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] FIELD OF THE DISCLOSURE The present disclosure relates to personal care devices for performing personal care actions on a subject, and more particularly to methods and apparatus for determining the position of a personal care device on a body part of a subject. [Background technology]

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

[0003] A technique for determining the position of a personal care device is known from WO 2020 / 182698, in which an apparatus for performing a therapeutic action on a body part includes one or more direction sensors for measuring the orientation of the apparatus and one or more motion sensors for measuring the movement of the apparatus. In this technique, a three-dimensional (3D) representation of the body part is obtained, having normal vectors for respective positions on the surface of the body part, and the motion and direction measurements are processed to determine a sequence of positions and orientations of the apparatus during the therapeutic action. The sequence of orientations and positions of the apparatus is compared with the normal vectors and their respective positions to determine the position of the apparatus on the surface of the body part. However, although this technique allows for determining the position of the apparatus on the body part, a 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 a skin surface of a subject. The method includes receiving data representing a measured curvature of the skin surface within a first region of the skin surface in contact with the personal care device. 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 multiple regions of the subject's skin surface contained in a database. 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, thereby augmenting the position determination. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, there is a need for improvements in detecting the location of a personal care device during a personal care operation. [Means for solving the problem]

[0006] According to a first particular 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 a position of the personal care device on a body part of the subject, the personal care device comprising: 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 to output a corresponding orientation measurement signal; a surface displacement sensor configured to measure two-dimensional displacement of the personal care device relative to a skin surface of the body part and to output a corresponding surface displacement measurement signal; a processing unit configured to determine a position of the personal care device on the body part based on a skin contact signal indicative of whether the personal care device is in contact with a skin surface of the body part, the surface displacement measurement signal, and the orientation measurement signal; It has.

[0007] According to a second aspect, there is provided a computer-implemented method for determining a position of a personal care device on a body part of a subject, the personal care device being configured to perform a personal care action on the subject, the method comprising the steps of: using an orientation sensor in the personal care device to measure a three-dimensional angular orientation of the personal care device relative to Earth's gravity over time and outputting a corresponding orientation measurement signal;

[0008] using a surface displacement sensor within the personal care device to measure two-dimensional displacement of the personal care device relative to a skin surface of the body part and outputting a corresponding surface displacement measurement signal;

[0009] determining, by a processing unit, a position of the personal care device on the body part based on the orientation measurement signals, the surface displacement measurement signals, and a skin contact signal indicative of whether the personal care device is in contact with a skin surface of the body part; It has.

[0010] According to a third aspect, there is provided a computer program product including a computer readable medium having computer readable code embodied therein, the computer readable code being configured, when executed by a suitable computer or processor, to cause the computer or processor to instruct the computer or processor to perform a method according to the second aspect or any embodiment thereof.

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

[0012] Exemplary embodiments will now be described, by way of example only, with reference to the following drawings, in which: [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram of an exemplary personal care device in the form of a rotary shaver. [Figure 2] FIG. 2 is a top view of the personal care device of FIG. 1. [Figure 3] FIG. 1 is a block diagram of a personal care device according to some embodiments. [Figure 4] 1 is a flowchart illustrating an exemplary method according to the present disclosure. [Figure 5] FIG. 10 is a block diagram illustrating some substeps of a location detection algorithm according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] Figure 1 is a simplified diagram of a personal care device 2 to which the techniques described herein may be applied or used. Figure 2 shows a top view of the personal care device 2 shown in Figure 1. Although in Figure 1 the personal care device 2 is in the form of an electric shaver / rotary shaver, it will be understood that the techniques described herein may be applied to any type of personal care device 2, such as a foil shaver, a beard trimmer, or any other type of hair cutting device, a photoepilation device, a skin massager, a skin measurement device (e.g., for measuring skin properties), etc.

[0015] The personal care device 2 comprises a body 3 that is held in the user's hand and a cutting head 4 in the form of a shaving portion that includes a plurality of cutting elements 5 for cutting / shaving hair. Each cutting element 5 includes one or more rapidly rotating circular blades or foils (not shown in FIG. 1 ). When the cutting head 4 is positioned over a face and moved, 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 a different arrangement of the cutting elements 5.

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

[0017] 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 and to output a corresponding orientation measurement signal representing the measured orientation. The orientation measurement signal comprises a time series of orientation measurement samples according to a sampling rate of the orientation sensor 6. In some embodiments, the orientation sensor 6 comprises a gyroscope 8 and, optionally, an accelerometer 7, and the orientation sensor 6 may also comprise a processor or processing unit for processing measurement signals provided by the accelerometer 7 and gyroscope 8 to determine the orientation measurement signal. In some implementations, the accelerometer 7 and gyroscope 8 are part of an inertial measurement unit (IMU) 12, while in other implementations the accelerometer 7 and 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., three dimensions), and output an acceleration measurement signal representative of the measured (3D) acceleration. The acceleration measurement signal comprises a time series of acceleration measurement samples according to the sampling rate of the accelerometer 7. The measured acceleration includes acceleration due to gravity.

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

[0020] The surface displacement sensor 10 is configured to measure 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. The surface displacement measurement signal includes a time series of surface displacement measurement samples according to the sampling rate of the surface displacement sensor 10. The surface displacement sensor 10 may be an optical displacement sensor similar to those used in computer mice. Thus, the surface displacement sensor 10 may include a light source for emitting light onto the skin surface and an optical 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 may include a low-resolution grayscale camera (e.g., having a resolution of 8x8 pixels or 16x16 pixels) that captures images of the surface at a high or very high frame rate, and the surface displacement is calculated by analyzing patterns in the captured images. The surface displacement sensor 10 is positioned 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 may be located on or near the cutting element on the cutting head 4.

[0021] The orientation sensor 6 (and gyroscope 8 and optional accelerometer 7, if present) and surface displacement sensor 10 are integral with or otherwise in fixed positions within the personal care device 2 such that movement of the personal care device 2 is directly measured by the orientation sensor 6 and surface displacement sensor 10. The positions and orientations of the orientation sensor 6 (and gyroscope 8 and optional accelerometer 7, if present) and surface displacement sensor 10 relative to each other are known. In addition, the positions and orientations of the orientation sensor 6 (and gyroscope 8 and optional accelerometer 7, if present) and surface displacement sensor 10 relative to the portion of the personal care device 2 that contacts the skin surface during a personal care operation are also known. For example, a calibration procedure may be performed during manufacture of the personal care device 2, or during initial setup, or during product design, so that 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 allow measurements from the sensors to be related to movement of the personal care device 2 relative to the skin surface.

[0022] As discussed further below, in determining the position of the personal care device 2 on a subject, it is useful to know whether the personal care device 2 is in contact with a skin surface. 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.

[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 a 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 that measures the pressure with which the personal care device 2 is pressed against the surface, a proximity sensor, or a capacitive sensor. The proximity sensor can be based on any suitable technology, such as light, sound, or ultrasound, and utilizes time-of-flight measurements to determine the proximity of the sensor 14 to the skin surface (and therefore the proximity of the personal care device 2 to the skin surface, given that the location of the sensor 14 on the personal care device 2 is known). It will be appreciated that some types of skin contact sensors 14 can provide a binary output of a skin contact signal that indicates whether the personal care device 2 is in contact with the skin surface at that moment.

[0024] In an alternative embodiment, the personal care device 2 does not include a separate skin contact sensor 14, and instead the skin contact signal is derived 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 can measure the displacement of the personal care device 2 across the skin surface, whereas 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] 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 herein. In the embodiment shown in FIG. 3, 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 the base unit of the personal care device 2, such as a docking station or charging stand. Additionally, if the direction sensor 6 comprises an accelerometer 7 and a gyroscope 8, the processing unit 22, or a separate processor or processing unit included within or associated with the direction sensor 6, may be provided to determine the direction measurement signals.

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

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

[0028] Processing unit 22 can be implemented in numerous ways using software and / or hardware to perform the various functions described herein. Processing unit 22 comprises one or more microprocessors or digital signal processors (DSPs), which can be programmed using software or computer program code to perform the necessary functions and / or to control the components of processing unit 22 to perform the necessary functions. Processing unit 22 can also be implemented as a combination of dedicated hardware (e.g., amplifiers, preamplifiers, analog-to-digital converters (ADCs) and / or digital-to-analog converters (DACs)) to perform some functions and processors (e.g., one or more programmed microprocessors, controllers, DSPs, and associated circuitry) to perform 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 include or be associated with a memory unit 24. The memory unit 24 may store data, information, and / or signals (including measurement signals, any results of processing of measurement signals, or any intermediate results) used by the processing unit 22 in controlling the operation of the personal care device 2 and / or in performing or executing the methods described herein. In some implementations, the memory unit 24 stores computer-readable code that may be executed by the processing unit 22 to cause the processing unit 22 to perform 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 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 memory chips, optical disks (such as compact disks (CDs), digital versatile disks (DVDs), or Blu-ray disks), hard disks, tape storage solutions, or solid-state devices, including memory sticks, solid-state drives (SSDs), memory cards, etc.

[0030] In the embodiment shown in FIG. 3 , the personal care device 2 further comprises an interface circuit 26 that enables data connection to and / or 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 (e.g., 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 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 that enable the personal care device 2 to output information or data to a user of the personal care device 2, such as information indicative of 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 may include any suitable input component, including, but not limited to, a keyboard, a keypad, one or more buttons, switches, or dials, a mouse, a trackpad, a touchscreen, a stylus, a camera, a microphone, etc., and / or the user interface 28 may include any suitable output component, including, but not limited to, a display unit or screen, one or more lights or light elements, one or more loudspeakers, a vibration element, etc.

[0032] It will be understood that actual implementations of the personal care device 2 will include additional components to those shown in Figure 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 mains power source, for example to charge the battery.

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

[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 relative to the Earth's gravity over time, and in particular during use of the personal care device 2 when performing a personal care activity. The direction sensor 6 outputs direction measurement signals representing the orientation around the three measured axes. The direction sensor 6 continuously outputs the direction measurement signals as 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 relative to the skin surface of the body part over time during use of the personal care device 2 in performing a particular personal care activity. The surface displacement sensor 10 outputs a corresponding surface displacement measurement signal representative of the measured displacement. The surface displacement sensor 10 continuously outputs the surface displacement measurement signal as it measures the surface displacement.

[0036] It will be appreciated that steps 101 and 103 occur simultaneously while the personal care device 2 is in use.

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

[0038] In some embodiments, a skin contact sensor 14 is provided to measure whether the personal care device 2 is in contact with a skin surface and generate a skin contact signal, in which case the method further includes a skin contact sensor 14 within the personal care device 2 that measures, particularly during use of the personal care device 2 in performing a personal activity, whether the personal care device 2 is in contact with the skin surface for a period of time. The skin contact sensor 14 outputs a corresponding skin contact signal indicative of whether the personal care device 2 is in skin contact or not. The skin contact sensor 14 continuously outputs the skin contact signal once skin contact is measured. In an alternative embodiment, a separate skin contact sensor 14 is not present 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 embodiments where the orientation sensor 6 comprises 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 while the personal care device 2 is in use when performing a particular personal care activity. The accelerometer 7 generates acceleration measurement signals representative of the measured acceleration along three axes, and the gyroscope 8 generates gyroscope measurement signals representative of the measured rotation about the three axes. The method can include determining a 3D angular orientation (represented by the orientation measurement signals) 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 a starting position of the personal care device 2 on the skin surface of the body part. The processing unit 22 may use this starting position to determine a 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 direction 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 to be a default position on the skin surface. For example, a user of the personal care device 2 may always start a personal care operation on the right cheek (e.g., may 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 an average starting position detected during previous personal care operations. In another alternative, the starting position may be determined based on the direction measurement signal. In this case, a geometric model of the body part may 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 the processing unit 22 executing a location detection algorithm that includes 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 relative to the body part from the direction measurement signals.

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

[0045] In some embodiments, step 105 may include deriving from the direction measurement signal a 3D angular orientation of a 2D reference plane of the surface displacement sensor from which the 2D displacement of the personal care device 2 is measured. The 2D displacement measurements represented by the surface displacement measurement signal are 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, this process converts the 2D displacement measurements by the surface displacement sensor 10 into 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 from which the 2D displacement of the personal care device 2 relative to the skin surface is measured.

[0046] In some embodiments, the position of the personal care device 2 on the body part can be determined by the processing unit 22 determining a first position estimate of the personal care device 2 from the surface displacement measurement signals and the orientation measurement signals, determining a second position estimate of the personal care device 2 from the orientation measurement signals, e.g., as described above, combining the first and second position estimates to determine a filtered position estimate, determining a projection of the filtered position estimate onto a geometric model of the body part, and 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 with the geometric model.

[0047] In an embodiment in which the orientation sensor 6 includes an accelerometer 7 and a gyroscope 8, the orientation measurement signal can be determined as follows: The accelerometer 7 can measure the direction of gravity. Gravity appears in measurements as a vector with a length of 1g pointing toward the ground. This provides a reference that can be used to determine the orientation of the personal care device 2 relative to Earth's gravity or the ground surface. However, because the accelerometer 7 measures all accelerations, it also measures accelerations caused by moving the personal care device 2 through space. Therefore, while gravity measurements are oriented correctly on average, they are noisy and unstable in the short term. The gyroscope 8 can measure device rotation around three axes, which is fast and accurate. However, it cannot measure the direction of gravity. Therefore, the absolute angular orientation of the personal care device 2 relative to Earth's gravity cannot be calculated using the gyroscope alone. Furthermore, the gyroscope measurement signal contains small measurement errors. The relative angular orientation is calculated by integrating the rotation rate over time. Therefore, this relative angular orientation estimate will drift away from its actual value over time due to measurement errors and cumulative errors. To combine strengths and overcome weaknesses, the outputs of both sensors 7 and 8 are combined in a smart way. Essentially, the accelerometer measurements are used to calculate the direction of the Earth's gravity field or the direction of a long-term stable ground surface, while the gyroscope measurement signal is used to accurately track fast, short-term angular orientation changes. One way to do this is to use a complementary filter that effectively applies a low-pass filter to the gravity orientation signal derived from the accelerometer measurements, a high-pass filter to the gyroscope measurement signal, and combines both filtered signals to obtain the final orientation measurement signal. Note that two of the three components of orientation available in the orientation measurement signal are absolute, roll angle, and pitch angle. These axes are perpendicular to the direction of gravity; therefore, orientation changes along these axes can be measured by the accelerometer as changes in the direction of gravity. Because the yaw axis is aligned with gravity, rotation along this axis does not appear as a change in the direction of gravity.This yaw axis can be thought of as an axis running straight down from the top of the head, and therefore measurements of left and right movement of the personal care device are completely relative (gyroscope only). The foregoing is why a start position should be set or derived. Without a start position, the algorithm can, for example, assume that the user started in the center of the face, when in fact the user started on the right cheek.

[0048] Assuming that the starting position of the personal care device 2 is known, the first position estimate may be a relatively accurate position of the personal care device 2 on the skin surface. However, without correction, the first position estimate will drift and become less accurate over larger displacements. Therefore, embodiments provide that the first and second position estimates are combined to address this drift issue.

[0049] In some embodiments, the first and second position estimates 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 signals and the direction measurement signals) is high-pass filtered and the second position estimate (i.e., the position estimate derived from the direction measurement signals) is low-pass filtered. The effect is to slowly pull the first position estimate toward the second position estimate, thereby preventing it from drifting while allowing accurate short-term surface displacement sensor information to pass through the filter.

[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 the (fully relative) yaw angle measurement. The idea is that a person cannot turn their head left or right more than 180 degrees. If the person turns their head, but not the personal care device 2, the orientation sensor 6 (IMU) will not measure this, and the IMU-based position estimate (second position estimate—IMU-only position) will be inaccurate. However, as the user continues to shave, the measured IMU-only position will move outside the boundaries of the head model. This can be detected, and the second position estimate can be moved so that the resulting position is again inside the head model. Similarly, if the user turns both their head and personal care device 2, this will appear inaccurate as the personal care device 2 moves left / right across their face in the IMU-only position estimate. Again, the physical constraints of the head model can be used to correct the position estimate. For both of these methods, the correction is complete as soon as the user completely covers the beard area from left to right after moving their head. For the other two angles, it is assumed that the user keeps their head straight on average.

[0051] The block diagram of Figure 5 illustrates some of the logical substeps of an embodiment of the position detection algorithm described above. While Figure 5 is directed to an embodiment in which the personal care device 2 is an electric shaver and the personal care activity is shaving the face and neck, it can be understood that the substeps of Figure 5 can be applied to other types of personal care devices 2 and / or other types of personal care activities. In Figure 5, the accelerometer 7 and gyroscope 8 are considered to be part of the IMU. Additionally, the electric shaver includes a skin contact sensor 14.

[0052] 5, when the electric shaver 2 is activated / switched on, the IMUs 7 and 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 output of the IMU, i.e., acceleration measurement signals (indicating acceleration in three orthogonal directions (e.g., designated ax, ay, and 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., surface displacement measurement signals (indicating two-dimensional displacements (e.g., designated dx and dy), are input to a surface displacement measurement signal (SDMS) processing block 54. The output of the skin contact sensor 14, a skin contact signal, is input to a block 58, which detects from the skin contact signal whether the electric shaver is in contact with the skin surface. Based on the output of the block 58 and the state of the electric shaver's on / off button, a block 56 detects whether a shaving operation has started.

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

[0054] The IMU data fusion block 52 determines, from the gyroscope measurement signal and the acceleration measurement signal, an orientation measurement signal, which is a three-axis angular orientation (also referred to as "device orientation") in a global coordinate system. Thus, the IMU data fusion block 52 determines, from the acceleration measurement signal and the gyroscope measurement signal, an orientation measurement signal that represents the 3D angular orientation of the personal care device 2 relative to the Earth's gravity during a personal care operation. In particular, as explained in detail above, the acceleration measurement signal is used to calculate a long-term stable ground plane orientation, and the gyroscope measurement signal is used to accurately track fast short-term orientation changes. Both signals are combined to obtain the 3D device orientation (orientation measurement signal) relative to the ground plane. The IMU data fusion block 52 outputs the three-axis direction signals 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, which 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 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 aforementioned "first position estimate" of the electric shaver 2 from the surface displacement measurement signals received from the surface displacement sensor 10 and the orientation measurement signals 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 signals. The 2D reference plane is the plane on 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 orientation of the 2D reference plane, thereby converting the 2D displacement measurements represented by the surface displacement measurement signals into three dimensions. This results in a raw 3D "track" of the electric shaver over time. The first position estimate is the most recent 3D position sample within the 3D track. This first position estimate is provided to the filtering and anchoring block 62. The first position estimate may also take into account the estimated starting position output by the starting position estimation block 60.

[0057] The IMU position processing block 61 determines the above-mentioned "second position estimate" of the electric shaver 2 from the device orientation signal. 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 start 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 indicated 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 personal care device long axis with the geometric model surface, 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 predetermined orientation relative to the local skin surface direction.

[0058] 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 (note that the connection from the face detection block 58 to the filtering and anchoring block 62 is not shown in FIG. 5). Briefly, 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 the second position estimate combined with knowledge or information about the shaver 2 being located on the neck or face. Based on this, a fixed second position estimate is determined. The anchored second position estimate is used to filter drift from the first position estimate using a complementary filter.

[0059] More specifically, the filtering and anchor block 62 can use the most recent complementary filtered position estimate to determine whether the electrical device is over the face region or within the neck region. An 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 over the face region, the anchor position is equal to the IMU-only position. If the most recent filtered position is within the neck region, the IMU-only position estimate is downgraded to the neck region. This corrected / downgraded position estimate is then used as the anchor position. This anchor position is then used to filter 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 anchoring block 62 determines the position of the electric shaver as the second position estimate. Similarly, if the indication from the on-face detection block 58 indicates that the electric shaver is again in contact with the skin surface after a period when the electric shaver was not in contact with the skin surface but before the surface displacement measurement signal indicated that the electric shaver had moved relative to the skin surface, the filtering and anchoring block 62 determines the position of the electric shaver on the body part as the 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 is moving relative to the skin surface in continuous contact with the skin surface since the electric shaver last resumed contact with the skin surface, the filtering and anchoring block 62 determines a filtered position estimate for the electric shaver by combining the first and second position estimates using complementary filters. 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 by the second position estimate.

[0062] The filtered position estimate is output to a beard model projection block 64, which projects the filtered position estimate onto a geometric model 63 of the face (particularly the facial and neck beard region) 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 with the geometric model. In some embodiments, the face / beard geometric model 63 may be a sphere, while in other embodiments, a geometric model 63 that is more representative of the subject's actual face / beard shape may 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 region, e.g., a cylinder. It will be appreciated that in embodiments in which an electric shaver (or other type of personal care device) is used on a body part other than the face / beard, a geometric model 63 appropriate for that body part may be used (e.g., a cylindrical model for the arms or legs).

[0063] Thus, improvements are provided in detecting the position of a personal care device during a personal care operation. In particular, the techniques of the apparatus herein provide that the position of the personal care device on a body part is determined based on an orientation measurement signal, a surface displacement measurement signal, and a skin contact signal indicative of whether the personal care device is in contact with a skin surface of the body part.

[0064] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing 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 articles "a" or "an" do 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 measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program can be stored or distributed on a suitable medium, such as an optical storage medium or a solid-state medium provided together with or as part of other hardware, but also in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. 1. A personal care device for performing a personal care operation on a subject, the personal care device configured to determine a position of the personal care device on a body part of the subject, the personal care device comprising: 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; and the personal care device further comprises: a surface displacement sensor configured to measure two-dimensional displacement of the personal care device relative to a skin surface of the body part and to output a corresponding surface displacement measurement signal; a processing unit configured to determine a position of the personal care device on the body part based on a skin contact signal indicative of whether the personal care device is in contact with a skin surface of the body part, the surface displacement measurement signal, and the orientation measurement signal; A personal care device comprising:

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

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

4. 10. The personal care device of claim 1, wherein the surface displacement sensor is an optical displacement sensor.

5. 5. A personal care device according to any one of claims 1 to 4, wherein the orientation 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 to output the corresponding orientation measurement signal.

6. A personal care device according to any one of claims 1 to 4, 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 a skin surface of the body part; determining a position of the personal care device on or relative to the body part from the direction measurement signals if the personal care device is determined to be (i) not in contact with the skin surface, or (ii) to resume contact with the skin surface after a period of not in contact with the skin surface and before being moved relative to the skin surface; determining a position of the personal care device on the body part from the orientation measurement signals and the surface displacement measurement signals if the personal care device is determined to be in contact with the skin surface and after being moved relative to the skin surface in continuous contact since the last resumption of contact; 5. A personal care device according to any preceding claim, configured to determine a position of the personal care device on or relative to the body part by performing:

8. Determining the position of the personal care device on the body part from the orientation measurement signals and the surface displacement measurement signals comprises: deriving from the direction measurement signals a three-dimensional angular orientation of a two-dimensional reference plane of the surface displacement sensor, along which two-dimensional displacement of the personal care device relative to the skin surface is measured; combining the two-dimensional displacement of the personal care device relative to the skin surface represented by the surface displacement measurement signals with a three-dimensional angular orientation 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; 8. The personal care device of claim 7, comprising:

9. the processing unit, when the personal care device is determined to be in contact with a skin surface of the body part and after being moved relative to the skin surface in continuous contact since the last resumption of contact, determining a first position estimate of the personal care device from the surface displacement measurement signal and the orientation measurement signal; determining a second position estimate of the personal care device from the direction measurement signals; 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; determining a position of a personal care device on the body part from the projection; 8. The personal care device of claim 7, configured to perform the following:

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

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

12. 5. The personal care device of claim 1, wherein the body part is the subject's head or the subject's head and neck.

13. 5. A personal care device according to any one of claims 1 to 4, wherein the personal care device is an electric shaver.

14. 1. A computer-implemented method for determining a position of a personal care device on a body part of a subject, the personal care device being configured to perform a personal care action on the subject, the method comprising: using an orientation sensor within the personal care device to measure a three-dimensional angular orientation of the personal care device relative to the Earth's gravity over time and outputting a corresponding orientation measurement signal. and the method further comprises: using a surface displacement sensor within the personal care device to measure two-dimensional displacement of the personal care device relative to a skin surface of the body part and outputting a corresponding surface displacement measurement signal; determining, by a processing unit, a position of the personal care device on the body part based on the orientation measurement signals, the surface displacement measurement signals, and a skin contact signal indicative of whether the personal care device is in contact with a skin surface of the body part; A method comprising:

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

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