Dynamic resonance frequency control for a resonant-type smooth impact drive mechanism actuator

Multimodal piezoelectric actuators combine multiple vibration modes to achieve specific motions for precise actuation, or to enhance the output performance. For such a combination, the operating frequency ratio is necessarily an integer constraint. However, the resonance frequencies of target modes can be mismatched in assembly, and shift easily during operation, limiting the actuator applications. Therefore, we proposed a dynamic resonance frequency control method for multimodal piezoelectric actuators and applied it to a resonant-type smooth impact drive mechanism actuator. Passive piezoelectric parts were deployed on a Langevin transducer and connected with a field effect transistor (FET) switch. As a pulse width modulation (PWM) signal continuously adjusting the electrical boundary of these passive parts, the first longitudinal L1 mode's resonance frequency was dynamically controlled to match the third L3 mode's frequency with a ratio of two, generating a quasi-sawtooth displacement to drive a rotor. Experimental results indicated that the prototype's L1 frequency can be continuously tuned from 25.715 to 24.76 kHz at 27 ℃, and the corresponding frequency ratio was adjusted from 1.953 to 2.028. Multimodal resonance frequency static matching was confirmed by changing the switching signal's duty ratio. The L1 and L3 mode driving voltages were 50 Vp-p, and 23 Vp-p, respectively, and the speed of the rotor was 133.7 r/min. Dynamic resonance frequency control was realized with a feedback control system. As the driving PZT temperature increased to 70.5 ℃, both modes were matched and maintained resonance for 400 s. The results demonstrate that this method is conducive to improving actuator performance.