Patent ID: 8653835

Claim:
A device for measuring a distance between a headrest and a head, comprising: a plurality of sensing electrodes which are provided in a headrest provided on a seat of a vehicle for sensing capacitances between a head of a human body sitting on the seat and the headrest, the sensing electrodes being provided side by side along a height direction of the headrest; a detecting circuit which detects capacitance values which are based on the capacitances from the plurality of sensing electrodes; and distance measuring means which measures an electrode-head distance indicating a distance between the headrest and the head, in accordance with detection results detected by the detecting circuit, wherein when the sensing electrode located at a highest position of the headrest or the sensing electrode located at a lowest position thereof among the plurality of sensing electrodes does not show a largest capacitance, the distance measuring means measures the electrode-head distance by calculating, on a two-dimensional coordinate system representing positions of the plurality of sensing electrodes on its one axis and the capacitance values detected by the detecting circuit on its other axis, a distance calculation angle formed by a line which connects a point representing the position and capacitance value of the sensing electrode located at the highest position of the headrest and a point representing the position and capacitance value of the sensing electrode from which a largest capacitance value is detected and a line which connects a point representing the position and capacitance value of the sensing electrode located at the lowest position of the headrest and the point representing the position and capacitance value of the sensing electrode from which the largest capacitance value is detected, and when the sensing electrode located at the highest position of the headrest or the sensing electrode located at the lowest position thereof shows the largest capacitance, the distance measuring means measures the electrode-head distance by calculating, on the two-dimensional coordinate system, an angle of a slope of a line which connects the point representing the position and capacitance value of the sensing electrode located at the highest position of the headrest and the point representing the position and capacitance value of the sensing electrode located at the lowest position of the headrest.