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

Abstract

According to one aspect, a personal care device for performing a personal care operation on a subject is provided, and the personal care device is configured to determine the position of the personal care device on a body part of the subject. The personal care device includes an orientation sensor configured to measure a three-dimensional (3D) angular orientation of the personal care device with respect to the gravity of the earth and output a corresponding orientation measurement signal, a surface displacement sensor configured to measure a two-dimensional displacement of the personal care device with respect to the skin surface of the body part and output a corresponding surface displacement measurement signal, and 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.

Description

Technical Field

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

Background Art

[0002] Personal care devices can be provided for many different types of personal care operations such as shaving, hair clipping, hair removal, skin massage, and the like. It can be useful for the position of a personal care device on a subject's body to be determined in real time or near real time during a personal care operation. 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, and so on.

[0003] Techniques for determining the position of a personal care device are known from International Publication No. WO 2020 / 182698, where a device for performing a treatment operation on a body part comprises one or more direction sensors for measuring the orientation of the device and one or more motion sensors for measuring the movement of the device. In this technique, a three-dimensional (3D) representation of the body part having a normal vector for each position on the surface of the body part is obtained, the motion measurements and the direction measurements are processed to determine a sequence of the position and orientation of the device during the treatment operation, and the sequence of the orientation and position of the device is compared with the normal vector and the respective positions of the normal vector to determine the position of the device on the surface of the body part. However, this technique enables the determination of the position of the device on the body part, but higher accuracy of the determined position of the personal care device on the body part is desirable.

[0004] EP 3 800 644 A1 discloses a computer-implemented method for determining the position of a personal care device relative to the skin surface of a subject. The method includes receiving data representative of the measured curvature of the skin surface within a first region of the skin surface with which the personal care device is in contact. An indication of the position of the first region of the skin surface on the subject is determined by comparing the measured curvature with curvature information for a plurality of regions of the subject's skin surface included in a database. The position of the personal care device can be determined more accurately by obtaining 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, an IMU is used to estimate the orientation of the personal care device relative to the gravitational field and increase the positioning.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] Therefore, there is a need for an improvement in detecting the position of a personal care device during a personal care operation.

MEANS FOR SOLVING THE PROBLEMS

[0006] According to a first specific aspect, there is provided a personal care device for performing a personal care operation on a subject, the personal care device being configured to determine the position of the personal care device on the body part of the subject. The personal care device includes an orientation sensor configured to measure a three-dimensional 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 a two-dimensional 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 a skin contact signal indicating whether the personal care device is in contact with the skin surface of the body part, the surface displacement measurement signal, and the direction measurement signal having.

[0007] According to a second aspect, a computer-implemented method for determining the position of a personal care device on a body part of a subject is provided, the personal care device being configured to perform a personal care operation on the subject. The method includes using a direction sensor in the personal care device to measure a three-dimensional angular orientation of the personal care device with respect to the earth's gravity over time and output a corresponding direction measurement signal,

[0008] using a surface displacement sensor in the personal care device to measure a two-dimensional displacement of the personal care device with respect to the skin surface of the body part and output a corresponding surface displacement measurement signal,

[0009] determining, by a processing unit, the position of the personal care device on the body part based on the direction 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 having.

[0010] According to a third aspect, a computer program product is provided that includes a computer-readable medium having computer-readable code embodied therein, the computer-readable code being configured to cause a computer or processor to execute the method according to the second aspect or any embodiment thereof when the instructions are executed by a suitable computer or processor.

[0011] These and other aspects will be apparent from and will be described with reference to the embodiments described hereinafter.

[0012] Exemplary embodiments are described by way of example only with reference to the following drawings.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0014] FIG. 1 is a schematic diagram of a personal care device 2 to which the technology described herein can be applied or used. FIG. 2 shows a top view of the personal care device 2 shown in FIG. 1. In FIG. 1, the personal care device 2 is in the form of an electric shaver / rotary shaver, but the technology described herein can be applied to any type of personal care device 2 such as a foil shaver, beard trimmer, or any other type of hair cutting device, photoepilation device, skin massager, skin measurement device (e.g., for measuring skin characteristics), etc.

[0015] The personal care device 2 comprises a body 3 held in the user's hand and a cutting head 4 in the form of a shaving portion including a plurality of cutting elements 5 for cutting / shaving hair. Each cutting element 5 comprises one or more rapidly rotating circular blades or foils (not shown in FIG. 1). When the cutting head 4 is placed and moved on the face, the hair on the face is cut by the cutting elements 5. Although the cutting head 4 is shown in FIG. 1 as including three cutting elements 5 arranged in a triangle, it will be understood that the rotary shaver 2 can have a different number of cutting elements 5 and / or cutting elements 5 arranged differently.

[0016] Various sensors present in or on the personal care device 2 are also shown in FIG. 1. Thus, FIG. 1 shows a personal care device 2 comprising a direction sensor 6 and a surface displacement sensor 10.

[0017] The direction sensor 6 is configured to measure the three-dimensional (3D) angular orientation of the personal care device 2 with respect to the earth's gravity over time and output a corresponding direction measurement signal representing the measured orientation. The direction measurement signal includes a time series of direction measurement samples according to the sampling rate of the direction sensor 6. In some embodiments, the direction sensor 6 comprises a gyroscope 8 and optionally an accelerometer 7, and the direction sensor 6 can also comprise a processor or processing unit for processing the measurement signals provided by the accelerometer 7 and the gyroscope 8 to determine the direction measurement signal. In some implementations, the accelerometer 7 and the gyroscope 8 are part of an inertial measurement unit (IMU) 12, while in other implementations, the accelerometer 7 and the gyroscope 8 are separate sensors.

[0018] The accelerometer 7 is configured to measure the acceleration of the personal care device 2 over time along three axes, for example, three orthogonal axes (i.e., 3D), 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 includes the acceleration due to gravity.

[0019] The gyroscope 8 is configured to measure the rotation of the personal care device 2 over time about three axes, for example, three orthogonal axes, and output a gyroscope measurement signal representing the measured (3D) rotation. The gyroscope measurement signal includes time-series rotation measurement samples corresponding to the sampling rate of the gyroscope 8.

[0020] 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 a body part and output a corresponding surface displacement measurement signal representing the measured displacement. The surface displacement measurement signal includes time-series surface displacement measurement samples corresponding to the sampling rate of the surface displacement sensor 10. The surface displacement sensor 10 may be an optical displacement sensor similar to that used in a computer mouse. Thus, the surface displacement sensor 10 can include a light source for emitting light onto the skin surface and a light sensor or camera sensor for measuring the light reflected by the skin surface, and the surface displacement measurement signal is derived from the measured light. For example, the surface displacement sensor can include a low-resolution grayscale camera (e.g., having a resolution of 8×8 pixels or 16×16 pixels) that captures images of the surface at a high frame rate or a very high frame rate, and the surface displacement is calculated by analyzing the pattern within the captured images. The surface displacement sensor 10 is disposed within the personal care device 2 such that the surface displacement sensor 10 can observe and measure the skin surface when the personal care device 2 is in contact with the skin surface. As shown in FIG. 2, the surface displacement sensor 10 can be disposed on or near a cutting element on the cutting head 4.

[0021] The movement of the personal care device 2 is directly measured by the direction sensor 6 and the surface displacement sensor 10. Thus, the direction sensor 6 (and, if present, the gyroscope 8 and optional accelerometer 7) and the surface displacement sensor 10 are integral with the personal care device 2 or are in a fixed position therein. The positions and orientations of the direction sensor 6 (and, if present, the gyroscope 8 and any accelerometer 7) and the surface displacement sensor 10 relative to each other are known. Additionally, the positions and orientations of the direction sensor 6 (and, if present, the gyroscope 8 and 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 personal care operations are also known. For example, a calibration procedure can be performed during the manufacture of the personal care device 2, or during initial setup, or during product design, as a result of which the relative positions and orientations are determined. The positions and orientations of the sensors relative to the portion of the personal care device 2 that contacts the skin surface during use enable the measurements from the sensors to be related to the movement of the personal care device 2 relative to the skin surface.

[0022] As further discussed below, it is useful to know whether the personal care device 2 is in contact with the skin surface when determining the position of the personal care device 2 on the subject. Accordingly, a skin contact signal is required that includes a measurement of whether the personal care device 2 is in contact with the skin surface of the body.

[0023] In some embodiments, the personal care device 2 can include a skin contact sensor 14 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 may be a pressure (force) sensor, a proximity sensor, or a capacitance sensor that measures the pressure with which the personal care device 2 is pressed against the surface. The proximity sensor can be based on any suitable technology such as light, sound, ultrasonic waves, etc., and uses time-of-flight measurements to determine the proximity of the sensor 14 to the skin surface (and thus the proximity of the personal care device 2 to the skin surface since the position of the sensor 14 in the personal care device 2 is known). It will be understood that some types of skin contact sensors 14 can provide a binary output of the skin contact signal indicating whether the personal care device 2 is in contact with the skin surface at that instant.

[0024] In an alternative embodiment, the personal care device 2 does not include a separate skin contact sensor 14. Instead, the skin contact signal is derived by processing a surface displacement measurement signal. For example, when the personal care device 2 is in contact with the skin surface, the surface displacement sensor 10 can measure the displacement of the personal care device 2 across the skin surface, while when the personal care device 2 is not in contact with the skin, the surface displacement sensor 10 cannot measure the surface displacement, which can be identified from the surface displacement measurement signal.

[0025] Figure 3 is a block diagram of an exemplary personal care device 2 configured to determine the position of the personal care device 2 on a body part of a subject in accordance with the apparatus techniques described herein. In the embodiment shown in Figure 3, the processing executed to determine the position of the personal care device 2 is executed by a processing unit 22 within the body 3 of the personal care device 2. However, in an alternative embodiment, it can be understood that the processing executed to determine the position of the personal care device 2 can be executed by a processing unit that is part of the base unit of the personal care device 2, such as a docking station or a charging stand. Additionally, when the direction sensor 6 includes an accelerometer 7 and a gyroscope 8, a separate processor or processing unit included within or associated with the processing unit 22 or the direction sensor 6 can be provided to determine the direction measurement signal.

[0026] The processing unit 22 generally controls the operation of the personal care device 2 and enables the personal care device 2 to execute the apparatus methods and techniques described herein. Briefly stated, the processing unit 22 is configured to determine the position of the personal care device 2 on the body part based on the direction measurement signal, the surface displacement measurement signal, and the skin contact signal.

[0027] The processing unit 22 is configured to receive the direction measurement signal and the surface displacement measurement signal from the respective sensors 6, 10. In embodiments 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. Accordingly, the processing unit 22 can include or be provided with one or more input ports or other components for receiving measurement signals from the sensors 6, 10, 12. The processing unit 22 can also include or be provided with one or more output ports or other components for communicating with other components of the personal care device 2.

[0028] The processing unit 22 can be implemented in a number of ways using software and / or hardware to perform the various functions described herein. The processing unit 22 can include one or more microprocessors or digital signal processors (DSPs) programmed using software or computer program code to perform the necessary functions and / or to control the components of the processing unit 22 to perform the necessary functions. The processing unit 22 can be implemented as a combination of dedicated hardware (e.g., amplifiers, preamplifiers, analog-to-digital converters (ADCs) and / or digital-to-analog converters (DACs)) for performing some functions and a processor (e.g., one or more programmed microprocessors, controllers, DSPs, and associated circuitry) for performing other functions. Examples of components that can 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).

[0029] The processing unit 22 may comprise or be associated with a memory unit 24. The memory unit 24 stores data, information, and / or signals (including measurement signals, any results of the processing of measurement signals or any intermediate results) used by the processing unit 22 when controlling the operation of the personal care device 2 and / or when executing or performing the methods described herein. In some implementations, the memory unit 24 stores computer-readable code that may be executed by the processing unit 22 such that the processing unit 22 performs one or more functions including the methods described herein. The memory unit 24 may comprise any type of non-transitory machine-readable medium such as a cache or system memory including volatile and non-volatile computer memories 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 solid-state device including a memory chip, an optical disk (such as a compact disk (CD), digital versatile disk (DVD), or 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.

[0030] In the embodiment shown in FIG. 3, the personal care device 2 further includes an interface circuit 26 that enables data connection to and / or data exchange with other devices, including any one or more of a smartphone, laptop, smartwatch, computer, and other user devices. Any data connection can be direct or indirect (e.g., via the Internet), and thus, the interface circuit 26 can enable a direct connection between the personal care device 2 and a network or between the personal care device 2 and another device (such as a smartphone) via any desired wired or wireless communication protocol. For example, the interface circuit 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), LTE-Advanced, etc.). In the case of a wireless connection, the interface circuit 26 (and thus, the personal care device 2) can include one or more suitable antennas for transmitting / receiving via a transmission medium (e.g., air). The interface circuit 26 is connected to the processing unit 22.

[0031] The personal care device 2 can 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, for example, 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 a determined location of the personal care device 2. The user interface 28 can include any suitable input components, including but not limited to a keyboard, keypad, one or more buttons, switches or dials, a mouse, trackpad, touch screen, stylus, camera, microphone, etc., and / or the user interface 28 can include any suitable output components, including but not limited to a display unit or display screen, one or more lights or light elements, one or more loudspeakers, vibration elements, etc.

[0032] It will be understood that the actual implementation of the personal care device 2 may include additional components relative to what is shown in FIG. 3. For example, the personal care device 2 may also include a power source such as a battery, or components to enable the personal care device 2 to be connected to a main power source, for example, to charge a battery.

[0033] The flowchart of FIG. 4 shows an exemplary method executed by the personal care device 2 in accordance with the techniques described herein. As described above, the personal care device 2 is for performing personal care operations such as hair cutting, shaving, photoepilation, skin massage, etc. on a subject. The body part on which the personal care operation is performed can be the head of the subject, the face of the subject, or the head / face and neck of the subject.

[0034] In step 101, the direction sensor 6 within the personal care device 2 measures the 3D angular orientation of the personal care device 2 with respect to the earth's gravity over time, particularly during use of the personal care device 2 when performing a personal care operation. The direction sensor 6 outputs a direction measurement signal representing the measured orientation around three axes. The direction sensor 6 continuously outputs the direction measurement signal when the orientation is measured.

[0035] In step 103, the surface displacement sensor 10 within the personal care device 2 measures the 2D displacement of the personal care device 2 with respect to the skin surface of the body part during use of the personal care device 2 when performing a specific personal care operation. The surface displacement sensor 10 outputs a corresponding surface displacement measurement signal representing the measured displacement. The surface displacement sensor 10 continuously outputs the surface displacement measurement signal when measuring the surface displacement.

[0036] It will be understood that steps 101 and 103 are performed simultaneously during use of the personal care device 2.

[0037] In step 105, the processing unit 22 determines the position of the personal care device 2 on the body part based on the direction 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. The processing unit 22 can execute step 105 in response to the execution of computer program code that can be stored in a computer-readable medium such as the memory unit 24, for example.

[0038] In some embodiments, a skin contact sensor 14 for measuring whether the personal care device 2 is in contact with the skin surface and generating a skin contact signal is provided. In this case, the method particularly includes the skin contact sensor 14 within the personal care device 2 that measures whether the personal care device 2 is in contact with the skin surface over time, especially during use of the personal care device 2 when performing a personal action. The skin contact sensor 14 outputs a corresponding skin contact signal indicating whether the personal care device 2 is in skin contact. The skin contact sensor 14 continuously outputs a skin contact signal when skin contact is measured. In an alternative embodiment, a separate skin contact sensor 14 does not exist within 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.

[0039] In an embodiment where the direction 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 during use of the personal care device 2 when performing a specific personal care action. The accelerometer 7 generates an acceleration measurement signal representing the acceleration measured along three axes, and the gyroscope 8 generates a gyroscope measurement signal representing the measured rotation around the three axes. The method can include determining the 3D angular orientation (represented by the direction measurement signal) of the personal care device 2 from the output signals of the three-axis accelerometer 7 and the three-axis gyroscope 8.

[0040] 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 can use this starting position to determine the current position of the personal care device 2 on the skin surface. In particular, the processing unit 22 can determine the current position by processing the direction measurement signal, the surface displacement measurement signal, and the skin contact signal in order to determine or estimate the movement of the personal care device 2 from the starting position. The starting position can be estimated as the default position on the skin surface. For example, the user of the personal care device 2 can always start a personal care operation on the right cheek (for example, can start a shaving operation on the right cheek), or on the 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 can be determined based on the direction measurement signal. In this case, the geometric model of the body part can be used in combination with the direction measurement signal when determining the starting position of the personal care device 2.

[0041] In some embodiments, step 105 includes a processing unit 22 that executes a position detection algorithm including several 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.

[0042] 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 with respect to the body part from the direction measurement signal.

[0043] Similarly, if it is determined that contact with the skin surface has resumed after a period when the personal care device 2 was not in contact with the skin surface, and before the surface displacement measurement signal indicates that the personal care device 2 has 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 direction measurement signal.

[0044] However, since the personal care device 2 is in contact with the skin surface and the personal care device 2 has resumed contact with the skin surface last, if it is determined that the personal care device 2 is in continuous contact with the skin surface, the processing unit 22 determines the position of the personal care device 2 on the body part from the direction measurement signal and the surface displacement measurement signal.

[0045] In some embodiments, step 105 can include deriving the 3D angular direction of the 2D reference plane of the surface displacement sensor on which the 2D displacement of the personal care device 2 is measured from the direction measurement signal. Then, the 2D displacement measurement value represented by the surface displacement measurement signal is combined with the 3D angular direction 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, this process converts the 2D displacement measurement value by the surface displacement sensor 10 into the 3D displacement of the personal care device 2 relative to the body part by considering the 3D angular direction of the 2D reference plane on which the 2D displacement of the personal care device 2 relative to the skin surface is measured.

[0046] In some embodiments, the processing unit 22 determines a first position estimate of the personal care device 2 from the surface displacement measurement signal and the direction measurement signal, and for example, determines a second position estimate of the personal care device 2 from the direction measurement signal as described above, combines the first position estimate and the second position estimate to determine a filtered position estimate, determines the projection of the filtered position estimate onto the geometric model of the body part, and determines the position of the personal care device 2 on the body part by determining 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 can be determined from the intersection of the projection of the filtered position estimate and the geometric model.

[0047] In an embodiment where the direction sensor 6 includes an accelerometer 7 and a gyroscope 8, the direction measurement signal can be determined as follows. The accelerometer 7 can measure the direction of gravity. Gravity appears as a vector with a length of 1g pointing towards the ground in the measurement value. This provides a reference that can be used to determine the direction of the earth's gravity or the personal care device 2 relative to the ground plane. However, since the accelerometer 7 measures all accelerations, it also measures the accelerations caused by moving the personal care device 2 through space. Therefore, although the gravity measurement is generally in the correct direction on average, it is noisy and unstable in the short term. The gyroscope 8 can measure the rotation of the device around three axes. It is fast and accurate. However, it cannot measure the direction of gravity. Therefore, the absolute angular direction of the personal care device 2 relative to the earth's gravity cannot be calculated using only the gyroscope. Furthermore, the gyroscope measurement signal contains small measurement errors. The relative angular direction is calculated by integrating the rotation speed over time. Therefore, this relative angular direction estimate drifts away from the actual value over time due to measurement errors and cumulative errors. To combine the strengths and overcome the weaknesses, the outputs of both sensors 7 and 8 are combined in a smart way. Essentially, the accelerometer measurement values are used to calculate the direction of the earth's gravity field or the direction of the long-term stable ground plane, and the gyroscope measurement signal is used to accurately track high-speed short-term angular direction changes. One way to do this is to effectively apply a low-pass filter to the gravity direction signal derived from the accelerometer measurement values, apply a high-pass filter to the gyroscope measurement signal, and use a complementary filter that combines both filtered signals to obtain the final direction measurement signal. Note that two of the three components of the direction obtained in the direction measurement signal are the absolute, roll angle, and pitch angle. These axes are perpendicular to the direction of gravity, and therefore, changes in the direction of these axes can be measured by the accelerometer as changes in the direction of gravity. Since the yaw axis is along the direction of gravity, rotations along this axis do not appear as changes in the direction of gravity.This yaw axis can be considered as the axis running straight down from the top of the head. Therefore, the measurement of the left - right movement of the personal care device is completely relative (using only the gyroscope). The above is the reason why the starting position should be set or derived. Without a starting position, the algorithm can assume, for example, that the user starts at the center of the face, but in reality, the user starts at the right cheek.

[0048] 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 a larger displacement, the first position estimate drifts and the accuracy decreases. Therefore, embodiments provide that the first position estimate and the second position estimate are combined to address this drift problem.

[0049] In some embodiments, the first position estimate and the second position estimate are combined using a complementary filter. The complementary filter can function as a combination of a high - pass filter and a low - pass filter. In some embodiments, the complementary filter can operate such that the first position estimate (i.e., the position estimate determined from the surface displacement measurement signal and the direction measurement signal) is high - pass filtered and the second position estimate (i.e., the position estimate derived from the direction measurement signal) is low - pass filtered. The effect is that the first position estimate is slowly pulled towards the second position estimate, thereby allowing accurate short - term surface displacement sensor information to pass through the filter while preventing it from drifting.

[0050] In some embodiments, the geometric model of the body part described above can also be used to correct for long-term changes in the orientation of the body part. The physical constraints defined by the model are used here to correct the position estimate. This mechanism can be used to correct (fully relative) yaw angle measurements. The idea is that a person cannot turn their head more than 180 degrees from side to side. Instead of the personal care device 2, when a person turns their head, the orientation sensor 6 (IMU) does not measure this, and the position estimate by the IMU (the second position estimate - the position using only the IMU) becomes inaccurate. However, as the user continues shaving, the measured position using only the IMU moves outside the boundaries of the head model. This can be detected, and the second position estimate value can be moved so that the resulting position is again within the head model. Similarly, when the user turns both their head and the personal care device 2, this appears inaccurate because the personal care device 2 moves left / right across the face in the position estimate using only the IMU. In this case as well, the physical constraints of the head model can be used to correct the position estimate. For both of these methods, the correction is completed as soon as the user has moved their head and completely covered the beard area from left to right. For the other two angles, it is assumed that the user generally keeps their head straight.

[0051] The block diagram of FIG. 5 shows some of the logical sub-steps of an embodiment of the position detection algorithm described above. FIG. 5 is directed to an embodiment where the personal care device 2 is an electric shaver and the personal care operation is shaving the face and neck, but it can be understood that the sub-steps of FIG. 5 can be applied to other types of personal care devices 2 and / or other types of personal care operations. In FIG. 5, the accelerometer 7 and the gyroscope 8 are considered to be part of the IMU. Additionally, the electric shaver comprises a skin contact sensor 14.

[0052] Therefore, in FIG. 5, when the electric shaver 2 is activated / switched on, the IMUs 7, 8 are initialized (e.g., activated), and the block 50 and the IMU data fusion block 52 are activated. The direction sensor 6 can be considered to include the IMU and the IMU data fusion block 52. The outputs of the IMUs, i.e., the acceleration measurement signals (indicating accelerations in three orthogonal directions (e.g., denoted as ax, ay, az)) and the gyroscope measurement signals (indicating three-dimensional rotational speeds), are input to the IMU data fusion block 52. The output of the surface displacement sensor 10, i.e., the surface displacement measurement signal (indicating two-dimensional displacement) (e.g., denoted as dx, dy), is input to the surface displacement measurement signal (SDMS) processing block 54. The skin contact signal, which is the output of the skin contact sensor 14, is input to a block 58 that detects whether the electric shaver is in contact with the skin surface from the skin contact signal. Based on the output of the block 58 and the state of the on / off button of the electric shaver, the block 56 detects whether the shaving operation has started.

[0053] When the block 56 detects that the shaving operation has started, the start position estimation block 60 is initialized to estimate the start position of the electric shaver. As described above, the start position can be estimated as the default position of the electric shaver (e.g., the right cheek), as the average of the start positions of a number of previous shaving operations, or based on the direction measurement signal. The estimated start position is output to the SDMS processing block 54 and the IMU position processing block 61. The estimated start position can be used to initialize the position estimate value (e.g., the position estimate value derived from the direction measurement signal), and / or the position estimate value derived from both the direction measurement signal and the surface displacement measurement signal. In some embodiments, the start position estimation block 60 can estimate the start position based on the position estimate determined by the IMU position processing block 61. The estimated start position can always be assumed to be within the face region, and during the shaving operation, the start position estimation can be corrected and updated based on the physical limits of the beard / face hair region.

[0054] The IMU data fusion block 52 determines a direction measurement signal in the three-axis angular direction (also referred to as the "device direction") in the global coordinate system from the gyroscope measurement signal and the acceleration measurement signal. Thus, the IMU data fusion block 52 determines a direction measurement signal representing the 3D angular direction of the personal care device 2 with respect to the earth's gravity during a personal care operation from the acceleration measurement signal and the gyroscope measurement signal. In particular, as detailed above, the acceleration measurement signal is used to calculate the long-term stable ground contact direction, and the gyroscope measurement signal is used to accurately track high-speed short-term direction changes. The two signals are combined to obtain the 3D device direction (direction measurement signal) with respect to the ground contact. The IMU data fusion block 52 outputs the three-axis direction signal to the SDMS processing block 54 and the IMU position processing block 61.

[0055] In some embodiments, the IMU data fusion block 52 can also determine a signal representing the linear acceleration of the personal care device 2 (i.e., the acceleration of the personal care device 2 excluding gravity) from the rotation measurement signal of the gyroscope 8 and the acceleration measurement signal of the accelerometer 7, and the linear acceleration is provided to one or more subsequent blocks (e.g., the IMU position processing block 61) within the algorithm. In this case, the acceleration measurement signal can identify the direction of gravity, and the acceleration due to gravity can be removed from the acceleration measurement signal.

[0056] The SDMS processing block 54 determines the above "first position estimate" of the electric shaver 2 from the surface displacement measurement signal received from the surface displacement sensor 10 and the direction measurement signal received from the IMU data fusion block 52. In particular, the SDMS processing block 54 derives the 3D angular direction of the 2D reference plane of the surface displacement sensor 10 from the direction measurement signal. The 2D reference plane is the plane in which 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 direction of the 2D reference plane, thereby converting the 2D displacement measurement value represented by the surface displacement measurement signal into three dimensions. Thereby, the raw 3D "tracking" of the electric shaver is obtained over time. The first position estimate is the latest 3D position sample within the 3D track. This first position estimate is provided to the filtering and anchor block 62. The first position estimate can also take into account the estimated start position output by the start position estimation block 60.

[0057] The IMU position processing block 61 determines the above "second position estimate" of the electric shaver 2 from the device direction signal. Thus, the IMU position processing block 61 determines the second position estimate using only the measurements from the IMU (accelerometer 6 and gyroscope 8). The second position estimate is output to the filtering and anchor block 62 and can also be output to the start position estimation block 60. In some embodiments, the second position estimate is determined from the device direction signal by using a geometric (3D) model of the subject's face / head, as shown by 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 long axis of the personal care device with the geometric model surface, or by comparing the 3D angular direction of the shaver with the local surface direction of the geometric model surface, and assuming that the user holds the shaver in a predetermined direction relative to the local skin surface direction.

[0058] Filtering and anchor block 62 receives a first position estimate from the SDMS processing block 54, a 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 (note that the connection from the face detection block 58 to the filtering and anchor block 62 is not shown in FIG. 5). Briefly stated, the filtering and anchor block 62 determines the anchor position, filters the first position estimate, and obtains the next filtered position. The anchor position is a second position estimate combined with knowledge or information about the shaver 2 on the neck or face. Based on this, a fixed second position estimate is determined. The anchored second position estimate is used to filter the drift from the first position estimate using a complementary filter.

[0059] More specifically, the filtering and anchor block 62 can use the most recently complementarily filtered position estimate to determine whether the electric device is on the face region or within the neck region. Next, the IMU anchor position estimate is calculated by combining the face / neck position type with the IMU-only position estimate. If the most recently filtered position is on the face region, the anchor position is equal to the IMU-only position. If the most recently filtered position is within the neck region, the IMU-only position estimate is lowered to the neck region. And this corrected / lowered position estimate is used as the anchor position. This anchor position is used to filter the drift from the surface displacement position estimate (using a complementary filter).

[0060] If the indication from the on-face detection block 58 indicates that the electric shaver is not in contact with the skin surface, the filtering and anchor block 62 determines the position of the electric shaver as a second position estimate. Similarly, if the indication from the on-face detection block 58 is after a period when the electric shaver is not in contact with the skin surface but before the surface displacement measurement signal indicates that the electric shaver has moved relative to the skin surface, and the electric shaver is again indicated to be in contact with the skin surface, the filtering and anchor block 62 determines the position of the electric shaver on the body part as a second position estimate.

[0061] If the indication from the on-face detection block 58 indicates that the electric shaver is in contact with the skin surface and the electric shaver has resumed contact with the skin surface so that the electric shaver is moving relative to the skin surface with which it is in continuous contact, the filtering and anchor block 62 determines a filtered position estimate for the electric shaver by combining a first position estimate and a second position estimate using a complementary filter. In some embodiments, the filtering and anchor block 62 operates such that the filtered position estimate is derived primarily from the first position estimate with minor correction by the second position estimate.

[0062] The filtered position estimate is output to a beard model projection block 64 that projects the filtered position estimate onto a geometric model 63 of the face (particularly the beard area of the face and neck) to determine the position of the electric shaver. In some embodiments, block 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 face / chin beard geometric model 63 can be a sphere, but in other embodiments, a geometric model 63 that more represents the actual shape of the subject's face / chin beard can be used. If the position of the personal care device on the neck is also to be considered, the geometric model 63 may include a portion representing the neck area, such as a cylinder. It will be appreciated that in embodiments where the electric shaver (or other type of personal care device) is used on a body part other than the face / chin beard, a geometric model 63 suitable for that body part can be used (e.g., a cylindrical model in the case of an arm or leg).

[0063] Accordingly, an improvement is provided in detecting the position of a personal care device during a personal care operation. In particular, the apparatus technique herein provides that the position of the personal care device on the body part is determined based on a direction 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.

[0064] Variations to the disclosed embodiments can be understood and achieved by those skilled in the art who practice the principles and techniques described herein, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain means are recited in mutually different dependent claims does not indicate that a combination of these means cannot be used to advantage. A computer program may be stored or distributed on a suitable medium, such as an optical storage medium or a solid state medium supplied together with or as part of other hardware, but it may also be distributed in other forms, such as via the Internet or other wired or wireless electrical communication systems. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A personal care device for performing a personal care operation on a subject, 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 a direction sensor configured to measure a three-dimensional angular orientation of the personal care device with respect to the gravity of the earth over time and output a corresponding direction measurement signal and having, the personal care device further a surface displacement sensor configured to measure a two-dimensional displacement of the personal care device with respect to the skin surface of the body part and output a corresponding surface displacement measurement signal; and a processing unit configured to determine the position of the personal care device on the body part based on a skin contact signal indicating whether the personal care device is in contact with the skin surface of the body part, the surface displacement measurement signal, and the direction measurement signal A personal care device having the above components.

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

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

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

5. The personal care device according to any one of claims 1 to 4, wherein the direction sensor comprises a three-axis accelerometer, a three-axis gyroscope, and a processor configured to determine a three-dimensional angular orientation of the personal care device from output signals of the three-axis accelerometer and the three-axis gyroscope and output the corresponding direction measurement signal.

6. The personal care device according to any one of claims 1 to 5, wherein the processing unit is configured to estimate a starting position of the personal care device 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 direction measurement signal.

7. The processing unit processing the skin contact signal to determine whether the personal care device is in contact with the skin surface of the body part; when the personal care device is determined to be (i) not in contact with the skin surface, or (ii) after a period of not being in contact with the skin surface and before being moved relative to the skin surface and it is determined to resume contact with the skin surface, determining the position of the personal care device on or relative to the body part from the direction measurement signal; when the personal care device is determined to be in contact with the skin surface and after being moved relative to the skin surface with which it has been continuously in contact since the last resumption of contact, determining the position of the personal care device on the body part from the direction measurement signal and the surface displacement measurement signal; A personal care device according to any one of claims 1 to 6, configured to determine the position of the personal care device on or relative to the body part by performing the steps above. **Claim 8** The step of determining the position of the personal care device on the body part from the direction measurement signal and the surface displacement measurement signal comprises: deriving a three-dimensional angular direction of a two-dimensional reference plane of the surface displacement sensor, in which a two-dimensional displacement of the personal care device relative to the skin surface is measured, from the direction measurement signal; combining the two-dimensional displacement of the personal care device relative to the skin surface represented by the surface displacement measurement signal with the three-dimensional angular direction of the two-dimensional reference plane of the surface displacement sensor to determine a three-dimensional displacement of the personal care device relative to the body part; A personal care device according to claim 7, having the steps above. **Claim 9** When the personal care device is determined to be in contact with the skin surface of the body part and after being moved relative to the skin surface with which it has been continuously in contact since the last resumption of contact, the processing unit determines a first position estimate of the personal care device from the surface displacement measurement signal and the direction measurement signal; determines a second position estimate of the personal care device from the direction measurement signal; combines the first position estimate and the second position estimate to determine a filtered position estimate; Determining a projection of the filtered position estimate onto the geometric model of the body part; Determining the position of the personal care device on the body part from the projection; The personal care device according to claim 7 or 8, configured to perform.

10. The personal care device according to claim 9, wherein the position of the personal care device on the body part is determined from an intersection of the projection of the filtered position estimate and the geometric model.

11. The personal care device according to 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 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 device according to any one of claims 1 to 12, wherein the personal care device is an electric shaver.

14. A computer-implemented method for determining the position of a personal care device on a body part of a subject, the personal care device being configured to perform a personal care operation on the subject, the method comprising: Measuring, using an orientation sensor within the personal care device, a three-dimensional angular orientation of the personal care device with respect to the Earth's gravity over time and outputting a corresponding orientation measurement signal; The method further comprising: Measuring, using a surface displacement sensor within the personal care device, a two-dimensional displacement of the personal care device with respect 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. A method.

15. A computer program product having a computer-readable medium with computer-readable code configured to cause a computer or processor to perform the method according to claim 14 when the code is executed by the appropriate computer or processor.

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