Surface treatment device and method

Abstract

A sensor is provided for sensing layer removal from a surface. A head has an abrasive portion for contacting the surface and a conducting portion inside the head. This device has a sensor design which provides self-generation of a sensor signal with no power supply to the device head. This simplifies the design of the sensor head, and means it can have a design which is easy to clean with no parts which are easily damaged. In one set of examples, the device is a skin treatment device.

Claims

1. A skin treatment device, comprising; a head; an abrasive ring disposed at an end of the head for contacting a skin surface; and a sensor for sensing layer removal from the skin surface, the sensor comprising: a contact electrode; a handle electrode; a circuit adapted to measure a voltage between the contact electrode and the handle electrode; a triboelectric generator for generating charge in response to movement of the abrasive ring over the skin surface, wherein the triboelectric generator is used as a sensor for measuring a parameter which is dependent on a level of layer removal, signal from the sensor comprising the charge generated by the generator; a voltage measuring circuit for measuring a voltage between the contact electrode and the skin surface; and a voltage rate measuring circuit for measuring a rate of change of the voltage between the contact electrode and the skin surface, wherein the contact electrode is shielded by a non-conduction portion, and the contact electrode is configured not to be in physical contact with a user during use of the skin treatment device.

2. The skin treatment device as claimed in claim 1, wherein the contact electrode comprises a metallic disc which functions as a passive induction electrode.

3. The skin treatment device as claimed in claim 1, wherein the abrasive ring is adapted to contact the skin.

4. The skin treatment device as claimed in claim 1, further comprising a suction system.

5. The skin treatment device as claimed in claim 1, wherein the handle electrode is configured to be in electrical contact with a user during use of the skin treatment device.

6. The skin treatment device as claimed in claim 1, wherein the handle electrode has an area of between 10 and 250 square centimeters.

7. The skin treatment device as claimed in claim 1, further comprising: an output device and a controller for controlling the output device, which is adapted to provide an output warning when the skin treatment should be ceased based on the measured parameter.

8. The skin treatment device as claimed in claim 1, wherein the abrasive ring comprises a ceramic material or rubber.

9. The skin treatment device as claimed in claim 1, wherein the contact electrode comprises a metal disc, which functions as a passive induction electrode.

10. A skin treatment device, comprising: a head; an abrasive ring disposed at an end of the head for contacting a skin surface; and a sensor for sensing layer removal from the skin surface, the sensor comprising: a contact electrode; a handle electrode; a circuit adapted to measure a voltage between the contact electrode and the handle electrode; a triboelectric generator for generating charge in response to movement of the abrasive ring over the skin surface, wherein the triboelectric generator is used as a sensor for measuring a parameter which is dependent on a level of layer removal, a signal from the sensor comprising the charge generated by the generator; a voltage measuring circuit for measuring a voltage between the abrasive ring and the skin surface, wherein the abrasive ring is adapted to receive electrons from the skin caused by a triboelectric effect caused by the triboelectric generator.

11. The skin treatment device as claimed in claim 10, wherein the contact electrode comprises a metallic disc which functions as a passive induction electrode.

12. The skin treatment device as claimed in claim 10, wherein, the abrasive ring is adapted to contact the skin.

13. The skin treatment device as claimed in claim 10, further comprising a suction system.

14. The skin treatment device as claimed in claim 10, wherein the handle electrode is configured to be in electrical contact with a user during use of the skin treatment device.

15. The skin treatment device as claimed in claim 10, wherein the handle electrode has an area of between 10 and 250 square centimeters.

16. The skin treatment device as claimed in claim 10, wherein the abrasive ring comprises a ceramic material or rubber.

17. The skin treatment device as claimed in claim 10, further comprising: an output device and a controller for controlling the output device, which is adapted to provide an output warning when the skin treatment should be ceased based on the measured parameter.

18. The skin treatment device as claimed in claim 10, wherein the contact electrode comprises a metal disc, which functions as a passive induction electrode.

19. The skin treatment device as claimed in claim 10, wherein the sensor further comprises a voltage rate measuring circuit for measuring a rate of change of the voltage between the contact electrode and the skin surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a skin treatment system;

(3) FIG. 2 shows the skin before and after treatment;

(4) FIG. 3 shows the effect of the treatment on the skin resistance based on tape stripping;

(5) FIG. 4 shows the skin treatment device in more detail;

(6) FIG. 5 shows in simplified form a voltage amplifier circuit for detecting the triboelectrically generated charge;

(7) FIG. 6 shows an simplified equivalent circuit for the sensor system when in contact with the skin; and

(8) FIG. 7 shows the results of an experimental use of the system.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(9) The invention provides a sensor for sensing layer removal from a surface. A head has an abrasive portion for contacting the surface and a conducting portion. A generator is used for generating charge in response to movement of the abrasive portion over the surface. The generator is used as a sensor for measuring a parameter which is dependent on the level of layer removal, the sensor signal comprising the charge generated by the generator.

(10) This device has a sensor design which provides self-generation of a sensor signal with no power supply to the device head. This simplifies the design of the sensor head, and means it can have a design which is easy to clean with no parts which are easily damaged.

(11) In one set of examples, the device is a skin treatment device. The invention will be described in detail with reference to an implementation for a skin treatment device.

(12) The invention makes use of charge generation induced by rubbing or contact between materials. This may be based electrostatic charging, although preferred examples make use of the triboelectric effect. The triboelectric effect is a physical phenomenon that has been known for a long time. Due to the triboelectric effect (also known as triboelectric charging, contact electrification or triboelectrification) certain materials become electrically charged after they come into contact with another different material through friction. Especially dry skin (stratum corneum) is highly triboelectrically active as often experienced in everyday life e.g. static discharges as shooting sparks when touching objects like a door handle.

(13) The triboelectric effect is based on a series that ranks various materials according to their tendency to gain electrons (become negatively charged) or lose electrons (become positively charged). This series is for example disclosed in A. F. Diaz and R. M. Felix-Navarro, A semi-quantitative triboelectric series for polymeric materials: the influence of chemical structure and properties, Journal of Electrostatics 62 (2004) 277-290. The best combinations of materials to create static electricity are one from the positive charge list and one from the negative charge list (e.g. PTFE against copper, or fluorinated ethylene propylene (FEP) against aluminum). Skin tends to become positively charged when brought in contact with other materials. This means skin is an electron donor and on the top of the triboelectric list. The end of this list includes electron acceptors such as various rubber compounds including for example santoprene rubber, hypalon rubber, butyl rubber, ethylene propylene diene monomer (EDPM) rubber, polydimethylsiloxane (PDMS), as well as polytetrafluoroethylene (PFTE, Teflon).

(14) For generating triboelectric charge when contact is made with the skin, the rubbers (and Teflon) listed above are examples of suitable materials, although others (such as aluminum oxide ceramic) will be known to those skilled in the art, by consulting the triboelectricity series.

(15) The triboelectric generation process involves the conversion of mechanical energy into electrical energy through a coupling between two main physical mechanisms: contact electrification (tribocharging) and electrostatic induction.

(16) This invention makes use of the triboelectric effect (and capacitive coupling) as a sensor principle for sensing the thickness of the top layer of a layered structure, such as the stratum corneum in the case of the skin, rather than for electricity generation or power harvesting.

(17) With increased removal of the stratum corneum which is a compact dense and insulating layer of dead, keratin filled corneocytes the skin becomes more hydrated and potentially less electrified as more hydrated, viable epidermal skin layers are accessed. Consequently skin layer resistance decreases and electrostatic charges cannot built up.

(18) FIG. 1 schematically shows an embodiment of the microdermabrasion device 1. The device 1 comprises a vacuum system, with a pump 2 and a channel 4. A removable device tip (a cap or head) 6 is provided. The pump 2 can suck air into the channel 4, and the channel has a channel inlet at the device head 6. The channel inlet is surrounded by a channel rim 7. This channel rim 7 facilitates gliding of the device head 6 over the skin (not shown). The device head 6 for example comprises a microdermabrasion zone configured remote from the channel inlet. The microdermabrasion zone is in the form of an abrasive ring which for example circumferentially surrounds the channel rim 7. The microdermabrasion zone includes abrasive structures such as aluminum oxide particles (20-100 m) bonded on an outer surface.

(19) Optionally, the head may be driven to rotate, oscillate or vibrate to assist the abrasive removal of a portion of the skin outer layer.

(20) The device is a hand held battery operated device, and it is shown sitting on a recharging station 10. The invention is not limited to handheld devices but may also relate to split devices, i.e. for instance a device with a main part, especially for providing the vacuum, and a tube with an abrasive treatment part, that can be moved at least partly independent of the main part.

(21) More details about this general type of device may for example be found in WO 2014/191149 and WO 2014/136013.

(22) In accordance with this invention, the device is modified so that the head 6 functions as one electrode of a charge generator, for example a triboelectric charge generator. It comprises an abrasive ring 8 (FIG. 4) on which charges are generated. There is also an induction electrode on the back of the ring inside the device head. A handle electrode 12 is provided, as well as circuitry for measuring a parameter (for example a voltage between the ring 8 and the handle 12) which is dependent on the generated charges and the skin impedance (which determines the charge leakage). The parameter is measured using the charges generated by the generator.

(23) The device 1 may have an output device 14 such as a display, microphone or a haptic output device, for providing output information to the user to assist them in using the device.

(24) FIG. 2 shows the top two layers of the skin, namely the stratum corneum 20 and the other layers 22 of the epidermis, beneath which is the dermis. The left part shows pre abrasive treatment and the right part shows post abrasive treatment. The stratum corneum is smoothed and thinned, and the epidermis is thickened.

(25) Preferred examples of the device of the invention use a single electrode triboelectric generator as sensor producing a triboelectric charge, to determine a value which is related to the rate and/or amount of skin exfoliation during a treatment with the skin rejuvenation device.

(26) When the level of exfoliation is reached that offers an optimal balance between rejuvenation and the prevention of skin irritation (skin rash) a signal issued by the output device 14 tells the end user to move on to the next untreated piece of skin.

(27) The sensor principle is based on the coupling of triboelectric effect and capacitive coupling. The rubbing of the rejuvenation device against skin causes an electrical charge build-up. The charge leaks then away through the skin. The rate of this process depends on the skin conductance.

(28) The stratum corneum 20 is a resistive barrier for the skin conductance. Exfoliation of the stratum corneum lowers this barrier, causing the tribo-generated charge to leak away faster.

(29) This effect is shown in FIG. 3, which is taken from T. Yamamoto and Y. Yamamoto, Electrical properties of the epidermal stratum corneum, Medical and Biological Engineering (March 1976), pp. 151-157. It shows the resistance of the stratum corneum (y-axis) as a function of a number of tape stripping actions carried out (x-axis). The solid dots are experimental values and the open dots are theoretical values. It shows clearly the relationship between resistance and the removal of stratum corneum due to repeated tape strippings.

(30) FIG. 4 shows an embodiment the device in more detail. A conducting ring inside the head 6 functions as a contact electrode 26 on which charges are induced, whereas the ring 8 is provided on the outside of the head, for example glued. After triboelectrification, there are positive charges at the skin surface 20 as shown. The sensing modality is based on the triboelectric effect and capacitive coupling. The triboelectrically generated voltage is shown as V between the contact electrode 26 and the handle electrode 12. The handle electrode has a contact area with the hand for example of 10 to 250 cm.sup.2 for example 10 to 150 cm.sup.2. The contact electrode 26, in the form of a conducting ring, inside the head 6 functions as a contact or induction electrode and it responds to the surface charge build-up on the abrasive ring 8 by means of capacitive coupling. A high impedance voltage meter (e.g. >10.sup.11) is used to measure the potential difference between the contact electrode 26 and the end user, as present at the handle electrode 12. A high impedance is used to prevent charge from leaking away via the metering circuit. The metal hand contact 12 on the handle of the device ensures a low resistance electrical contact to the end user. The size of this contact needs to be sufficient as not to disturb the measurement of the tribo generated charge. For example, a size of 10 to 150 cm.sup.2 is typically appropriate. The abrasive ring is for example made out of aluminum oxide (Al.sub.2O.sub.3) ceramic particles, a material at the opposite end of the triboelectric series to skin. The contact electrode 26 is a metallic ring into which charges are induced, whereas the abrasive ring is typically an insulator. The abrasive ring 8 is however not limited to insulators. If the abrasive ring is made of a conductive material, it can also be used as the contact electrode 26. In such an example, the abrasive ring 8 and the contact electrode 26 are the same component.

(31) The rubbing action used to perform the abrasion thus results in the generation of charges by the triboelectric effect, and these result in a voltage across the capacitance defined between the user and the abrasive ring 8 and therefore the contact electrode 26.

(32) The charges results in temporary voltage peaks. The height of the voltage peaks observed by a sensor circuit, caused by the triboelectric effect and brought about by the scrubbing of the device against the skin, is a measure of the exfoliation of the skin. When a threshold is met, for example when the peak is lowered by a defined percentage, a signal is given to the end user to move on to the next skin spot.

(33) In a more sophisticated example, the time derivative of the rising slope of the voltage signal may be used as a measure of stratum corneum removal. The time derivative of the voltage of the slope diminishes when the stratum corneum is removed since it is the sum of a charge build-up by the triboelectric effect brought about by a rubbing movement and the leaking away of charge through the upper skin layers to the body.

(34) The sensed signals will be comparable for rubbing actions with equal speed and pressure. However, variations in the expected signals can be taken into account in the signal processing. The voltage may be measured using a capacitive coupling sensor, for measuring the voltage between the contact electrode 26 in the head 6 and the handle contact 12.

(35) An example of a suitable voltage measuring circuit for measuring a capacitive coupling voltage is described in US 2008/0287767A1. Indeed, the signal measured in this previous application will be orders of magnitude smaller, so the required sensing circuitry may be somewhat simpler.

(36) A basic outline of the sensor circuit is schematically shown in FIG. 5. The circuit is the input stage of a signal processing circuit for which the contact electrode 26 and handle electrode 12 provide inputs. The circuit comprises a differential amplifier 40, such as an operational amplifier, with a non-inverting input 41, an inverting input 42, and an output 43. The contact electrode 26 is connected to the non-inverting input of the amplifier 40. The amplifier has a very high input impedance, for example 200 T. The amplifier 40 is basically connected as a buffer amplifier, having its inverting input 42 connected to its output 43, so that the amplifier's output 43 carries the same voltage signal as the amplifier's inverting input 42. The circuitry may have further signal processing components, or the amplifier's output may be connected straight to the handle electrode 12. The output signal is interpreted by a controller, which in turn controls the output device 14 to provide feedback to the user.

(37) In use, when placed in close proximity to a person's body, the abrasive ring 8 has a capacitive coupling with the body. The capacitance value of this coupling is typically in the order of a few pF. The input of the amplifier 40 has an input resistance which, in a suitably selected amplifier, may be approximated by infinity. However, it is desirable to provide a defined leak-resistance to zero voltage level, which is provided by a resistance 44 connected between the amplifier's positive input terminal and ground. The combination of coupling capacitance and leak-resistance forms a high-pass filter.

(38) The elbow frequency of this high-pass filter is as low as possible, for example of the order of 0.2 Hz. This leads to a design value of 100 G or higher for the input resistance 44.

(39) The handle electrode 12 is connected to the inverting input 42 through a potential divider 46a, 46b.

(40) There are no circuit voltages applied to the inputs 26, 12 of the amplifier. Instead, charge generated by the triboelectric effect are induced in the contact electrode 26, so that electrons flow between the contact electrode 26 and the body of the user in contact with the handle electrode 12. These charges create a measurable potential across the inputs 26, 12. The voltage changes over time as the charge leaks to the body, and the way the voltage changes is a function of the capacitance between the inputs 26,12 and the resistance of the skin, which in turn is a function of the level of skin abrasion.

(41) FIG. 6 shows an approximate equivalent circuit. The amplifier circuit of FIG. 5 is shown as 50. Between the inputs, there is a series connection of the body resistance 52 of approximately 1 k, the skin resistance 53, a voltage source 54 representing the voltage generated by the triboelectric effect, the skin capacitance 56 (between the abrasive ring 8 and skin surface) and the capacitance 57 between the ring 8 and the contact electrode 26. The readout electronics essentially comprises an amplifier 50 having a very large input impedance.

(42) In use, triboelectrically generated charges are generated at the skin and the ring 8. The ring 8 is also capacitively coupled to the contact electrode 26. Charges are therefore inducted on the electrode.

(43) The amplifier 50 measures the voltage difference between the handle electrode 12 (which is at the voltage potential of the user) and the contact electrode 26 in the head of the device. An amplifier with a very large input impedance is used to prevent the charges leaking away too fast to be measured.

(44) The system has been tested, by performing sampling of the amplifier voltage at 10 Hz. In the test, measurements of 100 samples were taken, taking 10 seconds. The results are shown in FIG. 7, which plots the voltage versus the sample number (i.e. every 0.1 s). During the first 20 samples nothing was done, and then 4 consecutive strokes of about 20 cm long were performed on the inner forearm (hairless skin area). The skin resistance is the dominating parameter in the leaking away of charge built up by the triboelectric effect, brought about by rubbing the two different materials (skin and the head 6) together. The four consecutive strokes can be seen in FIG. 7, each causing a corresponding voltage spike V1 to V4. The magnitude of the voltage spike diminishes along the sequence of consecutive strokes, indicating a faster charge leakage rate, caused by a decreased skin resistance and rising skin hydration level. This decreased skin resistance is caused by the partial abrasion of the stratum corneum by the abrasive material of the device head, thereby exposing a more hydrated skin layer to the skin surface.

(45) The device may be calibrated to enable more accurate evaluation of the data.

(46) A first calibration approach may take account of differences in the way the device is used, for example the stroke length and stroke speed. The device may be designed for operation with a certain stroke length, controlled contact pressure and speed, but the user may for example be able to provide, as an input, that they prefer longer or faster strokes, or shorter or slower strokes. The settings used to interpret the measured signals from the amplifier may then be adjusted accordingly.

(47) There may also be calibration for a particular users' skin. This may be carried out by performing a test routine, whereby the user performs a number of and type of strokes which they consider suitable. By monitoring the change in electrical characteristics for these reference strokes, a threshold may then be set so that the same degree of skin abrasion may be provided in future strokes, with the device indicating to the user when the same amount of skin treatment has been completed as in the reference cycle.

(48) To perform a system calibration check with the microdermabrasion device, testing against two suitable materials from the triboelectric series (e.g polyamide/Nylon and polyimide/Kapton, or polyamide and polyethylene, polyamide and polyester) could be carried out. For example, the user may perform multiple passes against a reference template (having two different materials) or a tape that may be applied to the skin. These reference signals are then taken and compared with an internal calibration curve to check whether the system is within specifications.

(49) To tolerate for different users, an individual baseline reference curve may be created and then compared with a reference graph (for example from a validation study showing the relationship between tribovoltage and skin level removed). When the measured voltage dropped to for example 30% of its initial value, the treatment may be instructed to be stopped.

(50) Another option is to learn from treatment results. The treatment duration may be monitored and the sensing data saved. This data may then be compared with reference strokes made by the user before each dermabrasion treatment. The treatment curves can also be also stored in the system to provide continuous feedback to the user and coach him or advise him on personalized device settings and a preferred treatment duration. This can be done also in combination with other skin property measurements such as skin moisture.

(51) When the voltage is sampled at a high enough sampling rate (10 Hz or more), the stroke duration can be determined. When a stroke is performed very slowly, the triboelectrical charge does not accumulate, but leaks away through the skin. A reference stroke over a known length combined with a measured stroke duration can function as a calibration step.

(52) It will be clear from the description above that one main area of interest is for microdermabrasion devices. However, the principles explained above may be employed for any surface treatment process which removes part of a surface layer which thereby changes the electrical charge retaining and/or generating properties of the remaining layer structure.

(53) The term substantially herein, such as in in substantially consists, will be understood by the person skilled in the art. The term substantially may also include embodiments with entirely, completely, all, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term substantially may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term comprise includes also embodiments wherein the term comprises means consists of. The term and/or especially relates to one or more of the items mentioned before and after and/or. For instance, a phrase item 1 and/or item 2 and similar phrases may relate to one or more of item 1 and item 2. The term comprising may in an embodiment refer to consisting of but may in another embodiment also refer to containing at least the defined species and optionally one or more other species.

(54) Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

(55) The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

(56) It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb to comprise and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words comprise, comprising, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of including, but not limited to. The article a or an preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. 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.

(57) The invention further applies to a device comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

(58) The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.