Personal care device and method for determining position of personal care device on body part

Abstract

According to one aspect, there is provided a personal care device (2) for performing a personal care procedure on a subject, the personal care device (2) configured to determine a position of the personal care device (2) on a body part of the subject. The personal care device (2) comprises: an orientation sensor (6) configured to measure a three-dimensional (3D) angular orientation of the personal care device (2) over time with respect to earth gravity and to output a corresponding orientation measurement signal; a surface displacement sensor (10) configured to measure a two-dimensional (2D) displacement of the personal care device (2) relative to a skin surface of the body part and output a corresponding surface displacement measurement signal; a processing unit (22) configured to determine a position of the personal care device (2) on the body part based on the orientation measurement signal, the surface displacement measurement signal, and a skin contact signal indicative of whether the personal care device (2) is in contact with a skin surface of the body part.

Description

Technical Field

[0001] The present disclosure relates to a personal care device for performing a personal care operation on a subject, and more particularly to a method and apparatus for determining a position of a personal care device on a body part of a subject. Background Art

[0002] Personal care devices can be provided for many different types of personal care operations, such as shaving, hair cutting, hair removal, skin massage, etc. During a personal care operation, it may be useful to determine the position of the personal care device on the subject's body in real time or near real time. For example, knowledge of the position of the personal care device can be used to monitor the performance of the personal care operation, adjust the operating characteristics of the personal care device, provide guidance to the user of the personal care device, etc.

[0003] A technique for determining the position of a personal care device is known from WO2020 / 182698, wherein the device for performing a treatment operation on a body part includes one or more orientation sensors for measuring the orientation of the device, and one or more movement sensors for measuring the movement of the device. In this technique, a three-dimensional (3D) representation of the body part is obtained, the 3D representation having normal vectors corresponding to positions on the surface of the body part, movement measurements and orientation measurements are processed to determine a position and orientation sequence of the device during the treatment operation, and the orientation and position sequence of the device are compared with the normal vectors and the corresponding positions of the normal vectors to determine the position of the device on the surface of the body part. However, although this technique is capable of determining the position of the device on the body part, it is desired that the determined position of the personal care device on the body part has higher accuracy.

[0004] EP3800644A1 discloses a computer-implemented method for determining the position of a personal care device relative to a subject's skin surface. The method includes receiving data representing the measured curvature of a skin surface within a first region of the skin surface in contact with the personal care device. By comparing the measured curvature with curvature information of multiple regions of the subject's skin surface contained in a database, a position indication of the first region of the subject's skin surface is determined. The position of the personal care device can be more accurately determined by acquiring additional data, such as displacement data of the personal care device acquired by a sensor such as an inertial measurement unit (IMU). In some examples, the IMU is used to estimate the orientation of the personal care device relative to a gravitational field to increase position determination.

[0005] Therefore, there is a need for improved detection of the position of personal care devices during personal care operations. Summary of the invention

[0006] According to a first specific aspect, a personal care device for performing a personal care operation on a subject is provided, the personal care device being configured to determine the position of the personal care device on a body part of the subject. The personal care device comprises: an orientation sensor configured to measure the three-dimensional 3D angular orientation of the personal care device relative to the earth's gravity over time, and output a corresponding orientation measurement signal; a surface displacement sensor configured to measure the two-dimensional 2D displacement of the personal care device relative to the skin surface of the body part, and output a corresponding surface displacement measurement signal; a processing unit configured to determine the position of the personal care device on the body part based on the orientation measurement signal, the surface displacement measurement signal, and a skin contact signal indicating whether the personal care device is in contact with the skin surface of the body part.

[0007] According to a second aspect, a computer-implemented method for determining a position of a personal care device on a body part of a subject is provided, wherein the personal care device is configured to perform a personal care operation on the subject. The method includes using an orientation sensor in the personal care device to measure the three-dimensional 3D angular orientation of the personal care device relative to the earth's gravity over time, and outputting a corresponding orientation measurement signal; using a surface displacement sensor in the personal care device to measure the two-dimensional 2D displacement of the personal care device relative to the skin surface of the body part, and outputting a corresponding surface displacement measurement signal; and determining, by a processing unit, the position of the personal care device on the body part based on the orientation measurement signal, the surface displacement measurement signal, and a skin contact signal indicating whether the personal care device is in contact with the skin surface of the body part.

[0008] According to a third aspect, there is provided a computer program product comprising a computer readable medium embodying computer readable code, the computer readable code being configured such that when executed by a suitable computer or processor, the computer or processor causes the computer or processor to perform the method according to the second aspect or any embodiment thereof.

[0009] These and other aspects will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Exemplary embodiments will now be described, by way of example only, with reference to the following drawings, in which:

[0011] Figure 1 is an illustration of an exemplary personal care device in the form of a rotary shaver;

[0012] Figure 2 yes Figure 1 A top view of a personal care device;

[0013] Figure 3is a block diagram of a personal care device according to some embodiments;

[0014] Figure 4 is a flowchart illustrating an exemplary method according to the present disclosure; and

[0015] Figure 5 is a block diagram illustrating some sub-steps of a position detection algorithm according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0016] Figure 1 is a simplified illustration of a personal care device 2 to which the techniques described herein may be applied or used. Figure 2 Shows Figure 1 A top view of the personal care device 2 is shown. Figure 1 In the figure, the personal care device 2 is in the form of an electric shaver / rotary shaver, but it should be understood that the technology described herein can be applied to any type of personal care device 2, such as a metal foil shaver, a beard trimmer or any other type of hair cutting device, hair removal device, skin massager, skin measurement device (for example, for measuring skin properties), etc.

[0017] The personal care device 2 comprises a body 3 to be held in the hand of a user and a cutting head 4 in the form of a shaving part comprising a plurality of cutting elements 5 for cutting / shaving. Each cutting element 5 comprises one or more rapidly rotating circular blades or foils ( Figure 1 When the cutting head 4 is placed on the face and moved, the hair on the face is cut by the cutting element 5. Figure 1 2 is shown as including three cutting elements 5 arranged in a triangle, but it should be understood that the rotary shaver 2 may have a different number of cutting elements 5 and / or cutting elements 5 arranged differently.

[0018] Figure 1 Also shown are various sensors present in or on the personal care device 2. Thus, Figure 1 A personal care device 2 comprising a position sensor 6 and a surface displacement sensor 10 is shown.

[0019] The orientation sensor 6 is configured to measure the three-dimensional (3D) angular orientation of the personal care device 2 relative to the earth's gravity over time, and output a corresponding orientation measurement signal representing the measured orientation. The orientation measurement signal includes a time series of orientation measurement samples according to the sampling rate of the orientation sensor 6. In some embodiments, the orientation sensor 6 includes a gyroscope 8 and optionally includes an accelerometer 7, and the orientation sensor 6 may also include a processor or processing unit for processing the measurement signals provided by the accelerometer 7 and the gyroscope 8 to determine the orientation measurement signal. In some embodiments, the accelerometer 7 and the gyroscope 8 are part of an inertial measurement unit (IMU) 12, but in other embodiments, the accelerometer 7 and the gyroscope 8 are independent sensors.

[0020] The accelerometer 7 is configured to measure the acceleration of the personal care device 2 along three axes (e.g., three orthogonal axes, i.e., three-dimensional axes) over time, and output an acceleration measurement signal representing the measured (3D) acceleration. The acceleration measurement signal includes a time series of acceleration measurement samples according to the sampling rate of the accelerometer 7. The measured acceleration will include the acceleration due to gravity.

[0021] The gyroscope 8 is configured to measure the rotation of the personal care device 2 about three axes (eg three orthogonal axes) over time and output a gyroscope measurement signal representing the measured (3D) rotation. The gyroscope measurement signal comprises a time series of rotation measurement samples according to a sampling rate of the gyroscope 8 .

[0022] The surface displacement sensor 10 is configured to measure the two-dimensional (2D) displacement of the personal care device 2 relative to the skin surface of the body part, and output a corresponding surface displacement measurement signal representing the measured displacement. According to the sampling rate of the surface displacement sensor 10, the surface displacement measurement signal includes a time series of surface displacement measurement samples. The surface displacement sensor 10 may be an optical displacement sensor similar to those used in a computer mouse. Therefore, the surface displacement sensor 10 may include a light source for emitting light onto the skin surface, and a light sensor or camera sensor for measuring light reflected by the skin surface, wherein the surface displacement measurement signal is derived from the measured light. For example, the surface displacement sensor may include a low-resolution grayscale camera (e.g., with a resolution of 8×8 pixels or 16×16 pixels) that captures an image of the surface at a high or very high frame rate, and calculates the surface displacement by analyzing patterns in the captured image. The surface displacement sensor 10 is arranged in the personal care device 2 so that the surface displacement sensor 10 is able to observe and measure the skin surface when the personal care device 2 is in contact with the skin surface. As Figure 2 As shown, the surface displacement sensor 10 may be arranged on or near a cutting element on the cutting head 4 .

[0023] The position sensor 6 (and if present, the gyroscope 8 and the optional accelerometer 7) and the surface displacement sensor 10 are integrated with the personal care device 2, or are otherwise located in a fixed position within the personal care device 2, so that the movement of the personal care device 2 is directly measured by the position sensor 6 and the surface displacement sensor 10. The position and orientation of the position sensor 6 (and if present, the gyroscope 8 and the optional accelerometer 7) and the surface displacement sensor 10 relative to each other are known. In addition, the position and orientation of the position sensor 6 (and if present, the gyroscope 8 and the optional accelerometer 7) and the surface displacement sensor 10 relative to the portion of the personal care device 2 that contacts the skin surface during the personal care operation is also known. For example, a calibration procedure can be implemented during the manufacture of the personal care device 2 or during the initial setting or during the product design to determine the relative position and orientation. The position and orientation of the sensor relative to the portion of the personal care device 2 that contacts the skin surface during use enables the measurement value from the sensor to be associated with the movement of the personal care device 2 relative to the skin surface.

[0024] As discussed further below, knowing whether the personal care device 2 is in contact with the skin surface is useful when determining the location of the personal care device 2 on the subject. Therefore, a skin contact signal is needed that includes a measurement of whether the personal care device 2 is in contact with the skin surface of the body.

[0025] In some embodiments, the personal care device 2 may include a skin contact sensor 14, which is configured to measure whether the personal care device 2 is in contact with the skin surface of a body part, and output a corresponding skin contact signal. The skin contact signal includes a time series of skin contact measurement samples according to the sampling rate of the skin contact sensor 14. The skin contact sensor 14 can be a pressure (force) sensor, a proximity sensor, or a capacitive sensor that measures the pressure on the surface of the personal care device 2 pressed against. The proximity sensor can be based on any suitable technology, such as light, sound, ultrasound, etc., and utilizes time-of-flight measurement to determine the proximity of the sensor 14 to the skin surface (and therefore determine the proximity of the personal care device 2 to the skin surface, because the position of the sensor 14 in the personal care device 2 is known). It should be understood that some types of skin contact sensors 14 can provide a binary output in the skin contact signal, indicating whether the personal care device 2 is in contact with the skin surface at this moment.

[0026] In an alternative embodiment, the personal care device 2 does not include a separate skin contact sensor 14, but rather derives the skin contact signal by processing the surface displacement measurement signal. For example, when the personal care device 2 is in contact with the skin surface, the surface displacement sensor 10 will be able to measure the displacement of the personal care device 2 on the skin surface, and when the personal care device 2 is not in contact with the skin, the surface displacement sensor 10 will not be able to measure the surface displacement, which can be identified from the surface displacement measurement signal.

[0027] Figure 3 is a block diagram of an exemplary personal care device 2 that is configured to determine the location of the personal care device 2 on a body part of a subject according to the techniques described herein. Figure 3 In the illustrated embodiment, the processing performed to determine the position of the personal care device 2 is performed by a processing unit 22 within the body 3 of the personal care device 2. However, it will be appreciated that in alternative embodiments, the processing performed to determine the position of the personal care device 2 may be performed by a processing unit that is part of a base unit of the personal care device 2 (e.g., a docking station or charging station). Furthermore, where the orientation sensor 6 includes an accelerometer 7 and a gyroscope 8, a processing unit 22 or a separate processor or processing unit included in or associated with the orientation sensor 6 may be provided for determining the orientation measurement signal.

[0028] Processing unit 22 generally controls the operation of personal care device 2 and enables personal care device 2 to implement the methods and techniques described herein. Briefly, processing unit 22 is configured to determine the position of personal care device 2 on a body part based on position measurement signals, surface displacement measurement signals, and skin contact signals.

[0029] The processing unit 22 is configured to receive the orientation measurement signal and the surface displacement measurement signal from the corresponding sensors 6, 10. In an embodiment where the personal care device 2 includes a skin contact sensor 14, the processing unit 22 is also configured to receive the skin contact signal. Therefore, the processing unit 22 may include or contain one or more input ports or other components for receiving measurement signals from the sensors 6, 10, 12. The processing unit 22 may also include or contain one or more output ports or other components for communicating with other components of the personal care device 2.

[0030] The processing unit 22 may be implemented in a variety of ways using software and / or hardware to perform the various functions described herein. The processing unit 22 may include one or more microprocessors or digital signal processors (DSPs) that may be programmed using software or computer program code to perform the desired functions and / or control the components of the processing unit 22 to perform the desired functions. The processing unit 22 may be implemented as a combination of dedicated hardware (e.g., amplifiers, preamplifiers, analog-to-digital converters (ADCs) and / or digital-to-analog converters (DACs)) that perform some functions and processors (e.g., one or more programmed microprocessors, controllers, DSPs, and associated circuitry) that perform other functions. Examples of components that may be used in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, DSPs, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs).

[0031] The processing unit 22 may include or be associated with a storage unit 24. The storage unit 24 may store data, information, and / or signals (including measurement signals, any results of measurement signal processing, or any intermediate results) for use by the processing unit 22 in controlling the operation of the personal care device 2 and / or executing or implementing the methods described herein. In some embodiments, the memory unit 24 stores computer-readable code that can be executed by the processing unit 22 so that the processing unit 22 implements one or more functions, including the methods described herein. The memory unit 24 may include any type of non-transitory machine-readable medium, such as a cache or system memory, including volatile and non-volatile computer memory, such as random access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM) and electrically erasable PROM (EEPROM), and the memory unit may be implemented in the form of a memory chip, an optical disk (e.g., a compact disk (CD), a digital versatile disk (DVD) or a Blu-ray disk), a hard disk, a tape storage solution or a solid-state device, including a memory stick, a solid-state drive (SSD), a memory card, etc.

[0032] exist Figure 3In the illustrated embodiment, the personal care device 2 also includes an interface circuit device 26, which can be connected to and / or exchange data with other devices, including any one or more of a smart phone, a laptop, a smart watch, a computer, and other user devices. Any data connection can be direct or indirect (e.g., via the Internet), and therefore the interface circuit device 26 can realize the connection between the personal care device 2 and the network via any desired wired or wireless communication protocol, or the direct connection between the personal care device 2 and another device (such as a smart phone). For example, the interface circuit device 26 can operate using WiFi, Bluetooth, Zigbee or any cellular communication protocol (including but not limited to Global System for Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE), Advanced LTE, etc.). In the case of a wireless connection, the interface circuit device 26 (and the personal care device 2) may include one or more suitable antennas for transmitting / receiving through a transmission medium (e.g., air). The interface circuit device 26 is connected to the processing unit 22.

[0033] The personal care device 2 may also include one or more user interface components 28 that enable a user of the personal care device 2 to input information, data, and / or commands into the personal care device 2, and / or enable the personal care device 2 to output information or data to the user of the personal care device 2, such as information indicating the performance of a personal care operation, the coverage of a personal care operation, and / or any other information related to or derivable from the determined location of the personal care device 2. The user interface 28 may include any suitable input component(s), including but not limited to a keyboard, a keypad, one or more buttons, switches or dials, a mouse, a track pad, a touch screen, a stylus, a camera, a microphone, etc., and / or the user interface 28 may include any suitable output component(s), including but not limited to a display unit or display screen, one or more lights or light elements, one or more speakers, a vibration element, etc.

[0034] It should be understood that actual implementations of the personal care device 2 will include Figure 3 Additional components shown. For example, the personal care device 2 may also include a power source, such as a battery, or components for enabling the personal care device 2 to be connected to a mains power source, such as components for charging a battery.

[0035] Figure 4The flowchart in illustrates an exemplary method performed by a personal care device 2 according to the techniques described herein. As described above, the personal care device 2 is used to perform personal care operations on a subject, such as hair cutting, shaving, hair removal, skin massage, etc. The body part on which the personal care operation is performed can be the subject's head, the subject's face, or the subject's head / face and neck.

[0036] In step 101, the orientation sensor 6 in the personal care device 2 measures the 3D angular orientation of the personal care device 2 relative to the earth's gravity over time, particularly during the use of the personal care device 2 in performing personal care operations. The orientation sensor 6 outputs an orientation measurement signal, which represents the measured orientation around three axes. When measuring the orientation, the orientation sensor 6 continuously outputs the orientation measurement signal.

[0037] In step 103, the surface displacement sensor 10 in the personal care device 2 measures the 2D displacement of the personal care device 2 relative to the skin surface of the body part over time, particularly during the use of the personal care device 2 in performing a personal care operation. The surface displacement sensor 10 outputs a corresponding surface displacement measurement signal representing the measured displacement. When measuring the surface displacement, the surface displacement sensor 10 continuously outputs the surface displacement measurement signal.

[0038] It should be understood that step 101 and step 103 occur simultaneously during use of the personal care device 2 .

[0039] In step 105, the processing unit 22 determines the position of the personal care device 2 on the body part based on the position measurement signal, the surface displacement measurement signal, and the skin contact signal indicating whether the personal care device 2 is in contact with the skin surface of the body part. The processing unit 22 can perform step 105 in response to executing a computer program code, which can be stored on a computer readable medium, such as the storage unit 24.

[0040] In some embodiments, a skin contact sensor 14 is provided to measure whether the personal care device 2 is in contact with the skin surface and generate a skin contact signal, in which case the method further comprises the skin contact sensor 14 in the personal care device 2 measuring whether the personal care device 2 is in contact with the skin surface over time, particularly during the use of the personal care device 2 in performing a personal care operation. The skin contact sensor 14 outputs a corresponding skin contact signal indicating whether the personal care device 2 is in contact with the skin. When measuring skin contact, the skin contact sensor 14 continuously outputs a skin contact signal. In an alternative embodiment, there is no separate skin contact sensor 14 in the personal care device 2, and the processing unit 22 is configured to process the surface displacement measurement signal from the surface displacement sensor 10 to determine the skin contact signal.

[0041] In an embodiment where the orientation sensor 6 includes an accelerometer 7 and a gyroscope 8, the accelerometer 7 measures the acceleration of the personal care device 2 over time, and the gyroscope 8 measures the rotation of the personal care device 2 over time, particularly during use of the personal care device 2 in performing a personal care operation. The accelerometer 7 generates an acceleration measurement signal representing the acceleration measured along 3 axes, and the gyroscope 8 generates a gyroscope measurement signal representing the rotation measured around the 3 axes. The method may include determining the 3D angular orientation of the personal care device 2 (represented by the orientation measurement signal) from the output signals of the 3-axis accelerometer 7 and the 3-axis gyroscope 8.

[0042] In some embodiments, in step 105, the processing unit 22 may be configured to estimate the starting position of the personal care device 2 on the skin surface of the body part. The processing unit 22 may use the starting position to determine the current position of the personal care device 2 on the skin surface. In particular, the processing unit 22 may determine the current position by processing the orientation measurement signal, the surface displacement measurement signal and the skin contact signal to determine or estimate the movement of the personal care device 2 from the starting position of the personal care device 2. The starting position may be estimated as a default position on the skin surface. For example, the user of the personal care device 2 may always start a personal care operation on their right cheek (for example, may start a shaving operation on their right cheek), or start a personal care operation above their upper lip, etc. Alternatively, the starting position may be determined by the processing unit 22 based on the average starting position detected during the previous personal care operation. In another alternative, the starting position may be determined based on the orientation measurement signal. In this case, when determining the starting position of the personal care device 2, the geometric model of the body part may be used in conjunction with the orientation measurement signal.

[0043] In some embodiments, step 105 includes the processing unit 22 executing a position detection algorithm, which includes a plurality of sub-steps. First, the processing unit 22 processes the skin contact signal to determine whether the personal care device 2 is in contact with the skin surface.

[0044] If it is determined that the personal care device 2 is not in contact with the skin surface, the processing unit 22 determines the position of the personal care device 22 on or relative to the body part from the position measurement signal.

[0045] Similarly, if it is determined that the personal care device 2 has resumed contact with the skin surface after a period of time without contact with the skin surface and before the surface displacement measurement signal indicates that the personal care device 2 has been moved relative to the skin surface, the processing unit 22 determines the position of the personal care device 2 on the body part from the orientation measurement signal.

[0046] However, if it is determined that the personal care device 2 is in contact with the skin surface, and the personal care device 2 has been moved relative to the skin surface with which it is in continuous contact since the personal care device 2 last resumed contact with the skin surface, the processing unit 22 determines the position of the personal care device 2 on the body part from the orientation measurement signal and the surface displacement measurement signal.

[0047] In some embodiments, step 105 may include deriving a 3D angular orientation of a 2D reference plane of a surface displacement sensor in which the 2D displacement of the personal care device 2 is measured from the orientation measurement signal. The 2D displacement measurement represented by the surface displacement measurement signal is then combined with the 3D angular orientation of the 2D reference plane of the surface displacement sensor to determine the 3D displacement of the personal care device 2 relative to the body part. Effectively, the process converts the 2D displacement measured by the surface displacement sensor 10 into a 3D displacement of the personal care device 2 relative to the body part by taking into account the 3D angular orientation of the 2D reference plane in which the 2D displacement of the personal care device 2 relative to the skin surface is measured.

[0048] In some embodiments, the processing unit 22 may determine a first position estimate for the personal care device 2 from the surface displacement measurement signal and the orientation measurement signal, for example in the manner described above, determine a second position estimate for the personal care device 2 from the orientation measurement signal, combine the first position estimate and the second position estimate to determine a filtered position estimate, determine a projection of the filtered position estimate on a geometric model of the body part, and determine the position of the personal care device 2 on the body part from the projection. In some embodiments, the position of the personal care device 2 may be determined from the projection of the filtered position estimate and the intersection of the geometric model.

[0049] In an embodiment where the orientation sensor 6 includes an accelerometer 7 and a gyroscope 8, the orientation measurement signal can be determined as follows. The accelerometer 7 is capable of measuring the direction of gravity. Gravity is shown in the measurement as a vector whose length is 1g pointing to the ground. This provides a reference that can be used to determine the orientation of the personal care device 2 relative to the earth's gravity or the ground plane. However, the accelerometer 7 measures all accelerations, and therefore also measures the acceleration caused by moving the personal care device 2 in space. Therefore, the gravity measurement is noisy and unstable in the short term, although on average it will point to the correct direction. The gyroscope 8 is capable of measuring the rotation of the device around 3 axes. The gyroscope is fast and accurate. However, the gyroscope cannot measure the direction of gravity. Therefore, the absolute angular orientation of the personal care device 2 relative to the earth's gravity cannot be calculated using only a gyroscope. In addition, the gyroscope measurement signal contains very small measurement errors. The relative angular orientation is calculated by integrating the rotation speed over time. Due to measurement errors and cumulative integration errors, the relative angular orientation estimate will therefore deviate from the actual value over time. In order to combine advantages and overcome disadvantages, the outputs of the two sensors 7, 8 are combined in a clever way. In essence, the accelerometer measurement value is used to calculate the long-term stable earth gravity field direction or the ground plane direction, and the gyroscope measurement signal is used to accurately track the fast short-term angular azimuth change. One way to do this is to use a complementary filter, which effectively applies a low-pass filter to the gravity direction signal obtained from the accelerometer measurement, applies a high-pass filter to the gyroscope measurement signal, and combines the two filtered signals to obtain the final azimuth measurement signal. It should be noted that two of the three components of the azimuth generated in the azimuth measurement signal are absolute, i.e., the roll angle and the pitch angle. These axes are perpendicular to the direction of gravity, so the accelerometer can measure the azimuth changes of these axes as changes in the direction of gravity. The yaw axis is in a straight line with gravity, so the rotation along this axis will not be displayed as a change in the direction of gravity. The yaw axis can be considered as an axis extending vertically downward from the top of the head, so the measurement of the left and right movement of the personal care device is completely relative (only gyroscope). The above is why the starting position should be set or derived. For example, without a starting position, the algorithm might assume that the user started at the center of the face, when in fact they started at the right cheek.

[0050] Assuming that the starting position of the personal care device 2 is known, the first position estimate can be a relatively accurate position of the personal care device 2 on the skin surface. However, without correction, over larger displacements, the first position estimate drifts and the accuracy decreases. Therefore, an embodiment provides a combination of the first position estimate and the second position estimate to address this drift problem.

[0051] In some embodiments, a complementary filter is used to combine the first position estimate and the second position estimate. The complementary filter may act as a combined high pass filter and low pass filter. In some embodiments, the complementary filter may operate such that the first position estimate (i.e., the position estimate determined from the surface displacement measurement signal and the orientation measurement signal) is high pass filtered, and the second position estimate (i.e., the position estimate derived from the orientation measurement signal) is low pass filtered. The effect is that the first position estimate is slowly pulled toward the second position estimate, which prevents it from drifting, while still allowing accurate short term surface displacement sensor information to pass through the filter.

[0052] In some embodiments, the geometric model of the above-mentioned body part can also be used to correct the long-term change of the orientation of the body part. The physical constraints defined by the model used herein are used to correct the position estimate. This mechanism can be used to correct the (completely relative) yaw angle measurement. The idea is that a person cannot turn more than 180° to the left or right. When a person turns their head instead of the personal care device 2, the orientation sensor 6 (IMU) will not measure this, and the position estimate of the IMU (the second position estimate-only IMU position) will become incorrect. However, since the user will continue to shave, the measured IMU position will move out of the limit of the head model. This can be detected, and the second position estimate can be moved in such a way that the resulting position is again inside the head model. Similarly, when the user turns their head and personal care device 2, this will be mistakenly displayed as the personal care device 2 moving left / right on the face in the position estimate of only the IMU. Similarly, the physical constraints of the head model can be used to correct the position estimate. For both methods, as long as the user completely covers the beard area from left to right after moving their head, the correction will be completed. For the other two angles, it is assumed that the user keeps his head straight on average.

[0053] Figure 5 The block diagram in FIG. 1 illustrates some logical sub-steps of an embodiment of the above-described position detection algorithm. Figure 5 For the embodiment where the personal care device 2 is an electric shaver and the personal care operation is shaving the face and neck, it will be appreciated that Figure 5 The sub-steps in can be applied to other types of personal care devices 2 and / or other types of personal care operations. Figure 5 In the embodiment of the present invention, the accelerometer 7 and the gyroscope 8 are considered to be part of the IMU. In addition, the electric shaver comprises a skin contact sensor 14.

[0054] Therefore, in Figure 5In the embodiment of the present invention, when the electric shaver 2 is activated / switched on, the IMU 7, IMU 8 are initialized (e.g., activated) - box 50 - and the IMU data fusion box 52 is activated. The orientation sensor 6 can be considered to include an IMU and an IMU data fusion box 52. The output of the IMU, namely the acceleration measurement signal (which indicates acceleration in three orthogonal directions (e.g., represented as ax, ay, az)) and the gyroscope measurement signal (which indicates three-dimensional rotation speed) are input to the IMU data fusion box 52. The output of the surface displacement sensor 10, namely the surface displacement measurement signal (which indicates a two-dimensional displacement ((e.g., represented as dx, dy)) is input to the surface displacement measurement signal (SDMS) processing box 54. The output of the skin contact sensor 14, the skin contact signal, is input to the box 58, which detects whether the electric shaver is in contact with the skin surface from the skin contact signal. Based on the output of the box 58 and the state of the on / off button of the electric shaver, the box 56 detects whether the shaving operation has started.

[0055] When the frame 56 detects that the shaving operation has begun, the starting position estimation frame 60 is initialized to estimate the starting position of the electric shaver. As described above, the starting position can be estimated as a default position of the electric shaver (e.g., the right cheek), as an average of the starting positions of multiple previous shaving operations, or based on the orientation measurement signal. The estimated starting position is output to the SDMS processing frame 54 and the IMU position processing frame 61. The estimated starting position can be used to initialize a position estimate (e.g., a position estimate derived from the orientation measurement signal), and / or a position estimate derived from the orientation measurement signal and the surface displacement measurement signal. In some embodiments, the starting position estimation frame 60 can estimate the starting position based on the position estimate determined by the IMU position processing frame 61. The estimated starting position can always be assumed to be in the facial area, and during the shaving operation, the starting position estimate can be corrected and updated based on the physical limitations of the beard / facial hair area.

[0056] The IMU data fusion box 52 determines an orientation measurement signal from the gyroscope measurement signal and the acceleration measurement signal, which is a 3-axis angular orientation in a global coordinate system (also referred to as "device orientation"). Therefore, the IMU data fusion box 52 determines an orientation measurement signal representing the 3D angular orientation of the personal care device 2 relative to the earth's gravity during the personal care operation from the acceleration measurement signal and the gyroscope measurement signal. In particular, as described above, the acceleration measurement signal is used to calculate the long-term stable ground plane direction, and the gyroscope measurement signal is used to accurately track rapid short-term orientation changes. The two signals are combined to obtain the orientation of the 3D device relative to the ground plane (orientation measurement signal). The IMU data fusion box 52 outputs the 3-axis orientation signal to the SDMS processing box 54 and the IMU position processing box 61.

[0057] In some embodiments, the IMU data fusion block 52 may also determine a signal representing the linear acceleration of the personal care device 2 (i.e., the acceleration of the personal care device 2 other than gravity) from the rotation measurement signal of the gyroscope 8 and the acceleration measurement signal of the accelerometer 7, wherein the linear acceleration is provided to one or more subsequent blocks in the algorithm (e.g., the IMU position processing block 61). In this case, the acceleration measurement signal is able to identify the direction of gravity, and the acceleration due to gravity is removed from the acceleration measurement signal.

[0058] The SDMS processing block 54 determines the above-mentioned 'first position estimate' of the electric shaver 2 based on the surface displacement measurement signal received from the surface displacement sensor 10 and the orientation measurement signal received from the IMU data fusion block 52. In particular, the SDMS processing block 54 derives the 3D angular orientation of the 2D reference plane of the surface displacement sensor 10 from the orientation measurement signal. The 2D reference plane is the plane where the surface displacement sensor 10 measures the 2D displacement of the electric shaver 2 relative to the user's skin. The SDMS processing block 54 combines the measured 2D displacement of the electric shaver 2 with the derived 3D angular orientation of the 2D reference plane, thereby converting the 2D displacement measurement represented by the surface displacement measurement signal into three dimensions. Over time, this will produce the original 3D 'track' of the electric shaver. The first position estimate is the most recent 3D position sample in the 3D track. The first position estimate is provided to the filtering and anchoring block 62. The first position estimate can also take into account the estimated starting position output by the starting position estimation block 60.

[0059] The IMU position processing block 61 determines the above-mentioned 'second position estimate' of the electric shaver 2 from the device orientation signal. Therefore, the IMU position processing block 61 therefore determines the second position estimate using only measurements from the IMU (accelerometer 6 and gyroscope 8). The second position estimate is output to the filtering and anchoring block 62, and may also be output to the starting position estimation block 60. In some embodiments, the IMU position processing block 61 determines the second position estimate from the device orientation signal by using a geometric (3D) model of the subject's face / head, as shown in the 3D model block 63. In particular, the IMU position processing block 61 can determine the second position estimate by calculating the intersection of the personal care device length axis with the surface of the geometric model, or by comparing the 3D angular orientation of the shaver with the local surface orientation of the geometric model surface, and assuming that the user holds the shaver in a predefined orientation relative to the local skin surface orientation.

[0060] The filtering and anchoring block 62 receives the first position estimate from the SDMS processing block 54, the second position estimate from the IMU position processing block 61, and an indication from the face detection block 58 indicating whether the electric shaver is in contact with the skin surface (it should be noted that Figure 56. The connection from the face detection block 58 to the filtering and anchoring block 62 is not shown in FIG. 6. In short, the filtering and anchoring block 62 determines an anchor position and filters the first position estimate to obtain a next filtered position. The anchor position is a second position estimate combined with knowledge or information about the position of the shaver 2 on the neck or on the face. Based on this, an anchored second position estimate is determined. The anchored second position estimate is used to filter out drift of the first position estimate using a complementary filter.

[0061] In more detail, the filtering and anchoring block 62 can use the most recent complementary filtered position estimate to determine whether the electronic device is in the face region or in the neck region. The IMU anchor position estimate is then calculated by combining the face / neck position type with the IMU-only position estimate. If the most recent filtered position is in the face region, the anchor position is equal to the IMU-only position. If the most recent filtered position is in the neck region, the IMU-only position estimate is reduced to the neck region. And this modified / reduced position estimate is used as the anchor position. The anchor position is used to filter out drift from the surface displacement position estimate using a complementary filter.

[0062] If the indication from the face detection block 58 indicates that the electric shaver is not in contact with the skin surface, the filtering and anchoring block 62 determines the position of the electric shaver as a second position estimate. Similarly, if the indication from the face detection block 58 indicates that the electric shaver is in contact with the skin surface again after a period of time without contact with the skin surface, but before the surface displacement measurement signal indicates that the electric shaver has been moved relative to the skin surface, the filtering and anchoring block 62 determines the position of the electric shaver on the body part as a second position estimate.

[0063] If the indication from the face detection block 58 indicates that the electric shaver is in contact with the skin surface, and the electric shaver has been moved relative to the skin surface with which it is in continuous contact since the electric shaver last resumed contact with the skin surface, the filtering and anchoring block 62 determines a filtered position estimate of the electric shaver by combining the first position estimate and the second position estimate using a complementary filter. In some embodiments, the filtering and anchoring block 62 operates such that the filtered position estimate is derived primarily from the first position estimate, with a small correction made based on the second position estimate.

[0064] The filtered position estimate is output to a beard model projection frame 64, which projects the filtered position estimate onto a geometric model 63 of the face (particularly the beard region of the face and neck) to determine the position of the electric shaver. In some embodiments, frame 64 determines the position of the electric shaver from the intersection of the projected filtered position estimate and the geometric model. In some embodiments, the geometric model 63 of the face / beard can be a sphere, but in other embodiments, a geometric model 63 that better represents the actual face / beard shape of the subject can be used. If the position of the personal care device on the neck is also to be considered, the geometric model 63 can include a portion representing the neck region, such as a cylinder. It should be understood that in embodiments where the electric shaver (or other type of personal care device) is used on a body part other than the face / beard, a geometric model 63 suitable for that body part can be used (for example, a cylindrical model in the case of an arm or leg).

[0065] Thus, improvements in position detection of personal care devices during personal care operations are provided. In particular, the techniques described herein provide for determining the position of a personal care device on a body part based on an orientation measurement signal, a surface displacement measurement signal, and a skin contact signal indicating whether the personal care device is in contact with the skin surface of the body part.

[0066] By studying the drawings, the disclosure and the appended claims, those skilled in the art can understand and implement changes to the disclosed embodiments when practicing the principles and techniques described herein. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "one" or "an" does not exclude multiple. A single processor or other unit can implement the functions of several items listed in the claims. The fact that certain measures are cited only in mutually different dependent claims does not indicate that the combination of these measures cannot be used advantageously. The computer program may be stored or distributed on a suitable 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. Any figure marks in the claims should not be interpreted as limiting the scope.

Claims

1. A personal care device (2) for performing a personal care operation on a subject, the personal care device (2) being configured to determine a position of the personal care device (2) on a body part of the subject, wherein the personal care device (2) comprises: an orientation sensor (6), the orientation sensor being configured to measure the three-dimensional 3D angular orientation of the personal care device (2) relative to the earth's gravity over time, and output a corresponding orientation measurement signal; Characterized in that the personal care device (2) further comprises: a surface displacement sensor (10) configured to measure a two-dimensional (2D) displacement of the personal care device (2) relative to a skin surface of the body part and output a corresponding surface displacement measurement signal; and A processing unit (22) is configured to determine the position of the personal care device (2) on the body part based on the orientation measurement signal, the surface displacement measurement signal and a skin contact signal indicating whether the personal care device (2) is in contact with the skin surface of the body part.

2. The personal care device (2) according to claim 1, wherein the personal care device (2) further comprises a skin contact sensor (14), the skin contact sensor being configured to measure whether the personal care device (2) is in contact with the skin surface of the body part and output the skin contact signal.

3. The personal care device (2) according to claim 1, wherein the processing unit (22) is configured to process the surface displacement measurement signal to determine the skin contact signal.

4. The personal care device (2) according to any one of claims 1 to 3, wherein the surface displacement sensor (10) is an optical displacement sensor.

5. A personal care device (2) according to any one of claims 1 to 4, wherein the orientation sensor (6) comprises a 3-axis accelerometer (7), a 3-axis gyroscope (8) and a processor (22), the processor being configured to determine the 3D angular orientation of the personal care device (2) from output signals of the 3-axis accelerometer (7) and the 3-axis gyroscope (8), and output the corresponding orientation measurement signal.

6. A personal care device (2) according to any one of claims 1 to 5, wherein the processing unit (22) is configured to estimate the starting position of the personal care device (2) on the skin surface of the body part (i) as a default position, or (ii) based on an average starting position detected during a previous personal care operation or (iii) based on the orientation measurement signal to estimate the starting position of the personal care device (2) on the skin surface of the body part.

7. The personal care device (2) according to any one of claims 1 to 6, wherein the processing unit (22) is configured to determine the position of the personal care device (2) on or relative to the body part by: processing the skin contact signal to determine whether the personal care device (2) is in contact with the skin surface of the body part; determining a position of the personal care device (2) on or relative to the body part from the position measurement signal if the personal care device (2) is determined to be (i) out of contact with the skin surface, or (ii) restored to contact with the skin surface after a period of time without contact with the skin surface and before being moved relative to the skin surface; and If the personal care device (2) is determined to be in contact with the skin surface and has been moved relative to the skin surface with which it is in continuous contact since the last time the contact was restored, the position of the personal care device (2) on the body part is determined from the orientation measurement signal and the surface displacement measurement signal.

8. The personal care device (2) of claim 7, wherein determining the position of the personal care device (2) on the body part from the position measurement signal and the surface displacement measurement signal comprises: deriving a 3D angular orientation of a 2D reference plane of the surface displacement sensor (10) from the orientation measurement signal, wherein a 2D displacement of the personal care device (2) relative to the skin surface is measured; and The 2D displacement of the personal care device (2) relative to the skin surface represented by the surface displacement measurement signal is combined with the 3D angular orientation of the 2D reference plane of the surface displacement sensor (10) to determine the 3D displacement of the personal care device (2) relative to the body part.

9. The personal care device (2) according to claim 7 or 8, wherein the processing unit (22) is configured to, if the personal care device (2) is determined to be in contact with the skin surface of the body part and after having been moved relative to the skin surface with which it is in continuous contact since the last restoration of the contact: determining a first position estimate for the personal care device (2) from the surface displacement measurement signal and the orientation measurement signal; determining a second position estimate for the personal care device (2) from the orientation measurement signal; combining the first position estimate and the second position estimate to determine a filtered position estimate; determining a projection of the filtered position estimate onto a geometric model of the body part; and The position of the personal care device (2) on the body part is determined from the projection.

10. The personal care device (2) of claim 9, wherein the position of the personal care device (2) on the body part is determined from an intersection of the projection of the filtered position estimate and the geometrical model.

11. The personal care device (2) of claim 9 or 10, wherein the first position estimate and the second position estimate are combined using a complementary filter.

12. The personal care device (2) according to any one of claims 1 to 11, wherein the body part is the head of the subject, or the head and neck of the subject.

13. The personal care appliance (2) according to any one of claims 1 to 12, wherein the personal care appliance (2) is an electric shaver.

14. A computer-implemented method of determining a position of a personal care device on a body part of a subject, wherein the personal care device is configured to perform a personal care operation on the subject, the method comprising: Using an orientation sensor in the personal care device to measure (101) the three-dimensional 3D angular orientation of the personal care device relative to the earth's gravity over time, and outputting a corresponding orientation measurement signal; Characterized in that the method further comprises: Using a surface displacement sensor in the personal care device, measuring (103) a two-dimensional (2D) displacement of the personal care device relative to a skin surface of the body part, and outputting a corresponding surface displacement measurement signal; and The position of the personal-care device on the body part is determined (105) by a processing unit based on the position measurement signal, the surface displacement measurement signal, and a skin contact signal indicating whether the personal-care device is in contact with the skin surface of the body part.

15. A computer program product comprising a computer readable medium embodying computer readable code, the computer readable code being configured to, when executed by a suitable computer or processor, cause the computer or processor to perform the method of claim 14.

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