SE542305C2 - Arrangement and system for wearable balance meter - Google Patents

Abstract

The invention relates to an arrangement (10) and a system for determining the ability of an object to remain in balance. The object is constituted by a bipedal animal, a bipedal bird or a bipedal robot, and it has an anterior- posterior extent and a medio-lateral extent. The arrangement comprises a monitor unit (30) monitoring the anterior-posterior and mediolateral acceleration of the object, and a computing unit (50) computing the displacement and movement of the object’s centre element. It integrates the anterior-posterior acceleration and the medio-lateral acceleration and performs an adjustment so that low acceleration and small displacement coincide in time. The invention also relates to a garment comprising such a system.

Description

ARRANGEMENT AND SYSTEM FOR WEARABLE BALANCE METER Field of the invention The present invention relates to an arrangement and system for determining the ability of an object to remain in balance, where the object is constituted by a bipedal animal, a bipedal bird or a bipedal robot; as well as a garment comprising such a system.

Background art Falis among older adults is a major public health concern. Balance problems are a major cause of falis. Balance problems make it difficult for a person to maintain an upright and stable position when sitting, standing, and walking. 75% of Americans older than 70 years are diagnosed as having "abnormal" balance. Once a balance problem has been determined in a person, there are a number of ways to address the causes. For example, the person's physician may adjust or change a medical prescription, or a physical therapist may help improve the person's strength and stability.

Good balance amounts to the ability to adequately balance the body’s Centre of Mass (COM) over its base of support in sitting, standing, and walking. Current field evaluation tools for determining the ability of a person to maintain balance in standing utilize expensive force platforms that are impractical to use in settings other than clinical research. Such platforms measure the ability to maintain balance in an indirect way, by determining the fluctuations of the Centre of Pressure (COP) from the ground reaction forces recorded from a person standing on the platform. The measurement of COP is considered as the Gold Standard currently but there exists a consensus that COM is the physically more relevant measure.

In order to make the assessment of a person's ability to balance in standing more accessible, development of wearable stand-alone electronic devices has been described in several clinical research projects. A modern accelerometer would seem a preferred choice to base such a device upon, given that it tends to be miniaturized, low-power and low-cost. However, it is a well-known fact to those of ordinary skill in the art, that a straightforward double integration of the acceleration signal to derive a displacement value, would amplify any errors in the acceleration value to such a degree that it would render the device useless in this respect.

Due to the difficulties involved in deriving an exact displacement by use of a modern accelerometer as the sole sensing component, such wearable devices tend to either a) rely on Inertial Measurement Units comprising a combination of accelerometers, gyroscopes and/or magnetometers to derive a more precise measurement of a person's movement, or b) use simplistic approaches such as the "Jerk" measure (based on a derivative of the measured acceleration) or the "Inverted Pendulum" principle (based on a simple trigonometric model that views the person as a swiveling rod).

To summarize, there is a need in the art for a method and system for determining the ability of a person to maintain balance, that comprises low- cost and low- power accelerometers and that delivers reliable measurements of the displacement and movement of a person's trunk and/or Centre of Mass. In this way, a low-cost and low- power solution can be designed so that measurement of a person's ability to adequately balance in standing, also outside the clinical environment, is facilitated, so that required action may be taken more readily, to preclude fall injuries.

Summary of the invention The following is intended to be a summary of the invention and is not intended to limit the scope of the invention.

It is an object/aim of the present invention to provide an arrangement and a system for determining the displacement and movement of a person's trunk and/or Centre of Mass. It is a further object to provide a robust stand-alone lowcost and low- power unit that can be worn and that determines and communicates the ability of a person to maintain balance in standing.

While the concept of measuring balance in standing has been implemented many years ago, those devices tend to be immobile, expensive, and/or power consuming. The simplicity of design of the arrangement and system described in this application are such as to overcome the previous shortcomings of the previous designs.

As a first example, there is provided a method for determining the displacement and movement of a person's trunk and/or Centre of Mass, comprising the steps of a) monitoring at least the anterior- posterior and medioiaterai acceleration of the person, and b) computing the displacement and movement of the person's trunk and/or Centre of Mass by means of at least integrating the anterior-posterior acceleration and the medio-iaterai acceleration and performing an adjustment so that low absolute acceleration and small displacement coincide in time.

The anterior-posterior acceleration refers to the acceleration in a direction generally parallel with the person's walking direction. The medio- lateral acceleration refers to the acceleration along an axis running from side to side, and the longitudinal acceleration is the acceleration along an axis substantially perpendicular to the horizontal plane, i.e. substantially perpendicular to both the anterior-posterior axis and the medio-iaterai axis.

The measured acceleration may for example be the momentary acceleration. This may thus give continual information on the displacement and movement of a part of the person's trunk that is indicative of the displacement and movement of the Centre of Mass.

In some examples, the accelerations of step a) are monitored on a reference point over the lumbar spine of the person.

The displacement and movement of a person's trunk and/or Centre of Mass is not readily measured. A reference point over the lumbar spine as an indicator of Centre of Mass during standing and walking is a feasible alternative.

An example of a method for determining the displacement and movement of a person's trunk and/or Centre of Mass using accelerometer data, comprises capturing current accelerometer data, computing acceleration and determining the points in time where absolute acceleration in the horizontal plane is low. Further, said acceleration in the horizontal plane is integrated twice to derive displacement in the horizontal plane. This displacement is compensated for drift by adjusting so that displacement in the horizontal plane is zero for each point in time where absolute acceleration in the horizontal plane is low. A computer program product and a device are also described.

It is known, to those of ordinary skill in the art, that it is not possible to derive reliable displacement over more than a second or so through double integration of accelerometer data alone, due to cumulative errors.

The first example is based on the insight that the physiology of a person's balancing mechanism introduces boundary conditions that allow an efficient reduction of the cumulative error that would result when deriving displacement information through double integration. Thus, the inventors have found a method that achieves a good approximation of the actual trunk and/or Centre of Mass displacement based solely on accelerometer data. A person applies almost no force when the Centre of Mass is positioned over the centre of the person's base of support. Thus low absolute acceleration and a centered position closely coincide in time.

The first example thus provides a convenient method for detecting balance problems and may thus raise an alarm before further damage, such as a fall, occurs.

It is to be understood that more than the anterior-posterior and mediolateral acceleration may be measured. As an example, the acceleration along three mutual orthogonal axes of the person, wherein two of the axes correspond to the anterior-posterior and the medio-lateral direction, respectively, may be measured in step a).

It is further to be understood that step a) may be performed continually, and the step of deriving the displacement and movement of the person's trunk and/or Centre of Mass may trigger other events, such as computing average sway values indicative of postural control.

Consequently, the specific acceleration pattern may function as a trigger event to communicate the findings.

In some examples, the accelerations of step a) are monitored over the lumbar spine of the person.

The lumbar spine of the person is closely coupled dynamically to the person's Centre of Mass. The acceleration may also be measured on other parts of the body that are coupled dynamically to the person's Centre of Mass.

Consequently, the acceleration may be measured on the trunk of the person, close to where the Centre of Mass is located. The inventors have found that normal acceleration levels experienced by this part of the person are within 0-2.0 g.

Thus, the inventors have found that performing a running adjustment by calibrating the displacement to zero at the points in time when absolute acceleration in the horizontal plane is low, enables reliable tracing of the displacement of a person’s trunk and/or Centre of Mass.

In some examples, the method is further comprising the step of c) measuring and analysing a person's ability to adequately balance based on a set of predefined criteria.

Estimating the person's ability to adequately balance is advantageous since this provides for different actions depending on the type and/or severity of balance problems. Different problems may require different safety actions, and it is very important that action be taken according to the severity, since otherwise the person may experience a harmful event. If for example the value is very poor due to medication, this may require immediate response by a treating physician, whereas a more gradual decline can be met by a training program administered by a physio-therapist over a period of weeks or more.

In some examples, the predefined criteria of step c) are predefined sway measures.

As an example, a predefined sway measure may correspond to a not so severe balance dysfunction, and a rapid deterioration in sway measure may correspond to a balance dysfunction that requires immediate attendance. As an example, the sway measure may be compared to predefined criteria that correspond to different balance dysfunctions.

Thus, the movement of a person's trunk may be used for estimating a person's ability to adequately balance. Thus, step c) may comprise comparing the ratio of the spread of the anterior-posterior displacement and the spread of the medio-lateral displacement, with a predefined value.

A step of estimating the ability to balance by comparing the results from step b) with predefined values means that the results from the estimation of the acceleration may be used as a "fingerprint" that is compared with predefined acceleration values, wherein different predefined values or "fingerprints” correspond to different balance problems. Thus, previous empirical data may be used to calibrate the method with information of what results obtained from step b) that correspond to the different balance problems. Thus, the step of "comparing with predefined values" may include a linear or non-linear fit of the monitored acceleration data to different calibration functions.

In some examples, step a) comprises monitoring the acceleration along three mutual orthogonal axes of the person, wherein two of the axes correspond to the medio-lateral and anterior-posterior acceleration, respectively, and step b) comprises computing the displacement and movement of the person's Centre of Mass by means of integrating the anterior-posterior acceleration and performing an adjustment so that low absolute acceleration and small displacement coincide in time, and step c) comprises determining the person's ability to adequately balance by measuring a sway value that is the ratio of the spread of the anteriorposterior displacement and the spread of the medio-lateral displacement. The spread may for example be given by the variance of the respective measure.

In step a) the acceleration may thus be measured in the direction along three mutual orthogonal axes, i.e. in three perpendicular directions. One direction may thus be along the vertical axis that is generally perpendicular to the horizontal plane.

The COM sway signal consists of the anterior-posterior and mediolateral time plot of the COM displacement during the test following Image available on "Original document" The conventional definition whereby the AP axis is the horizontal trace of the anterior-posterior plane aimed ahead of the person, and the ML axis is the horizontal trace of the medio-lateral plane aimed towards the right side of the patient, is recognized and accepted.

The origin of the coordinates is placed on an average value of the respective trace over the acquisition interval. The acquisition interval should not be less than 25 seconds. The sampling frequency should be at least 50 Hz.

Starting from the COM sway signal COM(t) the following can be extracted. 1) The two basic Stabilometric Graphs, namely the Stabilogram, i.e. the time plot of the two coordinates AP, ML, and the Statokinesiogram, or the ML vs AP plot as a function of time, 2) A set of parameters that describe the COM sway signal COM(t), such as Spectral Harmonic Analysis, "random walk", Sway Density, Fractal Analysis , Chaotic and Stochastic Analysis, and more.

As an example, a predefined sway measure may be a Stochastical Analysis that determines the ratio of sway variability (RMS: Root-mean- square) of the COM(t) signal in the anterior-posterior direction over the medio-lateral direction.

In the case of a set of n values measured for the anterior-posterior direction Image available on "Original document" In the same way the RMS in the medio-lateral direction follows MLRMS= Image available on "Original document" The ratio of sway variabilities thus follows R = APRMS/MLRMS. Different sway measures may thus correspond to different types and/or degrees of balance dysfunction. Further, changes in a person's sway measure over time may thus correspond to different types and/or degrees of balance dysfunction.

Measuring or estimating the acceleration vector may comprise estimating the momentary absolute value of the acceleration vector at the frequency at which the acceleration is monitored in step a) Thus, to clarify, the method of the first example may comprise a) monitoring the acceleration along three mutual orthogonal axes of the person, wherein two of the axes correspond to the anterior-posterior acceleration and the medio-lateral acceleration, respectively, b) computing the displacement and movement of the person's trunk and Centre of Mass by means of at least integrating the anterior-posterior acceleration and the medio-lateral acceleration and performing a running adjustment so that low absolute acceleration and small displacement coincide in time, and c1) estimating the person's ability to balance in standing by computing a sway measure for the displacements of step b). c2) estimating the type and/or severity of any balance dysfunction by comparing the sway measure of step d) with predefined criteria that correspond to different balance impairments.

As discussed above, step a), b), and c) may be performed continuously, or step b), as well as step d) may be performed after step a).

The acceleration of step a) may for example be measured at a frequency of 64 Hz. The displacement and movement of the person's trunk and Centre of Mass may be computed at the same frequency, and the momentary displacement may thus be used to estimate the person's ability to balance in standing and to estimate the type and/or severity of any balance dysfunction.

In the examples described above, the "specific period of time" may be a long enough time interval such that a reproducible measure of sway variability is obtained.

The specific period of time may for example be over 30 seconds.

It is also to be understood that e.g. both the momentary acceleration and/or a maximum value of the acceleration may be monitored and estimated. This may e.g. aliow diagnosing balance foliowing a number of different approaches in parallel, e.g. one measure may be particularly suited for the detection of defects due to degenerative disorders of the central nervous system such as Parkinson’s disease, another may be suited for the detection of defects that may follow a stroke.

As an example of the above examples, a result from step d) of a ratio of sway variabilities R measured over time interval M, wherein R may be the ratio of the RMS value for the displacements for the anterior-posterior direction, over the RMS value for the displacement for the medio-lateral value, is compared with the ratio levels R1and R2(R1< R2)· The levels of R1and R2may be determined based on empirical data and may be different depending on the measure used for sway, e.g. the RMS value. If R is below R1, it is concluded that there is no balance impairment, if R is between R1and R2there is moderate impairment , and if R is above R2, then there is significant impairment.

As a first aspect of the present invention, there is provided an arrangement, as defined in the appended claim 1, for determining the ability of an object to remain in balance, where the object is constituted by a bipedal animal, a bipedal bird or a bipedal robot.

As a second aspect of the present invention, there is provided a system for measuring and analysing a person's ability to adequately balance in standing, and for the communication of the findings, comprising at least one sensor for monitoring at least the medio-lateral and the anterior-posterior accelerations of the person, and a control unit adapted to perform adjustment, so that low absolute acceleration and small displacement coincide in time.

Terms and definitions used in connection with the first and second aspect of the invention are as defined in the first example above.

The system of the second aspect of the invention may thus be used in the method as defined by the first example above.

It is to be understood that a person may be equipped with several systems according to the present disclosure. The systems may be located on different parts of the body.

The sensor for monitoring the acceleration may be an accelerometer. The accelerometer refers to an electromechanical device that measures acceleration forces. Such forces measured by the accelerometer maybe static, i.e. forces that do not change in direction or amplitude, or dynamic, i.e. forces that change. The constant force of gravity experienced on the Earth's surface is static. Forces other than gravity may be static or dynamic. For example, swaying movement of a person's trunk and Centre of Mass is associated with dynamic forces.

Consequently, in embodiments of the second aspect, the sensor is adapted to monitor static forces. This may determine the angle with which the person’s body and/or the accelerometer's placement on the body, is tilted.

In embodiments of the second aspect, the sensor is adapted to monitor dynamic forces. By sensing dynamic acceleration forces, one can analyse the movement of the person.

The sensor or accelerometer may of course be adapted to measure both static and dynamic acceleration forces.

The sensor or accelerometer further measures acceleration in three mutual orthogonal axes, i.e. in three perpendicular directions. One direction may be along the general anterior-posterior direction.

The sensor or accelerometer may be integrated within an electronics module or be an externally connected accelerometer.

In embodiments of the second aspect, the sensor or accelerometer has a digital output. A digital accelerometer tends to produce a pulse width modulated signal: A square wave of constant frequency may be produced, and the time interval during which the voltage is high corresponds to the acceleration measured.

Further, in embodiments of the second aspect, the sensor or accelerometer has an analogue output. An analogue accelerometer produces a continuous voltage that is proportional to the acceleration measured.

Whether to use an analogue or digital accelerometer may depend on the hardware of the control unit with which to interface the accelerometer. If, for example, a microcontroller with purely digital input is used, a digital accelerometer is the most straightforward solution. On the other hand, if a microcontroller with AD-conversion capability is used, such as a PIC family one, or even a completely analogue based circuit is used, analogue may be the preferred choice.

In embodiments of the second aspect, the control unit comprises a microcontroller.

The control unit may amplify and filter the acceleration signals and also store the monitored signals or processed signals in a storage unit.

The control unit may for example be a standard microcontroller or a more complex microprocessor, on a printed circuit board with an internal or external signal processor such as an Arduino or Raspberry type board.

The control unit may be sealed in a waterproof, corrosion resistant housing and may be connected to the sensor for measuring acceleration or other probes on one side through a waterproof connector. This housing allows the system to be used in a hospital environment where water and/or moisture are a problem and frequent cleaning may be necessary.

The system of the second aspect of the invention may be powered by means of an external battery, such as a lithium-ion battery. The system may also be powered by other means, for example by connecting to an electrical outlet.

In the context of the present disclosure, a person's ability to adequately balance may be defined as the ratio of average sway computed from the corresponding displacement measured, over 30 seconds time, in the anterior-posterior direction divided by the average sway in the medio-lateral direction over the same time. This ratio may directly be converted into a measure of the person's ability to maintain balance. There are numerous sway measures that may be used.

In embodiments of the second aspect, the at least one sensor or accelerometer is adapted to measure acceleration levels of 0-2.0 g along all three mutual orthogonal axes, wherein the medio-lateral and the anteriorposterior axes are two of those axes.

One "g" is the Earth's level of gravitational force at the sea surface, i.e. 9.81 m/s2. The inventors have realized that acceleration measurements of to about 2.0 g may be sufficient to monitor sway of a person's trunk and/or Centre of Mass. Thus, the system may be equipped with rather non-complex accelerometers or sensors, but still be able to give information concerning the movement of the person’s Centre of Mass.

In embodiments of the second aspect, the sensitivity of the accelerometer or sensor is about 0.02 g. Such sensitivity or resolution may be enough or preferred for allowing the monitoring of the movement of the person’s trunk and/or Centre of Mass.

In embodiments of the second aspect, the at least one accelerometer or sensor has a bandwidth of about 64 Hz.

The bandwidth relates to the possible number of independent acceleration level measurements per time unit. The inventors have found that a bandwidth of about 50 Hz may be enough for monitoring the movement of the person's trunk and/or Centre of Mass according to the present disclosure. Thus, little bandwidth may be required for the proposed system. However, a sensor or accelerometer having a larger bandwidth may be used.

In embodiments of the second aspect, the at least one sensor or accelerometer is adapted to be mounted over a person’s lumbar spine. This means that the sensor may for example be adapted to be mounted by an adhesive patch, clipped to clothing worn by the person, integrated into garment worn by the person, or by means of a belt.

Normal acceleration levels experienced by this part of the body are 0-1.5 g In embodiments of the second aspect, the at least one sensor or accelerometer is adapted to be mounted on a person's leg.

In embodiments of the second aspect, the control unit is mounted together with the sensor.

If for example the sensor is mounted on the back of the person also the control unit may be mounted together with the sensor on the back of the person. This means that the control unit may be composed of a simple circuit instead of e.g. a microprocessor. Further, by mounting the control unit together with the sensor, the power consumption may be decreased. As the system has on-board algorithmic intelligence, it may not require communication to external data processing for measuring and analysing a person's ability to adequately balance.

In embodiments of the second aspect, the sensor or accelerometer is mounted directly over a person's lumbar spine, and the control unit is mounted on another part of the person. This could be an option in applications where advantage can be drawn from there being an extant control unit serving more than one purpose.

In embodiments of the second aspect, the sensor or accelerometer is mounted on a person's leg, and the control unit is mounted on another part of the person. This could be an option in applications where advantage can be drawn from there being an extant control unit serving more than one purpose.

In embodiments of the second aspect, the system is further comprising a wireless transceiver for transmitting acceleration data and/or information about the displacement and movement of the person's trunk and/or Centre of Mass, and/or measures deduced thereof.

The wireless transceiver may be mounted together with the at least one sensor and/or together with the control unit. If the sensor and control unit are mounted together, the wireless transceiver may transmit information about the displacement and movement of the person's trunk and/or Centre of Mass, and/or measures deduced thereof, to e.g. a caregiver or another person that has interest of the information, such as a relative. If the sensor and control unit are mounted separately, the wireless transceiver may transmit acceleration data from the sensor to the control unit for further analysis and further transmit information from the control unit to e.g. the caregiver. The wireless transceiver may for example be a GPRS-unit. However, an additional low- power local-area wireless network communication function, such as provided by Zigbee or Bluetooth technologies, may also be used in order to provide communication with e.g. the caregiver in the absence of GPRS coverage.

In embodiments of the second aspect, the system is further comprising a storage unit for storing the monitored acceleration data.

The system may thus basically gather accelerometer data and store the data in the storage unit and further transmit the data via GPRS with the transceiver to the control unit when there is GPRS coverage. If GPRS communication cannot be established due to lack of GPRS coverage the storage may store the acceleration data locally to be transmitted as soon as GPRS communication is established. Once data is transmitted successfully via GPRS, any data that has been stored in the storage unit may be deleted.

The storage unit may be part of the control unit, and may be mounted together with the at least one sensor.

In embodiments of the second aspect, the system further comprises at least one gyroscope and/or at least one magnetometer.

This may improve precision of acceleration measurement, and values deduced thereof.

The gyroscope and/or magnetometer may be mounted together with the at least one sensor.

In embodiments of the second aspect, the system is furthermore arranged to perform preliminary data processing to determine critical and noncritical balance impairments into three action related characteristics: 1) no balance impairment, 2) moderate balance impairment, and 3) significant balance impairment.

The system may furthermore be arranged to, after preliminary data processing as described above, immediately send significant impairment messages to the caregiver in order to intervene.

The system may furthermore be arranged to send the moderate impairment message to a back office server for additional processing. The back office server may be arranged to prepare and send reports to users or provide access to the data for their account over the internet. The back office server may furthermore be arranged to analyse, compare and/or combine the data with stored data relating to the same person, i.e. previous history.

In embodiments of the back office server, it may be arranged to: • Receive and store acceleration and time stamp data, from each person in a structured form.

• Compile this information, by background processes, into sets of data that represent specific information of interest, such as development of sway measures over time.

• Trigger functions that warn the user e.g. in case of sway measures in excess of a given threshold, or sway measures that deteriorate over time at a given rate.

In embodiments of the second aspect, the system functions may be described as: • acceleration measurement in 3 dimensions at 64 Hz intervals with time stamp, • Digital Signal Processing of the acceleration measurements such as thresholding, averaging as well as frequency analysis, • potential for integrating further sensor modules, such as a GPS module and/or gyroscope and/or magnetometer, • secure wireless communication via for example GPRS, • continually storing, by the CPU, of each accelerometer measurement to a local memory, for example a local flash memory in the format of a RAM-disk, • connection, by separate CPU process(es), to the GPRS network at predetermined intervals, for example immediately following a monitoring session. If the connection is successful, data may be packaged and encrypted and then transmitted to a back office server. If a receipt is received from the back office server that the transmission has been successful, the corresponding data is removed from the local memory. If connection either cannot be established, or a transmission attempt is unsuccessful, data is kept until the next transmission attempt, for example 2 minutes later.

As a third aspect of the invention, there is provided a garment comprising at least one system according to the second aspect, wherein the at least one system is mounted to the garment.

The third aspect thus provides a garment in which the displacement and movement of a person's trunk and/or Centre of Mass may be monitored in convenient ways using the system as disclosed in relation to the second aspect above.

As a further example, there is provided the use of at least one acceleration sensor mounted over the lumbar spine of a person for measuring the displacement and movement of a person's trunk and/or Centre of Mass.

The terms and definitions used in relation with the further example are as defined in relation to the other aspects of the invention above.

As discussed above, the inventors have found that it is advantageous to measure the acceleration over the lumbar spine of the person, since it gives a better measure of the displacement and movement of the person's trunk and/or Centre of Mass, which facilitates the computation of sway measures considerably.

In some examples, the at least one acceleration sensor is adapted to monitor the acceleration along three mutual orthogonal axes.

As a yet further example, there is provided the use of at least one acceleration sensor mounted on the leg of a person for measuring the displacement and movement of a person's trunk and/or Centre of Mass.

The terms and definitions used in relation with the yet further example are as defined in relation to the other aspects of the invention above.

In some examples, the at least one acceleration sensor is adapted to monitor the acceleration along three mutual orthogonal axes.

Brief Description of the Drawings Some embodiments of the present invention are illustrated as an example and are not limited by the figures of the accompanying drawings, in which like references may indicate similar elements and in which: FIG. 1 - Figure 1 depicts the functional components of a system according to an embodiment of the present disclosure.

FIG. 2 - Figure 2 depicts a schematic drawing of an example of apparatus configured for attaching to a person’s trunk or on a person’s leg.

FIG. 3 - Figure 3 depicts diagrammatically the positioning of an apparatus over a person's lumbar spine.

FIG. 4 - Figure 4 depicts diagrammatically the positioning of an apparatus on a person’s leg.

FIG. 5- Figure 5 depicts two curves showing, from an example simulation, acceleration values in the anterior-posterior direction (indicated by a solid line), and corresponding measured acceleration values, that include synthetically added noise (indicated by dots).

FIG. 6 - Figure 6 illustrates the accumulated displacement error that results from computing displacement by double integration of the acceleration with noise. The two curves show the actual displacement in the anterior- posterior direction (solid curve), and displacement derived from the measured acceleration values with added noise (dashed curve), respectively.

FIG. 7 - Figure 7 illustrates a process for computing the displacement of the Centre of Mass using an adjustment method according to an embodiment of the present disclosure.

FIG. 8 - Figure 8 illustrates a workflow for a running adjustment method according to an embodiment of the present disclosure. Rhombic boxes correspond to decision points, horizontal flows out of which correspond to “no", vertical flows correspond to "yes".

FIG. 9 - Figure 9 depicts two diagrams that are aligned in time. The data depicted in the upper diagram corresponds to the data depicted in Figure 5, The data depicted in the lower diagram depicts three curves showing actual displacement in the anterior-posterior direction, displacement derived from the measured acceleration values with added noise, and displacement derived by using a running adjustment method according to an embodiment of the present disclosure.

FIG. 10 - Figure 10 depicts three curves showing actual displacement in the anterior-posterior direction, displacement derived from the measured acceleration values with added noise, and displacement derived by using an adjustment method according to an embodiment of the present disclosure.

FIG. 11 - Figure 11 depicts a real-life measurement of the displacement of the Centre of Mass in the anterior-posterior and medio-lateral directions derived by an adjustment method according to an embodiment of the present disclosure.

FIG. 12 - Figure 12 illustrates a process for analysing displacement data.

Detailed Description of Preferred Embodiments The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well as the singular forms, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising", when used inthis specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one having ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

In describing the invention, it will be understood that a number of techniques and steps are disclosed. Each of these has individual benefit and each can also be used in conjunction with one or more, in some cases all, of the other disclosed techniques. Accordingly, for the sake of clarity, this description will refrain from repeating every possible combination of the individual steps in an unnecessary fashion. Nevertheless, the specification and claims should be read with the understanding that such combinations are entirely within the scope of the invention and the claims.

New methods and systems for Wearable Balance Meter are discussed herein. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident, however, to one skilled in the art that the present invention may be practiced without these specific details.

The present disclosure is to be considered as an exemplification of the invention, and is not intended to limit the invention to the specific embodiments illustrated by the figures or the description below.

The present invention will now be described by referencing the appended figures representing preferred embodiments.

Figure 1 depicts the functional components of a system according to an embodiment of the present disclosure.

The system comprises a self-contained primary unit 10.

The signal generation 30 may comprise sensors such as at least one accelerometer for monitoring the acceleration. The at least one accelerometer monitors acceleration in three dimensions continually and real-time analysis of such acceleration data determines the ability of a person to maintain balance. Depending on the result, a warning may be communicated to the person measured upon and/or another person or system.

The signal processing 20 may include Peak and Hold circuits which measure peak values over predetermined intervals over the complete low- pass regime. The signal processing may also comprise Fast Fourier Transforming (FFT) circuits that permit analysis of forces at preselected frequencies. Further, the signal processing may comprise correlator circuits that permit isolation and amplification of forces that are only of significance if detected from more than one source, or from a single source but with a time offset between two signal values.

Figure 2 depicts a schematic drawing of an example of apparatus configured for attaching to a person's trunk or to a person's leg by means of a belt. The housing 11 is attached to a belt 90 with a mechanism for adjusting the belt length 91. Whatever the way in which the housing is attached to the user's body, it is desirable for it to be attached firmly to the body so that it moves together with the part of the body to which it is attached. In that way, the data gathered by the signal generation unit is more representative of the motion of the user's body.

Figure 3 depicts diagrammaticaliy the positioning of an apparatus to a person’s lower back by means of a belt 90.

Figure 4 depicts diagrammaticaliy the positioning of an apparatus to a person's leg by means of a belt 90.

The following example further explains how an accelerometer signal may be processed in order to determine the displacement and movement of a person's trunk and/or Centre of Mass.

An inherent problem in determining a displacement from accelerometer data lies in the fact that any errors in the acceleration measured will cumulate in the process of double integration, deriving velocity, and then displacement.

We let ?(t) denote the acceleration as a function of time. The derived velocity will then follow v(t) = Image available on "Original document" The derived displacement follows Image available on "Original document" To illustrate the effect of noise when deriving a displacement value from acceleration measurements, a simplistic model of a case of anterior- posterior acceleration and displacement follows.

The model initially assumes an anterior-posterior displacement that is represented by three cosine functions of identical amplitude but different frequency and phase. Thus, displacement is centered on zero on average. The maximum amplitude is scaled so as to correspond to a typical value for Centre of Mass displacement of a few centimeters.

From this displacement model, through double derivation, the resulting acceleration can be derived. To this derived modeled acceleration, a measurement error is added in the form of random values evenly distributed around a zero value.

Figure 5 depicts two curves from such an example model. The solid line indicates the modeled acceleration values in the anterior-posterior direction. The dots indicate the modeled measured acceleration values, i.e. with synthetically added noise.

Figure 6 depicts two curves that result from double integration of the modeled acceleration without (as a solid line) and with (as a dashed line) the added noise. It is clearly visible that the noise results in a cumulative displacement error, a drift.

Figure 7 illustrates a process for computing the displacement of the Centre of Mass using an adjustment method according to an embodiment of the present disclosure.

Figure 8 illustrates a workflow for an adjustment method according to an embodiment of the present disclosure. Rhombic boxes correspond to decision points, horizontal flows out of which correspond to "no", vertical flows correspond to “yes". At the onset, the number of buffered values n equals zero and indices n1and n2are set to NULL. At regular or non-regular intervals, acceleration anand time tnare captured and buffered. If there is more than one buffered value (n ! = 0)) the current integral value for velocity vnand displacement dnare computed and buffered. If at a certain point in time the sign of the acceleration value changes, a low acceleration level has occurred and this point in time is noted. If at least two such low acceleration levels have occurred (n1! = NULL and n2! = NULL) the displacements from n1, inclusive, to n2, inclusive, are adjusted so that displacement equals zero at n1and n2, e.g. following Image available on "Original document" Figure 9 depicts two diagrams that are aligned in time. The data depicted in the upper diagram corresponds to the data depicted in Figure 5. The data depicted in the lower diagram depicts three curves showing i) modeled displacement in the anterior-posterior direction (solid line), ii) displacement derived from the measured acceleration values, i.e. with synthetically added noise (dashed line), and iii) displacement derived by using an adjustment method according to an embodiment of the present disclosure (dotted line).

Figure 10 depicts three curves showing i) actual displacement in the anterior-posterior direction (solid line), ii) displacement derived from the measured acceleration values, i.e. with synthetically added noise (dashed line), and iii) displacement derived by using an adjustment method according to an embodiment of the present disclosure (dotted line).

Figure 11 depicts a real-life measurement of the displacement of the Centre of Mass in the anterior-posterior and medio-lateral directions derived by using an adjustment method according to an embodiment of the present disclosure.

The algorithms described above enable a unit carried by a user to measure the displacement of the trunk and/or Centre of Mass in anterior- posterior and mediolateral directions in real time. In this way a person's ability to adequately balance can be measured and analysed and the findings be communicated.

Figure 12 illustrates a process for analysing displacement data.

Although the present invention has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention, are contemplated thereby, and are intended to be covered by the following claims.

In the embodiments presented, the invention is applied to a human, but this is obviously just an example. Clearly, the invention may equally well be applied to other bipedal animals such as ostriches, nandus or emus and alternatively it may be applied to bipedal robots. What in a human and in birds would be denoted torso, would for a bipedal robot not necessarily be denoted in that particular way, so the more generalized term centre element may be used. What in a human and in birds would be denoted legs, would for a bipedal robot not necessarily be denoted in that particular way, so the more generalized term appendage may be used.

Claims (13)

Claims

1. An arrangement (10) for determining the ability of an object to remain in balance, where the object is constituted by a bipedal animal, a bipedal bird or a bipedal robot, where the object has an anterior-posterior extent and a medio-lateral extent, where the arrangement (10)comprises a monitor unit (30) monitoring at least the anterior-posterior and mediolateral acceleration of the object, and a computing unit (50) computing the displacement and movement of the object’s torso and/or the object’s centre of mass by means of at least integrating the anterior-posterior acceleration and the medio-lateral acceleration and performing an adjustment so that the displacement is set to zero when the acceleration is low.

2. An arrangement according to claim 1, wherein the accelerations of step a) are monitored on the centre element of the object using at least one acceleration sensor attached to the object.

3. An arrangement according to claim 1, wherein the accelerations of step a) are monitored on a leg of the object using at least one acceleration sensor attached to the object.

4. An arrangement according to claim 1, wherein the computing unit further d) estimates the object’s ability to balance in place by computing a sway measure for the displacements of step b).

5. An arrangement according to claim 4, wherein the computing unit further c2) estimates the type and/or severity of any balance dysfunction by comparing the sway measure of step d) with predefined criteria that correspond to different balance impairments.

6. A system for determining the ability of an object to maintain balance, the system comprising an arrangement (10) provided on the object and an external unit arranged elsewhere, where the arrangement and the external unit are provided with means (70, 80) for communication between them, and where the object is constituted by a bipedal animal, a bipedal bird or a bipedal robot, where the object has an anterior-posterior extent and a medio-lateral extent, the arrangement comprising at least one sensor (30) for monitoring at least the anterior-posterior and medio-lateral acceleration of the object, and a control unit (50) adapted to compute the displacement and movement of the object’s torso and/or the object’s Centre of Mass by means of at least integrating the anterior-posterior acceleration and the medio-lateral acceleration and performing an adjustment so that the displacement is set to zero when the acceleration is low.

7. A system according to claim 6, wherein the at least one sensor is adapted to measure acceleration levels of up to 2.0 g.

8. A system according to any one of claims 6-7, wherein the at least one sensor has a bandwidth of about 100 Hz.

9. A system according to any one of claims 6-8 wherein the at least one sensor is adapted to be mounted on the object.

10. A system according to any one of claims 6-9 wherein the at least one sensor is adapted to be mounted on the torso of the object.

11. A system according to any one of claims 6-10 wherein the at least one sensor is adapted to be mounted at a lower portion of the torso of the object.

12. A system according to any one of claims 6-9 wherein the at least one sensor is adapted to be mounted on a leg of the object.

13. A garment comprising at least one system according to claim 6.