Vibration shape tuning for selective vibration node shifting in a multimodal longitudinal ultrasonic system.

Ultrasonic excitation is widely applied to enhance process performance and efficiency. Multimodal vibration excitation, as employed in advanced ultrasonic motors, offers the potential to generate multi-degree-of-freedom motion within a single compact actuator, enabling complex trajectories, higher torque densities, and improved integration in precision systems such as robotics, haptics, and micro-positioning. However, simultaneous excitation of multiple vibration modes often leads to misalignment of nodal and antinodal positions between modes, which can degrade energy transfer, reduce driving efficiency, and compromise precise control of localized energy delivery. This raises the central research question: Can the vibration node of one mode be selectively shifted without disturbing the behavior of another mode, thereby enabling reliable and synchronized multimodal excitation? In this work, we propose a tuning strategy in which additional piezoelectric ceramics are strategically integrated into the ultrasonic system. By adjusting their electrical terminal conditions, we influence the vibration distribution of modes individually. Both modeling and experimental validation demonstrate that this approach enables selective shifting of the vibration node of one mode over a wide range of 16 mm, while leaving the other mode unaffected. These findings provide a practical pathway for synchronizing nodes and antinodes of multiple vibration modes in ultrasonic systems and lay the groundwork for more robust multimodal excitation strategies in advanced manufacturing and precision actuation processes.