| 摘要 |
PROBLEM TO BE SOLVED: To facilitate the continuous change in sound volume by moving detecting plates directly or indirectly according to the movement of spring plates and detecting the movements of these detecting plates by detectors which output signals in accordance with the relative distances from the detecting plates. SOLUTION: When a string 6F is pushed by the finger and is displaced in an arrow direction, a sliding piece connected with this string 6F is pulled to a left direction and a leaf spring is pulled to an inner side as well, by which the distance between the leaf spring and a guide wall 32 is decreased to L2. As a result, a light shielding plate 4Fe is moved leftward and the luminous flux emitted by a light emitting diode 5Fa is not shielded any more and, therefore, the quantity of the light received by a photosensor 5Fb is increased. When the string 6F is opened at a dash (picking), the light shielding plate 4Fe returns to the right direction at a dash and the quantity of the light received by the photosensor 5Fb decreases sharply. At this time, the suitable threshold value is preferably determined. The sharp decrease of the output of the photosensor 5Fb at the time of the restoration thereof (return of the string) after the output once falls below the threshold value is detected. Detection is thus made that the string 6F is struck (striking is executed). |
