| 摘要 |
PROBLEM TO BE SOLVED: To correctly detect the movement of a hammer or pseudo-hammer of keyboard instrument, etc. SOLUTION: An optical filter 70 which is disposed on a rotating shaft 71 of a hammer shank 2a is rotated integrally with the hammer shank 2a. A light emitting surface 201a which radiates light via the optical filter 70 and a light receiving surface 201b which receives the light are disposed opposite to each other. The optical filter 70 has a gray scale by which the quantity of transmitted light is attenuated in proportion to rotational angle of the hammer shank 2a and, therefore, the rotational angle of the hammer, for example, can be found by the change of received light quantity in the light receiving surface 201b. |
