Method and apparatus for controlling feedback regarding motion of a rotary shaver performed by a user

Abstract

The present invention relates to a method (100) of controlling feedback to a user regarding motion of a rotary shaver performed by the user, the method comprising the steps of: obtaining motion data from a motion sensor (12) monitoring the motion of the rotary shaver (8) performed by the user; determining shape and size of the monitored motion based on the obtained motion data, the shape indicating if the monitored motion is circular or linear; and generating a control signal configured to trigger feedback of a first type to the user if the monitored motion is determined to be a linear motion having a size above a threshold and to trigger feedback of another type, different from the first type, to the user if the monitored motion is determined to be a circular motion or a linear motion having a size equal to or below the threshold.

Description

FIELD OF THE INVENTION

[0001] The invention relates to a method and apparatus for controlling feedback to a user regarding motion of a rotary shaver performed by the user of the rotary shaver based on motion shape and size detection.BACKGROUND OF THE INVENTION

[0002] Shaving motions are important for the shaving performance of rotary shavers that comprise one or more hair-cutting units each comprising an external cutting member with an annular array of hair-entry openings and an internal cutting member with an annular array of cutting blades that rotates relative to the external cutting member. Shaving motions are the motions performed by a user of a rotary shaver when moving the shaver relative to the face during shaving (in the following, "shaving motions" may occasionally also be referred to as "motions"). To increase the shaving performance, motion guidance can provide motion feedback to the user, alarming the wrong shaving motions and promoting the right shaving motions. For rotary shavers, in general the right shaving motions are rotational respectively circular shaving motions, and the wrong motions are linear shaving motions, i.e. stroke-like reciprocating shaving motions. However, this alarming respectively correction advice should not distract the user and should suit to the size and the limitations of the shaver.

[0003] WO2018 / 206805 A1 discloses a method of providing feedback to a user of a rotary shaver regarding motion of the rotary shaver performed by the user, the method comprising the steps of receiving, during at least one time interval, at least one motion type determined for the motion of the rotary shaver performed by the user, wherein the motion type is selected from a set of predefined motion types that comprises small rotational motion and one or more other predefined motion types; determining a degree of occurrence in the time interval of each of the motion types in the set of predefined motion types based on the at least one motion type received during the time interval; determining from the determined degree of occurrence of each of the motion types in the set of predefined motion types which motion type has a highest degree of occurrence in the time interval; and providing feedback to the user to increase a degree of occurrence of small rotational motion of the rotary shaver if the determined motion type having the highest degree of occurrence is one of the other predefined motion types.

[0004] Improvements in the controlled feedback regarding the motion of a rotary shaver performed by a user are desired to further improve the shaving performance.SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to provide accurate feedback to a user of a rotary shaver regarding motion of the rotary shaver performed by the user.

[0006] In a first aspect of the present invention, a method of controlling feedback to a user regarding motion of a rotary shaver performed by the user is provided, the method comprising the steps of: obtaining motion data from a motion sensor monitoring the motion of the rotary shaver performed by the user; determining shape and size of the monitored motion based on the obtained motion data, the shape indicating if the monitored motion is circular or linear; and generating a control signal configured to trigger feedback of a first type to the user if the monitored motion is determined to be a linear motion having a size above a threshold and to trigger feedback of another type, different from the first type, to the user if the monitored motion is determined to be a circular motion or a linear motion having a size equal to or below the threshold.

[0007] In a second aspect of the present invention, an apparatus for controlling feedback to a user regarding motion of a rotary shaver performed by the user is provided, the apparatus comprising a processing unit configured to: obtain motion data from a motion sensor monitoring the motion of the rotary shaver performed by the user; determine shape and size of the monitored motion based on the obtained motion data, the shape indicating if the monitored motion is circular or linear; and generate a control signal configured to trigger feedback of a first type to the user if the monitored motion is determined to be a linear motion having a size above a threshold and to trigger feedback of another type, different from the first type, to the user if the monitored motion is determined to be a circular motion or a linear motion having a size equal to or below the threshold.

[0008] In a third aspect of the present invention, a system for controlling feedback to a user regarding motion of a rotary shaver performed by the user is provided, the system comprising: an apparatus for controlling feedback to a user regarding motion of a rotary shaver performed by the user according to the present invention; a rotary shaver; and a motion sensor configured to monitor the motion of the rotary shaver.

[0009] In yet further aspects of the present invention, there are provided a corresponding computer program which comprises program code means for causing an apparatus according to the present invention to carry out the steps of the method according to the invention when said computer program is carried out on the processing unit of the apparatus, as well as a non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by the processing unit, causes the method according to the invention to be performed.

[0010] Preferred embodiments of the invention are defined in the dependent claims. It shall be understood that the apparatus, system, computer program and medium according to the present invention have similar and / or identical preferred embodiments as the method according to the invention, in particular as defined in the dependent claims and as disclosed herein.

[0011] It has been found that on some portions of the face the user of the rotary shaver cannot easily perform rotational respectively circular shaving motions, like under the nose area and around a single hair. On these portions of the face it is normal for a user to perform small sized linear shaving motions. To provide accurate feedback to the user regarding the shaving motion, i.e. the motion of the shaver relative to the user's face performed by the user, such shaving motions should be detected and not be classified as wrong motions. In particular, it is desirable to only correct or alarm the user when he is making wrong shaving motions which lead to reduced shaving performance that he can reasonably avoid. In particular, this is the case when the user makes large sized linear (stroke-like) shaving motions.

[0012] The present invention is based on the idea to provide more accurate feedback to the user regarding the shaving motions by only correcting the user when he is making wrong shaving motions that he can reasonably improve upon. Given that on some portions of the face the user is even forced to perform linear shaving motions, like under the nose area and around single hairs, these assumed wrong shaving motions are differentiated from wrong shaving motions that can be reasonably avoided. The user cannot perform large sized linear shaving motions under the nose as he can perform on other portions of the face, such as the cheeks. Therefore, according to the present invention motion shape and size detection is used to differentiate between wrong (large) linear shaving motions and acceptable (small) linear shaving motions.

[0013] According to the present invention, feedback of a first type is provided to the user of a rotary shaver in case the detected shaving motion is a wrong motion that the user can reasonably improve upon, i.e., in case the detected shaving motion is determined to be a linear motion having a size above a threshold representing a large (sized) linear motion and a correction of the motion performed by the user should be made. The feedback of the first type may indicate incorrect / non-preferred motion that can reasonably be avoided. It may be or represent an alarm or an advice to the user to start smaller and / or more circular motion.

[0014] In case the detected motion is determined to be a correct or a non-preferred but acceptable motion that the user cannot reasonably improve upon, and no correction of the motion performed by the user is needed, feedback of another type, different from the feedback of the first type, is provided to the user. In other words, feedback of the other type is provided in case the detected motion is determined to be rotational (or circular) motion or linear motion of a size below the threshold (i.e. small linear motion). The feedback of the other type might be feedback, which is provided to the user in case the detected motion is determined to be a correct motion or a non-preferred but acceptable motion that the user cannot reasonably improve upon. The feedback of the other type might be feedback, which is provided to the user in case that feedback of the first type is not provided. The feedback of the other type may thus indicate correct / preferred or acceptable motion. It may be or represent an advice to the user to continue performing motions like the last motion(s).

[0015] Feedback may be provided in any form that can be sensed by the user, such as audible feedback, visual feedback, haptic feedback, feedback in the form of text and / or images, etc. The feedback of the other type generally differs from the feedback of the first type. Not providing or issuing feedback of the first type may be considered as an embodiment of feedback of the other type which is different from the feedback of the first type. For example, in case feedback is provided by means of an LED, feedback of the first type may be provided by switching on the LED and feedback of the other type may be provided by switching off the LED or by changing one or more of the color, light intensity, blinking frequency, etc. of the LED. According to the present invention, continuous feedback can thus be provided to the user.

[0016] The feedback of the first type may be regarded as an alarm / alert or a recommendation, while the feedback of the other type may be regarded as a confirmation of correct motion or advice to continue with the same type of motion.

[0017] The (shaving) motion of the shaver is the motion performed by the user of the rotary shaver when moving the shaver relative to the face during shaving. The shaving motion of the shaver may be divided into a plurality of single motions. In particular, a single motion of the shaver can be defined as a continuous contact of the shaver with the skin between an initial point, respectively location, at which the shaver makes contact with the skin and a final point at which the shaver loses contact with the skin. Alternatively, a motion of the shaver can also be defined in that it ends when it reaches a point on the skin for a second time during continuous contact with the skin. The end of the motion might then initiate the start of a next motion. The motion of the shaver on the user's skin can be described by a location trail.

[0018] The location trail can be described as an imaginary line defined by following the motion of the shaver on the user's skin, wherein the shaver is in continuous contact with the skin. The location trail defines a series of locations that the shaver successively passes through as it moves along the trail.

[0019] The expression size of a motion can be described by the maximum distance that the shaver travels on the skin during one motion. The maximum distance can be the distance between the starting location of a shaver motion on the user's skin and the most distant location on the location trail, wherein the most distant location defines a longest direct line to the starting location. In other words, the maximum distance can be a maximum displacement of the shaver on the user's skin without losing contact to the skin. Alternatively, the expression size of a motion may describe a length of the location trail of the motion.

[0020] In an embodiment of the method according to the invention, the feedback of the other type is feedback of a second type if the monitored motion is determined to be a circular motion and feedback of a third type if the monitored motion is determined to be a linear motion having a size equal to or below the threshold. As mentioned above, the feedback of the other type is different from the feedback of the first type and may be of the second type or the third type. The feedback of the second type and the feedback of the third type may be of the same kind or even identical or may be different from each other. For example, the feedback of the second type may advise the user to continue circular motions, and the feedback of the third type may be provided to the user by not providing or issuing the feedback of the first or second type or may advise the user to better perform circular motions if possible. The feedback of the second type as well as the feedback of the third type may each be provided in any form as described above, e.g. in any form that can be sensed by the user, such as audible feedback, visual feedback, haptic feedback, feedback in the form of text and / or images, etc.

[0021] In an embodiment of the method according to the invention, the control signal is configured to suppress the feedback of the first type if the monitored motion is determined to be a circular motion or a linear motion having a size below the threshold. As explained above, small linear motions may be unavoidable in certain situations (e.g. when shaving under the nose area). Thus, according to this embodiment, feedback of the first type is suppressed or the trigger to issue the feedback of the first type is not generated or suppressed if the monitored motion is determined to be a circular motion or a linear motion having a size equal to or below the threshold. For instance, although for large linear motions an alarm as feedback of the first type may be generated, it may not be issued for small linear motions. In this way, the credibility of the feedback may be improved. In another embodiment of the method according to the invention, the control signal configured to trigger feedback of the first type is not generated, if the monitored motion is determined to be a circular motion or a linear motion having a size below the threshold.

[0022] In a further embodiment of the method according to the invention, the method further comprises a step of providing feedback to the user based on the generated control signal. The feedback may be provided by the shaver or by an external entity, e.g. a smartphone or other user device that is communicatively coupled with the shaver, such as an external display.

[0023] In a further embodiment of the method according to the invention, determining the size of the monitored motion includes the steps of: obtaining a plurality of latest samples of the monitored motion from the obtained motion data; smoothening the obtained motion data, in particular the plurality of the latest samples; extracting a trend from the smoothed motion data; determining a difference between a maximum and a minimum value of the trend; and thresholding the difference to determine if the size of the monitored motion exceeds the threshold.

[0024] The latest samples can be motion data representing the monitored motion. In particular, each sample may be a 3D value (x, y, z-value) of the motion data. The samples may be taken during a time interval, wherein a sampling frequency defines a number of samples taken during the time interval. The sampling frequency may be defined by the motion sensor or may be set in advance. The latest samples may be samples of one or of a plurality of motions of the shaver that the user performed last in the past.

[0025] Smoothening of the obtained motion data can for example be performed by using mean average filtering of the obtained motion data to remove noise.

[0026] Extracting the trend from the smoothed motion data may be performed by computing a trend line that shows the general direction of the smoothed motion data, respectively of the samples, over time. This can be a straight line or a line comprising many individual straight lines in case linear regression is used to extract the trend. Alternatively, this can be a curved line or a line comprising many individual curved lines in case polynomial regression or exponential smoothing is used to extract the trend. Alternatively, this can be a combination of straight and curved lines. In particular, the method which is used to extract the trend may be selected depending on the characteristics of the motion data.

[0027] Determining the difference between a maximum and a minimum value of the trend can be performed by computing the peak-to-peak difference of maximum and minimum values of the trend. Particularly, a local spread over the monitored interval of the latest samples can be detected this way. It has been found that as a (stroke) length of the monitored motion decreases, the spread decreases. In other words, the spread of the motion data over the monitored interval of the latest samples corresponds to the length of the monitored motion. To threshold the difference, the difference may be compared to a set value as the threshold.

[0028] In a further embodiment of the method according to the invention, a number of the latest samples is set in advance or is determined by a time interval. The number may be predetermined or set by a user or may be dynamically adapted.

[0029] In a further embodiment of the method according to the invention, extracting the trend from the smoothed motion data is performed using exponential smoothing or by performing linear regression, wherein a gravity component is extracted from the obtained motion data. By extracting the gravity component from the obtained motion data, respectively acceleration data, linear acceleration data can be achieved. Usually, the gravity component can only be extracted reliably from an acceleration signal by using a gyroscope as well. However, it has been observed that for the shaving application the motions of the shaver are generally of an oscillatory nature. Removal of the gravity component using linear regression without the need for a gyroscope can thus be achieved.

[0030] In a further embodiment of the method according to the invention, the threshold is a predetermined value or is computed based on the motion data. For example, to compute the value of the threshold based on the motion data the threshold may be determined based on a predefined upper bound on the fraction of time that alarms are generated. In this case, there may be a learning period during the initial phase of a shaving session to adapt the threshold to the (specific) motions performed by the present user. In case the threshold is a predetermined value, the value may be related to a dimension of the rotary shaver, in particular a diameter of a round hair-cutting unit of the rotary shaver. The value may be between 90% and 180% of said diameter. In particular, the value may be between 18 mm and 45 mm. Preferably, the value may be between 25 mm and 35 mm. For reference, a typical diameter of a hair-cutting unit of a rotary shaver is approximately 20 mm to 25 mm, although other values of the diameter can be used.

[0031] In a further embodiment of the method according to the invention, the step of determining a size of the monitored motion based on the obtained motion data is carried out only if the shape of the monitored motion is determined to be linear. In other words, only the samples representing a linear motion are further analyzed. In this way, the required computing power can be reduced.

[0032] In a further embodiment of the method according to the invention, determining the shape of the monitored motion includes the steps of: obtaining a plurality of latest samples of the monitored motion from the obtained motion data; smoothening the obtained motion data, in particular the plurality of the latest samples; extracting a trend from the smoothed motion data; computing features from the remaining linear motion data or the trend, in particular such as speed, amplitude, and motion ratio; running a machine learning model to compute, based on the computed features, a likelihood of the monitored motion being a circular motion; and determining that the monitored motion is a circular motion if the computed likelihood is more than 50%, and determining that the monitored motion is a linear motion if the computed likelihood is less than 50%.

[0033] In particular, said steps of obtaining, smoothening and extracting may be performed in the same way as described above.

[0034] The features can be computed from the obtained motion data. For example, in case the obtained motion data is acceleration data, speed data can be computed by integration of the linear acceleration data over time. Motion ratio and amplitude can be computed by first integrating twice and then estimating motion ratio and amplitude. In case the monitored motion is a circular motion, the three-dimensional linear acceleration data (being acceleration minus the gravity component) can be taken to approximate a three-dimensional position of the shaver. One-dimensional speed can thus be approximated by taking the successive differences of pairs of samples in the set of latest samples, and computing the Euclidean Distance of each difference, and further taking the average therefrom, and multiplying the average with the sampling frequency. One-dimensional amplitude can be estimated by taking the Euclidean Distance of the three-dimensional linear acceleration data and taking its mean value. The motion ratio can be estimated by taking the Euclidean Distance of the three-dimensional linear acceleration data and computing its standard deviation divided by its mean value.

[0035] The machine learning model may utilize the computed features as input. The machine learning model may further utilize samples of monitored motion(s) of the rotary shaver from previous shaving sessions of the user as input. The machine learning model may output the likelihood of the monitored motion being a rotational, respectively circular motion as a percentage or a comparable value. Alternatively, the machine learning model may output a likelihood of the monitored motion being a linear or stroke-like motion as a percentage or a comparable value. It is understood that the stated percentage values are to be considered as examples and may be adjusted to suit the specific requirements of the application. In particular, a degree of circularity of the monitored motion can be determined, whereby the degree is maximum when the motion is a circle.

[0036] In a further embodiment of the method according to the invention, determining the size of the monitored motion may be based on ground truth motion sizes of the monitored motion of the rotary shaver. In particular, the ground truth motion size may be utilized for tuning parameters of the machine learning model or for tuning at least one parameter of an algorithm configured to determine shape and / or size of the monitored motion based on the obtained motion data. The ground truth motion size may be determined based on the location trail of the monitored motion. Particularly, the ground truth motion size may be determined based on detecting the end of a previous motion and the start of the next motion.

[0037] In a further embodiment of the method according to the invention, determining the size of the monitored motion is based on an AI model, wherein each sample obtained in a shaving session is annotated using the ground truth motion size of the monitored motion, in particular wherein a LSTM-based (Long Short-Term Memory) network is trained using the binary cross-entropy loss-function, which penalizes the disparity between the predicted labels and the ground truth labels, using as input either the obtained motion data only, or the obtained motion data in combination with the computed features. Particularly, the ground truth motion size may be utilized to tune at least one parameter of the AI model.

[0038] In one example, the AI model is trained in advance to the use of the AI model in the method according to the invention. The AI model may be trained based on a collected dataset of one or more shaving sessions as inputs for the AI model, where the ground truth motion size has been determined, based on camera data and / or gyroscope data. Next to these inputs, the inputs may further comprise (x, y, z-value) triples from a motion sensor, respectively from an accelerometer. Training is performed by feeding the AI model with these inputs. The training is performed based on the type of AI model used. For an LSTM-based network, weights of internal parameters are estimated in an iterative fashion. However, alternative networks may also be suitable. The output (during the training of the AI model) is a yes / no classification. After training has been performed, the model can be used in the method according to the invention, whereby only the obtained motion data, respectively the accelerometer data is available. During the operation of the method according to the invention, the AI model may output an indication that can be utilized to determine the size of the monitored motion.

[0039] In another example, supervised learning is used to train the AI model on a dataset of motion data, respectively acceleration data of at least one shaving session, which included a mix of large and small motions (motions having a size above, respectively below a threshold). Each sample of motion data, respectively acceleration data has been annotated as either part of a large linear motion or not. The model in this example is an LSTM-based network. It takes a sample of acceleration data and the computed features as input to determine if the sample is a part of a large linear motion. Leveraging its memory capabilities, the LSTM-based network analyzes the temporal evolution of motions and functions as a binary classifier, outputting "True" for large linear motions and "False" otherwise. The dataset in this example comprises motion data of 25 sessions from 13 unique users, annotated using the ground truth motion size of the monitored motion based on a camera based system, wherein the monitored motion of each session is split into single motions, if multiple motions have been performed during the session. The network may for example be trained over 100 epochs, respectively run-throughs using binary cross-entropy loss to minimize the disparity between predicted labels and ground truth labels. For validation, a 13-fold cross-validation may be performed.

[0040] In a further embodiment of the method according to the invention, determining shape and size of the monitored motion can be determined after obtaining every (single) sample or once after obtaining a defined number of samples, in particular wherein the determined shapes and sizes can be smoothed using for example a moving average or a moving median filter. In this way, the feedback can be customized according to a required frequency of feedback or speed of response.

[0041] In a yet further embodiment of the method according to the invention, the step of providing feedback to the user can be based on the computed likelihood of the monitored motion being a circular motion, and the determined size of the monitored motion directly. Particularly, a feedback color displayed to the user can be based on the determined circularity of the monitored motion and / or the determined size of the monitored motion. The feedback color may be displayed during the shaving session by means of a light ring or other light element arranged on the rotary shaver.

[0042] In an embodiment of the apparatus according to the invention, the apparatus further comprises a feedback unit configured to provide feedback to the user based on the control signal. The feedback unit is for providing the feedback to the user regarding the motion of the rotary shaver performed by the user. The feedback unit is configured to provide the feedback based on the control signal generated by the processing unit. The feedback can be in any suitable or desired form, including one or more of a visual element, an audible element, a haptic (tactile) element, etc.

[0043] In a further embodiment of the apparatus according to the invention, the feedback unit comprises a light ring or other light element configured to provide optical feedback to the user. The light element may be provided on the shaver, in particular on a handle of the shaver. The light ring may be provided on the handle of the shaver circumferentially about a longitudinal axis of the handle. The light element may display the feedback color.

[0044] In an embodiment of the system according to the invention, the apparatus is part of the rotary shaver or of a separate device, in particular a digital mobile device, communicatively coupled to the rotary shaver. The separate device may be a smartphone, tablet, personal digital assistant (PDA), smart mirror, etc. Alternatively, the separate device may be a cloud-based system.

[0045] In a further embodiment of the system according to the invention, the system further comprising a feedback unit configured to provide feedback to the user based on the control signal generated by the processing unit, the feedback unit is arranged in the rotary shaver or in the separate device. The separate device and the shaver may be communicatively coupled, e.g. by use of Wi-Fi or Bluetooth or via cable.

[0046] In a further embodiment of the system according to the invention, the motion sensor comprises an accelerometer arranged in the rotary shaver.BRIEF DESCRIPTION OF THE DRAWINGS

[0047] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. In the following drawings Fig. 1(a) shows a diagram of rotational, respectively circular motion of a rotary shaver. Fig. 1(b) shows a diagram of linear motion of a rotary shaver. Fig. 1(c) shows a diagram of a location trail of an exemplary motion of the rotary shaver. Fig. 2 shows a schematic diagram of an apparatus for controlling feedback according to the present invention. Fig. 3 shows a schematic diagram of an embodiment of a system for controlling feedback according to the present invention. Fig. 4 shows a flowchart of an embodiment of a method for controlling feedback according to the present invention. Fig. 5 shows a flowchart of a further embodiment of the method according to the present invention. Fig. 6 shows an exemplary embodiment of the system according to the present invention comprising a feedback unit arranged in the rotary shaver. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] As noted above, an object of the invention is to provide feedback to a user on the (shaving) motion of a rotary shaver performed by the user. A rotary shaver is a type of shaver that cuts hairs using hair-cutting units that comprise one or more circular blades that rotate rapidly. Preferably, the rotary shaver is to be moved over the skin using a rotational motion, in particular circular motion, so that the shaver for example follows an approximately circular path on the skin of the user. A rotary shaver typically comprises at least two hair-cutting units, and preferably three hair-cutting units arranged in a triangle, although rotary shavers having different numbers of hair-cutting units and / or arrangements are available. It has been found that moving a rotary shaver with small rotational, respectively circular motions provides an improved shaving performance. Particularly, shaving performance can be improved in terms of reducing skin irritation.

[0049] Fig. 1(a) shows a diagram of rotational, respectively circular motion of a rotary shaver 8. Fig. 1(a) further shows a shaving unit 200 of the rotary shaver 8, the shaving unit 200 having three round hair-cutting units 202 arranged in a triangular configuration. The geometrical center or midpoint of the shaving unit 200 is marked as 204. Distance A is shown that is the diameter of the shaving unit 200 and in particular is the diameter of a circle that circumscribes the shaving unit 200. In a typical shaving unit 200, the distance A is approximately 5cm - 6cm, although other sizes can be used, and for reference the typical diameter of a hair-cutting unit 202 is approximately 2cm - 2.5cm, although again other sizes can be used.

[0050] The (shaving) motion shown in Fig. 1(a) is a single circular motion of the shaver 8, respectively the shaving unit 200. Dashed circle 206 shows the circular path taken by the center 204 of the shaving unit 200. Shaver 8' represents the shaver 8 after approximately 180 degrees of a full rotation along the circular path 206. Dashed circle 206 can be described as a location trail of the motion. The location trail in Fig. 1(a) is a closed circular contour around a center point 208 of the circle 206. In an alternative embodiment however, the motion might also be defined as a rotational or a circular motion, if the location trail 206 is no geometrical circle, but instead an approximately circular or elliptical path. The location trail 206 can describe the shape of the motion.

[0051] In the example in Fig. 1(a) the diameter of the circular path 206 of the rotational motion is equal to the diameter A of the shaving unit 200. However, the diameter of the circular path 206 can be smaller or greater than the diameter A, describing circular motions of different sizes.

[0052] Fig. 1(b) shows the shaving unit 200 as shown in Fig. 1(a) in a diagram of a linear motion of the rotary shaver 8. The (shaving) motion shown in Fig. 1(b) is a single linear motion of the shaver 8, respectively the shaving unit 200. Dashed line 210 shows a straight, respectively linear path taken by the center 204 of the shaving unit 200. In Fig. 1(b) the shaver 8 is in its initial position and the shaver 8' represents the shaver 8 in its final position. Dashed line 210 can be described as the location trail of the motion. The location trail in Fig. 1(b) is a straight line. However, in an alternative embodiment, the motion might also be defined as a linear motion, if the location trail 210 is no geometrical straight line, but instead an approximately straight line (an example of this is shown in Fig. 1(c)). The location trail 210 can describe the shape of the motion.

[0053] The linear motion of Fig. 1(b) is of a determined size. Since in this example, the motion is represented by a straight location trail, the size of the motion can be described by the length of the location trail 210 of the motion. In the example in Fig. 1(b), the length of the straight path 210 of the linear motion is equal to twice the distance B of the shaving unit 200. However, the length of the straight path 210 can be smaller or greater than the distance B, describing linear motions of different sizes.

[0054] Fig. 1(b) illustrates an exemplary definition of the size of a linear motion. A linear motion having a size below a threshold, respectively a small linear motion can be, for example, a stroke where the length of the stroke is such that there is at least one point on the user's skin that is always covered by the shaving unit 200, i.e. in contact with the shaving unit 200, during the linear motion. Following this definition, a linear motion having a size above a threshold, respectively a large linear motion can be a stroke wherein the length of the stroke is such that there is no point on the user's skin that is always covered by the shaving unit 200 during the linear motion. Fig. 1(b) shows a linear motion with a stroke length at the boundary between small linear motion and large linear motion according to this definition. In other words, this can be an example how geometrical dimensions of the shaver 8, in particular of the shaving unit 200 may be used as the threshold. This will be described in the following.

[0055] For example, distance B can be defined to be the same length as the diameter of a hair-cutting unit 202. It will be appreciated from Fig. 1(a) that in this example 2*B is slightly smaller than distance A in Fig. 1(a). In this definition, therefore, small linear motion is a stroke along the straight path with a length that is equal to or less than the distance 2*B. Dashed line 210 shows the straight path, respectively location trail 210 taken by the shaving unit 200 when the length of the path is 2*B. Thus, it can be seen that there is a point 212 on the user's skin at the midpoint of the straight path 210 that will always be covered during the linear motion if the stroke length is equal to or less than 2*B. Any stroke lengths greater than 2*B will imply that the midpoint of the path 210 on the user's skin will not always be covered by the shaving unit 200 during the linear motion, and in this example stroke lengths greater than 2*B are considered to be large linear motion. It will be appreciated that in alternative embodiments a different definition of large linear motion and small linear motion can be used, for example wherein large linear motion is a stroke motion with a length greater than distance A in Fig. 1(a) and small linear motion is a stroke motion with a length equal to or smaller than distance A. In this example, distance B defines the threshold. Particularly, 2*B is the threshold.

[0056] An alternative definition of a small linear motion can be provided by defining an alternative threshold. The threshold may be adapted to the need of the specific application, e.g. for using the shaver 8 on specific portions of the body, like under the nose area or around a single hair. Particularly, an average stroke length under the nose may be used to define the threshold, wherein data of a plurality of users may be provided to determine the average stroke length. Or a measured stroke length under the nose of a specific user may be used to define the threshold. A method to determine the size of the motion will be explained with reference to Figs. 4 and 5.

[0057] Fig. 1(c) shows a diagram of a location trail 220 of an exemplary (shaving) motion of the rotary shaver 8. The rotary shaver 8 may be the same as in Figs. 1(a), 1(b). The location trail 220 may be used to determine shape and / or size of the motion, particularly by tuning at least one parameter of an algorithm configured to determine shape and / or size of the monitored motion based on the obtained motion data. In other words, the motion can be described by the location trail 220. In this example, the location trail 220 can be represented by motion data. Therefore, it is possible to compute features from the motion data representing the location trail, in particular such as speed or via the acceleration a change of direction of the motion. Alternatively, the location trail 220 may be used to determine the shape of the motion for example, by running a machine learning model to compute, based on the computed features, a likelihood of the motion being a circular motion.

[0058] In Fig. 1(c) the motion may for example be determined as linear motion since in this instance, the likelihood of a circular motion may be less than 50%. Alternatively, or in addition, the motion can be classified as a linear or stroke-like motion as shown in Fig. 1(c) by analyzing the geometry of the location trail 220. The location trail 220 in Fig. 1(c) is not a closed contour. In this example, this can indicate a linear motion. The location trail of the linear motion starts at the starting location P0, respectively initial point of contact, and ends at a most distant location P5, respectively most distant point, in the maximum (direct) distance d05, wherein both points are connected by a continuous path. In comparison the distance from the location P0 to the location P6 is d06, which is less than d05. In Fig. 1(c), the location trail 220 makes no change of direction in the opposite direction. However, between the locations P5 and P6 there is a change of direction in the opposite direction. Therefore, the location trail 220 ends in the location P5. In other words, the location trail 220 of the motion reaches a maximum distance d05 before a change in direction occurs and the distance decreases d06, indicating a linear motion.

[0059] The following therefore describes how to determine the size of a linear motion using the location trail 220. The size of the motion can be described by the maximum distance that the shaver 8 travels on the skin during one motion. The maximum distance can be as described above the distance between the starting location P0 and the most distant location P5 on the location trail, wherein the most distant location defines a longest direct line d05 to the starting location P0. Based on a threshold, the size of a motion can then be classified as small or large by thresholding the maximum distance d05. In Fig. 1(c) the threshold may be defined as same as in Fig. 1(b).

[0060] Further, since the location trail 220 in this instance can be understood as a geometry that is derived directly from the motion data, the ground truth motion size of the monitored motion may be determined based on the location trail 220. In Fig. 1(c), the ground truth motion size can be determined based on detecting the end of a previous motion (for example ending in P0) and the start of the next motion (for example starting in P05). In other words, the ground truth motion size can be determined based on the distance d05 between the locations P0 and P5. In particular, every single distance d01 to d45 following the location trail 220 may be used in combination with the changes in direction between locations next to each other of the locations P0 to P5 to determine the ground truth motion size.

[0061] In an alternative embodiment the location trail 220 may be a closed contour and may represent a rotational or circular (shaving) motion. In this instance, the maximum distance may be a maximum diameter of the closed contour. The maximum distance can then be subjected to a threshold to determine the size of the motion. Particularly, the threshold may be defined by a ratio of a diameter of the shaving unit 200 to a diameter of the closed contour of the location trail (see for example the location trail 206 and diameter A in Fig. 1(a)).

[0062] Fig. 2 shows a schematic diagram of an apparatus 2 for controlling feedback to a user regarding motion of a rotary shaver performed by the user according to an aspect of the present invention. The apparatus 2 comprises a processing unit 4 and may optionally further comprise a feedback unit 6. In some embodiments, the apparatus 2 may be implemented as or may be part of an external device, in particular an electronic device, such as a smartphone, tablet, personal digital assistant (PDA), laptop, desktop computer, smart mirror, etc. In other embodiments, the apparatus 2, and particularly the functionality according to the invention provided by the apparatus 2, may be part of the rotary shaver.

[0063] The processing unit 4 generally controls the operation of the apparatus 2. The processing unit 4 is particularly configured to obtain (i.e. retrieve or receive) motion data from a motion sensor monitoring the motion of the rotary shaver performed by the user and to generate a control signal configured to trigger feedback to the user.

[0064] The motion data may be a signal from the motion sensor. The motion data may be measurements of motion of the rotary shaver acquired by the motion sensor, e.g. an accelerometer arranged in the rotary shaver. The motion data may represent single or multiple motions of the rotary shaver performed by the user.

[0065] The processing unit 4 may be any kind of means configured to process signals, in particular motion data, and determine shape and size of the monitored motion there from. It may be implemented in software and / or hardware, e.g. as a programmed processor or computer or app on a user device such as a smartphone, smartwatch, tablet, laptop, PC, workstation, rotary shaver, etc.

[0066] The processing unit 4 can comprise or be associated with a memory unit (not shown in Fig. 2), such as a volatile or non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM. The memory unit can be used for storing program code that can be executed by a processor in the processing unit 4 to cause the apparatus 2 to perform the various functions and methods described herein. In particular embodiments, the program code can be in the form of a smart phone application or tablet application.

[0067] The processing unit 4 may be directly coupled or connected to the motion sensor to obtain the motion data directly from the motion sensor. Alternatively, processing unit 4 may obtain (i.e. retrieve or receive) these signals from a storage, buffer, network, or bus, etc. The processing unit 4 may thus e.g. utilize a (wired or wireless) communication interface or data interface, such as a Bluetooth interface, Wi-Fi interface, LAN interface, HDMI interface, direct cable connector, or any other suitable interface allowing signal transfer to the processing unit 4.

[0068] In some embodiments, the processing unit 4 can be configured to obtain information, in particular shape and size, of the monitored motion of the shaver performed by the user via signals from another component of the apparatus 2 and therefore the processing unit 4 can include or comprise one or more input ports or other components for receiving the information, as mentioned above, from the other component. In other embodiments, the processing unit 4 can determine shape and size of the monitored motion based on the obtained motion data obtained by the processing unit 4. Therefore, the processing unit 4 can include or comprise one or more input ports or other components for obtaining motion data of the monitored motion of the rotary shaver from the motion sensor.

[0069] In some embodiments, the processing unit 4 can signal the control signal to a feedback unit 6. In particular, the processing unit 4 may be configured to signal the determined shape and size of at least one motion of the shaver to another component of the apparatus 2. Therefore, the processing unit 4 can comprise one or more output (ports) or other components for signaling the control signal to be provided to the feedback unit 6. The output may generally be any interface that provides the determined signal or information, e.g. transmits it to another device or provides it for retrieval by another device (e.g. a smartphone, computer, tablet, etc.). It may thus generally be any (wired or wireless) communication or data interface.

[0070] The feedback unit 6 is for providing feedback to the user on the monitored motion of the rotary shaver performed by the user. The feedback can be in any suitable or desired form, including one or more of a visual element, an audible element, a haptic (tactile) element, etc., and the feedback unit 6 can be in a form that is able to provide or output those elements. The visual element can comprise a message in the form of letters, numbers, symbols, pictures, a video message, etc. and therefore the feedback unit 6 can comprise or be a display screen, such as that used on a smart phone, tablet, smart mirror or other personal electronic device. Alternatively (or in addition), the visual element can be provided using one or more lights (e.g. one or more light emitting diodes (LEDs)) having one or more colors (e.g. red, orange, yellow, green, etc.). In a preferred embodiment the visual element can be a light ring, particularly provided on the handle of the shaver or on or around the shaver head. Preferably, the light ring is provided on the handle of the shaver circumferentially about a longitudinal axis of the handle (see e.g. Fig. 6). The audible element can comprise a tone or beep, a verbal message, etc., and therefore the feedback unit 6 can comprise a speaker for generating the required audio. The haptic element may comprise a vibration of a particular intensity and / or duration, and therefore the feedback unit 6 can comprise a component that can generate vibrations, for example a vibration motor. It will be appreciated that the feedback to be provided may comprise multiple forms of feedback (e.g. visual and audible), and therefore feedback unit 6 can be configured or capable of providing feedback of the appropriate form(s). It will be appreciated that certain devices, for example a smart phone or tablet, typically comprises components capable of providing the different forms of feedback set out above.

[0071] It will be appreciated that the apparatus 2 may comprise additional components to those shown in Fig. 2. For example, the apparatus 2 may comprise a power source, such as a battery, or a power interface component, such as plug, for connecting to the apparatus 2 to a mains power supply. The apparatus 2 may also or alternatively comprise a user interface that can enable a user to interact with the apparatus 2, for example to activate or deactivate the apparatus 2, and / or to control one or more settings or operations of the apparatus 2. The user interface can comprise any one or more of a touch screen, button, switch, keypad, keyboard, mouse, stylus, etc.

[0072] Fig. 3 shows a schematic diagram of an embodiment of a system 7 for controlling feedback according to the present invention. The system 7 may comprise the apparatus 2 of any one of the embodiments described above. The system 7 further comprises a rotary shaver 8 and a motion sensor 12 configured to monitor motion of the rotary shaver. In Fig. 3 a specific embodiment of the apparatus 2 is shown as part of the system 7. In this embodiment, the apparatus 2 is a separate device to the rotary shaver or may be part of a separate device to the rotary shaver. The system 7 comprises the apparatus 2, respectively the separate device and the rotary shaver 8. The apparatus 2, respectively the separate device, which may also be referred to as a feedback device, comprises a processing unit 4 and feedback unit 6 as described above, and may further comprise a transceiver or receiver unit 10 that is configured to receive signals, particularly motion data, from the rotary shaver 8. The transceiver or receiver unit 10 can be configured to operate according to any desired wireless or wired communication standard, for example Ethernet, Bluetooth, Wi-Fi, ZigBee, NFC, or any 3rd, 4th or 5th generation cellular telecommunications standard or any one of the communication systems mentioned above.

[0073] The rotary shaver 8 comprises a motion sensor 12, a shaver processing unit 14 and may further comprise a transceiver or transmitter unit 16. The transceiver or transmitter unit 16 is configured to transmit signals from the rotary shaver 8 to the feedback device 2. The transceiver or transmitter unit 16 can be configured to operate according to any desired wireless or wired communication standard, for example Ethernet, Bluetooth, Wi-Fi, ZigBee, NFC, or any 3rd, 4th or 5th generation cellular telecommunications standard, as required in order to communicate with the transceiver or receiver unit 10 in the feedback device 2.

[0074] The motion sensor 12 is configured to monitor, particularly measure, the motion of the rotary shaver 8 during use of the shaver 8 by the user. The motion sensor 12 can be configured to generate motion data, representing motion of the shaver 8. The motion sensor 12 is preferably integral with or otherwise fixed to the shaver 8 so that the motion sensor 12 directly measures the motion of the rotary shaver 8 performed by the user. In some embodiments, the motion sensor 12 is an accelerometer, for example that measures acceleration along three orthogonal axes. Alternatively or in addition, the motion sensor 12 can comprise a gyroscope or a magnetometer.

[0075] The shaver processing unit 14 may generally control the operation of the rotary shaver 8, for example by activating and deactivating one or more hair-cutting units to affect a shaving or other hair cutting operation. The shaver processing unit 14 can be implemented in numerous ways, with software and / or hardware, similarly to the processing unit 4 in the feedback device 2.

[0076] The shaver processing unit 14 is connected to the motion sensor 12 and is configured to obtain motion data from the motion sensor 12 monitoring the motion of the rotary shaver 8 performed by the user. In other words, the processing unit 14 is configured to receive or retrieve measurements of the motion of the rotary shaver 8 from the motion sensor 12, for example via an input port to the shaver processing unit 14.

[0077] Generally, there may be different options to process the motion data, to generate the control signal and to provide the feedback to the user. Further, there may be different options regarding in which device the motion data are processed, in which device the control signal is generated and in which device the feedback is provided to the user. Independent of the location of the respective units performing these steps it holds that the control signal is configured to trigger feedback of a first type if the monitored motion is determined to be a linear motion having a size above a threshold, wherein the control signal is further configured to trigger feedback of another type, different from the first type, if the monitored motion is determined to be a circular motion or a linear motion having a size below the threshold. In other words, feedback of the first type (e.g. an alert or recommendation) is provided in case of small linear motions, whereas in other cases of motion feedback of the other type (e.g. a confirmation, a signal to continue, etc.) is provided. Particularly, the processing unit generates the control signal configured to trigger feedback of a first type only if the monitored motion is determined to be a linear motion having a size above a threshold.

[0078] In some embodiments, the shaver processing unit 14 may output the motion data (e.g. raw acceleration data) of the motion to the transceiver or transmitter unit 16 for transmission to the feedback device 2 for subsequent processing performed by the processing unit 4. In this case the processing unit 4 may generate the control signal and the feedback unit 6 may provide feedback to the user based on the control signal.

[0079] Alternatively, the feedback unit 6 may be arranged in the rotary shaver 8. In this case, the processing unit 4 may generated and output the control signal to the rotary shaver 8, respectively the feedback unit 6 in the rotary shaver 8.

[0080] In alternative embodiments, the shaver processing unit 14 processes the obtained motion data to determine shape and size of the monitored motion based on the obtained motion data and generates the control signal. In this case, the shaver processing unit 14 may output the control signal to the transceiver or transmitter unit 16 for transmission to the feedback device 2, respectively to the feedback unit 6. In this case, the system 7 may comprise an apparatus 2, that is part of the rotary shaver 7 and the apparatus 2 may comprise the processing unit 14.

[0081] In another embodiment of Fig. 3 the feedback device 2 is part of the rotary shaver. In this embodiment, the feedback unit 6 is arranged in the rotary shaver 8. In other words, the shaver 8, by means of the processing unit 4, is configured to process the obtained motion data and generate the control signal and feedback is provided to the user by the feedback unit 6 that is arranged in the shaver 8 as well in this embodiment.

[0082] The feedback unit 6 is configured to provide feedback to the user based on the control signal. Particularly, the feedback unit 6 can be used to give feedback to the user on the shaving behavior. The feedback may be feedback of a first type or another type, different from the first type. As explained above by reference to different embodiments, the feedback unit 6 can be arranged in the rotary shaver 8 or in the separate device 2. While shaving using the rotary shaver 8 equipped with an accelerometer or other motion sensor 12, the motion of the shaver 8 is monitored by the motion sensor 12. The motion sensor 12 is configured to generate motion data, representing motion of the shaver 8. Further, the obtained motion data is then analyzed by the processing unit 4. If the user moves the shaver 8 using rotational motions, e.g. the shaver 8 follows a generally circular or elliptical path on the body of the user, the user can be notified via the feedback unit 6 that the monitored motion is correct. If the user moves the shaver 8 using small linear motions, e.g. the shaver 8 follows a generally linear, straight or stroke-like path on the body of the user, wherein the motion has a size below a threshold, the user can be notified via the feedback unit 6 that the monitored motion is correct. Correct motion is indicated by feedback of the other type. However, if the user deviates from performing correct motions described above with the shaver 8, in particular if the user moves the shaver 8 using large linear motions having a size above the threshold which is considered as wrong / incorrect motion, the user can be notified via the feedback unit 6 that the motion should be changed, in particular to rotational motion. Wrong / incorrect motion is indicated by feedback of the first type.

[0083] In an exemplary embodiment, the feedback unit 6 may comprise a light ring as a visual element configured to provide visual feedback to the user. The light ring may be provided on the shaver, in particular on a handle of the shaver. The light ring may display a feedback color. For example, for providing feedback of the first type (indicating incorrect / non-preferred motion) in case the monitored motion is determined to be a linear motion having a size above the threshold, the light ring may emit red light. To provide feedback of the other type (indicating correct / preferred motion), in case the monitored motion is determined to be a circular motion or linear motion of a size smaller than the threshold, the light ring emit green light (or may be switched off). The feedback color(s) may, of course, be any other suitable color(s). Further, in addition to or instead of colors other parameters may be controlled, like intensity of the light, periodicity of blinking of the light, etc.

[0084] Fig. 4 shows a flowchart of an embodiment of a method 100 of controlling feedback to a user regarding motion of the rotary shaver 8 performed by the user according to the present invention. The steps of the method 100 may be carried out by the apparatus 2, wherein the main steps of the method can be carried out by the processing unit 4. The method 100 may e.g. be implemented as computer program running on a computer or processor. In addition, some steps may be performed by the feedback unit 6.

[0085] In a first step 102, motion data from a motion sensor 12 monitoring the motion of the rotary shaver 8 performed by the user is obtained. The motion data can be data representing measurements of at least one motion. In some embodiments, the motion data are received or retrieved from the motion sensor 12 by the processing unit 4.

[0086] Next, in step 104, the shape of the motion is determined based on the motion data, the shape indicating if the monitored motion is determined to be rotational, respectively circular or linear, respectively stroke-like. In some embodiments, the shape of the motion is determined by the processing unit 4 in the same or similar way as described above with reference to Figs. 1(c) and 3.

[0087] In step 106, the size of the motion is determined based on the motion data. In some embodiments, the size of the motion is determined by the processing unit 4 before, after or in parallel to step 104. In a preferred embodiment, step 106 is carried out after step 104. In an alternative preferred embodiment of the method 100, as shown in Fig. 4, step 106 is carried out only if the shape of the motion is determined to be linear. The processing unit 4 may determine the size of the motion from acceleration data. Particularly, the processing unit 4 may utilize the ground truth motion size of the monitored motion to tune parameters of an algorithm configured to determine the size of the monitored motion.

[0088] Next, in steps 108, 109, a control signal is generated by the processing unit 4, 14. The control signal as generated in step 108 is configured to trigger feedback of a first type, particularly only, if the monitored motion is determined to be a linear motion having a size above a threshold. The control signal as generated in step 109 is configured to trigger feedback of another type, different from the first type, if the monitored motion is determined to be a circular motion or a linear motion having a size below the threshold. The control signal may be generated (step 109) directly after step 104, if the determined shape of the motion is determined to be rotational, respectively circular to trigger feedback of the other type.

[0089] In some embodiments of the method 100, step 110 follows step 108 and step 111 follows step 109. In steps 110, 111, feedback is provided to the user based on the control signal. In step 110, feedback of the first type is provided, if the determined size of the motion is above the threshold. In step 111, feedback of the other type is provided, if the determined size of the motion is below the threshold. The feedback triggered by the control signal is provided by the feedback unit 6 included in a separate device or by a feedback unit included in the shaver 8. For example, feedback of the first type can be provided by means of a light ring of the feedback unit 6 illuminated in red. Feedback of the other type can be provided by means of the light ring illuminated in green.

[0090] The feedback of the first type is provided to the user in case the detected motion is a wrong motion that the user can reasonably improve upon so that the user may change the motion to improve shaving performance. For instance, the feedback of the first type may advise the user to start smaller and / or more circular motion.

[0091] The feedback of the other type is provided to the user in case the detected motion is a correct motion or is a wrong or non-preferred but acceptable motion that the user cannot reasonably improve upon, and no correction of the motion performed by the user is needed. Particularly, in case that the detected motion is determined to be a rotational, respectively circular motion or a linear motion of a size below the threshold, the feedback of the other type may advise the user to continue performing motions like the last ones or latest one. In particular, the feedback of the other type can be feedback of a second type if the monitored motion is determined to be a circular motion and feedback of a third type if the monitored motion is determined to be a linear motion having a size equal to or below the threshold. For example, feedback of the second type can be provided by means of the light ring of the feedback unit 6 illuminated in green. Feedback of the third type can be provided by means of the light ring illuminated in blue or is switched off or alternatively, the light ring may illuminate in green with a light intensity or blinking frequency different to the feedback of the second type. It is understood that these are only examples, and that the skilled person will be aware of many possibilities for varying the form of the feedback, as described above.

[0092] Fig. 5 shows a flowchart of a further embodiment of the method 100 according to the present invention. Fig. 5 particularly illustrates an exemplary embodiment of implementing step 106 in more detail, wherein determining the size of the motion further includes steps 112 to 120.

[0093] In step 112, a plurality of latest samples of the monitored motion from the motion data is obtained. This means that, for example, the latest 50 samples of the monitored motion are obtained from the motion data. However, every other suitable number of samples may be considered. Alternatively, the number of obtained samples may be determined by a set period of time, respectively a time interval of monitoring the motion of the shaver 8.

[0094] Next, in step 114, the motion data, in particular the plurality of the latest samples, is smoothed. This can for example be performed by using mean average filtering of the motion data to remove noise. Those skilled in the art will be aware of various techniques that can be used to smoothen the motion data.

[0095] Next, in step 116, a trend from the smoothed motion data is extracted. In particular, a trend line is computed that shows the general direction of the obtained motion data, respectively of the samples, over time. In particular, each sample may be represented by a point on the trend line. The step 116 can include performing a linear regression to compute the trend line. This results in the trend being a straight line or a line comprising many individual straight lines. In this case a plurality of samples is represented by the line that is approximated to the points of the plurality of samples, wherein each point may represent a computed feature of each sample. Alternatively, the step 116 can include performing a polynomial regression or an exponential smoothing to extract the trend. This results in the trend being a curved line or a line comprising many individual curved lines. In an alternative embodiment, the step 116 can include performing a linear regression and / or a polynomial regression and / or an exponential smoothing to compute the trend line. In a preferred embodiment, the step 116 is performed by providing a decreased weight for each sample depending on the time difference to the latest sample or depending on the difference in number count of the samples, wherein a greater difference in time or number count to the latest sample results in a larger decrease in weight of each sample. This can e.g. be achieved by exponential smoothing.

[0096] Next, in step 118, a difference between a maximum and a minimum value of the trend is determined. For example, the step 118 can be performed by computing a peak-to-peak difference of maximum and minimum values of the trend. Particularly, the step 118 may include detecting a local spread over the monitored (time) interval of the latest samples.

[0097] Next, in step 120, the difference between the maximum and the minimum value of the trend is subjected to a threshold to determine if the size of the motion exceeds the threshold or not. After the latest sample is obtained and the steps 112 to 118 are carried out, the difference of the trend is compared to the threshold. In case the difference of the trend of the latest samples is above the threshold, thresholding the trend indicates that the (latest) monitored motion has a size above the threshold. In case the difference of the trend of the latest samples is below the threshold, thresholding the trend indicates that the (latest) monitored motion has a size below the threshold. In the following based on the determination of the size of the motion, steps 108, 109 of the method 100 (as illustrated in Fig. 4) can be executed based on the result of step 120.

[0098] Fig. 6 illustrates an exemplary embodiment of a rotary shaver 8 according to the invention comprising means for providing feedback to the user. In this embodiment, a feedback unit is provided in the form of a light ring 20 located on the handle 22 of the shaver 8. Alternatively, or in addition, the feedback can be provided in the form of a display screen 24. As described above, feedback can be provided in various ways, e.g. as visual feedback (as shown in Fig. 6), audible feedback (e.g. by means of a loudspeaker or sound generator) and / or as haptic feedback (e.g. by means of a vibration unit). The shaver 8 may further provide controls and / or interactive elements 26, 28 configured to input user controls and / or provide feedback to the user.

[0099] As shown in Fig. 6, the light ring 20 is switched on in a certain color (e.g. red) to indicate feedback of the first type. This way, the light ring 20 provides feedback indicating incorrect or non-preferred (large linear) motion. This feedback may be understood by the user to start smaller linear motion and / or, even more preferred, more circular motion.

[0100] Feedback of the other type may be provided by the light right 20 by showing a different color (e.g. green) or turning dark / being switched off (i.e., by not providing feedback of the first type). In particular, in case the feedback of the other type may be feedback of the second type, the feedback of the second type may be provided by the light right 20 by showing the different color (e.g. green) and in case the feedback of the other type may be feedback of the third type, the feedback of the third type may be provided by the light right 20 turning dark / being switched off. This way, the feedback indicates correct, respectively preferred or acceptable motion, i.e. circular motion or linear motion of a size smaller than the threshold. This feedback may be understood by the user to continue performing the current motion(s).

[0101] The feedback may be provided for every single detected motion or once after a defined number of detected motions or after a time interval or at regular or irregular intervals. Further, feedback may be provided in case an incorrect / undesired motion is detected.

[0102] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0103] 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 element 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.

[0104] A computer program may be stored / distributed on a suitable non-transitory medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0105] Any reference signs in the claims should not be construed as limiting the scope.

Examples

Embodiment Construction

[0048]As noted above, an object of the invention is to provide feedback to a user on the (shaving) motion of a rotary shaver performed by the user. A rotary shaver is a type of shaver that cuts hairs using hair-cutting units that comprise one or more circular blades that rotate rapidly. Preferably, the rotary shaver is to be moved over the skin using a rotational motion, in particular circular motion, so that the shaver for example follows an approximately circular path on the skin of the user. A rotary shaver typically comprises at least two hair-cutting units, and preferably three hair-cutting units arranged in a triangle, although rotary shavers having different numbers of hair-cutting units and / or arrangements are available. It has been found that moving a rotary shaver with small rotational, respectively circular motions provides an improved shaving performance. Particularly, shaving performance can be improved in terms of reducing skin irritation.

[0049]Fig. 1(a) shows a diagra...

FIELD OF THE INVENTION

[0001] The invention relates to a method and apparatus for controlling feedback to a user regarding motion of a rotary shaver performed by the user of the rotary shaver based on motion shape and size detection.BACKGROUND OF THE INVENTION

[0002] Shaving motions are important for the shaving performance of rotary shavers that comprise one or more hair-cutting units each comprising an external cutting member with an annular array of hair-entry openings and an internal cutting member with an annular array of cutting blades that rotates relative to the external cutting member. Shaving motions are the motions performed by a user of a rotary shaver when moving the shaver relative to the face during shaving (in the following, "shaving motions" may occasionally also be referred to as "motions"). To increase the shaving performance, motion guidance can provide motion feedback to the user, alarming the wrong shaving motions and promoting the right shaving motions. For rotary shavers, in general the right shaving motions are rotational respectively circular shaving motions, and the wrong motions are linear shaving motions, i.e. stroke-like reciprocating shaving motions. However, this alarming respectively correction advice should not distract the user and should suit to the size and the limitations of the shaver.

[0003] WO2018 / 206805 A1 discloses a method of providing feedback to a user of a rotary shaver regarding motion of the rotary shaver performed by the user, the method comprising the steps of receiving, during at least one time interval, at least one motion type determined for the motion of the rotary shaver performed by the user, wherein the motion type is selected from a set of predefined motion types that comprises small rotational motion and one or more other predefined motion types; determining a degree of occurrence in the time interval of each of the motion types in the set of predefined motion types based on the at least one motion type received during the time interval; determining from the determined degree of occurrence of each of the motion types in the set of predefined motion types which motion type has a highest degree of occurrence in the time interval; and providing feedback to the user to increase a degree of occurrence of small rotational motion of the rotary shaver if the determined motion type having the highest degree of occurrence is one of the other predefined motion types.

[0004] Improvements in the controlled feedback regarding the motion of a rotary shaver performed by a user are desired to further improve the shaving performance.SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to provide accurate feedback to a user of a rotary shaver regarding motion of the rotary shaver performed by the user.

[0006] In a first aspect of the present invention, a method of controlling feedback to a user regarding motion of a rotary shaver performed by the user is provided, the method comprising the steps of: obtaining motion data from a motion sensor monitoring the motion of the rotary shaver performed by the user; determining shape and size of the monitored motion based on the obtained motion data, the shape indicating if the monitored motion is circular or linear; and generating a control signal configured to trigger feedback of a first type to the user if the monitored motion is determined to be a linear motion having a size above a threshold and to trigger feedback of another type, different from the first type, to the user if the monitored motion is determined to be a circular motion or a linear motion having a size equal to or below the threshold.

[0007] In a second aspect of the present invention, an apparatus for controlling feedback to a user regarding motion of a rotary shaver performed by the user is provided, the apparatus comprising a processing unit configured to: obtain motion data from a motion sensor monitoring the motion of the rotary shaver performed by the user; determine shape and size of the monitored motion based on the obtained motion data, the shape indicating if the monitored motion is circular or linear; and generate a control signal configured to trigger feedback of a first type to the user if the monitored motion is determined to be a linear motion having a size above a threshold and to trigger feedback of another type, different from the first type, to the user if the monitored motion is determined to be a circular motion or a linear motion having a size equal to or below the threshold.

[0008] In a third aspect of the present invention, a system for controlling feedback to a user regarding motion of a rotary shaver performed by the user is provided, the system comprising: an apparatus for controlling feedback to a user regarding motion of a rotary shaver performed by the user according to the present invention; a rotary shaver; and a motion sensor configured to monitor the motion of the rotary shaver.

[0009] In yet further aspects of the present invention, there are provided a corresponding computer program which comprises program code means for causing an apparatus according to the present invention to carry out the steps of the method according to the invention when said computer program is carried out on the processing unit of the apparatus, as well as a non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by the processing unit, causes the method according to the invention to be performed.

[0010] Preferred embodiments of the invention are defined in the dependent claims. It shall be understood that the apparatus, system, computer program and medium according to the present invention have similar and / or identical preferred embodiments as the method according to the invention, in particular as defined in the dependent claims and as disclosed herein.

[0011] It has been found that on some portions of the face the user of the rotary shaver cannot easily perform rotational respectively circular shaving motions, like under the nose area and around a single hair. On these portions of the face it is normal for a user to perform small sized linear shaving motions. To provide accurate feedback to the user regarding the shaving motion, i.e. the motion of the shaver relative to the user's face performed by the user, such shaving motions should be detected and not be classified as wrong motions. In particular, it is desirable to only correct or alarm the user when he is making wrong shaving motions which lead to reduced shaving performance that he can reasonably avoid. In particular, this is the case when the user makes large sized linear (stroke-like) shaving motions.

[0012] The present invention is based on the idea to provide more accurate feedback to the user regarding the shaving motions by only correcting the user when he is making wrong shaving motions that he can reasonably improve upon. Given that on some portions of the face the user is even forced to perform linear shaving motions, like under the nose area and around single hairs, these assumed wrong shaving motions are differentiated from wrong shaving motions that can be reasonably avoided. The user cannot perform large sized linear shaving motions under the nose as he can perform on other portions of the face, such as the cheeks. Therefore, according to the present invention motion shape and size detection is used to differentiate between wrong (large) linear shaving motions and acceptable (small) linear shaving motions.

[0013] According to the present invention, feedback of a first type is provided to the user of a rotary shaver in case the detected shaving motion is a wrong motion that the user can reasonably improve upon, i.e., in case the detected shaving motion is determined to be a linear motion having a size above a threshold representing a large (sized) linear motion and a correction of the motion performed by the user should be made. The feedback of the first type may indicate incorrect / non-preferred motion that can reasonably be avoided. It may be or represent an alarm or an advice to the user to start smaller and / or more circular motion.

[0014] In case the detected motion is determined to be a correct or a non-preferred but acceptable motion that the user cannot reasonably improve upon, and no correction of the motion performed by the user is needed, feedback of another type, different from the feedback of the first type, is provided to the user. In other words, feedback of the other type is provided in case the detected motion is determined to be rotational (or circular) motion or linear motion of a size below the threshold (i.e. small linear motion). The feedback of the other type might be feedback, which is provided to the user in case the detected motion is determined to be a correct motion or a non-preferred but acceptable motion that the user cannot reasonably improve upon. The feedback of the other type might be feedback, which is provided to the user in case that feedback of the first type is not provided. The feedback of the other type may thus indicate correct / preferred or acceptable motion. It may be or represent an advice to the user to continue performing motions like the last motion(s).

[0015] Feedback may be provided in any form that can be sensed by the user, such as audible feedback, visual feedback, haptic feedback, feedback in the form of text and / or images, etc. The feedback of the other type generally differs from the feedback of the first type. Not providing or issuing feedback of the first type may be considered as an embodiment of feedback of the other type which is different from the feedback of the first type. For example, in case feedback is provided by means of an LED, feedback of the first type may be provided by switching on the LED and feedback of the other type may be provided by switching off the LED or by changing one or more of the color, light intensity, blinking frequency, etc. of the LED. According to the present invention, continuous feedback can thus be provided to the user.

[0016] The feedback of the first type may be regarded as an alarm / alert or a recommendation, while the feedback of the other type may be regarded as a confirmation of correct motion or advice to continue with the same type of motion.

[0017] The (shaving) motion of the shaver is the motion performed by the user of the rotary shaver when moving the shaver relative to the face during shaving. The shaving motion of the shaver may be divided into a plurality of single motions. In particular, a single motion of the shaver can be defined as a continuous contact of the shaver with the skin between an initial point, respectively location, at which the shaver makes contact with the skin and a final point at which the shaver loses contact with the skin. Alternatively, a motion of the shaver can also be defined in that it ends when it reaches a point on the skin for a second time during continuous contact with the skin. The end of the motion might then initiate the start of a next motion. The motion of the shaver on the user's skin can be described by a location trail.

[0018] The location trail can be described as an imaginary line defined by following the motion of the shaver on the user's skin, wherein the shaver is in continuous contact with the skin. The location trail defines a series of locations that the shaver successively passes through as it moves along the trail.

[0019] The expression size of a motion can be described by the maximum distance that the shaver travels on the skin during one motion. The maximum distance can be the distance between the starting location of a shaver motion on the user's skin and the most distant location on the location trail, wherein the most distant location defines a longest direct line to the starting location. In other words, the maximum distance can be a maximum displacement of the shaver on the user's skin without losing contact to the skin. Alternatively, the expression size of a motion may describe a length of the location trail of the motion.

[0020] In an embodiment of the method according to the invention, the feedback of the other type is feedback of a second type if the monitored motion is determined to be a circular motion and feedback of a third type if the monitored motion is determined to be a linear motion having a size equal to or below the threshold. As mentioned above, the feedback of the other type is different from the feedback of the first type and may be of the second type or the third type. The feedback of the second type and the feedback of the third type may be of the same kind or even identical or may be different from each other. For example, the feedback of the second type may advise the user to continue circular motions, and the feedback of the third type may be provided to the user by not providing or issuing the feedback of the first or second type or may advise the user to better perform circular motions if possible. The feedback of the second type as well as the feedback of the third type may each be provided in any form as described above, e.g. in any form that can be sensed by the user, such as audible feedback, visual feedback, haptic feedback, feedback in the form of text and / or images, etc.

[0021] In an embodiment of the method according to the invention, the control signal is configured to suppress the feedback of the first type if the monitored motion is determined to be a circular motion or a linear motion having a size below the threshold. As explained above, small linear motions may be unavoidable in certain situations (e.g. when shaving under the nose area). Thus, according to this embodiment, feedback of the first type is suppressed or the trigger to issue the feedback of the first type is not generated or suppressed if the monitored motion is determined to be a circular motion or a linear motion having a size equal to or below the threshold. For instance, although for large linear motions an alarm as feedback of the first type may be generated, it may not be issued for small linear motions. In this way, the credibility of the feedback may be improved. In another embodiment of the method according to the invention, the control signal configured to trigger feedback of the first type is not generated, if the monitored motion is determined to be a circular motion or a linear motion having a size below the threshold.

[0022] In a further embodiment of the method according to the invention, the method further comprises a step of providing feedback to the user based on the generated control signal. The feedback may be provided by the shaver or by an external entity, e.g. a smartphone or other user device that is communicatively coupled with the shaver, such as an external display.

[0023] In a further embodiment of the method according to the invention, determining the size of the monitored motion includes the steps of: obtaining a plurality of latest samples of the monitored motion from the obtained motion data; smoothening the obtained motion data, in particular the plurality of the latest samples; extracting a trend from the smoothed motion data; determining a difference between a maximum and a minimum value of the trend; and thresholding the difference to determine if the size of the monitored motion exceeds the threshold.

[0024] The latest samples can be motion data representing the monitored motion. In particular, each sample may be a 3D value (x, y, z-value) of the motion data. The samples may be taken during a time interval, wherein a sampling frequency defines a number of samples taken during the time interval. The sampling frequency may be defined by the motion sensor or may be set in advance. The latest samples may be samples of one or of a plurality of motions of the shaver that the user performed last in the past.

[0025] Smoothening of the obtained motion data can for example be performed by using mean average filtering of the obtained motion data to remove noise.

[0026] Extracting the trend from the smoothed motion data may be performed by computing a trend line that shows the general direction of the smoothed motion data, respectively of the samples, over time. This can be a straight line or a line comprising many individual straight lines in case linear regression is used to extract the trend. Alternatively, this can be a curved line or a line comprising many individual curved lines in case polynomial regression or exponential smoothing is used to extract the trend. Alternatively, this can be a combination of straight and curved lines. In particular, the method which is used to extract the trend may be selected depending on the characteristics of the motion data.

[0027] Determining the difference between a maximum and a minimum value of the trend can be performed by computing the peak-to-peak difference of maximum and minimum values of the trend. Particularly, a local spread over the monitored interval of the latest samples can be detected this way. It has been found that as a (stroke) length of the monitored motion decreases, the spread decreases. In other words, the spread of the motion data over the monitored interval of the latest samples corresponds to the length of the monitored motion. To threshold the difference, the difference may be compared to a set value as the threshold.

[0028] In a further embodiment of the method according to the invention, a number of the latest samples is set in advance or is determined by a time interval. The number may be predetermined or set by a user or may be dynamically adapted.

[0029] In a further embodiment of the method according to the invention, extracting the trend from the smoothed motion data is performed using exponential smoothing or by performing linear regression, wherein a gravity component is extracted from the obtained motion data. By extracting the gravity component from the obtained motion data, respectively acceleration data, linear acceleration data can be achieved. Usually, the gravity component can only be extracted reliably from an acceleration signal by using a gyroscope as well. However, it has been observed that for the shaving application the motions of the shaver are generally of an oscillatory nature. Removal of the gravity component using linear regression without the need for a gyroscope can thus be achieved.

[0030] In a further embodiment of the method according to the invention, the threshold is a predetermined value or is computed based on the motion data. For example, to compute the value of the threshold based on the motion data the threshold may be determined based on a predefined upper bound on the fraction of time that alarms are generated. In this case, there may be a learning period during the initial phase of a shaving session to adapt the threshold to the (specific) motions performed by the present user. In case the threshold is a predetermined value, the value may be related to a dimension of the rotary shaver, in particular a diameter of a round hair-cutting unit of the rotary shaver. The value may be between 90% and 180% of said diameter. In particular, the value may be between 18 mm and 45 mm. Preferably, the value may be between 25 mm and 35 mm. For reference, a typical diameter of a hair-cutting unit of a rotary shaver is approximately 20 mm to 25 mm, although other values of the diameter can be used.

[0031] In a further embodiment of the method according to the invention, the step of determining a size of the monitored motion based on the obtained motion data is carried out only if the shape of the monitored motion is determined to be linear. In other words, only the samples representing a linear motion are further analyzed. In this way, the required computing power can be reduced.

[0032] In a further embodiment of the method according to the invention, determining the shape of the monitored motion includes the steps of: obtaining a plurality of latest samples of the monitored motion from the obtained motion data; smoothening the obtained motion data, in particular the plurality of the latest samples; extracting a trend from the smoothed motion data; computing features from the remaining linear motion data or the trend, in particular such as speed, amplitude, and motion ratio; running a machine learning model to compute, based on the computed features, a likelihood of the monitored motion being a circular motion; and determining that the monitored motion is a circular motion if the computed likelihood is more than 50%, and determining that the monitored motion is a linear motion if the computed likelihood is less than 50%.

[0033] In particular, said steps of obtaining, smoothening and extracting may be performed in the same way as described above.

[0034] The features can be computed from the obtained motion data. For example, in case the obtained motion data is acceleration data, speed data can be computed by integration of the linear acceleration data over time. Motion ratio and amplitude can be computed by first integrating twice and then estimating motion ratio and amplitude. In case the monitored motion is a circular motion, the three-dimensional linear acceleration data (being acceleration minus the gravity component) can be taken to approximate a three-dimensional position of the shaver. One-dimensional speed can thus be approximated by taking the successive differences of pairs of samples in the set of latest samples, and computing the Euclidean Distance of each difference, and further taking the average therefrom, and multiplying the average with the sampling frequency. One-dimensional amplitude can be estimated by taking the Euclidean Distance of the three-dimensional linear acceleration data and taking its mean value. The motion ratio can be estimated by taking the Euclidean Distance of the three-dimensional linear acceleration data and computing its standard deviation divided by its mean value.

[0035] The machine learning model may utilize the computed features as input. The machine learning model may further utilize samples of monitored motion(s) of the rotary shaver from previous shaving sessions of the user as input. The machine learning model may output the likelihood of the monitored motion being a rotational, respectively circular motion as a percentage or a comparable value. Alternatively, the machine learning model may output a likelihood of the monitored motion being a linear or stroke-like motion as a percentage or a comparable value. It is understood that the stated percentage values are to be considered as examples and may be adjusted to suit the specific requirements of the application. In particular, a degree of circularity of the monitored motion can be determined, whereby the degree is maximum when the motion is a circle.

[0036] In a further embodiment of the method according to the invention, determining the size of the monitored motion may be based on ground truth motion sizes of the monitored motion of the rotary shaver. In particular, the ground truth motion size may be utilized for tuning parameters of the machine learning model or for tuning at least one parameter of an algorithm configured to determine shape and / or size of the monitored motion based on the obtained motion data. The ground truth motion size may be determined based on the location trail of the monitored motion. Particularly, the ground truth motion size may be determined based on detecting the end of a previous motion and the start of the next motion.

[0037] In a further embodiment of the method according to the invention, determining the size of the monitored motion is based on an AI model, wherein each sample obtained in a shaving session is annotated using the ground truth motion size of the monitored motion, in particular wherein a LSTM-based (Long Short-Term Memory) network is trained using the binary cross-entropy loss-function, which penalizes the disparity between the predicted labels and the ground truth labels, using as input either the obtained motion data only, or the obtained motion data in combination with the computed features. Particularly, the ground truth motion size may be utilized to tune at least one parameter of the AI model.

[0038] In one example, the AI model is trained in advance to the use of the AI model in the method according to the invention. The AI model may be trained based on a collected dataset of one or more shaving sessions as inputs for the AI model, where the ground truth motion size has been determined, based on camera data and / or gyroscope data. Next to these inputs, the inputs may further comprise (x, y, z-value) triples from a motion sensor, respectively from an accelerometer. Training is performed by feeding the AI model with these inputs. The training is performed based on the type of AI model used. For an LSTM-based network, weights of internal parameters are estimated in an iterative fashion. However, alternative networks may also be suitable. The output (during the training of the AI model) is a yes / no classification. After training has been performed, the model can be used in the method according to the invention, whereby only the obtained motion data, respectively the accelerometer data is available. During the operation of the method according to the invention, the AI model may output an indication that can be utilized to determine the size of the monitored motion.

[0039] In another example, supervised learning is used to train the AI model on a dataset of motion data, respectively acceleration data of at least one shaving session, which included a mix of large and small motions (motions having a size above, respectively below a threshold). Each sample of motion data, respectively acceleration data has been annotated as either part of a large linear motion or not. The model in this example is an LSTM-based network. It takes a sample of acceleration data and the computed features as input to determine if the sample is a part of a large linear motion. Leveraging its memory capabilities, the LSTM-based network analyzes the temporal evolution of motions and functions as a binary classifier, outputting "True" for large linear motions and "False" otherwise. The dataset in this example comprises motion data of 25 sessions from 13 unique users, annotated using the ground truth motion size of the monitored motion based on a camera based system, wherein the monitored motion of each session is split into single motions, if multiple motions have been performed during the session. The network may for example be trained over 100 epochs, respectively run-throughs using binary cross-entropy loss to minimize the disparity between predicted labels and ground truth labels. For validation, a 13-fold cross-validation may be performed.

[0040] In a further embodiment of the method according to the invention, determining shape and size of the monitored motion can be determined after obtaining every (single) sample or once after obtaining a defined number of samples, in particular wherein the determined shapes and sizes can be smoothed using for example a moving average or a moving median filter. In this way, the feedback can be customized according to a required frequency of feedback or speed of response.

[0041] In a yet further embodiment of the method according to the invention, the step of providing feedback to the user can be based on the computed likelihood of the monitored motion being a circular motion, and the determined size of the monitored motion directly. Particularly, a feedback color displayed to the user can be based on the determined circularity of the monitored motion and / or the determined size of the monitored motion. The feedback color may be displayed during the shaving session by means of a light ring or other light element arranged on the rotary shaver.

[0042] In an embodiment of the apparatus according to the invention, the apparatus further comprises a feedback unit configured to provide feedback to the user based on the control signal. The feedback unit is for providing the feedback to the user regarding the motion of the rotary shaver performed by the user. The feedback unit is configured to provide the feedback based on the control signal generated by the processing unit. The feedback can be in any suitable or desired form, including one or more of a visual element, an audible element, a haptic (tactile) element, etc.

[0043] In a further embodiment of the apparatus according to the invention, the feedback unit comprises a light ring or other light element configured to provide optical feedback to the user. The light element may be provided on the shaver, in particular on a handle of the shaver. The light ring may be provided on the handle of the shaver circumferentially about a longitudinal axis of the handle. The light element may display the feedback color.

[0044] In an embodiment of the system according to the invention, the apparatus is part of the rotary shaver or of a separate device, in particular a digital mobile device, communicatively coupled to the rotary shaver. The separate device may be a smartphone, tablet, personal digital assistant (PDA), smart mirror, etc. Alternatively, the separate device may be a cloud-based system.

[0045] In a further embodiment of the system according to the invention, the system further comprising a feedback unit configured to provide feedback to the user based on the control signal generated by the processing unit, the feedback unit is arranged in the rotary shaver or in the separate device. The separate device and the shaver may be communicatively coupled, e.g. by use of Wi-Fi or Bluetooth or via cable.

[0046] In a further embodiment of the system according to the invention, the motion sensor comprises an accelerometer arranged in the rotary shaver.BRIEF DESCRIPTION OF THE DRAWINGS

[0047] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. In the following drawings Fig. 1(a) shows a diagram of rotational, respectively circular motion of a rotary shaver. Fig. 1(b) shows a diagram of linear motion of a rotary shaver. Fig. 1(c) shows a diagram of a location trail of an exemplary motion of the rotary shaver. Fig. 2 shows a schematic diagram of an apparatus for controlling feedback according to the present invention. Fig. 3 shows a schematic diagram of an embodiment of a system for controlling feedback according to the present invention. Fig. 4 shows a flowchart of an embodiment of a method for controlling feedback according to the present invention. Fig. 5 shows a flowchart of a further embodiment of the method according to the present invention. Fig. 6 shows an exemplary embodiment of the system according to the present invention comprising a feedback unit arranged in the rotary shaver. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] As noted above, an object of the invention is to provide feedback to a user on the (shaving) motion of a rotary shaver performed by the user. A rotary shaver is a type of shaver that cuts hairs using hair-cutting units that comprise one or more circular blades that rotate rapidly. Preferably, the rotary shaver is to be moved over the skin using a rotational motion, in particular circular motion, so that the shaver for example follows an approximately circular path on the skin of the user. A rotary shaver typically comprises at least two hair-cutting units, and preferably three hair-cutting units arranged in a triangle, although rotary shavers having different numbers of hair-cutting units and / or arrangements are available. It has been found that moving a rotary shaver with small rotational, respectively circular motions provides an improved shaving performance. Particularly, shaving performance can be improved in terms of reducing skin irritation.

[0049] Fig. 1(a) shows a diagram of rotational, respectively circular motion of a rotary shaver 8. Fig. 1(a) further shows a shaving unit 200 of the rotary shaver 8, the shaving unit 200 having three round hair-cutting units 202 arranged in a triangular configuration. The geometrical center or midpoint of the shaving unit 200 is marked as 204. Distance A is shown that is the diameter of the shaving unit 200 and in particular is the diameter of a circle that circumscribes the shaving unit 200. In a typical shaving unit 200, the distance A is approximately 5cm - 6cm, although other sizes can be used, and for reference the typical diameter of a hair-cutting unit 202 is approximately 2cm - 2.5cm, although again other sizes can be used.

[0050] The (shaving) motion shown in Fig. 1(a) is a single circular motion of the shaver 8, respectively the shaving unit 200. Dashed circle 206 shows the circular path taken by the center 204 of the shaving unit 200. Shaver 8' represents the shaver 8 after approximately 180 degrees of a full rotation along the circular path 206. Dashed circle 206 can be described as a location trail of the motion. The location trail in Fig. 1(a) is a closed circular contour around a center point 208 of the circle 206. In an alternative embodiment however, the motion might also be defined as a rotational or a circular motion, if the location trail 206 is no geometrical circle, but instead an approximately circular or elliptical path. The location trail 206 can describe the shape of the motion.

[0051] In the example in Fig. 1(a) the diameter of the circular path 206 of the rotational motion is equal to the diameter A of the shaving unit 200. However, the diameter of the circular path 206 can be smaller or greater than the diameter A, describing circular motions of different sizes.

[0052] Fig. 1(b) shows the shaving unit 200 as shown in Fig. 1(a) in a diagram of a linear motion of the rotary shaver 8. The (shaving) motion shown in Fig. 1(b) is a single linear motion of the shaver 8, respectively the shaving unit 200. Dashed line 210 shows a straight, respectively linear path taken by the center 204 of the shaving unit 200. In Fig. 1(b) the shaver 8 is in its initial position and the shaver 8' represents the shaver 8 in its final position. Dashed line 210 can be described as the location trail of the motion. The location trail in Fig. 1(b) is a straight line. However, in an alternative embodiment, the motion might also be defined as a linear motion, if the location trail 210 is no geometrical straight line, but instead an approximately straight line (an example of this is shown in Fig. 1(c)). The location trail 210 can describe the shape of the motion.

[0053] The linear motion of Fig. 1(b) is of a determined size. Since in this example, the motion is represented by a straight location trail, the size of the motion can be described by the length of the location trail 210 of the motion. In the example in Fig. 1(b), the length of the straight path 210 of the linear motion is equal to twice the distance B of the shaving unit 200. However, the length of the straight path 210 can be smaller or greater than the distance B, describing linear motions of different sizes.

[0054] Fig. 1(b) illustrates an exemplary definition of the size of a linear motion. A linear motion having a size below a threshold, respectively a small linear motion can be, for example, a stroke where the length of the stroke is such that there is at least one point on the user's skin that is always covered by the shaving unit 200, i.e. in contact with the shaving unit 200, during the linear motion. Following this definition, a linear motion having a size above a threshold, respectively a large linear motion can be a stroke wherein the length of the stroke is such that there is no point on the user's skin that is always covered by the shaving unit 200 during the linear motion. Fig. 1(b) shows a linear motion with a stroke length at the boundary between small linear motion and large linear motion according to this definition. In other words, this can be an example how geometrical dimensions of the shaver 8, in particular of the shaving unit 200 may be used as the threshold. This will be described in the following.

[0055] For example, distance B can be defined to be the same length as the diameter of a hair-cutting unit 202. It will be appreciated from Fig. 1(a) that in this example 2*B is slightly smaller than distance A in Fig. 1(a). In this definition, therefore, small linear motion is a stroke along the straight path with a length that is equal to or less than the distance 2*B. Dashed line 210 shows the straight path, respectively location trail 210 taken by the shaving unit 200 when the length of the path is 2*B. Thus, it can be seen that there is a point 212 on the user's skin at the midpoint of the straight path 210 that will always be covered during the linear motion if the stroke length is equal to or less than 2*B. Any stroke lengths greater than 2*B will imply that the midpoint of the path 210 on the user's skin will not always be covered by the shaving unit 200 during the linear motion, and in this example stroke lengths greater than 2*B are considered to be large linear motion. It will be appreciated that in alternative embodiments a different definition of large linear motion and small linear motion can be used, for example wherein large linear motion is a stroke motion with a length greater than distance A in Fig. 1(a) and small linear motion is a stroke motion with a length equal to or smaller than distance A. In this example, distance B defines the threshold. Particularly, 2*B is the threshold.

[0056] An alternative definition of a small linear motion can be provided by defining an alternative threshold. The threshold may be adapted to the need of the specific application, e.g. for using the shaver 8 on specific portions of the body, like under the nose area or around a single hair. Particularly, an average stroke length under the nose may be used to define the threshold, wherein data of a plurality of users may be provided to determine the average stroke length. Or a measured stroke length under the nose of a specific user may be used to define the threshold. A method to determine the size of the motion will be explained with reference to Figs. 4 and 5.

[0057] Fig. 1(c) shows a diagram of a location trail 220 of an exemplary (shaving) motion of the rotary shaver 8. The rotary shaver 8 may be the same as in Figs. 1(a), 1(b). The location trail 220 may be used to determine shape and / or size of the motion, particularly by tuning at least one parameter of an algorithm configured to determine shape and / or size of the monitored motion based on the obtained motion data. In other words, the motion can be described by the location trail 220. In this example, the location trail 220 can be represented by motion data. Therefore, it is possible to compute features from the motion data representing the location trail, in particular such as speed or via the acceleration a change of direction of the motion. Alternatively, the location trail 220 may be used to determine the shape of the motion for example, by running a machine learning model to compute, based on the computed features, a likelihood of the motion being a circular motion.

[0058] In Fig. 1(c) the motion may for example be determined as linear motion since in this instance, the likelihood of a circular motion may be less than 50%. Alternatively, or in addition, the motion can be classified as a linear or stroke-like motion as shown in Fig. 1(c) by analyzing the geometry of the location trail 220. The location trail 220 in Fig. 1(c) is not a closed contour. In this example, this can indicate a linear motion. The location trail of the linear motion starts at the starting location P0, respectively initial point of contact, and ends at a most distant location P5, respectively most distant point, in the maximum (direct) distance d05, wherein both points are connected by a continuous path. In comparison the distance from the location P0 to the location P6 is d06, which is less than d05. In Fig. 1(c), the location trail 220 makes no change of direction in the opposite direction. However, between the locations P5 and P6 there is a change of direction in the opposite direction. Therefore, the location trail 220 ends in the location P5. In other words, the location trail 220 of the motion reaches a maximum distance d05 before a change in direction occurs and the distance decreases d06, indicating a linear motion.

[0059] The following therefore describes how to determine the size of a linear motion using the location trail 220. The size of the motion can be described by the maximum distance that the shaver 8 travels on the skin during one motion. The maximum distance can be as described above the distance between the starting location P0 and the most distant location P5 on the location trail, wherein the most distant location defines a longest direct line d05 to the starting location P0. Based on a threshold, the size of a motion can then be classified as small or large by thresholding the maximum distance d05. In Fig. 1(c) the threshold may be defined as same as in Fig. 1(b).

[0060] Further, since the location trail 220 in this instance can be understood as a geometry that is derived directly from the motion data, the ground truth motion size of the monitored motion may be determined based on the location trail 220. In Fig. 1(c), the ground truth motion size can be determined based on detecting the end of a previous motion (for example ending in P0) and the start of the next motion (for example starting in P05). In other words, the ground truth motion size can be determined based on the distance d05 between the locations P0 and P5. In particular, every single distance d01 to d45 following the location trail 220 may be used in combination with the changes in direction between locations next to each other of the locations P0 to P5 to determine the ground truth motion size.

[0061] In an alternative embodiment the location trail 220 may be a closed contour and may represent a rotational or circular (shaving) motion. In this instance, the maximum distance may be a maximum diameter of the closed contour. The maximum distance can then be subjected to a threshold to determine the size of the motion. Particularly, the threshold may be defined by a ratio of a diameter of the shaving unit 200 to a diameter of the closed contour of the location trail (see for example the location trail 206 and diameter A in Fig. 1(a)).

[0062] Fig. 2 shows a schematic diagram of an apparatus 2 for controlling feedback to a user regarding motion of a rotary shaver performed by the user according to an aspect of the present invention. The apparatus 2 comprises a processing unit 4 and may optionally further comprise a feedback unit 6. In some embodiments, the apparatus 2 may be implemented as or may be part of an external device, in particular an electronic device, such as a smartphone, tablet, personal digital assistant (PDA), laptop, desktop computer, smart mirror, etc. In other embodiments, the apparatus 2, and particularly the functionality according to the invention provided by the apparatus 2, may be part of the rotary shaver.

[0063] The processing unit 4 generally controls the operation of the apparatus 2. The processing unit 4 is particularly configured to obtain (i.e. retrieve or receive) motion data from a motion sensor monitoring the motion of the rotary shaver performed by the user and to generate a control signal configured to trigger feedback to the user.

[0064] The motion data may be a signal from the motion sensor. The motion data may be measurements of motion of the rotary shaver acquired by the motion sensor, e.g. an accelerometer arranged in the rotary shaver. The motion data may represent single or multiple motions of the rotary shaver performed by the user.

[0065] The processing unit 4 may be any kind of means configured to process signals, in particular motion data, and determine shape and size of the monitored motion there from. It may be implemented in software and / or hardware, e.g. as a programmed processor or computer or app on a user device such as a smartphone, smartwatch, tablet, laptop, PC, workstation, rotary shaver, etc.

[0066] The processing unit 4 can comprise or be associated with a memory unit (not shown in Fig. 2), such as a volatile or non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM. The memory unit can be used for storing program code that can be executed by a processor in the processing unit 4 to cause the apparatus 2 to perform the various functions and methods described herein. In particular embodiments, the program code can be in the form of a smart phone application or tablet application.

[0067] The processing unit 4 may be directly coupled or connected to the motion sensor to obtain the motion data directly from the motion sensor. Alternatively, processing unit 4 may obtain (i.e. retrieve or receive) these signals from a storage, buffer, network, or bus, etc. The processing unit 4 may thus e.g. utilize a (wired or wireless) communication interface or data interface, such as a Bluetooth interface, Wi-Fi interface, LAN interface, HDMI interface, direct cable connector, or any other suitable interface allowing signal transfer to the processing unit 4.

[0068] In some embodiments, the processing unit 4 can be configured to obtain information, in particular shape and size, of the monitored motion of the shaver performed by the user via signals from another component of the apparatus 2 and therefore the processing unit 4 can include or comprise one or more input ports or other components for receiving the information, as mentioned above, from the other component. In other embodiments, the processing unit 4 can determine shape and size of the monitored motion based on the obtained motion data obtained by the processing unit 4. Therefore, the processing unit 4 can include or comprise one or more input ports or other components for obtaining motion data of the monitored motion of the rotary shaver from the motion sensor.

[0069] In some embodiments, the processing unit 4 can signal the control signal to a feedback unit 6. In particular, the processing unit 4 may be configured to signal the determined shape and size of at least one motion of the shaver to another component of the apparatus 2. Therefore, the processing unit 4 can comprise one or more output (ports) or other components for signaling the control signal to be provided to the feedback unit 6. The output may generally be any interface that provides the determined signal or information, e.g. transmits it to another device or provides it for retrieval by another device (e.g. a smartphone, computer, tablet, etc.). It may thus generally be any (wired or wireless) communication or data interface.

[0070] The feedback unit 6 is for providing feedback to the user on the monitored motion of the rotary shaver performed by the user. The feedback can be in any suitable or desired form, including one or more of a visual element, an audible element, a haptic (tactile) element, etc., and the feedback unit 6 can be in a form that is able to provide or output those elements. The visual element can comprise a message in the form of letters, numbers, symbols, pictures, a video message, etc. and therefore the feedback unit 6 can comprise or be a display screen, such as that used on a smart phone, tablet, smart mirror or other personal electronic device. Alternatively (or in addition), the visual element can be provided using one or more lights (e.g. one or more light emitting diodes (LEDs)) having one or more colors (e.g. red, orange, yellow, green, etc.). In a preferred embodiment the visual element can be a light ring, particularly provided on the handle of the shaver or on or around the shaver head. Preferably, the light ring is provided on the handle of the shaver circumferentially about a longitudinal axis of the handle (see e.g. Fig. 6). The audible element can comprise a tone or beep, a verbal message, etc., and therefore the feedback unit 6 can comprise a speaker for generating the required audio. The haptic element may comprise a vibration of a particular intensity and / or duration, and therefore the feedback unit 6 can comprise a component that can generate vibrations, for example a vibration motor. It will be appreciated that the feedback to be provided may comprise multiple forms of feedback (e.g. visual and audible), and therefore feedback unit 6 can be configured or capable of providing feedback of the appropriate form(s). It will be appreciated that certain devices, for example a smart phone or tablet, typically comprises components capable of providing the different forms of feedback set out above.

[0071] It will be appreciated that the apparatus 2 may comprise additional components to those shown in Fig. 2. For example, the apparatus 2 may comprise a power source, such as a battery, or a power interface component, such as plug, for connecting to the apparatus 2 to a mains power supply. The apparatus 2 may also or alternatively comprise a user interface that can enable a user to interact with the apparatus 2, for example to activate or deactivate the apparatus 2, and / or to control one or more settings or operations of the apparatus 2. The user interface can comprise any one or more of a touch screen, button, switch, keypad, keyboard, mouse, stylus, etc.

[0072] Fig. 3 shows a schematic diagram of an embodiment of a system 7 for controlling feedback according to the present invention. The system 7 may comprise the apparatus 2 of any one of the embodiments described above. The system 7 further comprises a rotary shaver 8 and a motion sensor 12 configured to monitor motion of the rotary shaver. In Fig. 3 a specific embodiment of the apparatus 2 is shown as part of the system 7. In this embodiment, the apparatus 2 is a separate device to the rotary shaver or may be part of a separate device to the rotary shaver. The system 7 comprises the apparatus 2, respectively the separate device and the rotary shaver 8. The apparatus 2, respectively the separate device, which may also be referred to as a feedback device, comprises a processing unit 4 and feedback unit 6 as described above, and may further comprise a transceiver or receiver unit 10 that is configured to receive signals, particularly motion data, from the rotary shaver 8. The transceiver or receiver unit 10 can be configured to operate according to any desired wireless or wired communication standard, for example Ethernet, Bluetooth, Wi-Fi, ZigBee, NFC, or any 3rd, 4th or 5th generation cellular telecommunications standard or any one of the communication systems mentioned above.

[0073] The rotary shaver 8 comprises a motion sensor 12, a shaver processing unit 14 and may further comprise a transceiver or transmitter unit 16. The transceiver or transmitter unit 16 is configured to transmit signals from the rotary shaver 8 to the feedback device 2. The transceiver or transmitter unit 16 can be configured to operate according to any desired wireless or wired communication standard, for example Ethernet, Bluetooth, Wi-Fi, ZigBee, NFC, or any 3rd, 4th or 5th generation cellular telecommunications standard, as required in order to communicate with the transceiver or receiver unit 10 in the feedback device 2.

[0074] The motion sensor 12 is configured to monitor, particularly measure, the motion of the rotary shaver 8 during use of the shaver 8 by the user. The motion sensor 12 can be configured to generate motion data, representing motion of the shaver 8. The motion sensor 12 is preferably integral with or otherwise fixed to the shaver 8 so that the motion sensor 12 directly measures the motion of the rotary shaver 8 performed by the user. In some embodiments, the motion sensor 12 is an accelerometer, for example that measures acceleration along three orthogonal axes. Alternatively or in addition, the motion sensor 12 can comprise a gyroscope or a magnetometer.

[0075] The shaver processing unit 14 may generally control the operation of the rotary shaver 8, for example by activating and deactivating one or more hair-cutting units to affect a shaving or other hair cutting operation. The shaver processing unit 14 can be implemented in numerous ways, with software and / or hardware, similarly to the processing unit 4 in the feedback device 2.

[0076] The shaver processing unit 14 is connected to the motion sensor 12 and is configured to obtain motion data from the motion sensor 12 monitoring the motion of the rotary shaver 8 performed by the user. In other words, the processing unit 14 is configured to receive or retrieve measurements of the motion of the rotary shaver 8 from the motion sensor 12, for example via an input port to the shaver processing unit 14.

[0077] Generally, there may be different options to process the motion data, to generate the control signal and to provide the feedback to the user. Further, there may be different options regarding in which device the motion data are processed, in which device the control signal is generated and in which device the feedback is provided to the user. Independent of the location of the respective units performing these steps it holds that the control signal is configured to trigger feedback of a first type if the monitored motion is determined to be a linear motion having a size above a threshold, wherein the control signal is further configured to trigger feedback of another type, different from the first type, if the monitored motion is determined to be a circular motion or a linear motion having a size below the threshold. In other words, feedback of the first type (e.g. an alert or recommendation) is provided in case of small linear motions, whereas in other cases of motion feedback of the other type (e.g. a confirmation, a signal to continue, etc.) is provided. Particularly, the processing unit generates the control signal configured to trigger feedback of a first type only if the monitored motion is determined to be a linear motion having a size above a threshold.

[0078] In some embodiments, the shaver processing unit 14 may output the motion data (e.g. raw acceleration data) of the motion to the transceiver or transmitter unit 16 for transmission to the feedback device 2 for subsequent processing performed by the processing unit 4. In this case the processing unit 4 may generate the control signal and the feedback unit 6 may provide feedback to the user based on the control signal.

[0079] Alternatively, the feedback unit 6 may be arranged in the rotary shaver 8. In this case, the processing unit 4 may generated and output the control signal to the rotary shaver 8, respectively the feedback unit 6 in the rotary shaver 8.

[0080] In alternative embodiments, the shaver processing unit 14 processes the obtained motion data to determine shape and size of the monitored motion based on the obtained motion data and generates the control signal. In this case, the shaver processing unit 14 may output the control signal to the transceiver or transmitter unit 16 for transmission to the feedback device 2, respectively to the feedback unit 6. In this case, the system 7 may comprise an apparatus 2, that is part of the rotary shaver 7 and the apparatus 2 may comprise the processing unit 14.

[0081] In another embodiment of Fig. 3 the feedback device 2 is part of the rotary shaver. In this embodiment, the feedback unit 6 is arranged in the rotary shaver 8. In other words, the shaver 8, by means of the processing unit 4, is configured to process the obtained motion data and generate the control signal and feedback is provided to the user by the feedback unit 6 that is arranged in the shaver 8 as well in this embodiment.

[0082] The feedback unit 6 is configured to provide feedback to the user based on the control signal. Particularly, the feedback unit 6 can be used to give feedback to the user on the shaving behavior. The feedback may be feedback of a first type or another type, different from the first type. As explained above by reference to different embodiments, the feedback unit 6 can be arranged in the rotary shaver 8 or in the separate device 2. While shaving using the rotary shaver 8 equipped with an accelerometer or other motion sensor 12, the motion of the shaver 8 is monitored by the motion sensor 12. The motion sensor 12 is configured to generate motion data, representing motion of the shaver 8. Further, the obtained motion data is then analyzed by the processing unit 4. If the user moves the shaver 8 using rotational motions, e.g. the shaver 8 follows a generally circular or elliptical path on the body of the user, the user can be notified via the feedback unit 6 that the monitored motion is correct. If the user moves the shaver 8 using small linear motions, e.g. the shaver 8 follows a generally linear, straight or stroke-like path on the body of the user, wherein the motion has a size below a threshold, the user can be notified via the feedback unit 6 that the monitored motion is correct. Correct motion is indicated by feedback of the other type. However, if the user deviates from performing correct motions described above with the shaver 8, in particular if the user moves the shaver 8 using large linear motions having a size above the threshold which is considered as wrong / incorrect motion, the user can be notified via the feedback unit 6 that the motion should be changed, in particular to rotational motion. Wrong / incorrect motion is indicated by feedback of the first type.

[0083] In an exemplary embodiment, the feedback unit 6 may comprise a light ring as a visual element configured to provide visual feedback to the user. The light ring may be provided on the shaver, in particular on a handle of the shaver. The light ring may display a feedback color. For example, for providing feedback of the first type (indicating incorrect / non-preferred motion) in case the monitored motion is determined to be a linear motion having a size above the threshold, the light ring may emit red light. To provide feedback of the other type (indicating correct / preferred motion), in case the monitored motion is determined to be a circular motion or linear motion of a size smaller than the threshold, the light ring emit green light (or may be switched off). The feedback color(s) may, of course, be any other suitable color(s). Further, in addition to or instead of colors other parameters may be controlled, like intensity of the light, periodicity of blinking of the light, etc.

[0084] Fig. 4 shows a flowchart of an embodiment of a method 100 of controlling feedback to a user regarding motion of the rotary shaver 8 performed by the user according to the present invention. The steps of the method 100 may be carried out by the apparatus 2, wherein the main steps of the method can be carried out by the processing unit 4. The method 100 may e.g. be implemented as computer program running on a computer or processor. In addition, some steps may be performed by the feedback unit 6.

[0085] In a first step 102, motion data from a motion sensor 12 monitoring the motion of the rotary shaver 8 performed by the user is obtained. The motion data can be data representing measurements of at least one motion. In some embodiments, the motion data are received or retrieved from the motion sensor 12 by the processing unit 4.

[0086] Next, in step 104, the shape of the motion is determined based on the motion data, the shape indicating if the monitored motion is determined to be rotational, respectively circular or linear, respectively stroke-like. In some embodiments, the shape of the motion is determined by the processing unit 4 in the same or similar way as described above with reference to Figs. 1(c) and 3.

[0087] In step 106, the size of the motion is determined based on the motion data. In some embodiments, the size of the motion is determined by the processing unit 4 before, after or in parallel to step 104. In a preferred embodiment, step 106 is carried out after step 104. In an alternative preferred embodiment of the method 100, as shown in Fig. 4, step 106 is carried out only if the shape of the motion is determined to be linear. The processing unit 4 may determine the size of the motion from acceleration data. Particularly, the processing unit 4 may utilize the ground truth motion size of the monitored motion to tune parameters of an algorithm configured to determine the size of the monitored motion.

[0088] Next, in steps 108, 109, a control signal is generated by the processing unit 4, 14. The control signal as generated in step 108 is configured to trigger feedback of a first type, particularly only, if the monitored motion is determined to be a linear motion having a size above a threshold. The control signal as generated in step 109 is configured to trigger feedback of another type, different from the first type, if the monitored motion is determined to be a circular motion or a linear motion having a size below the threshold. The control signal may be generated (step 109) directly after step 104, if the determined shape of the motion is determined to be rotational, respectively circular to trigger feedback of the other type.

[0089] In some embodiments of the method 100, step 110 follows step 108 and step 111 follows step 109. In steps 110, 111, feedback is provided to the user based on the control signal. In step 110, feedback of the first type is provided, if the determined size of the motion is above the threshold. In step 111, feedback of the other type is provided, if the determined size of the motion is below the threshold. The feedback triggered by the control signal is provided by the feedback unit 6 included in a separate device or by a feedback unit included in the shaver 8. For example, feedback of the first type can be provided by means of a light ring of the feedback unit 6 illuminated in red. Feedback of the other type can be provided by means of the light ring illuminated in green.

[0090] The feedback of the first type is provided to the user in case the detected motion is a wrong motion that the user can reasonably improve upon so that the user may change the motion to improve shaving performance. For instance, the feedback of the first type may advise the user to start smaller and / or more circular motion.

[0091] The feedback of the other type is provided to the user in case the detected motion is a correct motion or is a wrong or non-preferred but acceptable motion that the user cannot reasonably improve upon, and no correction of the motion performed by the user is needed. Particularly, in case that the detected motion is determined to be a rotational, respectively circular motion or a linear motion of a size below the threshold, the feedback of the other type may advise the user to continue performing motions like the last ones or latest one. In particular, the feedback of the other type can be feedback of a second type if the monitored motion is determined to be a circular motion and feedback of a third type if the monitored motion is determined to be a linear motion having a size equal to or below the threshold. For example, feedback of the second type can be provided by means of the light ring of the feedback unit 6 illuminated in green. Feedback of the third type can be provided by means of the light ring illuminated in blue or is switched off or alternatively, the light ring may illuminate in green with a light intensity or blinking frequency different to the feedback of the second type. It is understood that these are only examples, and that the skilled person will be aware of many possibilities for varying the form of the feedback, as described above.

[0092] Fig. 5 shows a flowchart of a further embodiment of the method 100 according to the present invention. Fig. 5 particularly illustrates an exemplary embodiment of implementing step 106 in more detail, wherein determining the size of the motion further includes steps 112 to 120.

[0093] In step 112, a plurality of latest samples of the monitored motion from the motion data is obtained. This means that, for example, the latest 50 samples of the monitored motion are obtained from the motion data. However, every other suitable number of samples may be considered. Alternatively, the number of obtained samples may be determined by a set period of time, respectively a time interval of monitoring the motion of the shaver 8.

[0094] Next, in step 114, the motion data, in particular the plurality of the latest samples, is smoothed. This can for example be performed by using mean average filtering of the motion data to remove noise. Those skilled in the art will be aware of various techniques that can be used to smoothen the motion data.

[0095] Next, in step 116, a trend from the smoothed motion data is extracted. In particular, a trend line is computed that shows the general direction of the obtained motion data, respectively of the samples, over time. In particular, each sample may be represented by a point on the trend line. The step 116 can include performing a linear regression to compute the trend line. This results in the trend being a straight line or a line comprising many individual straight lines. In this case a plurality of samples is represented by the line that is approximated to the points of the plurality of samples, wherein each point may represent a computed feature of each sample. Alternatively, the step 116 can include performing a polynomial regression or an exponential smoothing to extract the trend. This results in the trend being a curved line or a line comprising many individual curved lines. In an alternative embodiment, the step 116 can include performing a linear regression and / or a polynomial regression and / or an exponential smoothing to compute the trend line. In a preferred embodiment, the step 116 is performed by providing a decreased weight for each sample depending on the time difference to the latest sample or depending on the difference in number count of the samples, wherein a greater difference in time or number count to the latest sample results in a larger decrease in weight of each sample. This can e.g. be achieved by exponential smoothing.

[0096] Next, in step 118, a difference between a maximum and a minimum value of the trend is determined. For example, the step 118 can be performed by computing a peak-to-peak difference of maximum and minimum values of the trend. Particularly, the step 118 may include detecting a local spread over the monitored (time) interval of the latest samples.

[0097] Next, in step 120, the difference between the maximum and the minimum value of the trend is subjected to a threshold to determine if the size of the motion exceeds the threshold or not. After the latest sample is obtained and the steps 112 to 118 are carried out, the difference of the trend is compared to the threshold. In case the difference of the trend of the latest samples is above the threshold, thresholding the trend indicates that the (latest) monitored motion has a size above the threshold. In case the difference of the trend of the latest samples is below the threshold, thresholding the trend indicates that the (latest) monitored motion has a size below the threshold. In the following based on the determination of the size of the motion, steps 108, 109 of the method 100 (as illustrated in Fig. 4) can be executed based on the result of step 120.

[0098] Fig. 6 illustrates an exemplary embodiment of a rotary shaver 8 according to the invention comprising means for providing feedback to the user. In this embodiment, a feedback unit is provided in the form of a light ring 20 located on the handle 22 of the shaver 8. Alternatively, or in addition, the feedback can be provided in the form of a display screen 24. As described above, feedback can be provided in various ways, e.g. as visual feedback (as shown in Fig. 6), audible feedback (e.g. by means of a loudspeaker or sound generator) and / or as haptic feedback (e.g. by means of a vibration unit). The shaver 8 may further provide controls and / or interactive elements 26, 28 configured to input user controls and / or provide feedback to the user.

[0099] As shown in Fig. 6, the light ring 20 is switched on in a certain color (e.g. red) to indicate feedback of the first type. This way, the light ring 20 provides feedback indicating incorrect or non-preferred (large linear) motion. This feedback may be understood by the user to start smaller linear motion and / or, even more preferred, more circular motion.

[0100] Feedback of the other type may be provided by the light right 20 by showing a different color (e.g. green) or turning dark / being switched off (i.e., by not providing feedback of the first type). In particular, in case the feedback of the other type may be feedback of the second type, the feedback of the second type may be provided by the light right 20 by showing the different color (e.g. green) and in case the feedback of the other type may be feedback of the third type, the feedback of the third type may be provided by the light right 20 turning dark / being switched off. This way, the feedback indicates correct, respectively preferred or acceptable motion, i.e. circular motion or linear motion of a size smaller than the threshold. This feedback may be understood by the user to continue performing the current motion(s).

[0101] The feedback may be provided for every single detected motion or once after a defined number of detected motions or after a time interval or at regular or irregular intervals. Further, feedback may be provided in case an incorrect / undesired motion is detected.

[0102] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0103] 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 element 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.

[0104] A computer program may be stored / distributed on a suitable non-transitory medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0105] Any reference signs in the claims should not be construed as limiting the scope.

Examples

Embodiment Construction

[0048]As noted above, an object of the invention is to provide feedback to a user on the (shaving) motion of a rotary shaver performed by the user. A rotary shaver is a type of shaver that cuts hairs using hair-cutting units that comprise one or more circular blades that rotate rapidly. Preferably, the rotary shaver is to be moved over the skin using a rotational motion, in particular circular motion, so that the shaver for example follows an approximately circular path on the skin of the user. A rotary shaver typically comprises at least two hair-cutting units, and preferably three hair-cutting units arranged in a triangle, although rotary shavers having different numbers of hair-cutting units and / or arrangements are available. It has been found that moving a rotary shaver with small rotational, respectively circular motions provides an improved shaving performance. Particularly, shaving performance can be improved in terms of reducing skin irritation.

[0049]Fig. 1(a) shows a diagra...

Claims

1. A method of controlling feedback to a user regarding motion of a rotary shaver performed by the user, the method comprising the steps of: - obtaining motion data from a motion sensor monitoring the motion of the rotary shaver performed by the user; - determining shape and size of the monitored motion based on the obtained motion data, the shape indicating if the monitored motion is circular or linear; and - generating a control signal configured to trigger feedback of a first type to the user if the monitored motion is determined to be a linear motion having a size above a threshold and to trigger feedback of another type, different from the first type, to the user if the monitored motion is determined to be a circular motion or a linear motion having a size equal to or below the threshold.

2. The method as claimed in claim 1, wherein the feedback of the other type is feedback of a second type if the monitored motion is determined to be a circular motion and feedback of a third type if the monitored motion is determined to be a linear motion having a size equal to or below the threshold, wherein the feedback of the second type and the feedback of the third type are different from each other or are of the same kind or identical.

3. The method as claimed in claim 1 or 2, wherein the control signal is configured to suppress the feedback of the first type if the monitored motion is determined to be a circular motion or a linear motion having a size below the threshold.

4. The method as claimed in any one of the preceding claims, further comprising a step of providing feedback to the user based on the generated control signal.

5. The method as claimed in any one of the preceding claims, wherein determining the size of the monitored motion includes the steps of: - obtaining a plurality of latest samples of the monitored motion from the obtained motion data; - smoothening the obtained motion data, in particular the plurality of the latest samples; - extracting a trend from the smoothed motion data; - determining a difference between a maximum and a minimum value of the trend; and - thresholding the difference to determine if the size of the monitored motion exceeds the threshold.

6. The method as claimed in claim 5, wherein a number of the latest samples is set in advance or is determined by a time interval.

7. The method as claimed in claim 5 or 6, wherein extracting the trend from the smoothed motion data is performed using exponential smoothing or by performing linear regression, wherein a gravity component is extracted from the obtained motion data.

8. The method as claimed in any one of claims 5 to 7, wherein the threshold is a predetermined value or is computed based on the motion data, in particular wherein the predetermined value is between 90% and 180% of a diameter of a round hair-cutting unit of the rotary shaver or wherein the predetermined value is between 25 mm and 35 mm.

9. An apparatus (2) for controlling feedback to a user regarding motion of a rotary shaver (8) performed by the user, the apparatus comprising a processing unit (4) configured to: - obtain motion data from a motion sensor (12) monitoring the motion of the rotary shaver performed by the user; - determine shape and size of the monitored motion based on the obtained motion data, the shape indicating if the monitored motion is circular or linear; and - generate a control signal configured to trigger feedback of a first type to the user if the monitored motion is determined to be a linear motion having a size above a threshold and to trigger feedback of another type, different from the first type, to the user if the monitored motion is determined to be a circular motion or a linear motion having a size equal to or below the threshold.

10. The apparatus (2) as claimed in claim 9, further comprising a feedback unit (6) configured to provide feedback to the user based on the control signal generated by the processing unit (4).

11. A system (7) for controlling feedback to a user regarding motion of a rotary shaver (8) performed by the user, the system comprising: - an apparatus (2) as claimed in claim 9 or 10; - a rotary shaver (8); and - a motion sensor (12) configured to monitor the motion of the rotary shaver performed by the user.

12. The system as claimed in claim 11, wherein the apparatus (2) is part of the rotary shaver (8) or of a separate device, in particular a digital mobile device, communicatively coupled to the rotary shaver.

13. The system as claimed in claim 12, further comprising a feedback unit (6) arranged in the rotary shaver (8) or in the separate device.

14. The system as claimed in any one of claims 11 to 13, wherein the motion sensor (12) comprises an accelerometer arranged in the rotary shaver (8).

15. A computer program comprising program code means for causing the apparatus as claimed in claim 9 or 10 to carry out the steps of the method as claimed in any one of claims 1 to 8 when said computer program is carried out on the processing unit (4) of the apparatus (2).

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