Velocity calculating device, velocity calculation method, and navigation device

1. A velocity calculating device comprising:

a vertical acceleration detector mounted on a moving body, the vertical acceleration detector detecting an acceleration in a vertical direction generated due to an undulation of a contact surface that is in contact with the moving body;

a horizontal angular velocity detector mounted on the moving body, the horizontal angular velocity detector detecting an angular velocity around a horizontal axis that is perpendicular to a direction of travel of the moving body, the angular velocity being generated due to the undulation of the contact surface; and

circuitry configured to

calculate a correlation coefficient that represents a degree to which an acceleration in the direction of travel of the moving body is mixed into the acceleration in the vertical direction in accordance with an attachment angle with which a body including the vertical acceleration detector and the horizontal angular velocity detector is attached to the moving body;

calculate a true acceleration in the vertical direction by subtracting the acceleration in the direction of travel mixed into the acceleration in the vertical direction from the acceleration in the vertical direction, the acceleration in the direction of travel mixed into the acceleration in the vertical direction being calculated on the basis of the correlation coefficient; and

calculate a velocity of the moving body in the direction of travel of the moving body on the basis of the true acceleration in the vertical direction and the angular velocity around the horizontal axis.

2. The velocity calculating device according to claim 1 ,

wherein the circuitry is configured to calculate the correlation coefficient only when the acceleration in the direction of travel is larger than a predetermined threshold.

3. The velocity calculating device according to claim 2 ,

wherein the circuitry is configured to calculate a final value of the correlation coefficient by using, as an input, a new correlation coefficient that is obtained by sampling a plurality of outputs from the vertical acceleration detector and the horizontal angular velocity detector and by performing processing using a low pass filter.

4. The velocity calculating device according to claim 3 ,

wherein the circuitry is configured to change a gain of the low pass filter in accordance with a magnitude of the acceleration in the direction of travel.

5. The velocity calculating device according to claim 1 , wherein the circuitry is further configured to:

calculate a second correlation coefficient that represents a degree to which a yaw angular velocity of the moving body around the Z axis is mixed into the angular velocity around the horizontal axis in accordance with the attachment angle with which the body is attached to the moving body;

calculate a true angular velocity around the horizontal axis by subtracting the yaw angular velocity mixed into the angular velocity around the horizontal axis from the angular velocity around the horizontal axis, the yaw angular velocity mixed into the angular velocity around the horizontal axis being calculated on the basis of the second correlation coefficient; and

calculate the velocity of the moving body in the direction of travel of the moving body on the basis of the true acceleration in the vertical direction and the true angular velocity around the horizontal axis.

6. The velocity calculating device according to claim 5 ,

wherein the circuitry is further configured to calculate the second correlation coefficient only when the yaw angular velocity around the Z axis is higher than a predetermined threshold.

7. A method of calculating a velocity, the method comprising the steps of:

detecting an acceleration in a vertical direction generated due to an undulation of a contact surface that is in contact with a moving body by using a vertical acceleration detector mounted on the moving body;

detecting an angular velocity around a horizontal axis that is perpendicular to a direction of travel of the moving body by using a horizontal angular velocity detector mounted on the moving body, the angular velocity being generated due to the undulation of the contact surface;

calculating a correlation coefficient that represents a degree to which an acceleration in the direction of travel of the moving body is mixed into the acceleration in the vertical direction in accordance with an attachment angle with which a body including the vertical acceleration detector and the horizontal angular velocity detector is attached to the moving body by using a correlation coefficient calculator;

calculating a true acceleration in the vertical direction by subtracting the acceleration in the direction of travel mixed into the acceleration in the vertical direction from the acceleration in the vertical direction by using a predetermined true vertical acceleration detector, the acceleration in the direction of travel mixed into the acceleration in the vertical direction being calculated on the basis of the correlation coefficient; and

calculating a velocity of the moving body in the direction of the travel of the moving body on the basis of the true acceleration in the vertical direction and the angular velocity around the horizontal axis by using a velocity calculator.

8. A navigation device comprising:

a vertical acceleration detector mounted on a moving body, the vertical acceleration detector detecting an acceleration in a vertical direction generated due to an undulation of a contact surface that is in contact with the moving body;

a horizontal angular velocity detector mounted on the moving body, the horizontal angular velocity detector detecting an angular velocity around a horizontal axis that is perpendicular to a direction of travel of the moving body, the angular velocity being generated due to the undulation of the contact surface; and

circuitry configured to

calculate a correlation coefficient that represents a degree to which an acceleration in the direction of travel of the moving body is mixed into the acceleration in a vertical direction in accordance with an attachment angle with which a body including the vertical acceleration detector and the horizontal angular velocity detector is attached to the moving body;

calculate a true acceleration in a vertical direction by subtracting the acceleration in the direction of travel mixed into the acceleration in a vertical direction from the acceleration in a vertical direction, the acceleration in the direction of travel mixed into the acceleration in a vertical direction being calculated on the basis of the correlation coefficient;

calculate a velocity of the moving body in the direction of travel of the moving body on the basis of the true acceleration in the vertical direction and the angular velocity around the horizontal axis;

calculate an angular velocity around the vertical axis perpendicular to the direction of travel;

calculate an angle by which the moving body has rotated on the basis of the angular velocity around the vertical axis; and

calculate a position of the moving body on the basis of the velocity in the direction of travel that is calculated by the velocity calculator and the angle that is calculated by the angle calculator.