Development of a moving coil actuator for an automatic piano

This paper describes the development of Moving Coil Actuator for Automatic Piano. To obtain the desired tone volume, the servo system is performed by a follow-up control which uses the signal wave form. The capacity of the actuator has a torque of 1.33Nm/A, a thrust of 13.3N/A at the swing stroke point, and the frequency responses up to 60Hz. As a result of the experiments, the actuator is capable of generating enough force up to attain saturation of a movement of a piano's action, and of controlling a wide range of hammer struck string velocity down to the smallest tone volume. Also, the optimum signal wave form is found by analyzing the motion of the key and the hammer. The actuator is realized to produce the stable tone to the smallest tone volume and to perform the repetition of the sound pressure range of about 18 dB at 15 Hz.