Keyboard apparatus

A keyboard apparatus comprising:

• plural keys that extend along a longitudinal axis in the direction of each of the keys, and pivot in the vertical direction about a support by the operation of depressing the keys and releasing the keys;
• plural electronic actuators that respectively apply a reaction force against the operation of depressing the plural keys, each of the electronic actuators including a movable member that displaces in the vertical direction interlocked with the pivot movement of each of the plural keys;
• plural reflection plates that are fixed to the movable members of the plural electronic actuators respectively in such a manner that an axis orthogonal to a surface of each reflection plate intersects the longitudinal axis of the keys, wherein the light reflectance of each of the reflection plates changes along the displacing direction of each of the movable members;
• and
• plural optical sensors, each of which is arranged at the position apart from the longitudinal axis of each of the keys in the lateral direction in such a manner that the distance between each reflection plate and each optical sensor is substantially constant whereby any clatter effect along the longitudinal direction is minimized, emits light toward each of the plural reflection plates, receives reflected light from each of the plural reflection plates so as to output an electrical signal according to the quantity of the received light, and detects displacement of the movable members of the plural electronic actuators,
• wherein each of the optical sensors is composed of a light emitting device that faces each of the reflection plates and emits light toward the reflection plate, and a light receiving device that faces each of the reflection plates and receives light from the light emitting device reflected by the reflection plate so as to output an electric signal according to the quantity of the received light, and
• wherein each of the optical sensors is arranged so that a light beam emitted from the light emitting device intersects the displacing direction of the movable member.