Skin treatment device and method of controlling skin treatment device

Abstract

A skin treatment device that provides feedback to the user about the force or pressure they apply. In addition to providing feedback indicating that the pressure is too high, correct or too low, there is another type of feedback indicating that there is no contact between the skin and the device when the force or pressure is below a minimum threshold. This avoids providing the same feedback information when the user applies too low a pressure as when the user deliberately releases the device from contact with the skin.

Description

Technical Field

[0001] The present invention relates to skin treatment devices, such as shavers and epilators and other grooming devices. In particular, the present invention relates to skin treatment devices which provide feedback to a user regarding the performance of their skin treatment procedure. Background Art

[0002] Skin treatment, such as hair removal, typically involves the application of a device, such as a razor, against the skin.

[0003] The performance of a skin treatment device will depend on the pressure applied to the skin. For example, it is known that the performance of a shaver depends on the pressure applied.

[0004] It has been proposed to provide feedback on shaving pressure in order to guide the user to apply pressure within a range that is optimal for the shaving process. For example, US2016 / 0046028 discloses force / pressure sensing and provides a warning if the user applies too much force.

[0005] It has also been proposed to use pressure sensing to control skin treatment devices. For example, EP 3183992 discloses an epilator that uses force feedback to control the drive speed of the epilator motor.

[0006] US2018 / 0000219 A1 discloses a depilatory device with a control unit, which is capable of analyzing the contact pressure of a user pressing a depilatory unit of the depilatory device against the skin: comparing the contact pressure with at least one threshold contact pressure, and providing feedback to the user whether the contact pressure is less than, equal to or greater than the at least one threshold contact pressure. In one embodiment, the contact pressure is compared with a lower threshold, a first upper threshold, and a second upper threshold. When the contact pressure is lower than the lower threshold, the depilatory performance is too low, prompting the user to apply a greater force to the depilatory device. When the contact pressure is higher than the first threshold, the friction on the skin will cause skin irritation, prompting the user to apply a smaller force to the depilatory device. When the contact pressure is higher than the second threshold, the drive unit of the depilatory device may be damaged, and the user is prompted to apply a smaller force to the depilatory device, or the control unit may stop the drive unit.

[0007] EP 3513927 A1 discloses a razor having a sensor for measuring the shaving pressure applied to the blade cartridge and having an illumination device, such as a multi-color LED, for indicating a subset of information to a user. In one embodiment, when the sensor detects that the shaving pressure is optimal, the illumination device illuminates a first color (e.g., green), and when the sensor detects that the shaving pressure is above the optimal range, the illumination device illuminates a second color (e.g., yellow or red). The notification to the user of the optimal shaving pressure sensed by the sensor compared to the high shaving pressure or the low shaving pressure can change over time based on learning the user's preferences and shaving behavior.

[0008] US2019 / 0061183 A1 discloses an electric shaver, which includes a sensor for detecting the pressure or force of the working head of the shaver against the skin. The shaver also includes a control unit and a light emitter to indicate the detected pressure or force to the user. The control unit can change the color of the emitted light according to the detected pressure or force. For example, green light can represent a relatively low force, while yellow light can represent an average force and red light can represent a relatively high force. Advantageously, the color can be changed gradually or continuously to give precise feedback. In one embodiment, the calibration device can calibrate the relationship between the color and the detected force based on the user history of the detected force.

[0009] Users appreciate the feedback provided to provide them with guidance. However, feedback can also be a cause of annoyance if it is clearly irrelevant or incorrect. The inventors have found that providing unwanted feedback is a particular cause of annoyance when users deliberately pause their skin treatment routine. Summary of the invention

[0010] The invention is defined by the claims.

[0011] According to an example of one aspect of the present invention, there is provided a skin treatment device, comprising:

[0012] Skin treatment head;

[0013] a force or pressure sensor for determining the force or pressure with which the skin treatment device is maintained against the user's skin during use;

[0014] an output device for providing output information to a user related to the force or pressure determined by the sensor; and

[0015] a controller for controlling the output device based on the force or pressure determined by the sensor,

[0016] The controller is adapted to control the output device to:

[0017] providing a first indication when the force or pressure determined by the sensor is within a range between a first threshold and a second threshold that is higher than the first threshold, the first indication indicating that the force or pressure applied by the user is within a range for an optimal skin treatment result;

[0018] providing a second indication different from the first indication when the force or pressure determined by the sensor is above a second threshold;

[0019] providing a third indication different from the first indication and the second indication when the force or pressure determined by the sensor is below a first threshold and above a third threshold that is below the first threshold; and

[0020] When the force or pressure determined by the sensor is below a third threshold value and corresponds to non-contact of the skin treatment head with the skin, a fourth indication different from the first, second and third indications is provided.

[0021] The third threshold is below the typical minimum pressure or force generated during normal skin treatment, even for a user applying relatively low force. In particular, the fourth indication is provided when the force or pressure determined by the sensor corresponds to non-contact of the skin treatment head with the skin. Thus, the third threshold is set at a sufficiently low level that the pressure or force generated when there is no skin contact is typically below the third threshold.

[0022] The skin treatment device provides feedback to the user about the force or pressure applied during use, so that, for example, the user can be guided to apply the most suitable force or pressure for effective use of the skin treatment device. The range of force or pressure values ​​between the first threshold and the second threshold corresponds to a range of force or pressure values ​​that advise the user of optimal skin treatment results, in particular with the aid of corresponding feedback of the first indication.

[0023] When the force or pressure (determined by the sensor) is above the second threshold, this indicates that the pressure applied is too high. The output device then provides a different (second) indication to the user. Thus, there is real-time feedback about the user's performance in performing the skin treatment. When the force or pressure is below the first threshold, this indicates that the pressure applied is too low. The output device then provides a different (third) indication to the user.

[0024] In this way, the feedback system can be used to encourage the user to apply more force, less force, or maintain the same force to optimize the effectiveness of the skin treatment.

[0025] According to the invention, there is an additional third threshold, the purpose of which is to distinguish between contact and non-contact as described above. Below this (lowest) third threshold, there is another different (fourth) indication. Providing the same feedback information as when the user applies too low a pressure when the user deliberately releases the device so that it is not in contact with the skin is found to be annoying to the user and undermines the user's trust in the feedback system.

[0026] Additionally, real-time force or pressure feedback can be used in other ways, such as controlling motor speed as a function of applied pressure. Alternatively, motor drive power can be varied based on sensed pressure to maintain a more constant speed despite different motor loads caused by different pressures.

[0027] The third threshold value is (or corresponds to) a force in the range from 0.1N to 0.5N, for example.

[0028] This is the force threshold used to distinguish between contact and non-contact.

[0029] The controller may be adapted to control the output device to provide the fourth indication only if the force or pressure determined by the sensor is below the third threshold for longer than the first time threshold.

[0030] If there is a very brief interruption, such as may also occur when the user is actively performing skin treatment (e.g., moving the skin treatment device over the contours of the body may cause a very brief non-contact time), the feedback (i.e., the first indication to the third indication) is not paused. The indication may remain in its previous state, or it may be set to the third indication while the time threshold is counted.

[0031] For users who typically apply light pressure, brief periods of no contact may also occur. Therefore, feedback is only paused when the user intentionally implements a break in the skin treatment.

[0032] The controller may be adapted to switch the skin treatment device between the active state and the inactive state and, when the force or pressure determined by the sensor is below a third threshold, control the output device to provide a fourth indication while maintaining the skin treatment device in the active state.

[0033] When the fourth indication is provided, the device thus remains active so that the entire skin treatment operation is not interrupted. The provision of feedback information that is not relevant is suspended, but once contact is restored, the user can continue the skin treatment operation. Therefore, the device is not completely turned off. For example, the user can simply move the skin treatment device from one part of the body (e.g., the face) to another part, so the device should not be turned off for a short interruption of the skin treatment operation. This provides a more pleasant user experience, which can better encourage the user to adjust the use of the skin treatment device based on the feedback given by the first to third indications.

[0034] The skin treatment device may further comprise a motor for driving the skin treatment head, and the controller may be adapted to activate the motor in the active state and deactivate the motor in the inactive state.

[0035] Thus, when non-contact is detected, the motor remains activated so that skin treatment can be resumed without delay.

[0036] If the force or pressure determined by the sensor is below the third threshold for longer than a second time threshold which is greater than the first time threshold, the controller may be adapted to switch the skin treatment device to an inactive state. If there is a long break in contact, this indicates that the user may have forgotten to switch off the skin treatment device. Thus, contact detection may also be used to implement an automatic switch-off function, whereby the device switches to an inactive state to save power.

[0037] The output device may comprise a light output device, and the first, second and third indications may each comprise a light output having a respective different colour.

[0038] The user can see the light output in use either directly or in a reflector. Simple color coding provides simple feedback to the user, e.g. red = too hard, green = OK, yellow = too light. Flashing speed and / or brightness may be used alternatively or additionally. Furthermore, auditory or tactile feedback (e.g. for people with vision difficulties) may be used additionally or alternatively.

[0039] The fourth indication may be no light output (but optionally, as described above, the device is still active). Alternatively, a different type of light output may be used than used to provide feedback during use (i.e., the first, second and third indications). The fourth indication may be a flashing light output.

[0040] The force or pressure sensor may be arranged to measure the force or pressure exerted mutually between the skin treatment head and the skin.Alternatively, the skin treatment device further comprises a handle coupled to the skin treatment head, and the force or pressure sensor may then be arranged to measure the force or pressure exerted mutually by the handle and the skin treatment head.

[0041] Thus, the force or pressure measured may be an external force or pressure applied by the skin to the skin treatment device (i.e., to an external pressure sensor), or an internal force or pressure generated between components of the skin treatment device. The force or pressure sensor may include a pair of components separated by a spring force, and a sensor for measuring the proximity of the two components, such as a magnetic sensor (e.g., a Hall sensor).

[0042] The output device for example comprises a light output device near the skin treatment head.This provides an easily visible indication which can be seen directly or in a reflector.

[0043] The controller may be adapted to derive a performance rating regarding a skin treatment procedure performed by the user based on the force or pressure determined by the sensor during the skin treatment procedure.

[0044] By ignoring periods of no contact, rather than treating them as periods of insufficient pressure being applied, the performance rating can be more accurate.

[0045] Skin treatment devices include, for example, electric shavers, wherein the skin treatment head comprises a shaving head.

[0046] The present invention also provides a method of controlling a skin treatment device, the skin treatment device comprising: a skin treatment head; a force or pressure sensor for determining the force or pressure with which the skin treatment device is maintained against the skin of a user during use; and an output device for providing output information to the user related to the force or pressure determined by the sensor, wherein the method comprises:

[0047] When the force or pressure determined by the sensor is between a first threshold and a second threshold that is higher than the first threshold, controlling the output device to provide a first indication indicating that the force or pressure applied by the user is within a range for an optimal skin treatment result;

[0048] When the force or pressure determined by the sensor is above the second threshold, controlling the output device to provide a second indication different from the first indication;

[0049] When the force or pressure determined by the sensor is below the first threshold and above a third threshold that is below the first threshold, controlling the output device to provide a third indication different from the first indication and the second indication; and

[0050] When the force or pressure determined by the sensor is below a third threshold and corresponds to non-contact of the skin treatment head with the skin, the output device is controlled to provide a fourth indication different from the first, second and third indications.

[0051] The method is preferably performed during non-therapeutic skin treatments such as hair cutting.

[0052] The method may include controlling the output device to provide the fourth indication only when the force or pressure determined by the sensor is below the third threshold for longer than the first time threshold.

[0053] The invention also provides a computer program comprising computer program code means adapted to implement the above method when said program is run on a computer.

[0054] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] For a better understanding of the invention, and in order to more clearly show how the invention may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0056] Figure 1 A skin treatment device in the form of a shaver is shown;

[0057] Figure 2 Shown in Figure 1 Examples of force or pressure sensors used in devices;

[0058] Figure 3 The electronic components used to implement the present invention are shown;

[0059] Figure 4 shows different outputs that may be provided in response to different sensed forces or pressures; and

[0060] Figure 5 A method of controlling a skin treatment device is shown. DETAILED DESCRIPTION

[0061] The present invention will be described with reference to the accompanying drawings.

[0062] It should be understood that the detailed description and specific examples, although indicating exemplary embodiments of the device, system and method, are only for illustrative purposes and are not intended to limit the scope of the invention. These and other features, aspects and advantages of the device, system and method of the present invention will become better understood from the following description, the appended claims and the accompanying drawings. It should be understood that the drawings are only schematic and are not drawn to scale. It should also be understood that the same reference numerals are used in all drawings to represent the same or similar parts.

[0063] The present invention provides a skin treatment device that provides feedback to the user about the force or pressure applied by the user. In addition to providing feedback indicating that the pressure is too high, correct or too low, there is another type of feedback indicating that there is no contact between the skin and the device when the force or pressure is below a minimum threshold. This avoids providing the same feedback information when the user applies too low a pressure as when the user deliberately releases the device from contact with the skin.

[0064] Figure 1 A skin treatment device in the form of a shaver 10 is shown.

[0065] The shaver comprises a skin treatment head 12 (i.e. shaving head) and a force or pressure sensor 14 for determining the force or pressure with which the skin treatment device (particularly the head 12) is held against the user's skin during use. The force of the pressure sensor preferably has a resolution corresponding to 0.1N or better.

[0066] The operation of the device is explained with reference to the applied force or pressure. It should be understood that pressure and force can be considered similar. A force or pressure sensor typically measures the force applied to a sensing area of ​​the sensor, which force therefore corresponds to a specific pressure.

[0067] The shaving head in this example has three rotating shaving units 13, and they are driven by a motor 16 in a handle 15 of the shaver. The handle 15 is coupled to the treatment head 12. However, other types of shaving heads are equally applicable.

[0068] The output device 18 is used to provide the user with output information related to the pressure applied by the user. This information is used to guide them during the skin treatment process (i.e., when shaving in this example).

[0069] The output device 18 comprises, for example, one or more LEDs in the upper back area of ​​the shaver body (near the shaving head). The one or more LEDs face outwards in normal use of the shaver so that they are easily visible in the shaving mirror, but the light output is preferably also directly visible. Therefore, the purpose is to make the output device visible to the user directly or reflected by the mirror during use. There may be different colored LEDs to provide different color outputs associated with different applied pressures. The light output may additionally or alternatively be made to flash (i.e., blink), wherein the flashing rate indicates the applied pressure. Brightness levels may also be used as part of the feedback system.

[0070] Any other light output device may be used at any suitable location or combination of locations. Tactile feedback may also (or alternatively) be used. Similarly, audible feedback may also (or alternatively) be used.

[0071] The controller 20 is used to control the output device (and the motor) based on the detected force or pressure.

[0072] The controller 20 controls the output device to generate various indications.

[0073] When the force or pressure is between a first threshold and a higher second threshold, a first indication (e.g., color) is provided that corresponds to a range of force or pressure values ​​that the user is advised to apply for optimal skin treatment results. Thus, the first indication indicates that the force or pressure applied by the user is within the range for optimal skin treatment results. This tells the user that they are performing the skin treatment correctly.

[0074] When the force or pressure is above a second threshold, a second indication (different from the first indication) is used. This tells the user to apply less force.

[0075] When the applied force or pressure is below the first threshold and above the third threshold (the third threshold is lower than the first threshold), a third indication is used (the third indication is different from the first indication and the second indication). This tells the user to apply more force.

[0076] The third threshold is lower than the usual minimum pressure or minimum force generated during normal skin treatment, even for users applying relatively small forces. In particular, the third threshold is set at a sufficiently low level that the pressure or force generated when there is no skin contact is usually lower than the third threshold. The third threshold is, for example, (or corresponds to) a force in the range of 0.1N to 0.5N.

[0077] When the force or pressure is below a third threshold, a fourth indication (different from the first to third indications) is used. In particular, the fourth indication is provided when the force or pressure determined by the sensor corresponds to non-contact of the skin treatment head with the skin.

[0078] Thus, there is real-time feedback regarding the user's performance in performing the skin treatment in order to encourage the user to apply more force, less force, or maintain the same force to optimize the effectiveness of the skin treatment.

[0079] As an example only, Th1 may be 1.5N and Th2 may be 3N.

[0080] The fourth indication means that the feedback used for users applying too low a pressure is different from the feedback used for users intentionally releasing the device from contact with the skin. The fourth indication may, for example, be provided only when the force or pressure is below the third threshold for longer than the first time threshold.

[0081] The first time threshold is, for example, in the range of 0.1 seconds to 2 seconds.

[0082] If there is a very brief interruption, such as moving the shaver from one side of the face to the other, normal feedback (ie the first to third indications) may still be provided.

[0083] The fourth indication may be a fourth color. Conversely, it may be a transition from a continuous color to a flashing color. However, the fourth indication may include providing no output at all. However, it is not part of the automatic shutoff function, so once contact is reestablished, the device remains (preferably) immediately ready to continue the skin treatment operation.

[0084] For example, the skin treatment device may have an active state (e.g., the motor is running) and an inactive state (the motor is not running). Then, when the force or pressure is below a third threshold, the skin treatment device operates in the active state. Thus, the device remains active, thereby not interrupting the entire skin treatment operation. The provision of feedback information that is not relevant is suspended, but once contact is reestablished, the user can continue the skin treatment operation. This provides a more pleasant user experience, which can better encourage the user to adjust the use of the skin treatment device based on the feedback given by the first set of instructions.

[0085] Alternatively, the active state may stop the motor, but in a state where it will be driven immediately upon detection of contact. Thus, the force or pressure sensor remains active and the device is not in a closed state.

[0086] Contact sensing enabled by the third threshold may also be used to implement a full-off function.For example, if the force or pressure is below the third threshold for a time longer than the second time threshold, the skin treatment device may be switched to an inactive state.

[0087] The second time threshold is, for example, in the range of 5 seconds to 1 minute.

[0088] Figure 2 An example of an embodiment of a force or pressure sensor is shown. It shows an internal component of the shaver in the form of a support 30 to which the shaver head 12 is mounted. The support is biased away from the body of the shaver (e.g. handle 15) by spring means 32. Therefore, the greater the force applied to the head 12 in the direction of the body, the closer the head moves to the body.

[0089] The distance is sensed by a magnetic sensor including a magnet 34 and a Hall sensor 36 .

[0090] This is just one possible example of an internal force sensor. Alternatively, the force or pressure sensor may be external and in contact with the skin.

[0091] Figure 3 Electronic components used to implement the present invention are shown.

[0092] As shown, the force or pressure sensor 14 provides its output to the controller 20 , and the controller controls the motor 16 and the driving of the output device 18 .

[0093] Figure 4 Illustrated are different outputs that may be provided in response to different sensed forces or pressures.

[0094] When the force or pressure determined by the sensor is between a first threshold Th1 and a second higher threshold Th2, a first indication "I1" is provided. This is the range for an optimal skin treatment result and the output is, for example, a green light "G".

[0095] The second indication "I2" is used when the force or pressure is above the optimal range, and the output is, for example, a red light "R".

[0096] The third indication “I3” is used when the force or pressure is below the optimal range but still above the third threshold Th3 and the output is, for example, yellow light “Y”.

[0097] The fourth indication "I4" is used when the force or pressure is below the third threshold Th3 and in this example the light is off. However, the device remains "active".

[0098] Figure 4 An additional (optional) threshold value Th4 is shown, above which there is an automatic shut-down function to protect the device.

[0099] In addition to providing real-time feedback as described above, the controller can derive a performance rating for the skin treatment procedure performed by the user based on the force or pressure sensed during and throughout the skin treatment procedure. For example, a percentage rating representing the time that an optimal pressure range is reached can be generated. This performance rating is made more accurate by ignoring periods of no contact, rather than treating them as periods of insufficient pressure being applied.

[0100] Figure 5 A method of controlling a skin treatment device is shown.

[0101] In step 50, the force or pressure is measured and compared with three threshold values ​​Th1, Th2, Th3. Figure 5 There is no indication in the method Figure 4 The fourth threshold is shown.

[0102] The first to third indications are provided in steps 52 , 54 and 56 .

[0103] If the force or pressure is below the third threshold, a timer is started in step 58 (during which the pressure or force continues to be monitored) to determine whether the contact has been released for longer than the first time threshold tth1 During this period, the previous feedback indication may be provided. Alternatively, the feedback may default to the third indication.

[0104] If the first time threshold is reached, a fourth indication is provided in step 60 .

[0105] The timing may continue, and if the non-contact continues for a second duration t th2 (which may be the total non-contact time or a new timing count starting from the time the fourth indication is provided), the timing may be determined in step 62 (during which the pressure or force continues to be monitored). If the second duration is reached, the automatic shut-off function is implemented in step 64.

[0106] Feedback to the user may additionally be provided by an app (e.g. running on a smartphone). This is particularly useful for performance analysis rather than real-time analysis. Thus, after the skin treatment is finished, the user may access a performance report on their mobile device.

[0107] Real-time force or pressure feedback can additionally be used in other ways, such as controlling motor speed as a function of applied pressure. Alternatively, motor drive power can be varied according to the sensed pressure to maintain a more constant speed despite the different motor loads caused by different pressures.

[0108] Contact sensing may also be used to provide automatic activation of the motor when contact is sensed. If the motor remains running when the fourth indication is provided, it may be set to a lower motor speed which is increased back to the desired level once contact is reestablished.

[0109] The invention is not only applicable to mechanical shavers as described above. It can be applied to shavers based on laser cutting, epilators or other skin treatment devices, such as beard trimmers, body groomers, scissors and skin cleaning brushes. It can also be applied to monitoring devices for measuring skin parameters, such as devices that capture images of the skin when the user applies the appliance to the skin.

[0110] By studying the drawings, the disclosure and the appended claims, those skilled in the art can understand and implement variations of the disclosed embodiments when practicing the claimed invention. 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 can implement the functions of several items described in the claims. The fact that certain measures are recited in mutually different dependent claims does not mean that a combination of these measures cannot be used to advantage. The computer program may be stored / distributed on an appropriate medium, such as an optical storage medium or solid-state medium provided 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 telecommunications systems. If the term "suitable for" is used in a claim or specification, it should be noted that the term "suitable for" is intended to be equivalent to the term "configured to". Any figure marks in the claims should not be interpreted as limiting the scope.

Claims

1. A skin treatment device (10), comprising: Skin treatment heads (12); a force or pressure sensor (14) for determining the force or pressure with which the skin treatment device is held against the skin of a user during use; an output device (18) for providing output information to the user related to the force or pressure determined by the sensor; as well as a controller (20) for controlling the output device according to the force or pressure determined by the sensor, Wherein, the controller (20) is adapted to control the output device to: providing a first indication (I1) when the force or pressure determined by the sensor is within a range between a first threshold (Th1) and a second threshold (Th2) higher than the first threshold, the first indication indicating that the force or pressure applied by the user is within a range of forces or pressures recommended to be applied by the user for optimal skin treatment results; providing a second indication (I2) different from the first indication when the force or pressure determined by the sensor is above the second threshold (Th2); and providing a third indication (I3) when the force or pressure determined by the sensor is below the first threshold (Th1) and above a third threshold (Th3), the third indication being different from the first indication and the second indication, the third threshold (Th3) being lower than the first threshold; The invention is characterized in that when the force or pressure determined by the sensor is lower than the third threshold value (Th3) and corresponds to the non-contact between the skin treatment head (12) and the skin, the controller (20) is suitable for controlling the output device (18) to provide a fourth indication (I4) different from the first indication (I1), the second indication (I2) and the third indication (I3).

2. The skin treatment device according to claim 1, wherein the third threshold value (Th3) is or corresponds to a force in the range of 0.1N to 0.5N.

3. A skin treatment device according to claim 1, wherein the controller (20) is adapted to control the output device (18) to output the force or pressure determined by the sensor only when the force or pressure is below the third threshold for a period longer than a first time threshold (t th1 ), provide the fourth indication.

4. The skin treatment device according to any one of claims 1 to 3, wherein the controller (20) is adapted to: switching the skin treatment device between an active state and an inactive state; and When the force or pressure determined by the sensor is below the third threshold value (Th3), the output device is controlled to provide the fourth indication (I4) while maintaining the skin treatment device in the active state.

5. The skin treatment device according to claim 4, further comprising: A motor (16) for driving the skin treatment head, wherein the controller is adapted to activate the motor (16) in the active state and deactivate the motor in the inactive state.

6. The skin treatment device according to claim 4, wherein the controller (20) is adapted to control the sensor to detect a change in the applied force or pressure when the time for which the applied force or pressure determined by the sensor is below the third threshold (Th3) is longer than a second time threshold (t th2 ) long, the skin treatment device is switched to the inactive state, the second time threshold (t th2 ) is greater than the first time threshold (t th1 ).

7. The skin treatment device according to any one of claims 1 to 3, wherein the output device (18) comprises a light output device, and the first indication, the second indication and the third indication each comprise a light output having a respective different color.

8. The skin treatment device according to claim 7, wherein the fourth indication comprises: No light output; a light output color different from the light output colors of the first indication, the second indication, and the third indication; or Flashing light output.

9. The skin treatment device according to any one of claims 1 to 3, wherein: The force or pressure sensor (14) is arranged to measure the force or pressure exerted mutually by the skin treatment head and the skin; or, The skin treatment device further comprises a handle (15) coupled to the skin treatment head, and the force or pressure sensor is arranged to measure the force or pressure exerted by the handle and the skin treatment head on each other.

10. A skin treatment device according to any one of claims 1 to 3, wherein the output device (18) comprises a light output device proximate to the skin treatment head.

11. The skin treatment device according to any one of claims 1 to 3, wherein: The controller (20) is adapted to derive a performance rating for a skin treatment procedure based on the force or pressure determined by the sensor during a skin treatment procedure performed by the user.

12. A skin treatment device according to any one of claims 1 to 3, comprising an electric shaver, wherein the skin treatment head (12) comprises a shaving head.

13. A method of controlling a skin treatment device, the skin treatment device comprising a skin treatment head; a force or pressure sensor for determining the force or pressure with which the skin treatment device is held against the skin of a user during use; and an output device for providing output information related to the force or pressure determined by the sensor to the user, wherein the method comprises: when the force or pressure determined by the sensor is between a first threshold and a second threshold that is higher than the first threshold, controlling (52) the output device to provide a first indication indicating that the force or pressure applied by the user is within a range of forces or pressures recommended to the user for optimal skin treatment results; When the force or pressure determined by the sensor is above the second threshold, controlling (54) the output device to provide a second indication different from the first indication; and controlling (56) the output device to provide a third indication different from the first indication and the second indication when the force or pressure determined by the sensor is below the first threshold and above a third threshold, the third threshold being lower than the first threshold; The method is characterized in that the method comprises: when the force or pressure determined by the sensor is lower than the third threshold value and corresponds to non-contact between the skin treatment head and the skin, controlling (60) the output device to provide a fourth indication different from the first indication, the second indication and the third indication.

14. The method according to claim 13, comprising: The output device is controlled to provide the fourth indication only when the force or pressure determined by the sensor is below the third threshold for longer than a first time threshold.

15. A computer program comprising computer program code means adapted to implement the method according to any one of claims 13 to 14 when said program is run on a computer.

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