrical tension may be reduced below 100V, further improving safety,

[0110] Furthermore, the fluid contained in the shell 114 may comprise a hydroscopic substance, such as glycerol and calcium chloride, in order to more effectively retain / contain the fluid. The draw-back of containing the fluid in a shell 114 / cavity is that they are usually not diffusion tight and, given a small size, the fluid may rapidly leave the shell 114. Indeed, it is unlikely that the shell 114 will be completely impervious to fluid, so a hydroscopic substance may be used to ensure that sufficient fluid remains in the shell 114.

[0111] In some embodiments, the hydroscopic substance may be a hydroscopic salt, such as calcium chloride. This may provide a dual advantage of retaining fluid within the shell, while reducing the resistivity of the fluid within the shell.

[0112] As also demonstrated in Fig. 2, the shell 114 may further comprise a plurality of rigid protrusions 116 on an outer surface of the shell 114. The rigid protrusions 116 may be formed by metals or ceramics in a polymer matrix. These may provide adequate cleaning action to break down hard substance, even when the shell 114 is formed of a flexible material.

[0113] Fig. 3 describes yet another alternative of the cleaning element 110 configuration. Specifically, the cleaning element 110 comprises a tip portion 118a and a body portion 118b. In this case, generation of the bubble in the space 112 affects movement of the tip portion relative to the body portion, and / or movement of the tip and body portion together by means of a rocket impulse effect.

[0114] In other words, instead of accelerating a part of the cleaning, the whole bristle may be accelerated towards the tooth. This can be accomplished by forming a bubble jet sideways (relative to a longitudinal direction of the cleaning element 110). The advantage of this particular design is that the tip portion does not just exhibit a normal force (relative to the longitudinal direction) responsive to bubble generation, but also a sideways / pivoting acceleration. This helps to create a tangential force to suitable to remove hard material on the target cleaning surface.

[0115] Generally, the force magnitude and dynamics of the generated bubble may be tuned and controlled. As disclosed above, surrounding surface integrity can be assured by using high frequency, but small amplitude force from the generation of the bubble. This force can be used to break down hard, brittle substances, but may not impact soft tissue. The combination of design of the cleaning element 110 (i.e., shape, space 112 shape, and material selection), and power provided by the heat source 120 (e.g., RF power) will determine the force produced by the generated bubble. Thus, with certain design of the cleaning element 110, the force produced by the bubble can be controlled with power supplied by the heat source 120.

[0116] In some implementations, this allows the applied force to be changed during operation (by altering the power supplied by the heat source 120). That is, a user may change the power according to their experiential preference. As another example, the personal care device may be equipped with position sensors, and the power may be changed based on the position of the personal care device. For example, when the personal care device is positioned such that the cleaning element 110 is positioned on an exposed root surface (due to retracted gums) the power supplied by the heat source 120 may be lowered to not damage the softer tooth root.

[0117] To further enhance safety and efficiency of the device, the operation may be restricted to situations where the cleaning element 110 is positioned near to hard material on the surface to be cleaned (e.g., tartar deposits). One way to achieve this is to track the position of the personal care device relative to the target cleaning surface using optical or electromagnetic methods. Only if a specific cleaning element 110 is close to the target cleaning surface is the heat source 120 activated, and therefore removal performed. Alternatively, or additionally, a force / bending detector of the cleaning element 110 may be used to establish when the cleaning element 110 is in contact with a surface. Only an established contact results in activation.

[0118] To be more selective, other sensors and methods of determining proximity to a target cleaning surface may be utilised. One method may be the addition of electrodes at the tip of the cleaning element 110, which may use electrical impedance spectroscopy to identify hard substances on the surface. A more complex but effective method would be to identify hard substances optically.

[0119] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. If a computer program is discussed above, it may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. If the term "adapted to" is used in the claims or description, it is noted the term "adapted to" is intended to be equivalent to the term "configured to". Any reference signs in the claims should not be construed as limiting the scope.

[0120] The block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). It will also be noted that each block of the block diagrams, and combinations of blocks in the block diagrams, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

Claims

CLAIMS:

1. A personal care device comprising: a cleaning element (110) comprising a space (112) for retaining a fluid; and a heat source (120) configured to generate a bubble in the space by evaporating fluid retained by the space, wherein: the generation of the bubble in the space affects movement of the cleaning element; or the generated bubble impacts a cleaning area of a user during use of the personal care device.

2. The personal care device of claim 1, further comprising a controller (130) configured to control the heat source (120) to generate the bubble in the space at a target frequency, and optionally wherein the target frequency is between 200Hz and 20kHz, and preferably between 1kHz and 5kHz.

3. The personal care device of claim 1 or 2, wherein the heat source (120) is an RF pulsed power source.

4. The personal care device of claim 3, wherein the RF pulsed power source comprises a first electrode and a second electrode physically separated within the space (112), and wherein the RF pulsed power source is configured to generate the bubble by providing a current between the first electrode and second electrode through the fluid in the space.

5. The personal care device of claim 4, wherein the RF pulsed power source further comprises a first capacitor provided in series between the first electrode and the RF pulsed power amplifier, and a second capacitor provided in series between the second electrode and the RF pulsed power amplifier.

6. The personal care device of claim 4 or 5, wherein the RF pulsed power source further comprises a transformer electrically coupling the first electrode and the second electrode to the RF pulsed power amplifier.

7. The personal care device of any of claims 3-6, wherein the RF power source comprises a metal structure provided within the space, and the RF power source is configured to generate the bubble by providing a current through the metal structure, and optionally wherein the metal structure comprises one or more Wollaston wires.

8. The personal care device of any of claims 3-7, further comprising: a sensor arrangement configured to measure a load impedance of the RF pulsed power source; and a controller configured to switch off the RF pulsed power source responsive to the measured load impedance meeting a predetermined safety criterion.

9. The personal care device of any preceding claim, wherein the space is enclosed by a shell (114) defining a volume containing the fluid, and optionally wherein the fluid contained in the shell comprises a solution having high salinity.

10. The personal care device of claim 9, wherein the fluid contained in the shell (114) comprises a hydroscopic substance, and optionally wherein the hydroscopic substance is at least one of glycerol and calcium chloride.

11. The personal care device of claim 9 or 10, wherein the shell (114) is formed of a flexible substance, and further comprises a plurality of rigid protrusions (116) on an outer surface of the shell.

12. The personal care device of any preceding claim, wherein the cleaning element comprises a tip portion (118a) and a body portion (118b), wherein generation of the bubble in the space (112) affects movement of the tip portion relative to the body portion.

13. The personal care device of any preceding claim, wherein the heat source (120) is configured to generate the bubble by evaporating 10-30pm3of fluid in the space (112) in less than 100ns.

14. The personal care device of any preceding claim, wherein the fluid is provided to the space (112) during use of the personal care device.

15. An oral care device according to any preceding claim, wherein the cleaning element(110) is flexible.

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