Resonance frequency tracking control of ultrasonic transducer for diminished haptics

Previously, 'diminished haptics' in which real surface texture can be transformed was proposed. Strong intensity ultrasonic vibration was applied to realize demonstration of the concept. To enjoy the demonstration, the intensity of the ultrasonic vibration on solid surface should be maintained. The ultrasonic transducer fabricated for this purpose consisted of a Langevin type ultrasonic transducer and a horn whose end was shaped in square. Large vibration amplitude can be acquired at resonance of the whole transducer as longitudinal vibration mode. On the other hand, resonant frequency easily changes due to operating conditions. To keep the amplitude, the resonant frequency should be tracked by real time. Tracking control with phase detection was applied with a newly developed control system. Step responses of oscillating frequency as results of tracking control are reported. The results show successful tracking control.