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WO2009031064A2 - Procédé d'extraction de composantes vectorielles inertielle et gravitationnelle de vecteurs d'accélération mesurés par un accéléromètre - Google Patents

Procédé d'extraction de composantes vectorielles inertielle et gravitationnelle de vecteurs d'accélération mesurés par un accéléromètre Download PDF

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Publication number
WO2009031064A2
WO2009031064A2 PCT/IB2008/053399 IB2008053399W WO2009031064A2 WO 2009031064 A2 WO2009031064 A2 WO 2009031064A2 IB 2008053399 W IB2008053399 W IB 2008053399W WO 2009031064 A2 WO2009031064 A2 WO 2009031064A2
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WO
WIPO (PCT)
Prior art keywords
acceleration
estimate
accelerometer
vector
inertial
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/IB2008/053399
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English (en)
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WO2009031064A3 (fr
Inventor
Bin Yin
Victor M. G. Van Acht
Nicolaas Lambert
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Koninklijke Philips NV
Original Assignee
Koninklijke Philips Electronics NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Koninklijke Philips Electronics NV filed Critical Koninklijke Philips Electronics NV
Publication of WO2009031064A2 publication Critical patent/WO2009031064A2/fr
Publication of WO2009031064A3 publication Critical patent/WO2009031064A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/103—Measuring devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
    • A61B5/11—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor or mobility of a limb
    • A61B5/1126—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor or mobility of a limb using a particular sensing technique
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C21/00—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00
    • G01C21/10—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration
    • G01C21/12—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning
    • G01C21/16—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning by integrating acceleration or speed, i.e. inertial navigation
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/02—Details of sensors specially adapted for in-vivo measurements
    • A61B2562/0219—Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/103—Measuring devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
    • A61B5/11—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor or mobility of a limb
    • A61B5/1118—Determining activity level
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/103—Measuring devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
    • A61B5/11—Measuring movement of the entire body or parts thereof, e.g. head or hand tremor or mobility of a limb
    • A61B5/1121—Determining geometric values, e.g. centre of rotation or angular range of movement
    • A61B5/1122—Determining geometric values, e.g. centre of rotation or angular range of movement of movement trajectories

Definitions

  • the present invention relates to a method and a device for extracting inertial and gravitational acceleration vector components from acceleration vector measured by an accelerometer when the absolute orientation of the accelerometer coordinate system relative to the earth coordinate system varies over time.
  • An activity monitor based on the measurement of acceleration of a human body is getting more widely used.
  • the applications range from those in medical and healthcare domain where the monitor aids to analyze and evaluate patients' vital body signs such as ECG and EMG signals to improve the quality of diagnosis, to those in consumer lifestyle domain where it enables the estimation of the amount as well as the way of energy expenditure associated with physical activities so that people can know how healthy their lifestyles are and make plans for improvement if necessary.
  • PAs human's daily physical activities
  • An AM device consists of, nowadays typically, a single or multiple tri-axial (3D) accelerometers.
  • a DC accelerometer measures both gravitational and inertial accelerations.
  • the gravitational components in three axes of the sensor coordinate system will give the orientation (or tilt), relative to the earth- fixed reference coordinate system, of the body part where the sensor is attached. This is depicted graphically in Figure 1 showing on the left side a sensor coordinate system and on the right side an earth- fixed reference coordinate system. If the orientation information is available, inertial accelerations in both the sensor and earth-fixed coordinate systems can be readily obtained.
  • the information about orientation and inertial accelerations will significantly improve the performance of activity recognition algorithms, in terms of the number of postures and motions that can be recognized and the accuracy of the recognition results, especially combined with a prior knowledge of the sensor orientation relative to the relevant anatomical axis of the wearing subject.
  • the orientation of a sensor coordinate system relative to the earth-fixed reference coordinate system may be defined as the absolute orientation and that relative to the relevant anatomical axis of its wearing subject as the relative orientation.
  • the absolute orientation of the sensor can be readily expressed in the form of rotation matrix, Euler angles or Quaternion.
  • Separating gravitational components from inertial ones when a subject stays relatively static can be realized by low-pass filtering or simply averaging the readout from each sensor axis over a certain time interval ⁇ David Mizell, Using Gravity to Estimate Accelerometer Orientation, Proceedings of the 7th IEEE ISWC, 2003).
  • the inertial components are negligible, so a simple averaging usually gives good results.
  • the readout of an accelerometer from its three axes results from both gravitational and inertial accelerations, plus that the absolute orientation of the sensor changes in time because of the subject's movement, meaning both gravitational and inertial components in all three axes' readout are time-varying.
  • the low-pass filtering or averaging method will have difficulties in reliably separating the gravitational and inertial accelerations.
  • Extra inertial sensors can help.
  • the use of a 3D gyroscope and a 3D magnetometer on top of a 3D accelerometer has been disclosed (MTi and MTx User Manual and Technical Documentation, Xsens Technologies B. V., 2006).
  • the magneto and accelerometers are responsible for measuring inertial accelerations as well as slow, usually under 1 Hz, rotational movements, while the gyroscope follows absolute orientation changes during fast rotational movements.
  • the problem with this reference is that the gyroscopes are generally expensive and, more importantly, power-hunger, so they are not ideal for portable and wireless applications, like in a body-worn AM device.
  • the object of the present invention is to overcome the above mentioned drawbacks by providing a method and a device where the acceleration readout of an accelerometer alone suffices to estimate the absolute orientation and inertial accelerations and that is also able to follow the variation of the absolute orientation if the subject wearing the device is moving.
  • Ji is a cost function for measuring the distance between
  • V g V a - V 1 and V g
  • E ⁇ may be considered to give an averaged value, or mean, of a variable.
  • a variable S[k] takes values S[O], S[I], ..., S[N-I], S[N] at sampling moments 0, 1,...,N-I and N, an approximation of E ⁇ S[k] ⁇ will be (S[O]+S[l]+...+S[N-l]+S[N])/(N+l). This may be reforming by saying that target function J is minimized in least mean square (LMS) sense.
  • LMS least mean square
  • the temporary estimate V g is given by: with V a [k] being a sequence of the acceleration readout data from the 3D-accelerometer in a discrete time domain, k being the sampling moment, and 2K+1 the number of samples around V a [k] .
  • V g acceleration vector By defining the estimate for the gravitational V g acceleration vector in that way, a very reasonable first estimate for the acceleration vector is typically provided because the inertial acceleration tends to average to something close to zero. As an example, if a subject runs with certain acceleration it will after some time slow down (otherwise the subject would approach an infinite speed).
  • the temporal estimate V g [k] will be close to the gravitational acceleration vector V .
  • the sampling rate is preferably selected such that both the increase and the decrease around the inertial acceleration V a [k] are covered (it will sum up to something close to zero).
  • the temporary estimate V g is determined using low-pass filtering method.
  • the acceleration readout vectors V a [k] are received in discrete time or in a continuous time domain.
  • discrete time domain is meant that a sampling domain, where the readouts from the accelerometer are discrete (e.g. every 1/10 of second data are collected), but this may just as well be done in a continuous time domain meaning that the data are continuously collected.
  • the sum in the equation for the estimate for the gravitational vector V g [k] would be replaced by an integral, and therefore the complete method including the definition of J and update of unknowns is to be implemented in a continuous time domain.
  • the present invention relates to a computer program product for instructing a processing unit to execute the above mentioned method steps when the product is run on a computer or computerized device.
  • V [k] for the gravitational acceleration vector V and an estimate V 1 [k] for the inertial acceleration vector J 1 oc ⁇ [k] - V 1 [k] - V [k]) ⁇
  • J 2 being proportional to the difference between the actual length of the gravitational vector V g and the length of the difference of the acceleration readout vector V a [k] and the estimate V 1 [k] for the inertial acceleration vector
  • the device is selected from: - a three axial accelerometer, an activity monitor (AM), a rehabilitation monitoring system adapted to record limb trajectories during exercising,
  • AM activity monitor
  • rehabilitation monitoring system adapted to record limb trajectories during exercising
  • Fig. 1 depicts graphically when a three axial (3D) accelerometer coordinate system in Fig. l(a) is moving relative to an earth fixed coordinate system shown in Fig. l(b),
  • Fig. 2 depicts the relationship of the accelerometer readout vector V a , the gravitational acceleration vector V g and the inertial acceleration vector V 1 in the accelerometer coordinate system,
  • FIG. 3 shows that in principle, any point on the sphere satisfies equation (6)
  • Fig. 4 is a flowchart of a method according to the present invention
  • Figs. 5-6 show experimental results depicting orientation estimation with a slowly moving Xsens unit
  • Figs. 7-8 show experimental results depicting orientation estimation for relatively fast movement.
  • Figure 1 depicts graphically when a three axial (3D) accelerometer coordinate system 101 in Fig. l(a) is moving relative to an earth fixed coordinate system 102 shown in Fig. l(b), where the y-axis is considered to be west and the x-axis is considered to be local magnetic north. The latter is shown as a left-handed system, but in a right handed system the z axis points upwards.
  • the subject 100 moves, e.g. the subject is running and the 3D-accelerometer is placed in the sole of the shoe, the accelerometer coordinate system moves with respect to the fixed earth fixed coordinate system.
  • the measured acceleration consists of an inertial acceleration V 1 and gravitational acceleration V g , i.e.
  • V a V + V g . (1)
  • Equations (2)-(4) may be expressed both in discrete (or sampling) domain signal where where where x, y, and z may be expressed as a function of sampling moment k, i.e. x a (k), ya(k) and z a (k).
  • x a (k) i.e. x a (k), ya(k) and z a (k).
  • z a (k) i.e. x a (k), ya(k) and z a (k).
  • the present invention may just as well be implemented in continuous domain signals. In the following, the discrete domain signal will be used.
  • the aim of the present invention is to extract the gravitational and the inertial acceleration components from the acceleration readout V a of the accelerometer such that the inertial acceleration and the absolute orientation of the subject wearing the accelerometer may be followed over time.
  • the problem of extracting the gravitational and the inertial acceleration components from the acceleration readout V a of the accelerometer is not one step solvable because the number of unknown components in the vector V g and V 1 is six, while the number of equations is only four, namely equations (2)-(5).
  • Figure 2 depicts the relationship of the accelerometer readout vector V a , the gravitational acceleration vector V g and the inertial acceleration vector V 1 in the accelerometer coordinate system.
  • the radius of the sphere is one, i.e. after the normalization of the acceleration vector V g .
  • Figure 3 shows that in principle, any point on the sphere satisfies equation (5), and this leads to arbitrary solutions V ' g and V ' , , which illustrates the abovementioned problem of having unknowns more than equations.
  • a tracking algorithm or a method which learns V 1 using temporarily estimated gravitational acceleration vector V g , and meanwhile corrects the estimate of V g if its length does not equal one. In this manner, the algorithm achieves the goal effectively in two steps each of which has a reduced number of unknowns.
  • a first step (Sl) 401 a sequence of acceleration readout vectors V a [k] are generated by the accelerometer, where k is the sampling moment. This means that e.g. every second the acceleration is measured. The sampling moment k may be considered as time, i.e.
  • a temporal estimate V g [k] for the gravitational acceleration vector V g is determined (S2) 403 for a given moment k.
  • V a [k] being a sequence of the acceleration readout data from the 3D-accelerometer in a discrete time domain
  • k being the sampling moment
  • 2K+1 the number of samples around V a [k] for averaging.
  • V 1 [k] is chosen. This value can in principle be arbitrarily chosen, but usually it is initialized to be zero.
  • the second step in the two step process (S5) 409 is to improve the estimates for the gravitational and the inertial vectors, if J; and J 2 are not substantially equal to zero.
  • the term substantial means up to a certain noise level, or when a pre-defined threshold value (e.g. the difference is equal or lower than 0.001) is reached.
  • the method solved this in an iterative way. Assuming that neither J; nor J 2 equal to zero, the following steps are, according to one embodiment, performed:
  • V g [k + l] V a [k + l] - V, [k +
  • Equation 9 shows an improved estimate is determined for both the inertial and the gravitational acceleration vectors, namely V 1 [k + 1] and V g [k + 1] for the subsequent moment k+1. Parallel to this a new estimate is determined for the gravitational vector, namely ⁇ - m] in accordance to equation 6 and step (S4) 407 is repeated. Accordingly, the target function J is minimized in a least mean square sense
  • V g usually, one can get a reasonably good V g simply by low-pass filtering or averaging V a , in particular, in the case of cyclic movements, like walking or cycling where V g varies around its nominal value, or more generally, when the gravitational component V g varies slowly compared to the inertial component V 1 . Although there are exceptions, normal body movements in daily activities mostly fall into those categories.
  • the proposed method Since only acceleration data are needed, the proposed method, therefore, provides a useful and more efficient and cost-effective way to extract both orientational and inertial acceleration information compared to the prior art solutions.
  • An Xsens inertial measurement unit consisting of 3D gyroscopes, 3D accelerometers and 3D magnetometers, is used to obtain 3-dimensional acceleration data as well as reference gravitational components, see MTi and MTx User Manual and Technical Documentation, Xsens Technologies B.V., 2006, hereby incorporated by reference.
  • the sampling frequency is 100Hz.
  • the proposed algorithm, or the method discussed previously, runs on the acceleration data and the extracted gravitational components ⁇ x g ,y g ,z g ) are compared with the reference ones.
  • Figure 9 shows a device 900 according to the present invention comprising a receiver (R) 901 and a processor (P) 902.
  • the receiver for receiving a sequence of acceleration readout vectors V a [k] from the device, and the processor adapted, for a given sampling moment k perform the method steps as disclosed in Fig. 4.
  • the device may be a three axial accelerometer, an activity monitor (AM), a rehabilitation monitoring system adapted to record limb trajectories during exercising, a vital body parameter measuring device, a joystick, and the like.
  • the device may further comprise a memory having stored therein an algorithm to perform the method steps as disclosed in Fig. 4.
  • the device may also be a computer, e.g.
  • LAP LAP, laptop, PC computer, mobile telephone and the like, which is capable of receiving the acceleration readout vectors V a [k] measured by an accelerometer and thus process the data external, such that the gravitational and the inertial acceleration components are extracted from the acceleration readout vectors V a [k] .

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
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  • Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)
  • User Interface Of Digital Computer (AREA)
  • Length Measuring Devices With Unspecified Measuring Means (AREA)

Abstract

Cette invention porte sur un procédé d'extraction de composantes vectorielles d'accélération inertielle Vi et gravitationnelle Vg d'un vecteur d'accélération Va = Vi + Vg mesuré par un accéléromètre lorsque l'orientation absolue du système de coordonnées d'accéléromètre par rapport au système de coordonnées de la terre varie au cours du temps. Une séquence de vecteurs de lecture d'accélération Va [k] venant de l'accéléromètre est reçue. Pour un moment d'échantillonnage donné k, une estimation temporelle (I)g [k] est déterminée pour le vecteur d'accélération gravitationnelle Vg, l'estimation temporelle étant déterminée dans le système de coordonnées d'accéléromètre à l'aide des vecteurs de lecture d'accélération venant de l'accéléromètre. Une première estimation pour le vecteur d'accélération inertielle (II)i [k] est établie à zéro. Une mesure de la différence entre le vecteur de lecture Va [k] et la somme de (I)g [k] + (II)i [k] est déterminée et une mesure de la différence de longueur entre l'estimation (II)g [k] et le vecteur d'accélération gravitationnelle réelle Vg est déterminée. Si les mesures déterminées ne sont pas sensiblement égales à zéro, les estimations (II)g [k] et (II)i [k] sont remplacées par l'estimation améliorée suivante, et les étapes mentionnées ci-dessus sont répétées.
PCT/IB2008/053399 2007-09-03 2008-08-25 Procédé d'extraction de composantes vectorielles inertielle et gravitationnelle de vecteurs d'accélération mesurés par un accéléromètre Ceased WO2009031064A2 (fr)

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EP07115496 2007-09-03
EP07115496.7 2007-09-03

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WO2009031064A3 WO2009031064A3 (fr) 2009-07-02

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120209117A1 (en) * 2006-03-08 2012-08-16 Orthosensor, Inc. Surgical Measurement Apparatus and System
RU2580893C2 (ru) * 2010-08-04 2016-04-10 Конинклейке Филипс Электроникс Н.В. Мониторинг сигналов жизнедеятельности организма во время движения
KR20210049044A (ko) * 2020-05-15 2021-05-04 베이징 바이두 넷컴 사이언스 테크놀로지 컴퍼니 리미티드 위치 정보 결정 방법, 장치 및 기기
US12220222B2 (en) 2015-01-28 2025-02-11 Koninklijke Philips N.V. Device and method for determining and/or monitoring the respiratory effort of a subject

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TWI419537B (zh) * 2009-12-23 2013-12-11 Inventec Appliances Corp A mobile phone for measuring balance and a method of measurement
CN106767776A (zh) * 2016-11-17 2017-05-31 上海兆芯集成电路有限公司 移动设备及求取移动设备姿态的方法
TWI737237B (zh) * 2020-03-25 2021-08-21 國泰醫療財團法人國泰綜合醫院 足部慣性量測系統

Family Cites Families (3)

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FI118745B (fi) * 2003-07-09 2008-02-29 Newtest Oy Automaattinen liikuntalajien tunnistusmenetelmä ja liikuntalajitunnistin
KR100653315B1 (ko) * 2005-01-04 2006-12-01 주식회사 헬스피아 중력방향의 자동인식이 가능한 휴대형 단말기를 이용한운동량 측정방법
JP4967368B2 (ja) * 2006-02-22 2012-07-04 ソニー株式会社 体動検出装置、体動検出方法および体動検出プログラム

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120209117A1 (en) * 2006-03-08 2012-08-16 Orthosensor, Inc. Surgical Measurement Apparatus and System
RU2580893C2 (ru) * 2010-08-04 2016-04-10 Конинклейке Филипс Электроникс Н.В. Мониторинг сигналов жизнедеятельности организма во время движения
US9833171B2 (en) 2010-08-04 2017-12-05 Koninklijke Philips N.V. Monitoring of vital body signals during movement
US12220222B2 (en) 2015-01-28 2025-02-11 Koninklijke Philips N.V. Device and method for determining and/or monitoring the respiratory effort of a subject
KR20210049044A (ko) * 2020-05-15 2021-05-04 베이징 바이두 넷컴 사이언스 테크놀로지 컴퍼니 리미티드 위치 정보 결정 방법, 장치 및 기기
KR102595677B1 (ko) * 2020-05-15 2023-10-27 아폴로 인텔리전트 커넥티비티 (베이징) 테크놀로지 씨오., 엘티디. 위치 정보 결정 방법, 장치 및 기기

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WO2009031064A3 (fr) 2009-07-02

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