DETERMINATION DEVICE, DETERMINATION METHOD, AND COMPUTER PROGRAM PRODUCT

1 . A determination device, comprising:

a first measurement unit fixed to a body unit to be attached to an attachment surface, and configured to measure acceleration in at least one direction;

a first calculator configured to calculate inclination information that indicates inclination of the attachment surface based on the acceleration measured by the first measurement unit during a first period;

a storage configured to store therein the inclination information calculated by the first calculator;

a second calculator configured to calculate difference information that indicates a difference between the inclination information stored in the storage and inclination information newly calculated by the first calculator;

a determination unit configured to determine that an attached state of the body unit with respect to the attachment surface changes when the difference information continuously indicates a difference equal to or greater than a predetermined value during a second period; and

an output unit configured to output information based on a determination result obtained by the determination unit.

2 . The device according to claim 1 , wherein

the first calculator is configured to calculate a vector that indicates the inclination of the attachment surface as the inclination information, and

the second calculator is configured to calculate at least one of an inner product, angle, and cosine value of the angle formed by the vector stored in the storage and a vector newly calculated by the first calculator as difference information.

3 . The device according to claim 1 , wherein

the first measurement unit is configured to continuously measure acceleration in a plurality of directions,

the first calculator is configured to calculate the vector that indicates the inclination of the attachment surface as the inclination information based on the acceleration in the plurality of directions, and

the second calculator is configured to

calculate at least one of an inner product, an angle, and a cosine value of the angle as first information, each of the inner product, the angle, and the cosine value being formed by the vector stored in the storage and a measurement axis of the acceleration in each of the plurality of directions,

calculate at least one of an inner product, an angle, and a cosine value of the angle as second information, each of the inner product, the angle, and the cosine value being formed by a vector newly calculated by the first calculator and a measurement axis of the acceleration in each of the plurality of directions, and

calculate a difference between the first information and the second information corresponding to the first information as difference information.

4 . The device according to claim 1 , wherein the output unit is configured to output information based on the determination result obtained by the determination unit through communication.

5 . The device according to claim 1 , wherein the first measurement unit is configured to continuously measure at least acceleration in a gravity direction.

6 . The device according to claim 1 , wherein

the attachment surface is on a surface of a living body, or in a position substantially identical to the surface of the living body, and

the device further comprises a controller configured to control so that the first period starts when the controller estimates that the living body is continuously in a stationary state based on the acceleration continuously measured by the first measurement unit or when the controller acquires a predetermined signal from outside.

7 . The device according to claim 6 , wherein the first calculator calculates the inclination information that indicates the inclination of the attachment surface, after performing a filtering process on the acceleration measured by the first measurement unit during the first period, the filtering process eliminating variation in the acceleration caused by a respiration or temporary movement of the living body.

8 . The device according to claim 6 , further comprising a second measurement unit configured to measure a living body signal, wherein the output unit is configured to further output information based on a measurement result obtained by the second measurement unit.

9 . A determination method comprising:

measuring acceleration of a body unit to be attached to an attachment surface in at least one direction;

calculating inclination information that indicates inclination of the attachment surface based on the acceleration measured during a first period;

storing the calculated inclination information;

calculating difference information that indicates a difference between the stored inclination information and inclination information newly calculated;

determining that an attached state of the body unit with respect to the attachment surface changes when the difference information continuously indicates a difference equal to or greater than a predetermined value during a second period; and

outputting information based on a determination result obtained at the determining.

10 . A computer program product comprising a computer-readable medium containing a program executed by a computer, the program causing the computer to execute:

calculating inclination information that indicates inclination of an attachment surface based on acceleration of a body unit to be attached to the attachment surface in at least one direction, the acceleration being measured during a first period;

storing the calculated inclination information;

calculating difference information that indicates a difference between the stored inclination information and inclination information newly calculated;

determining that an attached state of the body unit with respect to the attachment surface changes when the difference information continuously indicates a difference equal to or greater than a predetermined value during a second period; and

outputting information based on a determination result obtained at the determining.