Force control for the fingers of the piano playing robot — A gain switched approach

In this paper, a force controller design is considered for the fingers of the piano playing robot with a gain switched controller. Music playing robot is one kind of the service robots. In addition to playing music with the score, for a service robot, the robot, can play sweet sounds. In order to play a melodious music sound like musician, besides the robot can play the right note and right rhythm, the punching force of the fingers are controlled just right while the robot playing. In the proposed system, the finger is driven by a cylindrical linear motor. To play sounds of light, heavy, slow and anxious, the punching force of the finger is tuned according to the music score by controlling the cylindrical linear motor. Considering the playing requirements and load characteristics, the force controller is designed by a gain switchable controller to achieve the functions of force controllable and fast response. Also, the sound spectrum analysis is applied to analyze the quality of the robot's playing for the key punching and the force controlling in the viewpoint of frequency domain. Based on the sound spectrum analysis for a musician playing, the force controller of the finger is designed to lead the robot playing is closing to human playing. Through the FPGA-based implementation, each finger of the robot owns its independent control loop with parallel control structure designing to get the finger's action rapidly and precisely. From the experiments of the prototype, the results have given the verification about the practical control method and the realizable implementation.