Wearable device, posture measurement method, and non-transitory recording medium
Accelerations (Ax, Ay, Az) in directions along (X′, Y′, Z′) detected by an acceleration sensor 10 are converted, based on a correction angle γ, which is an angle between a first detection axis X′ and a first posture axis X, into accelerations (Bx By, Bz) in directions along three posture axes (X, Y, Z). A pitch angle α and a roll angle β, which indicate a posture of a portion to which the wearable device is attached, are calculated based on the accelerations (Bx By, Bz) obtained by the conversion based on the correction angle γ.
1. A wearable device capable of measuring a posture of a portion of a body to which the wearable device is attached, the wearable device comprising:
an acceleration sensor configured to detect respective accelerations in directions along three detection axes that are orthogonal to each other; and
a posture angle calculation unit configured to calculate, based on the accelerations detected by the acceleration sensor, a posture angle around at least one posture axis of three posture axes that define a reference of the posture of the portion, to which the wearable device is attached, with respect to a direction of gravity, the three posture axes being orthogonal to each other,
wherein a coordinate system obtained by rotating a detection coordinate system, defined by the three detection axes, around one of the detection axes by a correction angle and by moving the detection coordinate system in parallel matches a posture coordinate system defined by the three posture axes, the correction angle being formed between the detection axis and the posture axis,
wherein the posture calculation unit converts, based on the correction angle, the accelerations in the directions along the three detection axes detected by the acceleration sensor into accelerations in directions along the three posture axes,
wherein the posture calculation unit calculates, based on the accelerations at the three posture axes obtained by the conversion, the posture angle around the at least one posture axis,
wherein the wearable device includes an acceleration obtaining unit configured to obtain, upon a signal being input, the accelerations detected by the acceleration sensor, the signal indicating that a predetermined motion of, while maintaining the posture angle at two of the posture axes, changing the posture angle at one of the posture axes that forms the correction angle with one of the detection axes is being performed,
wherein the wearable device includes a correction angle calculation unit configured to calculate, based on the accelerations obtained by the acceleration obtaining unit when the predetermined motion is being performed, the correction angle,
wherein the three posture axes are composed of a first posture axis, a second posture axis, and a third posture axis,
wherein the three detection axes are composed of a first detection axis that forms the correction angle with the first posture axis, a second detection axis that forms the correction angle with the second posture axis, and a third detection axis that forms the correction angle with the third posture axis,
wherein the acceleration sensor detects a first acceleration in a direction along the first detection axis, a second acceleration in a direction along the second detection axis, and a third acceleration in a direction along the third detection axis, respectively,
wherein the correction angle calculation unit calculates, based on first accelerations, second accelerations, and third accelerations obtained at a plurality of timings when the predetermined motion is being performed, first rotation angles around the first detection axis and second rotation angles around the second detection axis at the respective timings,
wherein the correction angle calculation unit calculates respective ratios between the first rotation angles and the second rotation angles at the plurality of timings,
wherein the correction angle calculation unit calculates an average value and a variance of the ratios calculated for the plurality of timings,
wherein the correction angle calculation unit sets, based on the average value and the variance, an average value range of the ratios,
wherein the correction angle calculation unit specifies ratios included in the average value range,
wherein the correction angle calculation unit calculates an adjusted average value that is an average value of the specified ratios, and
the correction angle calculation unit obtains the correction angle based on the adjusted average value.
2. The wearable device according to claim 1 ,
wherein the predetermined motion is a motion of changing the posture angle at the first posture axis while maintaining the posture angle at the second posture axis and the third posture axis.
3. The wearable device according to claim 1 , comprising:
a storage unit configured to store information for the correction angle used to convert the accelerations in the posture angle calculation unit or
a communication unit configured to process a communication signal including information for the correction angle used to convert the accelerations in the posture angle calculation unit.
4. A posture measurement method, by a computer of an attached wearable device, for calculating a posture angle around at least one posture axis of three posture axes that define a reference of a posture of a portion of a body, to which the wearable device is attached, with respect to a direction of gravity, the three posture axes being orthogonal to each other,
wherein the wearable device includes an acceleration sensor configured to detect respective accelerations in directions along three detection axes that are orthogonal to each other,
wherein a coordinate system obtained by rotating a detection coordinate system, defined by the three detection axes, around one of the detection axes by a correction angle and by moving the detection coordinate system in parallel matches a posture coordinate system defined by the three posture axes, the correction angle being formed between the detection axis and the posture axis,
the posture measurement method comprising:
a step of converting, based on the correction angle, the accelerations in the directions along the three detection axes detected by the acceleration sensor into accelerations in directions along the three posture axes;
a step of calculating, based on the accelerations at the three posture axes obtained by the conversion, the posture angle around the at least one posture axis;
a step of obtaining, upon a signal being input, the accelerations detected by the acceleration sensor, the signal indicating that a predetermined motion of, while maintaining the posture angle at two of the posture axes, changing the posture angle at one of the posture axes that forms the correction angle with one of the detection axes is being performed; and
a step of calculating the correction angle based on the accelerations obtained in the step of obtaining the accelerations when the predetermined motion is being performed
wherein the three posture axes are composed of a first posture axis, a second posture axis, and a third posture axis,
wherein the three detection axes are composed of a first detection axis that forms the correction angle with the first posture axis, a second detection axis that forms the correction angle with the second posture axis, and a third detection axis that forms the correction angle with the third posture axis,
wherein the acceleration sensor detects a first acceleration in a direction along the first detection axis, a second acceleration in a direction along the second detection axis, and a third acceleration in a direction along the third detection axis, respectively, and
wherein in the step of calculating the correction angle,
a first rotation angle around the first detection axis and a second rotation angle around the second detection axis are calculated based on the first acceleration, the second acceleration, and the third acceleration obtained in the step of obtaining the accelerations when the predetermined motion is being performed;
a ratio between the first rotation angle and the second rotation angle is calculated; and
the correction angle is obtained based on the ratio.
5. The posture measurement method according to claim 4 ,
wherein the predetermined motion is a motion of changing the posture angle at the first posture axis while maintaining the posture angle at the second posture axis and the third posture axis.
6. The posture measurement method according to claim 4 ,
wherein in the step of calculating the correction angle,
based on first accelerations, second accelerations, and third accelerations obtained at a plurality of timings in the step of obtaining the accelerations when the predetermined motion is being performed, first rotation angles and second rotation angles at the respective timings are calculated;
respective ratios between the first rotation angles and the second rotation angles at the plurality of timings are calculated;
an average value and a variance of the ratios calculated for the plurality of timings are calculated;
an average value range of the ratios is set based on the average value and the variance;
ratios included in the average value range are specified;
an adjusted average value that is an average value of the specified ratios is calculated; and
the correction angle is calculated based on the adjusted average value.
7. A non-transitory recording storing a program for causing a computer of an attached wearable device to execute a posture measurement method for calculating a posture angle around at least one posture axis of three posture axes that define a reference of a posture of a portion of a body, to which the wearable device is attached, with respect to a direction of gravity, the three posture axes being orthogonal to each other,
wherein the wearable device includes an acceleration sensor configured to detect respective accelerations in directions along three detection axes that are orthogonal to each other,
wherein a coordinate system obtained by rotating a detection coordinate system, defined by the three detection axes, around one of the detection axes by a correction angle and by moving the detection coordinate system in parallel matches a posture coordinate system defined by the three posture axes, the correction angle being formed between the detection axis and the posture axis,
the posture measurement method comprising:
a step of converting, based on the correction angle, the accelerations in the directions along the three detection axes detected by the acceleration sensor into accelerations in directions along the three posture axes;
a step of calculating, based on the accelerations at the three posture axes obtained by the conversion, the posture angle around the at least one posture axis;
a step of obtaining, upon a signal being input, the accelerations detected by the acceleration sensor, the signal indicating that a predetermined motion of, while maintaining the posture angle at two of the posture axes, changing the posture angle at one of the posture axes that forms the correction angle with one of the detection axes is being performed; and
a step of calculating the correction angle based on the accelerations obtained in the step of obtaining the accelerations when the predetermined motion is being performed
wherein the three posture axes are composed of a first posture axis, a second posture axis, and a third posture axis,
wherein the three detection axes are composed of a first detection axis that forms the correction angle with the first posture axis, a second detection axis that forms the correction angle with the second posture axis, and a third detection axis that forms the correction angle with the third posture axis,
wherein the acceleration sensor detects a first acceleration in a direction along the first detection axis, a second acceleration in a direction along the second detection axis, and a third acceleration in a direction along the third detection axis, respectively, and
wherein in the step of calculating the correction angle,
a first rotation angle around the first detection axis and a second rotation angle around the second detection axis are calculated based on the first acceleration, the second acceleration, and the third acceleration obtained in the step of obtaining the accelerations when the predetermined motion is being performed;
a ratio between the first rotation angle and the second rotation angle is calculated; and
the correction angle is obtained based on the ratio.