WO2018004345A1

WO2018004345A1 - Method and module for analyzing a posture of a person

Info

Publication number: WO2018004345A1
Application number: PCT/NL2017/050435
Authority: WO
Inventors: Paulus Cornelius Helder; Bodo Rosenhahn
Original assignee: H.T. Technology B.V.
Priority date: 2016-07-01
Filing date: 2017-06-30
Publication date: 2018-01-04
Also published as: NL2017090A; NL2017090B1

Abstract

The invention relates to a method for analyzing a posture of a person. The method comprises emitting by an acoustic emitter, an acoustic signal, receiving by a first and second microphone, the acoustic signal, obtaining a reference state of the person in a reference posture, storing the reference state, obtaining a first state of the person in a first posture; and comparing the first state with the stored reference state and when the first state exceeds a comfort zone generating an alert, In this way an early alert can be given to the person when the person is exceeding comfort postures.

Description

Method and module for analyzing a posture of a person

FIELD OF THE INVENTION

The invention relates to a method and apparatus for analyzing a posture of a person.

BACKGROUND OF THE INVENTION

In the known method the person carries the apparatus attached at a belt around the body of, for example, an elderly person. The person carrying the apparatus can move freely through his environment, for example, a house. Furthermore, the known apparatus can be provided with accelerometers. When the person falls the known apparatus may detect the fall by analyzing the signals of the accelerometers and may give an alert e.g. if the signals, i.e. if one the accelerations exceeds a threshold. The alert can be an audio signal or physically transmitted to the person or can be a silent alert transmitted to a third party via a telecommunication network.

The method can also be used for analyzing a golf swing of a golf player or a tennis stroke of a tennis player.

An example of the known method and apparatus can be found in

US2010/0049096.

A drawback of the known apparatus is that the apparatus may give the alarm after the person has fallen and is laying on the ground. A further drawback is that a person carrying the apparatus with a belt around one's body is not experienced as comfortable.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method and apparatus for analyzing a posture of a person with improved accuracy of representing the posture of the person.

According to a first aspect of the invention this object is achieved in a method for analyzing a posture of a person using an apparatus comprising an orientation device, the method comprising:

emitting, by an acoustic emitter, an acoustic signal;

receiving, by a first and second microphone, the acoustic signal; obtaining a reference state of the person in a reference posture from the received signals;

storing the reference state;

obtaining a first state of the person in a first posture; and

comparing the first state with the stored reference state and when the first state exceeds a comfort zone generating an alert; wherein the comfort zone is defined as the zone wherein a person is in standing posture and is still able to correct his/her posture and wherein, when the person exceeds a threshold tilt angle and is entering a dangerous area, wherein the person may exhibit an unstable posture and has a higher risk of falling.

The invention is based on the insight that the measured reference state

representing the posture of the person in the reference state can be used to compare this reference state with the measured first state and when the difference between the first state and the reference is exceeding the comfort zone the alert is generated warning the person to correct his/her posture.

Other applications of the method according to the invention can be in sports, for example, in playing golf or tennis wherein the method provides an alert when the person is not in a preferred position for making an effective swing or strike.

In an embodiment the method comprises determining a triangle, wherein the vertices coincide with a first position, a second and a third position corresponding to a first, a second and a third reference point at the body in the reference posture;

providing a reference line defined as an altitude line through a first vertex to a side opposite the vertex,

determining the first position, the second and the third position corresponding to the first, second and third reference points at the body in the first posture; and

providing a first line defined as the altitude line through the first vertex to the side opposite the vertex;

wherein the reference state corresponds to the reference line and the first state corresponds to the first line.

The method can be repeated to obtain multiple reference states for different reference postures of the person in a standing or walking posture and the comfort zone is based on the obtained multiple reference states. The reference points coincide with the vertices of a triangle wherein for example, a top or first vertex corresponds with a point on one of the feet of a person.

In a further embodiment comparing the reference state and the first state comprises determining an angular difference between the reference line and first line and the comfort zone is defined by a threshold tilt angle between the reference line and the first line. In this way the reference state and the first state are represented as a reference line and a first line through a point at one of the feet, and a point at the neck or one of the shoulders. The comfort zone can be based on an average or median of the angular differences in the multiple reference states. The comfort zone can be defined as a range of tilt angles between the obtained reference line and the first line that have a value between 0 and a threshold value θτ. After the comfort zone is defined, the comfort zone is stored in the apparatus and the apparatus is ready for use.

When the person is moving or walking the direction of the first line is changing with respect to the direction of the reference line.

Thereafter, in an operating mode, the person wearing the apparatus can move freely through his/her environment, for example, a house or living, the first state is periodically obtained and compared to the comfort zone. If the obtained position is within the comfort zone the apparatus does not generate the alert, and if the obtained first state exceeds the comfort zone the apparatus generates the alert. The person wearing the apparatus, when hearing the alert, can then correct his/her posture. In this way the risk of falling of the person is reduced.

The invention is based on the insight that alerting the person in an earlier stage compared with the known methods, provides a larger opportunity for the person to correct his or her posture in a standing posture and return to a stable posture. To improve coordination of the body the person can be trained to be able to correct his/her posture within ones capability.

In a further embodiment determining the first, second and third position comprises: generating an acoustic signal at the first position and receiving the acoustic signal at the second and the third positions; determining a difference in a first time of arrival of the acoustic signal between the first position and the second position and a second time of arrival between the first and the third position; wherein the first reference point is selected from a point of one of the feet of the person and the second and third reference points are selected from respective points at the neck or the shoulders of the person; and determining the second and third positions with respect to the first position based on the determined difference.

In a further embodiment generating the acoustic signal comprises

generating a digital signal corresponding to a frequency modulated signal around a center frequency wherein the frequency modulation is based on a pseudo-random modulation; and converting the digital signal to the acoustic signal. In this way the sound from the sound transmitter can be uniquely characterized.

In a further embodiment the method comprises converting the received acoustic signals in a first received digital signal and a second received digital signal;

filtering the received first and second digital signal with a band filter with the center frequency of the frequency modulated signal;

wherein determining the difference in time of arrival is based on a cross correlation function with a sliding window between the first and second filtered digital signals. The difference in time of arrival corresponds to a phase difference due to a difference in path length.

In a further embodiment the method comprises receiving the acoustic signal at a fourth and a fifth reference position; determining a difference in a third time of arrival of the acoustic signal between the first reference point and the fourth reference point and a fourth time of arrival between the first and the fifth reference points; wherein the fourth reference point and fifth reference points are selected from respectively a point at an elbow and a wrist of an arm of the person; determining the positions of the first, fourth and fifth reference points based on the determined difference; determining a reference arm state or a first arm state based on the respective determined fourth and fifth positions in the reference state or the first state; wherein the reference state is based on the reference line and the reference arm state, and the first state is based on the first line and the first arm state.

In this way a further indicator of an instable posture of the person can be obtained. An instable posture in this document refers to the posture wherein the person is exposed to a higher risk of falling compared to its reference posture. Experiments have shown that the position of the arm, i.e. the wrist and the elbow with respect to the body can be an additional indicator of the posture of the person. In this way the reference state and the first state represent a posture of the body including the position of one the arms.

In a further embodiment determining the reference arm state or the first arm states comprises determining a reference projection of a line segment between the determined fourth and fifth position on the reference line; determining a first projection of the line segment between the determined fourth and fifth position on the first line;

determining the respective reference arm state and the first arm state based on the reference projection and the first projection in respectively the reference posture and the first posture.

In this way the reference arm state and the first arm state can be derived in an easy way relative to the reference cone and the first cone.

In an embodiment generating the alert comprises generating a sound signal, a visual signal or a haptic signal at a part of the body of the person and/or or an RF signal.

The haptic signal can be for example a mechanical vibration signal or an electric stimulus signal.

According to a second aspect of the invention this object is achieved by an apparatus for analyzing a posture of a person comprising

a memory for storing data;

an output device;

an acoustic emitter for emitting an acoustic signal;

a first and a second microphone for receiving the acoustic signal; and

a control unit, wherein the control unit is arranged

to obtain a reference state from the received acoustic signals in a reference posture ; to store the reference state;

to obtain a first state of the person in a first posture and

to compare the first state with the stored reference state and when the first state exceeds a comfort zone generating an alert; wherein the comfort zone is defined as the zone wherein a person is in standing posture and is still able to correct his/her posture and wherein, when the person exceeds a threshold tilt angle and is entering a dangerous area, wherein the person may exhibit an unstable posture and has a higher risk of falling.

In a further embodiment of the apparatus, the control unit is arranged to determine a triangle, wherein the vertices coincide with a first position, a second and a third position corresponding to a first, a second and a third reference point at the body in the reference posture from the received acoustic signals;

to provide a reference line defined as an altitude line through a first vertex to a side opposite the vertex,

determine the first position, the second and the third position in the first posture from the received acoustic signals; and

to provide a first line defined as the altitude line through the first vertex to a side opposite to the vertex;

In a further embodiment of the apparatus, the controller is further arranged to generate an acoustic signal at the first reference point and receiving the acoustic signal at the second and the third positions;

to determine a difference in a first time of arrival of the acoustic signal between the first positions and the second positions and a second time of arrival between the first and the third positions; wherein the first reference point is selected from a point of one of the feet of the person and the second and third reference points are selected from respective points at the neck or the shoulders of the person; and

determine the positions of the second and third positions with respect to the first position based on the determined difference.

In a further embodiment of the apparatus, the controller is further arranged to generate a digital signal corresponding to a frequency modulated signal around a center frequency wherein the frequency modulation is based on a pseudo-random modulation; and

converting the digital signal to the acoustic signal.

In a further embodiment the control unit is further arranged to convert the received acoustic signal in a first received digital signal and a second received digital signal;

to filter the received first and second digital signal with a band filter with the center frequency of the frequency modulated signal; and

to determine the difference in time of arrival based on a cross correlation function of the first and second filtered digital signals. In a further embodiment the apparatus comprises a garment comprising the first and second microphones at second and the third positions, when the person is wearing the garment, nearby the neck or one of the shoulder of the person.

In a further embodiment the apparatus is provided with a garment comprising the second and the third microphones at the second and the third positions, when the person is wearing the garment, nearby the neck or one of the shoulder of the person. The garment is for example a shirt.

In a further embodiment the apparatus is provided with a third and a fourth microphone and the control unit is further arranged to determine a fourth and a fifth positions using the third and fourth microphones for respectively the reference posture and the first posture; and

to determine a reference arm state or a first arm state based on the determined fourth and fifth positions respectively in the reference posture and the first posture.

In a still further embodiment the control unit is arranged to

determine a projection of the segment between the fourth and fifth position on the reference line or the first line;

determine a reference length or a first length of the determined projection; and the respective reference arm state and the first arm state are determined from the determined reference length or the determined first length in respectively the reference posture and the first posture.

BRIEF DESCRIPTION OF DRAWING

The above and other, more detailed aspects of the invention will be elucidated and described hereinafter, by way of example, with reference to the accompanying drawing. Therein:

Fig. 1 shows schematically an apparatus according to an embodiment of the invention; Fig. 2 shows schematically an orientation module;

Fig. 3 diagrammatically shows a person provided with the sound emitter and

microphones; Fig. 4 shows diagrammatically the position of the sound emitter and the first and second microphones.

Fig. 5 shows diagrammatically a reference state and a first state;

Fig. 6 shows a flow diagram of an embodiment of the method according to the invention; and

Fig. 7 shows diagrammatical a projection of the segment between a fourth and fifth position

DETAILED DESCRIPTION OF EMBODIMENTS

In the figures same numerals indicated like parts.

The invention is explained with reference to Figs. 1- 7. Fig. l shows schematically an apparatus 1 according to an embodiment of the invention. The apparatus 1 comprises a controller 3, a memory 4, an input module 5, an output device 6, a communication unit (7), an orientation device 10, and a first power supply 8.

The first memory 4 can be used for storage of data and programs. The input module 5 can comprise a first switch. The output device 6 can comprise a speaker, a buzzer, a light source, or an electronic-mechanic transducer for generating mechanical vibrations to a part of the body of the person wearing the electronic module 1 or an apparatus for generating an electric stimulus to a body part, for example a hand of the person.

Furthermore, the processor 3 is further arranged to control the memory 4, the orientation device 10, the input module 5 and output device 6 and the communication module 7.

The communication module 7 can comprise a wireless communication module, for example, a Bluetooth or WIFI module or a wired communication module, for example a USB module. This communication unit can also be used for communication with a computing module 13 for example a laptop, or table computer or smartphone. The communication module 7 can be used to connect a computing device 13 ( not shown) for example a laptop computer, a table computer or a smartphone to the apparatus 1. Furthermore, the first controller 3, the memory 4, the input module 5, the output device 6, the communication unit 7 and the first power supply or battery 8 can be mounted at a small PCB and/or integrated in a small package that the person can carry in a belt.

Fig.2 shows schematically the orientation device 10 comprising a sound emitter

21, first and second microphones 22, 23 according to an embodiment of to the invention. The sound emitter 21, for example can be a speaker or ultrasonic transducer and a first and second microphone. The frequency range of the speaker can be between 6kHz and 15 kHz. The frequency of the ultrasonic transducer can be in the range between 6 kHz and 60 kHz.

Furthermore, the orientation device comprises a digital-to-analog converter 24. And an analog-to-digital converter 25, both connected to the controller 3. The sound emitter 21 is connected with the controller 3 via the digital-to-analog converter 24. The microphones 22, 23 are connected via the analog-to-digital converter 25 to the controller 3. The microphones 22, 23 are sensitive in a frequency range that corresponds to the frequency of the emitted sound of the sound emitter 11. For example in the range between 6 kHz and 16 kHz.

Fig.3 shows a diagrammatically a person 30 provided with the apparatus, the sound emitter 21 and the microphones 22, 23. The sound emitter 21 can be attached to a first reference position on a first reference point on an ankle of the person by an anklet 31. The first and second microphones 22, 23 are attached to or integrated in a garment, for example a shirt 32, that is worn by the person 30. The microphones are attached such that when the person is wearing the shirt, the first microphone 22 is at a second reference position on a second reference point on the neck of the person, and the second

microphone 23 is at a third reference position on a third reference point on one of the shoulders of the person. Alternatively the first and second microphones 22, 23 are integrated in the shirt 32 such that when the person 30 is wearing the first and the second microphones 22, 23 are positioned nearby the respective left and right shoulder of the person. In both examples, the distance SI or S2 between the first and second microphones

22, 23 is assumed to be substantially constant. The reference points corresponds to the vertices of a triangle, wherein the first vertex correspond to the first reference point, in this example that can be one of the ankles. The altitude is defined a line through a vertex of the triangle perpendicular to a line containing the base, i.e the side opposite to the vertex.

Fig. 3 also shows a coordinate system x,y,z, wherein the z-axis coincides with the direction of gravity

The apparatus 1 is attached to the person via a belt 33.

In an embodiment of the invention the distance between the sound emitter 21 and the respective microphones 22, 23 is determined based on the difference between a first time of arrival of a first sound signal emitted by the sound emitter and received by the first microphone 22 at the second position and a second time of arrival of the first sound signal received by the second microphone 23 at the third position.

In an embodiment the method comprises the steps of:

composing a digital signal by the processor, the digital signal may comprise a plurality of samples for example 22500. The sampling frequency is 44100 Hz. The digital signal can comprise 5000 sequences of 0.001 s. The length of each sequence is then 441 samples and a duration of the digital signal is 5s. Each sequence represents a signal with a frequency that is the sum of a center frequency of, for example, 500 Hz plus a modulation frequency of (a -0.5) x 200 Hz, wherein a is random number between 0 and 1 that can be determined by a random generator in software for the respective sequences. The composed signal is stored in the memory 4.

The composed signal is then transferred to the sound emitter via the digital to analog converter 24. The sound emitter 21 converts the composed signal into a sound signal. The sound signal can be repeatedly transmitted. The first and second microphones 22, 23 respectively receive the sound signal. The microphones 22, 23 convert the received sound signals in electrical signals and send the electrical signals to the AD converters 25. The AD converters 25 convert the electric signal into a first and second received digital signal.

In the next step the processer determines the time difference between the time of arrival of the first and second sound signal at the first and second microphone 22, 23 on basis of a cross-correlation function with a sliding window on the first and second received digital signals. In an embodiment filtering can be applied on the received digital signals to remove unwanted disturbances. An example of such a filter can be a band filter.

The band filter is realized as a digital filter in the frequency domain. Thereto the received digital signals in the time domain are converted to the frequency domain by a FFT. The converted digital signals in the frequency domain are then multiplied by a window with a center frequency of 500 HZ and a bandwidth of 200 Hz. The multiplied signals are converted back to filtered first and second digital signals in the time domain.

The time difference correspond to the phase difference of the received sound signals.

In a next step the processor determines path lengths LI and L2 from the time difference using an optimization algorithm, for example a Jacobian method.

A Jacobian method is a first-order optimization algorithm. The method comprises taking steps proportional to the negative of the gradient (or of the approximate gradient) of the function at the current point in order to determine a local minimum of a function using gradient descent.

In this embodiment the reference positions are denoted by (Αχ,Αγ,Αζ) and

(Βχ,Βγ,Βζ) of the first and second microphones 22,23 in a reference coordinate system (given in the unit mm) and the position the emitter 21 is denoted by (Χ,Υ,Ζ). The spatial disparity dVca be calculated by using the difference in time of arrivals of a sound wave at the first microphone 22 compared to the second microphone 23 : Assuming the speed of sound with approx. 340000 mm/s and the sampling frequency of 44kHz, that is 44000 signals per second, a signal disparity of D results in dY=(D x 340000/44100) mm. The value dV encodes the delay of the arrival of the time signal as a spatial displacement. Since all values are expressed in terms of mm it is now possible to define the following error function to optimize for (X, Y,Z):

V((-4x - x)² + (Ay - Y)² + (Az - Z)²)- V((5x - X)² + (By - Y)² + (Bz - Z)²) -dV (1) If all values are known, Equation (1) must become zero, thus computing the

Jacobian of Equation (1) with respect to the unknowns (Χ, Υ,Ζ) can be used for a gradient descent optimization: The Jacobian results then in

J3 =[ (2Bx - 2X)/(2((Bx - X)² + (By - Y)² + (Bz - Z)²)¹/²)) - (2Ax - 2X)/(2((Ax - X)² + (Ay - Y)² + (Az - Z)²)¹/²)),

(2By - 2Y)/(2((Bx - X)² + (By - Y)² + (Bz - Z)²)¹/²) -

(2Ay - 2Y)/(2((Ax - X)² + (Ay - Y)² + (Az - Z)²)¹/²)),

(2Bz - 2Z)/(2((Bx - X)² + (By - Y)² + (Bz - Z)²)¹/²) -

(2Az - 2Z)/(2((Ax - X)² + (Ay - Y)² + (Az - Z)²)¹/²))] (2) Given an arbitrary start position for (Χ,Υ,Ζ), e.g. the origin, the error e can be computed by inserting the values in Eql. The vector v=-Inv(J3)e, where Inv denotes the pseudo inverse of J3, gives the update step for (Χ,Υ,Ζ). This can be iterated by computing a new error value until convergence. Fig. 4 shows schematically the position of the sound emitter 21 and the positions of the first and second microphones 22, 23. The path length LI and L2 can now be determined by the computational optimizing algorithm that matches the distance LI and L2 to the difference of respective time of arrival at the first and second microphones 22,23.

In a further embodiment the apparatus can be provided with a third microphone on the other shoulder. The third microphone 23' can be attached to the shirt near the other shoulder or the neck of the person depending on the configurations of the other microphones 22, 23.

The apparatus can also be provided with a gravity sensor 34 mounted between the microphones 22, 23 to obtain an angle between a longitudinal axis through the spine of the person and the axis z of the coordinate system in the direction of the gravity. The reference state can be determined for different reference postures of the person and the comfort zone can be based on the obtained reference states for the respective positions, for example, by averaging the respective directions of the reference lines obtained for multiple reference postures or applying a median value on the directions. A threshold tilt angle φτ between a measured first line and the reference line defines a safe zone, wherein a person is positioned to be exposed to a low risk of falling and wherein the person is still able to control his/her standing posture.

SI shows a distance between the neck and the shoulder. S2 shows the distance between the respective shoulders point.

Fig. 5 shows diagrammatically a reference state drawn in a solid line, and a first state drawn in a dashed line of a person. Furthermore, Fig. 5 shows also an orthogonal system Rx, Ry and Rz, wherein the Rz axis is the direction of gravitation. The reference state of the person can be represented by a reference line 51 through a first reference position 52 perpendicular to a guide line through the second and third reference positions 53, 54, wherein the first position 52 corresponds to the first position of the sound transmitter 21 at the ankle of the person. The second reference point 53

corresponds to the determined second position of the first microphone 22 and the third reference point 54 corresponds to the determined third position of the second microphone 23. A reference tilt angle between the longitudinal axis through the spine of the person and the Rz axis can be obtained from the gravity sensor 34.

In an operating state of the apparatus, wherein the person can walk in the room, the apparatus determines a first state of a posture of the person from the path length LI, L2 from the measured sound signals as described above. The first state of the person can be represented by a first line, dashed line, 5 through the first reference point 52' and perpendicular to a guide line through the second and third reference points 53', 54'. The distance SI between the determined second and third positions corresponding to the first and second microphones 22, 23 is considered substantially constant. The first, second and third positions coincide with the first, second and third vertices of a triangle, the reference line 51 and the first line 51 'correspond respectively to the altitude lines from the first vertex to the opposite side of the triangle in the reference state and the first state.

In this embodiment the comfort zone is defined by a threshold tilt angle between Rz-axis and the reference line 51, when the person is moving in the room the apparatus determines periodically the tilt angle between the direction of the first line 51 ' and the Rz- axis and when the tilt angle exceeds the threshold value φτ the apparatus controls the output of the output device to generate an alert, for example a ligh signal, a sound signal or mechanical vibration signal via the electro-mechanic transducer or an electric stimuli signal on a body part of the person. In fig. 5 the reference line 51 coincides with the Rz- axis.

Fig. 6 shows a flow diagram of a first embodiment of the method according to the invention. In operation, when the person is wearing the shirt 32 the apparatus 1 generates, when the person is leaving the comfort zone an alert. In this way the person is alerted and can correct his/her posture and reduces the chance that the person comes in a dangerous posture wherein the person is exposed to a high risk of falling.

In the reference mode the person is wearing the sound emitter 21 attached to the first reference point at one of the feet and the person also is wearing the shirt 32 whereto the first microphone 22 is attached at the second reference point close to the spine between the shoulders of the person and whereto the second microphone 23 is attached at the third reference point close to one of the shoulders of the person. Alternatively the second reference point can be on the first shoulder of the person and the second microphone can be attached at the third reference point on the other shoulder of the person.

In the reference mode the apparatus 1 is calibrated to the person in order to determine the comfort zone. In the operating mode the apparatus alerts the person wearing the apparatus 1 when the person is leaving the comfort area and exposed to a high risk of falling.

In the reference mode, the apparatus is measuring the second position and the third position of the first and second microphones 22, 23.

A personal coach or nurse can now determine the comfort zone by analyzing the different postures of the person, for example, when the person is walking or standing, and he or she may ask the person to take some reference postures, while the apparatus 1 is measuring the second and third positions of the first and second microphones 22, 23 with respect to the first position of the sound emitter 21 for the respective postures. When the personal coach has analyzed the different postures of the person, the personal coach can set a comfort area, by setting the comfort area corresponding to a threshold tilt angle φτ between the reference line obtained from one or multiple measurement for the reference posture and the first line obtained in a first state when the person is walking around.

This first step 60 can be repeated several times to obtain a reliable reference.

The personal coach or nurse can then store the threshold tilt angle φτ in the apparatus by touching the input module 5. The first microprocessor 3 is arranged to sense the input module 5 in a further step 61 and, when the input module detects an input, the method proceeds to step 62 and stores the corresponding threshold tilt angle φτ as the comfort zone in the memory.

In an embodiment of the method according to the invention this can be done automatically, thereto in step 60 the processor can obtain a series of first and second positions when a person is walking or moving in his/her apartment and/or living and the processors determines the first reference state from the obtained series of tilt angles.

For example by an average of the obtained tilt angle or the median of the obtained tilt angles.

The reference state can be represented using a reference line 51 through the first reference point representing the position of the sound emitter 21 and perpendicular to the guide line through the first and second reference points representing the determined positions 53,54 of the first and second microphones 22 and 23.

In an operating mode, when the person is wearing the sound emitter 21 and the microphones 22, 23 the person can move or walk freely in the person's living, house or outside.

In step 63 the processor 3 measures the first state from the determined second and third positions of the first and second microphones 22, 23. The first state can be represented by a first line 5 through the first position of the sound emitter 21 and perpendicular to the guide line through the second and third positions 53', 54' of the first and second microphones 22 and 23.

In a next step 64 the processor compares the tilt angle between the direction of the first line 51 ' and the reference line 51 with the stored threshold tilt angle and when the tilt angle is larger than the stored threshold tilt angle φτ the method proceeds to the next step 65, wherein the controller 3 controls the output device to generate the alert. The alert can comprise generating a sound, flashing light or a haptic signal, for example a mechanical vibration at the first measuring point or an electric stimulus on a body part, e.g. the left or right hand of the person, or transmitting a RF signal to a central control room.

After hearing or sensing the signal the person can correct his or her posture. In this way early detection of dangerous postures and subsequent alerting the person reduces the chance on falling of the person. Steps 63 to 65 can be periodically repeating, for example, this period is 10ms sees. A dynamic change of posture of the person can be determined by repeating steps 63 to 65, for example at a period of 100 ms.

In a further embodiment the number of microphones of the orientation device is extended with a third and fourth microphone 26, 27. The third microphone 26 can be attached in the shirt 40 nearby an elbow of an arm of the person and the fourth

microphone 27 can be integrated in a bracelet 50 and worn on the wrist of the selected arm. Fig. 3 shows also the third and fourth microphone 26, 27.

In this embodiment in step 60 the controller 3 can further determine the fourth and fifth positions of the respective third and fourth microphones 26, 27 in a similar way as described with respect to the first and second microphones 22, 23.

And in step 62 a reference arm state is determined from the reference projection Pr of the line segment 28 between determined fourth and fifth positions of the third and fourth microphones 26, 27.

Fig. 7 shows schematically the positions of the transmitter 21, the first and second microphones 22, 23 and the third and fourth microphones 26, 27.

Furthermore, fig. 7 shows the line segment 28 and the projection Pr of the line segment 28 between the fourth 26 and fifth positions 27 on the reference line 29 in a reference position of the person and a first projection PI of the line segment 28' between the fourth position 26 and fifth position 27'of the third and fourth microphones 26, 27' on the first line in a first posture of the person.

Furthermore, Fig. 7 shows the second position 22 near the neck of the person, the third position 23 near the shoulder of the person, the fourth position 26 on the elbow of the person and the fifth position 27 on the wrist of the person.

The line segment 28 represents the underarm of the person in the reference posture and the line segment 28' represents the underarm of the person in the first posture.

The method can be extended in that the reference state is determined by the reference line and the reference arm state in a reference posture of the person and that first state is determined by the first line and the first arm state in a first posture of the person. Therefore, in step 60 the first controller also determines the reference arm state from the projection Pr and in step 63 the first controller determines the first arm state from the first projection PI of the line segment 28' between the fourth position 26 and fifth position 27 on the reference line 29. In Fig. 7 the first line coincides with the reference line 29. The line segments 28, 28' represent the underarm of the person in respectively, the reference posture and the first posture.

Furthermore, the fourth position 26 in the reference state coincides with the fourth position 26 in the first state. The reference state can now be defined by the threshold tilt angle φτ and/or the reference projection Pr. The angle between the reference line and the first line and the reference projection and the first projection can define a reliable comfort zone.

In step 64 the processor 3 compares the first state and the reference state and when the first state exceeds the comfort zone, the method proceeds to step 65 wherein the processor 3 generates the alert. In this example the reference state is defined by threshold tilt angle φτ and/or the threshold difference between the reference projection and the first projection Δτ. In order to detect dynamically the posture of the person, the first state can be periodically determined, for example this period can be in the range between 1 sec and 1 ms., for example 10 ms.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

Claims

1. Method for analyzing a posture of a person, the method comprising:

emitting, by an acoustic emitter, an acoustic signal;

receiving, by a first and second microphone, the acoustic signal;

obtaining a reference state of the person in a reference posture from the received acoustic signals;

storing the reference state;

obtaining a first state of the person in a first posture; and

comparing the first state with the stored reference state and when the first state exceeds a comfort zone generating an alert, wherein the comfort zone is defined as the zone wherein a person is in standing posture and is still able to correct his/her posture and wherein, when the person exceeds a threshold tilt angle and is entering a dangerous area, wherein the person may exhibit an unstable posture and has a higher risk of falling

2. The method according to claim 1, further comprising

determining a triangle, wherein the vertices coincide with a first position, a second and a third position corresponding to a first, a second and a third reference point on the body in the reference posture ;

determining the first position, the second and the third position in the first posture; and providing a first line as the altitude line through the first vertex to the side opposite to the first vertex in the first posture,

3. A method according to claim 2, wherein comparing the reference state and the first state comprises determining an angular difference between the reference line and first line and the comfort zone is defined by a threshold tilt angle between the reference line and the first line.

4. A method according to claim 2 or 3, wherein determining the first, second and third position comprises:

generating an acoustic signal at the first position and receiving the acoustic signal at the second and the third position;

determining a difference in a first time of arrival of the acoustic signal between the first and second position and a second time of arrival between the first and the third positions; wherein the first reference point is selected from a point of one of the feet of the person and the second and third reference points are selected from respective points at the neck or the shoulders of the person; and

determining the second and the third positions with respect to the first position based on the determined difference.

5. The method according to claim 4, wherein generating the acoustic signal comprises

generating a digital signal corresponding to a frequency modulated signal around a center frequency wherein the frequency modulation is based on a pseudo-random modulation; and

converting the digital signal to the acoustic signal.

6. The method according to claim 5, wherein the method further comprises converting the received acoustic signals in a first received digital signal and a second received digital signal;

wherein determining the difference in time of arrival is based on a cross correlation function with a sliding window between the first and second filtered digital signals.

7. The method according to claim 4 to 6, wherein the method further comprises receiving the acoustic signal at a fourth and a fifth position corresponding to a fourth and a fifth reference point;

determining a difference in a third time of arrival of the acoustic signal between the first position and the fourth position and a fourth time of arrival between the first and the fifth positions; wherein the fourth and fifth reference points are selected from respectively a point at an elbow and a wrist of an arm of the person;

determining the positions of the fourth and fifth positions based on the determined difference;

determining a reference arm state or a first arm state based on the respective determined fourth and fifth positions in the reference state or the first state;

wherein the reference state is based on the reference line and the reference arm state, and the first state is based on the first line and the first arm state.

8. The method according to claim 7, wherein determining the reference arm state or the first arm states comprises

determining a reference projection of a line segment between the determined fourth and fifth position on the reference line;

determining a first projection of the line segment between the determined fourth and fifth position on the first line;

9. The method according to any of the claims 1 to 8, wherein generating the alert comprises generating a sound signal, a visual signal or a haptic signal at a part of the body of the person and/or or an RF signal;

10. Apparatus for analyzing a posture of a person comprising

a memory for storing data;

an output device;

an acoustic emitter for emitting an acoustic signal;

a first and a second microphone for receiving the acoustic signal; and

a control unit, wherein the control unit is arranged

to obtain a first state of the person in a first posture and to compare the first state with the stored reference state and when the first state exceeds a comfort zone generating an alert; wherein the comfort zone is defined as the zone wherein a person is in standing posture and is still able to correct his/her posture and wherein, when the person exceeds a threshold tilt angle and is entering a dangerous area, wherein the person may exhibit an unstable posture and has a higher risk of falling.

11. Apparatus according to claim 10, wherein the control unit is arranged to determine a triangle, wherein the vertices coincide with a first position, a second and a third position corresponding to a first, a second and a third reference point on the body in the reference posture from the received acoustic signals;

to provide a reference line defined as an altitude line through a first vertex and and a side opposite to the vertex ,

to determine the first position, the second and the third position in the first posture from the received acoustic signals; and

to provide a first line defined as the altitude line through the first vertex to a side opposite the first vertex ;

12. Apparatus according to claim 11, wherein the controller is further arranged to generate an acoustic signal at the first position and receiving the acoustic signal at the second and the third positions;

to determine a difference in a first time of arrival of the acoustic signal between the first position and the second position and a second time of arrival between the first and the third positions; wherein the first reference point is selected from a point of one of the feet of the person and the second and third reference points are selected from respective points at the neck or the shoulders of the person; and

to determine the second and third positions with respect to the first position based on the determined difference.

13. Apparatus according to claim 11 or 12, wherein the controller is further arranged to generate a digital signal corresponding to a frequency modulated signal around a center frequency wherein the frequency modulation is based on a pseudo-random modulation; and

converting the digital signal to the acoustic signal.

14. Apparatus according to any of the claims 11 -13, wherein the controller is further arranged

to convert the received acoustic signal in a first received digital signal and a second received digital signal;

to determine the difference in time of arrival based on a cross correlation function with a sliding window of the first and second filtered digital signals.

15. Apparatus according to any of the claims 11-14, wherein the apparatus comprises a garment comprising the first and second microphones at positions, when the person is wearing the garment, nearby the neck or one of the shoulder of the person.

16. Apparatus according to claim 15, wherein the apparatus is provided with a third and a fourth microphone and the controller is further arranged to determine a fourth and a fifth positions using the third and fourth microphones for respectively the reference posture and the first posture; and

determine a reference arm state or a first arm state based on the determined fourth and fifth positions respectively in the reference posture and the first posture .

17. Apparatus according to claim 16, wherein the controller is arranged to

determine a reference projection of a line segment between the fourth and fifth position in the reference posture on the reference line;

determine a first projection of a line segment between the fourth and fifth position in the first posture on the first line; and the respective reference arm state and the first arm state are based on the reference projection and the first projections in respectively the reference posture and the first posture.