KR20190056647A - Device for measuring angle of ankle based on inertial sensors - Google Patents

Abstract

According to an embodiment of the present invention, a device for measuring an angle of an ankle joint based on an inertial sensor calculates an angle (ρ) of an ankle joint (J) with rotary axes (X, X′). To this end, the device for measuring an angle of an ankle joint based on an inertial sensor comprises: a first inertial sensor attached to a first part of a human body based on the ankle joint (J); a second inertial sensor attached to a second part of the human body on the opposite side of the first part based on the ankle joint (J); and a processing unit calculating the angle (ρ) of the ankle joint (J) based on a unit vector (j1) in an axial direction of the rotary axes (X, X′) viewed by the first inertial sensor and a unit vector (j2) in an axial direction of the rotary axes (X, X′) viewed by the second inertial sensor.

Description

TECHNICAL FIELD [0001] The present invention relates to an inertial sensor-based ankle joint angle measuring device,

Embodiments relate to an inertial sensor-based ankle joint angle measuring apparatus.

The ankle joint is a joint that absorbs the shock applied to the foot and shank during walking of the human body and enables the human body to walk forward. The ankle joints should have sufficient flexibility to absorb impacts applied to the feet and shin during contact with the ground while the human body is walking. Accordingly, the ankle joint of the human body has a moving axis to cope with various spatial shapes, and the axis during walking of the human body is angled with respect to a virtual horizon when viewed from above. Or when the foot that is in contact with the ground is viewed from the side, it moves at an angle to the ground. These axes are also referred to as " torsional axes ". In addition, various large and small bones constituting the ankle joint are firmly connected by a connective tissue (e.g., ligament) so that the ankle joint is strong enough to withstand the driving force applied to the foot and shin during walking of the human body.

On the other hand, spasticity refers to upper motor neuron syndrome caused by damage to the central nervous system, resulting in hyperexcitability of renal reflexes with rate-dependent characteristics. This rigidity prevents the human body from walking. If stiffness persists, joint pain and deformation will occur. Objective evaluation of the ankle joint is required to treat such stiffness. The evaluation of the ankle joint is mainly made by measuring the angle of the ankle joint in the clinical field. For example, the modified tardieu scale (MTS) is an evaluation tool. However, current medical practitioners mainly use angle gauges to measure the angle of the ankle joint, so the measurement accuracy of the ankle joint is lowered, and the device for accurately measuring the angle of the ankle joint is very expensive commercially and is often difficult to operate. Therefore, there is a demand for a device for measuring the angle of the joint, which is convenient and easy to use by medical personnel in the clinical field.

There is an example of measuring the angle of the ankle joint using the inertial sensor in response to the above requirement. The ankle joints are shorter than other joints in the human body, inertial sensors are small enough to be used for ankle joints, lightweight, portable and cost effective. According to the method of measuring the angle of the ankle joint using the inertial sensor disclosed up to now, the angle of the ankle joint can be measured without considering the torsion axis of the ankle joint whose angle changes during the dorsiflexion and plantar flexion, Was measured. In addition, since the inadequate sensor position of the inertia sensor reduces the accuracy of the angle measurement of the ankle joint, it is necessary to provide a guide for the movement of the ankle joint based on the anatomical location of the ankle joint. .

For example, Japanese Laid-Open Patent Publication No. 2003-319920 discloses an apparatus and method for evaluating joint motion function.

An object of the present invention is to provide an inertial sensor-based ankle joint angle measuring apparatus for calculating an angle of ankle joint in consideration of a torsional axis of an ankle joint.

An object of the present invention is to provide an inertial sensor-based ankle joint angle measuring apparatus for measuring an angle of an ankle joint without guiding the movement of the ankle joint even if an inertial sensor is installed on an arbitrary portion of the human body based on the ankle joint will be.

An inertial sensor-based ankle joint angle measuring apparatus for calculating an angle? Of an ankle joint J having an axis of rotation X (X ') according to an embodiment includes an ankle joint J, A first inertial sensor attached to the portion; A second inertial sensor attached to a second portion of the human body opposite to the first portion with respect to the ankle joint J; And a unit vector (j1) in the axial direction of the rotation axis (X; X ') viewed from the first inertial sensor and a unit vector in the axial direction of the rotation axis (X; X' of the ankle joint (J) based on the angle (j2) of the ankle joint (J).

Wherein the processing unit is configured to calculate a value obtained by multiplying a unit vector j1 in the axial direction of the rotation axis X (X ') viewed from the first inertia sensor by a first set rotation matrix and a value obtained by multiplying the rotation axis The angle? Of the ankle joint J can be calculated based on a value obtained by multiplying the unit vector j2 in the axial direction of the ankle joint X by the set second rotation matrix.

Wherein the processing unit calculates a product of the unit vector j1 in the axial direction of the rotation axis X and the first rotation matrix viewed from the first inertial sensor by the rotation axis X ' The unit vector j2 in the axial direction of the first rotation matrix and the second rotation matrix can be set to be equal to the product of the unit vector j2 in the axial direction and the second rotation matrix.

Wherein the first inertial sensor is attached to a first portion of the human body at random with the orientation of the first inertial sensor being attached and the orientation of the second inertial sensor is randomly attached to the second portion of the human body .

The processing unit calculates the angular speed g2 in the axial direction of the rotation axis (X; X ') viewed from the first portion based on the angular velocity g1 measured by the first inertia sensor and the angular velocity g2 measured by the second inertia sensor And the unit vector j2 in the axial direction of the rotation axis X (X ') viewed from the second portion can be calculated.

Wherein the processing unit corrects the angular velocity g1 measured by the first inertial sensor to a first orthogonality value orthogonal to the ankle joint plane perpendicular to the rotation axis and an angular velocity g2 measured by the second inertia sensor to the ankle joint plane The unit vector j1 in the axial direction of the rotation axis X, X 'viewed from the first portion, and the unit vector j2 in the axial direction of the rotation axis X, X' viewed from the second portion on the basis of the difference value of the second ortho- ') In the axial direction can be calculated.

Wherein the processing unit calculates the unit vectors at a point at which the sum of the difference between the first orthogonal projection value and the second orthographic projection value is minimized in the axial direction of the rotation axis (X; X ') viewed from the first portion And a unit vector (j2) in the axial direction of the rotation axis (X; X ') viewed from the second portion.

The processing unit may calculate the unit vectors at a point where a sum of squares of difference values between the first orthogonal projection value and the second orthogonal projection value is minimized with time based on the Gauss-Newton method.

The inertial sensor-based ankle joint angle measuring apparatus according to one embodiment can calculate the angle of the ankle joint considering the torsional axis of the ankle joint.

According to the inertial sensor-based ankle joint angle measuring apparatus according to an embodiment, the angle of the ankle joint can be measured without guiding the movement of the ankle joint even if the inertial sensor is installed on an arbitrary portion of the human body based on the ankle joint.

The effects of the inertial sensor-based ankle joint angle measuring device according to one embodiment are not limited to those mentioned above, and other effects not mentioned may be clearly understood by those skilled in the art from the following description.

FIG. 1 is a block diagram schematically showing an inertial sensor-based ankle joint angle measuring apparatus according to an embodiment.
FIG. 2 is a view showing a first inertial sensor and a second inertial sensor according to an embodiment attached to a first portion and a second portion of a human body, respectively, with reference to an ankle joint.

Hereinafter, embodiments will be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In the following description of the embodiments, detailed description of known functions and configurations incorporated herein will be omitted when it may make the best of an understanding clear.

In describing the components of the embodiment, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected or connected to the other component, Quot; may be " connected, " " coupled, " or " connected. &Quot;

The components included in any one embodiment and the components including common functions will be described using the same names in other embodiments. Unless otherwise stated, the description of any one embodiment may be applied to other embodiments, and a detailed description thereof will be omitted in the overlapping scope.

Referring to FIGS. 1 and 2, an inertial sensor-based ankle joint angle measuring apparatus 100 according to an embodiment may calculate an angle of an ankle joint having a rotation axis X (X '). The inertial sensor-based ankle joint angle measuring apparatus 100 may include a first inertial sensor 110, a second inertial sensor 120, and a processing unit 130.

As used herein, the term "axis of rotation" refers to the axis of rotation of the ankle joint, and the axis of rotation may be thought of as a torsion axis that becomes the center of rotation of the ankle as it flexes or extends. Accordingly, the ankle joint can be considered to behave like a mechanical hinge joint. However, the movement of the ankle is not limited to a specific motion.

The angle of the ankle joint as used herein refers to an angle formed by the rotation axis X of the ankle joint J before exercise and the rotation axis X 'of the athletic joint J after exercise as the ankle bends or stretches. (?). That is, the ankle joint has a twist axis.

,

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으로 표현될 수 있다.The first inertial sensor 110 measures acceleration, angular rate and predetermined time period represented by the local coordinate system x1, y1, z1 of the first inertial sensor 110 . The inertia values, angular velocity and angular velocity, which are the inertia values measured by the first inertial sensor 110,

,

And

. ≪ / RTI >

,

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로 표현된다. 여기서, 각가속도는 3차 근사한 값을 사용한다.The second inertial sensor 120 may measure the acceleration, the angular velocity, and the predetermined time interval represented by the local coordinate system (x1, y1, z1) of the second inertial sensor 120. [ The inertia values, the angular velocity and the angular acceleration, which are the inertia values measured by the second inertia sensor 120,

,

And

Lt; / RTI > Here, the third-order approximation value is used for the angular acceleration.

Here, the " local coordinate " measured by the inertial sensor is referred to as a virtual space in which the inertia values measured by the inertial sensor are expressed based on the position where the inertial sensor is attached.

The first inertial sensor 110 may be attached to the first portion of the human body with reference to the ankle joint J and the second inertial sensor 120 may be attached to the ankle joint J with respect to the ankle joint J, And can be attached to the second portion of the human body.

Here, the position of each of the inertial sensors 110 and 120 attached thereto and their respective orientations are considered to be unknown. In particular, the axis of each inertial sensor itself does not necessarily coincide with the rotation axis X (X ') of the ankle joint J.

1, a first part of the human body is shown as a shank and a second part of the human body is shown as a foot. However, the present invention is not limited thereto and the first part may be a foot and the second part may be a shank. have. In other words, the attaching positions of the first inertial sensor 110 and the second inertial sensor 120 may be mutually changed.

The processing unit 130 reads the unit vector j1 in the axial direction of the rotating shaft X viewed from the first inertial sensor 110 and the unit vector j1 in the axial direction of the rotating shaft X viewed from the second inertial sensor 120. [ the angle? of the ankle joint J can be calculated based on the angle? 2.

First, the unit vector j1 in the axial direction of the rotation axis X as viewed from the first inertial sensor 110 and the unit vector j2 in the axial direction of the rotation axis X as viewed from the second inertia sensor 120 The method of calculation will be described.

The first inertial sensor 110 measures the acceleration of the ankle joint J viewed from the first portion at every predetermined time (expressed in the local coordinate system of the first inertial sensor 110), the acceleration of the ankle joint J around the ankle joint J, The radial acceleration and the tangential acceleration due to the rotation of the sensor 110, the angular velocity of the ankle joint J, and the angular acceleration thereof can be measured.

The second inertial sensor 120 measures the acceleration of the ankle joint J viewed from the second portion at every predetermined time (represented by the local coordinate system of the second inertial sensor 120), the acceleration of the ankle joint J around the ankle joint J, The radial acceleration and the tangential acceleration due to the rotation of the sensor 120, the angular velocity of the ankle joint J, and the angular acceleration thereof can be measured.

The inertia values such as the acceleration and angular velocity measured by the first inertial sensor 110 and the inertia values such as the acceleration and the angular velocity measured by the second inertial sensor 120 are calculated based on the ankle joint J viewed from the first inertial sensor 110, The unit longitudinal direction vector j2 of the rotational axis X of the ankle joint J viewed from the second inertial sensor 120 and the unit longitudinal direction vector j2 of the rotational axis X of the ankle joint J are calculated Can be used.

The angular velocity of the ankle joint J measured by the first inertial sensor 110 and the angular velocity of the ankle joint measured by the second inertial sensor 120 are different from each other only by the orientation of the vector and the rotation matrix, The projection to the joint plane is assumed to have the same length at the same time. Here, " ankle plane " refers to a plane perpendicular to the axis of rotation of the ankle joint.

The inertia values measured by the first inertia sensor 110 and the inertia values measured by the second inertia sensor 120 described above may be expressed as " the angular velocity of the ankle joint J measured by the first inertial sensor 110, The angular velocity of the ankle joint measured by the sensor J must satisfy the assumption that the angular velocity of each of the ankle joint planes is the same at the same time, . At this time, the angular velocity measured by the first inertial sensor 110 is converted into a first orthogonality value orthogonal to the ankle joint plane and an angular velocity measured by the second inertia sensor 120 to the difference between the second orthogonality value orthogonal to the ankle joint plane The unit length direction vectors j1 and j2 can be calculated by minimizing the value. These unit length direction vectors (j1, j2) can be expressed through angle parameters (e.g., spherical coordinate system components) as shown in Fig.

In one embodiment, when a value obtained by summing up values obtained by squaring the difference between the first orthogonal projection value and the second orthogonal projection value at every predetermined time is defined as a 'square error', until the square error becomes smaller than the setting size The unit length direction vectors (j1, j2) can be calculated by minimizing the square error. For example, the processing unit 130 may calculate unit length vectors j1 and j2 using a Gauss-Newton algorithm.

The unit vector j1 in the axial direction of the rotation axis X and the rotation axis X in the direction of the second inertia sensor X are calculated from the first inertial sensor calculated on the basis of the above- A method of calculating the angle p of the ankle joint J based on the unit vector j2 of the ankle joint J will be described.

The first inertial sensor 110 and the second inertial sensor 120 each have a reference frame represented by a local coordinate system while the first inertial sensor 110 and the second inertial sensor 120 Are assumed to have the same common fixed reference frame.

The orientation of the first inertial sensor 110 with respect to this fixed reference frame and the orientation of the second inertial sensor 120 with respect to the fixed reference frame are represented by rotation matrices R1 (t) and R2 (t), respectively.

The rotation matrix R1 (t) transforms the unit vector j1 in the axial direction of the rotation axis X (X ') viewed from the first inertial sensor 110 into a fixed reference frame, and the rotation matrix R2 (t) The unit vector j2 in the axial direction of the rotation axis X (X ') viewed from the inertial sensor 120 is converted into a fixed reference frame. In other words, the unit vector j1 in the axial direction of the rotation axis X (X ') viewed from the first inertial sensor 110 is multiplied by the rotation matrix R1 (t), and the rotation axis R1 (J1, j2) are transformed into a common fixed reference frame by multiplying the unit vector j2 in the axial direction of the reference frame (X, X; X ') by the rotation matrix R2 (t) to be represented in a common coordinate system.

Here, a vector obtained by multiplying the unit vector j1 in the axial direction of the rotation axis X (X ') viewed from the first inertial sensor 110 by the rotation matrix R1 (t) and a vector obtained by multiplying the rotation axis The rotation matrices R1 (t) and R2 (t) can be set such that the vector multiplied by the rotation matrix R2 (t) is equal to the unit vector j2 in the axial direction of the X axis X '.

The angle p of the ankle joint J is a vector obtained by multiplying the unit vector j1 in the axial direction of the rotation axis X (X ') viewed from the first inertial sensor 110 by the rotation matrix R1 (t) Is determined by the angle between the vector obtained by multiplying the unit vector j2 in the axial direction of the rotation axis X (X ') viewed from the second inertial sensor 120 by the rotation matrix R2 (t).

As described above, the basic concept described above can be applied to various embodiments. It should be noted that the above description is only one method for calculating the angle? Of the ankle joint J, and the embodiments are not necessarily limited to the above.

The method according to an embodiment may be implemented in the form of a program command that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions to be recorded on the medium may be those specially designed and configured for the embodiments or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI > or equivalents, even if it is replaced or replaced.

Claims (8)

An inertial sensor-based ankle joint angle measuring device for calculating an angle of an ankle joint having a rotation axis,
A first inertial sensor attached to a first portion of the human body based on the ankle joint;
A second inertial sensor attached to a second portion of the human body opposite to the first portion with respect to the ankle joint; And
A processing unit for calculating an angle of the ankle joint based on a unit vector in the axial direction of the rotation axis viewed from the first inertial sensor and a unit vector in the axial direction of the rotation axis viewed from the second inertia sensor;
An inertial sensor-based ankle joint angle measuring device.
The method according to claim 1,
Wherein the processing unit includes a value obtained by multiplying a unit vector in the axial direction of the rotation axis viewed from the first inertia sensor by a first rotation matrix and a unit vector in the axial direction of the rotation axis viewed from the second inertia sensor, Wherein the angle of the ankle joint is calculated based on a value obtained by multiplying the angle of rotation of the ankle joint by a two-rotation matrix.
3. The method of claim 2,
Wherein the processing unit calculates the product of the unit vector in the axial direction of the rotation axis viewed from the first inertia sensor and the first rotation matrix by the unit vector in the axial direction of the rotation axis viewed from the second inertia sensor and the second rotation matrix And sets the first rotation matrix and the second rotation matrix so that the first rotation matrix and the second rotation matrix are equal to each other.
The method according to claim 1,
Wherein the first inertial sensor is attached to a first portion of the human body at random with the orientation of the first inertial sensor being attached and the orientation of the second inertial sensor is randomly attached to the second portion of the human body An inertial sensor based ankle joint angle measuring device.
The method according to claim 1,
Wherein the processing unit calculates the unit vector in the axial direction of the rotation axis viewed from the first portion based on the angular velocity measured by the first inertia sensor and the angular velocity measured by the second inertia sensor, An inertial sensor-based ankle joint angle measuring device for calculating the unit vector in the axial direction of the ankle joint.
6. The method of claim 5,
The angular velocity measured by the first inertial sensor is converted into a first orthogonality value orthogonal to the ankle joint plane perpendicular to the rotation axis and an angular velocity measured by the second inertia sensor to a second orthogonality orthogonal to the ankle joint plane, And calculates a unit vector in the axial direction of the rotation axis viewed from the first portion and a unit vector in the axial direction of the rotation axis viewed from the second portion based on the difference value of the value.
The method according to claim 6,
Wherein the processing unit includes unit vectors in the axial direction of the rotation axis as viewed from the first portion and unit vectors in the axial direction of the rotation axis viewed from the first portion as unit vectors at a point where the sum of the difference between the first orthogonal projection value and the second orthogonal projection value is minimized, And a unit vector in the axial direction of the rotating shaft as viewed from the two parts.
8. The method of claim 7,
Wherein the processing unit includes an inertial sensor based ankle joint angle measurement unit that calculates the unit vectors at a point at which a sum of squares of difference values of the first orthogonal projection value and the second orthogonal projection value is minimized based on a Gauss- Device.

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