Variable step identification of resonance frequency for percussive ultrasonic drilling based on wavelet decomposition

In order to accomplish the in-situ exploration mission on the surface of asteroids, the probes rely on anchoring mechanisms for reliable attachment. Percussive ultrasonic drill characterized by low drilling pressure and energy consumption is suitable for anchoring environments with weak surface gravity. In order to improve the anchoring efficiency of percussive ultrasonic drill on asteroid surfaces, this paper proposes a fast resonant frequency identification method with variable step scanning based on wavelet decomposition. The series resonant impedance and phase angle of the percussive ultrasonic drill are compared for stability under different conditions, from which the phase angle with higher stability is selected as the judgment for the resonant state. The impedance detail waveform and the phase angle approximation waveform are extracted by the wavelet decomposition, which are applied to adjustment of the frequency step and the judgment of the resonance state, respectively. A variable frequency step scanning algorithm adjusted with phase angle, impedance, and scanning speed is designed based on the investigation of the minimum time step and the maximum frequency step allowed for ultrasonic drill frequency scanning. The experimental results prove that the proposed variable frequency step scanning algorithm and the traditional fixed frequency step scanning algorithm have the same resonance identification results for percussive ultrasonic drill. When the initial frequency differs from the resonant frequency by 39 Hz, the proposed variable frequency step scanning algorithm reduces the identification time from about 5 s to less than 3 s.