Repetitive Motion Control Algorithm Based on Cosine Feedforward Method and Its Application to Underwater Bionic Propulsion System

The conventional proportional integral derivative(PID) control algorithm will generate amplitude attenuation and phase lag in the periodic sinusoidal motion follow-up, and the larger the load is, the more serious the amplitude attenuation and the phase lag are, which makes the conventional PID control algorithm cannot meet the high-precision follow-up requirement of the bionic propulsion motion. And for a repetitive controller designed for periodic repetitive motion, its compensation output may be delayed for one motion cycle once external disturbance exists, which leads the controller not to be applicable for the underwater variable load operating conditions. The above controllers cannot meet the performance requirements for the underwater bionic propulsion system. Therefore, this paper proposes a cosine feedforward compensation control algorithm based on the feedforward control idea to combine the conventional PID controller for an underwater propulsion system in variable load conditions. A composite feedforward controller is hence constructed to eliminate the amplitude and phase errors of sinusoidal follow-up. Experimental results show that the repetitive motion control algorithm based on cosine feedforward method is more effective than the conventional PID control method, and under variable load conditions it can still achieve accurate follow-up of a given sinusoidal motion command with about 60% reduction in the phase difference compared with the results without compensation.