HK1089981B - Ultrasound applying skin care device - Google Patents

Description

Skin care device applying ultrasonic waves

Technical Field

The present invention relates to an ultrasonic wave applied skin care device for applying ultrasonic waves to the skin of a user in order to accelerate the metabolism of skin tissues, thereby making the skin beautiful and healthy.

Background

WO98/51255 discloses a similar ultrasound applying skin care device having an applicator head for generating and transmitting ultrasound to the skin of a user. The apparatus includes a load detection circuit for detecting whether the applicator head is loaded by contacting the skin, thereby saving energy when the applicator head is not in contact with the skin and safely applying the ultrasonic waves when the applicator head is in contact with the skin. To determine whether the applicator head is loaded or unloaded, the device relies on an electrically equivalent impedance in the applicator head that varies with the load on the applicator head and compares the corresponding voltage applied to the applicator head to a reference voltage. However, when the applicator head emits ultrasonic waves at a relatively high frequency, for example, several MHz or more, it may sometimes be difficult to distinguish an unloaded state from a loaded state on the basis of an electrically equivalent impedance due to an increase in the influence of parasitic resonance occurring in the applicator head.

Japanese patent laid-open No. 7-59197 discloses an ultrasonic vibrator element that reduces vibrations occurring near the periphery of the vibrator element. The vibrator element has the form of a disc and upper and lower disc-shaped electrodes are provided on opposite surfaces of the disc, respectively. Each electrode has a diameter smaller than that of the vibrator element in order to keep the outer periphery of the vibrator element uncovered in an attempt to cancel unwanted vibrations propagating in the radial direction, thereby allowing desired ultrasonic vibrations to progress in the thickness direction of the vibrator element.

The parasitic resonance can be reduced to some extent by the structure disclosed in japanese patent laid-open No. 7-59197. After studying the behavior of high-frequency ultrasonic vibrations, the inventors have found that vibrations occurring at the center of the applicator head can be effectively suppressed so as to reduce unwanted parasitic resonances to such an extent that the applicator head can exhibit electrically equivalent impedances sufficiently different from each other when loaded and unloaded, respectively, to easily discriminate between the loaded and unloaded states.

Disclosure of Invention

Based on the above findings, the present invention has been accomplished to provide an ultrasound applying skin care device capable of effectively and safely applying ultrasound to enhance skin care.

The skin care device of the present invention comprises: a housing having an applicator head for applying ultrasound to a user's skin; and a driver circuit that provides an electrical pulse for actuating the applicator head to deliver ultrasound to the skin. The applicator head includes: a vibrator element that generates ultrasonic waves; and a horn (horn) having a mounting face and a skin-facing face for contacting the skin. The horn carries a vibrator element on a mounting surface to transmit ultrasound waves to the skin. The vibrator element and horn are integrated into a combined vibration mass that resonates with an electrical pulse from a driver circuit to transmit the resulting vibration to the skin. The combined vibration mass gives a first electrically equivalent impedance when normally loaded by contacting the skin and a second electrically equivalent impedance when unloaded. The apparatus includes a load detection circuit that monitors whether the combined vibration mass emits the first or second electrically equivalent impedance and provides a load detection signal only when the first electrically equivalent impedance is seen. Also included in the apparatus is a control circuit that limits or stops the electrical pulse when the load detection signal is not received within a predetermined time period. The present invention is characterized in that the combined vibration mass has a structure that restricts vibration at a central portion of the vibration mass in order to reduce parasitic resonance, thereby distinguishing a first electrically equivalent impedance from a second electrically equivalent impedance. In this way, the load detection circuit can successfully decide whether the applicator head is in contact with the skin or not, whereby the control circuit can be made to reliably restrict the generation of ultrasonic vibrations when the applicator head is unloaded.

Preferably, the vibrator element comprises a piezoelectric element in the form of a disc having flat upper and lower end faces provided with upper and lower electrodes, respectively, wherein the electrical pulse is applied through the upper and lower electrodes. At least one of the upper electrode, the lower electrode, and the piezoelectric element has a central opening responsible for suppressing vibration at the center of the combined vibration mass.

In addition to the central opening, at least one of the upper and lower electrodes may be dimensioned to have a diameter smaller than that of the piezoelectric element, so as to leave the peripheral portion of the piezoelectric element uncovered as well, to reduce unwanted vibrations near the periphery of the piezoelectric element.

Alternatively, at least one of the upper and lower electrodes is divided into a plurality of identical segments by at least one slit (slit). The slit extends diametrically so as to leave the center of the piezoelectric element and the diametrically extending band portion uncovered to restrict vibration at the center of the vibration mass.

Instead of providing the slits extending in diameter, at least one of the upper and lower electrodes may be configured to have at least one slit that does not cover the central portion of the piezoelectric element for the same purpose of restricting the vibration at the center of the vibration mass.

In conjunction with or separately from the provision of the central opening in at least one of the upper electrode, the lower electrode, and the piezoelectric element, the horn may be configured as a central hole in the form of a through hole or a cavity for restricting the vibration at the center of the vibration body.

Further, instead of being formed with the central opening, the upper electrode may be covered with an elastic member that absorbs the vibration of the central portion of the vibration mass so as to reduce parasitic resonance.

Further, the upper electrode may be covered with a solder bump at the center thereof, the solder bump being used to electrically connect the upper electrode to a lead wire drawn from the driver circuit. The welding block adds a weight to the center of the combined vibration mass to suppress vibration at the center portion thereof.

Furthermore, it is preferred that the horn is formed as an integral part of a rim (rim) surrounding the horn, and the rim is adapted to secure the horn to the housing. Defined between the horn and the rim is a limiter that limits the propagation of the ultrasound waves towards the rim, thereby concentrating the ultrasound waves at the horn to effectively transmit the ultrasound waves through the horn to the skin. The limiter may be in the form of a cavity formed along the boundary between the horn and the rim.

Preferably, the control circuit is designed to receive the first electrically equivalent impedance in order to vary the intensity of the ultrasonic waves generated at the vibrator element in dependence on the value of the first electrically equivalent impedance. Just as the first electrically equivalent impedance will vary depending on the pressure at which the horn or the combined vibration mass is held against the skin of the user, the device can vary the effect or strength of the ultrasound applied to the skin depending on the pressure, thereby optimally applying the ultrasound to the skin of the user to enhance the skin care result.

Further, the apparatus preferably includes a motion detection circuit that monitors whether the combined vibration mass is moving and provides a motion detection signal when the vibration mass is so moving. Connected to the control circuit to receive the motion detection signal and the control circuit controls the driver circuit to stop or limit the electrical pulse when the motion detection signal is not continuous over a critical duration, even if the presence of the load detection signal is detected within a predetermined time period.

These and other objects and advantageous features of the present invention will become more apparent from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.

Drawings

FIG. 1 is a front cross-sectional view of an ultrasound applying skin care device according to a preferred embodiment of the present invention;

fig. 2A to 2C show an improper use state of the above apparatus;

fig. 3 is a circuit block diagram of the above apparatus;

fig. 4 is a circuit diagram illustrating a driver circuit, a load detection circuit, and a motion detection circuit in the above circuit;

fig. 5A to 5F are waveform diagrams illustrating the operations of the load detection circuit and the motion detection circuit;

FIG. 6 is a circuit diagram illustrating a temperature sensing circuit in the above circuit;

FIG. 7 is a flow chart illustrating the operation of the device;

FIG. 8 is a top view of the applicator head in the above apparatus;

FIG. 9 is a cross-sectional view of the applicator head;

fig. 10 to 12 are partial views illustrating modified structures of the applicator head;

FIG. 13 is a schematic view illustrating the relationship between the wavelength of ultrasonic waves of different frequencies and the combined vibration mass of the applicator head;

FIG. 14 is a graph illustrating, for comparison purposes, the electrically equivalent impedance of the vibration mass given in a normal loaded state, an unloaded state, and an abnormally loaded state, respectively, without a structure to reduce parasitic resonance;

FIG. 15 is a top view of a vibrator element;

FIG. 16 is a cross-sectional view of a vibrator element;

fig. 17 is a diagram illustrating an electrically equivalent impedance of a vibrating body given to the combined vibrating body in a normal loaded state, an unloaded state, and an abnormally loaded state, respectively, according to an embodiment of the present invention;

fig. 18 and 19 are a top view and a sectional view of a vibrator element according to a modification of the above embodiment;

fig. 20 and 21 are a top view and a sectional view of a vibrator element according to yet another modification of the above embodiment;

fig. 22 and 23 are top views illustrating still another modification of the above embodiment;

fig. 24 and 25 are a top view and a sectional view of a vibrator element according to yet another modification of the above embodiment;

fig. 26 and 27 are top views illustrating still another modification of the above embodiment;

fig. 28 and 29 are a top view and a sectional view of a vibrator element according to more modifications of the above embodiment;

fig. 30 and 31 are sectional views illustrating modifications of the above embodiment;

FIGS. 32 and 33 are a top view and a cross-sectional view of a vibrator element according to yet another modification of the above embodiment; and

fig. 34 and 35 are a top view and a sectional view of a vibrator element according to more modifications of the above embodiment.

Detailed Description

Fig. 1 illustrates a skin care device applying ultrasonic waves according to a preferred embodiment of the present invention. The skin care device is used for facial care or skin massage to enhance metabolism of skin tissue to make skin beautiful and healthy. The device includes a hand-held handle housing 10 having an applicator head 100 at one end thereof, the applicator head 100 being adapted to contact the skin of a user for applying ultrasound thereto. The applicator head 100 includes: a vibrator element 110 in the form of a piezoelectric element that generates ultrasound waves, and a horn 120 that transmits the ultrasound waves to the skin S. The piezoelectric element is formed to haveA flat upper surface and a flat lower surface, which are covered with upper and lower electrodes 111 and 112, respectively, to which electric pulses are applied to generate ultrasonic vibrations. The vibrator element 110 and the horn 120 are integrated into a combined vibration mass M, which is caused to resonate by the electric pulse to generate and apply the resonant ultrasonic vibrations to the skin S. Preferably, the device is designed to generate ultrasound waves having a frequency of 1MHz to 10MHz and at 0.1W/cm²To 0.2W/cm²The intensity of which transmits it to the skin. Furthermore, it is preferred to use a gel or similar fluid F at the interface between the horn and the skin to facilitate the transmission of the ultrasound waves to the skin S.

As will be described later in detail, the apparatus is equipped with a protector for limiting or stopping the ultrasonic vibrations transmitted to the skin when the applicator head 100 is not in the normal loaded state of fig. 1, i.e., the applicator head is kept in any one of the incorrect states. As shown in fig. 2A to 2C, the incorrect state includes: an unloaded state in which the applicator head 100 is away from the skin (fig. 2A); a partially contacted state in which the applicator head 100 is only partially facing the skin (fig. 2B); and a direct contact state in which the applicator head 100 is in a state of facing the skin, but no fluid F is used at the interface therebetween (fig. 2C).

As shown in fig. 3, the apparatus includes: a driver circuit 20 for providing electrical pulses across the electrodes 111 and 112 of the piezoelectric element 110; a load detection circuit 40 for detecting a load state of the applicator head 100; a motion detection circuit 50 for detecting the motion of the applicator head 100; a temperature sensing circuit 60 for sensing the temperature of the piezoelectric element 110; a display driving circuit 170 for displaying an operation state of the device; and a control circuit 80 for controlling the above circuits. The driver circuit 20 is energized by a power supply 1 accommodated in a power pack 2 converting a commercial AC line voltage into a DC voltage. Also included in the device is a monitoring circuit 90 for monitoring the ultrasound generated and applied to the skin of the user based on the electrically equivalent impedance of the combined vibration mass M.

The device 10 is designed to generate ultrasound while the horn 120 is held in actual contact with the user's skin. To this end, a load detection circuit 40 is provided to detect whether an appropriate load is applied as a result of the horn 120 being in contact with the user's skin through the fluid F. When the horn 120 is not in contact with the skin or fails to transmit the ultrasonic waves successfully, the load detection circuit 40 determines that the horn 120 or the vibration mass M is not loaded, and limits the generation of the ultrasonic waves. Details of the load detection implemented in the present invention will be discussed later. In use, when applying ultrasound, it is desirable to move the applicator head 100, i.e., the combination slowly across the skin. Otherwise, when the applicator head 100 stays at a portion for a long time, there is a potential risk of causing cold burn (cold burn) in the skin. In view of this, the motion detection circuit 50 is provided to allow continuous ultrasound application when the applicator head 100 is moving at an appropriate rate, and to otherwise disable or limit the generation of ultrasound. In addition, the control circuit 80 includes a timer that stops generating the ultrasonic wave after the apparatus is used for a preset time. That is, the timer counts the time only when the load detection signal from the load detection circuit 40 indicates that the applicator head 100 is kept in normal contact with the skin and when the motion detection signal from the motion detection circuit 90 indicates that the applicator head 100 is not staying at a site for a long time. The timer operates to continue generating the ultrasonic wave for a preset time. In addition, after the preset time elapses, the control circuit 80 gives an instruction to stop supplying the electric power to the driver circuit 20, thereby terminating the ultrasonic wave generation.

When the vibrating body is subjected to abnormal vibration with a temperature rise due to a failure of the driver circuit 20 or the like, the temperature sensing circuit 60 provides an output indication of the abnormal temperature rise to the control circuit 80 in response to the output from the temperature sensor 15 located adjacent to the horn 120, the control circuit 80 then responding to stop the driver circuit 20.

As shown in fig. 4, the driver circuit 20 includes an inverter (inverter) that converts a DC voltage from the power source 1 into an AC voltage. Provided at the output of the inverter is a transformer T having a primary winding 21 and a secondary winding 22. The primary winding 21 is connected in series with the FET 23 and the current sensing resistor 27 across the power supply 1 and cooperates with the capacitor 24 to form a parallel resonant circuit which provides a resonant voltage across the primary winding 21 when the FET 23 is switched off. The piezoelectric element 110 is connected in parallel with the secondary winding 22 so as to perform ultrasonic vibration by an AC voltage or an electric pulse introduced at the secondary winding 22. A feedback winding 25 is coupled to the primary winding 21 to feed the output of the driver circuit back to the FET 23. A bipolar transistor 26 is connected in the gate-emitter path of FET 23 for controlling FET 23. Connected across the power supply 1 is a series combination of a start-up resistor 28 and a capacitor 29, the junction of which is connected through a feedback winding 25 to the gate of FET 23 to give FET 23 a bias. When the capacitor 29 is charged by the power supply 1 to develop a voltage that is the threshold of the FET 23, the FET becomes conductive to lower the drain voltage of the FET 23. At this time, the feedback winding 25 generates a feedback voltage applied to the gate of the FET 23, thereby increasing the current flowing through the FET. Subsequently, when the voltage developed across current sensing resistor 27 reaches a predetermined level corresponding to the increased current through the FET, transistor 26 becomes conductive to turn off FET 23. Accordingly, the resonance circuit of the primary winding 21 and the capacitor 24 becomes effective to generate resonance. At the end of one period of resonance, the feedback voltage introduced by the feedback winding 25 reaches a voltage that turns on the gate of the FET 23, thereby turning the FET on again. The above operation is repeated to maintain the resonance voltage or the electric pulse so as to oscillate the piezoelectric element 110. The frequency of the resonant circuit is set to be variable in the range of 1MHz to 10 MHz.

Connected between the base of transistor 26 and resistor 27 is a variable resistor 30 whose value can be varied to adjust the timing of turning on transistor 26 to adjust the resonant frequency. It is to be noted at this point that the resonant circuit is controlled by the control circuit 80 to give intermittent oscillations with rest periods between adjacent pulse trains Vp as shown in fig. 5A.

The transformer T includes an auxiliary winding 91 cooperating with a rectifying circuit which rectifies the output of the auxiliary winding 91 to constitute a monitoring circuit 90, while the monitoring circuit 90 gives a monitoring output indicative of the state of the ultrasound applied to the skin of the user. The monitoring output Vx includes a low-frequency component given as a result of moving the applicator head 100, and the frequency of the low-frequency component is lower than that of the ultrasonic vibration. More precisely, the voltage appearing across the auxiliary winding 91 includes, in addition to the high-frequency component indicative of the ultrasonic vibration, a low-frequency component derived from the vibration in the electrically equivalent impedance of the combined vibration mass M upon contact with the load, and from the frictional sound that appears in response to the applicator head 100 moving across the skin of the user. The monitoring output Vx is obtained by rectifying the voltage appearing across the auxiliary winding 91 and is fed to the load detection circuit 40 and the motion detection circuit 50 for load detection and motion detection.

The load detection circuit 40 has a comparator 41 that compares the monitoring output Vx from the monitoring circuit 90 with a reference level Vref. The monitoring output Vx has a waveform pattern as shown in fig. 5B. When the output Vx becomes lower than the reference level Vref, the comparator 41 supplies a high-level load detection signal SL to the control circuit 80 as an indication that the applicator head 100 is kept in normal contact with the skin of the user. When the load detection signal SL is not received continuously for a predetermined period of time, the control circuit 80 stops the operation of the driver circuit 20 or disables the power supply 1. In this embodiment, the load detection signal SL is generated when the monitoring output Vx is smaller than the reference level Vref, taking into account that the resonance voltage is lowered due to the presence of the load, that is, the increase in the impedance of the combined vibration mass M.

In addition, the output Vx indicative of the impedance of the combined vibration mass M is also fed to the control circuit 80. When the output Vx is equal to the reference level Vref or greater, the control circuit 80 operates to change the output voltage of the power supply 1 in inverse proportion to the value of the output Vx. That is, the combined vibration mass M is held against the skin of the user with a greater pressure, and the control circuit 80 operates to lower the intensity of the ultrasonic waves applied to the skin, and vice versa. According to this result, the ultrasonic waves can be adjusted depending on the pressure at which the combined vibration mass M is held against the skin, so that the ultrasonic waves are transmitted at an optimum intensity to enhance the skin care effect.

It is possible that: in order to break the impedance match with the resonance circuit, the resonance circuit of different configuration may change the impedance characteristic of the combined vibration mass M, thereby causing the monitoring output to increase in the presence of the load. In this case, the load detection signal SL is supplied when the monitor output Vx exceeds the reference level Vref. Furthermore, it is also possible to limit or reduce the ultrasonic energy in a state where no load is detected, and also to change the ultrasonic energy in accordance with the value of the monitoring output.

Further, as shown in fig. 5D, the monitoring output Vx is fed to the motion detection circuit 50 in the form of an output Vx' through a capacitor 51. The motion detection circuit 50 includes a low-pass filter 52 and a decision circuit 53. As shown in fig. 5E, the high-frequency component in the output Vx' is removed by the filter 52 so as to give a low-frequency output VL that is independent of components that are not caused by the movement of the applicator head 100. The low-frequency output VL thus obtained is fed to the two comparators 55 and 56 of the decision circuit 53 and compared with the respective thresholds TH1 and TH2 (TH1> TH2), respectively, to supply the control circuit 80 with a high-level motion detection signal SM (shown in fig. 5F) over a period in which the output VL is higher than the threshold TH1 or lower than the threshold TH 2. TH1 and TH2 may be adjusted by variable resistors 57 and 58. The control circuit 80 counts the time period of the high-level motion detection signal SM for a predetermined duration Tc (for example, 15 seconds), and determines that the applicator head 100 has made an appropriate movement when the sum of the counted times exceeds a predetermined reference within the duration Tc. Otherwise, the control circuit 80 determines that no appropriate motion has been made and provides a limit signal that limits the driver circuit 20.

Driver circuit 20 includes a transistor 84 connected in parallel with transistor 26 across the gate-source path of FET 23 and to control circuit 80 through optocoupler 81. Thus, when the limit signal is received from the control circuit 80, the transistor 84 is turned on to thereby turn off the FET 23 to disable the driver circuit 20. Although in this embodiment the limit signal acts to stop the driver circuit 20. The invention is not limited to this feature and may be arranged to control the driver circuit 20 or the voltage 1 to reduce the ultrasonic vibrational energy.

As shown in fig. 6, the temperature sensing circuit 60 includes a first temperature sensing unit 61 and a second temperature sensing unit 62, both of which receive an output from the thermistor 15 for sensing temperature. The first temperature sensing unit 61 has a temperature controller 65, and the output of the thermistor 15 is fed to the temperature controller 65 through a resistor 63 and a capacitor 64. When the temperature sensed by the thermistor 15 is found to exceed the predetermined reference temperature, the temperature controller 65 issues a stop signal to the driver circuit 20 through the photo-coupler 66. The optocoupler 66 has a transistor 68 connected in the base-emitter path of the transistor 84 so that the stop signal causes the transistor 84 to turn on to stop the oscillation of the driver circuit 20. Hysteresis is given to the temperature control so that after the temperature of the horn 120 sensed by the thermistor 15 becomes higher than the reference temperature, the driver circuit 20 is allowed to resume oscillation only after the sensed temperature becomes lower to a temperature level lower than the reference temperature. When the sensed temperature becomes lower than the temperature level, the temperature controller 65 responds not to issue the stop signal, thereby resuming the oscillation of the driver circuit 20. The second temperature sensing unit 62 includes a comparator 69 that operates to turn on the transistor 160 when the temperature sensed by the thermistor 15 exceeds a predetermined reference, thereby turning on the transistor 163 of the photo-coupler 161 and thus disabling the power supply 1 connected to the transistor 163. As a guarantee of the response to the horn 120 which is abnormally heated even if the temperature controller 65 constituted by the microprocessor fails to operate, the predetermined reference for the comparator 69 is set to be higher than the reference temperature of the temperature controller 65 for stopping the ultrasonic oscillation.

The operation of the apparatus applying ultrasonic waves will now be described with reference to fig. 7. After the power switch is turned on, the depression of the start button actuates the driver circuit 20, causing the piezoelectric element 110 to start generating ultrasonic waves and starting the timer. At this time, the temperature sensing is performed on the horn 120 so that when the first temperature sensing unit 61 sees the temperature exceeding, for example, 45 °, the display driving circuit 70 gives a temperature warning that the horn 120 is overheated and causes the timer and driver circuit 20 to stop. Load detection is available when the sensed temperature is found to be below 45 ℃ at a step after the timer is started, and subsequent motion detection is available if a load detection signal is issued as an indication that the applicator head 100 is loaded. When the load detection signal is not issued, a no-load warning is displayed for a limited period of time, for example, 40 seconds, prompting the user to bring the applicator head 100 into contact with the skin. After the 40 seconds of no-load detection signal has elapsed, control is performed to display a warning to stop the operation, and stop the timer and ultrasonic wave generation. The motion detection is performed in the presence of the load detection signal so that when the motion detection signal is issued within, for example, 15 seconds, display of normal operation is performed and an instruction to count down is given to the timer. After a predetermined operation time of, for example, 10 minutes has elapsed in this state, the driver circuit is stopped. When the pause button is pressed within 10 minutes, the driver circuit is stopped, but the timer operation continues to count down. When the restart button is pressed within 10 minutes, the driver circuit resumes generating the ultrasonic wave.

Although the above embodiments are designed so that the control circuit disables the driver circuit when no load or no motion is detected, the present invention is not limited to this feature and is designed to reduce the ultrasonic energy upon such detection.

Referring now to fig. 8 and 9, the details of the applicator head 100, i.e., the combination of the piezoelectric element 110 and the horn 120, will be discussed. The piezoelectric element 110 is made of ceramic, and is formed as a circular disk having a uniform thickness, and upper and lower electrodes 111 and 112 are provided on upper and lower surfaces of the circular disk, respectively. The horn 120 is made of aluminum and is made as a circular disk having a surface area slightly larger than that of the piezoelectric element 110 and having a uniform thickness. As shown in fig. 9, the electric pulse from the driver circuit 20 is applied to the electrodes 111 and 112 through the leads 101 and 102 that are respectively soldered to the upper electrode 111 and the horn 120. The horn 120 is formed as an integral part with a tubular rim 130 surrounding the horn 120. A rim 130 projects upwardly from the periphery of the horn 120 and is secured at its upper end to the housing 10 to support the applicator head 100 to the housing. The upper end of the rim 130 is fitted into the mouth 12 of the housing 10 with the elastic damping ring 132 interposed therebetween. The horn 120 has: a flat mounting surface 121 for carrying thereon the piezoelectric element 110 in close contact relation; and a flat skin-facing face 122 for contacting the skin S with the fluid F applied to the skin S. The piezoelectric element 110 is fixed to the horn 120 so that they are integrated into the combined vibration mass M resonating with the electric pulses from the driver circuit 20 to generate the ultrasonic waves to be transmitted to the skin. A restrictor 140 in the form of a cavity extends between the horn 120 and the rim 130 to restrict the propagation of ultrasonic vibrations towards the rim 130 so as to effectively focus the ultrasonic waves to the skin of the user, as indicated by the arrows in figure 9. That is, the cavity 140 functions to isolate the rim 130 from the combined vibration mass M of the piezoelectric element 110 and the horn 120 in practice with respect to the ultrasonic vibration. As a result of forming the cavity 140, a reduced thickness bridge 142 remains for connecting the horn 120 and the rim 130. The reduced thickness (t) of the bridge 142 is selected to be different from an integer multiple of a quarter of the wavelength of the ultrasonic waves (t ≠ n · λ/4, where n is an integer) to effectively limit propagation of the ultrasonic vibrations toward the edge 130. As shown in fig. 10 and 11, the cavity 140 may be filled with a suitable medium 144 for blocking ultrasonic vibrations, or the cavity 140 may be smoothed with a rounded edge 146. Further, as shown in FIG. 12, other cavities 148 of different depths may be formed in concentric relation to the cavity 140.

As shown in fig. 13, the total thickness (T) of the combined vibration mass M of the piezoelectric element 110 and the horn 120 is selected to be half the wavelength (T ═ λ/2) of the ultrasonic wave vibrating at the fundamental frequency of, for example, 1MHz, so that the combined vibration mass M can also resonate at frequencies of integral multiples of the fundamental frequency (for example, 2 times, 3 times, and 4 times the fundamental frequency) while forming antinodes on the skin-facing surface 122 of the horn 120 and at the upper surfaces of the electrodes 111, as schematically illustrated in the drawing.

In order to efficiently transmit the ultrasonic power to the skin with the lowest loss and also to discriminate the normally loaded state from the abnormally loaded or unloaded state when the combined vibration mass M is actuated in the vicinity of the resonance frequency, the piezoelectric element 110 is designed to have a structure that restrains the vibration at the center of the combined vibration mass M to reduce unwanted parasitic resonance, which would otherwise make it difficult for the load detection circuit 40 to discriminate the normally loaded condition from the unloaded or abnormally loaded condition. That is, as shown in FIG. 14, when the vibration mass M is in the unloaded condition or the abnormally loaded condition, the fluctuation brought in by the parasitic resonance is superimposed on the electrically equivalent impedance curve associated with the frequency variation as shown by the dotted line. According to this result, it becomes difficult to distinguish the normally loaded state from the unloaded or abnormally loaded state based on the impedance of the vibration mass M in the vicinity of the resonant or antiresonant frequency. Therefore, in the state where the vibration mass M is normally loaded, it becomes almost impossible to extract the varying impedance indicating the contact pressure of the vibration mass M within the allowable range as indicated by the arrowed line in the drawing, in the vicinity of the resonance or anti-resonance frequency, without changing the intensity of the ultrasonic wave in accordance with the pressure held by the combined mass M against the skin of the user.

FIGS. 15 and 16 show a preferred structure for reducing the undesired parasitic resonance to such an extent that the load detecting circuit 40 can discriminate the normally loaded condition from the unloaded or abnormally loaded condition with reference to the electrically equivalent impedance of the combined vibration mass M. In this structure, the central opening 114 is formed to extend at the centers of the upper electrode 111, the piezoelectric element 110, and the lower electrode 112 to suppress the vibration at the center of the piezoelectric element 110, and thereby suppress the vibration at the center of the vibration mass M. With this result, the combined vibration mass M exhibits a definite impedance characteristic curve in relation to frequency in the unloaded or abnormally loaded state as shown by the dotted line in FIG. 17, which can be well distinguished from the impedance curve exhibited by the vibration mass in the normally loaded state, as shown by the solid line indicated in the same figure.

As is apparent from fig. 17, the vibration mass M can give an electrically equivalent impedance completely different from that given in the normally loaded state when subjected to the unloaded or abnormally loaded state. As explained hereinbefore with reference to the monitoring circuit 90, with this difference, the load detecting circuit 40 can successfully recognize an abnormally loaded or unloaded condition simply by monitoring the voltage reflecting the electrically equivalent impedance of the vibration mass M. In this result, it becomes possible to extract the impedance varying with the contact pressure of the vibration mass M within the allowable range, as indicated by the arrowed line in the figure, in the vicinity of the resonance or antiresonance frequency. Accordingly, as long as the vibration mass M is in a normally loaded state, the intensity change of the ultrasonic wave can be performed in accordance with the pressure of the combination mass M held against the skin of the user.

In conjunction with the central opening 114, at least one of the upper and lower electrodes 111 and 112 may be formed to have a diameter smaller than that of the piezoelectric element 110, so as to reduce the vibration at the periphery of the piezoelectric element, and thus the combined vibration mass M, to further reduce the parasitic resonance. For example, as shown in fig. 18 and 19, the central opening 114 may be formed in at least one of the electrode and the piezoelectric element.

Furthermore, as shown in fig. 20 and 21, the electrodes 111 and 112 may be divided into four identical segments or portions 117 by diametrically extending slits 116. The slit extends through the center of the electrode so as to leave the center of the piezoelectric element and the diametrically extending band portion uncovered, thereby suppressing vibrations at the uncovered center and the band portion, and thereby reducing unwanted parasitic resonance so as to also achieve the impedance characteristic of fig. 17.

Alternatively, as shown in fig. 22 and 23, one or both of the electrodes 111 and 112 may be divided into two or eight segments 117 for the same purpose.

Further, it is possible to give a slit 116A having closed ends also in the piezoelectric element 110 and the electrodes 111 and 112 as shown in fig. 24 and 25, or a slit 116B having one end opened, or a parallel slit 116C in at least one of the electrodes and the piezoelectric element as shown in fig. 26 and 27.

Fig. 28 and 29 show a modification of the above embodiment in which the center hole 134 is formed in the horn 120 in alignment with the center opening 114 to further suppress the vibration at the center of the combined vibration mass M and thereby largely reduce the undesired parasitic resonance. As shown in fig. 30, the combination M may have a central aperture 134 only in the horn 120. In this example, as shown in fig. 31, the central hole 134 may have the form of a cavity.

Fig. 32 and 33 show an alternative structure in which an elastic member 150 is fixed to the center of the upper electrode 111 for absorbing and thereby suppressing vibration on the center of the piezoelectric element 110. The elastic member 150 is preferably made of silicone rubber. Instead of providing the elastic element 150, it is also possible to give a weight on the center of the electrode 111 for suppressing the vibration on the center of the piezoelectric element 110 and thereby reducing the undesired parasitic resonance at the center of the combined vibration mass M. The weight is given by the solder bumps 160 or lands used to electrically connect the electrodes 111 to the leads 101 from the driver circuit 20.

It is confirmed that the structure disclosed herein for reducing the undesired parasitic resonance by suppressing at least the vibration at the central portion of the combined vibration mass M is found to be effective in separating at least the unloaded condition from the loaded condition in accordance with the electrically equivalent impedance of the vibration mass M in the frequency range of 1MHz to 10 MHz. In this regard, the apparatus of the present invention may be configured to not react to the abnormal load condition shown in fig. 2C and thereby allow use without the fluid F.

It is to be noted in this connection that the respective structures shown with reference to fig. 15, 16, 18 to 35 can be appropriately combined to reduce unwanted parasitic resonances. Further, when considering the electrodes, the above structure for reducing the vibration at the center of the vibration mass may be given to one of the electrodes while leaving the other electrode to substantially entirely cover the corresponding face of the piezoelectric element 110.

Claims (15)

1. An ultrasound applying skin care device comprising:

a housing having an applicator head for applying ultrasound to a user's skin; and

a driver circuit giving electrical pulses for actuating the applicator head to generate ultrasound waves;

the applicator head includes:

a vibrator element that generates ultrasonic waves; and

a horn having a mounting surface and a skin-facing surface adapted to contact skin, the horn carrying the vibrator on the mounting surface to transmit the ultrasound to the skin through the skin-facing surface, the vibrator element and the horn being integrated in a combined vibration mass resonating with an electrical pulse of a resonant frequency from the driver circuit to generate ultrasound, the combined vibration mass giving a first electrically equivalent impedance when normally loaded by contact with the skin and a second electrically equivalent impedance when unloaded,

a load detection circuit connected to monitor whether the combined vibration mass presents a first or second electrically equivalent impedance and to provide a load detection signal only when the first electrically equivalent impedance is monitored,

a control circuit which limits or stops the electric pulse when the load detection signal is not received within a predetermined period of time, wherein

The combined vibration mass has a structure that restrains vibration at a central portion of the combined vibration mass so as to reduce parasitic resonance, thereby making the first electrically equivalent impedance different from the second electrically equivalent impedance to discriminate therebetween.

2. The ultrasound applying skin care device as set forth in claim 1, wherein said vibrator element comprises a piezoelectric element in the form of a disc having flat upper and lower end faces, and upper and lower electrodes are attached to said upper and lower end faces, respectively, and said electric pulses are applied to said upper and lower electrodes.

3. The ultrasound applying skin care device as set forth in claim 2, wherein at least one of said upper electrode, said lower electrode, and said piezoelectric element has a central opening to suppress vibration at a center of said combined vibration mass.

4. The ultrasound applying skin care device as set forth in claim 2, wherein each of said upper electrode, said lower electrode, and said piezoelectric element has a central opening to suppress vibration at a center of said combined vibration mass.

5. The ultrasound applying skin care device according to claim 3, wherein at least one of the upper electrode and the lower electrode has a diameter smaller than a diameter of the piezoelectric element such that a peripheral portion of a corresponding end face of the piezoelectric element is not covered.

6. The ultrasound applying skin care device according to claim 2, wherein at least one of said upper and lower electrodes is divided into a plurality of identical segments by at least one slit, said at least slit extending diametrically so that a center of said piezoelectric element and a diametrically extending band portion are uncovered.

7. The ultrasound applying skin care device of claim 2, wherein at least one of the upper and lower electrodes has at least one slit leaving a central portion of the piezoelectric element uncovered.

8. The ultrasound applying skin care device as set forth in claim 2, wherein said horn has a center hole for suppressing vibration at a center of said combined vibration mass.

9. The ultrasound applying skin care device as set forth in claim 3, wherein said horn has a center hole for suppressing vibration at a center of said combined vibration mass.

10. The ultrasound applying skin care device as set forth in claim 2, wherein the upper electrode is covered at the center thereof with an elastic member for absorbing the vibration at the center of the combined vibration mass.

11. The ultrasound applying skin care device as set forth in claim 10, wherein said elastic member is silicone rubber.

12. The ultrasound applying skin care device as set forth in claim 2, wherein said upper electrode of said piezoelectric element is covered at its center with a solder bump for electrically connecting the upper electrode to a lead wire led out from said driver circuit, and the solder bump adds weight to the center of the piezoelectric element.

13. The ultrasound applying skin care device as set forth in claim 1, wherein said horn is formed as an integral part with a rim surrounding said horn and connected to said housing, said horn and said rim defining therebetween a limiter limiting propagation of the ultrasound vibrations toward said rim,

wherein the limiter is defined by a cavity formed at a boundary between the horn and the rim.

14. The ultrasound applying skin care device as set forth in claim 1, further comprising:

a motion detection circuit that monitors whether the combined vibration mass is moving and provides a motion detection signal when the vibration mass is so moving;

the control circuit controls the driver circuit to stop or limit the electrical pulse when the load detection signal is not received within the predetermined time period or when the motion detection signal is not continuous over a critical duration even if the presence of the load detection signal is detected within the time period.

15. The ultrasound applying skin care device as set forth in claim 1, wherein said control circuit receives said first electrically equivalent impedance to vary the intensity of the ultrasound generated on said vibrator element in accordance with the value of said first electrically equivalent impedance.