WO2008018810A2

WO2008018810A2 - Body kinetics monitoring system

Info

Publication number: WO2008018810A2
Application number: PCT/PT2007/000034
Authority: WO
Inventors: José AUGUSTO AFONSO; José Higino GOMES CORREIA; Hélder Raul PEIXOTO DA SILVA; Luís Alexandre MACHADO DA ROCHA
Original assignee: Universidade Do Minho
Priority date: 2006-08-07
Filing date: 2007-08-07
Publication date: 2008-02-14
Also published as: PT103551A; WO2008018810A3; WO2008018810B1

Abstract

The present invention relates to a sensing system for the monitoring of posture, orientation and movement of a body in a three dimensional space, differentiating among the various stationary states and transient states in what the user can be. Sensing modules are composed by three-axis accelerometers, three-axis magnetometers and interfacing electronics. The device is encapsulated, enabling its use in adverse and harsh environments. The data monitored by the sensing modules are transmitted in real time, by the local communication device, to the central communication device, using a 2.4 GHz RF transceiver. Generic applications derived from the analysis of the monitored data include not only the rectification of a user's incorrect body posture, thereby avoiding injuries, but also the acceleration of the healing process in therapy or the simple monitoring of a user's physical activity. Being compact and encapsulated, this device can be used to monitor and analyze the movement of athletes in physical activity, e.g. a swimmer.

Description

DESCRIPTION "BODY KINETICS MONITORING SYSTEM"

Field of the invention

The present invention is generically related to sensors, more particularly with a system for acquisition of data relative to posture, orientation and movement of the human body. Application fields of this invention include the monitoring and analysis of physical activity in athletes as well as the evolution of therapy in patients.

Background of the invention

The monitoring of joint movements in living beings, with particular interest in human beings, is very useful for various applications, such as the body posture monitoring.

Electronic sensors have been developed for the measurement of angles between various parts of the body and joint movement angles, as described in US6871413. This document discloses a device containing inclinometers, a cable and connecting points. Each inclinometer contains pairs of accelerometers orthogonally oriented to each other, A/D converters, a multiplexer, a voltage regulator and a microprocessor. The microprocessor calculates the angle of each inclinometer in relation to other inclinometer. However, this system is unable to measure angles that are orthogonal to the gravity field.

The document US2003/0158699A1 discloses inclinometers containing three orthogonal accelerometers and three orthogonal magnetometers which are used to measure Earth' s magnetic and gravity fields, from which the pitch, roll and yaw angles are calculated. Low-pass filters are used to minimize the inertia effects at the accelerometers, which could interfere with the accuracy of the measurements. This invention allows multiple devices to be connected to a single bus. The US 2003/0158699 also discloses the orientation sensors for the calculation of the pitch, roll and yaw angles from Earth's magnetic and gravity fields. This device can measure angles from 0 to 360 degrees in the yaw and pith axes, and from -70 to +70 degrees in the roll axis. The yaw output is compensated for pitch and roll errors using embedded algorithms. However, the systems of these two patents do not perform the correction of the vertical component of the magnetic field.

The limitation of the movement to a maximum prescribed angle is given by US 5,823,975, US4,958,145, US5,089,808 and US5,128,655. These documents disclose limiting devices that allow the movement restriction to a maximum angle during the rehabilitation of a user. US5823975 discloses a communication device that provides information about the user's current state and progress. The devices are equipped with a visual or vibratory alarm to prevent the user from exceeding the prescribed limits to the movements to be executed, providing an immediate response regarding the said movements. However, the devices described in this document do not detect the posture, movement or orientation of the user' s body, mainly warning if an inclination angle has been exceeded.

US 5,593,431 discloses how to determine the physical posture of the user in relation to the Earth' s gravity field. It consists of a device with two or three DC accelerometers with measurement axes orthogonally mounted inside a housing. When the device is implanted, these axes are aligned with the axes of the user's body. The activity and position signals of the user's body, which are monitored by the sensors, might be stored and/or used to monitor the effect of the therapy in the user. This device provides multi-axis readings, stable position and monitoring of physical activity along two orthogonal axes, thus allowing a way to differentiate the posture of the user in rest and in activity. However, this device can not measure angles orthogonal to the gravity field. Moreover, it can not be used in adverse or harsh environments.

US2005/0126026A1 discloses a sensing system that distinguishes bending, sitting and standing positions, the sensor data being stored in a storage device versus time. It is capable to detect and indicate low/high activity in relation to the one prescribed, when a joint is stationary for a long time or in case of repetitive activities that might cause stress injury.

The present invention, unlike the documents previously presented, allows the correction of the magnetic field, given that it has different values in different locals and it is not parallel to the horizontal reference plane of the Earth. This correction constitutes a significant advantage since it allows the elimination of measurement errors associated with the influence of Earth' s magnetic field, thereby allowing the achievement of accurate monitoring values .

The communication between sensing modules can take place using a serial interface or a radiofrequency (RF) network, the data measured by the sensors being transferred in real time to the central communication device. The sensing modules and the local communication device can also be encapsulated thus allowing their use in adverse and harsh environments .

Summary of the invention

The main objective of the present invention is to provide a system for data gathering on posture, orientation and movement of the human body with a resolution of 1 degree in a three dimensional space.

One of the objectives of the present invention is to create a system that distinguishes the user's sitting, bending/rising and standing/lying positions, distinguishing in each said position the different postures the user might undertake.

The system detects and warns when the user remains for too long stationary, in a determined position, or with too little activity, and also detects and warns about repetitive activities.

This system corrects the magnetic field, since it is not parallel to Earth's horizontal reference plane.

The sensing modules and the local communication device are contained in a housing that allows their use in adverse or harsh environments (e.g. underwater, under unstable climatic conditions, etc.).

The sensing modules and the local communication device have a small and compact dimension in order to ensure comfort and flexibility to the user, allowing unobtrusive execution of physical activity. An advantage of the present invention is the possibility of using wireless communication (radiofrequency) , being its power consumption extremely low.

The sensing modules and the local communication device can be integrated in a textile basis (suit, shirt, pants, etc.)

These and other objects, characteristics and advantages of the present invention characterize a device to be placed at a living being, containing sensors, a processing unit and a data storage system for a potential failure transferring data to a central communication station, since these are sent in real time.

The system can be used for the monitoring of up to 60 users simultaneously using the same central communication device.

Brief description of the drawings

Many aspects of the present invention will be better understood with reference to some drawings thereof. The devices in the drawings are not necessarily at scale, being instead attention drawn into the main aspects of the present invention. The drawings are included without any limitative aspect and mainly aiming to provide a better understanding of the following description:

Figure Ia:

Schematic view of the sensors' arrangement on the user's body using wired communication.

Figure Ib: Schematic view of the sensors' arrangement on the user's body using wireless communication.

Figure 2:

Block diagram of a sensing module.

Figure 3:

System of axes according to figure 1.

Figure 4a:

Overall system of the invention (wired communication) .

Figure 4b:

Overall system of the invention (wireless communication) .

Figure 5:

Block diagram of the local/central communication device.

Detailed description of the invention

The sensing system (Figure 4a and 4b) of the present invention performs the monitoring of posture, orientation and body movement in a three dimensional space in real time, differentiating the user's several types of posture at sitting, bending/rising and vertical/horizontal positions .

The present inventors developed an electronic system that monitors in real time the body position and posture. This monitoring process, for instance, allows the user to correct his body posture in order to avoid a lesion. In therapy sections, it allows the user to correct his exercise in order to accelerate the healing process. It also allows controlling movements and exercises to avoid that a prescribed maximum angle is exceeded. It can also be used to assess the movement and posture of an athlete carrying out physical activities, such as a swimmer. This is made possible by the compactness of the system and by the possibility of its encapsulation, this allowing its use in adverse environments.

The system (figure 4a and 4b) contains a network of sensing modules (17) connected to the local communication unit (16,6) using a serial interface (12), Figure 4a, or connected to the central communication device (15) by means of a radiofrequency network (RF) (13,19), figure 4b. The data collected from the sensors are:

• Transmitted in real time by the local communication device (16,6) using radiofrequency (RF) (19) to the central communication device (15, figure 5) , in the case of figure 4a;

• Transmitted in real time by the sensing modules (17) using radiofrequency (RF) (13) to the central communication device (15, Figure 5) , in the case of figure 4b.

Both Earth' s gravity and magnetic fields are used to detect the posture of body and limbs. The gravitational force is used to detect the inclination while Earth' s- magnetic field is used to measure the rotation of the body in relation to the axis, perpendicular to the gravity field.

The inclination of a limb or body is measured using three- axis accelerometers (7), figure 2. These measure the angular difference between the accelerometer position and the gravity field. Similarly with rotation, three-axis magnetometers (8) are used, each measuring the angular difference between the magnetometer's position and Earth's magnetic field. The use of accelerometers (7) and magnetometers (8) in the sensing modules (figure 2) , allows the measurement of rotation and inclination of each limb or body part.

Special attention to the location of the sensing modules in the body was given, due to the accelerations caused by limb movements. In order to minimize this effect, the accelerometers are placed at the rotation center of the arms (shoulders) (1,2) and legs (hip) (3,4), where the acceleration due to limb rotation is zero, as one might observe in figures Ia and Ib. Thus, the rotation angles are easily obtained from the accelerometers readings.

The sensor network is comprised by sensing modules. Each module (figure 2) contains a three-axis accelerometer (7) and a three-axis magnetometer (8) that are used to obtain the pitch (θ), roll (φ) and yaw (φ) angles for each joint (figures Ia and Ib) . The module (5) , figure 1 and Ib, preferably placed on the back, monitors the inclination and orientation of the spine and acts as the reference module for the other sensors. By calculating the difference between the measured angles at the shoulders and hip in relation to the reference module, the angles of these joints are found.

Given the gravity field, g = [a_x,a_y,a_z) , and the magnetic field, m — \m_x,m_y,m_z), and by using the system of axes illustrated in figure 3, the pitch (θ) and roll {φ) angles for the reference module (5) are given by θ =

The angles can be calculated up to 360 degrees, taking into consideration the signals concerning each angle. The readings from the magnetic sensors can be compensated for the roll and pitch at the horizontal plane (Earth's horizontal reference) by using the equations

X₁₁ = m_z cosθ -m_x ήΩ.θsm.φ - m_y s\τ\θcosφ

' II ' Y_H = m_x cos_$9 - m_y smφ

The yaw angle ( φ ) is calculated using the equation

ø . ( Ill )

The equation (II) will be valid if the magnetic field vector is located at the Earth's horizontal reference plane, which is not the present case, since the magnetic vector points to the magnetic north pole, yet having a component in the vertical axis. In order to solve this problem, the magnetic sensor measurements are rotated along an axis located at the plane parallel to the surface of the Earth and rotated by 90 degrees from the horizontal component of the Earth' s magnetic field.

The rotation vector v =(a_x,a_y,a_z)x(m_x,m_y,m₂) (IV) corresponds to the vector product of the gravity and magnetic fields, while the rotation angle (V) is

obtained from the angle between the gravity field and the magnetic field. After calculating the rotation vector and angle, the rotation matrix is given by

v u + c V_yV_χU - V₂S V₂V₁U + V _yS

M ¹ r_rnot = V_χV_yU + V_χS V_yU + C V₂V_yU - V_xS (VI) .

V_xV₂U - V_yS V_yV₂U + V_χS v_zu +c wherein 5 = sin(α), c = cos(α) and w=l-cos(α)

The readings obtained by the magnetic sensors are compensated by the equation m_rot =M_rotm (VII) .

After this rotation of the magnetic vector to the horizontal plane, the roll and pitch angles are compensated by the equations:

X_H = m_rot cos θ — m_rot sin θ sin φ — m_rot sin θ cos φ

(VIII ) .

^YH = ^mrot_x ^{COS (}P - ^mro_ty ^{Sin <}P

Figure 2 illustrates the block diagram of a sensing module. The module is a hybrid microsystem with sensors. Due to its small dimension, low power consumption and the use of standard material and techniques applied in the semiconductor industry, low costs are foreseen for the manufacture of the sensing modules when manufactured at a large scale.

Once the movement of human limbs is of 5 Hz for internally generated movements, second order low-pass filters (9) with cutoff frequency of 40 Hz are placed at the sensors output (7,8) in order to reduce the noise and improve the resolution of the measurements. The differential measurement also eliminates any magnetic interference from Earth's magnetic field.

A 3D magnetic sensor (8) consisting of three magnetoresistive sensors with Wheatstone bridges (aligned at the three axes) is directly connected to a signal processing block (10) , while the accelerometer (7) is connected to the second order low-pass filter (9) . The signal processing block comprises three instrumentation amplifiers which convert the variations in the magnetoresistive bridges into voltage. The second order filters (9) are implemented using transconductance amplifiers, which are very appropriate to implement filters in integrated circuit drawings due to their small dimension when compared with the large area occupied by capacitors and resistors used in passive filters.

After being filtered, the signals are converted into digital signals by means of an analog to digital converter (ADC) (11) .

In the case of figure 4a, the digital signals are sent through serial interface (12) to the microprocessor (18) of the local communication device (16) .

The monitored data received by the local communication device are stored in the storage unit (memory flash) (20) and sent by RF (19) to the central communication device (15) , figure 5, in real time, at a sampling rate between 1 and 50 Hz. If the data transmission fails, these are retransmitted to the central communication device.

In the case of figure 4b, the digital signals are directly sent, by means of RF transmission (13) , to the microprocessor (18) of the central communication device (16) .

After receiving the data in the central communication device, figure 5, these are monitored/analyzed by a PC (14) for possible actions/modifications, e.g., in the assessment of physical activity or therapy progress in living beings.

It should be pointed out that the previously described embodiments of the present invention are only possible implementation examples, merely presented to provide a clear understanding of the principles of the present invention. Many variations and modifications might be applied to the previously mentioned embodiments, without extending the scope of the invention. All those modifications and variations must be included in the scope of this disclosure and present invention, and must be protected by the following claims.

Claims

1. A system for monitoring— posture, orientation and movement of bodies in space comprising sensing modules, processing unit, storage unit and communication unit, comprising a device that applies a .method for correction of the vertical component of Earth' s magnetic field that comprises the following steps:

defining the gravity field data, g = [a_x,a_y,a₂) , and the magnetic field data, m = \m_x,m_y,m₂); calculating the pitch {θ) and roll {φ) angles using the equation (I) ;

( I )

calculating the correction factors by means of the rotation vector (IV) , which corresponds to the vector product of the gravity and magnetic fields, and the rotation angle (V) , which corresponds to the angle between the gravity and magnetic fields;

v = (a_x,a_y,a₂)x(m_x,m_y,m₂) (IV)

a =^-zrccos[(a_x,a_y,a₂).(m_x,m_y,m₂)] (V)

applying the correction factors with the rotation matrix (VI) wherein the readings from the magnetic sensors are compensated by equation (VII) ; v_xu + c V_yV_xU - V₂S V₂V_xU + V_yS

M = v_xv_yu + v₂s V_yU + C v₂v_yu -v_xs (VI)

V_xV₂U - V_yS v_yv_zu + v_xs v]u + c wherein 5 = sin(α), c = cos(α) and w=l-cos(α)

<_t=M_rotm (VII)

compensating of the yaw (φ) angle for roll (φ) and pitch (θ) movements using equation (VIII) being its value determined by equation (III) ;

X₁₁ = m_rot! cos θ - m_m sin θ sin φ - m_rot sin θ cos φ

(VIII )

^YH = ™_ro_tl ∞^S<P -^mro_ly ^S™ <P

arctan —-\ (III)

2. A system for monitoring posture, orientation and movement of the human body, according to claim 1, characterized in that one of the sensing modules (reference module) is located in the trunk zone.

3. A system for monitoring posture, orientation and movement of the human body, according to claim 1, characterized in that the sensing modules are located in body areas where the linear acceleration caused by the rotation of the limbs is zero.

4. A system for monitoring posture, orientation and movement of the human body, according to claim 1, characterized in that the sensing modules have power consumption lower to 50 mW, provided by batteries.

5. A system for monitoring posture, orientation and movement of the human body, according to claim 1, characterized in that the sensing modules have compact dimensions and a volume inferior to 5 cm³.

6. A system for monitoring posture, orientation and movement of the human body, according to claim 1, characterized in that the communication unit is composed by a central communication device and one or more local communication devices.

7. A system for monitoring posture, orientation and movement of the human body, according to the preceding claims, characterized in that the sensing modules register their position in relation to Earth' s gravity and magnetic fields and transmit data through the local communication device to the central communication device, providing the posture, orientation and movement of the body.

8. A system for monitoring posture, orientation and movement of the human body, according to claim 6, characterized in that the local communication device sends the monitoring data to the central communication device in real time at a sampling rate between 1 and 50 Hz.

9. A system for monitoring posture, orientation and movement of the human body, according to claim 6, characterized in that the local communication device can be integrated in the sensing modules, allowing direct wireless communication with the central communication device.

10. A system for monitoring posture, orientation and movement of the human body, according to claim 9, characterized in that the wireless communication takes place by radiofrequency (RF) at 2.4 GHz, allowing the connectivity with personal devices (cellular phones, PDAs, laptop computers, etc.).

11. A system for monitoring posture, orientation and movement of the human body, according to claim 1, characterized in that the storage unit stores de monitored data, retransmitting them afterwards to the central communication device in case of transmission failure.

12. A system for monitoring posture, orientation and movement of the human body, according to claim 1, characterized in that the sensing modules and local communication devices are housed in hermetic materials, allowing their operation in adverse or harsh environments.

13. A system for monitoring posture, orientation and movement of the human body, according to the preceding claims, characterized in that the reference module, the sensing modules and the local communication device can be embodied in a textile basis.